ML20066L317
| ML20066L317 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 01/31/1991 |
| From: | Palusamy S, Roarty D, Vora V WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | |
| Shared Package | |
| ML19312B425 | List: |
| References | |
| WCAP-12856, NUDOCS 9102060397 | |
| Download: ML20066L317 (108) | |
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-i Structural Evaluation of-.the.
Farley Units:1_and:2 Pressurizer -! Surge Lines,1Considering the Effects of-- Thermal' Stratification ~ y
~~
Janua_ry-1991 T. H. Liul S. Tendon L'. M. Valasek M. A. Gray R. Brace-Nash P..- L . ' Strauch'-
-C. Ng-i Verified by: -^ 4 ' Verified by: _ _ -
l D.~H. Roarty & V.-V. Vora
)
t Approved by: m,~ e / Approved by: " . du-
< .5. 5. jP lusamy, Manager .R. B. Patel,: Manager-j.
Diagnostics and Monitoring- . System-Structural Analysis- - Technology and; Development i ( [ .} L WESTINGHOUSE ELECTRIC ~ CORPORATION - l Nuclear and Advanced Technology' Division i P.O. Box 2728 Pittsburgh, Pennsylvania 15230-2728 l c 1991 Westinghouse Electric Corp.
<en.io s m ue l
y - . - - - , , .. . ..<r..- --e . ..v- . , + + , , ,~
I { TABLE 0F-CONTENTS i$
- Section Title ' Page':
Executive Summary iii 1.0 Background and= Introduction 1-1 1.1 Background :. 1-1 1.2 Description of-Surge Line Stratification ~ 1-3 1.3 Scope of~ Work 1-4~ 2.0 Surge Line Transient and.TemperatureiProfi k Development. 2-1 , 2.1 _ General Approach 2 2. 2_ System Design Information !2 2.3 . Development of Normal and Upset: Transients 2-3 2.4 : Monitoring Results and 0perator-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 2.8 ' Striping Transients 2-12 3.0 Stress Analysis 3-1 3.1 -Surge Line Layouts 3 .3.2 Pir J System Global Structural-Analysis' 3-3s 3.3 Local Stresses - Hethodology'and Results- .3 3.4- Total Stress from Global'and-Local Analysis 3 _7 3.5 Thermal _ Striping '3-8'
~
4.0 Displacements and Support Loadings- 4-1
.i 6058s/012391:10 j m, , ,.- . . - . _ - . - . - - - , , - , - - . - . . . - , , , - , - . ,. , . .
TABLE OF CONTENTS-(Continued) Section Title Page 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 Thermal Striping 5-9 , 5.4 Fatigue Usage Results 5-10 6.0 Summary and Conclusions 6-1 7.0 References 7-1 Appendix A Computer Codes -A-1 Appendix B USNRC Bulletin 88-11 B-1 Appendix C Transient Development Details C-1
' 5055s/012391 10 jj
L l 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 result from the difference in densities between the hot leg < water and generally hotter pressurizer _ water. Stratification with large-temperature differences 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 plant heatup and cooldown. This report has been prepared to demonstrate compliance with the requirements of NRC Bulletin 88-11 for Farley Units 1 and 2. Prior to the issuance of the bulletin,-the Westinghouse Owners Group had a program in place to investigate the issue, and recommend actions by member utilities. That program provided. the technical basis for the plant specific transient development _ reported here for the Farley units. This transient development utilized a number of' sources, including plant operating procedures, surge line monitoring data, and historical records for each unit. This transient information was used as input to a structural ~and stress analysis of the surge line for both-units. A. review and comparison of the piping and support configurations for the units led to the conclusion that the -surge lines are nearly identical, and .thus one analysis could be-done to apply to both units, for the stratification transient development and= structural analysis. The existing configurations for both Farley units have been analyzed by this
'WCAP. The results of the analysis indicate contact between the pipe and the whip restraints on both units. Even with this contact,Lthe analysis has determined that Unit 1 pipe stress is withinLcode allowables. With respect to the Unit 2 pipe whip restraint gaps, it-is Alabama Power Company's. intent to-develop a Leak-Before-Break analysis for the surge'line (separate from this effort) to justify removal of the pipe whip restraints on the-pressurizer soss, m suo
_$g
WESTINGHOUSE CRoC:QltTARY CLAs3 2 surge line. The results of that analysis will be submitted to the NRC for approvar at a later date, if necessary, Alabama Power Company will also modify the spring cans on both units to ensure sufficient travel allowance. This analysis work also demonstrates that the requirements of NRC1 Bulletin 88-11 and code requirements are satisfied, assuming that proper whip restraint
~
gaps are established and sufficient travel allowances in the spring cans are assured. The analysis results are summarized in the. table which follows, 4 4.u.niaisi io
$y
_ __-__a
SUMMARY
OF RESULTS, AND STATUS OF 88-11 QUALIFICATION FARLEY 1 FARLEY 2 Ope ating History Date of commercial operation 12-1-77 7-30-81 Years of wate-solid heatups 0 0 Years of steam-bubble heatups 13 9 System delta T limit 320*F 320'F Number of exceedonces 0 2 Code Information Code used for analysis ASME Section !!!, 1986 Edition Maximum Stress and Usage Factor Results Equation 12 stress / allowable (ksi) 40.4/51.4 40.4/51.4 Fatigue usage / allowable 0.7/1.0 0.7/1.0 Pressurizer Surge Nozzle Results-Equation 12 stress / allowable (ksi) 45.6/80.1 45.6/80.1 Fatigue usage / allowable 0.2/1.0 0.2/1.0- - l Support Modifications Required Ensure sufficient Ensure sufficient l travel allowance in travel allowance in all spring cans if all spring cans.and whip restraint gaps sufficient gaps in are opened. all pipe whip restraints (See Table 4-1) (See Table 4-1)
-Remaining Actions by Utility Support modifications Support and identified above restraint modifications identified above.-
i Status of 88-11 Requirements All analysis requirements met after
. actions above are completed.
uswomeno y
_ . . . . _ . . . - - .- . . _ . . - - . - . . . . . . . - . - . _ _ . - ~_. .. l l SECTION
1.0 BACKGROUND
AND INTRODUCTION i Farley Units 1 and 2 are three loop pressur Oed ' water reactors, designed to be as nearly' identical as practical, in both hardware and operation. 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 lines for each of these units.
The operation of a pressurized water reactor requires the primary coolant loop . to be water sol'id, and this is accomplished through a pressurizer _ vessel,. connected to the loop by the pressurizer surge line. The Farley three loop arrangement is shown in Figure 1-1. The pressurizer vessel 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' 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%. The steam bubble _provides-a-pressure i cushion effect in the event of sudden changes-in RCS mass inventory. Spray-
~
operation reduces system pressure-by condensing'some of 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 leg of one of the coolant loops by the surge = line, a 14 inch schedule 160 stainless steel pipe, a portion of which-is almost horizontal, but slightly pitched down toward the-hot leg. 1.1 Backaround During the period from 1982 to 1988, a number of utilities reported unexpected-movement of the pressurizer surge line, as evidenced by crushed insulation, gap closures :in the pipe whip restraints, and in some cases unusual snubber - movement. Investigation of this problem revealed that the movement was caused by thermal stratification in the surge line.
**"d' 1-1
. _ _ _ _ _ .. _:_ ._.,. _ -u _ _
Thermal stratification had not been considered in the original design of any pressurizer surge line, and was known to have been the cause of service-induced cracking in feedwater line piping, first discovered in 1979. Further instances of service-induced cracking from thermal stratification surfaced in 1988, with a crack in a safety injection line, and a separate occurrence with a crack in a residual heat 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 have 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 B. The bullet'n 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 for which a detailed plant specific analysis had been performed. Since this evaluation was unable to demonstrate the full design life for all plants, a generic justification for continued operation was developed for use by each of the WOG plants, the basis of which was documented in references 1 and 2. The WestinghoJse 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 realistic approach than could be obtained from a single bounding analysis for all plants, and the results were published in June of 1990 (3). soswoumio 1-2
.l 'h y L The foilowup to the Westinghouse 0wners: Group = Program is a' demonstration of 2 the applicability of reference [3] to each_ individual-unit, and the 3 performance of evaluations which could not' be. performed' on a generic basis. The goal of this report is to _ accomplish these followup actionsi and to therefore complete the requirements of the NRC' Bulletin 88-11 for Farley Units l 1 and 2. 1.2 Description of Surge Line Thermal Stratification - a It will be useful to describe the phenomenonLof stratification, before dealihg:
' ~
with its effects. Thermal stratification .in the pressurizer surgeiline is the j direct result of the difference in' densities between the pressurizer water ande k the generally cooler RCS 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-1 pressurizer and the' hot leg increases and as the insurge or outsurge flo( i rates decrease. J
~
At power, when the difference in temperature between the pressurizer and hotL [ 1eg is relatively small, __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-_1arge asL320*F, in
- which case the effects of stratification-are significan.t,!and must bel '
accounted for. L 1 ' L Thermal' stratification intthe surge line causes two effects: l o Bending of the pipe is diffvent-than that predicted in the: original-design. o Potentially reduced fatigue life of the piping due to the ' higher - stress resulting from stratification and-thermal oscillations ; (striping), f 5065s101239 h10
}.3
+ q. .,' -y w.w.,w--~ p.-e+ . , -r.r.. ,e+-1m e ..r ww -v e,, w . - - - + e wwwww, %
l 3 1.3 Scope of Work The primary purpose of this work was to develop transients applicable to the Farley units which include the effects of stratification and to evaluate those effects on the structural integrity of the surge lines. 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 and operator interviews, and historical data on plant operation. The resulting transients were used to perform an analysis of the surgeline, wherein the existing support configuration was modeled, and surge line displacements, stresses and support loadings were determined; This analysis and its results are discussed in Section 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. sessimimi io _1 4
l l l G O O vv R v Q t (3 &V i . V I m
> < J c:: _ . -
- 5 H. _
W figuio 1-1. Schematic of Farley Units 1 and 2 Loop Layout i l h lh 1-5
SECTION 2.0 SURGE LINE TRANSIENT AND TEMPERATURE PROFILE DEVELOPMENT 2.1 General Approach The transients fur the pressurizer surge line were developed from a number of sources, including the most recent systems standard design transiente. The heatup and cooldown transients, which involve the majority of tne severa stratificatior, cccurrences, were developed from review of operating procedures, operator interviews, monitoring data and historical records for each unit. The total number of heatup and cooldown events specified remains unchanged at 200 each, but a number of sub-events have been defined to reflect stratification effects, as described in more detail later. The normal and upset transients, except for heatup and cooldown, for the Farley Units 1 and 2 surge lines 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 eiu.e insurge/outsurges (I/O in the table) or fluctuations (F). Insurge/outsurge transients are generally more severe, because they result in the greatest temperature change in the top or bottom of the pipe. Typical teniperature profiles for insurges and outsurges are shown in Figure. 2-1. Transients identified as fluctuations (F) typically involve low surge flow rates and smaller temperature differences between the pressurizer and hot leg, so the resulting stratification stresses are much lower. This type of cycle is importan; to include in the analysis, but is generally not the major contributor to fatigue usage. The development of transients which are applicable to Farley Units 1 and 2 was bcsed on the work already accomplished under prograins completed for the l l l l mwmmm z.1 l
Westinghouse Owners Group (1,2,3)*. In this work all the Wescinghouse plants were grouped based on the similarity of their response to stratification. The three most important factors influencing the effects of stratification were fouhd to be the structural layout, support configuration, and plant operation. The transient development for the Farley units took advantage of the similarity in the surge line layouts,-as well as the similarity of the plants' operating procedures. Thus one set of transients was deemed applicable to both units, e The transients developed here, and used in the structural analysis, have taken advantage of the monitoring data collected on several Westinghouse plants, as well as operator interviews and historical operation data for the Farley units. Each of these will be discussed in the sections to follow. 2.2 System Desian Information P The thermal design transients for a typical Reactor Coolant System, including the pressurizer surge line, are defined in Westinghouse Systems Standard Design Criteria 1.3, Revision 1. The design transients for the surge line consist of two major categories: (a) Heatup and Cooldown transients (b) Normal and Upset operation transients (by de'inition, the emergency and faulted transients are not considered in the ASME Section Ill fatigue life assessment of components).
- Numbers in brackets refer to references listed in Section 7.
ioss.<o u r"" 2-2 s
d in the eva'uation of surge line stratification, the typical FSAR chapter 3.9 l definition of normal and upset wign events and the number of occurrences of the desigt. events remains unchanged. The total number of current heatup-cooldown cycles (200) remains unchanged. However, sub-events and the associated number of occurrences (" Label",
- Type" and " Cycle" columns of tables 2-2a and 2-?b) have been defined to reflect stratification effects, as described later.
2.3 Development of Normal and Upset Transients Transients in the surge line were characterized as either insurges or outsurcas (1/0) or fluctuations (F). Insurges and outsurges are the more severe transients and result in the greatest change in temoerature in the top or bottom of the pipe. An insurge may cool the entire pipe cross section significantly, to very close to the temperature of the RCS hot leg. Conversely, an outsurge can sweep the lino and heat the pipe to close to the temperature of the pressurizer. The typical behavior of insurge'and outsurge therni transients is shown in figure 2-1. Fluctuations, as opposed to the insurge-outsurge transients, are caused by relatively insignificant surges and result in variations in the hot-cold interface level. These variations in the interface level do net change the overall ginbal displacement of the pipe and hence are analyzed as changes in local stress only. The redefinition of the thermal fluid conditions experienced by-the' surge line durint normal and upset transients was necessary to reflect the indirectly observed fluid temperature distributions. These redefined thermal fluid
' conditions were developed based on the existing design transient systen parameters assumed to exist at the time of the postulated transient and the knowledge gained from.the monitoring programs. The redefined thermal fluid conditions conservatively account for the thermal stratification phenomena.
I smimmuo g 4 -
J To determine the ncemal and upset pipe top-to-bottom temperature difference, "oi strat " (table 2-1), the following conservatism was introduced. (-----
............ja.c.e
(........................................................ .................
...............'.........................................)a,c.e
[.......................................................................... i ...............................................................................
.....................................)a,c.e 2.4 Monitorina Results and Operator Interviews 2.4.1 Monitoring Monitoring was performed on Farley Unit 2, using temporary sensors on the surge line piping, as shown in figure 2-2. This data, along with monitoring information collected as part of the Westinghouse Owners Group generic detailed analysis (3) was utilized in this analysis. . 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 various circumferential and axial locations, in all cases these temperature sensors were securely clamped to the piping outer wall using clamps, taking care to properly insulate the area against heat loss due to thermal convection or radiation.
5055,'012391 10 24
a The farley Unit 2 temperature sensor configuration at a given pipe location consists of five sensors mounted as shown in figure 2-2. Temperature sensor configurations were mounted at various axial locations. The multiple axial locations give a good picture of how the top to bottom temperature distribution may very along the longitudinal axis of the pipe. In addition, the pressurizer surge line monitoring program utilized displacement sensors (lanyards) mounted at four axial locations to detect vertical and horizontal movements, as shown in .igure 2-2. Typically, data were collected at (---
------Ja.c.e intervals or less, during periods of high system delta T.
Existing plant instrumentation was used to record various system parameters. These system parameters were uteful in correlating plant conditions with stratification in the surge line. A list of typical plant parameters monitored is given below. [...................................... ,
........................................... ........)a,c.e l
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, i 2.4.2 Operational Practices l An operations interview was conducted at the Farley plant on October 6, 1989. The two Farley units operate with similar if not identical operating 1 1 S0$$s@ 2391'10 2-5 u
1 procedures, so the discussion that follows is a d icable to both Farley Units 1 and 2. Since the meximum temperature difference between the pressurizer and 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 tne cooldown process. In both heatup and cooldown, the plant has an administrative limit of 320'F on temperature difference between pressurizer and reactor coolant system. L 2.5 Historical Operation In the analysis, all heatups and cooldowns were assumed to reach the maximum system delte T values discussed in the previous section. A review af historical records from each of the two units (operator legs, surveillance test reports, etc.) was performed. From this review, two pieces of information were extracted; a characteristic maximum system delta T distribution for these units, and the number of maximum delta T exceedences. The number of heatups and cooldowns experienced to date and their associated system delta temperature values are listed in Table 2-3. This data is presented graphically in Figure 2-5. The historical operation data for both units are listed below. Due to the fact that both units operate similarly, the effective average of the two units as percentages of total occurrences is shown graphically in Figure 2-6. This average was considered in the transient development process. Unit 1 Unit 2 Numoer of humber of System (aT) Heatups Percent of Heatups Percent-of
' Range ('F) & Cooldowns Occurrences & Cooldowns Occurrences
[......
.....F.. .. .. .. ..
...) ,
80M,02391 10 g.g
The above table was used to ensure that the transients analyzed for Farley Units 1 and 2 encompassed the prior operating history of both units. J 2.6 Development of Heatup and Cooldown Transients The heatup 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 Farley Units 1 and 2. The transients were developed based on monitoring data, historical operation and operator interviews conducted at a large number of plants, including Farley. For each monitoring location, the top-to-bottom differential temperaturc (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 was termed the system delta T. From the pipe and system delta
- information collectel in the WOG effort, individual plants' monitoring data were reduced to categorize stratification cycles (changes in relatively steady-state stratified conditions) using the rainflow cycle counting method. This method considers delta T range as opposed to absolute values.
[....................................................................... t .................................... _; ........................... j f ce
.................................................)a 60t$s /012391 10 2-7
t 1ria resulting distributions (for 1/0 transients) were cycles in each RSS range above 0.3, for each mode (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 l determined by multiplying the average number of occurrences in each RSS range by two. Therefore, there is margin of 100% on the average number of cycles per heatup in each mode of operation. 2.6.1 Pipirg Transients Transients, which are represented by delta T pipe with a corresponding number of cycles were ieveloped 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 WOG plants (generic distributhn). 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 only a few heatups and cooldowns, for modes 4, 3 and 2, the delta T system was defined by one maximum value for each mode. 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. (-------------------------------------------
...................................)a,c.e The transients for all modes were then enveloped in ranges of AT p4pg, i.e., all cycles from transients within each ATp$p, range were added and assigned to the pre-defined
, ranges. These cycles were then applied in the fatigue analysis with the maximum ATpgp, for each range. The values used are as follows:
m w o m eiio 2-8
i i i For Cycles Within Pipe Delta T Range- Pipe Delta T- l i [.......... f f l
.......... ...)a,c,e This grouping was done to simplify the fatigue analysis. The actual number of cycles used for the analysis for each-sub-event in heatup and cooldown is i shown in Table 2-2.
t 2.6.2 Hot Leg Nozzle Transients 1 Because of main coolant pipe. flow effects the stratification transients loadings at the reactor coolant hot leg nozzle are different.- These I 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 lina pipe weld. Based on the monitoring, a set of transients were developed for the L nozzio region to reflect conditions when stratification could occur in the i nozzle, Table 2-2b. The primary factor affecting these' transients _was the' -- flow in the main coolant pipe. Significant stratification was.notH only when , the reactor ecolant pump was not operating in the-loop with the surge line. ! Trar.sients were then developed using a' conservative number of " pump trips." Thefatigueanalysisofthenozzlewasthenpehformedusing~the" nozzle transients" of Table 2-2b and_the pipe transients of_ Table 2-2a. The analysis
- included both the stratification loadings from.the nozzle transients, and the i-pressure and bending loads from the piping transients.. ,
4 un.mneno 2-9 q
. , , , , ., , , , , , _ _;. - i - .. . . - - - - - _ . - - - _ , , . . . . - - . , --- ,, ,_ , u.. ._- -_._.,___..J.-._.. - , . . ~ . _ . ,
2.6.3 Summary The final result of this complex process is c table of transients corresponding to the sub events of the heatup and cooldown process. A mathematical description of the process is given in Appendix C. {------------ *
......)a,c.e The critical location is the location with the highest combination of pipe delta T and number of stratification cycles.
The total transients for heatup and cooldown are identified as hcl thru HC9 for the pipe, and hcl thru HC8 for the nozzle as shown in tables 2-2(a) and 2-2(b)respectively. Transients HC7 thru HC9 for the pipe and HC7 and HC8 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 Farley operating records, there were two events in which the system delta T exceeded the transient basis upper limit of (-------------------------------------------
.......................................................................ja.c.e 2.7 Axial Stratification Profile Develeoment
, In addition to transients, a profile of the (-------------------------------- ace
.....) . .
mwmnue 2-10
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a _O em 8 8 8 8 u 4 8 8 0 8 8 8 8 0 e g he e a e a 8 G A 8 e 8 8 4 4 8 0 8 8 8 s **
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These three configurations are illustrated in Figure 2-9. The Farley units f a l l unde r the c a tegory of (---- - "-- --- ~~--" - ~ --- ---- -
........................ ........................]a,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 practices to provide a realistic yet somewhat conservative portrayal of the pipe delta T along the surge line. The combination of the hot / cold interface and pipe delta T as functions of distance along the surge line forms a profile for each individual plant analyzed. Since Farley Units 1 and 2 have similar surge line configurations, the profile applies to both units. 2.8 Stripino Transients The transients developed for the evaluation of thermal striping are shown in table 2-4. [........................................................................... l l ............................................................................ l l l l
......................................................)a,c.e
" ' " " ' 2-12
i l l 1 Striping transients use the labels HST and CST denoting striping transients (ST). T:ble 3-4 centr'ns a summary of the HST1 to HST8 and CST 1 to CST 7 thermal striping transients which are similar in their definition of events to the heatup and cooldown 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(3). Section 5 contains more information on specificelly how the striping loading was considered in the fatigue evaluation, l i ? 9 50$%/012391;10 2 13
- m. a..s +
TABLE 2-1 l SURGE LINE TRANSIENTS WITH STRATIFICATION l NORMAL AND UPSET TRANSIENT LIST ( l TEMPERATURES (*F) MAX NOMINAL LABEL TYPE CYCLES AT. PR2 T RCS T l otrat [.......................
......................... . . . h .
l ......................... . . . . . I l ......................... . . . . .
......................... . e . .
l l
..................M........ ... . . . g
)&,C,0 6066s/0123911 0 g.}4
TABLE 2-1 (Cont'd.) SURGE LINE TRANSIENTS WITH STRAl 'ICATION NORMAL AND UPSET TRANSIENT LIST TEMPERATURES ('F) MAX NOMINAL LABEL TYPE CYCLES AT PRZ T RCS T Strat [...................W... .
. . . e .
939MW999999994999999999 W G # # # GOSeteethemWS$9mesmtems S S # 6 h SSODettemmm99WWWWWmDWDM S S e W W
#W999ee9999999999WW99mm 9 9 @ W D SemeOSeem99meWSOWempeme m W G W G 999999999999D9999966999 W e e m W G59999993m99999999999W9 e e e e e W999598999999996##999D9 S D W e h SWSSMDWDemM499 mms 99WWW9 e e e e m 99WWeemmemWSWeW999bemes e e e e e 99999999999999999999999 9 e e a p WWWWWWSDOWSS#WemeWemO99 m e e e p #S9999999999999990' G9999 m e e a y @DWSSS$9peSmee9999999We a e e y 3
he9meSeheWWWheestemesme e e e e e DOWeepteemeS&WWWW9999mm p S e e a OppmephapeWODOWMDememem e e e e e WWDeptemehWWWWeBSeeDOWW D e e e g 9WWWSSO99mDhemmeSmeOSD$ e e e e e Ommem W9999999999999999W92D999999999266999999hSGSWemmemettemmetemmememmegememmogeme W WWeememamegeDemem&SWhammeememmetheteemmeeth p GSpeemmememememDOWeemmwemeDOSeeSemetemWWWSS
. ..S...... 8C0, ,
............................e.....]
6ee6vo1:20u0 g.15
TABLE 2-2a SURGE LINE PIPE TRANSIENTS WITH STRATIFICATION - FARLEY UNITS 1 AND 2 HEATUP/COOLDOWN (HC) - 200 CYCLES TOTAL TEMPERATURES ('F) MAX NOMINAL LABEL TYPE CYCLES AT PRZ T RCS T Strat , [.. . . . . .
, ...............Ja,c,e i son.Sunuo 2-16 l
TABLE 2-2b SURGE LINE N0ZZLE TRANSIENTS WITH STRATlflCATION - FARLEY UNITS 1 AND 2 HEATUP/COOLDOWN (HC) - 200 CYCLES TOTAL TEMPERATURES (*F) HAX NOMINAL LABEL TYPE CYCLES AT PRZ T RCS T Strat (.. . . . . . WWeh e e e W W 99nm 6 9 6 9 9 eeWD D e e e m DeWe e e a e D M***
- a m O 9 eOOO 9 m e o o ee9m M e a e e en e e W e a go ge e
- W D e Op 1
............... ....... .]8,C,e ms.,oun no 2-17
TABLE 2-3 HISTORICAL COLLECTION OF HEATUPS AND COOLDOWNS FARLEY UNITS 1 AND 2 l l l Farley Unit 1 i Number of System AT Number of Events Heatup & Cooldown Events Range ('F) Experienced to Date** Considered in 40 Year Heatups Cooldowns Design [......
...... .... .... ....)a,c.e l
Farley Unit 2 1 Number of System AT Number of Events Heatup & Cooldown Events Range (*F) Experienced to Date** Considered in 40 Year 1 Heatups Cooldowns Design [.......
. . . . . . .... .... ....)a,c.e *Two cycles per event were assumed, resulting in four cycles at AT > 320'F. **0nly those with a maximtm System AT available are listed. - 6055s41m1'10 2-18
TABLE 2-4 SURGE LINE TRANSIENTS - STRIP]NG FOR HEATUP (H) and C00LDOWN (C) [............ Label -------- --------------
.................................................................]a,C,e l
605bs /C12391.10 2-19
- a,c.e.
v t Figure 2-1. Typical Insurge-Outsurge (1/0)-Temperature Profiles l 483)s/132000 10 -- 2-20
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.S 9
O t ! N 1 l G l k 3 l @ E \ l 2 e 1- f: E. 2-22
m a U. N I I N T c 9 m N w e en c D A 4 b 9 6 L Q w Im D Q c 2 o 8 v Y i N m l 3
..e.n E
i i i e i g
=-
E 2 t 2-23
- 3
_ . _ _ . . _ . . . _._ _ _ .._..._ . .. _ . _ _ .. . _ . _ _ _ . . - ~ . . _ .. - . . _ . _. . _ . . - . r._. _ . . . _ . . . . _ . a,c,e 4 i l 1 1 i t A' j . t
- )
f 1 l 4 i u
- t o.
1.
=. , -h Figure 2-5.
~
Historical Heatups-and Cooldowns for.Farley Units 1 and 2 t Compared with the Number.of Events Usedii.n. the Analysis l-son.nne se g.gg. u *t-= vm 4 ** y- V pr ieur e ggrpi-p+.ap g >--g rey w rer9-y M y et%+yA g 7$= sy 7y y9-- pg.5 W=u-PkP*g*qT-9p'"41- ~
a.c.e
'?
lX Figure 2-6. Sumary of Historical . Data from the Farley Units I and 2, Shown as an Effective Average for Both Units Compared to the Distribution Used in this Analysis
x a.c.o to e ro w Figure 2-7. Exa w le Axial Stratification Profile for low Flow Conditions w iw.im. ..
O U O N
).
ces H w e s= x (U L 9 6 M e 99 heum C 6 Ca. 0 6 2-w L e i N G L 3
.m
^
I t t t 2-27 __m____-.m_mm-mm~.au-
a,:,e I l i l Figure 2-9. Geonstry Considerations aon.n uno ,o y gg
]
SECTION 3.0 STRESS ANALYSES The flow diagram (figure 3-1) describes the pror,edure to determir.e the effects of thermal stratification on the pressurizer surge lin& based on transients develeped in section 2.0. (--- ------------------------------------------
............. 3a,c,e 3.1 Surge Line Layouts The Farley Units 1 & 2 surge line layouts are documented in reference (4).
The Unit 1 design is a replicate of the Unit 2 design. The layout is shown schematically in figure 3-2. Below is a table summarizing the existing Ferley surge lir,e support configurations. Support label Support Type Unit 1 , Unit 2 Spring RC-R1 2RC-R1 Snubber RC-R7 2RC-R2 Spring RC-R2 2RC-R3 Pipe Whip Restraint PSR-1 PSR-1 Pipe Whip Restraint PSR-2 PSR-2 Pipe Whip Restraint PSR-3 PSR-3 Pipe Whip Restraint PSR-4 PSR-4 Pipe Whip Restraint PSR-5 PSR-5 Pipe Whip Restraint PSR-6 PSR-6 Pipe Whip Restraint PSR-7 PSR-7 Pipe Whip Restraint PSR-8 PSR-B Pipe Whip Restraint PSR-9 PSR-9 mwomet ie 31 __m_.___
1 Since snubbers and springs allow thermal growth, the Farley Units 1 & 2 surge lines have essentially similar support configurations for the thermal stratification analysis. The piping size is 14 inch schedule 160 and the pipe material is stainless steel for the surge lines in both units. Farley Unit I surge line pipe has SA 376-Type 316, Farley Unit 2 has SA 376-Type 304 Experience with the analysis of thermal stratification has indicated that surge line layout has a significant effect on the resulting stratification induced global pipe bending moments. One of the important factors regarding surge line layout was found to be (----------------------------------------
.......................................... ...)a,c,e For the existing support design the Farley Units 1 and 2 surge line design also includes nine pipe whip restraints. These pipe whip restraints have gaps ranging from 0" to 2.625" between the restraint and pipe. The actual gaps in pipe whio restraint (PWR) for both units were modeled. For the spring hangers, the actual travel allowances were also modeled in Unit 2 model. For Unit i design, travol allowar.ce was assumed to be sufficient (since there was no evidence of spring cans bottoming out from walkdown information).
Based upon a review of whip restraint drawings and the visual inspection reports I43 of Farley Units 1 and 2 pressurizer surge lines, it was concluded ! that some of the whip restraints impeded vertical motion due to stratification. Furthermore, the spring can 2RC-3 was actually found to be bottomed out in 1988. The travel allowance of this support was increased in i 1988 to accommodate the stratification displacements. The structural evaluation addressed by this WCAP assumes that proper whip l restraint gaps have been established and sufficient travel allowance in the spring cans have been assured for the future operation. With respect to the 605WOt 2391 10 3.g
f pipe whip restraint modification to ensure proper gaps, it is Alabama Power Company's intent to develop Leak-Before-Break analysis for the surge line (separate from this effort) to justify removal of the pipe. whip restraints on the pressurizer surge line. The results of that analysis will be subndttad to the NRC for approval at a later data. Alabama Power Company will also modtfy the spring cans to ensure sufficient travel allowance foi future operation. 3.2 Piping System Global Structural Analysis The piping system was modeled by pipe, elbow, and linear and non-linear spring elements using the ANSYS c aputer code. The geometric and material parameters are included. [-----------------------------------------------------------
.........................____................................ 3a,c,e The stiffness of snubber suppo-ts and spring hangers are neglected in the model because they are inconsequential for the therri.al condition although the potential for these members exceeding their displacement tolerance are verified, as discussed.
For the Farley surge line design, under the thermal stratification loadings, many unintended thermal constraint conditions were predicted to occur at the nipe 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, lets than adequate gap-clearance for the higher displacements resulting from stratification existed in the pipe whip restraints. [--------------------------------------- t ............__.............
......____............................._3a,c,e The hot-cold temperature interface along the length of a surge line (------
g ... .. .................. ................................... ....... ....s3 '.,e
$ I l g
1,
[......................................................-..............s ....
...............................................-.....................ja,c.e Each thermal profile loading defined in section 2 was broken into (--------
...........)oi t .e Table 3-1 shows the loading cases considered in the analysis. Within each operation the (-------------------------------------
1
...~ .,........................................................... ..........
............................. 3a,c e Consequently, all the thermal transient loadings defined in section 2 could be evaluated.
The presse ~2er and RCL temperature listed ii. teb's 3 . ef'.oct the approximate system 6T. System temperatures are used te define the boundary n displacements at both RCL and pressurizer nozzles, q
?n order to meet the ASME Section Ill Code Stress limits, global structural models of the Farley Units 1 and 2 surge lines were developed using the informstion provided by reference (4) and the ANSYS general purpose finite elemen; computer code. The model was constructed using (-------------------
.._. -......... .....)a,c,e to reflect the layout of straight pipe, bends and field welds as shown in Figure 3-2, [-------------------------------------
...................................ja,c,e (see table 3-2b For the stra'.ified condition, (---------------------------------------------
..... .........._................j c,e a 60:5,/012391 10 34
=- The global piping stress analyses were baseo on two models-due to the difference in bottomed out spring and pipe whip restraint gap conditions between the two units. The first model represents-the existing Unit 1 suppurt and restraint configuration and the second model represents the existing Unit 2 support and restraint configuration. For the future support configuration, both models were assumed totally free from any thermal constraint caused by l pipe whip restraint contacts and/or spring can bottomed out. The results of the ANSYS global structural analysis provided thermal expansion moments. The ASME Section 111 equation (12) stress intensity range was evaluated for both support configurations, for the existing support configuration, a sys'em t delta T = 337'F. was evaluated for Unit 2 and delta T = 320-i for Unit 1. For the future support configuration, a system delta T = 320*F was evaluated for-both units, In all cases, excluding the Unit 2 existing configuration, the maximum ASE equation (12) stress intensit" range in the surge line was found i to be under the code allowable of 3Sm. Maximum equation (12) and equation (13) stress intensity ranges are shown in table 3-3. From this table, it should be noted that, for Unit 1, modifications to the whip restraint gaps are not necessary, as leg as suffi. ient travel allowances are provided in the spring cans. For snit 2, both spring can travel allowances and whip restraint gaps require ver'fication. The pressurizer nozzle loads from pipe thermal stratification were also evaluated according to the requirements of the ASME code. The evaluation included the calculations of primary plus secondary stress. intensities and the fatigue usage factors. The maximum stress intensity is 45.6 ksi compared to the code allowable value of 80.1 ksi, and-the maximum fatigue usage factor is reported in Section 5. It was found that the Farley pressurizer nozzle met the code stress requirements, in order to superimpose local and global stresses, several stress analyses ! were performed using the 3-0 pipe model. (--------------------------------
...............__................................. .........__..........)8,c,e soss,/otanHo 3-5 , . . ~
[............................................................................
...................................]a.c e 3.3 Local Stresses-Methodology and Results 3.3.1 Explanation of Local Stress Figure 3-3 depicts the local axial stress components in a beam with a sharpls nonlinear metal temperature gradient. Local axial stresses develop due to the rostraint 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 ' :al axial stress would not exist. (-------------- ....................e ............................ ............... ....... ..............................................]a,c,e 3.3.2 Finite Element Model of Pipe for Local Stress A short description of tne pipe finite element model is shown in-figure 3-4.
The model with thermal boundary conditions is shown in figure 3-5. Due to symmetry of the geometry and thermal loading, only half of the cross section - was required for modeling and analysis. [---"------------------------------- l
............__ ...........................e.._,,........................
l
........................]a,c,e t
i seswomo io l 3-6 1
l i 1 l [........................................................................ ) 1 1
.............................................)a,c.e l 1
3.3.3 Pipe Local Stress Results Figure 3-6 shows the temperature distributions through the pipe wall (------
........__...............................................................s ..........)a,c e 3.3.4 PCL Hot Leg Nozzle Analysis
[........................................................................... l 1
.......____ .. 3a,c,e A summary of stresses for unit loading is shown in l table 3-5.
3.4 Total Stres,s_from Global and Local Analyses [_____.................................__.................................
...__.......e................__....e..........h......__...............s ..h ..............)a,c.e s " $ ' ""
3-7
[........................................................................
................__3a,c.e 3.5 Thermal Striping 3.5.1 Background At the time when the feedwater line cracking problems in PWR's was 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 flow rate conditions. (See figure 3-11 which shows the thermal striping , fluctuation in a pipe). Inermal striping was verified to occur during subsequent flow model tests [B) .
Results of the flow model tests were used to establish boundary conditions for tha stratificatin, analysis and to provide striping oscillation data for evaluating high cycle fatigue. Thermal striping was also examined during water model flow tests performed for D the Liquid Metal Fast Breeder Reactor (LMFBR) primary pipe loopI93 The
, stratified flow was observed to have a dynamic interface region which escillated in a wave pattern. These dynamic nseillations were shown to produce significent fatigue damage (primary crack initiation). The same interface oscillations were observed in experimental studies of thermal striping which were performed in Japan by Mitsubishi Heavy Industries [10) ,
The thermal striping evaluation process was discussed in detail in reference 3. soss.,oun no 3.g
3.5.2 Therm >' scriping Stresses 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 3-12 which shows a typical temperature distribution through the pipe wall). [.__..............___...........-.........................................
.............__ __.......)a,c.e The peak stress. range and stress intensity was calculated from a 3-D finite element analysis. [--------------------------~------------------------------ '1
_...................ja,c,e The methods used to determine alternating < stress intensity are defined in the ASME code. Several locations were evaluated in order to determine the location where stress intensity was a maximum. Stresses were intensified by K 3 to account for the worst stress concentration for all piping elements in the surge line. The worst piping : element was the butt weld. [__......__...__ ..... ......._________.........................__....... 1 1 ................___.........__........................____... ...... _________..............__.............ja,c.e 3.5.3 Factors Which Affect Striping Stress The factors which affect striping are discussed br afly below: t............__._____ ..__..........._...............................__
.......................____.....................................____...)a,c,e i
4 l 1 coe w oi m n o 39
[.......................................................................
......]6,C,9
(.. .................................... ...................................
'l
..............................e... ...e ........... ......................
i
............. 4................................................ 1
.........]8,C,e s
6056,/6 a leoto 3.g
- i 1
.~. - - . - . . _. . . . . - _ - . . . .
(.. . ............ .....................................................
..............................8,C,0- .
i l l i 1 h t
)
'Y 5055s/01239 h10 3.]
Y,
- , ,,,,-e, e e-e- e
TABLE 3-1 TEMPERATURE DATA USED IN THE ANALYSIS Max Type of System Analysis Pressurizer RCL T T Pipe Top Bot Operation AT(*f) Cases Temp (*F) Temp ('F) ('F) ('F) AT ('F) [............ ...
. ... ... ... ... ...)a,c,e.
M 1 4 son.,o mouc 3-12 !
l I l { 1 l TABLE 3-2 COMPARISON OF WESTDYN AND ANSYS PIPING THERMAL DISPLACEM%TS AND SUPPORT LOADS FOR A TYPICAL SURGE LINE MODEL*
........................___..... a,c.e :
[................................... 3 t i l
- The existing support configuration was used in this study.
sese: wo 3-13 l I
..q n
l
. =-i
-TABLE:3 ;
e 40mmary of: Far. ley Surge Line- j; ThermalLStratification: Stress Results. O J 1 y Unit 1- LUnit 2" , a Support Configuration- Support EConfiguration A
'ASME Code Equation: Existing + Future *1 -Existing + Future
- LCode A11owablear l i
_.(ksi); !(ksi). ~~(ksi) -(ksi) L(ksi): -j q a 12 48.7- --4 0. 4 l - 55.4 40.4: 51.4 13 40.0 40;0- 40.0 _ 4 0. 0 '- '48.6 y f l. l l 1 Future support configuration represents no bottcmingioutlsf-spring canst and no pipe ~ whip restraint contact .underlallithermalgloadings .with maximum !
.slfstem AT = 320'F-
.i..
+ Existing support configuration represents 1the actual:spH n.g; bottom:out 1
~
and/or PWR contact condition;under allLthermal:loaciings%ith maximum , ej systemAT=?337*F1(for: Unit 2);and-320'F (for. Unit ~1)' q
. If.the system ATlis maintained at 310*F.for Unit >2, theiEquationT12
- L -stress will be 50.96 ksi. '
L a- 'Corservative envelope _of..the tWo Units. y .i j 1 i V65s/012391:10 3. } 4 ;, ;! t . _ '~
- f)- ([
, . ,. .. . ,, . . , , - - . , . - - . . , .-.a-.c..... . . . . - , ..-,,...-.~....,;.-.....l
TABLE 3-4 FARLEY SURGE'LINE MAXIMUM LOCAL AXIAL STRESSES AT (------------------Ja,c,e (14 inch Schedule 160) Local Axial Stress (psi) Location Surface Maximum Tensile Maximum Compressive [. ______ ...... ..... __....a.c,e
......]
[..........................................................)a,c,e 1 i t 1 1 i oces. m n u 3-15
' J V
_,. <r we e
i h-
~ TABLE 3-5=
SUMMARY
OF. PRESSURE AND BENDING = INDUCED STRESSES IN THE SURGE LINE RCL N0Z2LE FORLUNITTLOAD: CASES All Stress in psi- ! Linearized Stress -Peak Stress Intensity Range- Intensity Range-Diametral Unit Loading- .. Location Location- Condition-- Inside; ;0utside= .Insido : Outside-4 ca.c.e. : [.......... .....: . . . . . . . . - .. . ... ..... .. ....., ;
.i o
.......... ..... ........ ...... :..... ....^ .....
_a 4 a
.i y
........- .... ..... -....- - .....< 3 s
a
. . .. .J q wum neno.
=3-16' k
. - ________m.-__-__._m.____.-. m
l l TABLE 3 6 i STRIPING FREQUENCY AT 2 MAXIMUM L1 CATIONS FROM 15 TEST RUNS
- m. i Total '
l Frequency (H2) Duration
# Cycles
% %. % Lgth, in i Min (Duration) Max (Duration) Avg (Duration) Seconds e.__............
t
. ... .. e.. WB. ..e .. m.G+....
. . . up .. ... . WB ... .. .Em.....
e . . m . GA........m
..M@... . .W - .. .M. .. Q.M M. ..M ..
m .m. .. ... .. m We . $s . . . m m es .
. ... .. . Es EIB Sp. . GB . .. Em . . . . 58
. . ED.e.. . ED.. M. ..W GW ... .. .. . et e GBGB
. We . em up e ... .. .We .. .......
]
l l l l l cess.,oian uo 3-17 l
- a c,e 1
l_ Figure 3-1. Schematic of Stress Analysis Precedure . m .,an niio 3.ig
e I ! 3250 ' ~
~
3258 3240 I 223a
- 2216 3215 234 T .
- ~
~g '
2212 2217 2218 ~
-k %p
.5 '3205 s - , g 4u ol O
/ -
I\ ga. A i: '. Nz .. l' figure.3-2. Pressurizer.-Surge Line Layout: farley Units 1.& 2
. nma ,n; so 2
. , , _ ._ , - , , ,~ ..,m.-_ . . _, m y
t L t
- d .c.e .
I
<a 5
. m. '
o
+
6 i 4 i 1
- 'j j .-
t
. Figure 3-3. Loca! Axial $ tress in Piping Due to Thermal Stratification
- imcom ..
A .e-
'*m*#- % #A p.r .* ._]n__
__,,_m_--'e '%*'*' *'e-##b'N-v'a--*' c- 'e9- W *did
- eN -A e #
?*---*"+gew.M*e -Sow-> a s.m y 4 _
,,g,,._
4,c.e i l. i Figure 3-4. Local Stress - Finite Element Models/ Loading 4m.<oimmi io 3-21
i 1
-. a , c . e ,
1 Figure 3-5. Piping Local Stress Model and Thermal Boundary Conditions o n ,e m .iio 3-22
a,c,o I, 1 i l l I i l l l l l l f Figure 3-6. Surge Line Temperature Distribution at ( Ja,c.e Axial Locations l 4633s/011791 to 3-23 i
,, e,c,o l a
Figure 3-7. Surge Line Local Axial Stress Distribution at ( ]C l Axial locations 4e n.m " " 3-24 1
e,c,o P f
' mumana.
Figure 3-8. Surge Line Local Axial Stress are Inside Surf ace at [ ]"'C'8 Axial Locations 4,n.,on ni io 3-25
-. . . . . - - . - . . . . . . . . . . . . . - . . . .~ .. .
. - . . . . ~ . .
f[
.~a , c , e I
f' t
.y
?!
-i,
- e
+
i -?
?l l
% a Figure 3-9. -Surge.Line Local Axial Stress-on:Outside Surfac9 at. 1
-[ la,c.e Axial Locat' ions-1.
1- - 49131/011791 to , n l
4 I
' a,c,e!
1 t j-
~
1
.w f\.)
N. 't i t i i 4 2 5 i- : Figure 3-10. Surge Line RCL Nozzle 3-D WECAN Model: 14 Inch Schedule.160 . m> 4.ini .e 1 r
?
w , _.3,i._
, - .L- - .,~--. ;~ , . ~ - - . ~ . ~ , - - - -
.~.l. , - -r - - - .- , --
,y._ - . . -- .-I
a,c,e Figure 3-11. Thermal Striping Fluctuation
.e u. m " " ' "
3-28
1 l l
- a ,:, e Figure 3-12. Thermal Striping Temperature Distribution . swoorei io 3-29
SECTION 4.0 DISPLACEMENTS AND SUPPORT LOADINGS The Farley specific support displacements along the surge lines were calculated under the thermal stratification and normal thermal loads for both existing and future support configurations. Table 4-1 shows the maximum values of the support displacements in the surge line. Nodes associated with supports and global coordinates are shown in figure 3-2. The support displacements listed in Table 4-1 along with displacements due to other loadings should be verified for the future support configuration, to ensure that the spring hangers and snubbers have enough travel allowance, insufficient allowance would result in an unevaluated condition for thermal stratification. For the displacements at pipe whip restraint locations, enough gaps should be also 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 thermal conditions. From the stress analysis in Section 3, it is not necessary to modify the Unit 1 existing spring can travel allowances or to open up the whip restraint gaps. However, in the future, if whip restraint gaps are opened, the spring cans must be modified to provide sufficient travel allowances according to the future configuration displacements listed in Table 4-1. For Unit 2, since the spring cans have been already modified to accommodate stratification, only modification of whip restraint gaps is necessary for future operation. Such modification will be performed in conjunction with the Leak-Before-Break application, c 5055s 412391 10 4.}
~ ..
l l TABLE 4-1 I Farley Unit 1 Maximum Support Displacement Under Thermal Stratification & Normal Operation Condition Displacements (inches) at Support Locations Existing Future QoportConfiguration Support Configuration Support Node .DX DY D2 DX -DY DZ RC-R1 2216 0.79 0.38/-0.11 +0.1/-0.42 0.79 -0.16 0.11/-0.42 RC-R7 2217 0.86 +0.33/-0.13 +0.14/-0.3- 0.86 -0.37 0.14/-0.32 RC-R2 2238 1.45 -1.1 +0.31/-0.22 1.45 -3.04 0.14/-0.22 ! Displacement at Whip Restraint Locations l Existing r uture Support Configuration Support Configuration Support Node DX DY DZ DX DY DZ I 2PSR-1 3258 0.26 -0.45 0.15/-0.21 0.26/-0.03 -0.53 0.04/-0.21 2PSR-2 3254 0.57 -0.65 0.09/-0.52 0.57 -1.35 -0.52 2P5R-3 3250 1.17 -1.13 0.16/-0.58 1.17 -2.66 -0.58 l 2PSR-4 3240 1.44 -1.16 0.291-0.3 1.44 -3.06 0.11/-0.30 2PSR-5 234 1.36 -0.79 0.34/-0.02 1.36 -2.62 0.22/-0.02 2PSR-6 2218 1.00 0.08/-0.16 0.23/-0.13 1.00 -1.01 0.19/-0.13-2PSR-7 3215 0.72 0.40/-0.09 0.05/-0.55 0.72 0.02/-0.09- 0.07/-0.55 2PSR-8 2212 0.52 0.29/-0.05 -0.88 0.52 0.21/-0.05 -0.88 2PSR-9 3205 0.16 0.02/-0.004 -1.21 0.16 0.03/-0.004 -1.21 6 % 5s/012391.10 4.g
TABLE 4-1 (continued) Farley Unit 2 Maximum Support Dit acement Under Thermal Stratification & Normal Operation Condition Displacements (inches) at Support Locations Existing ~ Future Support Configuration Support Configuration Support Node .[DC DY DZ DX DY DZ 2RC-R1 2216 0.79 0.53/-0.13 0.04/-0.42 0.79 -0.33 0.09/-0.42 2RC-R2 2217 0.86 0.48/-0.15 0.07/-0.32 0.86 -0.57 0.12/-0.32 2RC-R3 2238 1.45 -0.70 0.26/-0.22 1.45 -3.45 0.09/-0.22= Displacement at Whip Restraint Locations Existing Future Support Configuration Support Configuration Support Node DX DY D2 DX DY D2 PSR-1 3258 0.26 -0.45 0.13/-0.22 0.26/-0.07 -0.58 0.01/-0.22 PSR-2 3254 0.56 -0.44 0.05/-0.53 0.56 -1.50 -0.53 PSR-3 3250 1.17 -0.74 0.11/-0.59 1.17 -2.98 -0.59 PSR-4 3240 1.44 0.74 0.24/-0.31 1.43 -3.47 0.06/-0.31 PSR-5 234 1.36 -0.47 - 0.28/-0.03 1.36 -3.03 0.17/-0.03 PSR-6 2218 1.00 0.26/-0.19 0.15/-0.13 1.00 -1.28 0.17/-0.13 PSR-7 3215 0.72 0.53/-0.11 0.01/-0.55- 0.72 -0.11 0.06/-0.55 l PSR-8 2212 0.52 0.39/-0.05 -0.88 0.52 0.14/-0.05 -0.88 PSR-9 3205 0.16 0.03/-0.004 -1.21 0.16 0.03/-0.004 -1.21
,, _ . e 43
SECTION 5.0 ASME SECTION 111 FATIGUE USAGE FACTOR EVALVATION 5.1 Methodolooy Surge lite fatigue evaluations have typically been performed using the methods of ASME Saction 111, NB-3600 for all piping components [-------------------
........................................ ...................ja,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 global 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, [---
................__...............__.__ .....)a,c.e 5.1.1 Basis The ASME Code, Section 111, 1986 (Reference [6]) Edition was used to evaluate fatigue on surge lines with stratification loading. This was based on the requirement of NRC Bulletin 88-11 ( Appendix B of this report) to use-the " latest ASME Section III requirements incorporating high cycle fatigue".
m woim'" 5-1
Specific requirements for class 1 fatigue evaluation of piping components are j given in NB-3653, These requirements must be met for Level A and Level B type l 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. The'se 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 Stress Classification The stresses in a component are classified in the ASME Code based on the nature of the stress, the loading 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. Tabla 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 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 indices 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 f b055s /012391 10 5-2
1 i i determine nominal stress based on straight pipe dimensions. (------ - l
.............................................)a,c.e For the RCL nozzles, three dimensional (3-0) finite element analysis was used as described in Sect-ion 3.0. (----------- -------------------------------- ..................................................................... 3a,c.e Classification of local stress due to thermal stratification was addressed with respect to the thermal transient stress terms in the NB-3653 equations.
Equation 10 includes a Ta-Tb term, classified as "0" stress in NB-3200,-which represents stress due to differential thermal expansion at gross structural i discontinuities. (--------------------------------------------------------- 1 1 1
...............................__..........)a,c,e The impact of this on the selection of components for evaluation is discussed in Secticn 5.1.3.
l sess m :3s u e 5-3
Stress Combinations , The stresstes in a given component due to pressure, moment and local thermal i l stratification loadings were calculated using the finite element models l described in Section 3.0. (--------------------------------------------- t
....................................e....... e..........................
e.e..e................................................e...................
......e.........ja,c.e This was done for specific components as follows:
\ \ (.. . .... .....................e.....................e................ !
................e...........................e... ..................
....m...m..e-e........WW-........W....W............S.........e8.....
.e.....W..et...
- e. M-...ee80m...e..... G .eeeeW...em.S. OpW.W .......GS..e.W..m.GD....W..
......ene...m....e......ee-e.e...m.meefe.......e...m..m....W.........
ee......me..e ee.m. G. ...me. __.......ee_e..e........................................ , e.eeee.e.eee.....m..e......m....en........em.....m ee......e.. m.....W...
.. e....W ............ene.....eetem.mase.e...ege..e.....e..e...e...
...e............e.ee...m......e......e. enee..eeseeee..e...e eeeee e em . En e . e e es e . e . e e et. . e m . . en . en . . . . en . e e e . . . m . Opeaenam gy.geege.gg,g.
.........ep..45........G................e . es . as ge . . e es . . . ep og . e . . . g . g - en e3. m . . m - em e . ep . . . . en . . . et . en e up ..Em....e... 3... . et es as em . . . . . gD . . en l
l l = e . . . = = . -en. . . . . . . . . .e.. . . . e . . . . - . . . . . . . . . . . . . . . . .e.. e i l I l m.m.ee.es.....e..........m.es...e.................sen... .......... i ..==.= ..en.... .===..... =- e..en.. .........On ............ee i
.ao-eene......en.ae.........m...ene..eeee.... mas. eee-ee.eem.em.es.e
___e._..........e.....e.... .........e....___
.......... .....e)a,c,e 1
4 g
l 1 1 l l l l [.. .............................................................. l I ! 1 1
....................................................._ 3a,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 that certain points in the finite element models consistently produced the worst case fatigue stresses and resulting usage factors, in each stratified axial location. (------------------------------
..................................... WID.........................e........
.........................We.........................................m........
................................................]a,C,e
" " * " 5-5 i _
Equation 12 Stress . Code Equation 12 stress represents the maximum range of stress due 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 i discontinuities. Based on the transient set defined for stratification, the design pressures were not significantly different from previous design transients. Design mechanical loads ere 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. [--------------------------------------------------- - , ..................__ .....................................................)a,c.e Thermal Stress Ratchet The requirements of NB-3222.5 are a function of the thermal transient stress and pressure stress in a component, and are inaependent of the global moment loading. As such, these requirements were evaluated for controlling components using applicable stresses due to pressure anc stratification-transients. 50$$s/012 Nil 5-6
l 1 Allowable Stresses i 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, [--------------------------------------
......................................)a,c.e The method to evaluate usage factors using stresses determined according to Section 3.0 is described below.
5.2 Fatigue Usage 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 leadcases were developed for the usage evaluation. [-------------------------------------- __..........__.......___.......______....)a,c,e Each loadcase was assigned the number of cycles of the associated transient as defined in Section 2.0. These were irput to the usage factor evaluation, along with the stress data as described above, soswomouc 5-7
m _ 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. 1
- 2) For each value of Salt, the design fatigue curve was used to determine the maximum number of cycles which would be allowzd if this type of cycle were the only one acting. These values, Ny ,
N ...N , were determined from Code Figures 1-9.2.1 and I-9.2.2, 2 n curve C, for austenitic stainless steels.
- 3) Using the actual cycles of each transient loadset, ny , n 'U 2 n' calculate the usage factors U , U ***U This-3 2 n from U$ = n4M. 5 is done for all possible combinations. Cycles are used up for each~
combination in the order of decreasing Salt. When N $ is greater 11 than 10 cycles, the value of U is taken as zero.- (.................................................................
................)a,c,e
- 4) The cumulative usage factor,-Ucum, was calculated as Ucum =-01+
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. sm.<o un uo 5-8 l
1 , \- 5.3 Fatigue Due to Thermal Striping The usage factors calculated using the methods of Section 5.2 do not include the effects of thermal striping. (----------------------------------
.......................... 3a,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.
[.....................__....................................................
------]a,c.e The methods used to determine alternating-stress-intensity are defined in the ASME ccde. Saveral locations were evaluated in-order to determine the location where stress intensity was a maximum.
l l 1 1 5055s/012391 to 5-9
,. .. . . . = . . . . - -
Thermal striping transients are shown at a AT level and number of cycles. The striping aT for each cycle of every transient is assumed to attenuate and follow the sicpe 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 (--Ja,c,e seconds. Fluctuations are then calculated at each temperature step. Since a constant frequency of (------Ja,c.e is used in all of the usage factor calculations, the total fluctuations per step is constant and becomes: , [.............................................)a,c,e Each striping transient is a group of steps with (----Ja,c,e fluctuations per step. For each transient, the steps begin et the maximum AT and decreases by (--]a,c.e 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 [-----]a,c,e This is reflected in the results to be discussed below. 5.4 Fatioue Usage Results NRC Bulletin 88-11 (7) 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 striping at various locations in the surge line. Total stresses included sess'" " 5-10
----_____m_ _ _
[.......................................................................
...................................)a,c.e The total stresses for all transiants in the bounding set were used to form combinations to calculate I
alternating stresses and resulting fatigue damage in the manner defined by the Code. Of this total stress, the stresses in the 14 inch schedule 160 pipe due to (--------------------------~~~~--------- ------------~~~~~-----------------
................................................................)a.c.e-The maximum usage f actor on Farley surge lines occurred at (------------------
....................................................................)a'c.e ,
For the (------------------------------------------------------------------- l
-----Ja,c,e the maximum cumulative usage f actor of 0.7 was calculated. I l
2 It is also concluded that the Farley pressurizer surge nozzles will meet the code stress allowables under the cyclic loading from pipe thermal stratificaticn, and meet the fatigue usage requirements of ASME Section III, with a cumulative usage factor equal to 0.2, em.omemo 5-11
TABLE 5-1 CODE / CRITERIA o ASME B&PV Code, Sec. Ill, 1986 Edition-NB3600 NB3200 o Level A/B Service Limits Primary Plus Secondary Stress Intensity 5 35m (Eq. 10) Simplified Elastic-Plastic Analysis Expansion-Stress, S, 5 35m (Eq. 12)' Global Analysis Primary Plus Secondary Excluding Thermal Bending < 35m ! (Eq. 13) Elastic-Plastic Penalty factor 1.0 $ ,K s 3.333 Peak Stress (Eq.11)/ Cumulative Usage Factor (Ucum) Salt " Kep S /2 (Eq.14) Design Fatigue Curve Ucum 5 1.0 l l soss.ionm to 5-12 1 _ _ _ __ ___. ____ _ _ . ._ - , . ~ , _ _
TABLE 5-2
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 i K, 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 < 35m 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 l son.<omouc 5-13
- a,c.e Figure 5-1. Striping Finite Element Model
. u. omei ie 5-14 l
1 a ,c .e l Figure 5-2. Attenuation of Thermal Striping Potential by Holecular Conducti<n (Interface Wave Height of One Inch) u n.zo n n i i. 5-15
SECTION 6,0
SUMMARY
AND CONCLUSIONS The subjet: of pressurizer surge line integrity has been under intense investigation since 1988. The NRC issved Bulletin 68-11 in December of 1988, but the Westinghouse Owners Group had put a program in place earlier that j year, and this allowed all members to make a timely response to the bulletin. The Owners Group programs were completed in June of 1990, and have been followed by a series of plant specific evaluations. This report has documented the results of the plant specific evaluation for the Farley Nuclear Units. Following the general approach used in developing the surge line stratification transients for the WOG, a set of transients and stratification profile were developed specifically for farley. A study was made of the historical operating experience at the Farley units, and this information, as well as plant operating procedures and monitoring results, was used in development of the transients and profiles. From the stress analysis in Section 3 and fatigue evaluation in Section 5, it is not neces w y to modify the Unit 1 existing spring can travel allowances or to open up the whip restraint gaps. However, in the future, if whip restraint ' gaps are opened, the spring cans must be modified to provide sufficient travel allowances according to the future configuration oisplacements listed in Table 4-1. For Unit 2, since the spring cans have been already modified to accommodate stratification, only modification of whip restraint gaps is necessary for future operation. Such modification will be performed in conjunction with the Leak-Before-Break application. The results of this plant specific analysis demonstrated acceptance to the requirements of the ASME Code Section 111, including both stress limits and fatigue usage, for the full licensed life of the units. This report demonstrates that the Farley plants have now completely satisfied the requirements of NRC Bulletin 88-11. mwoms, to 6-1
SECTION
7.0 REFERENCES
- 1. Ceslow, B. J., et al. "Weatinghouse Owners Group Bounding Evaluation for Pressurizer Surge Line Thermal Stratification" Westinghouse Electric Corp.
WCAP-12278, (proprietar; cless 2) and WCAP-12278 (non proprietary), June 1989.
- 2. Coslow, B. J., et al., Westinghouse Owners Group Pressurizer Surge Line Thermal Stratification Program HUHP-1090 Summary Report," Westinghouse Electric Corp. WCAP-12508 (proprietary class 2) and WCAP 12509 (ntn 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. Alabama Power Co. Letter NDS-90-2043, 10/18/90 from J. E. Garlington.
- 5. Farley Units 1 and 2 Surge Line Piping Analysis, Westinghouse Central File ALA-145-15B and APR-145-153.
- 6. ASME B&PV Code Section III, Subsection NB, 1986 Edition.
- 7. " Pressurizer Surge Line Thermal Stratification," USNRC Bulletin 88-11, December 20, 1988.
- 8. " Investigation of Feedwater Line Cracking in Pressurized Water Reactor Plants," WCAP-9693, Volume 1, June 1990 (Westinghouse Proprietary Class 2).
- 9. Woodward, W. S., " Fatigue of LMFBR Piping due to Flow Stratification,"
ASME Paper 83-PVP-59, 1983. 5055s/012191 10 7.}
- 10. 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 ff.
- 11. Holman, J. P., Heat Transfer, McGraw Hill Book Co., 1963.
- 12. Yang, C. Y., " Transfer Function Method of Thermal Stress Analysis:
Technical Basis," Westinghouse Electric WCAP 12315, Westinghouse Proprietary, May 1990, i 1 i i 7-2
APPENDIX A LIST OF COMPUTER PROGRAMS This appendix lists and summarizes the computer codes used in the pressurizer surge line thermal stratification analysis. The codes are: i
- 1. WECAN
- 2. STRFAT2
- 3. ANSYS l
- 4. FATRK/ CMS A.1 WECAN t,,1.1 Description 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 ano 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 eierents are replaced by corresponding structural elements. Pressure and external loeds 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. sossceuwuo A-1
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 isoperametric elements. These problems are an integral part of 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 Description STRFAT2 is a program which computes the alternating peak stress on the inside surface 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 insida curface of a pipe if the program assumptions are considered to apply for the particul u
~
pipe being evaluated. l For striping the fluid temperature is a sinusoidal variation with numerous Cycles. The frequency, convection film coefficient, and pipe material properties are input. The program computes maximum alternating stress based on the maximum l l difference between inside surface skin temperature and the average through wall temperature, e ,v2" A-2
A.2.2 hatureUsed 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.3 ANSYS A 3.1 Description 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 and RHR lines are STlf 20 (straight pipe), STlf 60 (elbow and bends) and STIF14 (spring-damper for supports). A.3.3 Pro; ram Verification As described in section 2.1, the application of ANSYS for stratification has
, been independently verified by comparison to WESTDYN (Westinghouse piping) analysis code) and WECAN (finite element code). The results from ANSYS are also verified against closed form solutions for simple beam configurations.
N 50555/012391 10 43 i 1
a A4 FATRY/ CMS A,4.1 Deser 9 An FATRK/ CMS I19) is a Westinghouse developed computer code for fatigue tracking (FATRK) as used in the Cycle Monitoring System (CMS) for structural components of nut. lear power- plante. The transfer function method'is used for-transient thermal stress calculations. The oending stresses-(due.to global i stratification effects, ordi.ary thermal expansion and seismic) and the j pressure stresses are aho included. The fatigue usage factors are evaluated in accordance with thr sguidelines given in the ASME-Boiler and= Pressure Vessel i Code, Section Ill, Subsections NB-3200 and NB-3600. Tbs principal stress direct'ons are albwed to vary and the worst-bending stress combinations- are considered to obtain the most conservative fatigue results. i 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 acaitional-condition necessary-for data flowing.1 The program prints out the total usage factors, and the transients pairing information which determine ' the stress range magnitudes and number of cycles. The detailed stress data
$mayalsobeprinted, wwouwi io A-4
A.4.3 frocramVerification FATRK/ CMS is verified according to Westinghouse procedures with several levels ! of independent calculations as described below = (1) transfer function method of thermal stresses as compared with direct WECAN finite element analyses. (2) combined stresses as compared with hand calculptions and WECEVAL analyses. (3) The fatigue usage factor results as compared with WECEVAL analyses. - 4 a nis.m mei io A-5
. - . . . i APPEND!X 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, e
I I m., emet ic g.1
l OMB No. 3150-00M NRCB 88 11 UNITED STATES NUCLEAR REGULATOPY COMMIS$10N OFFICE OF NUCLEAR REACTOR DEGULATION WASHINGTON, D.C. 20!!5 December 20, 1988 NRC BULLETIN NO. B8 11: PRES $URIZER SURGE LINE THERMAL STRAT!FICATION Aceressees: All holders of rating licenses or construction permits for pressurized water
.mactors (NRs).
Purpose:
The purpose of this bulletin is to (1) rc< quest that addressets establish and implement a program to confim 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 ratsolve this issue. _ Description of Circumstances: , The licensee for the Trojan plant has observed unexpected movement of the pressurizer surge line during inspections performed at each refueling outage since 1902, when monitoring of the line movements began. During the last refueling outage, the Itcenset found that in addition to unexpected gap clo-sures in the pipe whip restraints, the piping actually contacted two re-straints. Although the licensee had repeatedly adjusted shims and gap sizes based on resolved. analysis of various postulated conditions, the problem had not been The most recent investigation by the licensee confirmed that the movement of piping was caused by themal stratification in the line. This phenomenon was not considered in the original piping design. On C;tober 7, 1988, the staff issued Infomation Notice 88 80, " Unexpected Piping Movement 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 ascen 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 June 16,1979), " Cracking in Piping Connected to Reactor Coolant Systems." 22,1988), " Thermal Stresses in 8812150118 8-2
NRCB 88 11 December 20, 1988 Page 2 of 5 Discussion: piping stress that may exceed design limits for fatigue The and stresse problem :an be more through Contact acute with pipe when whip the piping expansion is restricted, such as restraints. Plastic deformation can result, which pairment canoflead the to high local stresses, low cycle fatigue and functicnal im-line. thermal stratification occurs in the pressuritetAnalysis performed by the Trojan lice cooldown, and steady-state operations of the plant. surge line during bestup, 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 understood, as the hot water flows (at a 'very low flowrote) from the pressurizer through the surge line to the hot leg piping, the hot water rides on a layer of cooler water, causing the upper part of the pipe to be heated The differential to a highercould temperature temperature be as hithan the lower part (see Figure 1). conditions during typical plant operations.gh as 300'F, based on expected Under this condition, differential thermal expansion of the pipe metal can cause the pipe to deflect signifi-cently. plant, the line deflected downward and when the surFor the specific whip restraints. it underwent plastic deformation, ge lir.e contacted resulting two pipe in permanent deformation of the pipe. The Trojan event demonstrates that thermal stratification in the pressurizer The licensing basis according to 10 CFR 50.556 for all PW vessel Code Sections !!! and XI and to reconcile the evaluation when any significant differences are observed between measured da and the analytical results for the hypothesized conditions. indicates that the thermal stratification phenomenon could Staff evaluation occur in all PWR surge surge line.lines and may invalidate the analyses supporting the integrity of the The staff's concerns include unexpected bending and thermal striping (rapid oscillation of the themal 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 RtQuested: 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
NRCB 88 11 Dece:bar 20, 1988 Page 3 of 6 This inspection shoulo detemine any gross discernable distress or structural damage in the entire pressurizer 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 eperation over 10 years (i.e., low power license prior to January 1.1979) are reouested to demonstrate that the pressurizer surge line meets the apt.licable design codes
- and other FSAR and regulatory comitmentt for the licensed life of the plant, consider-ing the phenoraenon of thermal stratification and thermal striping in the fatigue and stress evaluations. This may be accomplished by performing a plant specific or gentric bounding analysis, if the 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 addressees in performing action 1.a may affect the analysis, the licensee should verify that the bounding analysis remains valid, if the opportunity to perfom the visual inspection in 1.a does not occur within the periods specified in this requested item, incorpora-tion 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 continue ( coeration or bring the plant to cold shutdown, as appropri-ate, and Mplement items 1.c and 1.d below to develop a detailed a analysis of the surge line, c. If the analysis in 1.b does not show compliance with the recuirements and licensing commitments stated therein for the duraticn of the operating license, the licensee is requested to obtain plant specific data tions.onThe thermal stratification, thermal striping, and line deflet-licensee may choose, for example, elther to install instruments on the surge line to detect temperature distribution and thermal movements or to obtain data through collective efforts, such as from other plants with a similar surge line design, if the latter option geometry is and selected, the licensee should demonstrate similarity in operation, d. Based on the applicable plant specific or referenced data, licensees are reouested to update their stress and fatigue analyses to ensure conpliance with applicable Code requirements, incorporating any observations from 1.a above. later than two years af ter receipt of this bulletin.The analysis should be co If a licensee Section 111 requirements incorporating high cycle fatigue.* Fa B-4
~_%m s NRCB 88-11 December 20, 1988 Page a of 6 is uneble to show compliance with the applicable design codes and other FSAR and regulatory comitments, the licensee is requested to 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 1.icenses:
- a. Before issuance of the low power license, applicants are requested te demonstratethatthepressurizersurgelinemeetstheapplicable design codes and other FSAR and regu atory comitments for the licensed life of the plant. This may be accomplished by performing a plant specific or generic bounding analysis. The analysis should include consideration of therinal stratification and thermal striping to ensure that fatigue and stresses are in compliance with applicable code limits. The analysis and hot functional testing should verif that piping thermal deflections result in no adverse consequences,y 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 reo4ested to either monitor the surge line for the effects of thennal 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 requested to update stress and 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 hRC any discernable distress and damage observed in Action 1.a along with corrective actions taken or plans and 1 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 nomal operation is restricted to the duration that compliance is-actually demonstrated.
B-5 l
NRCB 88-11 December 20, 1988 Page 5 of 6 2. Addressees who car.not meet the :chedule cescribed in Items 1 or 2 of Actions Recuested are requirea to submit to the NRC within 60 days of receipt of this 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 reovested in !tems Ib, la or 2 of Actions Recuested have been performed and that the results are available for inspection. The letter shall include the justification for continued operation, if appropriate, a description of the analytical coproaches used, and a sumary 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 addition, 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 comunications are in order. The lettersATTN: Comission, required above shall be addressed to the U.S. Nuclear Regulatory Document Control Desk, Washington 0.C. 20555, under oath or affirmation under the provisions of Section 182a, Atomic Energy Act of 195a. as amended. Administrator.In addition, a copy shall be submitted to the appropriate Regional This recuest is covered by Office of Management and Budget Clearance Number 3150-0011 which expires December 31, 1989. The estimated overage burden hours ( is approximately 3000 person-hours per licensee response, including assessment of the new requirements, searching data sources, gathering and analyzing the l ' data, and preparing the required reports. Thate 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 raoietion exposure is approxt:nately 3.5 person-rems per licensee response. Coments on the accuracy of this estimate and suggestions to reduce the burden may be directed to the Of fice of Management and Budget, Room 3208, New Execu-tive Offict Building, Washington. 20503, and to the U.S. Nuclear Regula-tory Commission, Records and Repo.0.C. rts Management Branch. Office of Administration and Resource Management, Washington,_0.C. 20555. B-6.
NRCB 88 11 December 20, 1988 Page 6 of 6 If you have any Questions about this matter please centtet one of the techni. cal contacts regional listed below or the Regional Administrator of the appropriate office. bl a es . Rossi Dir' ctor Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical Contacts: S. N. Hou, NRR (301) 492 0904 S. S. Lee, NRR (301) 492 0943 N. P. - Kadambi . NRR (301)4921153 Attachments: "
- 1. Figure 1 *
- 2. List of Recently Issued NRC Bulletins
-i e
d 1
.j B-7
llll.;:j;6. ,e. Surge Line Strati"ication O..
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