Method research and effect analysis of fuel-assembly bowing on neutron-physics simulations of HPR1000

Abstract

The fuel-assembly bowing is widely observed in PWR, due to the complex operational environment in the core. After the fuel-assembly bowing, the three-dimensional (3D) water-gap distributions around the fuel assemblies would be deviated from the nominal values. From the view of neutron physics, the variations of water gap would result in over-moderation or under-moderation of the neutrons locally, hence impact the results of the neutronics simulations. In order to estimate the neutronics effects of the fuel-assembly bowing, our home-developed Bamboo-C code system based on the two-step scheme has been improved. In the lattice code LOCUST, the few-group constants were generated with different sizes of water gaps around the fuel assembly. In the core code SPARK, the neutron-diffusion solver has been improved to consider the geometry-grid variations due to the whole-core fuel-assembly bowing. For the method verifications, two test cases of HPR1000 with different kinds of fuel-assembly bowings have been designed and simulated, with corresponding reference results provided by the Monte-Carlo code NECP-MCX. The verification results show that well-agreed eigenvalue and assembly-averaged power distributions can be provided by the improved Bamboo-C code.