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:
al such as the following are not effectively examined: a. Material volume near the front surface because of near- field effects, cladding disturbance, or electronic gating. b. Material volume near the surface because of surface roughness or unfavorable flaw orientations. c. Volumes shadowed by insulation or part geometry. In some cases, as much as 1 inch (25.4 mm) or more below the surface is not examined because of the electronic gate setting. This means that the unexamined volume may contain flaws that would be unacceptable according to Section XI, ASME Code, as follows: a. Without evaluation (deeper than approximately 0.2 inch). b. Even after evaluation (deeper than approximately 0.85 inch). Assuming an aspect ratio of 0.1, according to IWB-3510.1, Section XI, ASME Code, flaws 0.2 inch deep would be unacceptable for a 9-inch wall thickness. Typically a BWR reactor pressure vessel (RPV) wall in the beltline region is 6 inches thick and a PWR-RPV wall is 8.5 inches thick. During flaw evaluation, where the wall temperature is high and the available toughness is high, and the calculated critical surface flaw depth (ac) exceeds the wall thickness (t), ac is taken9 as the wall thickness. According to IWB-3600, Section XI, the allowable end-of-life size is af = 0.1a.. Flaws exceeding this allowable value, which would 8"Ultrawnic Examination Comparison of Indication and Actua1 Flaw in RPV," Ishi Kawajima-Harima Industries Co., Ltd., January 1976. 9,Flaw Evaluation Procedures: ASME Section XI-EPR1M" NP-719-SR, special report, August 1978. 1.150-5 be 0.85 inch for a PWR and 0.65 inch for a BWR, will have to be repaired. The above example illustrates the importance of blanking out the electronic indication signals and not examining the surface volume to a depth of 1 inch. Since the flaws that can be missed because of electronic gating may be larger than the flaws permitted with or without evaluation, this unexamined volume is important and needs to be identified. In certain