A Comprehensive Review of Post-Closure Safety Assessment Program for Near-Surface Disposal Facilities

Near-Surface Disposal Facilities (NSDFs) constitute a widely implemented solution for the management of low- and very low-level radioactive waste, for which a robust post-closure safety assessment is essential to ensure the long-term protection of humans and the environment. This review provides a comprehensive synthesis of disposal design concepts, safety assessment methodologies, and regulatory frameworks relevant to the post-closure phase of NSDFs, with emphasis on internationally accepted practices. Major disposal configurations, including trenches, vaults, tumuli, and engineered landfill-type facilities, are examined with respect to their structural design, engineered components, and interactions with natural site characteristics. The performance of engineered barriers such as final cover systems, drainage layers, concrete structures, and geomembranes is evaluated alongside natural barriers governed by site-specific geological, hydrogeological, and geochemical conditions that control radionuclide retention and transport over extended timescales. The paper reviews the regulatory and methodological foundations of post-closure safety assessment, including the stepwise approach recommended by international organizations, the development and documentation of safety cases, and the systematic application of the Features, Events, and Processes (FEPs) methodology for constructing credible system evolution scenarios. Deterministic and probabilistic assessment approaches are compared to illustrate their complementary roles in addressing uncertainty and characterizing long-term system behavior. Assessment timeframes extending from the institutional control period to several hundred years and, where relevant, to tens of thousands of years are discussed in relation to barrier degradation, radionuclide decay, and increasing uncertainty. Key radionuclides influencing post-closure impacts and dominant groundwater-related exposure pathways are identified to demonstrate how the integrated consideration of disposal design, barrier performance, scenario development, modeling approaches, and regulatory acceptance criteria underpins the demonstration of long-term safety for NSDFs.

کلیدواژه ها:

Near-surface disposal facilities ، Radioactive waste ، Post-closure safety assessment ، Engineered barrier systems ، Radionuclides transport ، Long-term safety case