Neutronics Analyses Of Dispersion Fuels For Core Conversion Of Nirr-1

The modification of Miniature Neutron Source Reactor (MNSR) facilities from 90% HEU cores to below 20% LEU systems as part of the on-going worldwide effort of converting Research Reactors from highly enriched uranium (HEU) cores to low enriched uranium (LEU) cores under the auspices of Reduced Enrichment for Research and Test Reactors (RERTR) program. In this work, neutronics feasibility studies of three dispersion fuels have been performed using the Monte Carlo N-Particle Transport (MCNP) code to determine their suitability for the conversion of Nigeria Research Reactor-1 (NIRR-1) from HEU (>90%) to LEU (<20%) fuel. The potential LEU dispersion fuels investigated in this work include U3Si, U3Si2, and U9Mo, each enriched to 19.75%. The following reactor core physics parameters were computed for the LEU fuel options; clean cold core excess reactivity (rex), control rod (CR) worth, shut down margin (SDM), neutron flux distributions in the irradiation channels and kinetics data (i.e. effective delayed neutron fraction, βeff and prompt neutron lifetime, lf ). Results are compared with experimental and calculated data of the current HEU core and indicate that it would be feasible to use any of the LEU fuel options for the conversion of commercial MNSR in general and NIRR-1 in particular from HEU to LEU.

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