Investigation on accident management measures for VVER-1000 Reactors

A consequence of a total loss of AC power supply (station blackout) leading to unavailability of major active safety systems which could not perform their safety functions is that the safety criteria ensuring a secure operation of the nuclear power plant would be violated and a consequent core heat-up with possible core degradation would occur.

Currently a study which examines the thermal-hydraulic behaviour of the system is being performed. This paper focuses on the possibilities for delay or mitigation of the accident sequence to progress into a severe one by applying accident management measures. The strategy “Primary circuit depressurization” as a basic strategy, which is realized in the management of severe accidents is being investigated. By reducing the load over the vessel in severe accident conditions, prerequisites for keeping the state of the primary circuit are being created. The time-margins for operators’ intervention as key issues are being also assessed.

The analyses are performed applying the GRS (Gesellschaft für Anlagen- und Reaktorsicherheit mbH) thermal-hydraulic system code ATHLET. Comparative analysis of the accident progression for a station blackout event for a reference German PWR and a reference VVER-1000, taking into account the plant specifics is being investigated.