A novel eddy current method for thickness and conductivity measurement of cladding tube

Zirconium-based cladding suffers material degradation including wall thinning and conductivity variation after long-term service in harsh environments, threatening structural integrity and raising fuel leakage risks. Periodic eddy current testing (ECT) of cladding thickness and conductivity is thus essential for safety evaluation, benefiting from ECT’s non-contact, fast and highly sensitive features. This work presents a multi-parameter measurement method using a triple-coil multi-frequency ECT system. The sensor with two excitation-reception coil pairs realizes decoupled detection of lift-off, thickness and conductivity of zirconium alloy cladding. A simplified theoretical model clarifies electromagnetic responses at different frequencies. At high frequencies, lift-off has a linear correlation with the logarithmic real part of coil inductance change. At low frequencies, cladding thickness follows an exponential relation with the imaginary inductance ratio between two receiving coils, whereas conductivity is linearly proportional to the absolute imaginary inductance. These relations allow simultaneous measurement of thickness and conductivity while suppressing lift-off interference. Experiments on zirconium alloy cladding specimens verify the proposed method, yielding relative errors less than 1.8% for both parameters.