Bubble nucleation process in a metal tritide modeled using a cellular automaton

The modeling of the 3He bubble nucleation phase that occurs during the aging of metal tritides such as palladium tritide is undertaken using a cellular automaton describing the material at the atomic scale. In that model, using simple rules of cell state change, the physical phenomena involved in the bubble nucleation, namely tritium diffusion, formation of 3He by radioactive tritium decay, 3He diffusion, 3He self-trapping, bubble growth, influence of pre-existing trapping sites such as vacancies, are taken into consideration. Calculations steps are related to physical time through the decay of tritium atoms into 3He atoms which is characterized by a half-life of 12.32 years.That work has shown that the bubble density and distribution are almost stable within a few days of aging – typically 5–10 –, whatever the input parameters, the system making created bubbles to grow thereafter instead of creating new ones. The reached bubble density is very dependent on the 3He mobility – related to temperature for instance – during the first days of aging. The smaller it is, the higher the density. With a larger density of trapping sites, bubbles appear earlier and their density is higher. These results are discussed and compared to available experimental and theoretical works on palladium tritide.

► We model the first stage (He bubbles formation) of the aging of Pd tritide. ► We use a cellular automaton in which a cube of matter is modelled at the atomic scale. ► Physical phenomena are modelled by means of simple rules of cell state change. ► Simulations showed that almost all He bubbles are nucleated within a few days only. ► Bubble density depends on He mobility and initial concentration of trapping sites.