Search

The determination of the solubility of helium in liquid lithium and in lead-lithium eutectic systems is of crucial importance for the assessment of the reliability, safety and efficiency of future nuclear reactor plants based on fusion technology. In this way, an important aspect to be considered concerns the possibility of accumulations of gas inside the so called breeding blankets of the reactors, due to the low solubility of helium, leading to potentially undesired effects. In the present work we have performed molecular dynamics simulations in order to examine the characteristics of the solubility of helium in alkali metals along a temperature interval that covers near ambient conditions up to temperatures of the order of a 1000 K. Our methodology relied on the classical Kirkwood perturbative approach, which involves the gradual coupling between the infinite diluted He atom and the solvent. Such insertion proceeds along three stages that involved a previous incorporation of a softly interacting cavity that prevented singularities due to the harshly repulsive nature of the actual He-Li potential. Simulated structure factors predicted by the force fields of the different alkali metals were found to be in excellent agreement with available experimental information. Moreover, at all thermal conditions, our results of Henry's constants predict a steady volatility reduction with increasing temperatures, in good agreement with available experimental data. Furthermore, Henry's law volatility constants increase as the sizes of the atoms of the host alkali metals become more comparable to the size of the He atom (the predicted solubility increases with the size of the alkali atoms), and are coherent with the scarce experimental data available., The authors thank L.A. Sedano and A. Awad for fruitful discussions. J.M. and L.B. acknowledge financial support from the Generalitat de Catalunya (project “FusionCAT”, number J-02603) and from the EUROfusion project (HORIZON-101052200-EUROfusion). J.M. and E.A-G. thank financial support of project PID2021-124297NB-C32 funded by Ministerio de Ciencia e Innovación MCIN/AEI/10.13039/5011000-11033 “A way of making Europe” by the “European Union NextGenerationEU/PRTR”. J.M. gratefully acknowledges financial support from the Generalitat de Catalunya (Grant 2021 SGR 01411). E.A-G. has been awarded a fellowship at the Polytechnic University of Catalonia by the Spanish “Consejo de Seguridad Nuclear” through the ARGOS Chair of Nuclear Safety and Radiation Protection., Peer Reviewed, Postprint (published version)

Tritium self-sufficiency in fusion nuclear reactors will be based on the neutron capture by lithium in the so-called breeding blankets of the reactor, a nuclear reaction that will produce helium along with tritium. The low solubility of helium in liquid metals could cause the eventual formation of helium bubbles, which may have a negative impact on the performance of the breeding blanket in a way that has yet to be fully understood. In this work, we provide deep insight into the behavior of lithium and helium mixtures at experimentally operating conditions (800 K and pressures between 1 and 100 bars) using a microscopic model suitable to describe the interactions between helium and lithium at the atomic level, in excellent agreement with available experimental data. The simulations predict the formation of helium bubbles with radii around 10 Å at ambient pressure with surface tension values in the range of 0.6–1.0 N/m. We also report the cohesive energies of helium and the work of formation of the cluster of atoms, as well as a quantitative estimation of the Hildebrand and Kumar cohesion parameters. Our results indicate that the segregation between He and Li atoms is strong, and once a bubble is formed, it never dissociates., Postprint (author's final draft)