ML20209F634

Submits Supplemental Response to GL 94-03, Intergranular Stress Corrosion Cracking of Core Shrouds in Bwrs, for Unit 2.Rev 0 to 1H61R & GE-NE-B13-02010-33NP Repts & Revised Pages to Summary Rept Previously Submitted,Encl

ML20209F634
Person / Time
Site:	Limerick
Issue date:	07/09/1999
From:	Geoffrey Edwards PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20209F638	List: ML20209F634 ML20209G021
References
GL-94-03, GL-94-3, NUDOCS 9907160090
Download: ML20209F634 (8)

Text

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4 Ctation Support Department l GL 94-03 y

PECO NUCLEAR nco%c-1 965 Chestertarook Boulevard A Unit of PECO Energy wam m twe July 9,1999 I Docket No. 50-353 License No. NPF-85 i

U.S. Nuclear Regulatory Commission i Attn: Document Control Desk Washington, DC 20555

Subject:

Llrrerick Generating Station, Unit 2 Revision to Supplemental Response to Generic Letter 94-03 Summary of Core Shroud Inspection Results ,

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Dear Sir / Madam:

By letter dated June 24,1999, PECO Energy submitted a supplemental response to Generic Letter (GL) 94-03, *Intergranular Stress Corrosion Cracking of Core Shrouds in Boiling Water l Reactors,"for Limerick Generating Station (LGS), Unit 2. The information provided in our June j 24,1999 letter, contained a Summary Report discussing the inspection results and evaluations associated with the LGS, Unit 2, reactor vessel core shroud examinations that were perfomied i during the last refueling outage (i.e.,2R05).  !

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Included as an attachment in the Summary Report (i.e., Attachment 5) was General Electric (GE) Report GE-NE B13-02010-33P, 'The Evaluation of Limerick Unit 2 Shroud Cracking for at /

Least One Fuel Cycle of Operation," dated June 1999. In our June 24,1999 letter, we indicated that GE requested that this report be withheld from pubne disclosure since it included information i I

of a proprietary / confidential nature. GE's request was submitted in accordance with the requirements of 10CFR2.790(a)(4) and a supporting affidavit was provided. At the time of the submittal, we also indicated that a non-proprietary version of the GE report was in preparation e.

and would be submitted at a later date upon completion. Accordingly, this letter forwards the j ,

non-proprietary version of Attachment 5 (i.e., GE Report GE-NE-B13-02010-33NP). g i in addition, this letter also provides several revised pages to the Summary Report previously L0 Q'kaj submitted by our letter dated June 24,1999. These revised pages are necessary in order to I provide clarification regarding the proprietary nature of Attachment 2, and to clarify the evaluation assumptions for considering through-wall cracking. Specifically, the title page for Att9chment 2 (i.e., Report No.1H61R, dated May 1999) inadvertently contained a proprietary disclaimer statement. This document is a non-proprietary report and a replacement title page (with the disclaimer statement deleted) is attached. The Summary Report also discussed evaluations and through-wall cracking assumptions. The information provided was based on preliminary data provided by Structural integrity Associates (SIA). The affected pages from the Summary Report have been revised to reflect the most current data concerning the through-wall cracking assumptions, and are attached. ,

i 9907160090 990709 PDR ADOCK 05000353 p PDR

July 9,1999

, Page 2 If you have any questions or require additional information, please do not hesitate to contact us.

Very truly yours, b l Fort Garrett D. Edwards Director- Licensing Attachments / Enclosure cc: H. J. Miller, Administrator, USNRC, Region I (w/ attachments / enclosure)

A. L. Burritt, USNRC Senio' rResident inspector, LGS (w/ attachment / enclosure) l l

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Docket No. 50-353 GL 94-03 June 24,1999 (Revised) 2R05 Final Report Page 4 of 92 The extent of core shroud weld inspections performed during 2R05 include:

57.41% of the length of weld H-1, 396.78" 4 57.44% of the length of weld H-2, 397.05" 61.53% of the length of weld H-3, 400.36"

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63.79% of the length of weld H-4, 415.08" 61.41% of the length of weld H-5, 399.61" 59.50% of the length of weld H-6, 346.69" 59.09% of the length of weld H-7, 372.69" Total 2,728.26*

The extent of these weld inspections is graphically depicted on the attached weld maps for welds H-1, H-2, H-3, H-4, H-5, H-6 and H-7 (Attachment 2). 1 RESULTS:

The extent of examination of these welds varied depending on accessibility. All accessible weld lengths were examined. The examination coverage achieved was sufficient to quantify the core shroud structural integrity. 3 Circumferential indications were found in the weld heat affected zone (HAZ) at welds H-1, H-2, H-3, H-4, H-5, and H-6. No indications were observed at the H-7 weld. Attachment 1 contains the General Electric (GE) Nuclear Energy, IJT Report summarizing the extent of each weld examination, their results and weld maps depicting the general location of the as-found indications.

EVALUATIONS:

Due to the large number of UT indications detected during 2R05 it was not practical during the outage to determine the true nature (i.e., geometric, metallurgical or flaw) of each reflector. Accordingly, all as-found surface connected indications were conservatively assumed to be flaws. Pursuant to the LGS, Unit 2, inspection plan in response to Generic Letter 94-03, submitted by letter dated January 12,1999, the initial evaluations considered all identified crack indications to have through-wall depth. Additionally, the weld lengths which were not inspected due to inaccessibility, were assumed to have through-wall cracks.

Detailed evaluations, including flaw depth sizing, were then performed; however, there was no change to the conservative assumptions for the uninspected regions.

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. Docket.No. 50-353 GL 94-03 June 24,1999 (Revised) 2R05 Final Report Page 14 of 92 Interim Report Limerick Generating Station - Unit 2 t Core Shroud Ultrasonic Examination Prepared for PECO Energy

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Prepared by:

GE Nuclear Energy )

l Report No.: 1H61R, Rev. 0

]i May 1999 l Original Signed By:

Prepared By: Date:

.lohn Hayder% GE Inspection Services, Sr. NDE Specialist LevelIII UltrasonicMethod ,

1 Original Signed By:

Reviewed By: Date: ,

Richard Keck, GE Inspection Services, Project Manager 1

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Original Signed By:

Reviewed By: Date:

Thornas Anderson, PECOEnergy,ISIEngineer l

1H61R 4 l

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'. l Docket Ao 50-353 GL 94-03 June 24,1999 (Revised) 2R05 Final Report Page 52 of 92 May 14,1999 SIR-99-061 RAM-99-053 rmattson@structint.com Mr. Richard E. Ciemiewicz PECO Energy Systems 965 Chesterbrook Blvd.,63B-3 Wayne, PA 19087-5691

Subject:

Evaluation of Limerick, Unit 2 Shroud Examination Results

Dear Rich:

Structural Integrity Associates (SI) has performed an evaluation of the ultrasonic examination results recorded during the 1999 inspections of shroud circumferential welds H1 through H7 at Limerick, Unit 2, in order to determine acceptance for continued operation. The evaluations performed and documented l herein were designed to justify operation without reinspection of these welds for at least one two year operating cycle. The evaluations were performed following the approach used in the BWR Vessel and intamals Project (BWRVIP) shroud evaluation guidelines [1], based on limit load and linear elastic fracture mechanics (LEFM) techniques. The following sections of this report describe the methodology used to evaluate each weld and the resulting safety margins. l INSPECTION AND EVALUATION METHODOLOGY The inspection and evaluation approach employed at Limerick, Unit 2 provides the necessary information for determination of the required amount of unflawed material to meet specified safety margins, including the appropriate amount for postulated crack growth and nondestructive examination detection and sizing uncertainties. Ultrasonic examination (UT) techniques were utilized which provided complete through-thickness interrogation of all welds. Due to accessibility limitations, the circumferential extent of examination of these welds varied. However, sufficient weld length was adequately interrogated to quantifiably demonstrate the condition, and hence, the structural integrity of all welds evaluated. Because both limit load and LEFM assessments have been performed, evaluation methodologies will be addressed separately with respect to structural integrity evaluation.

ACCEPTANCE CRITERIA The core shroud is a core support structure which provides lateral support for the fuel. The applicable codes, standards and classification for the core shroud are as follows:

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SIR-99-061/ RAM-99-053 t

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Docket No. 50-353 GL 94-03 June 24,1999 (Revised) 2R05 Final Report Page 53 of 92 j l

l e The core shroud is classified as a safety-related component.

The core shroud is not an ASME Code, Section til component. However, the original design is in accordance with the intent of Section lll of the ASME Code.

e lhe evaluation of the core shroud was performed in accordance with the requirements of the BWRVIP's shroud evaluation guidelines [1].

I FLAW EVALUATION RESULTS Based upon the inspection data reported in 1999, flaw evaluations were performed to justify continued operation, with the results documented herein. The analyses were performed using limit load as the failure criterion for each of the welds. The analyses performed take into account the distribution of good material at each weld around the circumference of the shroud. In addition, the H4 weld, which is the most highly irradiated, was evaluated using the LEFM methodology.

Substantial conservatisms were built into the evaluation to account for the weld area examined, the weld area which was not examined, evaluation guidelines' detection and sizing uncertainties, crack growth, and the evaluation guidelines' flaw proximity criteria as applied to adjacent flaws. The specific conservatisms utilized in this evaluation are as follows: I

1. All areas not examined were considered cracked through-wall for all evaluations. I

2. A bounding crack growth rate (5 x 104inches / hour)[1] in the length and depth directions was applied to all identified flaws, as well as to all the uninspected regions.

3. UT inspection uncertainty factors were applied to all identified indications, as well as to uninspected regions.

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. 4. ASME Code,Section XI proximity criteria for adjacent flaws were applied, after accounting for crack growth and inspection uncertainties.

5. ASME Code,Section XI pressure boundary safety margins were applied to these evaluations even though the core shroud is not a primary pressure boundary.

6. Dead weight of the shroud and supported components was conservatively ignored.

The conservative assumptions described above were applied to each of the horizontal welds examined in this report. Table 1 documents the input data. Tables 2 through 8 present tne results of the ultrasonic examination for each of the horizontal welds evaluated in this report.

1 l ; SIR-99-061/ RAM-99-053 i

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'. 1 Docket No. 50-353 GL 94-03 June 24,1999 (Revised) 2R05 Final Report l Page 54 of 92 The results of the limit load analyses for each of the horizontal welds examined are presented in Table 9.

based upon the stresses reported in Table 1, and the examination results reported in Tables 2 through 8, based on the inspection results contained in Appendix A. Based upon the stresses reported in Table 1, l the upset condition govems for welds H2 through H7, while the faulted condition govems for weld H1.

One observes from Table 9 that the factors-of-safety for the upset condition vary from 4.50 to 15.15, and for the faulted condition the factor-of-safety is 1.89. This compares to ASME Code minimum factors-of-safety of 2.77 and 1.39, respectively, specified for pressure boundary components [1]. One should note that the conservatisms utilized in this study are as described previously in this section.

Finally, an evaluation of the H4 weld was performed using the LEFM methodology to determine the applied stress intensity factor resulting from the bounding loading conditions. The results of this analysis  ;

demonstrate that the 150 ksidinch material toughness, which is presented in the evaluation guidelines

[1] as the acceptable fracture toughness for this material under irradiation conditions, is met. Table 10 l illustrates that the evaluation guidelines [1] minimum required factors-of-safety have been met for weld H4.

SUMMARY

Based upon a review of the examination data for circumferential welds Hi through H7, there is substantial ,

margin for each of these welds under conservative, bounding conditions to allow for continued operation for  !

at least one twenty-four month cycle. The analyses performed included limit load analyses under bounding design basis conditions, and LEFM evaluations for the postulated highest fluence weld. The evaluations were performed with the assumption that all regions uninspected were cracked through-wall for all calculations. Additionally, all uninspected areas and areas with reported cracking were grown in the l ,

l length and depth directions at the bounding crack growth rate of 5 x 104 inches / hour, and increased in ,

length and depth by UT uncertainty factors. Required safety margins were used, and were exceeded in all -!

cases.

Very truly yours, Prepared by: Reviewed by:

Original Signed By: Original Signed By:

R. A. Mattson, P. E. M. L. Herrera, P. E.

pq Attachments l

l SIR-99-061/ RAM-99-053 l.

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Non-Proprietary Document l

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