ML24241A012
| ML24241A012 | |
| Person / Time | |
|---|---|
| Issue date: | 08/28/2024 |
| From: | Leslie Terry NRC/NRR/DNRL/NCSG |
| To: | |
| References | |
| Download: ML24241A012 (1) | |
Text
Loss of Steam Generator Tube Integrity From Wear at Tube Support Plates NRC Staff Perspective
NRC Public Meeting w ith SGTF September 5, 2024 Corrosion and Steam Generator Branch, NRR/DNRL ACRONYMS
- EPRI - Electric Power Research Institute
- SGTF - EPRI Steam Generator Task Force
- MA - Mill Annealed
- TSTF - Technical Spec ifications Task Force
- TT - Thermally Treated
- RFO - Refueling Outage
- EFPM - Effective Full Power Months
- ISPT - In situ Pressure Test
- TS - Technical Specifications
- 3xNOPD - 3 Times Normal Operating
- OA - Operational Assessment Pressure Differ ential
- CMOA - Condition Monitoring Operational
- NDE - Nondestructive Examination Assessment
- TSP - Tube Support Plates
- PWR - Primary Water Reactor
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- Original SG TS until 2005
- Prescriptive surveillance requirements PWR Fleet SG
- TSTF-449 (2005)
Technical - Performance based TS framew ork Specifications History
- TSTF-510 (2011)
- Extended inspection periods, deleted mid-points
- TSTF-577 (2021)
Yellow shade = TSTF-577
Tube Material
Alloy 600MA Alloy 600TT Alloy 690
Inspect Inter val Unchanged at From 48 to From 72 to (maximum) 24 EFPM 54 (72) EFPM 96 EFPM
Inspect Period From 60 to From 120, 96, 72 From 144, 120, 24 EFPM to 54 (72) EFPM 96, 72 to 96 EFPM
3 Background - Operating Experience
- 9 flaws (4 tubes) did not satisfy condition monitoring analytically and required ISPT
- Based on ISPT, 2 tubes failed to meet TS structural integrity performance criterion (3xNOPD)
- Revised OA was nonconservative:
- Sub-population of aggressive wear (low rows) not recognized
- Assumed tapered wear shape in low rows instead of flat wear
4 NRC Staff Perspective
- This operating experience resulted from an inadequate OA and NDE calibration/sizing error, not from a TSTF -577 issue
- Loss of tube integrity due to wear at support structures shoul d not happen; degradation readily detected and sized with eddy current inspection
- Although tubes failed at or near the 3xNOPD criteria, t he revised OA for wear at TSPs also allowed for an additional operating cycle. The inspection interval was limited by t ube wear at anti -vibration bars
5 Discussion Topics
- Are any generic changes needed?
- EPRI guidelines
- Tube wear calibration standards and sizing techniques
- OA techniques
- What is industrys expected level of internal vendor review and licensee review/acceptance of SG CMOA documents?
- For longer inspection intervals or challenging CMOAs, should the OA technique parameters/assumptions that are most sensitive to changing the time between inspections be highlighted within the CMOA?
- When are third party CMOA reviews prudent?
- Licensees internal expertise
- OA results approaching acceptance criteria
6 References
- Technical Specifications Task Force, TSTF-577, Revised Frequencies For Steam Generator Tube Inspections, Final Traveler Safety Evaluation, ADAMS Accession No. ML21098A188
- Licensee Event Report, Event 56834, Steam Generator Tube Degradati on Indicated by Failed In-Situ Pressure Testing, ADAMS Accession No.
- Notice of Violation, NRC Inspection Report 05000382/2024013, ADAMS Accession No. ML24228A261
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