Certain EDF reactor steam generators in service could contain an anomaly similar to that affecting the Flamanville EPR vessel

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The analyses carried out by EDF since 2015 conclude that certain steam generator channel heads could contain a zone comprising a high carbon concentration which could lead to lower than expected mechanical properties. These steam generators equip 18 reactors of the 900 and 1450 MWe plant series.

These analyses were performed at the request of ASN to identify the equipment of the reactors in service which could be affected by an anomaly similar to that in the Flamanville EPR vessel.

ASN asked EDF to demonstrate the mechanical strength these channel heads, which were manufactured by Creusot Forge and by a foundry in Japan (JCFC). ASN considers that the initial demonstration data provided, on the basis of which EDF kept the equipment concerned in service, need to be confirmed. It therefore asked EDF to carry out additional investigations on the channel heads concerned.

These steam generator channel heads are hemispherical forged parts constituting the lower part of the steam generators. They contribute to containment of the primary system water¹. These components are essential for safety. The quality of their design, manufacture and in-service monitoring is therefore extremely important.

Furthermore, analyses of the other forged components making up the vessel, the pressuriser and the steam generators and liable also to be concerned by this anomaly are ongoing. ASN will make sure that they contribute to complete experience feedback from the anomaly detected on the Flamanville EPR vessel and that all possible consequences for the safety of the installations are identified.

These elements will be presented at the 24th June 2016 meeting of the Advisory Committee for nuclear pressure equipment. Representatives from the OPECST, HCTISN and ANCCLI have been invited to attend as observers.