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Alternative High-Level Waste Treatments at the Idaho National Engineering and Environmental Laboratory 13 Summary of Conclusions and Recommendations In a committee report of this type, with all of the information provided in the form of written reports and/or oral presentations, almost any observation or comment beyond a restatement of the material presented can be seen as a conclusion and/or recommendation. That is, a technical discussion of process steps leads naturally to committee statements of conclusions and recommendations. Chapters 2 through 12 contain many such statements. The reader is referred to them for a complete statement of committee views. What follows is a summary of the most important of these views. WHAT SHOULD BE DONE: SODIUM-BEARING LIQUID WASTE (CHAPTERS 4 AND 12) The committee believes that the sodium-bearing waste (SBW) [currently contained in tanks not approved under the Resource Conservation and Recovery Act (RCRA)] should be solidified in the near future with a process to be selected from a comparison study of proven methods that can be adapted for use on the SBW. The solid form produced should, if practical, be made acceptable for shipment to the Waste Isolation Pilot Plant (WIPP) or another suitable transuranic (TRU) waste repository. Any non-TRU low-level waste (LLW) fraction should be processed in a form acceptable for disposal in a LLW repository [e.g., the Nevada Test Site (NTS)]. Possible routes to accomplish this are described in Chapter 12. If calcination of SBW (option 6 of Chapter 12) is done, the calcine product should be stored separately from the existing high-level waste (HLW) calcine inventory. Since SBW is not HLW, it is counterproductive to convert it to HLW (via mixing) or force it into a scenario designed for HLW because that decreases the options for processing and ultimate disposal (with a concomitant decrease in program flexibility). WHAT SHOULD BE DONE: HLW CALCINE (Chapter 11) The committee could identify no significant present hazard to public health or to the environment due to the storage of solid calcine in the bins at INEEL, which have been designed to be secure for at least 500 years. The need for immediate action and a rush to select a long-term treatment option appear unwarranted, in the committee's view, especially in comparison to significant inventories of HLW at other DOE sites that are in liquid form in underground tanks, some of which have leaked.
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Alternative High-Level Waste Treatments at the Idaho National Engineering and Environmental Laboratory In contrast to the SBW storage situation, the committee recommends that no action to process the HLW be taken until it is clear where the material will be sent, what disposal form(s) is(are) acceptable, and that a viable transportation pathway is approved. The processing of calcine can be deferred so long as the bins maintain their integrity. This approach may require future modifications to the bins if necessary to ensure safe storage. In the meantime, the interim storage of HLW calcine in the bins is more practical than near-term treatment in view of several important considerations: the radiation hazard associated with the near-term retrieval and processing of the calcine; the integrity and long design life of the bin sets; and the isotopic composition of the INEEL calcine, which differs from other major Department of Energy (DOE) HLW inventories in its relative abundance of transuranic isotopes that decay significantly over the timescale associated with the design life of the bin sets. Additionally, interim bin storage of calcine is more practical than any other option because of the absence of an approved pathway to a different destination. The only near-term action should be improved confinement and stabilization of the bins, ventilation system, and associated equipment. The hygroscopic content of the calcine requires that there be adequate protection from atmospheric moisture if "caking" is to be avoided. A risk assessment is strongly recommended to identify which of these and other actions are most important to reduce risk. The risk assessment should also substantiate that this interim storage of a mixed HLW with significant TRU content in a near-surface environment (a storage which would probably require regulatory relief) poses a low risk at present and in the foreseeable future to workers, the public, and the environment. The committee believes that a risk analysis will show that extended interim bin storage of calcine is a low risk (and low cost) course of action. However, the committee emphasizes that this course should be subject to continued review and updating of comparative risks as additional information may be developed in the decades to come with respect to site availability, acceptable waste forms for such a site, and available transportation to such a site. This recommendation does not challenge the general strategy of geologic disposal for HLW, which is an issue outside the scope of this study, but emphasizes that decisions on the ultimate fate of the INEEL HLW should be postponed pending the resolution of waste management issues noted above and pending the results of adequate risk analyses.1 In this recommendation to defer processing of HLW calcine until site(s), route(s), and waste form specifications are firmly established, no time period is specified for the duration of interim bin storage. Limitations to this time period could come from a technical assessment of bin integrity over time, and/or regulatory and other requirements. To expand on (1), the information provided to the committee does not specify the failure mode (e.g., corrosion or seismic stability) that is the most limiting for bin integrity, and does not indicate whether 500 years signifies a mean time to failure or another design criterion. The 1 If bin storage of HLW calcine persists for more than a generation, then this recommendation does counter the general view (OECD. 1995) of having the present generation "dispose" of its own long-lived radioactive waste in geologic repositories; instead, for INEEL HLW calcine, the present generation would "manage" this waste. Such a bin storage strategy is consistent with the "stepwise implementation of plans for geological disposal" that might take place "over several decades" and is also consistent with the admission of "the possibility that other options could be developed at a later stage'' that is expressly stated in OECD (1995: p. 9).
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Alternative High-Level Waste Treatments at the Idaho National Engineering and Environmental Laboratory committee recommends that during any period of interim bin storage, continuing verification of bin integrity is essential. To expand on (2), if the Licensing Requirements for the Independent Storage of Spent Nuclear Fuel and High-Level Radioactive Waste (10 CFR 72) were to apply to INEEL bin storage, then a regulatory license could be granted for up to 20-40 years, with any renewals for time periods beyond that contingent upon sufficient technical justification to satisfy the requirements for a license extension. Such matters of regulatory strategy were not examined in detail by the committee, and would require attention in the event that resolution of ultimate disposal site(s), route(s), and waste form specifications is not attained in the near future. As a final observation, the committee believes that, along with good science and engineering, a major consideration in deciding how (and whether) to process any radioactive waste for long-term conditioning is that of the risks being added and/or mitigated. The fundamental purpose of environmental regulations [such as those of RCRA, the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), and United States Nuclear Regulatory Commission (USNRC) directives] and radioactive waste policy legislation must be, in the committee's view, minimization of risk to human health and the environment in a cost-effective and meaningful manner. A driving consideration in deciding upon a radioactive waste management strategy should be an identification, definition, and evaluation of the "trade-offs" (i.e., comparative risks) for the alternatives being considered, including those of limited or no processing. Such risk assessment calculations provide information on risk reduction strategies and are required to decide among alternatives in an informed and objective manner. Consequently, the committee believes that a risk analysis for the actions recommended above for both HLW calcine and SBW should be conducted promptly, and should include a comparison of the risks associated with INEEL HLW calcine and SBW to the risks associated with site inventories of other radioactive wastes. A sufficiently rigorous analysis should be performed to establish the current risks and to assess the changes in risk due to treatment options. In the committee's view, at least until the issues identified here are resolved, the risks (and costs) of repackaging the HLW calcine, with no certainty that it can ever be shipped outside of Idaho, may far exceed the risks (and costs) of continued interim bin storage. CONCLUSIONS AND RECOMMENDATIONS SPECIFIC TO INDIVIDUAL PROCESS STEPS Conclusions and recommendations pertinent to specific steps of HLW processing options are given below. They are of major importance only if the above recommendations with respect to SBW and calcine are not pursued. Further details are provided in Chapters 2 through 10. Calcine Characterization (Chapter 2) The present database with actual aged calcine is inadequate to assure that processing goals can be achieved or to allow definition of processing methods without excessive technical risk. In addition, there appears to be no realistic sampling plan to add to this database by retrieving actual aged calcine, nor a characterization plan for such calcine. Actual aged calcine is crucial for testing purposes. Characterization of additional calcine samples from many bins is necessary to define retrieval and treatment issues adequately. The existing database for all work with actual calcine is inadequate as a foundation to design a treatment plant. Analytical data appear to be incorrect and inconsistent in some (too many) cases (see Chapter 2). This
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Alternative High-Level Waste Treatments at the Idaho National Engineering and Environmental Laboratory inaccuracy of analytical data is cause for concern because it calls into question not only the state of knowledge of calcine characteristics, but also the validity of projections based on the data. Adequate samples to characterize the waste, along with a sampling and analysis plan with appropriate quality controls, are necessary to collect essential data, determine properties such as solubility and dissolution of calcine in nitric acid, support development studies of treatment processes, and support risk analysis calculations. Most process development should be done with actual aged calcine. Retrieval of Calcine from Bins (Chapter 2) It is likely that calcine can be retrieved from the bins, but operational problems should be expected. The existing database is inadequate to define the problems that might arise and to evaluate how to resolve them. For example, the presence of hygroscopic constituents in the HLW calcine raises the issue of whether "caking" has occurred, which would prevent simple pneumatic transfers from being fully effective. A limited sampling and characterization plan would diminish uncertainties in retrieval and processing, thereby reducing the risk, and should receive high priority. The quantity of residual calcine allowed to remain in the bins after retrieval should be rationally defined. Consideration should be given to the handling of retrieved calcine with respect to providing stable and uniform feed for downstream processing (i.e., blending). Calcine Dissolution (Chapter 2) The proposed dissolution approach probably can be made to achieve the desired separations levels. However, the risk is substantial that the program will fail to achieve the separations goals (especially Class A requirements) without a substantial and sustained test program using actual aged calcine. The unknowns associated with the quantity and nature of radionuclides in undissolved solids (UDS) translate into uncertainty and risk in the design of a processing operation. The root cause of this concern is a lack of sufficient characterization and testing data with actual aged calcine. Solid-Liquid Separation (Chapter 3) Both physical and chemical characterization data for UDS from actual aged calcine are extremely limited and inadequate to define the solid-liquid separation (SLS) system, or even to show that SLS requirements can be met with a practical system. Such characterization data are necessary to establish requirements for the removal of solids and to identify and test promising approaches for achieving these requirements. Because entrained solids will degrade the attainable decontamination factor (DF) and jeopardize process operability in all downstream decontamination operations, efficient removal of particles down to very small sizes is required. Therefore, a key requirement for successful performance is the highly efficient removal of solids from the feed to any downstream chemical separations process (as estimated in Chapter 3, a factor greater than 105 is needed). A reported study of the most promising SLS approach, single crossflow filtration, indicated limited effectiveness and problems caused by pore blockage. The apparent near-absence of a viable SLS program suggests that the necessity for effective SLS is not fully appreciated. The SLS program as presently conceived constitutes a region of unreasonably high technical risk.
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Alternative High-Level Waste Treatments at the Idaho National Engineering and Environmental Laboratory In addition to the characterization program noted above, priority should be given to evaluating and testing at least two different methods for SLS. This work should be done with actual waste from SBW tanks and dissolved calcine rather than surrogates. Process residuals, secondary waste streams, emulsions, and problems with plugging are the types of concerns that should be resolved in such testing. Cesium Ion Exchange (Chapter 3) Three inorganic ion exchange materials have been tested for removal of Cs from both SBW and dissolved calcine under a limited range of conditions. The selected materials are reasonable but unproven candidates, and they are subject to uncertain future availability. Other promising sorbents have not been tested. Results to date are inconsistent and so limited that system performance cannot be predicted with a reasonable degree of confidence. The choice of sorbent has changed recently and cannot be considered to be well defined. Evaluation has been limited to ion exchange column operation with elution and sorbent regeneration to allow repetitive cycles with a given batch of sorbent. It is questionable that the Cs DF required for Class A product can be achieved because, in subsequent loading cycles, residual Cs left on the column will slowly elute. If an elutable sorbent cannot be used to achieve sufficient decontamination of the waste stream, both the basis for selection of the sorbent and the mode of operation would be different, and final waste generation would likely be increased. The committee notes that Cs ion exchange is not required for a Class C waste product. Extensive testing of promising Cs separations methods with actual waste solutions is required to demonstrate process viability. Particular problem areas relate to performance (DF and capacity) in subsequent cycles following elution, accumulation of solids or other constituents that do not elute, system operability with high volumetric throughputs, and secondary waste generation. Consideration of systems other than columns may be necessary. Strontium Separation (Chapter 3) The committee concurs with previous review groups that strontium extraction (SREX) is a promising approach for removing 90Sr from SBW and dissolved calcine. However, the committee also believes that a number of significant technical difficulties described in Chapter 3 make achievement of Class A separations unacceptably risky without substantial additional chemical process information. In agreement with the feasibility study (Fluor Daniel, Inc., 1997), the committee recommends sustained tests of the complete extraction, strip, wash, and acid-rinse subsystems. Critical process vulnerabilities to be investigated should include solvent extraction recycle and degradation, impurity buildup in the organic phase, temperature effects, and formation of precipitates and emulsion. In particular, the behavior of RCRA constituents such as Pb and Hg needs to be clarified in tests with a range of actual aged calcines, because of known difficulties in stripping Pb and Hg from the organic phase and the formation of interfacial Pb precipitates.2 Additional process testing is needed to solve these difficulties in order to demonstrate the capability to meet Class A separations requirements, which are extraordinarily demanding and therefore likely to require significant resources. 2 The Pb and Hg constituents also pose interference problems for TRU separations.
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Alternative High-Level Waste Treatments at the Idaho National Engineering and Environmental Laboratory TRUEX Separations (Chapter 3) TRU separations have been proposed by using the TRUEX solvent extraction process applied to a feed solution consisting of calcine dissolved in acid. However, several of the nonradioactive chemical constituents of INEEL HLW calcines will complicate the successful extraction of the relatively small mass of TRU elements present. The chemical process design will depend on the chemical composition of a TRUEX feed solution and its inherent variability, as derived from the variations in calcine compositions upon retrieval and after any subsequent blending operations. In particular, the HLW calcines contain significant quantities of chemicals (e.g., Zr and Fe) that may directly compete with the actinides in interactions with TRUEX chelating agents (e.g., CMPO; see Appendix F). The few laboratory-scale extractions that have been performed to date on actual aged calcine confirm this suspected interference but provide no practical alternative chemistry to solve this problem. Therefore, TRUEX processing may not work effectively or operationally for the full range of feed compositions without major head-end chemical steps to remove interfering species. If the range of chemical constituents in redissolved calcine solutions warrants the use of complex head-end treatments, both the complexity and operational costs of processing would increase significantly. In this event, a comprehensive reexamination of the TRU separation technology should be considered. If significant TRU separations are required, then sufficiently large-scale demonstrations are necessary using actual aged calcine to test for the operability of a process under flow-sheet conditions. These tests are particularly important in view of limitations on the present knowledge of (and control on) the variability in the chemical composition of the feed. Several of the nonradioactive species present in dissolved calcine can chemically interfere with the extractant to degrade the level of separation that is achieved. Also, solid residues (typically fluoride and phosphate precipitates) that can be formed during the back-extraction step can physically damage, or even destroy, centrifugal contactor cascades and thus force total plant failures. In view of these problems, the operability and efficacy of a large-scale TRUEX process under currently proposed flowsheets using dissolved calcine solution should be critically assessed prior to the commitment of significant resources. This "scale-up" assessment cannot be done from experiments and characterization data obtained to date. This current status of INEEL TRUEX development efforts indicates that it would be premature to propose TRUEX partitioning to remove actinides from redissolved INEEL calcine to meet Class A limits in a large-scale process. The process development required to extract actinides from the chemically diverse feeds that can be formed from retrieved calcine is, in the committee's opinion, a challenge that is properly characterized as first-of-a-kind chemical processing design work. Therefore, an adequately funded chemistry investigation is needed to resolve outstanding issues. In this effort, nuclear and radiochemical processing expertise within the DOE and national laboratory systems and in private, including foreign, companies should be engaged more extensively. General Conclusions On Chemical Separations (Chapter 3) Challenges have been noted above for cesium, strontium, and actinide separations in a large-scale process designed to produce from the calcine a low-activity waste (LAW) stream meeting Class A limits. Before committing to large-scale SREX and TRUEX processing to meet Class A separations requirements, the following issues should be resolved: Effects during processing and final disposition of mixed waste species. Mixed waste constituents, particularly the RCRA metals Hg and Pb, complicate both SREX and
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Alternative High-Level Waste Treatments at the Idaho National Engineering and Environmental Laboratory TRUEX operations, and potentially cause both the high-activity waste (HAW) and LAW streams to be classified as mixed waste. Testing with actual aged calcine. Additional testing with a sufficient range of actual aged calcines is necessary to confirm the limited results obtained to date with surrogates. These tests should include reagent recycle and sequencing of unit operations using actual solutions, and should be long enough in duration to demonstrate long-term operability. Scale-up demonstrations. A successful pilot-scale demonstration of the proposed chemical separations process should be conducted prior to the commitment of resources to a full-scale system. Since downstream unit operations can be negatively impacted as a result of even minor changes in upstream operations, the testing should use actual aged calcine, full sequencing of operations, and reasonable run duration. Vitrification (Chapter 5) Among various solidification options, vitrification has been investigated extensively at INEEL and elsewhere. Frit glass compositions and simulated waste glasses have been developed for different calcine compositions. In general, the chemical durability of these glasses has been found to be satisfactory. The major effort remaining to complete this work is in the vitrification of the HLW resulting from the separation option, for which research is under way to develop an appropriate waste glass composition. In this research effort, a wider range of glass compositions, including phosphate glasses, should be explored. Vitrification facility plans have been made, and in some cases pilot-scale melting has been conducted. Experience at other DOE sites and laboratories may provide some useful guidance for these efforts. The composition of calcine waste feed to a melter would depend on the retrieval and blending strategy. Methods to mix calcine recovered from several bins should 'minimize the variation in the overall composition of the blend. A large supply (perhaps a 1-month to 1-year supply) of blended feed might be necessary to ensure stable, continuous production of a vitrified waste form. Since it will be necessary to adjust the glass frit composition to compensate for variations in the blended calcine composition, a glass frit compositional effort should be planned to continue during the entire vitrification period. Alternatives To a Borosilicate Vitrification in a Continuous Melter (Chapters 5 and 7) A concern of the committee is whether borosilicate vitrification in a continuous melter is the best solidification option for the INEEL calcines. Although INEEL calcines are, like Hartford and Savannah River tank waste, classified as high-level, they differ in important ways. The INEEL calcines may be distinguished from these other HLW inventories by their relatively higher content of Ca, Al, Zr, and F and relatively lower content of Na. The high alumina and zirconia content of the calcine is expected to result in a low waste loading in a borosilicate glass type because of the low solubility of these oxides at the planned melting temperature of 1150 °C. In view of the unique compositions of some of the wastes at INEEL and the loading problems they pose in borosilicate glass formulations, other solidification options, such as glass-ceramics, nonborosilicate glasses, and single-use melters, may be more advantageous by offering a satisfactory final form at lower cost or with higher waste loading or easier processing. In particular, a single-use melter offers the possibility of very high waste loadings while avoiding many of the problems inherent to continuous melters. Immobilization options (e.g., phosphate glass production, or partial vitrification; see Chapter 7 for a more complete list)
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Alternative High-Level Waste Treatments at the Idaho National Engineering and Environmental Laboratory other than borosilicate glass production also appear to have merit and therefore should be con-sidereal. In practice, this means that these other options should be included in a comparison of options, as in the Environmental Impact Statement (EIS) analysis, especially if the subset of options in the EIS involve extensive aqueous processing prior to vitrification and/or a large volume of HLW glass. Cementitious Options (Chapter 6) Cementation processes can be used to produce a HLW grout as well as a LLW grout. The cementation options proposed in DOE literature are all quite similar insofar as unit operations and equipme nt are concerned. All involve mixing of dry materials with liquid and subsequent placement of the semi-liquid material in containers. The major differentiation between the options is what has occurred to the waste prior to mixing with cement and what waste form results from the constituents after cementation. Any of the cementation options could be made to work easily and with reasonably low equipment costs. The direct cementation options (i.e., without chemical processing steps prior to waste immobilization), as compared to the options that contain processing steps, contain less risk and fewer personnel exposure hazards and produce lower overall waste volumes, albeit the volume of high-activity waste (HAW) may be much larger. There would still be a significant amount of work to be done to develop a cementation process. Representative samples of the various calcines must be obtained to characterize their composition and quantity of each type. Sampling of waste tanks of SBW is necessary for the same reason. Knowledge of compositions is required so that appropriate recipes for cementation can be developed. A pilot line (not necessarily full scale) needs to be set up and run first with simulated compositions (cold runs) and then installed in a hot cell for demonstration runs to prove processing feasibility and to produce samples for testing. To fully specify process requirements, work on resolving issues of RCRA constituents (e.g., delisting) should be initiated immediately. Similar development work would be needed for any treatment process, to test its viability on a sufficiently large scale on actual aged calcine. There are inadequate data to support the contention that cementitious waste forms can be made more quickly, more cheaply, more simply, and more safely than other (e.g., vitrified) waste forms. That contention may be tree, but it should be established by thoughtfully designed experimental programs and an analysis of comparable data (a full-scale demonstration of the process is not required). Although cement-based processes applied to INEEL HLW may prove to be relatively straightforward, the quantity of final waste that is acceptable to produce and the qualification of the cementitious waste form for suitable disposal are the major issues that would need to be resolved to make cementation a fully viable option. Other Alternative Waste Forms (Chapter 7) The committee has been presented with a number of alternative waste forms that could eliminate the need to redissolve the already solidified waste (calcine). Two important criteria for evaluating any type of waste form are (1) the ease of producing it with minimum exposure to workers, and (2) its long-term physical integrity and chemical durability which reduces the exposure to persons in the future. Unfortunately, only limited substantive data were presented to the committee for each of these waste forms, and in some cases, such as the simulated spent fuel (SSF), no data are available at this time. The limited data for these alternative waste forms indicates a lack of current support for exploring these possibilities, with several documents given to the committee dating back to
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Alternative High-Level Waste Treatments at the Idaho National Engineering and Environmental Laboratory the early 1980s (e.g., Post, 1981). Much of the data needed to compare and analyze alternative waste forms is available in the published literature; therefore, expensive experimental programs are not necessarily needed to provide at least some of the missing data. As an example, Table 7.1 compares the properties of a sintered glass waste form prepared at the University of New Mexico to reported literature on partially vitrified waste forms prepared at INEEL. Similar compilations of comparative data could and should be made for each alternative waste form that is considered to have a reasonable potential for practical use. Summary of HLW Immobilization Options This report identifies attractive features of several immobilization methods, including: (1) SSF, (2) cementation, (3) phosphate-based glasses, (4) a glass/ceramic (specifically, those made by cold or hot pressing or by embedding calcine in a glass shroud made by "partial vitrification"), and (5) options other than continuous Joule-heated vitrification melters (e.g., a single-use melter). Each of these methods has some merit, with potentially attractive features as well as uncertainties and potential problems that have been identified in Chapters 5-7. From these chapters, the committee concludes that many waste forms and processes for their creation can be identified. For example, Chapters 6 and 7 cite cementation and SSF as probably less costly processes than direct vitrification for the HLW calcine, but they produce final waste forms that would require further development and proper qualification for acceptance for disposal. None of these immobilization proposals logically can be selected until the definitive criteria, set in pan by the approved disposal pathway, have been established. As a further consideration, the committee has identified the following features as a useful basis to compare the different immobilization methods and to gauge their challenges and likelihood of success. These other features are: waste form properties, including durability; waste loading and net material additions;3 relative maturity and technical risk; operability and processing ease; worker and public risks; environmental releases and risks; regulatory requirements and challenges; estimated relative cost; unit size;4 other controls on the process environment,5 production experience,6 3 This is the net amount of material added in pretreatment, processing, and/or immobilization steps. In general, to minimize final waste volumes, the least amount of net material should be used. The net material would in-elude consideration of recycled materials that are recovered and reused. 4 This is the repeatable unit that defines the process conditions and properties, which in mm impact issues such as safety and throughput. The unit size would determine the amount of calcine that is retrieved, characterized, and processed at one time, to include consideration of sufficient blending for feed homogeneity. In principle, there can be differences between the unit size used in research and developmental testing, the unit size used for full-scale production, and the unit size used for qualification of the waste form (e.g., the whole production unit could undergo qualification/validation, or just a test sample). The criterion useful in evaluating immobilization options is whether the scale set by the unit size is adequate (for testing or for throughput). In particular, the test unit size must be large enough to provide a basis for scale-up to production size with considerable confidence. 5 Apart from environmental and safety controls that would be needed, other process conditions, such as the redox environment, may need controls that should be considered if they pose a technical challenge or limitation.
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Alternative High-Level Waste Treatments at the Idaho National Engineering and Environmental Laboratory For example, in relative maturity, the technologies discussed in Chapters 2-7 might be assessed as shown in Table 13.1. The relative maturity is, as shown above, only one feature among many valid technical considerations that are useful to consider in an inter-comparison of options. Tank and Bin Set Closure Issues (Chapter 8) Closure operations for the tanks and bin sets will require inventive engineering solutions that are practical and feasible with current technology. However, clean closure of the tanks and bin sets is impractical, insofar as some residual radioactivity, and possibly hazardous chemical constituents, will remain in the facilities. The options for closure of the tank farm and bin sets that are proposed in DOE literature are all possible from a technical standpoint. The health and safety of the public and the personnel performing the closure process is undefined pending agreements on acceptance criteria and the means for calculating risk. Assuming rational judgment and prudent management, it would be reasonable to expect that all options will result in very low risk. Based on its review, the committee believes that the technical success of the closure process would be enhanced by the following initiatives: Develop and innovate sampling strategies that focus on needs derived from a risk analysis of closure. If a risk-based closure is the operational driver for regulatory agreements, then sampling and analyses are needed to make this risk assessment sufficiently credible. For the risk information required, it may be insufficient to rely on sampling and analyses done for other purposes (such as process control of future separations of HLW, LLW, and hazardous chemicals and material balances of process schemes). Consider the possible advantages of restructuring the calcine retrieval and transport project (CRTP) and bin set closure project (BSCP) programs into three functional responsibilities: (a) movement of calcine internal to the bin and piping (retrieval and decontamination), (b) movement of objects and facilities external to the bins (containment assurance), and (c) movement of material into the bins (stabilization). The present programs have potentially too many interfaces that may hinder the effective coordination of efforts. Conduct essential testing such as proof-of principle tests and mock-up testing, and qualify key remote processes such as visual inspection of the tanks and bins, maneuverability, and bottoms management. Tank decontamination, which is scheduled first, could be used as a test-bed to qualify features to be used for bin decoction. Also, the test program should anticipate process failure and develop and test recovery measures. The closure program plans reviewed by the committee seem to be related to decisions based on risk analyses that are not independent of other Idaho Chemical Processing Plant (ICPP) and INEEL facility closures. Filling the tanks and bins with hazardous or LLW waste, storing road-ready HLW canisters, retaining the calcine in the bins, removing the tanks and bins by clean closure, and discarding them at another location on the site all contribute to the risk equation in the postclosure period. Each of these tasks has components of risk that should be considered in a comprehensive assessment. 6 Relevant expertise could be derived at least in part from users of similar equipment and related technology. These sources might need to be tapped to surmount challenges, particularly those unforeseen initially. For example, the SSF concept is similar to commercial nuclear fuel fabrication technology, which provides somewhat relevant production experience.
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Alternative High-Level Waste Treatments at the Idaho National Engineering and Environmental Laboratory Table 13.1 Qualitative Estimations of Relative Maturity of Various Technologies, Some Proposed by DOE and Some by the Committee, that are Useful in HLW Calcine Treatment Process Relative Maturity Bulk Calcine Retrieval Techniques Not proven technology but likely to work. Retrieval of Smaller Samples Proven technology (demonstrated in 1979). Dissolution of Calcine Feasible but uncertainties remain due to lack of extensive testing on actual aged calcine. Solid-Liquid Separations (SLS) Techniques are available but have not been integrated into a system because the system requirements are not yet fully defined. The SLS system requires substantial development and testing. Cs, Sr, and TRU Separations Tested on lab scale, mostly with simulants; limited testing with actual aged calcine. The application on INEEL HLW calcine poses problems (e.g., with constituents that interfere with separations processes) that require significant developmental testing, scale-up, and process integration. Cementation Feasible technology for HLW but not yet proven widely for HLW in general and INEEL HLW in particular. SSF Not yet demonstrated on HLW; development and testing needed to validate the concept. Continuous Melter-Borosilicate Glass Proven technology on some HLW, but formulation must be developed for the INEEL HLW compositions high in Zr, Al, and/or CaF2. Phosphate Glass Proven technology on some HLW, but further development and testing needed on INEEL HLW. Single-Use Melter Demonstrated technology for radioactive waste but further development and testing needed on INEEL HLW. Glass/Ceramic (Via Hot Isostatic Pressing) Proven technology on INEEL HLW (but safety and throughput concerns provide limitations). Glass/Ceramic (Via Cold Pressing followed by Sintering or Hot Uniaxial Pressing) Demonstrated technology for radioactive waste, but further development and testing needed on INEEL HLW. Partial Vitrification (Via Embedding Calcine) Demonstrated technology for radioactive waste, but further development and testing needed on INEEL. HLW. Common to all Immobilization Processes Qualification of waste form, regulatory approval for process and product(s), and large-scale testing of the process(es) are needed to categorize the technology as fully mature and implementable on INEEL HLW calcine.
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Alternative High-Level Waste Treatments at the Idaho National Engineering and Environmental Laboratory To expand on this issue, residuals of SBW and HLW calcine will remain at the INEEL site regardless of any option considered to process these wastes. For SBW, a portion of sludge on the tank floor may be unrecoverable and therefore destined for in-situ grouting and burial. A fraction of the calcine inventory may also be unrecoverable during retrieval and decontamination practices, and similarly destined to be grouted in place. The types and quantities of these wastes remaining on site can be analyzed in performance assessment calculations as defining the end state of remediation (NRC, 1999; Appendix B). The recovery of residual waste, and the mounts left in place, should be assessed in various scenarios to determine relevant ''trade-offs" such as the cost benefits and risk reductions that are achieved. These assessments of closure options should be used to guide decisions of tank closure criteria and specifications. Establishing a Disposal Path (Chapter 9) The viability of any out-of-state transportation and disposal option for INEEL HLW calcine (or for waste products made from HLW calcine) is highly uncertain at present. Therefore, the program cannot rationally select a processing option based on a currently established disposition pathway for the waste products. Until such a pathway is defined, the calcine should not be processed to yield a product that is less amenable to further processing than the current calcine. To expand upon the present state of uncertainty for HLW repositories, many aspects of the planned Yucca Mountain repository are uncertain and subject to change, including (1) whether DOE will be able to proceed with its construction, (2) what strategy will be followed to emplace waste, (3) how repository capacity will be allocated among various types of defense waste, (4) whether the current legal limitation of 70,000 MTHM will be changed by Congress in future legislation, and (5) waste acceptance criteria, which may be expanded and revised. The "second repository program" is even more uncertain and subject to change. The INEEL HLW could be relegated to this second repository program, insofar as the Yucca Mountain repository, if built, is slated to be filled by 2035. The waste form performance and waste acceptance criteria for the second repository program are not yet known, and may differ from those of the first repository, if indeed a second repository is mandated. Waste Management Strategy (Chapter 10) To meaningfully compare and decide among processing options that produce different waste forms, more information than is currently available is needed on (1) viable disposition pathways for waste streams and the requirements they impose on the waste forms, and (2) characterization of the calcine and SBW. Each of these inputs is needed to establish a credible basis for an informed choice between different proposed processing technologies and different waste forms (e.g., glass, cement, or a glass/ceramic). In order to properly focus on where the HLW is to be sent, an overall waste management plan is needed. To be truly comprehensive, such a plan would encompass all site inventories of radioactive wastes and other nuclear materials. A key element of such a plan is a firm knowledge of where the material is to go and what form it would be in to be acceptable. Until those issues are resolved, the selection of any technical option is without a proper basis. One purpose of a waste management plan is to treat uncertainties that prevent the full resolution of the technical issues in Chapters 2-8, the regulatory issues in Chapter 9, and the other program planning considerations in Chapter 10. The DOE planning approach in the past
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Alternative High-Level Waste Treatments at the Idaho National Engineering and Environmental Laboratory has been to make explicit planning assumptions [e.g., Wichmann et al. (1996) makes the assumptions that Federal environmental policies, strategic policies, and national priorities will remain unchanged; that treated INEEL HLW will be sent to the second (currently hypothetical) HLW geologic repository after 2065; that INEEL waste management activities may be licensed by other agencies, such as the USNRC; that Federal and State of Idaho environmental policies, statutes, codes and orders will remain unchanged; and that Congress will provide the funding necessary to meet the DOE's agreements with the State of Idaho]. The committee views these assumptions as an inadequate way to resolve uncertainties, and therefore proposes that the disposal conditions be firmly established prior to the selection of a treatment option. The committee recommends aggressive efforts to establish these disposal conditions. However, in practice, for the current situation, given that Yucca Mountain is to be filled by 2035 and a second repository program may not be identified for several decades, the firm establishment of disposal conditions may not be forthcoming in the near future, in which case following the recommendation of this report may translate into a suspension of effort in the near term to process the calcine into a different waste form. At this stage in the process, acquiring data to replace or validate key assumptions is a more informative and useful activity than conducting design studies and cost estimates that are based on assumptions yet to be validated. In addition to addressing uncertainties, other important features of a waste management plan, in the committee's view, are to adopt approaches that achieve risk and cost reductions and that support the thoughtful use of science and engineering in developing disposal strategies and waste forms. CHAPTER SUMMARY Table 13.2 summarizes some of the major recommendations of this chapter. As noted previously, these conclusions and recommendations in Chapters 2 through 10 are of major importance only if the conclusions and recommendations regarding Chapters 11 through 12 at the beginning of this chapter are not followed. These recommendations from Chapters 11 through 12 are, in the committee's view, feasible and readily implementable. In contrast, the recommended activities from Chapters 2 through 10 involve a pursuit of not only separations and immobilization challenges associated with processing the calcine, but also regulatory and other challenges. In the committee's view, working through the various challenges of this latter course of action is a formidable task that would likely require resources external to the INEEL HLW program. The alternatives for calcine treatment have substantial uncertainties and as yet unresolved technical difficulties.
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Alternative High-Level Waste Treatments at the Idaho National Engineering and Environmental Laboratory Table 13.2 Summaries of Major Recommendations Component or Topic Recommendation of lifts report Calcine Risk assessments should be performed to assess bin integrity and on-and off-site risks of continued interim bin storage and processing and disposal options. Processing should be deferred until: (1) the final repository location, disposal form, and transportation parameters are established; (2) an appropriate treatment method is identified, based on (a) sufficient characterization data of and testing with actual aged calcine, and (b) pilot plant testing at a realistic scale; and (3) further risk assessments confirm that such treatment constitutes less of a risk to human health or the environment than continued bin storage. SBW Identify suitable non-calcination solidification methods and select ore to solidify this waste in the near term as a high priority. Tank Closure Establish closure criteria; in this effort, consider using a risk basis. Determine the data needs and develop an appropriate sampling and analysis plan. Waste Management Plan A plan should be developed to resolve the uncertainties identified in tiffs report These uncertainties are of a technical, regulatory, offer legal, and/or DOE policy nature. The trade-offs among various alternatives should be exhibited and used in decision making. If the above recommendations are not followed, then the recommendations below apply. Characterization Adequately sample and characterize the calcine and SBW to reduce uncertainties in retrieval, dissolution, SLS, and other downstream processes. Calcine Dissolution Testing on actual aged calcine is recommended to reduce uncertainties and risks. Solid-Liquid Separations SLS system requirements should be developed, after present unknowns and uncertainties in waste characterization and separations requirements are resolved. Testing with actual waste is needed to provide base information. Cs, Sr, and TRU Separations Furuher testing is needed, particularly on actual aged calcine and on flue behavior of potentially interfering species in sufficiently large-scale demonstrations. Solidification Options for HLW Calcine: Vitrification A wider range of options should be explored, particularly alternatives to borosilicate vitrification in a continuous melter. Such alternatives include single-use melters and phosphate-based glasses. Cementation Further developmental work is needed. Other Immobilization Options Further developmental work is needed on methods such as "Simulated spent fuel" and glass ceramics produced by cold pressing and sintering, hot uniaxial pressing, or partial vitrification, all of which methods at this stage have merit and should be considered further. Disposal Requirements Establish disposal requirements in order to know (1) whether separations processing to reduce HLW volume is appropriate, and (2) which HLW immobilization process (and waste form) to select.
Representative terms from entire chapter: