Level 2 incident on INES scale concerning back-up diesel generators at Tricastin nuclear power plant

ASN rated at level 2 on INES scale an incident reported by EDF on February 16, 2011 concerning back-up diesel generators at Tricastin NPP.

The back-up diesel generators are used to supply safety systems of reactors in the event of loss of power by the national network. Each nuclear reactor is equipped with two back-up diesel generators. An additional back-up generator is available for all reactors on the same site. Each of these groups is sufficient to supply the systems necessary to ensure the safety of the reactor shutdown.

A periodic test conducted at the EDF Blayais NPP highlighted the failure of a back-up diesel generator. The first elements of the analysis undertaken by EDF and its supplier have been reported to ASN on February 7, 2011. They show a premature degradation on bearing bushings, which are mechanical components designed to minimize friction between moving parts of back-up diesel generators.

On French nuclear power plants, 26 back-up diesel generators are equipped with the same type of bearing bushings which are therefore potentially sensitive. ASN has asked EDF to submit a corrective action plan.

The first EDF proposals have been submitted to ASN. ASN, with the support of IRSN, currently assesses these proposals which include the installation of new bearing bushings and the implementation of a new operating procedure for the diesel generators involved.

At all EDF sites, other than Tricastin NPP, where this type of bearing bushings exist (Blayais, Bugey, Chinon, Cruas, Dampierre, Gravelines, Saint-Laurent), each reactor has at least one back-up generator, in the reactor or on the site, equipped with a different brand of bearing bushing which do not have this defect. The anomaly is rated by ASN on these sites at level 1 on the INES scale.

However, on reactors 3 and 4 of Tricastin NPP, two back-up diesel generators and the additional back-up diesel generator common to all reactors of the site are equipped with bearing bushing potentially sensitive. Therefore, on this site, the anomaly is rated by ASN as incident Level 2 on the INES scale. The ASN division of Lyon is currently conducting an inspection at Tricastin NPP.

Press Contact:
Evangelia Petit, Head of Press Relations, Tel. : +33 1 40 19 86 61, evangelia.petit@asn.fr