Faulty fossil dating
According to Power magazine, an ASN press relations officer, who requested anonymity in line with ASN rules, said more nuclear power plants with suspect parts will be inspected in the next few weeks.
"We are now finding carbon segregation problems from components coming from both Le Creusot and Japan Casting & Forging.
This is not yet a full-blown crisis for the nuclear industry, but it is putting serious strain on the finances of French nuclear giant EDF and causing electricity price rises across western Europe. France is reopening mothballed coal plants and burning more coal than it has for 32 years.
Neighbors, including Germany, which normally takes cheap nuclear power from the French, are also powering up old fossil fuel plants and exporting the electricity to France at premium prices.
The anomalies were first discovered in 2014 at the plant being built at Flamanville in northern France.
Excess carbon was found in the plant's pressure vessel.
And the Japan Times reported that Japan Casting & Forging Corporation is now also under scrutiny by the country's Nuclear Regulation Authority because it supplied French plants.
By Paul Brown A third of France's nuclear reactors have been shut down by industry regulators as revelations emerge about the supply of sub-standard parts.
As investigations into falsified documents and excess quantities of carbon in steel continue, more closures are expected.
The carbon content is well above specified safety limits, leading to fears that there could be catastrophic failures in plants currently operating.
The second, related, problem is forged, falsified or incomplete quality control reports about the components themselves.
But as more forged documents and potentially faulty parts have come to light, the French regulator ASN has begun insisting on shutdowns and inspections to ensure plants are safe.