ML072750013

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9/25/2007 Licensee Handouts for Meeting Re San Onofre Nuclear Generating Station, Unit 3 - Reclassification of Control Rod Drive Mechanism 56 NDE (Non Destructive Examination) Indication
ML072750013
Person / Time
Site: San Onofre Southern California Edison icon.png
Issue date: 09/25/2007
From:
Southern California Edison Co
To:
Office of Nuclear Reactor Regulation
Kalyanam N, NRR/DORL/LPL4, 415-1480
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ML072750008 List:
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Download: ML072750013 (30)
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September 25, 2007 Reclassification of Control Rod Drive Mechanism (CEDM) 56 NDE Indication Southern California Edison (SCE)

San Onofre Nuclear Generating Station (SONGS) Unit 3 1

Purpose

  • Based on all information available to date, SCE has reclassified the indication in CEDM 56 as No Detectable Defect (NDD)

- Discuss the technical basis for the reclassification

- Discuss the licensing issues associated with the reclassification 2

Non Destructive Examination Results for San Onofre Unit-3 Control Element Drive Penetration 56 Southern California Edison 3

Key Points

  • Determination

- The indication in CEDM 56 is not a defect

- Code Relief for Flaw Evaluation is not required

  • Basis

- Repair of CEDM 56 was based on refuted data

- All supplemental exams were negative for PWSCC

- Indication in CEDM 56 lacks PWSCC features

- Indication is consistent with grain noise

- Current evaluation methodology would conclude no defect is present in CEDM 56 4

Technical Presentation Overview

- Background

- Evaluation

- Conclusion

- Future plans regarding inspections and head replacement

- Discussion 5

Background

  • CEDM 56 identified as special interest during reactor vessel head inspection in RFO 12
  • Weld overlay was applied to J-groove weld and penetration OD surfaces to ensure that CEDM 56 was returned to service in a conservative configuration
  • Code Relief was needed to temporarily allow evaluation of a flaw having depth greater than 0.75 t pending final NDE evaluation and repair planning
  • Supplemental examination techniques were developed to investigate whether indication in CEDM 56 is PWSCC 6

Background

Inspection & Repair History

  • Cycle 12 refueling outage (RFO-12) Jan 2003

- SCE Commitment to NRC Bulletin 2002-01

- Westinghouse demonstrated inspection technology

- Ultrasonic time of flight diffraction (TOFD) indications observed in 4 penetrations

- Supplemental surface eddy current (ET) ruled out PWSCC

  • Cycle 13 refueling outage (RFO-13) Oct 2004

- NRC Order EA-03-009 using Westinghouse demonstrated NDE

- Indications in 4 CEDMs appeared to have grown

- Supplemental ET data was not consistent with apparent growth

- Embedded Flaw repairs implemented to ensure conservatism

- Indication in CEDM 56 exceeded Code limit for evaluation (figure 1)

  • Cycle 14 refueling outage (RFO-14) Oct 2006

- NRC Order EA-03-009 using Westinghouse demonstrated NDE

- Supplemental NDE designed for CEDM 56

- No discernable changes in CEDM 56 indication 7

Background

Figure 1 CEDM 56 Indication Profile 8

Background

CEDM 56 Inspection Detail SI, Special Interest RFO-12 RFO-13 RFO-14 NDD, No Defect Detected January 2003 October 2004 October 2006 CBH, Cleared By History Bulletin 02-01 EA-03-009 EA-03-009 TOFD (Volumetric) SI SI SI / CBH Bare Metal (Visual) NDD NDD NDD Leak Path Assessment NDD NDD NDD ID ET (Surface) NDD NDD NDD J-weld ET (Surface) NDD NDD Penetration OD ET (Surface) NDD NDD Penetration OD TOFD (informational) NDD Overlay PT (Surface) NDD NDD Ultrasonic shear Wave (axial & circumferential) NDD High Resolution TOFD >75%

Standard Examination Supplemental Examination 9

Evaluation

  • Approach
  • Determination of No Growth
  • Review of Industry Experience 10

Evaluation Approach

  • WesDyne (Westinghouse)

- Perform a consistent evaluation of base scope NDE data for indications of growth in CEDM 56 (and CEDMs 32, 57, and 64) from RFO 12, 13, and 14

- Assess supplemental NDE data from CEDM 56 to determine possibility of a PWSCC flaw

- Evaluation and assessment performed by

  • Level III with extensive experience in RVH TOFD
  • Chief Engineer, recognized authority in NDE
  • ANATEC

- Third party review of NDE data and Westinghouse evaluation

  • Level III with extensive experience in RVH TOFD
  • Concluded not attributable to PWSCC

- Analysis, review, oversight, and ownership of results 11

Evaluation Determination of No Growth

  • Reanalysis of all inspection data on a consistent basis concluded no discernable change since first detected in RFO12.

Refueling Original Reanalysis outage Analysis RFO 12 55.7 % t-w 74.4 % t-w RFO 13 77.6 % t-w 74.3 % t-w RFO 14 70.2 % t-w 74.4 % t-w *

  • RFO14 High resolution probe positioned indication at just over 75% t-w (>0.75 t) 12

Evaluation Inconsistent with PWSCC

- Automated J-weld and OD Eddy Current concluded no surface connected PWSCC

  • ET is a very effective exam for detection of PWSCC surface & near surface connections
  • A 0.7 surface or near-surface crack is readily detected (figure 2)
  • Lack of surface connection refutes PWSCC

- Indication was dispositioned as grain noise

  • Large population of distributed reflectors (figure 3) 13

Evaluation Inconsistent with PWSCC

- Manual OD scan employing TOFD & ET (informal)

  • ET: No crack like features
  • TOFD: No lateral wave interruption

- J-weld ET: No crack like features

- No effect from repair on ID exam 14

Evaluation Inconsistent with PWSCC

- Confirmed no discernable change

- High Resolution probe measured maximum indication depth at just over 75% from OD surface (could not withdraw 0.75t relief request)

- Ultrasonic shear wave exams detected no evidence of a crack-like flaw

  • No shadowing of distributed reflectors
  • Continuous observation of overlay weld interface (figure 4)

- Axial crack would obscure view of overlay interface

- Transparency of indication is consistent with grain noise, not PWSCC 15

Evaluation Review of Industry Experience

  • Beaver Valley (BV) J-weld and OD ET exams had clear detection of PWSCC

- Indication in CEDM 56 penetration OD would be larger and more easily detected if PWSCC

- CEDM 56 J-weld scan found no crack-like indications

  • BV TOFD included typical PWSCC characteristics that are lacking in CEDM 56

- No loss of backwall signal

- Crack tip diffraction response not evident

- Indication has not changed since detection

  • Application of updated WesDyne analysis procedures would determine CEDM 56 as NDD 16

Evaluation Technical Summary

  • Ultrasonic TOFD (tip diffraction) technology is very sensitive, and commonly detects normal material structures in addition to real defects

- Real cracks affect TOFD inspection results in a predictable way

  • Backwall reflections should be suppressed over certain angles
  • Distributed reflectors should be obscured behind crack faces
  • Characteristic tip diffraction signal response

- CEDM 56 penetration includes TOFD features typical of grain noise, and not PWSCC

  • Confirmed growth in a TOFD indication over time is compelling evidence of PWSCC

- Uniform analysis of RFO 12, 13, and 14 examination data has concluded that no discernable change in indication has actually occurred

  • Supplemental NDE is standard practice for validating TOFD indications

- Eddy Current is a reliable confirmatory test for PWSCC surface connection.

Supplemental ET of J-weld & Penetration OD in RFO 12 and 13 refuted PWSCC hypothesis.

- There was no shear wave obscuration of backwall features or distributed reflectors which would be expected behind a crack face 17

Conclusion

  • Summary of Facts

- PWSCC disposition in RFO 13 was based on refuted data

- All supplemental exams were negative for PWSCC

- Indication in CEDM 56 lacks PWSCC features

- Indication is consistent with grain noise

- Current Westinghouse evaluation methodology would conclude no defect is present in CEDM 56

- The indication in CEDM 56 is not a defect

- Code Relief for Flaw Evaluation is not required 18

Future Plans

  • Continue with EA-03-009 examinations every refueling outage
  • Respond to any new indications or unexpected changes as appropriate
  • Replace the SONGS 3 Reactor Vessel Head during RFO 17 (approximately Fall of 2012) 19

Licensing Licensing correspondence associated with CEDM 56 20

Licensing

  • Relief Request ISI-3-8:

- Contingency submitted prior to RFO 13 Embedded Flaw Repair (< 75% t-w) --

Used for 3 CEDMs during RFO 13

  • Submitted December 3, 2003
  • Supplemented March 15, 2004
  • Approved May 5, 2004
  • No Commitments made at this time 21

Licensing

  • Relief Request ISI-3-13:

- Submitted during RFO 13 Embedded Flaw Repair (>75% t-w) Specifically for CEDM 56

  • Submitted October 26, 2004
  • Supplemented December 2, 2004*
  • Approved December 23, 2004
  • *Commitment: SCE will identify a long-term repair method and implement that repair in RFO 14 22

Licensing

  • Meeting with NRC Staff:

- March 2, 2006, presented long term disposition of CEDM 56

- Existing repair is adequate for one cycle

- SCE will inspect to validate stability

- SCE will submit 2 relief requests

  • If no discernable growth - Operate 1 cycle (ISI-3-21)
  • Contingency repair alternative (ISI-3-22)
  • Teleconference with NRC Staff

- March 22, 2006, agreed to above approach 23

Licensing

  • Relief Request ISI-3-21: Allowing 1 cycle of operation contingent upon no discernable growth (<0.02)

- Submitted May 11, 2006 (Prior to RFO 14)

- Teleconference November 14, 2006 (During RFO 14)*

- Supplemented November 20, 2006 (During RFO 14)**

- Verbal Approval December 1, 2006 (During RFO 14)

- Written Approval February 7, 2007

  • SCE informed NRC no discernable growth
    • Commitment: SCE to either reclassify as NDD and withdraw Relief Requests ISI-3-21 and ISI-3-22 or will repair during RFO 15 24

Licensing

  • Relief Request ISI-3-22: Contingency repair in RFO 14 to allow operation to RFO 15 if growth was greater than or equal to 0.02 (no discernable growth) 25

Licensing

  • Based on all information available to date, SCE reclassified the indication in CEDM 56 as NDD

- August 31, 2007, SCE documented completion of NDE evaluation and withdrew Relief Request ISI-3-21 26

Questions 27

Figure 2: Comparison of penetration tube ET results for OD PWSCC Beaver Valley OD CEDM 56 28

Figure 3: Vertical (UT) slice of CEDM 56 (gray section) showing indication and grain noise throughout penetration tube base material 29

Figure 4: Unobstructed detection of OD weld overlay interface on CEDM 56 Overlay weld interface 70° /40° circumferential shear wave UT analysis of CEDM 56 30

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