Long-term behavior of vacancy defects in Pu-Ga alloy: Effects of temperature and Ga concentration

Vacancy and its clusters are among the most important defects induced by self-irradiation in plutonium-gallium (Pu-Ga) alloys. For decades-long stockpiles, the generation and evolution of vacancy defects could cause void swelling and helium bubble formation, resulting in the ageing of the Pu-Ga alloys. Therefore, to shed light on the ageing mechanisms caused by vacancies in Pu-Ga alloys, the long-term behaviour of vacancy defects in Pu-Ga alloys is simulated employing an AKMC model parameterized by molecular statics calculations. By tracking the number of vacancy defects, the size distribution of vacancy clusters, and the largest vacancy clusters over time, we found that temperature and Ga concentration significantly influence the evolution of vacancy defects in Pu-Ga alloys. Temperature changes could affect the clustering behaviour of mono vacancies, and critical temperatures initializing the nucleation of vacancy clusters are observed. On the other hand, adding Ga contents in Pu-Ga alloys could increase the migration energy of and attractive interaction among vacancies, leading to increased vacancy cluster numbers at high temperatures.