Investigation of deuterium cross section data by integral testing: ZED-2 measurements of high-enriched uranium fuel substituted into a natural uranium core

Historical ZED-2 measurements of an HEU fuel rod substituted into a lattice of NU rods were analysed to determine their reactivity sensitivity to differences between the neutron elastic scattering cross-sections of deuterium from different evaluated nuclear data libraries. The differences in the deuterium nuclear data concern the angular probability distribution at neutron energies below 3.2 MeV. These ZED-2 experiments were selected due to the presence of HEU fuel in D₂O, since analyses of other critical experiments involving solutions of HEU fluoride in D₂O show substantial sensitivity (∼10 mk) to these differences in the deuterium nuclear data. This analysis shows that the existing ZED-2 HEU experiments are insufficiently sensitive to resolve the discrepancy between the different deuterium data libraries. Further analysis of hypothetical configurations with high sensitivity shows that the sensitivity to the angular probability distribution of deuterium is strongly correlated with the leakage of fast neutrons, and it is recommended that further experiments to address this deuterium nuclear data issue be designed/evaluated to maximize this quantity. (author)