Analysis of the thermal feedback effect and nuclides flow effect on the fuel-cycle characteristics of Molten Salt Reactors

The main feature of Molten Salt Reactors (MSRs) is the use of fluid fuel which continuously flows through the primary circuit. The adoption of fluid fuel in the MSRs leads to strong coupling between the neutronics, thermal-hydraulics, fuel-cycle, and salt reprocessing. To accurately model the special phenomena caused by fluid fuel, a code system named TANSY has been developed. The code system has the capability to simulate the online refueling, the online reprocessing, the flow of delayed neutron precursors and the drift of nuclides accurately. To verify the fuel-cycle analysis capability of the code, neutronics benchmark problem of the Molten Salt Fast Reactor was simulated. The numerical solutions calculated by TANSY agree well with the reference results. After verification, it is applied to analyze the thermal feedback effect and nuclides flow effect on the characteristics of the fast-spectrum MSRs. From the numerical results, it has been concluded that both effects have a small influence less than 1% on the time evolution of the actinides. But it is also found that the thermal feedback effect has a relatively high impact about 8% on the feeding rate of the fissile nuclide because of its influence on the criticality and neutron spectrum. The nuclides flow effect has a relatively high impact about 5% on the time evolution of the nonsoluble fission products such as ¹³⁵Xe in the core because of the high reprocessing rate of such elements.