CFD-simulation of the VVER-440 steam generator with porous media model

The detailed flow field of water and steam mixture on the secondary side of horizontal and vertical steam generators of nuclear power plants (NPP) is fairly unknown. This is because of the lack of large experimental devices and the difficulties related to the measurements in real NPP's due to the complex geometry. Two-phase flow in a complicated 3D geometry is also very challenging to solve numerically. If the flow fields and temperatures of water and steam could be solved numerically, it would be useful in steam generator life time management and accident analysis. In this work, VVER-440 type steam generator is modelled with 3-D Euler-Euler 2-phase ANSYS FLUENT 12.0 model. Certain simplifications are made, of which the most significant is the modeling of primary tubes as porous media. Required physical models (source and interaction terms) are implemented in the computational fluid dynamics (CFD) -solver by using user defined functions. The primary circuit of the steam generator is calculated with the APROS system code model. The obtained temperature distribution of the primary circuit is interpolated to the three-dimensional CFD grid describing the porous media model tube banks. This approach provides a realistic temperature distribution to be used as boundary condition for the CFD simulations. Validation simulations are performed with feed water injection in the middle of the tube banks. Void fractions and velocities in few locations are compared to available measurement data. In addition the location of the mixture layer is discussed. Sensitivity analyses are performed by studying grid dependency, velocity formulation and the effect of the water mass on the results. With the validated model nominal power simulations with current feed water manifold are also made with the emphasis on the particle tracking.