The Evaluation of the Effective Kinetic Parameters and Reactivity of the IPEN/MB-01 Reactor for the International Reactor Physics Experiment Evaluation Project

The evaluation of the experiments of the effective delayed neutron parameters and reactivity performed in the IPEN/MB-01 research reactor facility has been successfully accomplished. The evaluated data are of very good quality and fulfill the requirements of a benchmark. The recently released MCNP6 together with the ENDF/B-VII.1, JENDL-4.0, JEFF-3.1.1, ENDF/B-VII.0, and JENDL-3.3 nuclear data libraries has been employed to calculate the effective delayed neutron parameters adopting the benchmark model of the IPEN/MB-01 reactor available in the International Handbook of Reactor Physics Benchmark Experiments. The analysis reveals that all these nuclear data libraries produced satisfactory results for β_eff, β_eff/Λ, and Λ. The same cannot be said for determining the reactivity using the Inhour equation. It was shown that there is a clear tendency to increase the deviation with the absolute value of the reactivity for negative periods. Only JENDL-3.3 and JEFF-3.1.1 produced results that are inside the 3σ range of the benchmark value uncertainty. Specifically for the case of ENDF/B-VII.1, a good part of this discrepancy is due to the decay constant of the first group of delayed neutrons, which is overestimated according to the experimental value measured in the IPEN/MB-01 reactor.