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Gap Analysis to Support Extended Storage of Used Nuclear Fuel

The U.S. Department of Energy Office of Nuclear Energy (DOE-NE), Office of Fuel Cycle Technology, has established the Used Fuel Disposition Campaign (UFDC) to conduct the research and development activities related to storage, transportation, and disposal of used nuclear fuel and high-level radioactive waste. The mission of the UFDC is to identify alternatives and conduct scientific research and technology development to enable storage, transportation and disposal of used nuclear fuel (UNF) and wastes generated by existing and future nuclear fuel cycles. The Storage and Transportation staff within the UFDC are responsible for addressing issues regarding the extended or long-term storage of UNF and its subsequent transportation. The near-term objectives of the Storage and Transportation task are to use a science-based approach to develop the technical bases to support the continued safe and secure storage of UNF for extended periods, subsequent retrieval, and transportation.

While both wet and dry storage have been shown to be safe options for storing UNF, the focus of the program is on dry storage at reactor or centralized locations. Although the initial emphasis of the program is on commercial light-water reactor uranium-oxide fuel, DOE-owned research and defense used nuclear fuels as well as alternative and advanced fuel concepts being investigated by the DOE will be addressed later in this program. Because limited information is available on the properties of high burnup fuel (exceeding 45 gigawatt-days per metric tonne of uranium [GWd/MTU]), and because much of the fuel currently discharged from today’s reactors exceeds this burnup threshold, a particular emphasis of this program is on high burnup fuels.

Until a disposition pathway, e.g., recycling or geologic disposal, is chosen and implemented, the storage periods for UNF will likely be longer than were originally intended. The ability of the important-to-safety structures, systems, and components (SSCs) to continue to meet safety functions over extended times must be determined and demonstrated. In addition, the ability of these SSCs to meet applicable safety functions when the used nuclear fuel is transported must be ensured. To facilitate all options for disposition and to maintain retrievability and normal back- end operations, it is considered an important objective of this program to evaluate the likelihood that the used nuclear fuel remains undamaged after extended storage. This does not preclude consideration of other options, such as canning of all UNF, from a total systems perspective to determine overall benefit to nuclear waste management.

This report documents the initial gap analysis performed to identify data and modeling needs to develop the desired technical bases to enable the extended storage of UNF. For most SSCs important to safety, additional data are required, often because there are limited data on the new materials used in more modern fuels or dry storage cask systems or because the effects of high burnup and extended storage are not fully known. Based upon the importance of the SSC to licensing a dry storage system or an independent spent fuel storage installation (ISFSI), the potential effects of extended storage or high burnup on the degradation mechanism, and a combination of the data needs, regulatory considerations, likelihood of occurrence, the consequence of degradation, the means to remediate the degradation, and the impact of degradation on cost, operations, and future waste management strategies, a research and development (R&D) priority (Low, Medium, or High) is assigned. The R&D priority cannot be higher than the ranking assigned for importance to licensing; obviously, a structure, system, or component ranked of Low importance to licensing does not require a Medium or High priority for R&D. However, a structure, system, or component can be of High importance to licensing, but the R&D needs can be lower depending on the prioritization criteria.

The degradation mechanisms identified in this report are limited to those during normal dry storage operations and potential off-normal conditions. Impacts of degradation mechanisms on demonstrating compliance with design basis accidents including those initiated by natural phenomena are not discussed in this report. This report is meant to be a living document that will be updated as additional technical data become available and as policy decisions are implemented. Future revisions will include formulating the technical bases for consideration of accidents and natural phenomena during extended dry storage. In addition, future revisions will compare the gap analysis generated as part of the UFDC with similar analyses developed by the U.S. Nuclear Waste Technical Review Board, the U.S. Nuclear Regulatory Commission, Electric Power Research Institute, and international organizations. A similar gap analysis effort is under way as part of the UFDC to examine the needs to meet transportation requirements. Once the transportation work is completed, the results will be consolidated in a consistent manner in a revision to this report to form a single set of gaps and congruous direction for addressing these gaps to meet applicable storage and transportation requirements.

There are several cross-cutting needs for dry storage. These cross-cutting needs are key to detecting, understanding, and evaluating the extent of many of the degradation mechanisms, as well as both determining and validating alternate means of demonstrating compliance with specific regulatory requirements. Table S-1 provides a summary of cross-cutting needs and the proposed work to address those needs.