State-owned South African power utility Eskom says unit 1 of the Koeberg NPP has achieved a significant milestone in upgrade work at the plant after mechanical work for replacement of the steam generators was completed. This is the most significant part of the complex project and Eskom is now able to proceed with other outage activities that could not be undertaken in parallel with replacement of the steam generators. Once the outage activities are completed, the reactor will be reloaded with fuel in preparation for its return to service. Commissioning operations, including the necessary tests of the new steam generators, will take place while the unit is synchronised to the grid.

The two 930 MWe (net) pressurised water reactors at Koeberg, built by Framatome, began commercial operation in 1984 and 1985. They generate about 5% of the South Africa’s electricity. In 2014, Eskom signed a ZAR4.4bn ($240m) contract with Areva (now Orano) to design, manufacture and install the replacement steam generators. They were made in China under subcontract by Shanghai Electric Power Equipment Company.

Replacement of the steam generators at unit 1 had originally been planned for the first half of 2021, with those of unit 2 to be replaced between January and May 2022. However, this was delayed mainly because of concerns about possible power shortages while the units are offline. The current licence expires in 2024-2025 and in 2021 Eskom applied to South Africa's National Nuclear Regulator to extend the operating licence. Eskom submitted the safety case for long-term operation in support of the application in July 2022. The regulator has two years to conclude the review and provide an outcome. No safety concerns have been identified that would preclude long term operation.

Koeberg 1 is now planned to be commercially available on 3 November. Because of the delays, the outage of unit 2 has been postponed until 7 November to ensure that there is no simultaneous shutdown of both units and that resources in place to begin the initial for the unit 2 outage.

Eskom said replacement of the steam generators was a first of its kind complex nuclear project to be performed at Koeberg and is the last major plant component out of the three to be replaced on the unit as part of the Long-Term Operation (LTO) project. The other two components – the replacement of the Refuelling Water Storage Tanks and the Reactor Vessel Closure Heads – have been replaced in previous years on both units. The replacement of the steam generators is the last of the large components that Eskom needed to replace in support of its application to operate the Koeberg units for another 20 years. The new steam generators are also more efficient and will produce an additional 27 MWe.

Eskom said the Koeberg units have operated safely and reliably for almost 40 years. “The amendment of the operating licence will enable Koeberg to continue providing safe, clean, and reliable power to the grid, and playing the essential role of stabilising supply in the Western Cape, which unit 2 has safely continued to do with an excellent energy availability factor of 94.87%, while unit 1 was on outage.”

Image: Koeberg nuclear power plant (courtesy of Eskom)