town of Miharu with a population of 18,000 is located directly 45 km west of
the crippled Fukushima Daiichi Nuclear Power Plant (FDNPP) in Fukushima
prefecture, Japan. The municipal government led an initiative by itself of
distributing and administering potassium iodine tablets to its residents who
are under 40 years old at 13:00 hrs on March 15, 2011. After all, Miharu has
become the sole municipality in Japan to administer the tablets in response to
the nuclear accident following the Great East Japan earthquake on March 11,
2011. This action taken by Miharu stirred controversy and was criticized by the
Fukushima municipal government as well as some mass media at that time.
However, after four years since the disaster, there has been no official
assessment by the prefectural or Japanese government on this unique case.
Its examination offers invaluable lessons to be incorporated into evacuation
procedures and responses in the future nuclear accidents, while the present
Japanese administration seeks early resumption of nuclear power plants which
have been shut down since the FDNPP accident. In fact, one nuclear power plant
has resumed operation as the first reactor to do so since the disaster as of
this writing, while a few more plants are expected to follow.
In this colloquium, it will be argued that the timing of ingesting the
iodine tablets was indeed appropriate based on the early radiation monitoring
conducted independently by one of the residents in the town. According to this
measurement, a radioactive plume from FDNPP passed over the town between around
13:30 hrs and 15:30 hrs on March 15, and there was no further major fallout
after that. Thus, the Miharu residents who ingested the tablets as advised by
the municipal government did so about a half hour prior to the arrival of
radioactive 131I. Effectiveness of ingesting the stable iodine lasts for 24
hours, and nearly 100 % of 131I is averted if the tablet is taken prior to or
immediately after inhalation of the radionuclide. In addition, an estimated
dosage of external exposure to radiation on the school children of the town
will be presented.
T Koike et al 2014 J. Radiol. Prot. 34 675 doi:10.1088/0952-4746/34/3/675
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