ML091540015

Technical Specifications Changes TS-418 and TS-431 - Extended Power Uprate (EPU) - Response to Round 24 Request for Additional Information (RAI) EMCB.209 Regarding Steam Dryer Analyses

ML091540015
Person / Time
Site:	Browns Ferry
Issue date:	05/29/2009
From:	West R Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
EMCB.209, TAC MD5262, TAC MD5263, TAC MD5264, TVA-BFN-TS-418, TVA-BFN-TS-431
Download: ML091540015 (5)

Text

Tennessee Valley Authority, Post Office Box 2000, Decatur, Alabama 35609-2000 May 29, 2009 TVA-BFN-TS-418 10 CFR 50.90 TVA-BFN-TS-431 U.S. Nuclear RegulatoryCommission ATTN: Document Control Desk Mail Stop OWFN, P1-35 Washington, D. C. 20555-0001 In the Matter of

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Docket Nos. 50-259 Tennessee Valley Authority

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50-260 50-296 BROWNS FERRY NUCLEAR PLANT (BFN) - UNITS 1, 2, AND 3-TECHNICAL

-SPECIFICATIONS (TS) CHANGES TS-418 AND TS-431 - EXTENDED POWER UPRATE (EPU) - RESPONSE TO ROUND 24 REQUEST FOR ADDITIONAL INFORMATION (RAI) EMCB.209 REGARDING STEAM DRYER ANALYSES (TAC NOS. MD5262, MD5263, AND MD5264)

By letters dated June 28, 2004 and June 25, 2004 (ADAMS Accession Nos.

ML041840109 and ML041840301), TVA submitted license amendment applications to NRC for the EPU of BFN-Unit 1 and BFN Units 2 and 3, respectively. The proposed amendments would change the operating licenses to increase the maximum authorized core thermal power level of each reactor by approximately 14 percent to 3952 megawatts.

The enclosure provides the response for draft Round 24 RAI EMCB.209. This RAI is associated with the steam dryer stress analyses performed for EPU.

TVA has determined that the additional information provided by this letter does not affect the no significant hazards considerations associated with the proposed TS change. The proposed TS change still qualifies for a categorical exclusion from environmental review pursuant to the provisions of 10 CFR 51.22(c)(9).

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U.S. Nuclear Regulatory Commission Page 2 May 29, 2009 No new regulatory commitments are made in this submittal. If you have any questions regarding this letter, please contact J. D. Wolcott at (256) 729-2495.

I declare under penalty of perjury that the foregoing is true and correct. Executed on this 2 9 th day of May, 2009.

Sicerely,

. G. West Site Vice President

Enclosure:

Response to Round 24 Request for Additional Information (RAI) EMCB.209 Regarding Steam Dryer Analyses

U.S. Nuclear Regulatory Commission Page 3 May 29, 2009 Enclosure cc (Enclosure):

State Health Officer Alabama State Department of Public Health RSA Tower - Administration Suite 1552 P.O. Box 303017 Montgomery, Alabama 36130-3017 Ms. Eva Brown, Project Manager U.S. Nuclear Regulatory Commission (MS 08G9)

One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852-2739 Ms. Heather J. Gepford, Branch Chief U.S. Nuclear Regulatory Commission Region !1 Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303-8931 NRC Resident Inspector Browns Ferry Nuclear Plant 10833 Shaw Road Athens, Alabama 35611-6970

ENCLOSURE TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)

UNITS 1, 2, AND 3 TECHNICAL SPECIFICATIONS (TS) CHANGES TS-431 AND TS-418 EXTENDED POWER UPRATE (EPU)

RESPONSE TO ROUND 24 REQUEST FOR ADDITIONAL INFORMATION (RAI) EMCB.209 REGARDING STEAM DRYER ANALYSES NRC RAI EMCB.209 (Unit 1)

While conducting the steam dryer inspections during the Unit 2 Cycle 15 refueling outage, the licensee found the TB-3/4-01, TB-3/4-02, and TB-3/4-03 tie bars to be broken. The inspections also revealed that the TB-5/6-01, TB-5/6-02, and TB-1/2-02 tie bars were bent. Deformation of the center divider plate between banks 3 and 4 was also observed by the licensee. In addition, crack-like indications were noted on the TB-4/5-02 and TB-1/2-01 tie bars. This recent operating experience provides an opportunity to confirm the accuracy of the current approach of dynamic stress analysis of BWR steam dryer using the acoustic circuit model (ACM) Revision 4 to predict the dryer pressure loading for each planned dryer configuration for the three Browns Ferry units.

Therefore, TVA is requested to provide a Unit 2 dryer stress analysis for the existing dryer configuration, based on the dryer pressure loading for the current licensed thermal power [105 percent original licensed thermal power (OLTP)], as predicted by the ACM Rev. 4 Code, in order to demonstrate the analytical predictability of the above noted deformations of the tie bars and the center divider plate, as well as failures of certain tie bars.

TVA Response to EMCB.209 (Unit 1)

Fatigue cracking of tie bars has been observed since 2001 in plants operating at both OLTP and uprated power levels. These failures have been discussed in General Electric (GE) Services Information Letter (SIL) No. 644, "BWR Steam Dryer Integrity," and BWRVIP-139, "BWR Vessel and Internals Project Steam Dryer Inspection and Flaw Evaluation Guidelines." As discussed in these reports, the potential for cracking is related to the cross section of the tie bar itself because the tie bar must withstand the displacements and stresses imposed on these structures. BFN follows the inspection guidelines of BWRVIP-1 39 which include inspections of the tie bars.

During the current refueling outage on Unit 2, the steam dryer inspection has identified failed tie bars, tie bars with crack indications, bent tie bars, and deformation of the center divider plate.

Bent tie bars had been identified during previous inspections and were a pre-existing condition.

Replacement tie bars are being installed for the bent /failed tie bars and the bent tie bar with crack indications. The remaining tie bar with crack indications (not bent) will have a weld repair performed. The replacement tie bars are the re-designed tie bars with modified attachments to the dryer banks designed for EPU conditions. The replacement center tie bars have retainer lugs to hold the center divider plate in place instead of the welds that were used on the original angle iron tie bars.

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The ACM predicts steam dryer pressure loading which is used in the finite element model (FEM) stress analysis methodology to assess normal operation flow induced vibration (FIV) stresses.

The bending/deformation of the tie bars and center divider plate are not believed to be the result of FIV stresses and, therefore, would not be expected to be predicted by the ACM and FEM stress analyses. The tie bars failures, however, are indicative of fatigue failures and can be further evaluated by the stress analyses that have been performed for the BFN steam dryers.

TVA has previously identified failed tie bars on Unit 3 in 2003 and evaluated the analytical predictability of the tie bar failures in the response to. RAI EMCB. 134/101 provided by the March 6, 2008 submittal, "Response to Round 15 RAI Regarding Steam Dryer Analyses, Group 2." That evaluation was based on stresses at the tie bar connections to the vane banks for the FEM of the Units 2 and 3 steam dryer with minimal EPU modifications using a steam dryer load at current licensed thermal power (CLTP) conditions which included the 218 Hertz source and did not remove low flow noise. While the FEM included the modified GE designed tie bars, an approximation of stresses in the installed angle iron tie bars was performed based on cross section differences. This evaluation concluded that the stress analysis utilizing the ACM Revision 4 methodology correlates with the operational failure of the original angle iron tie bars.

TVA does not have a FEM that reflects the configuration of the Unit 2 steam dryer with the original angle iron tie bars. Therefore, the evaluation previously provided on the Unit 3 tie bars is the best available information for evaluating predictability. The tie bar failures on Unit 2 were similar to the previous failures of the Unit 3 tie bars. In both units, the tie bar failures were indicative of fatigue cracking and involved complete severing of the angle iron tie bar through its cross section. The previous evaluation for Unit 3 provided in the response to RAI EMCB. 134/101 was performed with a FEM that reflected both the Unit 2 and Unit 3 steam dryer configuration, and was based on the Unit 2 steam dryer load calculated from the Unit 2 main steam line strain gage signals at CLTP conditions. Therefore, the previous Unit 3 evaluation equally applies to the tie bar failures that were identified on Unit 2 and adequately demonstrates the analytical predictability of the stress analysis for Unit 2.

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