EXECUTIVE SUMMARY
INTRODUCTION
In this report the Committee on Electrometallurgical Techniques for DOE Spent Fuel addresses the portion of its charge that it should carry out an ongoing evaluation of Argonne National Laboratory's (ANL's) R&D activity on electrometallurgical techniques for treatment of DOE spent fuel, including their specific application to Experimental Breeder Reactor II (EBR-II) spent fuel. However, delay of the EBR-II fuel treatment demonstration pending completion of an environmental assessment prevented the committee from assessing that portion of the R&D activity. Consequently, the committee focused its attention largely on the ANL program's efforts to develop and test waste forms.
SPENT FUEL OPERATIONS
Since the briefings received by the committee in November 1995, ANL-West (ANL-W) staff have proceeded by using nonradioactive surrogate fuels and have installed equipment for the ultimate production of mineral and metal waste forms. The scale of the demonstration project has been reduced from previous plans, and if additional obstacles develop during completion of the National Environmental Policy Act (NEPA) review, hot operation could be delayed further.
WASTE FORM DEVELOPMENT AND TESTING
ANL staff provided the committee with detailed descriptions of the equipment and processing conditions involved in ANL's waste form preparation. These appear to be well designed and likely to provide satisfactory results. An operational procedure for hot isostatic pressing (HIP) has been established that seems to allow reproducible preparation of the waste form. The results of hot isostatic pressing of zeolite showed the conversion of zeolite A to sodalite and in some cases nepheline. These phase transitions indicate a collapse of zeolite A; the transition to sodalite is accompanied by a decrease in intracrystalline void volume (the site of occluded salt and nuclides). Such a decrease could result in the partial expulsion of the nuclides into the glass matrix under certain conditions.
FINDINGS AND RECOMMENDATIONS
The committee learned from ANL that substantial progress has been made in the development and testing of waste forms, although it is also clear that this work is in its early stages. At the conclusion of this preliminary phase, the committee expects that the development program will achieve a sharper focus.
Questions raised by external groups about the adequacy of the existing environmental assessment have caused a delay in the demonstration processing of EBR-II spent fuel at ANL-W. The proposed quantity of fuel to be treated has been decreased but appears to be sufficient for demonstration of the process under radiochemical operating conditions. The committee continues to believe that the demonstration with irradiated fuels is the most important element in DOE's evaluation of the applicability of the electrometallurgical technology to treatment of other DOE nuclear fuels and other materials.
Consequently, the committee recommends that DOE assign high priority to authorization of hot operations at ANL-W.
The phase transformations during hot isostatic pressing of the loaded zeolite raise important issues of salt and nuclide partitioning and their effect on the overall performance of the GBZ waste form.
The committee recommends that ANL's ongoing studies be extended to include efforts aimed at defining the phase changes in the salt-loaded zeolite during hot isostatic pressing and determining the fate of the salt, which would no longer be as well isolated from the environment.
New, revised test and analysis protocols may be required before the release behavior of these new waste forms can be modeled with confidence.
The committee recommends that attention be given to establishing the performance of both the zeolite and metal waste forms under conditions relevant to their disposal in a geologic repository.
An effective and integrated waste form development and testing program will need to involve collaborative efforts between both ANL sites.
The committee recommends that the several aspects of ANL's substantial effort in waste form development be integrated into a formal, comprehensive program plan.
The committee also recommends that ANL establish a program of regular, formal meetings between ANL personnel and staff of the DOE's Yucca Mountain project as a useful (and perhaps essential) step in guiding ANL's future testing program.
The committee reiterates its earlier view on evaluating the ANL process in a “global” context once the process has been demonstrated.
The committee recommends that upon satisfactory completion of the demonstration with EBR-II fuel, the electrometallurgical technique should be evaluated in the broader context of alternative technologies for processing spent nuclear fuel.
