Document: NRC Regulatory Guide
Document ID: c55ba6c5-aa2d-4ad6-aba2-2001e16524ab
Document Type: regulatory_guide
Title: Ultrasonic Testing of Reactor Vessel Welds During Preservice and Inservice Examinations (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1221/ML12216A015.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.150
CFR Part: 
CFR Title: 

Content:
n to keep track of these from one examination to the other. Similarly, characteristics of other UT system components such as the pulser, receiver, amplifier, and video display screen may vary from one examination to another, and all these characteristics can influence the magnitude of the flaw indications. Therefore, well-defined'criteria for supple- mentary UT procedures are needed so that it will be possible to correctly characterize flaws, estimate flaw growth, and have reproducible results from inspections performed at different times using different equipment. P In many instances, the rate of flaw growth can be even more important than the flaw size. For example, if a flaw is found in an RPV nozzle or belt-line region and it can be demonstrated without doubt that the flaw will not grow and has not been growing, a rather large flaw can be tolerated. Crack initiation and growth is also a potential problem in cases where it is probable that no crack exists, but where there is a cluster of small rounded inclusions. These clusters of inclusions should be monitored by UT to ensure absence of cracks and crack growth. Where the rate of flaw growth is expected to be large or is uncertain, even a small flaw may be of concern. To permit determination of growth rate, the UT procedures should be such that results of successive UT examinations can be compared. With present procedures, these results cannot be compared because of variation in instrument system characteristics. UT instrument system characteristics depend on the characteristics of the system's different components. Variation in the characteristics of calibration blocks can also affect results. Guidelines are needed so that uncertainties in flaw charac- terization may be reduced or eliminated. The safety of the components is evaluated with the help of fracture mechanics. Flaw sizes need to be known for fracture mechanics evalua- tions. Uncertain determination of flaw sizes leads to uncer- tainties in the