Reliability of core cooling in WWER-440 reactors of type 213 in loss-of-coolant accidents

Possible problems are discussed of the emergency core cooling system of the WWER-440 reactor of type 213 during extensive loss-of-coolant accidents which are related to the manner in which the system is supplied with electric power. Big loss-of-coolant accidents are best dealt with using low pressure subsystems whose pumps require a continuous supply of electric power. The initial concept used in nuclear power plants in Jaslovske Bohunice and Dukovany involved diesel generators for supplying the pumps of the low pressure subsystem. In the Mochovce nuclear power plant the power supply concept reckons with supplies from the own power mains in addition to diesel generators. Both concepts may under certain circumstances cause 25 to 30 secs outages of electric power to the low pressure subsystem, which increases the danger of reactor core meltdown. The suggested design combines the advantages of both concepts and excludes their disadvantages. The reactor core cooling outage is reduced to 5 to 10 secs. (Z.M.)