Isotope Effect in Hydrogen Isotope Exchange Reaction on First Wall Materials

Hydrogen isotope exchange reaction is an essential reaction to understand tritium behavior in a fusion reactor because non-negligible amount of tritium is considered to be trapped to the surface of various materials through the isotope exchange reaction. However, a quantitative consideration of the isotope exchange reaction on candidates for the first wall material has not been done yet. In this study we experimentally quantify the hydrogen isotope exchange reaction rates between hydrogen isotope in a gas phase and hydrogen isotope on the surface of isotropic graphite, C/C composite and SiC. The isotope effect is observed in every material used in this work. The reaction rate between H₂-gas and D- surface is faster than that between D₂-gas and H-surface in every material, though no isotope effect has been observed on the surface of solid breeder materials or metals as stainless steel, aluminum and copper in previous studies. It is also certified that the isotope effect on SiC surface is the largest among three materials studied in this work. The isotope effect in the isotope exchange reaction for various combination of hydrogen isotopes are estimated using Bigeleisen)s equation.