XI
Conclusions

As discussed in the previous chapters, there is uncertainty in some of the major phases of the Department of Energy’s (DOE’s) tank waste remediation program. DOE has only recently made public its justification for tank waste disposition decisions and many of its quantitative examinations of questions relevant to the committee’s charge. Even in these documents, however, there are no clear, definitive answers to some of the questions that Congress posed to the committee in its request for this study (see discussion of congressional charge to the committee, below). In what follows, the committee summarizes the messages it means to convey by its general and site-specific findings and recommendations (detailed findings and recommendations can be found in Chapters III through IX).1 The committee also provides abbreviated answers to the questions that Congress asked.

FINDINGS AND RECOMMENDATIONS

Summarized below are the committee’s general and site-specific findings and recommendations (see Chapters III through IX for details).

1. DOE’s overall approach is workable but there are technical and programmatic challenges in reaching the goals of the tank remediation program.

DOE’s overall approach for managing its tank wastes and the framework in which this must be done is workable: to the maximum extent practical, retrieve the waste from the tanks and separate the recovered waste into high- and low-activity fractions; and dispose of both waste remaining in tanks and recovered low-activity waste on-site in a manner that protects human health and the environment. Nonetheless, DOE faces technical and programmatic challenges in implementing this approach. Examples of technical challenges include retrieving waste from tanks with significant obstructions at the Savannah River Site and from tanks with leaks at the Hanford Site and assessing the uncertainties in the performance of planned waste processing approaches, such as the deliquification, dissolution, and adjustment (DDA) process at the Savannah River Site and the bulk vitrification process at Hanford.2 Programmatic challenges are those affecting the success of the tank cleanup program, such as budgetary challenges and regulatory challenges (see Chapter VIII).

2. Decisions about planned disposal activities require multiple inputs and should not be dictated solely by schedule conformance.

Basing tank management and waste disposition decisions only on performance assessments to demonstrate compliance with performance objectives is inadequate because such assessments do not take into account all of the various factors that could be important to decisions such as the evolution of the full risk profile (risks across the site under different exposure scenarios) over time; compliance with federal facilities agreements; changes in costs and changes in how people value health and the environment; progress to build confidence in the program; and other site risks, among others. All of these factors are increasingly uncertain the further into the future that people attempt to anticipate conditions.

DOE uses conformance to a schedule (i.e., meeting milestones) as one of three criteria in determining what constitutes removal of waste to the maximum extent practical in the Section 3116 draft waste determination for Tanks 19 and 18 at the Savannah River Site. While meeting agreed-upon schedules and milestones is important and in many cases legally enforceable, a schedule-driven approach could lead

1

This chapter is essentially the same as the précis of the report’s findings and recommendations found in the summary.

2

Other technical challenges concerning waste retrieval, processing, immobilization, and monitoring are described in Chapters III, IV, V, and VII.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 121
Tank Waste Retrieval, Processing, and On-Site Disposal at Three Department of Energy Sites: Final Report XI Conclusions As discussed in the previous chapters, there is uncertainty in some of the major phases of the Department of Energy’s (DOE’s) tank waste remediation program. DOE has only recently made public its justification for tank waste disposition decisions and many of its quantitative examinations of questions relevant to the committee’s charge. Even in these documents, however, there are no clear, definitive answers to some of the questions that Congress posed to the committee in its request for this study (see discussion of congressional charge to the committee, below). In what follows, the committee summarizes the messages it means to convey by its general and site-specific findings and recommendations (detailed findings and recommendations can be found in Chapters III through IX).1 The committee also provides abbreviated answers to the questions that Congress asked. FINDINGS AND RECOMMENDATIONS Summarized below are the committee’s general and site-specific findings and recommendations (see Chapters III through IX for details). 1. DOE’s overall approach is workable but there are technical and programmatic challenges in reaching the goals of the tank remediation program. DOE’s overall approach for managing its tank wastes and the framework in which this must be done is workable: to the maximum extent practical, retrieve the waste from the tanks and separate the recovered waste into high- and low-activity fractions; and dispose of both waste remaining in tanks and recovered low-activity waste on-site in a manner that protects human health and the environment. Nonetheless, DOE faces technical and programmatic challenges in implementing this approach. Examples of technical challenges include retrieving waste from tanks with significant obstructions at the Savannah River Site and from tanks with leaks at the Hanford Site and assessing the uncertainties in the performance of planned waste processing approaches, such as the deliquification, dissolution, and adjustment (DDA) process at the Savannah River Site and the bulk vitrification process at Hanford.2 Programmatic challenges are those affecting the success of the tank cleanup program, such as budgetary challenges and regulatory challenges (see Chapter VIII). 2. Decisions about planned disposal activities require multiple inputs and should not be dictated solely by schedule conformance. Basing tank management and waste disposition decisions only on performance assessments to demonstrate compliance with performance objectives is inadequate because such assessments do not take into account all of the various factors that could be important to decisions such as the evolution of the full risk profile (risks across the site under different exposure scenarios) over time; compliance with federal facilities agreements; changes in costs and changes in how people value health and the environment; progress to build confidence in the program; and other site risks, among others. All of these factors are increasingly uncertain the further into the future that people attempt to anticipate conditions. DOE uses conformance to a schedule (i.e., meeting milestones) as one of three criteria in determining what constitutes removal of waste to the maximum extent practical in the Section 3116 draft waste determination for Tanks 19 and 18 at the Savannah River Site. While meeting agreed-upon schedules and milestones is important and in many cases legally enforceable, a schedule-driven approach could lead 1 This chapter is essentially the same as the précis of the report’s findings and recommendations found in the summary. 2 Other technical challenges concerning waste retrieval, processing, immobilization, and monitoring are described in Chapters III, IV, V, and VII.

OCR for page 121
Tank Waste Retrieval, Processing, and On-Site Disposal at Three Department of Energy Sites: Final Report to retrieval and closure actions that may later be judged insufficient. In addition to DOE, several other parties play an important role in the ultimate success of DOE’s program: Congress, the Environmental Protection Agency, the Nuclear Regulatory Commission, host states, American Indian nations, local governments, and other stakeholders. A risk-informed, transparent, participatory, and consistent decision-making process facilitates the involvement of these parties and enhances the effectiveness of the process. 3. Tank cleanup is a multidecade project allowing opportunities to improve the efforts to retrieve waste from the tanks The milestones to close all tanks are at least a decade away (ranging from 2016 to 2032).3 Of all 246 high-level waste tanks, only 2 have been closed (i.e., grouted) so far, and about 14 are being prepared for closure.4 However, the cleanup of each tank will provide DOE with experiences that can be used to improve cleanup of the others. Following closure, modification of stabilized tank waste that is left onsite will be difficult, meaning that the form, concentration, and mass of tank waste left on-site will basically be fixed. Retrieval of waste from each tank will be somewhat different because each tank’s specific combination of waste type, tank design and construction, and operation history is unique. Complete closure of all tanks will involve many one-of-a-kind and first-of-a-kind endeavors that would be carried out more effectively by building on experience with tank waste remediation. DOE is learning from its experience to date, but there still are substantial opportunities to continue to improve its program with respect to waste retrieval, processing, immobilization, and disposal, monitoring compliance and performance assessment, decision making, and research and development. Each of these opportunities is discussed in greater detail below. Waste Retrieval (see Chapter III) Depending on the particular requirements of individual tanks, DOE should use the most effective sequence and combination of waste retrieval tools to ensure that waste is removed to the maximum extent practical. When the limit of a given technology is reached, DOE should utilize, when necessary, other waste retrieval tools (already available or to be developed) so that the maximum extent practical is not contingent solely upon what technology has already been deployed or the proposed tank cleanup schedule. Reaching the limit of a given technology does not in itself demonstrate that all practical efforts for retrieval have been made. The committee continues to believe that DOE should decouple the schedule for tank waste removal from the schedule for tank closure on a case-by-case basis, particularly in the case of tanks with significant heels (radioactive material remaining after planned retrieval operations are complete), as is likely in tanks with obstructions and/or with recalcitrant waste. In these tanks, more time may be needed to implement additional waste retrieval methods. DOE should not make decisions based solely on schedule conformance. Decoupling will enhance future opportunities to remove additional radioactive material from these tanks as retrieval technologies are improved. If implemented properly, decoupling for individual tanks need not delay the final closure of the tank farms. There is little technical advantage in the accelerated closure of the tanks. Waste Processing (see Chapter IV) When selecting a waste processing technology, DOE should take into account the impacts, flexibility, and robustness of processing facilities and waste forms. The Savannah River Site uses the DDA process to free up tank space, but the committee has concerns about the amount of radioactive material that the DDA process would allow to be disposed as low-activity waste on-site. The committee also has concerns about the bulk vitrification option for Hanford’s supplemental low-activity waste treatment (see site-specific concerns, below). The cost and risks to workers, members of the public, and the environment if the processes should fail to perform acceptably, along with schedule uncertainties, need to be taken into account in making decisions among alternatives. Waste Immobilization (see Chapters V, VI, and IX) The committee agrees with DOE’s selection of cementitious material (grout) as the most appropriate material for tank closure and does not foresee the development of better alternatives. However, the committee has concerns about DOE’s understanding of the very-long-term performance of the grout used to inhibit water flow and immobilize waste in closed tanks. As a result, the committee recommends further short- and long-term research and development on the performance of cementitious materials. These efforts should be tailored to the formulations of grout planned for use in tank closures and waste immobilization and to the demands DOE places on their long-term performance in its performance assessments. 3 Currently, the closure schedule for Hanford is 2024 for single-shell tanks and 2032 for double-shell tanks; at the Savannah River Site, the closure milestones are 2022 for Type I, II, and IV and 2028 for Type III tanks; at Idaho, the six-phase tank closure process began in 2005 and will reach completion in 2016. No milestone has been selected for closing the Idahobins. 4 DOE has officially submitted a waste determination to close the following tanks: Tanks 18 and 19 at the Savannah River Site, Tanks WM-180 through 186, and tanks WM-103 through WM-106 at the Idaho site (see Table F-1 in Appendix F). A separate state and USNRC review required under the Hanford Federal Facility Agreement is underway for Hanford’s Tank C-106.

OCR for page 121
Tank Waste Retrieval, Processing, and On-Site Disposal at Three Department of Energy Sites: Final Report Performance Assessments and Monitoring Compliance (see Chapters VI and VII) The committee views monitoring programs and performance assessments as iterative, interrelated, evolutionary activities that require updating as new information becomes available and as changes occur at the site. The sites have not yet, for the most part, developed plans for post-closure monitoring so the committee is not able to comment on them. DOE Order 435.1 requires that plans for closure of high-level waste facilities include a monitoring plan and further requires that iterations of performance assessments for low-level waste disposal facilities continue through facility closure and beyond, as needed (DOE, 2001a). It is understandable that post-closure monitoring is not DOE’s highest priority right now, given that closure of the tank farms is still decades away. Plans are needed, however, before closure because some of the components of monitoring systems should be built into the closure system. DOE should begin to build provision for monitoring into its tank closures and disposal facilities and develop plans for a post-closure monitoring program, ensuring that post-closure monitoring and the updating of performance assessments are given appropriate attention as the site progresses toward closure and beyond. External and independent peer review of DOE’s draft waste determinations and performance assessments introduced by Section 3116 of the NDAA has led to demonstrable improvement in DOE’s analyses (such as incorporating sensitivity studies) and the technical documents that are being prepared. This in turn has sharpened the understanding of DOE’s rationale, assumptions, analysis, and conclusions. DOE should continue to seek transparent, independent peer review of critical data and analyses used to support decisions about tank waste retrieval, processing, and disposal even if review is not required under the NDAA. Decision Making (see Chapter VIII) Determining how clean is clean enough for tank waste retrieval, separation, and disposal is a decision in which DOE must consider a range of technical and nontechnical factors. The question does not have a unique, numerical solution. In such decisions, DOE should take into account, in addition to the performance assessments results for specific locations at specific times, how the risks from the materials left on-site vary over space and time; technical capabilities for waste retrieval and radionuclide separation from the removed wastes; cost, both in terms of dollars spent and worker doses incurred per increment of risk reduction achieved; and the potential risks from other wastes to be left on-site. Given the technical and programmatic challenges in DOE’s waste management environment, one way to improve decision making is to adopt a more risk-informed, participatory, transparent, and consistent decision-making process. Such a process, as recommended in a previous National Research Council report (NRC, 2005b), would give regulators, Congress, the public, and especially DOE a clearer idea of the challenges and choices that DOE faces. It also will make DOE’s planning more robust, in the sense that it is more likely to succeed in its mission. DOE has taken steps to improve its transparency in its most recent draft waste determinations and performance objectives demonstration documents, which describe how DOE reached its decisions and provide supporting data and analyses for understanding the rationale for its decisions (Sams, 2004; Buice et al., 2005; DOE-ID, 2005a; DOE-SRS, 2005a; Rosenberger et al., 2005). The committee commends this improvement and encourages DOE to continue to increase transparency, accessibility, participation, and peer review in all aspects of its tank waste management program. Research and Development (see Chapter IX) As DOE is in the initial stages of retrieval and closure, and as the committee continues to see delays in key pieces of the tank program (e.g., Salt Waste Processing Facility at the Savannah River Site and Waste Treatment Plant at Hanford; see below), it is increasingly clear that there is more time for implementing a research and development program that could improve waste retrieval, tank stabilization, and low-activity waste immobilization. DOE should initiate a targeted, aggressive, collaborative research and development program focused on (1) options for chemical cleaning of tanks; (2) emerging technologies to assist in tank waste removal, including robotic enhancements to current waste retrieval technologies; and (3) near- and long-term performance and monitoring of tank fill materials as they interact with the environment. Based on experience with the Environmental Management Science Program,5 Tanks Focus Area,6 and similar programs, a 10-year program on the order of $50 million per year would seem appropriate to generate the technological know-how needed for continuous improvement of tank waste management. Site-Specific Findings and Recommendations Savannah River Site Compliant Tank Volume for Processing Needs Tank wastes at the Savannah River Site occur in three different physical forms: a salt solution, a water-soluble 5 DOE’s Environmental Management Science Program (EMSP) was created by the 104th Congress to stimulate basic research and technology development for environmental cleanup of the nation’s nuclear weapons complex (NRC, 1997a). 6 The Department of Energy’s Tanks Focus Area (TFA) was funded by DOE’s Office of Science and Technology to provide technical assistance with issues related to tank wastes at the Savannah River Site, Hanford Site, Idaho National Laboratory, Fernald Site, and West Valley Demonstration Project.

OCR for page 121
Tank Waste Retrieval, Processing, and On-Site Disposal at Three Department of Energy Sites: Final Report saltcake, and an insoluble sludge. All phases contain radioactive materials. For the last 10 years, the site’s Defense Waste Processing Facility has immobilized sludge in glass and poured the glass into steel canisters, which are stored pending shipment off-site for disposal in a high-level radioactive waste repository. DOE has stated that it needs open volume in compliant waste tanks7 for secondary wastes from sludge treatment to ensure that sludge removal from non-compliant tanks continues apace and the Defense Waste Processing Facility continues to operate at full capacity. DOE ultimately plans to use the Salt Waste Processing Facility to remove radionuclides from most of the salt solution and saltcake phases of the tank waste, which occupy most of the volume in compliant waste tanks. To obtain open tank volume for waste inputs before the Salt Waste Processing Facility is operational and for efficient operation of that facility, DOE plans to use two interim processes: DDA and a separate, low-throughput chemical processing unit. Because of the recently announced 26-month delay in startup of the Salt Waste Processing Facility, DOE has been forced to reexamine its alternatives in obtaining that open tank volume. The committee reemphasizes its concern8 that too much waste will be processed through the DDA if it is a standalone process. There are two principal reasons for this concern. First, as described in DOE’s plans as of 2005 (when the committee’s interim report was prepared), DDA would send large amounts of radioactive material to the Saltstone Vaults, orders of magnitude more than was originally envisioned. Second, because of the 26-month delay in operation of the Salt Waste Processing Facility, it is possible that additional radioactive material could be disposed in saltstone if DDA has to operate longer than previously expected. In its salt waste determination (DOE, 2006), DOE said it intends to put no more radioactive material in the saltstone than described in the draft salt waste determination (DOE-SRS, 2005b); but DOE has not yet proposed any solutions to the tank space problem arising from the 26-month delay. Thus, the committee could not evaluate the problem further. The committee reiterates, however, that DOE should seek alternatives to the DDA process, either by slowing waste inputs (slowing operations or gaining efficiencies) or by finding storage alternatives for the least hazardous of the tank wastes to free up storage space. Point of Compliance DOE’s point of compliance (the location where compliance with performance objectives is determined) for its F Tank Farm is 1.6 kilometers (1 mile) away from the facility boundary, rather than the standard 100 meters (109 yards) away. When DOE uses a nonstandard point of compliance, it should state clearly the potential exposures closer to the disposal facility in case assumptions about human behavior and institutions do not turn out to be true. The selection of the point of compliance has both policy and technical dimensions. The committee believes that those technical dimensions should be stated clearly and prominently so that the policy decision is well informed. Estimated Doses from the Predicted Waste Residuals in the F Tank Farm In estimating the residual tank inventories for its performance assessment calculations for the F tank farm, DOE assumes that future efforts to clean out tanks will be much more effective than they were for most of the tanks that have already been cleaned out. The committee views this assumption as both optimistic and unsupported. Without a technical basis for the inventory estimates, the committee does not have confidence in the results of the performance assessment for the F Tank Farm.9 Hanford The challenges DOE faces at Hanford are significant and varied, but given that the revised performance assessment for the single-shell tank farms at Hanford had not been issued by the end of 2005, the committee was unable to evaluate DOE’s plans with respect to several elements of the charge from Congress. However, the committee has concerns about the technical performance and safety features of the bulk vitrification option for supplemental low-activity waste treatment. Each site is pursuing different technologies for immobilizing its non-high-level tank waste—grout at the Savannah River Site, steam reforming at the Idaho site, and vitrification in the Waste Treatment Plant and bulk vitrification10 at Hanford. The Hanford bulk vitrification process is currently less well developed technically than either the Savannah River Site saltstone or the Idaho National Laboratory steam reforming. Before selecting an immobilization technology at Hanford, DOE should sponsor a detailed, transparent, independent, technical review of bulk vitrification versus other options, focusing on process risks and uncertainties. Idaho National Laboratory Idaho faces smaller, simpler challenges than either the Savannah River or Hanford Sites in cleaning out the tanks. Less spent fuel was reprocessed at the site—all of it with the 7 Compliant waste tanks meet the Resource Conservation and Recovery Act requirements for storage of hazardous waste. Noncompliant tanks do not meet those requirements (e.g., full secondary containment). 8 See the committee’s interim report (NRC, 2005a). The summary of that report can be found in Appendix E. 9 No tank closures have been proposed yet for the H Tank Farm. 10 Bulk vitrification is the lead candidate for the Hanford supplemental low activity waste process; however, the preferred technology has not yet been officially selected.

OCR for page 121
Tank Waste Retrieval, Processing, and On-Site Disposal at Three Department of Energy Sites: Final Report same process; most of the tank waste was calcined and resides as granular solids in bins; and what liquid waste was stored in the tanks did not separate substantially into sludge and salt because the waste was left in its acidic state. The Idaho National Laboratory is making good progress in dealing with its liquid wastes. However, it remains to be seen whether the solidified waste (the calcine) stored in bins will be as easy to remove as projected by the site. CONGRESSIONAL CHARGE TO THE COMMITTEE The committee’s charge from Congress contains six specific topics. Each topic is presented below and is followed by the committee’s response. Topic 1: The “Department’s understanding of the physical, chemical, and radiological characteristics of the waste referred to above, including an assessment of data uncertainties.” The committee believes that DOE has reached a point in its analysis of the physical, chemical, and radiological characteristics of the waste in the tanks where further understanding would not change its overall approach substantially. DOE’s knowledge of the waste in the tanks is sufficient for waste retrieval. DOE needs to know the waste composition in greater detail for processing purposes and to confirm compliance with performance objectives, but this must be done after waste retrieval when mixing makes representative sampling of the retrieved waste possible and when samples of the tank heels can be taken. Even then, the waste composition need only be known sufficiently for reliable and efficient processing to take place. Some processing methodologies, such as steam reforming and grouting, do not require detailed feed characterization, whereas others, such as vitrification, may require greater knowledge and control of the waste characteristics. When these requirements are very stringent, it may be necessary to look for processing and immobilization technologies that accommodate a wider range of feed characteristics. The costs and the risks to workers, members of the public, and the environment if the processes should fail to perform acceptably have to be taken into account for each processing option. For different processes and different locations, the knowledge required may be different. Topic 2: “Any actions additional to those contained in current plan that [DOE] should consider to ensure that the plan will comply with the performance objectives of Part 61 of Title 10, Code of Federal Regulations”. 10 CFR 61.41 states: “Reasonable effort should be made to maintain releases of radioactivity in effluents to the general environment as low as is reasonably achievable.” After DOE shows that its plans meet the dose limits, DOE should further demonstrate how its plans for waste retrieval and immobilization meet ALARA requirements to protect workers, the public, and the environment now and in the future. In Section 3116(a)(2) of the NDAA, a criterion for on-site disposal is that the waste “has had highly radioactive radionuclides removed to the maximum extent practical.” The risks posed depend on the assumed location and time at which the performance criteria must be met. DOE has issued only a few documents detailing how it determined what amounts of material left in a tank would be acceptable. There is not sufficient information available to evaluate whether all of the components of importance to such decisions have been taken into account. However, it would be advantageous to have a common process that illustrates how risks under each option are likely to change over space and time, which would be useful in determining what wastes can be disposed on-site. An illustrative and extremely simplified example of such a process is given in Chapter X. Topic 3: “The adequacy of the Department’s plans for monitoring disposal sites and the surrounding environment to verify compliance with those performance objectives.” Monitoring is important in performance assessment model validation exercises and for early detection of failures. It also allows remedial actions to be taken at the earliest possible time, thereby minimizing human and environmental impact and cost. The committee judges that monitoring within the disposal facility is the most desirable location for the early detection of problems, followed by detection in the vadose zone, and finally by detection in the nearest aquifer. The committee’s overall impressions are that the sites’ monitoring programs are satisfactory at fulfilling their current goals, which in most cases are site characterization and operations monitoring to assess regulatory compliance. However, the committee believes that the DOE plans for monitoring should go beyond the requirement of verifying compliance with performance objectives. DOE should start planning its post-closure monitoring programs so that provision for monitoring can be built into closure plans and designs. Topics 4 and 5: “Existing technology alternatives to the current management plan for the waste streams mentioned above and, for each such alternative, an assessment of the cost, consequences for worker safety, and long-term consequences for environmental and human health;” and any “technology gaps that exist to effect improved efficiency in removal and treatment of waste from the tanks at the Hanford, Savannah River, and Idaho sites.” The committee had to operate within schedule constraints, which limited the extent to which it could evaluate technology alternatives. Such evaluation was particularly difficult because DOE was able to provide only limited information on cost, worker safety, and long-term human and environmental health consequences of technology alternatives for tank waste management. However, it is apparent that DOE should continue to adapt existing and develop new tech-

OCR for page 121
Tank Waste Retrieval, Processing, and On-Site Disposal at Three Department of Energy Sites: Final Report nologies for effective waste retrieval, with emphasis on tanks with obstructions and recalcitrant waste. Additionally, the committee recommends a targeted aggressive, collaborative research and development program on chemical cleaning of the tanks, mechanical waste retrieval, and tank filling materials for tank stabilization. The committee recommends support at approximately $50 million per year to focus on technologies that could become available in the near term (within 10 years) in time to be implemented during the tank cleanup program. Topic 6: “Any other matters that the committee considers appropriate and directly related to the subject matter of the study.” Following are issues that the committee believes are important, but either DOE’s plans are not detailed enough at this time to make specific recommendations or the issues are independent of tank management plans: Remediation of pipelines, leaking underground pipes and interwall spaces in double-walled tanks, and other auxiliary equipment in the tank farms could be challenging, particularly at Hanford where there are about 100 plugged pipelines (see Chapter III). Although the Idaho National Laboratory should focus on tank wastes first, some consideration should be given to the calcine waste and bins and their disposition (see Chapter III). DOE needs regulatory approvals for the off-site disposal of some Hanford tank waste and Idaho sodium-bearing tank waste. The philosophy and methodology for post-closure monitoring needs to be developed and articulated. Attention should be paid to long-term stewardship, post-closure monitoring, and the meaning of “in perpetuity,” and rigorous (within the limits of long-term prediction) planning for these activities should commence. A focus on these issues is important and would incorporate, but extend beyond, DOE’s tank waste management plans (see Chapters VII and VIII). FINAL WORDS DOE is progressing slowly, sometimes through no fault of its own, to remediate its high-level waste tanks at Hanford, Savannah River, and Idaho. Because this is largely a first-of-a-kind activity, some problems with chosen remedies should be expected. This should be seen as part of the learning curve for the process. However, the process can be improved by a more focused, experimental (adaptive) approach and by following a risk-informed, consistent, and transparent methodology, such as the one outlined in a previous National Research Council report Risk and Decisions About Disposition of Transuranic and High-Level Radioactive Waste (NRC, 2005b). This methodology involves analyses of risks, benefits, costs, and alternatives in a transparent environment that would allow meaningful stakeholder involvement, adaptation to surprises that will be encountered along the way, and continuous learning both from experience and from an ongoing focused R&D program.