Method of operating nuclear power plants at start-up and shutdown

Purpose: To curtail the time where the structural materials are exposed to a temperature where they are liable to undergo stress corrosion cracking by operating the reactor so that the temperature fluctuation speed of coolants within a temperature range where stress corrosion cracks are liable to occur assumes a value greater than a predetermined value. Method: The temperature of reactor water is measured at the inlet part of a recirculation pump, and the temperature of reactor water is supplied to a control rod driving mechanism. A command of extraction or insertion of control rods from a computer in which the extraction or insertion is memorized beforhand is produced as output by this signal, and the extraction or insertion of the control rods is carried out on the basis of the command. In the temperature range where the stress corrosion crackings are difficult to occur, the reactor is operated so that the temperature fluctuation speed of the coolants assumes a predetermined value, and in the temperature range where stress corrosion crackings are liable to occur, the reactor is operated so that the temperature fluctuation speed of the coolant assumes a value greater than the predetermined value. (Yoshino, Y.)