Cattenom power plant;
Credit: EDF
On Wednesday 7 October 2026, the Grand Ducal Fire and Rescue Corps (CGDIS) reported that during recent maintenance on production Unit 3 at the Cattenom nuclear power plant errors in the testing of safety valves were uncovered.
According to the CGDIS, on Sunday 27 September, as part of the shutdown of Production Unit No. 3 for scheduled maintenance, the teams at the Cattenom nuclear power plant carried out tests on valves in the shutdown reactor cooling system (RRA)* to verify that they were functioning properly. These four safety valves open automatically when the pressure reaches a predetermined value in order to protect the system against possible overpressure.
On Tuesday 29 September, additional analyses revealed a calculation error had been made during these tests. This error resulted in the four valves concerned being slightly over-calibrated, meaning that their opening pressure was set higher than the expected value (by a few tenths of a bar). As soon as this deviation was detected, the teams brought the valves back into compliance.
The CGDIS confirmed that this event had no actual impact on the safety of the facilities: the valves remained operational throughout the entire period concerned. However, if they had been called upon to operate, this calibration deviation could have caused a limited delay in their opening.
In accordance with the plant's operating rules, the valves concerned were considered unavailable for the duration of the deviation. Because a permanent requirement associated with this unavailability was not complied with, the Cattenom nuclear power plant reported, on Monday 5 October a Level 1 event on the INES scale, which has seven levels, to the French Nuclear Safety and Radiation Protection Authority.
* The shutdown reactor cooling system (RRA) removes the residual heat produced by the fuel after the reactor has been shut down. It is used during shutdown phases to maintain cooling of the primary circuit under safe conditions.
