Flamanville, Paluel, Belleville, Nogent and Penly nuclear power plants: ASN rates a significant safety event affecting the emergency diesel generator sets at level 2 on the INES scale

On 31 January 2020, EDF reported a significant safety event concerning seismic resistance defects on certain equipment contributing to the operation of the emergency diesel generator sets of several of its 1300 MWe reactors.

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The emergency diesel generator sets provide a redundant electrical power supply to certain safety systems in the event of the loss of off-site electrical power. If off-site electrical power supply is lost as a result of an earthquake, the operation of the emergency diesel generator sets could no longer be guaranteed owing to these defects.

These defects, identified during the inspections stipulated by ASN in its resolution 2019‑DC-0662 of 19 February 2019, are of three types:

• incorrect installation of piping elastomer couplings,
• corrosion of certain portions of the pipes or their supports,
• connection faults in certain electrical cabinets.

This event had no consequences on the personnel, nor on the environment. However, given the potential consequences of a malfunction of the two emergency diesel generator sets of a given reactor in the event of an earthquake, this event is rated level 2 on the INES scale (International Nuclear Events Scale which has 7 levels in ascending order of severity) for the following eight reactors:

• reactors 1 and 2 of the Flamanville NPP,
• reactors 1, 3 and 4 of the Paluel NPP,
• reactor 1 of the Belleville-sur-Loire NPP,
• reactor 1 of the Nogent NPP,
• reactor 2 of the Penly NPP.

The event is rated level 1 on the INES scale for eight other reactors, where the scope of the flaws was lesser and would not have led to the loss of the two emergency diesel generator sets in the event of an earthquake. This concerns the following reactors:             

• reactor 2 of the Paluel NPP,
• reactor 2 of the Saint-Alban NPP,
• reactor 2 of the Belleville-sur-Loire NPP,
• reactors 1 and 3 of the Cattenom NPP,
• reactor 1 of the Penly NPP,
• reactor 2 of the Chooz NPP,
• reactor 1 of the Civaux NPP.

For the reactors concerned, all of the defects detected were repaired or, with regard to the incorrect installation of certain elastomer couplings, were subject to reinforced monitoring until the next reactor outage, when they will be replaced. Repairs are in progress for Flamanville NPP reactor N° 2, which is currently shut down.

During the course of its inspections, ASN ensures that these defects are corrected.

ASN resolution 2019-DC-0662 of 19 February 2019 also requires other inspections on the electrical power sources of the NPPs. These inspections are currently ongoing.

Similar defects were found by EDF on the emergency diesel generator sets of some of its 900 MWe reactors and were the subject of a significant event rated level 1 on the INES scale in October 2019.