Relationship between Individual External Doses, Ambient Dose Rates and Individuals' Activity-Patterns in Affected Areas in Fukushima following the Fukushima Daiichi Nuclear Power Plant Accident

Wataru Naito; Motoki Uesaka; Chie Yamada; Tadahiro Kurosawa; Tetsuo Yasutaka; Hideki Ishii

doi:10.1371/journal.pone.0158879

Relationship between Individual External Doses, Ambient Dose Rates and Individuals' Activity-Patterns in Affected Areas in Fukushima following the Fukushima Daiichi Nuclear Power Plant Accident

PLoS One. 2016 Aug 5;11(8):e0158879. doi: 10.1371/journal.pone.0158879. eCollection 2016.

Authors

Wataru Naito¹, Motoki Uesaka¹, Chie Yamada¹, Tadahiro Kurosawa², Tetsuo Yasutaka³, Hideki Ishii⁴

Affiliations

¹ Research Institute of Science for Safety and Sustainability, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan.
² National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan.
³ Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan.
⁴ Fukushima Future Center for Regional Revitalization, Fukushima University, Fukushima, Japan.

Abstract

The accident at Fukushima Daiichi Nuclear Power Plant on March 11, 2011, released radioactive material into the atmosphere and contaminated the land in Fukushima and several neighboring prefectures. Five years after the nuclear disaster, the radiation levels have greatly decreased due to physical decay, weathering, and decontamination operations in Fukushima. The populations of 12 communities were forced to evacuate after the accident; as of March 2016, the evacuation order has been lifted in only a limited area, and permanent habitation is still prohibited in most of the areas. In order for the government to lift the evacuation order and for individuals to return to their original residential areas, it is important to assess current and future realistic individual external doses. Here, we used personal dosimeters along with the Global Positioning System and Geographic Information System to understand realistic individual external doses and to relate individual external doses, ambient doses, and activity-patterns of individuals in the affected areas in Fukushima. The results showed that the additional individual external doses were well correlated to the additional ambient doses based on the airborne monitoring survey. The results of linear regression analysis suggested that the additional individual external doses were on average about one-fifth that of the additional ambient doses. The reduction factors, which are defined as the ratios of the additional individual external doses to the additional ambient doses, were calculated to be on average 0.14 and 0.32 for time spent at home and outdoors, respectively. Analysis of the contribution of various activity patterns to the total individual external dose demonstrated good agreement with the average fraction of time spent daily in each activity, but the contribution due to being outdoors varied widely. These results are a valuable contribution to understanding realistic individual external doses and the corresponding airborne monitoring-based ambient doses and time-activity patterns of individuals. Moreover, the results provide important information for predicting future cumulative doses after the return of residents to evacuation order areas in Fukushima.

MeSH terms

Fukushima Nuclear Accident*
Geographic Information Systems
Humans
Japan
Linear Models
Radiation Dosage*
Radiation Dosimeters
Radiation Monitoring
Surveys and Questionnaires

Grants and funding

This work was supported by JSPS KAKENHI grant number 15H02854(WN), 26241023(TY). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.