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Weapons of Mass Destruction (WMD)

B.3.0 TANK WASTE ALTERNATIVES

The following sections describe each of the tank waste alternatives. Elements common to all tank waste alternatives are described in Section B.3.0. The discussion includes a general description of the alternative followed by a description of the construction activities that would be involved if the alternative would be implemented. The discussion continues with a description of the process/operations and ends with a discussion of key issues associated with implementing the alternative. Engineering data for each alternative may be found in Section B.11.0. Each alternative includes the continuation of routine operations discussed in Section B.1.1.7.

Section B.3.1 - B3.4 are unavailable electronically.

B.3.5 EX SITU INTERMEDIATE SEPARATIONS ALTERNATIVE

B.3.5.1 General Description

Ex situ alternatives would require removing the waste from the tanks for treatment and separating the waste into high- and low-level components. The benefit of separating the waste would be to minimize the volume of HLW requiring offsite disposal and reduce the amount of radioactivity for disposal in near-surface vaults onsite. Ex situ alternatives would dispose of HLW at a potential geologic repository, which is assumed to be at Yucca Mountain, Nevada (see Section B.10 for further discussion) .

This alternative involves retrieving as much of the waste as practicable from the tanks and separating it into HLW and LAW streams. Each waste stream would be vitrified into glass. The HLW would be transported offsite to the potential geologic repository and the LAW would be placed in retrievable near-surface disposal vaults at the Hanford Site (WHC 1995j).

It should be noted that the design information for all of the alternatives is at an early planning stage. The details of implementing the selected alternative(s) are likely to change as the planning and design process matures. Therefore, these alternatives are intended to represent an overall plan for remediation rather than a definitive design. Any aspect of the alternative could change as the design process optimizes details of the plan; however, the overall plan for the alternative would not change. This alternative would involve the actions described in the following text.

Retrieval

Slurry pumping would be used to extract DST waste. Hydraulic sluicing would be used to remove SST waste. If hydraulic sluicing does not meet waste retrieval requirements, robotic arm-based retrieval methods would be used. Robotic-arm removal of solid waste saltcake within the tanks would require using a crusher to produce fine particulate material that could be slurried and pumped from the waste tank to the receiving or blending tank(s). Once the waste is removed and converted to a slurry form it would be pumped via pipe line(s) from the tank farms to a pretreatment facility.

In addition, the robotic arm would be used to remove solid waste such as piping and instrument trees from the tank. This type of solid waste would require remote mechanical handling for separate treatment prior to disposal as low-level waste.

Pretreatment

Pretreatment would consist of performing sludge washing, enhanced sludge washing, solid/liquid separation, and ion exchange to separate the waste into HLW and LAW streams. The solids in the waste would be washed to dissolve salts to the extent practical, and the salt solutions would be added to the supernatant for Cs removal. The sludge remaining in the tanks would be transferred to the HLW vitrification facility. The Ex Situ Extensive Separations alternative includes using multiple pretreatment modules designed to minimize the volume of HLW.

Immobilization

The LAW would be pumped into a LAW vitrification facility where it would be concentrated and mixed with glass formers (e.g., borosilicate and silica) and vitrified. Vitrification is a high-temperature process in which the waste is blended with additives and fused into a glass-like form suitable for disposal. The vitrification facility would have pollution abatement controls to ensure that effluents and emissions are within regulatory standards.

The washed sludges mixed with the separated Cs would be routed from a temporary storage facility to a HLW vitrification facility where they would be mixed with glass formers and fused into glass. The HLW glass would be sent to an onsite interim storage facility where it would be stored before shipment to a permanent potential geologic repository. The HLW vitrification facility would include pollution abatement controls to ensure that all effluents and emissions are within regulatory standards.

Disposal

The disposal of radioactive waste is regulated by DOE and the U.S. Nuclear Regulatory Commission (NRC). DOE's guidance for classifying waste is contained in DOE Order 5820.2A, Radioactive Waste Management (DOE 1988). The Order classifies waste into HLW, low-level waste, and TRU waste. Specific guidance includes near-surface disposal of low-level waste and deep geologic disposal of HLW and TRUs. The NRC regulates and licenses the disposal of radioactive materials from non-DOE facilities and the disposal of HLW for DOE facilities through regulations contained in 10 CFR 60. The Nuclear Waste Policy Act provides the statutory framework for NRC regulation of HLW disposal. The NRC guidance on waste classification is contained in 10 CFR Part 61. Currently, DOE disposal of low-level waste is not regulated by the NRC, although NRC rulings regarding waste treatment and waste feed limitations would affect classifying waste that is subject to HLW disposal requirements.

The vitrified LAW glass would be put into large disposal containers and placed into a near-surface retrievable disposal facility on the Hanford Site. 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 50 years) if a different method of disposal was determined to be necessary. A Hanford Barrier would be constructed over the retrievable LAW disposal site to inhibit migration of contaminants and intrusion by humans, plant roots, or burrowing animals. Markers would be used to identify the location of the storage disposal facility. Security and administrative controls would be implemented and maintained indefinitely to protect workers and the public. For the purpose of calculating the potential impacts, it is assumed that the controls will be terminated after 100 years.

The vitrified HLW glass, following canister packaging into HMPCs, would be placed in an aboveground interim storage facility at the Hanford Site. The glass would then be shipped to the potential geologic repository for permanent disposal.

B.3.5.2 Facilities to be Constructed

The alternative includes constructing a tank waste retrieval and transfer facility, a sludge washing (separations) facility, the vitrification and process support facilities, onsite LAW disposal facilities, and temporary HLW storage facilities.

Tank Waste Retrieval and Transfer Facilities

The retrieval and transfer facilities would include bridging structures over the tanks to support the equipment, the off-gas treatment systems, four transfer annex buildings, one waste staging and sampling facility, and the transfer piping system (WHC 1995n). The bridge structures would span the tanks to transfer the equipment loads to foundations outside the perimeter of the tank. The structures, which would be movable or relocatable from tank to tank, would include a vertical, 24-m (80-ft) -high container to house equipment withdrawn from the tank while the entire assembly was relocated to another tank. Operating areas in the structures would be provided with HEPA ventilation equipment to maintain the pressure gradient required between the process, operating, and uncontrolled areas.

After being retrieved from the tanks, the waste would be transferred to the sludge washing tanks. The waste transfer system would include two transfer annexes in the 200 East Area and two transfer annexes and a waste staging and sampling facility in the 200 West Area. The transfer annexes and waste staging and sampling facility are shown in Figures B.3.5.1 and B.3.5.2. The inter farm and cross-site transfer piping would also be part of the system.

Figure B.3.5.1 200 East Area Tank Waste Transfer Facilities

Figure B.3.5.2 200 West Area Tank Waste Transfer Facilities

The transfer annexes would include multi-story facilities that contained tanks to store, blend, and dilute the slurry, equipment to crush oversize solids (saltcake and hardened sludge) , and pumps to transfer the slurry to the processing facility or, in the 200 West Area, to the waste staging and sampling facility.

The buildings would be built of concrete, approximately 25 m (80 ft) on each side, 11 m (35 ft) high, and extend 5 m (16 ft) below grade to allow the earth to serve as shielding. The facility would include the process equipment, a maintenance bridge crane, a decontamination area, an HVAC system with HEPA filters, a control room, and other features necessary for facility operations. The waste staging and sampling facility would pump the waste from the 200 West Area to the replacement cross-site transfer system for transfer to the processing facility in the 200 East Area. This facility would also be built of concrete, but would be larger than the transfer annexes. It would be approximately 73 m (240 ft) long, 23 m (75 ft) wide, 12 m (40 ft) high, and extend approximately 12 m (40 ft) belowgrade. Process equipment would include six agitated slurry tanks and two transfer pumps.

The processing facility would include a maintenance bridge crane with a repair bay, a decontamination bay, an HVAC system with HEPA filters, and an attached structure for emission/effluent monitoring. Except for the initial installation, tank farm piping would be rearranged during operation to accommodate the needs of the operation. Transfer piping between the tank farms and the transfer annexes and between the waste staging and sampling facility would be constructed as part of this alternative.

The replacement cross-site transfer line between the 200 West and 200 East Area lines would consist of two 8-cm (3-in.) -diameter stainless-steel pipes, each encased in a 15-cm (6-in.) -carbon-steel outer pipe to provide secondary containment as required by Federal and State regulations and DOE design criteria (see discussion in Section B.1.1.8). The lines would be sloped (at least 0.25 percent to preclude accumulation of solids) and buried, bermed, or appropriately shielded for radiation and freeze protection. The pipeline would be designed to prevent corrosion from the metal pipes contacting the soil. Both pipelines would be insulated with polyurethane foam and covered with a fiberglass jacket. A diversion box would connect the new transfer line to existing pipelines to facilitate liquid waste transfer between the 200 West and 200 East Areas. A booster pump located in the diversion box would provide the power to transfer waste slurries at the minimum required velocity to prevent the lines from clogging. A vent station would be located at the high point of the transfer system. The function of the vent station would be to introduce air into the lines after a transfer to allow draining the primary containment pipes. Both the diversion box and the vent station would be equipped with stainless-steel liners and would have provisions for washing down radioactive contamination, collecting accumulated liquid, and routing the liquid back to the tank farms. All process piping would have sufficient earth cover to reduce personnel exposure to as low as reasonably achievable, and would not exceed 0.05 millirem per hour (mrem/hr) at grade. The diversion box and cover would attenuate radiation levels to 0.05 mrem/hr at the surface.

Separations Facility

Separations would consist of two major process steps, sludge washing and Cs ion exchange. Other radionuclides would be removed, if required, to conform to the limits for LAW. The Cs ion exchange would be performed in the low-activity vitrification facility. The general arrangements for separations and low-activity vitrification are shown in Figures B.3.5.3 and B.3.5.4; however, the final design decision about washing the tank sludges has not yet been made. It is possible that an alternate method such as washing on crossflow filters may be used. Because in-tank washing represents a bounding condition for sludge washing, it will be described in detail in this appendix. Sludge washing would be done in DSTs that would be modified to accommodate the process. A mixer, decant pumps, and sludge transfer pumps would be added to the tanks through existing risers in the tank dome. New surface tanks would be installed for process chemicals, and surface piping would be rearranged to accomplish the objectives of the washing operation. Surface facilities would include three 20-m3 (700-ft3) process tanks, a tank ventilation system with HEPA filters to isolate the tank atmosphere, pump service and decontamination facilities, and an operations building. The ventilation system would allow the tanks to breathe as the waste level varied during transfer and mixing operations. The tank ventilation system, which would use HEPA filters, would be centrally located to serve the sludge washing system.

Figure B.3.5.3 Ex Situ Intermediate Separations Layout

Figure B.3.5.4 Pretreatment/Low-Activity Waste Facility Layout (Sheet 1 of 7)

Figure B.3.5.4 Pretreatment/Low-Activity Waste Facility Layout (Sheet 2 of 7 )

Figure B.3.5.4 Pretreatment/Low-Activity Waste Facility Layout (Sheet 3 of 7 )

Figure B.3.5.4 Pretreatment/Low-Activity Waste Facility Layout (Sheet 4 of 7 )

Figure B.3.5.4 Pretreatment/Low-Activity Waste Facility Layout (Sheet 5 of 7 )

Figure B.3.5.4 Pretreatment/Low-Activity Waste Facility Layout (Sheet 6 of 7 )

Figure B.3.5.4 Pretreatment/Low-Activity Waste Facility Layout (Sheet 7 of 7 )

The pump service and decontamination facilities would be arranged around a central chamber mated to tank nozzles and would contain equipment removed from the tank. The equipment would be flushed with fresh water as it was removed, and the central chamber would finally be filled with lead shot before the entire assembly was transferred to a LAW disposal facility. Each internal tank pump would have a dedicated confinement chamber.

The operations building would be a 590-m2 (6,400-ft2) single-story block structure that would house a motor control center and a control room for the washing operation. Change rooms, operations offices, and a lunch room would also be included.

Low-Activity Waste Vitrification Facility

The LAW waste vitrification facility would be sized to produce 200 mt (220 tons) of vitrified waste per day in two production trains. It would contain seven operational areas, including feed receipt and sampling, Cs ion exchange, melter operations, cullet processing, cullet matrix operations, cold chemical makeup, and off-gas treatment areas.

The facility would have an overall footprint of 90 m (290 ft) wide by 75 m (250 ft) long with an overall height of 40 m (130 ft), of which 20 m (65 ft) would be belowgrade. In addition to the process level, which would be belowgrade, the facility would have two other levels, one at grade and the other at +9 m (30 ft). Overall, the facility would have a total area of approximately 6,800 m2 (73,000 ft2).

The process level would include feed receipt and sampling, Cs ion exchange, process evaporation, and cullet processing areas. Feed receipt and sampling would occur in six 200-m3 (7,100-ft3) tanks that would receive feed from six 400-m3 (14,300-ft3) tanks external to the building. The Cs ion exchange area would include a single stage of 12.5-m3 (440-ft3) columns and supporting tanks. The cullet processing area would consist of quench tanks below the evaporator and 18 cullet storage tanks.

The facility's other two levels would provide space for support services and additional process equipment. The grade level of the facility would provide space to support canister filling operations, instrumentation for the process equipment, melter operations, process evaporator for LAW melter feed, maintenance areas, and sulfur operations. The +9-m (30-ft) level would provide electrical services and cold chemical makeup systems.

Low-Activity Waste Cullet Disposal

Under the Ex Situ Intermediate Separations alternative, LAW cullet would be disposed onsite. The cullet would be mixed with a matrix material in the vitrification facility and placed into disposal containers (approximately 2.6 m3 [92 ft3]), which would then be transported to onsite disposal vaults. A total of 66 vaults would be constructed. Each vault would be an estimated 37 m (120 ft) long by 15 m (50 ft) deep. The vaults would be engineered concrete structures.

The requirements for using a matrix material and specific matrix material requirements have not been established. The use of a matrix material for the LAW waste form has been included as being representative of waste form matrices for bounding the transportation and resource impacts.

When all of the LAW glass has been placed in final storage, a Hanford Barrier would be constructed over the storage site. Hanford Barrier performance objectives are discussed in Section B.6.0.

High-Level Waste Vitrification Facility

The HLW vitrification facility would have six operational areas that would include feed receipt and sampling, process evaporation, melter operations, maintenance areas, canister loading, cold chemical makeup, and off-gas processing (Figure B.3.5.5). The facility would have an overall height of 45 m (150 ft), of which 13 m (45 ft) would extend belowgrade. In addition to the process level, the facility would have three other levels at -13 m (-45 ft), +13 m (+45 ft), and +20 m (+65 ft). The facility's dimensions would be 55 by 165 m (175 by 545 ft) with an area of 8,800 m2 (94,700 ft2).

Figure B.3.5.5 High-Level Waste Vitrification Facility Plant - 0.00 Meters (at Grade) (Sheet 1 of 5)

Figure B.3.5.5 High-Level Waste Vitrification Facility Plant - 20 Meters ( Sheet 2 of 5 )

Figure B.3.5.5 High-Level Waste Vitrification Facility Plant - Section A ( Sheet 3 of 5 )

Figure B.3.5.5 High-Level Waste Vitrification Facility Plant - Section B ( Sheet 4 of 5 )

Figure B.3.5.5 High-Level Waste Vitrification Facility Plant - Section C ( Sheet 5 of 5 )

The facility's process levels would contain feed receipt and sampling equipment, centrifuges, process evaporation equipment, melter operations equipment, and the maintenance area. The feed tanks would be located in an adjacent structure. Three other areas would provide the remainder of the support facilities. The 13-m (45-ft) level would house the canister loading and handling equipment. The +20-m (+65-ft) level would provide crane maintenance and cold chemical storage makeup.

The final HLW glass form would be a glass canister measuring 0.61 by 4.57 m (2.0 ft by 15 .0 ft). The HLW interim onsite storage facility would allow enough interim storage space for all of the HLW glass produced. After the HLW campaign concluded, the canisters would be transported in the HMPCs (four canisters per HMPC) to the potential geologic repository for final disposal.

Support Facilities

Each of the process facilities would provide its own process support equipment. Common utilities and cold chemical areas would provide headers for service to support the process systems in the plants. These common services would include:

  • Medium pressure steam and condensate;
  • Instrument and plant compressed air;
  • Cooling water;
  • Sanitary water;
  • Process water;
  • Demineralized water;
  • Raw water and fire water;
  • Sanitary sewer;
  • Nonradioactive liquid waste processing;
  • Cold chemical bulk storage and makeup;
  • Oxygen; and
  • Electrical power.

Support facilities that would provide for nonprocess and personnel activities would include the following.

  • The Operations Support Building would serve as the administration building for the complex. It would have 19,000 m2 (21,000 ft2) of floor space with approximately 40 percent dedicated to offices and the remaining 60 percent dedicated to office support functions (e.g., conference rooms, lunch rooms, utility rooms, equipment areas, storage rooms, and supply rooms).
  • The Regulated Entrance Building would be the single point of entry into the facility for maintenance and operation personnel. The building would provide 6,500 m2 (70,000 ft2) of space for security operations, health physics, change rooms, lunch rooms, and a first aid clinic.
  • The 2,100-m2 (22,500-ft2) Operations Control Building would house the central control room for the entire TWRS Treatment Complex as well as space for control support functions.
  • The Bulk Cold Chemical Building would be a one-story building approximately 90 by 90 m (300 by 300 ft) providing 8,360 m2 (90,000 ft2) of floor area. The building would store anhydrous ammonia, kerosene, nitric acid, LAW form matrix materials, sodium hydroxide, and sulfur. Chemical makeup would also be located in this building.
  • The Switch Gear/Generator Building would be a 90- by 90-m (300- by 300-ft), single-story structure. It would house switch gear and be unoccupied.
  • The Mechanical Utilities Building would be a single-story, 90- by 90-m (300- by 300-ft) building. It would house plant air compressors, an instrument air system, chillers, a demineralized water system, and a process steam and condensate system.
  • Four small pumphouses external to the Mechanical Utilities Building would pressurize fire-water and cooling-water systems.

Other support facilities would include a cooling tower (60 by 90 m [200 by 300 ft]), a fabrication shop (45 by 90 m [150 by 300 ft]), mock-up shops (45 by 90 m [150 by 300 ft]), three warehouses (45 by 90 m [150 by 300 ft]), and a switchyard. The switchyard would include a 120 by 150 m (400 by 500 ft) substation consisting of incoming 230-kilovolt (kV) dead-end towers feeding a double-ended bus with a single tie breaker. The bus would feed redundant transformers rated 230 to 13.8 kV, with a capacity of approximately 100,000 kV-ampheres. The 13.8-kV transformer secondaries would feed a double-ended switchgear, located in a switchgear building that would include utility monitoring and control equipment.

B.3.5.3 Description of the Process

Overview

The overall tank waste treatment process would include 1) retrieving the waste; 2) separating the LAW from the HLW; 3) vitrifying each waste stream separately; 4) disposing of the LAW onsite; 5) temporarily storing the HLW; and 6) transporting the HLW to the potential geologic repository at a future date. Separating the HLW from the LAW would be accomplished with a liquid/solid separation process (many of the HLW constituents are insoluble) and a subsequent ion exchange step to recover Cs (which is partially soluble and has allowable concentration limits in the LAW) from the liquid phase. Other radionuclides would be removed, if required, to conform to the limits for LAW. The HLW and LAW would be vitrified in separate but similar processes. The vitrification process would include feed-preparation systems, the vitrification process itself, off-gas treatment systems, wastewater processing systems, glass-handling systems, and a number of utility and support systems. Figures B.3.5.6 and B.3.5.7 illustrate the process.

Figure B.3.5.6 Ex Situ Intermediate Separations Alternative - Separations and LAW Vitrification Process

Figure B.3.5.7 Ex Situ Intermediate Separations Alternative - HLW Vitrification Process

Sludge washing would be performed with approximately four modified DSTs. Sludge washing may also be done on filters or in centrifuges. The supernatant aqueous phase would be pumped to the LAW vitrification facility where the first operation would be Cs recovery. The sludge from sludge washing would be transferred to the freestanding HLW vitrification facility as would be the Cs recovered in the LAW facility. The vitrified LAW cullet would be placed in containers and transported to vaults for onsite disposal. The HLW would be temporarily stored in casks on a pad near the HLW facility before being shipped to the potential geologic repository for permanent disposal.

Tank Waste Retrieval and Transfer

The Tri-Party Agreement (Ecology et al. 1994) includes a milestone that directly impacts the TWRS program. Milestone M-45-00 requires tank waste residues not exceeding 10.2 m3 (360 ft3) in each 100 series tank, and tank residues not exceeding 0.85 m3 (30 ft3) in each 200 series tank. Thus, this milestone provides the basis for the 99 percent removal requirement.

Most of the SST waste would be removed by reslurrying the waste with a hydraulic jet. This process, referred to as sluicing, would remove the slurry with a pump to remove all but a 1 percent heel of waste from the tanks. The sluicers would dislodge and erode the sludges and dislodge, dissolve, and/or breakup the saltcake creating a slurry, which would be pumped to a DST where it would be allowed to settle. The supernate would be recycled to the sluicing jets to continue the recovery process. Reusing the saturated supernate would minimize saltcake dissolution and reduce the liquid volume in the process. Controlling the liquid volumes would be important because virtually all of the water added to recover and transfer the waste would need to be removed by evaporation before vitrification.

Currently, there are several technologies available for use in sluicing systems, one of which is presented in Figure B.3.5.8. Considerable experience on tank sluicing on which a design can be based exists, as the SSTs were previously sluiced to recover U sludges from 1952 to 1957 and again to recover Sr sludges from 1962 to 1978.

Figure B.3.5.8 Sluicing Arrangement for Single-Shell Tank Waste Retrieval

In some instances, the sluicing operation may not be able to remove sufficient waste to meet the removal requirement. A recovery system based on a robotic arm would be used as a backup for the SSTs. A robotic arm would provide additional flexibility to position sluicing jets and pumps and extended capability to recover additional waste by using tools and equipment. Arm-based systems would also provide for dismantling and recovering internal tank hardware that would otherwise interfere with sludge retrieval. Figure B.3.5.9 is a conceptual view of the robotic arm. It is estimated that 24 sluicing systems and 12 robotic arm systems would be required. This estimate is based on the proposed retrieval and transfer schedule, the life and reliability of the equipment, and the amount of sludges that will be difficult to retrieve.

Figure B.3.5.9 Robotic Arm-Based Arrangement for Single-Shell Tank Waste Retrieval

Because the solids in the DSTs may not be compacted into the dense material that occurs in the SSTs, the principal technology used for retrieving the DST waste would be mixer pumps. The pumps would be installed in existing DST risers. The pumps rotating hydraulic jets would breakup and mobilize the sludge, and vertical turbine pumps would transfer the slurry. Unlike the SST equipment that would be moved from tank to tank, each DST would be permanently equipped with two to four mixer pumps. A sluicing system would be provided as a backup to the mixer pumps. It is assumed that six of the 28 DSTs (20 percent) would use sluicing to retrieve waste that could not be retrieved with mixer pumps (WHC 1995n).

After retrieval, the waste from the SSTs would be either transferred directly to process facilities or the DSTs for interim storage. The waste transfer annexes would be the primary means for transferring waste, but container transport could be selectively used for small waste volumes and tank heels. Four waste transfer annexes would be constructed, two in the 200 West Area and two in the 200 East Area. In addition, a waste staging and sampling facility would be provided in the 200 West Area.

The waste transfer annexes would be located close to clusters of SST farms to receive waste slurry from the SSTs, condition the slurry, and pump it within the 200 East Area to DST storage or the processing facility. In the 200 West Area, the waste transfer annexes would pump to the staging and sampling facility that in turn would pump the waste to the 200 East Area processing facilities. Slurry conditioning would include dissolving, diluting, and reducing the size of entrained solids.

Waste would be recovered from approximately 60 MUSTs by sluicing and then transported by the LR-56(H) truck or a containerized transfer system to the transfer annexes for discharge to the process. Approximately 120 trips or more with the 3,800-L (1,000-gal) LR-56(H) truck would be required to nearly empty the tank waste volumes tabulated (see Appendix A, Table A.2.3.1) for 28 of the MUSTs.

For purposes of this EIS, it is assumed that an average, or nominal, feed would be the input to the processing plant. The concept of nominal feed is an averaging of the feed during the duration of waste treatment operations. For the ex situ alternatives, the retrieval function would be designed to deliver a nominal feed to the processing plant. The actual feed would vary depending on tank inventories and retrieval sequences. The Facility Configuration Study (Boomer et al. 1994) identified the following five design feed streams that would be addressed in the engineering design of the proposed treatment facility:

  • Nominal feed, average feed over plant life;
  • Shielding basis feed, highest radionuclide concentration feed used for shielding design;
  • Safety/regulatory assessment feed, bounding radionuclide feed used for accident analysis;
  • Criticality assessment feed, feed with bounding fissile material content used to define criticality controls; and
  • Variability assessment feed and range of feed compositions that might be expected during plant operation.

Sludge Washing

One of the primary purposes of the sludge washing step would be to dissolve constituents that limit the waste loading of the HLW such as aluminum, chromium, and phosphorous. Sodium hydroxide solutions would be used during enhanced sludge washing to solubilize aluminum, chromium, and phosphorous, which have limited solubility in water alone. Approximately 85 percent of the aluminum, 75 percent of the chromium, and 70 percent of the phosphorous would be recovered from the HLW and sent to the LAW vitrification facility. The supernatant solutions from the sludge washing process would be forwarded to the separations facility for Cs recovery.

Feed to the sludge washing process would be a slurry of insoluble sludges suspended in an aqueous solution of soluble waste. The solids would contain most of the HLW and, except for Cs and some complexed waste, the solution would contain limited HLW. The HLW (solids slurry at approximately 50 percent by weight would be separated from the liquids in a counter-current decantation operation that would use existing DSTs. Sludge washing could also be done outside the tanks on filters or in centrifuges. The waste slurry would be allowed to settle (separation by mechanical means may be required) to 50 percent total solids by weight, the supernatant would be transferred to the separations facility, and supernatant from a previous wash would be added to the solids remaining in the tank. After two washes with successively cleaner water the aqueous phase of the slurry would contain fewer soluble salts and the slurry could be transferred to the HLW vitrification facility.

Low-Activity Waste Processing

Cesium Recovery

For purposes of the EIS, it has been assumed that the only soluble radionuclide that would be removed would be Cs. It may become necessary to provide further liquid processing to remove additional radionuclides from the LAW to the extent required to meet onsite disposal requirements. This additional liquid processing could include organic destruction and Sr and Tc removal. The impacts to be expected as a result of additional liquid processing would be a small decrease in the amount of LAW and a small increase in the amount of HLW.

The Cs is soluble in alkaline solutions and in sufficient concentrations is a HLW. A minimum of 85 percent of the Cs would be removed from the feed to the LAW melter by an ion exchange process. Four ion exchange columns preceded by a submicron prefilter would be arranged so that three of the columns would load in series while the fourth column was being regenerated. Nitric acid would be used to elute the Cs and sodium hydroxide, and wash water solutions would be used to regenerate the resin in the fourth column. The fourth column would be returned to service once the first column was loaded. The columns would be sized for continuous operation. The Cs solution would be characterized, concentrated by evaporation, and transferred to the HLW vitrification facility.

The LAW remaining following the separations processes would contain approximately 17 million curies (MCi) of radioactivity including 10 MCi Cs and Ba, 6.8 MCi of Sr and Y, 2.59E-02 MCi of Tc-99, and a total of 1.22E-02 MCi of TRU isotopes.

Feed Conditioning System

The primary functions of the feed conditioning system would be to 1) mix and concentrate the LAW feed; 2) provide for chemical adjustment and sampling; and 3) supply a controlled and monitored feed to the melter. The feed conditioning system would be made up of the following:

  • Six 380,000-L (100,000-gal) sample/holding tanks located in an underground vault adjacent to the vitrification building;
  • One 36,000-L (9,500-gal) evaporator feed tank, which would also be used to collect the various aqueous plant recycle streams;
  • One steam-heated evaporator; and
  • Four 36,000-L (9,500-gal) melter feed adjustment tanks.

The feed would be held in the six sample/holding tanks for sampling and analysis before being forwarded to the single evaporator feed tank and evaporator, which would be in continuous operation. The evaporator concentrate would be divided into four streams and continuously forwarded to two pairs (four) of melter feed adjustment tanks. At this point, the evaporator concentrate would be sampled and analyzed before being transferred to two pairs of melter feed tanks. Each pair of melter feed tanks would supply a melter in a staggered cycle so that the melters would receive a continuous feed.

The LAW evaporator feed tank would provide a place for blending various recycle waste streams from the LAW vitrification building, such as melter off-gas quench liquid, cullet fines slurry, and filter wash from the six off-gas HEPA filters. The tank would have an agitator to ensure complete mixing. From this tank the blended stream would be pumped to the evaporator.

The steam-heated LAW evaporator would continuously receive the blended stream containing about 2 weight percent suspended solids and about 18 weight percent dissolved solids. Evaporated water would rise to the overhead condenser through mist-eliminators to minimize the carry-over of contamination. The evaporator overhead would generate condensate that would be sent to the process condensate recycle tanks. The evaporator bottoms would contain about 5 weight percent suspended solids and about 47 weight percent dissolved solids. This bottoms stream would be split in half to serve the two melter trains, and would be continuously pumped to one of the available LAW melter feed adjustment tanks in each of the two trains. The LAW melter feed adjustment tanks and the downstream melter feed tanks would be located in the chemical process cell. The tanks, cooling coils, and piping in the chemical process cell would have a no-maintenance design. The tanks, pumps, and agitators would be located below ports in the cell roof so that they could be removed into shielded flasks for transport to maintenance.

Bulk Flux System

Bulk fluxes include silica, alumina, borate, and calcium oxide. The bulk flux system would include receiving and storage silos with a pneumatic loading system; a conveyor discharge system with batching capabilities; a batch mixer; and pneumatic transfer to a day bin, which would feed the melter. The fluxes would be selected, proportioned, and blended to complement the analysis of the waste feed tank so that the desired vitreous product is produced.

Oxygen Plant

The final design selection of the LAW melter has not yet been made. For purposes of analysis this alternative would include a vortex melter that would be fuel-fired, although ultimately other melter designs could be chosen. The melter would be fired with oxygen to reduce the volume of flue gas and minimize the formation of NOx. The oxygen would be supplied by a pressure-swing adsorption unit with stored liquid oxygen available as backup.

Vitrification System

The vitrification system would combine the waste and flux in the desired proportions, heat them to the temperature required for vitrification, and evaporate the aqueous phase of the solution in the waste slurry. In the vortex melter this process would happen very rapidly. There would be two parallel vitrification systems, each with a 100-mt/day capacity for glass product. Each vitrification system would include a flux-feed system, waste injection system, burner system, vortex melter, glass separator, and a glass quench system. The flux-feed system would include a pneumatically supplied day bin and a weighfeeder with air locks.

The waste slurry would be fed to the combustion chamber of each melter at a 0.061-m3/min (16-gal/min) rate. There the semi-volatiles and volatiles would be burned off and the remaining solids and waste oxides would be combined with glass forming oxides. The combustion fuel, kerosene, would be pumped to the combustion melter along with 100 percent gaseous oxygen. The incoming waste slurry from the LAW melter feed tank would be mixed uniformly with the glass forming oxides in a mixing and injection valve mounted on top of the combustion chamber. The glass oxides would be gravity fed from head bins and carefully metered by weigh feeders into the mixing and injection valve. The hot combustion gases and by-products would flow axially through the cyclone, creating a rotating gas flow. The heavier premelted glass solids would be deposited along the refractory wall by the action of the rotating gases (centrifugal force) and form a thin film as they flowed axially through the cyclone. The hot combustion gases and by-products would continue heating the glass while in the cyclone to finish dissolving the waste oxides into the glass matrix. The hot combustion gases would be approximately 50 C (120 F) hotter than the glass melt film, which would be 1,300 C (2,370 F).

The glass separators would function as reservoirs to refine the glass and remove entrained gases. Each glass separator would be close-coupled to a quench flume where the molten glass would be fractured into cullet. The final design decisions concerning the LAW glass form have not yet been made. While this alternative is based on the concept of glass cullet, ultimately, other forms such as canisters or monoliths could be chosen. Also close-coupled to each glass separator would be a quench tower that would cool the melter off-gas and collect the condensables.

Cullet Slurry Handling

The cullet slurry handling system would include a quench flume, wet roll crusher, cullet catch tank, slurry catch tank, washing trommel screen, and a transfer pump to recycle fines and quench water back to the evaporator feed tank. There would be two production trains in the cullet handling system for the LAW plant. Molten glass from the glass separator would be discharged to the quench flume where it would make contact with water and fracture into cullet. The cullet would pass through a wet roll crusher to break up any oversized pieces and drop into the cullet catch tank. Steam from the quenching operation would be condensed and recycled to the quench tank. The cullet slurry would be pumped from the cullet catch tank to a trommel screen where it would be dewatered and washed to remove adhering fines. The fines would be returned to the cullet catch tank with any excess water and recycled to the feed conditioning system.

Dry-Cullet Handling

The product handling system, which would fill the casks, would include a combination dryer/storage bin and a pneumatic transfer system. In the dry-cullet handling system, the cullet would be dried and transported via a pneumatic conveyor to the cullet storage bin, where it would be sampled and held until analyses are complete. Accepted cullet would be pneumatically transferred to the day bin, while rejected material would be recycled to the melter feed tank as off-specification material. The cullet in the day bin would be fed forward to the waste form matrix mixer.

Cullet Transfer to Vaults

This alternative is based on mixing the cullet with matrix material and placing the mixture into disposal containers. The disposal containers would provide a means for handling LAW and retrieving them at a future time if required. The LAW disposal containers would be transported using a specialized transporter and placed into the disposal vaults.

Off-Gas Systems Description

Overview

The main off-gas systems would be the melter off-gas system, vessel off-gas system, condenser vessel off-gas system, bin vent off-gas system, and the pneumatic vessel off-gas system. Each of the tank waste alternatives would make extensive use of recycle streams in the process to recycle back into the treatment process volatile radionuclide and chemical constituents captured in the off-gas systems. 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., Tc-99 and mercury [Hg]) 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.

The melter off-gas system would receive the hot combustion gases from the glass separator. The gases leaving the melter would contain products of combustion, steam, volatilized radionuclides from the feed, and entrained particulates from the rapid water evaporation in the feed slurry. This gas would also contain nitrogen and sulfur dioxide (SO2) from the decomposition of process feed constituents. The off-gas would be first quenched with scrub water, which would condense the water vapor and remove particulates, and water-soluble contaminants. Excess condensate from the melter off-gas system would be recycled to the HLW evaporator feed tank. The scrubbed melter off-gas would undergo further cooling and successive stages of HEPA filtration to remove radionuclide particulates, after which SO2 would be adsorbed from the gas and subsequently converted into elemental sulfur by a Claus unit. Finally, the partially treated gas would pass through a catalytic de-NOx reactor, where NOx would be converted into nitrogen and water vapor before passing through another HEPA filter and discharging to the atmosphere.

Melter Off-Gas System

The primary functions of the melter off-gas system would be to 1) cool and quench the melter off-gas; 2) remove radionuclides and certain chemical constituents; 3) catalytically destroy SO2; and 4) recover elemental sulfur to permit the release of these emissions to the atmosphere consistent with regulatory requirements. An additional function would be to provide a differential pressure confinement boundary for the melter.

The gas cooling and quenching portion of the melter off-gas system would consist of two identical parallel trains, each dedicated to a single melter. Each train would consist of a quench tower, a venturi scrubber and separator, and a mist eliminator. Each train would include a dedicated cooler, chiller, scrub solution tank, scrub solution recirculating pump, and scrub solution transfer pump. The radionuclide removal portion of the melter off-gas system would include two operating trains and one standby train of sub-micron particulate filtration and blowers. The emissions abatement portion of the melter off-gas system would consist of a single operating train of catalytic NOx destruction, SO2 removal, and sulfur recovery equipment.

Melter off-gas flow from each of the two melters would be quenched from 1,360 to 75 C (2,480 to 170 F) by direct, counter-current contact with 32 C (90 F) water in a refractory-lined quench tower. Entrained particulates would also be scrubbed from the off-gas in the quench tower. The scrub water and condensed moisture from the bottom of the tower would drain by gravity back to the scrub solution tank for re-use. The quenched off-gas would be contacted with scrub water in a venturi scrubber to further remove entrained particulates. The separator would receive the venturi scrubber discharge and separate the off-gas from the scrub water, which would gravity drain to the scrub solution tank.

A chiller would cool the off-gas leaving the separator to 30 C (86 F) before it would enter the mist eliminator. The mist eliminator would use glass fiber candle elements to remove mist and particulates from the off-gas stream. A continuous water spray would help clean condensate and particulates from the candle elements. The rinse from the mist eliminator would gravity drain to the scrub solution tank. The liquid mixture from the scrub solution tank would be cooled to 32 C (90 F) in the cooler and would be recycled back to the quench tower and venturi scrubber. A purge of excess process condensate plus associated solids would be continuously discharged from each scrub solution tank and collected in the scrub filter tank. The solution would then be recycled from the tank back to the evaporator feed tank for treatment. A small bleed stream would be taken from this recycle stream to prevent a buildup of certain volatile radionuclides and chemical constituents. This secondary waste stream would be stabilized by an appropriate low temperature process (such as grout).

The off-gas from each mist eliminator would flow to one of three identical parallel trains of filters. Two of the three trains would be in operation with the third train on standby. Each train would consist of a heater, two back-washable metal HEPA filters in series, and a blower. These metal HEPA filters would be high-efficiency metal fiber filters that would be back-washable for removal of radioactive particulates. The heater and washable metal HEPA filters would be remotely maintainable and located inside a hot cell. The blowers would be located in a contact-maintenance room. The heater would raise the off-gas temperature to prevent any condensation of moisture, which would increase filter pressure drop, reduce filter efficiency, and cause acid gas corrosion in the equipment and piping. The back-washable metal HEPA filter would remove submicron radioactive particulates from the off-gas stream. The blowers would draw the off-gas through the system and provide a pressure confinement boundary for all of the equipment, including the melter relative to the remote cells.

The filtered off-gases discharged from the blowers would be combined and then processed to remove SO2 and catalytically destroy NOx. The combined melter off-gas stream would first be blended with pure oxygen and the recycled tailgas from the downstream Claus unit before entering the tube side of the melter off-gas heat exchanger. Oxygen addition would help SO2 absorption and catalytic NOx destruction. In the exchange, the melter off-gas would be heated to 400 C (750 F) by exchange with the hot effluent gas from the NOx catalytic reactor. The melter off-gas would then be sent to one of three copper oxide (CuO) bed absorbers containing CuO-impregnated alumina sorbent. Approximately 90 percent of the SO2 would be absorbed and converted to copper sulfate in the presence of oxygen in the SO2 absorber.

With one CuO bed serving as an SO2 absorber, the remaining two CuO beds would be in the sulfate reduction mode and the SO2 absorber regeneration mode, respectively. For sulfate reduction, a reducing gas stream containing hydrogen would reduce the copper sulfide and liberate gaseous hydrogen sulfide. The hydrogen would be produced by catalytically cracking ammonia to nitrogen gas and hydrogen. The hydrogen sulfide rich effluent would be sent to the Claus unit, which would recover the sulfur in its elemental form. The tailgas from the Claus unit would be recycled to join the melter off-gas downstream of the blowers. The SO2 absorber regeneration would prepare the CuO bed for SO2 absorption service by passing air across the absorber bed to oxidize the copper to CuO. Air leaving absorber regeneration would be sent to the vessel off-gas system for treatment.

From the SO2 absorber, the melter off-gas would be preheated to 500 C (932 F) in an electric heater before entering the NOx reactor. The NOx reactor would contain a catalyst bed for the selective catalytic reduction of NOx to produce nitrogen and water vapor in the presence of ammonia. The treated off-gas stream would be cooled to 66 C (150 F) or less as it passed first through the shellside of the melter off-gas heat exchanger, and then through the water-cooled melter off-gas discharge cooler prior to release to the process exhaust system.

Process Area Ventilation (Other Off-Gas Systems)

The primary function of the vessel off-gas, condenser vessel off-gas, bin vent off-gas, and pneumatic vessel off-gas systems would be to decontaminate vessel vent gases to meet regulatory requirements for stack release. An additional function of these systems would be to provide a pressure differential on process areas relative to the surrounding cells or vaults to prevent the out-migration of radioactive materials. Each of these systems would consist of a vent collection header, filter preheaters, metal HEPA filters, and blowers. The off-gases from the process vessels would be collected by the vent header and routed to one of two identical parallel trains of filtration. Each train would consist of a heater, two back-washable metal fiber HEPA filter and a blower. Both of these back-washable metal HEPA filters would be high-efficiency metal fiber filters that would be remotely maintainable and would be located inside a hot cell. The blower would be located in a contact maintenance room. The heater would raise the off-gas temperature to prevent the downstream condensation of moisture, which would increase filter pressure drop and reduce filter efficiency. The back-washable metal HEPA filters would remove submicron radioactive particulated from the gas stream. Following filtration, the vent gases would be pressurized by the two 100-percent capacity blowers before being discharged to the HVAC exhaust system.

In the process exhaust system, the melter off-gas would be combined with processed gas streams from other portions of the process and a stream of supply air. The combined flow of supply air and process gas streams would be exhausted through a high-efficiency metal fiber HEPA filter followed by a conventional paper HEPA filter and blower prior to being exhausted to the stack and discharged to the atmosphere. The metal HEPA filter would be remotely maintainable and located inside a hot cell. The conventional HEPA filter and blower would be located in a contact maintenance room.

Process Liquid Waste System

All of the process liquid waste from the LAW vitrification facility would be in the form of process condensate from contaminated process streams. The process condensate recycle tanks and the pH adjustment tank would be located inside an underground vault near the LAW vitrification building.

The process condensate recycle tanks would accumulate the continuously generating condensate, and sequester the contents while awaiting the analytical results of sampling. On-specification liquid would be transferred to the pH adjustment tank, but off-specification liquid would be returned at a controlled rate to the HLW evaporator feed tank for rework. To accommodate the occasional need to recycle off-specification liquid waste, the condensate recycle tanks would be sized so that two of the three tanks would be used to process the normal forward flow of on-specification liquid. The third tank would be used for short-term storage of off-specification waste.

Each process condensate recycle tank would have a 295,000-L (78,800-gal) capacity, and a working capacity of 274,000 L (73,000 gal). About 18 hours would be required to fill a single tank. With the two operating tanks alternately receiving the incoming feed, the time available for sampling, analysis, and pump-out of a tank would also be about 18 hours. Each tank would be agitated to ensure complete mixing. Each tank would have a sampling device and two motor-driven transfer pumps.

From a filled recycle tank, on-specification condensate would be transferred in batches to the pH adjustment tank every 18 hours. The adjustment tank would have the same capacity and type of associated equipment as the recycle tank. In the adjustment tank, a measured volume of sodium hydroxide would be added, based on previous sampling and analyses. The contents of the tank would then be sampled and analyzed prior to being transferred out of the facility. The normal destination for effluent that would meet acceptance criteria would be the Liquid Effluent Retention Facility from which the liquid waste would be transferred to the Effluent Treatment Facility for treatment and final disposal. On nonroutine occasions, off-specification liquid from the pH adjustment tank could be transferred to the tank farms.

Process Steam and Condensate System

The process steam and condensate system would provide 1,000 kilopascals (150 pounds per square inch-gauge) steam for the heating requirements of closed-loop process steam users. To minimize the amount of potentially radioactive material leaving the area, the process steam and condensate building would be located in the vitrification building. The process steam and condensate system would include the process steam generator, process steam condensate condenser and cooler, process condensate pumps, process condensate collection tank, particulate filter and ion exchange unit, and distribution piping for process steam and condensate. The HEPA filters would be provided on the process condensate collection tank vent discharge.

Process Cooling-Water System

The process cooling-water system would be capable of maintaining process tanks at 50 C (122 F) or less, during normal process operations and idle or shutdown periods. The process cooling water system would include heat exchangers, recirculation pumps, distribution piping, an expansion tank with HEPA filters on the tank vent, and a chemical addition tank. To minimize the amount of potentially radioactive material leaving the area, the process cooling water system would be located in the vitrification building.

Melter Cooling-Water System

The melter cooling-water system would remove heat from the melter during normal process operation. It would include heat exchangers, recirculation pumps, distribution piping, an expansion tank with HEPA filters on the tank vent, and a chemical addition tank. To minimize the potential for radioactive contamination outside of the facility, the process cooling water system would be located in the vitrification building.

Process Chilled-Water System

The process chilled-water system would remove heat from process streams, which would be cooled to below 27 C (80 F). This system would include a process water chiller, a process chilled-water expansion tank with HEPA filters on the tank vent, and a process chilled-water pump. To minimize the amount of potentially radioactive material leaving the area, the process chilled-water system would be located in the vitrification building.

Cold Chemical Vent System

The cold chemical vent system would provide vapor control on vents from cold chemical feed and decontamination tanks, drain catch tanks, and other potentially radioactive sources throughout the vitrification building. This system would include HEPA filters, blowers, and piping.

Breathing Air System

The breathing air system would provide breathing quality air for respirators. The source of this air would be breathing air bottles that would be located outside of the vitrification building. The breathing air stations, which would be the distribution system for breathing air, would be located inside the building. The building could also be served by portable breathing air carts.

Health Physics System Vacuum System

The health physics system vacuum system would provide a dedicated central vacuum system to support health physics monitoring and sampling systems. This system would provide constant flow rates for the monitors and samplers at various locations in the vitrification, regulated entrance, and operations control buildings, and the vitrification building annex. Each location would include HEPA filters, blowers, and piping. Buildings external to the process facilities would have their own dedicated health physics system. The health physics system vacuum system provided in buildings external to the process facilities would be located with the other shared facilities.

Potentially Radioactive Liquid Waste Processing System

The potentially radioactive liquid waste processing system would collect and store liquid waste from potentially contaminated areas. This waste would be analyzed for radioactivity. If the waste was determined to be radioactive, it would be transferred to radioactive waste processing for further treatment. If the waste was not radioactive, it would be transferred to nonradioactive waste processing. Facilities within the vitrification building would include drain catch tanks, pumps, transfer pumps, and HEPA filters. An externally located part of the potentially radioactive liquid waste collection system would convey potentially radioactive waste from the regulated entrance building and the repair shops to the main part of the system in the vitrification building.

Cold Chemicals System

The cold chemicals receipt, makeup, and distribution system would include all facilities required to receive, store, prepare, and feed cold chemicals to the process, neutralization, and decontamination facilities. The portion of the system that would be located within the vitrification building would include the cold chemical feed and decontamination tanks, their associated transfer pumps, and distribution piping.

High-Level Waste Processing

The HLW vitrification facility would be a freestanding, single train plant designed to produce 20 mt/day (22 tons/day) of of HLW glass. It would be essentially a small-scale version of the LAW vitrification facility performing similar processing and requiring similar support and utility systems.

Feed Conditioning System

The HLW vitrification facility would receive HLW slurry from the sludge washing operation and Cs solution from the LAW separation facility. After sampling, water would be removed first by centrifuging and then evaporating the centrate. The solids and the slurry from the evaporator would be recombined to feed the HLW melter feed system. As in the LAW vitrification facility, the feed would be sampled and analyzed. Based on the resulting analyses, fluxes would be added to provide the desired vitreous product, a borosilicate glass that would contain 20 percent waste oxides.

Vitrification System

A cold cap melter would be included in the alternative for HLW vitrification as the most thoroughly researched melter in the size required for this production level. The melter would use joule heating, in which current is passed through the molten charge that serves as the resistance element for the furnace. This type of furnace would have a crust over the surface of the melt that would receive the slurry feed, hence the term cold cap. The water in the slurry would be evaporated from the cold cap, and the dried waste would sink as the bottom of the cap entered the melt.

At this stage the HLW vitrification process would deviate from the LAW vitrification process. Instead of producing cullet as in the LAW process, the hot glass would be semi-continuously poured into cylindrical stainless-steel canisters, which would be 0.61 m (2 ft) in diameter and 4.57 m ( 15 ft) high. The quench flume, trommel, pneumatic transfer equipment, and a number of bins proposed for LAW vitrification would not be required to support HLW vitrification.

Canister Fill Operations

A canister would be moved from storage into position under a filling tube that would be lowered to mate tightly with the canister. The fill tube would contain a passage for molten glass to flow into the canister and a separate passage for air to vent out of the canister. The canister would be filled with molten glass. After canister filling was completed, the filled canister would then be transferred to the canister weld cell where it would be welded shut.

A transfer cart would move the canister into the decontamination cell from the weld cell. The crane would lift the canister from the cart and move it to a decontamination area. Decontamination solution would be sprayed onto the canister followed by a water rinse. After the canister dried, the crane would transport it to the smear test cell, where the canisters would be smear-tested for surface contamination. If the canisters failed the test they would be returned to the decontamination cell. If the canisters passed the test they would be forwarded to the load-out cell. Canisters would enter the load-out tunnel on a transfer cart. The tunnel would have a crane that would remove the canister from the cart and place it into an HMPC overpack container (four canisters per overpack).

Full HMPCs would be removed from the load-out well with the cask staging building crane. The cask lids would then be bolted on. The casks would be smear-tested, inspected, and then transferred to temporary storage pads pending shipment to the potential geologic repository for disposal.

Post Remediation

When processing of the tank waste has been completed, the processing facilities would be decontaminated and decommissioned in the following manner.

  • Processing equipment would be decontaminated sufficiently to allow onsite disposal in a low-level waste burial ground.
  • Processing facilities would be decontaminated to the extent possible and then entombed in place. The exact materials that would be used to cover processing facilities have not been decided.

B.3.5.4 Implementability

Issues related to implementing this alternative can be grouped into the following categories.

  • Some of the technologies involved in this alternative are first-of-a-kind and thus do not have a performance history. In particular, the robotic-arm concept for retrieval and the fuel-fired melter for producing LAW glass have been used as applicable concepts. In neither case is there performance history, particularly with the radioactive waste.
  • Processes for retrieving, separating, and immobilizing waste often have been based on engineering judgement and assumptions. Performance of key processes (e.g., sludge washing) has been assumed in the absence of extensive quantitative data. Quantitative performance requirements have not been established for many of the processes and functions. Further process testing to determine equipment sizes is necessary before plant engineering could proceed.
  • Cost estimates for this alternative have a high degree of uncertainty because many processes are first-of-a-kind systems.
  • Retrieval criteria specifying recovery of 99 percent of the waste volume in each tank may not be achievable. Recovery of less tank waste would have a direct bearing on classifying the waste remaining in the tank.
  • While the robotic arm being considered for backup to the sluicing operation has been designed and built, it has not been tested and therefore may not perform as assumed.
  • Facility requirements for shielding have not been generated and exposure during retrieval is based on engineering judgement.
  • Recovery of DST waste by agitating with turbine pumps has not been demonstrated. If the turbine pumps do not perform as expected, then additional retrieval methods would be necessary.
  • The vortec melter, which has been selected as a concept for this alternative, has been demonstrated on generic glass-making feedstock but not tested on the actual feeds that will be used in this process. The off-gases from a fuel fired melter may contain elevated levels of Cs, sodium, or radionuclides. The capture of large amounts of impurities in the scrubbers may result in a large quantity of liquid to be recycled or treated in a separate facility. The magnitude of the recycles stream has not been completely evaluated.
  • The proposed LAW waste form is unique and has not been used before.
  • The engineering data that served as a basis for this alternative were developed using cullet in a matrix material as a LAW form for onsite disposal.
  • A performance assessment has not been completed defining the LAW waste form requirements for retrievable storage and disposal at the Hanford Site, and DOE and NRC have not yet completed negotiations on what constitutes "incidental waste" for disposal of LAW at Hanford. Additional separations steps may therefore be required to meet LAW disposal criteria. The laboratory data now available on enhanced sludge washing are limited. There may be a need to evaluate additional alternate pretreatment methods for certain classes of waste.

The following development or demonstration activities would be necessary if this alternative is selected for implementation:

  • Design and test tank retrieval systems;
  • Evaluate sludge washing;
  • Evaluate the Cs ion exchange;
  • Evaluate separable phase organic treatment;
  • Test and evaluate the HLW melter;
  • Test and evaluate the LAW melter;
  • Evaluate melter off-gas treatment systems;
  • Balance and determine the flowsheets size of recycle streams to accurately estimate equipment size and costs;
  • Conduct performance assessment activities;
  • Evaluate alternative approaches to durability testing; and
  • Evaluate acceptance strategies for LAW and HLW waste forms.

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.

B.3.6 EX SITU NO SEPARATIONS ALTERNATIVE

B.3.6.1 General Description of the Alternative

The Ex Situ No Separations alternative is similar to the Ex Situ Intermediate Separations alternative except that there would be no separation of the waste into LAW and HLW; all waste would be handled as HLW. All of the waste would be vitrified or calcined without any pretreatment and placed in interim storage before being shipped to the potential geologic repository for final disposal. Consequently, there would be no LAW to be disposed of onsite.

Under the calcination option of this alternative, the waste would be calcined rather than vitrified. Calcination is the process of heating precipitates or residues to a temperature that is sufficiently elevated to decompose chemical compounds such as hydroxides or nitrates. Calcination differs from vitrification in that calcination temperatures would not necessarily cause the waste to melt and form a glass. Instead, the primary reaction product would be sodium carbonate. All of the waste would be retrieved from the tanks and calcined without any pretreatment. The calcined product (a dry powder) would be placed in large canisters for interim onsite storage before being shipped to the potential geologic repository for final disposal. For this alternative, no LAW would be disposed of onsite.

B.3.6.2 Facilities to be Constructed

Tank Waste Retrieval and Transfer Facilities

The facilities that would be constructed for recovering and transferring tank waste to the calcination or vitrification facility are exactly the same for both alternatives with one exception. There would be no requirement for sludge washing for the No Separations alternative. The waste would be pumped directly from the Transfer Annex or the Waste Staging Facility to the receipt and sampling system at the processing plant (vitrification or calcination facilities).

Vitrification Facility

If vitrification is chosen for this alternative, a vitrification facility would be constructed. The single vitrification facility for the Ex Situ No Separations alternative would be similar to the Ex Situ Intermediate Separations alternative LAW vitrification facility with a few exceptions. The No Separations (Vitrification) facility would not have Cs ion exchange columns or LAW vaults for onsite near surface disposal. In place of the matrix and cullet mixing and containerization system it would have a system for packaging the cullet in canisters and overpacking them into HMPCs, which would be placed on interim storage pads to await offsite transport (Figure B.3.6.1).

Figure B.3.6.1 Ex Situ No Separations Facility Layout

Because all of the waste would be considered high-level, separate HLW and LAW vitrification facilities would not be required. All of the waste would be vitrified in a single facility that would be virtually the same size as the LAW facility in the Ex Situ Intermediate Separations alternative (Section B.3.5). The off-gas treatment facilities would be identical in function to those described for the Ex Situ Intermediate Separations alternative.

Calcination Facility

If calcination is chosen for this alternative, a calcination facility would be constructed instead of a vitrification facility. The calcination facility would have a receiving and sampling system as in the Ex Situ Intermediate Separations facility. The calcination facility would not have a Cs ion exchange circuit, nor would the facility form cullet. Instead, it would have a system for processing the hot calcine and placing it in canisters. The canisters would be overpacked into HMPCs and placed on an interim storage pad and subsequently transported to the potential geologic repository for disposal. All of the waste would be calcined in a single facility. Because no engineering has been done for this alternative, the size of the facility has been estimated using engineering judgement. It is estimated that the calcination facility would be approximately the same size as the LAW facility in the Ex Situ Intermediate Separations alternative.

Support Facilities

All of the support facilities required for the Ex Situ Intermediate Separations alternative (Section B.3.5) would also be required in the same size and the same quantity for the Ex Situ No Separations alternative. As stated previously, there would be no LAW vaults for onsite waste disposal, but an increased area would be required for interim storage of the shipping casks for the HLW produced by the Ex Situ No Separations process.

The support systems for the calcination process would be essentially the same as those for the other ex situ alternatives. These would include:

  • Fuel receipt and storage area;
  • Process steam and condensate;
  • Cooling water supply and return;
  • Sugar receipt and storage area;
  • Breathing air and other bottled gases;
  • Electrical supply;
  • HVAC and process ventilation; and
  • Health protection facilities.

B.3.6.3 Process Description

The process for the Ex Situ No Separations alternative is similar to the Ex Situ Intermediate Separations alternative except that the waste would not be separated into LAW and HLW, because all waste would be HLW. This HLW would be vitrified or calcined and transported to the potential geologic repository for disposal. Figure B.3.6.2 illustrates the process.

Figure B.3.6.2 Ex Situ No Separations Alternative - Process Flow Diagram

Vitrification Process

In the Ex Situ No Separations alternative, there would be no sludge washing or Cs extraction process. The waste recovered from the tanks would be pumped via the Waste Transfer Annexes or the Waste Staging Facility directly to the receiving area of the vitrification facility. Other than deleting the Cs extraction process, there would be no change to the receiving process. The main process flow would be identical with the Ex Situ Intermediate Separations alternative from the evaporator through the day bin, which feeds the equipment that mixes the molten sulfur with the glass cullet in that process. In the Ex Situ No Separations alternative, the day bin would feed a cullet containerization system. The recycle systems, off-gas systems, liquid waste systems, and utility support systems would also be functionally identical to those of the Ex Situ Intermediate Separations alternative. Each of the tank waste alternatives would make extensive use of recycle streams in the process to recycle volatile radionuclide and chemical constituents captured in the off-gas systems back into the treatment process. These recycle streams would be used to minimize the generation of secondary waste. A bleed stream would be required for the off-gas system for vitrification and calcination to avoid a continuous buildup of certain volatile radionuclide and chemical constituents, namely Tc-99 and Hg, in these recycle streams. For comparison purposes, it has been assumed that the bleed stream percentage would be the same (at 1 percent of the recycle stream) and that this secondary waste stream would be stabilized by some low temperature process (such as grout).

The canister-filling process would be similar to the canister-filling operation in the HLW facility in the Ex Situ Intermediate Separations alternative although with larger equipment. The Ex Situ Intermediate Separations alternative would produce 20 mt/day of HLW glass. The Ex Situ No Separations alternative would produce 200 mt/day of HLW glass. Other differences are that the container would be filled with loose cullet. The container would be a 1.67-m (5.5- ft) diameter by 4.57-m (15 -ft) long canister that would be overpacked in an HMPC, which would be the same type of container used to overpack the HLW canisters described in the Ex Situ Intermediate Separations alternative.

Calcination Process

Calcination is the process of heating precipitates or residues to a temperature that is sufficiently elevated to decompose chemical compounds such as hydroxides or nitrates. It differs from vitrification in that calcination temperatures do not necessarily cause the reacting materials to melt and form a glass. Consequently, the final product of calcination is a solid or semi-solid, if certain products have been partially fused during the calcination process. Calcination techniques for solidifying radioactive waste similar to the TWRS waste have been studied previously, but no recent results are available. Sugar calcination refers to a process in which sugar is mixed with the tank waste prior to calcination. The calcination process would consist of evaporating the remaining feed liquid water content and the sodium nitrate, nitrite and hydroxide salts reacting with sugar and oxygen to form sodium carbonate salt, nitrogen oxide, carbon dioxide, and water vapor. Pure oxygen would be supplied to the calciner for these reactions. The oxygen would also combust the organic materials present in the feed to produce carbon dioxide gas and water vapor. Because sodium carbonate has a sufficiently high melting point, 850 C (1,560 F), it would remain as a solid in the calcining process rather than melting. Without reacting with sugar, sodium nitrate melts at 308 C (586 F) and sodium nitrite melts at 271 C (520 F).

Feed Preparation

Because all of the tank waste would be calcined, the waste feed to this process would be identical to the feed to the HLW vitrification melter in the Ex Situ Intermediate Separations alternative (Section B.3.5). Because the feed components would not be separated, all of the calcined product would be considered HLW. The primary function of the feed preparation system would be to mix measured amounts of sugar with the tank waste prior to calcination. Each batch of tank waste would be analyzed to determine the sugar requirements. A weighed amount of bulk dry sugar would then be added, and the mixture would be agitated until the sugar was dissolved.

Calcination

The prepared feed, after first being screened to separate small amounts of coarse solids and foreign objects, would be pumped to the feed nozzles of a spray calciner. The calciner would be an indirectly fired vessel consisting of a number of 20-cm (8-in.) diameter vertical tubes. The vessel is a box design approximately 9 by 9 m (30 by 30 ft) with an approximate height of 4.6 m (15 ft). This particular configuration would limit the reacting mass within the calciner as the reaction of the sugar could be very rapid and large quantities of sugar and nitrates could react violently. The calcination reactions would take place inside the tubes. The tubes would be heated by combustion of kerosene fuel with oxygen outside the tubes and the resulting hot off-gases exhausted directly to the atmosphere, probably after some indirect heat recovery operation. These gases would consist of only products from the combustion of kerosene with oxygen and should require no treatment as they would contain only very low levels of SOx and NOx due to the presence of small amounts of sulfur and nitrogen in the kerosene.

The feed for the calciner would consist of a slurry containing approximately 50 percent by weight solids (dissolved and suspended). Atomizing steam at the rate of approximately one-half of the feed rate (on a mass basis) would be added to ensure proper dispersion of the spray inside the calciner tubes. The atomized waste droplets would lose their water by evaporation and be heated to reaction temperature by the indirectly heated tubes as they fell through the length of the tube. The chemical reactions of the waste with the sugar would take place with the release of NOx gases and the formation of solids, which would be collected at the bottom of the calciner. The calciner would operate at a temperature between 700 and 800 C (1,300 and 1,470 F).

The evaporated water and injected steam for atomization along with the gaseous products from calcination would be exhausted to a ceramic candle filter where particulates would be removed from the hot gases, and then processed similar to vitrification off-gas treatment. The solids removed from the ceramic filter would be collected with the solids from the calciner for further processing and compaction. The ceramic filter equipment envelope would be approximately 9 m (30 ft) in diameter by 18 m (60 ft) high.

Compaction

The calcined solids would consist of a hot, fine powder with a low bulk density, and would require compaction to increase its bulk density. This fine powder would be hot processed in a roll-type compactor machine to produce small pellets or briquettes of high bulk density. The bulk density of the briquettes would be approximately 90 percent of the theoretical density of the solids. After compaction, the product briquettes would be screened to remove fines, air cooled, and transferred to the HLW cyclone bin for feeding into the canisters. The fines collected from screening the briquettes would be returned to the feed bin for recycle to the compactor machine.

Canister Operations

After the calcined product briquettes were transferred to the HLW cyclone bin, the vitrification process canister filling operation flowsheet would be used. The calcined briquettes would be placed in 1.67-m (5.5 -ft) diameter by 4.57-m (15 -ft) long canisters identical to the canisters used for glass cullet for Ex Situ No Separations alternative. A major difference is the quantity of calcine briquettes to be disposed. The Ex Situ No Separations alternative would produce 92 mt/day (100 tons/day) of HLW calcine briquettes. The number of canisters required for calcine briquettes would be 10,300 , approximately 65 percent less than the 29,100 required for vitrification.

Off-Gas Treatment

Off-gas processing for calcination would be the same as that used for off-gas processing for vitrification. The HLW off-gas system would receive hot gases from the HLW calciner ceramic candle filter. The gases would be cooled and scrubbed with water to remove most of the remaining particulates and water soluble materials, which would be recycled to the process feed tanks. A small bleed stream from this recycle stream would be required to prevent a buildup of certain volatile radionuclides and chemical constituents. This secondary waste stream would be stabilized by some low temperature process (such as grout). The scrubbed off-gas would pass through a mist eliminator to remove fine water droplets and then through metal HEPA filters to remove the majority of the radionuclide particulates. The off-gas would then flow to an SO2 adsorption process and a catalytic NOx reactor before being discharged to the atmosphere. The amount of NOx emissions estimated for the calcination process would be approximately five times larger than estimated for the vitrification process. The difference is caused by the assumption that reaction products of nitrites and nitrates for the calcination process would be NOx, whereas for the vitrification process the assumption also includes a large quantity of nitrogen as a reaction product.

Post Remediation

When tank waste processing has been completed, the processing facilities would be decontaminated and decommissioned in the following manner.

  • Processing equipment will be decontaminated sufficiently to allow onsite disposal in a low-level waste burial ground.
  • Processing facilities will be decontaminated to the extent possible and then entombed in place. The exact materials that would be used to cover processing facilities have not been decided.

B.3.6.4 Implementability

Issues associated with implementing this alternative include the following.

  • The Ex Situ No Separations (Vitrification) option has the same uncertainties as those listed for the Ex Situ Intermediate Separations alternative (Section B.3.5.4). In addition, this option would result in a large volume of vitrified HLW ( 2.91 E+05 m3 [1.0E+07 ft3]). The calcination option would also produce a large volume of calcined HLW (1.0E+05 m3 [ 3.7 E+06 ft3]); however it is approximately 65 percent less than the volume of vitrified HLW.
  • The calcination step using sugar as a reductant has had limited laboratory testing and the proposed facilities are conceptual. Calcination as a unit operation has been in use for many years on an industrial scale. No design or engineering has been completed for the process or support facilities. Consequently, the processing steps have been based on experience and engineering judgement. It is estimated that the consumption of fuel (kerosene) for calcination would be approximately 10 percent of that required for vitrification. Steam use for calcination would be higher than for vitrification due to the atomization steam required for feeding the calciner. Electrical power for calcination would be approximately 70 percent of that required for vitrification.
  • The process design parameters for calcining, such as feed rate, temperature, reagent addition, and mass and energy balances remain conceptual in nature. A substantial part of the flowsheet for calcination and vitrification would be the same; implementation of the calcination and vitrification options is estimated to be of approximately the same size and complexity. As a result of this similarity, the nature of most support services is estimated to be similar for calcination and vitrification. Exceptions to this are that raw water use for the calcination option is estimated to be approximately 10 percent of that for vitrification, and sanitary water use for calcination is estimated to be approximately 70 percent of that for vitrification.
  • It is estimated that the calcination and vitrification options would be approximately the same in size and complexity and therefore would have approximately the same costs for capital, monitoring and maintenance, decontamination and decommissioning, and research and development. Differences in cost occur in the operating category due to reduced cost of HLW casks/canisters and HLW disposal fees for calcination relative to vitrification (see Section B.10.0 for further discussion) . The operating costs for calcination are estimated to be approximately 60 percent of that for vitrification, resulting in an estimated overall cost for calcination that is approximately 60 percent of that for vitrification.
  • Further laboratory and pilot-plant testing is required for calcining, particularly for analyzing reaction products including the nature of the gas streams and off-gas treatment methods. The calciner and off-gas processing may require different sizes and types of equipment from the ones conceptualized for the EIS.
  • Processes for retrieving, pretreating, and immobilizing waste often have been based on engineering judgement and assumptions, performance of processes (e.g., sludge sluicing, robotic arm solids removal, and producing HLW glass with a high waste loading) has been assumed in the absence of extensive quantitative data. Further process testing (vitrification or calcination) to determine equipment size would be necessary before plant engineering could proceed.
  • Retrieval criteria that specifies recovering 99 percent of the waste volume in each tank may not be achievable. Recovering less tank waste would have a direct bearing on classifying the waste remaining in the tank.
  • Performance requirements for shielding have not been generated. Exposure during retrieval is based on engineering judgement.
  • Recovery of DST waste by agitating with turbine pumps has not been demonstrated. If the turbine pumps do not perform as expected, then additional retrieval methods would be necessary.

This alternative would meet all applicable regulations for disposal of hazardous, radioactive, or mixed waste assuming that the hazardous waste components would be adequately treated during waste processing and vitrification or calcining. However, the HLW forms (soda-lime glass or calcine) may not meet the current standard waste form (borosilicate glass) specified in the waste acceptance requirements (see Volume One, Section 6.2). The vitrified cullet waste form, with its high surface-area-to-volume ratio may not be acceptable for disposal at the potential geologic repository. These wastes forms might not be acceptable and would require acceptance criteria resolution, which could result in delayed acceptance. The compacted powder calcine also might not meet the waste acceptance requirement for immobilization of particulates.

B.3.7 EX SITU EXTENSIVE SEPARATIONS ALTERNATIVE

B.3.7.1 General Description of the Alternative

The Ex Situ Extensive Separations alternative is similar to the Ex Situ Intermediate Separations alternative but involves performing additional complex chemical separations processes to separate the HLW components from the recovered tank waste. The purpose of the Ex Situ Extensive Separations alternative is to process tank waste to produce a minimum number of vitrified HLW canisters, and reduce the curie loading of LAW to NRC Class A or as low as reasonably achievable, which ever is lower (WHC 1995c). Under the Ex Situ Extensive Separations alternative, the waste would be recovered from the tanks and a complex series of processing steps would be performed during pretreatment to separate HLW from LAW. A series of chemical processing operations would be used to separate HLW elements such as U, Pu, Np, thorium, americium, lanthanide (rare earth metals) series elements, Cs, Sr, and Tc from the waste. Under this alternative, the activities to be performed following pretreatment would be very similar to those included in the Ex Situ Intermediate Separations alternative. The HLW would be vitrified, stored onsite, and disposed of at the potential geologic repository. The LAW would be vitrified and placed in retrievable containers in a near-surface, disposal facility at the Hanford Site. This alternative would create a smaller volume of HLW being sent to the potential geologic repository. The resulting LAW requiring onsite disposal would be approximately the same volume but would have a lower radionuclide concentration than the Ex Situ Intermediate Separations alternative (WHC 1995e).

B.3.7.2 Facilities to be Constructed

The main processing facilities would consist of an integrated pretreatment (chemical processing) and HLW vitrification facility and a detached LAW vitrification facility. The integrated pretreatment-HLW vitrification facility would be operated and maintained remotely, and the detached LAW vitrification facility would be contact operated and maintained (Figure B.3.7.1).

Figure B.3.7.1 Ex Situ Extensive Separations Facility Layout

Integrated Pretreatment - High-Level Waste Vitrification Facility

The integrated facility would have an overall size of 94 by 230 m (310 by 770 ft) and a height of 40 m (130 ft), of which 20 m (65 ft) would extend belowgrade. The facility would be divided into three levels: a processing level, a level at grade, and a level at 12 m (40 ft) abovegrade. It would contain:

  • Sludge washing and dissolution;
  • Alkaline liquid processing;
  • Acidic liquid processing;
  • Destruction, recovery, and recycle of bulk chemicals;
  • Feed receipt and sampling;
  • Chemical makeup; and
  • HVAC.

The HLW vitrification portion of the integrated facility would have an overall size of 30 by 140 m (100 by 460 ft) and a height of 28 m (92 ft), of which 11 m (36 ft) would extend belowgrade. The facility would include:

  • Melter operations;
  • Maintenance areas;
  • Canister loading;
  • Cold chemical makeup; and
  • HVAC.

Detached Low-Activity Waste Vitrification Facility

The LAW vitrification facility would have an overall size of 24 by 75 m (80 by 250 ft) with a height of 21 m (70 ft). The building would be aboveground and would include a process level, a grade level, and a level at +9 m (+30 ft). The facility would be divided into the following areas:

  • Feed receipt and sampling;
  • Melter operations;
  • Cullet processing;
  • Cold chemical makeup; and
  • HVAC.

B.3.7.3 Process Description

The overall waste treatment process would include recovering and transferring the waste from the tanks, separating the HLW from the LAW, vitrifying the HLW, vitrifying the LAW, shipping the HLW offsite, and disposing of the LAW in onsite vaults in retrievable containers . The separation processes would include sludge washing, caustic and acid leaching, solvent extraction and ion exchange of acidic solutions, ion exchange of alkaline solutions, and recycling water, nitric acid, and sodium hydroxide to reduce HLW volumes. A process flow diagram is provided in Figure B.3.7.2.

Figure B.3.7.2 Ex Situ Extensive Separations Alternative - Process Flow Diagram (Sheet 1 of 2)

Figure B.3.7.2 Ex Situ Extensive Separations Alternative - Process Flow Diagram ( Sheet 2 of 2 )

Tank Waste Retrieval and Transfer

Recovering waste from SSTs and DSTs would not change from one ex situ process to another. Tank waste retrieval and transfer would be dependent on the content of the tanks, but would not be dependent on the processing of the waste. The recovery and transfer of the tank waste for the Ex Situ Extensive Separations alternative would be the same as that for the Ex Situ Intermediate Separations alternative. A full discussion of tank waste retrieval and transfer can be found in Section B.3.5.

Solids Separation and Dissolution

Liquid/Solid Separation

The Ex Situ Extensive Separations process would use centrifuges for separating liquid and solids in various stages of processing. These separations would occur after tank retrieval, complexing agent destruction, caustic dissolution, acid dissolution, and the chromium removal step. Several stages of liquid and solid separation would be used because supernate entrainment in the solids from the centrifuge would be assumed to make up about 12 percent of the centrifuge feed.

Destruction of Complexing Agents

The liquid resulting from liquid and solid separation would be treated by a wet air oxidation process to destroy organics, including complexing agents and ferrocyanides. The use of an organic destruction process is considered essential to break down the complexing agents that hold metal ions (such as Sr) in solution and prevent their extraction by subsequent processing. The wet air oxidation process has previous commercial application. In this process the liquid would be held at 325 C (620 F) and 14,000 kPa (2,000 psi) for 1 hour. The metals that would be released from their complexes would precipitate as hydroxides upon cooling. Hydroxides of Sr, nickel, calcium, and iron would occur along with coprecipitated TRU elements and lanthanides. Oxygen and hydroxide would react with organic constituents to form carbonates, oxalates, nitrogen, ammonia, and hydrogen.

Caustic Leach

Caustic leach is the first of three dissolution steps that would be used to reduce the amount of insoluble sludge that would ultimately be processed as HLW. Several hours of digestion at approximately 90 C (200 F) in appropriately designed reactors would be used to dissolve the desired elements. The caustic leach would be 4 molar in sodium hydroxide to solubilize aluminum, nickel ferrocyanide, and cancrinite. The liquid from caustic leaching would be added to the liquid from the initial liquid and solid separation, and the combined stream would be sent to the complexing agent destruction process. The solids from caustic leaching would then be sent to the first acid leach.

First Acid Leach

The first acid leach would be in a mixture that is 4.5 molar in nitric acid and approximately 0.3 molar in oxalic acid. This leaching operation would be expected to solubilize about 90 percent of the following substances: Cr+3, Fe+3, Fe(CN)6-3, Mn+2, MnO2, Ni+3, PO4-3, Pu+4, SO4-2, and Zr+4. The solids from the first acid leach would then be sent to the second acid leach, while the liquid from both acid leaches would be combined and sent to solvent extraction of acidic liquid.

Second Acid Leach

The second acid leach would be in a mixture that is 4.5 molar in nitric acid and approximately 1 molar in hydrofluoric acid. This leaching operation would solubilize the remaining solids to the maximum extent possible. Most of the undissolved material from the second acid leach would be recycled to the caustic leaching operation, while a minor fraction of the undissolved solids would be sent to the HLW vitrification operation.

Purification of Acid Soluble Radionuclides

Tributyl Phosphate Extraction of Transuranic Compounds

The active extractant for this solvent extraction process would be the same as used in the PUREX process, which is 30 percent TBP in a hydrocarbon diluent. In the first extraction, U, Pu, and Np would be extracted into the organic phase. The extracted Pu and Np would be selectively stripped into an aqueous phase and sent to the HLW vitrification process. The U would be stripped separately in a third processing step, and recovered for reuse by re-extraction and re-stripping. This U (approximately 1,400 mt [1,500 tons]) would be available for reuse if a market for the U could be found.

N-diisobutylcarbamoylmethylphosphine Oxide Solvent Extraction

The raffinate from the first TBP cycle would be sent to a N-diisobutylcarbamoylmethylphosphine oxide (CMPO) solvent extraction process to remove trivalent lanthanides, americium, and bismuth. The solvent would be 0.2 molar CMPO and 1.4 molar TBP in a hydrocarbon diluent, which has also been proposed for the transuranic extraction (TRUEX) process. Americium and trivalent lanthanides would be stripped from the organic phase into dilute nitric acid. Bismuth would be removed separately in a separate wash step with a sodium carbonate and EDTA solution.

Am and Lanthanide Ion Exchange

This separation would be accomplished by band displacement cation exchange using cation exchange resins loaded in sequence. Concentrate from CMPO stripping would be loaded on the resin in preparation for separation by displacement cation exchange. Elution of the resin would be with diethylenetriaminepentaacetic acid (DTPA) onto a second zinc-loaded resin. Continued elution would occur through a series of columns established discrete bands of metal ions in sequence depending on the formation constants of the metal ion DTPA complexes. The elution effluent would be divided into three portions. The first and third portions would be sent to the LAW process stream. The second portion would be sent to the HLW process stream.

Crown Ether Solvent Extraction

The raffinate from CMPO extraction would contain Cs, Sr, and Tc, and would require further processing to remove these elements. This raffinate would be concentrated by evaporation, and subsequently contacted with a crown ether solvent (0.2 molar in diluent) to remove these elements. They would be stripped in a second contact, and the strip solution would be concentrated by evaporation and then sent to the HLW process stream.

Ammonium Phosphomolybdate Ion Adsorption

The final acidic processing step would use ammonium phosphomolybdate (APM) to remove Cs from the raffinate from the crown ether extraction process. The adsorbent would be 10 percent APM on an alumina substrate. Because Cs cannot readily by eluted from APM, the loaded sorbent would be transferred to the caustic leach step of the sludge dissolution process. The caustic leach would dissolve 90 percent of the sorbent, releasing Cs into the basic leach liquid.

Removal of Radionuclides From Alkaline Liquid

Cesium Ion Exchange

The combined liquid from caustic leach and complexant destruction would be evaporated to 7 molar sodium hydroxide and put through ion exchange columns containing a resorcinol-formaldehyde ion exchange resin that removes Cs from basic solutions. Four ion exchange columns would be used, with three used for extraction, and the fourth undergoing elution with 1 molar formic acid. The eluted Cs would be sent to HLW process stream.

Strontium Removal by Silicotitanate

The basic stream from Cs ion exchange would be sent to a column containing crystalline silicotitanate, where the Sr in solution would be adsorbed irreversibly. The Pu and Cs could also be adsorbed on the silicotitanate. Because elution is not possible, the loaded adsorbent would be transferred to the acid dissolution reactors, where the silicotitanate would be dissolved, releasing Sr into acid solution.

Technetium Ion Exchange

The raffinate from Sr removal would be sent to strong base anion exchange columns where Tc would be removed as the pertechnetate ion (TcO4-). Elution from the ion exchanger would be by 6 molar nitric acid. The eluant would be concentrated by evaporation and sent to HLW treatment. Nitric acid would be recovered from the evaporator overheads and recycled. The raffinate from Tc removal would be sent to the LAW process stream.

High-Level Waste Concentration and Denitration

From the separation steps described previously, the HLW streams would be combined and concentrated by vacuum evaporation to remove nitric acid until the remaining liquid was a 3 molar nitric acid. The dilute overheads from the evaporator would be sent to acid recovery for reuse as a bulk chemical. The 3 molar nitric acid and the raffinate from the Cs ion exchange process would be combined and undergo denitrification by reaction with sucrose. Sufficient sucrose would be supplied to achieve 0.5 molar nitric acid in the liquid after sucrose conversion. This liquid would be fed to a HLW centrifuge process along with undissolved solids from the final acid dissolution step. The NOx produced would be sent to the acid recovery system for conversion to nitric acid.

Low-Activity Waste Concentration

The LAW streams from the previously described sections would be combined and concentrated by evaporating water to a 7 molar sodium hydroxide solution. The evaporator bottoms product would form the feed to the LAW calcination process, while the evaporator overheads would be used for dilution water or recycled to wash operations in the various separation processes. The LAW remaining following the separations processes would contain approximately 0.32 MCi of radioactivity including: 7.0E-02 MCi of Cs and Ba, 1.10E-02 MCi of Sr and Y, 1.56E-04 MCi of Tc-99, and 1.22E-03 MCi of TRU isotopes.

Recovery and Reuse of Bulk Chemicals

The recovery and reuse of bulk chemicals would take place in four major unit operations. These would be water evaporation and reuse, nitric acid distillation, nitrate destruction, and recovery and recycle of sodium hydroxide. Water from the various process evaporators would ultimately be routed to a wash water tank, where the recycled water would be used to meet the dilution requirements of other parts of the process. Acidic evaporator overheads would be contacted with the NOx streams from the denitration and calcination steps. Hydrogen peroxide and air would be added to convert the NOx to nitric acid. The resulting dilute acid would be concentrated to recover the nitric acid, and the water formed would be used as recycle. The caustic slurry produced in the calcination operation would be evaporated to produce a strong sodium hydroxide solution, which would be recycled to meet process requirements. Excess caustic slurry would be disposed of with the LAW.

Removal of Heavy Metals

A chromium-reduction process would be included to reduce chromium (Cr)+6, which is mobile in groundwater, to Cr+3, which precipitates as the hydroxide and does not have a high mobility. While this would keep the Cr from entering the groundwater, the process would result in a Cr product that would require disposal as a mixed waste. The process would employ the addition of 1.5 molar ammonium hydroxide as a reductant, which would be expected to reduce 99 percent of the Cr. Nitrogen gas would evolve during the reduction reaction and would be vented to the process stack. Insoluble Cr would be removed after reduction by centrifuging, and the solids would be sent to a separate waste processing step.

Clean Salt Process

This process represents a concept that potentially would reduce the LAW volume. The primary salts produced by the process would be sodium nitrate and aluminum nitrate. There is a concern that Cs-137 would also be extracted by the process and cause Cs-137 to enter the LAW stream. Varying degrees of decontamination could be achieved by increasing the number of recrystallization stages that are used on the waste stream.

B.3.7.4 Description of Immobilization and Off-Gas Treatment

High-Level Waste Melter

The evaporator bottoms from the HLW evaporator would be routed to the melter feed section. After sampling, cooling, and adjusting the slurry, it would be transferred to the melter feed system. This would be a batch system, which would mix the slurry and glass-forming frit. This mixture would then be continuously fed to the HLW melter system. The high temperature of the melter would convert the incoming feed slurry to molten glass containing 20 percent waste oxides. The HLW melter would be joule-heated and operate at a temperature of 1,200 C (2,200 F). Volatilized melter feed components would form a separate off-gas stream that would pass to off-gas processing. Periodically the molten glass would be poured into cylindrical stainless steel canisters. The glass-filled canisters would be plugged and welded shut before being decontaminated to remove surface decontamination. The cooled canisters would be taken to interim onsite storage before final transportation to the potential geologic repository.

High-Level Waste Off-Gas Processing

The HLW off-gas processing for the Ex Situ Extensive Separations alternative is similar to the HLW off-gas processing for the Ex Situ Intermediate Separations alternative. Each of the tank waste alternatives that uses high-temperature processing (vitrification or calcination) would make extensive use of recycle streams to recycle back into the treatment process volatile radionuclide and chemical constituents captured in the off-gas systems. The recycle streams would be used to minimize the generation of secondary waste. For this alternative, 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, namely Tc-99 and Hg, in these recycle streams. For comparison purposes, it has been assumed for this alternative that the bleed stream percentage would be the same one percent of the recycle stream and that this secondary waste stream would be stabilized by some low temperature process (such as grout). The HLW off-gas system would receive hot gases from the HLW melter. The gases would be first cooled and scrubbed with water to remove most of the particulates and water soluble materials. The quenched off-gas would pass through a mist eliminator to remove fine water droplets and then through HEPA filters to remove the majority of the radionuclide particles. The scrubbed off-gases would flow to an SO2 adsorption process and a catalytic NOx reactor before being discharged. The SO2 would be removed by adsorption on CuO beds prior to NOx destruction. The desorbed sulfur as hydrogen sulfide would be converted into elemental sulfur by a Claus Unit, which would discharge its sulfur product to the LAW vitrification facility for use in LAW cullet disposal.

Low-Activity Waste Melter

Evaporator bottoms from the LAW evaporator would be sampled, cooled, and adjusted before being transferred to the LAW melter feed system. The melter feed and dry-glass formers would be fed into a combustion melter where they would combine and form molten LAW glass. The LAW glass would exit the melter and pass through a quenching and crushing stage resulting in pea-sized fractured glass known as cullet. The final design decision concerning the form of the LAW glass has not yet been made. While this alternative is based on the concept of glass cullet, ultimately other forms such as canisters or monoliths could be chosen. For purposes of calculating impacts for this EIS, it was assumed that the cullet would be analyzed to ensure that it meets product specifications, mixed with a matrix material, placed into large disposal containers, and transported to onsite vaults for disposal. The final waste form matrix for the cullet has not been specified. Various types of waste form matrices available are discussed in Section B.9.3.

Low-Activity Waste Off-Gas Processing

The LAW off-gas processing for the Ex Situ Extensive Separations alternative is similar to the LAW off-gas processing for the Ex Situ Intermediate Separations alternative. The LAW off-gas system would receive hot gases from the LAW melter. The gases would be first cooled and scrubbed with water to remove most of the particulates and water soluble materials. The quenched off-gas would pass through a mist eliminator to remove fine water droplets and then through HEPA filters to remove the majority of the radionuclide particles. The scrubbed off-gases would flow to an SO2 adsorption process and a catalytic NOx reactor before being discharged to the atmosphere. The recovered SO2 would be converted into elemental sulfur by a Claus Unit, which would discharge its sulfur product to the LAW vitrification facility for use in LAW cullet disposal.

Low-Activity Waste Calcination

The bottoms from the LAW and other feed streams would be fed to a modified plasma arc calcination process for destroying nitrate and recovering sodium hydroxide. The main modification would be using ammonia as the combustion fuel. The calciner feed would be heated to 800 C (1,470 F) under atmospheric pressure that would vaporize the contained water and destroy sodium nitrate. The calciner off-gases would be quenched, water scrubbed, reacted to remove NOx, filtered, and sent to the process stack. The calciner molten salt stream would then be redissolved in a water quench. The quench solution would be expected to contain the majority of the Cs and Tc.

Post Remediation

When processing of the tank waste has been completed, the processing facilities would be decontaminated and decommissioned in the following manner.

  • Processing equipment will be decontaminated sufficiently to allow onsite disposal in a low-level waste burial ground.
  • Processing facilities will be decontaminated to the extent possible and then entombed in place. The exact materials which will be used to cover processing facilities have not been decided.

B.3.7.5 Implementability

The Ex Situ Extensive Separations alternative has the same uncertainties for retrieving and transferring the waste as those listed for the Ex Situ Intermediate Separations alternative (Section B.3.5.4). In addition, this alternative consists of concepts that are intended to reduce the volume of HLW. Many of these concepts have no testing to affirm their applicability. The key issues relating to this alternative are:

  • The performance of key processes has been assumed in the absences of substantive data. Further testing and development would be required to ensure that the processes would function as intended and make the required separations; and
  • Quantitative performance requirements have not been established for many of the processes and functions. Further engineering would be dependent on developing a process that will meet the quantitative performance requirements.

The HLW canister s produced under this alternative would have a higher thermal loading than other alternatives and the assumed method of interim onsite storage, which relies on dry storage with passive cooling, would require further evaluation. This alternative may 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 are adequately treated during waste processing and vitrification.

B.3.8 EX SITU/IN SITU COMBINATION ALTERNATIVE S

B.3.8.1 General Description of the Alternative s

The Ex Situ/In Situ Combination 1 and 2 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 may be appropriate to implement different alternatives for different tanks. There is a wide variety of potential combinations of alternatives that could be developed, and there are many potential criteria that could be used to select a combination of alternatives for implementation. The Ex Situ/In Situ Combination 1 and 2 alternative s described in the following text were developed to bound the impacts that could result from a combination of alternatives, and are intended to represent a wide variety of potential alternatives that could be developed to remediate the tank waste.

The Ex Situ/In Situ Combination alternative s represent a combination of the In Situ Fill and Cap and Ex Situ Intermediate Separations alternatives. Under the approach used to represent this alternative, tanks would be evaluated on a tank-by-tank basis to determine the appropriate remediation method based on the contents of the tank. The objective would be to effectively treat the tank waste in a manner that has acceptable risk and less overall cost than the Ex Situ Intermediate Separations alternative. This objective could be achieved by selecting tanks for ex situ treatment based on their contribution to post-remediation risk. Those tanks that are not selected for ex situ treatment would be treated in situ by filling and capping. Waste from tanks selected for ex situ treatment would be retrieved from the tanks 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 as well as the LAW retrievable disposal vaults from ex situ treatment.

Ex Situ/In Situ Combination 1 Alternative

Approximately one-half of the volume of the tank waste would be treated by the ex situ method and one-half would be treated by the in situ method. By selectively retrieving tanks for ex situ treatment, approximately 90 percent of the contaminants that contribute to long-term risks would be disposed of ex situ while retrieving only 50 percent of the waste.

Ex Situ/In Situ Combination 2 Alternative

Approximately 30 percent of the volume of the tank waste would be treated by the ex situ method and 70 percent would be treated by the in situ method. By selectively retrieving tanks for ex situ treatment, approximately 85 percent of the contaminants that contribute to long-term risks would be disposed of ex situ while retrieving only 30 percent of the waste.

B.3.8.2 Selection Process

Ex Situ/In Situ Combination 1 Alternative

There are many potential criteria that could be used to develop a selection process. Additional waste characterization and analysis would be necessary to implement this alternative. The Ex Situ/In Situ Combination 1 alternative presented in the EIS is an alternative that was developed to represent the numerous alternatives that could be chosen. For example purposes, this EIS has examined a selection process based on retrieving those tanks containing substances that represent the greatest risk to human health. This example selection process may not be the exact selection criteria that would be chosen, but it illustrates the impacts of the Ex Situ/In Situ Combination 1 alternative.

The objective of the selection process was to examine the published characteristics of the radionuclides in the tanks and select the minimum number of tanks to be retrieved that would result in a risk of contracting cancer to a hypothetical onsite farmer in the future that would be comparable to the ex situ alternatives. Examining the risk calculations results for the Ex Situ Intermediate Separations alternative demonstrated that recovering 90 percent of the mobile constituents from the tanks would meet the established criteria and result in residual risks that fall between those for Ex Situ Intermediate Separations and In Situ Fill and Cap alternatives . The risk calculations showed that the long-term risks were caused by the mobility of four tank waste constituents: U-238, Tc-99, C-14, and I-129. Consequently, the selection process chosen was one in which 90 percent of these mobile constituents would be retrieved, assuming that 99 percent of the contents of any given tank could be retrieved. The selection process for the DSTs and SSTs was based on the same principle. Similarly, risk calculations showed that only a single chemical constituent, the nitrate anion, resulted in a Hazard Index (HI) value of greater than 1.0 for the hypothetical onsite farmer in the future. Because nitrate is present in all the tanks in amounts far exceeding those of the radionuclides (107,00 mt), virtually all of the tanks would have to be retrieved to recover 90 percent of this constituent.

The tank inventory for the SSTs showed the following amounts for the mobile species: U (1,423 mt); Tc-99 (1.64 mt); I-29 (0.24 mt); and C-14 (0.004 mt). The U is present in amounts almost 1,000 times greater than the remaining mobile elements. The selection process started by assuming retrieval of the tank with the greatest published U content, tank TX-113. The next tank selected was the one with the second highest U content, tank BY-104. The selection process was repeated until the cumulative U recovery was 90 percent, and was then repeated for the remaining three mobile elements until their cumulative recovery reached 90 percent. The results of this procedure, as displayed in Figure B.3.8.1, show that the cumulative retrieval of the constituents of concern would be 90 percent by the time that 60 SSTs have been retrieved. This procedure would also recover approximately 85 percent of the Cs and 65 percent of the Sr remaining in the SSTs.

Figure B.3.8.1 Ex Situ/In Situ Combination 1 - Single-Shell Tanks

For the DSTs, the procedure was similar, but modified slightly because the published data (WHC 1995d) do not report U in the DSTs. The selection process for the DSTs was to retrieve the tanks based on their Tc-99 content until the cumulative recovery was 90 percent, then retrieve additional tanks as required until the cumulative recovery of C-14 was 90 percent. The results of this modified procedure, as displayed in Figure B.3.8.2, show that the cumulative retrieval of Tc-99 and C-14 would be 90 percent when 10 selected tanks have been retrieved. This process would recover approximately 85 percent of the Cs and Sr in the DSTs. While the selection process was directed towards retrieving mobile groundwater radionuclides, an additional benefit was retrieving 69 percent of the nitrate and waste from 25 of the 50 current Watchlist tanks.

Figure B.3.8.2 Ex Situ/In Situ Combination 1 - Double-Shell Tanks

Ex Situ/In Situ Combination 2 Alternative

The selection process described for Ex Situ/In Situ Combination 1 was modified to provide for the ex situ treatment of the largest contributors to long-term risks (Tc-99, C-14, I-129, and U-238) while limiting the waste to be processed. This modified selection process also included Np-237 in the tank selection process. This modified selection criteria resulted in 25 tanks selected for ex situ treatment instead of 70 tanks, based on the currently available characterization data. The actual number of tanks selected would be based on future characterization of the tanks.

By selecting the appropriate tanks for ex situ treatment, up to 85 percent of the constituents that are the greatest contributors to long-term risk would be disposed of ex situ while retrieving approximately 30 percent of the waste. Under the Ex Situ/In Situ Combination 2 alternative with the retrieval of approximately 25 selected tanks, 85 percent of Tc-99, 80 percent of C-14, 80 percent of I-129, and 50 percent of the U-238 would be retrieved rather than 90 percent as with the Ex Situ/In Situ Combination 1 alternative (Figure B.3.8.3).

Figure B.3.8.3 Ex Situ/In Situ Combination 2 - Single- and Double-Shell Tanks

B.3.8.3 Facilities to be Constructed

Ex Situ/In Situ Combination 1 Alternative

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

The following list identifies the major activities that 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 facilities;
  • Construct a HLW vitrification facility;
  • Construct a LAW vitrification facility; and
  • Construct a LAW disposal facility (vaults).

For the in situ component of this alternative, the following construction activities would take place:

  • Install gravel handling systems; and
  • Construct gravel storage sites for stockpiles.

A detailed description of facilities to be constructed for the Ex Situ Intermediate Separations alternative is included in Section B.3.5.2. A description of facilities to be constructed for the In Situ Fill and Cap alternative is included in Section B.3.3.2.

Ex Situ/In Situ Combination 2 Alternative

Construction activities required for this alternative would involve constructing all of the facilities identified in the Ex Situ Intermediate Separations alternative and In Situ Fill and Cap alternative, but at a reduced scale (Figure B.3.8.4). For the ex situ portion, the volume of waste requiring treatment and immobilization would come from 25 tanks instead of 177 tanks. In situ treatment would be required for the remaining tanks.

Figure B.3.8.4 Ex Situ/In Situ Combination 2 Facility Layout

The following list identifies the major activities that 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 facilities;
  • Construct a HLW vitrification facility;
  • Construct a LAW vitrification facility; and
  • Construct a LAW disposal facility (vaults).

For the in situ component of this alternative, the following construction activities would take place:

  • Install gravel handling systems; and
  • Construct gravel storage sites for stockpiles.

A detailed description of facilities to be constructed for the Ex Situ Intermediate Separations alternative is included in Section B.3.5.2. A description of facilities to be constructed for the In Situ Fill and Cap alternative is included in Section B.3.3.2.

B.3.8.4 Description of the Process

Processing Retrieved Waste

The waste that would be retrieved under either of the combination alternatives would be treated using the process identified for the Ex Situ Intermediate Separations alternative. For further details of the process, see Section B.3.5.

Processing Nonretrieved Waste

Tanks that would not be selected for retrieval under either of the combination alternatives would be treated in situ using the methods identified in the In Situ Fill and Cap alternative. For further details of this alternative, see the In Situ Fill and Cap alternative in Section B.3.3.

Post Remediation

After remediation, tank farm closure and decontamination and decommissioning would take place. Tank farm closure would involve the following activities:

  • Retrieved tanks would be stabilized with gravel (in situ tanks would have been stabilized during in situ operations);
  • Tank farm structures such as MUSTs, pump pits, valve boxes, and diversion boxes would be stabilized with grout; and
  • Hanford Barriers would be constructed over SSTs, DSTs, and LAW retrievable disposal vaults.

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

B.3.8.5 Implementability

Because these alternatives represent a combination of alternatives, the implementability is also a combination of those issues identified in discussing the implementability of both the In Situ Fill and Cap alternative and the Ex Situ Intermediate Separations alternative (Sections B.3.3.4 and B.3.5.4, respectively). However, developing acceptable tank selection criteria is unique to the Ex Situ/In Situ Combination 1 and 2 alternatives and would require more complete and accurate waste characterization than currently exists . There are numerous ways to fully develop these alternatives. The final selection criteria would be based on tank characterization program results, short-term versus long-term risks, and additional development of the Ex Situ Intermediate Separations and In Situ Fill and Cap alternatives.

The in situ portion of these alternatives 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 these alternatives would meet all regulations for disposal of hazardous, radioactive, or mixed waste assuming that the hazardous waste components would be adequately treated during processing or vitrification.

B.3.9 PHASED IMPLEMENTATION ALTERNATIVE

B.3.9.1 General Description

The Phased Implementation alternative would provide a mechanism to implement tank waste remediation in a two-step process. The first phase would be a proof-of-concept demonstration phase of the separations and immobilization processes for selected tank waste. The first phase would use demonstration-scale treatment facilities. The second phase would involve scaling up or replacing the demonstration-scale processes to treat the remaining tank waste. The Phased Implementation approach could be applied to any of the tank waste alternatives involving waste treatment; however, for purposes of analysis the Ex Situ Intermediate Separations alternative with some additional separations was selected as a representative alternative for analysis (Figure B.3.9.1). The description of the Phased Implementation alternative and the estimates for resources and emissions were developed from the Ex Situ Intermediate Separations alternative. This basis included vitrified LAW glass cullet as a LAW form and vitrified borosilcate glass as a HLW form. Other types of glass or waste forms could be selected for HLW or LAW treatment; however, they would have to meet the repository acceptance criteria or performance assessment criteria.

Figure B.3.9.1 Phased Implementation

B.3.9.1.1 Phase 1

Under Phase 1, readily retrievable, well-characterized waste from the DSTs (including SST saltwell liquids transferred to DSTs) would be retrieved and processed in two separate demonstration facilities. One of the facilities would process liquid waste to produce an immobilized LAW, while the other facility would produce an immobilized LAW and vitrified HLW. The facility with both LAW and HLW immobilization could be constructed as separate facilities.

Retrieval

Liquid waste retrieval for LAW treatment would be accomplished by using existing waste transfer systems currently installed in the DSTs. The waste identified for HLW processing would be retrieved from selected tanks containing higher concentrations of HLW constituents. The waste identified for HLW processing would be sludge washed to reduce the volume of vitrified HLW. The washed sludges would be transferred directly to the HLW treatment facility for vitrification. The HLW that would be conditioned and retrieved under currently planned demonstrations for retrieval as sludge washing would be used as feed for HLW processing.

Separations

Separations would consist of performing a solid-liquid separation followed by additional chemical processing steps on the liquid stream to remove HLW and TRU constituents to the extent required to meet specifications for the immobilized LAW.

Immobilization

The LAW would be processed using a technology that would meet LAW acceptance specifications. The acceptance specifications would have specific requirements for size, chemical composition limits, isotopic content, and physical parameters. The immobilized LAW waste would be placed into containers for interim storage as future onsite near-surface disposal. For purposes of analysis in this EIS, vitrification was selected as the immobilization process.

The HLW would be processed into a borosilicate glass form that would meet the established waste form acceptance criteria at the potential geologic repository. The HLW would be placed into canisters and overpacked into HMPCs for handling and transport. The HMPCs would be transported to an onsite interim storage facility pending offsite disposal at the potential geologic repository.

Disposal

There would be no disposal component for Phase 1 of the Phased Implementation alterative. The immobilized LAW and HLW would be packaged and stored onsite in interim storage facilities and disposed of during the implementation of Phase 2.

B.3.9.1.2 Phase 2

Following the successful implementation of Phase 1, Phase 2 would be implemented to complete the tank waste remediation. Under Phase 2, the waste remaining in the tanks and MUSTs would be retrieved and processed in new full-scale facilities. The new full-scale facilities would be two 100 mt/day (110 ton/day) LAW facilities and one 10 mt/day (11 ton/day) HLW facility.

Retrieval

Waste retrieval for Phase 2 would involve constructing and operating a full-scale retrieval system that would be capable of retrieving as much waste as practicable (assumed to be 99 percent) from all SSTs, DSTs, and MUSTs. The waste retrieval systems and processes used for Phase 2 would be the same as those described for the Ex Situ Intermediate Separations alternative.

Separations

Separations would consist of the same processes described for the Ex Situ Intermediate Separations alternative, followed by additional chemical processing steps on the LAW stream to remove HLW and TRU constituents to the extent required to meet specifications for the immobilized LAW.

Immobilization

The HLW and LAW immobilization processes used during Phase 2 would be the same processes demonstrated during Phase 1.

Disposal

The disposal of immobilized HLW and LAW would be the same for the Ex Situ Intermediate Separations alternative. The immobilized LAW would be placed into disposal containers at the treatment facility and transported to an onsite near-surface retrievable disposal facility.

The vitrified HLW would be placed into canisters, packaged into HMPCs, and placed in an aboveground storage facility. The canisters would then be shipped to the potential geologic repository for permanent disposal.

B.3.9.2 Facilities to be Constructed

B.3.9.2.1 Phase 1

This alternative would involve constructing two independent waste treatment facilities. One facility would produce immobilized LAW and the other facility would produce immobilized LAW and vitrified HLW. Each treatment facility would be constructed with support facilities as required to support each operation, as shown in Figure B.3.9.2.

Figure B.3.9.2 Phased Implementation Facility Layout

Necessary pipelines would be constructed from the designated tanks in the 241-AP Tank Farm to the treatment facilities. Additional pipelines would be constructed between the existing waste transfer system and the HLW processing facility. These pipelines would either be buried or constructed on grade inside a shielded pipe run.

The existing Canister Storage Building would be modified to accommodate interim storage of HLW canisters. This would include modifying the underground vaults and ventilation system to accommodate the physical and thermal leaching associated with interim storage of all HLW produced during Phase 1.

The existing grout vaults would be modified to accommodate interim LAW storage of the containerized LAW 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.

Separations Facilities

Each of the waste treatment facilities would include an integral separations and immobilization facility. The separations facilities would include the processing equipment to filter solids and remove selected radionuclides from the waste stream.

Low-Activity Waste Immobilization

Both of the waste treatment facilities, which would include LAW immobilization facilities, would be sized to produce the equivalent of 20 mt/day (22 tons/day) of vitrified waste at a sodium oxide loading of 15 weight percent. This basis was used to estimate the required facility size and resource requirements.

The facility that only treated LAW would be smaller than the combined LAW plus HLW facility and would have an overall footprint of 40 by 120 m (130 by 390 ft). The facility that treated LAW and HLW would have an overall footprint of 60 by 120 m (200 by 390 ft).

High-Level Waste Immobilization

The HLW immobilization facility would be sized to produce the equivalent of 1 mt/day of vitrified waste at a waste oxide loading of 20 weight percent.

Support Facilities

Each of the processing facilities would require its own support facilities. These facilities would include:

  • Cold chemical storage, supply, and makeup;
  • Substation and electrical distribution;
  • Cooling tower;
  • Operations control;
  • Regulated entrance building;
  • Emergency generator;
  • Emergency response center;
  • Operations support buildings;
  • Process chemical storage; and
  • Process water and potable water lines. These would be installed to connect the sites with existing distribution lines in the 200 East Area.

B.3.9.2.2 Phase 2

Construction activities required for Phase 2 would involve constructing all of the facilities identified in the Ex Situ Intermediate Separations alternative, but with reduced scale waste treatment and support facilities (Figure B.3.9.3). Because Phase 1 operations would produce up to 13 percent of the immobilized LAW volume, the size of the treatment facilities required for the Phase 2 would be approximately the same as the ex situ treatment described for the Ex Situ Intermediate Separations alternative. The facilities that would be constructed for Phase 2 operations would include:

  • Waste retrieval and transfer facilities as described for Ex Situ Intermediate Separations;
  • Two separations and LAW treatment facilities that would be similar to the vitrification facility described for the Ex Situ Intermediate Separations alternative, each with a 100-mt/day (110-ton/day) capacity ;
  • A 10-mt/day (11-ton/day) HLW vitrification facility that would be similar to the HLW vitrification facility described for the Ex Situ Intermediate Separations alternative;
  • Support facilities that would provide utilities, resources, and personnel support to the Phase 2 treatment facilities;
  • A LAW disposal facility that would provide for retrievable disposal of LAW produced throughout Phase 1 and Phase 2 (this facility would be the same as the LAW disposal facility described for the Ex Situ Intermediate Separations alternative);
  • A HLW interim storage facility for interim storage of the HMPCs; and
  • Hanford Barriers over the LAW retrievable disposal facility and tank farms following waste remediation.

Figure B.3.9.3 Phased Implementation (Total Alternative) Facility Layout

B.3.9.3 Description of the Process

B.3.9.3.1 Phase 1

Overview

The following processes would be included to treat tank waste under Phase 1:

  • Retrieve selected waste for LAW treatment;
  • Retrieve selected waste for HLW treatment;
  • Transfer liquid waste for LAW treatment to a receiver tank;
  • Following sludge washing, transfer selected waste for HLW processing directly to the HLW plant;
  • Perform separations to remove Cs, Tc, Sr, TRU elements, and sludges from the LAW feed stream;
  • Store the separated Cs and Tc produced during separations at the treatment facilities, or package and transport the separated Cs and Tc to onsite interim storage for future waste treatment;
  • Return sludges containing Sr and TRU waste separated during LAW treatment to the DSTs for storage;
  • Vitrify both the LAW and HLW;
  • Place the vitrified HLW into canisters;
  • Place the vitrified LAW into containers; and
  • Transport the immobilized waste to onsite interim storage facilities.

Each waste treatment facility would be designed, built, and operated separately. It is assumed that the technologies selected for the separations and immobilization processes would produce a waste form that meets DOE specifications. Therefore, the process description for the Phased Implementation alternative has been developed using the Ex Situ Intermediate Separations alternative, with additional separations processing as a basis. This approach provides for analyzing the alternative using representative technologies.

Tank Waste Retrieval and Transfer

The first step in waste processing would be to recover and transfer waste to be treated at LAW facilities from the tanks to the DST feed tanks. The waste feed to the LAW facilities would be retrieved and transferred in batches from selected DSTs into two existing DSTs designated as feed tanks. Each LAW facility would have one designated DST as a feed tank. The waste feed stream for LAW treatment would be primarily DST liquid waste but could include SST saltwell liquids or SST waste recovered during retrieval demonstrations. The waste feed to the HLW plant would be retrieved and transferred separately. The selected waste for HLW treatment would be sludge washed and the washed solids would be routed directly to the HLW processing facility. The waste treated at the HLW facility would be HLW recovered directly from selected tanks and may or may not include the HLW that would be separated at the LAW treatment facilities.

Liquid waste retrieval and transfer would use equipment and systems currently in place in the DST farms. Sludge washing and slurry pumping using techniques identified for the Ex Situ Intermediate Separations alternative would be used to retrieve waste for treatment at the HLW facility.

Separations

For purposes of analysis, the separations processes described for the Ex Situ Intermediate Separations and Ex Situ Extensive Separations alternatives were used.

The specific technologies used for separations and immobilization have not been defined, and therefore are not specifically identified or discussed for this alternative. The separations and immobilization technologies used for waste immobilization would be controlled by waste product specifications, which would control the physical properties, chemistry, radionuclide content , and volume of the immobilized LAW and HLW.

Separations prior to LAW immobilization would be performed to remove the Cs, Tc, Sr, TRU elements, and entrained sludge particles from the waste stream. The separated Cs and Tc radionuclides would either be stored at the treatment facilities or packaged in canisters for onsite dry storage, the treated sludges along with the Sr and TRU elements would be returned to the DSTs for storage, and the treated liquid waste stream would then be immobilized.

Immobilization

The LAW waste stream would be immobilized using a technology to treat the waste that would yield a stabilized waste product similar to vitrified glass with regard to waste performance characteristics. Vitrification was assumed for purposes of evaluation. The immobilized LAW would be placed into canisters 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 immobilized LAW would be sealed in steel containers at the Phase 1 treatment facilities for interim storage and eventual onsite disposal. The sealed LAW containers would be transported to the four existing grout vaults nearby for temporary storage until the Phase 2 LAW onsite disposal vaults are ready to receive the containerized LAW material. The Phase 1 immobilized LAW would be transported to this new disposal vault site to be entombed with the Phase 2 LAW waste.

The DST waste would be retrieved and transferred to the receiver tanks or in the case of the HLW, directly to the HLW processing facility. Waste from the receiver tanks would be transferred to the treatment facilities on an as-needed basis. The HLW would be vitrified into borosilicate glass. The HLW plant would be designed to produce the equivalent of 1 mt/day of HLW glass at a 20 weight percent waste oxide loading. The vitrified HLW would be placed directly into canisters. The HLW canisters (0.61 m [2 ft] in diameter by 4.57 m [15 ft] long) would be placed in transportation casks and transported to the Canister Storage Building for interim storage. The canisters would be removed from the transportation casks and placed into storage tubes at one of the Canister Storage Building vaults.

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

B.3.9.3.2 Phase 2

Overview

The tank waste treatment process for Phase 2 would include 1) retrieving the waste from tanks; 2) separating the LAW from the HLW; 3) immobilizing the LAW stream; 4) vitrifying the HLW stream; 5) disposing of the LAW onsite; 6) temporarily storing the HLW; and 7) transporting the HLW to the potential geologic repository at a future date. The processes used for waste treatment during Phase 2 would be the same processes demonstrated during Phase 1 operations.

Tank Waste Retrieval and Transfer

The process used for waste retrieval and transfer during Phase 2 would be the same as the process described for retrieval under the Ex Situ Intermediate Separations alternative. Waste retrieval during Phase 1 mainly would consist of removing liquid waste from DSTs. These DSTs would require additional waste retrieval during Phase 2 to remove sludges and meet requirements for waste residuals.

Separations

Separations processes used during Phase 2 would be the same processes that were developed and demonstrated during Phase 1. The LAW remaining following the separations process would contain approximately 17 MCi of radioactivity, including 10 MCi of Cs and Ba, 6.8 MCi of Sr and Y, 2.59E-02 MCi of Tc-99, and a total of 1.22E-02 MCi of TRU isotopes.

Immobilization

Immobilization of the HLW and LAW streams during Phase 2 would use the same processes that were developed and demonstrated during Phase 1. The HLW treatment during Phase 2 would also include vitrifying the Cs and Tc waste that was separated to produce the LAW during Phase 1 operations. The operation of the Phase 1 treatment processes would allow for optimizing the processes used during waste treatment at the new Phase 2 facilities.

Post Remediation

The post-remediation process for this alternative would be the same as that described for the Ex Situ Intermediate Separations alternative. When tank waste processing has been completed, the processing facilities would be decontaminated and decommissioned in the following manner:

  • Processing equipment would be decontaminated sufficiently to allow onsite disposal in a low-level waste burial ground.
  • Processing facilities would be decontaminated to the extent possible and then entombed in place. The exact materials that would be used to cover processing facilities have not been defined.

B.3.9.4 Implementability

Because the Phased Implementation alternative is only a demonstration-scale facility, many of the implementability issues surrounding the ex situ alternatives are reduced in complexity. Issues relating to implementing this alternative can be grouped into the following categories:

  • Capability to produce immobilized waste within the waste form specifications developed; and
  • Successful operation of the Phased Implementation alternative (Phase 1) is critical to the follow-on implementation of Phase 2 (the completion of retrieval treatment and disposal activities).

Phase 1 shares some of the same implementability issues as the Ex Situ Intermediate Separations alternative and the Ex Situ Extensive Separations alternative because several of the separations and treatment processes that would be used during Phase 1 were assumed to be similar to the processes described for those alternatives. Performance of key processes has been assumed in the absence of substantive data. Cost estimates have a high degree of uncertainty because some of the processes are unproven.

The phased implementation approach provides the opportunity for significantly improving the process design and facility configuration for Phase 2. Lessons learned and processing experience gained during Phase 1 would be applied to the construction and operation of Phase 2 facilities. This approach would allow for increased operating efficiency during Phase 2.

During Phase 2, the waste would be retrieved from the tanks using the same processes as the other ex situ alternatives, and thus Phase 2 shares the same implementability issues regarding retrieval as the other ex situ alternatives.

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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