ML20246E027
| ML20246E027 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 06/30/1989 |
| From: | Bond C, Chang K, Raju Patel WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | |
| Shared Package | |
| ML19312B348 | List: |
| References | |
| WCAP-12306, NUDOCS 8907120070 | |
| Download: ML20246E027 (207) | |
Text
{{#Wiki_filter:_ _ - _ _ - _ 1 WESTINGHOUSE CLASS 3 WCAP-12306 l-
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EVALUATION OF THERMAL STRATIFICATION FOR THE SEABROOK UNIT 1 PRESSURIZER SURGE LINE June, 1989 E. L. Cranford B. F. Maurer C. Y. Yang M. Gray P. L. Strauch T. H. Liu L. M. Valasek i Verified by: ff'M- Verified by: M 8 K. C. Chang C. B. Bond / Approved by: \ b.bO Approved by: Vns R. 5. Patel, Manager G. 5. Palusamf( Manager Systems Structural Analysis Structural Materials and Development Engineering
!8907120070 89dT30 PDR' ADOCK 05000443 '-
Q. ' PDC
~ WESTINGHOUSE ELECTRIC CORPORATION Nuclear and Advanced Technology Division P.O. Box 2728 Pittsburgh, Pennsylvania 15230-2728 mm.mme ie
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ACKNOWLEDGEMENT
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- The authors wish to acknowledge the contributions made by R. L. Brice-Nash, B.
.: J. Coslow, E. ' R. Johnson, J. F. Petsche, D. H. - Roarty and T. A. Kozlosky in support of this. report.
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II e o_ ,. 333 l-
TABLE OF CONTENTS Section Title Page
SUMMARY
1.0 INTRODUCTION
AND UPDATE OF DESIGN TRANSIENTS 1-1 1.1 Introduction 1-1 1.1.1 System Description 1-1 1.1.2 Thermal Stratification In The Surge Line 1-2 1.1.3 Surge Line Stratification Program 1-3 1.2 Update of Design Transients 1-4 1.2.1 System Design Information 1-4 1.2.2 Stratification Effects Criteria 1-5 1.2.3 Plant Monitoring 1-5 1.2.4 Heat Transfer and Stress Analyses 1-10 1.2.5 Stratification Profiles 1-10 1.2.6 Deve?opment of Conservative Normal and 1-11 Upset Transients 1.2.7 Temperature Limitations During Heatup 1-12 and Cooldown 1.2.8 Historical Data 1-13 1.2.9 Development of Heatup and Cooldown Design 1-14 Transients With Stratification 1.2.9.1 i, ,]"'C Transients 1-15 1.2.9.2 1 Ja,c.e Transients 1-19 1.2.10 Striping Transients 1-19 1.3 Monitoring Data From Seabrook Unit 1 1-20 1.4 Conclusions 1-20 2.0 STRESS ANALYSES 2-1 2.1 Piping System Structural Analysis 2-1
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2.1.1 Introduction 2-1 2.1.2 Discussion on Typical Surge Line Analysis 2-2 2.1.3 Results for Seabrook Unit 1 Surge Line 2-5 un.fou w a gy
TABLE OF CONTENTS (cont.) Section Title Page 2.1.4 Additional Information on Linear Equivalent 2-5 Techniques 2.1.4.1 Introduction 2-5 2.1.4.2 Theory 2-6 2.1.4.3 Application 2-9 2.1.4.4 Discussion 2-9 2.1.5 Conclusions 2-9 2.2 Local Stress Due to Non-Linear Thermal Gradient 2-10 2.2.1 Explanation of Local Stress 2-10 2.2.2 Superposition of Local and Structural Stresses 2-10 2.2.3 Finite Element Model of Pipe for Local Stress 2-11 2.2.4 Pipe Local Stress Results 2-11 2.2.5 Unit Structural Load Analyses For Pipe 2-12 2.2.6 RCL Hot Leg Nozzle Analysis 2-12 2.2.7 Conservatism 2-12 2.3 Thermal Striping 2-13 2.3.1 Background 2-13 , 2.3.2 Additional Background Information 2-13 2.3.3 Thermal Striping Stresses 2-16 2.3.4 Summary of Striping Stress Considerations 2-17 2.3.5 Thermal Striping Total Fluctuations and Usage 2-18 Factor 2.3.6 Conservatism a,c,e 2-19 2.4 for Thermal Stress Calculation 2-19 2.4.1 Description of Methodology 2-20 2.4.2 Example 2-22 2.4.3 Comparison of Total Stresses for Seabrook 2-23 3.0 ASME SECTION III FATIGUE USAGE FACTOR EVALUATION 3-1 3.1 Code and Criteria 3-1 3.2 Previous Design Methods 3-1 3.3 Analysis for Thermal Stratification 3-1 un.w oo y j
t-i TABLEOFCONTENTS(cont.)
.- Section Title Page 3.3.1 Stress Input 3-2 3.3.2- Classification and Combination of Stresses 3-2 3.3.3 Cumulative Fatigue Usage Factor Evaluation 3-3 3.3.4 Simplified Elastic-Plastic Analysis 3-4 3.3.5 Fatigue' Usage Results 3-4 3.4 Conservatism in Fatigue Usage Calculation 3-5 3.5 References 3-5
4.0 CONCLUSION
S 4-1 APPENDIX A - LIST OF COMPUTER PROGRAMS A-1 9 6 4 mw=mae y$
I c LIST OF TABLES Table Titic Page - 1-1 Wi'0RTANT DIMENSIONLESS GROUPS FOR SIMILITUDE IN 1-21
- HYDRODYNAMIC TESTING -
1-2 STRATIFICATION POTENTIAL BASED ON RICHARDSON NUMBER 1-22 l 1-3 SURGELINE TRANSIENTS WITH STRATIFICATION HEATUP (H) 1-23 AND C00LDOWN (C) - 200 CYCLES TOTAL 1-4 SURGE LINE TRANSIENTS WITH STRATIFICATION NORMAL AND 1-24 UPSET TRANSIENT LIST 1-5 STRATIFICATION PROFILES 1-26 1-6 HEATUP - C00LDOWN TRANSIENTS 1-27 1-7 DESIGN TRANSIENTS WITH STRATIFICATION 1-28 1-8 OPERATIONS SURVEY 1-29 1-9 HEATUP DATA
SUMMARY
(PZR - HOT LEG) TEMP. DIFFERENCE AND 1-30 TIME DURATION FOR EACH PHASE 1-10 COOLDOWN DATA
SUMMARY
(PZR - HOT LEG) TEMP. DIFFERENCE AND 1-31 TIME DURATION FOR EACH PHASE 1-11 -TRANSIENT TYPES 1-32 1-12
SUMMARY
OF FATIGUE CYCLES FROM [' ]a,c.e 1-33 1-13
SUMMARY
OF PLANT MONITORING HEATUP/C00LDOWN TRANSIENTS 1-34 WITH STRENGTH OF STRATIFICATION (RSS) 1-14
SUMMARY
OF MONITORED-TRANSIENT CYCLES (ONE HEATUP) 1-36 1-15
SUMMARY
OF % TIMES AT MAXIMUM TEMPERATURE POTENTIAL RMTPg 1-37 1-16 SURGE LINE TRANSIENTS - STRIPING FOR HEATUP (H) AND 1-38 ! C00LDOWN(C) 2-1 COMPARISON OF WECAN AND ANSYS RESULTS FOR LINEAR 2-25 STRATIFICATION - Case 2 2-2 COMPARISON OF WECAN [' Ja,c.e AND 2-26 ANSYS [. j"' itESULTS FOR CASE 3 , un.mase in y$$ ,
I l
!I LIST OF TABLES (cont.)
Table Title Page
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2-3 TEMPERATURE DISTRIBUTIONS IN SEABROOK UNIT 1 2-27 i PRESSURIZER SURGE LINE i 2-4 THE EQUIVALENT LINEAR COEFFICIENTS J 4g 2-28 2-5 SEABROOKUNIT1SURGELjN['MAXIMUMLOCALAXIALSTRESSES 2-29 AT l ] 2-6
SUMMARY
OF LOCAL STRATIFICATION STRESSES IN THE SEABROOK 2-30 UNIT 1 SURGE LINE AT THE RCL N0ZZLE 2-7
SUMMARY
OF PRESSURE AND BENDING INDUCED STRESSES IN THE 2-31 SEABROOK UNIT 1 SURGE LINE RCL N0ZZLE FOR UNIT LOAD CASES 2-8 STRIPING FREQUENCY AT 2 MAXIMUM LOCATIONS FROM 15 TEST RUNS 2-32 2-9 FLOW RATES AND RICHARDSON NUMBER FOR WATER MODEL FLOW TESTS 2-33 2-10 RESULTS FROM TWO HIGHEST THERMOCOUPLE LOCATIONS 2-34 l 2-11 ASME CODE STRESS
SUMMARY
2-35 2-12 COMPARISON OF [ . Ja,c.e RESULTS WITH THOSE 2-36 , OBTAINED BY DIRECT WECAN ANALYSIS. LOCATION A 0F FIGURE 2-60 2-13 COMPARISON OF [ ]a,c e RESULTS WITH THOSE 2-37 , OBTAINED BY DIRECT WECAN ANALYSIS. LOCATION H OF FIGURE 2-60 2-14 COMPARISON BETWEEN [ Ja,c.e AND WECEVAL 2-38 RESULTS FOR SEABROOK l 4 O e soo2.m w a yjg$ i _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ 1
l LIST OF FIGURES Figure Title Page . 1-1 Simplified Diagram of the RCS 1-39 1-2 Reactor Coolant System Flow Diagram (Typical Loop) 1-40 1-3 RCS' Pressurizer 1-41 1-4 Estimate of Flow Stratification Pattern in Elbow Under 1-42 Pressurizer 1-5 Seabrook Unit 1 Pressurizer Surge Line Stratification 1-43 ASME III and Qualification Program
.1-6 Transient Development Flow Chart 1-44 1-7 [' j a.c.e Press,urizer Surge Line Monitering Locations 1-45 1-8 [" Ja,c.e Pressurizer Surge Line Monitoring Locations 1-46 1-9 [' Ja ,c.e Pressurizer Surge Line Monitoring Locations 1-47 1-10 [' j a,c.e Pressurizer Surge Line Monitoring Locations 1-48 1-11 Seabrook Unit 1 Pressurizer Surge Line Monitoring Locations 1-49 1-12 Reactor Coolant Pump Cut-off Transient Location Approximately 1-50 -
10' From RCL Nozzle Safe-End 1-13 Reactor Coolant Pump Cut-off Transient RCL Nozzle Safe-End 1-51 HL 1-14 Transient Typical of RC Pump Cut-off 1-52 1-15 Temperature Profile (6.5-inch ID Pipe) 1-53 1-16 Dimensionless Temperature Profile (14.3-inch ID pipe) 1-54 1-17 Surge Line Stratification 1-55 1-18 Surge Line Hot-Cold Interface Locations 1-56 1-19 Typical [' ja,c.e Temperature Profiles 1-57 1-20 Inadvertent RCS Depressurization (AT = 260'F in Surge Line) 1-58 1-21 Steam Bubble Mode Heatup 1-59 , 1-22 Steam Bubble Mode Cooldown 1-60 j a,c.e
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1-23 Heatup [ 1-61 asessesaseolo iX
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1.ISTOFFIGURES(cont.) i
.. Figure Title Page 1-24 Cooldown [' Ja ,c.e 1-62 1-25 Heatup [ ]"'C'* 1-63 1-26 Cooldown [ .]a,c.e 1-64 1-27 Heatup [ l a.c.e 1-65 1-28 Cooldown [' )"'C'" 1-66 1-29 Heatup i la.c.e 1-67 1-30 Cooldown [ la,c.e 1-68 1-31 Heatup [ 1"'C 1-69 1-32 Cooldown [' ]a,c,e 1 1-33 [* Ja,c.e Location 1 - Heatup (7 Days) 1-71 1-34 [' j a.c.e Location 1 - Heatup (4 Days) 1-72 1-35 [ j a.c.e Location 1 Fatigue Cycles - Heatup (11 Days) 1-73 *- 1-36 Thermal Cycle Distribution Assumed For One Heatup Cycle 1-74 1-37 [ -
a,c,. 1-75 1-38 Indication of Striping Thermal Cycles Assumed For One Heatup 1-76 1-39 Comparison of Design to Monitored Transients 1-77 1-40 Comparison of Design to Monitored Transients 1-78 2-1 Determination of the Effects of Thermal Stratification 2-39 2-2 Stress Analysis 2-40 2-3 Typical Pressurizer Surge Line Layout 2-41 2-4 Cases 1 to 4: Diametric Temperature Profiles 2-42 2-5 Case 5: Diametric and Axial Temperature Profile 2-43 2-6 Finite Element Model of the Pressurizer Surge Line Piping 2-44 General View I 3602s/062988:10 g i
LIST OF FIGURES (cont.) Figure Title Page . 2-7 Finite Element Model of the Pressurizer Surge Line Piping 2-45 Hot Leg Nozzle Detail - 2-8 Thermal Expansion of the Pressurizer Surge Line Under 2-46 Uniform Temperature 2-9 Case 2 (linear) Temperature Profile at Hot Leg Nozzle 2-47 2-10 Case 2 (linear) Temperature Profile at Pressurizer Elbow 2-48 2-11 Thermal Expansion of Pressurizer Surge Line Under Linear 2-49 Temperature Gradient 2-12 Bowing of Beams Subject to Top-to-Bottom Temperature Gradient 2-50 2-13 Case'3(Mid-PlaneStep): Temperature Profile at Hot Leg Nozzle 2-51 2-14 Case 3 (Mid-Plane Step): Temperature Profile at Pressurizer 2-52 Nozzle 2-15 Case 4 (Top Half Step): Temperature Profile at Hot Leg Nozzle 2-53 2-16 ~ Case 4 (Top Half Step): Temperature Profile at Pressurizer 2-54 Elbow 2-17 Case 5: Axial and Diametric Temperature Profile 2-55 2-18 Case 5: Axial and Diametric Temperature Profile at Hot Leg 2-56 *i Nozzle { 2-19 Case 5: Axial and Diametric Temperature Profile at Pipe Bend 2-57 2-20 Case 5: Axial and Diametric Temperature Profile at 2-58 Pressurizer Elbow 2-21 [-
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ja,c.e Profile 2-59 2-22 Seabrook Surge Line Model and Temperature Profile 2-60 2-23 Equivalent Linear Temperature 2-61 2-24 Local Stress in Piping Due to Thermal Stratification 2-62 l 2-25 Independence of Local and Structural Thermal Stratification 2-63 ) Stresses Permitting Combination by Superposition - 2-26 Test Case for Superposition of Local and Structural Stresses 2-64 ,1 2-27 Local Stress - Finite Element Models/ Loading 2-65 mowouwe io x3
LIST OF FIGURES (cont.)
.' Figure Title Page 2-28 Piping Local Stress Model and Thermal Boundary Conditions 2-66 2-29 Surge Line Temperature Distribution at [' la,c.e Axial 2-67 Locations 2-30 Surge Line Local Axial Stress Distribution at [' j a,c.e 2-68 Axial Locations 2-31 Surae (ige,LocalAxialStressonInsideSurfaceat 2-69 1 J Axial Locations 2-32 Surgeyge,LocalAxialStressonOutsideSurfaceat 2-70
[" J Axial Locations 2-33 Surge Line Temperature Distribution at Location [ Ja,c.e 2-71 2-34 Surge Line Loga}*gxial Stress Distrit,ttion at 2-72 Location [ ] 2-35 Surge Line Temperature Distribution at Location [ Ja,c.e 2-73 2-36 SurgeLineLogc}'gxialStressDistributionat 2-74 Location [ ] 2-37 Surge Line' Temperature Distribution at Location [ Ja,c.e 2-75 2-38 SurgeLineLoga}'gxialStressDistributionat 2-76 Location [ ] 2-39 Surge Line Temperature Distribution'at Location [ Ja,c.e 2-77 2-40 SurgeLineLoga},gxialStressDistributionat 2-78 Location [ ] 2-41 Surge Line Temperature Distribution at Location [ Ja.c.e 2-79 2-42 SurgeLineLoga}'gxialStressDistributionat 2-80 Location [ ] 2-43 Surge Line RCL Nozzle 3-D WECAN Model #1 2-81 2-44 Surge Line RCL Nozzle 3-D WECAN Model #2 2-82 2-45 Surge Line Nozzle Temperature Profile Due to Thermal 2-83 Stratification
. 2-46 Surge Line Nozzle Stress Intensity Due to Ther:nal 2-84 Stratification mamme io x$$
L i LIST OF FIGURES (cont.) Figure Title Page . I 2-47 Surge Line Nozzle Stress in Direction Axial to Surge Line Due 2-85 to Thermal Stratification 2-48 Surge Line Nozzle Stress Intensity Due to Pressure 2-86 2-49 Surge Line Nozzle Stress Intensity Due to Pressure 2-87 2-50 Surge Line Nozzle Stress Intensity Due to Bending 2-88 2-51 Surge Line Nozzle Stress in Direction Axial to Surge Line 2-89 Due to Bending Showing Magnified Displacement 2-52 Surge Line Nozzle Stress Intensity Due to Bending Showing 2-90 Magnified Displacement 2-53 Surge Line Nozzle Stress Intensity Due to Bending 2-91 2-54 Thermal Striping Fluctuation 2-92 2-55 Stratification and Striping Test Models 2-93 2-56 Water Model of LMFBR Primary Hot Leg 2-94 2-57 Attenuation of Thermal Stripin PotentialbyMggeglar 2-95 Conduction (Interface Wave Hei ht of I 1 - 2-58 Thermal Striping Temperature Distribution 2-96 2-59 Striping Finite Element Model 2-97 2-60 Finite Element Model used in the Example Also Showing the 2-98 Region Numbers and the Locations. Numbers in the Parentheses are Nodal Numbers 2-61 Stratified Transient Used in Example 2-99 2-62 Comparison of Stress Results Location A (Node 1) 2-100 2-63 Comparison of Stress Results Location H (Node 10) 2-101 xiii
SUMMARY
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This report presents the methods, data, analysis and qualification results for the Seabrook Unit 1 pressurizer surge line including thermal stratification. l The report is divided into four sections. Appendix A is a list of computer codes used in this work. The sections are presented in order, reflecting the icA cal progression of evaluations and analyses: o Section 1.0 " Introduction and Update of Design Transients" presents the methods and data used to update the design thermal transients to incorporate the effects of flow stratification in the surge line. o Section 2.0 " Stress Analysis" describes the global and local stress effects of stratification, including striping. o Section 3.0 "ASME III Fatigue Usage Factor Evaluation" provides the evaluation results of the ASME III fatigue life of the surge line subject to all design transients plus the effects of stratification. o Section 4.0 " Conclusions" summarizes the results of the evaluations of the effects of stratification in the surge line. o Appendix A " Computer Codes" is a list and description of computer codes ~used in this work. The work presented in this report leads to the following conclusions: (a) Based on plant monitoring results from [ la.c.e Westinghouse PWR's and flow stratification test data, the thermal design transien'ts for the surge line have been updated to incorporate the effects of stratification. nowomm io x$y u___ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
(b) The structural global and local stresses and loads in the surge line piping and support system meet ASME III Code allowables. The . maximum cumulative fatigue usage factor including the effects of striping is less than [ jC for 40 year design life , - compared to the Code allowable of 1.0. In summary, based on the' current understanding of the thermal stratification phenomenon, it is concluded that thermal stratification does not affect the integrity of the pressurizer surge line of the Seabrook Unit I nuclear power plant. The design life (forty years) and ASME III Code compliance are not affected. e
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l 3ec2e/ostees to XV
fL F SECTION 1.0
, INTRODUCTION AND UPDATE OF DESIGN TRANSIENTS
.. . 1.1 Introduction 3 i
1.1.1 System Description '! The primary function of the reactor coolant system (RCS) is to transport heat from the reactor core to the steam generators for the production of steam. The Seabrook Unit 1 RCS consists of four similar heat transfer loops connected to the reactor vessel (figure 1-1). Each loop contains a reactor coolant pump (RCP)andasteamgenerator. The system also includes a pressurizer, connecting piping, pressurizer safety and relief valves, and a relief tank. The flow path for a typical reactor coolant loop is from the reactor vessel to the inlet plenum of the steam generator (figure 1-2). High temperature reactor coolant flows through the U-tubes in the steam generator (transferring heat to the secondary water) and out of the U-tubes into the outlet plenum to the suction of the reactor coolant pump. The reactor coolant pump increases the pressure head of the reactor coolant which flows back to the reactor vessel. The pressurizer vessel (figure 1-3) contains steam and water at saturated' conditions with the steam-water interface level between 25 and 60% of the volume depending on the plant operating conditions. From the time the steam bubble is initially drawn during the heatup operation to hot standby conditions, the level is maintained at approximately 25%. During power ascension, the level is increased to approximately 60%. As illustrated in figure 1-2, the bottom of the pressurizer vessel is connected to the hot leg of one of the coolant loops by the surge line, a 14 inch schedule 160 stainless steel pipe. an.msa,o 71
l } I L The simplified diagram shown in figure 1-2 indicates the auxilicry systems that interface with the RCS. Of particular significance to surge line . stratification are the normal charging and letdown function provided by the Chemical and Volume Control System (CVCS), and the suction and return lines - l associated with the Residual Heat Removal System (RHRS). The former directly controls the RCS mass inventory and therefore affects flow in the surge line. The RHRS is used to remove heat from the RCS and thereby influences coolant temperature and consequently coolant volume through thermal expansion and contraction. Other systems which affect surge line flow conditions are main spray flow supplied to the pressurizer from one or two cold legs, and the pressurizer electric heaters. Spray operation does not significantly alter the total RCS mass inventory, but does reduce system pressure by condensing some of the steam in the pressurizer. The pressurizer heaters, when energized, generate steam and, as a result, increase RCS pressure. 1.1.2 Thermal Stratification In the Surge Line Thermal stratification in the pressurizer surge line is the direct result of the difference in densities between the pressurizer water and the generally , cooler hot leg water. The lighter pressurizer water tends to float on the cooler heavier hot leg water. The potential for stratification is increased as the difference in temperature between the pressurizer and the hot leg increases and as the insurge or outsurge flow rates decrease. j l At power, when the difference in temperature between pressurizer and hot leg l is relatively small (less than 50'F), the extent and effects of stratification have been observed to be small. However, during certain modes of plant heatup and cooldown, this difference in system temperature could be as large as 320*F, in which case the effects of stratification must be accounted for. A common approach for assessing the potential for stratification is to evaluate the Richardson Number (tables 1-1 and 1-2) which is the ratio of the thermal density head diametrically across the pipe to the fluid flow dynamic head. mamme 1-2
r-i l l Ri = gBDAT
'~
where' q j i Ri = Richardson number j l g = gravitation constant V = hot fluid velocity AT = hot-to-cold fluid temperature difference i D = pipe inside diameter 6 = coefficient of volumetric thermal expansion of water For a range of surge line flow rates from approximately 700 gpm down to a pressurizer spray line bypass flow of approximately 1 to 5 gpm, and AT = 320*F, the Richardson number is greater than the value of 1 which is required to initiate stratification. Thus under this range of conditions, the flow has the potential to be stratified due to the relatively large hot-to-cold fluid temperature difference combined with the low hot fluid velocity. To eliminate
. stratification (i.e., Ri smaller than 1) a flow velocity of over 2.4 fps (approximately 700 gpm) is needed (figure 1-4).
1.1.3 Surge Line Stratification Program The surge line stratification program for Seabrook Unit 1 consists of three major parts: (a) Update of design transients (b) ASME III stress and fatigue cumulative usage factor (CUF) evaluation (c) Temperature and displacement monitoring. i e 9 e i 1-3 L 1 1 _ _ _ _______-___- - _-_
Figure 1-5 shows the steps required to complete this program. I
.,i 1.2 Update of Design Transients 1 The method used to update the design transients for stratification is illustrated in_ figure 1-6 and is discussed in this section.
1.2.1 System Design Information The thermal design transients for the Seabrook Unit 1. Reactor Coolant System, including the pressurizer surge line, are defined in Westinghouse Systems Standard Design Criteria (SSDC) documents SSDC 1.3. The design transients for the surge line consist of two maior categories: (a) Heatup and Cooldown transients (b) Normal and Upset operation transients. By definition, the emergency and faulted transients are not considered in the ASME III Section NB '
' fatigue life assessment of components.
-l In the evaluation of surge line stratification, the FSAR chapter 3.9N definition of normal and upset design events and the number of occurrences of the design events remains unchanged.
The' total number of current design heatup-cooldown cycles (200) remains unchanged. However, sub-events and the associated number of occurrences (" Label", " Type" and " Cycle" columns of tables 1-3 and 1-4) are defined to reflect monitoring datc, as described later. 1 In all cases, the surge line fluid temperature distribution is modified from j the original uniform temperature to a stratified distribution with the maximum I
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temperature differentials and the associated nominal temperatures (" MAX AT strat " and " Nominal" columns on tables 1-3 and 1-4). , maa.mme io . i.4
i i l i 1.2.2 Stratification Effects Criteria d To determine the normal and upset pipe top-to-bottom temperature difference,
. "AT strat
" (tables 1-3 and 1-4), the following conservatism is introduced. -
l For a given event, the AT strat in the pipe will be the difference between j the maximum pressurizer temperature and the minimum hot leg temperature, even l though they do not occur simultaneously. l l [ l ga c.e 1.2.3 Plant Monitoring Surge line stratification data have been obtained from ( la,c.e Westinghouse plants. Figures 1-7 through 1-10 show the instrumentation. configu-ation for four of these plants. The data was obtained by continuous monitoring of the piping metal surface temperature, displacements and plant parameters. The pipe temperatures were obtained from RTD's located on the outside of surge line. Plant parameters were obtained from the plant computer. Figure 1-11 represents the Seabrook Unit 1 monitoring configuration. Temperature data from the other reference plant surge lines were reviewed. The data, in all cases, shows the presence of stratification in the surge lines. The stratification observed is assumed to behave under the influence of gravity and consequently will have an axial profile defined by the slope of nouenio 1-5 t
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the pipe. The data interpretation herein is an attempt to classify and characterize observed thermal conditions. . There are two basic causes of thermal stratification. Thermal stratification - can be initiated either by [- la.c.e or the'[. ;
]a.c.e This is the condition which this report addresses.
[' i f ja.c.e I M02s/0621M to
i L I i [ ':; .
.. 1 ja,c.e I
l The establishment of a highly stratified condition is best' described by j considering the following typical transient example. This transient is based on an observed reference plant transient which was caused by the cut-off of 4 the RCP in the same loop as the surge line. l
. Typical' Transient
Description:
(RCP Cutoff figure 1-12) [ 6 9 e ja.c.e nowown io 17
[ s
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i ja,c.e One interpretation of the cause and effects of the transient just described is as follows: [ 4 4 Ja,C,e 1 un.mua. io 1-8
a [ b
.i
.;a,c.e j
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The data are sufficient to characterize stratification temperatures in the
. pipe during critical operating transients and heatup-cooldown operation.
'Also, the data are sufficient to verify that the pipe movements are consistent with analytical predictions, within an ac' uracy c normally expected from hot functional and/or power ascension tests, as discussed in section 2.1.
The monitoring of plant parameters is sufficient to correlate measured temperature fluctuations to changes in operation. In particular, it is apparent that temperature fluctuations are due to flow insurge (into the pressurizer) and outsurge (oti of the pressurizer) which in turn are due to differential pressure in the system. While a simple quantitative mechanistic
-relationship between plant operation and insurge and outsurge has not been found, the data indicate that a steady state stratified condition can be altered by any of the following events:
an.mmio 19
I a) Expansion of the pressurizer bubble b) RCP. trip in the surge line loop . I c) Safety injection d) Large charging - letdown mismatch . e) Large spray rates I In light of these observations, the update of design transients is based on plant monitoring results, operational experience and plant operational procedures. Conservatism have been incorporated throughout the process in the definition of transients (cycles, AT) and in the analysis, as described in the report. - 1.2.4 Heat Transfer and Stress Analyses The correlation of measured pipe OD temperature to ID temperature distribution is achieved by heat transfer analysis as well as previous experience with flow at large Richardson numbers (Rini) (figures 1-15 and 1-16). These analyses and test data available to date show that a stratified flow condition, [ '
]"'C is a proper and conservative depiction of the flow .
condition inside the pipe at large AT and low flow rates (Ri>1). An additional conclusion from the heat transfer and stress analyses is that [ 3a,c.e 1.2.5 Stratification Profiles Table 1-5 summaries the major stratification profile characteristics. The monitored data shows a consistent axial temperature profile along the horizontal portions of the [ ]a,c.e surge lines monitored. nowommae 1-10 1
l i The axial temperature profile is a function of the geometric characteristics j of each line. Each line monitored showed a definite relationship betwoen j axial length of stratification and slope of the line. Figure 1-17 depicts a
. typical axial stratification profile. Note that the. actual length of stratification is dependent on the volume of the insurge. Low volume insurges tend to stratify a shorter distance along the line. Similarly large volume !
insurges stratify longer distances provided the slope of the line is low enough. As the slope increases, smaller sections of the line will be affected by stratification. The slope also affects the type of stratification interface. As the slope is increased the flow characteristics of the interface are affected. There are two basic interface types; one which is narrow and highly defined is characteristic of laminar flow. The other is characteristically wide and a product of turbulent flow. The flow becomes turbulent at the interface when forced to a higher level than gravity would normally dictate. Flow velocity is also an integral part of this relationship. Figure 1-18 shoes a cross section of the pipe with the various hot and cold fluid interface levels created by a laminar flow or static steady state conditions. 1.2.6 Development of Conservative Normal and Upset Transients Transients in the surge line were characterized as either due to insurges or outsurges (I/0) from the pressurizer or fluctuations. Insurges and outsurges are the more severe transients and result in the greatest change in tempera-ture in the top or bottom of the pipe. An insurge may cool the bottom of the pipe significantly, to very close to the temperature of the RCS hot leg. Conversely, an outsurge can sweep the line and heat the pipe to close to the temperature of the pressurizer. The thermal transients are shown in figure 1-19. Fluctuations, as opposed to the insurge-outsurge transients, are caused by relatively insignificant surges and result in variations in the hot-cold ir,terface level. These variations in the interface level do not change the overall global displacement of the pipe and hence.are modeled as changes in the depth of the interface zone. mwomn io 3 33
)
1. I j The redefinition of the thermal fluid conditions experienced by the surge line during normal-and upset transients was necessary in order to neglect the . indirectly observed fluid temperature distributions. .These redefined thermal fluid conditions were developed based on the existing design transient system
-{
l- parameters assumed to exist at the time of the postulated transient and the J knowledge gained from the monitoring programs. The redefined thermal fluid l conditions conservatively account for the thermal stratification phenomena.
]4 Several conservatism were introduced in the redefined normal and upset ;
thermal transients (tables 1-3, 1-4, 1-6 and 1-7). [ 3a,c.e
'(b) Full stratification cycles are assumed for all transients, except for steady state fluctuations, unit loading and unloading, and reduced temperature return to power, where level fluctuations are sufficiently conservative based on flow rate and observations.
(c) The temperature of stratification was based on the minimum hot leg temperature at any time during the transhnt (for bottom of pipe) and , the maximum pressurizer temperature (for tsp of pipe). Figure 1-20 shows a case where this resulted in a very conservative 260*F stratification transient although the maximum temperature difference at any point in time was about 50'F. (d) The current number of design cycles of each event is unchanged. The normal and upset transients modified to account for the stratification phenomena are listed in tables 1-3 and 1-4. 1.2.7 Temperature Limitations During Heatup and Cooldown The maximum permitted temperature difference between the pressurizer and the ,i hot leg for Seabrock Unit 1 is 320*F. Therefore the maximum possible nn.=n=x 1 12 ,
top-to-bottom temperature stratification is 320'F. Exysriences from available monitoring data indicate that the top-to-bottom metal temperature difference will be less than 0.9 of the 320*F. With the RCL cold, the pressurizer pressure (and therefore temperature) is limited by the cold overpressure mitigation system (COMS). Practically, plants operate to minimize downtime and heatup-cooldown time, when power is not being generated. The times at large AT are therefore i reasonably limited, as discussed later. 1.2.8 Historical Data Since not all heatup and cooldown parameters affecting stratification are formally limited by Technical Specification or Administrative controls, it is necessary to reconsider plant operational procedures and heatup-cooldown practices to update the original heatup and cooldown design transient curves of SSDC 1.3 (figures 1-21 and 1-22). To this end, a review of procedures, operational data, operator experience, and historical records was conducted for [ Ja.c.e Westinghouse PWR plants (table 1-8). Similarly, operations procedures for Seabrook Unit 1 were reviewed and heatup cooldown curves developed (shown in figures 1-23 and 1-24). The heatup and cooldown operations information acquired from this review is summarized in tables 1-9 and 1-10, [ ja c.e The information is divided into heatup and cooldown tables and diagrams. The diagram presents the pressurizer water and hot leg temperature profiles versus time. The various phases of the process are identified by letters along the diagrams' abscissa and in tables 1-9 and 1-10. 9 mu.mune in 3 13
1.2.9 Development of Heatup and Cooldown Design Transients With Stratification As described above,- the database of information used to update the heatup and cooldown transients included the following: - a) Typical heatup and.cooldown curves, as developed from review of procedures, operational data and cperators experience. b) Transients as monitored at [ la.c.e plants c) Historical records of critical heatup and cooldown temperatures The heatup and cooldown transients are presented in the following sections as [ la.c,e and in similar fashion to the normal and upset transients. Table 1-11 gives the general characteristics of the two types of transients observed. The heatup cooldown transient labels have the following logic:
- 1. Transients H1 through H12 correspond to insurge or outsurge transients postulatedduringheatups(H). ,
- 2. Transients HF1A through HF3 correspond to fluctuation transients postulated during heatups (HF).
- 3. Transients C1 through C9 correspond to insurge or outsurge transients postulated during cooldown (C).
- 4. Transient CF1 represents the fluctuation transients postulated for cooldowns(CF).
l ma2.mun.$o l 1_14
1.2.9.1 [ la,c.e Transients A) Monitoring Transient Summary For a given monitored.. location, plots of temperature differer.co versus time were generated (figures 1-33 and 1-34 are examples of relatively high transient activity). Two parameters were plotted, the pipe top to bottom temperature difference (labeled " surge line") and the pressurizer to hot leg temperature difference (labeled " system"). It is clear from figures 1-33 and 1-34 that for the observed heatups, [
),a,c,e for conservatism, the envelope from measured transients in all plants is applied to define the transients.
B) Fatigue Cycles The fatigue cycles were obtained using the technique illustrated on figure 1-35, [which reduces each transient to its temperature range, rather than its absolute magnitude. Table 1-12 is a summary of the approximate magnitude of each cycle shown in figure 1-35. The heatup and cooldown design transients with stratification used in the piping qualification conservatively accounts for the mean stress effect. Figure 1-36 provides a single heatup interpretation of the design transients. Note the relative severity of the design transients by comparing them with the actual thermal activity observed at the worst case plant (figure 1-33). [ ja.c.e Figure 1-37 l illustrates the difference between the design transients and the transients observed at plant A. un.ma. ie 1-15
r C) Strength of Stratification
- Plant monitoring data indicate that for the various transients observed the j AT in the pipe'(top to bottom).is not as large as the AT in the system -
(pressurizer to hot leg). The ratio of AT in the pipe to AT in the system will be referrsd to as " strength of stratification". [ ya.c e D) Number of Stratification Cycles (table 1-14) Plant monitoring data indicated the significant events which could occur . during a given heatup. [ e
- moa.=2 = io 1-16 p
ja,c.e E) Maximum Temperature Potential The key factor in thermal stratification of the surge line is the temperature difference between the pressurizer and hot leg (section 1.2). This tempera-ture difference is clearly maximized during the heatup and cooldown, when the plant is in mode 5 cold shutdown (hot leg less than 200*F) and the pressurizer bubble has been drawn with the reactor coolant pump running (pressurizer tema*- ture larger than 425'F). [ ja,c,e F) Final Cycles and Stratification Ranges ja,c.e [ !'e
.O mu m22= in 1_17
?
L. l :: ja,c.e
.For Heatup: 1 = 1 to 24. j = 1. to 6, k = 1 to 4 E-ja c.e
-Example: ,
['.
-)a,5,e G )'. Cooldown Transients -
The procedure used in heatup is applied to develop transients for plant cooldown. [ men. w :" " 1-18
~
, ga,c.e 1.2.9.2 [ Ja c.e Transients i
.ja,c e
~
1.2.10 Striping Transients Mean stress effects are included in determining the usage factor contributed by thermal striping. Fatigue cycles like those shown in figure 1-35 were not used in the development of the striping design transients. [ Ja,c.e It should be noted that each striping transient cycle is assumed to initiate a discrete hot to cold fluid interface that will be attenuated with time (see section 2.3 for discussion). Figure 1-38 shows the relative magnitude and frequency of the striping transients for one heatup or cooldown with respect to the system AT (PRZT - RCST). The highest pipe AT (pipe T top pipe Tbot) bserved during heatup never exceeded [ ).a.c.e However, the design striping transients consider [ }"'C transients at pipe AT's greater than [ ,)a,c.e l Striping transients use the labels HST and CST denoting striping transients (ST). [ ia,c.e
. J nu.m2 E.m 1 19
_- . ___- __a
i i 1 1.3 Monitoring Data from Seabrook Unit 1 Plant monitoring data obtained on November 30, 1988 was reviewed for transient activity. During this period, the pressurizer steam bubble was drawn. - pressurizer water temperature stead'ily rose from 172*F to 439'F, and hot leg temperature rose slightly from 116*F to 130'F. Approximately 39 minutes after all pressurizer heaters were activated for bubble formation, stratification was initiated at the monitored location (i.e. the top two RTDs showed significantly higher readings than the lower two RTD's). This is a result of pressurizer out flow (due to water being displaced by steam in the pressurizer) flowing along the top of the pipe toward the hot leg. Stratification at the monitored location continued as pressurizer water temperature increased, maximizing at a top-to-bottom temperature difference of 269'F. Stratification diminished after the Reactor Coolant Pump was activated, since loop turbulence mixed the fluid at the monitoring location, which is near the hot leg connection. , During the 10.5 hour period monitored, only three significant transients . occurred which resulted in temperature changes at the top of the pipe of 100'F or greater (the bottom of the pipe remained steady at about 125'F, + 10*F). These changes were 214'F, 162*F and 104*F. The monitoring data shows no excephi'>ns and is considered enveloped by the design basis transients with stratification used by this evaluation. 1.4 Conclusions Design transients were updated to incorporate stratification. The transients ; were developed to conservatively represent the cyclic effects of stratification. To illustrate the margin included in the development of heatup transients, a simplified fatigue factor calculation is provided in ') figures 1-39 and 1-40. This comparison indicates that the design transients , have a factor of conservatism of approximately [ ' ja,c.e nowon . in 1-20 i l
TABLE 1-1 ,. IMPORTANT DIMENSIONLESS GROUPS FOR SIMILITUDE IN HYDRODYNAMIC TESTING Peremesse Symeel Deensene Squneenes Weiecaen w f DAP 3ev8L Pgeoure secoceme occer easier 2 Caveemen autrear o 47. -8,p ev' 8 eeuwe enerence monie meus 3 moynees nuanoor me sv0. mosca escovese.s %ece j s Susuna nummer Sr 4V vonos snesong m- ) moven Nwee
$ Weser nummer We aOV' a meme 4ptespace soneen nuee 4 f%ues numeer Fr V8 gD inerne 4ptegrerey tesse 7 menoresen nummer mi Aapoiav* Simrancy meensisses forco iheestesseuse nuMWert
- 4. Euler numeer Eu AP'sWa p,,,,,,g,,,,,,,,,,,,
9 Prenen tweer #r C* nemmereum ehenroyitnormal e mewer io pues nummer Po av0C2 convesne neer veneer-(As = *n sensusewe rue veneer i1 Greenet nummer Gr L8 s's#4N8 Ssseysuy tenevassue Nwee
- 12. Asyesign nummer me L'a 3CpAaflas4 -
(Gr a Pn N0esENCLAfufE C = seosas nest p = aessesresen of grevey a = eenemy 7 = openews a = surtese uneen 7, e smet Num spesews
= = renne senasevey 7, = sua vasor preneure
# = veesnSow essensen esentent L O = cnerecurses errureens af = Rue senseratare enange V = nue messy
.onom semesng messeney an = vegnemy l
l men. ooria in 1 21
1 l-L 1' : TABLE 1-2 1 1 STRATIFICATION POTENTIAL BASED ON RICHARDSON NUMBER
. Stratification potential exists if Ri > 1 8,C,e I
l 1 h W 9 e i un.-m un io 1-22
i 1 l TABLE 1-3 SURGELINE TRANSIENTS WITH STRATIFICATION HEATUP (H) AND COOLDOWN (C) - 200 PLANT CYCLES TOTAL
~
a.C.e l l.
~* Input for maximizing moment range only I/O = Insurge - Outsurge F = Fluctuation e
nu.<azin in 1-23 _ --__- _ - _ _ a
_wn---~~,...-_ TABLE 1-4 SURGE LINE TRANSIENTS WITH STRATIFICATION NORMAL AND UPSET TRANSIENT LIST TEMPERATURES ('F) TRANSIENT MAX NOMINAL , LABEL TYPE CYCLES AT PRZ T RCS T 3
- ~
8,C,e l' l 4 N 1 l l J asowoesiae to 1.g l
(; ' ') (O TABLE 1-4 (Cont'd.) SURGE LINE TRANSIENTS WITH STRATIFICATION t NORMAL AND UPSET TRANSIENT LIST h .::
\
TEMPERATURES ('F) ] TRANSIENT MAX NOMINAL LABEL TYPE CYCLES AT PRZ T RCS T 3
- ~~~
a.C,e'
/ /
t. D weenn
'e *e zu.mnaio 1-25 I
l l TABLE 1-5 STRATIFICATION PROFILES [ e ja.c.e l e nowouuo in 1-26
l: TABLE 1-6 l: HEATUP - C00LDOWN TRANSIENTS ' o Transients Were Developed Based On: Typical Heatup Cooldown Curves Envelope (Plus Margin) of Events. (Transients) Monitored - Historical _ Data on Temperature Plateaus
-[
3a.c.e f f ' e man. main in 1-27
=
.q I
1 TABLE 1-7 , DESIGN TRANSIENTS WITH STRATIFICATION a
)
o Heatup and Cooldown Combined With Other Events o Design Transient Crite.ia l l l l ja,c.e
- o. Input for Local and Structural Analysis Defined - Plus Nozzle o Striping Transients Defined to Consider Maximum Stratification Cycles Regardless of Range -
t l l, mu. min io 1-28 l l
. . - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ J
l i TABLE 1-8 l OPERATIONS SURVEY 'j q I o Summary of Plants Surveyed NO. OF YEARS OF OPERATION l PLANT LOOPS (MAXIMUM) [ ! l 4
. ja,c.e o Reviewed Typical Heatup Cooldown Process o Reviewed Administrative / Tech Spec Limitations o Reviewed Historical Events and Time Durations o Developed Heatup - Cooldown Profiles newmwo 1-29 L-_-_____-________.
-. 0, .
~-
C. . a i. A . H. P-H. C A. E. R O. F N. O. I-T
- A R.
U-
- D Y
R EI A I NIT I . 9 U
- S D.
1 N. A' A E T L A E 4 B D C A N
. T P E U R T E A F E F .
H I D. P. I I E. T.
)
G E. L - T O H R Z.. P . ( 0 1 9 8 1 2 6 0
/
s 2 0 8 3 s ewo t _lltI ttlri1l IIi !! i! !
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8 8 l , 1-31
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--m7 TABLE 1-11 TRANSIENT TYPES ja.c.e
\
l un.mma in 1-32
F 7 TABLE 1-12
SUMMARY
OF FATIGUE CYCLES FROM [ PLANT.B]a,c.e
.2 .
'CycleL Delka. Range (*F) Cycle Delta Range (*F) p
- a,c.e s'
p. NOTE: Tha delta range represents the relative severity (AT) of each transient following the fatigue cycle approach. t. 9
. man.maimio 1-33 a _ _ _ _ _ _ _ _ _ _ = _ -_ _ _ - _ .
TABLE 1-13
SUMMARY
OF PL'ANT MONITORING HEATUP/COOLDOWN TRANSIENTS WITH STRENGTH OF STRATIFICATION (RSS) g, .)a,c.e r ;a,c.e p 3a,c.e Observed Observed Eterved i Cycles RSS(1) Cycles RSS(1) Cycles RSS (1) a,c.e OBSERVED TRANSIENTS GROUPED
~
BY STRENGTH OF STRATIFICATION (RSS) INTERVALS No. Observed % of RSS Cycles Total a,c.e I
- . j Note: The No. of groups is reduced by combining the intervals .70 < x 8 and .6 < x < .70 % of total = 3.4% for the interval-anca.mentas to 1 34 u _ _- -_ _-. <
TABLE 1-13 (cont.)
SUMMARY
OF PLANT MONITORING HEATUP/COOLDOWN TRANSIENTS f. WITH STRENGTH OF STRATIFICATION (RSS)'
.,. 'RSS J % of Transients i a,c.e RELATIVE NUMBER OF CYCLES OF STRENGTH OF STRATIFICATION (RNSSj)
AFTER GROUPING RSSj RNSSj' Strength of 1
% Transients (2) j Stratification (1) a,c.e f
Nomenclature: (1) Strength of Stratification (RSS) (2). Relative Number of Cycles of Strength of Stratification (RNSS) aca./mai n io 1-35 i __-_________-__-____-____-___0
L TABLE'1-14
SUMMARY
OF MONITORED TRANSIENT CYCLES (ONE HEATUP)
)
1 i Plant No. of Cycles ~ a,c.e A<g. Monitored Cycles: 15.75 = x; Selected No. of Design Cycles: 36.5 (added 30% to observed maximum number of cycles, planta) DESIGN DISTRIBUTION APPLIED TO MAX NUMBER OF . TRANSIENTS EXCEPTED MULTIPLIED BY 200 HEATUP OR C00LDOWN CYCLES - No. of Transients RSS a,c.e Total _ O mowenise in 1-36
TABLE 1-15
SUMMARY
OF % TIMES AT MAXIMUM TEMPERATURE POTENTIAL RMTP g HEATUP a,c.e e e t 3602: 4 82180-10 }.y
TABLE 1-16 SURGE LINE TRANSIENTS - STRIPING FOR HEATUP (H) and COOLDOWN (C)
~
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O a c.e d l 1 Figure 1-19. Typical [' Ja,e e Tegerature PMN e sen..im i. 1-57
i- i 1 4
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==ien is I.77
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Figure 1-40. Comparison of Design to Monitored Transients
== = u 1-78
- 1. - _ _ _ _ _ _ _ _ - - _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ - - - . .J
)
SECTION 2.0 \ STRESS ANALYSES
. Flow diagram figure 2-1 describes the procedure to determine the effects of thermal stratification on the pressurizer surge line based on transients developed in section 1.0. [~
3a,c.e Section 2.1 Addresses the structural or global effect of stratification Section 2.2 Addresses the local stress effects due to the nonlinear portion of the temperature profile Section 2.3 Addresses the total stress effects due to the oscillation of the hot-to-cold boundary layer (striping) plus the thermal stratification stress 2.1 Piping System Structural Analysis 2.1.1 Introduction The thermal stratification computer analysis of the piping system to determine the pipe displacement, support reaction loads as well as moment and force loads in the piping is referred to as the piping system structural analysis. These loads are used as input to the fatigue evaluation. The thermal stratification condition consists of both axial and diametric variations in the pipe metal temperature, as described in section 1.0. The model consists of straight pipe and elbow elements for the ANSYS computer code. [
]C ~
These studies verified the suitability of the ANSYS computer 3790s/062 fee 10 2'
p code for the thermal. stratification analysis. [ 1 . . ja,c,e
.2.1.2 ' Discussion On. Typical Surge Line' Analysis The piping _ layout for. a typical surgeline is shown in figure 2-3. The rigid support,.Ril, originally installed to' reduce deadweight and seismic. loads provides; resistance to the displacements caused by thermal stratification.
-[
4 e 1 1
,Jac
, ,e '
{ 3%/os2ess to l 2-2
~.- - __--,--__--_.--_n,-,.n-- ___ _ ---
4 [ O e S 4 e ja,c.e ! 1 O me.ame in 2-3 1 1_ _ _ _ _ . _ _ _ _ . . _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ ____ _
p w .
,1 I :l L. ..
l 1 Ja',c.e Based on the above discussion, the.ANSYS computer Code is suitable for the thermal stratification analysis. [ l ja.C,8 1 i [ -. Ja.C,0 i
. l veo maase.no -
t-L 4
~
ja,c.e 2.1.3 Results For Seabrook Unit 1 Surge Line The calculated piping stress due to thermal stratification for Seabrook Unit I surge line is reviewed to ensure that the system will not collapse in a
" hinge-moment" mechanism. The primary plus secondary stress limit for this piping stress is given by ASWE III, Section NB 3600, equation 12 as 3.0 Sm. <
The maximum stress intensity range, which occurs at the RCL hot leg nozzle, is 57.2 ksi, this is less than the Code allowable value of 61.5 ksi for the SA-182, F316N material. This corresponds to a bounding thermal stratification case with AT = 320*F between the pressurizer and:RCS hot leg. It should be noted that.the stress index for the hot leg nozzle in equation 12 were developed from finite element analysis of the RCL nozzle. A summary of maximum ASME code calculated stresses are presented in table 2-11. The ',oads on the two vertical rigid supports, 49-SG-01 (node 2070) and 49-3G-04 (node 5250) were 42 kips and 10 kips, respectively. For 49-SG-01,_ tre support has been analyzed to maximum loads of 90 kips in the +Y direction and 111 kips in the -Y direction. In combination with other dead weight, seismic and pipe break loads, sufficient margin exists at 49-SG-01 to account for the 42 kips due to thermal stratification load. For 49-SG-04, the previous design analysis load was 18 kips, which is greater than the load for the stratification case. Vertical displacements from the stratification cases were found to be less than available clearances at whip restraints with consideration of tolerances. 2.1.4 Additional Information on Linear Equivalent Techniques l 2.1.4.1 Introduction A review of the pressurizer surge line thermal stratification for several plants indicated that the actual stratification temperature profiles are veo. m eneae 2-5
.l 1
I better described by nonlinear diametric (cross-sectional) temperature distributions. .These temperature profiles will have effects on the global structural behavior of the surge lines in terms of loads and displacements.
.{ '
The use of isoparametric solid elements has made possible the study of - non-linear cross-sectional temperature profiles, such as step change of temperatures at mid plane. This study was performed using a model developed for the WECAN computer code. In order to achieve a less costly analytical solution, an alternative model using pipe and elbow elements was developed for the ANSYS computer code. These elements can only be loaded with a constant cross-section temperature or a linear top-to-bottom cross-section temperature. It, therefore, becomes necessary to establish an equivalent linear temperature profile which will result in the same deflections and loads in the piping system, as would a nonlinear temperature profile. It should be noted that there are differences in the WECAN and ANSYS models as described in section 2.1.2. These modeling differences will contribute to minor differ-ences when results'obtained from the analyses are compared. The purpose of the study and the comparison with the measured displacements is to verify the suitability of the ANSYS code for the thermal , gratification global analysis. The theoretical basis for the equivalent linear temperature profile is based , on a cantilever beam model and is summarized below. 2.1.4.2 Theory The closed form solution is determined for the free end vertical and axial displacements of a cantilever cylindrical beam subject to two types of stratification temperature profiles: a) linear equivalent variation from top to bottom; b) step change at distance Y, below the beam centerline. The axis of the beam (x-axis) lies in a horizontal plane. The solution is based on the following principles: [
)a,c,e sm.aum ie 2-6
v [.
, ja.c.e
- 5. For a cantilever beam subject to thermal stratification, the axial force (F) and bending moment (N) are zero at each cross section (A),
- thus, F=IA.o dA = 0 (2.1-5)
M=IA o y dA = 0 (2.1-6) The above equations are solved in closed form with the following results: [ g =:_-__-___________-______-___ _ _ . -
1> y! ' p l: I .. l:- 2 l 1, il f ja,c.e The solution for the equivalent linear temperature in the form of coefficients J ik isobtainedbyequating(2.1-7)with(2.1-9)and(2.1-8)with(2.1-10). I (2.1-11) l" (2.1-12) where
=.mamae 2-8 ,
1
)
_ _ __ _ _-___D
l
)
i i ja,c.e 2.1.4.3 Application - The' deflections and loads in the surge line for case 3 (step at mid plane) have been calculated by WECAN. The same step change temperature profile is converted to an equivalent linear temperature profile (case 3L) for ANSYS using the Jik c efficients with Y, = 0. Table 2-4 is an example for 14-inch schedule 140 pipe. The case 3 and case 3L temperature profiles used in the analyses are shown in figure 2-23c and 2-23d. The results are presented in table 2-2. i
- =
2.1.4.4 Discussion
.l The suitability of the ANSYS computer code for the thermal stratification global analysis is demonstrated by the comparisons between case 3 and case !
3L. WECAN and ANSYS pipe displacements on table 2-2 also confirm this. In addition, case 3L is. representative of the eleven analysis cases which represent various step temperature profiles along the pipe axis. I 2.1.5 Conclusions Analytical studies with the AWSYS and WECAN computer codes have confirmed the validity of using an equivalent linear diametric temperature profile to l* represent the thermal stratification for displacement and loads. Eleven cases , of thermal stratification were analyzed using the ANSYS code for the Seabrook !
~
Unit I surgeline. Results for all other cases of stratification were obtained . 2790e/D8220010 2-9 j
L by interpolation. The resulting loads on the pressurizer and hot leg nozzles are acceptable.. The surge line pipe stress satisfies the ASME III NB-3600 . ; l Code equation 12 limits. ' 2.2 Local Stress Due to Non-Linear Thermal Gradient 2.2.1 Explanation of Local Stress Figure 2-24 depicts the local axial stress components in a beam with a sharply nonlinear metal temperature gradient. Local axial stresses develop due to the restraint of axial expansion or contraction. This restraint is provided by the material in the adjacent beam cross section. For a linear top-to-bottom temperature gradient, the local axial stress would not exist. [ ja.c.e . 2.2.2 Superposition of Local and Structural Stresses - 4 For the purpose of this discussion, the stress resulting from the global structural analysis (section 2.1) will be referred to as " structural stress." [
.]'" Local and structural stresses may oe superimposed to obtain the total stress. This is true because linear elastic analyses are performed and the two stresses are independent of each other as summarized in figure 2-25.
Figure 2-26 presents the results of a test case that was performed to demonstrate the validity of superposition. As shown in the figure, the super-position of local and structural stress is valid. I ja c.e
*"2"
2-10 J
2.2.3 Finite Element Model of Pipe for Local Stress
~A short description of the pipe finite element model is shoim in figure 2-27.
The model with thermal boundary conditions is shown in figure 2-28. Due to symmetry of the geometry and thermal loading, only half of the cross section was required for modeling and analysis. [
,ja,c.e 2.2.4 Pipe Local Stress Results -
Figure 2-29 shows the temperature distributions through the 14 in. schedule 160 pipe wall [,j ja.c.e g e. e e 2-11 - _ _ - _ _ _ - _ _ _ _ - _ - _ _ _ - _ _ _ _ - - _ - _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ . _-_______-__-_____-_-_-__-____---_-_a
ja.c.e , 2.2.5 Unit Structural Load Analyses For Pipe In order to accurately superimpose local and global structural stresses, several additional stress analyses were performed using the 2-0 pipe model. [ ja.c.e 2.2.6 RCL Hot Leg Nozzle Analysis Two RCL surge line nozzle models were developed to evaluite the effects of thermal stratification. These two models are shown in figures 2-43 and 2-44. [ ja.c.e Figures 2-45 thru 2-53 present color contour plots of temperature and stress distributions in the surge line RCL nozzle. A summary of local stresses in the RCL nozzle due to thermal stratification is given in table 2-6. A summary of pressure and bending induced stresses for unit loading applied is shown in table 2-7. 2.2.7 Conservatism Conservatism in the local stress analysis are listed below: 2no.,=22= io 2-12
m t . r 1. The hot / cold fluid interface is assumed to have zero width. A more gradual change from hot to cold would significantly decrease local stresses. P . 2.- Stresses are based on linear elastic analysis even though stress levels exceed the material yield point. 2.3 Thermal Striping 2.3.1 Background At the time when the feedwater line cracking problems in PWR's were first discovered, it was postulated that thermal oscillations (striping) may i significantly contribute to the fatigue cracking problems. These oscillations were . thought to be.due to either mixing of hot and cold fluid, or turbulence in the hot-to-cold stratification layer from strong buoyancy forces during low flow rate conditions. '(See figure 2-54 which shows the thermal striping fluctuation in a pipe). Thermal striping was verified to occur during subsequent flow model tests. Results of the flow model tests were used to
~*
establish boundary conditions for the stratification analysis and to provide striping oscillation data for evaluating high cycle fati@ue. Thermal striping was also examined during water model flow tests performed for the Liquid Metal Fast Breeder Reactor primary pipe loop. The stratified flow was observed to have a dynamic interface region which oscillated in a wave pattern. (See figure 2-55 for test pipe sizes, thermocouple locations, and table 2-8 for typical frequency of striping oscillations.) These dynamic oscillations were shown to produce significant fatigue camage (primary crack initiation). The same interface oscillations were observed in experimental studies of thermal striping which were performed in Japan by Mitsubishi Heavy Industries. 2.3.2 Additional Background Information
~
Thermal striping was examined during 1/5 scale water model flow tests performed for the Liquid Metal Fast Breeder Reactor primary pipe loop. These
- =.an=io 2-13
tests were performed by Westinghouse at the Waltz Mills test facility. In order to measure striping, thermocouple were positioned at 5 locations in the , hot leg piping system (three in the small diameter pipe and two in the large diameterpipe.) The inside diameters of the large and small pipes were 6-1/2 . and 4 inches, respectively. Figure 2-56 shows the test setup and locations of the thermocouple. (Figure 2-55 shows test pipe sizes with circumferential position of thermocouple.) Thermocouple locations were selected [
,]C The thermocouple extended [ ]*' into the fluid. The flow rates and corresponding Richardson numbers for each pipe size are shown in table 2-9.
A total of (fifteen]"'C'* tests were performed and evaluated. Three parameters were measured during the water tests which help define thermal striping: frequency of fluctuations, duration, and amplitude of delta fluid temoarature. The [ Ja.c.e were recorded in the discussion of test results and are presented in table 2-10. l The frequencies of the temperature fluctuations from these test results were
~
reported to be in the range of ( Ja.c.e As shown in table 2-10, the [- -
~ '
~~~
ja,c3 [. ja,c.e In order to use the water test data for the surge line striping analysis, the test data.with a (~
] d was chosen to be used in the evaluation. From .
table 2-9, the [ ]C inch I.D. pipe with flow rates of [ me.=22= io 2-14 I
,)a,c.e for the pressurizer surge line. , When all other factors are equal, it has been shown that the thermal striping stress is [ Ja c.e A typical value of usage factor was calculated with the [
Ja.c.e ,, f,)) ,,, [_ , ja,c.e This distribution corresponded to [ Ja,c.e considered' to occur at a stress level calculated with frequencies of [
),a,c.e respectively. Calculations revealed that there was [
]"'C in the usage factor when a [
frequency of .30 hz was used_vs. the worst frequency distribution shown Ja,c.e Therefore,[ Ja,c.e was assumed in all usage factor calculations. For the Seabrook Unit 1 Pressurizer surge line, the frequency of f
.]a,c.e was used in the I.
in the determination of total number of cycles at each AT level.]**C The total calculated usage factor from striping was i
}"'Cd to account for any uncertainty in the selection of frequency or other variables.
As shown in table 2-10, the amplitude of AT varies from (
]"'C d of the full AT between the hot and cold fluid temperatures.
For the Seabrook Unit 1 Surge line, the amplitude was assumed to be at i 3a,c.e as shown by the curve in figure 2-57. This is conservative since a higher AT results in higher stress.
'~
- =.wwe 2-15
-_______-____-_L
I i l The maximum duration of thermal striping from table 2-10 shows that thermal striping occurred for [ Ja.c.e For the Seabrook Unit 1 , pressurizer surce line, thermal striping was considered to occur [
~\
ja.c.e ! l 2.3.3 Thermal Striping Stresses i Thermal striping stresses are a result of differences between the pipe inside surface wall and the average through wall temperatures which occur with time, due to the oscillation of the hot and cold stratified boundary. (See figure 2-58 which shows the typical temperature di'stribution through the pipe wall). I' ja,c.e The peak stress range and stress intensity is calculated from a 2-D finite element analysis. (See figure 2-59 for a description of the model.) [ Ja,c.e The methods used to determine alternating stress intensity are definec: in the ASME code. Several locations were evaluated in order to l determine the location where stress intensity was a maximum. Stresses were intensified by K3 to account for the worst stress concentra-tion for all piping element in the surge line. The worst piping elements were the butt weld and the tapered transition. i [
~
)a.c.e _
mo.ou m o 2-16
._- __ _ _ _ _ -_ _ _ _- ~
l 1 1 2.3.4 Sumary of Striping Stress Considerations [
~
.ja,C,8
[ e
,,,w ,,
,.g
i o . .- 4 i I! 1. 1 ' p ja.c.e , 2.3.5- Thermal Striping Total Fluctuations and Usage Factor Thermal striping transients are-shown at.a AT level and number of cycles. [ ja.c.e
- me.wmo 2-18
i ja c.e 2.3.6 Conservatism l The conservatism in the striping analt:is are: striping occiars at one location; surface film coefficients assume high values with constant flow; and conservative design transients are used. The major conservatism involves the combination of maximum striping usage factor with fatigue usage factor from all other stratification considerations. The [ ja c.e 2.4 Transfer Function Method For Thermal Stress Calculation a ,c ,- i 6 me.nmw io 2-19
- - - - - - - ----_-----_-___----__________a
g 3 If 1 1
' -- - a , c . e .-
E
, , . - t 2.4.1 ' Description of the Methodology-
_ a,c.e e O emaname om.mnee in 2-20
'i l
i
~ 8,C,0 1 1
1 1 a l 1
+
I . , i I I 1 i i 9 l l t e .uj
' 4 tb 3790s/062889 10 2-21
~
- a,c.e 2.4.2 Example
- - a,c.e l
i. I 1 I i f k 2 i l l l e M 1
=
l t ano..ou io 2-22
, a,c.e d
1 i i 2.4.3 Comparisen of Total Stresses for.Seabrook
- 8,C,e I e
m neo.meme io 2-23
, b, q
I i
- a,c.e ;
-1 E
l l
' REFERENCES a c.e 2.4-1.
2.4-2. Burghes,'D. and. Graham, A., Introduction to Control Theory Including , Optimal Control, John Wiley & Sons, 1980. 2.4-3. WECAN.- Westinghouse Electric Computer Analysis User's Manual,
'[see appendix A).
2.4-4 WECEVAL, WECAN Evaluation Users Manual (see appendix A). S
***'*" 2-24
s TABLE 2-1
. COMPARISON OF WECAN AND ANSYS RESULTS FOR LINEAR STRATIFICATION - Case 2 ,. (Displacements in Inches)
ANSYS/WECAN (JOBANSF) WECAN (AGJAQLN) ANSYS (PERCENTAGE) Ri1 UX a,c.e UY UZ (vert %al typical) Sp1 UX UY UZ Sp2 UX UY UZ First SD bend UX
'=
off HL UY UZ Second SD bend UX off HL' UY UZ Max.. UZ Average UZ l 37hM2M 10 2-25
s .4 t #
~~
.\
TABLE 2-2
. COMPARISON OF WECAN [ Ja,c.e AND ,g ANSYS[ ]a,c.e RESULTS FOR CASE 3 Case 3L/ Case 3 Location , Direction WECAN Case 3 ANSYS Case 3L (Percentage)
Rigid Ri1 UX a,c.e UY i UZ FZ Spring Sp1 UX-UY UZ Spring Sp2 UX UY UZ
' First Band UX UY UZ Second Bend UX UY UZ !
Hot Leg MX MY MZ AVERAGE UZ Case 3L.ANSYS: DCISKXY, 11/12/88 I me.= me 2-26
g L: . t 1
^ L ,* -
TABLE 2-3 .H TEMPERATURE DISTRIBUTIONS.IN SEABROOK UNIT 1 PRESSURIZER SURGE LINE n, (4' , , j! i -. F a 8
- 4 f .',
L' -
=
W . i 9
- voovosaase:to 2-27 i
1 m ,, .'* p !.: , 4 9 TABLE 2-4 p THEEQdIVILENTLINEARCOEFFICIENTSJ ik . o ,
-(14. inch - Schedule 140 Pipe)
[- .. e y- J J J i, . o hh he Jch'- cc N'
. A.C,8
[ e WEEumiu m 4 l me.ame io 2-28
TABLE 2-5
. SEABROOK UNIT 1 SURGE LINE
~ MAXIMUM LOCAL AXIAL STRESSES AT [ Ja,c,e Local Axial Stress (psi) Location Surface Maximum Tenst'e Maximum Compressive a,c.e n Note: Local thermal stresses shown are for a AT = 260*F. me.mua. io 2-29
( i t TABLE 2-6
SUMMARY
OF. LOCAL STRATIFICATION STRESSES , IN THE SEABROOK UNIT-1 SURGE LINE AT THE RCL N0ZZLE All Stress in psi !- Linearized Stress Peak Stress
- l. Intensity Range Intensity Range Lccation Location Inside Outside Inside Outside a c.e 9
m O me. mama 2-30 i
I 4 1, TABLE 2-7
SUMMARY
OF PRESSURE AND BENDING INDUCED STRESSES ,. IN THE SEABROOK UNIT l' SURGE LINE RCL N0ZZLE FOR UNIT LOAD CASES - All Stress in psi , I Linearized Stress Peak Stress Intensity Range Intensity Range Diametral Unit Leading Location Location Condition Inside Outside Inside Outside-a,c.e 0 0 l n===. i . 2-31
7.u , . ' ll Ni , I:: [,. 1 r
' TABLE 2-8 STRIPING FREQUENCY'AT 2 MAXIMUN LOCATIONS FROM 15 TEST RUNS ,
~
8,C,8 O W
- M i
9 6
. sm.wassao I 2-32 i
. _ _ - _ _ _ _ _ - _ _ _ _ _ _ _ _ .. t
= - - - - - - - ,
- L' ;. ;
. .! 3.
g ..:: l' : TABLE 2 .- FLOW RATES AND RICHARDSON NUMBER V ~ FOR WATER MODEL FLOW TESTS l'
'e Cold Water-i' Flow Rate.
. Pipe Section (GPM) Ri i ,. -
B,Coe enume 4 4
'W m oune m ain 2-33
%CY -
C (
) G L V A A I
T )
-p N S E E t
T L O % C . P Y C F ( O
% X.
( A M E D ) U S T E ., . _ I L L %C P Y M C A ( S N . O N I I T M A C ) O / C L N 5 E O E N S E I L I ( L L T C P A A Y H E U T R C T M O O U G I C T D sL T O I ) 0 R N 1 E O
- H I 2 T % T A
E T' R L S U B E D A H ( T G I :. H G V O A W T ) N M O O I R % T F ) A Z R S H U T ( D L ( U Y S C . E N X R E A U M Q ) E R N F O I _ % T _ A R U D ( N I M e _ p i P l a D l -_ l a m- _ S
- NtWA l
} ', 6: . TABLE 2-11 ASME CODE STRESS
SUMMARY
l;.. - a,c.). .; p ., O
*ASME Boiler and Pressure Vessel Code, Section III, 1977 Edition through 1979 Sunner Addenda. .t e
1 1 e
~
sm.mn.io 2-35
.Y TABLE 2-12 COMPARISON OF [- ]a,c,e RESULTS WITH ,
THOSE OBTAINED BY DIRECT WECAN ANALYSIS. LOCATION A 0F FIGURE 2-60 .. a,c.e Note: The stress unit in psi. l
-l e
am.mam.io 2-36 1 4
r' P'i c TABLE 2-13 COMPARISON OF [ .Ja,c.e RESOLTSWITH o, . THOSE'0BTAINED BY DIRECT WECAN'
._; ANALYSIS. LOCATION H OF FIGURE 2-60
< a,c.e r
{.', e i er Note: . The stress unit in psi.
.e.
l u me.mam-ia 2-37
-+ 1 1
\ f 4,J\ l 'r L~
f
. COMPARISON SETWEEN [ la, , 2-1)ANDWECEVALRESULTSFORSEA TABLE b
' g 'c 8,C,8 .. l- ' i l l-l l , e l .- ! 1. l
- - ~
- n w.m = io 2-38 l .:
u -- ._ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ .
i i;;..
., -n k.. .. Q \
w blTERMINATION OF THE EFFECTS Ort THERMAL $7 RATIFICATION a,c.e
-a
[. (:
- t. -
Figure 2-1. Determination of the Effects of Thermal Stratification e ini.iivm io 2-39
e,c.e l Figure 2-2. Stress Analysis "
- =. 2mo 2-40
~
Z n PRE 55URIZER X F %
, /
kJ
\
l J ) RCL HOT LEG
- Figure 2-3. Typical Pressurizer Surge Line Layout
~
3790s/062W 10 2-41
- r. _ _ _ _ _ . _ _ _ _ _ - _ - _ _ _ _ _ _ _ _ _ _ _ _ . _ - _ . - _ - _ - _ _ _ - - _ _ _ _ _ _ _ _
5 :' (' s Q 1 (P; 'e a,c e . 1 L
' }
- )
.i 1
4 Figure 2-4. Cases 1 to 4: Diametric Temperature Profiles l l
, . wei.,ivue ,o '
2-42
~
-s.:
Figure 2-5. Case 5: Diametric and Axial Temperature Profile us . im.. so . 2-43
j; < 1 i 9 l l '-1 1 .
-- a,c.e 1.
1
'h l
l i-t' . Figure 2-6. Finite Element Model of the Pressurizer Surge Line Piping General View 3.i. mien ,. . 2-44
i ,
.I e
'h l'-
_a .c .e .. t i 46' ? 4 Figure 2-7. Finite Element Model of the Pressurizer Surge Line Piping Hot Leg Nozzle Detai) sei.nsieme i. , 2-45
.. -l t ! 4
, 1
- - l a .c.e -
1 i 6 6
- Figure 2-8. Thermal Expansion of the Pressurizer Surge Line Under Uniform
~
Temperature 2-46
* ./'
$ 1.:
..( '.--- p t
u .;.
. _ a,c.e ' ' 40 ,
A
.+
L' . e
, 6-
. Figure 2-9. Case 2 (linear) Temperature Profile at Hot Leg Nozzle 3te3e/StatAB 10 2-47 a
_____-____-----_Q
f a,c.e i: P [h
. Figure 2-10. Case 2 (linear) Temperature Profile at Pressurizer Elbow mr..i n io 2-48
a.c.e . I: . .
,l
^
i .'s I. Fihre2-11. Thermal Expansion of Pressurizer Surge Line Under Linear Temperature Gradient
.4 .
se,.ns,ue ,o g_g i
9
- a,c,e 1
. Figure 2-12. Bowing of Beams Subject to Top-to-Bottom Temperature Gradient
. mwou= =
2-50 L__ _u_ _ _ _ _ _ _
py- . - . . . '" - - - ~ ' - - - - ' ' " - - - ~ ' ' - ~ - ' - ' " ' -- ' ' - - ~ - - - " " ' - - - ' ' ' ' ' ' " " - - - " - - - ' " - - - - - - - - - - - ' ' ' - - - ' - - - ~ - ~
,,--T '
~~~"'~"----'~-"--"~~-~--~7
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SECTION 3.0 _ASME SECTION III FATIGUE US*GE FACTOR EVALUATION L.: 3.1. Code and Criteria Fatigue.usoge factors' for the Seabrook Unit 1 surge line were evaluated based
.on the requirements of the ASME B & PV Code, Section III (reference 3-1),
Subsection NB-3600, for piping components. The more detailed techniques of NB-3200 were employed, as allowed by NB-3611.2. ASME III fatigue usage factors were calculated for [ ,]a,c.e points in the surge line piping using program WECEVAL (reference 3-2). 3.2 Previous Design' Methods Previous method of surge line piping fatigue evaluation used the NB-3653 techniques but with thermal transients defined by W SSDC 1.3 F(3-3] and 1.3.X [3-4), assuming the fluid surges to sweep the surge line piping with an axisymmetric temperature loading on the pipe inside wall. These evaluations produced typical usage factors of approximately i Ja c.e at gi.th butt welds,. [ ./ *" A at'albows and bends, and [ Ja,c.e at the RCL hot leg nozzle crotch region. Effects of stratification were not included in previous
' design analyses.
It must be noted that these usage factors are conservative since, in the design process, calculations are carried to the point where results meet code requirements, and are not further refined to reduce the usage factor. 3.3 Analysis for Thermal Stratification With thermal transients redefined to account for thermal stratification as described in section 1.0, the stresses in the piping components were established (section 2.0) and new fatigue usage factors were calculated. Due o to the non-axisymmetric nature of the stratification loading, stresses due to all leadings were obtained from finite element analysis and then combined on a stress component basis. me aum to 3-1
y- -
+
i I L3.3.1 Stress Input Stresses in' the pipe wall due to internal pressure, moments and thermal
- stratification loadings were obtained from the WECAN 2-D analyses of 14' inch, :.
schedule 160.- [ 3a.c.e- [ 3a,c,e - 3.ii.2 - ~ Classification and Combination of Stresses As described in 3.3.1 the total stress in the pipe wall was determined for each transient load case. _ Two types of stress were calculated - Sn (Eq 10), ' to determine elastic plastic penalty factors, K,, and Sp (Eq 11) peak stress. . For most components in the surge line (girth butt welds, elbows, bonds) no gross structural discontinuities are present. As a result, the
! code-defined "Q" stress (NB-3200), or C3ElaaT, abTb lin Eq (10) of NB-3600 is zero. Therefore, for these components, the Eq. (10) stresses are due to pressure and moment.
For the RCL hot leg no:zle, the results of the 3-D finite element WECAN analysis of the nozzle were used to determine "Q" stress for transients with stratification in the nozzle. Note also that the Eq. (10) stresses included appropriate stress intensification using the secondary stress indices from NB-3681. - m .,m m ein 3-2
Peak stresses, including the total surface stress from all loadings - g- . pressure, moment, stratification - were then calculated for each transient. [ ja,r,e 3.3.3 Cumulative Fatigue Usage Factor Evaluation Program WECEVAL uses the n S and p S stresses calculated for each transient to determine usage factors at selected locations in the pipe cross section. Using a standard ASME method, the cumulative damage calculation is performed according to NB-3222.4(e)(5). The inside and outside pipe wall usage factors were evaluated at [ . Ja,c.e through the pipe wall of the 2-D WECAN model. This includes:
- 1) Calculating the S nand S pranges, K , and S alt I " ***"Y possible combination of the [ la,8,e transient load sets.
- 2) For each value of Salt, use the design fatigue curve to determine the maximum number of cycles which would be allowable if this type of cycle were the'only one acting. These values, N1, N 2 *'N n '
- were determined from Code figures I-9.2.1 and I-9.2.2, curve C, for f austenitic stainless steels.
- 3) Using the actual cycles of each transient loadset supplied to L WECEVAL, n '"2'***"n, calculate the usage factors U ,
1 1 U ...U I"
- Ui * "i/N .g This is done for all possible 2 n 11 l
combinations. If N gis greater than 10 cycles, the value of Ug is taken as zero. e [ ja,c.e n o..,ar2= in 3-3 l l 1 -_- -
1 (
,ja,c,e q
~
- 4) The cumulative usage factor, Ucum, is calculated as Ucum =U1+ )
U2+".+U.n The code allowable value is 1.0. I 3.3.4 Simplified Elastic-Plastic Analysis When code Eq. (10),nS , exceeded the 3Sm limit, a simplified elastic plastic ! analysis was performed per NB-3653.6. This requires separate checks of expansion stress, Eq. (12), and Primary Plus Secondary Excluding Thermal Bending Stress, Eq. (13), and Thermal Stress Ratchet, and calculation of the elastic plastic penalty factor, Ka, which affects the alternating stress by Salt
- EeS p/2. The K, values for all combinations were automatically calculated by WECEVAL. Thermal stress ratchet is also checked by WECEVAL.
Eq. (13) is not affected by thermal stratification in the pipe where no gross structural discontinuities exist, but required to be verified at the nozzle. Eq. (12) was evaluated in the Global ANSYS analysis by checking the worst possible range of stress due to the expansion bending moments (section 2). 3.3.5 Fatigue Usage Results The maximum Usage factors were [ ]a.c.e at the RCL nozzle safe-end (node 5040, figure 2-22) and [ Ja.c e at the 5-D bend located underneath the pressurizer, (figure 2-22) which are less than the code allowable of 1.0. The above usage factors included tha effects of striping. The nature of striping damage is at c much higher frequency, varies in location due to fluid level changes and is maximized at a different location than the ASME usage factor caused by the global bending and local transient effects of thermal stratification. s !
"" "*" 3-4
I 3.4 Conservatism in Fatigue Usage Calculation The above calculated ASME usage factors contain the inherent conservatism known to be in the ASME Code methods. These include the conservatism in the elastic plastic penalty factor, K,, the method of combining loadsets based on descending Salt, and the factor of 2 on stress and 20 on cycles in the design fatigue curve. Also, due to input limitations in program WECEVAL, the maximum value of peak stress intensification for all loading types was used. This was conservative at girth butt welds, since Ky = 1.2, K2 " 1*0' K3 = 1.7 in NB-3681 and K=1.8 was used in WECEVAL for all stresses. 3.5 References 3-1. ASME Boiler and Pressure Vessel Code, Section III,1986 Edition. 3-2. WCAP-9376, WECEVAL, A Computer Code to Perform ASME BPVC Evaluations Using Finite Element Model Generated Stress States, April,1985.
~
(Proprietary] 3-3. W Systems Standard 1.3.F, Rev. O. (Proprietary) 3-4. W Systems Standard 1.3.X, Rev. 0 (Proprietary) W S no.. = 2 u io 3-5 i
s APPENDIX A r,
. LIST OF COMPUTER PROGRAMS , This appendix lists and summarizes the computer codes used in the analysis of stratification in the Seabrook Unit 1 pressurizer surge line. The codes are:
- 1. WECAN
- 2. WECEVAL
- 3. STRFAT2
- 4. ANSYS A.1 WECAN A.1.1 Description WECAN is a Westinghouse-developed, general purpose finite element program. It contains universally accepted two-dimensional and three-dimensional i isoparametric elements that can be used in many different types of finite element analyses. Quadrilateral and triangular structural elements are used for plane strain, plane stress, and axisymmetric analyses. Brick and wedge structural elements are used for three-dimensional analyses. Companion heat conduction elements are used for steady state heat conduction analyses and transient heat conduction analyses.
A.1.2 feature Used The temperatures obtained from a static heat conduction analysis, or at a specific time in a transient heat conduction analysis, can be automatically input to a static structural analysis where the heat conduction elements are replaced by corresponding structural elements. Pressure and external loads can also be include in the WECAN structural analysis. Such coupled thermal-stress analyses are a standard application used extensively on an
, industry wide basis.
an.mme A-1 i
l
.A.1.3 Program Verification Both the WECAN program and input for the WECAN verification problems, . ' currently numbering over four hundred, are maintained under configuration -
control. Verification problems include coupled thermal stress analyses for the quadrilateral, triangular, brick, _ and wedge isoparametric elements. These problems are an integral'part of the WECAN quality assurance procedures. When- t a change is made to WECAN, as part of the reverification process, the configured inputs for the coupled thermal-stress verification problems are < used to reverify WECAN for coupled thermal-stress analyses. A.2 WECEVAL A.2.1 Description WECEVAL is a multi puroose program which processes stress input to calculate ASME Section III, Subsection NB equations and usage factors. Specifically, the program performs primary stress evaluations, primary plus secondary stress-intensity range analysis, and fatigue analysis for finite C oment models generated and run using the WECAN computer program. Input to WECEVAL consists of card image data and data extracted frc:n the output TAPE 12's generated by WECAN's stress elements. The program reads the input data, performs the necessary calculations, and produces summary sheets of the results. The required stresses are read from the WECAN TAPE 12's and placed onto intermediate or restart files. The user may then catalog these files for use in later evaluations. The stress state for a particular loading condition is obtained by a ratio-superposition technique. This optimal stress state is formed by manipulating the signs of the applied loads to generate the largest possible stress magnitude. A.2.2 Feature Used g WECEVAL has many options and features which enhance its versatility. Among I those used for this evaluation were: mm. memo A-2
p
- 1. 'The' ability to' perform simplified elastic plastic analysis per NB-3228.5,
..' including the automatic calculation of Ke factors and removal of. thermal i bending stresses from the maximum range of stress intensity evaluations. -d
- 2. Built-in ASME fatigue curves ~plus provisions for accepting user-defined ~
fatigue curves.
- 3. Equivalent moment linearization technique, along with the ability to correct for the radius effects in cylindrical and spherical caometries, b
- 4. The ability to limit the interactions'among load conditions during the fatigue analysis,
- 5. Generating input' for the fatigue crack growth program FCG.
A.2.3 Program Verification
' WECEVAL is verified to Westinghouse procedures by independent calculations of ASME III NB Code equations and comparison to WECEVAL results.
A.3 STRFAT2 A.3.1 Description STRFAT2 is a program which computes the alternating peak stress on the.inside surface of a flat pl, ate and the. usage' factor due to striping on the surface. The program is applicable to be used for striping on the inside surface of a
~
pipe if the program assumptions are considered to apply for the particular , pipe being evaluated. For striping the fluid temperature is a sinusoidal variation with numerous I cycles. The frequency, convection film coefficient, and pfpe material properties are 'f input. I mw=mo A-3 _ _ _ _ _ a
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, The program computes ^meximum alternating stress based on the maximum difference between inside surface skin temperature and the average through wall.- temperature. ! ,W
- A.3.2. Feature Used a
The program is,used to calculate striping usage factor based on a ratio of actual cycles of stress for a specified length of time divided by allowable cycles of stress at maximum the alternating stress level. Design fatigue
. curves for several materials are contained into the program. However, the user'has the ~ option to input any other fatigue design curve,-by designating that the fatigue curve is to be user defined.
'A.3.3 Program Verification STRFAT2 is verified to Westinghouse procedures by independent review of the stress equations and calculations.
A.4 ANSYS a A.4.1 Description ANSYS is a public domain, general purpose finite element code. A.4.2 Feature Used The ANSYS elements used for the analysis of stratification effects in the surge line are STIF 20 (straight pipe), STIF 60 (elbow and bonds) and STIF14 (spring-damper'forsupperts). A.4.3 Program Verification 'p As described in section 2.1, the application of ANSYS for stratification has been independently verified by comparison to WESTDYN (Westinghouse piping]
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me.mune to A-4 . i
l' analysis code) and WECAN (finite element code, section 8.1). The results from
, ANSYS are also verified against closed form solutions for simple' beam configurations.
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o. t ENCLOSURE 3 TO NYN-89077 WESTINGHOUSE LETTER NO. CAW-89-083-PROPRIETARY INFORMATION NOTICE, AFFIDAVIT CAW-88-129 4 i 1 1 1 l l l l l l 1
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