Source Terms for Spent Fuel Transportation and Storage Cask Evaluation

NUREG/CR-6487 and Interim Staff Guidance (ISG)–5 provide guidance on source terms to use when evaluating the ability of spent fuel storage and transportation casks to meet containment regulations in 10 CFR Part 71 and 72. These source terms, while intended to be bounding are based only on the properties of lower burnup (?current limit is 62.5 GWd/MTU peak rod average) that has changed the properties of the fuel. The change in the mechanical properties of the cladding will increase the potential for multiple fracture sites in a rod. The formation of a fuel rim at higher burnup may change the propensity of the fuel to fracture under impact and the resulting particulate size distribution. The analysis in this paper accounts for fuel fracture that occurs during an accident event and removal of particulate from the cask cover gas prior to the gases release from the cask. This paper reevaluates the particulate release fractions using high burnup fuel properties. Uncertainties in the release fractions due to uncertainties in the fuel properties data base are also evaluated.