Some Trends in Radioactive Waste Form Behavior Revealed in Long-Term Field Tests

摘要

Results from long-term field tests with borosilicate glass, cement and bitumen waste forms containing actual intermediate-level radioactive waste are summarized and discussed in the paper. Leaching behavior of the waste forms was evaluated by monitoring the contamination of contacting water. Measured leach rates of the three waste-form materials were in a narrow range in shallow subsurface repositories, but varied in a wide range at an open testing site owing to weathering of bitumen and cement materials. The repositories were opened after 12-year testing for visual examination, sampling and analysis. All retrieved waste forms were in good physical condition. The study has not revealed any negative changes in the waste glass. Some ageing processes were detected in cement and bitumen waste forms, which can positively (bitumen) or negatively (cement) affect physical and containment properties of these waste materials. It has been established that a significant proportion of the radioactive inventory in the bitumen waste form became associated with the bitumen phase. Phase separation of this radioactive bitumen has shown, than the asphaltene fraction is responsible for the major part of the radioactivity retained by the bitumen.