The return of Koeberg's Unit 1 to commercial service has been delayed by a further 10 days as some critical tests are still to be completed before the reactor is started.

The last date that Eskom provided for the return of Unit 1 from the extension of life project was 3 November. It is now expected to be returned around 13 November. Unit 2 will then be taken offline to replace its steam generators. The extension project will give Koeberg a 20-year extension of its licence, which expires in July 2024. 

The entire project is massively behind the original schedule, which was planned for 2022 and was expected to take 12 months. It was first put out to tender in 2010.

In a detailed reply to questions, Eskom's head of nuclear, Keith Featherstone, said that the steam generator replacement was complete, but some tests remained before the turbine could be set spinning to prepare for synchronisation to the gird. The unit would be commercially available once all tests were complete.

Said Featherstone: "During the startup, as all the activities are in series and a precursor to the next activity, any emerging defect becomes a delay to the plan as it has to be fixed before the plan can continue.

"Achieving each of the milestones involves the completion of many tests to verify all the safety systems are operating correctly. Up until now, the delays that have been experienced are typically around the review of the stroke times of values measured during the performance of the tests, as we have to assess deviations from previous values and ensure they are adjusted properly."

Featherstone said the primary circuit was in what is called "hot shutdown condition" - in which it "operates at pressure of 155 bar and temperature close to 300 degrees C, but the reactor has not yet been started."

The schedule to complete the refurbishment on both units before the licence expires is under pressure. While Eskom expects replacing the steam generators in Unit 2 will be quicker, it has taken 10 months to do Unit 1. 

In a further complication, Unit 1 must be taken offline again in July 2024 for 200 days. This is to conduct pressure tests on the container building that still need to be done. There is, therefore a risk that the two units – which alone generate electricity worth two stages of loadshedding – will be offline simultaneously.

To avoid this, Eskom has applied to the National Nuclear Regulator (NNR) to revise the licence with two stop dates, one for each unit, as Unit 2 came into commercial operation more than a year after Unit 1. If granted this permission, Eskom can complete the pressure tests on Unit 1 before Unit 2 is taken offline. 

"We are still awaiting a decision from the NNR as to whether they will include separate dates for Unit 1 and Unit 2 … The planned 200-day shutdown of Unit 1 will only change once we have clarity on the long-term operating licence from the NNR as we do not know if they will impose any requirement," said Featherstone.