The “significant safety level one event” on the International Nuclear Event Scale (INES), which counts seven levels, occurred on Friday, January 29. The repair time following a scheduled test on the production unit no. 3 had been exceeded that day.
Teams at the Cattenom power station had carried out a test to check on the valves located on one of the two safety injection circuits of unit no. 3. In the event of an accident, this circuit enables boron water to be injected into the reactor’s primary circuit to ensure the cooling of its core.
However, during this test, the teams noticed a defect in the testing of these valves. In this type of situation, “our operating rules require us to initiate the reactor shutdown procedures or to proceed with repairs within the regulatory timeframe”, i.e. within eight hours, the power plant reports.
After this initial diagnosis, an electronic board also had to be repaired. “The incomplete requalification of the electronic board led us to underestimate the new deadline for starting the reactor shutdown operations, which was then requested within one hour”, the plant managers state.
During the various phases of the reactor shutdown, a definitive diagnosis made it possible to bring the equipment back into conformity and to carry out conclusive tests. The power plant teams were then able to interrupt the reactor shutdown procedures. Production unit no. 3 remained connected to the grid at reduced power and the event “had no impact on the safety of the installations”, the power plant assures. A second channel was operational.
