ASN gives final opinion on Flamanville EPR vessel

The mechanical properties of the vessel head and bottom head of the Flamanville 3 EPR reactor pressure vessel are adequate and are therefore serviceable, the French nuclear regulator has concluded. However, the Autorité de Sûreté Nucléaire (ASN) still requires the vessel head to be replaced by the end of 2024.

The mechanical properties of the vessel head and bottom head of the Flamanville 3 EPR reactor pressure vessel are adequate and are therefore serviceable, the French nuclear regulator has concluded. However, the Autorité de Sûreté Nucléaire (ASN) still requires the vessel head to be replaced by the end of 2024.

Illustration of an EPR reactor vessel head (Image: ASN)

Areva NP revealed its discovery of an anomaly in the composition of the steel in certain zones of the reactor pressure vessel's (RPV's) closure head and bottom head of the Flamanville EPR in April 2015. The engineering group initiated a test program to demonstrate that the mechanical strength of the steel is sufficient in all operating situations, including accident situations. Its conclusions were sent to ASN in December 2016.

On 29 June, ASN said it had provisionally ruled the unit can start up safely, at the end of 2018 as planned, but that the reactor pressure vessel head would need to be replaced once a new one has been produced.

It made its draft opinion on the anomaly in the steel used for the bottom head and vessel head available for public comment between 10 July and 12 September. It also made the examination report produced by ASN and France's Institute for Radiological Protection and Nuclear Safety (IRSN) available to the public, together with the opinion of its Advisory Committee for nuclear pressure equipment. The consultation attracted more than 13,000 comments.

ASN issued its final opinion yesterday, saying it considers that the anomaly "is not such as to compromise the commissioning of the reactor pressure vessel, provided that specific checks are carried out during operation of the installation". However, it added, "As the feasibility of these checks cannot at present be confirmed for the vessel head, ASN considers that the current head cannot be used beyond 2024."

ASN noted the commissioning of the Flamanville EPR reactor pressure vessel will also require authorisation, "issued more specifically in the light of the results of a hydrotest on the entire main primary system".

The regulator said that, with the support of IRSN, it is also continuing its review of the Flamanville EPR reactor commissioning authorisation application, "as and when it receives the files transmitted by EDF".

ASN's approval of the start of operations at Flamanville 3 is a European Commission precondition for approving EDF's planned takeover of Areva's reactor business.

Earlier this week, EDF said it is preparing for the next stage of system performance testing at the Flamanville EPR, with a view to the fuel loading and reactor start-up at the end of the fourth quarter of 2018. Cold tests will start in the second fortnight of December, with hot tests starting in July 2018.

Construction work began in December 2007 on the 1650 MWe unit at the Flamanville site in Normandy – where two reactors have been operating since 1986 and 1987. The dome of the reactor building was put in place in July 2013 and the reactor vessel was installed in January 2014. The reactor was originally expected to start commercial operation in 2013.

Researched and written
by World Nuclear News