Study on surface reaction in tritium release from solid breeding materials by using hydrogen isotopes

Abstract

Surface reactions in tritium release from lithium ceramics (mainly Li 2O) were studied by in-situ tritium release experiment TTTEx at the University of Tokyo using sweep gases of He + H 2O, D 2O and He + H 2, D 2. In the sweep gas of He + H 2O(D 2O), recombination of surface OT and OH was concluded to be the rate-determining step. Tritium release behavior for the sweep gas of He + H 2(D 2) was found to be influenced by the oxygen potential of the system. For the low-oxygen potential case which was obtained by dehumidification with He + H 2 gas, exchange reaction of surface tritium with hydrogen was proposed. On the other hand, recombination of surface tritium with dissociatively adsorbed hydrogen was considered as the mechanism for high oxygen potential system. A part of tritium was believed to be released as the chemical form of HT, the fraction of which was larger for lower oxygen potential.