Calculation and Benchmarking of an Azimuthal Pressure Vessel Neutron Fluence Distribution Using the Boxer Code and Scraping Experiments

The light water reactor BOXER code was used to determine the fast azimuthal neutron fluence distribution at the inner surface of the reactor pressure vessel after the tenth cycle of a pressurized water reactor (PWR). Using a cross-section library in 45 groups, fixed-source calculations in transport theory and x-y geometry were carried out to determine the fast azimuthal neutron flux distribution at the inner surface of the pressure vessel for four different cycles. From these results, the fast azimuthal neutron fluence after the tenth cycle was estimated and compared with the results obtained from scraping test experiments. In these experiments, small samples of material were taken from the inner surface of the pressure vessel. The fast neutron fluence was then determined from the measured activity of the samples. Comparing the BOXER and scraping test results gave maximal differences of 15%, which is very good, considering the factor of 10³ neutron attenuation between the reactor core and the pressure vessel. To compare the BOXER results with an independent code, the 21st cycle of the PWR was also calculated with the TWODANT two-dimensional transport code, using the same group structure and cross-section library. Deviations in the fast azimuthal flux distribution were found to be <3%, which verifies the accuracy of the BOXER results.