Koeberg Unit 1 Return Delayed to August as Eskom Completes Key Safety Repairs

Eskom has officially announced a revised return-to-service date for Koeberg Nuclear Power Station’s Unit 1, which will now resume operations by the end of August 2025 rather than the originally anticipated end-of-July timeline. The delay stems from additional maintenance work required on the unit’s newly installed steam generators, following the identification of minor defects during post-installation safety inspections.

In a detailed statement issued this week, the power utility assured South Africans that the extension is necessary to uphold international safety standards and does not pose any risk to the country’s current stable electricity supply, which has seen a dramatic reduction in load shedding in recent months.

Advanced Testing Detects Tube Defects

The need for the extension arose after Eskom engineers conducted eddy current inspections, a non-destructive testing method that evaluates the condition of steam generator tubing. During these inspections, defects were discovered in four tubes out of several thousand that were checked. These tubes are crucial components of the steam generator system, responsible for heat transfer in the reactor's closed-loop process.

In response to the findings, Eskom mobilised a team of local and international experts, who performed automated tube repairs using advanced tools. The utility reported that all identified issues were successfully resolved, ensuring the structural integrity and safe operation of the equipment going forward.

Completion of Legally Required Safety Tests

Beyond the generator maintenance, Koeberg Unit 1 also underwent the Integrated Leak Rate Test (ILRT)—a statutory safety requirement conducted every 10 years. This test involves pressurising the reactor building over 72 hours to verify its leak-tightness and structural soundness. Eskom confirmed that Unit 1 passed the ILRT with full compliance, demonstrating the resilience of its containment system.

“These critical repairs and tests reflect our absolute commitment to quality, safety, and environmental responsibility,” said Bheki Nxumalo, Eskom’s Group Executive for Generation.

Energy Security Remains Intact Despite Delay

Eskom was quick to reassure the public that the delay in bringing Unit 1 back online will not affect the national electricity supply or increase the risk of load shedding. Since mid-May, South Africa has experienced an unprecedented reduction in power cuts, with only 26 hours of load shedding recorded between 1 April and 10 July 2025.

The Winter Outlook Report, released in May, projects that South Africa will remain in a secure energy position until 31 August, provided that unplanned outages do not exceed 13,000MW. Even in a worst-case scenario—where outages rise to 15,000MW—load shedding would be capped at Stage 2 for no more than 21 days during the entire winter period.

Eskom emphasized that the planned return of 2,500MW this winter does not depend on Koeberg Unit 1, and the overall strategy accounts for staggered maintenance at key generation facilities.

Unit 2 Operating at Peak Performance

While Unit 1 remains offline for maintenance, Koeberg Unit 2 continues to operate at full capacity, supplying up to 946MW to the grid. As of June 2025, Unit 2 boasts an impressive Energy Availability Factor (EAF) of 99.38%, making it one of the most reliable energy units in Eskom’s generation fleet.

Once Unit 1 is fully repaired, its reactor core will be refuelled, tested, and synchronised back to the national grid, restoring the plant’s total capacity to approximately 1,860MW, or 5% of South Africa’s electricity supply.

To ensure continued reliability, Eskom follows a strategic policy of staggered outages between the two Koeberg units, with maintenance intervals scheduled every 16 to 18 months. This approach guarantees that both units are never offline simultaneously, preserving nuclear power’s essential contribution to baseload generation.

Nuclear Power Key to Energy Future

The extension of Unit 1’s maintenance timeline underscores Eskom’s long-term vision of investing in affordable, low-carbon baseload power, with nuclear energy seen as a central pillar in South Africa’s transition to a more sustainable and resilient energy system.

“Nuclear power remains a critical component of our country’s energy mix,” said Nxumalo. “Our team at Koeberg continues to deliver world-class work, ensuring long-term stability while supporting environmental goals.”

As winter continues, Eskom has urged customers to continue practising energy efficiency in homes and businesses, noting that public cooperation remains key in maintaining grid stability.