Ionizing radiation

Frequently asked questions

Preliminary Dose Estimation from the Nuclear Accident after the 2011 Great East Japan Earthquake and Tsunami


The process

Q8. How was the dose assessment conducted?

WHO established an International Expert Panel to make an initial assessment of the possible range of radiation doses received by people in Fukushima prefecture, other regions of Japan and worldwide as a consequence of the 11 March 2011 accident.

The International Expert Panel consisted of independent experts selected on the basis of their scientific competence and experience. The experts all served in individual capacities whether they participated in the Panel’s meetings or provided technical contributions from their respective institutions. All members of the panel completed and signed a Declaration of Interests; no conflicts of interest were identified for any of the experts. Experts from the International Atomic Energy Agency (IAEA) and the Food and Agriculture Organization of the United Nations (FAO) served as Panel members, and representatives of the UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and the Government of Japan participated as observers. The panel was first convened in June 2011 (see more on the timeline below).

Q9. Where did the data come from and how were they used?

For the dose estimates for Japan, the primary source of data was official reports published by the Government of Japan. Environmental monitoring data were not generally available for the rest of the world and so the expert panel used computer simulations to estimate doses outside Japan (e.g. simulation of the dispersion of radioactive material through the air based on existing information about the composition of the radioactive release). The input data were measurements of levels of radioactive material in the environment (e.g. levels of different radionuclides on the ground) and levels of activity concentration in foodstuffs.

Q10. What has been the timeline in the development of this report?

  • March 2011: the Great East Japan Earthquake.
  • June-July 2011: WHO established an International Expert Panel tasked to conduct an initial evaluation of radiation exposure of people worldwide as a result of the Fukushima accident and to compile a dose assessment report.
  • August-September 2011: The panel collected available data up to September 2011 and began to analyze the relevant input data and to perform the dose assessments.
  • October-December 2011: The panel reviewed and discussed the results and worked on the development of a preliminary dose assessment report.
  • January-April 2012: the preliminary report was compiled, reviewed by the panel of experts and finalized by WHO for publication.
  • May 2012: publication online of the preliminary report.

In parallel, WHO also convened in December 2011 a second group of independent experts, the WHO Health Risk Assessment Group, that is currently undertaking an assessment of potential health risks to members of the public (based on the doses assessed by the panel) as well as to workers (based on occupational dosimetry data provided by Japan). The preliminary Health Risk Assessment report will be published in summer 2012.

Q11. How will the Dose Assessment Report contribute to other studies?

The Dose Assessment Report forms one part of an overall health risk assessment of the global impact of the accident at the Fukushima Daiichi NPP that is being carried out by WHO. The findings of the health risk assessment will be included in the Health Risk Assessment Report, to be published by WHO in summer 2012.

This dose assessment should be considered as being preliminary. It is expected that future studies will be undertaken with additional input data and more refined assumptions. These studies may further consider the impact of protective measures already taken in Japan.

The present assessment will also inform a longer-term two-year scientific assessment of the radiological consequences of the Fukushima accident, to be published in 2013 by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). The two assessments are complementary. The UNSCEAR report will assess doses to workers and the public and will include an analysis of the impact on non-human biota, while WHO is focusing on doses and risks to humans. UNSCEAR has participated in the meetings of the International Expert Panel as an observer to ensure compatibility between the two assessments.

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