Oxide film thickness measurement of fuel rod cladding based on multi-frequency eddy current technology

The oxide film on the surface of the nuclear fuel rod cladding will seriously affect its thermal conductivity, increase the temperature of the fuel rod, accelerate the corrosion rate of the fuel rod, and bring potential safety risks to the reactor. So, it is necessary to accurately measure the thickness of oxide film. In this paper, a three-dimensional finite element simulation model of fuel rod cladding tube was constructed, and the multi-frequency detection of fuel cladding was simulated. The influences of excitation frequency, cladding tube conductivity and metal coating thickness on the measurement results of oxide film were analyzed. A method of accurately calculating the thickness of oxide film was proposed by combining multi-frequency measurement data to suppress the influence of interference factors. The results showed that the calculation error of the oxide film thickness was less than 1 micron, and the method can be used for quantitative characterization of the oxide film thickness of fuel cladding.