Level-2 incident involving the emergency diesel generator sets of the Bugey and Fessenheim nuclear power plants (NPPs)
A significant safety-related event concerning a deficiency in the earthquake resistance of the auxiliary systems of the emergency diesel generator sets of reactors 2 and 5 of the Bugey NPP and reactors 1 and 2 of the Fessenheim NPP was rated level 2 on the INES scale by ASN. A similar event concerning twenty 1300 MWe reactors was reported in an information notice dated 20th June 2017.
On 13 October 2017, EDF informed ASN that the failure to demonstrate the earthquake resistance of the auxiliary systems of the emergency diesel generator sets concerned not only the 1300 MWe reactors but also some of the 900 MWe reactors, namely reactors 2 and 5 of the Bugey NPP and reactors 1 and 2 of the Fessenheim NPP. Verifications are currently in progress on the Bugey NPP reactors 3 and 4, which could also be concerned.
Each of the 900 MWe and 1300 MWe reactors of the French NPP fleet is backed up by two emergency diesel generator sets. These generator sets provide a redundant electrical power supply to certain safety systems in the event of the loss of off-site electrical power, particularly further to an earthquake. The emergency diesel generator sets comprise a generator, a diesel engine and auxiliary systems (cooling, pre-lubrication systems, etc.).
The significant event concerns the failure to demonstrate the earthquake resistance of the anchors in the civil engineering of the diesel generator set auxiliary systems. If off-site electrical power is lost as a result of an earthquake, operation of the emergency diesel generator sets could no longer be guaranteed as a result of the failure of their auxiliary systems.
On 26th October 2017 ASN instructed EDF to perform the necessary strengthening work on the reactors concerned at the Bugey and Fessenheim NPPs.
In view of the potential consequences for NPP safety in the event of an earthquake, the event has been rated level 2 on the INES scale for the Bugey NPP reactors 2 and 5 and the Fessenheim NPP reactors 1 and 2.
With regard to the twenty (20) 1300 MWe reactors having formed the subject of a significant safety-related event notification on 20th June 2017 which was rated level 2 on the INES scale, EDF has carried out work to reinforce the anchors of the auxiliary systems of the emergency diesel generator sets of these reactors, as instructed by ASN in its resolution of 22nd June 2017. ASN has carried out inspections of this work.
For further informations :
 See the information notice published by ASN on 20th June 2017. It concerns the 1300 MWe reactors of the Belleville-sur-Loire, Cattenom, Flamanville, Golfech, Nogent-sur-Seine, Paluel, Penly and Saint-Alban NPPs.
 System for attaching an element (structure, system or equipment item) to a stable point which can take up the loads exerted on that element, notably in the event of an earthquake.