Search

The correlation between water desorption and tritium release from Li 4 SiO 4 pebbles was studied by temperature programmed desorption. The released water and tritium from irradiated samples were monitored simultaneously. The main peak for tritium release from the irradiated samples that were exposed to air for more than a month, was shifted from 500 to about 250 °C, as compared to that from the unexposed samples. The peak temperatures for water desorption and tritium release overlapped very well, suggesting a strong correlation between the two processes. Accordingly, a two-step mechanism, involving isotope exchange between the tritium trapped on the grain surface and the surface hydroxyls (–OH), and subsequent desorption of tritiated water through recombination of the –OH/–OT groups, was proposed to explain the tritium release behavior for the air-exposed samples. It is believed that the formation and desorption of surface hydroxyl groups at 200–300 °C can affect the behavior of tritium release from Li 4 SiO 4 significantly. [ABSTRACT FROM AUTHOR]

Abstract: 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 450K to 600K 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. [Copyright &y& Elsevier]