Investigating the Dependence of Hydrogen and Oxygen Generation from High-Purity Plutonium Oxides in Sealed Containers

Gas generation experiments are being conducted on moist high-purity plutonium oxides in sealed containers to study pressure changes over time. Hydrogen and oxygen are of particular interest because of their potential to form flammable mixtures in containers during transport or storage. A broad range of high-purity plutonium oxides was chosen to investigate dependencies of G(H2) (molecules of hydrogen per 100 eV) and the maximum pressures on radiation dose to the water, specific surface area and number of monolayers (ML) of water adsorbed on the plutonium oxide surface. The specific power of the materials ranges from 2.1 to 33.5 W kg-1, and the specific surface area (SSA) ranges from 0.8 to 21.5 m2g-1. Flammable mixtures of hydrogen and oxygen that persisted for months were observed in some containers. A set of kinetic models that assumed first order formation and consumption reactions were used to fit the partial pressures of hydrogen and oxygen to obtain the initial rates of production and the maximum partial pressures in the container. Initial rates of hydrogen formation and maximum partial pressures increase with the amount of adsorbed water for materials with the same SSA. Hydrogen and oxygen maximum pressures were proportional to the initial formation rate normalized to the specific power of the material but were not proportional to initial rate normalized to SSA. Results suggest that formation of hydrogen and oxygen is dependent on dose to the water and their consumption is dependent upon dose to them. In some materials, a back reaction forming hydrogen was observed, which may also be dependent on dose to the consumption product. G(H2)-values were found to be independent of the number of MLs of adsorbed water, over the limited range studied.