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Nagai, Haruyasu; Chino, Masamichi; Terada, Hiroaki; Katata, Genki
NIRS-M-252, p.137 - 149, 2013/03
It is urgent to assess the radiological dose to the public due to the Fukushima Daiichi Nuclear Power Plant accident. JAEA has been undertaking this task by computer simulation of radioactive materials in the environment. The source term of radioactive materials discharged into the atmosphere was estimated. Then, detailed analysis on the local and regional scale dispersion were carried out by WSPEEDI-II simulations. However, there were some discrepancies between calculation and airborne monitoring of surface deposition of 
Cs. The cause of these discrepancies was investigated by carrying out some parametric study with focus on uncertainties due to the deposition process. In these tests, most discrepancies were reduced by modifying wet deposition processes without changing any other conditions. Further examinations are necessary to formulate wet deposition processes properly and to provide more accurate simulation for assessment of the radiological dose to the public.
Takada, Chie; Kurihara, Osamu*; Kanai, Katsuta; Nakagawa, Takahiro; Tsujimura, Norio; Momose, Takumaro
NIRS-M-252, p.3 - 11, 2013/03
A massive earthquake and tsunami on March 11, 2011 resulted in an enormous amount of release of radioactivity to the environment. On the day after the earthquake occurrence, Japan Atomic Energy Agency (JAEA) started emergency radiological monitoring. The measurements with whole body counter (WBC) for the staff members who had returned from Fukushima started at the end of March. The measured activity of 
I due to inhalation for emergency staff varied from LLD to 7 kBq, which corresponded to a range of estimated initial intakes of 
1 to 60 kBq when extrapolated back to the date on which the staff started the operation in Fukushima. The measured activity of 
Cs and Cs were both in the ranges of LLD - 3 kBq. The range of initial intake of Cs to I was 11 when taking a median from all the measurements. The maximum committed effective dose of 0.8 mSv was recorded for a worker, a member of the 2nd monitoring team dispatched from March 13 to 14.
I and Cs resulting from the Fukushima Daiichi Nuclear Power Plant accidentChino, Masamichi; Terada, Hiroaki; Katata, Genki; Nagai, Haruyasu; Nakayama, Hiromasa; Yamazawa, Hiromi*; Hirao, Shigekazu*; Ohara, Toshimasa*; Takigawa, Masayuki*; Hayami, Hiroshi*; et al.
NIRS-M-252, p.127 - 135, 2013/03
We estimated the release rates and total amounts of I and Cs discharged into the atmosphere from March 12 to April 5, 2011. The applied method is a reverse estimation by coupling environmental monitoring data with atmospheric dispersion simulations under the assumption of unit release rate (1 Bq/h). It calculates release rates of radionuclides (Bq/h) by dividing measured air concentrations of I and Cs into calculated ones at sampling points. The estimated temporal variation of releases indicates that the significant release, over 10
Bq/h of I, occurred on March 15, following to relatively small releases, 10
10
Bq/h, but the release rates from March 16 are estimated to be rather constant on the order 10 Bq/h until March 24. The release rates have decreased with small day-to-day variations to the order of 10
10
Bq/h of I on the beginning of April. The estimated source term was examined on the point of the time trend, total releases and the ground depositions of Cs by using different atmospheric dispersion models with above source term and compared them with observed Cs deposition distribution. These examinations showed that the estimated source term was reasonably accurate during the period when the plume flowed over land in Japan.
