When tube bundles submerged in water vibrate, their dynamic behavior is affected by the surrounding fluid. In particular, the added mass of the fluid leads to changes in the vibration characteristics of the structure. In nuclear power plants, steam generator heat transfer tubes are arranged in dense bundles and operate under submerged conditions, making fluid–structure interaction an important consideration. In this study, a fluid–structure interaction analysis is performed for a submerged group of tube bundles representative of nuclear power plant steam generator heat transfer tubes. Using a finite element–based coupled fluid– structural analysis, the vibration responses of the tube bundle are numerically investigated. The effects of the surrounding fluid on the vibration characteristics of the tube bundle are examined. The results indicate that the presence of the fluid significantly influences the vibration behavior of the tube bundle.