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Weapons of Mass Destruction (WMD)

3.4 TANK WASTE ALTERNATIVES

This section describes the alternatives for remediating the tank waste. Additional details may be found in Volume Two, Appendix B.

3.4.1 Elements Common to Tank Waste Alternatives

3.4.1.1 Current Operations

Included in each alternative are the operations necessary to maintain the tanks and associated facilities until they are no longer required for waste management. Routine operations include the following activities:

  • Managing operations;
  • Operating and maintaining facilities and equipment;
  • Monitoring tanks to gather information including data on waste temperatures, liquid levels, and tank status;
  • Monitoring leak detection equipment, including drywells around the tanks for increases in radioactivity, groundwater monitoring, and in-tank liquid level monitoring;
  • Adhering to regulatory compliance and reporting;
  • Conducting security and surveillance of facilities and grounds;
  • Performing interim stabilization of SSTs by saltwell pumping;
  • Operating the 242-A Evaporator to concentrate waste;
  • Maintaining tank safety including diluting tank waste as necessary and maintaining adequate storage capacity; and
  • Characterizing MUST waste associated with TWRS.

The 242-A Evaporator is an existing facility in the 200 East Area. This facility, which recently has been upgraded, is used for routine operations and would continue to be used (until approximately 2005) for waste management under all of the tank waste alternatives.

The functions and activities for routine operations are the same for each alternative but the cost, schedule, and staffing levels vary according to the schedule for completion of waste treatment and subsequent closure of the tank farms. The impacts of these routine operations are included in the calculations of the impacts for each alternative (Section 5.0).

Included in all of the alternatives (except No Action) are upgrades to the existing waste transfer system. Waste transfer system upgrades would involve constructing buried waste transfer pipelines in the 200 East Area. These upgrades would provide for safe, reliable, and compliant waste transfer between waste-generating facilities and the tank farms. Selected valve pits and diversion boxes would be upgraded by installing liners to provide secondary containment in the event of a leak or spill. Also included are new jumper and cover installations for selected valve pits and diversion boxes. The various flow path combinations would be indicated on the new cover blocks. The replaced buried lines would be abandoned in place, whereas the replacement items such as valve and diversion box jumpers and box covers would be removed and disposed of onsite (WHC 1996c). These waste transfer system upgrades do not include the replacement cross-site transfer system.

Future additions of waste to the tank farms would occur during routine operations. Some of these waste additions would involve loading the waste as liquid or slurry into a tank truck or rail car at the generating facility, transporting to the tank farms, and unloading and transferring the waste into existing DSTs for storage. This waste could be transferred using existing rail or specialized truck (LR-56[H]) systems. Volume Two, Appendix B contains a description of the LR-56(H) truck, which was specially designed for the transport of nuclear waste. Waste will be generated and require transport to the tank farms from the following:

  • 300 Area laboratory facility cleanout;
  • Plutonium-Uranium Extraction (PUREX) Plant, Plutonium Finishing Plant (PFP), and B Plant cleanout;
  • T Plant decontamination waste;
  • Routine laboratory waste; and
  • K Basins cleanout.

Some f uture waste volume projections are provided in Volume Two, Appendix A.

In December 1995, all 177 tanks (Watchlist and non-Watchlist) were placed under flammable gas controls. Until the necessary characterization data are obtained, the tank farm systems will continue to operate under a conservative management program to maintain a safe operating envelope. These controls may slightly increase the cost of performing maintenance and monitoring activities on the tanks until the issue is resolved.

3.4.1.2 Multi-Purpose Canister

For comparison, it has been assumed that each of the ex situ alternatives would use a large multi-purpose canister for interim onsite storage and transportation to the potential geologic repository. This canister is designated the Hanford Multi-Purpose Canister. The Hanford Multi-Purpose Canister would be approximately 4.6 m (15 ft) long and 1.4 m (4.5 ft) in diameter and would be used as an overpack canister to house up to four individual HLW canisters depending on canister size. The sizing of the HLW canisters and the decision to use a multi-purpose overpack canister are in the conceptual stage and have not been finalized. There may be potential economic and handling benefits to using a multi-purpose canister for the TWRS program. There may be potential additional costs associated with using Hanford Multi-Purpose Canisters if future evaluations determine that the Hanford Multi-Purpose Canisters were not acceptable for disposal or if the Hanford Multi-Purpose Canisters would require costly changes in repository design and operations. Such a multi-purpose type canister has also been proposed as a waste package for commercial spent nuclear fuel. Additional information on canister sizing is presented in Volume Two, Appendix B.

3.4.1.3 Liquid Effluent Processing

Liquid effluent processing for all of the alternatives would be provided by the secondary radioactive liquid-waste processing system. This system, which has been constructed and currently is undergoing acceptance testing, is assumed to be permitted and operational in time to support each of the alternatives. The environmental impacts of this facility were analyzed in an environmental assessment (DOE 1992a). The secondary radioactive liquid-waste processing system consists of the Liquid Effluent Retention Facility, the Effluent Treatment Facility, and the State-approved land disposal site.

To be accepted into the effluent treatment facilities, waste must meet specific waste acceptance criteria. It is assumed that the liquid effluent streams generated at the waste processing facilities identified for the various alternatives would meet the waste acceptance criteria for the Liquid Effluent Retention Facility and the Effluent Treatment Facility.

The Liquid Effluent Retention Facility provides up to 49 million L (13 million gal) of temporary storage capacity for liquid waste. This storage capacity is provided by two 25 million-L (6.5 million-gal) lined and covered basins. An additional storage basin is provided for emergency backup. Waste accumulated in the Liquid Effluent Retention Facility basins would be sent to the nearby Effluent Treatment Facility for treatment.

The Effluent Treatment Facility provides the final processing step before disposal. This facility includes a treatment system to reduce the concentrations of radioactive and hazardous waste constituents in the effluent streams to acceptable levels. The treated effluent is held in storage tanks to allow for verification before being transferred to the State-approved land disposal site for discharge.

3.4.1.4 Major Assumptions and Uncertainties

To develop engineering data required to perform impact analyses for each of the alternatives discussed in the EIS, assumptions were made regarding the technologies that have been configured to create a remediation alternative. These assumptions were based either on the best information available, applications of a similar technology, or engineering judgement. By definition when an assumption is made, there is some level of uncertainty associated with it that can be expressed as a range for the assumed value that reasonably could be expected. This section identifies the major assumptions used for the alternatives. Additional information on assumptions is provided in Volume Two, Appendix B, Section B.8.0 and uncertainties in Volume Five, Appendix K.

In Situ Alternatives

It was assumed that there would be no leaks to the soil from the SSTs or DSTs during the administrative control period for the No Action, Long-Term Management, or In Situ Fill and Cap alternatives. This assumption is based on ongoing SST interim stabilization to remove pumpable liquids, the ability to detect and recover leaks from the space between the inner and outer liners of the DSTs, and ongoing monitoring activities within the tank farms. The SSTs and DSTs were assumed to maintain their structural integrity throughout the administrative control period under the No Action and Long-Term Management alternatives.

The In Situ Vitrification, In Situ Fill and Cap, and the in situ portion of the Ex Situ/In Situ Combination 1 and 2 alternatives were assumed to require additional characterization data to evaluate the acceptability of in place disposal and address RCRA land disposal requirement considerations. This requirement would be in addition to the current characterization requirements for the ex situ alternatives. These additional characterization efforts could involve extensive laboratory analysis of additional tank samples and may require modifications to the tanks to install additional risers for sampling access.

In Situ Vitrification

The in situ vitrification system was assumed to be capable of vitrifying each of the tanks to the required depth resulting in a consistent waste form. It was also assumed that the variation in waste composition and inventory from tank to tank would not impact the ability to produce an acceptable waste form.

In Situ Fill and Cap

The concentrated liquid waste contained in the DSTs was assumed to be acceptable for gravel filling. Under this alternative, the DST liquids would be concentrated using the 242-A Evaporator to remove as much water from the waste as possible, but the waste would still contain substantial volumes of liquid. It has been estimated that concentration by the 242-A Evaporator would reduce the current liquid volumes contained in the tanks by approximately one-third (WHC 1995f).

Ex Situ Alternatives

The major assumptions used for the ex situ alternatives are outlined in the following paragraphs and summarized in Table 3.4.1.

Table 3.4.1 Ex Situ Alternatives Major Assumptions

Retrieval Efficiency

Retrieval efficiency is the assumed percentage of the tank waste that would be retrieved. The amount and type of waste that would remain in the tanks after retrieval is uncertain. The Tri-Party Agreement (Ecology et al. 1994) set a goal for the SSTs that no more than 1 percent of the tank inventory would remain as a residual following waste retrieval activities. The engineering data for the waste retrieval and transfer function common to all ex situ alternatives was developed using 99 percent retrieval as a goal.

The residual contaminants left in the tanks either would be insoluble and hardened on the tank walls or bottom or of a size that could not be broken up or removed from the tanks. In either case, the residual would have low solubility because the retrieval technologies proposed would use substantial quantities of liquid in an attempt to dissolve or suspend the waste during retrieval. Because of the uncertainties regarding the amount and type of residual waste that would remain in the tanks, a conservative assumption was made to bound the impacts of the residual waste. For purposes of the analysis, it was assumed that 99 percent recovery would be achieved for ex situ alternatives, and the residual waste left in the tanks would contain 1 percent of all the original tank inventory, including the water-soluble contaminants. The water-soluble contaminants provide the long-term potential human health risk because they would be transported into the groundwater and then could be consumed by humans.

The assumption that 1 percent of the water-soluble waste would remain in the tanks yields an upper bound on the impacts that would occur under the ex situ alternatives. The In Situ Fill and Cap and Ex Situ/In Situ Combination 1 and 2 alternatives leave more waste in the tanks for disposal and provide an upper bound on the impacts associated with the amount and type of waste that is disposed of onsite.

Releases During Retrieval

To provide a conservative estimate of the impacts that could occur following retrieval, the analysis performed for the EIS assumed that each of the 149 SSTs would leak an average of 15,000 L (4,000 gal) to the soils surrounding the tank during retrieval operations. No leakage was assumed to occur from the DSTs during retrieval operations because DSTs have provisions for leak containment and collection. The leakage volume estimate was based on current information from the retrieval program and the assumption that the average leakage volume from an SST would be one order of magnitude lower than the maximum release volume estimated for tank 241-C-106 during sluicing operations (DOE 1995d). The leakage estimated for tank 241-C-106 was based on a series of conservative assumptions that would not be applicable for developing an average lead estimate for all SSTs. It was also assumed that the contaminant concentrations in the liquids released would be at maximum predicted concentrations; therefore, dilution of the waste during retrieval was not taken into account.

DOE is currently working with Ecology to define the operating envelope for allowable leakage during retrieval systems would include measures to detect and control leakage.

Nominal Case

A nominal case retrieval release and residual tank inventory was developed to assess the impacts that would result from nominal, as compared to bounding, assumptions for tank releases during retrieval and the residual waste left in the tanks following retrieval. Additional information on the nominal case is in Volume Two, Section B.3.

The nominal retrieval release inventory was developed by assuming that the waste would be diluted by one-third through the addition of water during waste retrieval. The nominal case retrieval release volume was assumed to be 15,000 L (4,000 gal) from each SST, and the contaminant concentrations were assumed to be two-thirds of the bounding case.

The nominal tank residual inventory was developed by modifying the bounding tank residual inventory to reduce the mobile constituents of concern based on solubility. The mobile constituents of concern were evaluated because of their contribution to post-remediation risk. The isotopes of carbon, technetium, and iodine were reduced in the nominal case tank residual inventory to 10 percent of the bounding tank residual inventory.

The nominal case for operation accidents was analyzed by using average tank inventory for the potential releases during accidents. This nominal inventory was developed by estimating the inventory of radioactive materials contained in the fuel from the single-pass reactors and N Reactor and sent to the tank farms. Reduction factors were applied to account for extracted plutonium, uranium, cesium, and strontium. This nominal radiological inventory is shown in Appendix E, Section E.1.0.

Operating Efficiency

The operating efficiency is a combination of the online efficiency and the production efficiency of the treatment facilities. The assumed operating efficiency is used in combination with the operating schedule to determine the size of the treatment facilities required to treat the waste. The 60 percent operating efficiency assumption was selected as a reasonable value for facility sizing. This value is considerably lower than operating efficiencies obtained in the commercial chemical processing industry to account for regulatory and safety requirements associated with nuclear waste processing. The operating efficiency for Phase 2 of the Phased Implementation alternative was assumed to be higher than the other alternatives to account for the phased implementation approach. Once a treatment facility is designed and constructed, the inability to achieve the assumed operating efficiency would result in a longer operating schedule.

Waste Loading

Waste loading or waste oxide loading is the percentage of waste that is in the final vitrified waste form. The waste oxide loading is controlled by the amount of glass formers that are added during the vitrification process. The higher the waste loading, the more waste contained in the vitrified glass, and the lower the overall waste volume. Conservative waste loading factors have been assumed for the ex situ alternatives. Current development work may result in the selection of higher waste loading factors. The sensitivity of the HLW and LAW volume and the engineering data to the waste loading assumptions is provided in Volume Two , Section B.8.0.

Blending Factor

Blending is the mixing of the wastes from different tanks during retrieval to obtain an average waste feed stream for treatment. Because there are 177 tanks that contain waste and the waste composition varies from tank to tank, it would be difficult to achieve a completely uniform blending of the waste during retrieval. To account for the uncertainties associated with achieving a uniformly blended waste feed stream, blending factors have been assumed for the HLW vitrification processes.

One of the major uncertainties associated with the ex situ alternatives is the volume of HLW that would be produced. The largest uncertainty range would be for alternatives that rely on an intermediate level of separations. The estimated volume of HLW produced is a function of the inventory and assumptions made for separations efficiencies , waste loading, and blending.

The waste loading and blending factors assumed for the ex situ alternatives represent a reasonable and conservative technical basis for the EIS. This basis was developed through an independent technical review (Taylor-Lang 1996). The assumptions made for waste loading and blending result in approximately 12,200 HLW canisters (1.17 m3 [41 ft3]) for the Ex Situ Intermediate Separations and Phased Implementation alternatives.

Assumption on Disposal of Hanford Site HLW in a Geologic Repository

For purposes of analysis, a geologic repository candidate site at Yucca Mountain, Nevada was assumed to be the final disposal site for all TWRS HLW sent offsite for disposal. Current legislation prohibits the placement, in the first repository, of spent fuel in excess of 70,000 mt (77,000 tons) of heavy metal or a quantity of solidified high-level radioactive waste from the reprocessing of such a quantity of spent fuel until a second repository is operating. DOE will evaluate the need for a second repository no sooner than year 2007.

Currently, Yucca Mountain is the only site being characterized as a geologic repository for HLW. If selected as the site for development, it would be ready to accept HLW no sooner than 2015. The potential environmental impacts that would occur at the geologic repository from the disposal of HLW from TWRS are not addressed in this EIS. Potential impacts at the repository will be addressed in an EIS that DOE will prepare in accordance with the Nuclear Waste Policy Act to analyze the site-specific environmental impacts from construction, operation, and eventual closure of a potential geologic repository for spent nuclear fuel and HLW at Yucca Mountain. Detailed evaluations to support decisions on the disposal of HLW from the Hanford Site would be made following completion of the repository EIS. The repository EIS will also asses the impacts of transporting spent nuclear fuel and HLW from various storage locations to the potential geologic repository.

Each of the ex situ alternatives addressed in this EIS include sufficient interim onsite storage facilities to store all of the immobilized HLW produced while awaiting offsite transport and disposal at the potential geologic repository. This would allow each of the alternatives to operate independent of the acceptance schedule for the potential geologic repository.

Safety Issues

Because of the uncertainty involved with the tank waste inventory and the application of some first of a kind technologies, there are uncertainties involved with the estimates of accidents. Therefore, a bounding approach was taken for the calculation of consequences from accidents. A full safety review of all aspects of the alternative selected would be performed during the final design phase, and changes could be made to the selected alternative to provide engineering or administrative controls to mitigate accidents unforeseen at the current time. This is a standard design procedure.

The possibility of driving heavy equipment over an unstabilized tank during construction or operations that could potentially result in a tank dome collapse was considered. To reduce the potential for this accident, engineered features would be installed and administrative controls would be used to prevent large vehicles from driving on top of the domes. These engineered barriers would be mechanical barriers such as closely spaced posts installed around the tanks or tank farms.

3.4.1.5 Waste Compositions

Vitrification, or glassmaking, is a waste stabilization and solidification technology that incorporates radioactive and hazardous waste into a glass matrix. This process involves blending the waste material with glass formers or additives and heating the mixture to glass-forming temperatures. The types of glass formers added to the waste define the resulting glass type.

Borosilicate glass is based on a composition of silicon dioxide, boron trioxide, sodium oxide, and lithium oxide. Borosilicate glass is the standard final waste form for treating high-level radioactive waste because of its durability and ability to accommodate a varied range of waste feeds (DOE 1990). Additionally, borosilicate glass is currently identified as the only standard HLW form that will be accepted at the potential geologic repository (DOE 1994g).

Other types of glass could be selected for the vitrification of HLW or LAW; however, they would have to meet the repository or performance assessment criteria. One example is the soda-lime glass that would be produced by the Ex Situ No Separations (Vitrification) alternative. Soda-lime glass consists of mainly silicon dioxide, sodium oxide, and calcium oxide.

Two types of vitrified waste forms described in the alternatives are monoliths and cullet. Monoliths would be produced by casting the molten glass into a canister, resulting in a single piece of glass. The cullet would be produced by quenching the molten glass in water following vitrification, resulting in gravel-sized pieces of glass.

Cullet would provide processing and material handling advantages for the high-capacity processing facilities. The disadvantage of cullet as a waste form is its high surface area-to-volume ratio, which results in lower long-term performance. Matrices or coating material can be used in conjunction with the cullet to improve the waste-form performance.

All of the ex situ alternatives that produce vitrified LAW for onsite disposal have assumed cullet in a matrix material as the waste form for onsite LAW disposal. This provides a conservative analysis of the long-term impacts resulting from onsite disposal of LAW.

Grouting the retrieved tank waste is a technology that could be applied to any of the ex situ alternatives in place of vitrifying the waste. Grout is a common solidification and stabilization technology employed in the management of hazardous and radioactive waste. Grout is a general term that refers to a waste form obtained by mixing waste with chemical additives to stabilize and immobilize the hazardous constituents.

The grouting process applied to the ex situ treatment of the tank waste would involve waste retrieval and transfer to a grout facility where the waste would be mixed with appropriate mixtures of grout formers. After the grout is mixed, it could be placed into containers or pumped into large vaults for solidification and disposal.

Grouting tank waste has been studied extensively at the Hanford Site as a technology for LAW disposal. Grouting of the LAW was selected as the treatment method in the Hanford Defense Waste EIS (DOE 1987). The LAW described in the Hanford Defense Waste EIS included liquid waste from the tanks (after separation of HLW components) and secondary waste from the HLW vitrification facility, which would consist of waste from canister decontamination, drying feed material, and recovered liquid from off-gas treatment.

Each of the alternatives that involve treating the waste would involve collecting small sample quantities (up to about 2.5 L [0.65 gal] per sample) of tank waste and shipping the samples to offsite locations for bench-scale waste treatment and immobilization performance demonstration and testing purposes. The general approach would include collecting grab and/or core samples from the tanks, verifying that the samples and sample contents meet appropriate specifications (using existing onsite laboratory facilities, including necessary laboratory preparatory work [e.g., preparing composite samples]), and appropriately packaging and transporting the samples to other DOE facilities or to private contractor facilities. Initially, collecting and transferring small quantities of such samples would be to support contractor selection for DOEs TWRS privatization initiative.

3.4.1.6 Waste Minimization

Each alternative would involve waste minimization practices for primary, secondary, and tertiary waste. Primary waste is the treated tank waste and capsule contents requiring disposal. Primary waste minimization practices would be used to control the volume of HLW and LAW requiring disposal.

Secondary waste is generated during handling and processing of the waste and includes off-gases, contaminated filters, spent ion-exchange resins, and liquid effluents. Secondary waste minimization would involve practices such as using metal high-efficiency particulate air filters that could be washed in place and reused. In some process configurations, spent ion-exchange resin would be fed into the waste treatment process to reduce the volume of secondary waste.

Tertiary waste generation primarily would be a function of the number of operating personnel and includes such things as personal protective equipment and other incidental waste. Secondary and tertiary waste would be divided into low-level waste and transuranic waste based on characterization. Secondary low-level waste would be disposed of at the onsite low-level waste burial grounds. Secondary transuranic waste would be retrievably stored for future packaging at the Waste Receiving and Processing Facility. Current plans are for disposal of transuranic waste at the Waste Isolation Pilot Plant. Liquid effluent from all alternatives would be treated at the Effluent Treatment Facility in the 200 East Area before release.

Each of the tank waste alternatives that use high-temperature processing (vitrification or calcination) would make extensive use of recycle streams to recycle volatile radionuclide and chemical constituents, which are captured in the off-gas systems, back into the treatment process. These recycle streams would be used to minimize the generation of secondary waste. It has been determined that a bleed stream would be required for each alternative to avoid a continuous buildup of certain volatile radionuclide and chemical constituents (e.g., technetium-99 and mercury) in these recycle streams. For comparison purposes, it has been assumed for each alternative that the bleed stream percentage would be 1 percent of the recycle stream and that this secondary waste stream would be stabilized by some low-temperature process.

Hanford Site waste minimization would involve the use of chemicals and materials from other Hanford Site facilities where appropriate. One example would be the conversion of the sodium from the Fast-Flux Test Facility cooling system to sodium hydroxide for use during enhanced sludge washing for the Ex Situ Intermediate Separations and Ex Situ Extensive Separations alternatives, or other alternatives using waste stream separation processing. The conversion facility, with its process-inherent safety issues, would require a cost and safety analysis.

3.4.1.7 Cost Estimates

Cost estimates are presented for each alternative. These estimates are based on conceptual designs and have an associated level of uncertainty. This uncertainty is accounted for in the cost uncertainty analysis and results in a cost range that is estimated for each alternative. Additional information on the cost uncertainty is provided in Volume Two, Section B.8.0.

Capital cost is included in the cost for the alternatives and includes the direct cost (i.e., materials, labor, and equipment for facility construction), construction management, project management, engineering, and contingency. The contingency is obtained by multiplying the sum of the capital cost components by a contingency factor. Each of the estimates includes a value for current operations, which is the estimated cost associated with routine operations identified in Section 3.4.1.1.

Research and development cost is included in the cost estimates for each alternative. This cost is assumed to provide for development of the technologies required to implement an alternative. The resolution of implementability issues identified for each alternative would be part of the development work; thus the research and development cost partially reflects the implementation uncertainties.

Repository fees for alternatives that include shipment of HLW to the potential geologic repository are discussed in Section 3.7.

The cost estimates for each of the alternatives were prepared using the same methodology and estimating practices to ensure comparability among the alternatives. Additional detail on the cost estimates is provided in Volume Two, Appendix B.

3.4.1.8 Facility Sizing

The design capacities for the full-scale ex situ processing facilities were developed using a consistent approach. Each facility was sized to treat the projected volume of waste within the schedule outlined in the Tri-Party Agreement using a consistent set of assumptions for total operating efficiency. The total operating efficiency for the ex situ vitrification facilities was assumed to be 60 percent. The operating efficiency for the Phased Implementation alternative during Phase 2 was assumed to be higher to account for the advantages of the phased implementation approach.

3.4.1.9 Facility Siting

A site evaluation process was conducted and four potential sites were identified as suitable locations for the onsite treatment and disposal activities for the ex situ treatment and disposal alternatives. A suitable site, which would accommodate all of the full-scale ex situ alternatives, is a combination of Sites B and C shown in Figure 3.4.1. This representative site is for ex situ tank waste remediation activities for the purpose of alternative evaluation in the EIS and does not preclude the other sites from ultimately being selected. Prior to selecting the representative site, one of the other sites, or a combination of sites, appropriate NEPA analysis would be completed. All of the full-scale ex situ alternatives are assessed as if they were located on this representative site.

The representative site is located close to a potential support facility for the 200 East Area infrastructure on vacant land, which has been disturbed partially by past actions. The location of the Phase 1 facilities for the Phased Implementation alternative is assumed to be Site B, maintaining Site C for Phase 2 facilities (WHC 1996).

3.4.1.10 Hanford Barrier

The Hanford Barrier would be a horizontal, abovegrade, engineered soil structure used to isolate the waste site from the environment by preventing or reducing the likelihood of wind erosion, water infiltration, and plant, animal, and human intrusion. It would be composed of 10 layers with a combined thickness of 4.5 m (15 ft), and placed over the top of the stabilized tanks and the LAW disposal sites. Each Hanford Barrier would extend 9 m (30 ft) beyond the perimeter of the area to be protected. For additional information on the Hanford Barrier, see Volume Two, Section B.6.0.

Figure 3.4.1 Potential Site Location

For purposes of analysis only, the earthen borrow material was assumed to be obtained from three potential borrow sites on the Hanford Site. The use of these sites to allow the potential impacts to be calculated does not mean that these sites would be used. The evaluation and selection of borrow sites for closure activities will be addressed in a future NEPA analysis.

3.4.1.11 Interim HLW Storage

Each of the ex situ alternatives would include sufficient interim onsite storage capacity to store all of the immobilized HLW produced while awaiting shipment to the potential geologic repository. Interim HLW storage would consist of placing Hanford Multi-Purpose Canisters on a concrete storage pad and placing a concrete shielding cover over each Hanford Multi-Purpose Canister. This method of interim

storage would be used for all ex situ alternatives except for Phase 1 of Phased Implementation. During Phase 1 HLW canisters would be placed in the Canister Storage Building for interim storage. The Canister Storage Building is a facility that is being constructed in the 200 East Area for storage of DOE spent fuel.

3.4.2 No Action Alternative (Tank Waste)

3.4.2.1 Overview

The No Action alternative would provide for continued storage and monitoring of tank waste. For purposes of assessing impacts, it is assumed that administrative controls (e.g., site security and management) would be maintained for 100 years. However, DOE and Ecology currently have no policies or plans that would permit the loss of administrative control for radioactive and hazardous material.

The SST waste would have minimal free liquid remaining and would be left in place and monitored. Existing DSTs and MUSTs would be left in place and monitored, similar to the SSTs. No construction activities would be involved with the No Action alternative.

The information used in describing this alternative was obtained from the No Disposal Action Engineering Data Package for the TWRS EIS (WHC 1995g and Jacobs 1996).

3.4.2.2 Process Description

For the SSTs, it is assumed that current operations to remove pumpable liquid (interim stabilization) from the tanks would be completed. This would result in SST waste that primarily is solid but contains some interstitial liquid (the interstitial liquid is held within the void spaces of the sludge and saltcake). The SSTs would be monitored for releases and indications of tank dome settling or collapse. The SSTs showing signs of deterioration would be filled with grout or gravel as a corrective action or emergency response.

The DST waste mainly is liquid; consequently, a tank leak from a DST would represent a greater threat to the environment than a tank leak from a SST because of the potential volume and migration of contaminants to the groundwater. The DSTs were put into service between 1971 and 1987, and all DSTs would exceed their 50-year design life during the No Action alternative. Monitoring and maintenance activities would continue to ensure safe storage of waste in the DSTs. This would include maintaining spare DST capacity and leak recovery from the annulus of a tank if a leak were detected. Spare DST capacity would be maintained within the existing DSTs through periodic operation of the 242-A Evaporator and waste minimization practices. If a DST were to fail, its waste would be transferred to other DSTs as an emergency response. Administrative controls would be maintained for items such as monitoring, routine maintenance, fire protection, and security throughout the 100-year administrative control period.

3.4.2.3 Construction

No construction activities would take place for this alternative.

3.4.2.4 Operations

Operations would involve continued monitoring and maintenance of the tank farms.

3.4.2.5 Post Remediation

There would be no post-remediation activities associated with the No Action alternative. It is assumed for purpose of analyses that administrative control of the area would be discontinued after 100 years, and human intrusion could occur.

3.4.2.6 Schedule, Sequence, Cost

The No Action alternative schedule is shown in Table 3.4.2. The cost for the No Action alternative is shown in Table 3.4.3.

Table 3.4.2 Schedule - No Action Alternative (Tank Waste)

Table 3.4.3 Cost - No Action Alternative (Tank Waste) 1

3.4.2.7 Implementability

The objective of the No Action alternative would be to provide continued management of the tank waste. This alternative would not provide remedial action for the tank waste. This alternative would provide for the continuation of current operations and, as such, does not present specific process uncertainties. There is some uncertainty in estimating the functional life of the DSTs. Current design life of the DSTs is approximately 50 years.

Extensive additional characterization would be required to address RCRA land disposal requirements if waste was left in place.

One implementability issue that would require additional analysis is the potential for interim stabilized SSTs to develop leaks. Following interim stabilization, an SST could contain as much as 190,000 L (50,000 gal) of interstitial liquid.

This alternative would not comply with Federal and State requirements for storing hazardous waste. When administrative control is assumed to be discontinued after 100 years, the waste left in place would not comply with State and Federal (including DOE Order 5820.2A) requirements for disposal of hazardous, radioactive, or mixed waste (Section 6.2).

3.4.3 Long-Term Management Alternative

3.4.3.1 Overview

The Long-Term Management alternative would provide continued storage and monitoring of tank waste and is similar to the No Action alternative except that the DSTs would be replaced twice during the 100-year administrative control period to prevent the release of DST liquid. For purposes of assessing impacts, it is assumed that administrative controls (e.g., site security and management) would be maintained for 100 years. However, DOE and Ecology currently have no policies or plans that would permit the loss of administrative control for radioactive and hazardous material.

The SST waste would have minimal free liquid remaining and would be left in place and monitored. The DST waste, which is currently 77 percent liquid, would be monitored, retrieved, and placed into new DSTs at 50-year intervals corresponding to the design life of the DSTs (Figure 3.4.2) . Existing MUSTs would be left in place and monitored similarly to the SSTs. Construction activities for the Long-Term Management alternative involve building new DSTs along with the retrieval, transfer, and evaporator facilities to accommodate two retanking campaigns for the DST waste during the 100-year administrative control period.

The information used in describing this alternative was obtained from the No Disposal Action Engineering Data Package for the TWRS EIS (WHC 1995g and Jacobs 1996).

3.4.3.2 Process Description

For the SSTs, it is assumed that current operations to remove pumpable liquid (interim stabilization) from the tanks would be completed. This would result in SST waste that is primarily solid but that contains some interstitial liquid (the interstitial liquid is held within the void spaces of the sludge and saltcake). The SSTs would be monitored for releases and indications of tank dome settling or collapse. The SSTs showing signs of deterioration would be filled with grout or gravel as a corrective action or emergency response.

The DST waste is mainly liquid, and consequently, a tank leak to the ground from a DST (both shells failing) would represent a greater threat to the environment than a tank leak from a SST because of the potential volume and migration of contaminants to the groundwater. The DST waste would be removed and transferred into new DSTs at two intervals corresponding to the 50-year design life of the tanks. The design life corresponds to a minimum length of service time that a tank would be expected to remain functional, though the DSTs may remain functional for more than 50 years. The DSTs were

put into service between 1971 and 1987, and the first retanking campaign would correspond to using the full 50-year service life of the newest DSTs, which were placed into service in 1987. The first retanking campaign for the 28 DSTs would begin in the year 2037. It is recognized that some DSTs would exceed their design life prior to the first retanking campaign; however, it is assumed that these tanks would be safely managed. Monitoring and maintenance activities would continue to ensure safe storage of waste in those DSTs that would exceed the 50-year design life. This would include maintaining additional DST capacity and leak recovery from the annulus of the DSTs.

Based on waste volume projections, each retanking campaign would require 26 new 3.8-million-L (1-million-gal) tanks to replace the existing DSTs. This estimate includes maintaining a spare tank for contingency. A total of two retanking campaigns would be required during the 100-year administrative control period.

Figure 3.4.2 Long-Term Management Alternative

Following retrieval, the empty DSTs would contain waste residuals and would be managed in the same manner as the SSTs. Administrative controls would be maintained for monitoring, routine maintenance, fire protection, and security throughout the 100-year administrative control period.

3.4.3.3 Construction

Construction activities for this alternative would consist of building 26 new DSTs along with the required retrieval and transfer systems for each DST retanking campaign. The 242-A Evaporator was assumed to be obsolete by the time the first retanking operation would take place, and a new evaporator would be constructed in the vicinity of the new DSTs for each retanking. A total of 52 new DSTs and 2 new evaporators would be built under this alternative.

3.4.3.4 Operations

Operations would involve continued monitoring and maintenance of the tank farms as well as retrieving and transferring the DST waste during the retanking campaigns.

  • Waste retrieval would be accomplished during a DST retanking campaign as follows.
  • Pump tank liquid (supernate) from existing to new DSTs.
  • Add water to existing tanks and use mixer pumps to suspend solid and sludge into a slurry.
  • Pump the slurry to the evaporator for water removal and volume reduction.
  • Pump concentrated slurry to new DSTs.
  • Send evaporator condensate and excess retrieval water to the Effluent Treatment Facility for treatment and discharge.

3.4.3.5 Post Remediation

There would be no post-remediation activities associated with the Long-Term Management alternative. The evaporator facility constructed with each set of new tanks would be decontaminated and decommissioned after each retanking campaign. It was assumed that administrative control of the area would be discontinued after 100 years, and human intrusion could occur.

3.4.3.6 Schedule, Sequence, Cost

The Long-Term Management alternative schedule is shown in Table 3.4.4. The two separate time periods shown correspond to building and transferring the DST waste to new tanks during the 100-year administrative control period. The overall cost for the Long-Term Management alternative is shown in Table 3.4.5.

Table 3.4.4 Schedule - Long-Term Management Alternative

3.4.3.7 Implementability

The objective of the Long-Term Management alternative would be to provide continued storage of the tank waste. This alternative would not provide remedial action for the tank waste. This alternative would provide for the continuation of current operations and, as such, does not present any process uncertainties. There is some uncertainty in estimating the functional life of the DSTs. Design life of the current DSTs is approximately 50 years. Many tanks are expected to exceed their design life; however, a structural integrity assessment has not been completed to date. One implementability issue that would require additional analysis would be the potential for interim stabilized SSTs to develop leaks. Following interim stabilization, an SST could contain as much as 190,000 L (50,000 gal) of interstitial liquid.

Table 3.4.5 Cost - Long-Term Management Alternative 1

Extensive additional characterization would be required to address RCRA land disposal requirements if waste was left in place.

This alternative would not comply with Federal and State requirements for storing hazardous waste. When administrative control is assumed to be discontinued after 100 years, the waste left in place would not comply with State and Federal (including DOE Order 5820.2A) requirements for disposal of hazardous, radioactive, or mixed waste (Section 6.2).

3.4.4 In Situ Fill and Cap Alternative

3.4.4.1 Overview

The In Situ Fill and Cap alternative would leave the tank waste in place for disposal. This alternative would involve containing the waste by evaporating excess water from the DST waste using the 242-A Evaporator; filling the tanks with gravel to prevent subsidence; and installing a Hanford Barrier over each tank farm. These actions would slow the migration of contaminants from the waste by removing water from the waste and using the Hanford Barrier to limit the amount of rainwater that would infiltrate through the waste to the water table. The current barrier design is composed of 10 layers of material with a combined thickness of approximately 4.5 m (15 ft) (WHC 1995i). Additional information on the Hanford Barrier is contained in Volume Two, Appendix B. Information used in describing this alternative is from the In Situ and Closure engineering data packages (WHC 1995f, i, and Jacobs 1996).

3.4.4.2 Process Description

The 242-A Evaporator would be used to remove most of the liquid in the DSTs. The tanks would be filled with basalt gravel using commercially available equipment. Gravel filling the tanks would prevent future tank dome collapse and loss of integrity of the Hanford Barrier.

3.4.4.3 Construction

Construction for this alternative would include activities to fill the tanks with gravel: installing gravel handling equipment required to convey the gravel from a stock pile to individual tanks and distribute the gravel evenly into the tank; modifying tank openings to accommodate gravel handling equipment, and constructing four gravel stockpile storage sites.

3.4.4.4 Operations

Operations would take place during a 9-year period between 2000 and 2009. Major activities during operations would include evaporating DST liquid in the 242-A Evaporator to remove as much water from the liquid waste as practical, and filling SSTs and DSTs with gravel.

3.4.4.5 Post Remediation

After all tanks were filled, the equipment used for gravel filling would be decontaminated and decommissioned. The MUSTs (both active and inactive) and ancillary equipment in the tank farms would be filled with grout, and a Hanford Barrier would be constructed over each tank farm. The regulatory aspects of closure are discussed in Section 6.2.

3.4.4.6 Schedule, Sequence, and Cost

The schedule of major activities associated with this alternative is presented in Table 3.4.6. These estimates include the cost necessary to fill each of the tanks with gravel and cover each tank farm with a Hanford Barrier. The estimated cost for this alternative is shown in Table 3.4.7.

Table 3.4.6 Schedule - In Situ Fill and Cap Alternative

3.4.4.7 Implementability

The primary issue associated with implementing this alternative would be the possibility of spontaneous or radiolytic decomposition reactions occurring in the tanks following the gravel fill operations. Following gravel filling operations, oxidizing chemicals would be in contact with organics and safely disposing of these waste combinations would require further investigation. The regulatory issues associated with this alternative are discussed in Section 6.2.

Table 3.4.7 Cost - In Situ Fill and Cap Alternative 1

This alternative would not meet the land disposal requirements of RCRA for hazardous waste. Near-surface disposal of HLW would not meet DOE policy to dispose of readily retrievable HLW in a potential geologic repository (Section 6.2).

3.4.5 In Situ Vitrification Alternative

3.4.5.1 Overview

The In Situ Vitrification alternative would immobilize all of the tank waste by vitrifying the tanks and their contents in place (Figure 3.4.3) .

This process would require the use of electrical resistance heating, referred to as joule heating, to create a high-temperature region of molten soil and waste that would solidify when cooled into a stable, glass-like form. During this process, various components of the waste either would be incorporated into the glass, destroyed, or vaporized into the off-gas treatment stream. A confinement facility would be constructed over each tank farm or smaller group of tanks to provide containment and collect the off-gases generated during vitrification for subsequent treatment. Each facility would span an entire tank farm or a smaller group of tanks and would be supported around the perimeter. Information and data used throughout this section to describe this alternative are from the Site Management and Operations contractor (WHC 1995f, i) and the TWRS EIS contractor (Jacobs 1996).

Operations for this alternative would involve preparing the tanks for vitrification, operating the vitrification equipment, and treating the off-gases. At least two vitrification systems would be in operation at all times during the operational phase.

Figure 3.4.3 In Situ Vitrification Alternative

Following remediation, the vitrified waste would be left in place for disposal. A Hanford Barrier would be constructed over each of the tank farms to reduce infiltration of precipitation, penetration by plant roots and burrowing animals, and to prevent inadvertent human intrusion.

3.4.5.2 Process Description

In situ vitrification is a thermal treatment process in which electricity would be used to generate a high-temperature region in the range of 1,450 to 1,600 degrees centigrade (C) (2,600 to 2,900 degrees Fahrenheit [F]). This would be accomplished by placing electrodes in a pattern at the surface of the soil. After the electrodes were energized and a current path established, the soil surrounding the

electrodes would begin to melt. As the process continued, the electrodes would be fed down into the melt and the molten region would spread down and out, melting waste, tank, and soil. The process would be controlled by varying the amount of electricity flowing to the electrodes to maintain the temperature and rate at which the melt progressed. The melt would be continued until an entire tank and its waste contents were vitrified (converted to glass).

As the waste heated to the vitrification temperatures, some of the waste would decompose into gases and be released. The remainder of the waste would be incorporated into the glass that formed during cooling and solidification of the molten material. The gases generated during the operation would be vented from the top of or from around the molten region and collected for treatment before atmospheric release. A Hanford Barrier then would be constructed over each of the tank farms.

This alternative would involve the following major steps:

  • Remove the maximum amount of water practicable from the DST waste by processing through the 242-A Evaporator;
  • Construct the Tank Farm Confinement Facilities;
  • Isolate the tanks electrically by disconnecting all support systems connections such as piping, instrumentation, and ventilation systems;
  • Fill the tanks with sand, which would function as a glass former and eliminate all empty space within the tanks;
  • Place electrodes and supply electrical current to melt waste;
  • Collect and treat the off-gases;
  • Decontaminate and decommission the Tank Farm Confinement Facilities;
  • Grout fill MUSTs and ancillary equipment that is not vitrified; and
  • Construct Hanford Barriers.

Removing liquid from the DSTs by pumping prior to vitrification would provide a more efficient operation and reduce the amount of vapor in the off-gas system. The liquid would be pumped to the 242-A Evaporator for evaporation. The concentrated waste would be returned to the tanks and the evaporator condensate would be treated at the Effluent Treatment Facility and discharged.

The Tank Farm Confinement Facility would be a free-span structure providing confinement to an entire tank farm. The Tank Farm Confinement Facility would consist of two main components: 1) the truss structure that would sit on a concrete foundation running around the perimeter of the tank farm; and 2) the confinement facility that would be suspended from the trusses. This would allow the entire tank farm to be enclosed without putting additional weight loads on the tank domes. The confinement facility would consist of an operating floor with removable panels to provide access to the tanks.

The confinement facility would also provide multi-zone ventilation to collect and treat the off-gases and maintain the operating zones ( Figure 3.4.4).

Before beginning the vitrification operation, each tank would be electrically isolated from all support systems. This would include disconnecting and removing piping, instrumentation wiring, and ventilation systems shared with other tanks. This would prevent potential accidents and damage resulting from stray electrical current. Piping and equipment removed to electrically isolate the tanks would be decontaminated as necessary for onsite burial or placed in the tank and vitrified with the waste.

Because the vitrification process would rely on electrical resistance heating to create the melt zone, two important parameters in the process would be the resistance (which would affect melt temperature) and maintaining a continuous electrical path through the material being heated. All of the tanks have a void

Figure 3.4.4 In Situ Vitrification Arrangement and Features

space between the surface of the waste and the dome of the tank. Those tanks with the least volume of waste have the largest void spaces. These void spaces would be filled with Hanford Site sand to act as a filler and a glass former. This would require a total of 540,000 m3 (714,000 cubic yards [yd3]) of sand compared to 230,000 m3 (304,000 yd3) of waste currently stored in the tanks.

After filling the tanks with sand, the electrodes would be placed at the surface of the existing soil. An estimated 19 electrodes, each approximately 30 cm (12 in.) in diameter, would be used for a standard 23-m (75-ft)-diameter tank. An off-gas hood would be placed over the area to be melted to collect the

off-gases for cooling and treatment. A conductive material such as graphite then would be placed between the electrodes to help start the melt. An electrical potential would be applied to the electrodes starting the melt. As the melt progressed down, the individual electrodes would be fed through the off-gas collection system and down into the melt zone.

Each vitrification system would be configured to melt approximately 225 metric tons (mt) (248 tons) per hour consuming 160 MW, which would be required to vitrify the tank waste and the material between the tanks during a 5-year period. This rate of power consumption is about 14 percent of the output from a 1,100-MW power plant (e.g., Washington Public Power Supply System No. 2 Nuclear Power Plant). The electrical power required to vitrify a tank would be approximately 25,000 MW-hours (about 1 day's output from the Washington Public Power Supply System No. 2 Nuclear Power Plant). Four vitrification units would be built with at least two units in continuous operation.

The off-gas system would collect and treat gases from the melt before releasing them to the atmosphere. The off-gases would contain the reaction products resulting from the thermal destruction of the nitrates, nitrites, organic compounds, and some of the more volatile radionuclides contained in the waste. The off-gases would undergo substantial treatment before being released to the atmosphere. Specific control equipment used in the treatment of the off-gases would quench and cool the off-gases, remove radionuclide particulates, and remove nitrogen oxides and sulfur oxides.

Following vitrification operations, each of the Tank Farm Confinement Facilities would be taken down and decontaminated and decommissioned. The MUSTs and ancillary equipment located outside of the vitrified area (limited by the Tank Farm Confinement Facilities) would be filled with grout. Decontamination and decommissioning of a Tank Farm Confinement Facility would require a substantial level of effort because of the amount of surface area that would be contaminated during the vitrification process.

A Hanford Barrier would be constructed over each of the tank farms as well as those MUSTs that fall outside of the tank farm boundaries.

3.4.5.3 Construction

The main construction activity for this alternative would be building 18 Tank Farm Confinement Facilities to cover all of the tanks. The confinement facilities would be constructed in one of five configurations. The smallest configuration would cover a 2 by 2 tank farm (i.e., a tank farm that is two tanks wide by two tanks deep) and the largest would cover a 4 by 5 tank farm. The smaller Tank Farm Confinement Facility would be used for tank farms with two to four tanks.

Systems that would be constructed for the In Situ Vitrification alternative include the following:

  • Tank Farm Confinement Facilities to provide confinement and ventilation control, (18 facilities total);
  • Off-gas treatment systems to collect, treat, and filter process off-gases before discharge;
  • Handling system to fill tank domes with sand by transporting sand from stock pile and uniformly filling the tank dome spaces;
  • Electrical power distribution system to supply high-voltage power to the vitrification system;
  • New electrical substation to connect the power distribution system to the existing electrical grid;
  • Approximately 8 kilometers (km) (5 miles [mi]) of 115-kilovolt (kV) transmission line; and
  • Temporary 115-kV lines from transmission lines to individual tank farms in the 200 Areas.

3.4.5.4 Operation

Operations for this alternative would take place during an 11-year period between 2005 and 2016. This would include 3 years to start up the project, 3 years to shut down the project, and an additional 5 years until the vitrification process would take place. Activities that would take place during the operations phase include the following:

  • Remove and treat DST liquid in the 242-A Evaporator (treated slurry would be returned to tank);
  • Disconnect and remove piping, instrumentation, and ventilation system connections;
  • Fill tank void spaces with sand to provide an uninterrupted electrical path;
  • Install electrodes in the electrode feed system that would lower the electrodes into the molten region as it progressed down consuming the tank and waste;
  • Vitrify waste by starting the melt and controlling the applied power;
  • Operate an off-gas treatment system to collect, treat, and filter process off-gases before discharge; and
  • Treat liquid condensed in the off-gas system by evaporating to reduce the volume followed by low-temperature treatment or transporting to the Effluent Treatment Facility;

3.4.5.5 Post Remediation

When in situ vitrification was complete, the vitrified waste and the tank farms would be closed, and all facilities constructed for vitrifying the waste would be decontaminated and decommissioned. Activities that would take place include grout filling tank farm ancillary equipment (e.g., pump pits, diversion boxes, valve boxes) that would not be vitrified; constructing a Hanford Barrier over each tank farm; and decontaminating and decommissioning Tank Farm Confinement Facilities and equipment.

3.4.5.6 Schedule, Sequence, Cost

The schedule of major activities associated with this alternative is presented in Table 3.4.8.

The estimated cost for this alternative is shown in Table 3.4.9.

Table 3.4.8 Schedule - In Situ Vitrification Alternative

Table 3.4.9 Cost - In Situ Vitrification Alternative 1

3.4.5.7 Implementability

Implementability of a remedial alternative will be a function of two factors: the history of the demonstrated performance of a technology; and the ability to construct and operate the technology given the existing conditions at the Site. The primary issues applicable to the implementability of the In Situ Vitrification alternative include the following.

  • This alternative is more conceptual in design and development than the ex situ alternatives and thus has a higher degree of uncertainty associated with the supporting data.
  • In situ vitrification previously has not been performed and may not work on the scale described for this alternative. Substantial research, development, and demonstration activities would be required. Current commercial experience is limited to melting areas 15 m (49 ft) in diameter by 6 m (20 ft) deep, while this alternative assumes an entire tank that is 23 m (75 ft) in diameter by 18 m (60 ft) deep can be vitrified. Concerns with implementing this alternative are not as great for small tanks such as MUSTs or larger tanks with small volumes of waste. Multiple melts using smaller in situ vitrification systems could be used to vitrify larger diameter tanks .
  • The established safety envelope for much of the waste as it is stored in the tanks is dependent on the waste being wet. The vitrification process would dry out the waste before it was heated to melting temperatures and thereby raise the temperature of the waste and create the potential for initiating an uncontrolled reaction. This issue would require further analysis.
  • The Tank Farm Confinement Facility design is conceptual, and further development would be required for it to comply with current DOE facility design requirements.
  • The Tank Farm Confinement Facility could be difficult to construct because of the atypical nature of the design and restrictions associated with working in and around the tank farms. Smaller tank farm confinement facilities in a portable or moveable design could be used to replace the larger tank farm confinement facilities.
  • Inspection of the final waste form to confirm that all of the waste is stabilized and the waste form is acceptable for disposal would be difficult to perform. Reprocessing waste that fails to meet disposal criteria would involve remelting sections of the vitrified waste form, which could affect the operating schedule.
  • Decontamination and decommissioning of the Tank Farm Confinement facilities would be difficult because of the size of the facilities and the amount of surface area that would be contaminated.

Additional details on the implementability of this alternative are contained in Volume Two, Appendix B. This alternative could meet the RCRA land disposal requirements if hazardous waste is adequately treated during vitrification. Near-surface disposal of HLW would not meet DOE policy to dispose of readily retrievable HLW in a potential geologic repository (Section 6.2).

3.4.6 Ex Situ Intermediate Separations Alternative

3.4.6.1 Overview

Under the Ex Situ Intermediate Separations alternative, as much of the tank waste as practicable would be retrieved from each tank. This is assumed to be a minimum of 99 percent of the waste volume in each tank. The recovered waste stream then would be separated into HLW and LAW streams for vitrification in separate facilities (Figure 3.4.5 ). Separating the waste streams into HLW and LAW fractions would allow for processing and disposal methods best suited to the waste types and requirements.

The HLW stream would be vitrified and placed in canisters for disposal at the potential geologic repository. The LAW stream would be vitrified and quenched into glass cullet and placed into onsite near-surface vaults for retrievable disposal. Retrievable disposal means that the design of the disposal facility would be for permanent disposal, but the waste could be retrieved from the disposal facility within a certain amount of time (assumed to be approximately 50 years) if a different disposal method was determined to be necessary.

Information used throughout this section is from the Site Management and Operations contractor (WHC 1995 i, j, n) and the TWRS EIS contractor (Jacobs 1996).

Two vitrification facilities, one for HLW and one for LAW, as well as the shared support facilities, would be constructed. The HLW facility would be designed to produce 20 mt (22 tons) of HLW glass per day. The LAW facility would produce 200 mt (220 tons) of LAW glass cullet per day. The facilities are assumed to be located on the representative site in the 200 East Area, as shown in Figure 3.4.6. The vitrification facilities would be designed to treat all of the tank waste during a 21 -year operating period.

The following major operations would be implemented to treat waste under this alternative.

  • Retrieve the waste.
  • Pretreat the waste by sludge washing and enhanced sludge washing followed by separation of the liquid and solids.
  • Remove cesium from the liquid waste stream and transfer cesium to the HLW vitrification stream.
  • Transfer liquid and dissolved solids to the LAW vitrification facility.
  • Transfer solids (as a slurry) to the HLW vitrification facility.
  • Vitrify both HLW and LAW.
  • Pour the molten HLW into canisters.
  • Package the canisters into Hanford Multi-Purpose Canisters for interim storage and shipment.
  • Place the vitrified LAW in disposal containers.
  • Place the LAW disposal containers in onsite near-surface disposal vaults.
  • Ship the HLW canisters to the potential geologic repository.

Following the treatment phase, the processing facilities and storage tanks would be decontaminated and decommissioned. Contaminated materials and equipment from the processing facilities would be disposed of onsite in the low-level waste burial grounds. Noncontaminated materials and equipment from the processing facility would be entombed in place. Closure activities would be performed on the LAW disposal vaults and tank farms.

Figure 3.4.5 Ex Situ Intermediate Separations Alternative

Figure 3.4.6 Ex Situ Intermediate Separations Site Plan

3.4.6.2 Process Description

The first step in waste processing would be to recover and transfer waste from the storage tanks to the separations facility. The waste recovery function would retrieve and blend waste to provide, as close as possible, an average or blended feed stream that would be batch transferred to the separations facility. The Tri-Party Agreement requires that the retrieval function remove waste to the extent that SST waste residues meet specific volume requirements based on tank type, or that as much waste is removed as technically possible, whichever action results in the least residual volume (Ecology et al. 1994).

Two methods for removing waste from the SSTs would be hydraulic sluicing and robotic arm-based retrieval systems. Hydraulic sluicing would use pressurized water and recycled tank liquid sprayed from a nozzle to dissolve, dislodge, and suspend the waste into a slurry, which has a thick, soup-like consistency (Figure 3.4.7). The sluicing nozzles would be rotated and angled to direct the slurry to a pump for removal from the tank. Remote cameras installed with the retrieval system would aid in the waste recovery operation. Hydraulic sluicing has been performed in the past to recover tank waste and is assumed to be capable of recovering the majority of SST waste.

For those cases where hydraulic sluicing could not achieve 99 percent recovery, where sluicing would not be deployed because of a known leak, or where sluicing was to be discontinued because of tank leakage, robotic arm-based recovery systems would be used for waste recovery ( Figure 3.4.8 ). Robotic arm-based systems would allow using various engineered components on the end of a long-reach arm to minimize the addition of sluicing water to the tank or to provide remote cut up and removal of in-tank equipment. Recovered equipment, including hardware discarded in the tanks, would be containerized for onsite burial. A confinement structure would be needed over the enlarged tank access required by the arm-based systems.

Slurry pumping would be used for retrieving the waste from the DSTs (Figure 3.4.9 ) using mixer pumps to break up and suspend solids into a slurry. The current mixer pump design takes liquid from the upper liquid level and discharges it through nozzles approximately 0.6 m (2 ft) above the bottom of the tank. This directs the tank liquid at the solids that have settled in the bottom of the tank. Future DST mixer pumps would function in a similar manner. Future mixer pumps would be designed to accommodate the decreasing waste levels encountered during retrieval. The slurry would then be pumped out of the tank for transfer to the separations facility. Between two and four mixer pumps would be used in each DST. The retrieval for DSTs is assumed to be at least 99 percent.

The waste recovery system would consist of four waste transfer annexes and a waste staging and sampling facility. Each system would circulate sluicing liquid to the tanks as well as receive and accumulate slurry for batch transfer to the central separations facility located in the 200 East Area. The waste in the 200 West Area would be accumulated in the waste staging and sampling facility for cross-site transfer from the 200 West Area to the 200 East Area. A typical piping layout and location of a transfer annex are shown in Figure 3.4.10. The transfer annexes would be centrally located near groups of tank farms to expedite retrieval operations.

Figure 3.4.7 Sluicing Arrangement for Single-Shell Tank Waste Retrieval

Figure 3.4.8 Robotic Arm-Based Arrangement for Single-Shell Tank Waste Retrieval

Figure 3.4.9 Double-Shell Tank Mixer Pump Retrieval Arrangement

As a part of retrieval, piping would be installed to supply sluicing liquid to each tank and to transfer slurried waste from the tanks to the transfer annex or waste staging and sampling facility. The piping run from the transfer annexes or waste staging and sampling facility to the individual tanks would consist of three lines (i.e., supply, return, and spare). In the 200 West Area, waste transfer lines (one line and a spare) also would be installed to connect the waste transfer annexes to the waste staging and sampling facility. In the 200 East Area, transfer lines would be installed to connect the waste transfer annexes directly to the treatment facility. Waste retrieval and transfer lines all would be double-wall (encased) piping located on the ground inside concrete shielding enclosures. Locating these shielded transfer lines on the ground would facilitate removal following waste retrieval operations.

The waste retrieved in the 200 West Area would be collected in the waste staging and sampling facility, where it would be sent to the replacement cross-site transfer system for transfer to the treatment facilities located in the 200 East Area.

The waste transfer lines planned for the waste retrieval and transfer system would be used in conjunction with other waste transfer systems, such as the replacement cross-site transfer system and the waste transfer system upgrades, to meet the requirements for waste retrieval and transfer.

Waste contained in MUSTs would be retrieved using methods similar to those described for SST and DST waste retrieval. Waste recovered from MUSTs would be transported to the waste transfer system or directly to the treatment facilities in containers or a specialized truck (LR-56[H]) designed for the transport of nuclear waste (see discussion on LR-56[H] truck in Volume Two, Appendix B).

Figure 3.4.10 Slurry Transfer Piping and Facilities Layout

The next step in the process would be to separate the waste into LAW and HLW streams. The purpose of separations would be to split the waste volume into a small-volume HLW fraction and a larger-volume fraction that would be classified as LAW (Figure 3.4.11 ). This would reduce the volume of HLW requiring costly disposal at the potential geologic repository. The other goal of separations would be to limit the generation of additional waste during the separations processes.

The separations process would begin with a sludge wash followed by an enhanced sludge wash to remove the soluble components of the waste stream. The washing of solids and liquid-solid separation could be performed out-of-tank in a processing facility or in tank. For this alternative, sludge washing in the DSTs has been included as a representative process for analysis in the EIS. Future evaluation could result in the selection of other methods or combinations of methods, such as cross-flow filters or centrifuges. Most HLW constituents, which are made up of long-life and high-activity isotopes, are found as solid waste in the tanks and are intermixed with other nonradioactive solid waste. Washing the waste would involve adding water or sodium hydroxide solutions to dissolve a portion of the LAW solids and then separating the liquid and solids.

For SSTs, the dissolution of the waste would begin during retrieval when the waste is sluiced out of the SSTs and transferred. The second phase would take place in DSTs and the enhanced wash would dissolve some of the nonradioactive elements present in the solid waste and further reduce the volume of HLW. The third phase of separations would take place in the separations facility, which would be attached to the LAW vitrification facility. The third phase in the separations process would be to remove the cesium present in the liquid stream by ion exchange and feed it into the HLW stream. Cesium-137 is a high-activity isotope that is highly soluble and removing it from the liquid stream would allow the final LAW waste form to meet the assumed onsite LAW disposal criteria. Other radioisotopes, such as technetium, could also be removed during separations.

On receiving the waste from the separations operations, the waste would be sent to lag storage tanks within the vitrification facilities where it would be characterized before entering the melter feed section in either the HLW or LAW facility. In this area, the waste would be sampled, evaporated to remove excess water, and provided as a concentrated liquid or slurry feed stream to the melter.

The LAW vitrification facility and its support facilities would be designed to produce 200 mt (220 tons) of vitrified glass per day. This capacity would be provided by two melters operating in parallel, each making 100 mt (110 tons) of glass per day.

The glass product produced by each melter would be a combination of two separate material feed streams, the waste stream, and the glass formers. The energy source providing the heat to the melter would be separate kerosene and oxygen streams supplied directly to the melter. Fuel-fired melters have been included as a representative configuration for analysis in the EIS. Future evaluation may result in selection of another melter configuration. To make suitable glass with acceptable properties for waste immobilization, it has been determined that the LAW glass produced by this alternative would be limited to 15 weight percent sodium oxide in the glass. This means that glass formers would be added to the melter feed to maintain the required sodium oxide loading. Glass formers, primarily silica or sand and boron oxide, are similar to the components used to make commercial glass.

Figure 3.4.11 Ex Situ Intermediate Separations LW/LAW Separations Process Flow Diagram

The molten glass produced in the melter would flow into a water bath tank and be quenched into gravel-sized pieces of glass (referred to as cullet) and placed into containers approximately 1.8 m long by 1.2 m wide by 1.2 m high (6 ft long by 4 ft wide by 4 ft high) for onsite disposal. The engineering data supporting this alternative molten were based on a process that would blend the LAW glass cullet with a matrix material that would surround the glass cullet when placed into the disposal container. Disposing of LAW as glass cullet encapsulated by a matrix material has been included as a bounding condition for transportation and resource analysis in the EIS. Future evaluation of matrix materials and disposal forms may result in selecting other glass forms or eliminating the requirements for matrix materials. The potential benefits of a matrix material and glass cullet combination as a disposal waste form are reduced contaminant release rates and migration rates out of the disposal system. Additional details on matrix materials for LAW glass cullet are presented in Volume Two, Appendix B.

The HLW vitrification facility would be designed to produce 20 mt (22 tons) of HLW glass per day. This would be accomplished by using one electrically heated (joule-heated) melter making vitrified glass at 20 weight percent waste oxide. Following vitrification, the molten glass would be poured directly into a stainless-steel canister. The canisters then would be welded closed, the outside surfaces decontaminated, and the canisters placed into Hanford Multi-Purpose Canisters and transported to onsite storage pads for interim storage. Concrete shielding casks would be placed over the Hanford Multi-Purpose Canisters during interim storage.

Vitrifying waste would generate a large off-gas stream (gaseous air stream containing combustion gases) the would require mitigation measures to minimize air emissions. The off-gas treatment equipment would capture and partially recycle contaminants in the off-gas stream back into the melter feed stream.

3.4.6.3 Construction

New facilities that would be constructed for this alternative would include a HLW vitrification facility, a combined separations and LAW vitrification facility, a LAW disposal facility, an interim HLW storage facility, and multiple support facilities. When completed, the facilities would be in place to remove the waste from the tanks and provide the processing required to produce vitrified HLW for disposal at the potential geologic repository and vitrified LAW for disposal in onsite retrievable disposal vaults. Vitrification support facilities would support functions such as waste retrieval and transfer, utilities, raw material, storage and supply, and operations control. Several facilities and systems would be constructed for the Ex Situ Intermediate Separations alternative.

A retrieval and transfer system would be constructed to provide the facilities and systems to retrieve, blend, and transfer waste to the separations facility, which would include the following:

  • Waste transfer annexes that would support sluicing and slurry transfer (two in the 200 East Area and two in the 200 West Area);
  • Waste staging and sampling facility in the 200 West Area that would collect and blend batches of waste for cross-site transfer to the separations facility in the 200 East Area;
  • 24 SST sluicing systems;
  • 24 SST sluicing systems;
  • 24 SST sluicing systems;
  • Mixer pumps in DSTs (two to four mixer pumps per tank); and
  • MUSTs retrieval and transfer system (retrieval similar to SSTs except that transfer would be by truck or container).

Support facilities would be constructed to provide utilities, resources, and personnel support to the vitrification facility, which would include the following:

  • Mechanical utilities building (shared utilities);
  • Cooling tower that would provide process water cooling;
  • Cold chemical facilities that would provide bulk process chemical storage and chemical makeup;
  • Warehouses and other support facilities; Operations control and operations support buildings that would provide administrative offices and centralized control rooms; and
  • Electrical substation and 2.5 km (1.6 mi) of high-voltage electrical line.

A separation and LAW vitrification facility would be constructed that would separate the waste into HLW and LAW fractions and vitrify the LAW, which would include the following:

  • Sludge-washing systems (the first step in the HLW and LAW separation process);
  • Waste storage and sampling facility used for waste receipt and lag storage;
  • Cesium ion-exchange system that would remove cesium from the liquid stream sent to the LAW vitrification facility;
  • Melter feed system that would support the vitrification melter and include an evaporator, waste feed system, glass former handling systems, and fuel and oxygen supply systems;
  • Two 100-mt/day (110-ton/day) combustion LAW melters;
  • Cullet quench and handling system that would cool and fracture the molten glass into uniform-sized pieces and place them into containers;
  • Cullet transport system that would transfer the containers of LAW cullet to the disposal vaults;
  • Off-gas system that would collect, treat, and filter process off-gases before discharge; and
  • Recycle systems that would recycle contaminants captured in the off-gas system and undersized cullet from the cullet handling system back into the melter feed system.

A LAW disposal facility would be constructed that would provide retrievable disposal of the LAW. This facility would consist of LAW vaults (66 vaults) constructed belowgrade, each with a capacity to hold 5,300 m3 (7,000 yd3) of LAW. These vaults would be constructed throughout operational period.

A HLW vitrification facility would be constructed that would include the systems to support the HLW vitrification melter including centrifuges, an evaporator, glass former handling systems, a waste feed system, and an electrical power supply. This HLW vitrification system would include one 20-mt/day (22-ton/day) joule-heated HLW melter; an off-gas system that would collect, treat, and filter process off-gases before being discharged; a canister handling system that would remotely fill canisters with molten glass, weld on a lid, and decontaminate the outer surface of the canister; and recycle streams that would recycle contaminants captured in the off-gas system back into the melter feed system. A HLW interim storage facility also would be constructed that would consist of concrete storage pads for interim storage of the Hanford Multi-Purpose Canisters.

Hanford Barriers would be constructed for LAW retrievable disposal facility and tank farms. Hanford Barrier construction would occur after completion of LAW vitrification, and barrier construction at the tank farms would take place after waste removal and tank stabilization.

3.4.6.4 Operation

Operations for this alternative would take place in a 21-year period between 2001 and 2022 . These dates would comply with the schedule for tank waste treatment in the Tri-Party Agreement. Several activities would take place during the operations period. Waste retrieval would involve the following:

  • Sluice 110 SSTs. Sluicing is the preferred waste retrieval method and would be employed in as many tanks as possible where there would not be a high potential for leakage or an expected difficulty in waste recovery (engineering estimates were used to identify the number of SSTs that could be sluiced);
  • Robotic arm-based retrieval from 50 SSTs. This recovery method would be employed only for tanks with high leakage potential or difficult waste (11 SSTs would assumed to be subject to both types of retrieval); and
  • Slurry pump DST waste supplemented by sluicing or robotic arm-based retrieval if required.

Retrieval and confinement systems would be moved from tank to tank after completing waste retrieval from a tank. The SST sluicing systems would be moved 4 to 5 times during the 21-year operations time period and SST arm-based systems and confinement structures would be moved 4 times.

Waste would be separated to create separate HLW and LAW streams. This would involve sludge washing and enhanced washing with sodium hydroxide; solid/liquid separations evaporating the liquid stream to concentrate waste; and removing cesium from the LAW feed using ion exchange. The separated cesium-containing liquid stream that would come out of the ion-exchange process would be further evaporated and fed into the HLW stream. Waste would be transferred to the separation facility from the waste staging and sampling facility in the 200 West Area or from the transfer annexes in the 200 East Area.

The LAW vitrification facility would be operated to accomplish the following:

  • Receive and sample waste;
  • Evaporate water from waste and collect evaporator condensate for treatment or reuse for waste retrieval;
  • Operate two combustion melters. Fuel-fired melters have been included as a representative process detail for analysis in the EIS. Future evaluation may result in the selection of another melter configuration;
  • Quench molten glass to make cullet;
  • Size and dry cullet to uniform size for handling; recycle undersize cullet back to melter; and
  • Place cullet into disposal containers.

The LAW containers with vitrified cullet would be transported to nearby LAW retrievable disposal vaults.

The HLW vitrification facility would be operated to accomplish the following:

  • Receive and sample waste;
  • Separate solids and liquid with a centrifuge;
  • Evaporate excess water from liquid waste and collect condensate for treatment;
  • Operate one joule-heated melter with a capacity of 20 mt/day (22 ton/day);
  • Form glass at approximately 20 weight percent waste oxides;
  • Pour glass monoliths in 1.17-m3 (41-ft3) canisters; and
  • Package glass into Hanford Multi-Purpose Canisters, four glass monoliths per canister.

The off-gas treatment system at both HLW and LAW vitrification facilities would be operated to quench and cool off-gas; remove radionuclides and recycle to vitrification process; and destroy nitrogen oxides and recover sulfur from sulfur dioxides.

Liquid effluent from both HLW and LAW vitrification facilities would be treated by transferring liquid effluent to the Effluent Treatment Facility. The liquid effluent would be similar to the 242-A Evaporator condensate liquid that meets current waste acceptance criteria for the Effluent Treatment Facility.

The Hanford Multi-Purpose Canisters containing HLW would be transported to onsite interim storage pads and covered with a shielding casks for long-term storage. The stored canisters would be monitored and maintained through routine surveillance of the 12,200 HLW canisters (3,050 Hanford Multi-Purpose Canisters) pending offsite disposal, and the Hanford Multi-Purpose Canisters would be transported by rail to the potential geologic repository.

3.4.6.5 Post Remediation

To provide a basis for comparison in this EIS, it was assumed that each ex situ alternative would involve the same post-remediation activities. Following remediation, processing facilities would be decontaminated and decommissioned, SSTs and DSTs and ancillary facilities would be filled, and tank farms and LAW disposal vaults would be capped with a Hanford Barrier. Post-remediation activities are discussed in detail in Volume Two, Appendix B. Regulatory compliance aspects of closure are discussed in Section 6.2.

Post-remediation activities would include closing tank farms and decontaminating and decommissioning facilities. Closing tank farms would involve ensuring that the tanks would contain a residual equal to no more than 1 percent of the initial tank inventory and would be stabilized by gravel filling; tank farm structures, such as MUSTs, pump pits, valve boxes, and diversion boxes would be stabilized with grout; and Hanford Barriers would be placed over SSTs, DSTs, and LAW disposal vaults. Facility decontaminating and decommissioning would involve disposing of noncontaminated facilities onsite (entombed in place) and contaminated material and equipment at an onsite low-level waste burial ground.

3.4.6.6 Schedule, Sequence, Cost

A schedule of the major components of the Ex Situ Intermediate Separations alternative is shown in Table 3.4.10. Construction for waste retrieval and transfer would involve installing pipelines between the tanks and the transfer facilities throughout the retrieval period, which explains the difference in the construction periods shown. The cost estimate summary for the Ex Situ Intermediate Separations alternative is shown in Table 3.4.11.

Table 3.4.10 Schedule - Ex Situ Intermediate Separations Alternative

Table 3.4.11 Cost - Ex Situ Intermediate Separations Alternative 1

3.4.6.7 Implementability

Some of the technologies involved in this alternative would be first-of-a-kind and thus do not have a performance history. Performance histories would provide increased confidence in the feasibility of the technology and cost estimates. Other issues associated with implementing this alternative include the following.

  • The waste loading and canister size criteria have not been finalized, and future negotiations could result in different canister sizes and waste loadings. Waste loading in the glass would directly affect the volume of HLW and number of waste packages for disposal.

  • The proposed LAW form is unique and has not been used before.
  • Performance of key processes (e.g., solid/liquid separation) has been assumed in the absence of substantive data.
  • Cost estimates may have a high degree of uncertainty because some of the processes are first-of-a-kind.
  • Retrieval criteria based on recovering 99 percent of the waste volume in each tank are uncertain in that hardened sludge present in some tanks may be difficult to retrieve to the extent required to meet the retrieval criteria.
  • The disposal criteria for LAW have not been determined. When these criteria are decided on, additional separations steps could be required to meet LAW disposal criteria.
  • A performance assessment has not been completed defining the LAW form requirements for storage and disposal at the Hanford Site, and DOE and the Nuclear Regulatory Comission have not yet completed negotiations on what constitutes "incidental waste" for disposal of LAW at the Hanford Site. Additional separations steps therefore may be required to meet LAW disposal criteria.

The design of the HLW vitrification facility would be similar to the vitrification facility built at the DOE Savannah River Site. Following startup of the Savannah River facility, performance data would be available for application to this implementability analysis and enhancement of the alternative design. Other key technology development or demonstration activities identified for the TWRS program include the following:

  • Tank retrieval systems design and testing;
  • Sludge washing evaluation;
  • Solid/liquid separation;
  • Cesium ion-exchange evaluation;
  • HLW melter testing and evaluation; and
  • LAW melter testing and evaluation.

This alternative would meet all applicable regulations for disposal of hazardous, radioactive, or mixed waste assuming that the hazardous waste components are adequately treated during waste processing or vitrification.

3.4.7 Ex Situ No Separations Alternative

3.4.7.1 Overview

Under the Ex Situ No Separations alternative, as much of the tank waste as practicable would be recovered from each tank. This is assumed to be 99 percent of the waste volume in each tank. The recovered waste stream then would be vitrified or calcined and placed into containers for disposal at the potential geologic repository. All of the waste would be HLW and there would be no onsite LAW disposal of tank waste associated with this alternative.

Information and data used in describing the Ex Situ No Separations (Vitrification) alternative are from the Site Management and Operations contractor (WHC 1995c, i, n) and the TWRS EIS contractor (Jacobs 1996). Information and data used in describing the Ex Situ No Separations (Calcination) alternative are from the Site Management and Operations contractor (WHC 1995c) and the TWRS EIS contractor (Jacobs 1996).

One processing facility, as well as the support facilities, would be constructed. The HLW vitrification facility would be designed to produce 200 mt (220 tons) of HLW glass per day. The HLW calcination facility would produce 92 mt (100 tons) of HLW calcined briquettes per day. The calcination process would produce about 70 percent less HLW for disposal to the potential geologic repository than the vitrification process. The facilities are assumed to be located on the representative site in the 200 East Area similar to those shown for Ex Situ Intermediate Separations alternative (Figure 3.4. 6 ). The following major operations are associated with waste treatment under this alternative:

  • Retrieve waste;
  • Vitrify or calcine the HLW;
  • Place vitrified or calcined HLW in canisters;
  • Place the canisters into Hanford Multi-Purpose Canisters for interim storage and shipment; and
  • Ship the Hanford Multi-Purpose Canisters by rail to the potential geologic repository.

Following the treatment phase, the processing facilities and storage tanks would be decontaminated and decommissioned. Contaminated materials and equipment from the processing facilities would be disposed of onsite in the low-level waste burial grounds. Noncontaminated materials and equipment from the processing facility would be entombed in place. Closure activities, including filling the tanks and constructing Hanford Barriers, would be performed at the tank farms.

3.4.7.2 Process Description

The first step in waste processing would be to recover and transfer the waste from the storage tanks to the treatment facility. The waste recovery function would retrieve and blend waste to provide, as close as possible, an average or blended feed stream that would be transferred to the vitrification or calcination facility. A recovery rate of a minimum of 99 percent of the tank contents is a requirement for the retrieval function. The waste retrieval and transfer process for the Ex Situ No Separations alternative would be identical (without radioisotopic separation) to the process for the Ex Situ Intermediate Separations alternative (Section 3.4.6.2).

The waste received from the retrieval operations would be sampled, evaporated to remove excess water, and provided as a slurry feed stream to the melter or calciner in the HLW facility.

Vitrification Process

The HLW vitrification facility and its support facilities would be designed to produce 200 mt (220 tons) of vitrified glass per day. This capacity would be provided by two melters operating in parallel, each making 100 mt (110 tons) of glass per day.

The glass product produced by each melter would be a combination of two separate material feed streams, the waste stream and the glass formers. The energy source providing the heat to the melter would be separate kerosene and oxygen streams supplied directly to the melter. Fuel-fired melters have been included as a representative configuration for analysis in the EIS. Future evaluation could result in selection of another melter configuration. To make suitable glass with acceptable properties for waste immobilization, the HLW glass produced by this alternative would be limited to 20 weight percent sodium oxide in the glass. The glass formers, primarily silica or sand and calcium oxide, would be added to make a soda-lime glass and maintain the required sodium oxide loading.

The molten glass produced in the melter would flow into a water bath quench tank producing gravel-like glass cullet. The cullet would be screened for proper size, loaded into 10-m3 (360-ft3) stainless-steel canisters, and then placed into Hanford Multi-Purpose Canisters for interim storage and transport to the potential geologic repository.

Vitrifying waste would generate a large off-gas stream requiring mitigation measures to minimize air emissions. Treatment equipment would capture and recycle contaminants from the off-gas systems back into the melter feed stream.

Calcination Process

Calcination would heat precipitates or residues to a temperature high enough to break down chemical compounds such as hydroxides or nitrates. It differs from vitrification in that calcination temperatures would not necessarily cause the reacting materials to melt and form a glass. The final form of the calcined waste would be a dry powder material that would be hot processed in a roll-type compactor machine to produce small pellets or briquettes of high bulk density that would be loaded into 10-m3 (360-ft3) canisters, seal welded, and then placed into Hanford Multi-Purpose Canisters for interim storage and transport to the potential geologic repository.

The HLW calcination facility and its support facilities would be designed to produce 92 mt (100 tons) of calcined waste per day. This capacity would be provided by two spray calciners operating in parallel, each making 46 mt (50 tons) of calcined waste product per day. The same quantity of tank waste would be fed to the calciners as fed to the glass melters each day.

The prepared waste feed stream would be blended with sugar and pumped to the feed nozzles of a spray calciner, which would be externally heated by fuel-fired burners. The sugar supplied to the feed would act as a reducing agent to decompose the nitrate and nitrite in the waste to nitrogen oxides, carbon oxides, and water vapor. The atomized waste droplets would be dried through evaporation, and the remaining solids would react to release the gaseous decomposition products. The solid particles then would be collected in a tank and held at a temperature to allow further reaction. The product would be discharged to a roll-type compactor machine to produce small briquettes. The waste briquettes would be screened to remove the fines, if any, and then would be transported to the HLW cyclone bin by an air-cooled conveyor. The calcined product next would be transferred to a canister filling operation, where it would be placed in 10-m3 (360-ft3) canisters, identical to the canisters described for the Vitrification Process. The canisters would be welded shut, decontaminated, and placed in Hanford Multi-Purpose Canisters for interim storage and subsequent transport to the potential geologic repository.

Calcining waste would generate a large off-gas stream that would require mitigation measures to minimize air emissions. Treatment equipment would capture and recycle contaminants from the off-gas stream back into the calciner feed stream, if required. The calcined fines from the dust collection screen and hot gas filtering would be returned to the waste product tank as feed to the roll-type compactor machine.

3.4.7.3 Construction

New facilities that would be constructed for this alternative would include a HLW processing facility and multiple support facilities. A retrieval and transfer system identical to the system described for the Ex Situ Intermediate Separations alternatives (Section 3.4.6) would be constructed. When completed, the facilities would be in place to remove the waste from the tanks and provide the processing required to produce vitrified or calcined HLW. Support facilities similar to those described for the Ex Situ Intermediate Separations alternative (Section 3.4.6) would be constructed. Support facilities would supply waste retrieval and transfer, utilities, raw material, and operations control to the HLW processing facility.

A HLW processing facility would be constructed to include the systems to support the HLW vitrification melter including an evaporator, glass former handling system, and fuel and oxygen supply system. This HLW processing facility would include two combustion melters operating in parallel; a treated waste handling system that would remotely place the vitrified waste into canisters; and an off-gas system that would collect, treat, and filter process off-gases before being discharged.

A HLW processing facility would be constructed to include the systems to support the HLW calciner, including an evaporator, sugar addition system (dry bulk), fuel, oxygen, and hot gas filter system. This HLW processing facility would include two radiant heat spray calciners operating in parallel; a treated waste handling system that would remotely place the calcined waste into canisters; a roll-type compactor to densify the calcined product into briquettes; and an off-gas system that would collect, treat, and filter process off-gases before being discharged.

A HLW interim storage facility would be constructed consisting of concrete storage pads for interim HLW canister storage. In addition, Hanford Barriers for the tank farms would be installed after waste removal and tank stabilization.

3.4.7.4 Operation

Operations for this alternative would take place during a 17-year period between 2003 and 2020. Operations are the actions required to treat, store, and transport the waste. Several major activities would take place during the operations period. Waste would be retrieved and transferred in the same manner described for the Ex Situ Intermediate Separations alternatives (Section 3.4.6).

  • A HLW vitrification facility (vitrification option) would be operated to accomplish the following.
  • Receive and sample waste;
  • Evaporate excess water from waste;
  • Collect evaporator condensate for treatment;
  • Operate two combustion melters;
  • Form glass at approximately 20 weight percent sodium oxide;
  • Quench molten glass to make cullet;
  • Size and dry cullet to uniform size for handling, recycle undersize cullet back to melter; and
  • Place cullet into 10-m3 (360-ft3 ) canisters and overpack canisters into Hanford Multi-Purpose Canisters for storage and handling.

A HLW calcination facility (calcination option) would be operated to accomplish the following.

  • Receive and sample waste;
  • Evaporate water from waste;
  • Collect evaporator condensate for treatment;
  • Operate spray calciners; and
  • Place calcined product into 10-m3 (360-ft3) canisters and overpack canisters into Hanford Multi-Purpose Canisters for storage and handling.

An off-gas treatment system at the HLW facilities would be operated to quench and cool off-gas; remove radionuclides and recycle to process; and destroy nitrogen oxides and recover sulfur from sulfur dioxides.

Liquid effluent from HLW facilities would be treated by transferring liquid effluent to a retention basin for later transfer to the Effluent Treatment Facility. The HLW multi-purpose canisters would be transported to onsite interim storage pads. Stored canisters would be monitored and maintained through routine surveillance of the 29,100 HLW canisters of vitrified glass or 10,300 HLW canisters of calcined waste in interim storage pending offsite disposal. Hanford Multi-Purpose Canisters would be transported to the potential geologic repository.

3.4.7.5 Post Remediation

Following waste treatment operations, the tank farms would be closed and processing facilities decontaminated and decommissioned. Closing tank farms would involve ensuring that tanks contained a residual less than or equal to approximately 1 percent of the initial tank inventory; stabilizing tanks by gravel filling; stabilizing tank farm structures such as MUSTs, pump pits, valve boxes, and diversion boxes would be with grout or gravel; and placing Hanford Barriers over SSTs and DSTs.

Facility decontaminating and decommissioning activities would involve disposal of noncontaminated facilities onsite (entombed in place), and disposal of contaminated material and equipment at the onsite low-level waste burial ground.

3.4.7.6 Schedule, Sequence, Cost

A schedule of the major components of the Ex Situ No Separations alternative is shown in Table 3.4.12. Construction for waste retrieval and transfer would involve installing pipelines between the tanks and the transfer facilities throughout the retrieval period, which explains the difference in the construction periods shown. The cost estimate summary for the Ex Situ No Separations (Vitrification) alternative is shown in Table 3.4.13. The cost estimate summary for the Ex Situ No Separations (Calcination) alternative is shown in Table 3.4.14.

Table 3.4.12 Schedule Ex Situ No Separations (Vitrification or Calcination) Alternative

Table 3.4.13 Cost - Ex Situ No Separations (Vitrification) Alternative 1

3.4.7.7 Implementability

Some technologies involved in this alternative would be first-of-a-kind and thus do not have a performance history. Performance histories would provide increased confidence in the feasibility of technology and cost estimates.

Table 3.4.14 Cost - Ex Situ No Separations (Calcination) Alternative 1

Other issues would be associated with implementing this alternative. First, the vitrification option would have the same uncertainties as those listed for the Ex Situ Intermediate Separations alternative (Section 3.4.6). In addition, this alternative would result in a large volume of HLW. Second, calcination using sugar as a reducing agent on Hanford Site tank waste has had limited laboratory testing, and the proposed facilities, such as off-gas treatment, are conceptual. Calcination as a unit operation has been in use for many years on an industrial scale. The processing steps described for this alternative have been based on experience and engineering judgement. Third, the largest cost item for the Ex Situ No Separations (Vitrification) alternative would be the repository fee associated with disposal of the large volume of HLW.

This alternative would meet all applicable regulations for disposal of hazardous, radioactive, or mixed waste, assuming that the hazardous waste components were adequately treated during waste processing and vitrification or calcining. However, neither of the HLW forms (soda-lime glass and calcine) meet the current standard waste form (borosilicate glass) specified in the waste acceptance requirements for the potential geologic repository. The glass cullet waste form assumed for vitrification, with its high surface area to volume ratio, may not be acceptable for disposal at the potential geologic repository. The compacted powder calcine also would not meet the waste acceptance requirement for immobilization of particulates. In addition, the number of canisters of HLW produced under this alternative would greatly exceed the defense HLW limit of the first potential geologic repository (Volume One, Section 6.2).

3.4.8 Ex Situ Extensive Separations Alternative

3.4.8.1 Overview

The Ex Situ Extensive Separations alternative would be similar to the Ex Situ Intermediate Separations alternative except that multiple complex chemical separations processes would be performed to separate the HLW components from the recovered tank waste. These separations processes would concentrate and provide a smaller volume of HLW for disposal at the potential geologic repository, while at the same time provide a LAW that contained lower concentrations of radioactive contaminants than the Ex Situ Intermediate Separations alternative. Information and data used in describing the Ex Situ Extensive Separations alternative are from the Site Management and O perations contractor (WHC 1995e, i, n) and the TWRS EIS contractor (Jacobs 1996).

The Ex Situ Extensive Separations alternative would be similar to the Ex Situ Intermediate Separations alternative in that the waste recovered from the SSTs, DSTs, and MUSTs would be separated into HLW and LAW streams. The HLW would be vitrified and placed into canisters. The LAW would be vitrified and placed into onsite near-surface vaults for retrievable disposal.

3.4.8.2 Process Description

The first step in waste processing would be to recover and transfer the waste from the storage tanks to the separations facility. The waste recovery function would retrieve and blend waste to provide, as close as possible, an average or blended feed stream that would be transferred to the combined separations and HLW vitrification facility. A minimum recovery rate of 99 percent of the tank contents is a requirement for retrieval. The waste retrieval and transfer process for the Extensive Separations alternative would be identical to the process for the Ex Situ Intermediate Separations alternative (Section 3.4.6).

The term separations describes the process of separating the waste stream into HLW and LAW streams. Separations would split the waste volume into a smaller HLW fraction and a larger LAW fraction. This would reduce the volume of HLW requiring costly disposal at the potential geologic repository. The Ex Situ Extensive Separations alternative would include multiple processing steps for separating the tank waste, including the following.

  • Cross-flow filters and centrifuges would be used to perform liquid-solid separations.
  • Caustic leaching would be used to decrease the high-level solids fraction followed by additional sludge washing and liquid/solids separation.
  • Acid dissolution would be used to dissolve the HLW solids.
  • Solvent extracting and ion exchanging of acidic solutions would be used to concentrate HLW radionuclides.
  • Ion exchange would be used to remove cesium, strontium, and technetium from the alkaline LAW stream.
  • Recycling water, nitric acid, and sodium hydroxide would be used to reduce LAW volumes.

Following receipt of waste from the separations operations, the waste would enter the melter feed section in either the HLW or LAW facility. In this area of each facility, the waste would be sampled, evaporated to remove the excess water, and provided as a slurry feed stream to the melter.

The LAW vitrification facility and its support facilities would be designed to produce 200 mt (220 tons) of vitrified glass per day. This capacity would be provided by two combustion melters operating in parallel, each making 100 mt (110 tons) of glass per day. Fuel-fired melters have been included as a bounding condition for analysis in the EIS. Future evaluation may result in the selection of another melter configuration.

The glass product produced by each melter would be a combination of two separate material feed streams, the waste stream, and the glass formers. The energy source providing the heat to the melter would be separate kerosene and oxygen streams supplied directly to the melter. To make suitable glass with acceptable properties for waste immobilization, it has been determined that the LAW glass produced by this alternative would contain approximately 15 weight percent sodium oxide. Glass formers (primarily silica or sand and boron oxide), would be added to the melter feed to maintain the required oxide loading.

The molten glass produced in the melter would flow into a water bath tank and be quenched into gravel-like cullet, placed into large disposal containers, and transported to onsite near-surface vaults for disposal. The engineering data supporting this alternative were based on a process that would blend the LAW glass cullet with a matrix material before it was placed into the disposal containers. Disposing of LAW as glass cullet in a matrix material has been included as a bounding condition for analysis in the EIS. Future evaluation of matrix materials and disposal forms could result in selecting other glass forms, alternate matrix materials, or disposal without a matrix material.

The HLW vitrification facility would be designed to produce 1 mt (1.1 tons) of HLW glass per day. This would be accomplished using one electrically heated (joule-heated) melter making a vitrified glass containing approximately 20 weight percent waste oxides. Following vitrification, the molten glass would be poured directly into stainless-steel canisters. The canisters then would be welded shut, the outside surfaces decontaminated, and they would be placed into Hanford Multi-Purpose Canisters.

The sealed units would be transported to onsite interim storage pads where they would be covered with concrete shielding casks pending future transport to the potential geologic repository.

Vitrifying waste would generate a large off-gas stream requiring mitigation measures to minimize air emissions. Treatment equipment would capture and recycle contaminants from the off-gas stream back into the melter feed stream.

3.4.8.3 Construction

New facilities that would be constructed for this alternative would include a combined HLW vitrification and separations facility, a LAW vitrification facility, and multiple support facilities.

A retrieval and transfer system identical to the system described for the Ex Situ Intermediate Separations alternative (Section 3.4.6) would be constructed. When completed, the facilities would be in place to remove the waste from the tanks and provide the processing required to produce vitrified HLW for disposal at the potential geologic repository and vitrified LAW for disposal in onsite near-surface retrievable disposal vaults. Support facilities similar to those described for the Ex Situ Intermediate Separations alternative (Section 3.4.6) would be constructed. Support facilities would provide support functions to the vitrification facility, such as waste retrieval and transfer, utilities, raw material, and operations control. The facilities are assumed to be located on the representative site in the 200 East Area similar to those shown for the Ex Situ Intermediate Separations alternative (Figure 3.4. 6 ).

A combined separations and HLW vitrification facility would be constructed and include the following:

  • Separations facility that would perform the 15-unit separations processes;
  • Melter feed system, which would provide the melter with an evaporated waste feed stream, and a stream of glass formers;
  • Single 1-mt/day (1.1-ton/day) joule-heated HLW melter;
  • Off-gas system that would collect, treat, and filter process off-gases before release;
  • Canister handling system that would remotely fill canisters with molten glass; and
  • Recycle systems that would recycle contaminants captured in the off-gas system back into the melter feed system.

A LAW vitrification facility would be constructed and include the following:

  • Melter feed system that would include an evaporator, a glass former handling system, and a fuel and oxygen supply system to fire the melter;
  • Two 100-mt/day (110-ton/day) combustion melters;
  • Cullet quench and handling system that would cool and fracture the molten glass into uniform-sized pieces (cullet) and place them in disposal containers;
  • Cullet transport system that would transfer the LAW cullet in disposal containers to the disposal vaults;
  • Off-gas system that would collect, treat, and filter process off-gases before discharge; and
  • Recycle systems that would recycle contaminants captured in the off-gas system and undersized cullet from the cullet handling system back into the melter feed.

A LAW disposal facility would be constructed that would provide for retrievable disposal of the LAW. Vaults would be constructed throughout the operational period (66 vaults ), and vaults would be belowgrade with a capacity of 5,300 m3 (7,000 yd3 ) each.

A HLW interim storage facility would be constructed that would consist of concrete storage pads for interim storage of the Hanford Multi-Purpose Canisters.

Hanford Barriers for the LAW disposal facility and tank farms would be installed. Barrier construction for disposal vaults would commence after completion of LAW vitrification, and barrier construction for tank farms would take place after completion of waste removal and tank stabilization.

3.4.8.4 Operation

Operations for this alternative would take place in a 20-year period between the years 2003 and 2023. Several major activities would take place during the operations period. Waste would be retrieved in the same manner described for the Ex Situ Intermediate Separations alternative (Section 3.4.6). Waste would be separated as follows into HLW and LAW streams:

  • Sludge wash to remove water-soluble fractions;
  • Caustic leach to decrease the high-level solids fraction;
  • Acid dissolution to dissolve HLW solids;
  • Solvent extraction and ion exchange of acidic solutions;
  • Ion exchange of alkaline solutions; and
  • Recycling to reduce LAW volumes.

The LAW vitrification facility would be operated to accomplish the following.

  • Receive and sample waste;
  • Evaporate excess water from waste;
  • Collect evaporator condensate for treatment;
  • Operate two combustion melters (feed streams of oxygen, kerosene, waste, and glass formers);
  • Form glass at approximately 15 weight percent sodium oxide;
  • Quench molten glass to make cullet; and
  • Size and dry cullet to uniform size for handling, and recycle undersize cullet back to melter.

Vitrified cullet would be placed into disposal containers and transported to nearby LAW disposal vaults.

The HLW vitrification facility would be operated to accomplish the following.

  • Receive and sample waste;
  • Evaporate water from waste;
  • Collect evaporator condensate for treatment;
  • Operate one joule-heated melter
  • Form glass at approximately 20 weight percent waste oxides;
  • Pour glass monoliths 0.6 m (2 ft) in diameter by 4.5 m (15 ft) long; and
  • Overpack glass into Hanford Multi-Purpose Canisters, four glass monoliths per canister.

The off-gas treatment system at both HLW and LAW vitrification facilities would be operated to quench and cool off-gas, remove radionuclides and recycle to vitrification process, and destroy nitrogen oxides. The LAW vitrification facility also would recover sulfur from the sulfur oxides.

Liquid effluent would be transferred from the HLW and LAW vitrification facilities to the Effluent Treatment Facility. The HLW multi-purpose canisters would be transported to interim storage pads. Stored canisters would be monitored and maintained through routine surveillance of the Hanford Multi-Purpose Canisters in interim storage pending offsite disposal, and Hanford Multi-Purpose Canisters would be transported to the potential geologic repository.

3.4.8.5 Post Remediation

Following waste treatment operations, the tank farms would be closed and processing facilities would be decontaminated and decommissioned. Closing tank farms would involve ensuring that the tanks contained a residual less than or equal to approximately 1 percent of the initial tank inventory; stabilizing tanks by gravel filling; stabilizing tank farm structures such as pump pits, valve boxes, and diversion boxes with grout or gravel; and placing Hanford Barriers over SSTs, DSTs, and LAW burial vaults.

Facility decontaminating and decommissioning activities would involve disposal of noncontaminated facilities onsite (entombed in place), and disposal of contaminated material and equipment at the onsite low-level waste burial grounds.

3.4.8.6 Schedule, Sequence, Cost

A schedule of the major components of the Ex Situ Extensive Separations alternative is shown in Table 3.4.15. Construction for waste retrieval and transfer would involve installing pipelines between the tanks and the transfer facilities throughout the retrieval period, which explains the difference in the construction periods shown. The cost estimate summary for the Ex Situ Extensive Separations alternative is shown in Table 3.4.16.

Table 3.4.15 Schedule - Ex Situ Extensive Separations Alternative

Table 3.4.16 Schedule - Ex Situ Extensive Separations Alternative

3.4.8.7 Implementability

The Ex Situ Extensive Separations alternative would have the same uncertainties as the Ex Situ Intermediate Separations alternative, plus additional uncertainties associated with the chemical separations processes (Section 3.4.6.7). The key implementability issue associated with this alternative is that the performance of key separations processes has been assumed in the absence of substantive data. Further testing and development would be required to determine if the processes would function as intended to make the required separations.

The HLW canisters produced under this alternative would have a higher thermal loading than other alternatives and the assumed method of interim onsite storage, which would rely on dry storage with passive cooling, would require further evaluation. This alternative could require using a storage facility with active cooling to remove decay heat generated by the vitrified HLW.

This alternative would meet all applicable regulations for disposal of hazardous, radioactive, or mixed waste assuming that the hazardous waste components were adequately treated during waste processing and vitrification.

3.4.9 Ex Situ/In Situ Combination 1 and 2 Alternatives

3.4.9.1 Overview

The e x s itu/i n s itu c ombination alternatives were developed to assess the impacts that would result if a combination of two or more of the tank waste alternatives were selected for implementation. Because the tank waste differs greatly in the physical, chemical, and radiological characteristics, it might be appropriate to implement different alternatives for different tanks. There are a wide variety of potential combinations of alternatives that could be developed and criteria that could be used to select a combination of alternatives for implementation. Two ex situ/ i n situ c ombination alternatives were developed to bound the impacts that could result from a combination of alternatives, and are intended to represent a variety of potential alternative combinations that could be developed to remediate the tank waste.

The Ex Situ/In Situ Combination 1 and 2 alternatives represent a combination of the In Situ Fill and Cap and Ex Situ Intermediate Separations alternatives (Figure 3.4.12 ). Tanks would be evaluated on a tank-by-tank basis to determine the appropriate remediation method based on the contents of the tanks. The objective would be to effectively treat the tank waste in a manner that has acceptable risk and less overall cost than using the Ex Situ Intermediate Separations alternative for all tanks. This objective could be achieved by selecting tanks for ex situ treatment based on their contribution to post-remediation risk. The tanks that were not selected for ex situ treatment would be treated in situ by filling and capping. Two Ex Situ/In Situ Combination alternatives exist, one based on the recovery of approximately 90 percent of the long-term risk contaminants and the other based on recovery of approximately 85 percent of the long-term risk contaminants. See Volume Two, Section B.3.8 for discussion on tank selections methodology

Ex Situ/In Situ Combination 1

Waste from tanks selected for ex situ treatment would be retrieved and transferred to processing facilities for treatment. Closure activities would consist of filling those tanks selected for ex situ treatment with gravel and constructing a Hanford Barrier over all tank farms and the LAW retrievable disposal vaults from ex situ treatment. Approximately one-half of the volume of the tank waste would be treated using the ex situ method and one-half would be treated using the in situ method.

By selecting the appropriate tanks for ex situ treatment, approximately 90 percent of the contaminants that contribute to long-term risk would be disposed of ex situ while retrieving only 50 percent of the waste (Jacobs 1996). The process used to determine which tank waste would be retrieved for the purpose of analyzing this alternative is described in Volume Two, Appendix B. The human health risk associated with selectively retrieving tanks is discussed in Section 5.0.

Ex Situ/In Situ Combination 2

Waste from tanks selected for ex situ treatment would be retrieved and transferred to processing facilities for treatment. Closure activities would consist of filling those tanks selected for ex situ treatment with gravel and constructing a Hanford Barrier over all tank farms and the LAW retrievable disposal vaults from ex situ treatment. Approximately one-quarter of the volume of the tank waste would be treated using the ex situ method and three-quarters would be treated using the in situ method.

Figure 3.4.12 Ex Situ/In Situ Combination (1 and 2) Alternatives

By selecting the appropriate tanks for ex situ treatment, approximately 85 percent of the contaminants that contribute to long-term risk would be disposed of ex situ while retrieving only 25 percent of the waste (Jacobs 1996). The purpose of developing the Ex Situ/In Situ Combination 2 alternative was to analyze lower cost methods for remediation of the tank waste while maintaining long-term risk reduction. The process used to determine which tank waste would be retrieved for the purpose of analyzing this alternative is described in Volume Two, Appendix B. The human health risk associated with selectively retrieving tanks is discussed in Section 5.0.

3.4.9.2 Process Description

Ex Situ/In Situ Combination 1

The waste that would be retrieved for ex situ treatment would be treated using the process identified for the Ex Situ Intermediate Separations alternative (Section 3.4.6). The retrieved waste stream would be separated into HLW and LAW streams. Separations processes would include liquid solid separations followed by cesium recovery from the liquid stream, which would be fed back into the high-level stream. Both HLW and LAW streams would be vitrified in separate vitrification facilities. The HLW facility would be designed to produce 8 mt/day (8.8 tons/day) and the LAW facility would be sized to produce 120 mt/day ( 130 tons/day).

Following vitrification, the HLW would be poured into canisters. The canisters would be overpacked into Hanford Multi-Purpose Canisters (Figure 3.4.13 ) for onsite interim storage. The LAW would be quenched into gravel-like cullet, placed into disposal containers, and transported to onsite vaults for near-surface disposal. The engineering data supporting this alternative were based on a process that would blend the LAW glass cullet with a matrix material before placing it into the disposal containers. Disposing of LAW as glass cullet in matrix material has been included as a representative condition for analysis in the EIS. Future evaluation of matrix materials and disposal forms could result in selecting other glass forms, alternate matrix materials, or elimination of the matrix material.

Tanks not selected for retrieval would be treated in situ using the In Situ Fill and Cap process (Section 3.4.4). This process would involve reducing the DST liquid using the 242-A Evaporator, filling the tanks with gravel, and installing a Hanford Barrier over the tank farms.

Existing MUSTs (both inactive and active) would be filled with grout to stabilize the waste. All MUSTs would be covered with a Hanford Barrier during post remediation.

Figure 3.4.13 Hanford Multi-Purpose Canister (HMPC) System for High-Level Waste

Ex Situ/In Situ Combination 2

The waste that would be retrieved for ex situ treatment would be treated using the process identified for the Ex Situ Intermediate Separations alternative (Section 3.4.6). The retrieved waste stream would be separated into HLW and LAW streams. Separations processes would include liquid solid separations followed by cesium recovery from the liquid stream, which would be fed back into the HLW stream. Both HLW and LAW streams would be vitrified in separate vitrification facilities. The HLW facility would be designed to produce 5 mt/day (5.5 tons/day) and the LAW facility would be sized to produce 70 mt/day (77 tons/day).

Following vitrification, the HLW would be poured into canisters. The canisters would be overpacked into Hanford Multi-Purpose Canisters (Figure 3.4.13) for interim onsite storage and eventual transport to the potential geological repository. The LAW would be quenched into gravel-like cullet, placed into disposal containers, and transported to onsite vaults for near-surface disposal. The engineering data supporting this alternative were based on a process that would blend the LAW glass cullet with a matrix material before placing it into the disposal containers.

Tanks not selected for retrieval would be treated in situ using the In Situ Fill and Cap process

(Section 3.4.4). This process would involve reducing the DST liquid using the 242-A Evaporator, filling the tanks with gravel, and installing a Hanford Barrier over the tank farms. Existing MUSTs (both inactive and active) would be filled with grout to stabilize the waste. All MUSTs would be covered with a Hanford Barrier during post remediation.

3.4.9.3 Construction

Ex Situ/In Situ Combination 1

Construction activities required for this alternative would involve constructing all of the facilities identified for the Ex Situ Intermediate Separations alternative and the In Situ Fill and Cap alternative, but on a reduced scale. For the ex situ portion, the volume of waste requiring treatment and immobilization would come from approximately 70 tanks instead of 177 tanks. In situ treatment would be required for the remaining tanks.

The following major activities would take place during the construction phase for the ex situ component of the Ex Situ/In Situ Combination 1 alternative.

  • Install retrieval and transfer facilities.
  • Construct separations (pretreatment) facilities.
  • Construct an 8-mt/day (8.8-ton/day) HLW vitrification facility.
  • Construct a HLW interim storage facility.
  • Construct a 120-mt/day (130-ton/day) LAW vitrification facility.
  • Construct a LAW disposal facility (vaults).

For the in situ component of this alternative, construction activities would involve installing gravel handling systems, constructing gravel storage sites for stockpiles, and modifying tank openings to accommodate gravel handling equipment.

Ex Situ/In Situ Combination 2

Construction activities required for this alternative would involve constructing all of the facilities identified for the Ex Situ Intermediate Separations alternative and the In Situ Fill and Cap alternative, but on a reduced scale. For the ex situ portion, the volume of waste requiring treatment and immobilization would come from approximately 25 tanks instead of 177 tanks. In situ treatment would be required for the remaining tanks.

The following major activities would take place during the construction phase for the ex situ component of the Ex Situ/In Situ Combination 2 alternative.

  • Install retrieval and transfer facilities.
  • Construct separations (pretreatment) facilities.
  • Construct a 5-mt/day (5.5-ton/day) HLW vitrification facility.
  • Construct a HLW interim storage facility.
  • Construct a 70-mt/day (77-ton/day) LAW vitrification facility.
  • Construct a LAW disposal facility (vaults).

For the in situ component of this alternative, construction activities would involve installing gravel handling systems, constructing gravel storage sites for stockpiles, and modifying tank openings to accommodate gravel handling equipment.

3.4.9.4 Operations

Operations for the Ex Situ/In Situ Combination 1 and 2 alternatives would be a combination of the operations described for the Ex Situ Intermediate Separations alternative in Section 3.4.6 and the In Situ Fill and Cap alternative in Section 3.4.4, but on a reduced scale.

Waste retrieved from the tanks for treatment would be retrieved and processed in the same manner as described for extensive retrieval. The operation would be scaled down to accommodate the smaller waste volume to be treated.

Those tanks not selected for ex situ treatment would be remediated using the process described for the In Situ Fill and Cap alternative. The DST liquid in those tanks not selected for retrieval would be retrieved and reduced in the 242-A Evaporator. Following waste reduction operations for the DSTs, the tanks would be stabilized by filling with gravel.

3.4.9.5 Post Remediation

After remediation, tank farm closure and decontamination and decommissioning would take place. Tank farm closure would involve the following activities. First, retrieved tanks would be stabilized with gravel (in situ tanks would have been stabilized during in situ operations). Second, tank farm structures such as MUSTs, pump pits, valve boxes, and diversion boxes would be stabilized with grout. Finally, Hanford Barriers would be constructed over SSTs, DSTs, and LAW retrievable disposal vaults.

Decontamination and decommissioning of equipment and facilities would include disposing of noncontaminated material by in place entombing onsite and disposing of contaminated equipment and materials at the onsite low-level waste burial grounds.

3.4.9.6 Schedule, Sequence, Cost

Ex Situ/In Situ Combination 1

A schedule for the major components of the Ex Situ/In Situ Combination 1 selective retrieval alternative is shown in Table 3.4.17. This schedule covers both in situ and ex situ portions of the alternative. The estimated cost for this alternative is provided in Table 3.4.18.

Ex Situ/In Situ Combination 2

A schedule for the major components of the Ex Situ/In Situ Combination 2 alternative is shown in Table 3.4.19. This schedule covers both in situ and ex situ portions of the alternative. The estimated cost for this alternative is provided in Table 3.4.20.

Table 3.4.17 Schedule - Ex Situ/In Situ Combination 1 Alternative

Table 3.4.18 Cost - Ex Situ/In Situ Combination 1 Alternative 1

Table 3.4.19 Schedule - Ex Situ/In Situ Combination 2 Alternative

3.4.9.7 Implementability

Because this alternative represents a combination of alternatives, the implementability issues would be a combination of those issues identified for the implementability of both the In Situ Fill and Cap alternative and the Ex Situ Intermediate Separations alternative (Sections 3.4.4 and 3.4.6). Developing acceptable tank selection criteria would be an issue unique to the ex situ/in situ combination concept and would require more complete and accurate waste characterization than currently exists.

Implementability issues relating to both the in situ and ex situ portions of this alternative would include the following.

  • LAW form (glass cullets in a matrix material) is unique and has not been used before.
  • Successful performance of key processes (e.g., sludge washing) has been assumed in the absence of substantive data.
  • Final design of a combination alternative would consider retrieval and treatment of all DST liquids.
  • Cost estimates could have a high degree of uncertainty because these would be first-of-a-kind systems.
  • The ability to achieve retrieval criteria based on recovering 99 percent of the waste volume in each tank would be uncertain.
  • Incidental blending of waste during retrieval would be more uncertain for the ex situ/in situ combination alternatives because fewer tanks would be subject to retrieval. The affect of blending on HLW volumes for the combination alternatives would require further evaluation.
  • Additional separations steps could be required to meet LAW disposal criteria.

The in situ portion of this alternative would not meet the RCRA land disposal requirements for hazardous waste or DOE policy to dispose of readily retrievable HLW in a geologic repository. The ex situ portion of the alternative would meet all regulations for disposal of hazardous, radioactive, or mixed waste assuming that the hazardous waste components are adequately treated during processing or vitrification.

3.4.10 Phased Implementation Alternative

3.4.10.1 Overview

The Phased Implementation alternative includes remediating the tank waste in two phases. The first phase would be a demonstration of the separations and immobilization processes for selected tank waste. The second phase would involve scaling-up the demonstration processes and constructing larger treatment facilities to remediate the remaining tank waste.

This two-phased implementation approach could be applied to any of the tank waste alternatives involving ex situ waste treatment. However, for the purposes of analysis, the processes and activities described for the Ex Situ Intermediate Separations alternative, with some additional separations, was selected as the basis for developing the Phased Implementation alternative. This basis included vitrified glass cullet as a LAW form and vitrified borosilicate glass as a HLW form. Other types of glass or wastes forms could be selected for HLW or LAW treatment; however, they would have to meet the repository acceptance criteria or performance assessment criteria. The Phased Implementation alternative is presented in two parts; Phase 1 first, then Phase 2.

This alternative also could be implemented by decommissioning the two demonstration-scale facilities after the demonstration phase and constructing and operating two larger size facilities. The environmental impacts of each approach would be approximately the same.

Phase 1

During Phase 1, readily retrievable and well-characterized DST waste would be retrieved and processed in two separate demonstration facilities. The waste processed during Phase 1 could also include selected SST waste. One of the facilities would process liquid waste to produce immobilized LAW, while the other facility would produce immobilized LAW and vitrified HLW. The facility for both LAW and HLW immobilization could be constructed as separate facilities. Information used in describing this alternative was developed by the TWRS EIS contractor (Jacobs 1996).

The immobilized LAW would be sealed in containers at the treatment facilities and then transported to an interim onsite storage facility where it would be stored for disposal during Phase 2. The vitrified HLW would be placed in canisters and transported to an interim onsite storage facility, where it would be stored awaiting shipment and disposal at the potential geologic repository.

During Phase 1, canisters of vitrified HLW and canisters of separated radionuclides would be placed into shipping casks and transported to the onsite Canister Storage Building for interim storage. Each canister would be placed into a storage tube in one of the Canister Storage Building vaults. The Canister Storage Building is located in the 200 East Area and was constructed as an interim storage facility. The NEPA analysis for construction of the Canister Storage Building was performed under the K Basins Spent Nuclear Fuel EIS (DOE 1995j).

The Phase 1 immobilized LAW would be placed into disposal containers and transported to the existing grout vaults for interim storage until the permanent onsite disposal vaults were constructed during Phase 2. The NEPA analysis for the construction of the grout vaults was previously performed in the Hanford Defense Waste EIS (DOE 1987). The LAW placed in interim storage during Phase 1 would be retrieved and transported to the LAW disposal vaults during Phase 2.

Each of the LAW treatment facilities would operate for a 10-year period. The HLW treatment facility would operate for a 6-year period, which could be extended to a 10-year period.

The following operations would be implemented under Phase 1.

  • Retrieve selected liquid waste for LAW processing.
  • Retrieve selected DST and SST waste for HLW processing.
  • Transfer liquid waste to receiver tanks.
  • Transfer selected waste for HLW processing directly to the HLW facility.
  • Perform separations to remove cesium, technetium, strontium, transuranic elements, and sludge from the LAW stream.
  • Store separated cesium and technetium at the treatment facilities or package and transport to the Canister Storage Building for onsite interim storage pending future HLW waste treatment.
  • Return the sludge, strontium, and transuranic waste separated prior to LAW processing to DSTs for storage.
  • Immobilize the LAW and vitrify the HLW.
  • Place the vitrified HLW into canisters.
  • Place the immobilized LAW into containers.
  • Transport the immobilized waste to onsite interim storage facilities.

Phase 2

Phase 2 would be implemented to complete the remediation of the tank waste following successful implementation of Phase 1. Implementation of Phase 2 would involve the continued operation of Phase 1 facilities plus construction of two full-scale separations and LAW vitrification facilit ies and a full-scale HLW vitrification facility. Phase 2 would include the retrieval and treatment of the remaining DST and SST waste as well as the waste contained in the MUSTs. As much of the tank waste as practicable (assumed to be 99 percent) would be recovered from each tank. The recovered waste stream then would be transferred to one of the treatment facilities where it would be separated into HLW and LAW waste streams for immobilization.

The HLW stream would be vitrified, placed into canisters and then placed into Hanford Multi-Purpose Canisters for interim storage and disposal at the potential geologic repository . The LAW would be immobilized and placed into sealed containers similar to those used in Phase 1. The immobilized LAW would be placed into near-surface retrievable disposal vaults.

For purposes of analysis and in order to present a complete and representative alternative, the complete Phased Implementation alternative would include the following components:

  • Completion of the waste retrieval and transfer system as described for the Ex Situ Intermediate Separations alternative;
  • Construction and operation of the ex situ treatment facilities, similar to those described for the Ex Situ Intermediate Separations alternative, to provide the treatment capacity required to complete tank waste remediation; and
  • Construction and operation of interim HLW storage and LAW disposal vaults of the same size and type as described for the Ex Situ Intermediate Separations alternative to provide for interim HLW storage and LAW disposal.

3.4.10.2 Process Description

Phase 1

The first step in waste processing would be to recover and transfer selected waste for treatment. Liquid waste retrieval and transfer would use equipment and systems currently in place in the DST farms. Waste retrieved from selected SSTs also could be used as waste feed for the treatment facilities. The waste feed to the LAW facilities would be retrieved and transferred in batches from selected DSTs into two existing DSTs used as feed tanks. Each LAW facility would have one designated DST as a feed tank. The waste feed to the HLW facility would be retrieved, sludge washed, and transferred directly to the HLW processing facility. The waste treated at the HLW facility would be the HLW recovered from selected tanks and sludge washed and might or might not include the HLW separated out of the LAW stream.

The separations and immobilization technologies employed for waste immobilization would be based on waste product specifications, which would set the requirements for the physical properties, chemistry, radionuclide content, and volume of the immobilized LAW and HLW. During the demonstration phase, different types of waste would be processed to demonstrate process capability for easy, moderate, and difficult-to-process waste. For purposes of this analysis, the technologies employed would be assumed to be similar to those described for the other ex situ alternatives.

Separations prior to LAW immobilization would be performed to remove the cesium, strontium, technetium, transuranic elements, and entrained sludge particles from the waste stream to the extent required to meet LAW product specifications. The separated cesium and technetium would be stored at the treatment facilities or packaged in canisters for onsite dry storage; the sludge and other radionuclides would be returned to the DST farms for storage; and the remaining liquid waste stream then would be immobilized. The immobilization process would include evaporation of the waste stream followed by vitrification. The LAW processing facilities each would be designed to treat up to 3.8 million L (1 million gal) of liquid waste per year. This is equivalent to a treatment facility with a capacity of 20 mt (22 tons) of vitrified glass per day at a 15 weight percent sodium oxide waste loading, operating at an overall efficiency of 60 percent. The immobilized LAW would be placed into containers approximately 1.8 m long by 1.2 m wide by 1.2 m high (6 ft long by 4 ft wide by 4 ft high).

The HLW treatment process, which would involve only sludge washing and solid/liquid separations processes, would convert the entire waste feed stream into vitrified borosilicate HLW glass. The HLW facility would be designed to produce the equivalent of 1 mt/day (1.1 ton/day) of HLW glass at a 20 weight percent waste oxide loading. The HLW would be placed directly into 1.17-m3 (41-ft3) canisters for packaging in a Hanford Multi-Purpose Canister for interim storage.

Phase 2

Under Phase 2, the waste retrieval and transfer operations would use the same processes and would be subject to the same requirements for tank residuals as the retrieval and transfer function described for the Ex Situ Intermediate Separations alternative. Waste would be retrieved and blended for batch transfer to the treatment facilities. Radionuclides that previously had been separated from the LAW stream and placed in containers for storage would be transported to a HLW vitrification facility and blended with a HLW feed stream.

The HLW and LAW separations processes would be similar to those described for the Ex Situ Intermediate Separations alternative, but would include additional separations processes to remove strontium, technetium, and transuranic elements from the LAW stream to the extent required to meet the LAW product specifications.

During Phase 2, a HLW vitrification facility and two LAW treatment facilities would be constructed. The HLW vitrification facility would be designed to produce 10 mt (11 tons) of HLW glass per day. The LAW treatment facilities would each be designed to produce 100 mt (110 tons) of glass per day.

The LAW produced during Phase 1 and the LAW produced during Phase 2 would be disposed of onsite in near-surface retrievable disposal vaults.

3.4.10.3 Construction

Phase 1

The two facilities would be located on the east side of the 200 East Area within the area previously identified as the grout disposal area. Separate treatment and support facilities would be constructed (Figure 3.4.14 ). The following systems and facilities would be constructed:

  • Waste transfer systems - This would include pipelines from the receiver tanks to each of the treatment facilities and a separate pipeline to transfer HLW from the existing waste transfer system to one of the treatment facilities.
  • Electrical service to each of the sites - This would involve installing overhead power lines from the existing 200 East Area power grid to the designated sites.
  • Process water and potable water - These services would be installed to connect the sites with existing distribution lines in the 200 East Area.
  • Treatment facilities - This would include one separations/LAW processing facility and one separations/LAW/HLW processing facility.

Figure 3.4.14 Phased Implementation Facility Layout

Modify the Canister Storage building for interim storage of vitrified HLW. This would include modifying the underground vaults and ventilation system to accommodate the physical and thermal loading associated with interim storage of all HLW produced during Phase 1.

Modify the existing grout vaults to accommodate interim LAW storage during Phase 1 operations. This would include modifications to the existing vaults to allow placement and interim storage of the LAW disposal containers pending future retrieval and disposal during Phase 2.

Phase 2

Constructing new facilities for Phase 2 would include new treatment facilities with higher capacities than the Phase 1 demonstration facilities. The new facilities constructed during Phase 2 would include a HLW vitrification facility, two combined separations and LAW treatment facilities , a LAW disposal facility, an interim HLW storage facility, waste retrieval and transfer facilities, and support facilities ( Figure 3.4.15 ). The facilities that would be constructed for Phase 2 operations would include the following:

  • Waste retrieval and transfer facilities as described for Ex Situ Intermediate Separations;
  • Support facilities that would provide utilities, resources, and personnel support to the Phase 2 treatment facilities (these support facilities would be similar to those described for the Ex Situ Intermediate Separations alternative);
  • Two separations and LAW treatment facilities that would be similar to the LAW vitrification facility described for the Ex Situ Intermediate Separations alternative;
  • A LAW disposal facility for retrievable disposal of LAW produced throughout Phase 1 and Phase 2 (this facility would be similar to the LAW disposal facility described for the Ex Situ Intermediate Separations alternative);
  • A HLW vitrification facility that would be similar to the HLW vitrification facility described for the Ex Situ Intermediate Separations alternative;
  • A HLW interim storage facility for interim storage of the Hanford Multi-Purpose Canisters (this facility would be similar to the interim storage facility described for the Ex Situ Intermediate Separations alternative); and
  • Hanford Barriers over the LAW retrievable disposal facility and tank farms at the completion of remediation.

3.4.10.4 Operations

Phase 1

Operations under Phase 1 would take place simultaneously at the two treatment facilities. Both LAW facilities would operate for 10 years. The HLW treatment operations would take place for 6 years but could be extended to 10 years.

Figure 3.4.15 Phased Implementation (Total Alternative) Facility Layout

The waste (mainly DST liquid waste) would be retrieved and transferred to receiver tanks for LAW treatment. The waste then would be transferred from the receiver tanks to the treatment facilities on an as-needed basis. The HLW would be retrieved from selected tanks and transferred to DSTs for in-tank sludge washing. The washed HLW would then undergo solid/liquid separation followed by vitrification of the HLW.

Each facility would perform the necessary separations processes on the waste stream. Separated cesium and technetium radionuclides would be stored at the treatment facilities or packaged for interim onsite storage at the Canister Storage Building . The LAW stream would be vitrified to meet established performance characteristics. The HLW stream would be vitrified to produce borosilicate glass and then would be placed into canisters. The HLW produced would meet established acceptance criteria.

Each of the waste treatment facilities would operate off-gas treatment systems using control technologies for priority pollutants and radionuclides. The treatment of the off-gas would use processes and equipment similar to those described for the Ex Situ Intermediate Separations alternative.

Phase 2

Phase 2 operations would follow Phase 1 and would consist of the following:

  • Retrieve waste from the tanks and MUSTs. This operation would be the same as described for waste retrieval under Ex Situ Intermediate Separations alternative;
  • Perform sludge washing and solid/liquid separation; and
  • Operate the two LAW vitrification facilities and the HLW vitrification facility . Waste treatment operations would be similar to those described for the Ex Situ Intermediate Separations alternative but at a reduced scale.

3.4.10.5 Post Remediation

Following waste treatment and tank farm closure, decontamination and decommissioning would take place. Post-remediation activities for the Phased Implementation alternative would be the same as those described for the Ex Situ Intermediate Separations alternative. The tank farms would be closed and the processing facilities would be decontaminated and entombed in place.

3.4.10.6 Schedule, Sequence, and Cost

A schedule for the major components of the Phased Implementation alternative is shown in Table 3.4. 21 . The cost estimate for the Phased Implementation alternative was developed by combining applicable components from other ex situ alternatives and applying ratios as required to account for differences in facility sizes and capacities and the degree of separations in LAW and HLW. This approach inherently assumes that the Phased Implementation alternative would use similar types of processes and facilities to those described for the other ex situ alternatives. The estimated cost for the Phased Implementation alternative is shown in Table 3.4.22 .

Table 3.4.21 Schedule - Phased Implementation Alternative

Table 3.4.22 Cost - Phased Implementation Alternative 1

3.4.10.7 Implementability

Many of implementability issues identified for the ex situ alternatives would not be as well defined for the Phased Implementation alternative. Issues related to the implementability of phased implementation would include successfully producing immobilized waste that would meet waste form specifications. Successful implementation of Phase 1 would be required to start Phase 2.

Phase 1 would share some of the same implementability issues as the Ex Situ Intermediate Separations alternative because several of the processes were assumed to be similar. Performance of key processes was assumed in the absence of substantive data. Cost estimates could have a high degree of uncertainty because some of the processes are unproven.

The phased implementation approach would reduce uncertainties as compared to the other ex situ alternatives because the process would be demonstrated on a smaller scale and optimized before being used on a larger scale.

Retrieval criteria based on recovering 99 percent of the waste volume in each tank would be uncertain because hardened sludge present in some tanks could be difficult to retrieve, making it difficult to meet the retrieval criteria. This would be an implementability issue associated with Phase 2. The ability of the alternative to comply with regulatory requirements is discussed in Section 6.2.

This alternative would meet all applicable regulations for disposal of hazardous, radioactive, or mixed waste assuming that the hazardous waste components are adequately treated during waste processing or vitrification.



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