UPGRADING OF OPERATING NPP UNITS EQUIPPED WITH V-213 (THE CONCRETE VAULT TYPE 2) REACTORS TO ENHANCE SAFETY IN CASE OF SEVERE ACCIDENTS FOLLOWED BY REACTOR CORE AND REACTOR VESSEL DESTRUCTION

摘要

According to their functional destination thernsystems participating in managing the accidents with severerncore damage can be conventionally divided into tworngroups. Group 1 involves the systems that perform thernfunctions of reactor core cooling with the purpose ofrndecreasing the degree of core damage and limiting thernsource term. With this aim in view no special systems ofrnbeyond-design accidents managing are envisaged in therndesigns of NPPs equipped with VVER-type reactors. Thernabove functions are carried out by the systems of normalrnoperation. A number of systems and devices of beyonddesignrnaccidents managing (Group 2) is envisaged in thernprojects of NPPs equipped with VVER-type reactors withrnthe purpose to decrease the probability of protectivernbarriers system damaging. They involve: system of coriumrnretention inside reactor vessel and system of coriumrnretention inside reactor concrete pit.rnThe system of corium retention inside reactorrnvessel comprises interrelated channels that provide thernconditions of heat removal from reactor vessel due torncoolant natural circulation between the concrete pit andrnemergency pond. The system must provide retaining thernentire damaged core and all the internals inside the vessel with coolant available in the concrete pit and the minimumrnwater level in the emergency pond.rnThe system of corium retention inside reactorrnconcrete pit comprises the corium retention equipment andrncooling channels that connect the equipment and thernemergency pond. The system shall limit the generation ofrnexplosible corium-to-coolant interaction above thernspecified limits and to provide retaining the splintered fuelrnwith coolant available and no significant corium-to-pitrnconcrete interactionrnAlong with the systems and devices of beyond-designrnaccidents managing the paper covers the main approachesrnto concrete pits upgrading at the operating reactor plantsrnwith the aim to enhance the safety of NPPs equipped withrnVVER-type reactors.