Consistency analysis and nuclear data validation for two series of beryllium reflector critical benchmark experiments

TL;DR

This study improves beryllium nuclear data to resolve discrepancies in critical benchmark experiments, enhancing the consistency between calculations and measurements and providing insights into data reliability.

Contribution

The paper introduces improved secondary angular distributions for beryllium reactions, reducing the chi-squared discrepancy in benchmark experiments and advancing nuclear data validation methods.

Findings

Reduced chi-squared from 7.58 to 4.52 with improved data

Calculations now agree within 1 sigma of experimental uncertainty

Identified systematic differences between two benchmark series

Abstract

Neutron-induced nuclear reaction data on beryllium playing a crucial role in nuclear application. However, discrepancies have been observed in two closely related series of beryllium-reflector fast-spectrum critical benchmark experiments, HMF-058 and HMF-066, which are widely used in current nuclear data validation. In this work, we address these inconsistencies by improving the secondary angular distributions of the (n,n) and (n,2n) reactions of beryllium, thereby making the theoretical calculations (C) and experimental results (E) of these two series more consistent, and reducing the cumulative ${\chi^2}$ value from 7.58 using the ENDF/B-VII.1 to 4.52. All calculations based on the improved nuclear data agree with the experimental measurements within 1${\sigma}$ experimental uncertainty. Based on the latest comprehensive evaluation of uranium nuclear data, this consistency is slightly improved, and the cumulative ${\chi^2}$ value decreases to 4.36 once again. Despite these advances, systematic differences in the expected values of C/E between the two series still exist. The C/E values of the HMF-066 series are generally 230-330 pcm lower than those of the HMF-058 series, comparable to their experimental uncertainties of 200-400 pcm. Therefore, drawing a definitive conclusion about this systematic difference remains challenging. If the current improvement of differential nuclear data based on experimental data of ${^9}$Be is accurate, then the HMF-058 series experiments seem to be more reliable than the HMF-066 series.