Moisture and surface area measurements of plutonium-bearing oxides

Abstract

To ensure safe storage, plutonium-bearing oxides are stabilized at 950 °C for at least two hours in an oxidizing atmosphere. Stabilization conditions are expected to decompose organic impurities, convert metals to oxides, and result in moisture content below 0.5 wt%. During stabilization, the specific surface area is reduced, which minimizes readsorption of water onto the oxide surface. Plutonium oxides stabilized according to these criteria were sampled and analyzed to determine moisture content and surface area. In addition, samples were leached in water to identify water-soluble chloride impurity content. Results of these analyses for seven samples showed that the stabilization process produced low moisture materials (<0.2 wt%) with low surface area (≤1 m 2/g). For relatively pure materials, the amount of water per unit surface area corresponded to 1.7–3.4 molecular layers of water. For materials with chloride content >360 ppm, the calculated amount of water per unit surface area increased with chloride content, indicating hydration of hygroscopic salts present in the impure PuO 2-containing materials. The low moisture, low surface area materials in this study did not generate detectable hydrogen during storage of four or more years.