ML12339A741
| ML12339A741 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 11/30/2008 |
| From: | Cothron H Electric Power Research Institute |
| To: | Atomic Safety and Licensing Board Panel |
| SECY RAS | |
| References | |
| RAS 22624, 50-247-LR, 50-286-LR, ASLBP 07-858-03-LR-BD01 1016552 | |
| Download: ML12339A741 (26) | |
Text
United States Nuclear Regulatory Commission Official Hearing Exhibit Entergy Nuclear Operations, Inc.
In the Matter of:
(Indian Point Nuclear Generating Units 2 and 3) c.\..~RREG(J~)o ASLBP #: 07-858-03-LR-BD01 NYS000385 l~\
Docket #: 05000247 l 05000286 I- 0it Exhibit #: NYS000385-00-BD01 Identified: 10/15/2012 Submitted: June 19, 2012
'" ~ Admitted: 10/15/2012 Withdrawn:
<a.
'1"'4; 0-
! Rejected: Stricken:
" .***i' " Other:
Divider Plate Cracking in Steam Generators Results of Phase II: Evaluation of the Impact of a Cracked Divider Plate on LOCA and Non-LOCA Analyses 1016552 Technical Update, November 2008 EPRI Project Manager H. Cothron ELECTRIC POWER RESEARCH INSTITUTE 3420 Hillview Avenue, Palo Alto, California 94304-1338' PO Box 10412, Palo Alto, California 94303-0813' USA 800.313.3774' 650.855.2121' askepri@epri.com* www.epri.com
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Electric Power Research Institute, EPRI, and TOGETHER ... SHAPING THE FUTURE OF ELECTRICITY are registered service marks of the Electric Power Research Institute, Inc.
COPYRIGHT © 2008 ELECTRIC POWER RESEARCH INSTITUTE, INC. ALL RIGHTS RESERVED.
CITATIONS This report was prepared by Westinghouse Electric Company, LLC Nuclear Service Division P.O. Box 158 Madison, PA 15663 Principal Investigator C. Cassino This report describes research sponsored by the Electric Power Research Institute (EPRI).
The report is a corporate document that should be cited in the literature in the following manner:
Divider Plate Cracking in Steam Generators: Results of Phase II: Evaluation of the Impact of a Cracked Divider Plate on LDCA and Non-LDCA Analyses. EPRI, Palo Alto, CA: 2008.
1016552.
III
PRODUCT DESCRIPTION Cracking in the steam generator divider plate to stub runner welds has been reported by Electricite de France (EdF) plants. EPRI Report 1014982 describes results of a Phase I conservative detailed analysis of a crack in the divider plate to stub runner weld of a domestic Westinghouse-designed steam generator. Results of the Phase I analysis show that a completely degraded divider plate to stub runner weld would impact tube sheet displacement. Therefore, Phase II work began in 2008 to better understand crack initiation and growth in a divider plate to stub runner weld and the impact on plant accident analyses, American Society of Mechanical Engineers (AS ME) stress report fatigue limits, alternate repair criteria, and installed plugs and sleeves. This technical update provides a detailed analysis of the effect of a cracked divider plate on the behavior of a steam generator during normal and accident operating conditions.
Results and Findings The conclusion of the analysis in this report is that a cracked divider plate is not a safety concern with respect to loss of coolant (LOCA) and non-LOCA transients in the affected steam generator or loop.
Challenges and Objectives This report is intended for steam generator analysts and engineers in nuclear power. The report is primarily applicable to nuclear power plants that have Westinghouse-designed steam generators, without center stays or floating divider plates. The overall purpose of this report is to establish that divider plate cracking is not a safety significant issue for domestic plants. The specific goal of the analysis in this report is to determine the
- Bounding crack opening area (COA) that should be used in transient analyses for the case of a steam generator with a cracked divider plate
- Impact of steam generator divider plate cracking on LOCA analyses
- Impact of steam generator divider plate cracking on non-LOCA analyses Applications, Values, and Use The final report in 2009 will address:
- ASME Code stress report assumptions and an analysis of whether any structural criteria would be violated if the divider plate to stub runner weld is degraded
- Critical flaw sizes that must be detected if inspection of divider plate welds proves necessary
- The iinpact of a degraded divider plate on field repairs such as tube plugs EPRI Perspective The Westinghouse-designed steam generators are the only susceptible steam generators in the domestic fleet, and this is the only ongoing study on the impact of a degraded divider plate in the United States.
v
Approach Investigators relied on finite-element analysis to define the input conditions for a variety of thermal-hydraulic models. They adjusted the models as necessary to accommodate a flow path in the steam generator through the divider plate during transient conditions.
Keywords Divider Plate Cracking LOCA Stub Runner Weld Westinghouse Steam Generators Steam Generator Transients vi
CONTENTS 1 INTRODUCTION .................................................................................................................... 1-1 2 BOUNDING CRACK OPENING AREA ANALYSIS ............................................................... 2-1 3 ANALYSIS OF LOSS OF COOLANT ACCIDENT FORCES ................................................. 3-1 Impact of Steam Generator Vertical Divider Plate Cracking on LOCA Forces .................... 3-1 Impact of Steam Generator Vertical Divider Plate Cracking on Post-LOCA Long Term Cooling Analyses ........................... ;..................................................................................... 3-1 Calculation of the Minimum Mixed Mean Sump Boron Concentration ........................... 3-1 Hot Leg Switchover Time Calculation ............................................................................ 3-1 Flow Verification ............................................................................................................. 3-2 Conclusions .......................................................................................................................... 3-2 4 ANALYSIS OF NON-LOSS OF COOLANT ACCIDENT TRANSIENTS ................................ 4-1 Qualitative Scoping Analysis of Non-LOCA Transients for Steam Generator Divider Plate Crack Open Condition .......................................................................................................... 4-1 Plant Conditions with Divider Plate Crack Open ........................................................... .4-1 Qualitative Assessment of Bypass Flow .............................................................................. 4-2 Category #1 ..................................... ~ ............................................................................... 4-2 Category #2 ............................... ~ ........ ;........................................................................... 4-3 Category #3 ....................................................................................................................4-3 Category #4 ....................................................................................................................4-3 Category #5 ........................................................................................................:........... 4-4 Category #6 .....................................................................................................................4-4 Category #7 ....................................................................................................................4-4 Category #8 ....................................................................................................................4-4 Conclusions of Qualitative Assessment on Non-LOCA Transients ...................................... 4-5 5 QUANTITATIVE EVALUATION OF NON-LOCA STEAM GENERATOR TRANSIENTS ..... 5-1 Evaluation for Steady-State Conditions with the COA ......................................................... 5-1 Transient with the COA ........................................................................................................ 5-2
-Conclusions ............................ , ............................................................................................. 5-3 6 CONCLUSIONS ....................................................................... ~ ............................................. 6-1 7 REFERENCES .......................................................................................................................7-1 vii
-LIST OF FIGURES Figure 2-1 Plot of COA FEA Estimate for FLB Loading Assuming Zero Displacement of the Lower Crack Edge ...........................................................................................................................................................2-1 ix
LIST OF TABLES Table 2-1 COA Summary ........................................................................................................................... 2-2 Table 4-1 Non-LOCA Transients Based on Standard Non-LOCA Design Basis Events .......................... .4-7 xi
1 INTRODUCTION There have been several documented cases of crack indications in the divider plate to stub runner weld in steam generators in operation outside of the United States [1]. The function of the divider plate in most Westinghouse steam generators is to provide a separation between the cold and hot legs of the channel head as the primary water enters the steam generator. The divider plate is not considered a primary pressure boundary in the context of this analysis. In most Model F, Model D and Model 51 steam generators the divider plate is also not considered a structural component of the lower steam generator complex.
In most Model F, Model D and Model 51 Westinghouse pressurized water reactor (PWR) steam generators the divider plate is initially welded to the channel head and then attached to the tube sheet via a weld to a strip of metal on the primary side of the tubesheet called the stub runner. The weld between the stub runner and the divider plate is subject to bending and tension during regular operation of the steam generator. The tension on the divider plate occurs as the tube sheet bows from the difference between the primary and secondary operating pressures. The bending on the divider plate occurs because there is typically a temperature and a pressure difference between the hot leg and cold leg side of the tubesheet and divider plate. The weld that connects the stub runner and the divider plate in some steam generators consists of Alloy 600 material. This metal is susceptible to primary water stress corrosion cracking (PWSCC).
EPR! began Phase II work in 2007 to identify the impact of a degraded divider plate to stub runner weld on plant accident analyses, ASME stress report fatigue limits, alternate repair criteria, and installed plugs and sleeves.
This report summarizes a detailed analysis of the effect of a cracked divider plate on the behavior of the steam generator during normal operating and accident conditions. Section 2 provides a bounding crack opening area (COA) analysis. The final COA value is used in the accident analyses. Section 3 summarizes the impact of a degraded divider plate on loss of coolant accident (LOCA) forces. Section 4 summarizes the impact of a degraded divider plate on non-LOCA transients. Section 5 summarizes the quantitative analyses that were necessary for a few of the transient operating conditions.
1-1
2 BOUNDING CRACK OPENING AREA ANALYSIS The static finite element analysis (FEA) in Reference 1 calculated the displacements of the tube sheet assuming a constant maximum difference in pressure between the primary and secondary side of the tubesheet.
Figure 2-1 Plot of COA FEA Estimate for FLB Loading Assuming Zero Displacement of the Lower Cra~k Edge The eOA calculations assume that the lower edge of the crack is horizontal and the upper edge'-
of the crack conforms to the tubesheet displacements. See Reference 1 for a sketch of the assumed crack geometry for the calculations. The eOA for the divider plate crack is calculated using the trapezoidal rule, assuming that the displaced shape of the upper edge of the crack can be accurately represented by a series of trapezoids. This is a conservative assumption because approximating the curved shape using straight edges will tend to over estimate the eOA. The area of a trapezoid is calculated using the following equation:
Equation 2-1 2-1
Bounding Crack Opening Area Analysis Table 2-1 COASummary 2-2
3 ANALYSIS OF LOSS OF COOLANT ACCIDENT FORCES Impact of Steam Generator Vertical Divider Plate Cracking on LOCA Forces Impact of Steam Generator Vertical Divider Plate Cracking on Post-LOCA Long Term Cooling Analyses There are three types of analyses performed to ensure long term cooling following a postulated LOCA.
Calculation of the Minimum Mixed Mean Sump Boron Concentration Hot Leg Switchover Time Calculation 3-1
Analysis a/Loss a/Coolant Accident Forces Flow Verification Conclusions 3-2
4 ANALYSIS OF NON-LOSS OF COOLANT ACCIDENT TRANSIENTS Qualitative Scoping Analysis of Non-LOCA Transients for Steam Generator Divider Plate Crack Open Condition A qualitative analysis was performed to determine if any Non-LOCA transients would be affected by a cracked divider plate. The qualitative analysis suggested that the following conditions could be adversely affected by an open crack in the SG divider plate to stub runner weld:
Quantitative analysis of the above events was necessary to determine the impact to the safety margins. These events can be analyzed with the existing licensing basis RETRAN (Reactor Transient Analysis) models, with some modifications required to appropriately model the leakage pathway created by the cracked divider plate.
In the assessment of the non-LOCA transients, cracking is assumed in the weld between the steam generator tube sheet and the divider plate such that an opening is created along the top of the divider plate. No cracking is assumed between the divider plate and the channel head bowl.
The cracking is assumed only in one steam generator, and no cracking is assumed in other steam generators. It is also assumed that the SG tubes are not excessively bent or deformed by any lifting of the tube sheet.
Plant Conditions with Divider Plate Cracj( Open It is necessary to first determine the amount of the loop flow bypassing the steam generator tubes as a result of the bounding COA between the steam generator tubesheet and the divider plate.
The larger the amount of the bypass flow, the more pronounced the effect of the COA is expected. Hence, the minimum possible value of the form loss coefficient is assumed for the bypass geometry.
4-1
Analysis oJNon-Loss oJCoolant Accident Transients Qualitative Assessment of Bypass Flow Category #1 For the Non-LOCA transients in this category, the most limiting conditions for the primary criteria occur in a very short time, i.e., within one reactor. coolant system (RCS) loop cycle. As a result, the reduced SG heat transfer by the COAwould have either no impact or a negligible impact.
4-2
Analysis oJNon-Loss oJCoolant Accident Transients Category #2 The most limiting conditions for the primary criteria for the Non-LOCA transients in this category occur after several loop cycles. These transients assume that all loops are available, i.e.,
all reactor coolant pumps running. Asymmetric steam generator tube plugging (SGTP) conditions are analyzed with the maximum +/-5% difference among the loop flow rates. As these Non-LOCA events are primary system heat-up events due to reactivity anomalies (either positive or negative reactivity addition), the,primary heat generation is more dominate than the reduction in steam generator heat transfer area. Consequently, these Non-LOCA transients would have either no impact or an insignificant impact due to the COA. Hence, the current analyses results remain unchanged.
Category #3 Category #4 COA Resulting in Less Cooling in the Faulted Loop COA Resulting in Cooler Water on the Intact Loop 4-3
Analysis a/Non-Loss a/Coolant Accident Transients Category #5 Category #6 Category #7 Category #8 4-4
Analysis a/Non-Loss a/Coolant Accident Transients Conclusions of Qualitative Assessment on Non-LOCA Transients 4-5
Analysis oj Non-Loss oJCoolant Accident Transients Table 4-1 Non-LOCA Transients Based on Standard Non-LOCA Design Basis Events 4-7
Analysis oJNon-Loss oJCoolant Accident Transients Table 4-1 (continued)
Non-LOCA Transients Based on Standard Non-LOCA Design Basis Events 4-8
5 QUANTITATIVE EVALUATION OF NON-LOCA STEAM GENERATOR TRANSIENTS The qualitative evaluation of the non-LOeA analyses for the impacts of the crack opening between the stearn generator divider plate and tube sheet summarized in Section 4 is documented in Reference 4. The qualitative evaluation stated that the eOA would reduce the stearn generator heat transfer due to some of the loop flow bypassing the active heat transfer region of the tubes.
The reduction of the heat transfer was expected to be small, and therefore, the reduced heat transfer would not have an impact for a short duration. However, longer transients may have been adversely affected by the e~A, and the evaluation identified the following transients that may be adversely affected by the eOA:
Evaluation for Steady-State Conditions with the COA 5-1
Quantitative Evaluation ofNon-LOeA Steam Generator Transients Transient with the COA 5-2
Quantitative Evaluation ofNon-LOCA Steam Generator Transients Conclusions 5-3
6 CONCLUSIONS 6-1
7 REFERENCES
- 1. Divider Plate Cracking in Steam Generators: Results of Phase 1: Analysis of Primary Water Stress Corrosion Cracking and Mechanical Fatigue in the Alloy 600 Stub Runner to Divider Plate Weld Material. EPRI, Palo Alto, CA: 2007. 1014982.
- 2. Letter from Westinghouse to NRC, NSD-NRC-97-5092, "Core Uncovery Due to Loop Seal Re-Plugging During Post-LOCA Recovery," March 1977.
- 3. J. Tuunanen, et aI., "Experimental and analytical studies of boric acid concentrations in a VVER-440 reactor during the long-term cooling period ofloss-of-coolant accidents",
Nuclear Engineering and Design, Vol. 148, 1994, pp. 217-231.
- 4. LTR-CRA-07-257, Safety evaluation related to Steam Generator Divider Plate Cracking, December 5, 2007.
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