A study of the impact of mixed mode of fuel salt in plenum on steady-state performance of channel-type molten salt reactor

In this study, a coupled neutronics and thermal-hydraulics (THs) code named MOREL2.0, based on multi-group diffusion theory and multi-channel THs model, was employed to analyze a channel-type molten salt reactor TMSR-LF and the impact of different fuel mix mode in plenum on its steady-state performance was also discussed. MOREL2.0 adopts “two-step” calculation scheme, in which few-group homogenized parameters are generated by lattice code PIJ, and diffusion equation considering the drift of delayed neutron precursors is coupled with multi-channel THs model, and the least square method is implemented for cross-section feedback in coupling scheme. The numerical results indicate that TMSR-LF has negative reactivity coefficients in term of inlet fuel temperature and core power level, and the response of keff to mass flow is different for cases of nominal power and zero power, and keff decreases with the rise of time of fuel salt spent in external loop and gradually tends to steady. Different mix mode in plenum have a greater impact on the mass flow distribution and delayed neutron precursors distribution, but less impact on core lumped parameter such as keff and effective delayed neutron fraction.