Experimental and computational studies of two-phase flows in nuclear reactor systems

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Mixtures of gas and liquid flows are commonly encountered in heat exchangers, in components of nuclear reactors and other equipment in which boiling or condensation occurs. Such flows are very complex, but recent advances in measurement techniques and computational methods have permitted an in-depth examination of their characteristics. The objective of this project is to apply, and further develop, available experimental and computational fluid dynamics (CFD) methods to the study of two-phase flow characteristics in header-feeder systems of the type used in CANDU nuclear power plants. The main experimental tasks are: i) to modify an existing air-water flow loop by the addition of a versatile header/feeder model, in which different combinations of active inlet turrets and active feeders can be selected; ii) to assemble a database of measurements of gas and liquid flow rates in the feeder tubes of this model, while also documenting the turret inlet conditions and the flow patterns inside the header; and iii) to assess the effect of flow obstructions inside feeder tubes on the gas and liquid flow rates. The main task of the computational analysis is to perform CFD simulations of air-water flows at the same inlet flow conditions and in the same geometries as those of the experiments and to compare the simulation results to the measurements to verify the applicability of CFD as a tool for two-phase flow simulation at conditions and geometries of interest to nuclear safety analysis. The proposed experimental and numerical investigations will be conducted using state-of-the-art tools and will advance the technical capabilities of nuclear reactor designers and safety analysts. They are in direct support of the AECL air-water header facility tests. They will also assist the Canadian nuclear power industry in validating and improving existing multi-phase analytical tools and in maintaining a competitive position in this field of the world economy. This grant will enable uOttawa to educate several students and other personnel in nuclear reactor thermalhydraulics, thus providing the nuclear industry with a pool of prospective highly skilled research engineers to replace the currently retiring generation of such personnel.