Non-destructive assessment of oxide layer thickness on Zircaloy-4

The Nondestructive and Structural Testing Department is working at a project for the eddy current nondestructive assessment of oxide layer thickness on Zircaloy-4, which in the future might be applied to in-situ fuel channel testing, either in the decay pool or in the reactor. An eddy current technique for the assessment of the thickness of dielectric oxide layers on Zry-4 was developed which makes use of the fact that the induced magnetic flux density in a material is a function of lift-off (i.e. the distance between the probe and the conducting material). The larger this distance - e.g. the thicker the oxide layer - the smaller the magnetic flux density and the higher the voltage on the secondary coil of the probe. A linear relation was determined between voltage and oxide thickness and using this calibration function thickness of unknown layers could be determined. (author)