Document: NRC Regulatory Guide
Document ID: 8b2255d1-47a9-4dfe-ba41-568c561a89ee
Document Type: regulatory_guide
Title: Inspection of Water-Control Structures Associated with Nuclear Power Plants + HISTORY – HISTORY 01/2015 – DG-1245 , Proposed Revision 2 (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1325/ML13255A435.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.127
CFR Part: 
CFR Title: 

Content:
vulnerable areas that should be monitored. They may be susceptible to internal erosion at the planes of contact. Attention should also be focused on the slopes of the reservoir behind the dam or levee where unstable terrain may be a problem. Early stages of slope failure may be manifested in various ways, including buckling of concrete and asphaltic linings, leaning of trees and poles, and cracking and bulging of walls. Thorough surveillance of suspected unstable areas is essential when disturbance could jeopardize the safety of the dam or water control structure. These areas require careful and frequent inspection, sometimes supplemented by periodic measurement of precise level and triangulation nets, reading of slope indicators or tilt meters, and study of aerial photographs. Before filling a reservoir, records of piezometric levels, ground elevations, and background seismicity at the site should be compiled so that a comparison can be made with the effects of water loading. As soon as filling begins, inspection and monitoring should be performed. These activities should include regular patrol of the dam, water control structures and abutments; monitoring for seepage flows, changes in piezometric levels, and structural and foundation movements. These readings should be plotted and correlated with concurrent water levels. An increase in seepage flow and turbidity is a common symptom of piping as a result of impounded water penetrating and flushing out foundation openings. Although the most critical time in the life of a reservoir may be during its first filling when the design is checked against actual performance, several years may pass before the foundation and structures have fully adjusted to the loads. Thereafter, deformation will continue in response to cyclical load conditions. Attention should be focused on inspection and data collection during relatively rapid changes in reservoir water surface elevations. In addition, year-to-year conditions at high and