London — EDF's 900-MW Fessenheim-2 nuclear reactor may have to remain shut beyond the end of scheduled maintenance after French nuclear safety authority ASN said Tuesday it had suspended a certificate for one of the reactor's steam generators, in which several anomalies were discovered in June.
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"ASN has suspended the test certificate it issued to Areva NP in 2012 for a steam generator currently installed on reactor 2 of the Fessenheim nuclear power plant," ASN said.
"This suspension is consecutive to the detection of an irregularity in the manufacturing, by Areva's Creusot Forge factory, on one of the parts of this steam generator," ASN said in the statement.
ASN issues test certificates for the most important nuclear equipment, and these certificates are required for the commissioning of the equipment.
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The suspension of the test certificate, ASN said, would result in the Fessenheim-2 reactor remaining shut until Areva NP -- the reactor unit of Areva and owner of the Creusot Forge -- demonstrates the steam generators can meet the regulatory standards.
Le Creusot Forge manufactures forgings and castings for the large components of nuclear reactors.
ASN said it had asked Areva NP to send the agency details on how it intends to rectify the steam generator's problems.
Separately, Areva said Tuesday it acknowledged "ASN's decision dated July 18, 2016, taken as a precautionary measure, to suspend the test certificate on the secondary part of this component."
Areva NP said it was continuing its analysis in order to identify the appropriate measures to secure the lifting of the suspension, although previous technical analyses conducted by Areva NP experts had concluded, at this stage, the irregular findings were not detrimental to operational safety.
"However, in order to substantiate the robustness of the case, a similar part has just been cast and forged at Le Creusot plant to validate its mechanical and chemical characteristics," Areva said in the statement.
EDF shut the reactor June 13 for scheduled maintenance that was set to last until August 29 and submitted to ASN its preliminary analysis of the mechanical integrity of the generator June 15. It is not yet clear how long Areva's analysis will take.
The forging of the lower shell of the steam generator in 2008 was not conducted in accordance with the technical file submitted to ASN, the regulator said.
ASN said it had not been informed of the non-compliance of the steam generator until June 15. "Knowledge of this non-compliance would have led ASN not to issue a test certificate in 2012," the authority said.
ASN said in June that 85 irregularities in about 10,000 fabrication files from Le Creusot had been found involving components at 21 of EDF's 58 operating reactors.
The regulator also said at the time that the anomaly with the generator was due to an incomplete fabrication process, which led to a high carbon content in the lower part of the equipment.
A high carbon content can reduce fracture toughness of a material, reducing that material's ability to withstand the propagation of cracks.
--Benjamin Leveau, firstname.lastname@example.org
--Edited by Keiron Greenhalgh, email@example.com