Koeberg has two reactors. Since just before 1am on Thursday, neither of them has been making electricity.
A nuclear station of this kind is built to run flat out and stay there. It is not the plant you dial up when demand spikes and down when it falls; it sits underneath everything else on the grid, holding the same output day and night, which is what the word baseload means. Koeberg normally carries about 5% of the country's electricity that way. With both units down, more than 1.8 gigawatts of it is gone.
The unit that tripped, and the unit nobody mentioned
Eskom's statement on Thursday covers Unit 1, and only Unit 1. The unit was taken offline safely and within procedure after a turbine trip, the utility said, plant monitoring stayed stable throughout, nuclear safety was never compromised, and there was no risk to employees, the public or the environment. Losing Unit 1's capacity poses no risk to national supply either, it added, because Eskom has enough generation available and the grid remains stable and secure. The cause of the trip is under investigation.
What the statement does not say is that Unit 2 has been out of service since 26 April, on a 150-day refuelling and maintenance outage tied to the station's life-extension programme, and is not due back until November.
Sardines in the seawater intake
Thursday's trip was Unit 1's second interruption in seven days. On 21 August a cooling water pump shut itself down after marine material built up in the seawater intake, and Eskom halved the unit's output, roughly 465MW, for several days. Output had been brought back up to 70% less than a day before the turbine tripped.
The fish are a separate investigation. Dead sardines have washed up along the Western Cape coast through the month, and the environment department confirmed on 14 August that it had found genetic material from pilchard herpesvirus in sampled fish, including at lower levels in apparently healthy ones, which suggests the virus alone is not enough to kill them. Harmful algae, low oxygen and unusual ocean conditions are all still being examined.
Unit 2's six months out
The refuelling outage has had its own incidents. In May a crane stalled while lifting a 150-tonne low-pressure turbine rotor and dropped it into the wrong position; Eskom said recovery teams repositioned it, inspections found no significant damage, and the outage schedule was unaffected. In July the National Nuclear Regulator disclosed that it was reviewing airborne contamination events inside the Unit 2 reactor building, detected during testing of the unit's new steam generators. Both the regulator and Eskom said the events were contained, classified level 0 on the international scale, and posed no risk to the public.
Both units run on 20-year licence extensions granted after a multibillion-rand programme that replaced Unit 2's three steam generators, and this is Unit 2's first major inspection cycle since it returned at the end of December 2024. It is due back on the grid in November. Until then, whatever is holding the base load up, it is not Koeberg.
