ML20211H584

Rev 0 to Justification for Continued Operation W/Existing Weld Overlays at Hatch Unit 1

ML20211H584
Person / Time
Site:	Hatch
Issue date:	02/28/1987
From:	Gustin H, Riccardella P STRUCTURAL INTEGRITY ASSOCIATES, INC.
To:
Shared Package
ML20211H541	List: ML20211H537 ML20211H549 ML20211H584 ML20211H615
References
GPCO-12, SIR-87-004, SIR-87-004-R00, SIR-87-4, SIR-87-4-R, TAC-64777, NUDOCS 8702260216
Download: ML20211H584 (27)

Text

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Report No. SIR-87-004 Revision 0 Project No. GPCO-12 February, 1987 l

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Justification for Continued Operation With Existing Weld Overlays at Plant Hatch Unit 1

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Prepared by:

Structural Integrity Associates Prepared for:

I Georgia Power Company 7 !'E !? 7 Prepared by:

Date:

H.

L.

Gustip

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Reviewed and f

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Approved by:

[d

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M A

Date:

1. 2 /2 87 P.

C. Ricca"rdell'a I

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I mucu m 0702260216 y21 PDR ADOCK I

PDR G

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REVISION CONTROL SHEET SIR-87-004 I

SECTION PARAGRAPH (S)

DATE REVISION REMARKS I

Table of all 2-12-87 0

Initial issue.

Contents I

pg. ii List of all Tables pg. ill pg. I thru all 2-12-87 0

Initial issue.

pg. 23 I

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Table of Contents Section Page

1.0 INTRODUCTION

1 2.0 HISTORY OF WELD OVERLAY REPAIRS AT HATCH UNIT 1.

4 3.0 CRITERIA FOR EVALUATION, DESIGN, AND INSPECTION OF WELD OVERLAYS IN 1985/86 9

3.1 Criteria for Evaluation and Design 9

3.2 In-Process Inspection of Weld Overlays.

.11 4.0 REQUIREMENTS OF NUREG-0313, REVISION 2 (DRAFT)

.15 4.1 Acceptable Design Bases for Weld Overlay Repairs

.15 5.0 INSPECTION AND SURFACE IMPROVEMENT OF WELD OVERLAYS AT HATCH UNIT 1

.17 I

6.0 TREATMENT OF UNREPAIRED FLAWS AND IGSCC MITIGATION ACTIVITIES

.18 6.1 Unrepaired Flaws at Hatch Unit 1

.18 6.2 Mitigation of IGSCC Potential in Presently Unflawed Welds.

.18 7.0

SUMMARY

AND CONCLUSIONS.

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8.0 REFERENCES

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List of Tables Table Ea_gg I

2-1 Summary of Weld Overlay Activity for Plant Hatch Unit 1.

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3-1 Summary of Hatch Unit 1 Weld Overlay Design Versus As-Built Dimensions 13 6-1 Welds With Post-IHSI Flaw Indications (1985/86) 20 I

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1.0 INTRODUCTION

I Weld overlay repairs to intergranular stress corrosion cracking (IGSCC) were first applied at Hatch Unit 1 during the Winter 1982 Refueling Outage.

Additional repairs were applied during the 1984 and 1985/86 outages.

The affected systems include the stainless steel portions of the recirculation, residual heat removal (RHR),

and reactor water clean-up (RWCU) systems.

Between 1982 and the present, a total of 35 locations have been repaired using the weld overlay technique.

In addition, an overlay was applied to one unflawed weld (24B-R-12) to enhance inspectability.

An additional 9 indications have been treated with the Induction Heating Stress Improvement (IHSI) process, which has been shown to produce a favorable residual stress distribution which inhibits both growth of shallow flaws and initiation of new flaws.

No identified flaws have been left without either weld overlay or IHSI repair.

The flawed locations treated with IHSI would be acceptable for cycle by cycle operation by the criteria of [3).

During each of the aforementioned outage, weld overlays were designed and applied using the then current regulatory bases together with conservative treatments of flaw character [1,2).

During the 1985/86 outage, all previously applied weld overlays were re-evaluated in the as-built condition to the same criteria as were used for design of new repairs in 1985/86 [2].

The purpose of the re-evaluation was to provide a uniform basis for comparing weld overlay repair adequacy, and to eliminate any inconsistencies among the design bases employed at different times.

In cases where the as-built thickness of an earlier overlay was inadequate by the 1985/86 criteria, additional weld l

overlay material was added to produce an overlay which met the latest criteria in effect at that time.

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Tiie result of the 1985/86 effort is that all weld overlays applied to locations containing circumferentially oriented flaws were shown to be adequate to repair a 360 long, through original pipe wall circumferential flaw in the as-built condition, I

regardless of the nature of the original flaw.

This is a very conservative result.

In 1987, those overlays applied in 1982 will enter their fourth cycle of operation.

It is the intent of Georgia Power Company to operate Plant Hatch Unit 1

indefinitely with the existing stainless steel piping systems (including weld overlay repaired locations) in place.

This is justified for the following reasons:

I 1.

The weld overlays meet a very conservative design basis

[2].

I 2.

Weld overlay material 308L stainless steel is inherently resistant to further IGSCC propagation [6, attached].

3.

Weld overlay surface preparation activities conducted l

during the 1985/86 outage at Hatch Unit 1 meet EPRI inspectability recommendations

[5],

which have been demonstrated to be effective [6].

In July of 1986, the USNRC issued a draft version of NUREG-0313, Revision 2 [3], which represents the latest published regulatory position regarding weld overlay repairs.

The document presents criteria for acceptability and inspection of

overlays, and discusses long term inspection of weld overlay-repaired locations.

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i The present report, together with the attached generic report

[6],

addresses in

detail, the technical justification for contin)ted operation with the weld overlays at Hatch Unit 1.

Section 2 of this report discusses the histcry of weld overlays I

at Hatch Unit 1,

and presents information on the flaws detected in each location.

Section 3 discusses criteria employed in re-evaluation of all weld overlays, and summarizes the design (as re-evaluated) and as-built weld ove:-lay dimensions.

This section also includes a discussion of the in-process examination of weld overlays.

Section 4 discusses the critoria of [3] and compares these with the requirements of the re-evaluated design basis.

Section 5 briefly summarizes the surface finish improvement of all weld

overlays, which was performed during the._1985/86 refueling outage in 198'.

Section 6 reviews the treatment of those flaw locations identified in 1985/86 wh4.ch were not repaired by weld overlay, and discusses the IGSCC mitigation I

measures being taken by Georgia Power Company.

Section 7

summarizes the report and presents conclusions.

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2.0 HISTORY OF WELD OVERLAY REPAIRS AT HATCH UNIT 1 Weld overlays were first applied at Hatch Unit 1 during the winter, 1982/83 refueling outage.

Six repairs were applied at that time.

Since the first overlays at Hatch, an additional twenty-nine. such repairs have been applied as repairs to IGSCC flaws.

In cddition, one unflawed location was weld overlay repaired to ' simplify inspectability of the location.

In summary, a total of 36 weld overlays are currently in service at Hatch Unit 1.

Table 2-1 summarizes weld overlay activity at Hatch, listing the weld identification number, the flaw which lead to the repair as defined by the original inspection results, and the year in which the repair was applied.

This table shows that following the outage currently scheduled to begin April, 1987, six weld overlays will enter their fourth cycle of operation, seventeen will begin their third cycle, and thirteen will enter I

their second cycle of operation.

Although the original overlays at Hatch are more than four years old, it should be noted that all weld overlays at Hatch have been conservatively evaluated and upgraded to current standards.

During the 1985/86 refueling outage, several actions were taken to upgrade weld overlays to a conservative standard, consistent with the regulatory guidance in effect at the time.

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re-evaluation is discussed in detail in [2] and is summarized in Section 3 of this report.

During the 1985/86 maintenance / refueling outage at Georgia Power l

Company's Plant E.I.

Hatch Unit 1, which was the third outage at this unit during which activities were directed at the detection l

and rgpair of intergranular stress corrosion cracking (IGSCC) flaw' indications in the recirculation, reactor water cleanup, and residual heat removal stainless steel systems, Georgia Power Company identified 12 new locations which required weld overlay

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application to repair observed flaw indications.

During the 1982 and 1984 outages, a total of 23 weld overlays were applied to repair similar flaw indications.

In addition, during 1985/86 one unflawed weld (24B-R-12) was weld overlayed to improve inspectability of this weld.

Consequently, a total of 36 piping system locations were weld overlay repaired at Hatch Unit 1 as of the end of tile 1985/86 outage.

The weld overlay activity at I

Hatch Unit 1 during the 1985/86 outage is summarized below:

1.

All previously applied weld overlays were remeasured, and the as-built overlays were evaluated for conformance with current criteria.

For circumferential flaw indications, the design basis flaw was taken to be 360 long and 100% through original pipe wall.

Where necessary, weld overlay thickness was increased to meet this design basis.

I 2.

All weld overlays designed during 1985/86 were based upon an assumed 360 long, 100% through-wall flaw.

3.

No credit for the thickness of the first welding layer was taken for any veld overlay.

For previously applied weld

overlays, te M thickness was assumed to be 0.1".

For overlays applic during 1985/86, the actual first layer thickness was deducted from the reported as-built thickness.

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The surface finish of all weld overlays was improved by grinding to enhance inspectability of the weld overlay and the underlying pipe wall.

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Accessible welds without overlays in the recirculation, RHR, and RWCU systems (inside containment) were treated by Induction Heating Stress Improvement (IHSI) to mitigate the IGSCC susceptibility of these welds.

All treated welds were l

ultrasonically examination following IHSI.

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'I included the 12" recirculation safe-end to inlet nozzle welds and 28" safe-end to nozzle outlet welds.

I 6.

Following IHSI, a total of 9 welds were identified which contained IGSCC-like flaws requiring no repair other than IHSI.

These flaws were shown to be acceptable using fracture mechanics analyses based upon the criteria of NRC Generic Letter 84-11 [4] and ASME Section XI.

7.

Four welds were determined to have flaws unrelated to IGSCC.

These welds were shown to be acceptable by the methods of ASME Section XI.

The result of the above activities is that all weld overlays have effectively been re-evaluated and upgraded to the latest published standards as of early 1986.

Since that time the USNRC has published a draft version of NUREG-0313, Revision 2,

[3]

which documents the most recent regulatory position on weld overlay service life.

This document, although not officially issued yet, is generally favorable to the concept of weld overlay repairs as a long term resolution of IGSCC flaws in BWR piping, when coupled with other mitigating activities.

The criteria of this document as applied to weld overlays are summarized in Section 4 of this report.

The effects of these criteria as applied to the Hatch weld overlays, are discussed in the same I

section.

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TABLE 2-1 Sumary of Weld Overlay Activity for Plant Hatch Unit 1 WELD #

INSI?

PRE INSI POST lHS!

DISPOSITION I

FLAW DESCRIPTION FLAW OESCRIPil0N RWCU 6 D 4 No CIR. 1.6"X50%

OVERLAY 86 RWCU 6 D 5 No CIR. 1.5"X70%

OVERLAY 86 RWCU 6 D 18 No CIR. 1.25"X39%

OVERLAY 86 RWCU 6 D 18A No CIR. 1"X43%

OVERLAY 86 12AR F 2 NO CIR. 20 30%X360*

OVERLAY 84/ SURFACE FINISH 86 12AR F 3 NO CIR. 20 30%X360*

OVERLAY 84/ SURFACE FINISH 86 12AR F t YES CIR. 4"X13%

CIR. 3.2"X32%

OVERLAY 86 12AR G 3 No CIR. 2.1"X50%

OVERLAY 86 12AR G 4 YES CIR. 5.375"X 20%

LEAVE AS IS I

12AR H 2 NO CIR. 20 30%X360*

OVERLAY 84/ SURFACE FINISH 86 12AR N 3 No CIR. 20 30%X360*

OVERLAY 84/ SURFACE FINISH 86 12AR N 4 NO CIR. 5"X35%

OVERLAY 86 I

12AR J 3 NO CIR. 20 30%X360*

OVERLAY 84/ SURFACE FIN!$H 86 12AR K 2 NO CIR. 30%X360*

OVERLAY 84/ SURFACE FINISH 86 12AR K 3 NO CIR. 30%X360*

OVERLAY 84/ SURFACE FINISH 86 12BR A-4 YES CIR. 2"X22%

2.6"X26%

LEAVE AS IS I

12BR B 3 YES CIR. 1.35"X20%

THROUGH WALL AXIALS OVERLAY 86 12BR C 2 No CIR. 20 30%X360*

OVERLAY 84/ SURFACE FINISH 86 12BR C 3 No CIR. 25%X360*

OVERLAY 84/ SURFACE FINISH 86 I

12BR C 4 NO CIR. X39%

OVE2 LAY 86 12BR C-5 YES LAMINATION LAMINATION LEAVE AS IS 12BR D 2 NO CIR. X50%

OVERLAY 86 12BR D 3 NO CIR. 20%x360*

OVERLAY 84/ SURFACE FINISH 86 12BR E 2 No CIR. 25%X360*

CVERLAY 84/ SURFACE FINISH 86 12BR E 3 No CIR. 30%X360*

OVERLAY 84/ SURFACE FINISH 86 12BR E 4 YES CIR. 25%X2.5" CIR. 2.75"X19%(PIPE) LEAVE AS IS I

CIR. 2"X14%(SE) 208 D 3 NO CIR. 3"X32%

DVERLAY 82/ SURFACE FINISH 86 I

AXIAL X94%

208 D 4 YES AXIAL X 18%

LEAVE AS IS I

22AM 1 No AXIALX63%

DVERLAY 82/ SURFACE FIU.iH 86 22AM 4 No AXIALX72%

OVERLAY 82/ SURFACE FINISH 86 228M-1 No AX!ALX64%

OVERLAY 82/ SURFACE FINISH 86 22BM 4 NO AXIALX67%

CVERLAY 82/ SURFACE FINISH 86 I

22AM1 BC1 YES INT. CIR.: 8.8"X11%

GEOMETRY LEAVE AS IS 228M1 BC1 YES INT. CIR.:12.7"X29%

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TABLE 2-1 (continued)

I Summary of Weld Overlay Activity for Plant Hatch Unit 1 I

24A R-13 No AXIALX50%

OVERLAY 84/ SURFACE FINISH 86 248 R 13 NO AXIALX47%

OVERLAY 82/ SURFACE FINISH 86 28A 2 fES CIR. 1"X13%

LEAVE AS IS CIR. 5.25"X15%

28A 4 YES 7 AXIALS 14% MAX.

7 AXIALS 14% MAX.

LEAVE AS IS 28A 6 YES CIR. 2.5"X30%

AXIAL 0.3"X29%

LEAVE AS IS 2 AXIALS 28A 10 NO CIR. 50%X360*

OVERLAY 84/ SURFACE FINISH 86 I

28A 12 YES CIR. 14"X29%

OVERLAY 86 AXIALX41%

288 3 No CIR. 32%X360*

OVERLAY 84/SMFACE FINISH 86 l

288 4 No CIR. 31%X360*

LACK OF FUSION IN OVERLAY 84/ SURFACE FINISH 86

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WELD OVERLAY 288 8 YES 2 AXIALS: 0.25"X 24% LEAVE AS IS 288 10 YES 4 CIRC. 6.5" TOTAL LEAVE AS IS X 23%

2 AXIALS: 31%, 26%

288 11 No CIR. 49%X360*

OVERLAY 84/ SURFACE FINISH 86 l

288 16 YES SHORT CIR. 10%

CIR. 2.65"X24%

OVERLAY 86 AXIAL 20%

CIR. 4"X18%

CIR. 1.5"X40%

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3.0 CRITERIA FOR EVALUATION, DESIGN, AND INSPECTION OF WELD OVERLAYS IN 1985/86 3.1 Criteria for Evaluation and Design In order to produce a consistent design basis for all weld overlay repairs applied Hatch Unit 1,

all pre-existing weld overlays were re-evaluated in 1985/86

[2]

to determine their conformance with current criteria.

Where necessary, additional material was applied to pre-existing overlays to upgrade their design to the same standard as was used for design of new weld overlay repairs.

The following criteria formed the basis for weld overlay design and re-evaluation during the most recent I

and were applied to both new and pre-existing overlays.

outage, 1.

Where the original flaw indication was circumferential in orientation, the design basis flaw was taken to be through the original pipe wall and 360" in length.

This assumption negates uncertainty in flaw characterization, and eliminates the concern of potential butt weld low toughness due to use of flux-shielded weld processes (SMAW, SAW).

2.

Axially oriented flaw indications do not present a

structural integrity concern.

Those weld overlays previously applied to locations with only axial flaws were l

evaluated assuming that only leakage protection (2 layer weld overlay) and residual stress modification (to inhibit j

new flaw initiation) were required.

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No credit was taken for the first weld overlay layer.

4.

The as-built overlay thickness, minus 0.1" to allow for the I

first weld layer, was used in the evaluation.

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All previously applied welds were upgraded if they were determined to be insufficient to meet the above design bases.

Effectively, a new design was Aepared for each weld.

During the surface finish operation for these overlays (Section 5), the "new l

design" was used to guide material build-up and grinding 1

operations.

The as-built (post-surface finish) thickness for I

each overlay was compared with the new design to determine acceptability of each overlay.

The design and as-built dimensions for each evaluated overlay are presented in Table 3-1.

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The dimensions listed in the as-built columns represent the arithmetic average of measurements taken at 4

azimuthal locations.

It should be noted that the thickness of the as-built overlay meets or exceeds the design value in all cases.

As-built thicknesses are the average measured thickness values following deduction of 0.1" for each pre-existing overlay.

l Because of the conservative design approach employed at Hatch for both design of the most recent weld overlays, and re-evaluation of older overlays, weld overlays applied to locations containing circumferential flaws at Hatch have been shown to be sufficient to repair a 360 through-wall circumferentially oriented flaw.

There are 33 weld overlays in this category.

In addition, two overlays were applied to locations with only axially oriented flaws, and one overlay was applied to an unflawed location to simplify inspection.

The latter weld overlay is adequate to meet the design criteria applied to circumferential flaw repairs.

A detailed discussion of the design and re-evaluation of the Hatch weld overlays is presented in (2].

Subsequent to the completion of the 1985/86 work, Revision 2 of NUREG-0313 was issued in draft form for public comment [3].

This document represents the latest regulatory position regarding weld overlay service life.

A discussion of the criteria of this document is briefly presented in Section 4 and in more detail in INTEGRITY ASSOCIATESINC

I the appendix (6].

The draft NUREG introduces definition of three categories of weld overlay repairs.

These are:

1.

Standard Weld Overlays 2.

Designed Weld Overlays 3.

Limited Service Weld Overlays These terms are discussed in the next section of this report.

However, for the purposes of the present section, it is worth noting that 34 of the weld overlays at Hatch 1 may be categorized as standard weld overlays, and 2 may be categorized as designed weld overlays.

The designed weld overlays were applied to locations containing only axial flaws at Hatch.

These flaws do not present a structural concern.

The significance of this is that weld overlays in these two categories are considered in the NUREG to be acceptable for unlimited service life (that is, the I

NUREG does not limit the service life of such overlays) if adequate inservice inspection of the repairs is undertaken.

The actions taken by Georgia Power Company to enhance inspectability of the weld overlays at Hatch are summarized in Section 5.

3.2 In-Process Inspection of Weld Overlays I

As discussed above, the weld overlays at Hatch were designed j

using very conservative methods.

In addition, Georgia Power Company generally performed three conservative inspections of repaired locations during and after overlay application, to demonstrate weld overlay material IGSCC resistance and structural integrity.

These were:

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1.

Delta ferrite measurements of the first welding layer were made on each weld overlay.

During the 1985/86 outage, a delta ferrite level of 7.5 FN minimum was taken as the acceptance criteria for the first layer.

Delta ferrite content at or above the 7.5 FN level was considered to be

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indicative of minimal dilution of weld metal by base metal, and to demonstrate excellent IGSCC resistance of the first weld metal layer.

If the weld metal passed this examination, the examination described in (2) below was then performed.

If the layer did not pass the delta ferrite test, another layer was applied on top of the layer, and this new layer was examined to the same delta ferrite I

criterion as above.

The significance of the delta ferrite content of the weld metal is discussed in the appended report [6].

2.

A first weld overlay layer which passed criterion (1) above was then examined by the dye penetrant method to demonstrate that no flaws had " blown through" the layer.

The weld metal was then carefully cleaned prior to continuing with weld overlay application.

3.

The completed weld overlay was examined ultrasonically in accordance with EPRI-qualified procedures to demonstrate proper weld overlay bonding and quality and to provide a baseline inspection for future inservice inspections.

The above combination of inspections make up a

highly conservative demonstration of weld overlay integrity.

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l TABLE 3-1 I

Summary of Hatch Unit 1 Weld overlay Design Versus As-Built Dimensions I

Wcid Design As-Built Design As-Built Number Lenoth Lenoth Thickness

• Thickness' I

RWCU-6-D-4 2.0 2.820 0.167 0.208 RWCU-6-D-5 2.0 2.026 0.206 0.228 RWCU-6-D-18 3.5 3.090 0.1G5 0.205 RWCU-6-D-18A 4.0 3.539 0.165 0.231 I

12AR-F-2 3.2 3.823 0.250 0.500 12AR-F-3 3.2 4.190 0.263 0.271 12AR-F-4 4.0 4.528 0.257 0.389 12AR-G-3 4.0 4.517 0.250 0.253 I

12AR-H-2 3.2 3.810 0.246 0.420 12AR-H-3 3.2 4.469 0.250 0.331 12AR-H-4 4.0 4.414 0.306 0.366 12AR-J-3 3.2 4.194 0.257 0.279 12AR-K-2 3.2 4.764 0.251 0,278 12AR-K-3 3.2 4.284 0.270 0.358 I

12BR-B-3 4.0 4.113 0.242 0.340 12BR-C-2 3.2 4.066 0.'249 0.463 12BR-C-3 3.2 3.723 0.251 0.268 12BR-C-4 4.0 4.127 0.294 0.305 12BR-D-2 4.0 4.323 0.250 0.318 12BR-D-3 3.2 4.249 0.257 0.380 12BR-E-2 3.2 3.983 0.251 0.300 12BR-E-3 3.2 3.839 0.252 0.284 20B-D-3 5.0 9 143 0.330 0.408 I

Design Thickness is the result of the 1985/86 re-evaluation, and not the original design in the case of previously overlayed welds.

Design and As-Built Thickness takes no credit for the first overlay layer. mucTona INTEGRITY l

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TABLE 3-1 (continued)

Weld Design As-Built Design As-Built Number Lenath Lenath Thickness

• Thickness

• 22AM-1 5.2 6.332 0.37C 0.445 22AM-4 5.2 6.750 0.376 0.478 22BM-1 5.2 7.777 0.369 0.418 22BM-4 5.2 6.638 0.376 0.466

'l 24A-R-13 3.75 4.006 0.200 0.240 24B-R-12 Blend N/A 0.200 0.522 24B-R-13 5.6 8.010 0.200*

0.290 28A-10 4.2 4.643 0.480 0.533 1

l 28A-12 4.0 6.278 0.520 0.688 28B-3 6.0 6.152 0.440 0.509 28B-4 6.2 5.976 0.429 0.631 28B-11 4.2 4.720 0.493 0.648 28B-16 4.0 5.501 0.560 0.594 Design Thickness is the result of the 1985/86 re-evaluation, and r.ot the original design, in the case of previously overlayed welds.

Design and As-Built Thickness takes no credit for the first overlay layer.

Axial Flaw only.

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4.0 REQUIREMENTS OF NUREG-0313, REVISION 2 (DRAFT)

As noted previously in this report, the most recent published regulatory guidance on the acceptable service life of weld overlays is contained in the draft of NUREG-0313, Revision 2,

which was issued for public comment in

July, 1986

[3].

NUREG-0313, Revision 2

(draft) gives implicit approval for extended operation with weld overlay repairs in a piping system, contingent on an acceptable design basis for the overlay, and upon demonstration of inspectability of the overlay and some portion of the underlying piping component.

These criteria are discussed in greater depth in the attached report [6], and are summarized briefly below.

4.1 Acceptable Design Bases for Weld Overlay Repairs The NUREG

[3] defines two weld overlay categories which ar*

acceptable for long term operation.

These are:

1.

Standard Weld Overlay This category requires that the weld overlay thickness be sufficient to repair a circumferentially oriented flaw which is l

through the original component and which extends 360" i

circumferentially.

This is clearly a quite conservative design basis, since no credit is taken for strength of the remaining ligament of the original component.

This approach has another advantage in that it is not dependent upon the sizing accure.cy of the ultrasonic examination which originally detected the flaw.

'I The NUREG [3] considers weld overlays of this type to be suitable for extended service life, assuming the overlay and some portion of the underlying pipe wall can be adequately inspected every other fuel cycle.

The purpose of the inspection is to STRUCTUIULI.

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demonstrate that the design margin of the overlay is not being degraded by continued flaw propagation.

I 2.

Designed Weld Overlay I

This category takes some credit for the remaining pipe wall.

It applies to repair of circumferential flaws with circumferential extent of less than 10% of the total pipe circumference.

It also applies to repairs to locations containing only axial flaws.

The latter do not present a structural concern, even if through-wall.

A repair is applied to arrest further crack initiation by modification of the weld residual stress distribution and to provide a leakage barrier for through-wall axial flaws.

This category is also treated as acceptable for extended operation, with the same requirement on inspectability of the weld overlay and some portion of the underlying pipe material as was imposed I

for the standard weld overlay.

A detailed discussion of the NUREG requirements is contained in (3] and [6].

The weld overlays at Hatch Unit 1 all fall into one of these two acceptable categories (34 are standard and 2 are designed weld overlays applied to a::ially flawed locations).

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weld overlay locations have had their surfaces improved to enhance inspectability, as recommended in [5] and described in Section 5 of this report.

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5.0 INSPECTION AND SURFACE IMPROVEMENT OF WELD OVERLAYS AT HATCH UNIT 1 I

One of the earlier technical roadblocks which limited the service life of the weld overlay repair was the difficulty of ultrasonically inspecting the as-applied weld overlay material and the underlying pipe material.

This was a problem because without reliable inspection techniques, there was no objective way to demonstrate that the design margin of the repair was not degrading with time due to continued crack propagation as a result of ongoing IGSCC or other mechanisms.

The inspection difficulty was traceable in part to the irregular nature of the as-welded overlay surface, which made proper coupling of the ultrasonic crystal erratic.

EPRI has conducted a program to identify the surface finish improvement to as-welded overlays which is required to allow reliable inspection.

The results of I

the EPRI study are contained in [5].

All weld overlays at Hatch Unit 1 have had their overlay surface finishes improved to meet the recommendations of [5].

The weld overlay surfaces were improved during the 1985/86 outage.

This activity is summarized in Appendix B of the attached report [6].

As a result of the surface improvement effort at Hatch, Georgia Power has effectively demonstrated the capability to inspect the weld overlay material and a portion of the underlying pipe material of all overlays at Hatch.

The weld overlay surface improvement activities at Hatch in 1985/86 make all of the overlays inspectable to the requirements of NUREG-0313 Revision 2 [3]. STRUCTUIMI.

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6.0 TREATMENT OF UNREPAIRED FLAWS AND IGSCC MITIGATION ACTIVITIES 6.1 Unrepaired Flaws at Hatch Unit 1 During the 1985/86 incpection, 12 locations were identified as having flaws requiring assessment, in addition to the total of 35 to which weld overlays were applied.

Of the 12 evaluated flaw indications, 3 were traceable to fabrication defects and not to IGSCC.

These flaws were evaluated in accordance with the requirements of ASME Section XI, paragraph IWB-3500 and were shown to require no repair.

The balance of the unrepaired flaws were shown by fracture mechanics analysis to require no repair by the criteria of the governing regulatory guidance in effect at the time [4].

This analysis was based upon the use of location specific stress information and a

conservative crack growth l

correlation, as detailed in [2].

All unrepaired flawed locations were treated with the induction heating stress improvement process (IHSI) to mitigate further IGSCC flaw initiation and growth.

The analytical treatment of the IHSI process is discussed in [2].

'I The flaws discussed above which did not require a repair are summarized in Table 6-1.

These flaws would be acceptable for continued operation on a cycle by cycle basis under the criteria of [3].

6.2 Mitigation of IGSCC Potential in Presently Unflawed Welds The emphasis of the previous sections of this report is upon treatment of locations containing some form of flaw.

Georgia Power Company has also taken action to prevent initiatiion of new IGSCC flaws in susceptible systems.

In 1985 the IHSI process was STRUCTUIMI.

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successfully applied to a

total of 107 welds in the recirculation, residual heat removal, and reactor water clean up systems at Hatch Unit 1.

This process produces a compressive l

residual stress distribution in the inner portion of the l

component wall, which will inhibit future IGSCC initiation and growth of shallow flaws.

The welds treated included all 10 of the 12" recirculation riser to safe end welds, and both of the 28" recirculation safe end to outlet nozzle welds.

IHSI is recognized by NUREG-0313 Revision 2 [3] as an effective IGSCC mitigation process.

l In addition to the application of IHSI, Georgia Power is studying the possibility of implementing a hydrogen water chemistry HWC system at Hatch Unit 1.

Such a system, which effectively reduces the IGSCC inducing potential of BWR primary water by reducing free oxygen content in the water, has been demonstrated to be effective in arresting IGSCC initiation and growth.

Georgia Power Company is currently conducting pilot tests (" mini test")

for possible use of this type of system at Hatch Unit 1 in the near future.

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I Table 6-1 Welds With Post-IHSI Flaw Indications (1985/86)

I Weld Number I

Pre-IHSI Indication Post-IHSI Indication (if applicable) 12AR-G-4 N/A

1) Circ.: 5.375" x 20%

12BR-A-4

1) Circ.: 2" x 22%

1) Circ.: 2.6" x 26%

,E 12BR-C-5 Lamination in Safe-End No flaw observable l3 Base Material: 0.4" long after IHSI x 0.025" deep, 0.775"

'I from 0.D.

12BR-E-4

1) Circ.: 3.5" x 21%

1) Circ.: 2.75" x 19%

2) Circ.: 2.0~~ x 25%

2) Circ.: 2.0 x 14%

20B-D-4 N/A

1) Axial: 0.25" x 18%

2) Axial: 0.15" x 16%

I 28A-2 N/A

1) Circ.: 1" x 13%

2) Circ.: 5-1/4" x 15%

28A-4 N/A 7 Axial Flaws:

1) 0.2" x 9%

I

2) 1.05" x 11%

3) 1.35" x 10%

4) 1.3" x 8%

5) 1.35" x 10%

6) 1.25" x 10%

7) 1.35" x 13%

288-8 I

N/A

1) Axial: 0.25" x 24%

2) Axial: 0.25" x 16%

288-10 N/A

1) Circ.: 1-7/8" x 23%

'I

2) Circ.: 1-3/8" x 20%

3) Circ.: 2-7/8" x 17%

4) Circ.: 1/2" x 15%

5) Axial 31% (associated with #1)

6) Axial 26% (associated with #3) all on elbow side

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7.0

SUMMARY

AND CONCLUSIONS Georgia Power Company has conducted weld overlay repair design and application activities and flaw evaluations at Plant E.I.

Hatch Unit 1 since IGSCC was first detected in the recirculation and residual heat removal systems of this unit in 1982.

These activities have historically been done in a conservative manner I

and in accordance with all applicable regulatory requirements.

In 1985, all weld overlays were re-evaluated, considering the as-built weld overlay dimensions and assuming (in the case of l

repairs to circumferentially oriented flaws) that the flaw was through the original pipe wall and extended 360 circumferentially.

This re-evaluation activity forms the basis l

for correlation of the as-built Hatch weld overlays with the weld overlcy classifications contained in NUREG-0313 Revision 2

1 i

(Draft)

[3].

Thirty four of the thirty six weld overlays at Hatch can thus be considered to be " standard weld overlays".

The remaining two weld overlays, which were applied as repairs to locations containing axial flaws only, may be classified as

" designed weld overlays".

Both of these classifications are considered by the NUREG to be acceptable for extended service, l

subject to re-inspection every 3-1/2 years.

Georgia Power Company has improved the surface finish of all weld overlays at Hatch in accordance with the recommendations of EPRI

[5] to enhance inspectability of the weld overlays and to permit examination of the weld overlay material and a portion of the underlying pipe wall by ultrasonic methods.

In addition to the above activities regarding weld overlays, Georgia Power Company has applied IHSI to 107 welds in the recirculation, residual heat removal, and reactor water clean-up

systems, to minimize the potential for IGSCC initiation and further growth in the treated welds.

The possibility of l smxmmaI.

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implementing a hydrogen water chemistry system is also being evaluated for application at Hatch Unit 1.

The above activities are plant specific.

In addition, there has been extensive analytical, experimental, and field evidence developed industry-wide in the past five years which supports use of weld overlays as long term repairs IGSCC flawed locations in BWRs.

This evidence is summarized in the attached report [6].

Because of the plant specific and generic considerations summarized in the present report, the operation of the Hatch Unit 1

piping systems in their present configuration with weld overlays in place for the upcoming fourth and subsequent cycles is technically justified, and is in accordance with the most recent regulatory guidance.

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8.0 REFERENCES

1.

Structural Integrity Associates,

" Technical Justification for Continued Operation of Hatch Unit 1 With Existing Recirculation and RHR System Piping", Report No. SIR-85-010, Revision 1, June, 1985.

2.

Structural Integrity Associates, " Evaluation of IGSCC Flaw Indications and Weld Overlay Designs for Plant E.

I.

Hatch Unit 1,

Fall 1985/86 Maintenance / Refueling Outage", Report No. SIR-86-002, Revision 2, April, 1986.

3.

U.S.

Nuclear Regulatory Commission,

" Technical Report on Material Selection and Processing Guidelines for BWR Coolant Pressure Boundary Piping", NUREG-0313, Revision 2 (Draft),

issued for public comment July 11, 1986.

4.

U.

S.

Nuclear Regulatory Commission Generic Letter 84-11,

" Inspection of BWR Stainless Steel Piping", April 19, 1984.

5.

EPRI NDE Center, " Examination of Weld Overlaid Pipe Joints",

Final Report, August, 1986.

Prepared for EPRI RP-1570-2 and BWROG II T301-2.

6.

Structural Integrity Associates,

" Technical Justification for Extended Weld Overlay Design Life",

Report No.

SIR-86-021 (Draft), Prepared for EPRI, December 1986.

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