On Monday 18 August 2025, Luxembourg’s National Fire and Rescue Centre (Centre national d'incendie et de secours - CNIS) announced they had received a report from EDF-CNPE that a level 1 significant safety event had occurred following a planned maintenance outage at the Cattenom nuclear power plant.
According to the report, on Thursday 14 August 2025, during restart operations on Unit 3, operating teams carried out manoeuvres on the continuous treatment circuit of the primary circuit water. At 12:41, an incorrect configuration of two valves on this circuit (set to the closed position) caused water from the primary circuit to flow into a dedicated collection tank at a rate above the threshold specified by the operating rules. Once detected, the operating teams conducted investigations and restored the valves to the correct position at 16:25, stopping the water level increase in the tank.
According to EDF-CNPE, the primary circuit is a closed system containing pressurised water, which cools the reactor. During certain operating phases, such as reactor restarts, auxiliary tanks and systems collect and process primary circuit water for reuse. This transfer of water is monitored under the operating rules, which set limits on the flow leaving the primary circuit.
EDF-CNPE stressed that this event had no impact on plant safety and the water always remained in a closed circuit, with reactor cooling continuously ensured. However, the operating rules required the immediate application of a procedure to identify the cause of the abnormal water transfer.
As the anomaly was detected late, the procedure was not initiated straight away. This represented a non-compliance with the prescribed operating rules. As a result, a level 1 significant safety event (on the INES scale, which has 7 levels) was declared to the Nuclear Safety and Radiation Protection Authority.
