Keywords Dispersion models Gaussian plume models Computational Fluid Dynamics (CFD) Radioactive releases Buoyancy Turbulence Meteorology DECLARATION I, the undersigned, hereby declare that the work contained in this thesis is my own original work and that I have not previously in its entirety or in part submitted it at any university for a degree. Signature: ............................................................... Date:

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... i ABSTRACT Modeling of the dispersion of radionuclides around a nuclear power station T S Dinoko A thesis submitted to the Department of Physics, in partial fulfillment of the requirements for the degree of Magister Scientiae. Nuclear reactors release small amounts of radioactivity during their normal operations. The most common method of calculating the dose to the public that results from such releases uses Gaussian Plume models. We are investigating these methods using CAP88-PC, a computer code developed for the Environmental Protection Agency (EPA) in the USA that calculates the concentration of radionuclides released from a stack using Pasquill stability classification. A buoyant or momentum driven part is also included. The uptake of the released radionuclide by plants, animals and humans, directly and indirectly, is then calculated to obtain the doses to the public. This method is well established but is known to suffer from many approximations and does not give answers that are accurate to be better than 50% in many cases. More accurate, though much more computer-intensive methods have been developed to calculate the movement of gases using fluid dynamic models. Such a model, using the code FLUENT can model complex terrains and will also be investigated in this work. This work is a preliminary study to compare the results of the traditional Gaussian plume model and a fluid dynamic model for a simplified case. The results indicate that Computational Fluid Dynamics calculations give qualitatively similar results with the possibility of including much more effects than the simple Gaussian plume model. ii DEDICATION: 1) To my late father Nkoetsile Justice Dinoko, who always reminded me of the importance of education. "May your soul rest in peace", and 2) My family; Hilda (mother), Israel, Eric, Kagiso, Boitumelo and Mpho.  Omphemetse, Rorisang and Onalenna.  Oratile, Oarabile and Isago.  Eyana-Tshireletso and Enele-Refentse.  Onalerona(Ofile). iii ACKNOWLEDGEMENTS