French nuclear regulator Autorité de Sûreté Nucléaire (ASN) has accepted "in principle" Areva’s proposed methodology to demonstrate the strength of the reactor pressure vessel (RPV) of the EPR under construction unit 3 of the Flamanville nuclear power plant, and says a new mechanical and chemical testing programme proposed by Areva can go ahead.

In May, Areva sent ASN a proposed methodology, including additional tests, to justify the acceptability of the mechanical properties of the RPV top and bottom heads. ASN said Areva’s approach will build on the results of the new testing programme.

The results of the programme will be "an essential element" in ASN’s decision-making on the serviceability of the Flamanville 3 RPV top and bottom heads. ASN did not say when the test programme would begin, but said it would run over several months.

In April, ASN, Areva and Electricité de France (EDF) revealed that chemical tests had shown higher than average carbon content in the RPV, indicating a manufacturing flaw and potentially affecting the vessel’s ability to withstand the propagation of cracks. Areva has said independent experts will carry out an external review of Areva’s Creusot forge plant in France, which manufactured the RPV top and bottom heads for Flamanville 3. ASN said it has based its decision on the opinion and recommendations from the Permanent Expert Group for nuclear pressure vessels (GP ESPN).

On 15 December, Areva had outlined a major plan designed to "reinforce quality culture" at the Creusot Forge. This followed an external review of the plant after the anomalies were identified in the Flamanville 3 RPV steel. Areva said the "details and timeline" of the plan will be fixed before the end of 2015 and presented to ASN in January. British-French firm Lloyd’s Register Apave Limited was called in by Areva to conduct the external review last May. Areva said then that the review would focus on forging and inspections.

Areva said its plan "takes into account" the Lloyd’s Register review and also "responds to questions raised by findings reported since then. One concerned the tensile testing performed at Le Creusot’s laboratory and another related to welding defects on the thermal barriers of the reactor coolant pumps manufactured at the company’s Jeumont facility".

Latest findings "have been characterised, their consequences have been studied" and those findings concerning French nuclear plants operated by the country’s EDF Group have been provided to the ASN by Areva and EDF, Areva said. The "guiding principles" of Areva’s plan include creating a group of technical experts tasked with continuing to characterise and manage "any possible quality deviations that could be found at Le Creusot and Jeumont and then, in collaboration with its customers, to evaluate the consequences for the acceptability of the equipment manufactured".

Areva said: "In order to ensure an exhaustive quality review of Le Creusot and to understand all origins of these dysfunctions, Areva will mobilise both its internal audit organisation as well as independent experts. The company will include its other equipment manufacturing sites, Saint-Marcel and Jeumont, in this quality review."