Secondary source reconfiguration for a Westinghouse four-loop plant

Abstract

An approach is described for estimating the excore source range detector count rate for several secondary neutron source configurations. A case in which a Westinghouse four-loop plant considered relocating the secondary source fuel assemblies and switching from secondary source fuel assemblies with six secondary source rods to assemblies with two or four secondary source rods is presented. The excore detector count rate is first estimated computationally, by modeling the secondary source fuel assemblies and excore detectors in MCNP and predicting the detector count rate based on detector sensitivity in cps/nv listed in the detector manual. Since the excore detector response can vary greatly from cycle to cycle even for equilibrium loading patterns due to variations in detector response, benchmarking to actual excore source range detector count rates is presented. A correction factor for each individual source range detector is determined from the benchmark, then applied in the prediction of excore source range detector count rate for the proposed two or four secondary source rod configurations. The approach presented in this paper could also be used to perform an engineering evaluation on the feasibility of elimination of secondary sources.