Level 2 incident concerning the emergency diesel generator sets on the Belleville, Cattenom, Flamanville, Golfech, Nogent, Paluel, Penly and Saint-Alban NPPs

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ASN rated as level 2 on the INES scale a significant safety incident regarding the seismic resistance of the auxiliary systems of the emergency diesel generator sets of twenty 1300 MWe reactors on the Belleville, Cattenom, Flamanville, Golfech, Nogent, Paluel, Penly and Saint-Alban NPPs.

Each 1300 MWe reactor has two emergency diesel generator sets, which provide redundant electrical power supply to certain safety systems in the event of the failure of off-site electrical power supplies, more particularly in the wake of an earthquake. The emergency diesel generator sets comprise a generator, a diesel engine and auxiliary systems (cooling, pre-lubrication, etc. systems).

The significant event concerns the lack of demonstration of the ability of the civil engineering anchors of the diesel generator sets auxiliary systems to withstand an earthquake. It covers both design problems, which are generic to all the 1300 MWe reactors, and local problems relating to the poor condition or poor assembly of the anchors.

If off-site electrical power is lost as a result of an earthquake, the operation of the emergency diesel generator sets could no longer be guaranteed as a result of the failure of their auxiliary systems.

Insufficient seismic resistance of an emergency diesel generator set auxiliary system (cooling system surge tank) was initially detected by EDF in March 2017 in the Golfech NPP and then on all the 1300 MWe reactors. ASN had rated this event level 1 on the INES scale.

On 20 June 2017, EDF informed ASN that the lack of demonstration of the ability to withstand an earthquake was also liable to concern the other auxiliary systems of the two emergency diesel generator sets of twenty 1300 MWe reactors.

Therefore, ASN asked EDF to ensure that the anchors of all the diesel generator set auxiliary systems be reinforced within three weeks for at least one of the two emergency diesel generator sets and within one and a half months for the second, for each of the 20 reactors concerned. This request will be the subject of a formal ASN resolution within the coming days.

Given the potential consequences for the safety of the NPPs in the event of an earthquake, this event is rated level 2 on the INES scale for the reactors of Belleville, Cattenom, Flamanville, Golfech, Nogent, Paluel, Penly and Saint-Alban.

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