Computer simulation study of self irradiation in plutonium

There is clear experimental evidence that plutonium based materials exhibit density changes with time. By comparison to what is known for nuclear fuel cell aging, it is believed that this phenomenom could be linked to the radioactive alpha-decay of plutonium. Schwartz et al. have identified three possible age-related phenomena due to self irradiation in Pu alloys that would cause dimensional changes: the initial transient, helium accumulation and void swelling [A.J. Schwartz, M.A. Wall, T.G. Zocco, W.G. Wolfer, Philos. Mag. 85 (2005) 479]. Even if the later phenomenon has not yet been observed in naturally aged Pu alloys, the aim of this work is to examine its possible occurrence by means of a multi-scale modelling approach. We coupled classical molecular dynamics simulations (MD) to mesoscopic Monte Carlo ones (MMC) in order to predict the long-term evolution of point defects created by self irradiation in plutonium. In this article, we focus on the results obtained for the MD radiation damage simulations. We show that plutonium does not seem to behave like other metals under ion irradiation. The annealing process of the defects produced by a recoil nucleus is indeed very long compared to what is known for various other metals. An MD parametric study of displacement cascade simulations combining temperature and cascade energy will be exposed. At the end, we will present results of preliminary MMC simulations based on our MD data which show that the spatial correlation of the stable defects populations created by the cascades seems to have a great influence on the predicted swelling. (c) 2006 Elsevier B.V. All rights reserved.