Document: NRC Regulatory Guide
Document ID: 0b9a3243-ab39-402c-9f4b-215c6e4f79ab
Document Type: regulatory_guide
Title: Inservice Inspection of Ungrouted Tendons in Prestressed Concrete Containments (Rev. 3)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003740007.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.35
CFR Part: 
CFR Title: 

Content:
al grease leakage, a rec ommendation is made to compare the amount of sheathing filler grease removed with that being re placed. Regulatory Position 7 discusses the individual cri teria for evaluating inspection results as follows: In Regulatory Position 7.1, prestress monitoring criteria have been developed to ensure that any signs of systematic tendon force degradation are detected and investigated. Acceptance of 95% of the predicted force for two tendons out of three in Regulatory Posi tion 7.1.3 is a slightly relaxed criterion from Revision 2 of the guide. It should be recognized, however, that the primary objective is to compare the measured tendon forces against the predicted forces at the time of the lift-off testing. Regulatory Guide 1.35.1 pro vides guidance on establishing the predicted forces. A provision has been added to check the average of measured forces against the minimum required force in an average (hypothetical) tendon in a group. This provision is added as a result of a suggestion from the contractor (ORNL) and public comments. It should be recognized that each individual tendon force (measured) will have to be modified to reflect the condition of an average tendon. The contributing modifying factors would be the difference in installa tion forces and in the elastic shortening losses, as suming the time-dependent characteristics remain es sentially the same for the group of tendons. The loss of prestress from creep and shrinkage of concrete and stress relaxation of the tendon steel are time-dependent and are predicted on such a basis. The predicted tendon force may be represented by a sloped line in a semi-logarithmic graph. The trend of the actual effective tendon force is obtained by join ing the points on the graph representing the meas ured tendon forces in two or more surveillances of the same tendon or tendons in a group. By extending the trend line, one can determine when the effective tendon force will be below the minimum required.