French regulator says Flamanville 3 is safe to start

The French nuclear regulator has provisionally ruled that EDF's Flamanville 3 can start up safely, but that the head of its reactor pressure vessel (RPV) will need to be replaced by the end of 2024. The Autorité de Sûreté Nucléaire (ASN) said yesterday the unit, which is under construction in northwest France, is fit for operation despite issues with its steel.

Areva NP revealed its discovery of an anomaly in the composition of the steel in certain zones of the 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.

Cutaway of the reactor pressure vessel and core of  Flamanville 3 (Image: ASN)

ASN said yesterday it had "presented its position" regarding the RPV anomaly. It had relied on its nuclear pressure equipment department and IRSN's "analysis of files" that Areva NP and EDF had provided, it added.

The current closure head should not be operated beyond 2024, meaning the date by which a new one could be produced, it said.

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, but due to delays is now expected to start up in late 2018.

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.

New cover

In a statement yesterday, ASN said: "On the basis of the technical analyses carried out, ASN considers that the mechanical characteristics of the pressure vessel head and bottom head are adequate with regard to the loadings to which these parts are subjected, including accident situations. However, the anomaly in the chemical composition of the steel entails a reduction in the margins with respect to the fast fracture risk. ASN therefore considers that EDF must implement additional periodic inspections to ensure that no flaws appear subsequently."

"ASN observes that such inspections can be performed on the vessel bottom head and therefore considers that they must be implemented. However, the technical feasibility of similar inspections on the pressure vessel closure head is not established. ASN therefore considers that the use of the closure head must be limited in time. It notes that it would take about seven years to manufacture a new vessel head, which could thus be available by the end of 2024. In these conditions, ASN considers that the current closure head shall not be operated beyond that date."

ASN has made the "examination report" available on its website for public consultation, along with the opinion of its advisory committee for nuclear pressure equipment.

Public consultation will continue until September. ASN will also consult the French High Council for Technological Risk Prevention. It will finalise its opinion following these consultations in October.

The commissioning of the RPV of the Flamanville EPR will also require authorisation "issued more specifically regarding the results of a hydrotest on the entire main primary system", it said.

In April, ASN defined the preconditions for the resumption of forging operations at Areva's Le Creusot forge. The facility has been out of operation since December 2015 following the discovery of quality assurance issues. In May 2016, ASN said an ongoing quality audit at the forge - which Areva bought in 2006 - had identified "irregularities" in paperwork on some 400 plant components produced there since 1965. The issues "comprise inconsistencies, modifications or omissions in the production files, concerning manufacturing parameters and test results", it said.

The new RPV cover will be forged by Japan Steel Works and not by Le Creusot forge, Reuters said yesterday, quoting an unnamed source.

Researched and written
by World Nuclear News