A major earthquake, measuring 9.0 in the Richter scale shortly followed by a 15-metre tsunami disrupted the power supply and cooling of Fukushima Daiichi reactors causing a nuclear accident on 11 March 2011. The nuclear cores of three reactors largely melted in the first three days and led to the environmental release of substantial amounts of radioactive substances over a prolonged period.
In its report titled “Levels and effects of radiation exposure due to the nuclear accident after the 2011 great east-Japan earthquake and tsunami,” published on April 2 this year, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) stated that any increase in cancer among the public is unlikely following the accident. The committee concluded that cancer levels are likely to remain stable in the wake of the nuclear power accident.
Discernible changes in future cancer rates and hereditary diseases are not expected as the exposures people received were very low. “... the expected low impact on cancer rates of the population is largely due to prompt protective actions on the part of the Japanese authorities following the accident.” a press release from UNSCEAR revealed.
The committee estimated that people in Fukushima may receive on average less than 10 mSv due to the accident over their whole lifetime. This may be compared with 170 mSv lifetime dose from natural background radiation that people in Japan typically receive at the rate of 2.1 mSv annually.
According to the committee, the most important health effect is on mental and social well-being, related to the enormous impact of the earthquake, tsunami and nuclear accident, and the fear and stigma related to the perceived risk of exposure to radiation.
The committee noted the theoretical possibility that the risk of thyroid cancer among the group of children most exposed to radiation could increase and concluded that the situation needs to be followed closely.
Thyroid cancer is rare among young children. Specialists have observed an appreciable increase in thyroid cancer among children exposed during the accident at Chernobyl nuclear power station.
The Committee analyzed worker doses reported by the management and also independently assessed doses for some of the workers. Its assessments are broadly consistent with reported doses, but uncertainties remain for exposures during the early phase of the accident.
In the case of workers, the Committee concluded that no discernible increase in cancer or other diseases is expected; however, the most exposed workers will receive regular health checks.
The Committee estimated the effects of radiation exposure on both terrestrial and marine ecosystems and found that any effects would have been transient.
“For marine ecosystems, the possibility of effects on flora and fauna was limited to the shoreline area adjacent to the power station and the potential for effects over the long term was considered insignificant,” the UNSCEAR press release added
The estimates of the Committee for the releases of iodine -131 and caesium-137 , two of the more significant radio-nuclides from the perspective of exposures to people and the environment were lower by a factor of 10 and 5 respectively compared to the releases from Chernobyl.
Specialists consider that the conclusions of the committee are the most authoritative because of two reasons.
Firstly, the conclusions are based on estimates of the exposure of various population groups — including children. And secondly, the committee relied on scientific knowledge of health impacts following radiation exposure.
The General Assembly of the United Nations set up the UNSCEAR in 1955. “Its mandate in the United Nations system is to assess and report levels and effects of exposure to ionizing radiation.”
The United Nations General Assembly has designated 27 countries, including India, as members of the committee.
Since 1955, UNSCEAR issued 22 major publications. Governments and organizations universally rely on the Committee's estimates as the scientific basis to evaluate radiation risk and to establish protective measures. The International Commission on Radiological Protection (ICRP) bases its recommendations on the conclusions of UNSCEAR which in turn reviews and assesses levels of radiation exposures and effects on A-bomb survivors and other exposed groups on a long-term basis.
( Former secretary of the AERB)