ML20091E344
| ML20091E344 | |
| Person / Time | |
|---|---|
| Site: | Kewaunee  |
| Issue date: | 03/31/1991 |
| From: | Mel Gray, Tilda Liu, Valasek L WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | |
| Shared Package | |
| ML111661114 | List: |
| References | |
| WCAP-12842, NUDOCS 9111190267 | |
| Download: ML20091E344 (105) | |
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Hestinghouse Class 3 HCAP-12842 Structural Evaluaticn of the Kewaunee Pressurizer Surge Line, Considering the Effects of Thermal Stratification March, 1991 M. A. Gray T. H. Liu C. B. Bond L. M. Valasek R. Brice-Nash S. Tandon Verified by: h Verified by: Y Y' b - H. H. Bamfory V. V. Vora Mb Approved by Approved by: 0-S. S. Palusamy, Manager R. B. Patel, Manager Diagnostics and Monitoring System Structural Analysis Technology and Development Work Perforraed under Shop Order KFBP-964 and 145 HESTINGHOUSE ELECTRIC CORPORATION Nuclear and Advanced Technology Division P.O. Box 272C Pittsburgh, Pennsylvania 15230-2728 ' e 1991 Westinghouse Electric Corp. 5428s/091791:10
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TABLE OF CONTENTS Section Title Eage Executive Summary iii 1.0 Background and Introduction 1-1 1.1 Background 1-1 1.2 Description of Surge Line Thermal Stratification 1-3 1.3 Scope cf Work 1-4 s 2.0 Surge Line Transient and Temperature Profile Development 2-1 2.1 General Approach 2-1 2.2 System Design Information 22 2.3 Development of Normal and Upset Transients 2-3 2.4 Monitoring Results and Operator Interviews 2-4 2.5 Historical Operation 2-6 , 2.6 Development of Heatup and Cooldown Transients 2-7 2.7 Axial stratification Profile Development 2-10 2.8 Striping Transients 2-12 3.0 Stress Analysis 3-1
~
3.1 Kewaunee Surge Line Layout 3-1 3.2 Piping System Global Structural Analysis ? 3.3 Local Stresses - Methodology and Results 3-5 3.4 Total Stress from Global and Local Aralyses 3-6 3.5 Thermal Striping 3-7 4.0 Displacements at Support Locations 4-1 5428s/100191:10 i
TABLE OF CONTENTS (Continued) ,
.4 Section Title hgg 5.0 ASME Section III Fatigue Usage Factor Evaluation 5-1 5.1 Methodology 5-1 5.2 Fatigue Usage Factors 5-7 5.3 Fatigue Due to Therinal Striping 5-9 5.4 Fatigue Usage Results 5-10 6.0 Summary and Conclusions 6-1 7.0 References 7-1
-Appendix A Computar Codes A-1
,. Appendix B USNRC Bulletin 88-11 B-1 Appendix C Transient Development Details C-1 Appendix 0 Kewaunee Historical Data 0-1 m
~
i t 5428s/100191:10 11
EXECUTIVE
SUMMARY
Thermal stratification has been identified as a concern which can affect the structural integrity of piping systems in nuclear plants since 1979, when a leak was discovered in a PWR feedwater line. In the pressurizer surge line, stratification can restit from the difference in densities between the hot leg water and generally hotter pressurizer water. Stratification with large temperature differe .?s can produce very high stresses, and this can lead to integrity concerns. Study of the surge line behavior has concluded that the largest temperature differences occur during certain modes of plcnt heatup and cooldown. This report has been prepared to demonstrate compliance with the requirements of NRC Bulletin 88-11 for the Kewaunee plant. Prior to the issuance of the bulletin, the Westinghouse Owners Group had initiated a program to investigate the issue, and recommend actions by member uti'ities. That program provided the technical basis for the plant specific analysis repcrted here for the Kewaunee plant. The plant specific transient development utilized a number of sources, including plant operating procedures, industry and plant specific surge line monitoring data, and historical records for the plant. This transient information was used as input to a structural and stress analysis of the surge line for the plant. Separate analyses were completed for the structural and leak 'efore-break o (LBB) analyses, and the LBB analyses results are reported in a separate report [15].
. The results of the structural analysis, and the fatigue analysis which followed, showed that the Kewaunee pressurizer surge line meets the stress , limits and usage factor requirements of the ASME Code for the romainder of the design life of the plant. The calculated support displacement 2 resulting from stratification have also been provided for both the existing and fature support configurations, to ensure proper gaps in pipe whip restraints and sufficient travel allowances in the spring can, in order to allow free pipe movement at all thermal conditions. The structurai analysis which resulted in this recommendation is discussed in Section 4.
5428s/100191:10 iii
These analyses, along with modification of the whip restraint gaps and spring hanger travel allowance in 1992, led to the conclusion that the Kewaunee plant is in full compliance with the requirements of NRC Bulletin 88-11. . 5428s/091791:10 iv
l l
SUMMARY
OF-RESULTS, AND STATUS OF 88-11 QUALIFICATION
.00eratina Historv i Date of commercial operation 6-16-74 Years of water-solid heatups 0 Years of steam-bubble heatups 16 .
System delta T limit 320*F l
-Number of exceedances Three !
Maximum Stress and Usage Factor Resulti Equation 12 stress / allowable' (ksi) 52.3/53.0 Fatigue usage / allowable 0.97/1.0 Pressurizer Surge Nozzle Resulti Maximum stress-intensity range / allowable (ksi) 32.39/57.9 Fatigue usage / allowable 0.78/1.0 Restraint _ Modifications Reauired adjust pipe whip restraint gaps (Tables 4-1 and 4-2) Snrina Can Modification _ Required allow sufficient travel (Tables 4-1 and 4-2) Remainina Actions by Utility Schedule for modifications 1992 of spring hanger and restraints . Status of 88-11 Reautrements All analysis requirements met with l modification in 1992 l L l Results for future configuration. See Table 3-2 for results for pre:9nt l configuration. l l 5428s/091791:10 v l
-~.._._ . _ _ _ _ _ _ _ __
SECTION
1.0 BACKGROUND
AND INTRODUCTION Kewaunee is a two-loop pressurized water reactor, which began commercial
. operation on June 16, 1974. This report has been developed to provide the technical basis and results of a plant-specific structural evaluation for the effects of thermal stratification of the pressurizer surge line for the plant.
The operation of a pressurized water reactor requires the primary coolant loop to be water solid, and this is accomplished through a pressurizer vessel, connected to the loop by the pressurizer surge line. A typical two-loop arrangement is shown in Figure 1-1, with the surge line highlighted. The pressurizer ve3 contains steam and water at saturated conditions with the steam-water interface level typically between 25 and 60% of the volume, depending on the plant operating conditions. From the time the steam bubbla 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%. The steam bubble provides a pressure cushion effect in the event of sudden changes in Reactor Coolant System (RCS) mass inventory. Spray operation reduces system pressure by condensing some of c the steam. Electric heaters, at the bottom of the pressurizer, may be energized to generate additional steam and increase RCS pressure. As illustrated in Figure 1-1, the bottom of the pressurizer vessel is ! connected to the hot :eg of one of the coolant loops by the surge line, a 10 inch schedule 140 stainless steel pipe, a portion of which is horizontal. 1.1 RickGInund-During the period frcm 1982 to 1988, a number of utilities reported unexpected l- movement of the pressurizer surge line, as evidenced by crushed insulation, gap closures in the pice whip restraints, and in some cases unusual snubber movement. Investigation of this problem revealed that the movement was caused l ! by thermal stratification in the surge line. l 5428s/091791:10 1-1
~ . . - -
Thermal stratification had not been considered in the original design of any pressurizer surge line, and was only recently known to have been the cause of service-induced cracking in feedwater line piping, first discovered in 1979 * [14]. Further instances of service-induced cracking from thnrmal stratification surfaced in 1988, with a crack in ? safety injection line, and a separate occurrence with a crack in a residual . eat removal line. Each of the above incidents resulted in at least one through-wall crack, which was detected through leakage, and led to a plant shutdown. Although no through-wall cracks were found in surge lines, inservice inspections of one plant in the U.S. and another in Switzerland mistakenly claimed to nave found sizeable cracks in the pressurizer surge line. Although both these findings were subsequently disproved, the previous history of stratified flow in other lines led the USNRC to issue Bulletin 88-11 in December of 1988. A copy of this bulletin is included as Appendix 8. The bulletin requested utilities to establish and implement a program to confirm the integrity of the pressurizer surge line. The program required both visual inspection of the surge line and demonstration that the design requirements of the surge line are satisfied, including the consideration of stratification effects. Prior to the issuance of NRC Bulletin 88-11, the Westinghouse Owners Group had implemented a program to address the issue of surge line stratification. A bounding evaluation was performed and presented to the NRC in April of 1989. This evaluation compared all the WOG plants to those plants for which a detailed plant specific analysis had been performed. This evaluation demonstrated that all WOG plants could operate for an additional ten heatup/cooldown cycles, ano provided the basis for a i neric justification for , continued operation until a more thorough evaluation could be completed to ensure full design life [1], [2]. This WOG generic JC0 provided the basis for . the Kewaunee Nuclear Power Plant plant-specific justification for continued operation which was submitted to the NRC on May 24, 1989 [13]. The Westinghouse Owners Group implemented a program for generic detailed analysis in June of 1989, and this program involved individual detailed analyses of groups of plants. This approach permitted a more rcalistic 5428s/091791:10 1-2
approach than could be obtained from a single bounding analysis for all plants, and the results were published in June of 1990 [3).' The followup to the Westinghouse Owners Group Program is a demonstration of the applicability of reference [3] to each individual plant, and the performance of evaluations which could not be performed on a generic basis. The goal of this report is to accomplish these followup actions, and to therefore complete the requirements of the NRC Bulletin 88-i - for Kewaunee. 1.2 Descriotion of Surae Line Thermal Stratification It will be useful to describe the phenomenon of stratification, before dealing with its effects. Thermal stratification in the pressurizer surge line is the direct result of the difference in densities between the pressurizer water and the generally cooler RCS hot leg water. The lighter pressurizer water tends t3 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 ae the insurge or outsurge flow rates decrease. At power, when the difference in temperature b.5seen the pressurizer and hot leg is relatively small, the extent and effects of stratification have been observed to be small. However, during certain modes of plant heatup and cocidown, this difference in system temperature could be as large as 320*F, in which case the effects of stratification are significant, and must be accounted for,
, Thermal stratification in the surge line causes two effects:
o Bending of tha pipe is different than that predicted in the original design.
- Numbers in brackets refer to references listed in Section 7.
5428s/091791:10 1-3
o Potentially reduced fatigue life of the piping due to the higher stress resulting from stratification and striping. 1.3 SIspe of Work The primary purpose of this work was to develop transients applicable to the Kewaunee plant which include the effects of stratification and to evaluate these effects on the structural integrity of the surge line. This work will therefore complete the demonstration of compliance with the requirements of NRC Bulletin 88-11. The transients were developed following the same general approach originally established for the Westinghouse Owners Group. Conservatism inherent in the original approach were refined through the use of monitoring results, plant operating procedures, operator interviews, and historical data on plant operation. This process is detailed in Section 2. The resulting transients were used to perform an analysis of the surge line, wherein the existing support configuration was carefully modeled, and surge line displacements, stresses and support loadings were determined. This analysis and its results are discussed in Sections 3 and 4. The stresses were used to perform a fatigue analysis for the surge line, and the methodology and results of this work are discussed in Section 5. The summary and conclusions of this work are summarized in Section 6. I 5428s/100191:10 1-4
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SECTION 2.0 SURGE LINE TRANSIENT AND TEMPERATURE PR0flLE DEVELOPMENT 2.1 G1neral Approach The transients for the pressurizer surge line weie developed from a number of sources, including the most recent systems standard design transients. The heatup and cooldown transier.ts, which involve the majority of the severe stratification occurrences, were developed from review of the plant operating procedures, operator interviews, monitoring data and historical records for the plant. The total number of heatup and cooldown events specified remains - unchanged at 200 each, 'out a number of sub-tvents have been defined to reflect stratification effects, es described in more detail later. The normal and upset transients, except for hEatup and cooldown, for the Kewaunee surge line are provided in Table 2-1 For each of the transients the surge line fluid temperature was modified from the original design assumption of uniform temperature to a stratified distribution, according to the predicted temperature differentials between the pressurizer and hot leg, as listed in the table. The transients have been characterized as either insurge/outsurges (I/O in the table) or fluctuations (F). Insurge/outsurge transients are generally more severe, because they result in the greatest temperature chango '.n the top or bottom of the pipe. Typical temperature
~
profiles for insurges and outsurges are shown in Figure 2-1. Transients identified as fluctuations (F) typically involvo low surge flow rates and smaller temperature differences "etween the pressurizer and hot leg, so the resulting stratification stresses are much lower. This type of cycle is important to include in the analysis, but is generally not the major - contributor to fatigue usage. The development of transients which are applicable to Kewaunee was based on the work already accomplished under programs completed for the Westinghouse Owners Group [1,2,3]*. In this work all the Westinghouse plants were grouped
' Numbers in brackets refer to references listed in Section 7.
5428s/091791:10 2-1
based on the similarity of their response to stratification. The three most important factors-influencing the effects of stratification were found to he the structural layout, support configuration, and plant operation. - I l The transients developed here, and used in the structural analysis, have taken - , advantage of th6 monitoring data collected during the WOG program, as well as operator interviews and historical operation data for the Kewaunee plant. Each of these will be discussed in the sections which follow. 2.2 System Desian Information
)
The thermal design transients for a typical Reactor Coolant System, including the pressurizer surge line, are defined in Hestinghouse Systems Standard Design Criteria. The design transients for the surge lir.e consist of two major categories: (a) Heatup and Cooldown transients (b) Normal and Upset operation trcnsients (by definition, the emergency and faulted transients are not considered in the ASME Section III fatigte life assessment of components). In the evaluation of surge line stratification, the typical FSAR chapter 3.9 definition of normal and upset design events and the number of occurrences of the design events rerains unchanged. The total number of heatup-cooldown cycles (200) remains unchanged. However, . sub-events and the associated number of occurrences (" Label", " Type" and " Cycle" columns of Tables 2-1 and 2-2 have been defined to reflect , stratification effects, as described later. 5428s/100191:10 2-2
2.3 Stratification Ef fetts Criteria and_Aerelopment_ of Norml]_andjjple_t Transi ent.1
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3a ,c.e 5428s/091791:10 2-3
[ j a.c.e , [ a C,e 3 2.4 Monitorina Results and-Qperator Interviews 2.4.1 Moni toring Honitoring infonnation collected as part of the Westinghouse Owners Group generic detailed analysis [3] was utilized in this analysis. Monitoring was performed at plants with similar layout, in addition to the Kewaunee plant. The monitoring programs used existing and installed temporary sensors on the. surge line piping, as shown in Figure 2-2. The pressurizer surge line monitoring programs utilized externally mounted temperature sensors (resistance temperature detectors or thermocouples). The temperature sensors were attached to the outside surface of the pipe at j various circumferential and axial locations. In all cases these temperature sensors were securely clamped to the piping outer wall using hose clamps, , taking care to properly insulate the area against heat loss due to thermal convection cr radiation. . l l 5428s/091791:10 2-4
The typical temperature sensor configuration at a given pipe location consists of five sensors; however, the Kewaunee monitoring program used sesen, mounted
. as shown in Figure 2-2. Temperature sensor configurations were mounted at various axial locations, rho multiple axial locations give a good picture of how the top to bottom temperature distribution may vary along the longitudinal axis of the pipe. In addition, many pressurizer surge line monitoring programs utilized displacement sensors mounted at various axial locations to detect vertical movements, as shown in Figure 2-2. Typically, data were collected at [ 3a ,c.e intervals or less, during periods of high system delta T.
Existing plant instrumentation was used to record various system parameters. These system parameter; were useful in correlating plant actions with stratification in the surge line. A list of typical plant parameters monitored is given below. [ 3a ,c.e Data from the temporary sensors was stored on magnetic floppy disks and converted to hard copy time history plots with the use of common spreadsheet software. Data from existing plant instrumentation was obtained from the utility plant computer. 2.4.2 Operational Practices An operations interview was conducted at the Kewaunee plant on September 18, 1969. Since the maximum temperature difference between the pressurizer and 542Bs/091791:10 2-5
. . . . . . ~ . . - - - - _ - _ - . . _ . - .. - . - . - _ . - ...-.-,-
the reactor coolant loop occurs during the plant heatup and cooldown, operations during these events were the main topic of the interview. Figure 2-3 describes the heatup process, and Figure 2-4 is the corresponding - plot for the cooldown orocess. In both heatup and cooldown, the plant has an administrative limit of 320*F on i temperature difference between pressurizer and reactor coolant system. ; 2.5 Historical 0 aeration A review of historical records from the plant (operator logs, surveillance test reports, etc.) was performed. From this review, two pieces of information were extracted: a characteristic maximum system delta T for each heatup and cooldown recorded, and the number of delta T exceedances of 320*F , (Appendix D). The number of actual heatups and cooldowns experienced to date and their associated system delta temperature are described below for the plant. Number of Percentage of l System AT Heatup & Cooldown Heatup & Cooldown l Range (*F) Experienced to Date Occurrences [ l' i l 3a,c.e This information was used to ensure that the transients analyzed for Kewaunee . ! . encompassed the prior operating history of the plant. Comparison of the above table.to the numbers.used in the evaluation, as seen in Figure 2-5, confirmed , applicability to the plant. [ 3a ,c.e l l l 5428s/100191:10 2-6
2.6 Develcoment of Heatuo and Cooldgwn Transienti The heatco and cooldown transients used in the analysis were developed from a ) number of sources, as discussed in the overall approach. The transients were built upon the extensive work done for the Westinghouse Owners Group [1,2,3], coupled with plant specific considerations for Kewaunee. Plant specific considerations included past operating historical temperature data, and accounting for past and future operation with respect to whip restraint gap modi fications. The transients were developed based on monitoring data, historical operation and operator interviews conducted at a large number of plants, including Kewaunee. For each monitoring location, the top-to-bottom differential temperature (pipe delta T) vs. time was recorded, along with the temperatures of the pressurizer and hot leg during the same time period. The difference between the pressurizer and hot leg temperature wa. termed the system delta T. From t!.e pipe and system delta T information collected in the WOG[1,2,3] effort, individual plants' monitoring data was reduced to categorize stratification cycles (changes in relatively steady-state stratified conditions) using the rainflow cycle ounting method. This method considers delta T range as opposed to absolute values. [ a .c.e-3 The resulting distributions (for I/O transients) were cycles in each RSS range above 0.3, for each mude (5,4,3 and 2). A separate distribution was determined for each plant at the reactor coolant loop nozzle and a chosen critical pipe location. Next, a representative RSS distribution was 5428s/100191:10 2-7 l
- - _- _- - . . ~ -, - _ - - . - . - - _ - - - - _ - . - -
deterrhined by multiplying the average number of occurrences in each RSS range by two. Therefore, there is margin of 1007. on the average number of cycles per heatup in each mode of operation. - Transients, which are represented by delta T pipe with a corresponding number - 1 of cycles, were developed by combining the delta T system and cycle distributions. For mode 5, delta T system is represented by a historical system distribution developed from a number of HOG plants (generic distribution). Using data from a number of plants is beneficial as the resulting transients are more representative of a complete spectrum of ! operation than might be obtained from a smaller number of heatups and cooldowns. As discussed in Section 2.5, this historical delta T system distribution was shown to encompass the prior operating history of the Kewaunee plant. For modes 4, 3 and 2, the delta T system was defined by maximum values. The values were based on the maximum system delta T obtained from the monitored plants for each mode of operation. An analysis was conducted to determine the average number of cycles per cooldown relative to the average number of cycles per heatup. [ 3a .c.e The transient cycles for all modes were then envaloped in ranges of ATp3p,, i.e., all cycles from transients within each ATpipe range were added and assigned to the pre-defined ranges. These cycles were , then applied in the fatigue analysis with the mar mum ATp$p,_for each range. The values used are as follows: l
- l For Cycles Within Pipe Delta T Range Pipe Delta T
[ - l
-i
\ 3a,c.e 5428s/091791:10 2-8
This grouping was done to simplify the fatigue analysis. The actual number of cycles used in the analysis for the heatup and cooldown events is shown in 4 Table 2-2. 7_
. The final result of this complex process is a table of transients corresponding to the subevents of the heatup and cooldown process. A mathematical description of the process is given in Appendix C. [
3a ,c.e ; The critical location is the location with the highest combination of pipe delta T and number of stratification cycles. Because of main coolant pipe flow effects, the stratification transient loadings at the reactor coolant hot leg nozzle are different. These transients have been applied to the main body of the nozzle as well as the pipe to nozzle girth butt weld. Plant monitoring included sensors located near the nozzle to surge lia.c pipe eeld. Based on the monitoring, a set of transients was developed for the
- nozzle region to reflect conditions when stratification could occur in the nozzle. The primary factor affecting these transients was the flow in the main coolant pipe. Significant stratification was noted only when the reactor l coolant pump was not operating in the loop with the surge-line. Transients were then developed using a conservative number of " pump trips."
l l-l a,c.e Therefore, fatigue analysis of the nozzle was performed using the " nozzle transients" and the " pipe transients".
'The analysis included both the stratification loadings from the nozzle transients, and the pressure and bending loads from the piping transients.
l l. l I 5428s/091791:10 2-9'
Gnce the. transients were generated, it was necessary to determine how many cycles of each should be considered with the past and future restraint configurations (see Section 3,0) for Kewaunee. The maximem number of heatups - that the plant has experienced is 35 events, The past configuration resulted in more conservative stress ranges; therefore, an addit',;nal 6 heatup events - were considered with the past restraint configuration, bringing the total number of events considered with the past restraint configuration to 41. The additional 6 heatups will account for operations until the modifications are matt. The remaining 159 heatups were considered with the future restraint configuration. Transients that a:cour. for past and future restraint configuration are shown in Table 2-2 as " cycles before modification" and
" cycles af ter modification".
The total transients for heatup and cooldown are identified as hcl thru HC9 for the pipe, and hcl thru HC9 for the nozzle as shown in Tables 2-2(a) and 2-2(b) respectively. Trantients HC8 thru HC9 for the pipe and HC9 for the nozzle represent transients which occur during later stages of the heatup. As indicated in Section 2.5, based on a review of the Kewc aee operating records, there were three events in whicn the system delta T exceeded the transient basis upper limit of [ l l
)a,c.e 2.7 Axial Stratification Profile Develcomgni In addition to transients, a profile of the [
3a ,c e 5428s/100191:10 2-10
l I Two types.of profile envelope the stratified temperature distributions observed and predicted to occur in the line. These two profiles are [ I j a.c.e low flow profiles are characterized by a non-linear top to bottom temperature distribution in association with low fluid velocities. A typical low flow profile is shown in Figure 2-6. Low flow profiles are a function of the density difference between the two fluids and the flow rates of each. During low flow conditions the two fluids do not mix, because of the density difference, but prefer to separate with the heavier (colder) fluid filling the lower portions of the pipe. The interface, the point at which the two fluids meet, has a constant elevation along its entire length for steady state conditions. This characteristic is present because stratification is a gravity induced phenomenon. [ i l i j a,c e 5428s/100191:10 2-11
-These three configurations ar. 'Ilustrated in Figure 2-7. [
3a ,c.e Review and study-of the monitoring data for all the plants revealed a consistent pattern of development of delta T as a function of distance from the hot leg intersection. This pattern was consistent throughout the heat-up/cooldown process, for-a given plant geometry. This pattern was used along with plant operating procedures to provide a realistic set somewhat conservative portrayal of the pipe delta T along the surge line. The combination of the hot / cold interface and p1pe delta T as functions of distance along the surge line forms a signature profile for each individual plant analyzed. [
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2.8 Stricina Transients The transients-developed for the evaluation of thermal striping are shown in . Table 2-3.
' [ .-
j a,c.e 5428s/091791:10 2-12
Striping transients use the labels HST and CST denoting striping transients
-(ST). Table-2-3 contains a summary of the HST) to HST8 and CST) to CST 7
- . . thermal striping transients which are similar in their definition of events to the heatup and cooldownl transient definition.
-These striping transients were developed during plant specific surge line evaluations and are considered to be a conservative representation of striping
.in'the surge line[33. Section 5 contains more information on specifically how the striping loading was considered in the fatigue evaluation.
k h il 5428s/091791: 10 2-13
1 TABLE 12-1 SURGE LINE TRANSIENTS WITH STRATIFICATION NORMAL AND UPSET TRANSIENT LIST . TEMPERATURES (*F) . = MAX NOMINAL LABEL TYPE CYCLES AT PRZ T RCS T Strat-l t i I A 1-4 3a ,c.e i 5428s/091791:10: 2-14 y --
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-TABLE 2-1-(Cont'd.)
-SURGE LINE TRANSIENTS 1HITH STRATIFICATION ;
-' - ' NORMAL AND UPSET TRANSIENT LIST i
TEMPERATURES (*r) i MAX NOMINAL LABEL TYPE CYCLES AT PAZ T RCS T Shat [ , t
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TABLE 2-2a SURGE LINE PIPE TRANSIENTS WITH STRATIFICATION HEATUP/COOLDOWN (HC) - 200 CYCLES TOTAL - TEMPERATURES (*F) CYCLES CYCLES - MAX NOMINAL BEFORE AFTER LABEL TYPE CYCLES AT FRZ T RCS T HODIF' CATION MODIFICATION Strat [ L l _ja.c,e 5428s/091791:10 2-16
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TABLE 2-2b SURGE LINE N0ZZLE TRANSIENT 4 HITH STRATIFICATION
- HEATUP/COOLDOWN (HC) - 200 CYCLES TOTAL--
. TEMPERATURES (*F) CYCLES CYCLES
'HAX NOMINAL BEFORE AFTER LABEL TYPE CYCLES AT PRZ T RCS T MODIFICATION HODIFICATION Strat
[ !.. Ja.C,e i , 5428s/091791:10 2-17
. . . _ . . . _ . - _ . . . . . _ _ _ . . . . _ _ ~ . _ . . _ . - _ . _ . . . _ . . _ _ _ . _ _ - _.
TADLE 2-3
' SURGE LINE TRANSIENTS - STRIPING FOR HEATUP (H) and C00LDOWN (C)
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!. ! l!t l!lIlll llliI!ltt1I ,
SEC'uhN 3.0 STRESS ANALYSES
- The flow diagram (Figure 3-1) describes the procedure to determine the effects . of thermal stratificatio,+ :n the pressurizer surge line based on transients developed in section 2.0. [
j a c.e 3.1 Taway_n_ee n Surae Line layou.1 The Kewaunee surge line layout is documented in reference [5] and is shown schematically in Figure 3-2. Below is a table summarizing the existing Kewaunee surge line support configuration. Suooort tLode Tyng RR-134-1 1040 Pipe Whip Restraint RR-134 1050 Pipe Whip Restraint RR-li4-3 1060 Pipe Whip Restraint RR-134-4 1070 Pipe Whip Restraint RR-134-5 1100 Pipe Whip Restraint RR-134-6 1130 Pipe Whip Restraint RR-134-7 1160 Pipe Whip Restraint RR-134-8 1190 Pipe Whip Restraint RR-114-9 1215 Pipe Whip Restraint RC-H41' 1080 Spring Hanger It can be seen from the table above that the Kewaunee surge line contains no vertical rigid supports but many pipe whip restraints, which esually result in high thermal loads during stratification. As a result of the thermal stratification analysis, plans have been made to modify the available gap sizes at whip restraint locations in the near future-to allow sufficient gaps 5428s/091791:10 3-1
l l l for thermal stratification movement. Therefore, in the global structural analysis, two models were prepared for: (i) existing support configuration with. existing gaps, and (ii) future support configuration with all gaps large - enough and sufficient travel allowance in the spring can to accommodate all thermal conditions. - The piping size is 10 inch schedule 140 and the pipe material is stainless steel for the surge 'ine. Experience with the analysis of thermal stratification has indicated that surge line layout [ 3a ,c.e 3.2 Pioina System Global Structural Analvtii - The piping system was modeled by pipe, elbow, and linear and non-linear spring elements using the ANSYS computer code in Appendix A. The geometric and material parameters are included. [ l l l l j Ja ,c.e A linear spring element is used to model the spring hanger, and non-linear spring elements are used for the whip restrai-ts. The l potential .for the spring hanger exceeding its displacement tolerance should be checked, as-discussed in Section 4. . For the Kewaunee surge line design with the existing support configurations, , under the normal thermal and thermal stratification loadings, many unintended thermal constraint conditions occurred at the pipe whip restraint locations. This is mainly due to the fact that the pipe whip restraints were originally designed with the considerations of the normal thermal expansion loading only, and consequently, less than adequate gap clearance for the higher l 5428s/091791:10 3-2 l l
.m.___ _
I i displacements resulting from stratification can exist in the pipe whip l restraints. [ l a.c.e for the future support configuration, all pipe whip restraints are to be removed or gaps are to be
. opened large enough so (nat no unintended thermal constraint will occur.
t The hot-cold tamperature interface along the length of a surge line [
~
i ja.c.e . Each thermal profile loading defined in section 2 was broken into ( i a J .c.e Table 3.1 shows the loading cases considered in the analysis. Within each operLtion the [ Ja ,c.e Consequently, all the thermal transient loadings defined in section 2 could be evaluated. The pressurizer and PCL temperature listed in Table 3-1 reflect the approximate system AT. System temperatures are used only to define the ' l boundary displacements at both RCL and pressurizer nozzles.
, In order to meet the ASME-Section III Code stress limits, global structural models of the surge line for existing and future support configurations were I
[ developed using the information provided by reference (5) and the ANSYS l' general purpose finite element computer code. Each model was constructed l i using [ 3a ,c.e 54285/100191:10 3-3
- _ . _ . _ __au _ _. _ _ .. _ _ _ _ _ _ ..._ _ _._ _ _ . . _ _ .
..__ ..~ _. -
for the stratified condition, [ j a,c.e The global piping stress analyses wtre based on two models for Kewaunee. The first model represents the existing whip restraint gap configuration and the second model represents the future configur" Hon (without restraint contact). The results of the ANSYS global structura ,;'ysis provides the thermal expansion moments. The ASME Section III equation (12) stress intensity range was evaluated for both gapped and no restraint configurations. For the existing gapped configuration, sy?'em delta T's of 334'F 331*F and 321'F were evaluated in addition to 320'F. For the future (no restraint) configuration, a system delta T = 320*F was evaluated as discussed in Section 2.0. The maximum ASHE equation (12) stress intensity range in the surge line was found to be under the code allowable of 35m for future support configuration. Maximum equation (12) and equation (13) stres; intensity ranges are shown in Table 3-2. The presscrizer nozzle loads from thermal stratification in the surge line were also evaluated according to the requirements of the ASHE code. The evaluation using transients detailed in Reference (12) plus the moment loading from this analysis, included the calculations of primary plus secondary stress intensities and the fatigue usage factors. The maximum stress intensity range is 32.39 ksi comparing to the code allowable value of 57.9 ksi, and the maximum fatigue usage factor will be r ; ported in Section 5. It was found that . the Kewaunee pressurizer nozzle met the code stress requirements. In order to superimpose local and global stresses, several 7 tress analyses were performed using the 3-D pipe model. [ 3a ,c.e 5428s/100191:10 3-4
i ( 6 j a.c.e 3.3 LonLittents -Etth04010ayanLRe s ulti l 3.3.1 Explanation of Local Stress l l Figure 3-3 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. [ I t 3h,C .e 3.3.2- Finite-Element Model of Pipe for Local Stress A :hort description of the pipe finite element model is summarized below. The model with thermal boundary conditions is shown in Figure 3-4. Due to symmetry of the geometry and thermal loading, only half of the cross section us required for modeling and analysis. ( b j a,c.e 5428s/091791:10 3-5 1
.+---+im-----s.,--mm ,..+-----..-----,-,-,---w. --
.w-r m- w.s..--w -. .-,.,y,.--,.-----.-.,y----v-,---,,,va,- - -,%..v,-- ,-r-ev,+%-,-w. ,.3-,w---i.. e rm ee--ri-- sve-
[ j a.c.o 3.3.3 Pipe Local Stress Results Figure 3-5 shows the temperature distributions through the pipe wall [ j a.c.e 3.3.4 RCL Hot Leg Nozzle Analysis A detailed surge line nozzle finite element model was developed to evaluate the effects of thermal stratification. The model is shown in Figure 3-9. [ l a.c.e A summary of stresses in the RCL nozzle location 1 due to thermal stratification is given in Table 3-3. 3.4 Total Strns from Global anLLoral Analvth [ 3a ,c.e l L 5428s/091791:10 3-6
I 4 r F 3a ,c.e 3.5 1hermal Str1Dh g 3.5.1 Background At the time when the feedwater line cracking problems in PWR's were first discovered, it was postulated that thermal oscillations (striping) may , 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 flos rate conditions. (See Figure 3-10 which shows the thermal strlping 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 fatigue.
. Thermal striping was also examined during water model flow tests performed for the Liquid Metal fast Breeder Reactor primary ploe loop. The stratified flow
, was observed to have a dynamic interface region which oscillated in a wave pattern. These dynamic oscillations were shown to produce significant fatigue damage (prim &ry crack initiation), The same interface oscillations were l observed in experimental studies of thermal striping which were performed in l
l l 5428s/091791:10 3-7
i i Japan by Hitsubishi Heavy Industries. The thermal striping evaluation process was discussed in detail in reference [3), and is also discussed in references ! (7), (8), and (9). [ 3.5.2 Thermal Striping Stresses
- l Thermal striping stresses are a result of dif ferences between the pipe inside l
$Urface wall and the average through wall temp ratures which occur with time, due to the oscillation of the hot and cold stratified boundary. (See figure 3-11 which shows a typical temperature distribution through the pipe wall). [
j a.c.e The peak stress range and stress intensity was calculated from a 3-D finite t element analysis. ( 1 Ja .c.e The methods used to determine alternating stress intensity are defined in the ASME code. Severs 1 locations were 1 evaluated in order to determine the location where stress intensity was a ! maximum. Stresses were intensified by K3 to account for the worst stress concentration for all piping elements in the surge line, The worst piping element was the b'Itt weld. I l ..
)a,c.e 5428s/091791:10 3-8
. ~ . . . _ _ _ _ _ _ _ _ _ _ _ ___________ _ _ _ _ - . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ -
i i 3.5.3 Factors Hhich Affect Striping Stress ; i The factors which affect striping are discussed briefly below: i [ ! I t t r 1 I r i P f t T i. i
)a,c,e ,
5428s/091791:10 3-9
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i i
-5428s/091791:10 3-10
TABLE 3-1 TEMPERATURE DATA USED IN THE ANALYSIS Max . Type of System Analysis Pressurizer RCL T Top T Bot Pipe Operation AT(*F) Cases Temp (*f) Temp ('F) (*F) (*F) AT ('F) [ 3a ,c.e 5428s/091791:10 3-11
TABLE 3-2 , Summary of Kewaunee Surge Line Thermal Stratification Maximum Stress Results
- SUPIDILCQufi9urJLtitu 83HLCtdg_Lquq11cn Existingt f_uture* Cody A11stwable 12 58.7 52.3 53.0 13 44.2 44.2 50.1 Future represents the support configuration of no restraint contact and no spring can bottomed out witt system AT-320'F
+ Existing represents the cuirent support configurations with maximum system AT-334*F 5428s/091791:10 3-12
TABLE 3-3 KEHAUNEE SURGE LINE e MAXIMUM LOCAL AXIAL STRESS AT [ Ja .c.e (10" - 140) Local Axi&l Stress (psi) location Surface Maximum Tensile Maximum Compressive t j a,c.e 5428s/091791:10 3-13
j TABLE 3-4 STRIPING FRE JENCY AT 2 MAXIMUM LOCATIONS FROM 15 TEST RUNS Total Frequency (HZ) Du.ation -
# Cycles
% % % Lgth, in Min (Duration) Max (Duration) Avg (Duration) Seconds
[ j a.c.e 5428s/091791:10 3-14
...mm..._... ..__.. _ . _ . ._ . _ . =._ _ =..._-.__... .-_ _ ___ _ _ _ _ _ _
a,c.e 4 i t i f f I 4 i f i i t i Y t, Figure 3-1.. Schematic of Stress Analysis Procedure 5428s/091791':10 3-15
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u i l I Figure 3-3. Local Axial Stress in Piping Due to Thercal Stratification
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I t i l. f i t figure 3-4. Piping Local Stress Model and Thermal Boundary Conditions l- <
-5428s/091791:10 3-18 l.-
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_ -~ ... ..i,,..._ ..-. m . . , . . . . . ,-,_.,......_,.-.,--,,,.,,_m'..-,.-,., ,,m-,_,,,,_,_.
i a,c.e I 3 I t f I~ l i l i t t
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i, Figure 3-5. Surge Line Temperature Distribution it [ Ja .c.e Axial Locations 5428s/091791:10 3-19
a,c.e A i i t I i l I p ! i f I i I
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- i
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Figure 3-6. Surge Line Local Axial Stress Distribution at [ l a,c.e- 1 Axial Locations 5428$/091791:10 3-20 . __ _ - _ _ _ _. .__ _ _.._.__._-~.-. _.-. _ ._.. _ _ ..._._.__.._. _._ _.._.._.._.____.. _ ,- _. _ .- .,_.._-_.c._.-.
A.C.0 , . -Q 1 i I 4 i _J Figure 3-7. Surge Line Local Axial Strets on Inside Surface at [ Ja .c.e Axial Locations 5428s/091791:10 3-21
a,c.e l I 4 I l Figure 3-8. Surge Line Local Axial Stress on Outside Surface at a [ J .c.e Axial Locations 5428s/091791:10 3-22
a,c.e i l 4 s l Figure 3-9. Surge Line RCL Nozzle 3-D WECAN Model: 10 Inch Schedule 140 5428s/091791:10 3-23
a,c e Figure 3-10. Thermal Striping Fluctuation 5428s/091791:10 3-24
i i i
. i
- a c.e i
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b i i-I i l f l l t Figure-3-11. Thermal Striping Temperature Distribution
- 5428s/091791:10 3-25
-t
,- n ,,',-,,,n,
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-,.,,,r----n-,,+,,--n-,,;avn,--, Unw--~~ n n ,,.we w.cm-,,e,..w..-,,,,,_,, m,-,,,,m -en,,,,-..,-,, -r,,,,, -U,,, ,w< ne,,--- - - - . + , . , . , - , . . - - , - -
i l SECTION 4.0 l DISPLACEMENTS AT SUPPORT LOCATIONS The Kewaunee plant specific support displacements along the surge line were e calculated under the thermal stratification and normal thermal loads for both existing and future support configurations. Tables 4-1 and 4-2 show the maximum values.of the support displacements in the surge line. For the future : design consideration, the support displacements presented in the corresponding column of Tables 4-1 and 4-2 are provided for verification relative to their i design, l I All support displacements listed in Tables 4-1 and 4-2_should be verified, to j ensure that the spring hanger (RC-H41) has enough travel allowance. ; Insufficient allowance would result in an unevaluated condition for thermal i stratification. For the oisplacements at pipe whip restraint locations, enough gaps should be maintained between the pipe outside surface and the whip restraint surface so that the pipe will be free to move during all normal and stratified therma 1> conditions. t for the existing support configuration, the whip restraints predicted to contact the pipe are RR-134-2 and RR-134-4 under maximum thermal stratification, and RR-134-3, OR-134-4, RR-134-6, and RR-134-9 under normal thermal expansion, ,. l 5428s/091791:10 4-1
. . , _ , . _ _-_.. _ .-_ _ ._ _ _ . ~ _ _ _.._.... ____ _-
TABLE 4-1 Haximum Support Displacement * (inches)
- Under Thermal Stratification Q11platements at Supoort LotAttoni Existing future Confiauration ConfLquration +
Suonort Role 01 DX DI D2 DX DZ [ 3a ,c.e DisolacemenLat Whio R21 TEA 10.t_LQsitioni Existing future Confiauration ConfiayIAtlen + SEDDLt kQLt DX D1 DZ D1 D1 QL [ ja,c.e With maximum system aT-320*F during heat /cooldown and maximum system . AT-203*F during normal operation; and X alcng plant East, Y vertically upward, and Z by the right hand rule (see Figure 3-2). .
+ Future configuration represents no pipe whip restraint contact and no spring can bottomed out.
5428s/100191:10 4-2
TABLE 4-2
. Maximum Support Dispiacement' (inches)
Under Normal Thermal Expansion
\
Displacements at Supoort Locations i Existing future Confiauration . Conii.g.untion a S.URDRLt RQde DX D1 DI DX D1 QI g j a,c.e Disolacement at Whio Restraint Locationi Existing future Confiauration Confiagration + [ Sueoort flode DX D1 DI DX D.1 DI [ 3a ,c.e With surge.line uniform temperature of 653'F; and X along plant East, Y vertically upward, and Z by the right hand rule (see Figure 3-2).
& Future configuration represents no pipe whip restraint contact and no spring can bottomed out.
5428s/100191:10 4-3
SECTION 5.0 ASHE SECTION III FATIGUE USAGE FACTOR EVALUATION 5.1 Methodology Surge line fatigue evaluations have typically been performed using the methods of ASME Section III, NB-3600 for all piping components [ l a,c.e Because of the nature of the stratification loading, as well as the magnitudes of the stresses produced, the more detailed and accurate methods of NB-3200 were employed using finite element analysis for all loading conditions. Application of these methods, as well as specific interpretation of Code stress values to evaluate fatigue results, is described in this section. Inputs to the fatigue evaluation included the transients developed in section 2.0, and the globcl loadings and resulting stresses obtained using the methods described in section 3.0. In general, the stresses due to stratification were categorized according to the ASME Code methods and used to evaluate Code stresses and fatigue cumulative usage factors. It should be noted that, [ j a,c.e 5.1.1 Basis The ASME Code, Se tion III, 1986 (Reference [4]) Edition was used to evaluate fatigue on surge lines with stratification loading. This was based on the requirement of NRC Bulletin 88-11 [6] (Appendix 8 of this report) to use the
" latest ASME Section III requirements incorporating high cycle fatigue".
542Bs/091791:10 5-1
i Specific-requirements for class 1 fatigue evaluation of piping components are given in NB-3653. These requirements must be met for Level A and Level B type loadings according to NB-3653 and NB-3654. ~ According to NB-3611 and NB-3630, the methods of NB-3200 may be used in lieu ' of the NB-3600 methods. This approach was used to evaluate the surge line components under stratification loading. Since the NB-3650 requirements and equations correlate to those in NB-3200, the results of the fatigue evaluation are reported in terms of the NB-3650 piping stress equations. These equations and requirements are summarized in Table 5-1. The methods used to evaluate these requirements for the surge line components are described in the following sections. . 5.1.2 Fatigue Stress Equations
$ff13s Classification The stresses in a component are classified in the ASME Code cased on the nature of the stress, the loadirg that causes the stress, and the geometric characteristics that influence the stress. This classification determines the acceptable limits on the stress values and, in terms of NB-3653, the '
respective equation where the stress should be included. Table NB-3217-2 provides guidance for stress classification in piping components, which is reflected in terms of the NB-3653 equations. - The terms in Equations 10, 11, 12 and 13 include stress indices which adjust nominal stresses to account for secondary and peak effects for a given - component. Equations 10, 12 and 13 calculate secondary stresses, which are I obtained from nominal values using stress indices C1, C2, C3 and C3' for - pressure, moment and thermal transient stresses. Equation 11 includes the K1, K2 and K3 inoices in the pressure, moment and thermal transient stress terms in-order to represent peak stresses caused by local-concentration, such as ' notches and weld effects. The NB-3653 equations use simplified formulas to 5428s/091791:10 5-2
determine nominal s.ress based on straight pipe dimensions. [ l 3 ,c.e a Fct the RCL nozzles, three dimensional (3-0) finite element analysis was used as described in Section 3.0. [ 3a , ,e Classification of local stress due to tnermal stratification was addressed eith respect to the thermal transient stress terms in the NB-3653 equations. Equation 10 includes a Ta-Tb term, classified as "Q" stress in NB-3200, which
.: resents stress due to differential thermal expansion at gross structural
. sntinuities. [
Ja ,c.e The impact of this on the selection of components for evaluation is discussed in Section 5.1.3. i
-5428s/091791:10 5-3 <
Stress combinations The-stresses in a given component due to prtssure, moment and local thermal - stratification loadings were calculated using the finite element models
-described-in Section 3.0. [ '
38 ' This was done for specific components as follows:
- 1) [
j ,c.e a 5428s/091791:10 5-4
C) [ j a.C,e from the stress profiles created, the stresses for Equations 10 and 11 could be determined for any point in the section. Experience with the geometries and loading showed thac certain points in the finite element models consistently produced the' worst case fatigue stresses and resulting usage i factors, in each stratified axial location. [ l j a.c.e 5428s/091791:lv 5-5
Eggation 12 Stress Code Equation 12 stress represents the maximum range of stress Jue to thermal ' expansion moments as described in Section 3.2. This used an enveloping approach, identifying the highest stressed location in the model. By - evaluating the worst locations in this manner, the remaining locations were
- inherently addressed.
Equation 13 Stress Equation 13 stress, presented in Section 3.2, is due to pressure, design mechanical loads and differential thermal expansion at structural discontinuities. Based on the transient set defined for stratification, the design pressures were not significantly different from previous design transients. Design mechanical loads are defined by the design specification for surge lines built to the ASME Code. The "Ta-Tb" term of Equation 13 is only applicable at structural discontinuities. [ 3a ,c.e Ibermal Stress Ratchet J The requirements of NB-3222.5 are a function of the thermal transient stress and pressure-stress in a component, and are independent of the global moment loading. As such. these requirements were evaluated for controlling -
. components using applicable stresses due to pressure and stratification transients .
5428s/091791:10 5-6
Allowable Stresses j Allowable stress Sm, was determined based on note 3 of Figure NB-3222-1. For : secondary stress due to a temperature transient or thermal expansion loads ( restraint of free end deflection"), the value of Sm was taken as the average of the Sm values at the highest and lowest temperatures of the metal during the transient. The metal temperatures were determined from the transient definition. When part of the. secondary stress was due to mechanical load, the value of Sm was taken at the highest metal temperature during the transient. 5.1.3 Selection of Components for Evaluation Based on the results of the global analyses and the considerations for controlling stresses in Section 5.1.2, [ l a.c.e The method to evaluate usage factors using stresses determined according to Section 3.0 is described below. 5.2 Fatiaue Usaae Factors Cumulative usage factors were calculated for the controlling components using the methods. described in.NB-3222.4(e), based on NB-3653.5. Application of these methods is summarized below. Transient loadcases and Combinations From the transients described in Section 2.0, specific loadcases were
.- developed for the usage evaluation. [
j a,c.e Each loadcase was assigned the number of cycles of the associated transient as defined in Section 2.0. These were input to the usage factor evaluation, along with the stress data cs described above. 5428s/091791:10 5-7
-e_ g -,-e - .,-
. . - . - ~ - ._ . - - - . - . - . . --
Usage factors were calculated at controlling locations in the component as follows:
- 1) Equation 10. Ke, Equation 11 and resulting Equation 14 (alternating stress - Salt) are calculated as described above for every possible
- combination of the loadsets.
- 2) For each value of Salt, the design fatigue curve was used to e determine the maximum number of cycles which would be allowed if this type of cycle were the only one acting. These values, Ng ,
N ...N , were determined from Code Figures I-9.2.1 and I-9.2.2, 2 n curve C, for austenitic stainless steels.
- 3) Using the actual cycles of each transient loadset, n), n2 **"n' calculate the usage factors Uj , U 2 ...U n from U$ = ng /Ng . This is done for all possible combinations. Cycles are used up for each combination in the order of decreasing Salt. When N g is greater than 10 lI cycles, the value of U is taken as zero.
[ a ,c.e. 3
- 4) The cumulative usage factor, Ucum, was calculated as Ucum - U) +
U2 + ... + Un . To this was added the usage factor due to thermal striping, as described below, to obtain total Ucum. The Code allowable value is 1.0. . 5428s/091791:10 5-8
5.3. Fatigue Due to Thermal Stricina Yha usage factors calculated using the methods of Section 5.2 do not include the effects of thermal striping. [ i j a,c.e 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. This type of stress is defined as a thermal discontinuity peak stress for ASME fatigue analysis. The peak stress is then used in the calculation of the ASME fatigue usage factor.- [-
. Ja ,c.e The methods used to determine alternating stress intensity l .are defined in the ASME code. Several locations were evaluated in order to determine the location where stress intensity was a maximum.
L 5428s/091791:10 5-9 l
- t. , ,
Thermal striping transients are shown as a AT level and number of cycles. The striping AT for each cycle of every transient is assumed to attenuate and follow the slope of the curve shown on Figure 5-2. Figure 5-2 is conservatively represented' by a series of 5 degree temperature steps. Each step lasts [ 3a ,c.e seconds. Fluctuations are then calculated at each temperature step. Since a constant
- frequency of [ 3a ,c.e is used in all of the usage factor calculations, the total fluctuations per step is constant and becomes:
g )a.c.e Each striping transient is a group of steps with [ l a.c.e fluctuations per step. For each transient, the steps begin at tne maximum AT and decreases by a [ Jce steps down to the endurance limit of AT equal to [ Ja .c.e The cycles for all transients which have a temperature step at the same level were added together. This became the total cycles at a step. The total cycles were multiplied by [ Ja .c.e to obtain total fluctuations. This results in total fluctuations at each step. This calculation is performed for each step plateau from [ Ja .c.e to obtain total fluctuations. Allowable fluctuations and ultimately a usage factor at each plateau is calculated from the stress which exists at the AT for each step. The total striping usage factor is the sum of all usage factors from each plateau. The usage factor due to striping, alone, was calculated to be a maximum of [ Ja ,c.e This is reflected in the results to be discussed below.
- 5.4 Fatigue Usaae Relylti -
NRC Bulletin 88-11 requires fatigue analysis be performed in accordance with - the latest ASME III requirements incorporating high cycle fatigue and thermal stratification transients. ASME fatigue usage factors have been calculated considering the phenomenon of thermal stratification and thermal str'cing at various locations in the surge eine. Total stresses included [ Ja .c.e 5428s/091791:10 5-10
[ 8 'C 1 The total stresses for all transients in the bounding set were used to form combinations to calculate alternating stresses and resulting fatigue damage in the manner defined by the Code. Of this total
- stress, the stresses in the 10 inch schedule 140 pipe due to [
ya .c.e The maximum usage factor on the rewaunee surge line occurred at [ 3a ,c.e It is also concluded that the Kewaunee pressurizer surge nozzle will withstand the thermal stratification loading from the surge line and the transients detailed in reference [121, and meet the fatigue usage requirements of ASME Section III, with a maximum cumulative usage factor equal to ( ).a.c.e 5428s/091791:10 5-11 l
TABLE 5-1
SUMMARY
OF ASME FATIGUE REQUIREMENTS Parameter Description Allowable * (if applicable) Equation 10 Primary plus secondary stress intensity; < 35m if exceeded, simplified elastic-plastic analysis may be performed K e Elastic-plastic penalty factor; required for simplified elastic-plastic analysis when Eq. 10 is exceeded; applied to alternating stress intensity Equation 12 Expansion stress; required for simplified < 3Sm elastic-plastic analysis when Eq. 10 is exceeded Equation 13 Primary plus secondary stress intensity < 3Sm excluding thermal bending stress; required for simplified elastic-plastic analysis when Eq. 10 is exceeded Thermal Limit on radial thermal gradient stress to Stress prevent cyclic distortion; required for use Ratchet of Eq. 13 - Equation 11 Peak stress intensity - Input to Eq. 14 - Equation 14 Alternating stress intensity - Input to Ucum Ucum Cumulative usage factor (fatigue damage) < 1.0 5428s/091791:10 5-12
4 i -- : i ! I f= i 2
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i l. i i _ _ a,c.e -' i ll + i I
- i. ;
+
1 f- . i i k 1 1 3 i L-t l
. Figure 5-1. Striping Finite Element Model i l 1 5428s/0917h l:10 5-13
- a,c.e
( 1 I t Figure 5-2. Atter'ation of Thermal Striping Potential by Molecular Conduction (Interface Have Height of One Inch) 5428s/091191:10 5-14 .n u.a.-n..o n
SECTION 6.0
SUMMARY
AND CONCLUSIONS The subject of pressurizer surge line integrity has been under intense investigation since 1988. The NRC issued Bullet ~ v8-11 in December of 1988, but the Westinghouse Owners Group had put a progiam in place earlier that year, and this allowed all members to make a timely response to the Wiletin. The Owners Group programs were completed in June of 1990, and have ' oeen followed by a series of plant specific evaluations. This report has documented the results of the plant specific evaluation for the Kewaunee plant. Following the general approach used in developing the surge line stratification transients for the WOG, a set of transients and stratification l profile were developed specifically for Kewaunee. A study was made of the historical operating experience at the Kewaunee plant, and this information, as well as plant operating procedures and monitoring results, was used in development of the transients and profiles. As a result of the analyses, pipe whip restraint gaps and spring can travel allowance will be adjusted to accommodate thermal displacements due to normal-thermal expansion and thermal stratification. The date committed for the adjustments is 1992. The results of this plant specific analysis along with support modification demonstrated acceptance to the requirements of the ASME Code Section III, including both stress limits and fatigue usage, for the full licensed life of the plant. This report demonstrates that the Kewaunee plant
- has now completely satisfied the requirements of NRC Bulletin 88-11.
I-l l 5428s/091791:10- 6-1
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SECTION
7.0 REFERENCES
- 1. Coslow, B. J., et al., " Westinghouse Owners Group Bounding Evaluation for Pressurizer Surge Line Thermal Stratification," Westinghouse Electric Corp. WCAP-12278, (proprietary class 2) and WCAP-12278 (non-proprietary),
June 1989,
- 2. Coslow, B. J., et al., Westinghouse Owners Group Pressurizer Surge Line Thermal Stratification Program MUHP-1090 Summary Report," Westinghouse Electric Corp. WCAP-12508 (proprietary class 2) and WCAP 12509 (non-proprietary), March 1990.
- 3. Coslow, B. J. , et al., " Westinghouse Owners Group Pressurizer Surge Line Thermal Stratification Generic Detailed Analysis Program MUHP-1091 Summary Report," Westinghouse Electric Corp. WCAP-12639 (proprietary class 2) and WCAP-12640 (non-proprietary), June 1990.
- 4. ASME B&PV Code Section III, Subsection NB,1986 Editicq.
- 5. Wisconsin Public Service Corporation letter, from C. A. Tomes to S. S.
Palasamy, 10-15-90.
- 6. " Pressurizer Surge Line Thermal Stratification," USNRC Bulletin 88-11, December 20. 1988.
- 7. " Investigation of Feedwater Line Cracking in Pressurized Water Reactor
. Plants," Westinghouse Electric Corp. WCAP-9693, Volume 1 (proprietary Class 2).
- 8. Woodward, W. S. , " Fatigue of LMFBR Piping due to Flow Stratification,"
ASME Paper 83-PVP-59, 1983. 5428s/091791:10 7-1
. .. -.. ~ . . - . , . . .--. - . - - - - - . . . . --.- -
l
- 9. Fujimoto, T., et al., " Experimental Study of Striping at the Interface of '
Thermal Stratification" in Thermal Hydraulics in Nuclear Technology, K. H.
-Sun, et al., (ed.) ASME, 1981, pp. 73. '
- 10. Holman,-J. P., Heat Transfer, McGraw Hill Book Co., 1963. *
- 11. Yang, C. Y., " Transfer Function Method of Thermal Stress Analysis:
Technical Basis," Westinghouse Electric Corp. WCAP 12315 (proprietary).
- 12. Series 84 Pressurizer Stress Report, Section 3.1, Surge Nozzle Analysis, December 1974 (Westinghouse proprietary).
- 13. Hisconsin Public Service Corporation letter NRC-89-67, "Kewaunee Nuclear Power Plant, Justification for Continued Operation Regarding Pressurizer Surge Line Stratification," May 24, 1989.
- 14. Madeyski, A., et al., " Metallurgical Inves tigation of Cracks in the Steam Generator Feed Water Line of the Kevaunee Nuclear Power Generating Station," Westinghouse Electric Corp. WCAP-9673 (non-proprietary),
October 1979.
- 15. Bhowmick, D. C., et al., " Technical Justification for Eliminating Pressurizer Surge Line Rupture as the Structural Design Basis for Kewaunee Nuclear Plant," Hestinghouse Electric Corp. WCAP-12875 (Proprietary Class 2) and WCAP-12874 (non-proprietary).
i i 5428s/100191:10 7-2
APPENDIX A LIST OF COMPUTER PROGRAMS This appendix l'sts and summarizes the computer codes used in the analysis of stratification in the pressurizer surge line. The codes are:
- 1. HECAN
- 2. STRFIT2
- 3. ANSYS
- 4. FATRK/ CMS A.1 HECAM A.l.1 Descriotion WECAN is a Westinghouse-developed, general purpose finite element program. It contains universally accepted two-dimensional and three-dimensional 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.l.2 Feature Used The temperatures obtained from a static heat conduction analysis, or at a
, specific time in a transient beat conduction analysis, can be automatically input to a static structural analysis where the heat conduction elements are , replaced by correspon. ding structural elements. Pressure and external loads can also be included in the WECAN structural analysis. Such coupled thermal-stress analyses are a standard application used extensively on an industry-wide basis.
5428s/091791:10 A-1
A.1.3 Proaram 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 cf the WECAN quality assurance procedures. When 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 STRFAT2 A.2.1 Descriotion STRFAT2 is a program which computes the alternating peak stress on the inside surfact of a flat plate 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 ~)eing evaluated. For striping the fluid temperature is a sinusoidal variation with numerous cycles. The frequency, convection film coefficient, and pipe material properties are input. Tb? program computes maximum alternating stress based on the maximum , difference between inside surface skin temperature and the average through wall temperature. 5428s/091791:10 A-2
A.2.2 fra.tutellstd 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.2.3 Program Verification STRFAT2 is verified to Westinghouse procedures by independent review of the stress equations and calculations. A.: 1NSYS A.3.1 Rescrictlan ANSYS is a public domain, general purpose finite element code. A.3.2 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 bends) and STIF14 " (spring-damper for supports). A.3.3 Procram Verifica11gn As described in section 3.2, the application of ANSYS for stratification has
. been independently verified by comparison to WESTDYN (Westinghouse piping a analysis code) and WECAN (finite element code). The results from ANSYS are also verified against closed form solutions for simple beam configurations.
5428s/091791:10 A-3
A.4 FATRK/ CMS A.4.1 Descriution FATRK/ CMS is a Westinghouse developed computer code for fatigue tracking - (FATRK) as used in the Cycle Monitoring System (CMS) for structural components of nuclear power plants. The transfer function i2thod is used for transient thermal stress calculations. The bending stresses (due to global stratification effects, ordinary thermal expansion and seismic) and the pressure stresses are also included. The fatigue usage factors are evaluated in accordance with the guidelines given in the ASME Boiler and Pressure Vessel Code, Section III, Subsections NB-3200 and NB-3600. The code can be used both as a regular analysis program or an on-line monitoring device. A.4.2 Feature Used FATRK/ CMS is used as an analysis program for the present application. The input data which include the weight functions for thermal stresses, the unit bending stress, the unit pressure stress, the bending moment vs. stratification temperatures, etc. are prepared for all locations and geometric conditions. These data, as stored in the independent files, can be appropriately retrieved for required analyses. The transient data files ~ contain the time history of temperature, pressure, number of_ occurrence, and additional condition necessary for data flowing. The program prints out the total usage factors, and the transients pairing information which determine the stress range magnitudes and number of cycles. The detsiled stress data - may also be printed. A.4.3 Program Verification FATRK/ CMS is verified according to Westinghouse procedures with several levels of independent calculations. 5428s/091791:10 A-4
APPENDIX B USNRC BULLETIN 88-11 In December of 1988 the NRC issued this bulletin, and it has led to an extensive investigation of surge line integrity, culminating in this and other plant specific reports, The bulletin is reproduced in its entirety in the pages which follow. 5428s/091791:10 B-1
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i i CPB No. 3150-0011 NRCB 88-11 UNITED STATES NUCLEAR REGULATOPY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 December 20, 1988 NRC BULLETIN h0. 88-11: PRES $URIZER SURGE LINE THERMAL STRATIFICATION Addressees: All holders of operating licenses or construction permits for pressurized water reactors (PWRs).
Purpose:
The purpose of this bulletin is to (1) request that addressees establish and implement a program to confirm pressurizer surge line integrity in view of the occurrence of thermal stratification and (2) require addressees to inform the staff of the actions taken to resolve this issue. Description of Circumstances: The licensee for the Trojan plant has observed unexpected movecent of the pressurizer surge line during inspections performed at each refueling outage since 1982 when monitoring of the line movements began. During the last refueline surcs i' utage, the licensee found that in addition to unexpected gap clo-stra ... ae pipe whip restraints, the piping actually contacted two re-Although the licensee had repeatedly adjusted shims and gap sizes basec on analysis resolved. The most of various postulated conditions, the problem had not been recent investigation by the licensee confirmed that the movement of piping was caused by thermal stratification in the line. This phenomenon was not considered in the original piping design. On October 7, 1988, the staf f issued Information Notice 88-80, " Unexpected 7tpi-- Muvement Attributed to Thermal Stratification," regarding the Trojan experience and indicated that further generic communication may be forthcoming. The licensee larger-than-expected surge line displacement during power ascensi The concerns raised by the above observations are similar to those described in NRC Bulletins 79-13 (Revision 2 dated October Feedwater System Piping" and 88-08 (dated June22, 16,1988), 1979),""Thermal CrackingStresses in in
- Piping Connected tu Reactor Coolant Systems."
8812150118 B-2 1
l NRCB 88-11 f Cecember 20, '.g88 Page 2 of 6 l
, Discussion:
Unexpected piping movements are highly undesirable because of potatual rign piping stress that r'ay exceed design limits for fatigue and stresses. The problem can be more acute when the piping expansion is restricted, such as through contact with pipe whip restraints. Plastic deformation can resu'.t, which can lead to high local stresses, low cycle fatigue and functional in-priment of the line. Analysis performed by the Trofan licensee incicatec that thermal stratification occurs in the pressurizer surge line curing Featus, cooldown, and steady-state operations of the plant. During a typical plant heatup, water in the pressurizer is heated to about 440*F; a steam bubble is then formed in the pressurizer. Although the exact phenomenon is not thoroughly understooc, as the hot water flows (at a very 'cw flowrate) from the pressurizer through the surge line to the hot-leg picing, the hot water rides on a layer of cooler water, causing the upper part of the The differential temperature could be as high as 300'F, based on exp conditions during typical plant operations. Under this condition, differential thermal expansion of the pipe metal can cause the pipe to deflect signifi-cantly. For the specific configuration of the pressurizer surge line in the Trojan plant, the line deflected downward and when the surge line ' contacted two pipe whip restraints, deformation it underwent of the pipe. plJstic deformation, resulting in pemanent The Trojan event demonstrates tnat thermal stratification in the pressuri:er The licensing basis according to 10 CFR 50.55a for all PWRs r licensee meet the American Society of Mechanical Engineers Boiler and Pressurc-Vessel Code Sections III and XI and to reconcile the pipe stresses and fatigue evaluation when any significant differene.es are observed between measured data and the analytical results for the hypothesized Conditions. Staff evaluation indicates that the thennal stratification phenomenon could occur in all PWR surge surge line.lines and may invalidatts the analyses supporting the integrity of the The staff's concerns include unexpected bending and thermal e striping (rapid oscillation of the thermal boundary interface along the piping inside surface) as they affect the overall integrity of the surge line for its design life (e.g., the increase of fatigue). Actions Reauested: Addressees are requested to take the following actions: 1. For all licensees of operating PWRs: a. Licensees are requested to conduct a visual inspection (ASME, Section XI, VT-3) of the pressurizer surge line at the first available cold shutdown after receipt of this bulletin which exceeds seven days. B-3
NRCS 88-11 December 20, 1988 Page 3 of 6 This inspection should determine any gross discernable distress or structural damage in the entire pressuri:er surge line, including piping, pipe supports, pipe whip restraints, and anchor bolts. .
- b. Within four_ months of receipt of this Bulletin, licensees of plants in operation over 10 years (i.e., low power license prior to January 1,1979) are requested to demonstrate that the pressuri:er surge line meets the applicable design codes
- and other FSAR and regulatory comitments for the licensed life of the plant, consider-ing the phenomenon of thennal stratification and thermal striping in the fatigue and stress evaluations. This may be accomolished by performing a plant specific or generic bounding analysis. If tne latter option is selected, licensees should demonstrate applicability of the referenced generic bounding analysis. Licensees of plants in operation less than ten years (i.e., low power license after January 1,1979), should complete the foregoing analysis within one year of receipt of this bulletin. Since any piping distress observed by addresseas in performing action 1.a may affect the analysis, the licensee should verify that the bounding analysis remains valid. If the opportunity to perform the visual inspection in 1.a does not occur within-the periods specified in this requested item, incorpora-tien of the results of the visual inspection into the analysis should be performed in a supplemental analysis as appropriate.
Where the analysis shows that the surge line does not meet the requirements and licensing comitments stated above for the duration of the license, the licensee should submit a justification for continued operation or bring the plant to cold shutdown, as appropri-ate, and implement Items 1.c and 1.d below to develop a detailed analysis of the surge line.
- c. If the analysis in 1.b does not show compliance with the reouirements and licensing commitments: stated therein for the duration of the operating license, the licensee is requested to obtain plant specific data on thennal stratification', thermal striping, and line deflec-tions. The licensee may choose, for example, either to install instruments on the surge line to detect temperature distribution and thennal movements or to obtain data through collective efforts, such
- as from other plants with a similar surge line design. If the latter option is selected, the licensee should demonstrate similarity in geometry and operation. '
d. Based on the applicable plant spect fic or referenced data, licensees are recuested to update their stress and fatigue analyses to ensure compliance with applicable Code requirements, incorporating any observations from 1.a above. The analysis should-be completed no later than two years after receipt of this bulletin. If a licensee L
- Fatigue andlysis should be performed in accordance with the latest ASME Section !!! requirements incorporating high cycle fatigue.
! B-4
NRCB 88-11 December 20, 1988 Page 4 of 6 is unable to show compliance with the applicable design codes and other FSAR and regulatory corritments, the licensee is requested te submit a justification for continued operation and a description of the proposed corrective actions for effecting long term resolution.
- 2. For all applicants for PWR Operating Licenses:
- a. Before issuance of the low power license, applicants are requestec te demonstrate that the pressurizer surge line meets the applicable design codes and other FSAR and regulatory comitments for the licensed life of the plant. This may be accomplished by per#orming a plant-specific or generic bounding analysis. The analysis should include consideration of thennal stratification and thermal striping to ensure that fatigue and stresses are in compliance with applicable code limits. The analysis and hot functional testing shoulo verify that piping themal deflections result in no adverse consecuences, such as contacting the pipe whip restraints. If analysis or test results show Code noncompliance, conduct of all actions specified below is requested,
- b. Applicants are requested to evaluate operational alternatives or piping modifications needed to reduce fatigue and stresses to acceptable levels,
- c. Applicants are requested to either monitor the surge line for the effects of thermal stratification, beginning with hot functional testing, or obtain data through collective efforts to assess the extent of thermal stratification, thennal striping and piping deflections.
- d. Applicants are reauested to update stress ano fatigue analyses, as necessary, to ensure Code compliance.* The analyses should be completed no later than one year after issuance of the low power license.
- 3. Addressees are requested to generate records to document the development and implementation of the program requested by items 1 or 2, as well as any subsequent corrective actions, and maintain these records in accor-dance with 10 CFR Part 50, Appendix B and plant procedures.
Reporting Requirements:
- 1. Addressees shall report to the NRC any discernable distress and carrage observed in Action 1.a along with corrective actions taken or plans and schedules for repair before restart of the unit.
*If compliance with the applicable codes is not demonstrated for the full duration of an operating license, the staff may impose a license condition such that normal operation is restricted to the duration that compliance is actually demonstrated.
N5
NRCB 88-11 December 20, 1988 Page 5 of 6 2. Addressees who cannot meet the schedule oescribed in Items 1 or 2 of
- Actions Recuested are requireo to submit to the NRC within 60 days of receipt of tnis bulletin an alternative schedule with justification for the requested schedule.
- 3. Addressees shall submit a letter within 30 days after the completion of these actions which notifies the NRC that the actions recuested in !ters Ib, id or 2 of Actions Recuested have been performed and that the results are available for inspection. The letter shall include the justification for continued cperation, if appropriate, a description of the analytical approaches used, and a summary of the results.
Although not requested by this bulletin, addressees are encouraged to work collectively to address the technical concerns associated with this issue, as well as to share pressurizer surge line data and operational experience. In aedition, addressees are encouraged to review piping in other systems which may experience thermal stratification and thermal striping, especially in light of the previously mentioned Bulletins 79-13 and.88-08. The NRC staff intends to review operational experience giving appropriate recognition to this phenome-non, so as to determine if further generic communications are in order. The letters recuired Commission, above shall be addressed to the U.S. Nuclear ATTN: Document Regulatory Control Desk, Washington, D.C. 20555, under oath or affirmation under the provisions of Section 182a, Atomic Energy Act of 1954, as amended. Administrator.In addition, a copy shall be submitted to the appropriate Regicnal This recuest is covered by Office of Management and Budget Clearance Number 3150-0011 which expires December 31, 1989. The estimated average burden hours is approximately 3000 person-hours per licensee response, including assessment of the new requirements, searching data sources, gathering and analyzing the data, and preparing the required reports. These estimated average burden hours pertain only to these. identified response-related matters and.do not include the time for actual implementation of physical changes, such as test equipment installation or component modification. The estimated average raciation exposure is- approximately 3.5 person-rems per licensee response. . Comments on the accuracy of this estimate and suggestions to reduce the burden ., may be directed to the Office of Management and Budget, Room 3208, New Execu-tive Offict Building, Washington, D.C. l tory Commission, Records and Reports Management Branch, Of fice of20503, and Acministration and Resource Management, Washington, D.C. 20555. B6 l l
NRCB 88-11 December 20, 1988 Page 6 of 6 If you have any questions about this matter, please contact one of the techni-cal contacts listed below or the Regional Administrator of the appropriate regional office. a les E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical Contacts: S. N. Hou, NRR (301) 492-0904 S. S. l.ee, NRR (301) 492-0943 N. P. Kadambi, NRR (301) 492-1153 Attachments:
- 1. Figure 1
- 2. List of Recently Issued NRC Bulletins 9
l l B-7
mn:o Dece=ber 20, 7is Page >of Surce Line Stratification - t PZR m1 1 1 1 N Hot Flow from Pressurizer Thot = 425*F ( HL Stagnant Cold Fluid 1Q . Tcold = 125 F Figure 1 B-8 1
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APPENDIX D KEHAUNEE HISTORICAL DATA This appendix contains the summary of system delta t values for past operation of the Kewaunee plant. This was provided by Hisconsin Public Service Corporation to Westinghouse in refteente (5), and is included here for information. 5428s/091791:10 D-1
Page 1 of 3 Rev. 0 10-15 90 ,
*5 ATTACHMENT 1
SUMMARY
OF KNPP HISTORICAL MAXIMUM SYSTEM DELTA T VALUES SYSTEM DELTA T # % OF # % OF <+ RANGE HEATUPS OCCURRENCES C00LOOWNS OCCURRENCES Greater than 300 2 6 6 18 ., n 271 to 300 5 14 9 26 251 to 270 7 20 10 29 q 250 and below 21 60 9 26 ll 4 8 0 4 u 0-2 , t .. 8 ' '
"7
P39e 2 of 3 Rev. 0 10-15 90 ATTACHMENT 1 (Cont.) KNPP HISTORICAL MAXIMUM SYSTEM DELTA T VALUES EVENT DELTA T NUMBER H/V C/0 DATE RAX, CCHMENTS 1 90-1 04-1230 251.2 2 90-1 03-03-90 264.7 3 89-3 06-22-89 110.5
~
4 __ 89-3 06-17-89 246.2 5 89-2 04-08-89 164.3 6_ 89 2 04 n4-89 249.7 7 89-1 04-02-89 252.9 8 89-1 02-23-89 186.2 - 9 88-2 09-01-88 160.0 10 88-2 08-29-88 184.2 11 88-1 04-07-88 169.2 12 88-1 03-04-88 268.1 13 87-1 03-29-87 209.1 14 87-1 02-25-87 288.8 15 86-1 04-15-86 253.1 _ ___16 86-1 03-02-86 265.6 17 85-1 04-04-85 221.0 18 85-1 02-09-85 318.1 19 84-1 04-30-84 285.9 20 e4-1 03-18-84 260.8 21 03-1 ~ 05-07-83 298.9 22 83-1 l 03-21-83 275.7 23 82-1 05-16-82 249.4 ~ 24 82-1 04-12r82 313.9 4 25 81-1 05-30-81 149.7 26 81-1 04-25-81 284.4 27 '50-3 09E29-80 333.5 4I)320' 28 80-3 09-28-30 330.9 AT)320* 29 80-2 06-17-80 193.5 30 80-2 05-12-80 260.1 31 80-1 01-27-80 144.7 32 80-1 01-22-80
. 305.6 33 79-2 53-15-79 190.1 34 79-2 08-10-79 27E9 --
35 79-1 36 07-27-79 152.7 q 79-1 05 28-79 285.1 37 78-1 - 05-24-78 252.2 38 78-1 04-25-78 279.6 39 77-3 08-13-77 198.4 40 77-3 08-12-77 32E6 6TU20' 41 77-2 ___ 03-19 77 173.9 42 77-2 03-17-77 255.4 43 77-1 03-16-77 44 204.4 l 77-1 01-22-77 279.3 D-3
Page 3 of 3 Rev. 0 10-15-90 ATTACHMENT 1 (Cont.) EVENT DELTA T NUMBER H/U C/D DATE HAX. COMMENTS 45 76-4 05-18-76 178.9 46 76-4 05-09-76 203.9 47 76-3 04-03-76 143.2 48 76-3 04-02-76 137.5 49 76-2 03-28-76 280.2 - 50 76-2 03-27-76 277.8 51 76-1 03-23-76 261.9 52 76-1 02-15-76 262.3 53 75-4 11-02-75 293.1 54 75-4 ' 11-01-75 291.4 55 75-3 09-18-75 188.0 56 75-3 09-14-75 ' 160.3
~
57 75-2 07-18 75 141.0 58 75-2 07-18-75 144.2~ ^ 59 75-1 , 04-30-75 265.1 60 75-1 04-29-75 269.5 _ ] 61 74-5 10-13-74 262.3
~ ~ '
~
62 74-4 09-21-74 260.7 63 74-4 07-08-74 l'I6. 7 7 74-3 06-30-74 280.2
~~
65 74-3 03-26-74 ~ 304.2
~~
66 74-2 03-25-74 305.2
~ ~
~~~
67 74-2 03-21-74 298.5 68 74-1 03-14-74 242.6 69 74-1 02-04-74 164.7
~~
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