14.23. PWR shutdown to either a hot-standby or cold condition is ini­tiated by unloading the turbine-generator and corresponding plant systems automatically. For a hot-standby subcritical condition, the control rods are inserted, cooling loop flow is maintained with two of the four pumps, and the residual heat removal system is placed in service. To place the plant in cold shutdown condition, numerous adjustments to plant systems are needed, including blocking the action of the safety injection systems and increasing the dissolved boron concentration.

14.24. A BWR operational shutdown is one of short duration in which the reactor remains critical at about 0.01 percent of rated power and the turbine-generator is removed from the grid. Pressure is maintained and the steam produced is bypassed to the condenser, as needed. In an isolated shutdown, the reactor is not critical but the system is maintained at pressure with the residual heat removal system activated. For cold shutdown, the pressure is slowly reduced, with the cooling rate limited to about 50°C per hour and the residual heat removal system utilized.