A study on the optimal position for the secondary neutron source in pwrs

Abstract

This paper presents a new and efficient scheme to determine the optimal neutron source position in a model near-equilibrium PWR reactor, which is based on the OPR1000 Hanul Unit 3 Cycle 7 configuration. The proposed scheme particularly assigns importance of source positions according to local adjoint flux distribution. In this research, detailed pin-by-pin reactor adjoint fluxes are determined by using Monte Carlo KENO-VI code from solutions of the reactor homogeneous subcritical adjoint transport equations. The adjoint fluxes at each allowable source position are subsequently ranked to yield four candidate positions with the four highest adjoint fluxes. The study next simulates excore detector responses using the Monte Carlo MAVRIC code by assuming a neutron source installed in one of the four candidate positions. The calculation is repeated for all positions. These detector responses are later converted into inverse count rate ratio (ICRR) curve for each candidate source position. The study confirms that the optimal source position is the one with the highest adjoint fluxes, as it yields a more linear ICRR curve. The current work demonstrates that the adjoint flux-based approach can be used to determine efficiently the optimal geometry for a pair of neutron source and detector in a modern PWR core.