Evaluation of the Leaching Behavior of Heavy Metal Including Cement Solidified Waste in Simulated Radioactive Waste Disposal Facility Environment

Radioactive waste containing hazardous substances (mixed waste) frequently occurs around the world for reasons such as radiochemistry, nuclear species analysis, and nuclear decommissioning. These mixed wastes are thoroughly classified and disposed of in the United States, but not dealt with in other countries. Most countries distinct radioactive waste and hazardous waste separately, and there is no clear treatment standard for mixed waste with both properties. Inadequately treated mixed waste could cause crucial issues with both radiation and non-radiation hazard (chemical and biological).<br/>For proper disposal of mixed wastes, specific technical standards and regulatory guidelines are required. In order to set these standards, it is possible to consider the application of environmental regulations on hazardous substances. However, there are many differences between non-radioactive waste disposal facilities and radioactive waste depository such as the facility design, post-closure operating standards, and leachate creation. Therefore, rather than simply applying environmental regulations for disposal of mixed waste, appropriate regulations should be established in consideration of the radioactive waste disposal environment.<br/>In this study, the leaching behavior of hazardous substances which is frequently generated from the nuclear industry was tested in the simulated disposal condition. The target harmful substances were selected as lead, cadmium, and antimony focusing on heavy metals, and sample waste was produced by cement solidification method, which is commonly used for the disposal of hazardous and radioactive wastes. The leaching properties of these wastes were tested using TCLP, a leaching test method of hazardous waste, and ANS 16.1, a leaching test method of radioactive waste. Test conditions of leachate pH, leachate composition, and exposure dose were modified and applied to simulate the leachate environment. As a result, it was found that the leachability of the simulated waste increased significantly within the environment of the radioactive waste disposal facility compared to standard leaching test condition. In addition, as a result of the irradiation-leaching test, it was observed that the non-leached heavy metal(Cd) showed leaching though a small amount.<br/>Consequently, it was confirmed that Pb and Sb had increased leaching rate in the radioactive waste disposal environment. In the case of lead, it is expected that cement solidification is an inappropriate treatment method due to high leaching amount in cement solidification. Cd was not detected at all in the non-irradiation-leaching experiment, but it was observed that radiation could affect the leaching properties of heavy metals of detection in the irradiation-leaching experiment. Using this approach, it is possible to establish specific regulations for the disposal of mixed waste. It is suggested that wastes containing Pb should be treated with other method than cement solidification. Cd has a highly insoluble property in cement solidification, so cement solidification is considered an appropriate disposal method. In addition, both lead and cadmium show changes in leaching properties as a result of irradiation-leaching experiments, raising the necessity to establish proper leaching criteria in consideration of the expected dose exposure in the disposal facility.<br/>Acknowledgements<br/>This work was supported by the Nuclear safety Research Program through the Korea Foundation Of Nuclear Safety (KoFONS), granted financial resource from the Nuclear Safety and Security Commission (NSSC), Republic of Korea (No. 2003016 & No. 2203028).