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According to the US NRC:
“The steam generator is an integral part of the reactor coolant pressure boundary, and its integrity is important to the safe operation of the plant.” http://www.nrc.gov/docs/ML1320/ML13204A143.pdf
Today ASN, the French nuclear regulator, has stated that “analyses performed by EDF at ASN’s request since 2015 conclude that certain channel heads of the steam generators manufactured by Areva Creusot Forge or JCFC” [ Japan Casting and Forging Corporation] “contain a significant carbon concentration zone which could lead to lower than expected mechanical properties.” In other words, they are more likely to fail and could lead to a serious nuclear accident. An earlier ASN notice states that “in particular its resistance to crack propagation, are lower than anticipated.” See the earlier statement and more here: https://miningawareness.wordpress.com/2016/07/01/asn-possible-defects-in-areva-creusot-steam-generator-channel-heads-may-impact-countries-in-both-hemisperes-including-the-usa-us-nrc-snoozes
Today’s ASN press release continues: “These steam generators equip 18 reactors of the 900 and 1450 MWe plant series. Of these reactors, 12 are equipped with channel heads manufactured by JCFC liable to contain a particularly high carbon concentration.” (This seems to be within France only. There are probable problems worldwide, as reported in the summer. See entire press release below. Note that the English translation appeared today, but the original French appeared yesterday.)
Three years ago, in October of 2013:
“The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform addressees of instances of steam generator channel head and tubesheet degradation. Although the operating experience discussed is related to steam generators, the findings may relate to other structures, systems, and components.
[…] The steam generator channel head is typically made of carbon or low-alloy steel base material and is clad on the interior surface with a corrosion-resistant material such as stainless steel to protect the channel head’s base material…” http://www.nrc.gov/docs/ML1320/ML13204A143.pdf
Today’s Press Release from the French Nuclear Regulator [Inter-bracket comments by MA]:
“ASN requires that inspections be carried out within the next three months on the steam generators of five EDF reactors in which the steel contains a high carbon concentration 19/10/2016 10:31 am Communiqué de presse
ASN has asked EDF to carry out additional inspections within three months on certain channel heads of the steam generators  on 5 of its reactors, in which the steel is affected by a high carbon concentration. The performance of these inspections will require shutdown of the reactors concerned.” [Will the shutdown be immediate? What if something happens in the interim? Is that why France is about to run through a law making high level exposure to radiation acceptable during and a nuclear accident, starting next year? There was only one month to comment and most missed it. Where would nuclear accident refugees go? To Syria? Or perhaps Mosul?]
“The analyses performed by EDF at ASN’s request since 2015 conclude that certain channel heads of the steam generators manufactured by Areva Creusot Forge or JCFC  , contain a significant carbon concentration zone which could lead to lower than expected mechanical properties. These steam generators equip 18 reactors of the 900 and 1450 MWe plant series. Of these reactors, 12 are equipped with channel heads manufactured by JCFC liable to contain a particularly high carbon concentration.
EDF has provided ASN with data aiming to demonstrate the operating safety of the 12 reactors concerned.” [Notice that French state owned EDF is reportedly “aiming to demonstrate“. That suggests that they are setting out to prove what they want. It is not good science. EDF is owner-operator of the UK’s nuclear power stations too.] “Further to the analysis carried out with the support of IRSN and after technical discussions with EDF, ASN has concluded that additional inspections should be carried out within three months, without waiting for the scheduled refuelling outage of these reactors.” [While ASN still appears more serious than many regulators, waiting 3 months may not be serious enough. At least some of the Swiss towns and/or cantons will almost certainly sue France in the event of an accident – too late by then though. Basel has long complained about Fessenheim and Geneva recently filed suit about Bugey. ] “The purpose of these inspections will be to verify whether each of the channel heads concerned is in conformity with the file transmitted by EDF.
These inspections have been carried out or are in progress for 7 of the 12 reactors concerned  , on the occasion of scheduled outages. EDF has confirmed that it will carry out these inspections on the other 5 reactors within three months. ASN today issued a resolution requiring the performance of inspections on these reactors:
* Civaux NPP, reactor 1;
* Fessenheim NPP, reactor 1;
* Gravelines NPP, reactor 4;
* Tricastin NPP, reactors 2 and 4.
With the support of IRSN, ASN is also examining the substantiating data transmitted by EDF. This examination will take several weeks, or possibly longer, if additions are required to the file transmitted.
On 7th April 2015, ASN made public the discovery of an anomaly in the composition of the steel in certain zones of the vessel closure head and the vessel bottom head of the Flamanville EPR reactor. The detection of this anomaly led ASN to ask Areva NP and EDF to learn all possible lessons from this event.
Three processes are currently under way:
* on other components of the EDF reactors, the search for technical anomalies similar to that detected on the Flamanville EPR vessel. This search enabled EDF to identify similar anomalies on the channel heads of certain steam generators, which are the subject of this press release;
* manufacturing quality reviews on parts in the Areva NP manufacturing plants, which enabled Areva NP to detect irregularities in the manufacturing files from Creusot Forge;
* initiation of a review of BNI licensee monitoring of their contractors and subcontractors, of ASN oversight and of the alert mechanisms.
 A steam generator is a heat exchanger used to cool the primary system, which reaches high temperatures (320°C) in the reactor core. The channel head is a steel component with the shape of a portion of a sphere, situated at the base of the steam generator. It contributes to the containment of the water in the primary system.
 Japan Casting and Forging Corporation
 List of the 7 reactors on which inspections have been performed or are under way:
* Tricastin NPP, reactors 1 and 3
* Bugey NPP, reactor 4
* Dampierre NPP, reactor 3
* Gravelines NPP, reactor 2
* Saint-Laurent-des-Eaux NPP, reactor B1
* Civaux NPP, reactor 2”
Emphasis our own. Read original here: https://web.archive.org/web/20161019142339/http://www.french-nuclear-safety.fr/Information/News-releases/Additional-inspections-required-on-steam-generators-of-five-EDF-reactors French original and much more on the ASN dot fr web site (select English at upper right for official English translations)