An acute ingress of marine life, including fish and jellyfish, clogged a drum filter at Eskom’s Koeberg nuclear power station, causing unit 1 at the facility to trip on 10 March.

The state-owned electricity utility said on Friday that the unit was tripped manually in line with operating procedures.

“The reason for the manual trip was as a result of the increasing temperature on the secondary side of the plant to due to degraded heat removal (or cooling) capability because the pump that remained in service was supplying a heat exchanger that was degraded and not able to sufficiently remove heat,” the company said in a statement.

“The circulating cooling water system pump that tripped was due to low levels in the suction pit as a result of the drum filter that was clogged by an acute ingress of marine life.”

Normally, Koeberg units are able to survive a trip of one circulating cooling water system pump, the utility explained.

“The actions required from the operators are to reduce power to below 60% and to ensure that temperatures of various components on the secondary side stabilise. In this case, the temperature did not stabilise due to the heat exchanger remaining in service having reduced heat transfer efficiency and was planned for maintenance this week.

Cleared off

“The excess marine life and debris has been cleared off the drum filter and it is back in service,” Eskom said. “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 was not damaged, as had initially been feared.