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San Onofre Unit-3 RFO-15

San Onofre Unit-3 RFO-15. Rejectable PT indication in an Alloy-52 CEDM overlay repair weld. PT defect in CEDM #64 repair weld. Background. 2004 crack like indications in four CEDM nozzles repaired with A52 weld overlays (WCAP-15987) SE requires refueling interval Surface Exams

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San Onofre Unit-3 RFO-15

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  1. San Onofre Unit-3 RFO-15 Rejectable PT indication in an Alloy-52 CEDM overlay repair weld

  2. PT defect in CEDM #64 repair weld

  3. Background • 2004 crack like indications in four CEDM nozzles repaired with A52 weld overlays (WCAP-15987) • SE requires refueling interval Surface Exams • SE requires NRC notification if flaws are detected • 2006 all repair welds PTs were acceptable • 2008 CEDM 64 presents large, rapid PT bleed • In service defect is not expected in Alloy 52 • Necessitated NRC re-review of overlay repair • NRCactively supported the defect investigation

  4. Initial Assessment: Weld Porosity • Records show that a PT indication was ground out in in this area during fabrication • Observation reveals area contains numerous weld bead interfaces • Weld bead starts & stops prone to void formation • Evidence of prior grinding at the defect location • Replica of defect captured a small surface pore • “comma” shape pore approximately 1/16w x 1/32d • Weld porosity considered to be the likely cause • Could be repaired by grinding & weld buildup

  5. Observed features in defect area Weld bead starts & stops Area ground during installation 2004 2008 PT indication

  6. Replication of defect Weld pore exposed at defect location

  7. Investigation Process • “Emergent Issue Protocol” entered due to unexpected degradation in Alloy 52 • NEI & PWROG informed • EPRI Assessment ITG is lead IP • Peer team assembled • Boat Sample preparations initiated (day 2) • SCE proposed a limited “grind & replicate” • EPRI concurs with a 1/16th maximum grind limit • NRC requests preserving bottom of pit (~1/32nd limit) • PT after grinding resulted in a similar failure • Defect was extracted within a boat sample – cavity restored with weld repair

  8. Boat Sample Extraction Results • Sample extracted & cavity is re-welded • Actual head work completed in ~10-hours • 14 days after detection • extensive tool & procedure qualification • Did not impact the outage length • Emergent project resulted in about 3 Rem • Sample at 2.5 mR, very low contamination

  9. CEDM 64 Boat Sample New pore exposed on EDM’d surface Original Defect EDM’d side Wetted side

  10. On site radiograph shows void

  11. Approach to Destructive Exam • Destructive exam is an industry project • Alloy 52 question, Not a plant specific concern • Why did it take two cycles to manifest itself? • EPRI EOC authorizes financial support of lab work • Team formed to guide Destructive Examinations • Utilities, EPRI and NRC and Westinghouse represented • Examination plan developed & lab contracted • Results expected in late March

  12. Lessons Learned • Emergent Issue Protocol provides valuable framework for obtaining resources and capturing broad Industry issues • Establish and maintain confidence during emergent work • NRC remains concerned with in-service degradation of Alloy 690/52/152 • Be mindful of reporting requirements for Alloy 690/52/152 repairs • Generic issues are more challenging than the rework • Destructive Exam will provide definitive conclusion • Overlapping weld bead starts & stops create vulnerability • Initial NDE supports fabrication voids underlying indication

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