Simulation of the nucleation of helium 3 bubbles in a metal tritide using a cellular automaton

Palladium tritide is often used to store tritium. Helium 3 that appears as a decay product of tritium generates microscopic bubbles that can change mechanical and thermodynamical properties of palladium tritide. This study deals with the modeling of helium bubble growth. This modeling is based on a cellular automaton that describes the material at the atomic scale. This modeling takes into account the diffusion of tritium, the formation of helium through tritium beta decay, the diffusion of helium, the self-trapping of helium atoms, the bubble growth, and the presence of initial defects in palladium tritide. These different processes are simulated through the use of a set of simple rules governing the changes of state of the cells composing the automaton. This study has shown that the density of helium bubbles stabilizes quickly and is very dependent on helium diffusion. The more mobile helium is, the more bubbles. As a consequence, the controlling of the temperature of palladium tritide during the first days of storage is an important point to mastering palladium tritide aging. (A.C.)