Safety authority asks for steam generator measures
Electricité de France has been given until 30 September to implement preventative safety measures in steam generators at its French nuclear reactors including plugging tubes affected by an anomaly in anti-vibration measures
Electricité de France has been given until 30 September to implement preventative safety measures in steam generators at its French nuclear reactors including plugging tubes affected by an anomaly in anti-vibration measures.
France's Nuclear Safety Authority (Autorité De Sûreté Nucléaire, ASN) has released a letter issued to the utility on 24 April calling for some steam generator tubes to be plugged to prevent the risk of their rupturing. The company must also implement enhanced measures to detect leaks between primary and secondary coolant circuits pending the completion of the plugging work.
Steam generators provide the interface between the primary and secondary circuits of a pressurized water reactor (PWR), transferring heat from the water that circulates through the reactor itself (the primary circuit) to turn water into the steam that passes into the turbogenerators (secondary circuit). Each steam generator contains up to 5600 tubes through which water flows. During operation, steam tubes are subjected to vibrations which can lead to fatigue, eventually causing cracks. Anti-vibration bars in the steam generators counter this, but in the late 1980s it was discovered that if tubes were incorrectly positioned within the anti-vibration bars they would be subject to fatigue and cracking. Remedial work was undertaken to plug affected tubes in various plants around the world, including some 1500 tubes in 34 French PWRs.
In February 2008 a leak was discovered between the primary and secondary circuits of unit 2 at EdF's Fessenheim plant, caused by a tube which had not met the criteria requiring it to be plugged in the earlier operation. The ASN has therefore asked EdF to carry out investigations into the cause of the cracking, if necessary adapting the existing plugging strategy. In the meantime, ASN has given EdF until 30 September to plug all steam generator tubes not supported by the anti-vibration bars in all reactors affected by the anomaly.
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