The French nuclear safety authority has requested five of EDF's nuclear power units are taken offline for additional inspections on their steam generators within the next three months. The steel in parts of those components has been found to contain high concentrations of carbon.
The upper and bottom heads of the reactor pressure vessel for the EPR under construction at Flamanville 3 were manufactured at Areva's Le Creusot facility in September 2006 and January 2007, respectively. A high carbon content in those parts prompted Areva to review the company's quality management process in 2015 for some 400 heavy steel components made at the Creusot Forge plant since 1965.
|Steam generator channel head (Image: ASN)
The French regulator, the Autorité de Sûreté Nucléaire (ASN), subsequently requested Areva and EDF conduct an analysis to identify any other components in operating nuclear power reactors that could be affected by a similar anomaly to that of the Flamanville EPR vessel. The regulator also asked EDF to justify the mechanical resistance of the steam generator bottom heads that had been manufactured by Areva's Creusot Forge facility or by Japan Casting and Forging Corporation (JCFC).
In June, the ASN said it had identified 18 French nuclear power reactors operated by EDF - of both 900 MWe and 1450 MWe capacity - whose steam generators could contain high carbon concentrations. Of these, 12 are equipped with channel heads manufactured by JCFC "liable to contain a particularly high carbon concentration".
ASN said EDF has provided it with data aimed at demonstrating the operating safety of the 12 reactors concerned. However, the regulator called for additional inspections to be carried out to verify whether each of the channel heads concerned conforms with the data submitted by EDF.
These inspections, it noted, have already been conducted or are in progress during scheduled outages at seven of the 12 reactors.
ASN now requires inspections at the remaining five units - Civaux unit 1, Fessenheim unit 1, Gravelines unit 4, and Tricastin units 2 and 4 - are carried out within the next three months. It says the inspections, which can only be conducted when the reactors are offline, must be performed "without waiting for the scheduled refuelling outage of these reactors".
Steam generators are heat exchangers between the water circulating in the reactor's primary coolant 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. Their domed lower head is part of the primary circuit and therefore has an important safety role in ensuring cooling water is always available. There are three steam generators in 900 MWe pressurized water reactors, while 1450 MWe reactors feature four.
Researched and written
by World Nuclear News