Estimation of the maximum mass of graphite removed during phased work on the management of RBMK-1000 resource characteristics

The article describes a set of studies for estimating and substantiating the limit mass of graphite removed during the resource characteristic management of RBMK reactors. The limit mass is understood as the maximum mass of graphite that can be removed from the reactor core at the stages of resource characteristic management without violating the operational limits of neutron-physical characteristics during the operation of power units over a period of 45 years. The substantiation of the limit mass was made based on the detailed computational simulation of reactor operation for realistic operational scenarios of the third and fourth power units of the Leningrad NPP. Particular attention is paid to the change in the void coefficient for the predicted states of reactors. The uncertainty of the limit mass of removed graphite is analyzed. The trueness of the calculated predictive estimates of neutron-physical characteristics and the limit mass of removed graphite is confirmed by the measurement results. It is shown that, by taking into account the considered operational scenarios for the reactors of the third and fourth power units of the Leningrad NPP, nuclear safety is ensured.