Continuous Measurement of Zircaloy Corrosion in Air with an Ultrasonic Corrosion Monitor

摘要

The Ultrasonic Corrosion Monitor (UCM) produces a continuous, in-situ, real-time characterization of corrosion film formation. The monitor, which measures its own corrosion, has a film thickness measurement resolution of better than 0.1 mu m (0.004 mil). The technique is particularly well suited to severe or inaccessible environments, such as those experienced by nuclear materials, where standard corrosion measurement techniques require costly and time-consuming shutdown/measurement/startup cycles of the test facility. This report describes the physical basis for the UCM and presents the results of a corrosion experiment with a zircaloy ultrasonic monitor, which was exposed to 680 exp 0 F air for over 7200 h. Ultrasonic corrosion measurements are made by continuously measuring the time-of-flight of an extensional ultrasonic wave along the axis of a corroding waveguide, such as a thin wire. As the waveguide corrodes, the different ultrasonic transmission characteristics of the base metal and the continually growing corrosion film cause a continuous change in the effective time-of-flight, which can be analytically related to the corrosion film thickness. The results of the zircaloy corrosion experiment demonstrate that the corrosion film thickness determined by the ultrasonic monitor corresponds directly to that determined by standard weight gain measurements. However, a typical in-reactor corrosion test would have accumulated no more than five weight measurements during the exposure time of this experiment, whereas the UCM produces a continuous measurement and, therefore, promises a level of corrosion characterization that has heretofore been unavailable. The UCM is expected to aid considerably in understanding and characterizing zircaloy corrosion. More generally, the concept is applicable to a broad range of materials and environments. (ERA citation 10:010317)