The Effects of Wear Debris under Fluid Flow Environment on Fretting Wear Mechanism of Nuclear Fuel Cladding Tube Supported by Supporting Grid

Abstract

Nuclear cladding tubes are subjected to low-amplitude flow-induced vibrations (FIVs). Fretting wear occurs when two contacting surfaces are exposed to very low oscillation. Because nuclear cladding tubes are damaged by this fretting wear, it is necessary to try to evaluate the lifetime and improve the wear resistance of the tube. For this purpose, it is very important to clearly understand the damage mechanism of the tubes. Therefore, the present study undertook fretting-wear tests to investigate how the fluid that flows between the tube and the supporting grid affects the fretting wear. The governing damage mechanism consisted of abrasive wear and surface detachment behavior. In the case of the fluid flow environment, most of the wear debris was ejected from the contacting surfaces and this mode had a large effect on the maximum wear depth of the tube or wear amount. Additionally, the tests were performed under the water flow state as well as the water/air flow state. The result is that if the fluid flow exists, severe wear occurs through some mechanisms, such as two-body abrasion; further, the fluid flow decreases the contact load and attenuates the kinetics of oxidation. Because the severe wear due to two-body abrasion interrupted the formation of oxide film, wear amount was increased. Furthermore, even in the case of water/air flow environment, the worn surface was hardly oxidized due to extremely severe wear.