Tritium segregation to vacancy-type basal dislocation loops in α-Zr from molecular dynamics simulations

Abstract

Tritium interactions with irradiation-induced defects in α-Zr are important for understanding getter performance in tritium-producing burnable absorbed rods. Vacancy-type basal loops are prominent in α-Zr irradiated at high dose rates. As they generate substantial tensile strain fields, such loops can trap tritium atoms. For this reason, vacancy-type basal dislocation loops are potentially important for tritium transport, tritium solubility, and tritide precipitation. We perform molecular dynamics simulations of tritium distributions around vacancy-type basal dislocation loops of different sizes, across a temperature range of 700–1200 K. Tritium preferentially segregates to the dislocation core and, to a lesser extent, the stacking fault. Segregation energies are estimated by inverting the tritium concentration distributions by assuming that the Boltzmann distribution adequately describes partitioning between the bulk and core environments. Agreement between molecular dynamics calculated segregation energies and predictions from elasticity theory using the stress field obtained by spatially averaging the atomic virial stresses suggests that elastic interactions dominate the interaction between tritium and basal loops. We also find an attractive tritium–tritium interaction. This attractive interaction can increase the stability of tritium in the dislocation core, resulting in a higher relative tritium concentration as the overall tritium concentration of the system increases. This suggests that vacancy-type basal dislocation loops can increase tritium solubility in irradiated α-Zr and may serve as preferential sites for tritide precipitation.