Multi-physics numerical analysis of the fuel-addition transients in the liquid-fuel molten salt reactor

On-line refueling is one of the most unique merits of the liquid-fuel Molten Salt Reactor (MSR), which can dramatically improve the capacity factor of a nuclear power plant. However, the liquid-fuel addition to the fluid will change the reactivity of the core and hence the transient behavior should be carefully analyzed to guarantee the reactor safety. Therefore, a multi-physics coupling code named TANSY has been developed based on the OpenFOAM toolkit for MSR. It is capable of modeling the drift of nuclides in the online refueling process, the drift of delayed-neutron precursors, and the multi-physics coupling. For the code verifications, two transients have been simulated, including the Unprotected Loss Of Flow (ULOF) and Unprotected Loss Of Heat Sink (ULOHS) of the Molten Salt Fast Reactor (MSFR). After verifications, some special transients caused by the on-line addition of the fissile and fertile fuel for the fast-spectrum MSR were analyzed. The numerical results demonstrate that the fast-spectrum MSRs have excellent safety performance under the fuel-addition transient process due to the large negative temperature coefficient of the salt.