Inspection work has revealed tiny cracks on a penetration at the bottom of Gravelines 1's reactor pressure vessel. The power unit remains shut down until a repair has been made.
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 be inserted 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 six units of the Gravelines nuclear power plant (EDF)
The tiny cracks were discovered 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 such a defect has been found in France, although similar faults were dealt with in 2003 at the South Texas Project site in the USA.
EDF owns and operates Gravelines 1 along with France's 57 other power reactors. The company has 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 that 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 - a total of 54 units.
Researched and written
by World Nuclear News