Glass - Back to the Future!

Presenting Author:
Tsuyoshi Usami;

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 and Ca(OH)2, respectively. The glass, MoO3 and Ca(OH)2 were mixed, loaded into alumina crucible, heated to 1150C or 1300C at 10C/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 Na2O at 1150C as shown in Fig. 1.
On the other hand, when the glass contained a high concentration of Na2O, water-soluble Na2MoO4 was formed and agglomerated. These results were considered to be related to the following equilibrium. CaMoO4 + Na2O(in glass) <=> Na2MoO4 + CaO(in glass) Barium sulfate BaSO4 was chosen as the dispersing phase of the sulfur waste. B2O3 - SiO2 - BaO 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.%.