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Three dimensional steady‐state neutronics/thermal‐hydraulics coupled simulation for a molten salt reactor moderated by zirconium hydride rods

Zirconium hydride (ZrH) is considered as an alternative moderator in the molten salt reactor (MSR) due to its excellent slowing‐down ability, good thermal stability, and high radiation resistance. In the MSR, ZrH moderator is inserted in the form of rod into the fuel salt of the reactor core, and an axial and a transverse fuel salt flow occur between adjacent fuel salt channels. This inter channel flow mixing effect of fuel salt makes the molten salt reactor moderated by zirconium hydride rods (ZrH‐MSR) substantially different from other type of reactors in both neutronics and thermal hydraulics. Based on the multi‐group neutron diffusion theory and the subchannel thermal‐hydraulics model, a steady‐state analysis code for ZrH‐MSR was developed and verified in this work. Then, a 25 MWth ZrH‐MSR proposed by Transatomic Power Corporation was selected to evaluate its steady‐state characteristics due to its cost‐effective and simplified design. By applying this coupled code, the effects of control rod position, inlet fuel salt flow velocity, and residence time of fuel salt in the external loop on the distributions of the neutron fluxes, delayed neutron precursors (DNPs), and temperature for the 25 MWth ZrH‐MSR were analyzed in detail. The simulation results show that the control rod position influences the neutron fluxes greatly, which indirectly affects the distributions of DNPs and core temperature. The inlet fuel salt flow velocity and the residence time of fuel salt in the external loop have little influence on the neutron fluxes of the core but affect the distribution of DNPs significantly. These numerical results can provide valuable information for the research and design of ZrH‐MSR.