Providing Evidence for the Experimental Nuclear Data Validation of the 35 Cl(n,p) 35 S Reaction Channel

The Thermal/Epithermal eXperiments (TEX) critical integral experiment test beds provide an opportunity to test specific key nuclear data. One well-known shortfall in the current evaluated nuclear data libraries is the uncertainty associated with the 35Cl(n,p) cross section, especially in the fast neutron energy regime (>100 keV). Additionally, validation for the total 35Cl neutron capture cross section has been sparse, with only a handful of thermal benchmarks to validate against.This work sets out to provide critical validation for the 35Cl neutron capture cross section, specifically targeting the 35Cl(n,p) cross section at neutron energies above 1 MeV, for criticality safety applications and nuclear data validation. A novel experiment campaign, which was specifically designed to address the 35Cl(n,p) cross section, was performed. This experiment builds upon the highly enriched uranium (HEU) TEX baseline framework to single out the chlorine cross section, adding sodium chloride absorber plates interstitially accompanied by high-density polyethylene moderators to tune the neutron energy spectrum to various energy regions within the capture cross section.The novel experiments were assessed in comparison to the ENDF/B-VIII.0, ENDF/B-VIII.1, ENDF/B-VII.1, JEFF 3.3, JEFF 4.0, and JENDL5 nuclear data libraries using the MCNP6.3, COG11.3, and MONK12B neutron transportation codes. In general, the nuclear data codes underpredicted compared to the experimentally derived neutron multiplication factors (keff) suggesting a bias in the nuclear data.Recent differential measurements have shown promising results in the quest to constrain the 35Cl(n,p) and 35Cl(n,α) cross sections. Even with the most recent evaluation, there still exists a clear bias that remains unexplained. This study provides integral experiment results that attempt to reconcile the remaining issues in the cross sections and offer evidence regarding factors unlikely to contribute to the remaining observed bias.