Study of the segregation of helium in the eutectic lead-lithium alloy and other liquid metals for modelling bubble formation in tritium breeding blankets

In this thesis, the mixing of helium with liquid metals is studied from atomistic and computational perspectives using classical molecular dynamics methods. The main objective is to understand the microscopic mechanisms governing helium nucleation in various liquid metals, with particular emphasis on the lead–lithium eutectic.

The obtained results contribute to a better understanding of processes occurring in metal–gas systems, with applications in materials science and nuclear engineering. These mixtures are relatively exotic and have been scarcely studied due to the experimental difficulties associated with handling them. The work compiled in this thesis was motivated by the need to characterize tritium breeding blankets in future nuclear fusion reactors, where free neutrons interact with lithium atoms present in the lead–lithium eutectic alloy. In this process, not only is tritium produced, but helium is also released as a by-product. The reportedly low solubility of helium in various liquid metals suggests a strong tendency towards nanobubble formation within breeder modules. Consequently, understanding the underlying microscopic mechanisms governing helium dissolution, transport, and aggregation is essential for improving the efficiency, reliability, safety, and long-term sustainability of fusion energy conversion systems.

Interactions between helium and metal atoms, as well as the physical mechanisms governing noble-gas segregation, were analysed through numerical simulations. Throughout this thesis, the effects induced by thermodynamic conditions (temperature and solvent composition) were investigated. Although the main focus was placed on the lead–lithium eutectic system, the study was not restricted to this composition: various lead/lithium ratios and other pure liquid alkali solvents were also investigated.

In the first part of the thesis, interaction models for liquid metals and their mixtures with helium were proposed. The second part of the thesis corresponds to the studies of helium solubilities (Henry’s law constants) in alkali metals and lead–lithium alloys. Finally, for completeness and to obtain a more accurate representation of the mixtures, tritium was included through potential models developed in this work in order to predict the effects of the hydrogen isotope on the previous results.