Isotope Exchange Reaction Between Gaseous Hydrogen and Tritium on Li₂TiO₃ Grain Surface

Though litium ceramic materials such as Li₂O, LiA1O₂, Li₂ZrO₃, Li₄SiO₄, and Li₂TiO₃, are considered as the candidates for breeding materials in the blanket of a D-T fusion reactor, the release behavior of the bred tritium in these solid breeder materials has not been fully understood yet. We have pointed out that it is essential to understand such mass transfer steps as diffusion of tritium in the grain, absorption of water in the bulk of grain, and adsorption of water on the surface of grain, together with two types of isotope exchange reactions for estimation of the tritium inventory in a uniform solid breeder blanket under the steady-state condition. The rate of isotope exchange reaction-1 on Li₂TiO₃ is quantified in this study, where pebbles of Li₂TiO₃ from CEA, KHI, and NFI are used.It is observed in this study that the rate of isotope exchange reaction on Li₂TiO₃ becomes 2∼3 order smaller than other solid breeder materials when it is placed in the hydrogen atmosphere at high temperature. It is also observed that the color of Li₂TiO₃ changed to black in accordance with decrease of reaction rate.The observation obtained at the release experiment of bred tritium performed in Kyoto University Reactor that chemical form of tritium becomes HTO at the high temperature even when hydrogen of 100 Pa is added to the purge gas can be explained by decrease of isotope exchange reaction rate.Tritium inventory in the Li₂TiO₃ blanket in various conditions are also discussed in this paper.