PWR type nuclear power plants

Purpose: To reduce the pressure at an early stage in nuclear reactor primary coolant circuits for reducing the amount of radioactive materials released upon rupture accidents of heat conduction pipes in a stream generator. Constitution: A pressure gage for measuring the secondary circuit pressure and a pressure switch are disposed to the gas phase portion on the secondary side of the steam generator in addition to a proportional control of a pressurizer spray valve to actuate the pressurizer spray valve by the signal therefrom. In the case where the heat conduction pipes of the steam generator are destructed and the condensator can not be used, the reactor primary circuit pressure is decreased but the secondary circuit pressure is increased. Then, the pressure in the secondary coolant circuit is detected by the pressure gage and the pressurizer spray valve is actuated by the signal from the pressure switch to promote the pressure reduction in the primary coolant circuit. In this way, discharging flow rate of the primary coolants containing radioactive materials can be reduced and the amount of radioactive materials released from the main steam releaf valve and the main steam safety valve to the atmospheric air can be suppressed. (Yoshino, Y.)