Impact Wear Properties of Two Zr(-Sn)-Nb Zirconium Alloys with 316L Stainless Steel

The fuel element cladding serves as the first and most important safety barrier against the release of radioactive products into the environment in a pressurized water reactor (PWR). The loss of its integrity will not only bring huge economic losses, but also lead to major security threats. Therefore, improving the reliability of fuel and maintaining the integrity of nuclear fuel cladding is of great significance to the operation and long-term development of nuclear power. In the pressurized water reactor nuclear power plant, the debris constantly rubs and collides with the fuel rods under the continuous scouring of the coolant, resulting in the wear of the fuel rods and even the leakage of perforations. In this paper, two kinds of Zr(-Sn)-Nb zirconium alloy tubes were impacted by a 60° acute angle conical block of 316L stainless steel with an impact energy of 4.0 mJ for different cycles (N =10², 10³, 10⁴, 10⁵, 10⁶). 1 200 mg/L H₃BO₃+2.2 mg/L LiOH solution was flowed over the impingement contact surface at a flow rate of 10 mL/min. The impact wear behavior of zirconium alloy cladding under debris-induced fretting wear was simulated. After that, the dynamic response of the force, velocity and energy during the impact test was obtained by analyzing the data collected by the impact wear tester. Optical microscope, 3D morphology and scanning electron microscope were used to observe the surface and cross-sectional micro-morphology of the wear scars and measure the wear depth and wear volume. Combined with the analysis of wear debris components obtained by energy spectrometer, the impact wear performance and impact wear mechanism of two zirconium alloy tubes were studied. Before the impact wear test, the results of nano-indentation and ring compression test showed that Zr-Sn-Nb zirconium alloy had higher hardness and elastic modulus than Zr-Nb zirconium alloy, and was more compressive. The dynamic response of impact wear showed that the contact peak force and energy loss of Zr-Sn-Nb zirconium alloys were higher than those of Zr-Nb zirconium alloys. The impact wear test results showed that the wear depth and wear volume of Zr-Sn-Nb zirconium alloys were higher than those of Zr-Nb zirconium alloys. After 10⁵ cycles of impact, the wear area of the Zr-Nb zirconium alloy tube increased significantly, which was mainly due to the wear of the friction pair. When impacted with 316L stainless steel, the energy consumption of Zr-Nb zirconium alloy during impact was more, and the wear of zirconium alloy tube was more serious; The relative deformation between Zr-Sn-Nb zirconium alloy and 316L stainless steel impact block was larger, but the damage of the zirconium alloy tube itself was small. The results showed that the wear mechanisms of the two zirconium alloy pipes under impact wear were mainly plastic deformation and fatigue spalling. In the process of impact wear, the work hardening caused by the impact can effectively reduce the wear rate of the material. However, with the increased of the cycle of impacts: The plastic flow of the material at the edge of the wear scar leaded to the initiation and propagation of cracks to the zirconium alloy matrix; The extension and intersection of fatigue cracks at the center of the wear scar will cause fatigue spalling of the material, resulting in more serious wear and removal. Zr-Sn-Nb zirconium alloy had better resistance to impact wear of 316L stainless steel than Zr-Nb zirconium alloy. During the impact process, material migration occurred between the zirconium alloy tube and the friction pair, forming a wear debris accumulation layer with uneven distribution of Zr, O, C, and Fe elements.