The series of small earthquakes that shook Cape Town recently has raised fears that a larger seismic event could spell disaster for the ageing Koeberg nuclear power plant and those who live in its shadow.
On Saturday September 26, at 7pm, a 6.2 magnitude earthquake registered 1 600km off the coast of South Africa. At 8.41pm, a 2.5 magnitude tremor was reported in Durbanville.
According to the Council for Geoscience (CGS), the two quakes were not related.
On September 27, another 2.3 magnitude tremor hit 5km north of Durbanville.
On Tuesday November 17 at 12.27am, a 3.5 magnitude tremor was reported 60km off the Cape Town coastline.
The Southern African Faith Communities’ Environment Institute (Safcei) says an increase in seismic activity on the Milnerton fault line should ring alarm bells, especially since Eskom plans to extend Koeberg’s 40-year lifespan, due to end in July 2024, by another 20 years.
The Milnerton fault line caused one of the biggest earthquakes to ever hit Cape Town – the 1809 quake is estimated to have been a magnitude 6 event.
Francesca de Gasparis, Safcei’s executive director, has doubts about whether Eskom can be trusted to put people first in its decision-making about Koeberg.
“Has Eskom considered what will happen if we are hit by a massive earthquake on this existing earthquake fault, so close to our only nuclear power plant? We know from the nuclear disasters at Chernobyl and Fukushima, citizens were told not to worry, and that the government and the nuclear plants had everything under control. Yet, these are two of the biggest nuclear catastrophes of our time.
“Are we willing to take that chance with Koeberg when the information that should be in the public realm is being kept hidden? Firstly, the plant is old and secondly, we have no information about its current state. What if the next earthquake is even more powerful, which some scientists are saying is more than likely?”
A disaster on the scale of Fukushima or Chernobyl would be catastrophic for the country, she argues.
“In a worst-case scenario, the Koeberg evacuation plan would have to be implemented, and tens of thousands of people, possibly millions of people, would need to be evacuated.
And since radioactive contamination can make an area uninhabitable for hundreds of years, where would all these people find housing? Or schools for their children? Will there be enough services or jobs there, to cater for these new inhabitants?
“These are important questions which should be addressed in the open, with sufficient reliable evidence available for public scrutiny.”
Peter Becker, of Koeberg Alert Alliance, says Eskom’s response to their questions about the recent quakes was far from reassuring.
“We were brushed off by Eskom as no cause for alarm. But now, with a third and more intense earthquake, South Africans need to be aware of the risks associated with an aging nuclear plant so close to a fault zone and densely populated areas.
“The Council for Geosciences issued a tender [CGS-2020-033A], in October 2020, for a study of the seismic risks at the Koeberg site. It seems we are not alone in our concerns about how safe Koeberg is from earthquakes.”
Lewis Phidza, a stakeholder manager at Koeberg, says the plant continued to operate normally during the quakes with only a minor spike in vibrations on the turbine-driven pumps that feed water to the two nuclear-reactor units.
“Eskom wishes to assure the public that there are no safety concerns with regards to the Koeberg power station, which is designed to withstand a magnitude 7 earthquake.
In terms of the Richter scale, the amplitude of a tremor of 3.4 is much less than 0.1% of what Koeberg was designed to safely withstand. No damage was found or reported after inspections to the plant and other general areas.”
Mr Phidza says the reactors are built on what is known as a “nuclear island” that shields them from seismic activity.
“The foundations of the power station are anchored to the bedrock, and then the nuclear island ‘floats’ on a foundation of evenly spaced concrete pillars. Each of these pillars is topped by a seismic bearing, which isolates the nuclear island from the shaking of the ground during an earthquake, essentially acting as a shock absorber.”
However, Ms De Gasparis and Mr Becker question whether the neoprene pads that form part of this “shock absorber” system will last for another 20 years in a marine environment if Eskom plans to extend the life of Koeberg.
They say that while Koeberg was the first nuclear plant built with earthquake protection in the foundations in the form of a concrete “raft” resting on neoprene rubber pads, it didn’t have the horizontal failsafe buffers included in later designs.
They say this means that if the rubber pads do not perform as expected, or if there is an unexpectedly powerful earthquake, it could result in the foundation cracking. They want Eskom to explain whether the neoprene pads will last for another 20 years in a marine environment.
Mr Phidza says the neoprene layer will form part of the safety assessments that need to be carried out for the National Nuclear Regulator to grant Eskom permission to extend the life of the plant.
“As part of this exercise, Eskom has contracted the CGS to perform an independent review of the seismic risk in the area surrounding Koeberg, which is why CGS has issued an enquiry into the market for addition resources. This will be the first
such re-assessment of the Koeberg site.”
Mr Phidza says that during pre-design investigations for Koeberg, the Milnerton fault was mapped in a north-westerly direction about 8km offshore from where the plant is sited.
“It also extends in a south-easterly direction beneath the Milnerton area. The Milnerton fault may extend farther across the central Cape Flats and the north-eastern part of False Bay to a large fault exposed on-land between RooiEls and Betty’s Bay.