Research and Application of the Rehomogenization Method for PWR Core Neutron Physics Simulation

The “two-step” scheme based on assembly homogenization is widely applied in simulations for pressurized water reactor (PWR) cores in which the few-group constants of the fuel assembly are generated with the single-assembly simulation. However, the reflective boundary condition adopted in the single-assembly simulation can’t characterize the real environment in the core, especially the strong heterogeneity between the neighboring assemblies. In order to consider the environmental effects on the homogenized few-group constants, a rehomogenization method is proposed. In this method, the heterogeneous neutron spectral of single-assembly model of the reflective boundary condition is corrected with the homogeneous neutron spectral of the real core environment. Through definition and precalculation of the rehomogenization factors for few-group constants during the fuel assembly simulation, corresponding corrected constants can be recomputed during the core simulation to consider the environmental effects. This method has been implemented in our home-developed code Bamboo-C. For method verification, both the heavy reflector PWR EPR1750 and the baffle reflector PWR HPR1000 have been simulated. It can be observed that the biases of the eigenvalues can be notably reduced with the proposed rehomogenization method. The assembly-averaged powers of the peripheral fuel assemblies were also notably reduced, especially for the EPR1750, which indicates that the environmental effects can be appropriately solved with the rehomogenization method.