A 24-year-old man who was about to join the Nuclear Power Corporation of India Limited (NPCIL) and his parents were troubled by what they saw on a TV channel about the alleged damage to DNA by radiation. TV channels often go overboard and make unsubstantiated claims.
A 63-year-old person asked this writer whether the throat malignancy, which, his 33-year-old daughter was suffering from, was likely due to the possible radiation exposure he might have received while working in a nuclear power plant when he was 28 years old. The explanations offered appeared to have dispelled their doubts.
Is work in a nuclear power plant risky?
Several extensive epidemiological studies of nuclear power plant workers have shown that work in a nuclear power plant is not a risky occupation.
Radiation workers in nuclear industry like other radiation workers form a unique group. They are adult workers whose radiation doses received at work are regularly measured; these records are maintained.
Radiation protection specialists accept that ionising radiation at high dose levels can cause cancer. Nuclear power plant workers receive low doses of radiation.
Cancer induced by radiation is indistinguishable from those caused spontaneously or by other cancer-causing agents. Since there are no unique biomarkers for radiation-induced cancer, specialists depend on statistical methods to predict cancer incidence in a group of exposed workers.
Specialists have carried out long-term studies of these workers in many countries. Most of these studies have low statistical power.
To get statistically respectable population groups, specialists carried out a pooled study of radiation worker populations from 15 nations. The participants in this international collaborative study included 407,391 workers whose external radiation doses were individually monitored; the total follow up was about 5.2 million person-years.
The study published in Radiation Research in 2007 quite unexpectedly showed statistically significant increased risks per unit of occupational ionising radiation dose for mortality from solid cancer and from all cancers excluding leukaemia, compared to those of A-bomb survivors.
The observation that the radiation risk at low doses is more than that at high doses attracted wide attention. In the pooled analysis, Canadian workers had the highest cancer radiation risk estimates among the 15 countries. None of the other 14 country cohorts individually had significantly raised cancer mortality risk estimates. Exclusion of Canadian workers (4 per cent of the sample) from the pooled analysis changed the findings to statistically non-significant.
Critics questioned the data and the analytical validity of the study because of the apparent difference in the results between the Canadian and the 15-country studies.
A recent paper dispelled the disproportionate alarm caused by the pooled study.
A paper published on November 13, 2013 inthe British Journal of Cancer , indicated that the significantly increased risks for early AECL workers are most likely due to incomplete transfer of AECL dose records to the National Dose Registry.
Researchers reported that the analysis of the remainder of the Canadian nuclear workers (93.2 per cent) provided no evidence of increased risk; also the risk estimate was compatible with estimates that form the basis of radiation protection standards.
“Study findings suggest that the revised Canadian cohort, with the exclusion of early AECL workers, would likely have an important effect on the 15-country pooled risk estimate of radiation-related risks of all cancer excluding leukaemia by substantially reducing the size of the point estimate and its significance,” the researchers clarified.
Workers in nuclear power plants will receive some radiation dose. Nuclear Power Corporation of India Limited (NPCIL) has strict procedures in place to keep the doses to workers within the limits prescribed by the Atomic Energy Regulatory Board (AERB).
The AERB Annual Report of 2012-2013 published at (www.aerb.gov.in) indicates that in 2012 no radiation worker in any nuclear power plant exceeded the dose limits prescribed by AERB.
The average radiation dose varied from 0.35 mSv to 2.84 mSv, a fraction of the AERB annual dose limit of 30 mSV. Conclusions were similar in earlier years. At these doses, radiation risks, if any, are insignificant.
Since the dose limits are based on conservative assumptions, it is inconsequential if anyone receives, occasionally, a dose above the limit.
Radiation protection standards are based on studies by scholarly bodies such as the US National Academy of Sciences (NAS), Biological Effects of Ionizing Radiation Committee, the International Agency for Research on Cancer (IARC) and United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR).
They indicate that at low doses — similar to those received by nuclear power plant workers — radiation risks, if there are any, are negligibly small. Such risks are no risks at all. Work in a nuclear power plant is not a risky occupation.
Former Secretary, Atomic Energy Regulatory Board
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