NCRP Report No. 152, Performance Assessment of Near‑Surface Facilities for Disposal of Low Level Radioactive Waste
In the United States, low-level radioactive waste is defined as any radioactive waste arising from operations of the nuclear fuel cycle that is not classified as high-level waste (including spent fuel when it is declared to be waste), transuranic waste, or uranium or thorium mill tailings. Low-level waste is generated in many commercial, defense-related, medical, and research activities.
NCRP Report No. 152 provides a review of concepts underlying performance assessments of near-surface disposal facilities for low-level radioactive waste and approaches to conducting such assessments. This Report includes discussions on the nature and scope of performance assessment, accepted approaches to conducting all aspects of a performance assessment, and unresolved issues in conducting performance assessments and applying the results. Challenges in conducting and defending performance assessments at specific sites also are emphasized.
This Report discusses the different components that generally must be considered in a performance assessment, including: cover performance and infiltration; performance of concrete barriers (e.g., vaults, modular canisters, or bunkers); source term; flow and transport in the unsaturated (vadose) zone; flow and transport in groundwater (zone of saturation); flow and transport in surface water; atmospheric transport; biotic transport; and exposure pathways and radiological impacts.
Some of the challenges in modeling the performance of a disposal system when water is the medium in which releases are assumed to occur and a high level of performance of natural and engineered barriers is required to demonstrate compliance with performance objectives are discussed, including: cover performance and infiltration, concrete barriers, source term, unsaturated (vadose) zone flow and transport, and saturated zone flow and transport.
The point of view taken in this Report is that an appropriate balance between conservatism and more realistic approaches to performance assessment is largely a matter of judgment that should be applied on a site-specific basis.
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