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Tank Waste Retrieval, Processing, and On-Site Disposal at Three Department of Energy Sites: Final Report Appendix E Interim Report Summary and Follow-up This appendix presents the summary of the committee’s interim report (NRC, 2005a) and an overview of developments since that report. In this final report, the committee stands by the findings and recommendations presented in its interim report, and elaborates on some of them. SUMMARY OF THE COMMITTEE’S INTERIM REPORT The full text of the interim report is available on-line, free of charge, at http://www.nap.edu/catalog/11415.html. Summary In the Ronald Reagan National Defense Authorization Act of 2005 (Section 3146 of Public Law 108-375), Congress directed the Department of Energy (DOE) to request a study from the National Academies that evaluates DOE’s plans for managing certain radioactive wastes stored in tanks at its sites in Idaho, South Carolina, and Washington.1 The wastes addressed in this study are from reprocessing of spent nuclear fuel, exceed certain concentration limits,2 and are planned for disposal at the sites mentioned above. Congress asked the National Academies3 for an interim and a final report addressing this task. According to the Defense Authorization Act, the interim report “shall address any additional actions the Department should consider to ensure that the Department’s plans for the Savannah River Site, including plans for grouting the tanks, will comply with the performance objectives [of 10 CFR 614] in a more effective manner” (Section 3146 (e)(A)). This document fulfills the interim report request. Congress requested this study at the same time another provision of the same law (Section 3116) provided the basis for DOE, in consultation with the U.S. Nuclear Regulatory Commission (USNRC), to determine that tank wastes at the South Carolina and Idaho sites meeting certain listed criteria are not high-level waste (HLW).5 Such wastes may then be disposed of on-site. TECHNICAL BACKGROUND The Savannah River Site has 51 underground tanks that are used for storing 138,000 cubic meters (36.4 million gallons) of hazardous and radioactive waste from chemical processing of spent nuclear fuel and related operations.6 Tank construction and characteristics vary, but the typical tank is a large cylindrical carbon steel and reinforced concrete structure buried at a shallow depth (1 to 3meters below the surface). The tanks’ sizes range from about 2,800 cubic meters (m3) to 4,900 m3 (750,000 to 1.3 million gallons). The largest tanks are approximately 26 meters (85 feet) in diameter and 11 meters (35 feet) from the inner tank floor to the center of a domed ceiling. Most of the tanks are equipped with dense networks of vertical and horizontal cooling pipes, referred to as cooling coils (see Figure S-1). These cooling coils are used toremove heat produced by radioactive decay in the waste. Twenty-seven of the tanks have a full secondary containment (i.e., a tank inside another tank) and are considered “compliant 1 The full statement of task can be found in Appendix A. 2 These limits define the maximum radionuclide concentrations for Class C low-level waste for radioactive waste disposal facilities regulated by the U.S. Nuclear Regulatory Commission. The limits are found in Part 61, Title 10 of the Code of Federal Regulations (10 CFR 61) titled “Licensing Requirements for Land Disposal of Radioactive Waste.” For the purpose of this study, the committee interprets this concentration criterion to apply to the waste streams stored in tanks prior to waste processing. 3 The National Academies appointed a committee to carry out this study. Biographical sketches of committee members can be found in Appendix C. 4 The performance objectives of 10 CFR 61 can be found in Appendix A and contain four mandates: (1) protect the general population from releases of radioactivity, (2) protect individuals from inadvertent intrusion, (3) protect individuals during operations, and (4) provide stability of the site after closure. Regulatory guides use a time period of 10,000 years for the performance period. 5 The term “high-level waste” is used in this report according to its legal definition in the U.S. Code, Title 42, Chapter 108, Nuclear Waste Policy, Section 10101 (see page 13, footnote 8). There is no particular radioactivity concentration or dose limit associated with this definition. 6 Reprocessing operations at the Savannah River Site started in 1953 and continue on a reduced scale to this day. A map of the site can be found in Appendix E.
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Tank Waste Retrieval, Processing, and On-Site Disposal at Three Department of Energy Sites: Final Report FIGURE S-1 Photograph of the interior of a Type I tank (Tank 4) prior to receipt of wastes. SOURCE: Caldwell (2005a). tanks” under the site’s Federal Facility Agreement,7 which regulates storage and disposal of hazardous waste at the site. The remaining tanks do not have complete secondary containment and are considered noncompliant. Visual inspections and conductivity probes in the tanks and in the annuli of the tanks have shown that about half of the noncompliant tanks have leaked in the past (although the leaks were confined to the tank’s annulus in all but one case). Although the composition of waste in each tank varies, the tanks generally contain a bottom layer of a peanut-butter-like deposit of insoluble solids (referred to as sludge), a layer of crystalline solids (the saltcake), and a salt solution (the supernate). The term “salt waste” is sometimes used to refer to saltcake and supernate. Although the sludge represents less than 10 percent of the volume, it contains about half of the radioactivity in the waste tanks,8 mainly from insoluble actinides and strontium salts. The other half of the radioactivity is mostly in the supernate, where the soluble radionuclides, mainly cesium-137, are in solution. A fraction of the soluble radionuclides is also trapped as liquid in the interstices of the saltcake. DOE has argued that it is impractical to dismantle and remove the tanks after the waste has been retrieved because of the exposures incurred by workers from radioactive residues and because of the overall prohibitive costs of exhuming such large structures. The committee has not seen analyses to support this claim. For each tank, the general plan is to retrieve the bulk of the waste, clean up the tank to the “maximum extent practical,”9 and close the tank in place, according to milestones agreed to in the site’s Federal Facility Agreement. Because of practical limitations on waste retrieval, “emptied” tanks will still contain variable amounts of the radioactive waste (the “heel”), depending on the success of the retrieval and cleanup process. DOE plans to close emptied tanks by placing layers of engineered grout to encapsulate and stabilize the tank heel and a controlled low-strength material to provide structural support against tank collapse and act as a physical barrier that inhibits the flow of water through the residual waste. Tanks that do not have a concrete roof would have a high-strength layer of grout that would serve as an intruder barrier. An engineered cover to retard infiltration to the tanks after closure is also under consideration. DOE’s plan to manage the bulk of the waste retrieved from the tanks is to separate the radioactive from the nonradioactive components, the latter of which make up most of the waste volume. This processing generates two waste streams: (1) a high-activity waste stream, which will be immobilized and disposed off-site in a high- 7 This is an agreement among DOE, the Environmental Protection Agency, and the South Carolina Department of Health and Environmental Control and contains the plan for tank closure. 8 The radionuclides of concern for this study are short-lived but highly radioactive isotopes, such as strontium-90 and cesium-137 and their decay products; long-lived (>30 years) radionuclides such as uranium and plutonium isotopes; and especially long-lived and highly mobile radioisotopes, such as iodine-129, technetium-99, tin-126, selenium-79, and neptunium-237. 9 One of the criteria that DOE must use according to Section 3116 of the Defense Authorization Act to determine whether waste is not HLW and can be disposed as low-level waste (LLW) is if this waste has had highly radioactive radionuclides removed to the “maximum extent practical.” DOE is authorized to make this determination in consultation with the USNRC at the Savannah River and Idaho sites.
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Tank Waste Retrieval, Processing, and On-Site Disposal at Three Department of Energy Sites: Final Report FIGURE S-2 Waste flows in the Savannah River Site waste management plans. Note that the sizes do not necessarily scale with the sizes of the waste flows. level waste repository,10 and (2) a low-activity waste stream, which is to be disposed on-site. At the Savannah River Site, DOE already retrieves sludge and then processes and immobilizes it in glass at its Defense Waste Processing Facility (DWPF). These operations generate as a secondary product a relatively low-activity liquid waste, referred to as the DWPF recycle stream, which is returned to the HLW tanks. To separate highly radioactive constituents of the salt waste, DOE proposes to utilize three different processes11 that will be available at different times and have different capabilities. Two low-capacity processes are expected to be available sooner and are referred to as “interim” processing by DOE. These are the deliquification, dissolution, and adjustment (DDA) process, which could begin immediately upon approval of the waste determination by the Secretary of Energy in accordance with Section 3116 of the 2005 National Defense Authorization Act, consultation with the USNRC, and permitting by the state of South Carolina; and the actinide removal, modular caustic-side solvent extraction process (ARP/ MCU), which is expected to begin operations in 2007. A high-capacity chemical processing facility, called the Salt Waste Processing Facility, is scheduled to be available in 2009 and could be supplemented by the ARP, if needed. DOE indicated to the committee that the Savannah River Site is facing a “tank space crisis” because of net waste inputs from current waste processing and waste removal operations. To alleviate the tank space crisis, DOE is proposing to begin processing salt waste using DDA as soon as possible (see Figure S-2). The low-activity waste streams from these three processes will have varying concentrations of radioactivity and will be mixed with cementitious material to form “saltstone” and disposed on-site as a monolith in near-surface concrete vaults. FINDINGS AND RECOMMENDATIONS Although DOE, its regulators, and others worked with the committee to provide the information needed for this study, some data were not available (not yet collected, not yet generated, or not yet made public), and some plans had not yet been formulated or finalized when this report was written.12 Appendix B describes the main documents to which the committee had access and the missing 10 The high-activity waste stream is outside the scope of this report, which focuses solely on waste disposed on-site. 11 DOE refers to this as a two-phase, three-step approach. The committee has not adopted this way of describing the approach because it suggests that all wastes undergo each process, which is inconsistent with DOE’s plan. 12 The information-gathering phase for the interim report lasted from March through June 2005. Under the Federal Advisory Committee Act Amendments of 1997 (Public Law 105-153), any document provided to the committee from outside of the National Academies must be made available to the public, unless the document is exempt from disclosure under the Freedom of Information Act (Public Law 89-554) and its amendments. As a result, the committee could not accept any document that was undergoing security review, internal scientific review, or legal and policy review and was therefore not ready for public release.
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Tank Waste Retrieval, Processing, and On-Site Disposal at Three Department of Energy Sites: Final Report pieces of information to assess DOE plans for compliance with the performance objectives set forth in 10 CFR 61. Therefore, the committee was unable to evaluate fully what, if any, actions are needed for DOE to comply with these performance objectives. However, the committee was able to evaluate factors that reduce risk and recommends actions to (1) reduce the waste left on-site and (2) increase DOE’s understanding of the long-term performance of waste forms and other barriers to the release of radionuclides. These actions will increase confidence in DOE’s ability to comply with the performance objectives in general and conform with the requirement to take actions to make releases of radioactivity to the environment as low as reasonably achievable (ALARA), with economic and social considerations taken into account. Findings and recommendations address four major issues: (1) near-term and long-term risks; (2) the tank space crisis; (3) Class C limits and performance objectives; and (4) research and development needs. The following findings and recommendations are based on the information available to the committee at the time of writing this interim report and may be extended in the committee’s the final report. Near-Term versus Long-Term Risks Finding 1a: By far the greatest reductions in near-term probability and quantity of radionuclide and hazardous chemical releases to the environment are achieved by bulk removal and immobilization of liquid, salt, and sludge from the non-compliant high-level waste tanks. The tank heels that remain after bulk removal contain a smaller quantity of waste that is less mobile and constitutes a much lower near-term probability of release. Finding 1b: The Savannah River Site Federal Facility Agreement has schedules for waste removal from and closure of the noncompliant tanks. For some tanks, the tank-closure step immediately follows the waste-removal step, making them appear to be coupled. This coupling could limit the time available for tank-waste removal and consequently could determine how much waste can be removed to “the maximum extent practical.” A decoupled schedule is already planned for a limited number of tanks, as shown in Appendix F. Decoupling allows the consideration of a wider set of options for removing and/or immobilizing residual waste (especially for tanks that have significant obstructions that complicate waste removal), which could reduce long-term risks. Recommendation 1: DOE should decouple tank waste removal and tank closure actions on a case-by-case basis where there are indications that near-term (5-10 year) techniques could become available to remove tank heels more effectively, safely, or at a lower cost. In evaluating schedules for each tank, DOE should consider the risks from postponing tank closure compared with the risk reductions that could be achieved if the postponement improves heel removal. Although the committee believes that postponing tank closure need not extend the closure dates of the tank farms, DOE should work with theState of South Carolina to revise the schedule for closure of a limited number of the tanks that contain significant heels, if necessary. The committee agrees with DOE’s and South Carolina’s overall approach to cleanup at the Savannah River Site: bulk removal of the waste containing the majority of the mobile radionuclides is the highest priority to reduce release of radioactive materials to theenvironment in the near term. The noncompliant tanks, about half of which have a history of leakage, demand attention first, but nearly all of the tanks are beyond their design lifetimes. Filling a tank with grout is, from a practical point of view, an irreversible action, although it is conceivable to open a tank and excavate the grout if absolutely necessary. Moreover, postponing closure of some tanks for several years would appear to have essentially no effect on near- or long-term risk. The current approach of coupling cleanup and closure schedules forecloses options that may become available in the near future (e.g., using alternative technologies to reduce the radioactive heel [source] and/or using other types of immobilizing material to fill the tank). DOE should decouple cleanup and closure schedules, keep as many options open as practical, and regularly assess technology developments and alternatives to reduce long-term risks presented by the tank heels. DOE should make additional investments in research and development to enhance tank waste retrieval (reducing the source term), improve residual waste immobilization (stabilizing the source term), or reduce the ingress of water once the tanks are closed (protect the source term), as stated in Recommendation 4. In some cases, tank closure need not be delayed, such as in tanks that have small heels (i.e., as small as the heels in Tanks 16, 17, and 20) and/or low concentrations of radionuclides, or if risks specific to the tank require early closure (i.e., as soon as waste removal is completed). Conversely, delaying closure may be warranted for tanks with large heels or high concentrations of radionuclides. This approach need not necessarily affect the final closure date of the tank farm, which will occur later than 2022, the milestone for closure of the noncompliant tanks. If new technologies become available in the near future (i.e., 5-10 years), it may be possible to clean up and/or close tanks faster (possibly leaving less waste behind), thus meeting the final milestone for the tank farms. As DOE considers delaying closure for some tanks, it has to evaluate the advantages and disadvantages from both a risk and a cost perspective. If DOE can relax other constraints on tank waste removal, such as the tank space problem, delaying tank closure could free up funds planned for closure activities, and those funds could be devoted to enhancing waste removal, waste processing, and confidence in the near- and long-term performance of the waste immobilization and tank fill materials. Similarly, research and development require funds, but if they are successful they could result in lower costs and increased safety overall (see Finding and Recommendation 4). Tank Space Crisis Finding 2a: The lack of compliant tank space does appear to be a major problem because of continuing waste inputs and the anticipated future needs for space to support site operations and tank cleanup. As presently operated, sludge waste processing results in a net addition of waste to the compliant tanks. Salt waste processing will also require storage volume in compliant tanks for batch preparation and other operations. Finding 2b: DOE plans to use the deliquification, dissolution, and adjustment process to free up space in compliant tanks.
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Tank Waste Retrieval, Processing, and On-Site Disposal at Three Department of Energy Sites: Final Report While DOE analyses so far suggest that the wastes from this process would meet the performance objectives in 10 CFR 61, it achieves less radionuclide separation than other planned processes. While waste from the DDA process represents only 8percent of the volume of low-activity waste to be generated during salt waste processing, it contains 80-90 percent of the radioactivity that is projected to be sent to the Saltstone Disposal Vaults. Recommendation 2: DOE and other involved parties should consider options other than DDA to alleviate the impending crisis in usable storage in compliant tanks. Options include actions that (1) reduce waste inputs to the tanks, such as redirecting the DWPF recycle stream for disposition in the Saltstone Facility; and (2) actions that free up usable volume in compliant tanks, such as using noncompliant tanks not known to have leaked for emergency storage volume. Waste retrieval, processing, and tank cleaning operations continuously add secondary wastes to the tanks; in addition, space in compliant tanks is needed to prepare feeds for the high-level and salt waste processing facilities. Moreover, DOE is maintaining the equivalent of a full tank capacity—4,900 m3 (1.3 million gallons)— in empty compliant space for emergency purposes at all times. Hence the “tank space crisis.” DOE plans to address the tank space problem in the short term by implementing the DDA process. This process uses physical rather than chemical means to accomplish cesium separation (i.e., draining interstitial liquid present in the saltcake and then dissolving the saltcake and grouting it into saltstone (see Figure S-2).13 The saltstone from this process is expected to contain cesium concentrations that are two orders of magnitude higher than the waste from the chemical processes that eventually will be used in the Salt Waste Processing Facility (albeit still considerably lower than ClassC limits). Even these higher levels of cesium may not cause projected doses from the Saltstone Vaults to exceed dose limits, although as noted earlier, details underlying a performance assessment for DDA saltstone were not available for committee examination. However, this raises the following question: Does this process remove radionuclides to the maximum extent practical? The tank space crisis forces DOE to engage in increasingly complex operations to ensure that there is sufficient space to continue waste processing. Hence, the tank space crisis may increase the possibility of accidental worker exposure to radiation, the chance of operational accidents, and the chance of waste leakage during transfers. In its recommendation, the committee suggests alternative options to DDA to mitigate the tank space crisis. Class C Limits and Performance Objectives Finding 3: The future site-specific risks posed by wastes disposed of on-site is the primary issue of concern in this study. Such risks are determined by the radionuclide and chemical quantities and concentrations, their conditioning, their interactions with the environment, and their bioavailability, not by the relationship of radionuclide concentrations to generic limits such as those for Class C low-level waste. The National Defense Authorization Act Section 3116 requires the use of the performance objectives in 10 CFR 61 to limit and minimize these risks. Recommendation 3: When deciding what wastes may be disposed of on-site, DOE and other involved parties should ensure that discussions focus on how radionuclide and chemical quantities and concentrations, their conditioning, their interactions with the environment, and their bioavailability affect site-specific risk. The Class C limits are not a criterion for acceptability of on-site disposal of tank wastes from reprocessing of spent nuclear fuel under the present law but are sometimes discussed as if they were. The Class C limits were developed for a diverse commercial sector to establish limits on what is generally acceptable for near-surface disposal, based in part on assumptions about the overall set of wastes destined for disposal. According to Section 3116, comparison of radionuclide concentrations in waste to Class C limits is relevant to waste disposition decisions only procedurally, in that DOE must develop its disposal plans in consultation with USNRC. Rather than Class C limits, site-specific risk assessments are the bases for determining whether the facility meets the performance objectives in the regulations. These risks depend on radionuclide quantities and concentrations, their conditioning, and their interactions with the environment.14 The performance objectives and waste acceptance criteria constrain the overall quantity of radioactive material that can be disposed in a facility.15 Acceptable radionuclide concentrations (and/or inventories) and distributions should be determined as a result of a properly constituted and implemented risk assessment16 that takes into account measured and/or projected radionuclide concentrations, spatial variability of the concentrations, and attendant uncertainties. Such a risk assessment was not available at the time of report writing (see Appendix B). Congress recognized the importance of the performance objectives for evaluating site-specific near-surface disposal of waste in Section 3116 of the 2005 National Defense Authorization Act by explicitly including these objectives as the basis for determining whether waste is HLW instead of relying on the radionuclide concentrations that define the upper boundary of Class C waste. All substantive technical criteria that DOE’s determination must meet (e.g., performance objectives, remove highly radioactive radionuclides to the maximum extent practicable) apply irrespective of whether a waste is less than or greater than Class C. 13 DOE plans to send what it has identified as the least radioactive salt wastes from the tanks through the DDA process. 14 Regulatory guides for 10 CFR 61 state that 10,000 years is an appropriate time frame for the performance assessments. 15 Waste acceptance criteria take into account broader considerations than performance objectives, such as waste “processibility” (i.e., compatibility of waste and secondary products with the chemical and physical processes prior to disposal) and other site-specific requirements. 16 A recent National Research Council report Risk and Decisions about Disposition of Transuranic and High-Level Radioactive Waste describes a framework for decision-making processes in the presence of risk and uncertainties (NRC, 2005).
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Tank Waste Retrieval, Processing, and On-Site Disposal at Three Department of Energy Sites: Final Report Research and Development Needs Finding 4: Focused research and development could help DOE reduce the amount, improve the immobilization, and test some of the assumptions used in performance assessment of tank waste to be disposed of at the Savannah River Site. These actions could reduce the risks to humans and the environment and improve confidence in DOE’s risk estimates. These research and development activities could also increase DOE’s ability to demonstrate compliance with the performance objectives in 10 CFR 61. Recommendation 4: DOE should fund research and development efforts focused on providing deployable results within 5-10 years on the following topics: (1) in-tank and downstream processing consequences of chemical tank-cleaning options, (2) technologies to assist in tank-waste removal, including robotic devices, and (3) studies of the projected near- and long-term performance of tank-fill materials such as grout. To reduce long-term risks to the site and test the assumptions in the performance assessment, the committee recommends that DOE perform focused research and development to enhance tank waste retrieval and residual waste immobilization. Tank waste retrieval could be enhanced using better mechanical or chemical tools. Tank waste retrieval is currently performed using hydraulic technologies (i.e., water jets) and, to a certain extent, robotic devices and chemical cleaning agents (i.e., oxalic acid). The committee believes that additional research and development on mechanical tools, including but not limited to robotic devices and chemical cleaning could reduce the tank heels, especially in tanks with cooling coils. DOE should further evaluate the effectiveness of residual waste immobilization by conducting durability studies of grout (and alternative fill materials). These activities may increase confidence in DOE’s management plans or may cause DOE to revise some of the assumptions used in the performance assessment. Testing assumptions and improving DOE’s knowledge base might increase its ability to comply with the performance objectives specified in the law. Research and development activities should be limited to those technologies that are promising and at a near-deployment stage (i.e., they could provide results within 5 to 10 years, in time to be implemented during the tank closure process). All noncompliant tanks are scheduled to be closed by 2022. A technology developed in the next 5-10 years could be deployed in time to address the most challenging tanks (i.e., those with cooling coils). The committee believes that a nonradioactive test bed for retrieval technologies that can be adapted to simulate a variety of tank situations (i.e., recalcitrant heels, cooling coils, debris) should be maintained. The Pump Test Tank, a partial Type IV tank mockup at the mostly decommissioned TNX facility used for testing and equipment before deployment, and similar test beds at other sites, are candidates for this role. The Hanford Site also has a mockup of a single-shell tank used for similar purposes. The committee will further address the need for experimental retrieval facilities in its final report. FUTURE PLANS FOR THE STUDY The committee’s full task is to review and evaluate DOE’s plans to manage radioactive waste streams from reprocessed spent fuel that exceed the Class C concentration limits and are planned for onsite disposal at the Savannah River Site, the Idaho National Engineering and Environmental Laboratory, and the Hanford Reservation. Congress requested assessments of the following: DOE’s knowledge of the characteristics of the wastes; additional actions DOE should take in managing these wastes to comply with the performance objectives; monitoring plans; existing technologies and technology gaps for waste management; and any other matters that the committee considers appropriate and directly relevant. For its interim report, the committee was charged to examine whether DOE’s plans to manage its radioactive waste streams at the Savannah River Site will comply with the performance objectives of 10 CFR 61. Compliance with the performance objectives depends upon the amount of radioactive material left onsite, the manner in which it is immobilized, its interaction with the environment, and its interaction with ecological and human receptors. As noted above, some critical data, analyses, and plans were not available when this report was written: the performance assessment for closed tanks; plans for residual waste characterization; plans for tank annuli and tank-system piping; support for assumptions, estimated levels of conservatisms, and sensitivity analyses for performance assessment calculations; and long-term monitoring plans are examples of the missing information. In this interim report, the committee has fulfilled the charge to the extent possible by focusing mainly on the amount of waste left in the tanks and in the Saltstone Vaults at theSavannah River Site. The committee has made findings and recommendations on four major issues: near-term and long-term risks in the context of tank waste removal and the schedule for tank closure; the tank space crisis and options to alleviate the crisis; the roles of the Class C limits and the performance objectives in determining whether on-site disposal is acceptable; and research and development needs, particularly in-tank and downstream consequences of chemical cleaning options, technologies to assist in tank waste removal, including robotic devices, and studies of the projected near- and long-term performance of tank fill materials, such as grout. The committee is still examining the interactions of the tanks and the saltstone with the surrounding environment; the role of environmental monitoring; the role of the point of compliance in meeting the performance objectives; and the role of modeling inthe performance assessment. These topics are relevant to all three sites and will be addressed in the final report, along with the rest of the statement of task. For a substantive analysis, the information described above will be needed at all sites. In addition, because the wastes and the site conditions differ, the topics investigated in this report will also be examined at the Hanford and Idaho sites. These investigations at other sites will have an impact on the committee’s views on the Savannah River Site. Hanford will likely offer the committee the greatest challenge because it is the oldest site, has many tanks that have leaked, and has the most complicated wastes because of the various management practices and several chemical processes that generated the wastes, including the earliest processing technologies. The committee may also extend the comments on the Savannah River Site found in this report as additional information on this site becomes available during the period of this study.
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Tank Waste Retrieval, Processing, and On-Site Disposal at Three Department of Energy Sites: Final Report DEVELOPMENTS SINCE THE COMMITTEE’S INTERIM REPORT The committee has received direct and indirect feedback from DOE and the South Carolina Department of Health and Environmental Control (SCDHEC) on the findings and recommendations in its interim report. Inez Triay, U.S. Department of Energy Office of Environmental Management’s (DOE-EM’s) chief operating officer, informed the Nuclear and Radiation Studies Board on September 12, 2005, that while it agrees in principle with the findings and recommendations, DOE disagrees with some of the details. DOE (Triay, 2005) Reiterated its commitment to the schedule for closing tanks; Said that the committee misunderstood the tank space problem and the solutions the committee proposed were irrelevant or unworkable; Expressed that it had no concerns about the recommendation concerning the class C limits, except to note that the committee could be most helpful by sticking to the National Academies’ strengths, which are science and research; and Asked for more specific guidance on what research is needed. SCDHEC representatives in interviews with reporters reiterated SCDHEC’s commitment to the schedule for closing tanks and disagreed with the committee’s conclusion that delaying filling of tanks with grout would be beneficial from the perspective of risk. Postponement of Tank Grouting As noted in its final report, the committee remains convinced not only that postponing tank filling after tank cleanout should be kept as an option, but that DOE is already effectively doing this with some of its tanks at Savannah River Site. Some tanks are scheduled for waste removal years before they are scheduled for closure. This is likely to become an even more important option as DOE continues cleanup and encounters tanks from which waste retrieval promises to be more difficult. Tank Space Crisis Concerning the tank space crisis at SRS, the committee’s concerns have continued to increase. Quoting from the committee’s interim report: One committee concern is what will happen with salt waste processing if the [Salt Waste Processing Facility, SWPF] or the interim chemical processing cannot be brought into operation on schedule. The committee did not review the engineering readiness of the salt waste processing, but theschedule to bring the facilities on-line (ARP/MCU by 2007 and the high-capacity SWPF by 2009) and operating to specifications (i.e., processing waste at the expected throughput and meeting the waste acceptance criteria) is ambitious. Based on DOE’s prior experience with developing and initiating operations at major waste processing facilities, it is prudent to plan for the possibility that salt waste will not be removed from the tanks at the planned pace. In other words, DOE needs a contingency plan for tank space. More generally, the committee cautions that in a schedule-driven system there is the danger that wastes could be sent through the process that is currently available rather than the one that is most suited to the wastes. The committee recognizes, of course, that there are other considerations (e.g., safety, risk, and cost) involved in such decisions. The committee here offers some suggestions to reduce waste inputs to tanks and to free up compliant tank space. The committee suggested alternative options for the Defense Waste Processing Facility recycle stream. On this point, the situation was changing during the committee’s information gathering for the interim report, and the committee did not have the most current information when the interim report was released (see Sidebar E-1). By that time, DOE had already moved its concentrated Defense Waste Processing Facility recycle waste from compliant tanks to a noncompliant tank with no history of leakage. There also appeared to be some confusion about the committee’s suggestion that noncompliant (but nonleaking) tank space be used for emergency reserve. Some understood the committee to say that DOE should transfer waste into noncompliant tanks. Although this practice has been used on a temporary basis by DOE with approval from SCDHEC and could potentially be used to alleviate short-term space crises,17 this was not the committee’s suggestion. Instead, the committee suggested keeping the emergency reserve storage, which is empty tank space, in noncompliant tanks that have no history of leakage. Waste would be transferred into the reserve only in an emergency, such as a major leak discovered in another tank. Since the interim report was released, the main point the committee was making—that DOE and its regulators must think creatively to solve the tank space crisis—has become more salient. DOE has encountered additional significant delays in bringing the Salt Waste Processing Facility (SWPF) on-line. The facility is being redesigned due to seismic concerns raised by the Defense Nuclear Facilities Safety Board (Allison, 2005). DOE now expects a 26-month delay in the start of operations, from August 1, 2009, to September 30, 2011 (Terhune and Kasper, 2005). Although DOE has not stated the specific consequences of the delay, it previously emphasized that the schedule was crucial, and 17 In essence, this is what DOE has done with its concentrated DWPF recycle stream, which was stored in compliant tank space but now is in a noncomplaint (Type IV) tank.
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Tank Waste Retrieval, Processing, and On-Site Disposal at Three Department of Energy Sites: Final Report SIDEBAR E-1 The DWPF Recycle and Tank Space at SRS The Defense Waste Processing Facility (DWPF) receives tank waste and processes and immobilizes that waste in glass logs. Some 5,680 m3 (1.5 million gallons) per year of waste called DWPF recycle is sent back to the tank farms. DWPF recycle is a combination of several liquid waste streams from the DWPF, including overheadsa from the Melter Off-gas System and the Sludge Receipt and Adjustment Tank and the Slurry Mix Evaporator. The latter waste streams are collected in the Slurry Mix Evaporator Condensate Tank (SMECT). These “mildly contaminated” waste streams are alkalized with sodium hydroxide (1 molar) and corrosion-inhibited with sodium nitrite (1 molar) before being sent to noncompliant (Type IV) tanks: Tanks 21 and 22. They are then sent to the 2H evaporator system, which comprises the feed tank (Tank 43, Type III), the 2H evaporator, and the concentrate receipt (drop) tank (Tank 38, Type III). The drop tank takes the evaporator bottoms. The evaporator overheads are sent to the Effluent Treatment Facility. The evaporator bottoms sent to Tank 38 are essentially all concentrated supernate (liquor), with high concentrations of sodium hydroxide. Until recently (November 2004), the liquor was cycled back to the feed tank and run through the evaporator repeatedly. As a result, sodium hydroxide built up in the 2H evaporator system and the volume reductions achieved by evaporation worsened. In November 2004, DOE concluded it could, and had to, transfer the roughly 3,000 m3 (800,000 gallons) of liquor from the 2H evaporator system to another tank for storage to allow new DWPF recycle to be sent to the 2H evaporator. The concentrated liquor was stored temporarily in Tank 49, a Type III (compliant) tank, from November 2004 until April 2005 when it was transferred to Tank 24, a virtually empty Type IV (noncompliant) tank. Tank 49 had previously been emptied in preparation for its role as the DDA settling tank and, therefore, was available for temporary storage of the 2H evaporator liquor. Before the waste transfer to a noncompliant tank with no history of leakage (Tank 24) was approved, DOE expressed some concern that the waste would continue to occupy compliant tank space needed for salt waste operations, but that potential problem never became a reality. Considering the capacity in Tanks 21 and 22 and the 2H evaporator system, DOE projects that DWPF recycle will not have storage problems for several years to come. In the future, DOE plans to use the 2 molar DWPF recycle to adjust the sodium molarity of the dissolved saltcake (7.5-8 molar) down to the range that is best for saltstone feed (5-6 molar). The sodium molarity of the concentrated DWPF recycle stream in Tank 24 is 11. DOE notes that gibbsite and aluminosilicates (primarily cancrinite) will form if DWPF recycle or the liquor is mixed with other tank wastes, but these solids are expected to be resuspended easily in the liquids, rather than forming the agglomerated masses that have proven to be problems in the 2H evaporator and in tanks that have zeolite in the form of ion-exchange media. DOE said that the Savannah River Site has no way to get the DWPF recycle stream directly to the Saltstone Production Facility (Triay, 2005). Upon further discussion with DOE, the statement was clarified to mean that currently there is no way to bypass the tank farm entirely. In fact, an option explored by Mahoney and d’Entremont (2004) is to send a portion of the DWPF recycle stream to Tank 50, which is the feed tank for the Saltstone Production Facility. DOE did not select this option. In short, DOE can send the DWPF recycle stream to saltstone. However, without a new transfer line, DOE cannot avoid neutralizing the waste stream because it has to go through the tank farm to get to the saltstone facility. a Overheads are the vapors arising from waste in a waste evaporator. Once condensed, they constitute another liquid waste stream. this new delay can only exacerbate the tank space problems unless DOE (1) decreases the rate of waste additions from sludge processing and canyon operations; (2) increases the amount of waste sent through interim processing, including the deliqufication, dissolution, and adjustment (DDA) process, or (3) finds alternative storage options. In its interim report, the committee recommended that DOE consider options other than DDA to alleviate the impending crisis in usable storage in compliant tanks. DOE is examining what alternatives it has that will allow for continued full-capacity operation of the DWPF without increasing the radioactivity in saltstone above the amount the state has already agreed to (3-5MCi). DOE hopes to put forward a new strategy for salt processing and tank space in January 2006. Class C Limits In December 2005, the USNRC issued a Draft Interim Concentration Averaging Guidance for Waste Determinations (FR 74846 v. 70, n. 241, Dec. 16, 2005) that would allow averaging concentrations of residual waste in tanks over the volume of the grout in which the waste is mixed or that is needed to stabilize the waste. However, it would not allow averaging over the volume of the overlying grout because there is neither substantial mixing nor encapsulation. In essence, the committee’s recommendation that discussion focus on risk assessments rather than concentration limits or averaging is consistent with the USNRC’s draft interim guidance and prior Branch Technical Position (USNRC, 1995), which say that the determining factor for averaging is the impact on risk.
Representative terms from entire chapter: