PARIS (Reuters) - French utility EDF's Cattenom 1 nuclear reactor was stopped on Thursday after the French nuclear watchdog reported an incident caused by the "inopportune opening of a valve" that did not lead to a radioactive discharge.
A spokeswoman for nuclear watchdog ASN said the incident, which happened in the secondary circuit of the reactor located near the border with Luxembourg, was provisionally rated 1 on the INES scale out of a maximum 7.
"It's not every day that the internal emergency plan is triggered," Philippe Jamet, an ASN administrator told Reuters.
The internal emergency plan triggers procedures at a nuclear plant to stop a technical incident that has no impact on the environment or the population.
"It did not cause a safety problem that would really have had us unnerved, however. It wasn't a threat, there was never the threat of a (radioactive) leak."
"The water in the secondary circuit is not radioactive," he said.
The ASN, which was carrying an emergency exercise when the incident happened, is now assessing the situation with EDF, the plant's operator, Jamet said.
EDF said on the plant's Twitter account that the emergency plan had been triggered as a precaution and that the shutdown of the reactor was proceeding normally.
Reporting by Michel Rose; editing by Gus Trompiz