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Corrosion on nuclear reactors: “These microcracks could cause the rupture of this circuit”, warns an expert

Microcracks in nuclear reactors “could cause this circuit to break just when it is needed”, explained this Friday on franceinfo Yves Marignac, head of the nuclear expertise center at the n├ęgaWatt institute, member of the permanent group of experts on nuclear reactors of the Nuclear Safety Authority (ASN), while EDF has extended the shutdown of five nuclear reactors, where corrosion problems have been identified (in some cases until the end of 2022). EDF has launched an inspection of all the reactors in its fleet.

franceinfo: Should we be worried about these corrosions?

Yves Marignac: Yes, you have to be worried. These corrosions relate to microcracks appearing in the bends of a circuit which is essential for the emergency cooling of the reactors, if a reactor were to be in an accident situation. These micro cracks could cause this circuit to break just when it is needed. This means that some reactors could be affected by this very serious failure.

Was this problem foreseeable?

The phenomenon of stress corrosion, which corresponds to the appearance of microcracks within the steel under specific conditions, is a known and feared phenomenon in nuclear installations. He is under surveillance. But here the problem is that it was not anticipated that such corrosion could appear so soon. So, there is a whole questioning and that is why the situation is dramatic, since we have seen this phenomenon appear. But we don’t have very clear explanations on the reasons and the conditions of this appearance. Therefore, we cannot exclude that this same phenomenon does not exist on other reactors.

How long does it take to check all the reactors?

Yes and no. There is a first verification which will be long but which EDF is in the process of doing. It is a reading of the last checks. They are done every 10 years when the reactors are shut down and thoroughly inspected. So, we can see if there are things that we would not have seen or misinterpreted at the time and which would be clues to the appearance of these faults. But what is necessary is to go and inspect these reactors live, but to do so they have to be shut down. It’s complicated from the point of view of electrical safety, especially now where the electrical system is under high voltage.

Can we run out of electricity?

For years now, we have been warning of a growing dependence on our electricity system, on an aging nuclear fleet and therefore more and more likely to encounter this type of problem. We are in a situation where there is a practically impossible trade-off between precaution from a safety point of view and electrical safety. Closing more reactors would fuel the risk of supply shortages. We therefore have an impossible trade-off which will probably result in the fact of delaying safety in order to maintain electrical safety at all costs.

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