Analysis of the impact of different scenarios on the simulation results of unauthorized dilution of boric acid in the coolant of the primary circuit of the NPP-2006

Abstract Unauthorized dilution of boric acid in the reactor coolant due to improper operation of the chemical and volume control system (KBA) is a project mode with the violation of normal operation. The operator is obliged to identify unauthorized dilution within half an hour and stop feeding with pure condensate. The power unit has automation, which stops feeding on EP (emergency protection) and ATWS (Anticipated transient without scram) signals. The situation without the intervention of the operator and the failure of automation to stop dilution can be considered as a beyond design basis accident. The article presents an analysis of unauthorized boric acid dilution process in the primary circuit coolant of the NPP-2006 power unit up to the controlled state, either considering the operator's intervention after a 30-minute period of process, i. e. with a forced cessation of dilution, or without the operator's intervention until the tanks with pure condensate are completely emptied.