MULTI-FACET APPROACH FOR EVALUATING CRITICALITY RISKS DURING TRANSPORTATION OF COMMERCIAL SPENT NUCLEAR FUEL

The U.S. industry’s limited efforts at licensing transportation packages characterized as “high-capacity,” or containing “high-burnup” (>45 GWd/MTU) commercial spent nuclear fuel (CSNF), or both, have not been successful considering existing spent fuel inventories that will have to be eventually transported. A holistic framework is proposed for resolving several CSNF transportation issues. The framework considers transportation risks, spent fuel and cask-design features, and defense-in-depth in the context of present regulations as well as in the context of future potential revisions of regulations that would reflect a risk-informed, technically state-of-the-art approach. Within the boundary limits of the cases analyzed, the EPRI-sponsored work shows that there are no credible combinations of accident events, accident locations, and fuel misloading or reconfiguration that would result in a critical configuration during the transportation of spent nuclear fuel. The non-mechanistic criticality evaluation performed in the as-loaded or asdesigned configuration can be considered the bounding case for all conditions of transportation because this hypothetical reactivity case bounds all those normal and hypothetical accident cases that can credibly exist for a spent fuel transportation packages. Criticality during hypothetical transportation accidents should be a regulatory non-issue, as misallocation of regulatory requirements can lead to greater risks by overly restricting payloads.