Nuclear Fuel Cycle Technological Development

8-1

Vitrification Melter Improvement–Development of Long-Life High
Waste (HLW) Vitrification Melter–Level

Radioactive

LiquidGlass & HLW
Electrodes(2) Movable and remotely
exchangeable

Off gas(1) Skull layer to extend
life-time

Skull layer
Cooling jacket(Air or Water)
Molten glass

Fig.8-2 Outline of advanced melter and development objectives
To extend vitrification melter life-time from 5 years of the current design base to 20 years, corrosion rate must be decreased
drastically. (1) Skull layer formation technology and (2) Movable and remotely exchangeable electrodes are introduced for thispurpose.

In a vitrification melter, borosilicate glass cartridges filledwith high level radioactive liquid waste (HLW) are fed directly
into a melter and melted at high temperature around 1150°C.
Thus, the refractory melter wall is gradually corroded by thehigh temperature glass.
The Tokai Vitrification Facility (TVF) melter is designed
to be exchanged every five years because of corrosion of its
electrodes and refractory wall.
The objective of this development is to extend vitrificationmelter life-time from the 5 year standard upon which current
design is based to 20 years to reduce the economic burdenof high level radioactive waste management, by applying
advanced technologies (Fig.8-2).
Development of a new long-life vitrification melter for thispurpose is focused on establishing measures for preventing
corrosion of the refractory and electrode, and preventing
accumulation of noble metal particles at the bottom of themelter.
The new melter wall structure, which forms a skull layer(a solid glass layer or low-temperature high viscosity meltedglass layer) on the wall by cooling the wall, is being considered
as a measure against refractory wall corrosion. To prevent
electrode corrosion, a “commutative electrode structure” isbeing considered. This structure avoids fixing the current
electrodes within the refractory wall by inserting them fromthe top of the melter in an exchangeable configuration.
Moreover, basic tests of the corrosion rate are being carriedout for data on candidate materials for the refractory and theelectrode.
In the advanced melter, good drainage of noble metal will beattained by special temperature control of melted glass in thelower part of the melter. Viscosity of glass changes according
to glass temperature and concentration of noble metal. Thus weare continuing to gather basic data in our laboratory. In a normal
condition, glass temperature of a conical chamber decreases
as the radius decreases. To drain noble metal smoothly, higher
glass temperature along the wall of conical part than inside isnecessary. Glass viscosity along wall then becomes lower thanthat of glass near the center, resulting in flow of accumulated
noble metal rich glass along the wall and out of the melter. We
call this temperature distribution mode the “reverse viscosity
operation mode”.
We started advanced melter development in 2005 and will
promote melter design and related R&D activity until 2008,
aiming to determine the most feasible melter concept design.

Reference
Aoshima, A. et al., Vitrification Experience and New Technology Development in Tokai Vitrification Facility, Proceedings of European Nuclear Conference2007(ENC2007), Brussels, Belgium, 2007, 5p., in CD-ROM.

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JAEA R&D Review 2008