Correlation between the processes of water desorption and tritium release from Li4SiO4 ceramic pebbles

The correlation between water desorption and tritium release from Li4SiO4 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 Li4SiO4 significantly.