At the beginning of December 2016 the Swiss Federal Nuclear Safety Inspectorate (ENSI) requested the inspection of the steam generators at the Gösgen and Beznau nuclear power plants. Georg Schwarz, ENSI Deputy Director and head of the NPPs Division, explains the background and context in the following interview.
Last summer, the operators of Swiss nuclear power plants were obliged to examine the production documents of forged steel components within their plants in respect of possible falsifications. Now, ENSI has requested that the Beznau and Gösgen nuclear power plants inspect the components in their steam generators for elevated carbon values and possible effects on material toughness. For this purpose, the production documents must first be examined again. Is there a connection between these two issues?
Georg Schwarz: No. These are two different topics which must not be confused.
Could you explain that in more detail?
Concerning falsifications, we were able to issue an all-clear already in last August. All plants in Switzerland which have (or had) components in service from the Le Creusot forge in France, were able to confirm that the corresponding production documents did not contain any indication of falsifications.
In parallel, but independent of the falsification issue, information became available from France about potential material problems in the steam generators of pressurised water reactors. In a series of reactors, the forged steel components of the steam generators showed elevated carbon content. On 18 October 2016, the French nuclear supervisory authority ASN therefore instructed the operator of the French nuclear power plants, EDF, to subject the steam generators of twelve nuclear power plants to more detailed investigation and to demonstrate that they have the necessary material toughness in spite of the elevated carbon content. This, in turn, prompted ENSI to call for the inspection of the steam generators of the Swiss nuclear power plants Beznau and Gösgen.
And what about the other two nuclear power plants in Switzerland?
What does examination of the documents involve?
The examination of the production documents is a first step and serves as basis for the inspections of the steam generators themselves. In this case, however, it is not a search for potential falsifications, but rather for basic information on the material quality of the steam generators.
Is it still possible to trust these documents?
Yes. The investigations in summer revealed no indication of any falsifications.
In the inspections of the steam generators at Beznau and Gösgen requested by ENSI, the results of the corresponding investigations in France will probably also be considered. What is the current status in France?
In France, the investigations are largely completed and it has been demonstrated that the steam generators with an elevated carbon content are strong enough and do not pose a risk. The reactors which were disconnected from the grid for the investigations have either been reconnected to the grid by now, or will again be delivering power from January 2017. (For details see the chronology below).
In France, the plants had to be disconnected from the grid for the investigations. Why is this not necessary for Beznau and Gösgen?
In France, the nuclear power plants were not shut down immediately, either. In Switzerland we do not see any reason, from a safety point of view, to temporarily disconnect the plants concerned from the grid. The inspections on the steam generators can be performed during a routine maintenance outage.
Can you explain why in more detail?
The first checks in France in the past summer revealed that steam generators in 18 of the 58 French reactors require more detailed investigations. For 6 reactors these investigations could be completed fairly quickly so that by autumn 2016 only 12 reactors remained. ASN set a deadline of three months for the French NPP operator EDF to carry out the required measurements and calculations on the steam generators in the remaining reactors. To be able to perform this work, a reactor must be in shut-down mode. Seven of the reactors concerned were already in routine maintenance outage and they therefore decided to postpone their restart, five reactors initially continued operations. In the course of 2016, three were disconnected from the grid in order to perform the required measurements. The last two will be disconnected in January 2017.
In light of the developments in France, why is there any point in Beznau and Gösgen actually performing the investigations?
The steam generator is an important component of the primary circuit. From a safety point of view, it is appropriate to assess both the situation in the Swiss reactors and to what extent the results in France agree with the corresponding findings in the steam generators in the Swiss plants.
What precisely do the Beznau and Gösgen nuclear power plants have to check?
As stated, a first step will involve examining the production documents. This will result in information on affected components, manufacturer, manufacturing period, material, applied design specification and regulations, deviations during manufacture, details of the forging process, acceptance tests carried out, and test requirements. Based on these documents, a second step involves the derivation of a concept for the further safety assessment.
What result do you expect from the first step, the examination of the documents?
The aim of the in-depth examination of the production documents is to obtain fairly quickly a first overview of the manufacturing of the steam generators. This will result in first insights, based on which further steps can be decided upon.
When will the second step containing the non-destructive testing be performed?
This depends on the concepts. Potential inspections on the steam generators themselves will be performed during the regular maintenance outages of the nuclear power plants.
Is this inspection of the steam generators in any way related to the findings in the reactor pressure vessels, which were uncovered in the Belgian plants Doel 2 and Tihange 3 in 2013 and during 2015 in Beznau 1?
No. The findings in the reactor pressure vessels have nothing to do with the inspections of the steam generators. As already stated above, the trigger for the inspection of the steam generators was information from France stating that the steel of the steam generators potentially contains an elevated carbon content in certain areas.
Reactor pressure vessels and steam generators are different components.
Reactor pressure vessel
The fuel rods are contained in the reactor pressure vessel. The heat generated by the chain reaction is used to heat up the coolant.
In pressurised water reactors, steam production takes place in the steam generator, where the hot water of the primary circuit transfers heat energy to the secondary circuit.
Does this mean that the investigations concerning the steam generator will have no influence on the decision of whether Beznau 1, upon completion of the investigations into the reactor pressure vessel findings, can start up again?
Precisely, they have no influence at all.
From the reactor vessel closure head in Flamanville to the steam generators in Switzerland: a chronology
On the basis of findings in the French Flamanville nuclear power plant, various investigations have been triggered in France and Switzerland. These concern falsifications in the production documents from the Le Creusot forge, on one hand, and the material properties of the steam generators on the other hand.
|Topic “Findings in the Flamanville reactor pressure vessel”|
|On 7 April 2015, the French nuclear supervisory authority ASN informed the public that zones of elevated carbon content had been identified in the reactor vessel closure head and reactor vessel bottom of the French Flamanville 3 nuclear power plant, which is currently under construction.|
|Topic “Falsifications in the Le Creusot forge”||Topic “Carbon content in steam generator components”|
|2015||On 4 August 2015, ASN President Pierre-Franck Chevet wrote in an open letter that AREVA had decided to arrange an investigation into the production practices at the Le Creusot forge over the past few years by an independent body. These investigations were started in April 2015 at the instigation of the ASN.|
|2016||On 19 January 2016, the ASN made it known that within the context of a hearing on 8 December 2015 it had informed AREVA of the requirements for the investigation. According to these, the investigation had not only to extend back until 2010, but until at least 2004 because it was in this year that the first parts were forged for the Flamanville EPR.
The ASN first informed the public of the results of the investigation on 3 May 2016. It was established that there were irregularities in the production documents for 400 components manufactured at Le Creusot since 1965. These included both inconsistencies between the documents and production or inspection data as well as falsifications (changing of measurement and acceptance reports). Of the relevant 400 components, around 50 are in use in French nuclear power plants.
On 6 June 2016, ENSI required the Swiss nuclear power plants to gather information about whether components originating from the Le Creusot forge with potentially incorrect production documents were or are currently in use.
On 16 June 2016, the ASN could for the first time list those nuclear power plants in France where components of the primary circuit are affected by irregularities in the material properties. To perform additional examinations, the operator EDF took the reactor Fessenheim 2 offline in the middle of June 2016.
On 19 July 2016, the ASN informed the public that the authorisation for a steam generator of the Fessenheim 2 NPP had been suspended. It cited falsifications in the production documents as the reason. The steam generator vessel bottom produced in 2008 does not conform to the dossier that had been submitted to the ASN and was not forged in accordance with the applicable rules.
On 17 August 2016, ENSI informed the public that all plants in Switzerland which had or have components in use originating from the Le Creusot forge, could confirm that these components are not affected by any falsifications in production documents.
On 23 September 2016, the ASN for the first time published a list of the irregularities and falsifications uncovered in the production documents. At the same time, the French supervisory authority made it known that in 21 of the 23 cases uncovered, safety was not affected. Further investigations were announced in two cases, namely Gravelines 5 and Fessenheim 2 which are currently shut down.
|On 23 June 2016, the ASN informed the public for the first time that the vessel bottoms of steam generators could have zones with elevated carbon content. Under consideration were 18 reactors, 16 reactors with 900 MWe output and 2 with 1450 MWe output. Amongst the unaffected reactors were 18 reactors of 900 MWe, 2 reactors of 1450 MWe and all 20 reactors with a 1300 MWe output. The supervisory authority required the operator EDF to examine the steam generators from the Le Creusot forge and the Japanese JCFC forge using both non-destructive testing in respect of carbon concentration and using ultrasonic crack testing.
On 18 October 2016, the ASN ordered more detailed inspections of the steam generators in respect of the material carbon content in 12 reactors. Seven of the affected reactors were at that time already shut down for routine maintenance outage. Five other nuclear power plants received a deadline of three months.
On 26 October 2016, the ASN announced that within the context of a parliamentary hearing it had provided information that in the steam generators of 12 reactors, which had been manufactured by JCFC, the carbon content elevated.
On 5 December 2016, ASN announced that the documents requested from the operator EDF had been accepted in general. Furthermore, it requested reports for compensatory measures and other medium-term tests. It requested additional calculations for four plants. As soon as these are assessed by ASN, the ten 900 MWe nuclear power plants can start up again. According to ASN, EDF announced that the documents for the two 1450 MWe plants will be submitted soon.
On 9 December 2016, ENSI required that the pressurised water reactors in Switzerland, Beznau and Gösgen, examine their steam generators in a two-stage process.
According to Réseau de Transport d’Electricité RTE (dated 3 January 2017), 4 of 12 reactors subject to more in-depth investigation have been restarted until the end of 2016. 8 further reactors are planning to start up in January 2017.