An analysis of crud contribution to the maximum permissible release rates for reactor spent fuel shipments

The Office of Civilian Radioactive Waste Management is sponsoring a program to develop standardized methodologies for evaluating spent fuel source terms and demonstrating compliance of spent fuel shipping packages to the federal containment requirements. An important subtask of the program is the evaluation of the neutron-activated corrosion-product deposits (i.e., ''crud'') on irradiated fuel rod surfaces and the determination of the contribution of these ''crud'' deposits to the total activity available for release from cask containment. During transportation, crud may spall from the fuel rods, disperse and become suspended in the cavity medium (gas or liquid), and could be the major contributor to the total source term. An analysis of all available data on crud deposit activity concentration distributions, composition, spallation properties, particle size distribution, and crud friability was conducted for various light-water-reactor fuels for selected burnups and decay times. Assuming that crud is the only source of activity release, the maximum permissible leakage rates were estimated using these data for seven types of truck and rail shipping casks containing 1-year-cooled and 10-year-cooled spent fuel. The details and results of this analysis are presented in this paper. 2 refs.