Effect of Nuclear Data Libraries on PWR Ex-core Detector Response

Knowing the reactor power is of utmost importance for a safe operation of a nuclear power plant. In a typical pressurized water reactor during normal operation, reactor power is monitored by power-range detectors positioned outside the reactor core. With the aim to predict their response, a detailed core and ex-core model using Monte Carlo Neutron Transport Code MCNP were developed. Due to the ex-core position of neutron detectors, hybrid code ADVANTG is used to generate weight windows to speed up neutron transport outside the reactor core. To be able to use ADVANTG, fixed neutron source had to be reconstructed from the criticality core calculation. This paper focuses on the evaluation of the effect of different nuclear data libraries on the ex-core detector response. The deviation between ENDF/B-VII.0 and ENDF/B-VIII.0 nuclear data library on the ex-core detector response was evaluated to be similar to 9 %, by replacing the deficient evaluation of 56 Fe isotope included in the ENDF/B-VIII.0 nuclear data library, with the improved evaluation from the IAEA INDEN project, deviations decreased to similar to 5 %. Our results demonstrate the importance of correct description of prompt neutron spectra at high energy region and its impact on the ex-core detector response. It was concluded that the method using weighting of prompt neutron fission spectra for important isotopes with calculated reaction rates is the best approximation.