ML070570544
| ML070570544 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 02/16/2007 |
| From: | O'Grady B Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| TAC MC3743, TAC MC3744, TAC MC3812, TVA-BFN-TS-418, TVA-BFN-TS-431 | |
| Download: ML070570544 (11) | |
Text
February 16, 2007 TVA-BFN-TS-431 TVA-BFN-TS-418 10 CFR 50.90 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Stop OWFN, P1-35 Washington, D. C. 20555-0001 Gentlemen:
In the Matter of
)
Docket Nos. 50-259 Tennessee Valley Authority )
50-260
)
50-296 BROWNS FERRY NUCLEAR PLANT (BFN) - UNITS 1, 2, AND 3 -
TECHNICAL SPECIFICATIONS (TS) CHANGES TS-431 AND TS-418 -
EXTENDED POWER UPRATE (EPU) - OUTLINE OF APPROACH TO STEAM DRYER EVALUATIONS (TAC NOS. MC3812, MC3743, AND MC3744)
By letters dated June 28, 2004 and June 25, 2004 (ADAMS Accession Nos. ML041840109 and ML041840301, respectively),
TVA submitted license amendment applications to the 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 to 3952 megawatts.
As part of EPU applications for the BFN units, TVA has provided information needed by the NRC staff to evaluate the structural capability of the BFN steam dryers for the proposed EPU conditions. Because the NRC staff does not consider the information provided to date in the EPU applications to be sufficient to adequately evaluate the capability of the steam dryers to maintain their structural integrity at the proposed conditions, TVA has undertaken additional steps to address NRC concerns, as outlined in the enclosure to this letter.
U.S. Nuclear Regulatory Commission Page 2 February 16, 2007 By letter dated January 31, 2007, TVA stated that an outline of a revised steam dryer approach would be provided as part of the steam dryer stress analysis that is scheduled for submittal to NRC by April 2, 2007. To advance the review process, the enclosure to this letter is an outline of TVAs approach for providing the NRC staff with sufficient information regarding steam dryer evaluations and measures to demonstrate reasonable assurance that the BFN steam dryers will maintain structural integrity at extended power uprate conditions.
TVA anticipates that timely execution of the actions outlined will allow NRC to complete its draft safety evaluation for the EPU of the BFN units.
No new regulatory commitments are made in this submittal.
If you have any questions regarding this letter, please contact Bill Crouch at (256)729-2636.
Sincerely, Original signed by:
Brian OGrady
Enclosure:
Outline of Approach to Steam Dryer Evaluations
U.S. Nuclear Regulatory Commission Page 3 February 16, 2007 Enclosures cc: (Enclosures):
State Health Officer Alabama Dept. of Public Health RSA Tower - Administration Suite 1552 P.O. Box 303017 Montgomery, AL 36130-3017 U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303-3415 Mr. Malcolm T. Widmann, Branch Chief U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303-8931 NRC Senior Resident Inspector Browns Ferry Nuclear Plant 10833 Shaw Road Athens, Alabama 35611-6970 NRC Unit 1 Restart Senior Resident Inspector Browns Ferry Nuclear Plant 10833 Shaw Road Athens, Alabama 35611-6970 Margaret Chernoff, Project Manager U.S. Nuclear Regulatory Commission (MS 08G9)
One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852-2739 Ms. Eva A. Brown, Project Manager U.S. Nuclear Regulatory Commission (MS 08G9)
One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852-2739
U.S. Nuclear Regulatory Commission Page 4 February 16, 2007 JEM:LTG:BAB cc (w/o Enclosures)
M. Bajestani, NAB 1A-BFN A. S. Bhatnagar, LP 6A-C D. C. Matherly, Jr.
R. H. Bryan, Jr., LP 4J-C J. C. Fornicola, LP 6A-C R. G. Jones, POB 2C-BFN G. V. Little, NAB 1D-BFN R. F. Marks, Jr., PAB 1C-BFN B. A. Wetzel, BR 4X-C B. J. OGrady, PAB 1E-BFN K. W. Singer, LP 6A-C P. D. Swafford, LP 6A-C E. J. Vigluicci, ET 11A-K NSRB Support, LP 5M-C EDMS WT CA-K, (w/Enclosures) s:lic/submit/EPU/TS 418 and 431 - approach to steam dryer.doc
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) -
OUTLINE OF APPROACH TO STEAM DRYER EVALUATIONS Enclosed is TVAs Outline of Approach to Steam Dryer Evaluations for EPU.
BFN Steam Dryer Approach for EPU E-1
- 1.
Purpose This document provides an outline of TVAs approach for providing the NRC staff with sufficient information regarding steam dryer evaluations and measures to demonstrate reasonable assurance that the BFN steam dryers will maintain structural integrity at extended power uprate (EPU) conditions.
- 2.
Summary TVA will provide the NRC with its evaluations of the effects of the proposed EPU on the steam dryer and planned actions to reasonably assure that the steam dryer will operate safely considering the potential for flow-induced degradation.
As described herein, TVA has revised its approach to the evaluation of steam dryer at EPU conditions. Figure 1 illustrates the basic steps being taken.
Following TVAs July 26, 2006 (ADAMS ML062200279), submittal of a steam dryer stress analysis report and the identification of concerns by the NRC staff regarding certain inputs and assumptions affecting specific aspects of the analysis, TVA modified its approach to demonstrating the adequacy of the BFN steam dryers at EPU. The approach now includes the following:
Comprehensive analysis techniques that use actual BFN plant operating data; A re-assessment of the physical loads imposed on the steam dryer using an improved load definition methodology that more accurately represents acoustic forces and incorporates actual steam line pressure data obtained from BFN Unit 2; An additional steam dryer design modification; A revised stress analysis of steam dryer components using inputs and assumptions, including the treatment of damping and time steps that the NRC staff has previously found acceptable in the review of steam dryer analysis; and A power ascension program, based on a program previously found acceptable by the NRC, to verify acceptable steam dryer performance at EPU conditions.
BFN Steam Dryer Approach for EPU E-2
- 3.
Plant-Specific Operating Data During the fall of 2006, TVA entered a mid-cycle outage of Unit 2 to install 64 strain gages on the main steam lines for the purpose of obtaining fluctuating pressure information for plant conditions up to 105% of original licensed thermal power (OLTP). Arrays of eight strain gages were installed at two locations on each main steam line between the reactor pressure vessel nozzle and the main steam line safety relief valves. The strain gages were located at distances from the steam dome that, to the extent possible, match the Quad Cities Unit 2 gage locations that were used for the benchmarking of the acoustic circuit methodology (on a vertical section of the main steam piping, approximately 9 and 42 from the reactor vessel). The arrays were oriented to measure the circumferential strains (hoop stress) in the piping. The differential pressures inside the steam lines were then calculated based on the hoop stress. To improve the quality of the data collected, signal content originating from background electrical noise detected by the strain gages was removed. This information was used to more clearly define the actual data important in the development of the load definition.
The same strain gage installation will be made on Units 1 and 3 (Unit 1 prior to spring 2007 restart; Unit 3 during the spring 2008 refueling outage).
- 4.
Load Definition Improvements have been made in acoustic circuit modeling to provide greater correlation of low frequency (0 to 80 Hz) content. The model now includes load content to account for high frequency input, as well as low frequency input. The methodology has been benchmarked against in-plant measurements taken from the instrumented Quad Cities Unit 2 steam dryer.
Measured strain gage time history data obtained from the four main steam lines at BFN Unit 2 were processed by a dynamic model of the steam delivery system to predict loads on the full-scale steam dryer. These measured data were first converted to pressures, then positioned on the four main steam lines and used to extract acoustic sources in the system. A validated acoustic circuit methodology (ACM) was used to predict the fluctuating pressures anticipated across components of the steam dryer. This pressure loading was then provided for structural analysis to assess the structural adequacy of the steam dryer.
BFN Steam Dryer Approach for EPU E-3 The ACM analysis is divided into two distinct analyses:
a Helmholtz solution within the steam dome and an acoustic circuit analysis in the main steam lines. These solutions are matched at the main steam line entrances to predict pressure on the steam dryer.
The ACM has been validated with Quad Cities Unit 2 pressure sensor data collected on the steam dryer, and the load includes both an acoustic loading and a low frequency hydrodynamic loading.
Because of modeling uncertainties based largely on the scale and fluid medium, TVA will no longer base its load definition on the scale model testing previously used to evaluate the potential for adverse flow effects. Use of actual BFN steam line data will provide a better prediction of steam dryer loading under EPU conditions.
- 5.
Steam Dryer Modifications Modifications have been made to strengthen the Unit 1 steam dryer to reduce the effects of flow-induced vibration (FIV).
As a result, the modified steam dryer is more robust and able to accommodate greater loads. The modifications consisted of replacing the hood and cover plate with one-inch thick Type 304L stainless steel material, increasing weld dimensions, installing larger tie bars, and adding two external reinforcing stiffeners to the hood.
TVA plans on implementing the same modifications on Units 2 and 3 prior to EPU power ascension for each respective unit.
Following completion of the modifications, all three BFN steam dryers will be the same.
Additional details on the physical modifications to the steam dryer will be included in the stress analysis report that will be submitted to NRC by April 2, 2007.
BFN Steam Dryer Approach for EPU E-4
- 6.
Structural Integrity Analysis As discussed in TVAs letter of January 31, 2007 (ADAMS ML070310569), a revised steam dryer stress analysis report for all three BFN units will be submitted to NRC by April 2, 2007. The revised structural analysis will be based on the following inputs and assumptions to the finite element analyses:
- b. A 1% damping value;
- c. Nominal load condition with frequency shifts of +/-2.5%,
+/-5%, +/-7.5%, and +/-10%; and
- d. Acoustic pressure fluctuations from a three-second time history to ensure proper response in the low frequency components.
The end-to-end uncertainty analysis is being performed and will be included in the April 2, 2007, steam dryer stress analysis report. The end-to-end uncertainty will include the appropriate bias and uncertainties associated with:
- a. Steam line instrumentation and data collection,
- b. Acoustic circuit methodology, and
- c. Stress analysis methods.
- 7.
BFN Unit Similarity TVA is documenting a similarity review that considers reactor pressure boundary geometries, hydrodynamics, and other factors related to steam dryer stresses. Upon completion of Unit 2 and Unit 3 steam dryer modifications (incorporating the Unit 1 design modifications), the design of all three steam dryers will be the same. To verify expected loadings, fluctuating pressures on Unit 1 and Unit 3 main steam piping will also be measured prior to power ascension above currently licensed thermal power levels. These measurements will be compared to the Unit 2 operating data that were obtained during the fall of 2006, and additional evaluations or analyses will be performed as necessary.
BFN Steam Dryer Approach for EPU E-5 The results of the similarity review will be submitted to NRC by April 2, 2007, and will include the following elements:
- a. Steam line flow characteristics,
- b. Acoustic source locations,
- c. Steam dryer configuration,
- d. Steam dome configuration,
- f. Steam line geometries.
- 8.
Steam Dryer Monitoring Plan As stated in TVAs response to Request for Additional Information (RAI) EEMB-D-7 (TVA letter of July 26, 2006), TVA will implement a Steam Dryer Monitoring Plan (SDMP). The SDMP is based on the Vermont Yankee SDMP that was reviewed and accepted by the NRC staff prior to that plants EPU power ascension. The SDMP will procedurally control power ascension in accordance with pre-determined acceptance criteria (including stress limit curves) and provide for the close monitoring of plant parameters. Evaluations and action criteria will ensure that steam dryer integrity is maintained during the power ascension process. The SDMP will also require visual inspections of the steam dryer that follow GE Service Information Letter and BWRVIP recommendations. The comprehensive monitoring program includes provisions for FIV monitoring through system walkdowns and the use of accelerometers on selected plant components.
- 9.
Stress Limit Curves for Power Ascension Testing TVA will provide frequency-dependent stress limit curves that will become operating restrictions during EPU power ascension. The limit curves and their development will be further described in the steam dryer stress analysis report that will be submitted to NRC by April 2, 2007.
BFN Steam Dryer Approach for EPU E-6 Figure 1 Steam Dryer Evaluation Process Install main steam line strain gages Collect main steam pressure data (strain)
Acoustic Circuit Model Acoustic Load Finite Element Analysis Design and Install Steam Dryer Modifications Steam Dryer Component Stresses Stress Limit Curves Power Ascension Monitoring