Nuclear reactor

Purpose: To prevent cyclic thermal fatigue from being applied to a core structure by preventing variations in the power of the nuclear reactor due to a void effect occurring due to variations in the pressure of the reactor when closing a nuclear reactor isolation valve. Constitution: An escape tube is connected through a flow rate control valve capable of continuously controlling the opening to a main steam tube upstream of a reactor isolation valve, and a pressure detector is inserted into the pressure vessel. When the isolation valve is closed, the pressure vessel is maintained at predetermined pressure according to the output of the pressure detector to control the opening of the main flow rate control valve. An escape tube is connected through another pressure relief valve to the buffer valve, and when the pressure in the reactor cannot be maintained by the flow control valve alone, the pressure relief valve is operated to discharge the steam in the reactor into the pool water, thereby maintaining the pressure substantially constant. (Sekiya, K.)