Containment passive heat removal system (C-PHRS) removes heat from the containment in case of a LOCA and is designed to fulfil the following functions: (1) emergency isolation of service lines penetrating the containment and not pertaining to systems intended to cope with the accident; (2) condensation of the steam from the containment atmosphere; (3) retention of radioactive products released into the containment; (4) control of the iodine levels released into the containment atmosphere. The steam from the containment atmosphere condenses on the internal steel wall of the double-containment being cooled from the outside surface by the water stored in the tank.

The system operates due to natural circulation of the containment atmosphere and water storage tank. The design basis of this system is to condense the amount of steam equivalent to decay heat release within 24 hours after reactor trip without water storage tank replenishment. This system does not require electric power supply to operate. The system consists of four independent trains with the redundancy of 4 x 33%. A diagram of the passive heat removal system is shown in Figure XII-2.

FIG. XII-2. Passive heat removal system for LOCAs (1 — cooler of primary containment; 2 — discharge pipeline; 3 — emergency heat removal tank; 4 — make-up pipeline).