Test analysis of fuel rod fretting wear incorporating slip direction and contact shape

Fretting wear test is conducted for a PWR fuel rod. Five different shapes of the spacer grid spring are designed and fabricated. The tubes and the springs are made of Zircaloy-4. A fretting wear tester is specially designed for the present research, which is introduced in detail in this paper. The tests are conducted in air and at room temperature. The test conditions, i.e. the normal and shear forces on the contact, the slip range and the number of cycles, are set to be the same. The contact contour of the spring is a concave, a flat or a convex. The influence of the axial and transverse slip directions is also investigated to incorporate the actual tube motion caused by a flow-induced vibration in a reactor. A surface roughness tester is used to measure the wear depth and the contour of the worn surface of the tube. Wear volume is also evaluated, for which an algorithm using the signal processing technique is developed. It is found that the wear is severer when the slip direction is axial, and if the support has a convex contour