Investigation of the Effect of Wear and Oxidation on the Fatigue Strength Degradation of Zircaloy Cladding Tubes for Spent Nuclear Fuel

For a fundamental assessment of spent nuclear fuel integrity, the fatigue behavior of cladding tubes was investigated by evaluating the fatigue strength reduction factor (Kf) due to wear and oxidation-induced degradation. In this study, as wear geometry significantly influences fatigue life cycles leading to fracture, it was determined based on the contact conditions observed in commercial fuel designs. Wear and oxidation-affected cladding tubes were fabricated, along with reference specimens without wear, for comparative analysis. Fatigue tests were conducted by applying and releasing cyclic high internal rod pressures (<102 MPa) at 4 Hz to simulate operational conditions. The obtained average Kf for wear specimens was 1.04, based on an effective stress analysis relative to the unworn reference tube. However, oxidation led to a significantly greater reduction in fatigue life with Kf values exceeding 1.5, indicating more dominant role in fatigue degradation. It is noteworthy that oxidation‑induced metal wastage caused a significantly greater reduction in fatigue life than wear, thereby emphasizing the need for stringent corrosion control in dry storage environment.