Volume Reduction of Radioactive Concrete in Nuclear Facilities by Chemical Extraction Methods on Long-Lived Radioactive Nuclides

Leaching yields from an activated aggregate, removal yields from leachate, and overall mass balance relevant to the chemical procedure were investigated on radionuclides of ⁵⁹Fe, ⁶⁰Co, and ¹⁵²Eu to reduce volume of radioactive waste used in a nuclear reactor facility. The radioactive nuclides were leached with 7 M HNO₃ from the aggregate, then the 7 M HNO₃ solution was mixed with NaOH or NH₃ water to remove the nuclides as a precipitate. 70–80% of ⁶⁰Co and 60–70% of ¹⁵²Eu were leached from an activated aggregate. 100% of ⁵⁹Fe, more than 99% of ⁶⁰Co, and 94–98 % of ¹⁵²Eu were removed as a precipitate at pH higher than 4, 7, and 6, respectively. Removal rates became lower at pH lower than 4 for ⁵⁹Fe, 7 for ⁶⁰Co, and 6 for ¹⁵²Eu. It is basically possible to separate ⁶⁰Co and ¹⁵²Eu from precipitate of Fe at pH ∼ 4. The further separation to reduce volume of waste is not practical, because 20% of ⁶⁰Co and ¹⁵²Eu contained in the precipitate. 93% of volume reduction was achieved with one-step separation.