Atomistic simulations and theoretical predictions of helium nucleation in liquid Pb-Li eutectic alloy

Abstract

Liquid Lead-Lithium Eutectic (LLE) alloy is a promising candidate coolant and/or breeder to attain tritium self-sufficiency in the EU DEMO breeding blanket design. Liquid metals are characterized with excellent heat-transport properties, and a wide range of densities, melting points and low viscosities. More than 20 years ago, a potential helium nucleation issue in LLE was raised based on experimental observations, since helium is produced in a one-to-one mole ratio with tritium through nuclear breeding reactions of Li isotopes. Theoretical and numerical modelling investigations remained inconclusive due to the complexity of the system, i.e., multi-component system of liquid metal and a noble gas with extremely low solubility, thus challenging the validity of the relevant theories. In this study, ab initio and classical Molecular Dynamics methods are used to investigate the helium bubble formation in LLE. An Embedded Atom Method potential is developed to model liquid Li with enhanced performance and transferability to reproduced LLE characteristics. The nucleation phenomenon of helium is investigated by implementing the Mean First-Passage Time atomistic technique, and nucleation curves are produced for a variety of thermodynamic states. It is found that helium is in the regime of kinetic spinodal, which suggests that nucleation of small clusters is imminent, and bubble growth to a macroscopic-size is only a function of time.