The neutron streaming correction method in the homogenization of Pebble-bed HTGR reflector

Abstract

In pebble-bed high temperature gas-cooled reactors (HTGRs), the outside graphite reflector generally contains void regions, including the boring channels for control rods, absorber balls and coolant flow. Deterministic reactor physics calculation of HTGR is usually based on regular geometries, which requires pre-homogenization to the materials with void regions. However, the volume-weighted homogenization to the HTGR reflector can greatly overestimate the keff, due to the neutron streaming effect in the reflector channels. This paper proposes a convenient method of correcting the neutron streaming effect in the HTGR reflector, by adjusting the homogenized transport cross sections based on preservation of the neutron transmission probabilities. The proposed method has been implemented in the PANGU code for pebble-bed HTGR physics analysis and fuel cycle simulations. Numerical results suggest that the proposed method can effectively reduce the discrepancy in the homogenization of the HTGR reflector.