Single steam generator tube rupture

As with a single steam generator tube rupture, there is a discharge of radionuclides outside the containment. 

The steam generator tube rupture accident examined is the complete severance of a single steam generator tube. The accident is assumed to take place at power with the reactor coolant contaminated with fission products corresponding to continuous operation with a limited number of defective fuel rods within the allowance of the Technical Specifications (see Chapter 16 of Reference 5.6). The accident leads to an increase in contamination of the secondary system due to leakage of radioactive coolant from the reactor coolant system. In the event of a coincident loss of offsite power, or a failure of the condenser steam dump, discharge of radioactivity to the atmosphere takes place via the steam generator power-operated relief valves or the safety valves. 

For small-tube-rupture flows that simulated the flow from the single-ended rupture of up to 16 steam generator tubes in a PWR system initiated at the start of vessel refill, the core thermal response was strongly dependent on the magnitude... 

The steam generator (SG) tubes in many PWR plants of different vendors have shown several degradation phenomena during their operation, and these have weakened their function as the primary to secondary barrier. This degradation has been discovered by in-service inspection programmes and by the operational experience of many NPPs in which leaks ranging from minor leaks to complete single tube ruptures have been detected. So far no multiple tube rupture has occurred. 

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