Kinetic studies of the tritium release process in neutron-irradiated Li2O and LiOH

Tritium produced in Li2O(s) and LiOH(s) by the 6Li(n,α)T reaction was released mostly in the form of HTO(g) through heat treatment under vacuum. From rate measurements of the HTO(g) release process in the temperature range 530-700 K, however, a difference was found in the kinetic data between the two materials. The HTO(g) release from LiOH(s) was revealed to be controlled by desorption of HTO molecules in analogy with the thermal decomposition reaction of LiOH(s). On the other hand, the rate-determining step of HTO(g) release from Li2O(s) was found to be diffusion of tritium in the solid. The diffusion coefficients determined for Li2O samples, different in neutron fluence (nvt), were D = 1.9 x 10-2 exp[-(24.8 +- 2.5) x 103/RT] cm2/s at nvt = 5.4 x 1015 cm-2, D = 1.2 x 10-2 exp [-(24.9 +- 1.7) x 103/RT] cm2/s at nvt = 8.1 x 1016 cm2, and D = 5.1 x 10-3 exp[-(23.9 +- 1.7) x 103/RT] cm2/s at nvt = 8.9 x 1017 cm-2. (orig.)