ML20210V291

Provides Response to NRC Bulletin 96-003, Potential Plugging of ECCS Strainers by Debris in BWRs Per Request During 970821 Meeting

ML20210V291
Person / Time
Site:	Browns Ferry
Issue date:	09/16/1997
From:	Abney T TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
IEB-96-003, IEB-96-3, TAC-M96135, TAC-M96136, TAC-M96137, NUDOCS 9709230232
Download: ML20210V291 (7)

Text

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Termessee Vahey Authortty, Post Offee Box 2000, Decatur, Alabama 35609-2000 September 16, 1997-U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555

-Gentlemen: i In the Matter of ) Docket Nos. 50-259 Tennessee Valley Authority ) 50-260-50-296 BFN NUCLEAR PLANT BROWNS FERRY NUCLEAR PLANT (BFN) - NRC i- BULLETIN 96-03, POTENTIAL PLUGGING OF EMERGENCY CORE COOLING SYSTEMS (ECCS) STRAINERS BY DEBRIS IN BOILING-WATER REACTORS

-(TAC NOS M96135, M96136, M96137)

This letter provides information requested by.NRC during a meeting on August 21, 1997, between TVA management, General Electric and-the staff. Specifically, NRC requested that TVA describe any changes made in the BFN Long-Term Torus Integrity Program structural analysis, in response to NRC Bulletin.96-03.

The Enclosute provides the requested information. Additional detailed technical justification for.the changes described by the enclosure was presented to NRC during the August 21, 1997, meeting and therefore, is not repeated in the-enclosure.

There are no commitments contained in this letter.

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U.S._ Nuclear Regulatory Commission Page 2: 1 September _16, 1997 j If you have any questions, please telephone me at (205) 729-

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Mr. Mark S.' Lesser, Branch Chief U.S. Nuclear Regulatory Commission 61 Forsyth Street, S.W.

Suite 23T85 Atlanta, Georgia 30303 NRC Resident Inspector BFN Nuclear Plant 10833 Shaw Road-Athensi Alabama 35611 Mr. J. . F.. Williams, Project Manager

-U.S.-Nuclear Regulatory Commission-One White-. Flint, North 11555 Rockville Pike LRockville, Maryland 20852 M

ENCLOSURE TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)

UNITS 1, 2, AND 3 NRC BULLETIN 96-03 POTENTIAL PLUGGING OF EMERGENCY CORE COOLING SYSTEMS (ECCS) SUCTION STRAINERS BY DEBRIS IN

'3 OILING-WATER REACTORS This enclosure provides the inrormation requested by NRC during the August 21, 1997, meeting on NRC Bulletin 96-03. It describes L the changes made in the BFN.Long-Term Torus Integrity Program

) structural analysis, in response to NRC Bulletin 96-03.

I. Structural Design Basis The structural design basis for the ECCS strainers, penetrations, headers, and attached piping systems was established by the Long Term Torus Integrity Program (LTTIP)

Plant Unique Analysis Report (PUAR) (Reference 1) and the associated NRC Safety Evaluation Report (SER) (Reference 2).

II. Replacement Strainer Description The BFN ECCS suction replacement-strainers are General Electric (GE) stac).ed disc type strainers, approximately 45 inches in diameter and 49 inches tall. The strainers replace existing basket type which are approximately 24 inches in diameter and 20 inches tall. The replacement

-strainers will be securely fastened to previously existing 30-inch diameter flanges located approximately one foot inside the associated ECCS suction penetrations. No other mounting support or brace is required for the replacement strainers.

III. Updated Methodology and Criteria The BFN replacement strainers, associated ECCS suction header / piping systems, and penetrations have been structurally qualified to LTTIP design criteria and methodology as described in the PUAR with the following changes:

1. Effective Water Masses And Velocity Drag Coefficients The ECCS suction header / piping models were-modified by TVA-to represent the added mass of the replacement strainers and associated effective water mass in the axialiand cross axis directions. Replacement strainer stiffness was based on structural properties determined

-from a detailed-GE structural model.

The defined effective water mass for the BFN strainers-was based on analysis which was subsequently verified by test of the prototype strainer. The effective water mass used for structural analysis of the BFN strainers was more than 30 percent conservative in the critical cross-axis direction. ,

i Hydrodynamic drag load factors were based on comparison of the size,-location, effective water mass, and l

E velocity drag coefficients.for the replacement and previously existing strainers. Applied hydrodynamic drag loads for the existing strainers were defined'for the LTTIP by assuming the perforated wall basket. type-strainers to be solid wall cylinders. TVA calculated the applied hydrodynamic drag loads for the replacement strainers by multiplying the existing strainer applied loads for each loss of coolant accident (LOCA)' and main steam relief valve (MSRV) load case by the hydrodynamic load factors. TVA then calculated acceleration drag responses for each load case based on characteristic frequencies determined from the modified ECCS suction header / piping model. Acceleration drag responses dominated the overall drag loads.

Application of.the effective water masses and velocity drag coefficients in this manner is technically adequate, and consistent with the acceptance criteria considered in the BFN LTTIP SER (1.e. NUREG-0661-Appendix A Section .2:.14 and PUAR- Section 4) . There has been an increase in the accuracy of applied hydrodynamic load calculations for the: replacement strainers relative to the existing trainers.

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2. MSRV Load Reduction Factors Load reduction factors for the single and multiple MSRV torus dynamic response effects (0.5 and 0.6, respectively)-were defined by TVA based on correlation of the test results from the LTTIP post-modification in-plant MSRV tests, described in Appendix C of the PUAR, with the ECCS suction header / piping analyses for those conditions. While these factors were not utilized in l the original ECCS headet/ piping analysis, NUREG 0661 Appendix A Section 2.13.9 and PUAR Sections 4.2.2.1, i C.9.3, and C.10 indicate the method is acceptable. A margin of more than 50 percent is preserved between analytically predicted stresses in the ECCS header and penetration, using the load reduction factors, and the in-plant test measurements at those locations.

l The MSRV load reduction factors were applied to the torus dynamic response MSRV inertial inputs (e.g.,

response spectra) for the ECCS suction header / piping and associated torus penetrations analyses.

Application of the MSRV load reduction factors for the ECCS header / piping system removed some margin between the design loads for LTTIP modifications and the loads justified by the LTTIP post-modification in-plant MSRV tests. However, substantial margin is retained.

The acceptance criteria considered by the BEN LTTIP SER (i.e. NUREG-0661 Appendix A Section 2.13.9 and PUAR Section 4) permit use of MSRV in-plant test data in this manner. An increase in actual stresses was observed during the analysis for the replacement strainers.

Additional insitu test load reduction factors were justified and applied as allowed by existing design basis. The structural adequacy of the ECCS penetrations, header, and piping systems was confirmed within existing criteria.

3. Strainer Qualification The existing strainers were qualified for the LTTIP to a safety factor of three against structural failure.

Structural qualification of the replacement strainers and mounting bolts was performed using a detailed finite element model and enveloping inertia and drag loads.

The inertia loads were defined by reanalysis of the ECCS suction header / piping systems for the modified models.

Service levels for LTTIP load combinations were established per Mark I Containment Program Structural E-3

Acceptance Criteria - Plant' Unique Analysis Application Guide-(PUAR Reference 13) Table 5.1 for Class MC components. Strainer stresses comply with the allowable stress requirements of ASME Code Section III, 1989 Edition -(Subsection NC except' Subsection NG for welds) at applicable' service levels.

. Compliance wtth these ASME Code requirements, for the drag and inertia loads described above, ensures improved structural adequacy for the replacement strainers 1 relative to the existing strainers. The acceptance

, criteria considered by the BFN LTTIP SER (i.e. NUREG-0661 Appendix A Section 3 and PUAR Section 4) permit definition of allowable stresses for ECCS suction strainers in this manner.

Accordingly, the BFN LTTIP design criteria has been revised to:

1. Require the use of replacement strainer effective water masses and velocity drag coefficients based on GE test and analysis data for the strainers;

2. Require the definition of MSRV load reduction factors for the ECCS suction header / piping systems, penetrations, and s Tainers; and,

3. Establish the allowable- stress criteria for the replacement strainers._

1 IV. Conclusion

-While some reductions in structural' margin exist based _on new strainer mass and applied loads, the structural margin of safety for the torus has_been retained. _ Overall, the margin of; safety for-_the facility has been increased because the replacement strainers will have a significantly-larger surface-area; thus, increasing the plants tolerance to debris loading during a postulated LOCA.

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VI. References

1. TVA letter to NRC dated, January 25, 1985, in regards to BFN Nuclear Plant, Torus Integrity Long Term Program, Plant Unique Analysis Report (PUAR), TVA Report No. CEB-83-34, Revision 2, December 12, 1984

2. NRC letter to TVA dated, May 6, 1985, in regards to Safety Evaluation of BFN Nuclear Plant, Units 1, 2, and 3, Mark I Containment Long-Term Program, Dynamic Loads Review E-5 o

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