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Information on the Chernobyl Nuclear Power Plant accident

The Chernobyl Nuclear Power Plant accident happened on 26th April 1986 at 1.24 a.m. The accident was the result of a flawed reactor design, coupled with inadequately trained personnel operating the reactor at the time. The accident resulted in large parts of Southern Belarus and Northern Ukraine, together with a smaller area of western Russia being contaminated by radioactive isotopes of iodine and caesium which had been released into the atmosphere. A detailed account of the accident can be found on the World Nuclear Association’s webpages.

The accident destroyed the Chernobyl 4 reactor and resulted in the immediate deaths of 3 operators of the plant at the time of the accident (two from injuries acquired from the accident itself, and one from a heart attack), and 28 firemen who died within a few months of the accident from Acute Radiation Syndrome, as a result of their exposure to large doses of radiation. Exposure to radioiodine in fallout from the accident resulted in a large increase in thyroid cancer, but only in those who were children at the time of the accident. The increase became apparent within 4 years of the accident. Full details of the health effects of exposure to radiation after Chernobyl can be found in a number of UNSCEAR publications.


Why did the accident lead to an increase in thyroid cancer?

The explosion and fire in the graphite core of reactor 4 at the Chernobyl Power Plant led to the release of more than 1019 Bequerels (Bq) of radioisotopes including 1.8 x 1018 Bq of 131- iodine, 2.5 x 1018 Bq 133-iodine , and 1.1 x 1018 Bq 132- Tellurium, which decays to 132- iodine. Iodine is concentrated and bound in the human thyroid from about 3 months of intrauterine age; for this reason, exposure to the thyroid from 131- iodine is 1000-2000 times the average body dose. 131-I has a short physical half-life, which results in quick elimination from the environment. Patients who were born more than 9 months after the accident were therefore not exposed to radioiodine either in utero or as young children. Many of the children in the exposed areas of Belarus, Ukraine and Russia received thyroid doses in excess of 1Gy. The thyroid is known to be a particularly radiosensitive tissue. Studies following the atomic bombing of Japan in the 1940s have shown that those exposed under the age of 10, carried a higher risk of developing thyroid cancer until they were aged 40. The BEIR VII model of the risk of radiation induced thyroid cancer based on studies of groups of children exposed to external sources of radiation predicts a lifetime Excess Relative Risk (ERR) of around 10 per Gy for exposure in early childhood, falling to an ERR of about 2 per Gy at age 20 at exposure. The reason for this differential risk is not known, but is believed to result from a combination of factors, including the mitotic activity of the tissue at the time of exposure.

For further detailed information on the health risks of low dose radiation more generally, please see the Radiation Restatement published by the Oxford Martin School in 2017.


Why was the CTB set up?

By 1995 it was becoming apparent that several European research groups were unknowingly receiving material from the same patients for research, and that there were discrepancies in the pathological diagnoses being applied to the same tumour. Subsequently, a report to the EC confirmed that there had indeed been considerable overlap since 1995 among a number of EC-funded molecular biology projects. It was then recognized that a cooperative tissue bank would reduce the duplication of research effort and provide better scientific data on the health effects of the Chernobyl accident. The Chernobyl Tissue Bank (CTB) was established as an internationally supported project and following agreement on standard operating procedures and approval by the relevant political and ethical authorities, the CTB officially started collecting material on 1st October 1998