Neutron importance behavior in a VVER-1000 core during reactor operating cycle

In this work, we investigated the variation of neutron importance during reactor operating cycles for a VVER-1000 reactor. A more realistic approach of calculation of the neutron importance during burnup cycle has been implemented by using the MCNIC method. The simulation for neutron importance quantification during reactor operating cycle influenced by burnup and operational condition has been carried out. The results show that the maximum absolute relative difference in the core average neutron importance from the beginning of cycle to the end of cycle is within 15%.