Abstract: The overflow in the secondary of a steam generator of a nuclear-reactor plant, which occurs when one or more primary tubes conducting the coolant are ruptured, is controlled. The secondary of the steam generator, which contains the water that is converted to steam, is connected through valves to the pressurizer relief tank. The level of the liquid in the shell is monitored. An alarm is sounded when the level of the liquid in the generator reaches a predetermined height alerting the operator. When the level reaches a greater height, the valves are opened and the liquid in the shell is discharged into the pressurizer relief tank. The liquid in the tank is discharged into the containment sump when a disc is ruptured. The time taken after the rupture is 30 minutes as mandated by safety regulations. If, after the liquid in the shell reaches the level at which the valves are opened, the level drops to a height at which steam may be injected into the pressurizer relief tank, the valves are automatically closed.