(415e) Analysis of Radiolytic Hydrogen Generation from Water Adsorbed on Selected Plutonium Oxides

Radiolytic hydrogen generation from adsorbed moisture poses a safety risk for storage of plutonium oxide powders in sealed containers. Measurements have shown that during long-term storage the hydrogen pressure in such containers may either reach an equilibrium value or go through a maximum and then slowly decrease. The tempering of the gas generation rate with increasing pressure can result either from competing gas generation and consumption reactions whose relative rates change with pressure or perhaps over time or from an equilibrium in gas pressure or dissolved gas activity. The existence of an equilibrium gas pressure or activity is a more attractive explanation from the standpoint that it does not require a second reaction mechanism that is separate from water radiolysis.

A model is proposed in which the rate of radiolytic gas generation is limited by counterdiffusion of radiolytic hydrogen and oxygen gases and water vapor at the surface of the absorbed water. The limiting gas generation rate is shown to be lower than the intrinsic rate of water radiolysis. To confirm the existence of a limiting radiolytic gas generation rate, a perturbation analysis is used to calculate a characteristic frequency for fluctuations in the pressure generated during a gas generation test. Calculated and measured frequencies are compared.

Rates of radiolysis are analyzed for plutonium oxides from various sources, with differing isotopic compositions, morphologies related to processing conditions, and levels of moisture content.