France's Autorité de Sûreté Nucléaire (ASN) has lifted the suspension of the serviceability certificate for one of three steam generators installed at EDF's Fessenheim 2. The certificate was suspended in July 2016 after anomalies were detected in the steel of the steam generator's lower shell.
In June 2016, EDF had informed the ASN that parts of some steam generators at 18 of its 900MWe and 1450MWe nuclear power units might have anomalies similar to those found in the steel of Flamanville EPR reactor pressure vessel. EDF took Fessenheim 2 offline for scheduled maintenance and sent an 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. ASN subsequently suspended the test certificate for one of Fessenheim 2's 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 last week that technical analyses conducted since 2016 have concluded that the deviation detected did not compromise the integrity of the component but “to substantiate matters, two shells with identical characteristics (steel grade, ingot weight, dimensions of the part) were cast and forged at Le Creusot site”. These were then subjected to chemical analyses and mechanical tests the results of which were analysed by ASN and its technical arm, the Institute for Radiological Protection and Nuclear Safety, as well as by a group of experts. On 9 March, the ASN published its decision confirming the lifting of the suspension of the certificate noting that 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 said the mechanical properties of the material comply with the assumptions initially adopted in the design studies.