A passive residual heat removal system (see Figure XIII-3) is included in the design to remove heat from the reactor plant. The PHRS is designed in case of a station blackout including the loss of emergency power supply. The removal of residual heat should be provided without damage to the reactor core and the primary system boundary for an unlimited time. The PHRS consists of four independent trains, each of them being connected to the respective loop of the reactor plant via the secondary side of the steam generator. Each train has pipelines for steam supply and removal of condensate, valves, and an air-cooled heat exchanger outside the containment. The steam that is generated in the steam generators due to the heat released in the reactor; condenses and rejects its heat to the ambient air. The condensate is returned back to the steam generator. This occurs by natural circulation.

FIG. XIII-3. Principal diagram of PHRS.