The technical difficulties in the French nuclear power plants are expanding.

As the operator informed EDF, indications of stress corrosion were also discovered for the first time in a reactor of smaller design.

One of the four reactors in Chinon on the Loire with an output of 900 megawatts is affected.

There, too, weld seams of elbows that connect the safety injection system to the primary circuit are said to have cracks - a phenomenon that has so far only been seen in five reactors of the newer types with 1300 and 1450 megawatts of capacity in Civaux in western France, in Chooz in the Ardennes and in Penly in Normandy had been established.

Niklas Zaboji

Economic correspondent in Paris

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As EDF also reported, according to the latest investigations, there is a suspicion of corrosion not only in the older reactor in Chinon, but also in other newer reactors.

This means one of the reactors in Cattenom near the Saarland border, in Flamanville in Normandy and in Golfech in south-west France.

There, too, the investigations are now continuing in coordination with the ASN supervisory authority.

The systems do not produce any electricity during this time.

The same applies to the second reactor in Flamanville and two of the reactors in Bugey near Lyon.

Their assessment was also given priority by EDF because of the corrosion phenomenon.

The French power supply is threatened with further stress tests because of the reactor failures.

In the worst case, the entire power plant park would have to be checked, including the replacement of the affected components.

Between 1979 and 1988 there were 32 reactors with a capacity of 900 megawatts, which is more than half of the total of 56 reactors in operation.

There are 20 of the 1,300-megawatt reactors, which went online between 1985 and 1994, and the remaining four 1,450-megawatt reactors in 2000 and 2002. Little has been invested since then and only one new reactor has been commissioned.

In the past few weeks, the French network operator RTE has called in phases not to leave the washing machine running or to charge cell phones and electric cars at certain times of the day.

Even before the corrosion problems began to spread from December, RTE had forecast unusually lower power generation from the French nuclear reactors as maintenance work had been postponed due to the corona.

Most of the outages are now unscheduled - and have been extended due to the replacement of the affected components, in some cases until the end of this year.

As a result, only a little more than half of the approximately 61 gigawatts of capacity that the French nuclear power plant park has is currently available.

EDF recently announced that electricity production will fall to a 30-year low this year.

On the one hand, this has consequences for the energy supply: France gradually became an electricity importer again and increasingly purchased natural gas from abroad, even if its share in the electricity mix and dependence on Russia is lower than in Germany;

the share of nuclear energy in the French electricity mix is ​​currently almost 65 percent.

On the other hand, the power plant failures are straining the balance sheet of the power plant operator EDF, which is already highly indebted at more than 40 billion euros: It was not until the beginning of April that the shareholders injected 3.1 billion euros in fresh capital, the lion's share of which came from the French state, which holds 84 percent of the shares .

In addition, EDF had been ordered by the government to wholesale larger quantities of nuclear power to competitors at a state-regulated price below current prices.

This should reduce costs for households and companies.

EDF then had to procure expensive quantities on the market.

The shares of the energy group are currently listed at around 9 euros, around a third less than at the beginning of December.