A technical problem at the Koeberg nuclear power station posed no threat to the reactor or nuclear safety, authorities said on Monday. Unit 1 of the Koeberg power station was shut down on Sunday due to a technical fault on the main generator transformer, which resulted in the unit being isolated from the national grid.

The transformer had experienced an earth fault, which has now been addressed, power utility Eskom said.

"Eskom technicians are in the process of performing start-up tests in an effort to bring back to service Unit 1 of the Koeberg power station," the utility said.

Unit 1 is expected to be fully operational by the end of this week, which will increase capacity going into the weekend, according to Eskom.

The nuclear station is regularly shut down as part of Eskom's overall maintenance program for its fleet of power stations.

Every 16 to 18 months, each of the two units at Koeberg is shut down for refuelling, inspection and maintenance. The routine shutdowns are scheduled so as to avoid having both units out of service at the same time and to avoid the winter months in each year, the utility said.

During these routine planned outages, one-third of the used nuclear fuel is replaced with new fuel. Statutory inspection and maintenance is performed, and modifications, that will ensure that international safety standards continue to be met or that improve the plant performance, are implemented, said Eskom.

Koeberg nuclear power station, situated near Cape Town, is Africa's only nuclear power station. In the past, technical problems sometimes forced the station to shut down, raising fears for nuclear safety.