Document: NUREG-0800
Document ID: 04c894f5-e3ab-479e-8bca-0722777c79a7
Document Type: srp
Title: Revision 4 – January 2016
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1502/ML15027A401.pdf
Revision Date: 2023-06
Chapter: 11
Section ID: 11
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CFR Title: 

Content:
etardation factors, and travel times in instances where groundwater or surface water models were not used to describe the transport of radioactivity from the site to the point of entry in unrestricted areas, and L. assumed dilution factors applied beyond the point of entry in unrestricted areas in instances where groundwater or surface water models were not used to describe the movement of radioactivity between the point of entry into unrestricted areas and location of dose receptors. In assigning radionuclide distributions and concentrations for the relevant exposure scenario, the staff should consider whether the site conceptual model defines the release as through a surface water or groundwater pathway, and also consider conditions where surface water and groundwater resources could be impacted by a single event. For scenarios that include surface water pathways, the source term should consider both short and long-lived radionuclides. The rationale for including both types of radionuclides in surface water release scenarios is that releases to useable surface water resources and impacts would occur promptly with minimal time for retardation after a release. In assessing the movement of radioactivity in surface water bodies and streams, the dispersion of radioactivity is expected to be affected by various mechanisms, including near- and far-field mixing patterns, recirculation driven by current directions and flow rates, differences in temperatures in relation to the receiving water body, and impacts of tidal action, among others. For groundwater pathways, the source term should consider radionuclides that are expected to persist in groundwater, taking into account radioactive half-lives, distribution coefficients, retardation factors, and environmental mobility in groundwater. For scenarios involving groundwater, the rationale is that releases to useable water resources and impacts to users are assumed to occur over protracted time periods, years to decades,