Scientists say it is “quite conceivable” that the Koeberg nuclear power station could experience an earthquake greater than 8 on the Richter scale – and they have called for a “serious reassessment” of the earthquake hazard to Koeberg, which lies about 8km from the offshore Milnerton Fault.
Chris Hartnady, an international expert on geotectonics and technical director of the Umvoto science consultancy in Muizenberg, told the Cape Times: “I do not agree that there is ‘no risk’ … A ‘great’ earthquake, of 8 and above, is quite conceivable on the Milnerton Fault.”
After the nuclear crisis in Japan, triggered by an earthquake of 8.9, the authorities here have assured South Africans that Koeberg is not an earthquake risk. The National Nuclear Regulator said last week that the Koeberg plant was designed to withstand “earthquakes and tidal waves of a magnitude which are considered likely”.
Koeberg has been designed to withstand an earthquake with a magnitude of 7. The Milnerton Fault caused an earthquake in 1809 with an estimated magnitude of between 6.3 and 6.5.
But Hartnady, a specialist in seismic risk assessment, believes these assurances are wrong. His says the methods used to work out what is “likely” are outdated.
Hartnady says he has had an intense difference of scientific opinion with the seismology unit of the Council for Geoscience on the subject of the earthquake risk to Koeberg. The methods the council used to calculate the risk to Koeberg used an old approach to working out quake risks. They used a method which worked out a maximum possible quake strength for a region.
Hartnady says there is no such thing.
The new approach looks at the universality of earthquake distribution – and arrives at different answers: that a quake of more than 8 near Koeberg is quite possible.
Hartnady says the engineers who built the Fukushima nuclear plant had a “misplaced confidence” in this regional earthquake risk assessment, which was believed to be 7.9. They had probably arrived at this figure “simply by adding an arbitrary 0.4 to the largest known historical event, a 7.5 earthquake in November 1938”.
“The unfolding catastrophe that we are currently seeing is testimony to the absolutely pernicious effect of the very notion of a ‘regional maximum’ earthquake. Better that the nuclear industry accept upfront that there is no such thing – only a universal global maximum close to 9 – and adopt an ultra-conservative approach to design,” he says.
He believes the authorities should seriously reassess the geohazards to Koeberg, and pay far more attention to the tsunami hazard. And they should focus their reassessment on the pools where the spent fuel, still highly radioactive, is stored on site.
The spent fuel – essentially radioactive waste – in Japan has given rise to massive problems after the storage pools were damaged by the tsunami.
Last week, the cabinet approved a new 20-year electricity plan which sees 23 percent of all new electricity generation coming from nuclear. The three sites selected to build the new nukes are Koeberg, Bantamsklip near Pearly Beach and Thyspunt near St Francis.
But if the methods used to calculate the quake risk to Koeberg are outdated, it appears that the methods used recently to calculate the quake risks for the new nukes are not only outdated, but “incomplete and scientifically flawed”, according to seismology expert Andreas Späth.
In his critique of the environmental impact assessment’s quake risk, he says the methods used to conclude that none of the sites posed a risk were “disingenuous, scientifically flawed” and “all but meaningless”. - Cape Times