The French nuclear safety authority has accepted analyses submitted by EDF on the serviceability of ten of its 900 MWe reactors in which some steam generator parts were found to contain high concentrations of carbon. The utility will soon submit analyses for two 1450 MWe units.
In June, the French regulator, the Autorité de Sûreté Nucléaire (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 Japan Casting and Forging Corporation (JCFC) "liable to contain a particularly high carbon concentration". A high carbon content in steel can lead to mechanical properties lower than expected.
EDF has since provided ASN 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 to the data submitted by EDF. These inspections have already been conducted or are in progress during scheduled outages.
The data submitted by EDF has since been examined by ASN and France's Institute for Radiological Protection and Nuclear Safety (IRSN), who verified that the hypotheses and method used were acceptable. However, the ASN said the hypotheses of the EDF data will need to be confirmed by a test program on representative scale replicas of the components.
ASN has now sent EDF requests concerning "the additional inspections required, the compensatory operational measures to be implemented or reinforced and the additional tests or studies to be performed in the medium term".
ASN said yesterday, "Provided that its requests are taken into account, the generic demonstrations provided by EDF are acceptable for the 900 MWe reactors and can be used on each of the reactors concerned with a view to ASN authorizing their restart."
"Each reactor restart remains subject to the approval of ASN on the basis of a specific safety file," ASN said.
It added, "EDF informed ASN that it will shortly be sending its additional data regarding the 1450 MWe 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.
Last month, Japan's Nuclear Regulation Authority concluded that domestically produced nuclear power plant components are sufficiently strong for their intended purpose.
Researched and written
by World Nuclear News