Regulator asks EDF to extend Flamanville weld checks

EDF should consider extending checks on welds in the main secondary system of the EPR reactor under construction at Flamanville to other systems, the French nuclear safety regulator has said. Welding flaws were not detected during the manufacturing checks performed by subcontractors of Framatome but were identified during pre-service inspections by EDF prior to commissioning.

EDF should consider extending checks on welds in the main secondary system of the EPR reactor under construction at Flamanville to other systems, the French nuclear safety regulator has said. Welding flaws were not detected during the manufacturing checks performed by subcontractors of Framatome but were identified during pre-service inspections by EDF prior to commissioning.

The Flamanville EPR (Image: EDF)

The French utility announced on 10 April that the first quality deviation in the welding of the main secondary system was detected on 21 March during the initial comprehensive inspection. This inspection includes an examination of the welds in the primary and secondary systems - mainly using ultrasound and radiography - and allows an initial reference state of the plant to be established before it begins operating.

In a pressurised water reactor, steam generators transfer reactor core heat from the primary coolant loop into a secondary loop where it can be used to generate electricity. The secondary loop is a closed system in which steam produced in the steam generator is conducted towards the turbine. Once condensed, the water is returned to the steam generator.

The inspections identified around 150 welds in the secondary circuit that may not meet the required standards. EDF will carry out additional checks on those in order to identify exactly which ones are subject to quality deviations. It has also ordered a report into the causes and nature of the deviations, in order to define the necessary corrective actions and methods to be proposed to the French nuclear safety regulator, the Autorité de Sûreté Nucléaire (ASN), so as to meet safety requirements. EDF said it expects to complete the checks and the report by the end of May.

ASN said it carried out an inspection on the Flamanville EPR construction site on 10 April to examine how the welds on the main secondary systems were checked. "The inspection revealed that the organisation and working conditions during the manufacturing completion checks were on the whole prejudicial to the quality of the checks," according to ASN. "Inappropriate surveillance of this work by EDF and Framatome also failed to identify and remedy the difficulties being experienced by the operators."

The procedures proposed by EDF for carrying out the new checks are "appropriate", ASN said. However, it "considers that EDF should propose that these checks be extended to other systems". The regulator said it will issue a position statement on the corrective measures proposed by EDF, "notably in light of the results of the checks which will be sent to it next month".

The main steam letdown pipes - part of the main secondary system which direct the steam from the steam generator towards the turbine - is already subject to a deviation with respect to the correct application of "high-quality" requirements, EDF noted. This deviation was notified to ASN on 22 February and is also subject to the overall inspections initiated by EDF.

"Following the current checks and the licensing process by ASN, EDF will be able to specify whether the project requires an adjustment to its timetable and its costs," EDF said.

Construction work began in December 2007 on the 1650 MWe unit at the Flamanville site in Normandy - where two reactors have been operating since 1986 and 1987. The dome of the reactor building was put in place in July 2013 and the reactor vessel was installed in January 2014. The reactor was originally expected to start commercial operation in 2013, but owing to delays this is now expected late this year.

EDF's roadmap for the Flamanville 3 project, drawn up in September 2015, sees fuel loading and start-up of the reactor at the end of the fourth quarter of 2018. It also sets the project cost at EUR10.5 billion (at the 2015 rate, excluding interim interest).

Researched and written
by World Nuclear News