Structural health monitoring (SHM) is in urgent need and must be integrated into the nuclear-spent fuel storage systems to guarantee the safe operation. The dry cask storage system (DCSS) is such storage facility, which is licensed for temporary storage for nuclear-spent fuel at the independent spent fuel storage installations (ISFSIs) for certain predetermined period of time. Gamma radiation is one of the major radiation sources near DCSS. Therefore, a detailed experimental investigation was completed on the gamma radiation endurance of piezoelectric wafer active sensors (PWAS) transducers for SHM applications to the DCSS system. The irradiation test was done in a Co-60 gamma irradiator. Lead Zirconate Titanate (PZT) and Gallium Orthophosphate (GaPO4) PWAS transducers were exposed to 40.7 kGy gamma radiation. Total radiation dose was achieved in two different radiation dose rates: (a) slower radiation rate at 0.1 kGy/hr for 20 hours (b) accelerated radiation rate at 1.233 kGy/hr for 32 hours. The total cumulative radiation dose of 40.7 kGy is equivalent to 45 years of operation in DCSS system. Electro-mechanical impedance and admittance (EMIA) signatures and electrical capacitance were measured to evaluate the PWAS performance after each gamma radiation exposure. The change in resonance frequency of PZT-PWAS transducer for both in-plane and thickness mode was observed. The GaPO4-PWAS EMIA spectra do not show a significant shift in resonance frequency after gamma irradiation exposure. Radiation endurance of new high-temperature HPZ-HiT PWAS transducer was also evaluated. The HPZ-HiT transducers were exposed to gamma radiation at 1.233 kGy/hr for 160 hours with 80 hours interval. Therefore, the total accumulated gamma radiation dose is 184 kGy. No significant change in impedance spectra was observed due to gamma radiation exposure.
In this paper, a semi-analytical finite element (SAFE) approach is presented to model the guided-wave propagations in composite plates. The theoretical framework is formulated using finite element method (FEM) to describe the material variation along the thickness direction and assuming analytical solutions in the wave propagation direction. As with any finite element approach, the convergence study is first performed to ensure the accuracy of the solution. Then, the dispersive curves are obtained in terms of phase velocity, group velocity, and steering angle. In general, a wave packet in composite plates with anisotropic characteristics does not travel in the same direction as the phase velocity, and the difference is defined as steering angle. Knowledge of these properties in composite plates is important in guided waves based SHM applications. Finally, it is experimentally validated using the scanning laser Doppler vibrometer (SLDV) measurements of guided wave packets generated by a piezoelectric wafer active sensor (PWAS) in a unidirectional carbon fiber reinforced polymer (CFRP) composite plate. It will be shown that the SAFE approach achieves a good agreement with experimental results.