Core design study on CANDU-SCWR with 3D neutronics/thermal-hydraulics coupling

Using separated heavy water as moderator and supercritical water (SCW) as coolant introduces challenge for CANDU-SCWR to get a negative coolant void reactivity (CVR), due to which the moderator thickness of the fuel channel is optimized in this paper. When SCW flows through the core, there is a rapid variation in SCW density, which is directly related to the neutron spectrum and subsequently to the power distribution, so the 3D core neutronics/thermal- hydraulics coupling is needed to accurately evaluate the core coolant density and power distribution. In this paper, the neutronics calculation is computed with 3D fine mesh diffusion code while the thermal-hydraulic calculation is based on single channel model, they are coupled with each other automatically by a link code. Further, the in-core fuel management can be simulated by the link code to search the equilibrium cycle. Based on these calculation models, a CANDU-SCWR equilibrium core is designed with a thermal power of 2540 MW, the core equivalent diameter is 4.30 m and the active length is 5.94 m. A 3-batch fuel management scheme with a cycle length of 350 EFPD is used. The numerical results show that a high average outlet coolant temperature of 625 °C is achieved with a maximum cladding surface temperature less than 850 °C. The maximum linear heat generation rate is 50.6 kW/m, the average discharged burnup is 38.1 GWd/tU, and the CVR is negative throughout the cycle.