Comparative analysis of the contribution of short-lived radioiodines to the thyroid radiation dose for the population after the Chernobyl and Fukushima accidents

Purpose. To present results of the comparative analysis of the contribution of short-lived radioiodines to the thyroid radiation dose (TRD) in the population after two severe radiation accidents at nuclear reactors: the Chernobyl accident (1986) and the Fukushima accident (2011).

Material and methods. The contribution of short-lived radioiodines to the TRD is expressed in fractions of the TRD from ¹³¹I (the main dose forming radionuclide). This contribution takes into account the ratio between doses from inhalation and ingestion intake of ¹³¹I, the ratios between dose factors of the expected dose to the thyroid gland in the case of inhalation and ingestion intake of iodine and tellurium isotopes, the ratios between time-integrated concentration of iodine and tellurium isotopes at the ground-level air and in foodstuffs (milk).

Results. The typical contribution of short-lived radioiodines to TRD for the population accounts of few percent of dose to the thyroid gland from ¹³¹I following the Chernobyl accident as on March 15, 2011, the day of the main fallout after  the Fukushima accident — within 15%. For both accidents the leading role among the short-lived radioiodines in terms of dose to the thyroid for the public belongs to ¹³³I and ¹³²I (due to the intake of ¹³²Te and its radioactive decay to ¹³²I in the body).

Conclusion. Significant differences in estimates of the typical contribution of short-lived radioiodines to TRD for the population after two considered accidents can be explained by differences in the dominant pathways of the intake of radioiodine by population. The dominant pathway for the vast majority of the population in the contaminated areas following the Chernobyl accident was ingestion intake with locally produced cow’s milk. Following the Fukushima accident the dominant pathway was inhalation intake, because the Japanese authorities were able to quickly prevent the intake of radioiodine with foodstuffs.