Comparison of T-junction flow pattern of water and sodium for different geometries of power plant piping systems

The history of nuclear power plants experiences (such as Phenix NPP and Tomari NPP) shows the failure of the piping systems particularly at T-junction area with an elbow on the upstream. With regard to catastrophic consequences of piping break in the nuclear power plants and radioactive material release to the environment, it is essential to have reliable piping systems. For this purpose, several geometries and parameters are considered. For model validation the available experimental data for the water is compared with the results, which show very good agreement. The same procedure is carried out with the water and sodium for the dimensions of the failed T-junction in Phenix piping system. The change effects in the physical properties from the water to the sodium in a T-junction area with an elbow on the upstream are compared. Next, classifications of the sodium mixing jets are presented. Also the temperature and velocity patterns of the sodium in the two types of geometries like S and E, with three different dimensionless distances, are simulated. Finally, the most reliable geometry, minimum appropriate dimensionless distance and optimum mixing jet type are determined. The important parameters of these simulations are momentum ratio, dimensionless distance and velocity ratio. The results will be used to promote design and enhance the safety and reliability of the piping systems in nuclear power plants.

► Role of jets in thermal fatigue. ► Sodium/water flow pattern. ► Role of pipe geometry.