Use of flaw aspect ratios for pressurized thermal shock evaluations. Final report
Regulatory Guide (R.G.) 1.154 provides guidelines for assessing the integrity of pressurized water reactor (PWR) pressure vessels during pressurized thermal shock (PTS) transients. Currently, R.G. 1.154 specifies that {open_quotes}axial flaws with depths less than 20 percent of the wall thickness and all circumferential flaws should be modeled in infinite length{close_quotes}. During evaluation of the Yankee Rowe vessel it became apparent that there can be significant interaction between the flaw size and shape, cladding, and transient conditions. These complex interactions preclude using an infinite flaw length model to predict initiation of an existing flaw or to define inspection requirements for the range of variables associated with PTS evaluations. The purpose of this evaluation was to determine as a function of flaw aspect ratio the flaw and material conditions that would result in extension of axial flaws during a PTS event. Results indicate that: using an infinite aspect ratio to represent the spectrum of flaw aspect ratios that may exist in reactor pressure vessels is not appropriate for the range of conditions associated with PTS analyses; no single value of aspect ratio or location on the flaw boundary can be used to accurately represent the various flaw, transient, and material conditions important to PTS evaluations; an accurate representation of the influence of aspect ratio can be obtained by using aspect ratio as a random variable and evaluating both the maximum depth and cladding to base metal interface locations on the flaw boundary in the probabilistic fracture mechanics analysis; inspection requirements for flaw detection and sizing accuracy should be defined to maintain consistency between flaw aspect ratio and depth for PTS transients identified as significant risk contributors.
- Research Organization:
- Electric Power Research Inst., Palo Alto, CA (United States); Sartrex Corp., Rockville, MD (United States)
- Sponsoring Organization:
- Electric Power Research Inst., Palo Alto, CA (United States)
- OSTI ID:
- 88646
- Report Number(s):
- EPRI-TR--104894
- Country of Publication:
- United States
- Language:
- English
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