CONSEQUENCE ANALYSIS OF SPENT NUCLEAR FUEL RECONFIGURATION SCENARIOS

High-burnup fuel has different characteristics than low-burnup fuel with respect to cladding oxide thickness and hydride content, radionuclide inventory and distribution, heat load, fuel grain size, fuel fragmentation, and fission gas release to the rod plenum. High-burnup fuel may have a greater potential to reconfigure than low-burnup fuel because of higher irradiation damage. In addition, it appears that the fuel will be stored in a dry storage condition beyond the initial license. As the fuel decay heat decreases during storage times, fuel rod mechanical performance may be affected as a result of cladding material properties changes associated with hydride reorientation. The fuel cladding may become less ductile once the temperature decreases below the cladding’s ductile-to-brittle transition temperature. To improve understanding of the implications of potential fuel failure on the continued safety of storage casks and transportation packages, the U.S. Nuclear Regulatory Commission (NRC) has initiated a project with Oak Ridge National Laboratory (ORNL) to evaluate the potential consequences of fuel rod failure and reconfiguration with respect to satisfying the regulatory requirements for SNF storage and transportation systems in the areas of criticality, shielding (dose rates), containment, and thermal. The technical approach includes (1) development of credible failed fuel configurations and (2) evaluation of the impact of fuel failure/reconfiguration on the storage and transportation systems with respect to satisfying the 10 CFR 71 and 72 regulatory requirements for criticality safety, shielding, containment, and thermal design. The evaluated scenarios include possible effects from individual rod break, general cladding failures, rod/assembly deformation, and gross failure as a function of fuel type, burnup, and decay time.