Reactor 2 of the Penly nuclear power plant: a significant safety event concerning defective electrical components is rated level 2 on the INES scale

Reactor 2 of the Penly nuclear power plant: a significant safety event concerning defective electrical components is rated level 2 on the INES scale

On 18 December 2019, EDF reported a significant safety event relating to defective electrical components which put the backup systems of the Penly NPP reactor 2 out of service.

The equipment ensuring the safety of each NPP reactor is supplied with electrical power via two redundant electrical panels (channels A and B). These electrical panels supply power to the motors that actuate the valves and pumps of the backup systems and the reactor instrumentation and control panels.

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In the context of the Penly NPP reactor 2 refuelling and maintenance outage which began on 27 July 2019, EDF replaced the moving parts of these electrical panels. The work was carried out on channels A and B simultaneously, because it could not be carried out on channel A alone during a previous outage.

During restarting of the reactor backup and cooling pumps for post-work requalification, when the reactor was still shut down, anomalies led EDF to detect the malfunctioning of four electrical components as of 12 October 2019.

On 10 December, with the reactor still shut down but refuelled, EDF conducted investigations to determine the origin of these successive faults. The investigations revealed that 28 components replaced on the electrical panels were potentially defective. EDF then deemed the pumps of the backup and cooling systems of the reactor concerned by the anomaly to be unavailable.

This unavailability of several items of equipment important to safety had no consequences on people or the environment.

On account of the deterioration of the safety function due to the installation of defective components on electrical panels important to safety, and deficiencies in the licensee's organisation - as much in the preparation of the maintenance activities as in the late analysis of the successive faults - the event is rated level 2 on the INES scale (international scale of nuclear and radiological events, graded from 0 to 7 in increasing order of severity).

EDF is currently completing the replacement of the 28 potentially defective electrical components. The expert assessment of the first eighteen insertion contacts found eight of them, all from the same manufacturing batch, to have a manufacturing defect. EDF is currently checking which other reactors could be concerned by the defective parts and shall replace these parts where necessary.