ML102510346
| ML102510346 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 09/09/2010 |
| From: | Mel Holmberg NRC/RGN-III/DRS/EB1 |
| To: | |
| Shared Package | |
| ML102310165 | List: |
| References | |
| Download: ML102510346 (44) | |
Text
NRC Special Inspection NRC Special Inspection Team Exit Meeting Team Exit Meeting Davis Besse RPV Head Leakage Davis Besse RPV Head Leakage September 9, 2010 1
Welcome Welcome Anne Boland Di t
Director Division of Reactor Safety Division of Reactor Safety NRC Region III 2
Meeting Agenda
- Introductions
- Background
- Background
- NRC Special Inspection Scope & Results
- NRC Evaluation for Continued Operations
- NRC Evaluation for Continued Operations
- NRC Conclusions FENOC C t
- FENOC Comments
- Public Questions and Comments 3
Introductions - NRC
- Mark Satorius, Regional Administrator, Region III
- Anne Boland, Director, Division of Reactor Safety
- David Hills, Chief, Engineering Branch 1 g
g
- Jamnes Cameron, Chief, Reactor Projects Branch 6
Reactor Regulation (NRR)
- Mel Holmberg, Senior Metallurgical Engineer, SIT Lead Inspector
- Jay Collins Senior Materials Engineer SIT Member NRR Jay Collins, Senior Materials Engineer, SIT Member, NRR
- John Rutkowski, Senior Resident Inspector, Davis Besse
- Michael Mahoney, Project Manager, NRR Vikt i Mitl
/ P Ch d thil P bli Aff i Offi 4
- Viktoria Mitlyng / Prema Chandrathil, Public Affairs Officers
- Adam Wilson, Resident Inspector, SIT Member
Introductions - FENOC
- FirstEnergy Nuclear Operating Company (FENOC) 5
=
Background===
g
- March 12, 2010 - FENOC identified reactor pressure vessel (RPV) head flaw indications through NRC
(
)
g required examinations
- NRC safety focus on potential reactor coolant pressure boundary leakage resulted in dispatch of an pressure boundary leakage resulted in dispatch of an inspector specialized in material degradation
- NRC was concerned with the unexpected early onset of cracking/leakage & later with the number of nozzles affected
- March 16 2010 - Upgraded NRC response to a 6
March 16, 2010 Upgraded NRC response to a Special Inspection Team (SIT)
NRC Special NRC Special Inspection Scope &
Inspection Scope &
Results Mel Holmberg Mel Holmberg Senior Metallurgical Engineer SIT L d I t
NRC Inspection Focus Areas
- Extensive onsite NRC observation and evaluation of examinations and repairs evaluation of examinations and repairs
- Evaluation of previous non destructive
- Evaluation of previous non-destructive examinations for the replacement head
- Evaluation of FENOCs root cause analysis effort and report conclusions effort and report conclusions 8
Major SIT Activities
- Observation of each type of head examinations
- Review exam personnel qualifications R
i f h d
d
- Review of head exam procedures
- Review of historical video and written exam records
- Review of reactor coolant leakage measurement/trends
- Review of reactor coolant leakage measurement/trends
- Observation of the head repair process
- Review of repair personnel qualifications p
p q
- Review of repair procedures
- Review of FENOC root cause team investigation
- Review of FENOC analysis for head continued service 9
=
Background===
- 1975 - 2002: Head stored at Midland plant, but not maintained under a Quality Assurance program maintained under a Quality Assurance program
- 2002: Head subjected to a series of nondestructive examinations (NDE) to confirm integrity
- 2002: Original head replaced with unused head from the cancelled Midland Unit 2 plant March 2004: Power operation with the replaced head
- March 2004: Power operation with the replaced head
- 2003, 2005, 2006, 2008: Multiple bare-metal visual (BMV) head examinations completed - No boric acid
(
)
p deposits indentified 10
RPV Head Configuration 10 Access View Ports in Service Structure J-Nozzle Detail at Right Groove Weld at Right 11
SIT Observations - 2010 Outage g
- Applied multiple exam methods to head Applied multiple exam methods to head
- Minor leakage at nozzles #4 and # 67
- Repaired 24 nozzle locations with cracks 12
Ultrasonic (UT) Examinations
- Nozzle 4 - Three Axial Crack Indications 2
1 2
Visual (VT) Examinations
(
)
- Nozzle # 4 - Boric Acid Deposits 14
J-groove Weld Examinations
- Nozzle # 48 J groove Weld
- Nozzle # 48 - J-groove Weld
- Dye Penetratnt (PT) Examination 15
Head Repair Method
- Half-nozzle repair - 24 nozzles
- Roll expansion of the nozzle within the head
- Removal of the lower nozzle section and PT
- New Alloy 52M weld to attach nozzle to head
- Machine repair weld and nozzle inside surface
- High pressure water jet at inside nozzle surface.
16
CRDM Half Nozzle Repair CRDM Vessel Head Mockup CRDM Nozzle Vessel Repair Weld Vessel Head Removed CRDM Nozzle 17
Conclusions on Exams & Repairs
- Exams met NRC Requirements
- Appropriate nozzles were repaired
- Repaired nozzles met NRC requirements
- Head suitable to return to service 18
Direct Cause of Cracking SIT agrees with:
- Direct cause Primary Water Stress
- Direct cause - Primary Water Stress Corrosion Cracking (PWSCC) of CRDM nozzle and J-groove welds nozzle and J groove welds
- Early onset of cracking due to:
Early onset of cracking due to:
- Higher than expected head operating temperature temperature
- Nozzle material fabrication method 19
Factor for Early Cracking Head Operating Temperature
- Factor for early onset of PWSCC - higher head operating temperature than previously assumed
- Head hotter than the previously assumed hot leg temperature
- Caused by channeling of water directly from fuel assemblies 20
Vessel Flow -
Head Temperature 21 Reactor Vessel
Factor for Early Cracking S
tibl M t i l Susceptible Material
- Random (Poor) carbide distribution in the Alloy
(
)
y 600 CRDM nozzle material was a significant contributing cause
- Material samples from nozzles 4 and 10
- Distributed carbides identified
- Low heat treatment temperature
- Heat treatment process met ASME Code and p
NRC requirements 22
Random Carbide Distribution Grain Boundary 23 Carbides
Root Cause of Cracking SIT agrees with:
SIT agrees with:
- Root cause related to site staffs lack of sensitivity to susceptibility of this head to sensitivity to susceptibility of this head to cracking
- Replace head or do UT sooner p
- No performance deficiency - Licensee actions reasonable and met NRC requirements 24
Weaknesses in Root Cause and Narrow Corrective Action
- The root cause corrective actions were narrowly focused on preventing recurrence of cracking on the head the head
- Root cause weakness - No verification of site staff knowledge or training related to PWSCC
- No performance deficiency because FENOC met NRC requirements for head exams related to identification of PWSCC indicating training 25 to identification of PWSCC indicating training is adequate
NRC Identified Findings
- Weld repair procedure applied on nozzle # 4
- Weld repair procedure applied on nozzle # 4 26
Finding - PT Procedure for Nozzle Repairs
- Excessive wash time removes PT fluid from k
th t PT t
k cracks so that PT process may not work
- Procedure changed to limit water wash time t
10 i
t to 10 minutes
- Mockup used to demonstrate 10 minutes was an acceptable wash time an acceptable wash time 27
Finding - PT Procedure for Nozzle Repairs
- Potential violation of 10 CFR 50 Appendix B, Criterion IX - failure to use a procedure qualified in accordance with applicable Codes and Standards and Standards
- Finding of very low safety significance (Green)
(Green) 28
Finding - Procedure for Viewing PT on Nozzle # 61 Repair Weld Nozzle # 61 Repair Weld
- 14% of nozzle #61 repair area not examined
- Similar errors affected nine other nozzles
- Procedure changed to ensure complete exam area coverage and repeated 10 nozzle exams 29
Finding - Procedure for Viewing PT on Nozzle # 61 Repair Weld Nozzle # 61 Repair Weld
- Potential violation of 10 CFR 50 Appendix B, C i i
V f il d
i h Criterion V - failure to use procedure with adequate instructions to detect flaws in the repaired nozzles repaired nozzles
- Finding of very low safety significance (Green) 30
Finding - Weld Repair Procedure Applied on Nozzle # 4 Nozzle # 4
- FENOC failed to ensure weld procedure PS0140-002 maintained heat input below procedure qualification record (PQR)
N l
- 4 i
ld l t d
- Nozzle # 4 repair weld passes completed without meeting Code qualification tests W ld f b i t d ith hi h ld h t
Finding - Weld Repair Procedure Applied on Nozzle # 4
- Potential Violation of 10 CFR 50 Appendix B Potential Violation of 10 CFR 50 Appendix B, Criterion IX - failure to use Code qualified welding process on nozzle # 4
- Finding of very low safety significance (Green) 32
NRC Evaluation of Findings
- Cause of findings relates to an inadequate review of deficient vendor procedures
- FENOC oversight of work activities including contractors was not adequate to ensure that all requirements were being met
- IMC 0310 Item H.4.C - examples of a cross-i i
h f H cutting aspect in the area of Human Performance, Work Practices 33
Potential Violation of TS 3.4.13 - RCS Operational Leakage - Self-Revealed Operational Leakage - Self-Revealed
- Minor pressure boundary leakage at nozzles # 4 and # 67 and # 67
- Leakage was below detection thresholds
- No performance deficiencies associated with No performance deficiencies associated with monitoring for reactor coolant leakage
- No related performance deficiencies (e.g.
Accounting for the revised higher head temperature no additional head exams were required) required) 34
Head Operating Service Life
- Temperature heat treatment cold work and residual Temperature, heat treatment, cold work and residual stress - affect crack growth-rates
- Uncertainties bounded by FENOC commitments
- Uncertainties bounded by FENOC commitments to limit remaining head service life
- NRC will test a nozzle material for independent crack growth-rate measurements 35
NRC Evaluation for NRC Evaluation for Continued Safe Operations David Hills Engineering Branch Chief i
36 NRC Region III
NRC Evaluation for Continued Safe Operations Safe Operations
- NRC SIT confirmed the RPV head was returned to a condition suitable for service returned to a condition suitable for service
- FENOC originally proposed a 21 month operating cycle in a June 3 2010 Public operating cycle in a June 3, 2010 Public Meeting
- NRC identified uncertainties in ensuring low
- NRC identified uncertainties in ensuring low likelihood of leakage toward the end of the proposed operating cycle 37 proposed operating cycle
FENOC Resolution - NRC Evaluation
- Operating time (~15 months) consistent with i d d
t d
ti NRC k
th independent and conservative NRC crack growth rate calculations
- Replacing the head in 2011 earlier than previously planned (2014) was a safety focused decision that 38 p
(
)
y bounded uncertainties
NRC C l
i NRC Conclusions Mark Satorius Regional Administrator NRC Region III 39
Summary Conclusions
- Plant safety was not compromised.
- The NRC required exams worked as designed.
FENOC identified nozzle cracking/leakage well before structural integrity was challenged.
Th NRC d
d i
d i
- The NRC conducted an extensive and rigorous inspection to ensure that FENOC properly repaired the RPV head.
40 the RPV head.
Summary Conclusions (Continued)
(
)
p earlier than planned, was a safety conservative decision.
- Significant NRC action prior to plant startup -
June 23, 2010 Confirmatory Action Letter y
- The NRC will conduct a comprehensive head 41 C
p replacement inspection.
FENOC Comments 42
Public Questions &
C t
Comments 43
Questions/Comments Questions/Comments Contact the NRC Region III Office of Contact the NRC Region III Office of Public Affairs, 630-829-9500