The oldest and most numerous nuclear reactors would also be the least affected by the corrosion observed in the French fleet.

This rather paradoxical phenomenon could be explained by differences in design between these 900 MW reactors and those more recent, the president of the Nuclear Safety Authority (ASN) said on Tuesday.

"At this stage, in respect of stress corrosion, EDF has shut down or extended the scheduled outages of 12 reactors for in-depth expertise and, if necessary, repair", underlined Bernard Doroszczuk during the a hearing in front of parliamentarians.

small cracks

These corrosion problems were detected or suspected at the welds of the bends of the safety injection pipes – which allow the reactor to be cooled in the event of an accident – ​​connected to the primary circuit.

This so-called “stress” corrosion results in small cracks.

In detail, these are the four most recent and most powerful reactors (1,450 MW), known as the N4 level, five of the 20 1,300 MW reactors and three of the 32 900 MW reactors.

“At this stage, the N4 reactors, those at Civaux and Chooz, are the most affected (…).

And given the results of expertise carried out on a certain number of 900 MW reactors, it seems that these reactors are little or not at all affected by the phenomenon at this stage”, indicated Bernard Doroszczuk.

The analyzes "seem at this stage to favor a preponderant cause, which is linked to the geometry of the lines of the pipes", he continued.

The oldest reactors (900 MW) were in fact built according to a design directly inherited from the American group Westinghouse, while the design of the following models was “Frenchified”.

"If this hypothesis were confirmed, it could explain why the oldest reactors are not or only slightly affected," argued Mr. Doroszczuk.

29 out of 56 reactors shut down

He also said that EDF had submitted its control strategy for the entire fleet "last Friday".

Inspections will also be carried out during the ten-yearly inspections scheduled for certain reactors this year.

“If the results of these checks carried out during the ten-yearly outage revealed major defects, the strategy would have to be adjusted and perhaps provide for the precautionary shutdown of additional reactors”, declared the president of the ASN.

On its fleet of 56 reactors, EDF currently has 29 shut down.

It is therefore only “a part” which is unavailable for corrosion problems, underlined the nuclear policeman.


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