Background to the discovery of the anomaly affecting the Flamanville EPR reactor vessel (excessively high carbon content in the vessel closure head and vessel bottom head)

On 7th April 2015, ASN made public the discovery of an anomaly in the composition of the steel in certain zones of the vessel closure head and the vessel bottom head of the Flamanville EPR reactor.

The new regulations of 2005 relative to nuclear pressure equipment provide for the qualification of the manufacturing processes, not only by performing tests on the most sensitive zones (zones subject to the greatest mechanical stresses or weld zones), but also by performing tests on standard zones of pressure equipment.

Consequently, in July 2007 ASN reminded AREVA of the need to perform complementary tests on standard zones of the equipment intended for the Flamanville EPR.

AREVA sent the first file concerning the reactor vessel closure head and bottom head to ASN in 2008. A new file was sent in 2010 following discussions with ASN. These files mentioned some results of extremely partial tests aiming at identifying the orientation of the parts in blank condition, tests which were in no way able to demonstrate the quality of the standard zones of the vessel.

In March 2011 ASN therefore confirmed its requirement for complementary tests to be performed.

In 2012 AREVA proposed the corresponding test programme, and at the end of 2014 sent its first results to ASN, which has started analysing them.