Update: Eskom |


erection underneath the generator was required, hence the generator had to be purged of hydrogen.


Purging involves displacing one gas with another to prevent a combustible mixture. In this case hydrogen was purged with carbon dioxide to prevent the hydrogen from mixing with air/oxygen.


The operating department was tasked with the purging of hydrogen from the generator prior to the leak search. It appears air was introduced into the generator at a point where hydrogen was still present, creating an explosive mixture. The unit 4 generator experienced a hydrogen explosion when the hydrogen/air mixture reached the spontaneous combustion level, resulting in severe damage to the generator, exciter, turbo-generator auxiliaries and other equipment.


Seven employees were treated for shock (but thankfully there were no injuries or fatalities).


“The incident…seems to indicate procedural non-compliance and management failures”, said Phillip Dukashe, the group executive for generation.


Initial indications are that the cost of repairing the damage caused by the explosion will amount to an estimated R2.5 billion. The incident is “being used as a case study to improve internal processes going forward”, Eskom says, and in response it has taken corrective measures to safeguard its operations, employees, and assets. These include the appointment of a recovery manager, while the process of recruiting a multi-disciplinary team had commenced, Dukashe reported. “A process to assess the damage to property resulting from the explosion is underway, and is led by Eskom Rotek Industries (ERI) with technical support from GE.” GE is the OEM following its purchase of Alstom power businesses.


Eskom has also launched an insurance claim relating to the incident, and insurers have appointed technical assessors who are working with Eskom and GE’s engineers to evaluate the damage.


Initial indications are that the unit may not return to service until August 2024, but “we continue to explore avenues to accelerate the recovery of the unit”, said Dukashe. Dukashe also reiterated that the process to address the design defects of the Medupi and Kusile power stations is “progressing well.” Boiler plant modifications have been implemented on all six units at Medupi, except for a few specific components on unit 6. A boiler plant modification outage was currently underway at Kusile unit 2, following successful completion of boiler work on unit 1 during November 2021, with unit 2 expected to return to service in February 2022.


“Since the implementation of the solutions on Medupi unit 3, which was used as a pilot, the unit has been running at an average of 93% EAF for 8 weeks from an inspection outage in November 2021, an indication that


12 | March 2022| www.modernpowersystems.com


the interventions have begun yielding the desired outcomes,” said Dukashe. Eskom has had to address a wide range of major boiler defects on the new-build Medupi and Kusile units (involving mills, gas/air heaters, fabric filters, air and flue gas ducts, and reheaters) and a defect correction programme has been established in collaboration with the original boiler contractor (Mitsubishi Hitachi Power Systems, now Mitsubishi Power Africa), to develop, test and implement technical solutions in all the Medupi and Kusile units. Looking at the older units, Eskom group executive for transmission, Segomoco Scheppers, said the majority of Eskom’s coal power stations are operating past the midway of their operational life, at an average of 42 years, resulting in high levels of breakdowns. “As we continue to perform reliability, maintenance and refurbishment projects to address lack of power station reliability, an elevated risk of load shedding remains,” said Scheppers.


He added that Eskom will continue to rely on renewable energy sources to play a significant role to ease the pressure on the national grid, having contributed more than 3500 MW to the power system during the day on some days. “For example, on 1 November 2021, at 13:00, about 19% of the country’s demand was supplied by renewable generation,” said Scheppers. “While this is still low, we expect the renewables contribution to continue rising as additional capacity is brought online.”


Koeberg SG replacement postponed


The Koeberg 2 x 920 MWe PWR nuclear plant continues to be one of the most reliable power stations in the Eskom generation fleet, with the lowest “primary energy costs”, says Eskom, and “consistently playing a significant part in adding stability to the grid.”


Koeberg unit 2 was shut down on 18 January 2022 (following an uninterrupted 454 days of power generation since its previous outage) for a refuelling and maintenance


outage, the scope of which had been intended to include replacement of the three steam generators.


However, prior to the start of any irreversible work in relation to the steam generator replacement, Eskom and the main contractor, Framatome, performed a final review to ensure that “the steam generator work would be completed at the expected quality levels and in accordance with the outage schedule.” The review concluded there was a “high likelihood of the unit being returned to the grid later than currently planned.”


Due to the potentially severe impact of such a delay on the grid, the decision was made to defer the steam generator replacement to the next planned outage for this unit, scheduled for August 2023. This is to avoid the risk of impacting electricity supply during the high demand winter period, with an earlier than anticipated return to service of Koeberg 2 helping to reduce the risk of load shedding, says Eskom


Having completed its maintenance and refuelling outage, which is underway but without the SG replacement, Koeberg unit 2 will be returned to service during June 2022. This will help reduce the pressure on the rest of the generating fleet and limit the need for load shedding during the winter period. The unit 1 steam generator project will proceed as planned, starting in September 2022, says Eskom.


Steam generator replacement is a key part of Eskom’s LTO (long term operation) efforts to extend the operating life of the Koeberg plant by another 20 years beyond 2024/25. Considering that the power station has been largely depreciated, the steam generator replacement project, at a budgeted R20 billion for both units, is seen as “one of the most financially attractive projects in the Eskom portfolio”, the utility says.


The formal application to extend the Koeberg operating licence has been submitted to South Africa’s National Nuclear Regulator (NNR).


Above: Koeberg nuclear plant


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