ML072750013
| ML072750013 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 09/25/2007 |
| From: | Southern California Edison Co |
| To: | Office of Nuclear Reactor Regulation |
| Kalyanam N, NRR/DORL/LPL4, 415-1480 | |
| Shared Package | |
| ML072750008 | List: |
| References | |
| Download: ML072750013 (30) | |
Text
1 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
2 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
3 Non Destructive Examination Results for San Onofre Unit-3 Control Element Drive Penetration 56 Southern California Edison
4 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
5 Technical Presentation Overview
- Background
- Evaluation
- Conclusion
- Future plans regarding inspections and head replacement
- Discussion
6
- 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
Background
7 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
8 Background
Figure 1 CEDM 56 Indication Profile
9
>75%
High Resolution TOFD NDD Ultrasonic shear Wave (axial & circumferential)
NDD NDD Overlay PT (Surface)
NDD Penetration OD TOFD (informational)
NDD NDD Penetration OD ET (Surface)
NDD NDD J-weld ET (Surface)
NDD NDD NDD ID ET (Surface)
NDD NDD NDD Leak Path Assessment NDD NDD NDD Bare Metal (Visual)
SI / CBH SI SI TOFD (Volumetric)
RFO-14 October 2006 EA-03-009 RFO-13 October 2004 EA-03-009 RFO-12 January 2003 Bulletin 02-01 SI, Special Interest NDD, No Defect Detected CBH, Cleared By History
Background
CEDM 56 Inspection Detail Standard Examination Supplemental Examination
10 Evaluation
- Approach
- Determination of No Growth
- Inconsistent with Primary Water Stress Corrosion Cracking (PWSCC)
- Review of Industry Experience
11 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
- SONGS Engineering
- Analysis, review, oversight, and ownership of results
12 Evaluation Determination of No Growth
- Reanalysis of all inspection data on a consistent basis concluded no discernable change since first detected in RFO12.
74.4 % t-w
- 70.2 % t-w RFO 14 74.3 % t-w 77.6 % t-w RFO 13 74.4 % t-w 55.7 % t-w RFO 12 Reanalysis Original Analysis Refueling outage
- RFO14 High resolution probe positioned indication at just over 75% t-w (>0.75 t)
13 Evaluation Inconsistent with PWSCC
- RFO 12
- Automated J-weld and OD Eddy Current concluded no surface connected PWSCC
- 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)
14 Evaluation Inconsistent with PWSCC
- RFO 13
- 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
15 Evaluation Inconsistent with PWSCC
- RFO 14
- 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
16 Evaluation Review of Industry Experience
- 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
- 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
17 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
18 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
- SCEs Conclusion
- The indication in CEDM 56 is not a defect
- Code Relief for Flaw Evaluation is not required
19 Future Plans
- Continue with EA-03-009 examinations every refueling outage
- Respond to any new indications or unexpected changes as appropriate
20 Licensing Licensing correspondence associated with CEDM 56
21
- 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 Licensing
22 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
23 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
24 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
25 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)
26 Licensing
- August 31, 2007, SCE documented completion of NDE evaluation and withdrew Relief Request ISI-3-21
27 Questions
28 Beaver Valley OD CEDM 56 Figure 2: Comparison of penetration tube ET results for OD PWSCC
29 Figure 3: Vertical (UT) slice of CEDM 56 (gray section) showing indication and grain noise throughout penetration tube base material
30 Figure 4: Unobstructed detection of OD weld overlay interface on CEDM 56 70° /40° circumferential shear wave UT analysis of CEDM 56 Overlay weld interface