Journal of Applied Sciences1812-56541812-5662Asian Network for Scientific Information10.3923/jas.2008.780.787KhanbabaeiB. GhasemizadA. FarajollahiH. 5200885An accurate description of the fluid flow and heat transfer within a Pressurized Water Reactor, PWR, for the safety analysis and reactor performance is always desirable. In this study, a mathematical model of the fundamental physical phenomena which are associated to a typical PWR and governs the fluid dynamics in the reactor is presented. Using CFX, a Computational Fluid Dynamics (CFD) code, a three-dimensional flow distribution in the downcomer and the lower plenum of the reactor was also calculated. Due to computational limits, simplifications of the core, downcomer and the lower plenum of the reactor are introduced. Nevertheless, it has been shown that CFD improves our understanding of fluid flow and heat transfer in the Reactor Pressure Vessel (RPV).]]>Bieder, U. and E. Graffard,2007Bottcher, M.,2006Cartland, G.G.M.,2007Espinoza, S.,2006Fox, R.W. and A.T. McDonald,1978Hohne, T. and S. Kliem,2006Kliem, S.,2006Muralidhar, K. and T. Sundararajan,1995Rohde, U.,2007Scheuerera, M.,2005