Eskom responded to the report on Thursday by saying it was confident its seismic hazard assessment was adequate. The methodology used had taken account of various alternative models and interpretations, including the "extreme scenario" in De Wit’s report, it said.
"Eskom will also apply conservative decision-making in the design and operation of a future Thyspunt nuclear installation. It is confident that the data used and knowledge gained through the Thyspunt [probabilistic seismic hazard analysis] project is accessible to the broader scientific community, and that it has contributed to our understanding of the local and regional geology and the hazard posed by seismic events,"
The paper quotes studies that show the sea level has been rising along Nelson Mandela Bay at about 2mm a year over the past 36 years and may rise between 1m and 2m by the end of this century as the power station nears the end of its life. Nelson Mandela Bay is also particularly exposed to storm surges.
"From the above, one may conclude that the chance of seawater penetration into buried canyons and valleys beneath the Thyspunt dunes is more likely to increase into the future rather than stagnate or decrease," the report reads.
The PhD study explores the fault system that runs about 600km along the Cape mountains to Coega, and several fault systems nearby. The area has witnessed historic earthquakes such as the 6.3-magnitude Ceres-Tulbagh quake in 1969.
De Wit says new "paleo-seismicity work" outlined in the thesis confirms the fault "can be best considered ‘active’"; and a major earthquake and surface rupture occurred about 10,000 years ago along the Kango Fault segment, close to De Rust.
A conservative estimate of the magnitude of this paleo-earthquake is between 6.9 and 7.2, the study reads.
"The new work implies that the hazard for the southern to southeastern Cape should now be upgraded, to include local 7.0-magnitude events.
"If in future, for example such a similar earthquake occurs along the extended St Croix Fault offshore, it is likely to generate a large submarine slump, and possible significant local tsunami that would affect the coastal region, including Thyspunt," the report reads.
De Wit criticises Eskom for making little of its own technical work available on an open-source data bank, which would allow other scientists to scrutinise it. This, he says, is neither transparent nor international best practice.
The risks are compounded by indications from Eskom that it does not intend building a state-of-the-art nuclear plant that would include all the post-Fukushima safety features standard in GenerationIII reactors.