On February 4th 2004, November 7th 2005 and February 11th 2006, three primary-to-secondary leaks occurred at the Cruas Units 1&4 Nuclear Plants located in France. The leaks were due to circumferential cracks in steam generator (SG) tubes at the level of the 8th tube support plate (TSP). The origin of cracking was determined to be high cycle fatigue as a result of flow-induced vibration. The tubes had become susceptible to vibration and fatigue as a result of the buildup of deposits on the secondary side of the steam generator. This locally increased the flow velocities. This study details the main results of the safety analysis carried out by IRSN which includes an evaluation of TSP hole blockage by corrosion products, the thermal-hydraulic calculations used to check the water mass inventory, the water oscillation parameters and the mechanical analysis of the SG tubes and internals. This paper also describes the actions taken to remove the deposits by chemical cleaning and planned improvements to the chemistry conditions on the secondary-side.
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