III
Findings and Recommendations

PATHS TOWARD SOLUTIONS TO TANK WASTE PROBLEMS

As noted in the introduction, the committee has focused on actions that tend to (1) reduce the waste left on-site and (2) increase DOE’s understanding of factors that affect the near- and long-term risks associated with the waste. Before commenting on issues specific to the Savannah River Site, it is useful to summarize briefly the general philosophy and approach that the committee considers important given its mandate from the Congress.

The committee notes that the goal of management of tank wastes that are to be left on site is protection of public health and the environment. The committee endorses a risk-informed approach, as described in Risk and Decisions About Disposition of Transuranic and High-Level Waste (NRC, 2005). A risk-informed approach starts with risk but incorporates many other factors in a decision process that leads to the desired end states (goals). The performance objectives define those goals, and the performance assessments determine which courses of action will meet those objectives. There are well-defined procedures for setting performance objectives to meet an acceptable end state. Much of the concern and difficulty relating to cleanup of the tanks relates to choices among alternative end states that meet the minimum legal and regulatory requirements and are protective of public health and welfare. The alternatives may differ substantially in several dimensions, including the types of risks associated with the end state, information needed to evaluate risk, time until final cleanup goals are met, the risks through time prior to achieving the end state, costs, and a variety of other considerations such as cultural, social, and political, as well as local, regional, and national economic interests.

The challenge, therefore, is not in demonstrating that performance objectives can be met by a particular cleanup option, but in determining which cleanup options provide an appropriate balance of costs, protection of public health and the environment, and other relevant factors, including consideration of the steps necessary to achieve the selected end state.

The committee believes that the basis for choices could be made clearer, and a wider range of possibilities may become apparent, if DOE were to identify and assess cleanup as a sequence of decisions (see, e.g., NRC, 1996). Management, treatment, and eventual disposal of tank wastes at DOE sites involve a complex and interdependent set of decisions, characterized by uncertainties in the consequences of each decision element. Some parts of the sequence of decisions can be made without finalizing the entire sequence. A most fundamental element of sound decision making under uncertainty is to preserve options for action as long as possible, provided that waiting for information or



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Tank Wastes Planned for On-Site Disposal at Three Department of Energy Sites: The Savannah River Site - Interim Report III Findings and Recommendations PATHS TOWARD SOLUTIONS TO TANK WASTE PROBLEMS As noted in the introduction, the committee has focused on actions that tend to (1) reduce the waste left on-site and (2) increase DOE’s understanding of factors that affect the near- and long-term risks associated with the waste. Before commenting on issues specific to the Savannah River Site, it is useful to summarize briefly the general philosophy and approach that the committee considers important given its mandate from the Congress. The committee notes that the goal of management of tank wastes that are to be left on site is protection of public health and the environment. The committee endorses a risk-informed approach, as described in Risk and Decisions About Disposition of Transuranic and High-Level Waste (NRC, 2005). A risk-informed approach starts with risk but incorporates many other factors in a decision process that leads to the desired end states (goals). The performance objectives define those goals, and the performance assessments determine which courses of action will meet those objectives. There are well-defined procedures for setting performance objectives to meet an acceptable end state. Much of the concern and difficulty relating to cleanup of the tanks relates to choices among alternative end states that meet the minimum legal and regulatory requirements and are protective of public health and welfare. The alternatives may differ substantially in several dimensions, including the types of risks associated with the end state, information needed to evaluate risk, time until final cleanup goals are met, the risks through time prior to achieving the end state, costs, and a variety of other considerations such as cultural, social, and political, as well as local, regional, and national economic interests. The challenge, therefore, is not in demonstrating that performance objectives can be met by a particular cleanup option, but in determining which cleanup options provide an appropriate balance of costs, protection of public health and the environment, and other relevant factors, including consideration of the steps necessary to achieve the selected end state. The committee believes that the basis for choices could be made clearer, and a wider range of possibilities may become apparent, if DOE were to identify and assess cleanup as a sequence of decisions (see, e.g., NRC, 1996). Management, treatment, and eventual disposal of tank wastes at DOE sites involve a complex and interdependent set of decisions, characterized by uncertainties in the consequences of each decision element. Some parts of the sequence of decisions can be made without finalizing the entire sequence. A most fundamental element of sound decision making under uncertainty is to preserve options for action as long as possible, provided that waiting for information or

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Tank Wastes Planned for On-Site Disposal at Three Department of Energy Sites: The Savannah River Site - Interim Report resolution of uncertainties does not create greater offsetting risks to health and the environment or other costs. Actions that would eliminate important options should be delayed when possible because options have value. By structuring the path toward a final end state as a sequence of decisions (e.g., a tank closure decision or a saltstone processing decision), one can start to separate the decisions into decisions that clearly should be taken as soon as possible and those that potentially may be delayed until important uncertainties can be reduced (allowing a better choice to be made) or until new options become available (e.g., through operational experience, research, and technological innovation) that may make the decision easier (reduced risk at lower cost) and better informed. The committee’s findings and recommendations address four major issues: (1) near-term and long-term risks; (2) tank space crisis; (3) Class C limits and performance objectives; and (4) research and development needs. The following findings and recommendations are based on information available to the committee at the time of writing this interim report and may be extended if new information becomes available at the time the final report is written. 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 noncompliant 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 years) 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 the State of South Carolina to revise the schedule for closure of a limited number of the tanks that contain significant heels, if necessary.

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Tank Wastes Planned for On-Site Disposal at Three Department of Energy Sites: The Savannah River Site - Interim Report Rationale The bulk of the waste within the noncompliant tanks poses the greatest potential for environmental release in the near term, and if released into the environment it constitutes an essentially irretrievable source term of untreated hazardous material into the future. Therefore, most of the reduction in risk from such releases is achieved by bulk removal of these wastes. Removal of sludge in the heel, which contains most of the strontium salts (i.e., medium-lived radioactivity) and most of the insoluble actinides (i.e., long-lived radioactivity), will also reduce risks although it is more difficult to achieve. The committee agrees with DOE’s and South Carolina’s overall approach to tank waste removal at the Savannah River Site: bulk removal and immobilization of the waste is the highest priority to reduce the probability of release of radioactive materials to the environment in the near term. The noncompliant tanks, about half of which have a history of leakage, demand attention first but most of the tanks are beyond their design lifetimes. Residual waste left in the tanks poses a lower near-term risk because it is less mobile and, as such, has less potential for environmental release, and there is less of it to constitute a potential source term. However, wastes left in tanks for longer terms may result in increased risks due to aging and corrosion of the tanks, and the greater likelihood of extreme natural events with time. The milestones in the Federal Facility Agreement have been negotiated among DOE, the state, and EPA and are based on policy decisions; from a technical perspective, the schedule that the milestones imposes make tank waste removal and tank closure schedules appear “coupled” (i.e., one following the other as soon as possible) for some tanks. The disadvantage of closing tanks as soon as waste removal actions cease is that it forecloses near-term options to remove additional waste and/or to use improved immobilizing materials to fill the tank. Filling a tank with grout is essentially an irreversible action, although it is always conceivable to open a tank and excavate the grout if absolutely necessary. DOE should decouple cleanup and closure schedules, keep as many options open as practical for a limited period of time (i.e., 5-10 years), and regularly assess technology developments and alternatives to reduce long-term risks presented by the tank heels (radioactive source term). In some cases, such as tanks with large obstructions where retrieving all of the heel is particularly problematic, DOE should make additional investments in research and development to enhance tank waste removal (reducing the source term), to improve residual waste immobilization (stabilizing the source term), or to reduce the ingress of water once the tanks are closed (protect the source term); see Recommendation 4. A similar recommendation was made in a previous National Academies report for DOE’s Environmental Management Science Program (NRC, 2001). A qualitative assessment by DOE of the issues associated with aged and abandoned underground structures and vessels includes the potential for roof and side wall collapse; filling with water from runoff (bathtub effect); and internal seepage which can lead to overflowing, leaking, or leaching, and buoyancy (Langton et al., 2001). However, the committee is not advocating abandoning the empty tanks on-site and has seen no quantitative assessment of the risks of postponing tank grouting. According to DOE, the tanks are not in near-term danger of collapsing after bulk waste retrieval;54 indeed the structural support provided by the tank fill is not likely to be needed until DOE is ready for 54   It is the committee’s understanding that the geometry of the tanks is inherently stable (i.e., resistant to collapse). The emptied tanks, therefore, need not be filled until immediately prior to closure of the entire tank farm and placement of the engineered cap (if used).

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Tank Wastes Planned for On-Site Disposal at Three Department of Energy Sites: The Savannah River Site - Interim Report ultimate closure of the tank farm. In most cases, postponing closure of tanks that contain substantial amounts of residual waste for several years would appear to have essentially no effect on near- or long-term risk. In some cases, tank closure need not be delayed, such as in tanks that have small heels (i.e., as small as those in Tanks 16, 17, and 20) and/or low concentrations of radionuclides or if there are risks specific to the tank that require closure 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 dates of the tank farms, 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 closing the tank farms. There are specific advantages in delaying closure of the most challenging tanks. DOE needs time to gather operational experience for tanks with cooling coils and other major obstructions. DOE obtained good results in retrieving waste from Tanks 17 and 20, leaving behind very little residual waste. Tanks 18 and 19, which have undergone waste removal, are estimated to have an order of magnitude more radioactivity than Tanks 17 and 20, but the greater challenges lie ahead. DOE started its tank waste removal and closure campaign with Type IV tanks, which are simpler to work with because of the absence of cooling coils. This approach makes sense with respect to retrieval technology, because it allows DOE to learn from the simpler tanks before tackling the more complex ones. Tanks with coils may present an additional challenge because they are likely to have solids encrusted on the walls, bottoms, and the coils themselves. DOE has developed operational experience on in-tank activities, such as sampling, slurrying, pumping, removing waste heels with water jets (sluicing), and operating other remotely controlled equipment. In some cases, DOE may need more time than is allowed by the FFA closure milestone to apply what it has learned, test, identify any new challenges, and evaluate new technologies to maximize the removal of waste and stabilize residual waste in the more difficult tanks (see also Recommendation 4). The other advantage of decoupling tank waste removal and closure is that it would allow DOE the opportunity to enhance the effectiveness of tank closure. As previously noted, the long-term performance of the tank fill materials, especially Smart Grout, has not been adequately established. To lend confidence to the assumptions used in the performance assessment, a delay in tank closure would give DOE more time to evaluate grout formulation and techniques further and to conduct studies of projected long-term performance by laboratory and field testing of tank fill materials (see Recommendation 4). The committee recognizes that there are also drawbacks to delaying tank closure. The State of South Carolina told the committee that the state wants to see progress on closing out the tanks and does not favor a “piecemeal approach” to waste cleanup, decoupling bulk removal from tank closure (SCDHEC, 2005). It has been argued that unless previously agreed to milestones for tank closure continue to be met, progress will stall. Moreover, once equipment is in place for tank waste removal (e.g., the superstructure for in-tank operations), it is convenient to proceed to use the same equipment for closure, rather than moving it to another tank and re-equipping the first tank when it is ready for closure. The committee does not advocate decoupling the removal and closure schedule based only on the future possibility of discovering better technologies for cleanup and closure, without identifiable prospects. Rather, the idea is to develop or adapt specific technologies that are at least in the applied research stage and to research a narrow set of questions that, if answered, could enhance tank heel removal and closure effectiveness. In Recommendation 4, the committee suggests three promising topics that warrant further research and development efforts to achieve these two objectives.

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Tank Wastes Planned for On-Site Disposal at Three Department of Energy Sites: The Savannah River Site - Interim Report A reason for decoupling schedules concerns what is practical. The tank wastes must be dealt with and Congress has provided a means to do so. One element of Congress’ mechanism concerns removal of highly radioactive materials to the maximum extent practical. Ideally, all radioactive materials would be removed; in practice, waste cleanup decisions account for risks, costs, benefits, the likelihood of improvements, and other policy considerations. The committee is concerned that what is practical is being defined, in some cases, by an agreed upon schedule or what meets the performance objectives, not accounting for the ALARA requirement. The committee is also concerned that the cleanup not extend indefinitely into the future. Therefore, the committee has selected a time frame that is in reasonable accord with the overall schedule for tank farm closure. If substantially improved waste removal and closure can be achieved with no or little effect on the overall tank farm closure schedule, it would seem prudent to do so. Finally, as DOE considers delaying closure for some tanks, it has to evaluate 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, then 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 could, if successful, 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. 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 8 percent 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. Rationale As noted previously, compliant tank space is scarce and DOE often makes multiple transfers among tanks to ensure that there is sufficient operating space in specific tanks, such as tanks that are connected to an evaporator. As the compliant tank space diminishes,

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Tank Wastes Planned for On-Site Disposal at Three Department of Energy Sites: The Savannah River Site - Interim Report the needed transfers become more complex, even to the point of making transfers between the tank farms. Further, unless currently obligated compliant tank space is freed up, there will come a point when the tanks cannot accommodate more waste. DOE has indicated that without increasing the available compliant tank space, it faces a decision in the next year about whether and how to reduce waste additions. As noted in Section II, the DNFSB has raised concerns about tank space problems and the increased risks of accidents and worker exposures incurred as a result of the additional waste transfers that are required as space becomes more scarce (DNFSB, 2004). The committee shares these concerns and believes they deserve serious attention: DOE needs options to address this problem, even if new inputs are slowed, as recommended above. DOE plans to address the tank space problem in the near term by implementing the interim salt waste DDA process. The DDA process would alleviate some of the space problem. However, during the short time it will be in operation DDA would process less than 10 percent of the salt waste and would leave behind at least five times as much radioactivity in the saltstone compared to the ARP/MCU and the high-capacity processes that will treat the other 90 percent of the salt waste. Because grouting the LLW is an irreversible action, the decision to send the DDA waste stream directly to saltstone permanently commits a substantial amount of radioactivity to the site. In other words, although the DDA process would free up tank space, this tank space is attained at the cost of a large increase in radioactivity left on-site, compared to processing the waste through the planned chemical processing facilities (ARP/MCU and SWPF). Even these higher levels of radioactivity, primarily from 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, the separation achieved with DDA raises the question: Does this process remove radionuclides to the maximum extent practical? Table 4 compares the efficacies of salt waste treatment processes. The table shows that DDA is significantly less effective than ARP/MCU and the SWPF in removing radioactivity from salt waste. DOE indicated that up to 5 MCi of radioactivity could be sent to saltstone depending on the uncertainties in the characterization of the saltcake; if this were to be the case, the contribution of radioactivity sent to saltstone from DDA alone could increase to 4.5 MCi, which represents almost 90 percent of the total amount of radioactivity sent to saltstone from all three salt waste processes. Neither the model that generated the detailed inventory of the waste constituents nor the saltstone waste acceptance criteria55 were available to the committee for review. The committee, therefore, can neither endorse nor recommend changes to a phased salt waste processing approach that includes the DDA without this additional information. One committee concern is what will happen with salt waste processing if the 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 the schedule 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. 55   Waste acceptance criteria take into account performance objectives and broader considerations, 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.

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Tank Wastes Planned for On-Site Disposal at Three Department of Energy Sites: The Savannah River Site - Interim Report TABLE 4 Projected Efficacy of Salt Waste Treatment Facilities   DDA ARP/MCU SWPF Date expected to be in operation 2005 2007 2009 Date expected to cease operations 2009 2009 2019 Volume to be processed, million gallons 6.9 2.1 75 Volume to be sent to saltstone, million gallons 8.6 2.8 95.8 Radioactivity to be removed, MCia 8.8 3.4 217.1 Radioactivity to be sent to saltstone, MCi 2.5 0.3 0.2 Projected radioactivity removed, % 71.6 91.1 99.9 Projected share of radioactivity in the saltstone, % 83.3 10 6.7 a DOE indicated that due to the uncertainty associated with the current characterization of the saltcake waste, the actual radioactivity of the material going to saltstone may be as high as 5 MCi. Other uncertainties associated with radioactivity values and the time lines have not been determined. Values in curies include contributions from the daughter products of cesium-137 and strontium-90. Based on DOE’s prior experience with developing and initiating operations at major waste processing facilities,56 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. Reducing Waste Inputs (1) Reduction in DWPF recycle stream volume. As previously noted, a major source of new waste inputs to the tanks is from the DWPF recycle stream, which is a low-activity, high-volume waste stream. According to information provided by DOE (Fellinger and Bibler, 2004), the main contributor to radioactivity in this recycle stream is condensate from the melter off-gas (i.e., vapors and gases produced during melter operations). This off-gas contains a small amount of solids entrained in the steam produced when the waste slurry is evaporated in the melter. DOE’s analyses indicate that both the nonradioactive and the radioactive compositions of samples taken from the off-gas condensate tank, and subsequently the recycle concentrate tank, which collects all DWPF recycle stream, reflect the composition of the waste sludge that is being vitrified. According to the same analyses, the total radioactivity in the recycle stream amounts to about 0.001 Ci/liter with about two thirds of the radioactivity coming from cesium-137 and one third from alpha-emitting 56   Several Government Accountability Office reports have commented on the challenges of bringing online and operating large-scale waste processing facilities (GAO, 1997a, 1997b, 1999, 2003, 2004).

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Tank Wastes Planned for On-Site Disposal at Three Department of Energy Sites: The Savannah River Site - Interim Report isotopes. The DWPF recycle stream is therefore essentially a very dilute solution that carries traces of the original waste sent to the DWPF. Installing an evaporator at the DWPF to reduce the volume of the recycle stream would reduce waste inputs to the tanks. However, as noted before, DOE indicated that the earliest an evaporator could be brought on-line is 2010. While an evaporator would not now be able to alleviate the near-term tank space crisis without an expedited schedule, such an option should be investigated for longer-term waste management operations. Other longer-term options for consideration include the installation and use of temporary holding tanks as part of the sludge washing and DWPF recycle handling to reduce the waste generation from those operations or a change in operations of the DWPF. (2) Redirecting the DWPF recycle stream. The DWPF recycle waste stream could be grouted and sent directly to the saltstone facility. As noted above, DOE indicated that this stream is a low-activity waste stream and therefore could be disposed on-site as saltstone. DOE is currently sending the DWPF recycle stream to the tank farm because of future potential use in waste processing (e.g., batch preparation); however, this waste stream currently does not appear to be used for any purpose and the near-term benefits of more tank space may outweigh the long-term detriment of introducing additional water into the system. Freeing Up Existing Compliant Tank Space (1) DOE holds the equivalent volume of one empty tank in compliant tank space in reserve for emergencies. Holding such a reserve is sensible, but it is not clear that the space has to be in a compliant tank. Several Type IV tanks have no history of leakage, and some could provide emergency reserve. This would free up the equivalent of a full compliant tank. According to DOE and the South Carolina Department of Health and Environmental Control, DOE may store waste in noncompliant tanks if the waste is kept below the height of any historical or anticipated leak. Given that virtually all of the usable tanks are filled to capacity with very limited free working volume, the system is vulnerable to mishaps and perhaps to leaks, overflows, and possibly even tank or line failures with potential extensive releases to the environment. Therefore, it seems prudent to proceed apace to obtain the working volume to deal with unexpected circumstances while refining waste treatment processes for the long term (i.e., 10-20 years or more). 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.

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Tank Wastes Planned for On-Site Disposal at Three Department of Energy Sites: The Savannah River Site - Interim Report Rationale The Class C limits are not a criterion for the 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. In Section 3116 of the Ronald Reagan National Defense Authorization Act of 2005 (NDAA), Congress established criteria for determining that some waste from spent fuel reprocessing is not high-level waste and may be disposed of on-site at the Savannah River Site and the Idaho National Engineering and Environmental Laboratory. Congress implicitly divided the non-HLW destined for on-site disposal into two subclasses, depending on the concentrations of radionuclides in the waste in relation to Class C concentration limits in 10 CFR 61.55 (see Table 5). Therefore, at the Savannah River Site and the Idaho National Engineering and Environmental Laboratory (but not at Hanford), there are essentially three categories of reprocessing waste: HLW, non-HLW Class C or less and non-HLW greater than Class C, as shown in Table 5. The recent promulgation of the NDAA adds further complexity to the regulatory framework for tank waste at the Savannah River Site in that the “consultative” role of the U.S. Nuclear Regulatory Commission has not been defined in the NDAA and is now being applied for the first time. TABLE 5 Management Standards for Wastes Stored in HLW Tanks at the Savannah River Site and the Idaho National Laboratory HLW Non-HLW Class C or Less Non-HLW Greater than Class C Default classification of all highly radioactive wastes from reprocessing of spent nuclear fuel DOE, in consultation with the USNRC, may decide that the wastes do not require deep geologic disposal DOE, in consultation with the USNRC, may decide that the wastes do not require deep geologic disposal High-activity radionuclides removed to the maximum extent practical High-activity radionuclides removed to the maximum extent practical Disposal must meet performance objectives of 10 CFR 61, subject to USNRC monitoring and reporting to congressional committees Disposal must meet performance objectives of 10 CFR 61, subject to USNRC monitoring and reporting to congressional committees Disposal must be approved by host state Disposal must be approved by host state   DOE consults with USNRC on disposal plans Must be disposed of in deep geologic repository Need not be disposed of in deep geologic repository DOE develops disposal plan in consultation with USNRC NOTE: Standards established in Section 3116 of the Ronald Reagan National Defense Authorization Act of 2005.

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Tank Wastes Planned for On-Site Disposal at Three Department of Energy Sites: The Savannah River Site - Interim Report DOE and the Nuclear Regulatory Commission are now testing this process through the Salt Waste Process Determination (DOE, 2005a). The present study focuses on non-HLW, although the committee is encouraged to consider as much of the issue as is necessary to make meaningful recommendations. The committee draws several conclusions from the legal structure in Table 5: The non-HLW categories potentially apply to the reprocessing wastes planned for land disposal at the Savannah River Site, including tanks, tank heels, and saltstone in vaults. Whether a particular non-HLW meets or exceeds Class C criteria is relevant to its disposition only procedurally regarding USNRC roles in that DOE must consult with the USNRC on its disposal plans. The USNRC has a consultation and monitoring role in both of the non-HLW categories, but it has no decision-making role in either. Congress has mandated that the substantive disposal standards for non-HLW be the following: Removal of highly radioactive radionuclides “to the maximum extent practical.” Compliance with the performance objectives of Subpart C of 10 CFR 61. The performance objectives focus on ensuring that the dose to the public meets specific requirements and is as low as reasonably achieved (ALARA) below this level; protection of inadvertent intruders; ensuring that the occupational dose meets specific requirements and is ALARA below this level; and ensuring long-term stability of the disposal site including elimination of the need for active maintenance to the extent practicable. Disposal pursuant to a state-approved closure plan or state-issued permit. Risk to human health and the environment is not an explicit criterion in disposal decisions, though the performance objectives are proxies for human health risk to the extent that dose limits and ALARA are representative of this goal. In sum, within this regulatory structure, whether a particular waste stream meets or exceeds the definition of Class C makes little difference in terms of what is really at issue here—compliance with performance objectives and the protection of human health and the environment. This conclusion underlies Recommendation 3. Class C limits were not designed to be applied for legacy waste at DOE sites. These concentration limits for waste were developed for a diverse commercial sector to establish limits on what is generally (not site specifically) acceptable for near-surface disposal, based in part on assumptions about the overall set of wastes destined for disposal. It was never envisioned that one might have a large, near-surface disposal facility filled to capacity with waste at or near the Class C limit. Indeed, if the Class C limits alone were the criteria for acceptance of waste in the Saltstone Disposal Vaults, all of the cesium-137 in the high-level waste tanks at the Savannah River Site could potentially go into the saltstone. Congress recognized the importance of the performance objectives for evaluating site-specific near-surface disposal of waste in Section 3116 of the NDAA by explicitly including these objectives as the basis for management standards to be applied to waste in high-level waste tanks at the Savannah River Site and Idaho. Note, too, that the USNRC eliminated comparisons to Class C concentration limits in favor of a site-specific,

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Tank Wastes Planned for On-Site Disposal at Three Department of Energy Sites: The Savannah River Site - Interim Report performance-based approach for the West Valley Demonstration Project (USNRC, 2002; Vietti-Cook, 2000). Rather than Class C limits, site-specific risks (as calculated in performance assessments) are the bases for determining whether the facility meets the performance objectives in the regulations. Risks depend on radionuclide quantities and concentrations, their conditioning, and their interactions with the environment. It is possible that some Class C wastes may not be acceptable for near-surface disposal at a particular site and that some greater-than-Class C wastes may be acceptable for near-surface disposal at a another site as exceptions to the generic concentration limits. At the Savannah River Site, DOE proposes on-site disposal of certain wastes in known facilities (e.g., Saltstone Vaults, existing tanks). As a consequence, the relevant criterion concerning the maximum concentration of radionuclides acceptable for such disposal is whether performance objectives are met for those specific locations, which is supposed to be reflected in the “waste acceptance criteria” for each disposal facility. The allowable concentrations may be higher or lower than the Class C limits, but they would likely be based on relevant data, models, and assumptions rather than generic calculations. Risk evaluations must be done using a properly constituted “performance assessment” and associated uncertainty analysis for the specific situation at hand. A previous National Academies report (NRC, 2005) provides extensive guidance on how such risk assessments should be performed. Concerning the related issue of radionuclide concentration averaging, the committee draws similar conclusions to those described above. The actual distribution of radionuclides within the waste form and the waste form’s ability to immobilize the radionuclides affect risk. The performance assessment used to assess risks must use the actual distributions or conservative simplifications of those distributions. Concentration averaging that is used only to calculate radionuclide concentrations for comparison to the Class C limit is not relevant to risk. Such averaging will not be required for saltstone, the composition of which should be well known and is essentially homogeneous over large volumes. This way of thinking about concentration averaging is in agreement with the U.S. Nuclear Regulatory Commission’s guidance on these issues (Knapp, 1995). 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. Rationale To reduce long-term risks at the site and test the assumptions in the performance assessment, the committee recommends that DOE carry out focused research and

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Tank Wastes Planned for On-Site Disposal at Three Department of Energy Sites: The Savannah River Site - Interim Report development activities to improve capabilities for tank waste removal and closure. This recommendation implies that certain tanks should not be closed immediately after cleanup, as stated in Recommendation 1. The committee is not advocating delaying closure of certain tanks to perform long-term research and development activities: efforts should be limited to promising technologies that are at a near-deployment stage (i.e., they could provide deployable 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). Although the committee is lacking critical information to determine whether DOE’s management and closure plans will comply with the dose limits in the performance objectives, the committee believes that a focused research and development program aimed at reducing the amounts of waste left in the tanks or improving its immobilization may increase confidence in DOE’s plans or cause DOE to revise some of the assumptions used in the performance assessment. Validating assumptions and improving DOE’s knowledge base could increase its ability to comply with the performance objectives. Moreover, these research and development activities could support the development of contingency approaches to address unanticipated difficulties in baseline processes. These research and development activities would be carried out either in parallel with the current baseline approach to tank waste removal and closure or until a specific technology becomes ready to be deployed. These technologies will likely require pilot-scale tests with tank mockups and with surrogate heels to test their effectiveness before full-scale deployment. The committee believes that there are at least three critical topics warranting further research and development efforts.57 These topics represent the greatest technological challenges (i.e., waste retrieval and tank cleanup) and knowledge gaps (i.e., Smart Grout long-term performance). Research and development activities to address these topics are discussed below. In-Tank and Downstream Consequences of Existing and Advanced Chemical Cleaning Options As noted previously, DOE has demonstrated the efficacy of oxalic acid for the chemical cleaning of waste tanks but also uncovered potential drawbacks associated with criticality safety and downstream processing. DOE’s concerns about criticality issues are linked to the potential for selective removal of a neutron poison (e.g., iron hydroxide) from a phase containing significant quantities of fissile isotopes.58 DOE provided no indication that calculations have been carried out to substantiate these concerns. Oxalic acid may also interfere with downstream processing for further separation or immobilization of radionuclides. For example, foaming of organic chemicals could occur depending upon a number of conditions including chemical concentration, temperature, and mixing. Two paths can be explored: (1) research and development of cleaning agents other than oxalic acid that would not interfere with sludge or salt waste processes; or (2) research and development on ways to both predict and eliminate criticality concerns and downstream problems if oxalic acid is used as the cleaning agent. Examples of research to address downstream problems from oxalic acid could include destruction of oxalic acid and metal 57   Other topics may be added in the final report, as the committee gathers further information. 58   Fissile isotopes have a high probability of undergoing nuclear fission when struck by neutrons and, in the right quantities and configurations, can sustain a nuclear chain reaction.

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Tank Wastes Planned for On-Site Disposal at Three Department of Energy Sites: The Savannah River Site - Interim Report oxalates via ozone oxidation, chemical oxidation, and electrochemical oxidation (Patello et al., 1999; Nash et al., 2003). Savannah River Site personnel indicated that they are in communication with other national laboratories, DOE sites, and with Russian experts on tank cleaning technologies, particularly on chemical cleaning. The chemical species formed by radioactive elements have been identified as key parameters in understanding their dissolution and solution behavior in tank waste (Garnov et al., 2003; Nash et al., 2002). Over the past 30 years, significant advances have been made in metal-specific complexation and ligand design which exploit metal ion speciation in producing selective complexes. A number of these advances are based on biomimetic studies that evaluate specific metal ion-ligand interactions in natural systems (Raymond, 1990; Durbin et al., 1989). While metal-ligand interactions are primarily understood in the solution phase, ligands produced by bacteria (siderophores) will solubilize iron oxides, dissolve oxides of uranium and plutonium, and can be exploited in developing metal-specific reactions for solid phases (Brainard et al., 1992). These metal-specific ligand approaches have been used for the selective removal of radionuclides from the human body (see for example, Gorden et al., 2003). This same selective ligand approach has been applied to the area of radionuclide removal from tank waste (see, for example Nash et al., 2000). To date, these advances have not impacted the site’s tank waste removal operations but in the future they might offer cost-effective options for removing both solution and solid phase radionuclides from the tanks. Technologies to Assist in Tank Waste Removal, Including Robotic Devices Numerous technologies for retrieving residual high-activity waste from tanks at DOE sites have been developed to varying extents. The technologies mostly include tethered devices that may be either remotely controlled or robotic (i.e., programmable) and that maneuver along the bottom of a tank, as well as end-effectors deployed on the end of a mechanical arm. Such technologies are typically designed to gather, retrieve, and/or characterize relatively small amounts of residual waste remaining in the tank after bulk retrieval has been completed. Some devices have been deployed in the harsh environment represented by tanks containing high-activity wastes (Vesco et al., 2000; DOE, 2001d). However, the instances in which these devices have been deployed in tanks are relatively few and the devices have been tethered and not programmable or autonomous. Such devices and enhancements thereof appear to be suitable for the many DOE tanks that do not have internal structures such as cooling coils. Looking forward, DOE faces the need to retrieve waste from many large tanks containing cooling coils and other obstructions, especially at SRS. The baseline bulk retrieval approach consists of using water jets from the riser locations to spray material off the internal tank structures onto the bottom of the tank, consolidating it by sluicing, and pumping it from the tank. The potential limitations of bulk retrieval techniques are clear when one notes that the tanks containing a ‘jungle’ of cooling coils are 25 to 28 meters (75 to 85 feet) in diameter and up to 10 meters (30 feet) in height. The efficacy of bulk retrieval in tanks with coils is uncertain: good cleaning of tank surfaces appears to have been achieved in zones beneath the risers but the amount of residual waste remaining in the ‘dead zones’ between risers and in the tank periphery is unknown. However, the use of remotely controlled and robotic devices to retrieve residual tank waste also faces challenges as a result of the jungle of piping and other obstructions that severely limit the size and mobility of retrieval devices. According to the committee’s experts, no device—robotic or otherwise—is ready to be deployed in such tanks to recover residual waste. A few devices seem

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Tank Wastes Planned for On-Site Disposal at Three Department of Energy Sites: The Savannah River Site - Interim Report promising but require time for development and testing (see Sidebar 2), and significant investments. In general, since the 1970’s, robotic technology advances have paralleled the progress of the microprocessor, though with a lag of some years. The continued increase of processing power and speed has allowed robotic devices to make major advances in speed, precision, cost effectiveness, scope of applications and most critically, reliability. This is especially true in industrial applications. More exotic applications such as space, service, military and security robotics have also seen impressive gains commensurate with the funding level invested in development. Because the challenge of DOE tank waste cleanup is unique and the opportunities for deployment have been few due to the pace of the tank waste cleanup program, development and deployment of robotic devices for this purpose has only been attempted by a few teams. DOE’s previous work and experience on retrieval systems for residual wastes (e.g., the Fluidic Pulse Mixing and Retrieval System, the Modified Light Duty Utility Arm [Thompson et al., 1997; Magleby et al., 2002], previously cited deployments) is a worthwhile first step in a necessary continuing investigation. Robotic technologies will continue to advance and may accomplish in the future what is not possible today. The committee is planning to learn more about DOE’s research and development efforts on technologies for retrieving residual tank waste and may write more in the final report. In the interim, research and development investments in residual waste retrieval technologies suitable for tanks containing cooling coils or other obstructions appears prudent. Near-Term and Long-Term Performance Studies for Tank Fill Material As previously mentioned, DOE’s assumptions about the long-term performance of the tank fill materials, especially Smart Grout, have not been verified with empirical tests or SIDEBAR 2 USE OF TEST BEDS FOR THE STUDY OF RETRIEVAL TECHNIQUES Waste retrieval (bulk or heel) has not yet occurred in most tanks at the Savannah River Site. As noted in Section II, many of the tanks contain internal features such as cooling coils or other debris that promise to impede waste retrieval. In these situations, new technology or adaptations of existing technology may be desired or required. Adapting an existing retrieval technology or deploying a new retrieval technology in a radioactive environment can cost millions of dollars and failures can cost even more. Thus, it is technically prudent and cost-efficient to test retrieval technologies in nonradioactive test facilities (test beds) before attempting to deploy them. The usual approach to ensuring that a radioactive waste process will work consists of two steps: tests with the actual material on the laboratory scale to ensure that the process fundamentals are understood (e.g., sludge dissolution, pumpability), and tests with nonradioactive simulants on large or full scale to prove the design and the equipment (velocities, mass transfer).a DOE has operated such a test bed at the TNX facility at the Savannah River Site, but it is not clear that this test bed will be available in the future. 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, and debris) should be maintained. The Pump Test Tank is 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 committee will further address the need for experimental retrieval facilities in its final report. a   Lab scale tests and tests with simulants did not reveal the difficulties that emerged when DOE used the in-tank precipitation process to remove cesium from waste in Tank 48. That process, however, is rather different in nature than the type of waste removal and tank cleanup technologies that the committee describes here.

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Tank Wastes Planned for On-Site Disposal at Three Department of Energy Sites: The Savannah River Site - Interim Report even documented analytic reasoning. To lend confidence to the assumptions used in the performance assessment, DOE should further evaluate grout formulation and techniques and conduct studies of the near- and long-term performance of the grout by laboratory and field testing of tank fill materials. Experts at Savannah River (Dr. C. Langton and Mr. T. Caldwell) stated that based on tests they have concluded that there is effectively no mixing of grout with the insoluble tank heel, but the liquid is effectively absorbed by the grout or the dry cementitious materials deposited on top of the grout. Accordingly, DOE’s ongoing performance assessment does not take credit for mixing of the grout and heel but, as noted previously, assumes that the grout maintains its structural integrity for 1,000 years and its physicochemical integrity for 10,000 years. The basis for the 1,000-year assumption is taken from an earlier analysis done for the E-Area Vaults Performance Assessment (Martin Marietta Energy Systems et al., 1994). It appears that these assumptions have not been validated adequately either by literature review or by laboratory or field experiments. Moreover, despite requests, DOE has not presented evidence of long-term performance tests or modeling on grout to support these durability assumptions; therefore, the committee cannot assess the 1,000- and 10,000-year assumptions of physical and chemical durability of the Smart Grout. Although the committee acknowledges that a short research program (5 to 10 years) will not remove all uncertainties about the long-term performance of fill materials, such as cemented grout, research aimed at understanding the long-term performance of these materials in simulated tank field conditions and an assessment of projected service lifetime would provide a valuable insight to DOE’s assumptions. The concrete-durability research conducted by the Atomic Energy of Canada Limited for its near-surface disposal facility indicated that service life predictions can be made with some level of confidence from a 5- to 10-year laboratory test program. For example, DOE’s performance assessment takes credit for the tank fill materials, designed with objectives such as resistance to water infiltration and inadvertent intrusion for 1,000 years, as part of an engineered barrier system. The committee suggests conducting research and development activities to test these assumptions. Moreover, to lend confidence to the assumptions of the long-term integrity and durability of Smart Grout DOE should conduct laboratory and field research activities. Such activities could include high-temperature leach tests; grout-waste mixing tests; and tests to verify the effectiveness of the grout’s chemical properties on key radionuclides and hazardous metals, as well as the evolution of these properties with time. More basic research activities that could be performed in the same time frame include identifying and evaluating oxidation pathways and kinetics mechanisms for grout degradation. Some of these activities could also be conducted in parallel with saltstone to compare retention capabilities for the mobile radionuclides, such as technetium-99. Many of these research and development needs were identified by Westinghouse Savannah River Company at the committee’s meetings; the committee is not aware of any active research on tank fill materials performance for the Savannah River Site. Ongoing research on building materials, mainly for civil engineering purposes, could also provide a valuable insights for applications involving waste immobilization. The USNRC is cosponsoring research at the National Institute for Standards and Technologies on degradation mechanisms, mixing formulations, durability, and modeling of cementitious materials (Garboczi et al., 2005). Research and development on alternative grout placement technologies, such as jet grouting, to improve the degree of mixing of waste with grout could also yield results that are deployable in 5 to 10 years. Research and development work on jet grouting is already in progress at the Los Alamos National Laboratory (AEATES, 2004). An additional topic for research and development for which the committee does not yet have a recommendation concerns the environmental effects of the Saltstone Disposal

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Tank Wastes Planned for On-Site Disposal at Three Department of Energy Sites: The Savannah River Site - Interim Report Vaults, in light of the 3 to 5 MCi that DOE plans to there. Similarly, a study of the interaction of the tank fill material with the environment is warranted to determine the long-term impacts of waste residuals in the tanks. An updated, albeit partial, environmental impact statement for the Saltstone Vaults was provided to the committee. The environmental impact statement for all tank closures is not yet available (see Appendix B).