Calculation of the effects of Eu as impurity on the reactivity of the Miniature Neutron Source Reactors using the MCNP code

• Miniature Neutron Source Reactors (MNSRs) are modeled using the MCNP-4C Code.
• The effect of europium as impurity in MNSRs materials is studied completely.
• Decreasing europium in side reflectors of MNSRs by 35 ppm saves 6 fuel rods.
• 6 fuel rods can be saved by decreasing Eu in the bottom reflector by 220 ppm.

Europium is present as impurity in both the side and bottom reflectors in Miniature Neutron Source Reactors (MNSRs). Natural europium is formed of two isotope, namely: Eu-151 and Eu-153 both are good absorber of thermal neutrons. Results have shown the decreasing the natural europium content in the side reflector by 35 ppm would save about 6 fuel rods in MNSRs. While it is necessary to decrease the content of natural europium in the bottom reflector by about 220 ppm to save the 6 fuel rods from loading in the core of MNSRs.By comparing the weights of the two reflectors it comes out that the side reflector is more important for MNSRs as a component but europium is more efficient in the bottom reflector of MNSRs by about 20%.The choice of performing further purification of beryllium depends on the cost of purification in the country and the purpose of the reactor.