Eskom confident of Thyspunt seismic safety

South African nuclear utility Eskom said it is confident its probabilistic seismic safety studies for Thyspunt adequately characterise the site's seismic hazards. It denied allegations by a research institute that it had not shared its findings on the seismic safety of the Eastern Cape site.

Thyspunt is one of two potential sites for new nuclear power plants for which Eskom earlier this year submitted applications to the country's National Nuclear Regulator. The other site, Duynefontein, is in the Western Cape.

Eskom's statement was issued on 25 November in response to media reports citing a study published by the Africa Earth Observatory Network-Earth Stewardship Science Research Institute (AEON-ESSRI), based at the Nelson Mandela Metropolitan University in Port Elizabeth. The report, Geo-realities @ Thyspunt.za authored by AEON director Maarten de Wit, says the proposed nuclear plant site is at seismic risk from the Kango fault coupled with the presence of deep "canyons" in the bedrock, covered by sand and soft rock.

The report says that aquifer systems, valleys and canyons beneath the sands at Thyspunt "may not be able to protect large tidal swamps and/or tsunami waves from flooding across the bedrock below sea level". It also says a plant built at the site "could literally become a Fukushima prone to flooding from below". It adds that "there has not been open access to all the scientific data" from Eskom's site studies.

Eskom said extreme scenarios and alternative models and interpretations, such as those presented in the AEON report, were addressed by the SSHAC Level 3 (Senior Seismic Hazard Analysis Committee) methodology it used in its studies of Thyspunt. The US-developed methodology is the approach required by the US Nuclear Regulatory Commission for construction of new nuclear plants and is accepted as "one of the most comprehensive and rigorous approaches", the company said.

Eskom itself, and not the studies referred to by AEON, identified a segment of the Kango fault that was seismically active 10,000 years ago and then proceeded to quantify that risk. "That work was incorporated in the Thyspunt seismic hazard calculations and is reflected in the seismic design input that will be used for the design of the power stations," it said.

"Eskom would like to make it clear that the plan has always been to remove the sand and excavate into the bedrock to create a level horizon in competent material to eliminate the liquefaction risk. This is the same approach as was taken at the existing Koeberg Nuclear Power Station in the 1970s," it added.

Eskom said the AEON-ESSRI studies brought "no new data to the table as relates to the suitability of the Thyspunt site for nuclear power plant siting" and in fact used information based on research previously carried out and publicly shared by Eskom. The findings of the SSHAC study, completed in 2013, are freely available on the internet and the research has led to the publication of more than 20 scientific papers in the international scientific literature, the company said. "Suggesting that Eskom has not shared the data and findings of its own studies is patently untrue," it said.

The South African government last week announced plans to increase nuclear capacity by 1359 MWe by 2037 - less and over a longer timeframe than the previously announced target - under draft integrated resource and energy plans which are currently open to public consultation. Eskom has said it plans to invite applications from companies interested in building new nuclear plants by the end of this year.

Eskom operates the two-unit Koeberg nuclear power station, near Capetown.

Researched and written
by World Nuclear News