Why Koeberg Unit 1 was tripped – Jellyfish and fish blockage

Eskom has provided an update as to why Koeberg Unit 1 was manually tripped by its operators this week.

“The reason for the manual trip was as a result of increasing temperature on the secondary side of the plant, due to degraded heat removal (or cooling) capability,” said Eskom.

The reason for the degraded performance was because the pump that remained in service was “supplying a heat exchanger that was degraded and not able to sufficiently remove heat”.

“The circulating cooling water system pump that tripped was due to [a] low level in the suction pit as a result of the drum filter that was clogged by an acute ingress of marine life (jellyfish and fish),” said Eskom.

It stated the Koeberg units are typically able to survive a trip of one circulating cooling water system pump.

“The actions required from the operators are to reduce power below 60% and to ensure that temperatures of various components on the secondary side stabilises.”

“In this case, the temperature did not stabilise due to the heat exchanger remaining in service [having] reduced heat efficiency and was planned for maintenance this week,” said Eskom.

“The excess marine life and debris has been cleared off the drum filter and it is back in service. The level in the suction pit has sufficiently recovered and the circulating water system pump has been put back in service and no anomalies have been noted.”

The pump has not been damaged, said Eskom.

Eskom added that the technical assessments and regulatory approvals have been obtained to start and safely return Koeberg Unit 1 back on the grid.

“The current projected synchronisation will take place on Sunday,” said Eskom.


Eskom stated earlier this week that stage 4 load-shedding will continue until Friday.

Load-shedding shifted to stage 4 on Tuesday afternoon after the fault which occurred on the turbine section of Koeberg Unit 1.

Eskom said unplanned breakdowns or outages stood at 12,046MW on Tuesday afternoon, while planned maintenance outages were at 6,155MW.

Eskom advised South Africans that the stage of load-shedding may change at short notice because its ageing fleet is currently constrained, unpredictable, and vulnerable.

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Why Koeberg Unit 1 was tripped – Jellyfish and fish blockage