Flow Induced Vibration and Fretting Wear in PWR Fuel

Fuel rod fretting wear is due to complex combinations of factors. Excitation of the fuel rod and motion relative to its supports can be caused by coolant flow and mechanical forces. The amplitude of response for a given set of flow and mechanical forces is dependent on the fuel rod and its support system. The fuel rod mass and stiffness and location of supports along its length dictate the mode shapes and natural frequencies. The contact geometry between the support system and fuel rod is also an important factor. The two primary areas covered in this paper are 1) the types of flow conditions that may exist in a reactor core and how they would result in excitation of the fuel rod and 2) how the relative motion of the rod to its supports can result in fretting wear. Numerous testing techniques, ranging from microscopic, to single grid cell tests, to high temperature and flow full scale multiple fuel assembly tests, are discussed.