A 2014 incident in France's oldest nuclear plant, located near the German and Swiss borders, was more serious than previously reported, German media claimed Friday, reports Yahoo! News.
Flooding at the Fessenheim plant disabled electrical control systems and forced operators to launch an emergency reactor shut-down, reported public broadcaster WDR and Sueddeutsche Zeitung daily.
Operators decided to insert boron into the reactor cooling system, a procedure the report likened to "pulling the emergency brake", and which a nuclear safety expert said was a unique event in Western Europe so far.
The joint news report said that operators temporarily lost full control over the plant's reactor 1 in the April 9, 2014 incident after water had incapacitated one of two parallel reactor security systems.
The official reports by French nuclear safety agency ASN had not mentioned the use of boron, the media report said.
"I am not aware of any other case where a power reactor here in Western Europe suffered an incident in which it had to be shut down with the use of boron," nuclear safety expert Manfred Mertins was quoted saying.