Eskom had to shut down Koeberg Unit 1, but 'reserves' are enough to avoid load shedding

Nuclear power station Koeberg's Unit 1 had to be shut down last week for repairs, but it didn't necessitate load shedding because Eskom has enough emergency reserves, the South African power utility said.

Koeberg Unit 1 was recently granted a licence extension to run for another 20 years, until 21 July 2044, subject to conditions. A decision for the long-term operation of Unit 2 is expected next year, as the unit's steam generator replacement programme is still under way.

As part of the long-term operation of the plant, Eskom had to implement modifications at Koeberg, as well the replacement of key components such as the steam generators. Following the replacement of its steam generators in what was almost a year-long outage, Koeberg Unit 1 came onstream again in November 2023.

But on Wednesday, 11 September, Eskom had to shut down the unit after one of its isolation/block valves failed a three-monthly routine test, the company said in response to questions.

"The unit was shut down in order to restore redundancy of the steam pressure relief system in line with the operating technical specifications. At no point was the safety of the plant, staff, public or environment at risk," it said.

The unit is now in the process of being returned to service.

While Eskom did not name Koeberg as part of its unplanned outages in its weekly update on generation performance last Friday, it said that "all stakeholders who were required" to be notified were informed of the shutdown.

Eskom gave assurances that the country still has sufficient generation capacity, owing to its generation recovery plan. The power utility has surpassed 170 days without load shedding.

Unplanned outages of the generation units across its fleet averaged 11 190 megawatts (MW) – compared to 16 876 MW recorded for the same period (7 to 13 September) last year.

Koeberg Unit's 1 has a capacity of 920MW.

"Additionally, we have sufficient emergency reserves to handle any sudden changes in demand during peak periods," Eskom said.

"The issue has had no impact in the suspension of load shedding and the summer outlook remains in force."

The energy availability factor - a measure of generation fleet performance - from 1 April to 12 September averaged 63.6%, up 8.5 percentage points from 55.12% for the same period last year. This is largely due to a drop in unplanned outages, it said.