Flow-induced vibration (FIV), due to its large amplitude and frequent occurrence, is a serious problem associated with the cooling/heat-exchanger systems in nuclear plants. It diminishes coolant capacity and causes fatigue damage and failure, which can lead to catastrophic nuclear meltdown. To understand the behavior of this complex interactive vibration system and its effect on thermal performance, this study investigates experimentally and numerically across flow heat transfer of two different sized tandem circulars as a tractable representative model of cross flow heat exchanger in the presence of FIV. Comprehensive experiments, including FIV on downstream cylinder measured, vortex dynamics visualized and associated heat transfer measured and analyzed, buttressed with detailed numerical simulations are employed to obtain deeper understanding of these fully-coupled phenomena, to develop effective FIV countermeasures and hence increase the reliability of the nuclear-reactor cooling system. This will increase the public confidence on nuclear power plant safety in the UAE.