Coprecipitation of radioactive Ru with hydroxides has been studied for the purpose of the management of the high level waste from the nuclear fuel reprocessing. Aluminosilicate gel used as coprecipitant was prepared by addition of aqueous sodium hydroxide to sodium aluminate-sodium silicate solution containing ruthenium nitrate. Ruthenium quantitatively precipitates under the conditions, aluminate>4×10
-2M, Al/Si<0.5 and pH=6-9. Thermal transformations of aluminosilicate gels were examined by means of DTA and X-ray powder diffraction. Ruthenium is volatilized from aluminosilicate gel above 600°C. However, volatilization rate of Ru is suppressed by coating with mullite phase into which aluminosilicate ge1 transformes above 900°C. The amount of Ru volatilized in Ar-flow was reduced to about 10% of that in air-flow.
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