Document: NRC Regulatory Guide
Document ID: e5306f4f-dc8c-4f60-a71c-af7ad4080384
Document Type: regulatory_guide
Title: Aquatic Environmental Studies for Nuclear Power Stations + HISTORY - HISTORY 12/2014 – DG-4023 -Proposed New Guide
Source: NRC Regulatory Guide Division 4
Source URL: https://www.nrc.gov/docs/ML1318/ML13186A085.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-4.24
CFR Part: 
CFR Title: 

Content:
nearby habitats, such as heavy feeding on vegetation or changes in targeted prey species. A qualitative discussion of possible biotic displacement may be adequate. Analysts should confer with federal, state, and local resource agencies. Analyses can include a discussion of possible mitigation measures, such as regional habitat improvement projects to accommodate displaced individuals. Entrapment, Impingement, and Entrainment Analyses Cooling water withdrawal adversely affects not only habitats, as mentioned above, but also aquatic species at the individual and population levels through entrapment, impingement, and entrainment. Several factors, including type of cooling system, the design and location of the intake structure, and the amount of water withdrawn from the source waterbody, greatly influence the degree to which organisms become entrapped, impinged, or entrained. Potentially affected species include marine mammals, fish, shellfish, other aquatic invertebrates, and aquatic vegetation. Entrapment occurs when an aquatic organism swims or drifts into an area within the intake structure, often termed a forebay, from which the organism cannot escape to return to the natural aquatic ecosystem. For example, sea turtles often swim under booms or underwater curtain walls into forebays and cannot figure out how to return to the natural water body. Also, intake systems that have forebays fed only through a one-way pipeline from the natural water body often entrap many fish and invertebrates that will never escape unless they enter a fish-return system following impingement (some individuals may not ever be impinged and, therefore, remain entrapped indefinitely). Impingement occurs when the water withdrawal occurs at such a velocity that forces an individual against trash racks, trash bars, intake screens, or some other physical component of the intake structure such that the individual cannot swim, walk, crawl, or otherwise move away from the structure. Impingement