• Military

• WMD Menu                           

• Introduction
• Systems
• Facilities
• Agencies
• Operations
• Countries
• Hot Documents
• News
• Reports
• Policy
• Budget
• Congress
• Links

• Intelligence
• Homeland Security
• Space

3.2 SITE AND WASTE DESCRIPTION

3.2.1 Tank Waste

3.2.1.1 History

Tank waste is the by-product of producing plutonium and other defense-related materials. From 1944 through 1990, chemical processing facilities at the Hanford Site processed irradiated or spent nuclear fuel from defense reactors to separate and recover plutonium for weapons production. As new, improved processing operations have been developed over the last 50 years, processing efficiency has improved and the waste compositions sent to the tanks for storage have changed both chemically and radiologically. T and B Plants were the first separations facilities built at the Site. The separations processes carried out at these plants recovered only plutonium; consequently, all remaining components of the dissolved fuel elements, including uranium, were sent to the waste tanks.

Later, processes were developed to recover uranium, which was recycled back into the reactor fuel cycle. Many of the chemical processes associated with plutonium recovery from spent nuclear fuel involved dissolving the material in nitric acid. The resulting acidic waste streams were made alkaline by adding sodium hydroxide or calcium carbonate before being transferred to the tanks. These processing steps produced large volumes of sodium nitrate salts in the tanks. Table 3.2.1 shows the major processing facilities that served as sources of tank waste (see Figure 3.2.3 for location s ).

Table 3.2.1 Waste Generating Facilities

Chemical processing generated approximately 1.5E+09 liters (L) (4.0E+08 gallons [gal]) of waste. More than 1.1E+09 L (3.0E+08 gal) of waste was sent to underground storage tanks throughout the production period. Volume reduction practices were followed to maintain waste volumes within available tank space. The tanks were single-shell tanks (SSTs) or double-shell tanks (DSTs).

Through evaporation, concentration, and the past practice of discharging dilute waste to the ground, the waste volume has been reduced to approximately 2.1E+08 L (5.6E+07 gal) (Hanlon 199 6 ). Discharging SST liquid to the ground was stopped in 1966, and since then, no waste from SSTs or DSTs has been discharged to the ground intentionally.

3.2.1.2 Tank Farm Description

The first 149 waste storage tanks constructed were SSTs. An SST is an underground storage tank with carbon-steel sides and bottom surrounded by a reinforced concrete shell (Figure 3.2.1). The tops of the tanks are buried approximately 2.5 meters (m) (8 feet [ft]) belowground for radiation shielding. The larger tanks have multiple risers (shielded openings) that provide tank access from the surface. These risers provide access points for monitoring instrumentation, camera observation, tank ventilation systems, and sampling. Sixty-seven of the SSTs are known or assumed to have leaked 2.3 million to 3.4 million liters (600,000 to 900,000 gallons) of liquids (Hanlon 1996 ).

An ongoing vadose zone characterization program that was initiated in April 1995 (DOE 1995t) is providing new baseline characterization data on the potential contaminant distribution in the vadose zone beneath and in the vicinity of the SSTs. This has resulted in additional information for the SX Tank Farm. The characterization effort relies on geophysical logging of existing drywells using a spectral gamma logging system with a high-purity intrinsic germanium detection device to provide assays of gamma-emitting radionuclides near the drywells (Brodeur 1996).

Figure 3.2.1 Single-Shell Tank Configuration

Ten of the 15 tanks in the SX Tank Farm are assumed or verified as leaking, as discussed in Volume Five, Appendix K. Ninety-five drywells ranging in depth from 23 m (75 ft) to 38 m (125 ft) from ground surface were logged with the Spectral gama logging system in the SX Tank Farm. The most abundant and highest concentration radionuclide detected was cesium-137, which was detected in virtually every borehole (Brodeur 1996). Cesium-137 was detected at the following depths in several drywells: 23 m (75 ft) in drywells 41-09-03 and 41-08-07, 32 m (105 ft) in 41-09-04, 27 m (90 ft) in 41-11-10, and 38 m (125 ft) in 41-12-02.

Other gamma-emitting radionuclides detected include cobalt-60, europium-152, and europium-154, which were generally found near the surface and are believed to be the result of spills (Brodeur 1996). Cobalt-60 was found in drywell 41-14-06 only and was detected at a depth of 17 to 23 m (55 to 76 ft) below ground surface. The data are unclear as to whether relatively immobile contaminants such as cesium-137 would be found dispersed laterally within the vadose zone (i.e., at observed concentrations laterally several meters from the drywells) at the depths of over 30 m (100 ft) based on ambient conditions and vadose zone contaminant transport via advective flow in interstitial pore spaces. There may be other transport mechanism(s) occurring. The viability of any other potential transport mechanism has not yet been demonstrated but is one of the objectives of the ongoing investigations.

The last 28 tanks constructed were DSTs, which have two carbon-steel tanks inside a reinforced concrete shell (Figure 3.2.2). This design provides improved leak detection and containment of the waste. To the present time, no leaks have been detected in the annulus, the space between the inner and outer tanks. The space between the tanks houses equipment to detect and recover waste in the event that the inner tank develops a leak. Like the SSTs, the DSTs are buried belowground and have risers for tank monitoring and access.

The tanks are arranged in groups, referred to as tank farms, with each tank farm containing 2 to 18 tanks. The SST farms typically were interconnected in a series or cascade that allowed the waste to be pumped into the first tank, overflow into the next tank, and so on throughout the cascade series. This process allowed solid particles to settle into the first few tanks of a cascade and allowed the liquid in the last tank to be discharged into a crib (subsurface drain system). The practice of discharging tank waste to cribs no longer occurs. A summary of the number and size of SSTs and DSTs and their locations is shown in Table 3.2.2 and Figure 3.2.3.

Also included in the tank farm system are approximately 40 inactive and 20 active miscellaneous underground storage tanks (MUSTs). The inactive MUSTs, which are smaller than the SSTs and DSTs, were used for settling solids out of liquid waste before decanting the liquid to cribs, reducing the acidity of process waste, uranium recovery operations, collecting waste transfer leakage, and waste handling and experimentation. The active MUSTs still are used as receiver tanks during waste transfer activities or as catch tanks to collect potential spills and leaks. The volume of waste in all the MUSTs combined is less than one-half of 1 percent of the total tank inventory (WHC 1995n).

Figure 3.2.2 Double-Shell General Configuration

Figure 3.2.3 Tank Farm Locations in 200 East and 200 West Areas

Table 3.2.2 Size and Number of Tanks by Type

3.2.1.3 Waste Characterization

Tank waste characterization is the process of determining the physical, radiological, and chemical properties of the waste. Considerable historical data are available and have been used to estimate the contents of the storage tanks. Historical data provide a basis for an overall tank waste inventory and are compiled from invoices of chemical purchases and records of waste transfers and processing.

Historical-based data for SSTs and laboratory data and characterization reports for DSTs provide the basis for radioactive and mixed waste inventory estimates used in this EIS. These inventory estimates, as provided in Volume Two, Appendix A, are adequate for a detailed evaluation of impacts (WHC 1995d).

A considerable amount of inventory information is available from process records and past sampling activities. However, this information is not considered adequate to characterize the waste in individual tanks in support of safety issues and final design activities for remediation. There is an ongoing waste characterization program to better determine the contents of each tank through analyzing samples to help resolve safety issues and support design decisions for implementing the remediation alternative.

The tank waste is categorized as liquid, sludge, or saltcake. Liquid is made up of water and organic compounds that contain dissolved salts. The organics in liquid form, depending on the type, either are dissolved in the water or exist in separate phases. Liquid is present in the tanks as either free standing, where the liquid volume is relatively free of solid particles, or as interstitial liquid, where the liquid volume is contained within the void spaces surrounding the sludge and saltcake particles. Sludge is a mixture of insoluble (i.e., will not dissolve in tank liquid) metal salt compounds that have precipitated and settled out of solution after the waste was made alkaline. Saltcake is primarily sodium and aluminum salt that crystallizes out of solution following evaporation.

These three types of waste exist in the tanks in numerous combinations and proportions, which results in complex combinations of waste with varied physical and chemical properties. Sludge has been found with consistencies from mud to hardened clay. Layers of organic compounds have been found in some tanks floating on top of solid waste. Crusts have formed in some tanks where a layer of solid has formed on top of the liquid. Table 3.2.3 is a summary of the waste forms in both the SSTs and DSTs (Hanlon 1995). The percentages shown may change as additional data become available.

Table 3.2.3 Waste Form Summary

3.2.1.4 Ongoing Activities

All U.S. Department of Energy (DOE) facilities that store hazardous or radioactive materials require documented authorization bases that establish a range of operating parameters (e.g., temperature, pressure, concentration) within which routine operations are conducted. These authorization bases also evaluate the effects of potential accidents, abnormal events, and natural disasters.

Watchlist Tanks

The identification of tank safety issues and the concern for the potential of an uncontrolled release of high-level radioactive waste to the environment resulted in the passing of Public Law 101-510, Section 313, Safety Measures for Waste Tanks at the Hanford Nuclear Reservation (also known as the Wyden Amendment) in 1990. In response to this law, a program was created to identify tanks with potential safety problems. Many of the tank safety issues that became Watchlist tank categories were already known to DOE, and the maintenance and operations for these tanks were being reviewed and managed. The enactment of the public law and the establishment of the Watchlist provided a more formalized and rigorous basis for addressing specific tank safety issues. Safety issues associated with the tanks were grouped into four categories: flammable gas, ferrocyanide, high organic content, and high heat generation. Tanks having any of these characteristics, referred to as Watchlist tanks, are categorized as shown in Table 3.2.4 (Hanlon 1996 , Cowan 1996 ). There currently are 50 Watchlist tanks with several tanks listed in more than one category.

Table 3.2.4 Watchlist Tanks

Unreviewed Safety Questions

DOE has a formal administrative program to identify, communicate, and establish corrective actions for known or suspected operating conditions that have not been analyzed or that fall outside of the established authorization bases as an Unreviewed Safety Question. Following the identification of an Unreviewed Safety Question, a review is conducted, and corrective action is taken if applicable. Following the review process, the Unreviewed Safety Questions may be closed from an administrative standpoint, which means that conditions surrounding the safety issue have been analyzed. However, the conditions on which the safety issue is based still may exist and may require mitigation, controls, or corrective action. In this way, safety issues and Unreviewed Safety Questions are related. The safety issues that were identified under the Watchlist program also were analyzed as Unreviewed Safety Questions. Those issues that had not been addressed in the documented authorization bases were established as Unreviewed Safety Questions. Following the review processes, the Unreviewed Safety Question can be closed while the tank remains on the Watchlist. The Hanford Federal Facility Agreement and Consent Order (Tri-Party Agreement) requires the resolution of all existing Unreviewed Safety Questions by September 1998 (Ecology et al. 1994).

Technical evaluation has resulted in closing the following Unreviewed Safety Questions identified for the tanks: ferrocyanide (closed in March 1994); floating organic layer in tank 241-C-103 (closed in May 1994); and criticality (closed in March 1994). Criticality was addressed on a tank farm basis and did not result in identifying any individual tanks to be added as Watchlist tanks. Criticality, which would be an issue during tank waste retrieval and transfer, would be evaluated on a tank-by-tank basis during final design. Closure of the Unreviewed Safety Questions was accomplished by defining the parameters (e.g., concentrations and temperature) of potential reactions that could lead to an uncontrolled release, collecting physical and chemical data on the waste, and establishing safe operating specifications.

The remaining Unreviewed Safety Questions are undergoing resolution. Mitigative action has been implemented for tank 241-SY-101 (commonly known as 101-SY), the most widely known flammable-gas-generating tank. This mitigative action involved installing a mixer pump to control the periodic release of flammable hydrogen gas and provide a more frequent and gradual release of hydrogen. This mitigative action reduced the maximum concentration of flammable gas that can exist in the tank and greatly reduced the potential for an uncontrolled gas burn.

There is a safety screening and characterization program ongoing to determine if any additional tanks should be placed under special controls. Recently, all 177 tanks (Watchlist and non-Watchlist) were placed under flammable gas controls, which means that flammable gas may exist in all 177 tanks and special safety measures will be taken during maintenance, monitoring, and waste transfer activities. Until the necessary characterization data are obtained, the tank farm system will continue to operate under these special waste management requirements to maintain a safe operating envelope. Additional data may allow for relaxed operating procedures, where appropriate. Volume Four, Appendix E contains a more detailed description of the tank safety issues.

Continued Operations of Tank Farm System

Numerous tank waste activities are ongoing to provide continued safe storage of the tank waste until remediation measures are implemented. These activities consist of a number of routine activities as well as a number of additional activities required for safe storage.

Routine operations include management oversight, regulatory compliance and reporting activities, and operations and maintenance of facilities and equipment. Tank monitoring activities support waste management by gathering information on waste temperature, liquid levels, solid levels, and tank status. Leak detection activities involve in-tank liquid level monitoring, leak detection monitoring of the annulus for the DSTs, drywell monitoring around tanks for increases in radioactivity levels, and groundwater monitoring. Other routine operations include:

• Calculating operational waste volume projections by comparing projected waste volumes against tank capacity. The projections also provide for identification and management of risk that could negatively impact available tank storage space;
• Combining compatible waste types. Transferring tank waste between tanks and tank farms through the existing cross-site transfer system to provide the required tank space and to address safety issues;
• Implementing a waste minimization program to reduce the generation of new waste requiring storage in the tanks. This program includes job preplanning and identification of new technologies such as low-volume hazardous waste decontamination practices to limit the generation of new waste. The waste minimization program also includes a support program for other onsite organizations (non-TWRS) that generate waste to encourage waste minimization practices;
• Screening and characterizing the waste on a tank-by-tank basis to gather data in support of safety and remedial action design activities;
• Isolating and removing pumpable liquid from SSTs to reduce the potential for future leakage (interim stabilization by saltwell pumping);
• Operating the 242-A Evaporator to concentrate waste; and
• Treat ing the evaporator effluents at the Effluent Treatment Facility to remove the contaminants prior to discharge.

These activities are not within the scope of this EIS because they were addressed in previous National Environmental Policy Act (NEPA) documents: the Safe Interim Storage of Hanford Tank Waste EIS (Safe Interim Storage EIS) (DOE 1995i), the Waste Tank Safety Program Environmental Assessment (DOE 1993h), and the Disposal of Hanford Defense High-Level, Transuranic, and Tank Wastes at the Hanford Site (DOE 1987).

3.2.1.5 Planned Activities

Several tank waste activities are planned for implementation in the near future. These activities would address urgent safety or regulatory compliance issues.

Safe Interim Storage

One issue that requires action is the safe storage of tank waste in the interim period before implementing actions for the permanent remediation of tank waste. To address this issue, the Safe Interim Storage EIS was prepared to consider alternatives for maintaining safe storage of Hanford Site tank waste (DOE 1995i). The actions considered in the Safe Interim Storage EIS include interim actions to 1) mitigate the generation of high concentrations of flammable gases in tank 241-SY-101 ; and 2) contribute to the interim stabilization of older SSTs, many of which have leaked.

The most pressing interim need identified by DOE and the Washington State Department of Ecology (Ecology) was for a safe, reliable, and regulatorily compliant replacement cross-site transfer capability to move waste between the 200 West and 200 East Area tank farms. This transfer capability is needed because the 200 West Area has far less useable DST capacity than there is waste in SSTs. The replacement waste transfer capability would provide a safe, reliable, and regulatory compliant means to move waste from the 200 West Area to the available DST capacity located in the 200 East Area.

Based on tank waste management and operation activities when the Safe Interim Storage EIS was prepared, the following needs were addressed:

• Removing saltwell liquid from older SSTs to reduce the likelihood of liquid waste escaping from corroded tanks into the environment. Many of these tanks have leaked, and historically, new leaks, either known or assumed, have developed at a rate of more than one per year;
• Providing the ability to transfer the tank waste via a regulatorily compliant system to mitigate any future safety concerns and use current or future tank space allocations;
• Providing adequate tank waste storage capacity for future waste volumes associated with tank farm operations and other Hanford Site facility operations; and
• Mitigating the flammable gas safety issue in tank 241-SY-101.
• The alternatives evaluated in the Safe Interim Storage EIS provided DOE with the ability to continue safe storage of high-level tank waste and upgrade the regulatory compliance status with regard to the Resource Conservation and Recovery Act (RCRA) (40 Code of Federal Regulations [CFR] 260) and the Washington Administrative Code (WAC) Dangerous Waste Regulations (WAC 173-303).
• On December 1, 1995, DOE published the Record of Decision in the Federal Register (FR) (60 FR 61687). The decision was to implement most of the actions of the preferred alternative, including the following.
• Construct and operate a replacement cross-site transfer pipeline system.
• Continue operating the existing cross-site transfer pipeline system until the replacement system is operational.
• Continue operating the mixer pump in tank 241-SY-101 to mitigate the unacceptable accumulation of hydrogen and other flammable gases.
• Perform activities to mitigate the loss of shrub-steppe habitat.

The existing cross-site transfer system has been used to transfer waste from the 200 West Area to the 200 East Area for 40 years. This underground pipeline system is at the end of its original design life. Currently, four of six lines are out of service and unavailable to perform transfers because of plugging. The two useable lines do not meet current engineering standards such as double containment and leak detection, which are required for waste management facilities. The design and operation of the replacement cross-site transfer system will meet the requirements of RCRA and WAC for secondary containment and Tri-Party Agreement Milestone M-43-07, which required construction of the replacement cross-site transfer system to commence by November 1995. Construction of the replacement cross-site transfer system has begun and the system is scheduled to be operational in 1998.

DOE will continue to use the existing cross-site transfer system until the replacement cross-site transfer system is operational to provide access to 200 East Area DSTs for storage of 200 West Area facility waste and retrieved liquid waste from SSTs. Saltwell liquid retrieval will continue to reduce the risk to the environment from leaking SSTs. Operational procedures will ensure the integrity of the existing cross-site transfer system before any waste transfers. The current planning base estimates that the existing cross-site transfer system will operate for approximately 625 hours during 5 transfers before the replacement cross-site transfer system is operational in 1998.

The mixer pump in tank 241-SY-101 was proven to be effective in mitigating flammable gas as a safety issue in that tank during more than 1 year of operation. DOE and Ecology revised their preferred alternative between release of the Draft and Final Safe Interim Storage EIS, based on the demonstrated success of the mixer pump, and determined that the construction of new DSTs to resolve safety concerns was not necessary.

Based on new information available to DOE regarding nuclear criticality safety concerns during retrieval, transfer, and storage actions since the issuance of the Final Safe Interim Storage EIS, DOE has decided to defer a decision on the construction and operation of a retrieval system in tank 241-SY-102. Through an ongoing safety evaluation process, DOE recently revisited its operational assumptions regarding the potential for the occurrence of a nuclear criticality event during waste storage and transfers. Changes to the Tank Farm Authorization Basis for Criticality approved in September 1995 were rescinded by DOE in October 1995, pending the outcome of a criticality safety evaluation process outlined for the Defense Nuclear Facility Safety Board on November 8, 1995. Until these criticality safety evaluations are completed, the Site will operate under historic limits, which maintain reasonable assurance of subcritical conditions during tank farm storage and transfer operations.

Of the actions evaluated in the Final Safe Interim Storage EIS, only the retrieval of solids from tank 241-SY-102 was affected by the technical uncertainties regarding criticality. Based on the quantities of plutonium in tank 241-SY-102 sludge, retrieval of the solids falls within the scope of the criticality safety issues that will be evaluated over the next few months. As a result, a decision on retrieval of solids from tank 241-SY-102 was deferred in the Safe Interim Storage EIS Record of Decision (60 FR 61687). Pending the outcome of the technical initiative to resolve the tank waste criticality safety issue, waste transfers (primarily saltwell liquid) through tank 241-SY-102 will be limited to noncomplexed waste. Tank 241-SY-101 mixer pump operations, existing cross-site transfer system interim operations, replacement cross-site transfer system operations, saltwell liquid retrievals, and 200 West Area facility waste generation would occur within applicable criticality limits and be subcritical.

Privatization of Tank Farm Activities

Currently, DOE is considering contracting with private companies for waste remediation services for the tank waste. DOE is interested in encouraging industry to use innovative approaches and in using competition within the private marketplace to bring new ideas and concepts to tank waste remediation. The goal of the privatization effort is to streamline the TWRS mission, transfer a share of the responsibility, accountability, and liability for successful performance to industry, improve performance, and reduce cost without sacrificing worker and public safety or environmental protection. DOE issued a TWRS Privatization Request for Proposal in mid-February 1996 and has received two bids to treat tank waste (Briggs 1996). DOE plans to issue contracts to perform the first phase of the work in late summer 1996. As currently envisioned, DOE would select contractors to construct and operate commercial demonstration facilities for two tank waste separations and low-activity waste (LAW) immobilization facilities, one of which may include a high-level waste (HLW) vitrification facility. If these commercial demonstrations are successful, DOE may use the lessons learned from those demonstration facilities and proceed with contracting for full-scale facilities to remediate additional tank waste. The planning process for these privatization activities is not complete and is subject to the final decision concerning remediation of the tank waste, which is the subject of this EIS.

The potential environmental impacts associated with the activities included in the contracting strategy are analyzed in the EIS. The DOE plan is to require potential contractors to propose technologies that meet specified performance criteria for the waste product, as established by DOE. DOE will require potential offerers to submit environmental information and analyses reasonably available to them as a discrete part of their proposals. DOE will independently evaluate and verify the accuracy of the environmental data and analyses and, as appropriate, use the information to help ensure the consideration of environmental factors in the selection process in accordance with 10 CFR 1021.216.

DOE has received two proposals under the privatization initiative for constructing and operating demonstration-scale facilities for separating selected portions of the tanks waste into LAW and HLW fractions and immobilizing the separated waste. The two proposals would follow the same general approach described in the EIS for Phase 1 of the Phased Implementation alternative including; separating the waste into LAW and HLW streams, immobilizing the HLW by forming a borosilicate glass, and using high-temperature processes to generate immobilized LAW. Evaluation of the two proposals has shown that they would have similar overall environmental impacts and that the impacts would be less than or approximately the same as the impacts described in Phase 1 of the Phased Implementation alternative assessed in this EIS.

One proposal has the potential to substantially reduce the volume of LAW requiring disposal and would result in less disposal-related land disturbance. However, the total amount of radioactivity in the LAW would be approximately the same for both proposals, and the associated impacts on groundwater would be the same (i.e., small). This proposal also offers the potential for recycling a portion of the LAW, and some of the raw material used in LAW processing might be suitable for other beneficial uses within DOE or the nuclear industry. There is uncertainty about whether markets for these materials will be available. If such markets were not available then the potential benefits of LAW volume reduction would not occur and these materials would need to be disposed of. Differences between the proposals in environmental impacts associated with the use of resources such as fuel and from air emissions such as nitrogen oxides would be small.

DOE will also require selected offerers to submit further environmental information and analyses, and will use the additional information, as appropriate, to assist in the NEPA compliance process, including a determination under 10 CFR 1021.314 of the potential need for a supplemental EIS.

Tank Farm Upgrades

Upgrades to the tank farms are planned to improve the reliability of safety-related systems, minimize onsite health and safety hazards, upgrade the regulatory compliance status of the tank farms, and place the tank farms in a controlled, stable condition until disposal is complete. Upgrades planned include: 1) instrumentation including the automatic tank data gathering and management control system and the closed-circuit television monitoring to minimize personnel exposure; 2) tank ventilation to replace outdated ventilation systems; and 3) an electrical system to provide electrical power service with sufficient capacity and in compliance with current electrical codes. These three components of the tank farm upgrades are not addressed in the TWRS EIS but will be the subject of other analyses. Upgrades to the existing waste transfer system that would be used in conjunction with the replacement cross-site transfer system also are planned. Waste transfer system upgrades are included in the TWRS EIS and are discussed in Section 3.4.1.1.

Initial Tank Retrieval System

This project would provide systems for retrieving waste from up to 10 DSTs. Initial tank retrieval capabilities also would allow consolidation of compatible tank waste to create additional DST storage capacity and support passive mitigation such as diluting hydrogen-gas-generating Watchlist tanks, should that become necessary. Retrieval and transfer of waste from all tanks is addressed in this EIS, so the Initial Tank Retrieval System project is a subset of the actions included in this EIS and not addressed separately.

Hanford Tanks Initiative

Under this program, several waste retrieval activities discussed in the TWRS EIS would be demonstrated in support of the ex situ alternatives. This program would reduce the uncertainties associated with waste retrieval by developing and demonstrating the technologies required to meet retrieval requirements. The Hanford Tanks Initiative includes activities associated with waste retrieval and tank closure. Those activities associated with waste retrieval are covered under this EIS while activities associated with the closure would be the subject of future NEPA analysis.

This program would demonstrate equipment and systems for removal of tank residuals from tank 241-C-106 that are expected to remain following initial retrieval by sluicing. The objective would be to retrieve sufficient waste to meet waste retrieval requirements. This program also would attempt to develop technologies and criteria to retrieve waste from known or assumed leaking SSTs.

3.2.2 Cesium and Strontium Capsules

3.2.2.1 History

The cesium and strontium capsule program was initiated in the early 1970's to remove heat-generating cesium and strontium isotopes from the waste for safer storage. The waste used for this purpose either was existing waste retrieved from tanks or waste from the processing facilities enroute to the tanks. Removing cesium and strontium from the waste reduced the heat generation in the tanks and provided for safer storage of the waste remaining in the tanks.

The capsule fabrication program took place between 1974 and 1985 at the Waste Encapsulation and Storage Facility (WESF), which adjoins B Plant in the 200 East Area (Figure 3.2.4). Capsules were fabricated to hold the stabilized cesium chloride and strontium fluoride salts in an effort to provide a physical form for the cesium and strontium suitable for long-term storage.

3.2.2.2 Capsule Description

The capsules are double-walled, high-temperature metal alloy tubes that contain cesium and strontium (Figure 3.2.5). The capsules are stored in water-filled basins at WESF and are approximately 6. 7 centimeters (cm) (2.6 inches [in.]) in diameter and 51 cm (20 in.) in length. The decay reactions taking place within the capsules generate approximately 200 to 300 watts ( W ) of heat continuously from each capsule. Storing the capsules underwater provides radiation protection for workers as well as cooling for the capsules. Basins or pool cells are filled with water to a depth of 4 m (13 ft) and house metal storage racks to control capsule storage within the cells. WESF has a total of eight pools: five are active and used for capsule storage, one is used for temporary storage, and two are not used. The size and number of capsules are presented in Table 3.2.5. The capsules currently are classified as waste by-product, which means that they are available for productive uses if uses can be found.

Figure 3.2.4 Waste Encapsulation and Storage Facility

Figure 3.2.5 Typical Cesium and Strontium Capsule Configuration

The final classification of the cesium and the strontium would be made in correlation with the Nuclear Regulatory Commission (NRC) if and when the capsules are classified as waste.

3.2.2.3 Capsule Characterization

The chemical form of the cesium in the capsules is cesium chloride and the chemical form of the strontium in the capsules is strontium fluoride. The combined total capsule volume is approximately 2 cubic meters (m³) (70 cubic feet [ft³]) (WHC 1995h).

The cesium content of the capsules is primarily cesium-137, which has a half-life of 30.17 years. Cesium-137 decays to the stable isotope barium-137, either directly or through a two-step process, first into metastable barium-137m, and then to stable barium-137. Strontium capsules contain mainly strontium-90, which has a half-life of 28.6 years. Strontium-90 decays to yttrium-90 and then to the stable isotope zirconium-90. The quantities, heat loading, and radioactivity levels for the cesium and strontium capsules are presented in Table 3.2.6. Reduction in the number of curies, heat load, and concentration over time is due to radioactive decay of cesium and strontium into stable decay products.

Table 3.2.5 Cesium and Strontium Capsules

Table 3.2.6 Characteristics of Existing Capsules

3.2.2.4 Current and Planned Activities

The only ongoing and planned activities for the capsules are the continued storage of the capsules in WESF, return of the remaining cesium capsules to WESF, and attempts to find productive uses for the cesium and strontium capsules. Continued operations include monitoring capsule integrity and maintaining support facilities (ventilation, monitoring, radiation alarms, and waste handling systems).

DOE is in the early planning stages of considering whether the capsules should remain in WESF or be placed in alternative locations for storage. Among the possible alternatives are placing the capsules in the proposed Canister Storage Building originally planned to store HLW. DOE is currently upgrading WESF to operate independently of B Plant. No decisions have been made to proceed with any alternative storage options. For purposes of analyzing impacts in the TWRS EIS, it is assumed that the capsules will remain in WESF until ready for final disposition . If DOE proposes to change the method or location for the interim storage of the capsules, an appropriate NEPA review will be performed.

A cesium and strontium capsule management program will provide for management of the capsules until final disposition has been implemented.

Strontium capsules previously were used as heat sources, and the cesium capsules were used at commercial facilities for strengthening wood products, sterilizing medical products, and sterilizing saline solutions. Cesium and strontium capsules also have been used by DOE programs for research activities at Pacific Northwest National Laboratory, Sandia National Laboratory, and Oak Ridge National Laboratory. DOE has requested that all capsules be returned to the Hanford Site for storage at WESF (DOE). Some cesium capsules have not yet been returned, but plans call for all capsules to be returned to the Hanford Site by the end of 199 7. There are four strontium capsules located offsite that will not be returned to the Hanford Site.

DOE is pursuing alternative uses for the cesium and strontium capsules. If no future uses for these capsules are found, the capsules eventually would be managed and disposed of consistent with the Tri-Party Agreement (Ecology et al. 1994) and the TWRS EIS alternative selected for implementation.