Physical Property Changes in Aging Plutonium Alloys

Plutonium, because of its self-irradiation by alpha decay, ages by means of lattice damage and helium in-growth. These integrated aging effects result in microstructural and physical property changes. Because these effects would normally require decades to measure, studies are underway to asses the effects of extended aging on the physical properties of plutonium alloys by incorporating roughly 7.5 wt% of highly specific activity isotope 238Pu into weapons-grade plutonium to accelerate the aging process. This paper presents updated results of self-irradiation effects on enriched and reference alloys measured from immersion density, dilatometry, and mechanical tests. After nearly 90 equivalent years of aging, both the immersion density and dilatometry show that the enriched alloys at 35 deg. C have decreased in density by ∼0.19% and now exhibit a near linear density decrease, without void swelling. Both tensile and compression measurements show that the aging process continues to increase the strength of plutonium alloys. (authors)