Invariability of neutron flux in internal and external irradiation sites in MNSRs for both HEU and LEU cores

The effect of the control rod position on the values of the neutronic flux in the internal and external irradiation sites for the actual high enriched uranium UAl 4-Al fuel and U 3Si 2, U 3Si, UO 2, and U-9Mo low enriched uranium fuels has been investigated by using a 3-D model for MNSRs. Results show that the values of the neutron flux in these sites depend only on the radial distance of these sites from the control rod axis, but not on the control rod vertical position. The standard deviation and the variance coefficient are all less than 0.0088E12 and 0.812%, respectively except for the UO 2 fuel for which these two parameters are 0.0088 and 1.938%, respectively. These calculated values depend on the fuel type and enrichment for the same power of the core and not on the thickness of the annulus reflector. The invariability of the neutronic flux values with the vertical position of the control rod renders, MNSRs optimum tools for neutron activation analysis.