ASN rates a significant event affecting the emergency diesel generator sets on the Civaux, Gravelines and Paluel NPPs level 2 on the INES scale

A significant nuclear safety event concerning a deficiency in the earthquake resistance of the piping of the emergency diesel generator sets in the Civaux, Gravelines and Paluel NPPs was rated level 2 on the INES scale by ASN.

Each reactor has two emergency diesel generator sets, which provide redundant electrical power supply to certain safety systems in the event of the loss of off-site electrical power, more particularly in the wake of an earthquake.

The significant event concerns a risk of damage to the piping owing to their potential contact with the civil engineering structures of the emergency diesel generator sets in the event of an earthquake. This damage could lead to rupture of these pipes and failure of the emergency diesel generating sets.

EDF initially detected this deviation at the end of October 2018 on one of the two emergency diesel generating sets for reactors 2 and 3 of the Tricastin NPP. On 6 May 2019, EDF informed ASN that, following characterisation, it also concerned the two emergency diesel generating sets for the reactors of the Civaux, Gravelines and Paluel NPPs as well as one of the two emergency diesel generating sets for the reactors of the Fessenheim, Cruas, Saint-Laurent-des-eaux and Nogent NPPs, reactor 3 of the Dampierre NPP, reactors 2 and 3 of the Tricastin NPP and reactor 1 of the Le Blayais NPP.

Repairs were made to the reactors concerned, except for one emergency diesel generating set for reactor 4 of the Paluel NPP, which is currently shut down. This anomaly will be corrected before the reactor is restarted.

More particularly during the course of its inspections, ASN checks that these repairs are carried out satisfactorily. In its resolution of 19 February 2019, ASN also instructed EDF to inspect the conformity of the electricity sources for its nuclear reactors.

In the light of the potential consequences for NPP safety, ASN rates the event:

• level 2 on the INES scale for the reactors of the Gravelines, Paluel and Civaux NPPs;
• level 1 on the INES scale for the reactors of the Fessenheim, Cruas, Saint-Laurent-des-eaux, Nogent reactors, as well as for reactor 3 of the Dampierre