ML20198D998
| ML20198D998 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 10/31/1992 |
| From: | Bond C, Mel Gray, Palusamy S WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | |
| Shared Package | |
| ML19310D503 | List: |
| References | |
| WCAP-13510, NUDOCS 9212030282 | |
| Download: ML20198D998 (121) | |
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Westinghouse Class 3-(Non-Propriotary)
WCAP-13510 Structural Evaluation.of the Point Beach Units 1 & 2 Pressurizer Surge Lines, Considering the Effects of Thermal Stratification Oct'ober 1992 M. A. Gray T. H. Liu T. A. Kozlosky L. M. Valasek Verified by: # Id Verified by: i j C. B. Bond R. 'L. Brice-Nash Approved by: M '^ h /Y S. S. Palusamy,-Manager Approved by: hd b R. -II. Patel,- Manager -
Diagnostics and Monitoring- System Structural Analysis & Dev. .
Technology-Work Performed under Shop Orders.WXHP-964 and WXHP-145.
WESTINGHOUSE ELECTRIC CORPORATION'-
Nuclear.and Advanced Technology Division P.O. Box 2728 Pittsburgh, Pennsylvania 15230-2728 o 1992 Westinghouse Electric Corp.
WPF0630A:lb/110692:
TABLE OF CONTENTS Section Titig 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 Temperature Profile Development 2-1 2.1 General Approach 2-1 2.2 System Design Information 2-2 2.3 Development of Normal and Upset Transients 2-3 2.4 Monitoring Results and Operational Practices 2-5 2.5 Historical Operation 2-7 2.6 Development of Heatup and Cooldown Transients 2-8 2.7 Axial Stratification Profile Development 2-12 2.8 Striping Transients 2-14 3.0 Stress Analysis 3-1 3.1 Surge Line layouts 3-1 3.2 Piping System Global Structural Analysis 3-2 3.3 Local Stresses - Methodology and Results 3-4 3.4 Total Stress from Global and Local Analysis 3-6 3.5 Thermal Striping 3-7 4.0 Displacements at Support Locations 4-1 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 5-8 5.4 Fatigue Usage Results 5-10 6.0 Summary and Conclusions 6-1 ,
7.0 References 7-1 WPF0630A:lb/110692 i
TABLE OF CONTENTS (Continued)
Section Title Page Appendix A Computer Codes A-1 3
Appendix B USNRC Bulletin 88-11 B.1 Appendix C Transient Development Details C-1 3 Appendix D Update of Point Beach Historical Operating D-1
, Transient Set i I 4
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- WPF0630A
- lb/110692 11
EXECUTIVE
SUMMARY
Thermal stratification has been identified as a concern which can affect the l structural integrity of piping systems in nuclear plants since 1979, when a leak was discovered in a pressurized water reactor (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 piping integrity concerns. Study of the surge line behavior has concluded that the largest temperature differences occur during certain modes of plant heatu9 and cooldown.
This report has been prepared to demonstrate compliance with the requirements of NRC Bulletin 88-11 for Point Beach 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 to recommend actions by member utilities. That program provided the technical basis for the anelysis reported herein for Point Beach Units I and 2.
To demonstrate compliance with Bulletin 88-11, transients representing the stratification conditions had to be developed. The transient development utilized a number of sources, including plant operating procedures, surge line monitoring data from Point Beach Unit 1 and other similar plants, and historical records for each unit. This transient information was used as input to a structural and stress analysis of the surge lines for the two units. in conjunction with this effort, Wisconsin Electric has committed to future operation of the Point Beach Units within a 210*F limit on the system delta T (difference between pressurizer and hot leg).
The existing and future configurations for the Point Beach Units 1 and 2 surge 1.iaes have been analyzed as described in this WCAP. The results of the analyses indicate no contact between the pipe and pipe whip restraints on either unit for future operation. For Unit 1, the travel allowance at spring hanger RC-2 will be modified at the next refueling outage to accommonsie the thermal displacements for future operation.
.WPF0630A:lb/110692 iii
With the above modification, the ASME Code stress limits and cumulative usage factor requirements have been shown to be acceptable for the remainder of the licensed operation of both units. No whip restraint gap modifications are
, necessary to show Code acceptance.
This work has led to the conclusion that Point Beach Units 1 and 2 are in full I compliance with the requirements of NRC Bulletin 88-11, provided the spring
) hanger modification and operating limits summarized on the following page are implemented.
l i
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I i
i WPFC630A:1b/110692 iv
SUMMARY
OF RESULTS, AND STATUS OF 88-11 QUALIFICAT10N Unit 1 Unit 2 Operatina History through 1991 Date of commercial operation 12/21/70 10/1/72 Years of heatup/cooldoet operation 22 20 System delta T limit (past/ future) 320*F/210*F 320*F/210*F Number of 320*F oJT exceedances 0 0 Maximum Stress and Usage Factor Results Equation 12 stress / allowable (ksi) 51.8/52.9 56.1/57.9 Fatigue usage / allowable Excluding welded attachments 0.7/1.0 0.7/1.0 At welded attachments 0.99/1.0 -
Pressurizer Surge Nozzle Results ,_
Maximum stress intensity range / 32.4/57.9 32.5/57.9 allowable (ksi)
Fatigue usage / allowable 0.51/1.0 0.53/1.0 Remaining Actions by Utility Spring hanger modification required Allow sufficient travel allowance at spring haager RC-2 on Unit 1 Future operating procedure Limit maximum system tit to 210*F on modification both units Status of 88-11 Reauirements All analysis rv sirements met with above actions WPF0630A:1b/110692 v l
l 1
SECTION 1.0 BACKGROUND AND INTRODUCTION Point Beach Units 1 and 2 are two-loop pressurized 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 both of these units.
The operation of a pressurized water reactor requires the primary coolant loops to be water solid, and this is accomplished through a pressurizer 4
vessel, connected to one of the hot legs by the pressurizer surge line. A typical two-loop arrangement is shown in Figure 1-1.
The pressurizer vessel contains steam and water at saturated conditions with i
the steam-water interface level typically between 25 and 60% of the volume
- <pending 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% to 35%. During power ascension, the pressurizer level varies between 22% and 50% depending on reactor thermal power. The steam bubble provides a pressure cushion effect in the event of sudden changes in Reactor Coolant System (RCS) mass inventory. Spray operation reduces system pressure by condensing some of the steam. Electric
- heaters, at the bottom of the pressurizer, are energized to raise the liquid
, temperature to generate additional steam and incraase 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. The surge lines of both units are 10 inch schedule 140 stainless steel.
1.1 Background
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 WPF0630A:lb/110692 1-1
l l
e l movement. Investigation of this problem revealed that the movement was caused ;
by thermal stratification in the surge line.
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 o# 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 bulletin requested utilities to establish and implement a program to confirm the integrity of the pressurizer surge line. The program required both visual inspection of the surge line and demonstration that the design requirements of the surge lint are satisfied, including the consideration of l 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].*
oNumbers in brackets refer to references listed in Section 7.
WPF0630A:lb/110692 1-2
t i
i- The~ Westinghouse Owners Group implemented a program for generic detailed-
- analysis in June of 1989, and this program involved individual detailed l analyses of groups of plants. This approach permitted a more realistic l- approach than could be obtained from a single bounding analysis for all
< plants, and the results were published in June of 1990 (3].
-The followup to the Westinghouse Owners Group Program is a performance of I evaluations which could not be performed on a generic basis. The goal of this
! report is to accomplish these followup actions, and therefore ' complete the l requirements of NRC Bulletin 88-11, for Point. Beach Units 1. and 2. ;
i .
l 1.2 Descriotion of Surge t.ine Thermal Stratification- ,
i
- It will be useful to describe the phenomenon of stratification before dealing
! with its effects. Thermal stratification in the pressurizer surge line is the direct result of the difference in densities between the pressurizer water and I the generally cooler RCS hot leg water. -The warmer, lighter pressurizer water 1 tends to float on the cooler. Nvier hot leg water. The potential for .
I
- stratification is increased t ..e difference in temperature between the-l pressurizer and the hot leg increases and as the insurge or outsurge flow rates decrease.
j At power, when the difference in temperature between the pressurizer and hot l leg 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 large as 320*F,--in l which case the effects of stratification are significant, and must be.
accounted for.
l l- Thermal. stratification in.the surge line causes two effects:
[ _
- Bending of the -pipe different from that predicted in the original design.
t l
i j WPF0630A:lb/110692 1-3
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- Potentially reduced fatigue life of the piping due to the higher stress resulting from stratification and striping.
1.3 Scope of Work l
The primary purpose of this work was to develop.transi_ents which are i applicable to the Point Beach Units 1 and 2 surge lines, incorporating the effects of stratification, and to evaluate 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. Conservatisms inherent in the original approach were refined through the use of monitoring results from
' Point Beach Unit-.1 and similar plants, plant operating procedures, operator interviews, and historical data on plant operation. This process is discussed in Section 2.
L The resulting transients were used to perform analyses of the surge lines, wherein the existing support configurations were carefully modeled, and surge-I line displacements, stresses, support loads and nozzle loads were determined.
The analyses and their results are discussed in Sections 3 and 4.
l The stresses were used to perform fatigue analyses for the surge lines,.and the methodology and results of this work _are discussed-in'Secti_on 5'. The summary and conclusions of this work are presented in Section 6.-
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WP0475:lb/110392 15-
i SECTION 2.0 SURGE LINE TRANSIENT AND TEMPERATURE PROFILE DEVELOPMENT 2.1 General Approach The transients for the pressurizer surge line were developed from a number of sources, including the most recent Westinghouse Systems Standard Design transients. The heatup and cooldown transients, which involve the majority of the severe stratification occurrences, were developed from review of the design transients, plant 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 transient events within each heatup and cooldown cycle have been defined to reflect stratification effects, as described in more detail later.
The normal and upset transients, except for heatup and cooldown, used for the Point Beach 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 standard design assumption of uniform temperature to a stratified distribution, according to the predicted temperature differentials between the pressurizer and hot leg, as listed in the table. The transients have been characterized as either insurge/outsurges (1/0 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 temperature 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 st ess" are much lower. This type of cycle is important to include in the analysis, but is generally not the major contributor to fatigue usage.
In addition to the plant specific operating history mentioned above, the development of transients which are applicable to Point Beacn Units 1 and 2 was based on the work already accomplished under programs completed for the WPF0630A:lb/110692 2-1
Westinghouse Owners Group (1,2,3). In this work all the Westinghouse plants were grouped based on the similarity of their respcnse tc stratification. The three most important factors influencing the effects of stratification were-found to be the structural layout, support configuration, and plant operation.
The transient development for the Point Beach units took advantage of the similarity in the surge line layout for the two units, as well as similarities in the coerating procedures. A detailed comparison of the piping and support cunfigurations for the units appears in Section 3.1.
The transients developed here, and used in the structural analysis, have taken edvantage of the monitoring data collected during the WOG program, as well as historical operation data for the Point Beach units. Each of these will be discussed in the sections which follow.
2.2 System Desion Informatica The thermal design transients for a typical Reactor Coolant System, including the pressurizer surge line, are defined in 8"stinghouse Systems Standard Design Criteria.
The design transients for the surge line consist of two major categories:
(a) Heatup and Cooldown transients (b) Normal and Upset operation transients (by definition, the emergency and faulted transients are nb considered in the ASME Section III fatigue life assessment of components).
In the evaluation of surge line stratification, the transient events considered encompass the normal and upset design events defined in the Point Beach FSAR [16).
WPF0630A:lb/110692 2-2
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_ _ _ - _ _ - - - . _ . - - - - . _ . . - - . . . _ - ~ . _ - - _ - . _ _ . _ _ _ . -._ .. ..
2.3 Development of Normal and Upset Transients l
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) .u Table 2 I defines the total set of non heatup/cooldown normal and upset design transients used in the analyses. For all transients, the effects of global pipe movement due to stratification and the local effects of the fluid inside the pipe were appropriately included for each component analyzed.
Sections 3 and 5 describe the detailed evaluation of the welded attachment on Unit 1. For this component, the change in global loadings resulting from a modification of the structural configuration was incorporated in detail in the analysis. The total number of design transient cycles was unchanged from Table 21, but the corresponding global -loadings were distributed according to the cycles occurring before the structural change and those occurring after the change. To support this type of fatigue evaluation, a portion of the Transient Monitoring Program for Point Beach (14) was updated to include transient cycles through the time of the structural modification in-1989.
This update is described in Appendix D of this report. The data collected was used to justify the number of cycles of normal and upset transients occurring eith the prv modification loadings used in the fatigue evaluation of the Unit I welded attachment.
WPF0630A:lb/110692 2 ._
i 2.4 Monitorina Results and Operational Practices
]
I 2.4.1 Monitoring I Monitoring information collected as part of the Westinghouse Owners Group generic detailed analysis [3] was utilized in this analysis, in addition to monitoring dati from Point Beach Unit 1. Data used from Point Beach is
! discussed in Sections 2.5 through 2.7. The pressurizer surge line monitoring programs utilized externally mounted temperature sensors (resistance temperature detectors or thermocouples). The temperature sensors were 1 attached to the outside surface of the pipe at various circumferential and axial locations. These temperature sensors were securely clamped to the
$ piping outer wall, taking care to properly insulate the area against heat loss due to thermal convection or radiation.
4 The temperature sensor configuration used at Point Beach Unit 1 is shown in l Figure 2-2 and is typical of other WOG plant monitoring programs. Temperature j sensor configurations, consisting of four or five sensors, were mounted at various axial locations. The multiple axial locations give a good picture of 4
how the top to bottom temperature distribution may vary along the longitudinal l axis of the pipe. In addition, many other pressurizer surge line monitoring programs utilized displacement sensors mounted at various axial locations to detect horizontal and vertical movements. Typically, data was collected at
[ ]"" intervals or less, during periods of high system delta T.
Existing instrumentation for the monitored plants was used to record various system parameters. These system parameters were useful in correlating plant
- actions with stratification in the surge line. A list of typical plant parameters monitored at various plants is given below.
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Data from the temporary sensors was stored on magnetic floppy disks or tapes 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 computers.
2.4.2 Operational Practices Operator interviews were conducted at a number of plants, including Point Beach,aspartoftheWOGprogram(2). Since the inaximum temperature difference between the pressurizer and the reactor coolant loop occurs during plant heatup and cooldown, operations during these events were the main topic of the interviews. From the Point Beach interview, the general heatup and cooldown processes were categorized with plants using the " water-solid" approach [2].
In addition, the plant heatup and cooldown procedures for Point Beach were reviewed. The heatup and cooldown procedures limit the difference between pressurizer and spray temperature to 320'F. With respect to the surge line, spray temperature is less than or equal to hot leg temperature during heatup and cooldown, so the stated limits also inherently apply to the surge line temperature differential.
As part of the plant specific analysis, actual plant operating records were investigated, and it was found that there were heatup and cooldown events in the history of both units where the system delta T exceeded the 210*F limit assumed in the WOG generic analysis [3). In some instaness, this was due to a pressure test being performed with a steam bubble in the pressurizer.
Therefore, although the general plant heatup procedure-used the water-solid-approach, there were a substantial number of events with system delta-T higher WPF0630A:lb/110692- 2-6
than 210*F There were no events recorded for which system delta T exceeded the administrative 320'F limit.
For future operation Wiscr.nsin Electric has committed to revise their operating procedures to limit the system delta T to 210'F. The incorporation of past operating practice and future planned operations in the transient development process is discussed in the following section.
2.5 Historical Operation Historical records from Point Beach Units 1 and 2 (strip charts, operator logs, etc.) were reviewed and summarized in (7]. The purpose of the review was to obtain a distribution of maximum system delta T, and to identify heatup or cooldown events where the maximum system delta T exceeded the 210'F limit assumed for water-solid plants in the WOG generic analysis (3). The delta T distribution is expressed in terms of the number of events in a predetermined range as a percentage of the total number of events for which data was available. Due to the number of events with system delta T greater than 210'F, the past distribution was expressed in terms of maximum system delta T of 320'F. A summary of the results for available data is presented below.
Historical System AT Distributions - Basis for Past Operation i Unit 1 Unit 2 l
Number of Number of Envelope System AT Heatups or % of Heatups or % of % of Ranoe (*F) Cooldowns Total Cooldowns Total Total
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l For future operations, Wisconsin Electric plans to limit system delta T to 210*F. For analysis, a maximum future system delta T of 260'F was conservatively assumed, based on the maximum delta T for which ASME Ill Equation 12 could be qualified. The historical data distribution was then WPF0630A:lb/110692 2-7
determined based on the envelope percentages of maximum system delta T shown i% Past values above 260*F were assumed not to occur in the future, based on N '!Ti*r to be imposed for future operation. This resulted in the fo' lowing de ribution. ,
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HF A/.mcal System AT Distributions - Basis for Future Operation l l Unit 1 Unit 2 l Number of Number of Envelope b em AT Heatups or % of Heatups or % of % of
! Range (*F) Cooldowns Total Cooldowns Total Total
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1 Total events 53 37 1
This information was used to ensure that the transients analyzed for the Point
. Beach units encompassed the prior operating history of the units, and accounted adequately for future operation. Comparison of these system delta T distributions to that used in the analysis is illustrated in Figures 2-3 and 2-4. (
2
).o Development of the analytical system delta T distribution is discussed further in Section 2.6.
. 2.6 Development of Heatup and Cooldown Transients The hestup 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 Point Beach Units 1 and 2.
2.6.1 General Method The transients were developed based on monitoring data, historical operation
- and operator interviews conducted at a large number of plants. For each l
WPF0630A:lb/110692 2-8 l
monitoring location, the top to bottom differential temperature (pipe delta T) vs. time was recorded, along with the temperatures of the pressurizer and hot leg during the same time period. The difference between the pressurizer ani-hot leg temperature was termed the system delta T.
From the pipe and system delta T information collected in the WOG[1,2,3) effort, individual plants' monitoring data was reduced to categorize stratification cycles (changes in relatively steady-state stratified conditions) using the rainflow cycle counting method. This method considers delta T range as opposed to absolute values.
(
) .u The resulting distributions (for 1/0 transients) were cycles in each RS$ range i above 0.3, for each mode (5,4,3 and 2). Separate distributions were determined for the reactor coolant loop nozzle and for a chosen critical pipe location. Next, a representative RSS distribution was 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.
Transients, which are represented by AT, with a corresponding number of cycles, were developed by combining the system delta T and cycle distributions. For mode 5, system delta T is represented by the historical l distributions developed from plant operating records, and is represented in figures 2 3 and 2-4 as "Used in Analysis". As discussed in Section 2.5, these historical system delta T distributions encompass the prior operating history of the Point Beach units (Figure 2-3), and the assumed limits for future WPF0630A:1b/110692 2-9
operation (Figure 2-4). The analytical future system delta T distribution is also conservative compared to the WOG distribution for water-solid plants (3).
For modes 4, 3 and 2, the system delta T was defined by maximum values. The values were based on the maximum system delta T obtained from the monitored WOG plants for each mode of operation.
An analysis was conducted to determine the average number of stratification cycles per cooldown relative to the average number of stratification cycles ps heatup. (
).u The transients for all modes were then enveloped in ranges of AT,, i.e., all cycles from transients within each AT, range were added and assigned to the pre-defined ranges. These cycles were then applied in the fatigue analysis eith the maximum AT, for each range. The values used are as follows:
For C_vcles Within Pipe Delta T Range Pipe Delta T
[
).u This grouping was done to simplify the fatigue analysis. The actual number of cycles used in the analysis for the heatup and cooldown events is shown in Table 2-2.
The final result of this complex process is a table of transients corresponding to the subevents of the heatup and cooldown process. A mathematical description of the methodology used is given in Appendix C.
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WPF0630A:lb/110992 2-10
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stratification transient loadings at the RCS hot leg nozzle are different.
These transients have been applied to the main body of the nozzle as well as the pipe to nozzle girth butt weld. l Plant monitoring at Point Beach Unit 1 and at other WOG plants included sensors located near the RCS hot leg nozzle to surge line pipe weld. Based on the monitoring, a set of transients was developed for the nozzle region to reflect conditions when stratification could occurJin horizontal nozzles. The same phenomena that produced stratification in horizontal nozzles could also' [
produce an axisymmetric shock in the vertical nozzles. The primary factor affecting these transients was the flow in the main coolant pipe. In plants with horizontal nozzles, significant stratification was noted only when the reactor coolant pump in the loop with the surge line was not operating. The same " pump trip" phenomenon could cause a thermal shock in the vertical- t nozzles. Therefore, transients were developed using a conservative number of
" pump trips."
-[
_ ]" Therefore, the fatigue analysis- of the RCS hot leg nozzle included both the local effects of shocks at the nozzle i (" nozzle _ transients"),.and-the coincident pressure and_ bending loads caused by stratification i_n the piping (" pipe transients").
-WPF0630A:1b/110992 2-11 u
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2.6.3 Final Plant-Specific Transients The total transients for heatup and cooldown are identified as hcl through HC9
- for the pipe, and hcl through HC9 for the RCS hot leg nozzle, as shown in Tables 2-2a and 2-2b, respectively. Transients HC8 and HC9 for the pipe and HC9 for the nozzle represent transients which occur during later stages of the heatup. These transients account for past and future operation for both Point Beach units.
2.7 Axial Stratification Profile Development in addition to transients, a profile of the [
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Review and study of the monitoring data for the WOG plants revealed relatively I consistent patterns of development of delta T as a function of-distance from the hot leg-intersection. This pattern was essentially consistent throughout the heatup/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 combina-tion of the hot / cold interface and pipe delta T as functions of distance along the surga line forms a profile for'each individual plant analyzed.
The axial profiles used'for analysis of Point Beach Units 1 and-2 were developed using the general concepts discussed above and monitoring data from-
.th11t 1. The-general layout of Unit 2 is similar enough to 'that of Unit 1 to l apply the monitoring resultsito both surge lines. SurgeLline thermocouple data and plant < computer data were reviewed for two heatups and one cooldown
. period. .The data exhibited characteristics of both low and high flow WPF0630A:lb/110692- 13 - ,
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conditions discussed above, due to the effects of the riser off the hot leg.
1 Several consistent stratification profile patterns in the surge line piping were identified. The most non linear stratified condition occurred in the '
flat portion of the surge line, while the vertical portions remained at essentially uniform temperature, as expected. This axial profile is illustrated in figure 2-7, where the term " location" is defined in Figure 3 5.
Other axial profiles, exhibiting more linear vertical temperature distributions, were also considered appropriately in the global analyses and fatigue analyses discussed in subsequent sections of- this report.
4 l 2.8 Stripina Transients l
9 The transients developed for the evaluation of thermal striping are shown in
! Table 2-3.
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Striping transients use the labels HST and CST denoting striping transients (ST). Table 2-3 contains a summary of the HST1 to HS18 and CSTI 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). Obviously, striping does not occur in the vertical risers or hot leg nozzle, so the striping transients do not apply to these components. Section 5 contains more information on specifically how the striping loading was considered in the fatigue evaluation.
WPF0630A:lb/110692 2-14
TABLE 2-1 SURGE LINE TRANSIENTS WITH STRATlflCATION NORMAL AND UPSET TRANSIENT LIST - POINT BEACH UNITS 1 & 2 TEMPERATURES (*f)
MAX NOMINAL LABEL TYPE CYCLES A Tsi,,, PRZ T RCS T
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WPf0030A:lb/110692 2-15
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TABLE 2-1 (Continued)
SURGE LINE TRANSIENTS WITH STRATIFICATION NORMAL AND UPSET TRANSIENT LIST - POINT BEACH UNITS 1 & 2 TEMPERATURES (*F)
MAX NOMINAL LABEL TYPE CYCLES A T ,,,, PRZ T RCS T I
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SURGE LINE PIPE TRANSIENTS WITH STRATIFICATION - POINT BEACH UNITS 1 & 2 HEATUP/COOLDOWN (HC) - 200 OCCURRENCES TOTAL MAX TEMPERATURES NOMINAL
(*F) "'
LABEL TYPES CYCLES ATStrat PRZ T RCS T
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WPF0630A:lb/110692 2-17
TABLE 2-2b SURGE LINE N0ZZLE TRANSIENTS WITH STRATIFICATION - POINT BEACH UNITS 1 & 2 HEATUP/C00LDOWN (HC) 200 OCCURRENCES TOTAL TEMPERATURES (*F)
MAX (3) NOMINAL (1)
LABEL TYPE (2) CYCLES AT PRZ T RCS T
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TABLE 2 3 SURGE LINE TRANSIENTS - STRIPING FOR HEATUP (H) and C00LDOWN (C) - POINT BEACH UNITS 1 & 2 i
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Figure 2-1. Typical Insurge-Outsurge (1/0) Tenperature Profiles WP0475:lb/092992 2-20
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- _ a.c.e Figure 2-2. Point Beach Unit 1 Honitoring Locations WP0475:lb/092992 2 21
a.c.e Figure 2 3. Summary of Historical Data Distribution from Point Beach Units 1 and 2 Compared to Distribution used in Analysis for Past Operation WP0475:lb/092992 2-22
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Figure 2-4. Summary of Historical Data Distribution from Point Beach l Units 1 and 2 Compared to the Distribution used in Analysis for Future Operation WPO475:lb/092992 2-23
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Figure 2-5. Example Axial Stratification Profile for Low Flow Conditions WP0475:lb/092992 2-24
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Figure 2-6. Geometry Considerations WPO475:lb/092992 2-25
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5 Figure 2-7. Non-linear Temperature Profile for Point Beach Unit 1 WP0475:lb/092992 2-26
SECTION 3.0 j STRESS ANALYSES I The flow diagram (Figure 3 1) describes the procedure to determine the effects of thermal stratification on the pressurizer surge line based on transients developed in Section 2.0. [
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$ 3.1 Surae Line layouts The Point Beach Units 1 and 2 surge line layouts are documented in Reference 4
[6] and are shown in Figures 3-2 and 3-3. Below is a table summarizing the existing support configurations.
Unit 1 Unit 2 item Node Type item Node Tyng R-1 1090 Whip Restraint R-1 1090 Whip Restraint RC-1 1120 Spring Hanger R2 1100 Whip Restraint R-2 1130 Whip Restraint RC-1 1110 Spring Hanger R-3 1160 Whip Restraint R-3 1150 Whip Restraint R-4 1190 Whip Restraint RC-2 1180 Spring Hanger RC-2 1200 Spring Hanger R-4 1190 Whip Restraint R-5 1210 Whip Restraint RC-3 1220 Spring Hanger RC 3 1240 Spring Hanger It can be seen from the table above that both surge lines contain various spring hangers and whip restraints. In general, these supports can cause higher thermal loads if displacements from thermal stratification exceed travel allowances in spring hangers or gaps at whip restraints, b
a WPF0630A:1b/110692 3-1
For both units, the pipe size is 10 inch schedule 140, and the pipe material is stainless steel, SA 376-Type 316.
l 3.2 Pipina System Global Structural Analysis The Point faach Units 1 and 2 surge line piping systems were modeled separately using pipe, elbow, and linear and non-linear spring elements in the ANSYS computer code described in Appendix A. The geometric A material parameters are included. [
).u The hot-cold temperature interface along the length of a surge line [
ju, The thermal profile loading defined in Section 2 was broken into [
J'" Table 3-1 shows the loading cases considered in the analysis.
To encompass all plant operations, [
]"' Consequently, all the thermal transient loadings defined in Section 2 could be evaluated.
UPF0630A:lb/110692 3-2
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) ..o To calculate the ASME Section til Code stress limits, global structural models of the surge lines were developed using the information provided by Reference 6 and the ANSYS general purpose finite element computer code. Each model was constructed using [ ] *" ;
to reflect the layout of straight pipe, Fonds and field welds as shown in Figures 3-2 and 3 3.
For the stratified condition, [
]*" These temperature distributions were established from the transients, as discussed in Section 2.0. For both units, the maximum system AT was taken as 320'F for past conditions and 260*T for future conditions (based on modified future operating procedures). These correspond to maximum pipe delta T values of 304*F and 247'F, respectively, based on maximum relative strength of stratification of 0.95.
For Unit 1, the global piping stress analysis was based on the following three support configurations. The first and second configurations utilized travel.
allowances in spring hangers and gaps at whip restraints that were measured in .
walkdowns of the surge line (6). Travel allowances were calculated from measured loads. The first configuration represented the time before whip. restraints R-4 and R-5 were modified in 1989 to prevent interferer.ce, while the second represented the time after they were modified. Spring hanger RC-2 was' predicted to bottom out for both- configurations, and whip restraint R-4 was predicted to contact ~the pipe for-the first configuration. A third configuration in which nu.
springs could bottom out and no whip restraints could contact the pipe was also analyzed. To implement the third configuration, the travel allowance at spring hanger RC-2 would have to be increased, but no whip restraints would have to be modified for the-future operation.
For Unit 2, the global piping stress analysis was based on one support configuration. This configuration utilized travel allowances and gaps that WPF0530A:1b/ll1092 33
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eere specified on design drawings (6) because gap information for analysis was required at ambient conditions, and the Unit 2 VT-3 inspection was performed at hot standby. No spring hangers were predicted to bottom out, and no whip restraints were predicted to contact the pipe.
The results of the ANSYS global structural analyses provide the thermal expansion moments. The ASME Section 111 equation (12) stress intensity range was evaluated for both units. For a system AT of 260'F, equation (12) stresses were under the code allowable of 35m for the future configuration of ,
both units. Maximem equation (12) and equation (13) stress intensity ranges are shown in Table 3-2. For past conditions with a system AT of 320'F, equation (12) stresses would have exceeded the allowable stress (e.g., at the long radius elbows near the hot legs), based on conservative calculations.
However, visual inspections performed on the surge line revealed no indications of gross discernable distress or structurel damage [6]. The loads resulting from both past and future operating conditions wore included in the fatigue evaluation described in Section 5.0.
The pressurizer nozzle loads from thermal stratification in the surge line were also evaluated according to the requirements of the ASME code. The evaluation, using transients detailed in Reference (13] plus the moment loading from this analysis, calculated primary plus secondary stress intensities and the fatigue usage factors. For the pressurizer nozzles, the maximum stress intensity range is 32.5 ksi, compared to the code allowable value of 57.9 ksi. The maximum fatigue usage factor will be reported in '
Section 5. It was found that the Point Beach Units 1 and 2 pressurizer surge nozzles met the code stress and fatigue requirements for thermal stratification.
3.3 Local Stresses-Methodology and Results 3.3.1 Explanation of Local Stress Figure 3-4 depicts the local axial stress components in a beam wi'S a sharply nonlinear metal temperature gradient. Local axial stresses develop due to the WPF0630A:lb/110692 3-4 I
1
4 restraint of axial expansion or c ntraction. This restraint is provided by the material in the adjacent beam cross section. Fo- a linear top-to-bottom temperature gradient, tht local axial stress would not exist. [
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3.3.2 Finite Element Model of Pipe for Local Stress i
- The pipe finite element model with therma, boundary conditions is shown in Figure 3-5. [
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Figure 3-6 shows the temperature distributions through the pipe wall [
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3.3.4 RCL Hot Leg Nozzle Analysis Detailed finite element models were developed to evaluate the effects of the shocks on.the vertical hot leg nozzle due to outsurges and insurges. The <
nozzle model is shown in Figure 3-10.- Loading cases included [
]"' A summary of representative stresses for unit loading is shown in' Table 3-4.
3.3.5 Welded Attachment Analysis
-For Unit 1, a lug is welded to the pipe fto_ hold =in place a collar surrounding-the pipe at whip restraints'R-2, R-4, and R-5.. A walkdown of-the surge _line and subsequent stress analyses suggested that whip restraint R-4 had been contacting the pipe. ' Thus an additional mechanical load resulted on the lug during operation of the plant before R-4 and R-5 were modified-in 1989. This load was calculated from the global analysis of the -piping system.
Subsequently, to reduce conservatism in Code Case calculated stresses, a-finite element analysis of the lug subjected to this mechanical load was ,
performed to evaluate the effects of this additional' load. (See Figure 3-13.)-
The resulting. local stresses from the finite element analysis were used in the fatigue _ usage- factor calculation for-the-pipe at the lug location.
3.4 Total Stress from Glotal and local Analyses t
]ue
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discovered, it was postulated _ that. thermal oscillations (striping) .may
! - significantly contribute to the_ fatigue. cracking problems. . These oscillations e 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.thermalistriping.
F 'luctuation in a p_ip'e). LThermal striping was- verified to occur during.-
subsequent flow modelitests. Results .of the flow model tests 'were used to-WPF0630A:lb/110992 ~ 3-7
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l establish boundary conditions for the stratification analysis and to provide striping oscillation data for evaluating high cycle fatigue.
Thermal striping was also examined during water model flow tests performed for the Liquid Metal Fast Breeder Reactor (LMFBR) primary pipe loop. The stratified flow was observed to have a dynamic interface region which oscillated in a wave pattern. These dynamic oscillations were shown to produce significant f atigue 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. The thermal striping evaluation process was discussed in detail in References [3, 8, 9, and 10]. .
3.5.2 Thermal Striping 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 brundary. (See Figure 3-12, which shows a typical temperature distribution through the pipe wall). [
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The peak stress range and stress intensity was calculated from a 3-D finite element analysis. [
]"' The methods used to determine alternating stress intensity are defined in the ASME Code [4]. Several locations were evaluated to determine the location where stress intensity was a maximum.
Stresses were intensified by ASME Code NB-3680 factor K to account for the worst 3
stress concentration for all piping elements in the surge line affected by striping. The worst piping element was the butt weld.
WPF0630A:lb/110692 3-8
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3.5.3 Factors Which Affect Striping Stress The factors which affect striping are discussed briefly below:
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TABLE 3-1 TEMPERATURE DATA USED IN THE ANALYSIS Future Operation Max System Analysis Pressurizer RCL Temp T ,,, T,, Pipe AT(*F) Cases Temp (*F) (*F) (*F) (*F) AT (*F)
[
ju Past Operation Max System Analysis Pressurizer RCL Temp T1,, Tu, Pipe l
AT(*F) Cases Temp (*F) (*F) (*F) (*F) AT (*F)
[
j u..
WPF0630A:lb/110692 3-11
TABLE 3-2 l I
SUMMARY
OF POINT BEACH UNITS 1 AND 2 SURGE LINES THERMAL STRATIFICATION STRESS RESULTS i FOR FUTURE OPERATION 1 l I
ASME Unit 1 Unit 2 Code Stress Allowable Stress Allowable Eauation (ksi) (ksi) (ksi) (ksi) location
[
ju.
i e
WPF0630A:lb/111092 3-12
TABLE 3-3 POINT BEACH UNITS 1 & 2 SURGE LINE MAXIMUM LOCAL AXIAL STRESS AT ANALYZED LOCATIONS Profile Local Axial Stress (psi) location
- Surface Maximum Tensile Maximum Compressive
[
3.
i l
l WPF0630A:lb/110692 3-13
TABLE 3-4
SUMMARY
OF PRESSURE AND BENDING INDUCED STRESSES IN THE SURGE LINE RCL N0ZZLE FOR UNIT LOAD CASES Peak Stress Intensity Range (psi)
Diametral Unit loading Location Location Condition Inside Outside
[
j u.
b WPF0630A:1b/110692 3-14
TABLE 3-5 STRIPING FREQUENCY AT 2 MAXIMUM LOCATIONS FROM 15 TEST RUNS
- Cycles Frequency (HZ) Total Duration
% % % in
]
Min (Duration) Max luration) Ava (Duration) Seconds
[
1 5
3 .....
l WPF0630A:lb/110692 3-15
- a.c.e Figure 3-1. Schematic of Stress Analysis Procedure 4
WP0475:1b/092992 3-16
4
)
f 1
i a,c.e J
Figure 3-2. Pressurizer Surge Line Layout: Potnt Beach Unit I WP0475:lb/100292 3-17
1
_ a c.e Figure 3-3. Pressurizer Surge Line Layout: Point Beach Unit 2 WP0475:1b/100292 3-18
a,c.e i
l l
l l
l Figure 3-4. Local Axial Stress in Piping Due to Thermal Stratification WP0475:lb/100292 3-19 l
a,c.e Figure 3-5. Piping Local Stress Model and Thermal Boundary Conditions WPO475:1b/092992 3-20
a,c,e J
i Figure 3-6. Surge Line Temperature Distribution at [ ]'" Axial Locations WPO475:1b/092992 3-21
a r c,o
- Figure 3-7.- Surge Line Local Axial ' Stress Distribution at- [ . ]i" Axial' Locations WPO475:1b/092992 3-22
m,c,o Figure 3-8. Surge Line Local Axial Stress on Inside Surface at
[ ]"* Axial Locations WP0475:lb/100292 3-23
e,c,o 4
Figure 3-9. Surge Line local Axial Stress on Outside Surface at
[ ]'" Axial Locations WPO475:1b/092992 3-24
. . . - . . - - . . . . . - . . . .. . .- _-. . . - - . . . .- . - . -. .- - -~.. . -. .- . . ..- .
- a , c , e : .l r
w l
t l
i
\-
- Figure 3-10. _ Point Beach Surge Line RCL Nozzle 3-D WECAN Model WPO475:1b/092992 -
25 6- g e'- 1 vi yy y 9 m y y p
% y $' $ -Y.Y--- g = 9 '.i--' 97 **'*TP* y '*y---' yw
a,c.e Figure 3-11. Thermal Striping Fluctuation WP0475:1b/092992 3-26
i
- a,c.e I
Figure 3-12. Thermal Striping Temperature Distribution WPO475:lb/092992 3-27' l
)
-a,c.e C
Figure 3-13. Point Beach-Unit 1 Welded- Attachment
-Finite' Element.Model
. WPO475:lb/100292 28
SECTION 4.0 DISPLACEMENTS AT SUPPORT LOCATIONS Table 4-1 shows the surge line piping displacements for the highest AT conditions in Table 3-1 at the support and whip restraint locations for both units and for the future support configuration. Table 4 2 shows the maximum surge line piping displacements from the normal operating thermal condition.
Displacenents are shown for the condition in which no spring was bottomed out and no whip restraint contacts the pipe.
Based on the stress analysis in Section 3, no whip restraint gap modifications are necessary to satisfy the ASME Code requirements, provided that the future whip restraint gaps are not smaller than those displacements listed in Tables 4-1 and 4-2. Furthermore, for Unit 1, the travel allowances in spring hanger RC-2 will be modified to accommodate the piping displacements shown in Tables 4-1 and 4-2.
4 4
WPF0630A:lb/110692 4-1
TABLE 4-1 PIPING DISPLACEMENT UNDER STRATIFIED CONDITIONS
- l l
l i
l l
l l
i l
l
\
l 1
1 l
j u..
WPF0630A:lb/110692 4-2
TABLE 4 1 (continued)
PIPING DISPLACEMENT UNDER STRATIFIED CONDITIONS
- UNIT 2
[
3>
WPF0630A:lb/l10692 4-3 i
TABLE 4-2 l MAXIMUM P'PINC C DrtACEMENT UNDER NORitAL THERMAL CONDITIONS *
[
ju WPF0630A:lb/110692 4-4
SECTION 5.0 ASME SECTION 111 FAllGUE USAGE FACTOR EVALVATION 5.1 Methodoloav Surge line fatigue evaluations have typically been performed using the methods of ASME Section 111, NB-3600 for all piping components [
]'" Because of the nature of the stratification loading, as well as the magnitude of the stresses produced, the more detailed and accurate metheds 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 resuits, 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, [
pu
. 5.1.1 Basis The ASME Code, Section 111, 1986 Edition [4] was used to evaluate fatigue on sur;2 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 111 requirements incorporating high cycle fatigue." Specific requirements for WPf0630A:lb/110692 5-1
l class 1 fatigue evaluation of pfsing components are given in NB 3653. These requirements must be met for Level A and Level B type loadings according to NB 3653 and NB-3654.
l According to NB 3611 and NB 3630, the methods of NB-3200 may be used in lieu of the NB-3600 methods. This approach was used to evaluate the surge line components under stratification loading. Since the NB 3650 requirements and equations correlate to those in NB 3200, the results of the fatigue evaluation are reported in terms of the NB-3650 piping stress equations. These equations and requirements are summarized in Tables 51 and 5-2.
The methods used to evaluate these requirements for the surge line components are described in the following sections.
5.1.2 Fatigue St::ss 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. Table NB 3217 2 provides guidance for stress classification in piping components, which is reflected in terms of the NB-3653 equations.
The terms in Equations 10, 11, 12 and 13 include stress indices which adjust nominal stresses to account for secondary and peak effects for a given component. Equations 10, 12 and 13 calculate secondary stresses, which are 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 stru s 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 determine nominal stress based on straight pipe dimensions. For this l WPF0630A:lb/110692 5-2
s.
[
ju.
For the RCL nozzles, three dimensional (3-0) finite element analysis was used d
as described in Section 3.0. [
1 1
i ).u 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 "Q" stress in NB 3200, which represents stress due to differential thermal expansion at gross structural 1 discontinuities. [
i ju.
WPF0630A:lb/110692 5-3
. , - , - -,, -,. - ~ - - ,.,-.,r, e , n - -n'- ,
I Stress Combinations The stresses in a given component due to pressure, moment and local thermal stratification loadings were calculated using the finite element models described in Section 3.0. [
]'" This was done for specific con:ponents as follows:
I
) ..u UPF0630A:lb/110692 5-4
) .....
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. (
) . ...
1 j
WPF0630A:lb/110692 55
Ecuation 12 Stress Code Equation 12 stress represents the maximum range of stress due to thermal expansion moments as described in Section 3.2. Components along the entire length of the surge line were evaluated.
[g_uation 13 Stress Equation 13 stress, presented in Section 3.2, is due to pressure, design mechanical loads and differential thermal expansion at structural discontinuities. Based on the transient set defined for stratification, the design pressures were not significantly different from previous design transients. Design mechanical loads are defined as deadweight plus seismic OBE loads.
The "Ta Tb" term of Equation 13 is only applicable at structural discontinuities. [
ju.
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 independent of the global moment loading. As such, these requirements were evaluated for controlling
- components (RCL nozzles) using applicable stresses due to pressure and thermal transients.
Allowable Stresses Allowable stress, Sm, was determined based on note 3 of Figure NB 32221. 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 l
WPF0630A:lb/110692 56
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.
5.2 Fatique Usaae Factors Cumulative usage f?ctors were calculated for the controlling components using the methods described in NC 3222.4(e), based on NB 3653.5. Application of these methods is sunnarized below.
Transient loadcases and Combinations From the transients described in Section 2.0, specific loadcases were developed for the usage evaluation. [
) . ...
Each loadcase was assigned the number of cycles of the associated transient as defined in Section 2.0. These were input to the usage factor evaluation, along with the stress data as described above.
[
j u.
WPF0630A:lb/110692 5-7
l Usage factors were calculated at controlling locations in each component as follows:
- 1) Equation 10, Ke, Equation 11 and resulting Equation 14 (alternating stress - Salt) are calculated as described above for every possible combination of the loadsets.
- 2) For each value of Salt, the design fatigue curve was used to determine the maximum number of cycles which would be allowed if this type of cycle were the only one acting. These values, N,,
N,. . .N,, were determined from Code figures I 9.2.1 and I-9.2.2, curve C, for austenitic stainless steels. ,
- 3) Using the actual cycles of each transient loadset, ni , n,, . ..n,,
calculate the usage factors U i , U,. . .U, from U, = n/N,, This is done for all possible combinations. Cycles are used up for each combination in the order of decreasing Salt. When N, is greater than 10" cycles, the value of U,is taken as zero.
- 4) The cumulative usage factor, Ucum, was calculated as Ucum - U, + U,
+ ... + V,. 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.
5.3 Fatique Due to Thermal Striping The usage factors calculated using the methods of Section 5.2 do not include the effects of thermal striping. (
)u.
WPF0630A:lb/110692 5-8
[
]'"
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 strt.ss for ASME fatigue analysis. The peak stress is then used in the calculation of the ASME fatigue usage factor.
[
]"' 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.
Thermal striping transients are-shown as a AT level and number of cycles.
The striping AT for each cycle of every transient is assumed to-attenuate and follow the slope of the curve shown on Figure 5-2. Figure 5-2 is conservraively represented by a series of 5 degree temperature steps. Each steplasts-[ l" seconds.. Fluch ations t are then1 calculated at each-temperature step. Sinceaconstan, frequency.of( )*" is used in all of the usage factor calculations,' the_ total. fluctuations per step is constant and becomes:
[ ]"'
i WPF0630A:lb/110692 9
Each striping transient is a group of steps with [ )"' fluctuations per step. For each transient, the steps begin at the maximum AT and decreases by ( )"' steps dos.n to the endurance limit of AT equal to
( )*" 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 ( ]"' to obtain total fluctuations. This results in total fluctuations at each step. This calculation is performed for each step plateau from ( ]"' 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
( ]"' This is reflected in the results to be discussed below.
5.4 Fatique Usaae Results ,
NRC Bulletin 88 11 (5) 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 phenomer.on of thermal stratification and thermal striping at various locations in the surge line. Total stresses included the
[
]"' The total stresses for all transients in the bounding set were used to form combinations to calculate alternating stresses and resulting fatigue damage in the manner defined by the Code. Of this total stress, the stresses in the pipe due to
(
ju, For Unit 1, the maximum usage factor occurred at [
ju, WPF0630A:lb/110692 5-10 4
- _ . . . _ _ _ . - , _ _ . , _ - - . , - . , , . ,.m.m__-.,. . ...-----a...--,_,,.m _ ,, . ,. - - ... .-......m....-. _.__,....,A
l i
l 3.u lt is also concluded that the Point Beach Units 1 and 2 pressurizer surge nozzles meet the code stress allowables under the thermal stratification loading from the surge line and the transients detailed in Reference (13), and meet the fatigue usage requirements of ASME Section 111, with a maximum cumulative usage factor equal to [ J'".
l WPF0630A:lb/110692 5-11 1 , - .. - - .. . ..
i TABLE 5-1 l
CODE / CRITERIA
- Level A/B Service Limits
- Primary Plus Secondary Stress Intensity s 35m (Eq.10)
- Simplified Elastic-Plastic Analysis Expansion Stress, Se 13Sm (Eq.12) - Global Analysis
- Primary Plus Secondary Excluding Thermal Bending < 35m (Eq. 13)
Elastic-Plastic Penalty Factor 1.0 s Ke 5 3.333 Peak Stress (Eq. II)/ Cumulative Usage Factor (Ucum)
Salt " KepS /2 (Eq. 14)
Design Fatigue Curve Ucum 5 1.0 WPF0630A:lb/110692 5-12
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 E
Elastic-plastic penalty factor; required for simplified elastic plastic analysis when Eq. 10 is exceeded; applied to alternating stress intensity Equation 12 Expansion stress; required for simplified < 3Sm elastic-plastic analysis when Eq.10 is exceeded Equation 13 Primary plus secondary stress intensity < 3Sm excluding thermal bending stress; required for simplified elastic-plastic analysis when Eq. 10 is exceeded Thermal Limit on radial thermal gradient stress to Stress prevent cyclic distortion; required for use Ratchet of Eq. 13 Equation 11 Peak stress intensity - Input to Eq. 14 Equation 14 Alternating stress intensity - Input to Ucum Ucum Cumulative usage factor (fatigue damage) < 1,0 WPF0630A:lb/110692 5-13
- - a,c.e i
l Figure 5-1. Striping Finite Element Model WPO475:lb/092992 5-14
4 1
a,c.e j
l s
t Figure 5-2. Attenuation of Thermal Striping Potential by Molecular Conduction (Interface Wave Height of One Inch)
WP0475:lb/092992 5-15
- n. . w--wr m--
! SECTION 6.0 l
SUMMARY
AND CONCLUSIONS i
- The subject of pressurizer surge line integrity has been under intense j investigation since 1988. The NRC issued Bulletin 88-11 in December of 1988,
! but the Westinghouse Owners Group had put a program in place earlier that l l year, and this allowed all members to make a timely response to the bulletin.
l
! The Owners Group programs were completed in June of 1990, and have been i followed by a series'of plant specific evaluations. This report has j documented the results of the plant specific evaluations for Point Beach *
- Units 1 and 2.
i Following the general approach used in developing the surge line strati-
. fication transients for the WOG. a set of transients and stratification l profile were developed specifically-for the Point Beach Units. A study was
! made of the historical operating experience at both units, and this
) information, as well as plant operating procedures and monitoring results, was
- used in development of the transients and profiles. As a result of this effort, Wisconsin Electric will limit the system delta T to 210'F for future l
i operation of the Point Beach units.
l Based on the stress analysis in Section 3 and fatigue evaluation in Section 5, l it is not necessary to modify the existing whip restraint' gaps for ASME Code l
acceptability, provided sufficient travel-allowances are maintained in the
{ variable spring hangers in each plant. For Unit 1, the existing spring travel l allowance at spring hanger RC-2 will be modified to accommodate the thermal
! displacements shown in Tables'4-1 and 4-2. Such modification is necessary to
- validate the complete analysis.
- The results of the plant specific analyses, along with the support
- modification in the Unit I spring hanger and future operating procedures discussed above, demonstrate acceptance to the requirements of the ASME Code l Section-III, including both stress limits and fatigue usage for the full L
WPF0630A:lb/110692 6-1 s
'i
-.,-w.,,_. .-.-a.-s-.,, .,,-w,.: _ ,..,%c ,..y= -,[- c 4 . m ,. ,u,, .,,w .
,..,.m--,- ~-
licensed life of the plant. This report demonstrates that Point Beach Units I and 2 have completely satisfied the requirements of NRC Bulletin 8811.
l
! WPF0630A:lb/110692 6-2
SECTION
7.0 REFERENCES
- 1. Coslow, B. J., et al., " Westinghouse Owners Group Bounding Evaluation for Pressurtzer Surge Line Thermal Stratification", Westinghouse Electric Corp. WCAP-12277, (Proprietary Class 2) and WCAP-12278 (nonproprietary), June 1989.
- 2. Coslow, B. J., et al., " Westinghouse Owners Group Pressurizer Surge Line Thermal Stratification Program MUHP-1090 Summary Report," Westinghouse Electric Corp. WCAP-12508 (Proprietary Class 2) and WCAP-12509 (nonproprietary), 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. '
- 5. " Pressurizer Surge Line Thermal Stratification," USNRC Bulletin 88-11, December 20, 1988.
- 6. Wisconsin Electric letter no. NPL 92-0283, June 8, 1992.
- 7. Bond, C. B., " Compilation of Historical Surge Line System Delta T for Point Beach Units 1 and 2," Westinghouse letter report MT-DMT-447(91),
December, 1991.
[
- 8. " Investigation of Feedwater Line Cracking in Pressurized Water Reactor Plants," WCAP-9693, Volume 1, June 1990 (Proprietary Class 2).
- 9. Woodward, W. S., " Fatigue of LMFBR Piping due to flow Stratification,"
ASME Paper 83-PVP-59, 1983.
WPF0630A:lb/110692 7-1
)
i 10. Fujimoto, T., et al., " Experimental Study of Striping at the Interface of Thermal Stratification" in Thermal Hydraulics in Nuclear Technolvay, K. H. Sun, et al., (ed.) ASME, 1981, pp. 73.
l 11. Holman, J. P., Heat Transfer, McGraw Hill Book Co.,1963.
- 12. Yang, C. Y., " Transfer function Method for Thermal Stress Analysis:
Techni:ai Basis," Westinghouse Electric Corporation WCAP-12315 (Proprietary Class 2).
- 13. Series 84 Pressurizer Stress Report, Section 3.1, Surge Nozzle Analysis, 4
December 1974.
- 14. Bond, C. B. and Pepka, J. M., " Transient Monitoring Program for
- Wisconsin Electric Power Company, Point Beach Units 1 and 2 Phase I
- final Report," Westinghouse Electric Corporation WCAP-ll501 (Proprietary Class 2), October 1987.
- 15. Sargent & Lundy letter no. SL-WE-92-038, project no. 6904-35, dated June 19, 1992.
- 16. Point Beach Nuclear Plant, Unit Nos. I and 2, Final Safety Analysis Report, Section 4.1.
I i
WPF0630A:lb/110692 7-2
APPENDIX A LIST OF COMPUTER PROGRAMS This appendix lists and summarizes the computer codes used in the pressurizer surge line thermal stratification. The codes are:
- 1. WECAN
- 2. STRFAT2
- 3. ANSYS
- 4. FATRK/ CMS A.1 WECAN A.l.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 and triangular structural elements are used for plane strain, plane stress, and axisymmetric analyses. Brick and wedge structural elements are used for three dimensional analyses. Companion heat conduction elements are used for steady state heat conduction analyses and transient heat conduction analyses.
A.I.2 Feature Used The temperatures obtained from a static heat conduction analysis, or at a specific time in a transient heat conduction analysis, can be automatically input to a static structural analysis where the heat conduction elements are replaced by corresponding structural elements. Pressure and external loads can also be include in the WECAN structural analysis. Such coupled thermal-stress analyses are a standard application used extensively on an industry wide basis.
1 WPF0630A:lb/110692 A-1
A.l.3 Procram Verification Both the WECAN program and input for the WECAN verification problems, I currently numbering over four hundred, are maintained under configuration control. Verification problems include coupled thermal-stress analyses for the quadrilateral, triangular, brick, and wedge isoparametric elements. These ,
problems are an integral part of the WECAN quality assurance procedures. When f 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 Descr_iption STRFAT2 is a program which computes the alternating peak stress on the inside surface of a flat plate and the asage factor due to striping on the surface.
The program is applicable to be used for striping on the inside surface of a pipe if the program assumptions are considered to apply for the particular pipe being evaluated.
For striping the fluid temperature is a sinusoidal variation with numerous cycles.
The frequency, convection film coefficient, and pipe material properties are itput.
The program computes maximum alternating stress based on the maximum difference between inside surface skin temperature and the averege through wall temperature.
A,2.2 Feature Used 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 WPF0630A:lb/110692 A-2
4 cycles of stress at maximum the alternating stress level. Design fatigue curves for several materials are contained into the program. However, the l user has the option to input any other fatigue design curve, by designating l that the fatigue curve is to be user defined.
A.2.3 Proaram Verification STRFAT2 is verified to Westinghouse procedures by independent review of the stress equations and calculations.
4 A.3 ANSYS I
A.3.1 pescription ANSYS is a public domain, general purpose finite element code.
A.3.2 Feature Used The ANSYS elements used for the analysis of stratification effects in the surge line are STlf 20 (straight pipe), STIF 60 (elbow and bends) and STIF14 (spring damper for supports).
j A.3.3 Proaram Verification As described in Section 3.2, 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.
A.4 FATRK/ CMS A.4.1 Description FATRK/ CMS is a Westinghouse developed computer code for fatigue tracking
'FATRK) as used in the Cycle Monitoring System (CMS) for structural components WPF0630A:lb/110692 A-3
. . - _ - ~ _ - . . _ _ _ - - . -- ._ - __ --. __ _ - _ - _ _
of nuclear p,wer plants. The transfer function method is used for transient thermal stress calculations. The bending stresses (due to global stratification effects, ordinary thermal expansion and seismic) and the pressure stresses are also included. The fatigue usage factors are evaluated in accordance with the guidelines given in the ASME Boiler and Pressure Vessel Code, Section 111, Subsections NB-3200 and NB-3600.
The code can be used both as a regular analysis program or an on-line monitoring device.
A.4.2 Featuro used FATRK/ CMS is used as an analysis program for the present application. The input data which include the weight functions for thermal stresses, the unit bending stress, the unit pressure stress, the bending moment vs.
stratification temperatures, etc. are prepared for all locations and geometric conditions. These data, as stored in the independent files, can be appropriately retrieved for required analyses. The transient data files contain the time history of temperature, pressure, number of occurrence, and additional condition necessary for data flowing. The program prints out the total u< age factors, and the transients pairing information which determine the stress range magnitudes and number of cycles. The detailed stress data may also be printed.
A.4.3 Program Verification FATRK/ CMS is verified according to Westinghouse procedures with several levels of independent calculations.
WPF0630A:lb/110692 A-4
I APPENDIX B USNRC BULLETIN 88-11 In December of 1988 the NRC issued this bulletin, and it has led to an extensive investigation of surge line integrity, culminating in this and other plant specific reports. The bulletin is reproduced in its entirety in the pages which follow.
WPF0630A:lb/110692 B-1
.. j
0FB ho. 3150-0011
> NRCB 88-11 UNITED STATES NUCLEAR REGULATOPY COMMISSION OFFICE OF NUCLEAR REACTOR DEGULATION WASHINGTON, D.C. 20555 l
December 20, 1988 NRC BULLETIN NO. 88-11: PRESSURIZER SURGE LINE THERMAL STRATIFICATION Addressees:
All holders of operating licenses or construction permits for pressurized water reactors (PWRs).
Purpose:
The purpose of this bulletin is to (1) request that addressees establish and implement a program to confirm pressurizer surge line integrity in view of the occurrence of themal stratification and (2) require addressees to infom the staff of the actions taken to resolve this issue.
Description of Circumstances:
The licensee for the Trojan plant has observed unexpected movement of the pressuriter surge line during inspections performed at each refueling outage since 1982, when monitoring of the line movements began. During the last refueling outage, the licensee found that in addition to vnexpected 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 e resolveu nalysis of various postulated conditions, the problem had not been The most recent investigation by the licensee confirmed that thS movement of piping was caused by themal stratification in the line. This phenomenon was not considered in the original piping design. On October 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 comunication may be forthcoming. The licensee for Beaver Valley 2 has also noticed unusual snubber movement and significantly larger-than-expected surge line displacement during power ascension.
The concerns raised b NRC Bulletins 7913 (y the above observations are similar to those described in Revision 2, dated October 16, 1979), " Cracking in Feedwater System Piping" and 88-08 (dated June 22, 1988), " Thermal Stresses in Piping Connected to Reactor Coolant Systems."
8812150118 B-2
1 1
NRCB 88-11 December 20, 1988 Page 2 of 6 Discussion:
piping stress that may exceed design limits for fatigue The and stre problem can bewith through contact more acute pipe whipwhen the piping expansion is restricted, such as restraints.
Plastic deformation can result, which paiment canoflead the to high local stresses, low cycle fatigue and functional im-line.
thermal strattfication occurs in the pressurizer surge line during be cooldown, and steady state operations of the plant.
During a typical plant heatup, water in the pressurizer is heated to about 440'F; a steam bubble is then formed in the pressurizer. Although the exact phenomenon is not thoroughly understood, as the hot water flows (at a very low flowrate) from the pressurizer through the surge line to the hot. leg piping ,
the het water rides on a layer of cooler water, causing the upper part of the The differt tial temperature could bc as hipipe to be heated to a higher temper conditions 'uring typical plant operations.gh as 300'F, based on expected Under this condition, differential themal expe nsion of the pipe metal can cause the pipe to deflect signifi-cantly.
t plant, the line deflected downward and when the surFor the specif whip restraints, it underwent plastic deformation, ge line contacted resulting in pemanent two pipe defomation of the pipe.
l The Trojan event demonstrates that thermal stratification in the pressurizer The licensing basis according to 10 CFR 50.554 for all PW Vessel Code Sections !!! and XI and to reconcile the evaluation when any significant differences are 00 served between measured dat and the analytical results for the hypothesized conditions.
indicates that the thermal stratification phenomenon could Staffoccur evaluation in all PWR surgeline.
surge lines and may invalidate the analyses supporting the integrity of the The staff's concerns include unexpected bending and themal striping (rapid oscillation of the thermal boundary interface along the piping inside surface) as they affect the overall integrity of the surge line for its design life (e.g., the increase of fatigue).
Actions Requested:
Addressees are requested to take the following actions:
1.
For all licensees of operating PWR$:
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, e
B-3
NRCB 88 11 December 20, 1988 Page 3 of 6 This inspection should determine 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 operation over 10 years (i.e., low power license prior to January 1. 1979) are requested to demonstrate that the pressurizer surge line meets the applicable design codes
- and other FSAR and regulatory comitments for the licensed life of the plant, consider-ing the phenomenon of thermal stratification and thernal striping in the fatigue and stress evaluations. This may be accomplished by perfoming a plant specific or generic bounding analysis, if the latter option is selected, licensees should demonstrate applicability of the referenced ganeric 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 continued operation or bring the plant to cold shutdown, as appropri-
- ate, and implement Items 1.c and 1.d below to develop a detailed analysis of the surge line. '
3
- c. If the analysis in 1.b does not show compi' with the recuirements and licensing convoitments stated therein for se duration of the operating license, the licensee is requested to obtain plant specific data on thermal stratification, thermal striping, and line deflec-tions. The licensee may choose, for example, either to install instruments on the surge line to detect temperature distribution and themal movements or to obtain data through coll 6ctive efforts, such as from other plants with a similar surge line design, if the latter option is selected, the licensee should demonstrate similarity in geometry and operation.
d.
Based on the applicable plant specific or rehrenced data, licensees are reouested to update their stress and fatigue analyses to ensure compitance with applicable Code requirements, incorporating any observations from 1.a above. The analysis should be completed no later than two years aftor receipt of this bulletin. If a licensee
- Fatigue analysis should be performed in accordance with the latest ASME Section 111 requirements incorporating high cycle fatigue.
B-4
NRCB 88 11 Oecember 20, 1988 Page 4 of 6 is un6ble to show compliance with the applicable design codes and other FSAR and regulatory comitments, the licensee is requested te submit a justification for continued operation and a description of '
the proposed corrective actions for effecting long term resolution.
- 2. For all applicants for PWR Operatio Licenses:
- a. Before issuance of the low power license, applicants are requested te demonstrate that the pressurizer surge line r:etts the applicable design codes and other FSAR and regulatory corrnitnents for the licensed life of the plant. This may be accomplished by performing a plant-s;ecific or generic bcunding analysis. The analysis should include consideration of thermal stratification and thermal striping to ensure that fatigue and stresses are in compliance with appitcable 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 requested 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, th6nnel striping and piping deflections, d.
Applicants are requested to update stress and fatigue analyses, es 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 anu implementation of the program requested by items 1 or 2, as well 6; any subsequent corrective actions, and maintain these records in accor-dance with 10 CFR Part 50 Appendix B and plant procedures.
Report!ng Requirements:
1.
Addressees shall report to the hRC any discernable distress and damage observed in Action 1.4 along with corrective actions taken or plans and schedules for repair before restart of the unit.
- If compliance with the applicable codes is not demonstrated for the full duration of an operating license, the staff may impose a license condition sut.h that nonnal operation is restricted to the duration that compliance is actually demonstrated.
B-5
- - - _ - _ - a
NRCB 88-11 Deced.er 20, 1988 Page 5 of 6 2.
Addressees Actions Requested who cannot are meet the schedule oescribed in items i or ? of
'equired to submit to the NRC within 6G 4 5 of receipt of tnis bulletin an alternative schedule with justification for the recuested schedule.
3, Addressees shall submit a letter within 30 days after the completion of these actions which notifies the NRC th6t the actions recuested in !ters Ib,16 or 2 of Actions Recuested have been perforwed and that the iesults are available for inspection. The letter shall include the justification for continued operation, if appropriate, a description of the analytical approaches used, and a summary of the results, i
Although not requested by this bulletin, addressees are encouraged work
( collectively to address the technical concerns associated with this ,isue, as well as to share pressurizer surge line data and operational experience, In aodition, addressees experience thermal stratification are encouraged and to review piping in other systems which may therma!
the previously mentioned Bulletins 79-13 and 68-08. striping, especially in light of The NRC staff intends to review noti , operational experience giving appropriate recognition tt *is phenome-30 as 'o determine if further generic communications are der.
The letters ATTN:
Commission, required above shall be addressed to th' U.S. Nuclear Regulatory Document Control Desk, Washington, D.C. 20555, under oath or amended, as offirmation under the provisions of Section 182a, Atomic Energy Act of 1954, Administrator.in addition, a copy shall be submitted to the appropriate pegional This request is covered by Office of Management and Budget Clearance Number 3150-0011 which expires December 31, 1989.
The estimated average burden hours is approximately 3000 person-hours per licensee response, including assessment of data, theand new requirements, preparing searching the required data sources, gathering and analyzing the reports. These estimated average burden hours pertain only to these identified response-related matters and do not include the time fororactual installation component implementation of physical changes, such as test equipment modification. The estimated average raciation exposure is approximately 3.5 person-rems per licensee response.
Convents on the accuracy of this estimate and suggestions to reduce the burden may be directed to the Office of Management and Budget, Roorn 3208, New Execu-tive Offict Buildin?, Washington. 0.C.
tory Commission, req,rds and Reports Management Branch, Of fice of20503, and to the U.
Aaministration and Resour*> 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 contact one of the techni-cal contacts listed below or the Regional Administrator of the appropriate i regional office.
t i '
[f a les E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical Contacts: 5. N. Hou, NRR (301) 492-0904
- 5. S. Lee, NRR
. (301) 492-0943 N. P. Kadambi, NRR j (301) 492-1153 Attachments:
- 1. Figure 1
- 2. List of Recently Isseed NRC Bulletins i
4 4
0 4
i i
4 B-7
RC -
December 20, 986 Page I of i
i Surge Line Stratification -
)
\ .
i
'PZR aunx i
l Hot Flow from Pressurizer i Th = 425*F
( -
,I HL i
Stagnant Cold Fluid V Tcold = 125 F e
s Figure 1 l B-8
APPENDIX C TRANSIENT DEVELOPMENT DETAILS
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APPENDIX D j UPDATE OF. POINT BEACH HISTORICAL OPERATING TRANSIENT SET AUGUST, 1986 THROUGH JULY, 1992 INTRODUCTION AND BACKGROUND
! In August 1986, Westinghouse performed a program of historical operating
- transient data collection at the Point Beach-plant site as part_of the first
$ phase of a Transient and Fatigue Cycle Monitoring Program for that plant. The
- data was evaluated at Westinghouse and used as input to create an " Operating Transient Set" for the plant, which covered the time period from the initial-j cold hydrotest to July, 1986. The Operating Transient Set is summarized in Tables 3.5.1 and 3.5.2 of Westinghouse report WCAP-ll501 [ref. D-1].
1 l Currently in 1992, Westinghouse is. performing a Pressurizer Surge Line Plant i Specific Applicability Analysis for Point Beach 1 and 2. This analysis is l being used by WEPC0 to demonstrate validity of the Westinghouse Owners Group-l Surge Line Stratification Program conclusions [D-2] to the Point Beach Plant.
l _To support that analysis, the historical _ operating transient set from
{ Reference D-1 was updated as' described in this appendix, i TECHNICAL ISSUE AND TASK OBJECTIVE l Point Beach Unit I has welded attachments on the pressurizer surge line, and, ,
until May 1989, associated collars restricted the movement of the attachments 4
as part of the pipe whip restraint system. This configuration caused
- significant fatigue loading on the welded attachments. When the welded j attachment fatigue analysis was performed for the plant specific applicability
- analysis using 40 year design transients interpolated back to May 1989, qualification could not be demonstrated. However, if the actual-transients l
from Reference D-1 were forward extrapolated to May 1989, fatigue acceptability could be demonstrated.
To_ verify the assumption.that'the Reference D-1 results could be extrapolated, the Point beach Unit 1 operating transient history needed to be updated from 1
)-
j WPF0630A:1b/110692- D-1 4
. < ~ , - - , v ,
August 1986 through May 1989. The Special Projects group at WEPC0 was also interested in operating history data for the planned continuation of the Transient and Fatigue Cycle Monitoring Program. The Special Projects group was interested in both units, as well as updating the data to the present time, i .e. , July 1992. Since the offort to do this was not significantly different from the effort to simply update Unit 1 to May 1989, the operating history for both units was updated through July 1992.
METHODOLOGY To update the operating transient set, two Westinghouse engineers visited the site during the time period from August 27 through September 2, 1992, to collect operating history data from August 1986 through July 1992. This data was analyzed and categorized using the methods of Reference D-1. Tables 3.5.1 and 3.5.2 of Reference D-1 were then updated for both units. Two separate table updates were created; one covering the period up through May 1989, and the other through July 1992. These tables are reproduced as Tables D-1 and D-2 of this appendix.
RESULTS The actual accumulated cycles for Unit 1 through May 1989 were compared to the values based on extrapolation. On an overall basis, the actual cycles were within the extrapolation assumptions. Therefore, the basis of the number of cycles used for the Unit I welded attachment fatigue evaluation has been shown to be valid.
REFERENCES D-1 Bond, C. B. and Pepka, J. M., " Transient Monitoring Program for Wisconsin Electric Power Company, Point Beach Units 1 and 2 Phase I Final Report," Westinghouse Electric Corporation WCAP-ll501 (Proprietary Class 2), October 1987.
WPF0630A:lb/110692 D-2
D-2 Coslow, B. J., et al., " Westinghouse Owners Group Pressurizer Surge Line Thermal Stratification Generic Detailed Analysis Program MUHP-1091 l Summary Report," Westinghouse Electric Corp. WCAP-12639 (Proprietary Class 2) and WCAP-12640 (non-proprietary), June 1990, a
l i
i l
WPF0630A_:Ib/110692 D-3 i
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, TABLE D-1.1
SUMMARY
OF POINT BEACH OPERATING TRANSIENTS i
Actual No. Actual No.
of Occurrences of Occurrences Design Point Beach Through July, 1986 Through May, 1989 No. Design Transient Unit 1 Unit 2 Unit 1 Unit 2 (40 yr.) Transient Normal Conditions Unit loading. 1341"8 1478"' 1441 1569 .14,500 Yes Unit Unloading 1206"' 1353"' 1303 1438 14,500 Yes Reduced Temperature Return 11 -12 14 14 2,000 No .
to Power (Core Stretchout)-
2,000
.Small15tep Load Increase O O O O _Yes Small-Step Load Decrease 20' 20 21 23 2,000 Yes Large' Step load Decrease 33- 15 33 15 200 Yes with Steam Dump Turbine'Runbacks- 28 10 28 10 ;
0ther Large Steps 5 5 5 5 . ,
!- Baron Concentration Equalization 136 90 147 105 36,600 Yes
~
Test / Shutdown Conditions-
!' -Heatup '42 28 47 34 200 Yes ,
i
, "'See Appendix 1. and Tables. A1.1 through A1.8 for frequency distribution by magnitude and rate of power ,
, change.. Design numbers of. cycles are based on 0% to 100% and 100% to 0% at 5% Full Power / min and '-5% ,
s
~ Full Power / min.
5 WPF0630A'Ib/110692 : D-4' ,
_ m. . _ -. . . . . . _ . . . _ - . _ - - --- . _ _ _ . _ _ . _ . _ . _- -. _ _ _ _ _ . . _ _ - . - . _ . . . . _ - . _ -. .
l p .
l TABLE D-1.1 .j
SUMMARY
OF POINT BEACH OPERATING TRANSIENTS (Cont.)
Actual No. Actual No.
of Occurrences of Occurrences Design Point Beach .
Through July, 1986 Through May, 1989 No. Design ..
Transient . Unit 1 Unit _2 Unit I _ Unit 2 (40 yr.) Transient
- Cooldown- 41 27 46 33 200 Yes i Hot Standby Operation
, - Main-(Continuous)'Feedwater 194 172 203 187 25,000 Yes
- Auxiliary (Slug) Feedwater 194 172 203 187 2,000 No
. Refueling i :
- 11 12 14 15 80 No Turbine Roll Test 1 1 1 1 10 Yes
- Pressure Testing .
- A) Initial Primary Hydro. I 1 1 1 1 Yes '
B) -Subsequent & Alternate 23" 21" 25 21 50 Yes
, Subsequent Primary Pressure 8
C1) Primary-to-Secondary Leak 2" 7 2 7 5 Yes !
C2) 2000.psid.' , .
6*' 9*- 6 12 N/A No i
~ D) Additional Primary Pressure 11* 12* 15 18 N/A No
.(Tech.-Spec.' Requirement)
-- E) ' Initial Secondary Hydro. 2" 1* 2- 1 1 Yes F) -Secondary Pressure- :l* 1* 1 1 50. Yes --
G) -Secondary-to-Primary Leak- A:33" A:21" 34 25' 5 Yes I -B:28" 'B:21" 29- 25 1
.mFrom.information;in MT/SME/4542 transcribed'from Station Logs "From WEPC0 memo, 11/12/86 (See. Appendix-10,-page A10-8).
' "From discussions'with~ Point Beach ISI_ personnel,-11/20/86.
Additional -(Tech. spec.) pressure test performed once per outage
- One additional secondary hydro.- for replacement steam' generator:(Unit 1)
'"Fron WEPC0 memo,-11/12/86 (See Appendix 10, page A10-6)' .
' WPF0630Ailb/110692- D-5 q
- - _ _ - = = _ - _ _ _. .>
TABLE D-1.1
SUMMARY
OF POINT BEACH OPERATING TRANSIENTS (Cont.) ,
Actual No. Actual No.
of Occurrences of Occurrences Design Point Beach Through July, 1986 Through May, 1989 No. Design Transient Unit 1 Unit 2 Unit 1 Unit 2 (40 yr.) Transient Abnormal (Upset) Conditions Reactor. Trip from Power 42 30 44 33 400 Yes 28* 20" 29 22 230*
- A) No Excessive Cooldown * '
B) Excessive Cooldown 13" 9* 13 10 160*
5 5 2 10*
- C) Excessive Cooldown and SI 1 1 1 Loss of Load 0 0 0 1 80 Yes Loss of Power 0 0 0 0 40 Yes Control' Rod Drop 3 1 4 1 80 No Partial loss of Flow 0 1 0 2 80 Yes Primary Side Overpressurization 2 0 3 0 No 8
Excessive Feedwater Flow 2 2* 2 2 30* No S See Appendix 4, page A4-14 and Table A4.5 for additional breakdown by initial power level.
" Design numbers of cycles for (A), (B), (C) subcategories are from SSDC 1.3F.
"This transient,. as defined by the courses of the events and the available parameter data, is not described by the design basis. Based on the initial pressure increase, these events are similar to the Loss of Load transient.
- Estimated based on operator information (See Section 3.4.3.5).
i WPF0630A:ib/110692 0-6
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TABLE-D-1.2 i
SUMMARY
OF POINT BEACH AUXILIARY TRANSIENTS Actual No. Actual No.
- . of Occurrences of Occurrences Design Point Beach !
Through July, 1986 Through May, 1989 No. Design !
Transient / Initiating Event Unit 1 Unit 2 Unit l' Unit 2 (40 _yr.) Transient ;
Pressurizer Spray Actuation /
Normal Conditions: '! '
Heatup 42m 28"' 47 34 200* .Yes Cooldown to 400 psia. 41" 27 5 46 33 200m Yes ;
Cooldown'from 400 psia 41m 27 5 46 33 200* Yes Unit. Loading at 5%/ min. 80 102 80 '102 14,500 Yes
' Unit Unloading at 5%/ min. 84 148 86 148 14,500 Yes ;
Large Step Decrease. 33 15 33 15 200 Yes Small_ Step Load Increase 0 0 0 0 2,000 Yes-Small Step Load. Decrease 20 20 21 23 2,000 Yes >
Boron Concentration 136 90 147 105 36,600 Yes
- Equalization Abnormal (Upset) Conditions: 10 10 11 .10 690 5 -
Test Conditions- '
- Turbine Roll _ Test 1 1 1 1 10 Yes mTotals apply to each of the spray operations designated in Appendix 5, Table A5.3. .
< *These values are based Lon totals for. design numbers of cycles of abnormal events . identified in SSDC 1.3.F. '!
4 t !
i WPF0630A:lb/110692 D-7
TABLE D-1.2 ,
SUMMARY
OF POINT BEACH AUXILIARY TRANSIENTS (Cont.)
I Actual No. Actual No.
cf Occurrences of Occurrences Design Point Beach Through July, 1986 Through May, 1989 No. Design Transient / Initiatina Event Unit 1 Unit 2 Unit 1 Unit 2 (40 yr.) Transient PORV Opening /
Reactor Trips (all causes) 12" 9* 12 9 100 No Large Step Load Decrease 1 "' 2"' 1 2 Other. Conditions 1 0 RID Maintenance 3* 3* 4 4 60 No Charging Flow 50% Increase and 1,306* 1,420* 1,407 1,512 24,000 Yes Return Charging Flow 50% Decrease and 1,341" 1,478"' 1,441 '1,569 24,000 Yes '
Return Letdown Flow 60% Increase and 240* 267m 274 303 24,000 Yes Return ~ !
S 5 Letdown Flow Isolation:and IS 10 16 11 200 No 1 Return ,
Charging and Letdown Flow 6m 6m 7 7 60- Yes Isolation and Return RHR Operation /
Cooldown" 41 27 46 33 200 Yes' ,
Refuel ing" 11 12 14 15 80 No Low Head SIS 1 0 1 0 89 No High Head Sl* 1- 0 2 0 89 No j WPF0630A:1b/110692 D-8 l
l
TABLE D-1.2
SUMMARY
OF POINT PEAC11 AUXILIARY TRANSIENTS (Cont.)
" Estimated based on available strip chart data See Appendix 5.
"'See Section '3.4.1.4 and Appendix 2, pgs. A2-1 through A2-3.
- Estimated based on operator information.
- Assumed to occur for all load changes. See Appendix 5, pgs. A5-12 through A5-14.
" Estimated. See Section 3.4.4.5 and Appendix 5, pgs. A5-14 through A5-17.
- See Sections 3.4.4.6 and 3.4.4.7 for discussion of flow paths.
t
, WPF0630A:lb/110692 D-9 t
TABLE D-2.1
SUMMARY
.0F POINT BEACH OPERATING TRANSIENTS Actual No. Actual No.
of Occurrences of Occurrences Design Point Beach ,
Through July, 1986 .Through June, 1992 No. Design-Transient- Unit 1 Unit 2 Unit 1 Unit 2 (40 yr.) Transient Normal Conditions Unit Loading 1341"' 1478"' -1532 1643 14,500 Yes Unit Unloading 1206"' 1353* 1381 1505 14,500 Yes Reduced Temperature Return 11 12 17 16 2,000 No To Power (Core.Strechout)
Small Step Load Increase 0 0 0 0 2,000 Yes Small Step Load Decrease 20 20 22 25 2,000 Yes Large Step Load Decrease 33 15 43 18- 200 Yes )
with Steam Dump Turbine Runbacks 28 10 38 13 Other Large Steps 5 5 5 5 BoronIConcentration Equalization 136 90 170 118 36,600 Yes
' Test / Shutdown Conditions Heatup. 42 28 53 38 200 Yes
'*See Appendix. l .and-Tables A1.1' through A1.8 for frequency distribution by magnitude and rate of power change. Design numbers of cycles are ba',ed on 0% to 100% and 100% to 0% at 5% Full . Power / min ~ and -5% Full Power / min.
WPF0630A:lb/Il0692 0-10
3 u-L L h -+% 6h m W_.a..a TABLE D-2.1
SUMMARY
OF POINT BEACH OPERATING TRANSIENTS (Cont.)
Actual No. Actual No.
of Occurrences of Occurrences Design Point Beach Through July, 1986 Through June, 1992 No. Design Transient Unit 1 Unit 2 Unit 1 Unit 2 (40 yr.) Transient Cooldown 41 27 52 37 200 Yes Hot Standby Operation
- Main (Continuous) Feedwater 194 172 215 194 25,000 Yes
- Auxiliary'(Slug) Feedwater 194 172 215 194 2,000 No Refueling 11 12 19 17 80 No
' Turbine Roll Test 1 1 1 1 10 Yes Pressure Testing A) Initial Primary Hydro. I 1 1 1 1 Yes B) Subsequent & Alternate 23m 21* 25 23 50 Yes Subsequent Primary , assure 5
Cl) Primary-to-Secondary Leak 2 7" 2 7 5 Yes C2) 2000 psid 6* 9* 6 15 N/A No D) Additional Primary Pressure 11" 12* 21 24 N/A No (Tech. Spec. Requirement)
E) Initial Secondary Hydro. 2* 1* 3 1 1 Yes F) Secondary Pressure .l* 1* 1 1 50 Yes G) Secondary-to-Primary Leak A:33 S A:21 8 34 28 5 Yes B:28" B:21 8 29 28 S From information in MT/SME/4542 transcribed from Station togs SFrom WEPC0 memo, 11/12/86 (See Appendix 10, page A10-8)
- From discussions with Point Beach ISI personnel, 11/20/86
- Additional (Tech. Spec.) pressure test performed once per outage
- One additional secondary hydro. for replacement steam generator (Unit 1) 8From WEPC0 memo, 11/12/86 (See Appendix 10, page A10-6)
WPF0630A:Ib/110692 D-11
TABLE D-2.1 SUffiARY OF POINT BEACH OPERATING TRANSIENTS (Cont.)
Actual No. Actual No.
of Occurrences of Occurrences Design Point Beach Through July, 1986 Through June, 1992 No. Design Transient Unit 1 Unit 2 Unit 1 Unit 2 (40 yr.) Transient l
Abnormal (Upset) Conditions 30 46 34 400 Yes Reactor Trip from Power 42 5 230"
- A) No Excessive Cooldown 28 20" 30 23 l
Excessive Cooldown 13" 9" 14 10 160*
B) 8 m 1* 2 1 10m C) Excessive Cooldown and SI 1 0 0 0 2 80 Yes Loss of Load 0 0 0 0 40 Yes Loss of Power Control Rod Drop 3 1 4 1 80 No 0 0 2 80 Yes Partial Loss of Flow 1 0
- No Primary Side Overpressurization 2 0 3 2
8 2 5
2 2 30* No ;
Excessive Feedwater Flow )
- See Appendix 4, page A4-14 and Table A4.5 for additional breakdown by initial power level.
" Design numbers of cycles for (A), (B), (C) subcategories are from SSDC 1.3F.
"This transient, as defined by the courses of the events and the available parameter data, is not described by the design basis. Based on the initial pressure increase, these events are similar to the Loss of Load transient.
- Estimated based on operator information (See Section 3.4.3.5).
WPF0630A:lb/110692 D-12
TABLE D-2.2
SUMMARY
OF POINT BEACH AUXILIARY TRANSIENTS Actual No. Actual No. ,
- ~
of Occurrences of Occurrences Design Point Beach j.
Through July, 1986 Through June, 1992 No. Design
- Transient'/ Initiating Event Unit 1 Unit 2 Unit 1 Unit 2 (40 _yr.) Transient-Pressurizer Spray Actuation / j Normal Conditions: '
l Heatup.. .
42 5 28* 53- 38 200"' Yes Cooldown'to.400' psia '41* 27* 52 37 200"' Yes Cooldown from'400 psia 41* 27* 52. 37 200"' Yes Unit Loading at 5%/ min. 80 102 82 102 14,500 Yes .;
Unit Unloading at 55/ min. 84 148 96 148 14,500 Yes .;
Large Step Decrease 33 15 43 18 200 Yes 't
, ' Small Step Load Increase 0 0 0 0 2,000 Yes Small Step Load Decrease 20 20 22 25 2,000 Yes Baron Concentration Equalization 136 36,600 90 170 118 Yes Abnormal (Upset) Conditions: 10 10 11 10 690 5 -
Test Conditions:
Turbine Roll Test 1 .1 1 1 10 Yes '
4
- Totals apply to each of the spray operations designated in Appendix 5, Table'AS.3. .
- These values' are based on ' totals for design numbers of cycles of abnormal events identified in SSDC 1.3.F.
4
- WPF0630A:1b/110692 0-13
. ~ ,
. - -. - . -.-- -. - - - .-..... .-. -. .... - - - - . . . . . - . . - . -..- - - - - - . . . . ~ .
1 TABLE D-2.2
SUMMARY
OF POINT BEACH AUXILIARY TRANSIENTS (Cont.)
Actual No. Actual No. -!
of Occurrences .of Occurrences Design Point Beach
- . Through July, 1986 Through June, 1992 No. Design Transient / Initiating Event Unit 1. Unit 2 -Unit 1 Unit 2 (40 yr.) Transient PORY Opening /
Reactor Trips-(all causes) 12" 9" 12 9 100 No Large Step Load Decrease 1* 2" 1 2 Other Conditions 1 0 8 8 3
RTD Maintenance 3 3 4 4 60 No Charging Flow 50% Increase and '1,306" 1,420*- 1,498 1,585 24,000 Yes Return Charging. Flow 50% Decrease and 1,341* 1,478* 1,532 1,643 24,000 Yes Return Letdown' Flow 60% Increase and 240m 267m 315' 332 24,000 Yes
. Return Letdown Flow Isolation.and .15m 10m- 18 11 200 No Return Charging and Letdown Flow '6m 6m. 7 7 60 Yes
. Isolation and Return l
" Estimated based on available strip. chart data. See Appendix 5.
"See Section 3.4.1.4 and Appendix-2, pgs. A2-1 through A2-3.
" Estimated based on' operator information.
" Assumed to occur for all load changes. See Appendix 5, pgs. AS-12.through A5-14.
" Estimated. 'See Section 3.4.4.5 and Appendix 5, pgs.'AS-14 through A5-17.
WPF0630A:1b/110692' D-14 i
TABLE D-2.2
SUMMARY
OF POINT BEACH AUXILIARY TRANSIENTS (Cont.)
Actual No. Actual No.
of Occurrences of Occurrences Design Point Beach Through July, 1986 Through June, 1992 No. Design Transient / Initiating Event Unit 1 Unit 2 Unit 1 Unit 2 1_40 yr.) Transient RHR Operation /
Cooldown" 41 27 52 37 200 Yes Re fueling" 11 12 19 17 80 No Low Head SI S 1 0 1 0 89 No High Head Sl* 1 0 2 0 89 No "See Sections 3.4.4.6 and 3.4.4.7 for discussion of flow paths.
WPF0630A:lb/110692 D-15