Neutronics assessment of advanced shield materials using metal hydride and borohydride for fusion reactors

Neutron transport calculations have been performed to evaluate the capability of metal hydrides and borohydrides as advanced shielding materials. Some hydrides are characterized by considerably higher hydrogen content than polyethylene and solid hydrogen. The hydrogen-rich hydrides show superior neutron shielding capability compared to the conventional materials. A one-dimensional cylindrical model was used to do the neutron transport calculation. The shields are located at the inboard and outboard sides, and they are 30 and 70 cm in radial thickness, respectively. Mg(BH4)2, TiH2 and ZrH2 can reduce the thickness of the outboard shield by 23, 20 and 19%, respectively, compared to the combination of steel and water. Mixing Mg(BH4)2 with F82H produces large effects in the gamma-ray shielding. In the mixing ratio of 0.5, the gamma-ray flux was 300 times smaller than that of pure Mg(BH4)2, even though the fast neutron flux is 13% larger than that of pure Mg(BH4)2. In the neutron spectrum for Mg(BH4)2, the neutron flux in the energy range of less than 100 eV drastically reduced as compared to those of other materials, due to the effect of boron.