Stress corrosion: presence of a deep crack on the safety injection system of reactor 1 of the Penly NPP

Print View Posted on: 30 May 2023

Event Date: 06 March 2023 Event Type: Power Reactor
Event Location: France, PENLY-1 INES Rating: 2 (Final)

On 6 March 2023, EDF sent ASN an update of its significant safety event notification concerning the presence of stress corrosion cracks on several of its reactors. This update concerns reactor 3 of the Cattenom NPP and the reactors of the Civaux, Chooz B and Penly NPPs.

This update includes in particular the detection of a crack situated near a weld on a line of the safety injection system hot branch (RIS BC) of the Penly NPP reactor 1. The crack extends over 155 mm, i.e. about a quarter of the pipe circumference, with a maximum depth is 23 mm for a pipe wall thickness of 27 mm.

EDF considered that this line was not susceptible to stress corrosion, due in particular to its geometry. However, the weld underwent a double repair during reactor construction, which could have modified its mechanical properties and the internal stresses of the metal in this zone.

The presence of this crack means that the strength of this pipe is no longer demonstrated. The reactor safety case does however take into account the rupture of one of these lines.

In this update, EDF indicates that the inspections have also detected the presence of a thermal fatigue crack on lines considered to be susceptible to stress corrosion of the safety injection system (RIS) of reactor 2 of the Penly NPP and reactor 3 of the Cattenom NPP. The pipes in question were replaced under the programme EDF has initiated on the RIS system lines of the type P'4 reactors.

This event has no consequences on the personnel or the environment. Nevertheless, it affects the safety function associated with reactor cooling. Due to its potential consequences and the increased probability of rupture, ASN has rated this event level 2 on the INES scale for reactor 1 of the Penly NPP and level 1 for the other reactors concerned.

EDF is implementing an inspection programme on the repaired welds of the RIS and RRA systems. More than 150 welds have undergone expert assessments in the laboratory and the inspections are continuing, with an inspection programme covering all the reactors as from 2023.

ASN has asked EDF to revise its strategy to take into account these new findings. It will shortly give a position statement on this revised strategy.

INES Rating: 2 - Incident (Final)
Release beyond authorized limits? No
Overexposure of a member of the public? No
Overexposure of a worker? No

Contamination spread within the facility? No
Damage to radiological barriers (incl. fuel damage) within the facility? No

Degradation of Defence In-Depth Yes

Person injured physically or casualty? No
Is there a continuing problem? No

Julien Husse
Autorité de Sûreté Nucléaire (ASN)
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