Abstract
Cladding fatigue is a critical factor in the evaluation of the structural integrity and safety of nuclear fuel rods, which are typically subjected to multiaxial dynamic loading conditions within reactor systems during normal and off-normal operations as well as during spent fuel transportation. This report describes the fatigue testing of chromium-coated (Cr-coated) M5_Framatome cladding under the Framatome Cooperative Research and Development Agreement. The M5_Framatome cladding tubes were irradiated in Oak Ridge National Laboratory’s High Flux Isotope Reactor to various levels of displacements per atom. The fatigue data were developed under fully reversed cycling conditions at 5 Hz for both the nonirradiated and the irradiated conditions; the nonirradiated conditions served as a baseline. Fatigue life data points of Cr-coated, irradiated specimens are above the O’Donnell–Langer best estimate fatigue curve in the low-cycle region but below the O’Donnell–Langer best estimate curve starting from 0.31%. The test results indicate that the Cr-coated, irradiated cladding tube has a fatigue limit near 0.05% with 3 × 10^6 cycles as a fatigue limit threshold. The observed increase in flexural rigidity and decrease in hysteresis indicate that irradiation has hardened the Cr-coated cladding. These changes suggest that the cladding may become more susceptible to brittle fatigue failure under operational conditions, highlighting the need for further investigation into temperature effects and additional fatigue tests to fully characterize the effects of irradiation.
