Regulator approves Fessenheim 2 steam generator

13 March 2018

France's nuclear regulator has lifted the suspension of the serviceability certificate for one of the three steam generators installed at unit 2 of EDF's Fessenheim nuclear power plant. The certificate was suspended in July 2016 due to anomalies in the steel of the steam generator's lower shell.

Fessenheim - 460 (ASN)
Fessenheim (Image: ASN)

The steam generator components were forged at Areva's Le Creusot facility in 2008 and the Autorité de Sûreté Nucléaire (ASN) certified the component's conformity to safety standards in 2012.

In June 2016, EDF informed the ASN that parts of some steam generators at 18 nuclear power units - of both 900 MWe and 1450 MWe capacity - in France may have anomalies similar to those found in the steel of Flamanville EPR vessel.

EDF took Fessenheim 2 offline in June 2016 for a scheduled maintenance outage and two days later sent an initial analysis of anomalies detected in the steel of the component's lower shell to ASN. The deviation concerned the cropping rate of the steel ingot used to manufacture the shell.

The regulator announced the following month that it had suspended the test certificate for one of the Fessenheim 2 steam generators as its forging "had not been conducted in accordance with the technical dossier" submitted to it by Areva. These test certificates - issued following multiple inspections and hydraulic testing - are required for commissioning, ASN noted.

Framatome said yesterday that technical analyses conducted since 2016 have concluded that the deviation detected did not compromise the integrity of the component in operation. It added, "However, in order to substantiate matters, two shells with identical characteristics (steel grade, ingot weight, dimensions of the part) were cast and forged at Le Creusot site." Chemical analyses and mechanical tests were then carried out on those parts.

On the basis of its analyses, and in coordination with EDF, Framatome compiled a file which it submitted to ASN. This file was analysed by the ASN and the Institute for Radiological Protection and Nuclear Safety. It was also examined by a group of experts on 27 February this year. On 9 March, the ASN published its decision confirming the lifting of the suspension of the certificate for the steam generator.

ASN said it considered the manufacturing anomaly "does not call into question its aptitude for service and that the justification for its compliance with the regulations has been made". It noted that the mechanical properties of the material comply with the assumptions initially adopted in the design studies.

Researched and written
by World Nuclear News