Plutonium dioxide storage: Conditions for preparation and handling

Desorption and adsorption of plutonium dioxide are derived from production-scale experiments that demonstrate techniques of preparing weapons-grade material for extended storage. In combination with data from literature, results define conditions for preparing and certifying PuO{sub 2} and provide essential information for developing and implementing a repackaging process compliant with DOE standards for safe storage of plutonium. As demonstrated by loss-on-ignition (LOI) analysis, adsorbates are effectively removed by heating the oxide in air at 950 C for two hours. After oxides are fired at this temperature, specific surface areas are consistently less than 5 m{sup 2}/g. Due to this low surface area, water adsorption by fired oxide is limited to a maximum of 0.2 mass % at 50% relative humidity. Kinetic data for the adsorption process show that water is accommodated on the oxide surface by a sequence of distinct first-order steps comprising five types of adsorbate interaction and accumulating ten molecular layers of H{sub 2}0 at 100% humidity. An equation defining the humidity dependence of the adsorption rate during the first step is applied in estimating time periods that a fired oxide may remain in given configurations without detrimental adsorption. Particle size measurements show that the source terms for environmental dispersal of oxides prepared by hydride-catalyzed reaction of metal and by oxalate calcination are approximately 20 and 0.1 mass %, respectively, and that the values are reduced by firing. Evidence for a chemical reaction between dioxide and water is discussed and practical applications of the results to oxide stabilization and LOI analysis are presented