ML20209G021

GE-NE-B13-02010-33NP, Evaluation of Limerick Unit 2 Shroud Cracking for at Least One Fuel Cycle of Operation

ML20209G021
Person / Time
Site:	Limerick
Issue date:	06/30/1999
From:	Caine T, Mehta H, Stark R GENERAL ELECTRIC CO.
To:
Shared Package
ML20209F638	List: ML20209F634 ML20209G021
References
GE-NE-B13-02010, GE-NE-B13-02010-33NP, GE-NE-B13-2010, GE-NE-B13-2010-33NP, NUDOCS 9907160215
Download: ML20209G021 (15)

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Docket No. 50-353 GL 94-03 y -

\v; June 24,1999 2R05 Final Report Page 77 of 92 GEbclear Energy TECHNICAL SERV lCES GE-NE-813 02010-33NP GE Nuclear Energy DRF #BI3-02010 175 Curtner Avenue, San Jose, CA 95125 ClassII June 1999 THE EVALUATION OF ' LIMERICK UNIT 2 SHROUD CRACKING FOR AT LEAST '

ONE FUEL CYCLE OF OPERATION June 1999 i

Prepared for Limerick Unit 2 Prepared by

.) GE Nuclear Energy

';{ 175 Curtner Avenue

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San Jose, CA 95125 9907160215 990709 33 DR ADOCK 0

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une 4 9 05 nri Riport CENE-8f3 aart#J3WP pig 3 78 of 92 1.

THE EVALUATION OF LIMERICK UNIT 2 SHROUD CRACKING FOR AT LEAST ONE FUEL CYCLE OF OPERATION i

l June 1999 I Prepared by: M M1 R.R. Stark,%enior Engineer Struc 1 Assessment & Mitigation Veritied by: w~ -

H.S. Mehta Technical Leader l Structural Assessment & Mitigation j Approved by: YA bw T.A. Caine, Manager  ;

Structural Assessment & Mitigation  ;

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Do et No. 50-353 $4 June 24,1999 $05 knal R;pon GE"f-arnanome Pigs 79 of 92 l

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IMPORTANT NOTICE REGARDING CONTENTS OF THIS REPORT Please Read Carefully The only undertakings of th'c General Electric Company (GE) respecting information in this document are contained in the contract between PECO Energr and GE, and nothing contained in this document shall be construed as changing the contract. The use of this information by anyone other than PECO Energy, or for any purpose other than that for which it is intended under such contract is not authorized; and with respect to any unauthorized use, GE make no representation or warranty, expressed or implied, and assumes no liability as to the completeness, accuracy, or usefulness of the information contained in this document, or .

l that its use may not infringe privately owned rights. '

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• GL 94-03 Dockit No. 50-353.-

June 24,1999 ' 2R05 Final R: port ###""

Page 80 of 92 Table of Contents Subiect Pane No.

1.0 BACKOROUND.. . . . . . . . .. 4 2.0 ASSUMPTIONS . ... ...-.. ...- . . . . . . . . . . . . . . . . -6

' 3.0 STRUCTURAL EVALUATION METHODOLOGY .. ... . ............7 3.1 BWRVIP 01 Evaluation Methodology.- . . . . . _7 3.2 H3 Analysis. . . . . . . . . . . .. . . . . . . . . . .. .... 8 3.3 H4 Analysis. . .. . . . ...........8 3.3.1360*Part Through WallCrack Approach.. . . . . . . . . . . . . . . . . . . . . . .........8 3.3.2 CompoundCrack Approach . . . . . . . . . . .9 4.0 ANALYSIS RESULTS 12 5.0

SUMMARY

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6.0 REFERENCES

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. APPENDIX A: UT DATA . ...........: . . . . . . . . . . . . . . . .. . 15 1

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- *i hicket No. 50-353 GL 94-03 June 24,1999 [ [jna jpst sar sSessany

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1.0 BACKGROUND

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. An inspection was performed on the RPV shroud circumferential welds at Limerick Unit 2 during the Spring 1999 RF05 outage. The inspections consisted of a UT examination i of the circumferential welds. Figure 1-1 shows a typical map of the shroud welds.

During the inspections. indications were found in the H-3 and H-4 welds. The inspection

~ data for H3 and H4 is included in the Appendix.

Due to the extent of the cracking in the H3 and H4 welds, a detailed structural evaluation of the welds was performed.' The objective of this report is to describe the structural evaluation methodology performed and document the results of evaluation in support of

. at least one fuel cycle of operation (24 months) fol: awing RF05.

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L ' * ' * . Docket No. 50-353 GL 94-03 June 24' 1999 2R05 Finti Rrport pig) 82 of 92 sesessesper

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. 35' 60* 90* - 135' :80* 240* 270* 300* 30*

' i i ,. i 45' 85* .ev- 155* 225* 265*275* 315' l VI l V2 l V3 V4- V5 v6 i V7 i v8 j V9 l vt0 i vil 3

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_f Vla i V19 i v20 , v21  ! v22 Iv23 T<-a v24 v25 I Figure 1 1. Typical Shroud Weld Configuration l

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Docket N3. 50 353 GL 94-03 Jun3 24,1999 2R05 Final R:eport Pag) 83 of 92 GENE-#U@pf843WP 2.0 ASSUMfTIONS Several conservative assumptions were made throughout the repon. They included the following:

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1. A bounding crack growth rate of 5x10 inihr will be used for both length and depth.

2. 16.000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> of operation will be used in the evaluation, based on a 24 month cycle.

3. A.UT uncenainty of 0.131 inches will be used for crack depths, and a UT uncenainty of 0.5 degrees will be used for crack lengths (on each flaw tip). These values are consistent with BWRVIP-03 [1].

4. Crack growth and UT uncenainty were not included for uninspected regions when treated as through-wall flaws.

5. 'All other assumptions are stated in the body of the repon.

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• Dockrt No. 50-353 GL 94-03

.Jun3 24,1999 D5 e na}

9 spod 3.0 STRUCTURAL EVALUATION METHODOLOGY The methodology used in the structural evaluation of the observed cracking in the shroud H3 and H4 welds followed the guidelines outlined in BWRVIP-01. In case the required guidance available in BWRVIP-01 was not available, a verified conservative technical approach was used. This section describes the details of the evaluation methodology.

3.1 BWRVIP-01 Evaluation Methodology The BWRVIP-01, Rev. I report [2] has been reviewed and approved by the US Nuclear Regulatory Commission (NRC) with certain stipulations as described in the Reference 3 safety evaluation report (SER).

Section 4.0 of BWRVIP-01 describes the flaw evaluation methodology suggested for use in evaluating cracking in core shrouds. Three techniques for the flaw evaluation are recognized: (1) linear elastic fracture mechanics (LEFM), (2) limit load, and (3) elastic.

plastic fracture mechanics (EPFM). The LEFM methodology coupled in addition to the limit load approach is appropriate when the fluence level at a weld exceeds 3x10 2o n/cm2 (E>l MeV). At lower fluence levels, only limit load evaluation is necessary. The EPFM i approach may be used in lieu of LEFM when deemed necessary to demonstrate additional margin.

The LEFM approach described in BWRVIP-01 is based on the assumption of a through-wall circumferential flaw geometry in a cylindrical shell and provides for two types of corrections to the basic equation for stress intensity factor (K) calculation: (1) shell or curvature correction factor, and (2) the flaw interaction correction factor.

The limit load approach includes consideration of a distributed ligament length (DLL). A later BWRVIP report (Reference 4) included a computer program (DLL, Version 2.1) which incorporated the distributed ligament length limit load approach.

A bounding crack growth rate of 5x10~5 inch / hour is'specified in BWRVIP-01 and is consistent with the SER.

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1* f.7 .' Docket No. 50-353 GL 94-03 EU'24,1999 05 ni port Gew-su m 3.2 H3 Analysis I' ' Because the fluence for H3 is below 3x102 n/cm 2. only limit load analysis was performed. The limit load evaluation was conducted using the DLL computer program.

The cracking in H3 was found in both the inner and outer diameter of the shroud. To

simplify the analysis, all cracks on the inner part of the shroud were conservatively l- - assumed th be cracked to the largest initial crack depth observed on the inner diameter (0.39 inches). In the same way, all cracks on the outer part of the shroud were assumed to be cracked to the largest crack depth observed on the outer diameter (0.33 inches).' Since

j. cracks were found on both the inner and outer diameter of the shroud, the cracks were assumed to be grown in both depth directions (as well as length directions), and j combined appropriately. In addition all uninspected areas were assumed to be i

completely cracked through-wall.

3.3 H4~ Analysis l ' The H4 weld was considered to be in the beltline region (estimated peak fluence greater than 3x10 2o n/cm2 ) and therefore, both a limit load and an LEFM evaluation was  :

J conducted for this weld The limit load evaluation was performed using the same methodology as the H3 analysis.

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, TFor the LEFM evaluation. the following methodology was used. The crack configuration l

was analyzed using the DLL computer program which is based on the LEFM -

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methodology outlined in BWRVIP-01. This methodology is also consistent with the NRC staff pos'ition stated in Reference 3. Two cases were evaluated. These cases are described in the following sections.  !

3.3.1 360 Part Through-WallCrack Approach i l

This case assumed a 360* part through-wall crack with an initial depth (i.e., before the application of NDE uncertainty and projected crack growth) equal to the maximum j indication depth reported at the H4 weld. Thus, the initial crack depth assumed at the i inaccessible weld lengths was equal to the maximum measured depth in the inspected regions.

At Limerick'2, approximately 60% of the H4 weld was inspected and the maximum observed crack depth was 0.11 inches. Thus, the initial 360' part through-wall flaw depth assumed was 0.11 inch. The 0.11 inch crack depth was increased to account for crack  !

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' Docket No. 50-353 GL 94-03 Jun3 24,1999 2R05 Final Report Ptg3 86 of 92 car.ars4amuar growth (5x10 irvhr x 16.000 hrs) and UT uncertainty (0.131 in). The resulting end-of-cycle crack depth was found to be 0.11 +0.80+0.131=1.041 in.

BWRVIP-01 does not include guidance for the calculation of K for this configuration and, therefore, a fracture mechanics handbook solution was used. A typical handbook solution for a single edge notch flat plate (Reference 6) was conservatively applied. This approach is considered conservative since the flat plate solution includes the bending caused by the eccentricity of the applied load, which is not present in the cylindrical model. The solution is found by the following formula:

K = F

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• a) (4-1) where: K = stress intensity.

F = the geometrical scaling factor o = primary membrane plus primary bending stress. and a = crack depth 3.3.2 Compound Crack Approach in this approach a 360' part through-wall crack was first assumed with a constant initial depth equal to the maximum indication depth reported at the H4 weld (0.11 inches). This

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results in an end-of-cycle depth of(0.11+0.131+0.8) or 1.041 inch. Recall that 0.131 inch is the UT uncertainty value and 0.80 inch is the projected crack growth for one fuel cycle (16000 hot operating hourst using the bounding crack growth rate of 5x105 inch / hour. In addition. all uninspected weld lengths were assumed to be cracked through-wall to an extent consistent with Table 3 of BWRVIP-07 (Reference 7). That is, since the H4 inaccessible region was between 25-50%, and the defect rate in the accessible region was l

between 25-50%, the defect rate in the inaccessible region could be assumed to be 65%.

Thus, an additional 35% of uncracked material can be credited. Conservatively, the l additional uncracked material was placed in a location such that the longest through-wall l

crack would remain.

! The BWRVIP-01 does not provide explicit guidance for the LEFM evaluation of a compound circumferential crack geometry. Therefore, an altemate approach was used.

The K values were calculated using the LEFM option in the DLL computer program (which treats through-wall cracking and any interactions between multiple through-wall 9

D'ocket No. 50-353 '- GL 94-03 Jun3 24,1999 5 n port gg, cracks) with the applied stresses increased by a factor obtained from Reference 8 to account for the presence of a part through-wall 360' crack.

l Reference 8 provides the following analytical expression for the calculation of K for a compound circumferential crack geometry (Figure 4-1):

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K=i c. (nRO) ' F. (4-2) where: a, = Applied bending stress i F = F [1.0 + A(4.5967(0/n)" + 2.6422(0/n)4.24))

l F = [(1 +x)(1 x) (1.0 + 0.5x/(R/t)})*5 A = [0.125(R/t) - 0.25]o25 x = a/t R = Average radius of cylinder = Outer radius, R,- t/2 t = Cylinderthickness a = Crack depth in part through-wall crack 0 = Half angle of through-wall crack l

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. Dodket No. 50 353 GL 94-03 June 24,1999 2R05 Finil Report '

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COMPOUND CRACK-Figure 3-1 Compound Crack Geometry i

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'Docke't No. 50-353 GL 94-03 June 24,1999 2R05 Final Report GME-8fAsartsJmP Page 89 of 92 4.0 ANALYSIS RESULTS l

l The calculated membrane and bending stress magnitudes for the normal / upset and l

l emergency / faulted operating conditions are summarized in Table 4-1. For each case, the normal / upset condition was determined to be limiting.

The methodology discussed in the previous section was used to evaluate structural margins at the H3 and H4 shroud circumferential welds. The methodologies used are consistent with BWRVIP-01 methodology. The calculated and required safety factors are shown in Table 4-2. It is seen that each weld meets the structural margin requirements.

Table 4-1. Membrane and Bending Stresses for Normal / Upset and Emergency / Faulted Conditions Weld Pressure Axial Stress (ksi) Bending Moment Stress (ksi)

Location Upset Faulted Upset Faulted H3 0.300 0.724 0.935 1.583 H4 0.300 0.724 1.471 2.411 Table 4-2. H3 and H4 Results (Normal & Upset Conditions Were Limiting in All Cases)

Weld Limit Load Safety Factors LEFM Safety Factors Location Calculated SF Min. Calculated SF Calculated SF Min.

Required for Compound for 360" Required Flaw Flaw H3' l 6.51 2.77 - - -

H4 l 13.16 2.77 3.67 13.82 2.77

• H3 fluence is below 3x10" n/cm;. Thus. LEFM evaluation was not necessary.

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Docket No. 50 353 l June 24.1999 h05 nal Report Gest-sf u arts w Page 90 of 92 5.0

SUMMARY

The structural evaluation methodologies used in the evaluation of the H3 and H4 1

. circumferential welds for the Limerick Unit 2 shroud are consistent with the methodologies described in BWRVIP-01 and the corresponding US NRC SER. The evaluation determined that the welds meet the structural margin requirements for '

continued operation for at least one fuel cycle. .

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6.0 REFERENCES

1. BWRVIP-03, " Reactor Pressure Vessel and Internals Examination Guidelines,"

October 1995.

2. BWRVIP-01, Rev. 2, "BWR Core Shroud Inspection and Flaw Evaluation Guidelines," October i996.

3. Evaluation of "BWR Core Shroud Inspection and Evaluation Guidelines," GENE-523-113-0894, Revision 1,- Dated March 1995, and "BWRVIP Core Shroud NDE Uncertainty & Procedure Standard," Dated November 22,1994; USNRC. June 16, 1995.

4. BWR Core Shroud Distributed Ligament Length (DLL) Computer Program (Version 2.1), BWRVIP-20, December 1996.

5. ASME Boiler and Pressure Vessel Code,Section XI, Rules for In-Service Inspection of Nuclear Power Plant Components, American Society of Mechanical Engineers,  !

1989 Edition.

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6. Tada, H., Paris, P. and Irwin, G., "The Stress Analysis of Cracks Handbook", Del Research Corp.,1985 Edition.

7. BWRVIP-07," Guidelines for Reinspection of BWR Core Shrouds," February 1996. i

8. Zahoor, A., " Ductile Fracture Handbook." Volume 2, EPRI Research project 1757-69 October 1990.

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D6cket No. 50-353 GL 94 03

-Jun) 24' 1999 2R05 Finti Report Pags 92 of 92 saurcw APPENDIX A: UT DATA (See ATTACHMENT 2 to the PECO Energy Report)

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