Quality issue detected with Flamanville EPR welds

Quality deviations have been detected on certain welds of the main secondary system in the EPR reactor under construction at Flamanville, northern France, EDF announced today. The utility has informed the French regulator of the discovery, but has yet to determine whether the unit's start-up, expected at the end of this year, will be delayed.

Quality deviations have been detected on certain welds of the main secondary system in the EPR reactor under construction at Flamanville, northern France, EDF announced today. The utility has informed the French regulator of the discovery, but has yet to determine whether the unit's start-up, expected at the end of this year, will be delayed.

The Flamanville EPR (Image: Alexis Morin and Antoine-Soubigou/EDF)

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.

EDF said the first quality deviation in the welding of the main secondary system was detected on 21 March during the initial comprehensive inspection, a regulatory requirement prior to the reactor starting up. This inspection includes an examination of the welds in the primary and secondary systems, and allows an initial reference state of the plant to be established before it begins operating.

Each of the welds had been declared compliant by the consortium of contractors in charge of manufacturing the system, EDF noted.

Following the detection of deviations, EDF decided to carry out additional checks on the 150 welds in question 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.

EDF said it today notified the ASN of "a significant event relating to the detection of deviations in the performance checks of the welds".

The part of the main secondary system which directs 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.

"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 €10.5 billion (at the 2015 rate, excluding interim interest).

Cold functional tests - which verify the leak-tightness of the primary circuit - began at Flamanville 3 on 18 December and were completed on 6 January. Testing of the reactor building to confirm its airtightness was completed on 3 April. Hot functional tests - which involve checking the equipment under similar temperature and pressure conditions to those under which it will operate - are due to start in July.

The first-of-a-kind EPR at Finland's Olkiluoto plant has been under construction since 2005 and has seen several revisions to its start-up date. In October, the schedule for OL3 commencing regular electricity production was again revised from the end of 2018 to May 2019. The unit began functional hot tests in December.

The Taishan 1 EPR in China, which has been under construction since 2009, has completed functional hot tests and will be the first EPR to operate. It is expected to start up later this year, while Taishan 2 is scheduled to begin operating next year.

Researched and written
by World Nuclear News