Core and sub-channel analysis of SCWR with mixed spectrum core

The SCWR core concept SCWR-Mis proposed based on a mixed spectrum and consists of a thermal zone and a fast zone. This core design combines the merits of both thermal and fast SCWR cores, and minimizes their shortcomings. In the thermal zone co-current flow mode is applied with an exit temperature slightly over the pseudo-critical point. The downward flow in the thermal fuel assembly will provide an effective cooling of the fuel rods. In the forthcoming fast zone, a sufficiently large negative coolant void reactivity coefficient and high conversion ratio can be achieved by the axial multi-layer arrangement of fuel rods. Due to the high coolant inlet temperature over the pseudo-critical point, the heat transfer deterioration phenomenon will be eliminated in this fast spectrum zone. And the low water density in the fast zone enables a hard neutron spectrum, also with a wide lattice structure, which minimizes the effect of non-uniformity of the circumferential heat transfer and reduces the cladding peak temperature.The performance of the proposed core, including the neutron-physical and thermal-hydraulic behavior in sub-channel scale, is investigated with coupled neutron-physical/thermal-hydraulic simulation tools, which at the same time enables multi-scale analysis. During the coupling procedure, the thermal-hydraulic behavior is analyzed using a multi-channel code and the neutron-physical performance is computed with a 3-D diffusion code. Based on the core results, the pin-power reconstruction is carried out for each fuel assembly to predict the local pin-power distribution. Moreover, the sub-channel calculation is performed to obtain the thermal hydraulic parameters in each sub-channels and fuel rods. Based on the coupled analysis, measures to improve the performance of the SCWR-M core design are proposed and evaluated in this paper.The results achieved in this paper have shown that the mixed spectrum SCWR core concept (SCWR-M) is feasible and promising. One reference SCWR-M design is proposed for future analysis. (authors)