Moisture Adsorption Considerations for Packaging Plutonium Oxide

Compliance with DOE-STD-3013, Stabilization, Packaging, and Storage of Plutonium-Bearing Materials, requires plutonium oxide to be stabilized at high temperatures such that the material is non-reactive and has less than 0.5% wt. moisture adsorption [1]. Since plutonium oxide is known to readily adsorb moisture, compliance with the standard requires a sample of oxide material to be measured for moisture adsorption. The measurement is typically performed using thermogravimetric analysis (TGA). The sample must be representative of the actual oxide material in order for the TGA measurement to be valid. Obtaining a representative sample from an oxide powder container may be done using a core sampler or a grab sample method that accounts for potential spatial distribution of the oxides. A further complication with moisture sampling is that the plutonium oxide typically continues to adsorb moisture from the glove box ambient air for many hours or even days until equilibrium is reached. In typical oxide material handling operations, the material, both product and sample, is canned and bagged out prior to reaching a moisture level in equilibrium with the ambient relative humidity. In fact, given the strict moisture requirement for DOE-STD-3013 compliance, it is highly undesirable to allow for equilibrium moisture adsorption to be achieved. Given the dynamic nature of moisture adsorption, a technical basis for obtaining a representative sample is important for DOE-STD-3013 compliance. The technical basis not only includes how the sample is obtained, but more importantly, must account for all handling once the sample is physically separated from the product. This paper provides an analytical basis for moisture adsorption to define handling controls that assures a representative oxide sample is obtained.