This research examines the effect of radiolysis species (H 2 , O 2 , and H 2 O 2 ) upon crud deposition and growth and also the effect of their concentration within the crud. A 3-D transient diffusion model has been developed to simulate solute transport of these radiolysis products in porous crud layer. It attempts to explain the behavior of the porous crud growth on PWR fuel pins. This model employs a system of coupled mass transport and chemical interactions as the source term, which make the problem non-linear. A Monte Carlo technique is adopted to simulate the behavior of the different species.The direct application of this study to nuclear engineering research is to aid in the design of reactors with higher performance. With the deregulation of the U.S. power market, there is an incentive to extend the life and to enhance the performance and For the modeling of solute transport of radiolysis products, the present analysis considered two competing solute transport mechanisms within the porous crud deposits: molecular diffusion with a source term from the radiolysis and mass convection. Initially, the analytical model for the equilibrium state using the Laplace equation is summarized from the author's earlier work. Later, a transient diffusion equation was introduced using a random walk Monte Carlo technique coupled with a constant source term from radiolysis. This procedure by Ragheb was modified from a cartesian to a cylindrical geometry random walk. The molecular radiolysis species of hydrogen, oxygen, and hydrogen peroxide are the most stable radiolysis products that directly affect: (1) the oxidation-reduction reactions at the interface of crud/cladding and (2) the formation of nickel ferrite within the crud deposit. In a post-AOA crud, Bonaccordite (Ni 2 FeBO 5 ) is also observed in the nickel-ferrite. It is recommended that further investigations be performed incorporating the electrochemical interactions of these electroactive species.More detailed consideration of convective transport should be coupled with diffusion with a source term of radiolysis.