Out-of-pile tritium extraction from lithium orthosilicate-based ceramics

Ceramics based on the lithium orthosilicate (Li4SiO4) are candidates as blanket materials for forthcoming fusion reactors. Lithium ceramics, with controlled stoichiometry and microstructure, have been prepared by sol-gel route and sintering at 650-800deg C. The enhancement of the lithium conductivity is realized either by introducing mobile ion vacancies in the lithium sites of the orthosilicate type structure, or by formation of a composite material containing a few wt% of LiOH. Tritium extraction experiments, from out-of-pile, show no relation between the tritium release and the lithium bulk-diffusion within the grains. At low temperature, the tritium release is governed by water chemistry and can be described by OH-/OT- recombination and desorption. At high temperature, the tritium release is probably governed by surface reaction between adsorbed H2 and surface OT-. (orig.)