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:
the basic calibration block at "the start and finish of each examination, with any change in examination personnel and at least every 4 hours during an examination." However, the 1977 rules of Article 4 (T-433), Section V, which are referenced by Section XI and now apply to the examination of the RPV, require calibra- tion against the calibration block only "prior to use of the system." It is considered that the present 1977 ASME Code rules are not adequate to control potential problems in the variation of instrument performance characteristics. There- fore, the recommended calibration before and after each examination is a more reliable approach to instrument performance checks. The above position is not more con- servative than the previously accepted 1974 Code rules, but is more conservative if 1977 rules are considered. Considering the requirements of Article 4, Section V (1977), the above position will mean a calibration check each week the system is in use or before and after each RPV examination, whichever is less, instead of before each examination. A calibration check against the calibration block takes 15 to 30 minutes for manual UT and for automated UT equipment where provision is made to calibrate the equipment without having to remove the trans- ducers from the rotating scanning arm of the mechanized scanner. In some cases, transducers have to be removed from the scanning arm for calibration of the UT instrument; in these cases, a calibration check may take from 30 to 60 minutes. The added cost of the above would be in terms of additional time spent by the examiner and would occur each week or once for each RPV examination, depending on whether or not the examination is completed in less than a week. No additional radiation exposure is expected because of this position. 3. NEAR-SURFACE EXAMINATION AND SURFACE RESOLUTION This position recommends that an estimation of the capability to effectively detect defects at the metal front and back surfaces of the