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The structural integrity of a jet pump assembly of a boiling water reactor (BWR) under hydrodynamic loading was evaluated. This arrangement, which has a riser joined with a couple of jet pumps by the transition piece, is part of the reactor recirculation system. It is submerged in water under pressure. The main function is to induce forced flow through the core of the reactor. A dynamic structural analysis was carried out with the finite element method. The first ten modes of vibration and their natural frequencies were calculated. The first five natural frequencies are in the range between 25 Hz and 40 Hz. In this analysis, it was considered that the jet pump assembly is supported at the riser brace. The restrainer bracket keeps together the riser with the two jet pumps and there is free movement at the slip joints.

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Flow-induced vibrations occur in some of the internal components of a nuclear reactor. When specific conditions are present, these vibrations may result in excessive deformations or fatigue that can generate mechanical damage. Several boiling water reactor (BWR) of nuclear power plants (NPP) have experienced failures in the jet pump assembly due to flow-induced vibration (FIV) which could be caused by acoustic pulsations derived from recirculation pumps, vibration induced by turbulence and vibration induced by leakage at the slip joint. The purpose of this paper is to establish a viable numerical methodology to evaluate the fluid-structural interaction at the slip joint of a jet pump. In this analysis, the fluid-structural interaction was evaluated with the finite element method and finite volume method with ANSYS® code in the case of two steel plates with a divergent gap. Results show that a critical velocity could cause fluidelastic instability, if only one flow in a two-way fluid-structural interaction was considered. This is one of the phenomena that could take place at the slip joint of a jet pump assembly.