Criticality aspects of nuclear power reactor cores in the case of emerging nuclear fuels

Reactor cores of PWR and LMFBR, loaded with different commercial and emerging nuclear fuels, have been simulated and compared at BOI with respect to criticality with and without chemical shim, control rods and sodium. The different cases considered, within each of the reactor types, are grouped together according to their fissile content, when compared on the basis of the neutron multiplication factor (k_eff). For both PWR and LMFBR reactor types, the reactivity worths of the control rods do not change significantly when replacing commercial fuels by emerging ones. In the case of the LMFBR, the Na void reactivity effects are small and comparable using either emerging or commercial fuels. Hence, operation and control of the core at beginning of irradiation are similar for emerging or commercial fuels.