Tritium release behavior from neutron-irradiated Li₂+xTiO₃+y with 20wt% Li₂ZrO₃ pebbles under different atmospheres

Abstract

• LTZO had versatile water vapor release mechanisms that contributed to tritium release. • LTZO had an indigenous peak expected to result from the existence of ZrO2. • The surface reaction contributed the tritium release property from LTZO. • No significant tritium left in LTZO was observed after 900 °C heating. Solid tritium breeding materials are essential for the fusion reactors' fuel cycle. Hence, it is necessary to investigate how the bred tritium releases from them carefully. Li 2+x TiO 3+y with 20 wt% Li 2 ZrO 3 (LTZO) ceramic pebbles were recently developed by QST as an advanced tritium breeder. However, the tritium release behavior has not been fully understood yet. Considering the upcoming high-flux irradiation test and downstream tritium separation and purification system design and permeation loss, further investigation on water vapor release and tritium release properties from LTZO by isokinetic heating were carried out in this study. As a result, it was found that LTZO had diverse vapor release mechanisms, including the same ones as ordinary Li 2 TiO 3 ceramic pebbles and the ones derived from TiO 2 and ZrO 2 . These results suggested that HTO release would last until the water formation reaction between TiO 2 and ZrO 2 , and H 2 in the gas phase ceased. Regarding the tritium release property under different purge gas species, it was experimentally clarified that the surface reaction was the rate-determining step like the existing Li 2 TiO 3 pebbles. In the case of H 2 purging, chemically adsorbed water vapor release and thermal decomposition of LiOH were recognized. Residual tritium in the LTZO pebbles was never observed after 900 °C heating.