Particulars of neutron-physical calculations of sodium-cooled fast reactors with mixed oxide fuel

The neutron-physical characteristics of reactor systems with a fast spectrum, sodium coolant, and uraniumplutonium fuel load have been analyzed on the basis of computational studies of the BFS-62-3A critical assembly and a BN-600 hybrid core with mixed oxide fuel. The large differences in the spectra in an expanded thermal range to 1 keV for the central and peripheral regions with uranium oxide and mixed oxide fuel show that spatially differentiated fission and absorption cross sections must be used for the main uranium and plutonium isotopes in neutron-physical calculations.