Experimental investigation of tritium release from LiAlO2 and absorption into Zr

Tritium (T) production using a high-temperature gas-cooled reactor (HTGR) has been proposed to arrange initial T inventory for nuclear fusion reactors. For the establishment of this method, the behavior of T in a Li-loading rod (Li-rod), which contains LiAlO₂ and zirconium (Zr), needs to be understood. In this study, a powdered LiAlO₂ sample was heated in H₂ containing Ar gas flow to observe water formation reaction. Then, a powdered Zr sample was heated in humid Ar gas flow to investigate the temperature dependence of H₂O reduction rate on the Zr. Finally, a Zr-mixed LiAlO₂ sample, which had been neutron-irradiated in the Kyoto University Research Reactor (KUR), was preheated at 700 °C in a sealed quartz tube, and then heated in Ar gas flow to observe the release behavior of T from the sample. Released gaseous T (HT, T₂) and tritiated water vapor (HTO, T₂O) were separately collected using a pair of bubblers installed upstream and downstream of a copper oxide (CuO) bed, and the tritium concentration in each bubbler was measured using a liquid scintillation counter. Based on the results, it is suggested that LiAlO₂ should be in advance heated in reduction atmosphere to remove adsorbed water and unstable oxygen to suppress the release of T in chemical form of HTO, and Li-rod should be operated at higher temperatures over 700 °C to decrease the mass transfer resistance by an oxide layer on Zr.