article posted 02 Feb 2016
Tsuyoshi Usami1995 Graduated from University of Tokyo with a Doctor of Engineering.
1995 Joined Central Research Institute of Electric Power Industry.
1998-1999 Temporarily worked at Harwell Site of AEA Technology, U.K.
2003-2005 Temporarily worked at Tokai site of Japan Atomic Energy Agency.
Solidification of nuclear waste containing molybdenum and sulfur
Tsuyoshi Usami*, Kazuyoshi Uruga and Takeshi Tsukada
Central Research Institute of Electric Power Industry
Iwadokita 2-11-1, Komaeshi, Tokyo 201-8511, JAPAN
In the dissolution process of nuclear fuel reprocessing, zirconium molybdate is accumulated on the dissolver wall.
Liquid waste containing highly concentrated molybdenum (Mo) can be generated by washing dissolver, and is difficult
to vitrify because of the limited solubility of Mo in glass. In addition, there may be waste solution containing sulfuric
acid in the nuclear power plant. Sulfur is also difficult to dissolve in glass. For these wastes, the application of glass
ceramics in which crystals of water insoluble waste material are dispersed was investigated.
Borosilicate glass with dispersed calcium molybdate (CaMoO4
) was examined for Mo waste. To form the
dispersed phase, Mo and Ca were added as MoO3
The glass, MoO3
were mixed, loaded into alumina crucible, heated
to 1150°C or 1300°C at 10°C/min, kept for 2 h and then quenched. The observation results are listed in Table 1.
The chemical composition of the dispersed phase depended on the concentration of alkali elements in the borosilicate
glass and also on the temperature. About 15 wt% MoO3
was dispersed as CaMoO4 in glass containing 3.1 wt% of Na2
at 1150°C as shown in Fig. 1.
On the other hand, when the glass contained a high concentration of Na2
was formed and agglomerated. These results were considered to be related to the following equilibrium.
O(in glass) <=> Na2
+ CaO(in glass)
Barium sulfate BaSO4
was chosen as the dispersing phase of the sulfur waste. B2
was chosen as the glass, mixed with BaSO4
and heated. The result of the elemental mapping of the product is shown in Fig. 2.
It can be seen that S and Ba were well dispersed together. The concentration of SO3
in the product was about 15 wt.%.