Electricité de France (EdF) has found a generic design defect on 14 of its nuclear power units. The utility must make changes to safety system pipe supports in order to "completely guarantee" safety in an earthquake.
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The defect concerns three of the 262 supports for pipes that would supply water to steam generators in the event of a serious leak from the secondary coolant loop. EdF said its calculations showed that the supports "can not completely guarantee holding the piping during an earthquake" and that they would be modified either while the units were operating or at the next scheduled outage.
In a pressurized 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. This removal of heat is also important for nuclear safety because the reactor core requires constant cooling, even when the plant is shut down. The piping EdF is concerned about would ensure an adequate supply of water to the secondary loop so that this function could continue in the event it suffered a serious leak.
EdF operates 59 reactors across France of a number of related designs. The design defect is present in 14 of its 28 900 MWe units: at the Blayais, Chinon, Cruas, Dampierre, Gravelines, Saint-Laurent and Tricastin nuclear power plants which started operation between 1980 and 1984.
EdF said the issue became known during September 2005 at Cruas, in the Ardeche region. The company informed the Autorité de sûreté nucléaire (Nuclear Safety authority, ASN) on 28 May, categorising the defect as a generic compliance issue and grading it at Level 1 on the International Nuclear Event Scale.