ML20217J805

to Safety Evaluation of EPRI Topical Rept TR-105747, BWR Vessel & Internals Project,Guidelines for Reinspection of BWR Core Shrouds (BWRVIP-07)

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Issue date:	04/27/1998
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U.S. NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION DIVISION OF ENGINEERING SUPPLEMENT 1 TO THE SAFETY EVALUATION OF EPRI TOPICAL REPORT TR-105747 "BWR VESSEL AND INTERNALS PROJECT. GUIDELINES FOR REINSPECTION OF BWR CORE SHROUDS (BWRVIP-07)"

1.0 INTRODUCTION

By letter dated February 29,1996, as supplemented by letters dated July 17, May 21, and October 21,1996, and January 8,1997 (References 1,2,3,4, and 5, respectively), the Boiling Water Reactor Vessel and intemals Project (BWRVIP) submitted the Electric Power Research Institute (EPRI) Topical Report TR-105747, "BWR Vessel and Intemals Project, Guidelines for Reinspection of BWR Core Shrouds"(BWRVIP-07), for staff review and approval. In References 2 and 3, the BWRVIP clarified the content of the BWRVIP-07 report, and supplemented the content of the guidelines with additionalinformation in Reference 4. The BWRVIP further modified the guidelines in the BWRVIP-07 report in Reference 5.

On September 15,1997, the staff issued its safety evaluation (Reference 6) of the BWRVIP-07 report. The staff found the guidance generally acceptable but identified several open issues.

Representatives of the BWRVIP met with the NRC staff on November 5,1997, to discuss these issues and documented their proposed resolution in their submittal of November 26,1997 (Reference 7). The staff is issuing this supplement to its September 15,1997, SE to close the open issues.

2.0 DEFINITIONS in t'se staff's evaluation, several terms in the BWRVIP-07 report are referenced in discussion.

Fr r clarification, these terms are defined in the attachment.

3.0 STAFF EVALUATION For a detailed description of the issues discussed in this supplement, see Reference 6. These issues are considered as belonging to three categories: (1) issues upon which the staff and BWRVlP differ, (2) issues for which the response is incomplete, and (3) issues for which the BWRVIP response was adequate.

3.1 issues Upon Which the Staff and BWRVIP Differ

' The staff and the BWRVIP differ about the resolutions to the following issues. These issues all concem the use of Lmin, L' min, or Table 1 in the BWRVIP-07 report to determine reinspection intervals for Category B and C plants.

5NCLOSURE 9804300319 980427 PDR TOPRP EXIEPRI C PDR

2 lasue 3.1.1 1 Use of Lmin to Determine Reinspection Intervals for Category B Shrouds issue 3.1.1-2 Use of Option A to determine inspection Intervals for Category B Core Shrouds issue 3.1.13 (1) Use of Option B (L' min Equation) to Establish the Reinspection Intervals for Category B Core Shrouds issue 3.1.2-1 (1) Use of Lmin to Determine the Reinspection Intervals for Category C Core Shrouds issue 3.1.2-2 Use of the L' min Equation to Determine the Reinspection Inte;vals for Category C Core Shrouds issue 3.1.2-3 Use of Table 1 to Determine Reinspection Intervals for Category C Core Shrouds issue 3.1.3 Acceptable Altemative to Table 1 of the BWRVIP-07 report for Interim Use in determining Reinspection intervals (Table A)

Issue 3.2.4-1 Use of Option A for Reinspection of ring Segment Welds Staff Conclusion Because of uncertainties about crack initiation in the unflawed region and the lack of reinspection data to support the multiple-cycle reinspection intervals proposed in the BWRVIP-07 report, the staff has concluded that it is necessary to incorporate an additional conservatism into the Lmin, L' min, and Table 1 methodologies used to determine reinspection intervals. The staff has concluded that the reinspection interval (years), calculated according to the BWRVIP-07 guidelines, needs to be reduced to (n/2 + 1), when the calculated reinspection interval (n) is longer than two years. If the reinspection interval does not coincide with a refueling outage for the time calculated, the reinspection needs to be performed at the refueling outage that precedes the time calculated. After successful completion of at least three consecutive reinspections, the staff may remove the additional conservatism on a case-by-case basis when adequately justified.

1 3.2 lasues That Still Need to be Addressed The BWRVIP has not addressed the following issues:

lasue 3.1.1-4 and 3.1.2-4: Inspection of Vertical Welds The proposed reinspection of unrepaired core shrouds for both Category B and Category C plants is limited to horizorital(i.e., circumferential) welds only. The staff has concems about the functionability of the shroud if a vertical weld were to completely fail and an intersecting

- circumferential weld had extensively cracked. Therefore, the staff requested that BWRVIP-07 evaluate this potential condition and provide for inspecting the vertical welds to ensure functionality if such cracking of the circumferential welds were to occur.

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. BWRVIP Response The BWRVIP is currently developing inspection guidance for vertical welds. These guidelines will be submitted to the NRC when complete.

Staff Conclusion The staff will review the proposed inspection guidance when submitted. The staff has previously determined, in a plant-specific case, that the licensee could continue to safely operate. This was

. done using bounding crack growth rate calculations for the most severe vertical cracking seen to date. The staff considers the results to be applicable generically. Therefore, the staff has concluded that waiting for a timely submittal on this issue will not endanger public health and safety.

3.3 lasues Considered Closed Based on the BWRVlP's Response L issue 3.1.1-3 (2). (3): Use of Option B to Establish the Reinspection Intervals for Category B Core Shrouds This item concemed the assumption that the inspection uncertainty is not to exceed 2t (t = wall thickness). Previous analyses have used other values, including 4t. All values used for inspection uncertainties need to be demonstrated and technically justified.

BWRVIP Resoonse BWRVIP will revise the BWRVIP-07 report to require allinspection uncertainties be determined in accordance with the BWRVIP-03 guidelines.

Staff Conclusion The staff finds this response adequate. This issue is closed.

Issue 3.1.2-1 (2): Use of Lmin to Determine the Reinspection intervals for Category C Core Shrouds l The guidelines stated that if a Category C plant cannot be inspected for Lmin, the acceptability l

and inspection interval of the weld are to be determined on a case-by-case basis. The staff requests that such determinations be submitted to the NRC for review and approval.

BWRVIP Response Plant-specific analyses need to be submitted to the NRC for review and approval.

Staff Conclusion The staff finds this response adequate. This issue is closed.

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4 lasue 3.2.1-1: Recommended Generic Criteria Regarding Reinspection of Core Shroud Repair

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l Industry experience suggests that the generic recommendations of the BWRVIP-07 report may not be adequate for reinspection of components used in core shroud repair modifications. The staff recommended including a provision in the guidelines for expanding the inspection sample if degradation of the repair components is found.

BWRVIP Resoonse The BWRVIP stated that it will revise the guidelines to require expanding the sample if degradation of the repair components is discovered. it also proposed two reinspcc,tien options and will amend the guidelines to identify other options to verify bolt tightness.

Staff Conclusion l ' The staff finds this response adequate. This issue is closed.

Issue 3.2.1-2: Recommendation to Review Current Set of Assumptions Used in Analyses of Core Shroud Repair Modifications The staff recommended that the guidelines specify reviewing the design assumptions for the l repair and a pre-repair inspection for all future repairs to ensure the minimum ligaments L assumed present actually are present. The staff recommended an inspection schedule in its original SE.

BWRVIP Resoonse The BWRVlP proposed an attemative. The BWRVIP addressed this issue in its response to issue 3.2.1-1 above.

Staff Conclusion The staff finds this response adequate. This issue is closed.

Issue 3.2.2-1: Justification for Omitting Pre-Inspections of Components Used for the Core Shroud Repair Anchorages.

, The guidelines state that, in the absence of a pre-repair inspection, a licensee should perform an j; inspection in the first operating cycle after the repair is completed. However, the guidelines did not justify not performing a pre-repair inspection. Welds H8 and H9 need to be included in this l inspection to ensure that all the repair design assumptions are met.

l BWRVIP Response This provision will be deleted from the BWRVIP-07 report because it is outdated. The Shroud Repair Design Criteria (BWRVIP-02) report will be revised to clarify the requirements for pre-repair inspection of repair anchorages. Pre-repair inspections will not be specifically discussed l

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in the BWRVIP-07 report except to require that the pre-repair inspection requirements of the r-BWRVIP_-02 report have been met.

Staff Conclusion-The staff finds this response adequate. This issue is closed.

- lacue 3.2.2-2: Recommended Practices for Reinspections of Gussets, Brackets and Repair Anchorages The BWRVIP is currently preparing another document to address inspection requirements for welds H8 and H9, as well as the shroud support structure (which includes gussets and '

brackets). The staff recommended that licensees reinspect the repair anchorages and set the reinspection intervals according to those of the repair components. The staff recommended that it would be preferable to address welds H8 and H9 in anchorages associated with the repair in

. the context of these BWRVIP-07 guidelines (rather than in a separate document). i l

BWRVIP Response I The BWRVIP-07 report was prepared consistent with the staff's recommendation of addressing repair anchorage welds in this document rather than in a separate document. The H9 weld is typically not considered part of the repair anchorage and falls within the scope of inspections for the shroud support. Also, the H8 weld is typically not part of the repair anchorage.

The BWRVIP agrees that the frequency of reinspections of the repair assemblies and anchorages should be consistent and proposes a schedule as indicated in its response on repair assemblies.

Staff Conclusion The staff finds this response adequate. This issue is closed.

Issue 3.2.2-3: Recommendations for Technical Analyses to Verify the Effect of Cracking on Gusset Stiffness The guidelines state that minor cracking in a gusset weld would not affect the effectiveness of a shroud repair and that the stiffness of the gusset is not significantly affected if there is no gross through-thickness cracking. The staff recommended that the guidelines of the BWRVIP-07 report be amended to recommend that technical analyses be performed to verify the validity of this assumption.

BWRVIP Response BWRVIP-07 was prepared recognizing that cracking of a gusset weld would require specific analysis and disposition regardless of whether or not there is a specific requirement in this document. Therefore a recommendation for an analysis was not included.

A specific recommendation for technical analysis is included in the BWRVIP-38 report.

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6 Staff Conclusion i

The staff finds this response adequate. This issue is closed.

Issue 3.2.2-4: BWRVIP-07 Recommended Intervals for Reinspection of BWR Core Shroud Repair Assemblies The staff recommended a more conservative reinspection schedule for repair anchorages and adding a provision requiring sample expansion if degradation is found.

BWRVIP Response The BWRVIP addressed this issue in its response to issue 3.2.1-1 above.

Staff Conclusion -

The staff finds this response adequate. This issue is closed.

Issue 3.2.3-1: General issue Regarding the Proposed Guidelines for Reinspection of Vertical Welds in Repaired Shrouds The staff recommended reinspecting vertical welds needed to ensure structural integrity to confirm that the design assumptions remain valid and that licensees perform baseline inspections of the vertical welds. This recommendation replaces the existing guidelines which specify using Option A or Option B.

BWRVIP Resoonse The BWRVIP-02 and -07 reports will be revised to clarify requirements for inspecting vertical v.sids and address the NRC's concems.

Staff Conclusion i

The staff finds this response adequate and will review the schedule when provided. ]

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Jgue 3.2.3-2: Use of Option A or Option B for Reinspections of Vertical Welds in Repaired Core  !

Shrouds This item concemed the staff's recommendations about resolving shortcomings in Option A and

. Option B. The staff also recommended that licensees inspect the same location of some other ,

vertical welds at the same elevation; that samples include the vertical welds near the beltline i exposed to high fluence and that in selecting welds for reinspection, licensees should  :

emphasize welds with high susceptibility to IGSCC or irradiation-assisted stress corrosion l cracking (IASCC).- l BWRVIP Resoonse The BWRVIP-02 report is being revised to address the staff's concems about the pre-repair ,

inspection of vertical welds. '

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7 The BWRVIP-07 report is being revised to include requirements for the reinspection of vertical welds both for repaired and unrepaired shrouds and for sample emansion. In selecting welds for reinspection, the BWRVIP-07 report will require emphasizing vertical welds with high susceptibility to IGSCC or lASCC.

Staff Conclusion The staff finds this response adequate and will review the schedule when provided.

Issue 3.2.4-2: Use of Option B for Reinspections of Ring Segment Welds In this item, the staff made recommendations about baseline inspections and sampling of ring segment welds.

BWRVIP Response i

The BWRVIP-02 report is being revised to address the pre-repair inspection of ring segment welds.

The BWRVIP-07 report is being revised to include requirer:ents for the reinspection of ring segment welds both for repaired and unrepaired shrouds. In selecting welds for reinspection, the BWRVIP-07 report will require emphasizing vertical welds with high susceptibility to IGSCC or IASCO.

j Staff Conclusion i The staff finds this response adequate. This issue is closed.

4.0 FINAL CONCLUSIONS The staff concludes that the following changes are needed for the report to provide an  ;

acceptable level of quality for inspection and assessment of the subject safety-related core l shroud.

Because of uncertainties about crack initiation in the unflawed region and the lack of l reinspection data to support the multiple-cycle reinspection intervals proposed in the  !

BWRVIP-07 report, the staff has determined that the BWRVIP needs to incorporate an additional conservatism into the Lmin, L' min, and Table 1 methodologies used to

- determine reinspection intervals.

The staff concludes that the reinspection intervals (years) determined according to Lmin, L' min, and Table 1 methodologies need to be reduced to (n/2 + 1), when the calculated ,

reinspection interval (n) is longer than 2 years if the reinspection interval does not coincide with a refueling outage for the time calculated, the reinspection needs to be performed at the refueling outsp that precedes the time calculated. After successful completion of at least three consecutive reinspections, the staff may remove the  !

additional conservatism on a case-by-case basis when adequately justified. l t

8 Guidance regarding the inspection of vertical welds in unrepaired shrouds is needed and should be submitted for staff review in a timely manner.

The BWRVIP needs to revise the BWRVIP-07 report to include: (1) the changes stated above, (2) the inspection guidance for the vertical welds once the staff approves it, and (3) its proposed responses to the remaining issues, as discussed in Section 3.3, all of

, which are considered resolved.

l 5.0 BIBLIOGRAPHY AND REFERENCES

1. February 29,1996 - Letter from J.T. Beckham, Chairman - BWRVIP, to the U.S. Nuclear  ;

Regulatory Commission Document Control Desk, "'BWR Vessel and intemal Project, i Guidelines for Reinspection of BWR Core Shrouds (BWRVIP-07)' EPRI Report TR-105747, February 1996."

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2. July 17,1996 - Letter from V. Wagoner, Chairman - BWRVIP integration Committee, to  !

C. Carpenter, U.S. Nuclear Regulatory Commission: " Clarification to Core Shroud l Reinspection Guidelines."

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3. May 21,1996 - Letter from C.E. Carpenter, Lead Project Manager, U.S. Nuclear Regulatory Commission, to J.T. Beckham, Jr., Chairman - BWRVIP, submitting " Request for Additional information - Review of BWR Vessel and Intemals Project Proprietary Report, 'BWR Vessel and Intemals Project, Guidelines for Reinspection of BWR Core Shrouds (BWRVIP-07)."

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4. October 21,1996 - Letter from Larry Stewart, Acting on behalf of Robin Dyle, BWRVIP

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Technical Chairman, to the U.S. Nuclear Regulatory Document Control Desk, submitting the "BWRVIP Response to Request for Additional Information Regarding Proprietary Topical Report EPRI TR-105747."

5. January 8,1997 - Letter from W. Bilanin, Acting on behalf of Robin Dyle, BWRVIP .

Technical Chairman, to the U.S. Nuclear Regulatory Document Control Desk, submitting the

" Modification to BWRVIP Response to NRC Request for Additional Information on BWRVIP-07."

l 6. September 15,1997 - NRC letter to the BWRVIP submitting the staff s ' Safety Evaluation of EPRI Topical Report TR-105747 "BWR Vessel and Intemals Project, Guidelines for Reinspection of BWR Core Shrouds (BWRVIP-07)."

7. November 26,1997, Letter from Larry Steinert, BWRVIP, to U.S. Nuclear Regulatory Commission Document Control Desk," Response to NRC Staff Safety Evaluation of the BWR Vessel and Intemals Project BWRVIP-07 Report.

1 Technical Contacts: M. J. Banic W. H. Koo

9 DEFINITIONS OF TERMS USED IN THE BWRVIP-07 REPORT Category B plant: plants operated more than eight hot operating years with core shrouds made with Type 304L stainless steel (Iow carbon content) and average conductivity less than 0.3 S/cm during the first five cycles of operation.

Category C plant: plants operated more than six hot operating years with core shroud made with Type 304 stainless steel (high cart >on content) or plants operated more than eight hot operating years with core shrouds made of Type 304L stainless steel (Iow carbon content) and average conductivity greater than

0.3 S/cm during the first five cycles of operation.

Lmin: the minimum required length of uncracked weld, including two cycles of crack growth, to ensure the structural integrity of the weld.

L' min: the minimum required length of uncracked weld, including an allowance of crack growth up to a maximum of 6 years, to ensure the structuralintegrity of the weld.

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L' min is the sum of the minimum required length of sound weld (assuming inaccessible regions are 100 percent cracked) and the crack growth over the desired inspection interval (crack growth rate of 5 x 10~5 in/hr).

Option A: inspection strategy for category B plants that requires 100% inspection of all accessible areas of the shroud we!ds H3, H4, H5, and H7. If the cracking is found to be greater than 10 percent in any weld, then full inspections are required in accordance with the requirements for Category C plants.

Option B: Inspection strategy for category B plants that allows inspection of a length of l L' min for the welds specified in Option A.")

l t: the wall thickness Table 1: provides core shroud reinspection intervals for Category C plants. The reinspection intervalis a function of the degree of cracking and the stress levelin the weld.

Table 2: provides a summary of the crack length assumption used in determining the reinspection intervals in Table 1.

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It should be noted that Options A and B vary slightly depending on which welds are being discussed. To more fully describe these Options would require publicly providing information that the NRC staff has determined to be proprietary in nature.