Density changes in plutonium observed from accelerated aging using Pu-238 enrichment

In support of Stockpile Stewardship activities, accelerated aging tests on a plutonium alloy enriched with 7.3 at.% of Pu-238 is underway using dilatometry at 35, 50, and 65 degrees C and immersion density measurements of materials stored at 50 degrees C. Changes in density are expected from radiation damage in the lattice and helium in-growth. After 25 equivalent years of aging, the dilatometry data shows that the alloys at 35 degrees C have expanded in volume by 0.11-0.12% and have started to exhibit a near linear expansion behavior primarily caused by the helium accumulation. The average He-to-vacancy ratio from tested specimens was determined to be around 2.55. The model for the lattice damage and helium in-growth accurately represents the volume swelling at 35 degrees C. The density converted from the dilatometry corresponds well to the decreasing density trend of reference plutonium alloys as a function of time. (c) 2006 Elsevier B.V. All rights reserved.