Applicability of Hydride Materials for Radiation Shielding in Helical Reactor FFHR-d1

Performance and applicability of hydride shielding materials are investigated in the helical reactor FFHR-d1 design. Performance of ZrH₂ and TiH₂ in fast neutron shielding are close to that of WC, which is most effective among candidate materials, for both in-vessel and out-vessel use. The investigation confirms that neutron shielding performance of a two-layered ferritic steel (FS)/ZrH₂ or TiH₂ shield is similar to that of a one-layered ZrH₂ or TiH₂ shield with the same total thickness. This shielding property is an important feature to maintain consistency with the structure design of FFHR-d1. In attenuation of direct neutrons from the core plasma in a bending duct, the hydride duct walls show superior performance compared with FS + B₄C and WC duct walls. While controls for temperature (at <300 °C) and hydrogen concentration in the coolant gas would be required particularly for in-vessel use, the lower weight densities and quick decay of contact dose rates compared with other candidate materials would be reasons to select these hydride shielding materials.