Photo: Dr. Georg Schwarz
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.
But?
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?
Leibstadt and Mühleberg are boiling water reactors. They do not have steam generators and are therefore unaffected of this issue.
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.
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.