Destruction of Nuclear Organic Waste by Supercritical Water Oxidation: Scale-Up of the Process

In order to design and then define appropriate dimensions for a supercritical oxidation reactor, a 2D and 3D simulation of the fluid dynamics and heat transfer during the oxidation process has been performed. The solver used is a commercial code, Fluent 6.2. The turbulent flow field in the reactor, created by the stirrer is taken into account with a k-omega model and a swirl imposed to the fluid. In the 3D case the rotation of the stirrer can be modeled thanks to the sliding mesh model. The reactivity of the system is taken into account with a classical combustion model EDC. Comparisons with experimental temperature measurements validate the ability of the CFD modeling to simulate the supercritical water oxidation process. Simulation results provide us a view inside the reactor on the flow, temperature fields and the oxidation localization and development. Results indicate that the flow can be considered as piston-like, heat transfers are strongly enhanced by the stirring. Hence the scaling up of the reactor volume, to reach a treatment capacity of 1 Kg/h of pure organics, can be done regarding the necessary residence times and temperature distribution needed for a complete destruction of the organic matter.