ML20126H336

Rev 1 to Design Rept for Recirculation & Reactor Water Cleanup Sys Weld Overlay Repairs & Flaw Analysis at Brunswick Steam Electric Plant,Unit 1

ML20126H336
Person / Time
Site:	Brunswick
Issue date:	03/31/1985
From:	Gustin H, Kleinsmith M, Wenner T NUTECH ENGINEERS, INC.
To:
Shared Package
ML20126H312	List: ML20126H309 ML20126H336
References
CPL-21-103, CPL-21-103-R01, CPL-21-103-R1, CPL021.0103, CPL21.0103, NUDOCS 8506180315
Download: ML20126H336 (49)

Text

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NUTECH CONTROLLtv COPY CPL-21-103 Revision 1 l

March 1985.

! CPLO21.0103 DESIGN REPORT FOR RECIRCULATION AND REACTOR WATER CLEAN-UP SYSTEMS WELD OVERLAY REPAIRS AND FLAW ANALYSIS AT BRUNSWICK STEAM ELECTRIC PLANT UNIT 1 Prepared for:

Carolina Powe r and Light Company Prepared by:

NUTECH, Inc.

San Jose, California Prepared by: Reviewed by:

k.C hl

!! . E. Kleinsmith H. L. Gustin, P.E.

Consultant I Project Engineer Approved by: Issued by:

. Y,e . .

T. J b Wenne r, P.E. D. K. Yo[hida,P.E.

l Engineering Manager Project Manage r Da te : d - M - dY 8506180315 850614 5 DR ADOCK 050 mtagh

REVISION CONTROL SHEET TITLE. Design Report for Recirculation 00CUMENT FILE NUMBER: CPLO21.0103 and Reactor Water Clean-up Weld Overlay Repairs and Flaw Analysis at Brunswick Steam Electric Plant Unit 1 H. L. Gustin, P.E./ Project Engineer NAME / TITLE INITIA'L3 M. E. Kleinsmith/ Consultant I NN INITIALS NAME/ TITLE N AME / TITLE INITIALS N AME / TITLE INITIALS AFFECTED DOC PREPARED ACCURACY CRITERIA REMARKS DAGE(S) REV 8Y / DATE CHECK 8Y / DATE CHECK 8Y / DATE i-vi 0 Sfsf/i'J6-87 h Q t/?bhV //[.} 7/eijif Initial Issue 1-41 0 AftA'll87 f} >lty.:V gQ2 JT i-iii 1 J .2f FF b 3/N[gf J M V2z k Revised Report Title ,

10-14 1 Ne[/J.21-85 ihek );(1 gaz[sf Ad 3[edgr Added Weld I.D. Numbers i

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.. CEP 3 3.1.1 11 R EV 1 1

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CERTIFICATIOt! BY REGISTERED PROFESSIOtIAL ENGIt3EER I hereby certify that this document and the calculations contained herein were prepared under my direct supervision, or reviewed by me , and to the best of my knowledge are correct and complete. I f urther ce rtify that, to the best of my knowledge design margins required by the original Code of Construction have not been reduced as a result of the re pairs addressed here in. I am a duly Registered Professional Engineer unde r the laws of the State of Illinois and am compe tent to review this document.

Ce rtified by:

1..h..?.

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I 62-39110 REGISTERED

.b kg PROFESSIONAL Ik

• ENGINEER I e, CF j

kl gf H. L. Gustin

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1. 13/dr Registered Professional Engineer S ta te of Illinois j Registration No. 062-039110 CPL-21-103 iii Revision 1 nutg.gh

4 TABLE OF CONTENTS i:

Page LIST OF TABLES v LIST OF FIGURES vi

1.0 INTRODUCTION

1 2.0 REPAIR DESCRIPTION 6 3.0 EVALUATION CRITERIA 16 3.1 lbld Ove rlay Repair Crite ria 16 3.2 Flawed -Pipe Analysis Criteria 17 4.0 LOADS 18 4.1 Mechanical and Internal Pressure Loads 18 7

! 4.2 Thermal Loads 19 4.3 lbld overlay Shrinkage - Induced Loads 20 i

l 5.0 EVALUATION METHOD AND RESULTS 22 l 5.1 Code Evaluation - Section XI 22 1 5.2 Fracture Mechanics Evaluation 23 j 5.3 Overlay Shrinkage Ef fect on Recirculation 23 and RUCU Systems 6.0 LEAK-BEFORE-BREAK ASSESSMENT 28 6.1 Ne t Section Collapse 28 6.2 Leak Ve rsus Break Flaw Configuration 29 6.3 Axial Cracks 30 6.4 Multiple Cracks 31 6.5 Nondestructive Examination 31 6.6 Leakage De tection 32 6.7 Historical Experience - 33 j

7.0

SUMMARY

AND CONCLUSIONS 37 i

8.0 REFERENCES

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l CP L-21-103 iv

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LIST OF TABLES Table Title Page l.1 Brunswick Unit 1 Flaw Disposition 3 2.1 Wels! Ove rlay As-Built Dimensions 9 4.1 Summa ry of Total Stre sse s 21 5.1 Shrinkage Stresses at Recirculation System Flaw Locations 26 6.1 Ef fect of Pipe Size on the Ratio of the 34 Crack Iangth for 5 GPM Isak Rate and the Critical Crack Length i

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' CP L-21-103 y Revision l '

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l LIST OF FIGURES

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Figure Title Page 1.1 Conceptual Drawing of Recirculation System 5 2.1 Configuration of 12" Safe End to Pipe Weld 10 Ove rlay, 12-AR-A4 A and 12-AR-B4A 2.2 Configuration of 12" Safe End to Pipe ibld 11 ove rlay , 12-BR-F4A 2.3 Configuration of 12" Elbow to Pipe ibld Ove rlay 12 2.4 Configuration of 6" Elbow to Pipe Weld Overlay 13 2.5 Schematic Diagram of RUCU Ibid Inlay 14 2.6 Configuration of 4" Pipe to Weldole t Overlay 15 5.1 Brunswick Unit 1 Recirculation System Piping Model 27 6.1 Typical Result of Net Section Collapse Analysis 35 of Cracked Stainless Steel Pipe 6.2 Typical Pipe Crack Failure Locus for Combined 36 Through-wall Plus 360* Part-through Crack CPL-21-103 vi Revision l-

1.0 INTRODUCTION

f This report summarizes analyses performed by NUTECH to e valuate flaw indications in the Recirculation System

and to design weld overlay repairs on the Recirculation System and the Reactor Water Clean-Up (RWCU) System at Carolina Powe r and Light Company's Brunswick Steam Electric Plan t Unit 1 (Brunswick 1). One flaw indica-tion de tected . by ultrasonic (UT) examination was determined to be acceptable without repair for at least the next 6 months. Eleven ' flaw indications we re repaired by application of weld overlay. The purpose of E

4 each ove rlay is to arrest any further propagation of -

, intergranular stress corrosion cracking (IGSCC), and to restore original design safety margins to the weld. The flaw indications addressed in this report were detected

- during the November 1984 mid-cycle inspe ction .

Flaw indications were identified adjacent to 6 welds in ,

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the Recirculation System and adjacent to 6 welds in the RWCU System. All flaws are in Type 304 stainless steel ma te rial . Figure 1.1 shows the location of these flaw indications. Table 1.1 contains a description of each flaw indication -and the disposition of each.  ;

4 CPL-21-103 1

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During ~ the UT inspection of IGSCC susceptible welds in the RWCU, flaws were identified in welds. 6-RUCU-16 i

(inside containment) and 6-RWCU-17 (outside contain-i men t ) . Be tween the se two welds is weld X-14 which is part of the penetration flued head assembly, and which is inaccessible. CP&L made the conservative decision to

cut the process line outside of containment and inspect this weld from the inside. . The dye penetrant (PT) me thod wa s used . A circumferential flaw extending approximately 180* with significant bleed out was ide n tified. The inspectors de te rmined that the PT indications observed suggested the presence of a deep l,

CP&L and NUTECH agreed to repair this flaw by flaw. ,

{ application of weld me tal on the inside of the pipe at the ' af fected location. - This repair is comparable in concept . to the other ove rlay . repairs pe rformed at Brunswick Unit 1.

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t CPL-21-103 2 Revision 1 t

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Table 1.1 BRUNSUICK UNIT 1 FLAU DISPOSITION OVE RLAY DESIGN, INCHES Pipe ibld No. Flaw a T min 'l '2 Size 28-B-12-A 2.5"x10% N/A N/A N/A 28" Pipe Side 12-AR-A4A 1.6"x19% 0.19 1.5 (b) 12" Pipe Side 12-AR-B 2 A 2.0"x20% 0.19 1.5 1.5 12" Pipe Side 12-AR-B4A 1.0"x45% 0.19 1.5 (b) 12" Pipe Side 12-BR-F4 A 0.5x23% 0.19 1.5 (b) 12" 4.0"x9%

Pipe Side X-14-C 5.5" (c) 0.25 1.5 1.5 6" 2.0" (c)

Pipe Side RUCU-6-4A 1.25"x10% 0.16 1.5 1.5 6" Elbow Side RUCU-6-6A 2. 7 5" x31% 0.18 1.25 1.25 6" Elbow Side RUCU-6-7A 3.0"x81% 0.17 1.25 1.25 6" Elbow Side CPL-21-103 3

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Table 1.1 (Continued) ,

i BRUNSWICK UNIT 1 FLAU DISPOSITION OVERLAY DESIGN, INCHES Pipe a bl b2 ibld No. Flaw T min Size RWCU-6-8A 1.125"x23% 0.185 1.25 1.25 6" Pipe Side 1.125"x19%

Elbow Side RWCU-6-10A 2.75"x14% 0.17 1.25 1.25 6" Elbow Side 1-RR-4A10-A (d) 0.125 1.0 (e ) 4" ibidole t Side NOTES: a. All flaws are circumferential unless othe rwise noted.

b. Ef fe ctive length va ries (See Figures 2.1 and 2.2) .

c. Flaws de te cted from I.D. by P.T., assumed to be through-wall for measured length.

d. Leaking flaw. Unable to size due to geome tric ,

I constraints. Assumed to be either circumferential 2" long or axial 1/2" long. I

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e. Ove rlay to extend to and blend smoothly with we ldole t.

I CPL-21-103 4 l Revision 1 l nutagh

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o () X 14 PENETRATION

• PIPE WELD g n - 'o

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! O Figure 1.1 CONCEPTUAL DRAWING OF RECIRCULATION SYSTEM b

l 2.0 REPAIR DESCRIPTION i

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The UT and PT flaw indications requiring repair we re remedied by establishing additional " cast-in-place" pipe i

i wall thickness with weld me tal deposited ~ 360 degrees around and to either side of the existing weld, as shown a

in Figures 2.1 through 2.6. The weld-deposited band -

over the cracks provide s, as a minimum, wall thickness t

l equal to that required to meet the requirements of l Reference 1, as modified by Re fe rence 2. Also, a ,

f avorable compre ssive residual stress results from '

overlay application, which will tend to inhibit further crack initiation or. growth. The deposited weld me tal is type . 308L, which is - resistant to IGSCC propagation.

Table 2.1 presents de sign and as-built information for the overlay ' repairs applied to Brunswick k. -

P The flaw observed in weld X-14, which was not accessible from the outside of the pipe , was repaired by applying weld me tal on the inside of the pipe at the flawed i

location. This inside overlay (" inlay") was applied i i ,

around the entire circumference of the pipe, and extended axially approximately 5 inches, ' centered on the f

i flaw.

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i CPL-21-103 6 i Revision 1

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All weld ove rlay repairs we re inspected using non-destructive examination. The non-destructive examina-tion of the comple ted weld " inlay" applied to the X-14 penetration weld, Figure 2.5, included a PT examination (in accordance with ASME Section XI) of the comple ted overlay and 1" either side of it (to demonstrate that no new flaws had been opened by ove rlay application), UT 1

thickness, UT pre-se rvice ins pe ction (in accordance with ASME Section XI), and delta ferrite measurement af ter overlay comple tion. Non-destructive examination of the remaining weld ove rlays consisted of the foIlowing:

i

1) Surface examination of the first weld overlay layer by the liquid penetrant examination te chnique in accordance with ASME Section XI.

2) Delta ferrite measurement of the first laye r, using a Se ve rn gauge .

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3) Surf ace examination of the comple ted weld ove rlay by the liquid penetrant examination technique in accordance with ASME Se ction XI.

4) volumetric examination of the comple ted weld  ;

< 1 l ove rlay by the ultrasonic examination technique in -i i

accordance with ASME Section XI.

CPL-21-103 7 Revision 1

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5). Volume tric examination of the weld ove rlay and  ;

existing circumferential pipe weld by the ultrasonic examination technique in accordance with ASME Section XI (Re fe rence 1) .

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Table 2.1 l

t WELD OVERLAY AS-BUILT DIMENSIONS De s ign

• As-Built

• As-Built Weld I.D. Pipe Size Thickness Thickness Length 6-RWCU-4A 6" 0.16 0.217 2.771 6-RUCU-6A 6" 0.18 ,

0.473 2.808 6-RWCU-7A 6" 0.17 0.252 2.460 6-RWCU-8A 6" 0.185 0.189 2.890 6-RWCU-10A 6" 0.17 0.215 2.565 12- A R-A4 A 12" 0.19 0.351 2.515 12-AR-B2A 12" 0.19 0.205 3.450 12- AR-B 4 A 12" 0.19 0.262 2.200 12-BR-F4A 12" 0.19 0.290 2.620 1-RR-4A10-A 4" 0.125 0.409 1.732 PENT. X-14-C 6" 0.25 0.440 5.800

{

• Does not include first ove rlay laye r. -

1 CPL-21-103 9 Revision 1

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AS WELDED SUHFACE ACCEPTABLE FOR OVERLAY THIS AREA GROUND TO TAPER TRANSITIONS REMOVE MICROFlSSURES INCONEL fl00 1.5" 0.5

• O  : O > SAFE END MIN g

-0.19" MIN l '

WELD OVERLAY MMMMME/ ' E M/M

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e 45' NOMINAL (TYPI O 6 3 PLACES Weld Ntznbers: 12AR-A4A &

12AR-B4A l ._ _

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12", 0.57" WALL 12", 0.57" WALL SAFE END TO 304 SS PIPE 304 SS PIPE " PUP" PIECE WELD

" PUP"-PIECE TO SAFE END TO j PIPE WELD NOZZLE WELD

= DOES NOT INCLUDE FIRST OVERLAY LAYER THICKNESS.

I Figure 2.1

- CONFIGURATION OF SAFE END TO PIPE WELD OVERLAY i

(OVERLAY MICROFISSURES REMOVED)

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I oY AS WELDED SURFACE ,,

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PW ACCEPTAsLE FOR OVERLAY - -

' ' 0.25" MIN L TAPER TRANS4TSONS USE ETCil TO DEFINE MAN EDGE OF SAFE END TO

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TYPE sont PUP" PIECE WELD WELD OVERLAY ' '

f[f['ff$'b\\\\A7 s - e.s7*

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_ w J 46' NOMINAL (TYP)

[ Weld Nunber: 12BR-F4A --->

l I 12", 0.57" WAL L ,

88 LL k SAFE-END TO 304 SS PlPE " PUP" P9ECE WELO CA

PUP *-PIECE 10 i SAFE-ENO TO --

NOZZLE WELO

• DOES NOT INCLUDE FIRST OVERLAY LAYER THICKNESS i

l E TENT APPLIED FOn Figure 2.2

CONFIGURATION OF SAFE END TO PIPE WELD OVERLAY (THERMAL SLEEVE OMITTED) 1 1

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45' NOMINAL #

TYPE 30sL WELD CVERLAY

' l 1.5" MIN -

[ 12 , o.s7" Twicx WALL, p 33 PtPg

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3.0" MIN =

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I I Weld Number: 12AR-B2A, o

l A8 WELDEO SURPACE LONG ACCIFTASLE PCR RAOluS OVERLAY TAPgR ELECW TRANSmce.s PATINT APPUED PCM Figure 2.3 l CONFIGURATION OF 12" ELBOW TO PIPE WELD OVERLAY CPL- 21-.10 3 Revision f gd

i 48' NOMINAL TYPE 30BL WELD CVERLAY 1.25" MIN -

a a 8", 0.43" THICK WALL 24 Ss PIPE 0.14" TO --* l 0.10B" MIN

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2.5" MIN -

1 Weld bers: MCU-6-4A RWCU-6-6A {

MEU-6-7A i MCU-6-8A MCU-6-10A AsWELogo suRPACs LcNo ACC1PTA5LE PCR g ,ging OVEhLAY TAPER ELBCW TRANsmoNS PATENT APPLIED FOR Figure 2.4 CONFIGURATION OF 6" ELBOW TO PIPE WELD OVERLAY

- . CPL-21-103 13 Revision 1 O

I WELD INLAY PlPE

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1 Penetration Weld Ntrber 6" DIA., SCH. 80 TYPE 308L x-14.C WELD INLAY STAINLESS STEEL PIPE I ( V

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MINIMUM 3 TO 1 TAPER (TYP)  : 1.5" MIN 0.25" MIN J q

3.0" MIN l

PATENT APPLIED FOR Figure 2.5 j

l SCHEMATIC DIAGRAM OF RWCU WELD INLAY l

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CPL-21-103 14 Revision 1 n

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WELD NO.1-RR-4A10-A h

1.0" MIN NOTE 1 WELDOLET w l WV/////A *

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< /NV s THRU-WALL 6*: 0.337" THICK ,

FLAW LOCATION WALL, 304 SS PIPE NOTES:

1. OVERLAY SHALL EXTEND TO WELDOLET ON WELDOLET SIDE.

FINAL SURFACE OF WELD OVERLAY SHALL BLEND SMOOTHLY INTO CONTOUR OF WELDOLET.

2. THICKNESS OF OVERLAY SHALL BE 0.125" MINIMUM, NOT INCLUDING FIRST LAYER.

Figure 2.6 CONFIGURATION OF 4" PIPE TO WELDOLET OVERLAY CPL-21-103 15 Revision 1 0

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i 3.0 EVALUATION CRITERIA This section describes the criteria that are applied in this report to evaluate the acceptability of the weld overlay repairs and flawed pipe analysis. A Section III code stress evaluation was not performed as part of this analysis since the Section XI evaluations are conside red adequate.

3.1 Weld Overlay Repair Criteria Due to the nature of these re pa irs , the geome tric config-uration is not directly covered by Section III of the ASME Boiler and Pressure Vessel Code, which is intended for new construction. Howe ve r , ma te ria ls , fabrication procedures, and Quality Assurance requirements mee t applicable se ctions

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of the original construction code. In addition, since conditions conducive to IGSCC led to the need for repairs, IGSCC- resistant materials have been selected for the weld v

ove rlay repairs.

A conservative me thod was used to demonstrate the adequacy of weld overlay repairs. All relevant UT and PT indica-tions we re assumed t$ be through-wall for their measured length. The weld ove rlays we re then designed such that the net se ction limit load requirements of Reference 1 we re satisfied.

CPL-21-103 16 Revision 1

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l-I The ove rlay repair applied to the inside of weld X-14 was originally designed using IWB-3641 of ASME Section XI ( Re fe rence 1) as a basis. The as-built ove rlay thickness (See Table 2.1) was greater than the original

. pipe wall thickness, so further stress evaluation was unne ce ssa ry. The e f fe cts of the inside overlay on system performance (e.g., flow capability, etc.) we re evaluated by others under the direction of CP&L, and shown to be negligible.

3.2 Flawed Pipe Analysis Crite ria Weld 28-B-12 contained a circumferential flaw de termined to be 2.5" long with a depth of 10%. Due to its small l ini'tial size, the end-c f-cycle allowable flaw depth I defined in Table IWB-3641-1 of ASME Section XI

( Re fe rence 1) is 75% of the through-wall thickness. The NRC's Generic Lette r 84-11 ( Re fe rence 2) modifies this end-of-cycle allowable flaw depth by a factor of 2/3, causing it to become 50% of the through-wall depth.

The upcoming cycle length in this instance is 6 months due to the fact that the' inspection took place in mid-cycle.- The flaw was shown to be acceptable without repair for at least the- next 6 months, utilizing the crack growth law presented in Section 5.2. This crack growth law was obtained from a curve fit of data presented in NUREG-1061 ( Re ference 14).

CPL-21-103 17 Revision 1

f 4.0 LOADS The loads considered in the evaluation jof UT flaw indications included mechanical loads, internal pressure {

loads, dif fe rential the rmal expansion loads, and weld overlay-induced shrinkage loads. Mechanical and j inte rnal pressure loads are used in de signing weld overlays and are described in Section 4.1. Dif fe ren tial thermal and ove rlay shrinkage-induced loads are included for crack growth predictions. An explanation of the thermal transient conditions which cause differential thermal expansion loads is presented in Section 4.2, and the weld ove rlay shrinkage-induced loads are explained in Section 4.3.

4.1 Mechanical and In ternal Pressure Loads Internal pressure information for the Recirculation and RWCU Systems was obtained f rom Re fe rence 3. De adwe ight and seismic loads applied to the Recirculation System welds we re obtained f rcm Re fe rence 4. Re fe rence 5 supplied the deadweight and seismic loads applied to the RWCU System. Calculated stresses are included in Table 4.1 CPL-21-103 18 Revision 1 ,

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4.2 The rmal Loads yhe the rmal expansion loads for each weld in the Recirculation System were obtained from a computer i mode l

.i (Re fe rence 5 ) . The NUTECH ccmputer program PISTAN

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('Re fe rence 6) was used. Re fe rence 3 de fine s se ve rIl

'l type s of transients for which the Recirculation System is designed. The se transients we re conse rvatively g rou pe d into three compo s ite transients. The first compos ite transient is a start up/ shutdown transien t with a heatup or cooldown ra te of 100

• F pe r hou r . The second composite tran sien t consists of a 50*F step change in tempe rature with no change in pressure. The third composite transien t is an emergency event with a 416*F step change in tempe rature and a corresponding change in pressure of 1325 psi. In the five year design life , the re a re 38 startup/ shutdown cycle s, 2 5 small tempe rature change cycle s, and one emergency cycle.

Thermal expansion loads for the RUCU System welds we re obtained from Re fe rence 7.

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4.3 lbld ove rlay Shrinkage - Induced Loads Weld ove rlays cause a small amount of axial shrinkage beneath the overlay. The resulting loads are manifested as bending stresses in the remainde r of the piping system. Shrinkage loads in the Recirculation System were calculated using a PISTAR (Reference 6) piping mode l. Weld ove rlay shrinkage is discussed further in Section 5.2.

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CPL-21-103 20 ,

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Table 4.1

SUMMARY

OF TOTAL STRESSES Maximum Stress (PSI) Total Stress (PSI)

De ad Crack Wol We ld I . D. Ib igh t The rmal Se ismic Pressure Growth De sign 12" AR-A4A 311 4494 3823 7015 11820 11149 12" AR-B4A 591 4745 3108 7015 12351 10714 12" AR-B2A 409 3235 1985 7015 10659 9409 12" BR-F4A 323 2250 1534 7015 9588 8872 28"-B-12A 868 870 3053 6928 8666 10849 6" X-14-C 2159 10310 6495 4000 16469 12654 Pene tra tion ib ld 6"-RUCU-10A 561 2483 3322 4000 7044 7883 6"-RUCU-8A 366 4954 3560 4000 92'0 7926 6"-RWCU-7A 593 3718 913 4000 8311 5506 6"-RWCU-6A 483 3318 1074 4000 7801 5557 6"-RUCU-4A 572 2537 1837 4000 7109 6409 CPL-21-103 21 Revision 1 p,

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5.0 EVALUATION METHODS AND RESULTS The flawed welds shown in Table 1.1 we re identified by UT and PT inspections during the November 1984 mid-cycle inspection at Brunswick Unit 1. The se flawed welds we re evaluated using the methods of Section 3 to determine whether an ove rlay was necessary to meet the re quire-ments of Re ference 1 and 2. Only one flawed weld (28-B-12) was found to meet the requirements of References 1 and 2 without an overlay repair.

The application of weld ove rlays imposes a small amount of axial shrinkage at the weld location which produces secondary stresses on the remainder of the piping system. The analysis made to de te rmine the magnitude of this ef fect at each weld location and to address its significance is discussed in Section 5.2 5.1 Code Evaluation - Section XI All weld ove rlays we re de signed assuming flaws we re through-wall for their measured length. All overlay designs restore the safe ty margins required in Section IWB-3640 of ASME Section XI (Re fe rence 1) . The flaw in weld 28-B-12 mee ts the se requirements without repair and will not violate them for at least the next 6 months.

CPL-21-103 22 Revision 1 l

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5.2 Fracture tiechanics Evaluation The allowable end-of-cycle flaw depth was de te rmined

, from Refe rence 1 and 2. Calculation of crack growth due to IGSCC was based on Re ference 10 and NUTECH's computer t

program NUTCRAK ( Re fe rence 13 ) . Input to NUTCRAK included the as-measured flaw depth, a conservative residual stress distribution, and the following conse rva tive crack growth law.

3.59 x 10 -8 K 2.161 (Re fe rence 14) hh =>

Where da = dif ferential crack depth dt = dif ferential time K = s tre ss intensity at the crack tip 4

Based on this conservative analysis, it was predicted that the flaw in weld 28-B-12 would not exceed the end of cycle allowable crack depth for at least 41 months.

I 5.3 Ove rlay Shrinkage Ef fect on Recirculation and RWCU i

Systems The ef fects of the radial shrinkage are limited to the region adjacent to and directly underneath the weld i

CP L-21-103 23 Revision 1 l

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ove rlay. - Based on Re fe rence 8, the stress due to the radial shrinkage is less than the yield stress at distances greater than about 4 inches from either end of the ove rlay.

The ef fect of the axial weld shrinkage on the Recirculation System was evaluated with the NUTECH computer program PISTAR (Re fe rence 6 ) using the piping model presented in Figure 5.1. The measured shrinkages

! due to all ove rlays applied this outage , as well as those due to previously applied overlays, were impose d as boundary conditions on this model. Since the ASME Code does not limit weld residual stress, all stress

. indices we re set equal to 1.0.

The PISTAR program was used to elastically calculate s tre ss due to weld shrinkage . The maximum calculated stress for an IGSCC susceptible weld was 16.7 KSI at we ld 12-AR-B4. This wc ld is a 12" pipe-to-safe-end we ld on a recirculation rise r. This weld was overlaid. The above stress value does not include the stress reduction at this location due to the application of weld ma te rial . Table 5.1 give s the shrinkage stress for all welds in the recirculation system found to have flaws l this outage.

CPL-21-103- 24 Revision 1

Since . weld shrinkage-induced stresses are not limited by the AS!!E Code , the Code acceptability of these welds is not in= que stion. It is judged that stresses of the magnitude calculated will have negligible ef fect on the integrity or IGSCC susceptibility of these welds.

The RWCU System welds were not analyzed for weld overlay shrinkage-induced stresses, since a spool piece was removed from the af fected piping af ter the overlays were applied. Displacement-controlled stresses due to we ld overlay shrinkage were thereby relieved, and are therefore not a conce rn.

4 .

A i

I CPL-21-103 25 Revision 1

Table 5.1

SUMMARY

OF SHRINKAGE STRESSES AT RECIRCULATION SYSTEM FLAW LOCATIONS i

Shrinkage Weld Numbe r Ove rlay Stress (PSI) 2 8 -B A NO 121 12-AR-A4A YES 6787 4

, 12- AR-B 2 A YES 5330 12-AR-B4h YES 15517*

12-BR-F4A YES 654 i

• Includes allowance for additional wall thickness due to weld ove rlay application.

4 i

l CPL-21-103 26 Revision 1 l

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BRUNSWICK UNIT 1

( RECIRCULATION SYSTEM PIPING MODEL l

l CPL-21-103 27 Revision 1 gg

6.0 LEAK-BEFORE-BREAK ASSESSMENT The following considerations apply to welds with undetected flaws or welds with IGSCC flaws judged to be s=all encugh not to require repair. These censide ra- ,

tions for= the basis for continued plant cperatice for ancther fuel cycle .

6.1 Net Section Collacse 4

The ef fect of IGSCC cn the structural integrity of piping is evaluated through the use of a si=ple

" strength of saterials" approach to assess the lead carrying capacity of a piping sectica af ter the cracked portica has been renowd. Studies have shewn (Feference 10 and 11) that this approach gives a conservatiw ,

Icwe r-bcund esti= ate of the leads which would cause unstable fracture of the cracked section. Typical results of such an analysis are show. in Figure 6.1 (Re fe rence 10 ) . This figure defines the locus of li=iting crack depths and lengths for circu=ferential cracks which are predicted by the net sectico collapse me thod to cause failure. Curves are presented for both typical piping syste=s stresses and stress levels equal to ASME Code limits. Note that a ve ry large pe rcentage of pipe wall can be cracked be fore reaching these li=its CP L-21-103 23 Revision 1

l i.

(40% to 60% of circumference for through-wall cracks, and 65% to 85% of wall thickness for 360* part-through l

cracks). Also shown in Figure 6.1 is a sampling of cracks which have been detected in service, either through UT examination or leakage. In each case the re has been a significant margin between the size of the crack observed and that predicted to cause failure unde r service loading conditions.

6.2 Leak Ve rsus Break Flaw Configuration Perhaps of more significance to the le ak-be fo re-b re ak argumen t is the flaw configuration depicted in Figure 6.2. This configuration addressas the concerns raised i

by the occurrence of part-through flaws growing circumferentially before breaking through the outside surface to cause leakage. Figure 6.2 presents typical

! size limitations on such flaws based on the conservative ne t section collapse me thod of Section 6.1. Note that l

ve ry la rge crack sizes are predicted. Also shown on f

this figure are typical detectability limits for short t

i through-wall flaws (which are amenable to leak I

de te ction ) and long part-through flaws (which are i

ame nable to de tection by UT) . The margins be tween the detectability limits and the conservative, net section collapse failure limits are sub s tan tial . It is CPL-21-103 29 Revision 1

noteworthy that the likelihood of flaws deve loping which are. characterized by the vertical axis of figure 6.2 (constant depth 360* circumferential cracks) is so remote as to be conside red impossible. Material and stress asymme tries always tend to propagate one portion of the crack faster than the bulk of the crack front, which wiil eventually result in "le ak-be fo re-b reak" .

This observation is borne out by e xtensive fie ld e xpe rience with BUR IGSCC.

6.3 Axial Cracks Axial cracks can grow through the wall but remain short in the axial direction. This behavior is consistent with expectations for axial IGSCC since the presence of a sensitized weld heat-af fected zone is necessary, and this heat-affected zone is generally limited to approximately 0.25 inch on either side of the weld.

Since the major loadings in the net section collapse analysis are bending moments on the cross section due to seismic loadings, and since the se loads do not exist in the circumferential direction, the above le a k-be fo re-break arguments are even more persuasive for axially oriented cracks. The re is no known mechanism for axial cracks to lengthen before growing through-wall and leaking, and the potential rupture loading on axial cracks is less than that on circumferential cracks.

CPL-21-103 30 Revision 1

6.4  !!ultiple CracP.s Analyses pe rformed for EPRI ' Re fe rence 12 ) indicate that the occurrence of multiple cracks in a weld, or cracking in multiple welds in a single piping line does not invalidate the leak-be fore-break arguments discussed above.

6.5 Nonde structive Examination The primary means of nondestructive examination for IGSCC in BWR piping is ultrasonics. This method has been the subject of considerable research and develop-ment in - recent years, and significant improvements in its ability to de tect IGSCC have been achieved. Figure 6.2 illustrates a significant aspect of UT detection capability with respect to leak-be fo re-b reak. The ty pe s of cracking most likely to go undetected by UT are relatively short circumferential or axial cracks which are most amenable to detection by leakage monitoring.

Conve rsely, as part-through cracks lengthen, and thus become more of a concern with respect to leak-be fore-b re ak , they become more readily de tectable by UT.

i L

l One weld in the RCWU System, the X-14 penetration weld, was inaccessible to UT examination from the outside.

)

i e

CP L-21-103 31 Revision 1

i The re fo re , a portion of the adjoining piping was removed and the weld was inspected f rom the inside by the liquid l

l l pene tran t (PT) me thod. Flaws we re de tected by this j method and a subsequent " weld inlay" repair was made.

6.6 Leakace De tection 4

Typically, leakage de tection for BWR reactor coolant I system piping is through sump level and drywell activity monitoring. The se systems have sensitivities on the order of 1.0 gallon per minute (GPM). Plant te chnical specification and administrative limits typically require investigation / corrective action at 5.0 GPM unidentified leakage , or when the re is a 2.0 GPM increase in unidentified leakage in a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period.

Table 6.1 provides a tabulation of typical flaw sizes

( which cause 5.0 GPM leakage in various size piping assuming a membrane stress of S,/2 ( Re fe rence 10).

Also shown in this table are the critical crack lengths for through-wall cracks based on the net section i

l collapse method of analysis discussed above. For conse rva tism, the leakage values are based on pressure stress only, while the critical crack lengths are based on the sum of all combined loads, including seismic.

l c .

? l l l I CP L-21-103 32 l l Revision 1 I

Conside ring other normal ope rating loads in the le akage analysis would result in higher rates of leakage for a given crack size. Note that the re is considerable margin be tween the crack length which produces 5.0 GPM leakage and the critical crack length, and that this I

margin increases with increasing pipe size.

6.7 Historical Expe rience i

The above theories regarding crack de tectability have been supported by experience ( Re fe rence 12 ) . Indeed, of 1

j the large number of IGSCC inciderts to date in BWR piping, none have come close to violating the structural integrity of the piping.

1 I

1 CPL-21-103 33 Revision 1

i i

l l

Table 6.1 EFFECT OF PIPE SIZE ON THE RATIO OF THE CRACK LENGTH  ;

FOR 5 GPM LEAK RATE AND THE CRITICAL CRACK LENGTH (ASSUMED STRESS a = Sm / 2)

( REFERENCE 14)

NOMINAL CRACK LENGTH FOR CRITICAL CRACK gfg LENGTH Ig (in.) c PIPE SIZE 5 GPM LEAK (in.)

4" SCH 80 4.50 6.54 0.688 10" SCH 80 4.86 15.95 0.305 24" SCH 80 4.97 35.79 0.139 FCPt.83.0849 l

l

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CPL-21-103 34 Revision 1 Qd 1

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I O.4 @ Field Cata - Part-j I Througri Flaws i 9 C Field Cata - Laaks E Sm = 16.0 ksi

@ ag = A8.0 ksi ~

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Values at EECC F l

0 O 0.2 0.4 0.5 0.8 1.0 Fraccon of Circumfemes. 9/r Pot.as.as a Figure 6.1 TYPICAL, RESULT OF NET SECTION COLLAPSE ANALYSIS OF CRACKED STAINLESS STEEL PIPE

( REFERENCE 14 )

CPL-21-103 35 Revision 1 Qd

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PIPE CROSS SECTION 0.7 0.6 1

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i Figure 6.2 TYPICAL PIPE CRACK FAILURE LOCUS FOR COMBINED THROUGH-WALL PLUS 3600 PART-THROUGH CRACK CPL-21-103 3G Revision 1 gd

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7.0 SUttf1ARY AND CONCLUSION Evaluation of the repairs to the Recirculation and Reactor Water Clean-up Systems reported herein shows that the resulting stress levels are acceptable for all design condition s. The stress levels have been assessed f rom the standpoint of load capacity of the components and the resistance to crack growth.

Acceptance crite ria for the analyses have been established in Section 3.0 of this report which demon s tra te that:

1. The re is no loss of de sign safe ty margin ove r that provided by the current Code for Class 1 piping and pressure ve ssels (ASME Se ction III, Subsection NB).

2. During the design evaluation period of 5 years for each repair, the observed cracks will not grow to the point whe re the above safe ty margins would be reduced.

Analyses have been pe rformed and results are pre se n te d which demonstrate that the repaired welds satisfy these criteria by a large ma rg i n . Analyses have also been CP L-21-10 3 37 Revision 1 nutggb

~

performed which demonstrate that the un re pa ire d we ld satisfies these criteria by a large margin.

l Fur the rmore , it is concluded that IGSCC experience in the Reactor Recirculation and Reactor Water Cleanup

, Systems at Brunswick Unit 1 does not increase the 4

probability of a design basis pipe rupture at the plant. This conclusion expressly considers the nature of the cracking which has been repaired at Brunswick Unit 1, and the likelihood that other similar cracking i may have gone unde tected. The conclusion is based primarily on the extremely high inherent toughness and 4 ductility of the stainless steel piping material.

Cracks in such piping grow through-wall and leak before affecting its structural load carrying capacity.

CPL-21-103 38 Revision 1 N

8.0. REFERENCES

1) ASME Boiler and Pressure Vessel Code ,Section XI, 1983 Edition with Addenda through Winte r 1983, Paragraph IWB-3640, " Acceptance Criteria for Austenitic Steel Piping".

2) NRC Generic Le tter 84-11, dated April 19, 1984.

3) General Electric Design Specification 22A1417, Revision 2, File No. CPLO21.0013.

4) General Electric " Brunswick Recirculation Pipes Stress Results for Multi-Support Response Spectra Input from UE&C Me thod 1," Rev. O , 9/24/84, File No. CPLO21.0013.

5) " Weld overlay Shrinkage - Thermal Expansion, Brunswick 1," NUTECH Documen t No. CPL-09-302, Re v .

O , File No. CPLO 21.0013.

6) NUTECH Computer Program PISTAR, File No.

08.003.0300, Ve rs ion . 3. 2.

CPL-21-103 39 Revision 1

f 4

7) United Engineers RWCU Stress Calculations, Telecopied to Dean Yoshida of NUTECH Engineers 11-20-84, from Carolina Powe r and Light, UEC-14930, Re v. 11, 4-26-7 7, File No. CPLO21.0013.

8) NUTECH Re port NSP-81-105, Revision 2, " De s ign Report for Recirculation Safe End and Elbow

! Re pa irs , Monticello Nuclear Generating Plant,"

Decembe r 1982, File No. 30.1281.0105.

l 9) ASME Boiler and Pressure Vessel Code ,Section III,

1983 Edition with Addenda through Winter 1983.

10) EPRI-NP-2472, "The Growth and Stability of Stress l Corrosion Cracks in i arge-Diame ter BWR Piping, July 1982.

11) EPRI-NP-2261, " Application of Tearing Modulus Stability Concepts to Nuclear Piping," February 1982.

12) Presentation by EPRI and BWR Owners Group to U.S.

Nuclear Regulatory Commission, " Status of BUR IGSCC Development Program," Octobe r 15, 1982.

i l

CPL-21-103 40 Revision 1

13) NUTECH Compu'te r Program NUTCRAK, Ve rsion 2.0.2, File No. 08.039.0005.

14) NUREG 1061, "Inve stiga tion and Evaluation of Stress-Corrosion Cracking in Piping of Boiling Water Reactor Plants," Second Draf t, April 1984.

CPL-21-103 41 Revision 1 nutggb

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A 4-5 Comerate OMese NUTECH, ins.

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