CARBON STEEL TUBE SUPPORT PLATE DEGRADATION CONSEQUENCES ON STEAM GENERATOR TUBE BUNDLE INTEGRITY IN LOSS OF COOLANT ACCIDENT AND SEISMIC CONDITIONS

摘要

In April 1995, during its fourteenth refueling outage, degradation were found at Fessenheim 2 on the upper tube support plate (TSP) of two steam generators. As the degradations were located near an aseismic support, a safety analysis had to be performed. To evaluate corrective or preventive actions needed for affected steam generators in short or long term, studies were performed to determine the impact of considering an aseismic support as inefficient on tubes integrity in faulted conditions, which include LOCA and earthquake transient. In a second step, hypothetical larger degradations were defined to estimate safety margins available. Specific models and methods were defined. In particular, an elastoplastic modelling has been developed to precise impact of horizontal loadings on tubes integrity. Results were used to define maintenance policy to be implemented for next years.