Laser ultrasonics detection of an embedded crack in a composite spherical particle

Laser ultrasonics was applied to the manufacturing control of the integrity (no failure) of coated spherical particles designed for High Temperature Reactors (HTR). This control is of major importance, since the coating of the nuclear fuel kernel is designed to prevent from the diffusion of fission products outside the particle during reactor operation. The SiC layer composing the coating is particularly important, since this layer must be an impenetrable barrier for fission products. The integrity of the SiC shell (no crack within the shell) can be assessed by the ultrasonic vibration spectrum of the HTR particle, which is significantly changed, compared to the reference spectrum of a defect-free particle. Spheroidal vibration modes of defect-free dummy particles with a zirconium dioxide (ZrO2) core were observed in the 2–5 MHz range. A theoretical analysis is presented to account for the observed vibration spectra of defect-free or cracked HTR particles.

► Non-destructive testing and evaluation of High Temperature Reactor (HTR) nuclear fuel.
► Laser ultrasonics integrity control of manufactured HTR coated spherical particles.
► Vibration eigenfrequencies of defect-free dummy HTR particles in the 2–5 MHz range.
► SiC shell integrity of HTR particle assessed by ultrasonic spectrum.