Computational fluid dynamics applied in the evaluation of atmospheric dispersion modelling at site region

To estimate the radiological impact of airborne effluents discharged from the stack of nuclear power plant (NPP) exposing on the person who are not directly related to NPP operation (e.g. construction workers and NPP employees) at site region and considered as public, it is vital to obtain the spatial distribution of airborne pollutants due to atmospheric dispersion at site region. The air flow is substantially affected by the main structures of NPP and the application of Gaussian type atmospheric dispersion model is constrained within the range of several hundred meters away from NPP. Thanks to the increasing power of CPU power, Computational Fluid Dynamic (CFD) can be used in solving the transportation and dispersion of airborne pollutants in the vicinity of NPP site. In this study, a benchmark CFD model has been built to simulate dispersion close to site. Comparing the ground-level atmospheric dispersion simulation results by CFD model with that estimated by Gaussian model, it can be concluded that in neutral condition Gaussian model results remain conservative and the peak value of dispersion factor in two models differs in factor of 3. In unstable condition the CFD results are larger than Gaussian ones, which may be caused by the difference between two model solution methods to the strong vertical turbulent intensity of the air flow and the main structures of NPP illustrated by CFD model and Gaussian model. CFD model results reflect the building wake effect within the distance of about 100 m to 1 km from the release point at site region. (author)