This paper describes the results of ultrasonic examination of molten glass in the glass melter for the vitrification process of high-level radioactive liquid waste (HLW). The propagation and the attenuation of ultrasound in the molten glass were measured to study feasibility of detecting noble metal precipitates and the viscosity measurement of glass melter.
The ultrasonic propagation experiment at 2.25MHz were carried out in a simulant fluid (glycerin) at room temperature and the molten glass at 1000°C using ultrasonic wave guide rods. The wave guide rod materials used in this research are a nickel-based heat resistant alloy 690 and a high density isotropic graphite T-6 (Ibiden Co., Ltd.) with a corrosion resistant coating. Although the nickel-based alloy 690 has a favorable property such as superior structural integrity or corrosion resistant against molten glass at high temperatures, the ultrasonic attenuation was quite large thereby not suited for the wave guide rod. On the other hand, the wave guide rod made of high density isotropic graphite showed good capabilities of ultrasonic propagation both in glycerin and the molten glass at 1000°C.
The changes in ultrasonic intensity of reflecting echoes vs. distance were measured both in glycerin and the molten glass to obtain attenuation coefficient of ultrasound. Then, the viscosity of glycerin and molten glass was calculated from the result of ultrasonic attenuation measurement. The viscosity of glycerin and molten glass thus obtained showed good agreement with those obtained by ordinary viscous test.