An Assessment of the Use of Diluents in the Vitrification of Weapons-Grade Plutonium

A technical analysis was performed to determine the feasibility and utility of vitrifying weapons-grade plutonium (WGPu) with various diluents. The diluents considered were reactor-grade plutonium (RGPu) and several rare earths. The use of these diluents could affect both the usability of the material for weapons and long-term environmental safety. Blending RGPu with WGPu would increase the compressed critical mass of the WGPu mixture only slightly; but the blending would increase pre-detonation probabilities. Blends with the rare earths (notably Eu) would be highly effective in increasing the compressed critical mass. In addition to their effectiveness in increasing critical mass, the rare earths were investigated as criticality controllers due to their neutron absorption capabilities and insolubility in aqueous environments. Thorium (assumed as a Pu surrogate) and the rare earths Eu, Gd, and Sm were added to two standard frits (ARM-1 and SRL-165) and melted into glass. Aqueous leach tests were performed to measure rare earth leaching and determine the added elements effects on glass durability. Europium was much more leach resistant than boron in the glasses tested. The added elements had no negative effect on the environmental durability of the glasses tested at 90°C. No fission product releases were detected in the ARM-1 compositions (which contained numerous simulated fission products).

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