Alternative High-Level Waste Treatments at the Idaho National Engineering and Environmental Laboratory (1999)

The processing alternatives under consideration for the Idaho National Engineering and Environmental Laboratory (INEEL) high-level waste (HLW) calcine and sodium-bearing waste (SBW) will result in final waste forms whose classifications [e.g., high-level, transuranic (TRU), low-level, and/or mixed] and quantities will affect disposal options. Different disposal sites (not all of which currently exist), each with different and largely unknown acceptance criteria, will be needed for the various waste types. The regulatory and legal requirements discussed in Chapter 9 provide other numerous criteria to be accommodated. Designing a waste management and disposal plan to deal appropriately with these constraints is a challenge. In pans of the current plans, inconsistencies in logic arise, as discussed in this chapter.

In the committee's judgment, no waste treatment option should be selected until a substantive risk assessment is done of a no-action or minimal action alternative, particularly since the present calcine storage bins have a design life of approximately 500 years (Palmer, 1998; Dirk, 1994¹; Schindler, 1974),² after which time the radioactivity will have decreased greatly (see Chapter 11). Only one of the bin sets is believed to be "structurally unsound according to seismic criteria,"³ (Dahlmeir et al., 1998). This bin set does conform to ASME Boiler and Pressure Vessel Codes (Ibid, Engineering Design File "EDF-BSC-007," p. 2), and appears to be equivalent in performance to the rest of the bin sets except that the bins are flat on the ends rather than pan-shaped (Ibid, p. 4).

Insofar as storage of calcine in bin sets appears to be a low-risk configuration, there is no technical or risk basis, in the committee's judgment, to allocate billions of dollars for

processing such low-risk calcine, even if the processing program were low in technical risk. The committee believes that the Department of Energy (DOE) manages much higher risk radioactive waste configurations elsewhere. Therefore, it seems premature to do anything in the near future with the calcine, beyond possibly beefing up the confinement provided by the bin sets (e.g., by improving the protection against seismic events, water intrusion, atmospheric moisture, and wind).

The disposition of a low-level TRU waste (namely, SBW) by addition of nonradioactive chemicals (i.e., aluminum nitrate), calcination, and storage with HLW in the bins, thereby converting the SBW calcine to a HLW (via mixing) to create more HLW volume than existed to begin with, is unwise in the committee's judgment, because HLW will likely be more expensive and difficult to dispose of than low-level TRU waste. This approach would prevent the site from exploring TRU waste disposal options for the SBW.

Basing program plans on only two types of calcined materials (Al-type and Zr-type) could misrepresent the full suite of challenges associated with calcine dissolution and treatment, particularly because the relative CaF₂ content is arguably the component that most differentiates the various calcines. The CaF₂ content is potentially problematic because CaF₂ serves as (1) an undissolved solid in nitric acid dissolution and subsequent separations stages and (2) an undesirable ingredient in a borosilicate glass formulation. Another challenge for program plans is the choice to use ion exchange agents only available from either Czech universities or Russian institutes (see Chapter 3).

In the committee's view, a sound strategy would include efforts to reduce major uncertainties, unknowns, and assumptions, as by collecting characterization data and performing tests to validate key assumptions. It would be imprudent to adopt a high-risk, $5 billion-plus operation without collecting calcine characterization data or performing adequate tests. Likewise, 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 based on assumptions yet to be validated.

One decision in any remediation flowsheet (see Figure 1.5) is whether or not some separations will be done. As stated in the introduction to Chapter 3, a separations approach has merit if the cost savings associated with the reduced volume of final waste can be justified compared to the cost (and risk) of performing the separations. Therefore, reliable estimates are needed on both of these cost figures (and on the risk associated with operations). Unfortunately, one of these cost values depends on HLW disposal costs in the future (i.e., circa 2035), and potentially in a second repository, whose cost structure may differ from the first. Until

reliable cost information is available, as also noted in the previous chapter, one cannot assemble reliable figures to judge whether the separations process is a worthwhile approach.

Performance assessments are useful guides for determining waste form requirements, but such assessments have not been completed (Olson, 1998b). A performance assessment should be done to cover the contingency that the waste cannot be shipped and disposed of elsewhere and to define the requirements for keeping it on-site, particularly because a period of at least interim storage at INEEL is likely. Similarly, a performance assessment should be used to develop requirements on waste form properties (e.g., radioactivity concentrations and leach resistance) needed for shipping and disposal of the wastes at any site. This approach would be more rational than one that just adopted guidelines such as Class A or C limits without regard for the time period during which the waste will be contained. For example, if at least a few hundred years of containment is planned for, whether on-site or in off-site disposal, then ¹³⁷Cs and ⁹⁰Sr separations are unnecessary, and the only separations that may be justified are TRU separations.

Until the full suite of regulatory requirements for the complete pathway to disposal is defined, important relative advantages and trade-offs between various durable waste forms (e.g., glass, grout, and glass/ceramic) cannot be ascertained. Therefore, the committee believes that it is premature to decide which of these various durable waste forms to make.

In addition, the committee believes it unwise to convert calcine and SBW to forms that would be difficult to dissolve and process further in the future, should that be necessary. For SBW, the alternative is to consolidate it using a less "irreversible" solidification option, such as one of the candidate methods discussed further in Chapter 12. For the committee's views on near-term actions for the calcine, see Chapter 11.

Commercial spent fuel accounts for 90 percent of the contents of the proposed Yucca Mountain repository, as measured in metric tons of heavy metal (MTHM), and 95 percent of the radioactivity as measured in curies. Currently, DOE plans to directly dispose of this commercial spent fuel without processing to produce a more leach-resistant waste form. The co-disposed DOE HLW (representing 10 percent of the 70,000 MTHM legal limit and 5 percent of the projected curies deposited in Yucca Mountain) consists of DOE spent nuclear fuel (SNF) and other HLW forms, such as vitrified HLW from DOE sites. None of these non-SNF HLW forms logically can be expected to have a major impact on the analysis of the risk to the public because of their much smaller contribution to the total inventory of radioactivity. Moreover, some of the longer-lived radionuclides in DOE HLW may have been removed during reprocessing and recovery operations. In the committee's judgment, it is therefore difficult to rationalize requiring durable glass waste forms for these DOE HLW inventories. In this context, it is important to determine the comparative performance of different waste forms for defense HLW that is not DOE SNF.

Therefore, the committee believes it is premature to decide among various processing options (that produce different waste forms) without (1) a statement of waste form performance objectives and (2) a clear and consistent comparison of waste form performance. Although calcine is not currently an accepted waste form for ultimate disposal, there seems to have been no careful consideration of the performance requirements needed and of processing alternatives that achieve these requirements with minimal or no change to the calcine material form. For example, performance requirements might show the present (or slightly modified) form of the calcine to be suitable for direct disposal in a geologic repository (Rechard, 1995). Until this has been proven to be false, the committee believes that there is no rational basis for dissolving the calcine to process it to a different waste form.

Reducing the HLW volume and the number of canisters is an important perceived goal, even though the waste may never be shipped off-site. Current cost analyses, using certain assumptions, favor a reduction in volume (Palmer, 1998). By the time waste is shipped in the future, however, the conditions and assumptions that underlie cost calculations may differ. By then, it is not certain whether the transportation and disposal costs associated with the number of canisters would be the controlling cost element.

The right framework for considering disposal volume in a second HLW repository has yet to be established. Therefore, the committee believes that it is premature to base technical choices on waste volume reduction (which may not be important in the future) when other important considerations (e.g., impacts on risk reduction and worker safety, and the degree of technical risk of the proposed plans) are either poorly known or at odds with a strategy to process in order to reduce HLW volume. In particular, dissolution and separation operations on the existing calcine will result in potentially significant risks, costs, exposures, and time requirements. If significant costs and risks are incurred in these operations, the rationale to minimize HLW volume should be tempered with these considerations in guiding the selection of a processing option.

A legal and technically viable path should be established for the out-of-state transportation and disposal of the waste products that are to be made. In the committee's judgment, it is premature to develop a waste form without a developed and approved disposition pathway.

In addition, the committee was given the view (Wichmann, 1998) that there is a low probability that regulatory authority would ever be given to move the HLW in any form out of the state of Idaho. The committee has no basis for agreeing or disagreeing with this view, but believes it is prudent for the program to develop a course of action to follow if this proves to be tree. While the settlement agreement (see Appendix G) between the DOE and the state of Idaho requires that the HLW be prepared for out-of-state shipment, the program should address the alternative (i.e., retention of the waste in Idaho for the foreseeable future) in its contingency planning.

As discussed in Chapter 9, the current HLW repository acceptance criteria do not permit disposal in Yucca Mountain of hazardous materials regulated by the Resource Conservation and Recovery Act (RCRA). It seems incongruous to the committee to allow disposal of RCRA-hazardous waste in a contained facility on the INEEL site but not in a geologic repository.

An assumption common to all the INEEL HLW treatment options presented to the committee was that all such plans depend on delisting RCRA waste constituents. These delisting petitions to the appropriate regulatory authorities should be resolved expediently, or else contingency plans should be developed. The committee believes that it would be premature to select a treatment option without resolution of this issue, because the regulatory solution to the RCRA constituents is an important determinant on waste form requirements. Here calcine characterization data would be useful to confirm the concentrations of RCRA materials and the reasonableness of the position that materials such as organics did not survive the calcining process.

The RCRA constituents of the waste impose a potentially significant regulatory challenge. One challenge is in the success of confirmatory sampling and analysis to support delisting petitions for some (e.g., organic) RCRA constituents. For constituents not handled by delisting, some requirements on the final waste form(s) are likely, insofar as the RCRA Land Disposal Restrictions (LDRs) specify disposal criteria. If considerable heavy metals are present, the need to meet Toxic Characteristic Leaching Procedure (TCLP) criteria may impose stabilization requirements prior to disposal.

The committee has identified in this chapter some inconsistent elements in the INEEL HLW program planning, with the intention of elucidating where changes in approach might best be sought. These conflicting factors are presented in this chapter as issues relevant to any future decision about processing HLW calcine and SBW. The committee expects that resolution of these issues will assist any decision on alternative treatment technologies. The next two chapters deal with the committee's views of what should be done in light of the technical considerations in Chapters 2 through 8 and the regulatory and other factors considered in Chapters 9 and 10.