An adjustment and control method for atmospheric dump valves in nuclear power plants comprises setting a pressure setpoint value for the atmospheric dump valves of a steam turbine bypass system, adjusting an opening of the atmospheric dump valves by use of a difference between outlet pressure of a steam generator and the pressure setpoint (i.e. threshold) value of the atmospheric dump valves of the steam turbine bypass system; in this way, steam in a secondary system is discharged thereby reducing the excess pressure of the secondary system to achieve the pressure setpoint value of the atmospheric dump valves. The setpoint value can be set using computer programs or manually. In case of a breaking accident of heat transfer tubes of the steam generator, the atmospheric dump valves enable cooling to be triggered automatically. In this way, no operator intervention is required and the temperature of the steam generator is reduced at required rate so as to reduce the pressure and temperature of the reactor coolant loop, thus mitigating the safety risks to the reactor due to operator mis-operation following an accident.