Consequences of the Chernobyl reactor accident on the 137Cs internal dose to the Japanese population

The consequences of the Chernobyl reactor accident on the Japanese population are assessed, for the one-year period from May 1986, in terms of the internal dose due to 137Cs. First, the dose from 137Cs is assessed, for a group of healthy adult males, on the basis of their observed body burdens of 137Cs determined by whole body counting. The annual individual dose estimate thus obtained is 1.5 μSv, which is 6-15% and 3.7% respectively of the doses determined by whole body counting in UK and the Federal Republic of Germany. The temporal change in the average body burden is successfully explained here by a single-compartment model. Secondly, this latter model is used, along with the daily 137Cs intake data for each district in Japan, to calculate the dose for the whole of Japan. The estimates of the population dose and the average individual dose obtained are 148 man Sv, for the population of 120 million, and 1.24 μSv, respectively. Although comparatively small, these values nonetheless also include the residual contribution from past nuclear weapon tests. The average annual individual dose of 1.24 μSv corresponds to 0.7% of the dose from natural 40K in the body. Although whole body counting indicates that 137Cs burdens were still increasing as of May 1987, it is concluded that, in terms of radiocaesium, the effect of the Chernobyl reactor accident on Japan was negligible. (author)