Volume changes in δ-plutonium from helium and other decay products

Small changes in volume are observed in plutonium, and several potential mechanisms have been proposed. In this paper, we provide a detailed theoretical analysis of volume changes due to the accumulation of helium and daughter products generated in the radioactive decay of plutonium. It is shown that volume changes in δ-phase plutonium caused by Am, U, and Np are significant and compensate to some degree the swelling from helium bubble formation and growth. Comparison with experimental results obtained so far suggests that the decay products dominate the rate of volumetric change in the long run.