Experimental and computational study of the flux spectrum in materials irradiation facilities of the high flux isotope reactor

This report compares the available experimental neutron flux data in the High Flux Isotope Reactor (HFIR) to computational models of the HFIR loosely based on the experimental loading of Cycle 400. Over the last several decades, many materials irradiation experiments have included fluence monitors that were subsequently used to reconstruct a coarse-group energy-dependent flux spectrum. Experimental values for thermal (E < 0.5 eV) and fast (E > 0.1 MeV) neutron flux in the outer ring of the flux trap about the midplane are found to be 1.73 ± 0.20 and 1.06 ± 0.04·10¹⁵ n/cm ²-sec, respectively. The reactor physics code MCNP is used to calculate neutron flux in the HFIR at irradiation locations. The computational results are shown to correspond closely to experimental data for thermal and fast neutron flux with calculated percent differences ranging from 0.55-13.20%.