1. After a reactor is shutdown, a considerable amount of sensible (or stored) heat is still present in the fuel rods and heat continues to be generated by the decay of fission products and by fission caused by delayed neutrons.
2. The sensible heat and delayed fission heat are removed within about half a minute and then only the decay heat determines the cooling requirements.
3. The thermal power from this source is initially about 7% of the operating power at shutdown, then decreased to somewhat more than 6% after 1 second, to 1.3% after 1 hour and 0.4% after day.
4. The residual heat removal system also called shutdown cooling system is provided to remove the decay heat from the core to the cold shutdown temperature at controlled rate and maintains this temperature until the plant is started up again.
5. In some nuclear power plants, the residual heat removal system also serves as part of the emergency core cooling system, during the injection and recirculation phase following a Loss of Coolant Accident (LOCA)5. 在某些电厂，在LOCA后的注射和再循环阶段，停冷系统也作为应急堆芯冷却系统的一部分。
6. The residual heat removal system consists of two residual heat exchangers, two residual removal pumps and the associated piping, valves and instrumentation for operational control.
7. The inlet line to the residual heat removal system is connected to the hot leg of one of the reactor coolant loop, while the return lines are connected the cold legs of each of the reactor coolant loops.
8. The delay heat is transferred to the component cooling water circulating through the shell side of the residual heat exchangers.
9. The initial phase of reactor cooldown is accomplished by transferring heat from the reactor coolant system to the steam and power conversion system through the steam generator.
10. The second phase of cooldown starts with the residual heat removal system being placed in operation approximately four hours after reactor shutdown when the temperature and pressure of the reactor coolant system are approximately 180℃ and 2.94MPa, respectively.
11. Both residual heat removal pumps are utilized during refueling to pump borated water from the refueling water storage tank to the refueling cavity.
12. To assure reliability, the two residual heat removal pumps are connected to separate electric buses and each bus is automatically transferred to a separate emergency diesel supply.