South African power utility Eskom confirmed that Koeberg Unit 1 Reactor tripped at 16:30 on Monday, 30 August 2021, due to a fault on the electrical breaker to one of the primary coolant pumps.
In a media statement, Eskom explained that the reactor was then safely shut down by the operators, in compliance with the operating procedure.
Initial fault-finding ruled out any concerns on the primary pump or the motor itself. There are no nuclear safety concerns.
By mid-morning on Tuesday, 31 August the cause of the trip has been confirmed to be a faulty electrical protection relay, which tripped the primary motor. The secondary side was already fully conditioned and on standby, waiting for the reactor and the primary system to be returned to service.
Only once an assessment of the protection relay is complete, together with the analysis of the trip, the unit will be returned to service.
The unit shutdown and response were straightforward, and no safeguard systems were required to operate. The National Nuclear Regulator (NNR) does not need to approve the restart, although the regulator is kept informed of the situation, the findings and the actions being taken.
Koeberg Unit 1 reactor will be returned to service during the weekend of 5-6 September.