ASN authorises commissioning and operation of the Flamanville EPR reactor pressure vessel in certain conditions

On 9^th October 2018, ASN authorised the commissioning and operation of the Flamanville EPR reactor pressure vessel, subject to the performance of a test programme to monitor the thermal ageing of the steel in the residual carbon positive macro-segregation zone, plus specific inspections during operation of the facility. As the current state of knowledge does not enable the feasibility of these inspections to be confirmed for the vessel closure head, ASN set a service life limit at end of 2024 for the existing vessel closure head.

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This authorisation is based on the conclusions of the ASN opinion of 10^th October 2017 concerning the anomaly in the chemical composition of the steel of the vessel closure and bottom heads of the Flamanville EPR reactor, as well as on the additional data transmitted by Framatome in its authorisation application of 13^th July 2018.

The examination of this additional information by ASN did not compromise the conclusions of the 2017 opinion. Moreover, ASN verified compliance with the technical and regulatory requirements other than those concerning the chemical composition of the steel in the reactor vessel closure and bottom heads.

The ASN draft resolution was opened to public consultation on its website between 3^rd and 24^th September 2018. This consultation received more than 500 contributions. The summary of this consultation is available on the ASN website.

Following this consultation of the public and that of the Standing Sub-committee for Pressure Vessels of the High Council for the Prevention of Technological Risks, ASN supplemented its resolution in order to clarify certain points underpinning the requirements of article 2 of the resolution, concerning the thermal ageing programme and the technical feasibility of the pressure vessel closure head replacement operation.

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At the end of 2014, Areva NP revealed an anomaly in the chemical composition of the steel used in the Flamanville EPR reactor pressure vessel closure and bottom heads, which could impair its ability to withstand crack propagation. Areva NP then adopted an approach to demonstrate that the mechanical strength of the steel remained sufficient in all operating situations, including accidents.

On the basis of the analysis of the files transmitted by Areva NP and EDF, with the support of IRSN, and of the opinion of its Advisory Committee for nuclear pressure equipment, ASN issued an opinion on 10^th October 2017 concerning the anomaly in the chemical composition of the steel of the Flamanville EPR reactor pressure vessel closure and bottom heads.