A conical bottom shape was adopted for the 3rd melter to minimize accumulation of particulate noble metal elements contained in high-level radioactive liquid waste in the melter.

(a) A cold test using an aqueous non-radioactive solution (simulated waste solution) to represent high-level radioactive liquid waste was performed to evaluate the RuO₂ discharge rate. Mass of RuO₂ contained in each discharged glass was compared with the mass of RuO₂ in the simulated waste solution supplied to the melter. The vertical axis of the graph represents discharge rate, and the horizontal axis represents the number of glass batch. It is noted that RuO₂ not extracted in the previous discharge can leach into subsequent discharge, causing the discharge rate to exceed 100%. Average RuO₂ discharge rate of the 3rd melter was higher than that of the 2nd, indicating that RuO₂ discharge ability was improved by changing the bottom shape.

To continue moving forward in decommissioning the Tokai Reprocessing Plant, safe and steady vitrification of any remaining high-level radioactive liquid waste is very important.

At the Tokai Vitrification Facility, TVF, issues in operations due to the square pyramid shape of the conventional glass melters (1st and 2nd) were observed. The pyramid shape resulted in the accumulation of platinum group metals (Ru, Rh, Pd) from high-level radioactive liquid waste at the furnace bottom, which subsequently affected melter operations. To address this issue, fluid visualization experiments using simulated molten glass fluids and simulation analysis of melter operations were conducted. From the results, the design of the bottom shape in the new melter, the 3rd melter, was changed from a square pyramid to a cone shape (Fig. 1). Performance tests were carried out to verify operation conditions of the 3rd melter, and noble metal elements were confirmed to be less likely to remain in the melter and were smoothly discharged compared to previous melters. This provides a promising outlook for future stable operation (Fig. 2).

Looking ahead, installation of the 3rd melter at TVF is scheduled for early 2026, with operations expected to begin later that year.

Asahi, Y. et al., Design Details of Bottom Shape for the 3rd Glass Melter in TVF, JAEA-Technology 2021-026, 2022, 50p. (in Japanese).
Asahi, Y., Tone, M. et al., Experimental Verification of Operational Conditions for the 3rd Glass Melter in TVF, JAEA-Technology 2024-024, 2025, 271p. (in Japanese).

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