Tritium release kinetics in lithium orthosilicate ceramic pebbles irradiated with low thermal-neutron fluence

Tritium release kinetics in lithium orthosilicate (Li4SiO4) ceramic pebbles irradiated with low thermal-neutron fluence was studied by out-of-pile annealing experiments. It was found that the tritium produced in Li4SiO4 pebbles was mainly released as tritiated water vapor (HTO). The apparent desorption activation energy of tritium on the pebble surface was consistent with the diffusion activation energy of tritium in the crystal grains, indicating that tritium release was mainly controlled by diffusion process. The diffusion coefficients of tritium in the crystal grains at temperatures ranging from 450 K to 600 K were obtained by isothermal annealing tests, and the Arrhenius relation was determined to be D = 1 × 10−7.0 exp (−40.3 × 103/RT) cm2 s−1.