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:
e vessel (RPV) welds and RPV nozzle welds. The apparent low level of the reproducibility: of detection, location, and characterization of flaws leads to lengthy discussions and delays in the licensing process. Much attention is paid to the integrity of RPV welds during the licensing process because the failure probability of a reactor pressure vessel is considered to be sufficiently low to exclude it from consideration as a design basis accident. The assumption of a low probability relies heavily on regularly repeated inservice examination by ultrasonic testing (UT) of welds. 1.2 Need for Proposed Action As more reactors start producing power, as those in operation grow older, and as more inservice examinations are performed, the number of detected flaws with uncertain characteristics (size, orientation, and location) is likely to increase. Flaw characterization is essential for flaw evalua- tions required by the ASME Code and by NRC to determine the structural integrity of nuclear reactor components when such flaws exist. It is essential to have valid background data for the flaw evaluations required by Section XI of the ASME Code. Based on the information gathered according to ASME Code requirements, it is often difficult to assess whether or not the flaw has grown between examinations. The procedures now in use do not require the recording of certain information that can be important in later analysis for determining the location, dimensions, orientation, and growth rate of flaws. The lack of standardization in the use of UT equipment and procedures leads to uncertainty concerning the results obtained. For example, transducer characteristics such as beam spread, damping characteristics, and frequency for peak response are not defined, and there is no provision 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