Steam generator anomalies to extend Fessenheim 2 outage

A serviceability certificate for one of the three steam generators installed at unit 2 of the Fessenheim nuclear power plant, currently offline for maintenance, has been suspended by the French nuclear safety regulator. A number of anomalies were discovered last month in the steel of the component's lower shell.

A serviceability certificate for one of the three steam generators installed at unit 2 of the Fessenheim nuclear power plant, currently offline for maintenance, has been suspended by the French nuclear safety regulator. A number of anomalies were discovered last month in the steel of the component's lower shell.

The two-unit Fessenheim plant (Image: EDF)

Last month, EDF informed the ASN that parts of some steam generators at 18 nuclear power units in France may have anomalies similar to those found in the steel of Flamanville EPR vessel. At Fessenheim 2 this includes the steam generator's lower shells. Steam generators are heat exchangers between the water circulating in the primary circuit - at a temperature of about 350°C and a pressure of 155 bar - and the water in the secondary circuit that supplies steam to the turbines. There are three steam generators in 900 MWe pressurized water reactors, while the larger ones feature four.  

Outages impact production target

EDF yesterday revised its nuclear electricity generation target for 2016 to reflect expected extended outages at some of its plants.

The utility said output last month totalled 28.6 TWh, down 2.1 TWh compared with June 2015. Total output over the first half of 2016 was 205.2 TWh, 5.2 TWh less than in the first half of 2015.

EDF said it needs to demonstrate in the second half this year that "some components, mainly steam generators ... can operate in a fully safe mode". It added, "Taking into account ASN's examination schedule, extensions of part of the outages are expected over the second half of 2016".

As a result, EDF has revised its 2016 nuclear output target down from 408-412 TWh to 395-400 TWh.

An analysis in May of the internal production record for the component "established a divergence from the nuclear pressure equipment manufacturing standards", Areva said. They were forged at Areva's Le Creusot facility in 2008 and the ASN certified the component's conformity to safety standards in 2012.

EDF took Fessenheim 2 offline on 13 June for a scheduled maintenance outage and two days later sent an initial analysis of the detected anomalies to ASN which announced yesterday that it has 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. The regulator added that, had it been aware of this non-compliance, it would not have originally issued the certificate.

ASN has requested Areva submit a file detailing the approach it intends to take in order to demonstrate the steam generator meets regulatory standards.

Areva said the ASN took the decision to suspend the certificate "as a precautionary measure". The company said the technical analyses conducted by its own workers have so far concluded "the irregular findings are not detrimental to operational safety". It added that a similar part has just been cast and forged at Le Creusot to validate its mechanical and chemical properties.

Areva said it is "continuing its analysis in order to specify appropriate measures to secure the lifting of this suspension". Until that time, however, Fessenheim 2 must remain offline.

Researched and written
by World Nuclear News