PNNL

Abstract

The Hanford Spent Nuclear Fuel Project focuses its efforts on determining how to safely move the degraded N-Reactor spent fuel from water-stored basins to a dry storage facility. As part of this effort, the project initiated experimental studies to address issues relating to the chemical reactivity of the degraded/corroded metallic uranium material. The studies generated a limited set of data on chemical reaction rates of the N-Reactor spent fuel in dry air, moist air, and moist-inert atmospheres for comparison with published data on unirradiated/ irradiated metallic uranium. Based on the laboratory data, the project chose to use a conservative enhancement factor in analyzing the oxidation behavior of the spent metallic fuel. However, there is a need for the project to increase the fuel throughput for the drying treatment process by implementing certain design optimization steps. The study discussed in this paper re-evaluated the previous laboratory data in conjunction with the Cold Vacuum Drying (CVD) process experience and determined whether the built-in level of conservatism could accommodate the potential changes in the process without compromising public and worker safety. Evaluations based on laboratory data on samples taken from the N-Reactor spent fuel showed no reactivity enhancement in moist atmosphere. The established reaction rate constant was used to accurately determine the reactive surface areas of corroded N-Reactor fuel elements. The method was then used to provide a good estimate of the exposed uranium surface area in the loaded MCOs.