The two-unit facility supplies some 5% of the nation’s electricity and they are currently the only operating reactors in South Africa as well as the African continent.

While the nuclear units play a significant role in maintaining grid stability, since the start of the year only a single unit, or half the capacity, has been operating.

Both Koeberg 1 and 2 are PWRs. Unit 1 began construction in 1976 and commercial operations begin in July 1984. Construction on Unit 2 also began in 1976 but commercial operations didn’t begin until just about a year later than unit 1, in November 1985. Units 1 and 2 have net capacities of 924 MWe and 930 MWe, respectively. The state-owned power utility Eskom is responsible for operating the reactors as well as maintaining them and this year both are due to be shut down as part of a repair and maintenance programme.

The planned outage of unit 2, the 25th refuelling outage since commissioning, began on 18 January and originally had been planned as an outage lasting 155 days. This maintenance programme also included the replacement of the unit’s three steam generators and reactor pressure vessel head, which houses the nuclear fuel.

In March though, the company announced that, prior to the start of any irreversible work, Eskom and the main contractor Framatome (now Areva) performed a final review to ensure that the steam generator replacement work would be completed in a timely way while ensuring the quality levels of the work. However, the review concluded that there was a significant likelihood that the unit would not be returned to service before the peak demand winter season, exacerbating the challenges faced by an already constrained grid.

“Before we start cutting pipes, we conducted a final review to ensure that the steam generator replacement work would be completed at the expected quality levels and in accordance with the outage schedule. It was just too risky to continue with this work,” Oberholzer explained in a statement.

With the chance that the reactor may return to service later than planned-for June 2022 and the severe impact on consumers and businesses, if that was the case, a decision was taken to delay the steam generator element of the refurbishment until the following refuelling outage. This is currently planned for August 2023. Eskom insists that these deferred tasks in no way affect the safe operations of the plant as the steam generators undergo a full series of inspections and integrity tests as part of the standard refuelling outage. Riedewaan Barkadien, Eskom’s Chief Nuclear Officer, explained: “We have moved the replacement of the generators into a window that suits Eskom better,”

While the first phase of the current outage proceeded as planned, including the replacement of fuel and scheduled maintenance, the latest delay to the project is the second to be recently announced. Eskom laid the delays at the door of the global pandemic, which hampered the ability of the company to get resources to the site. Work on Unit 2 had initially been set for completion by mid-June. CEO André de Ruyter has said the work would now be finalised by the end of July, as NEi goes to press. Unit 2 had produced electricity for 454 days without interruption ahead of the January refuelling and maintenance shutdown.

Each weighing about 380 tonnes and some 20 metres long, the steam generator replacement is an important part of a US$1.2bn longer-term programme to extend the operational life of the plant by 20 years each. The original generators feature U-tubes that are susceptible to cracking. Once removed they will be temporarily stored on-site, before final disposal at the Vaalputs radioactive waste storage facility in the Northern Cape “as complete and sealed units”. It has been reported that the on-site facilities to store the old steam generators are not ready, which is one of the reasons for the changing schedule.

While the delay will not materially impact the life extension plan it does narrow the available window to complete the work. Koeberg’s current operating licences expire in 2024 for Unit 1 and 2025 for Unit 2. Steam generator replacement at both units is one of the upgrades required by the National Nuclear Regulator (NNR) to grant an extension to the operating licence. The Koeberg Long-Term Operation (LTO) plan is a series of activities that will enable Koeberg to operate to 2045. The plans are to be submitted along with supporting documentation to the NNR for evaluation and Eskom had planned to submit the required supporting documentation by June 2022.

As part of the review of the Koeberg LTO programme, an International Atomic Energy Agency (IAEA) 10-person team carried out a safety aspects of the LTO (SALTO) review during March 2022. “We observed that despite many challenges the plant has made progress in ageing management activities and preparation for safe LTO since the first Pre-SALTO mission in 2015,” said team leader Gabor Petofi, a Senior Nuclear Safety Officer at the IAEA. Koeberg management has also requested the IAEA schedule a follow-up mission to Koeberg in 2024.

“Eskom has incorporated some IAEA standards and guides into its policies and procedures, with a robust framework having been put in place for the life extension,” said Barkadien.

In a statement Katse Maphoto, Chief Director: Nuclear Safety and Technology of the Department of Minerals and Energy in South Africa, emphasised the importance of Koeberg LTO from national energy security and grid balancing perspective: “The government remains optimistic that the LTO project will benefit a lot from this IAEA mission recommendations for the power station to achieve the highest level of safety.” Indeed, the South African government has previously indicated a strong commitment to the future of nuclear energy. Alongside, the Koeberg LTO in October 2019 the country outlined plans to build 1 GW of new nuclear capacity by 2030.

Koeberg unit 1 is currently scheduled to shut down for its annual refuel and maintenance programme in September and the steam generator replacement on this unit will proceed as planned from October 2022. This is after the winter peak and is planned as a similar 155-day outage. Its reactor pressure vessel head was replaced several years ago.

Areva was the original manufacturer of the equipment at Koeberg and in August 2014, Eskom awarded the steam generator replacement contract to the company in a ZAR 4.3bn (US$258m) contract that was later challenged in court by Westinghouse. The installation of the replacement steam generators was originally scheduled to begin in 2018. Three of the steam generators have already been completely built and the remaining three are progressing well, Eskom says.

In August last year, US-based Jacobs announced it had been selected to carry out essential engineering modifications in preparation for the installation of the six replacement steam generators. Jacobs is responsible for construction management related to modifications to the secondary steam turbine system. The scope of work includes prefabrication of piping, pipe supports and modification, and piping replacement; installation of on-site scaffolding, rigging and lagging; vessel modifications and strengthening; and replacement of forced air cooler units. About 12.6 tonnes of asbestos roof sheets and 14.1 tonnes of structural steelwork were safely removed ahead of schedule.

“This project is vital to maintain the pivotal role of nuclear power in South Africa’s energy mix,” said Jacobs Energy Security and Technology Senior Vice President Karen Wiemelt, who added: “We also created a new design to install an independent seal cooling system with an independent power supply system.”

In March 2017 Canada-based L3 MAPPS won a contract to upgrade two simulators at Koeberg, taking into account the changes that the new steam generators will make to the plant performance. The two simulators will switch from PC/Linux simulation servers to PC/Windows-based computers running its latest Orchid simulation environment. The reactor core model will also be replaced. In 2013, L3 MAPPS completed work to upgrade the plant’s original simulator and also commissioned the second full-scope simulator at the site. That work was carried out under contracts signed in 2009.

In July, it was announced that Barkadien had tendered his resignation and is to join a Canadian nuclear utility after 26 years at Eskom. A previous Koeberg Station Manager, Keith Featherstone, will be acting in the Chief Nuclear Officer role while a replacement for Barkadien is recruited. “As the only nuclear power station in Africa, we have all played a role in keeping the plant safe, and the best place to work. The decision to resign was, therefore, by no means an easy decision,” said Barkadien.

In a related development, the current acting Station General Manager (PSGM), Nomawethu Mtwebana, is to temporarily join the World Association of Nuclear Operators (WANO) after the completion of the current outage of Unit 2. Mahesh Valaitham will become the acting Koeberg PSGM.

Returning Koeberg 2 to service will help reduce pressure on the rest of the Eskom generation fleet and will help mitigate the risk of further load-shedding over the winter period. The increase in load-shedding came on the back of higher levels of unplanned plant breakdowns, which averaged 26% of the fleet in the period ended March 2022. During this period the energy availability factor (EAF) averaged 62%.

“Planned maintenance is Eskom’s only weapon to try bring reliability and predictability to a neglected plant,” Eskom Chief Operating Officer Jan Oberholzer said, emphasising the challenge of maintaining its generation fleet. During the summer months around 12% of the total generation capacity had been taken offline for planned maintenance in preparation for the peak demand winter period.

The return to service of Koeberg 2 will add 920 MWe of much-needed power to the South African power system, reducing pressure on a constrained power system and limiting the need for load-shedding. Until then Eskom has urged South African residents to use electricity “sparingly”, especially during the morning and evening peaks, when capacity constraints require it to implement load-shedding as a “last resort” to protect the national grid. Nonetheless, due to low plant availability from 1 January to 10 May this year, load-shedding has been implemented for 32 days, six more than the 26 days of load-shedding during the same period in 2021.

This article first appeared in Nuclear Engineering International magazine.