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Home arrow Environment arrow Radiation Monitoring and Dose Estimation of the Fukushima Nuclear Accident

Conclusions

To assess the radiological dose to the public resulting from the month-long discharge of radioactive materials into the atmosphere from the Fukushima Daiichi Nuclear Power Plant accident, the source term is essential for computer simulations on the dispersion of radioactive materials in the environment. The Japan Atomic Energy Agency has been trying to estimate the source term of iodine and cesium discharged to the atmosphere in the studies on the preliminary source term estimation [1], detailed analysis on the local atmospheric dispersion [2], reestimation of source term for the early phase of the accident [3], and validation of source term by the regional-scale atmospheric dispersion simulation [4]. As the result of these studies, the release rates of 131I and 137Cs discharged into the atmosphere were estimated for the period from 12 March to 1 May 2011 (Table 15.1); those for the period from 12 March to 5 April are shown in Fig. 15.6. The total amounts of 131I and 137Cs discharged into the atmosphere in this period were 1.2 × 1017 and 8.8 × 1015 Bq, respectively.

These studies on the source term estimation of radioactive materials discharged to the atmosphere from the Fukushima Daiichi Nuclear Power Plant had been carried out within 1 year after the accident using limited monitoring data and plant information. In these analyses, some limitation of WSPEEDI was also found in the utilization of simple dry and wet deposition processes. The results indicated that more sophisticated deposition processes considering chemical form and particlesize distribution of radionuclide are necessary to better reconstruct the measured surface deposition pattern [41]. New data, for example, the special distribution of 131I deposition by airborne monitoring [42], have been reported after our source term estimation studies were made. Thus, more accurate and detailed source term estimation can be expected by using these additional data and the upgraded WSPEEDI with improved deposition processes.

Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

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