- Isotope main suspect behind 2010 Cobalt-58 scare
- Plant should be decommissioned says Koeberg Alert
- There is no known threshold beyond which radiation is considered safe
INFORMATION released by environmental organisation Koeberg Alert Alliance (KAA), point to ongoing reactor design problems associated with normal operations at the plant. In particular the production of elemental Tritium (3H) and tritiated water (3H2O) during the course of nuclear fission. The organisation has previously drawn attention to routine Tritium releases and the resulting contamination of borehole water and the water table surrounding Koeberg, in its submissions on the environmental impact of a previous project known as Nuclear 1 — is now concerned about further issues which have emerged from an informal forensic study of the discharge.
“Tritium levels of <3 TU are the “norm” at the Koeberg site but elevated levels of 4.8, 5.5 and 42 TU have been recorded in three boreholes within 50 m of the plant buildings”, suggests the initial report by SRK Consulting, which was conducted over a decade ago in 2010 and is still used by KAA as a baseline requiring further research.
The SRK report illustrates how widespread the Tritium issue has become.
“These levels are the result of known releases of tritiated steam and condensate and the pathways are as per the original design of the plant and are not due to uncontrolled releases or leaks,” claim SRK who concluded at the time: “The presence of tritium in groundwater at these levels does not pose a risk to people or the environment”.
The report however failed to explain a contamination incident inside the plant affecting 91 workers at the time the report was drafted, and in all likelihood the result of Tritium. The claim of zero health impact is also disputed by KAA.
According to the Nuclear Industry Association of South Africa (NIASA) “The greatest source of radioactivity in the reactor coolant circuit is, however, irradiation of the coolant itself. Neutron bombardment of nitrogen dissolved in the water gives rise to carbon-14. Moreover, irradiation of boron dissolved in the coolant water creates hydrogen-3, i.e. tritium, the radioactive isotope of hydrogen.”
“Radioisotopes such as cobalt-58, cobalt-60 and silver-110m arise as a result of wear or corrosion of reactor components. They become radioactive due to neutron bombardment as they circulate through the reactor with the primary circuit cooling water.”
Both Tritium and Tritiated Water are sources of beta particle radiation. It is suspected that elemental Tritium is the more likely culprit behind the production of Cobalt-58 dust affecting the workers, who would not ordinarily come into contact with the primary coolant.
At the time Eskom spokeswoman Karen de Villiers claimed the exposures to radiation caused by exposure to the dust particles were low, “about 0.5 percent of the annually allowed exposure limit.”
Co-58 has a half-life of 70.86 days, which is the ‘approximate time required for a quantity to reduce to half of its initial value’. The substance is a source of beta and gamma radiation. It would thus take 70 days to become half as radioactive, another 70 days to become a quarter and so on, and is thus radioactive for months.
Elemental Tritium is able to diffuse through metals, particularly in the presence of heat, and is a direct consequence of fission, where production of Tritium occurs in about “one atom per 10,000 fissions” as a direct consequence of the fission process. Tritiated Water (3H2O) is the result of neutron bombardment of water. Tritium has a half-life of 12 years, and a decay chain to Helium-3 (3H).
Although not considered chemically toxic, it is nevertheless a source of radiation, and impacts upon the longevity of the plant, which is nearing its design limits and is due for decommissioning in 2024.
With 2 neutrons and one proton, Tritium loses a neutron during the decay process creating beta particles which then interact with nickel parts inside the plant. Nickel, since it has 30 neutrons, loses a proton and gains a neutron to become radioactive Cobalt-58, which itself experiences its own decay chain.
This is the prevailing explanation for the 2010 contamination incident.
Since the Linear No-Threshold (LNT) model of radiation exposure states there is ‘no threshold beyond which radiation should be considered safe’, KAA consequently disputes the baseline findings of SRK Consulting, and thus the drafters of the initial report commissioned by the Pebble-bed Modular Reactor Company, to determine possible impact of the demonstration unit Koeberg.
LNT is a dose-response model used to estimate stochastic health effects such as radiation-induced cancer, genetic mutations and teratogenic effects on the human body due to exposure to ionizing radiation.
The model “statistically extrapolates effects of radiation from very high doses (where they are observable) into very low doses, where no biological effects are observed” and is disputed by members of the Nuclear Industry.
The LNT model is nevertheless the foundation of a “generally-accepted postulate that all exposure to ionizing radiation is harmful, regardless of how low the dose is, and that the effect is cumulative over lifetime.”
The National Nuclear Regulator currently deems anyone who accepts the LNT model, to be ‘opponents of nuclear power’, and thus Peter Becker was recently suspended from his position on the regulator as a civil society representative by Minister Gwede Mantashe.