Eskom nearly lost 920 MW of power to the grid when an individual at nuclear power station Koeberg cut the wrong valve.

The incident was reported in Eskom's newsletter to employees, Shutdown Times, on Tuesday.

While carrying out required maintenance on Unit 2, someone cut the valve of Unit 1, instead of the same valve on Unit 2, the newsletter read. This "significant error" could have had "devastating consequences."

Eskom had to implement a work stoppage following the incident, which could have resulted in the loss of the running unit. Koeberg's "high safety measures" managed to identify the error in time, to prevent any damage from being caused, according to spokesperson Sikonathi Mantshantsha.

According to the newsletter, this is the second time this incident has happened during this outage.

"This speaks to very poor human performance, and it is an unacceptable practise," the newsletter read.

According to Eskom - employees are equipped with the relevant training to correctly identify the unit and components they need to work on. Eskom implored employees to use situational awareness and be vigilant when working on the units.

Eskom acknowledged that fatigue might set in, "but we cannot afford to make such serious mistakes which could have resulted in serious repercussions," the newsletter read.

Asked whether Eskom is carrying out disciplinary action against the relevant individuals, Mantshantsha said that the individuals responsible have been interviewed and have been "cautioned" by Koeberg professionals.

Mantshantsha added that the incident was not such that warranted reportage to the regulator.

Both units at Koeberg have a capacity of 920 MW and are the largest generating units in Africa.

Koeberg Unit 1 has been safely online for 141 days, without any interruptions, said Mantshantsha.

Currently, Unit 2 is offline for maintenance and refuelling. Eskom was supposed to replace the steam generators at the unit during this outage. However, due to facilities not being ready, Eskom decided to delay the steam generator replacement to the next outage. Among these facilities was the construction of a building that was not yet complete. The building is meant to store the old, radioactive steam generators after their removal.

The delay in the steam generator replacement programme will ensure Unit 2 is back up and running in time for the high peak demand winter period, Fin24 previously reported.

Eskom is in the process of extending Koeberg's operational life by another 20 years.