Ceramic breeder material with catalytic function

In most current designs of D-T fusion reactor blankets employing ceramic breeder materials such as Li2O, LiAlO2, Li2ZrO3 and Li4SiO4, the use of a helium sweep gas containing 0.1% of hydrogen is contemplated to extract tritium efficiently via isotopic exchange reactions. However, at lower temperatures, the release process of tritium from the breeders is dominated by the desorption of tritiated water and are therefore rather slow. For this reason, there is still a need to develop techniques that contribute to the acceleration of the recovery of bred tritium. In our previous studies, the isotope exchange reactions and water adsorption on the surface of several solid blanket materials were investigated. The results revealed that these isotope exchange reactions proceed fast only at more elevated temperatures. Because of the strong temperature dependence of the exchange reactions, a considerable decrease in the reaction rate takes place as temperature is lowered. Taking into consideration that there is a broad temperature distribution within a blanket module, it is anticipated that the tritium bred in the regions of lower temperature will presumably be poorly recovered. The result could be an increased overall steady state tritium inventory in the blanket module. In order to obtain an improved recovery of tritium from a blanket over a broad range of temperatures, the effect of catalytic active metal additives, such as platinum and palladium, on the heterogeneous isotope exchange reactions at the breeder-sweep gas interface was examined. These catalytic additives are irradiated in the 14 MeV neutron field during the operation of fusion reactors, which could lead to the nuclear transmutation of Pd and Pt and thus change in the chemical properties of these noble metals. Moreover, there is a possibility that nuclear reactions cause induced radioactivity related to additive metals. The authors also investigate these aspects using cross sections of the nuclear reactions. (author)