Radiation Survey Along Two Trails in Mt. Fuji to Investigate the Radioactive Contamination Caused by TEPCO's Fukushima Daiichi Nuclear Plant Accident
Kazuaki Yajima, Kazuki Iwaoka, and Hiroshi Yasuda
Abstract Mt. Fuji is located approximately 300 km southwest of TEPCO's Fukushima Daiichi Nuclear Power Plant. We performed the radiation survey along two main Mt. Fuji's trails from 04:30 to 18:30 on July 9, 2011. We climbed Yoshida trail from Fuji-Subaru Line fifth station (2,300 m in altitude) to Yoshida-Subashiri top (3,720 m in altitude) and descended Subashiri trail from the Yoshida-Subashiri top to Subashiri new fifth station (2,000 m in altitude) on foot while measuring gamma rays. The dose rate 1 m above ground as measured using a NaI(Tl) scintil-
lation survey meter was within the range from 0.03 to 0.05 μSv/h throughout our measuring trip. We used a NaI(Tl) scintillation spectrometer for gamma-ray pulse
height spectra measurement. The gamma-ray pulse height spectra obtained at least 2,500 m in altitude on both Yoshida and Subashiri trails showed the peaks of two radioactive cesium isotopes (134Cs and 137Cs) and natural radioactive nuclides. It was confirmed that a radioactive plume released from the Fukushima Daiichi Nuclear Power Plant had arrived at least 2,500 m above sea level of Mt. Fuji.
Keywords Dose rate • Plume • Radiation survey • Radioactive contamination
A large amount of radioactive materials was released in the environment as a result of the TEPCO Fukushima Daiichi Nuclear Power Plant (NPP) accident caused by the Great East Japan Earthquake that occurred on March 11, 2011. The spread of the radioactive contamination had become a concern just after the accident. Mt. Fuji, which is 3,776 m above sea level and the highest mountain in Japan, is located approximately 300 km southwest of TEPCO's Fukushima Daiichi NPP. Because an environmental radiation monitoring level in Shizuoka City, which is approximately 50 km southwest from Mt. Fuji, rose on March 15 and 21–22, 2011, it is estimated that the radioactive plume released by TEPCO's
Fig. 6.1 Location of TEPCO's Fukushima Daiichi Nuclear Plant, Mt. Fuji, and Shizuoka City
Fukushima Daiichi Nuclear Power Station arrived around Mt. Fuji at those times . Figure 6.1 shows the locations of TEPCO's Fukushima Daiichi Nuclear Station, Mt. Fuji, and Shizuoka City.
Climbing Mt. Fuji is a very popular leisure activity and its trails are crowded with many climbers every summer. Thus, to reveal the radioactive contamination level of Mt. Fuji's trails before the summer season began, we performed the radiation survey along two main Mt. Fuji trails.