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INTRODUCTION
The U.S. Department of Energy (DOE) is nearing a decision on how to process 30 million gallons of high-level radioactive waste salt solutions 1 at the Savannah River Site (SRS) in South Carolina to remove strontium, actinides, and cesium for immobilization in glass and eventual shipment to a geologic repository. The department is sponsoring research and development (R&D) work on four alternative processes at Savannah River and at several national laboratories, and it plans to use the results to make a downselection decision in a June 2001 time frame. This decision will involve the selection of one or more alternatives for further R&D, pilot plant demonstration, and near the end of this decade, implementation to initiate processing of high-level waste at the site.
The department has requested technical advice from the National Research Council (NRC) to inform this downselection decision. In 1999, the DOE requested advice from the NRC on its efforts to identify potential processing alternatives and assess their technical feasibility. A National Research Council committee, hereafter referred to as the “2000 NRC committee,” was formed to undertake that work and issued its advice in an interim and final report (NRC, 1999, 2000, respectively). These reports raised numerous concerns about the processing alternatives and identified important issues to be addressed by the department's R&D program. The department's current R&D efforts are focused on addressing the issues identified in these reports.
Following the issuance of that final report, the DOE requested that the National Research Council continue to advise the department on the downselection process ( Appendix A). The present committee was formed to undertake this work. It comprises seven members of the first committee and two new members ( Appendix C). The committee was given the following charge:
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evaluate the adequacy of the criteria that will be used by the department to select from among the candidate processes under consideration;
1The waste to be processed includes supernate and salt cake that is stored in the underground high-level waste tanks at the site. The sludge portion of the waste is now being removed from the tanks, washed, and sent to the Defense Waste Processing Facility to be immobilized in glass.
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evaluate the progress and results of the research and development work that is being undertaken on these candidate processes; and
assess whether the technical uncertainties have been sufficiently resolved to proceed with downsizing the list of candidate processes.
The department also invited the committee, at its discretion, to provide comments on the implementation of the selected process.
This report focuses exclusively on the technical issues related to the candidate processes for radionuclide removal from high-level waste salt solutions at SRS. However, because final downselection must be based on a number of issues in addition to science and technology, the committee does not believe it is appropriate to recommend which process(es) should be selected. Rather, the committee has attempted to identify residual technical risks that should be a component of the decision-making process for downselecting the list of candidate processes. Some of these risks are a normal part of practice and scale up, while other risks encountered in the R&D program may reflect potential problems with the use of these process for radionuclide separation.
The present committee issued an interim report in March 2001 that addresses the first point of its charge. That report is reproduced in Appendix B and can be viewed on-line at http://www.nap.edu. It is not discussed further in this final report. The present report addresses the second and third points and the discretionary component of the charge.
The committee recognizes that the primary audience for this report is the assistant secretary for environmental management, who requested this study, her management team, other high-level DOE managers, and Congress. Therefore, the committee has striven to be concise rather than comprehensive and has intentionally avoided inclusion of the voluminous introductory and background sections that are a characteristic of many National Research Council reports. The final report of the 2000 NRC committee (NRC, 2000) provides an excellent summary of the high-level waste program at Savannah River, the candidate processing options, and the department's R&D program. That report is available for sale from National Academy Press and can be viewed on-line at http://www.nap.edu. Detailed technical background on cesium separation at the Savannah River Site and associated laboratories may be found in the DOE report Savannah River Site Processing Project Research and Development Plan (Pacific Northwest National Laboratory, 2000).
The information used to develop this report was obtained from briefings provided to the committee by the department and its contractors at the Savannah River Site, Oak Ridge National Laboratory (ORNL), and Argonne National Laboratory (ANL) at committee meetings in February
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and March 2001. A list of presentations received by the committee is provided in Appendix D.
The presentations to the committee were generally excellent. However, given the accelerated schedule for the R&D program and this review, complete, fully documented results generally were not available for the committee's review. The committee did, however, have an opportunity to discuss R&D results with the project scientists who attended its meetings. Therefore, the committee has used its best collective judgment in evaluating these results and formulating its findings and recommendations, but wishes to acknowledge that its evaluation is necessarily incomplete because of these information limitations. Similarly, given the tight schedule for this review, the committee has not performed an evaluation on how extensive any additional research and development needs to be. Instead, the committee has sought to identify those areas of technical risk that warrant further investigation.