A Comparative Study of the HEU, LEU Fuels: Assessing the Effect of the MNSR Fuel Burnup on the Effective Multiplication Factor and Neutron Fluxes

The GETERA and MCNP4C codes have been used to perform the core conversion analysis of the MNSR from the existing HEU to four potential LEU fuels. The effect of fuel burnup on the effective multiplication factor (keff) and the neutron fluxes in the irradiation sites was also investigated. Results showed that the “keff“ dropped sharply in the first days of the reactor operation time (Xe effect), then decreased slowly due to the fuel consumption. The axial thermal, epithermal and fast neutron flux distributions in the irradiation sites exhibited similar flux patterns for all types of fuel. The values of the axial thermal neutron flux were slightly lower in the LEU fuel. For the HEU fuel, the fuel residence time in the core was shorter than that for the LEU fuel. For both HEU and LEU cores, the changes in the neutron fluxes in the irradiation sites with burnup were negligible, so no burnup effect on the neutron fluxes was observed.