Monte Carlo neutronic simulations for a new approach to parametric INAA and Mo-99 production feasibility at MURR

Abstract

A novel approach to parametric instrumental neutron activation analysis at MURR has been established. In particular, a detailed MCNP5 steady-state model of the MURR core was developed. The model, which was based on the most recent continuous-energy neutron data from the ENDF and JEFF neutron libraries, was used to compute the local continuous-energy neutron flux distribution. By coupling the computed flux spectrum to the energy-dependent ([nu], [upsilon]) cross-sections for a range of nuclides, their intrinsic reaction rates were predicted in irradiation channel ROW2. The model was initially benchmarked by measuring the intrinsic ([nu], [upsilon]) reaction rates for a set of mostly dilute single-element standards in ROW2. Predictions of the intrinsic reaction rates for many nuclides, including those with high epithermal sensitivity and non-1/v behavior, are within [plus-minus] 5% of the measured values. Using predicted ([nu], [upsilon]) reaction-rates, trace-elemental concentrations were determined in NIST standard reference materials, bovine liver, obsidian and coal fly ash. The agreements with the certified concentrations were generally within [plus-minus]5%. The new methodology has produced better results for a greater number of elements than [kappa][subscript 0]. The model was also combined with MONTEBURNS and ORIGEN to test the feasibility of Mo[superscript 99] production at MURR from fissioning LEU. Results from a 5-gram low-enriched uranium target show predictions of Mo[superscript 99] end-of-irradiation yields are within 3% of the measured value. This dissertation entails a complete study of the MCNP5 model and the new neutron activation analysis method.