Integrated post-closure safety assessment of radioactive waste containing hazardous chemicals: A screening framework for radiological-chemical risk

Disposal of radioactive waste containing hazardous chemicals can generate post-closure radiological cancer risks, chemical cancer risks, and chemical non-cancer hazards. Existing assessments often treat radiological and chemical endpoints separately. This study develops an integrated post-closure assessment and screening framework that combines United States Environmental Protection Agency risk methods with AMBER dynamic compartment modeling, using the International Atomic Energy Agency Trench Case as a reference disposal system. A normalized generic assessment of selected metallic elements was used to compare radiological and chemical risk behavior and derive two endpoint-specific screening metrics: a critical radioactivity concentration for identifying when chemical cancer risk is small relative to radiological cancer risk, and a preliminary non-cancer trigger based on maximum leachate concentration relative to the drinking-water standard. A case-study application using documented mixed-waste inventory data from nuclear facilities evaluated complex waste types with associated radionuclides under normal-evolution and human-intrusion scenarios. Several cases triggered total cancer risk screening criteria under human intrusion, indicating the need for detailed assessment. The results are reference-scenario screening outcomes, not site-specific predictions. The framework supports prioritization of radioactive mixed waste for constituent-specific, pathway-specific, and site-specific assessment. This structure links time-dependent transport outputs with endpoint-specific decisions for waste management and regulation.