In this report, several works on mainly resuspension and eolian transfer of radioactive cesium due to wind, which is one of the most effective transfer processes of previously deposited radioactive particulate materials, are introduced. First, the mechanisms of the resuspension of particulate matter by wind as well as resultant dust storms and wind erosion are surveyed. Next, the papers related to resuspension and eolian transfer of radioactive aerosols originally emitted by the Chernobyl nuclear accident are reviewed. The measured fallouts and radioactivity concentrations show annual cycles, and their peak periods depend on the measured regions. Finally, the works that analyze the related effects of the accident at the Fukushima Daiich Nuclear Power Plant are reviewed, and some issues to be focused and resolved are summarized.
Evaluation of annual average of radionuclide concentration in surface air obtained from atmospheric dispersion factor is intended to determine a public dose as a primary source for the safety analysis of nuclear facilities in normal operation. Oarai Research and Development Center (ORDC) of the Japan Atomic Energy Agency have used fixed 5-year meteorological statistics for derivation of atmospheric dispersion factors as average conditions. To show that the meteorological statistics for any 5-year period could be used as representative data for evaluation of average conditions, annual average (1-year average) and 5-year average of evaluated radionuclide concentrations derived from the meteorological data observed over a 20-year period (1991-2010) at ORDC were analyzed. Fluctuations of evaluated radionuclide concentrations of any 5-year average were smaller than those of 1-year averages. Further, any 5-year averages were sufficiently convergent to 20-year average. Because any 5-year averages contained no rejections by the F-test (5% significance level), they were not statistically different to the rest of 20 years data set, instead that some of 1-year averages could be rejected. It means that any 5-year averages of radionuclide concentration evaluations are well representative for the safety analysis of normal operation of the nuclear facilities in ORDC.
The Japan Atomic Energy Agency has conducted a monthly monitoring of airborne 14C discharge at the forth research building (RI facility) of the Tokai Research and Development Center. In the current monitoring, 14C, which exists in various chemical forms in airborne effluent, is converted into 14CO2 with CuO catalyst and then collected using monoethanolamine (MEA) as CO2 absorbent. However, this collection method has some issues on safety management because the CuO catalyst requires a high heating temperature (600℃) to ensure a high oxidation efficiency and the MEA is specified as a poisonous and deleterious substance. To establish a safer, manageable and reliable method for monitoring airborne 14C discharge, we examined collection methods that use different CO2 absorbents (MEA and Carbo-Sorb E) and oxidation catalysts (CuO, Pt/Alumina and Pd/ZrO2). The results showed 100% CO2 collection efficiency of MEA during a 30-day sampling period under the condition tested. In contrast, Carbo-Sorb E was found to be unsuitable for the monthly-long CO2 collection because of its high volatile nature. Among the oxidation catalysts, the Pd/ZrO2 showed the highest oxidation efficiency for CH4 at a lower temperature.