In-situ tritium release experiments from solid breeding materials (TTTEx) — Released chemical form of tritium and its diffusivitees in Li 2O

Abstract

Experiments of in-situ tritium release from Li 2 O powder under neutron irradiation at high temperatures ( Φ = 10 8 n/cm 2 · s, 400–700 ° C) were conducted using the research reactor YAYOI at the University of Tokyo to study the chemical form of the released tritium and the tritium release kinetics. The chemical form of the released tritium was found to depend upon the experimental conditions such as (i) sweep gas chemistry, (ii) pre-treatment of the sample, and (iii) choice of structural material for the sample holder. It was concluded that the dependence of the chemical form of released tritium on these parameters can be explained by the thermodynamic equilibrium of the metal/oxide/hydrogen/water system. The tritium release kinetics, especially tritium diffusions in a crystal grain and through grain boundaries, were studied by utilizing several polycrystalline samples of different particle sizes. Diffusivities of tritium in the grain ( D g ) and through grain boundaries ( D int ) were calculated as D g (cm 2 /s) = 1.27 × 10 −5 exp(− 54.9(kJ/mol)/ RT ), D int (cm 2 /s) = 1.61 × 10 2 exp(− 95.1(kJ/mol)/ RT ) over the temperature range from 360 to 600 ° C.