South African utility Eskom and the National Nuclear Regulator have refuted media reports that the reinforced concrete containment buildings at the Koeberg nuclear power plant have suffered extensive corrosion and would not be able to prevent the release of radiation in the event of a severe accident. They say tests have confirmed the performance of the structures, to which repairs have already been made.

Koeberg, South Africa's sole nuclear power plant (Image: Eskom)

Media reports said the Koeberg Alert Alliance (KAA) had been notified of structural problems at Koeberg by a "concerned insider". The KAA says: "At one stage the concrete containment dome was found to have cracked around the entire 110 meter circumference."

In August 2020, KAA made two requests under the Promotion of Access to Information Act legislation. The first was a request for the latest report on chloride damage to the concrete reactor containment domes, and the second was related to damage to the stainless steel used in the structures of the plant. The anti-nuclear group said Eskom had provided it with a 31-page report which refers to repairs carried out up until 2018, has 11 pages entirely blacked out, and various other sections, photos and tables redacted with the reason given as "sensitive technical information".

"What is in the report is deeply disturbing and contradicts claims of safety," said KAA's Peter Becker. "There should be no need to hide the extent of the damage or the associated costs of the repairs. There is a great need for transparency from Eskom as the proposed 20-year extension of Koeberg's lifespan and additional nuclear builds are being debated."

Eskom refutes safety risks

However, Eskom said in a statement it is "fully cognisant of the risk of corrosion of civil structures" at the Koeberg plant in Duynefontein, 27km north of Cape Town, on the Atlantic coast.

"Ongoing testing on the Koeberg containment buildings, which house the reactor and associated nuclear components, have proven the structures to be capable of withstanding the most severe accident," the utility said. "This containment programme has been managed closely since construction."

Eskom noted these tests comprise quarterly and annual measurements to identify any abnormal movement (such as expansions, settling, etc), visual inspections to identify physical degradation (such as cracks, spalling, efflorescence) and by performing the Integrated Leak Rate Tests (ILRT) on a 10-yearly basis. "The results of the ILRTs have shown conclusively that the design functions of the containment buildings are met." It added the test results were compared with international plants of similar design and found to be in line with industry norms.

Reassurance from regulator

The National Nuclear Regulator (NNR) confirmed that the Koeberg plant currently complies with regular tests required by the regulator. "Furthermore, with the information at our disposal we can confirm that despite the concrete cracking and delamination observed on the outer surface, the containment structures remain currently effective for protecting the environment from radiation during accident conditions," it said yesterday.

NNR CEO Bismark Tyobeka said: "The Koeberg nuclear power station is continuously monitored to ensure that the operation of the plant complies with nuclear safety requirements at all stages of operation."

Eskom said the main concern to the long-term system health of the containment buildings is the deterioration of the externally exposed concrete surfaces due to chloride ingress that causes reinforcement corrosion and the potential effect on the pre-stressing tendons. It said concrete repairs have been implemented to reinstate areas of the external façades where spalling and delamination occurred due to reinforcement corrosion.

"A long-term solution to prevent rebar and tendon corrosion due to chloride ingress is the implementation of an induced cathodic protection system," Eskom added. "This is being implemented as previously recommended by a team of international civil engineering experts."

Construction of the Koeberg plant began in 1976, with unit 1 entering commercial operation in 1984 and unit 2 in 1985. With a total capacity of 1860 MWe, Koeberg's two pressurised water reactors can supply the equivalent of about 5.6% of South Africa's national energy needs, and currently about half of the energy demand of the Western Cape. Eskom is planning to extend the operation of the units by 20 years to 60 years each. The plant is undergoing a periodic safety review to identify safety improvements for the long-term operation period.

Researched and written by World Nuclear News