Affiliations: [a] Shanghai Nuclear Engineering Research and Design Institute Co., Ltd., Shanghai, China | [b] School of Energy and Power Engineering, Xi’an Jiaotong University, Shananxi, China | [c] Nuclear and Radiation Safety Center, Ministry of Environment and Ecology, Beijing, China
Correspondence:
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Corresponding author: Wenjie Bao, Shanghai Nuclear Engineering Research and Design Institute Co., Ltd., Shanghai 200233, China. E-mail: [email protected].
Abstract: The leakage or explosion of hazardous chemicals will seriously affect the operation safety of nuclear power plants. Therefore, in the nuclear safety review, it has been clearly proposed that the environmental risks of off-site toxic chemicals should be evaluated. When calculating the toxic chemical leakage accident, as HABIT model calculation result is based on the 2 min concentration limit condition assumed in RG1.78, and the longest duration is only 7.5 min, so it cannot be applied to the safety assessment of offsite toxic hazards. This paper presents a detail analysis of the impact on toxic chemical release using modified Gaussian plume algorithm model in ALOHA. The Gaussian plume algorithm is mainly used to calculate the plume diffusion emitted by continuous point sources, assuming that its concentration distribution obeys the empirical model of normal distribution. The plume is transported downwind at an average wind speed, ignoring turbulent diffusion downwind, with vertical and horizontal lateral diffusion described by diffusion parameters. The Gaussian plume algorithm has many advantages such as high computational efficiency and simple calculation method. Therefore, it has a wide application in the field of atmospheric diffusion. Calculation shows for the chlorine and ammonia leakage accident, chlorine’s influence area is much larger than ammonia. For ammonia, safe distance is about 3.5 km, but for chlorine, hydrogen fluoride and hydrazine, with the increase of storage capacity, their safety distance change slower at 8 km, which is consistent with HAD101/04. The storage amount of liquid ammonia shows an exponential increase, indicating that for liquid ammonia, the chemical safety control distance will not exceed 3.5 km. Conclusion of this paper has a long last meaning to NPP environmental assessment and safety evaluation, and full filled area of toxic chemicals quantitative analysis.
Keywords: Toxic chemical release, nuclear power plant, ALOHA, screen distance
