The PWR cooling system is provided in order to circulate the reactor coolant heated with the thermal energy generated in a reactor core and to generate high-energy steam by conducting heat exchange at a steam generator to drive a turbine, and has the following functions;
The major equipment that consists of the primary cooling system are described in the following;
(a) Reactor coolant pump
The reactor coolant pump, which is a vertical-type single-stage, circulates the coolant for heat transfer to a steam generator, and flow the coolant back into a nuclear reactor. This pump seal consists of three-seal structures to prevent coolant leakage to the outside. Moreover, a flywheel is provided in the top so as to ensure adequate coolant to a reactor core by extending the coast down of the pump even at a power loss.
(b) Steam generator
The steam generator is a vertical heat exchanger using heat transfer tubes of high-nickel alloy (Inconel), and such a structure to contain a steam-water separator and a moisture separator in the upper region. The coolant flows in from a bottom inlet nozzle, transfers heat to the heat transfer tubes, and flows out from an outlet nozzle. The feed water to the secondary side is supplied through a feed water piping, flows down between a lower shell and an internal shell, and flows upward in the heat-transfer-tube bundle after changing the direction at a tube sheet, absorbing the heat from the coolant, and a part of the water becomes steam. The mixture of rising steam and water is separated with the steam-water separator, the water circulates as feed water again, and the steam flows passes the moisture separator and flows out from a top outlet nozzle.
The pressurizer is provided with a liquid-immersion-type heater at the bottom end, and a spray, safety valves and relief valves in the upper region, and during normal operation, the inside of pressurizer is liquid in the lower one-half and steam in the upper one-half. The pressurizer and the high-temperature leg of the primary cooling system are connected with a surge pipe, which absorbs a pressure surge of the primary cooling system due to load fluctuation. Namely, when pressure of the reactor coolant system rises, the pressurizer pressure is lowered by water-spray operation. And, when pressure of the reactor coolant system goes down, heating by the heater raises the pressure, and the pressurizer acts to maintain the primary-coolant pressure at a rated value.