Pebble structure change of Li2TiO3 with excess Li in water vapor atmosphere at elevated temperatures

The pebbles of Li2TiO3 with excess Li, which is in a developmental stage in JAEA (Japan Atomic Energy Agency) as an advanced tritium breeding material, were exposed to water vapor at elevated temperatures. In the temperature rising process from room temperature to 900 °C, pore distribution and BET surface area were largely changed. The surface area decreased gradually by a sintering effect when maintained at 900 °C for a long time. The release of water vapor was observed at about 450 °C by the decomposition of LiOH in addition to the release of adsorbed water at the beginning of heating. A large release peak of CO2 was observed at 700 °C. This is caused by the decomposition of Li2CO3. A remarkable melt layer was formed on the pebble surface over 700 °C by melting of Li2CO3. The change of pebble structure and the influences of LiOH and Li2CO3 have to be taken into account, when the release behavior of bred tritium from Li2TiO3 pebbles is discussed.