Early Radiation Survey of Iitate Village, Which Was Heavily Contaminated by the Fukushima Daiichi Accident, Conducted on 28 and 29 March 2011

Abstract

Following the news that the radiation level in Iitate Village, located 25-45 km from the Fukushima Daiichi Nuclear Power Plant, was seriously increased, an urgent field survey was carried out on 28 and 29 March 2011. Radiation levels at 130 locations were measured inside a van that traveled throughout the village using a CsI pocket survey meter and an ionization chamber. Soil samples were also taken at five locations and submitted to gamma ray analysis using a Ge detector. A radiation exposure rate of more than 20 μSv h was observed in the southern part of Iitate Village. Volatile radionuclides such as iodine and cesium were found to be the main components of radioactive contamination. A trace amount of plutonium isotopes originating from the accident was also confirmed in several soil samples, the level of which was less than the global fallout. Based on the measured density of radionuclides at the highest contamination location during the present survey, an exposure rate of about 200 μGy h at 1 m above the ground was estimated at the time of the radioactive deposition on March 15. At this location, the cumulative exposure would reach 50 mGy in the middle of May 2011.

An early survey of the radioactive contamination of soil due to the Fukushima Dai-ichi Nuclear Power Plant accident, with emphasis on plutonium analysis

“…Imanaka et al (2012 (21 Aprill and 25 May, 2011) 1) Volatile radionuclides such as 131 I and 134,137 Cs were responsible for a large share of the radioactivity that was released. Higher deposition levels of these nuclides were observed in areas in a northwestern direction and in Okuma Town.…”

“…The accumulated level (inventory, Bq/m 2 ) per unit area was also calculated using the known soil sampler areas (Tables 3 and 4). The data from a γ-ray spectrometric analysis of soil samples from Iitate Village have already been reported by Imanaka et al ( , 2012.…”

Overview of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, with amounts and isotopic compositions of the released radionuclides

“…As for transuranic nuclides, there was some public concern as to whether or not plutonium (Pu), one of the most toxic elements, was released into the environment, because some mixed uranium (U) and Pu oxide fuel (MOX fuel) was used in Unit 3. To date, release of trace amounts of Pu isotopes from the FDNPP accident into the environment has been confirmed by measurements of Pu isotopic compositions in the environmental samples such as soil and litter [20][21][22][23]. And, the release of 239,240 Pu into the environment was found to be very small compared with that of radioactive Cs, being of the order of 10 -7 -10 -8 in 239,240 Pu/ 137 Cs activity ratios [25].…”

Estimation of -ray dose in air and soil from Fukushima Daiichi Power Plant accident

“…The ratio f i and decay constant λ i for each radionuclide, ( i = 129m Te, 129 Te, 131 I, 132 Te, 132 I, 134 Cs and 137 Cs) were taken from the literature [1, 9, 10, 11], and the values used are listed in Table 1. …”