KMID : 0364920130380020060
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Journal of Radiation Protection and Research 2013 Volume.38 No. 2 p.60 ~ p.67
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Influence of Modelling Approaches of Diffusion Coefficients on Atmospheric Dispersion Factors
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Hwang Won-Tae
Kim Eun-Han Jeong Hae-Sun Jeong Hyo-Joon Han Moon-Hee
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Abstract
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A diffusion coefficient is an important parameter in the prediction of atmospheric dispersion using a Gaussian plume model, and its modelling approach varies. In this study, dispersion coefficients recommended by the U. S. Nuclear Regulatory Commission¡¯s (U. S. NRC¡¯s) regulatory guide and the Canadian Nuclear Safety Commission¡¯s (CNSC¡¯s) regulatory guide, and used in probabilistic accident consequence analysis codes MACCS and MACCS2 have been investigated. Based on the atmospheric dispersion model for a hypothetical accidental release recommended by the U. S. NRC, its influence to atmospheric dispersion factor was discussed. It was found that diffusion coefficients are basically predicted from a Pasquill-Gifford curve, but various curve fitting equations are recommended or used. A lateral dispersion coefficient is corrected with consideration for the additional spread due to plume meandering in all models, however its modelling approach showed a distinctive difference. Moreover, a vertical dispersion coefficient is corrected with consideration for the additional plume spread due to surface roughness in all models, except for the U. S. NRC¡¯s recommendation. For a specified surface roughness, the atmospheric dispersion factors showed differences up to approximately 4 times depending on the modelling approach of a dispersion coefficient. For the same model, the atmospheric dispersion factors showed differences by 2 to 3 times depending on surface roughness.
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KEYWORD
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Hypothetical accidental release, Atmospheric dispersion factor, Dispersion coefficient, Plume meandering, Surface roughness
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