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ALTERNATIVES FOR HIGH-LEVEL WASTE SALT PROCESSING AT THE SAVANNAH RIVER SITE Summary At the request of the U.S. Department of Energy (DOE), the National Research Council formed a committee to provide an independent technical review of alternatives selected by representatives at the Savannah River Site (SRS), South Carolina, for processing the high-level radioactive waste (HLW) salt solutions stored at the site. This review, which is summarized in this report, addresses the following four charges in the committee's statement of task: Was an appropriately comprehensive set of cesium partitioning alternatives identified and are there other alternatives that should be explored? Was the process used to screen the alternatives technically sound and did its application result in the selection of appropriate preferred alternatives? Are there significant barriers to the implementation of any of the preferred alternatives, taking into account their state of development and their ability to be integrated into the existing SRS HLW system? Are the planned research and development (R&D) activities, including pilot-scale testing, adequate to support implementation of a single preferred alternative? HLW at Savannah River is currently being stored in 48 below-grade tanks in the F and H Areas at the site. Currently, the solid (sludge) portion of the tank wastes is being removed and immobilized in borosilicate glass in the Defense Waste Processing Facility (DWPF) for eventual disposal in a geological repository. What remains in the tanks after the removal of sludge is a highly alkaline salt that is present in both liquid (or supernate) and solid (or saltcake) forms. The salt contains cesium, strontium, actinides such as plutonium and neptunium, and other radionuclides. This HLW salt will be put into solution and then processed to remove these radionuclides for immobilization in glass in the DWPF. The remaining “decontaminated” salt solutions will be immobilized in grout at the site. The process originally developed to
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ALTERNATIVES FOR HIGH-LEVEL WASTE SALT PROCESSING AT THE SAVANNAH RIVER SITE accomplish this HLW processing—in-tank precipitation (ITP) using monosodium titanate to remove strontium and actinides and sodium tetraphenylborate (TPB) to remove cesium —encountered unexpected problems when operations first started on a large scale with real waste in 1995. Savannah River abandoned the ITP process in 1998 and is now attempting to select an alternative processing option. After an extensive review of possible processing options, Savannah River selected a primary alternative (a variation of the ITP process known as small tank TPB precipitation) and a backup option (an ion exchange process using crystalline silicotitanate, or CST ion exchange). At this point DOE requested that the National Research Council undertake the current study to review both the selection process and the processing options themselves, which included the primary and backup options along with two other options that were eliminated by SRS in the final stages of screening: caustic sidesolvent extraction and direct grout. Information on these processes is presented in Chapter 3, Chapter 4,Chapter 5,Chapter 6,Chapter 7 of this report. The committee issued an interim report on October 14, 1999 (National Research Council, 1999b; see Appendix B), that provided a partial response to the charges in the committee 's task statement. This final report provides a more comprehensive response to all four of the charges in the statement of task. Explicit responses to each of those charges are provided below. More details on these recommendations can be found in the main body of the report. Charge 1: Was an appropriately comprehensive set of cesium partitioning alternatives identified and are there other alternatives thatshould be explored? The committee finds that a comprehensive set of cesium partitioning alternatives was identified in the Savannah River Site's screening procedure, and it recommends that no further effort be expended in alternatives identification at this time. Additional details can be found in Chapter 2 of this report. Charge 2: Was the procedure used to screen the alternatives technically sound and did its application result in the selection of appropriate preferred alternatives? The committee finds that the screening procedure was cumbersome, complex, and lacked transparency to document the technical soundness of the evaluations. The selection of alternatives appears to be based primarily on the best judgment of experts using many qualitative factors, an appropriate technique whose merit was obscured by the attempt to quantify the qualitative judgements in voluminous documents. The screening procedure did, however, result in the selection of four potentially appropriate processing options. Additional details can be found in Chapter 2.
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ALTERNATIVES FOR HIGH-LEVEL WASTE SALT PROCESSING AT THE SAVANNAH RIVER SITE Charge 3: Are there significant barriers to the implementation of any of the preferred alternatives, taking into account their state of development and their ability to be integrated into the existing HLW processing system? The committee finds that there are potential barriers to implementation of all of the alternative processing options. The committee recommends that Savannah River proceed with a carefully planned and managed research and development (R&D) program for three of the four alternative processing options (small tank precipitation using TPB, crystalline silicotitanate ion exchange, and caustic side solvent extraction, each including monosodium titanate processing for removing strontium and actinides) until enough information is available to make a more defensible and transparent downselection decision. The budget for this R&D should be small relative to the total cost of the processing program, but this investment will be invaluable to overcoming many of the present uncertainties discussed in this report. Recommendations on the elements of this R&D program are provided in Chapter 3, Chapter 4,Chapter 5,Chapter 6. Additionally, the committee recommends that DOE hold good faith discussions with regulators to determine if the direct grout option is feasible should all of the other processing options, including those that are potentially viable but had been previously discarded, prove to be technically or economically impractical. Additional details on this recommendation can be found in Chapter 7. The committee makes additional recommendations to overcome more “global” barriers for implementing any of these processing options in Chapter 8 of this report. In particular, the committee recommends that the Savannah River Site implement a more fully integrated systems engineering approach for processing HLW salt solutions. This approach involves the possibility of tailoring of HLW salt processing to the contents of individual waste tanks, as well as possible changes to the order of radionuclide removal. Given the large variability in radionuclide content between tanks, it is not clear to the committee that SRS has adequately addressed whether all tanks should be subjected to the same processing operations. Analysis of this issue should be predicated on possible reduction in size, cost, and design requirements for selected processing options. The committee also recommends that DOE charter external technical review and oversight groups to guide, evaluate, and provide direction to the R&D needed to support this program and to the managers of the program responsible for making decisions. DOE Order 435.1 places responsibility for the salt processing program with SRS. Careful coordination will be required between DOE Headquarters staff and SRS managers to implement these recommendations. Charge 4: Are the planned research and development activities, including pilot-scale testing, adequate to support implementation of asingle preferred alternative? The answer to this charge's question, at the time the committee completed its information gathering, is “NO!” The committee makes numer-
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ALTERNATIVES FOR HIGH-LEVEL WASTE SALT PROCESSING AT THE SAVANNAH RIVER SITE ous recommendations in this report on the elements of an effective R&D program to address the remaining scientific and technical uncertainties with each of the four alternative processing options. R&D plans were being made by DOE as the committee finalized this report, so the committee has not had the opportunity to review and evaluate the final plan and its progress. Detailed recommendations on these R &D elements can be found in Chapter 3, Chapter 4,Chapter 5,Chapter 6,Chapter 7 of this report.
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