ML20206D544

Safety Evaluation of Topical Rept TR-107284, BWRVIP Vessel & Internals Project,Bwr Core Plate Insp & Flaw Evaluation Guideline (BWRVIP-25). Rept Acceptable for Insp & Flaw Evaluation of Subject safety-related Core Interal

ML20206D544
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Issue date:	04/28/1999
From:	NRC (Affiliation Not Assigned)
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o U.S. NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION SAFETY EVALUATION OF "BWRVIP VESSEL AND INTERNALS PROJECT. BWR CORE PLATE INSPECTION AND FLAW EVALUATION GUIDELINE (BWRVIP-2SL" EPRI REPORT TR-107284. DECEMBER 1996

1.0 INTRODUCTION

1.1 Background

By letter dated December 27,1996, the Boiling Water Reactor Vessel and intemals Project (BWRVIP) submitted the Electric Power Research Institute (EPRI) proprietary Reports TR-

, 107284, "BWR Vessel and Intemals Project, BWR Core Plate inspection and Flaw Evaluation '

Guideline (BWRVIP-25)," December 1996. This report was supplemented by a letter dated December 19,1997, which was in response to the stafi's request for additional information (RAl), dated March 14,1997.

The BWRVIP-25 report provides generic guidelines intended to present the appropriate inspection recommendations to assure safety function integrity of the subject safety-related reactor pressure vessel (RPV) intemal components it also provides design information on the core plate, gecmetries, weld locations, and potential failure locations for the several categories of boiling water reactors (BWR/2 through BWR/6).

1.2 Purpose The staff reviewed the BWRVIP-25 report to determine whether its guidance will provide  !

acceptable levels of quality for inspection and flaw evaluation of the subject safety-related RPV intemal components. The review considered the consequences of component failures,  !

potential degradation mechanisms and past service experience, and the ability of the proposed  !

inspections to detect degradation in a timely manner.

1.3 Organization of this Report Because the BWRVIP-25 report is proprietary, this SE was written so as not to repeat information contained in the report. The staff does not discuss in any detail the provisions of the guidelines nor the parts of the guidelines it finds acceptable. A brief summary of the contents of the BWRVIP-25 report is given in Section 2 of this SE, with a detailed evaluation in Section 3. The conclusions are summarized in Section 4. The presentation of the evaluation is structured according to the organization of the BWRVIP-25 report.

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ENCLOSURE

[ 2 2.0

SUMMARY

OF BWRVIP-25 REPORT i

The BWRVIP-25 report addresses the following topics:

Suscentibility Factors - The various types of material degradation mechanisms (e.g.,

fatigue, stress corrosion cracking, age embrittlement) that could impact the core plate are characterized. Materials, stress, and environmental factors are described in  !

general terms, followed by specific references to localized regions relative to plant operating experience for particular mechanisms and components.

Comoonent Descriotion and Function - The various core plate components are described in considarable detail by a series of illustrations along with brief descriptions of each component's function and materials / welding characteristics. Differences among the various models of BWRs (BWR/2, BWR 3-5, and BWR/6) are identified. .-

Potential Failure Locations and Safety Conseauences - Eatn of the' core plate components are addressed from the standpoint of inspection history, future susceptibility to degradation, and consequences of failures in terms of component q functions and plant safety. Based in these qualitative considerations, the BWRVIP-25  :

report makes recommendations as to the need for inspections for each of the lower -

plenum components. .

Backaround and insoection Historv- Data on service related failures of components are summarized. The major sources of such data are the various GE SILs and Rapid i information Communication Service Information Letters (RICSILs).

BWRVIP Insoection Guidelines - The guidelines recommend the specific locations, NDE methods, and inspection frequencies for examinations of core plate components.

Loads - This section defines the loading to be used in fracture mechanics 6 valuations to address the effects of detected flaws on structural integrity, and is based on the plant design and licensing basis. The various types of loads (e.g., pressures, seismic, etc.) of concem are listed.

3.0 STAFF EVALUATION With the exception of issues described below, this review finds that the guidance provided in the subject report to be acceptable. .

Item 3. Inspection Strategy The BWRVIP-25 report presents a conservative representative structural analysis of the core plate in order to determine which core plate locations require inspection to assure performance of core plate safety functions. The load magnitudes at various locations in the core plate were determined through finite element analysis. The finite element model consists of the core plate, including stiffener beam, stabilizer beams and rim and, in some cases, wedges. The core plate evaluation was broken into several parts by investigating the following scenarios:

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3 o' stiffener beam separation o ' tim hold-down bolts restraining the core plate

-o wedges restraining the core plate Based on the structural analysis presented in this report, the BWRVIP has determined that the rim hold-down bolts are the only core plate location which need to be addressed with a plant-specific inspection strategy. The BWRVIP has concluded that one of two plant-specific options for addressing the IGSCC susceptibility of the hold-down bolts can be selected:

1. inspect the core plate bolts to assure an adequate number are intact to prevent lateral displacement of the core plate; or, i

2. Install core plate wedges (BWR/6s already have wedges included in their designs) to strucerally replace the lateral load resistance provided by the rim hold-down bolts, in -

which case no inspections are required.

The BWRVIP-25 report presents a " baseline" approach for the first inspections performed.

Acceptable altematives to inspection to new BWRVIP requirements for the core plate are also presented for plants to consider, specifically involving plant-specific analysis or repairs and/or modifications. Reinspection scope and frequency have not been determined, but will be i

developed later based on " baseline" inspection results. l The staff believes that an initial baseline inspection should be comprehensive, and include all components that are practicable to inspect, based on tooling available. Further, the staff believes that a re-inspection schedule and scope, based on the performance and results of the initial baseline inspections, should be addressed. The staff requests that the BWRVIP address these in a revision to the BWRVIP 25 report.

Item 3.1.8 Location 8 - Aligner Pin Socket to Rim Welds The BWRVIP-25 report states that "[m]ovement of the core plate during a seismic event in such a way as to interfere with control rod insertion ... requires multiple failures of the rim hold-down bolts...." and "...as long as the critical number of bolts remain intact, lateral support for the core plate assembly is assured. ... Therefore, there is no safety consequences of failure at Location 8." ,

The BWRVIP's assumption for no safety consequences of failure at Location 8, that a critical number of rim hold-down bolts remains intact, is not adequately justified. The BWRVIP needs to either (a) expand its technical basis for this assumption, (b) expedite confirmatory inspections of the hold-down bolts, or (c) expedite replacement of the hold-down bolts with restraining wedges, as described in the " Top Guide / Core Plate Repair Design Criteria (BWRVIP-50)" report, dated May 14,1998 (presently under staff review).

L ltem 3.1.9 Location 9 - Core Plate Wedge Retainer The BWRVIP's technical basis for its assumption that the BWR/6 core plate wedge retainers "would remain in approximately their designed location and would perform their intended function," even if the tack-welded bolts used to retain the keepers failed, should be expanded l

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upon for accident and upset conditions, where it is assumed that the wedges are no longer restrained by bolts.

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4.0 CONCLUSION

S The staff has reviewed the BWRVIP-25 report and finds that the guidance of the report is acceptable for inspection and flaw evaluation of the subject safety-related core intemal components, except where the staff's conclusions differ from the proposed guidance, as discussed above. The staff requests that the BWRVIP review and resolve the issues raised above, and incorporate the staff's conclusions into revised BWRVIP-25 report. Please inform the staff in writing as to this resolution.

5.0 REFERENCES

i 1.- Cari Terry, BWRVIP, to USNRC, "BWR Vessel and intemals Project, Core Plate l Inspection and Flaw Evaluation Guidelines (BWRVIP-25)," EPRI Report TR 107284, l December 1996, dated December 27,1996.

2. Carl Terry, BWRVIP, to USNRC, "BWR Vessel and intemals Project, Top Guide j inspection and Flaw Evaluation Guidelines (BWRVIP-25)," EPRI Report TR-107285, I j December 1996, dated December 27,1996.  !

l l 3. C. E. Carpenter, USNRC, to Carl Terry, BWRVIP, " Proprietary Request for Additional J Inforraation - Review of BWR Vessel and Intemals Project Reports, 'BWR Core Plate insper tion and Flaw Evaluation Guidelines (BWRVIP-25),' and ' Top Guide Inspection l and Flaw Evaluation Guidelines (BWRVIP-26),'(TAC Nos. M97802 and M97803),"

dated March 14,1997.

l 4. Vaughn Wagoner, BWRVIP, to USNRC, "BWRVIP Response to NRC Request for Additional Information on BWRVIP-25 and BWRVIP-26," dated December 19,1997, i

Principal Contributors: C. E. Carpenter K.A.Kavanagh

, J. R. Rajan

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