Development of an anisotropic pressure fluctuation model for the prediction of turbulence-induced vibrations of fuel rods

Abstract

The vibration of fuel rods induced by the fast flowing coolant is a known challenge to nuclear power plant designers and operators. If not dealt with adequately, the vibrations could lead to undesirable wear and tear of the cladding, which, in turn, could result in fuel rod failures and costly unplanned outages of the power plant. Hence, knowledge of these vibrations is important in the design phase. Due to the increase in computational power, numerical tools are increasingly often used to assess flow-induced vibrations. As these vibrations are a result of the local axial turbulent flow, scale-resolving methods are typically required for accurate predictions. Such methods, though, are usually computationally too expensive to use for industrial nuclear applications. Medium resolution turbulence models such as URANS generally cannot be used as they only resolve the average flow conditions and not turbulent fluctuations. To overcome this limitation of the URANS models, an Anisotropic Pressure Fluctuation Model (AniPFM) has been developed, which is an improved version of the earlier developed isotropic version. Compared to the isotropic model the generated synthetic turbulence is now anisotropic and is correlated in time based on the transport and decorrelation of turbulence. The current paper gives an overview of the new AniPFM, and presents results for a first fluid–structure interaction test case, demonstrating it can indeed induce and sustain vibrations of a rod, and that results are improved compared to the old model.