Early Intake of Radiocesium by Residents Living Near the Tepco Fukushima Dai-ichi Nuclear Power Plant After the Accident. Part 2: Relationship Between Internal Dose and Evacuation Behavior in Individuals.

The Tokyo Electric Power Company's Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident exposed members of the public to radiation. This study analyses the relation between personal behavior data obtained from 112 out of 174 subjects who underwent whole-body measurements by the National Institute of Radiological Sciences (NIRS) during the period from 27 June to 28 July 2011 and their committed effective doses (CEDs) from Cs and Cs. The whereabouts of the 112 persons living in municipalities near the FDNPP (mainly, Namie town) on several days in March 2011 are graphed on maps. It was confirmed that most subjects started evacuation promptly and had left the 20-km-radius of the FDNPP by the end of 12 March. The individual CEDs were poorly correlated with the person's distances from the FDNPP at any day in March. Meanwhile, the percentage of persons remaining within the 20-km radius of the FDNPP was 100% at 16:00 on 12 March and 42.9% at 0:00 on 15 March for those with CEDs > 0.1 mSv, whereas the corresponding values were much lower for those with CEDs ≤ 0.1 mSv. This suggests that the time of evacuation would be one of the crucial factors for the early intake; however, more personal behavior data are needed to be analyzed to clarify the relevance to the individual internal dose.