Effectivity of a passive heat removal system for a new VVER reactor

This paper deals with different aspects of the functioning of the passive heat removal system (PHRS), which is proposed to transport the heat from the secondary system to the ultimate sink (in this paper to the atmosphere) in future reactors of the VVER-1000/88 concept. The PHRS consists of four subsystems, each connected to one of the four steam generators. The heat exchangers of the subsystem are installed outside the containment in separate chimneys. Steam from the steam generator is transported by means of natural circulation to the heat exchanger where it condenses. The condensate returns to the steam generator by means of gravitational forces. The potential of the PHRS to provide an essential contribution to the prevention of a severe core accident has been demonstrated; however, the costs for such a system are considerable. The existence of the PHRS with huge heat exchangers outside the containment increases the risk of a secondary leak. The benefits, costs, and disadvantages of the PHRS are being compared by Soviet organizations with those of other systems.