According to preliminary information available to ASN, the origin of the event that occurred at the reactor n°1 of the Cattenom NPP (Moselle) was an unexpected opening of a secondary system valve which resulted in a steam release. The reactor was automatically shut down at 13:25, according to procedures.
The steam release was stopped by closing a second valve (cf. schematic p. 2). EDF reduced the pressure and the temperature of the primary cooling system of the reactor. Conditions have now been reached to allow alignment of the normal shutdown cooling system. The connection should be completed in the short term. The reactor should then be returned to normal operating conditions. All safety systems are available. There have been no radioactive releases to the environment.
ASN preliminarily ranks the event at level 1 on the international INES scale, which has 7 levels.