Study on the photoacoustic method for accurate, online, in-situ, non-contact measurement of corrosion-related unidentified deposit thickness

The thickness of Corrosion-Related Unidentified Deposits (CRUD) on the surface of Pressurized Water Reactor (PWR) fuel cladding is one of the key factors affecting fuel performance. Accurate measurement of CRUD thickness is crucial for ensuring the safe operation of nuclear reactors. This paper presents an online, in-situ, non-contact CRUD thickness measurement method based on the photoacoustic effect, overcoming the issues of surface morphology changes and re-dissolution associated with traditional offline measurement methods. To validate the feasibility and accuracy of this method, an experimental system was established, and the signal transmission mechanisms involved in the thermal-fluid–solid multi-physics fields of the measurement method were explored using a simplified 1D mathematical model and 3D simulations. The results show that the method enables low-cost, high-precision measurements, requiring only a 532 nm wavelength, 700 Hz modulation frequency, and 3 W full power Pulse Width Modulation (PWM) pulsed laser as the signal excitation source, along with a piezoelectric transducer as the signal receiver. The simplified 1D mathematical model and 3D simulation results align well with experimental data, with a maximum error of ±10 %. The results show that under the same laser operating conditions, the CRUD thickness is approximately proportional to the output signal intensity with a good linear relationship. This measurement method and its mathematical model provide significant technical and theoretical support for studying the dynamic growth behavior of CRUD.