Qualification of afterheat removal passive system from reactor to manage blackout accidents

Abstract

Nuclear safety criteria and conditions for the maximum admissible temperatures of nuclear fuel and fuel claddings, for the pressure and coolant flow of the steam-driven emergency pump and for dimensions of using natural circulation are qualification criteria and conditions for operability and reliability of the presented afterheat removal passive system from the reactor to manage blackout accidents. The conservative heathydrodynamic model of qualification of afterheat removal passive system from the reactor is developed for blackout accident management. Calculation modelling with the presented conservative model has recognized that design blackout accident management strategy does not ensure nuclear safety conditions. The modernized accident management strategy with afterheat removal passive system from the reactor provides nuclear safety conditions. According to Prof. Korolev’s experiments, operability of the steam-driven emergency pump is provided when the reactor pressure is more than 0.3 MPa. For smaller pressure, the afterheat removal passive subsystem using natural circulation provides safety functions. The results of this work can be used to modernize nuclear power plants with the view of increasing the efficiency of blackout accident management, and to improve symptom-informed instructions and guidelines for the accident management of severe fuel damages. The proposed blackout accident management system can be supplemented with steam removal passive safety systems through steam generators of nuclear power plants with WWERs. The proposed passive system is effective only for blackout accidents and large loss-of-coolant accidents in the reactor (including the maximum design depressurization accident). The presented results are used for training, retraining and advanced training of specialists in Ukrainian nuclear energy.