LAUSR

Abstract This study presents a neutronic and thermal–hydraulic estimation to convert a Multi-Application Small Light Water Reactor (MASLWR) with UO2 core to the UO2 + ThO2 core or ThO2 with the minimum possible modifications in the geometry and main parameters of MASLWR core. The thorium considered in this work was already enriched in 233U. MCNPX 2.7.0 (Monte Carlo code) has been used to calculate neutronic parameters such as effective multiplication coefficient (Keff), the nuclear fuel evolution during the burn-up, and the power peaking factor (Pmax/Pav) in the radial direction of the MASLWR different cores. RELAP5 code also has been applied to calculate thermal–hydraulic parameters for fuel rod hot channel, such as the surface heat flux, the coolant channel temperature. The centerline temperature of the fuel was calculated axially and radially, as well as the departure from nucleate boiling (DNB) ratio. The results show that the utilization of thorium (enriched with 233U) fuel improves the overall performance characteristics of the MASLWR. Less or no burnable poisons may be used (especially at the beginning of the reactor cycle); longer reactor cycle and higher fuel burn-up can be achieved, and most attractive feature is its resistance to nuclear proliferation. Also, thermal–hydraulic analysis of fuel rods displayed that the ThO2 fuel rod has a lower axial centerline temperature than UO2, and the DNBR value is about 5.2 for both fuel types and occurred at 0.6 of the fuel height from the inlet side.