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Industry Presentations: Nov. 16, 2006 Public Meeting
	ML063210080
Person / Time
Site:	Wolf Creek
Issue date:	11/16/2006
From:	Robinson M; Duke Energy Corp, Electric Power Research Institute
To:	; Office of Nuclear Reactor Regulation
	Mensah T
References
	Download: ML063210080 (31)
	v • d • e

Alloy 82/182 Pipe Butt Weld Inspections MRP / NRC November 16, 2006 Mike Robinson, Duke Energy, MRP Chairman

Outline

Materials Initiative Background

MRP-139: What Is It And Why Are We Doing It

Review of Wolf Creek Findings

Recent Industry Activities to Incorporate the Wolf Creek Operating Experience

- Fleetwide Survey for Pressurizer Location Inspection and Mitigation Status

- White Paper Reviewing Key Safety Assessment Assumptions

- MRP Information Notice to PWR Owners

How Fleet compares to Wolf Creek

Materials Initiative Background

Indications found at WC discovered during inspections performed in accordance with MRP-139, industry guidance for inspection of dissimilar metal butt welds

MRP-139 guidance is mandatory in accordance with the industrys Material Initiative

An initiative is a formal commitment between industry CNOs to follow defined policy

The materials initiative is focused on supporting a proactive approach to managing degradation of the materials used in the pressure boundary of primary systems

Materials Initiative Background

The Materials Initiative was unanimously approved by NSIAC in May of 2003

MRP-139 was issued in August 2005. Its guidance on inspection methods and frequency is mandatory in accordance with the Materials Initiative

Materials Initiation has a process for deviations

Industry Perspective on WC Indications

We are reviewing the findings at WC and potential impact on our recommendations relative to safety significance.

Recognize NRC concerns on what has been reported for WC

Believe that fleet pressurizer DM welds condition is not an immediate nuclear safety concern

- 30+ years of operating history and experience without any significant leakage and no failures

- All PWR operators are using enhanced RCS leakage monitoring and take aggressive action at very low levels of leakage

- Original design basis included failures of piping. Margin built in designs to respond to these failures.

MRP-139 inspection program is working

Industry lessons learned from fall outages

- MRP-139 is living document and will be updated to reflect field experience and any new information.

MRP-139 Development

MRP-139 provides guidance for the volumetric and visual inspection of dissimilar metal butt welds in PWR primary systems

- Not dependent on any one analysis

- Technical Basis developed using a structured approach

Performed deterministic calculations

- Time from initial flaw to throughwall

- Time from 1 gpm to critical flaw

- Set initiation time to zero, set throughwall to 1 gpm leak

Performed probabilistic calculations

Evaluated the impact of a failure on plant operation

Knowledge of fundamentals of degradation mechanism

Condition of Alloy 82/182 welds (worldwide)

Inspection capabilities for various location types

- During review and approval process, conducted a third party review and industry resource assessment for implementation planning

During Development of MRP-139

Based on preliminary results from safety assessment calculations, MRP escalated prior bare metal visual recommendation for butt welds to needed requirement.

- MRP letter 2004-05: Each PWR perform a direct visual inspection of the bare metal at all Alloy 82/182 pressure boundary butt weld locations within the next 2 refueling outages.

- Deadline is found in MRP-2003-039 (2 outages from 1/20/2004)

- To prepare for volumetric inspections, MRP letter 2004-05 also included Good Practice

Obtain plant-specific information on weld joint configurations and available access to prepare for future volumetric examinations.

- BMVs have been completed for all plants and no leakage identified

BMVs continue

NRC Bulletin 2004-01: utilities committed to bare metal visuals until MRP-139 guidance

Analytical Considerations

Used best available, generally accepted analytical methods

- Cant fully capture complexities of PWSCC propagation

Destructive examinations have shown more complex crack morphologies that are clearly not k-dependent (MRP-115)

Limited ability to characterize these indications with current UT methods

- Determine whether flaws are service induced or fabrication flaws

- Determine whether all the flaws are in the same plane

- Determine whether there are several flaws close together or one flaw

Used temperature as initial method for prioritization and did not give credit for knowledge of weld repairs

MRP-139 Final Decisions

Augmented inspections beyond ASME Section XI requirements are the right thing to do

- Safety assessment supported ASME Section XI requirements including RI-ISI

- MRP-139 consistent with approach used for BWR piping in GL 88-01(NUREG 0313)

- Provides reasonable assurance that the potential for RCS pressure boundary leakage is minimized

- Assures continued safe operation

MRP-139 inspection requirements:

- Complement the previous industry-wide BMVs required by MRP Letter 2004-05.

- Establish BASELINE condition of the fleet

- Eliminate RI-ISI sampling for Alloy 82/182 welds

- Monitor condition of Alloy 82/182 butt welds

Track the occurrence of degradation

Detect onset of increased initiation as plants age

Validate models

- Increase inspection frequency for earlier detection as compared to current ASME code requirements

MRP-139 Implementation Schedule

More aggressive schedule implementation than ASME schedule for qualified examinations judged appropriate by industry.

- Baselines shall be complete for all butt welds by 2010

First priority: pressurizers primarily due to temperature and limited inspection capability

- 12/31/07 conveys an appropriate urgency

- Recognized that some utilities would have only one opportunity to make this deadline due to limited preparation time.

Evaluated impact on industry resources of aggressive schedule

What is a Deviation?

Industry Materials Initiative identified a process for deviations

- Similar to the relief request from ASME requirements

Required when mandatory elements will not be fully implemented or will not be implemented in a manner consistent with their intent OR when implementation exceeds allotted schedule.

Entered in site Corrective Action Programs

Technical justification will

- Provide basis for determining that the proposed deviation meets the same objective and intent, or level of conservatism exhibited by the original requirement

- Clearly state how long the deviation will be in effect

- Final concurrence from the responsible utility executive and a materials expert independent of utility

Industry Activities and Status

White Paper - will revise to support the next public meeting

Will address NRC comments

Key Safety Assessment Assumptions

Field Experience Summary

Review of Wolf Creek Findings

- Reported flaw length was not transferred to ID surface

Wolf Creek Operating Experience issued to industry

Completed MRP-139 Implementation Survey

MRP Letter 2006-044, Incorporation of Wolf Creek OE

- Sent to MRP Executive Committee

- Primary purpose to heighten awareness

Summary of Wolf Creek Indications Nozzle Reported Reported Aspect Nom ID Calc. ID Arc Length Length Depth Ratio (in.) Length (deg )

(in.) (a/t) (in.) 1 Relief 11.5 26% 21:1 5.71 7.7 155 Safety C 3.75 23% 8:1 5.71 2.5 50 Surge (1) 5.0 31% 9:1 11.88 4.0 39 Surge (2) 2.75 25% 5:1 11.88 2.2 21 Surge (3) 1.0 10% 2:1 11.88 0.8 8 1 - length is based on projecting flaw to ID surface.

NRC/NEI Public Meeting Wolf Creek DM Weld Indications Terry Garrett Vice President Engineering Wolf Creek Nuclear Operating Corporation November 16, 2006 14

NRC/NEI Public Meeting Wolf Creek DM Weld Indications November 16, 2006 In October 2006 all six pressurizer Dissimilar Metal (DM) welds inspected.

Mandatory Inspection per MRP-139.

Inspected per PDI-UT-10.

PDI UT-10 is an approved manual technique for detection and length sizing.

The UT examiner was qualified on PDI-UT-10 for detection.

Full Structural Weld Overlays were scheduled to be installed regardless of results. 15

NRC/NEI Public Meeting Wolf Creek DM Weld Indications November 16, 2006 Results Spray, A Safety & B Safety nozzle DM Welds - no indications.

Indications identified in Surge, C Safety & Relief nozzle DM Welds.

EPRI NDE Center performed a technical review and hands on evaluation of the examinations and results.

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NRC/NEI Public Meeting Wolf Creek DM Weld Indications November 16, 2006 Surge Nozzle Three circumferentially oriented planar indications that originate at or near the inside surface.

Based on informational sizing:

About 5 inches long* with a maximum through wall extent of approximately 31%.

About 2.75 inches long* with a maximum through wall extent of approximately 25%.

About 1 inch long* with a maximum through wall extent of less than 10%.

UT showed branched indications with multiple 17

NRC/NEI Public Meeting Wolf Creek DM Weld Indications November 16, 2006 C Safety Nozzle Circumferentially oriented planar indication that originates at or near the inside surface.

Informational sizing showed the indication to be approximately 3.75 inches long* with a maximum through wall extent of approximately 23%.

UT showed branched indications with multiple facets.

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NRC/NEI Public Meeting Wolf Creek DM Weld Indications November 16, 2006 Relief Nozzle Circumferentially oriented planar indication that originates at or near the inside surface.

Informational sizing showed the indication to be approximately 11.5 inches long* with a maximum through wall extent of approximately 26%.

UT showed branched indications with multiple facets.

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All indication lengths are projected lengths on the outside diameter

NRC/NEI Public Meeting Wolf Creek DM Weld Indications November 16, 2006 What happened Most probable mechanism for formation of the indications in the surge, C safety, and relief nozzle DM welds is PWSCC.

All indications were characterized as branched with multiple facets.

Indications are all located near the ID or ID connected.

All indications found in susceptible Alloy 82/182 Material.

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NRC/NEI Public Meeting Wolf Creek DM Weld Indications November 16, 2006 Actions Taken Performed Full Structural Weld Overlay on all six nozzles as previously planned prior to examinations.

All weld overlays passed PDI UT examination.

Performed extent of condition evaluation.

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Butt Weld Field Experience Summary of Alloy 182/82 Butt Weld Indications Date Plant Nozzle Indication Disposition Comments Location 1999 Ringhals 3 RV Hot Leg Axial Left in service Remove after 1 cycle - DE 2000 Ringhals 4 RV Hot Leg Axial Removed Boat sample 2000 Summer RV Hot Leg Axial Removed Through wall - DE (circ in clad) 2002 Tihange 2 PZR Surge Axial Left in service No growth - NOT PWSCC 2003 Tsuruga PZR Relief & Axial Removed Through wall -DE Safety 2003 TMI 1 Surge to Hot Axial Weld Overlay Leg 2005 Calvert Cliffs 2 Hot leg drain 2 axial & 1 Weld Overlay Circ attributed to fabrication -

Circ NOT PWSCC 2005 Calvert Cliffs 2 Cold leg drain Axial Weld Overlay Indication not reproducible after surface prep 2005 Cook 1 PZR Safety Axial Weld Overlay

Summary of Alloy 182/82 Butt Weld Indications Date Plant Nozzle Indication Disposition Comments Location 2006 Millstone 3 PZR Spray Axial & 2 Circs Weld Overlay Circs attributed to original fabrication LOF, Axial not characteristic of PWSCC 2006 SONGs 2 PZR Safety 5 Axial Weld Overlay ID NDE confirmed not surface PZR Spare 1 Axial connected, Fab RT review corresponded to UT -NOT PWSCC 2006 Davis Besse Cold leg drain Axial Weld Overlay ~1/4 long, attributed to construction 2006 Calvert Cliffs 1 PZR Relief Axial MSIP 2006 Calvert Cliffs 1 Surge to Hot Circ MSIP Aspect Ratio 6:1 Leg 2006 Calvert Cliffs 1 Hot leg drain Circ MSIP Aspect Ratio 6:1 2006 Wolf Creek PZR Relief Circ Weld Overlay Aspect Ratio 21:1 2006 Wolf Creek PZR Safety Circ Weld Overlay Aspect Ratio 8:1 2006 Wolf Creek PZR Surge 3 Circ Weld Overlay Aspect Ratio 9:1, 5:1, 2:1

Summary of Alloy 182/82 Butt Weld Indications

Three PWSCC flaws confirmed by DE were axial and two resulted in leaks

Historically most indications have been axial, recent NDE have identified circumferential indications

Several indications have had additional NDE confirm they are not surface connected - not PWSCC or attributed to previously accepted fabrication indications.

Summary of Pressurizer Inspections

19 PWRs do not have A82/182 dissimilar metal butt welds

- All 19 are older than Wolf Creek

11 PWRs have completed their inspections

- 8 of these are older than WC

26 PWRs will complete their inspections in 2007

- 17 of these are older than WC

13 PWRs will complete their inspections in 2008

- 6 of these are older than WC

Plant Inspection Status & Plans Not A600(19) 10 <=2006 (12)

Wolf Creek 8 2007 (25) 2008 (12)

Inspected 6

4

of Nozzles per Unit 2

0 0 5 10 15 20 25 30

-2 Not Inspected

-4

-6

-8

-10 EFPY (as of ~Feb. 2001)

Summary of Pressurizer Inspections

Statistically significant sample of Alloy 82/182 pressurizer locations has been completed today

- ~26% of Alloy 82/182 pressurizer locations have been inspected

- These inspections are equally distributed around Wolf Creek (1/2 older, 1/2 younger)

- By end of next outage season (Summer 2007), this sample will have increased to ~50%

- By end of 2007 ~80% will be completed

294 Domestic Alloy 82/182 BW locations on pressurizers

- 100% BMV inspections on all pressurizer locations

Only a few plants with an EFPY greater than Wolf Creek currently will exceed 12/31/07

Deterministic Analyses

Primary objective was to address the safety significance of postulated flaws in Alloy 82/182 butt welds

Specific analyses included

- Critical flaw size

- Time to through wall leak

- Time between 1 gpm/10 gpm and failure

- Leak rate as function of flaw size

- Margin between leak and failure

Additional scoping calculations have been done to evaluate the effects of flaw shape

The scoping analysis results do not significantly change the conclusions of the safety assessment

Preliminary Assessment: Effect of Flaw Shape Impact of Larger Aspect Ratio on time to failure: Westinghouse plants Location Years to Years from Total Total Total Total leak (6:1) 1 GPM Time Time Time Time to Critical 6:1 10:1 20:1 30:1 Surge 1.4 2.6 4.0 3.7 3.4 3.4 Safety 4.1 5.6 9.7 7.8 7.5 7.4 Relief Spray 1.1 2.6 3.7 3.4 3.3 3.2

Conclusions

Very small number of leaks/cracks given large numbers of locations worldwide

- Wolf Creek shapes are longer than anything seen to date

Deterministic analyses shows that flaw shape has only a small impact on safety assessment calculations

Probabilistic analysis showed impact of butt weld PWSCC on CDF is insignificant

Analyses for circumferential cracks show that 360 deg constant-depth circ flaws unlikely to occur

Not an immediate safety concern

ML063210080

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