The Koeberg nuclear power station in South Africa, 30 km north of Cape Town. (Photo: Esa Alexander)
Eskom has reached a crucial milestone in Koeberg Nuclear Power Plant Unit 1’s maintenance plan, even though it is weeks behind schedule.
The plant, with a capacity of 920 MW, is undergoing scheduled maintenance to enable the replacement of the steam generators.
The plant was shut down in December 2022 due to more load shedding and was expected to remain shut down for six months.
This is in line with the government’s Energy Action Plan Intervention One, which aims to guarantee that all power plants are adequately maintained and operate at peak efficiency to prevent further reductions in the energy availability of the energy company.
The energy supplier revealed that the power station’s first steam generator had been dismantled and stored in a storage facility.
“This is a major achievement for the Koeberg team, the contractor and the numerous local and international subcontractors involved in the project. We are very relieved to have reached this milestone as the steam generator replacement project has had numerous false starts during previous outages and some unexpected challenges during the current outage to get to this point in the project,” said Eskom Tuesday.
According to the electricity supplier, dismantling the steam generator is a dangerous operation due to its size.
“The logistics of moving the steam generators from their installed (vertical) position out of the container (horizontal at a height of 20m) to placing them on a flatbed trailer (horizontal) can only be appreciated if one considers the size and weight of each understands steam generator.
“Each of them is 22 meters high with a diameter of 4.5 meters (upper half) and 3.5 meters (lower half) and they each weigh more than 320 tons. From here all it takes is to take out the other two ready to lift and install the three new steam generators,” Eskom said.
Before the operation can be performed, many measures must be taken. These are some examples:
Remove the remaining two steam generators from their positions in the containment. Rigging the three new steam generators in their exact position in the containment building. Perform the 6 critical welds (2 per steam generator) that connect the steam generators to the primary system piping. Radiograph welds to ensure they meet code requirements. Reinstall all access platforms that allow people to work all the way up into the steam generators (seven floors of permanent structures and temporary scaffolding). Install all other piping connections (top steam pipe, feed water pipe, and all other minor sampling and instrumentation connections) as soon as access is available. In all cases, perform the required level of quality control. Install new thermal insulation over the entire surface of the steam generator and all piping that was worked on (approximately 120 tons were removed). Remove all temporary equipment that had to be installed to carry out the work safely (scaffolding (85 tons), lead shielding (70 tons), electrical services (22 distribution boards and 1 km of cabling), etc.).
Delay in resuming service
The return of the unit to service has been postponed, according to Eskom, as these actions need to be completed properly.
“After (these steps), we still need to complete the planned maintenance activities for the outage, commission all systems, refuel the reactor and return the unit to service. Due to the delays that have already occurred, the original return date for the unit is no longer feasible.
“Although every effort is being made to mitigate the impact, we are currently experiencing a few weeks delay. The Generation production plan is being optimized to minimize the impact of the expected delay on the system as much as possible.
“In accordance with the safety analysis conducted and submitted to the National Nuclear Regulator in support of the application to extend the life of the plant by 20 years, the steam generators are the final major component replacements required to ensure that Koeberg can operate safely for the requested additional operating time.
“Eskom therefore sees this milestone as an important step towards safely extending Koeberg’s life,” said Eskom.
Later this year, Koeberg’s second unit will be shut down for a similar period to replace its three steam generators.