An inspection found tiny cracks on a penetration at the bottom of the fifth largest nuclear power plant in the world, Nord, France-based Gravelines 1’s reactor pressure vessel. The power unit will remain shut down until officials can repair the cracks.
In France’s 900-MWe class pressurized water reactors, some 50 small tubes around 38 mm in diameter penetrate the bottoms of the reactor pressure vessels. They allow for instruments to insert through the vessel and into the reactor core, but their construction is important to nuclear safety because it represents part of the boundary of the pressurized cooling system.
The tiny cracks are within the pressure vessel in the area of welded alloy around the tube at Gravelines 1. The Nuclear Safety Authority (Autorité De Sûreté Nucléaire, ASN) said it was the first time they found this type of defect in France, although officials found similar faults in 2003 at the South Texas Project site in the U.S.
EDF owns and operates Gravelines 1 along with France’s 57 other power reactors. The company suggested a repair method to the ASN, which is reviewing the technique in collaboration with the Institute of Radiological Protection and Nuclear Safety (Institut de Radioprotection et de Sûreté Nucléaire, IRSN). In the meantime, the reactor will remain offline, said ASN, noting the detailed 10-year inspection that discovered the issue had required the removal of nuclear fuel. The cracks therefore have no current impact on safety.
EDF has been requested by the ASN to check all its 900 MWe and 1300 MWe reactors for similar cracks, which consists of 54 units.