Internal Radiation Dose of KURRI Volunteers Working at Evacuation Shelters After TEPCO's Fukushima Daiichi Nuclear Power Plant Accident

Yuko Kinashi, Kouta Kurihara, Keiko Fujiwara, Eiko Kakihana, Tomohiro Miyake, Tomoyuki Takahashi, Tatsuya Yamada, Hiroshi Yashima, Hidehito Nakamura, Kenichi Okamoto, and Sentaro Takahashi

Abstract We report the radiation doses encountered by 59 Kyoto University Research Reactor Institute (KURRI) staff members who had been dispatched to screen refugees for radiation at emergency evacuation sites 45–80 km from the Tokyo Electric Power Co. (TEPCO) Fukushima Daiichi Nuclear Power Plant. From March 20 to April 30, 2011, 42 members were dispatched to the emergency evacuation sites located 45–80 km from the power plant to examine the radioactive contamination affecting refugees. Continuously, from May 10 to May 23, 2011, 17 members were dispatched to Fukushima Prefecture to establish the Kyoto University Radiation Mapping (KURAMA) system. Body burdens of radioactive nuclides were estimated using a whole-body counter. The first team dispatched showed 1,300–1,929 Bq internal radiation activity from cesium (including 137Cs and 134Cs) and 48–118 Bq 131I. The internal doses of four members of the first team were estimated to be 24–39 μSv. The doses from internal exposure were almost similar to the cumulative external doses for the dispatch period (March 20–22, 2011) The external radiation doses of members dispatched after the second team had decreased from one third to less than one tenth of the external doses of the first dispatched team. The internal radiation doses of 55 members after the second team showed that 51 cases were undetectable and 4 cases showed doses of 2–15 μSv.

Keywords Cesium-134 • Cesium-137 • Internal radiation • Iodine-131 • Wholebody counter

Background

On March 11, 2011, an earthquake and tsunami struck the Tohoku area of Japan, causing serious damage to the Tokyo Electric Power Co. (TEPCO) Fukushima Daiichi Nuclear Power Plant, and a significant amount of radionuclides was released into the surrounding environment (Fuyuno 2011; Butler 2011). The radioactive plume spread over Fukushima Prefecture toward the end of March 2011.

Fifty-nine members as the total number of man-teams of the Kyoto University Research Reactor Institute (KURRI) had been dispatched to the emergency evacuation shelters in Fukushima Prefecture 45–80 km from the power plant to help the local governments in screening the radioactivity level of refugees. From March 20 to April 30, 2011, 42 members in teams consisting of 2–4 staff were dispatched 13 times to nine emergency evacuation shelters. From May 10 to May 23, 2011, 17 members in teams consisting of 2–5 staff were dispatched six times to Fukushima Prefecture to establish the Kyoto University Radiation Mapping (KURAMA) system. All screening teams, especially the earlier one, risked internal radiation exposure because of the radioactivity in the environment.

Two volunteers of the initial team who had a high external and internal radiation dose were followed up 513 days after the first dispatch.