In-situ measurement of hydrogen isotope behavior in high temperature LBE: Diffusivity, permeability, and solubility

Abstract

The Lead-Bismuth Fast Reactor (LBR) emerges as a promising concept due to its superior neutron economy, chemical stability, and thermal properties. From the nuclear safety standpoint, the focus has predominantly been on the behavior of 210Po and other fission products, while the issue of tritium in LBRs has not been sufficiently addressed due to the inconvenience of tritium experiments. Formation of tritium/helium bubbles induces significant local stress and volume expansion, leading to hardening and embrittlement of structural materials, thus expediting their degradation through irradiation effects. Current understanding of tritium transport within liquid Lead-Bismuth Eutectic (LBE) remains incomplete. To bridge this gap, a novel device employing the "permeation pot" method has been developed for the first experimental quantification of diffusivity, permeability, and solubility of hydrogen isotopes in liquid LBE. Notably, hydrogen diffusivity in this medium is found to be three to four orders of magnitude greater than in conventional 316L stainless steel structural material. Furthermore, the temperature-dependence of diffusivity in liquid metals is minimal compared to solids, as indicated by the activation energy. Conversely, solubility in 316L significantly surpasses that in LBE by three to four orders of magnitude. This discrepancy accelerates the tritium release from LBE to structural material, leading to the failure of the structural material.