Power utility Eskom says the Koeberg Unit 1 reactor tripped at 16:30 on August 30, as a result of a fault on the electrical breaker to one of the primary coolant pumps.
"Eskom can confirm 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," the utility assured the country on September 1.
Eskom expects the unit will be returned to service at the weekend.