MCNP Simulation of Physics Parameters of Dispersion Fuels for Conversion of NIRR-1 to LEU

Abstract

The Nigeria Research Reactor-1 (NIRR-1) is one of the Commercial Miniature Neutron Source Reactors (MNSRs) sited outside China and scheduled for conversion under the auspices of Reduced Enrichment for Research and Test Reactors (RERTR) program. Since 2006, the reduction in the fuel enrichment of MSNR facilities from greater than 90% HEU cores to less than 20% LEU cores has been embarked upon. Consequently in this work, the physics parameters of three dispersion LEU fuels, which include U 3 Si, U 3 Si 2 , and U 9 Mo enriched to 19.75% were determined by the MCNP code to investigate their suitability for the conversion of NIRR-1 to LEU. The following reactor core physics parameters were computed for the LEU fuel options: clean cold core excess reactivity (ρ ex ), control rod (CR) worth, shut down margin (SDM), neutron flux distributions in the irradiation channels and kinetics data (i.e. effective delayed neutron fraction, β eff and prompt neutron lifetime, l f ). 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 options for the conversion of commercial MNSR in general and NIRR-1 in particular from HEU to LEU.

Nigerian Research Reactor-1 (NIRR-1) Core Life-time Analysis using Winfrith Improved Multigroup Scheme-Argonne National Lab (WIMS-ANL) and REactor BUrnup System-Argonne National Lab (REBUS-ANL) Computer Code

“…The containment vessel is a tubular alloy container with a diameter of 0.6 m and a height of 5.6 m that is suspended in a reinforced concrete pool lined with stainless steel (SAR, 2012). The intrinsic safety of all MNSRs is related to the restricted core excess reactivity in the range 3.5-4.0 mk (Ibikunle et al, 2018). The current NIRR-1 core is powered by around 1.4kg LEU, and the clean cold core excess reactivity is 3.94 mk, as determined during on-site zero-power and criticality studies (Table 3.1) (CERT, 2019).…”

“…Since then, a worldwide effort has been made to restrict, and nally eradicate, the civil use of HEU (Travelli, 1993).Through use of High Enriched Uranium (HEU) to fuel research reactors instantly creates a slew of inescapable and obvious proliferation risks associated with material diversion and/or theft. Thus according sources, the US Department of Energy (DOE) established the Reduced Enrichment for Research and Test Reactors (RERTR) program in 1978 in response to rising concerns about proliferation and the ease with which state and nonstate actors may get nuclear weapons (Ibikunle et al, 2018, Feiveson et al, 2014and Simon et al, 2021. A miniature neutron source reactor (MNSR) is one of numerous research reactors worldwide that use HEU as fuel.…”