Outline of the Radiation Dose Estimation of Residents After the Fukushima Daiichi Nuclear Power Plant Accident

Sentaro Takahashi

Abstract The outline of research with relationship to the dose estimation of the residents, which was carried out by a variety of organizations and individuals, is summarized here. This research may be categorized into that for external dose and for internal dose estimation. In addition to the large-scale investigations carried out by governmental organizations, several important studies were carried out by small sectors and individuals.

Keywords Dose estimation • Dose reconstruction • External exposure • Health effects • Internal exposure • Radiation dose

Introduction

Many residents in the Fukushima Prefecture and neighboring areas were exposed to significant doses of radiation as a result of the radioactive nuclides that were accidentally released from TEPCO'S Fukushima Daiichi nuclear power plant. In the days immediately following the accident, radiation exposure was caused by isotopes of iodine and short-lived radionuclides. As time progressed, radiocesium, that is, cesium-134 and cesium-137, became the major source of radiation. The exposure pathways were external irradiation by radiocesium deposited in the environment and internal irradiation through consumption of foods contaminated with radiocesium.

Although an accurate estimation of the radiation dose was essential for predicting the health risks to residents and for adopting suitable and effective measures against the radiation risks, it was not easy to achieve an accurate dose assessment for residents because of the complexity of the exposure routes.

Soon after the accident, environmental monitoring of air dose rates and measurements of the concentrations of radioactive nuclides in various environmental materials, including soil, tap water, and food, were widely implemented by the Japanese and local governments, institutes, universities, small groups, and individuals. Some of the results of such monitoring were reported by news media as well as on Internet websites, used for dose estimation for residents, and published in scientific papers. In contrast with this environmental monitoring and these surveys, direct monitoring or measurement of individual radiation doses was not widely carried out in the early stages after the accident. Compared with environmental monitoring, there have not been many attempts to estimate actual radiation doses in the residents, except for large-scale surveys by governmental organizations.

The personal radiation dose is the most important parameter for planning and implementing suitable protective measures. Nevertheless, the attention of the public, governments, and even scientists has mainly been focused on environmental radiation dose and radioactivity, and not particularly on actual radiation dose in individuals, especially in the early stages after the accident. A detailed and easily understandable explanation of the concept of radiation dose assessment is provided in the excellent commentary article by Dr. Inaba in this book (see Chap. 4). In this chapter, we outline the activities performed in an attempt to monitor, measure, or estimate the personal radiation doses of the residents, based mainly on the information presented at the International Symposium on Environmental Monitoring and Dose Estimation of Residents after the Accident of TEPCO's Fukushima Daiichi Nuclear Power Stations, organized by Kyoto University Research Reactor Institute on December 2012 (hereafter referred to as “The Symposium”).