1. Engineered safety features (ESFs) are installed in the nuclear power plant to mitigate the consequences in the accidents.
2. The ESFs include such systems as emergency core cooling system, containment heat removal system (e.g., containment spray system), containment combustible gas control system, auxiliary feedwater system, component cooling water system and emergency power system.
3. The emergency core cooling system (ECCS) is designed to cool the reactor core and provide additional shutdown capability following loss of coolant accident (LOCA), steam generator tube rupture, or main steam line break.
4. The ECCS is divided into several subsystems consisting of both passive systems and active systems.
5. The passive systems consist of large volume tanks (accumulators) which are filled with borated water and pressurized with nitrogen gas.
6. The active systems consist of several pumping systems of varying discharge pressure and flow rates, e.g., high head injection system, low head injection system.
7. In order to meet the single failure criterion, it is necessary that each active component be duplicated.
8. All active components are actuated by an engineered safety system actuation signal (also known as safety injection signal).
9. All active systems use the refueling water storage tank as a source of water following the loss of coolant accident.
10. The operation of the emergency core cooling system following a loss of coolant accident can be divided into three modes: injection mode, cold leg recirculation and hot leg recirculation.
11. Cold leg recirculation mode will provide long term cooling for the core and hot leg recirculation mode will be used alternately provide reverse flow to the core.
12.The emergency core cooling system must meet the acceptance criteria, e.g., peak cladding temperature remains less than 1204℃.