Cementitious Wasteforms for Immobilization of Low-Activity Radioactive Wastes

Solidification of low-activity wastes with cementitious materials is a widely accepted technique that contains and isolates waste from the hydrologic environment. The radionuclides I-129, Se-75, Tc-99, and U-238 are identified as long-term dose contributors. The anionic nature of these radionuclides in aqueous solutions allows them to readily leach into the subsurface environment. Assessing the long-term performance of waste grouts requires understanding the speciation and interaction of radionuclides within the concrete wasteform, their diffusion when contacted with vadose zone porewater or groundwater, and the durability and weathering of concrete waste forms. An integrated laboratory investigation was conducted involving spectroscopic investigations, solubility tests, and quantifying diffusion and long-term durability under realistic moisture contents. Additionally, the study identified secondary phases or processes that influence radionuclide retention. Results yield critical insights into the behavior and fate of radionuclides immobilized within concrete wasteforms, underscoring the necessity for robust performance assessments for concrete waste forms under vadose zone conditions.