Tritium transfer from neutron-irradiated lithium to yttrium and gas phase

Evaluation of material damage by neutrons is an essential issue for the realization of deuterium - tritium fusion reactors. In a material irradiation facility such as the Advanced Fusion Neutron Source (A-FNS), the high-intensity neutron beam is generated by the reaction of a flowing lithium and a deuteron beam. At this time, tritium is produced as a by-product. For safety operation of the facility, it is important to understand tritium behavior in lithium and to control tritium appropriately by a hot trap using yttrium. In this work, tritium transfer behaviors from liquid lithium to yttrium and gas phase were investigated at 400, 500, and 600 °C by using the samples of lithium irradiated by thermal neutrons at the Kyoto University Research Reactor (KUR). It was shown that the higher the heating temperature and the longer the contact time of lithium and yttrium, the higher the tritium retention ratio in yttrium. It was indicated that removing the oxide layer on the surface of yttrium by soaking in hydrofluoric acid can significantly improve the rate of tritium transfer from liquid lithium to yttrium. When the irradiated lithium was heated, a certain amount of tritium was released to the gas phase, but a certain amount of tritium was left in the liquid lithium or yttrium. The amount of tritium released by heating to 600 °C from the lithium exposed to air for a short time before irradiation was much larger than that from the lithium that was not exposed to air.