A model for the evolution of gas pressure and composition during sealed storage of metallic uranium fuel

Abstract

A model has been developed to predict the pressure generation and concentrations of oxygen and hydrogen gas in a Multi-Canister Overpack (MCO) containing metallic uranium N Reactor fuel during staging, drying, conditioning, and storage at the Hanford Site. Ass0ciated uncertainties with each parameter were also calculated. The mechanisms that were included in the analysis were: -- Uranium Corrosion in which oxygen is consumed, or water is consumed and hydrogen is produced, -- Uranium Hydriding in which hydrogen is consumed, and -- Radiolysis in which water is consumed and hydrogen and oxygen are produced. The model characterizes the evolution of gases inside the MCO for the three ,egimes in which the fuel will be staged or stored. Prior to treatment the fuel will be immersed in water in the MCO. Proceeding the first treatment step, the MCO will contain no free water, but water vapor will contribute to a moist atmosphere. After the last treatment step, the inside of the MCO will be dry with only tightly-bound chemisorbed water remaining associated with sludge that will be present with the fuel. The model shows that for likely conditions inside the MCO, the container will not pressurize during its expected service life. The model also shows the effects that varying parameters have on the final pressure.