EDF is a major nuclear company in France. They notified the nuclear safety regulator of France which is the Autorité de Sûreté Nucléaire (ASN) on March 3rd of a significant event related to a design anomaly on three nozzles of the main primary system of the European Pressurized Reactor (EPR) currently under construction at Flamanville. The nozzles in question were manufactured in 2011 based on a 2006 design file. ASN has asked EDF to explain how it plans to deal with this problem.
The main primary system contains that water that is used to cool the reactor core and transfer energy in the form of heat from the nuclear reaction to the steam generator. This system consists of four piping loops installed in the reactor building. Several auxiliary systems are connected to the main primary system by the nozzles that are at issue. The largest nozzles are integral forgings made during manufacture of the main pipe. The small diameter nozzles (less than six inches) are connected to the main primary system piping by a “set-in” weld to the main pipe. Three of these nozzles are affected by the reported anomaly.
In 2006, in order to make it easier to inspect the “set-in” welds on the main piper, EDF and Framatome altered the design of these three nozzles to increase the diameter of the weld. When these design changes were made, the engineers did not identify the fact that the break size to be considered in the event that this weld ruptured now exceeded the diameter dictated by safety studies.
The design anomaly was identified by EDF and Framatome in 2013 after the pipes involved had already been manufactured. In 2014, EDF decided to deal with this anomaly by extending to these welds the break preclusion approach that was applied to the primary system pipes. This approach was implemented by EDF on certain pipes of the Flamanville EPR. It consisted of reinforcing the design, manufacture and in-service monitoring requirements. This was done in order to ensure that of any breaks in this equipment would be highly improbable. They felt that this removed the need to study all the consequences of a break in the installation’s safety case.
Following anomalies detected on the welds of the main steam letdown pipes in early 2017, the ASN asked EDF to examine the conformity of the main primary systems with the “break preclusion” baseline requirements. The subsequent ASN examination of the explanations supplied by EDF regarding the nozzles, at the end of 2020, revealed that the welds of these three nozzles did not comply with all the break preclusion requirements.
Before making a position statement, the ASN has asked EDF to reveal its strategy to deal with this anomaly. The ASN also requested that EDF identify the root cause and the reason for its belated detection. The regulator asked that EDF take corrective measures, especially to ensure that there are no other anomalies on the main primary system.
Framatome is supporting EDF. They said that they have launched a review aimed at determining the exact cause of the event. In order to propose an adequate repair plan, they also began reassessing the characteristics of the nozzles compared with the reference study.
In March of 2018, a quality deviation of the main secondary system was detected. This system conducts steam from the steam generator to the steam turbines. More deviations in secondary system welds were subsequently detected.
In June of 2019, the ASN requested that EDF repair eight containment penetration welds in the Flamanville EPR in which quality deviations had been discovered. There problematic welds are located in difficult-to-access areas of the reactor. In October of 2019, EDF adjusted the schedule and estimated cost of constructing the Flamanville EPR. The ASN said that, assuming that it approved its preferred option for repairing the welds using robots, the loading of fuel into the EPR would be further delayed until the end of 2022. The estimated cost of building Flamanville 3 would increase to about fourteen billion dollars up from an earlier estimate of about thirteen billion dollars. Construction began in December of 2007 on the one thousand six-hundred-and-fifty megawatt unit at the Flamanville site in Normandy. The EPR reactor was expected to begin commercial operation in 2013.