This paper describes the results of ultrasonic examination of the build-up of noble metal precipitates in the glass melter using a wave guide rod. The glass melter is used for the vitrification process of high-level radioactive liquid waste (HLLW).
A high density isotropic graphite T-6 (Ibiden Co., Ltd.) and a nickel-based corrosion and heat resistant alloy 690 were selected as candidate materials of wave guide rod. Ultrasonic propagation experiment with the frequency 0.5, 1.0 and 2.25 MHz was performed using the wave guide rods. The T-6 graphite wave guide rod in the simulant fluid (glycerin) showed a good capability of ultrasonic propagation and signal detection. However, the propagation of ultrasonic wave into molten glass was not possible due to the poor wetting of molten glass with the graphite. On the other hand, it was possible to propagate the ultrasonic wave into molten glass with the wave guide rod made of the nickel-based alloy 690. However, the intensity of reflecting echo signal was very small due to the large ultrasonic attenuation in the nickel-based alloy. The simulation study on the ultrasonic wave propagation using the three dimensional finite element method code ComWave showed good agreement with the experimental results.