ML20067D331
| ML20067D331 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse, Arkansas Nuclear  |
| Issue date: | 08/31/1993 |
| From: | Degrassi G BROOKHAVEN NATIONAL LABORATORY |
| To: | |
| Shared Package | |
| ML20065M224 | List: |
| References | |
| IEB-88-011, IEB-88-11, NUDOCS 9403080171 | |
| Download: ML20067D331 (30) | |
Text
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TECHNICAL EVALUATION REPORT EVALUATION OF THE BABCOCK AND WILCOX OWNERS GROUP
. PRESSURIZER SURGE LINE THERMAL STRATIFICATIDN PROGRAM TO ADDRESS NRC BULLETIN 88-11 Engineering Research and Applications Division Brookhaven NationalI.aboratory Upton, NY 11973 G. DeGrassi August 1993 l
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EXICUTIVE
SUMMARY
This report presents a summary of the Brookhaven National Laboratory Wilcox owners(BNL)
Grouptechnical (B&WOG)review and evaluation of the Babcock and the pressurizer surge line program to reevaluate the integrity of stratification. considering the effects of thermal thermal stratificationNRC Bulletin 88-11 identified the potential for in surge lines and requested all PWR licensees integrity structural to establish and lines.
of these implement a program to verify the The NRC Bulletin requested a number of specific actions including conducting visual inspections of the surge damage lines and supports for indications of structural or distress, performing bounding analyses to justify continued operation, establishing monitoring programs to obtain plant specific data on stratification, and updating stress and fatigue analyses to ensure compliance with applicable ASME Code requirements.
address the technical concerns associated with this issue. Licensee In response to address to the Bulletin, the concerns the B&WOG for all B&W plants. established a program Based on similarities in plant design and operation, B&WOG demonstrated that a generic loop plants:could be performed for the following six B&W lowered evaluation Arkansas Nuclear One Unit 1 Crystal River Unit 3 Oconee Units 1, 2, 3 Three Mile Island Unit 1 a Davis-Beese plant-specific Unit 1, the evaluation. only B&W raised loop plant required The B&WOG program consisted of several tasks including the collection and reduction of temperature and displacement data from a representative lowered loop plant, the assessment of operating practices and procedures, the collection and review of historical plant data, the developasnt of revised design basis thermal transients with consideration to thermal stratification and striping, and the structural and fatigue analysis and evaluation of the surge line piping and nozzles. The visual inspections of the surge lines required by Bulletin 88-11 were parformed by each licensee.
The methodology and results of the B&WOG program were published in B&W report BAW 2127 dated December 1990. The report concluded that all ASME Code stress and fatigue limits were met for tha lowered year loop plant surge lines for the remainder of their Corty design lives.
questions and concerns.
BNL reviewed the report and raised several BNL than participated in as NRC staff audit in February 1991 to discuss the concerns and i view the program in depth. The BNL findings were incorporated ta an NRC Safety Evaluation Report issued in July (SER) 1991. The reevaluation methodology was found to be acceptable with one l 111 l
l exception.
BNL disagreed with the B&W interpretation of stress indices used to calculate stresses in elbows. This left the code qualification of the elbows as an open item.
B&WoG subsequently proposed another approach to qualify the elbows.
BNL alternate the proposed participated in followup analysis NRC staff meetings to discuss methods.
when B&WOG performed an The issue was resolved elastic-plastic demonstrated that the surge line elbows analysis which meet the alternate requirements of ASME Code Section III Subsection NB-3228.4. The surge thermalline was shown to shake down after a few cycles of severe stratification loads with an acceptable amount of accumulated usage factor oflocal lessstrain than and 1.0.a maximum elbow cumulative fatigue The revised methodology and results were documented in B&W report BAW-2127 Supplement 2. Based on the additional that the information presented in the final report, BNL concluded B&WoG program adequately demonstrated that the lowered loop plant surge lines and nozzles will meet ASME Code stress and fatigue requirements for their forty year design lives with consideration of the thermal stratification and thermal striping phenomena.
that To provide additional confidence, BNL also recommended line licensees perform volumetric inspections of critical surge elbows as part of future ASME Code Section XI in-service inspections.
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TABL2 OF CONTENTS
1.0 INTRODUCTION
2.0
...................... 1 NRC BULLETIN 88-11 REQUIREMENTS . . . . . . . . . . . . 2 3.0
SUMMARY
OF B&WOG Ph0 GRAM .
. . . . . . . . . . . . . . . . 3 4.0 HISTORY OF RZVIEW PROCESS
. . . . . . . . . . . . . . . . 5
5.0 TECHNICAL EVALUATION
OF B&WOJ PROGRAM . . . . . . . . . . 6 5.1 Generic Application .
. . . . . . .. . . . . . . . . 6 5.1.1 Pressurizer Surge Line Design .
5.1.2 Plant Operations . . . . . . 6 5.1.3 . . . . . . . . . . . . . 6 BNL Evaluation . . . . . . . . . . . . . .7 5.2 Revised Design Basis Transients . . . . . . . . . . . 7 5.2.1 Monitoring Program and Stratification Correlations 5.2.2 . . . . . . . . . . . . . . . 7 Development of Thermal Striping Correlations . . . . . . . . . . . . . . . 8 5.2.3 Development of Revised Design Transients 8 5.2.4 BNL Evaluation . . . . . . . . . . . . . .
. 9 5.3 Stress and Fatigue Evaluation . . . . . . . . . . . . 9 5.3.1 Model Development and Analysis 5.3.2 . . . . . 10 Stress Analysis and Code Evaluation . . . 10 5.3.3 Fatigue Analysis and Code Eval . . 11 5.3.4 5.3.5 Nozzle Evaluation . . . . . . uation
. . . . . . 13 BKL Evaluation . . . . . . . . . . . . . 13 5.4 Structural Reevaluation of Surge Line Elbows . . . 16 5.4.1 Reevaluation Methodology and Results . . 16 5.4.2 BNL Evaluation . . . . . . . . . . . . . 18 5.5 Plant Specific Applicability of B&WOG Analysis . . 19 5.5.1 Applicability of Revised Design Basis Transients . . . . . . . . . . . . . . . 19 5.5.2 Appicability of Fatigue Analysis . . . . 20 5.5.3 BNL Evaluation . . . . . . . . . . . . . 20
6.0 CONCLUSION
S !
. . . . . . . . . . . . . . . . . . . . . . 21 l
7.0 REFERENCES
. . . . . . . . . . . . . . . . . . . . . . . 22 APPENDIX A ASME Code Inquiry and Response !
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1.0 INTRODUCTION
This. technical evaluation report (TER) presents a summary of and Wilcox owners Group (B&WOG) program )to the pressurizer surge . line in view of the ocourrence of thermal stratification as described in NRC Bulletin 88-11 (Ref.1). '
The existence of the thermal pressurizer Trojan plant surge whenlines in U.S. plants was first identified at thestratifica unexpected pipe movements were Licensee investigations determined observed. '
by thermal stratification in thethat the movements were line. caused found to be most severe during heatup' andThe stratification cooldown when was i temperature leg. differences existed between the pressuriser and the hotlarge part of the. pipe was heated to a higher temperature than part.
resultedThe in significantdifforentialpipe thermal expansion of the -pipe ~ metal deflections.
considered in the original piping design. This phenomenon was not was that The NRC staff's concern.
the additional bending acaents and loads introduced by this condition of the surge line. may invalidate the analyses supporting the integrity .
NRC Bulletin 88-11 requested all PWR licensees to take a-series actions These of actions to verifyconducting included the integrity of their surge lines.
visual' inspections for-analyses to justify continued operation, establishing programsstress updating to obtain and plant specific data on stratification, and applicable Code requirements. fatigue analyses to ensure -compliance with Subsequent to~the issuance'of the bulletin, the B&W Owners Group developed a program to address the requirements of the bulletin for B&W plants. The results.of the I
program were published in B&WOG report BAN-2127 in - December 1990 (Ref. 2 . t the repo)rt andthe prepared review. a request"for additional informa needed to complete held to discuss that RAI responses Meetings with B&W were subsequently greater detail. and to review: the program in.
Based on the additional information, BNL found the used to perform the ASME Code evaluation of the surge lin After further discussion with the NRC staff and BNL, B&W revised their methodology and reevaluated the elbows.
The revised methods and results were documented in B&WOG report BAW-2127 Supplement 2 which was issued in May 1992 (Ref. 3) . The BNL evaluation of this program is presented in this TER.
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2.0 NRC BULLETIN 88-11 REQUIREMENTS NRC Bulletin No. 88-11 requested all PWR licensees to establish and implement a program to confirm pressurizar surge line integrity in view of the occurrence of thermal stratification and inforts the -staf f of the actions taken to resolve this issue.
Licensees actions: of operating PWR's were requested to take the following Action 1.a - Perform a visual inspection walkdown (ASMZ Section XI, VT-3) at the first available cold shutdown ubich exceeds seven days.
Action 1.b - Perform a plant specific or generic bounding analysis to damonstrate that the surge line meets applicable design codes and other FSAR and regulktory commitments for the design life of the plant. The analysis is requested within four months for plants in operation over ten years and within one year for plants in operation less than ten years. If the analysis does not demonstrate compliance with these requirements, submit a justification for continued operation (JCo) and implement actions 1.c and 1.d below.
Action 1.c - obtain data on thermal stratification, thermal striping, and line deflec* ions either by plant specific monitoring or through collective efforts among plants with a similar surge line design. If through collective efforts, demonstrate similarity in geometry and operation.
Action 1.d - Perform detailed stress and fatigue analyses of the surge line to ensure compliance with applicable code requiraments incorporating any observations from 1.a. The analysis should be based on the applicable plant specific or referenced data and should be completed within two years. If the detailed analysis is unable to show compliance, subnit a JCo and a description of corrective actions for effecting long term resolution.
Although not required by the Bulletin, licensees were encouraged to work collectively to address the technical concarns associated with this issue, as well as to share pressurizar surge line data and operational experience. In response, the Babcock and Wilcox owners Group (B&WoG) developed and implemented a program to address the technical issues of surge line stratification in B&W plants. A summary of it.11 program is presented in the next section of this TER.
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3.0
SUMMARY
or B&WoG PROGRAM l The B&W owners Group Materials Committee- developed a comprehensive in NRC bulletin 88-11. program to address all technical concerns identified Based on similarities in design and -
operation, lowered loop B&WoG plants.was able to perform a generic evaluation for all j
They include the following six plants:
i Arkansas Nuclear.One Unit 1 Crystal River Unit 3 oconee Units 1,2,3 ' j l
Three Mile Island Unit 1 i i
The B&WoG determined that Davis-Besse Unit 1, 'which is the -
only B&W raised plant-specific loop plant, evaluation. differed significantly and required a- i The Davis-Besse analysis was beyond the scope of the BNL review and is not addressed in this TER. j The B&WOG p rogram was divided into two basic parts. The first' part surgeinvestigatud lines. the thermal hydraulic phenomena occurring in the !
development ofThe goal of the . first part of the program was the revised design basis thermal transients which l J
appropriately account for the effects of thermal stratification and -
thermal striping. - !
monitoring of the ThisoconeeeffortUnit included1 the instrumentation and surge line -to determine l
circumferential temperature profiles and displacements 'of the line under stratified flow conditions. It also involved the assessment of operating practices and procedures, and the collection and review limits Upper of historical plant data from all lowered loop B&W plants.
on surge- line differential _ temperatures were established based on 10CFR50 Appendix ~ G pressure /teaperature limits. Analytical correlations were developed to predict thermal stratification and thermal striping based on surge line flow rates 3 and differential temperatures. These-correlations were based on !
oconee measured data and on thermal striping experimental . data. l Based on the measured data, historical data'and upper limits, B&W '
established generic conservative magnitudes and numbers of thermal stratificatiou cycles for past and future operation. The and result of this part of the program was a revised set of design basis transients that were used as input to the surge line stress and fatigue analysis.
The second part of . the program addressed the structural-analyses needed. to assess the integrity of the surge . line and nozzles for the balance of the design life of each plant.- This {
required the development of a structural mathematical model of the surge line. A - structural loading analysis was performed by applying the revised design basis transients to this-model. This '
generated the internal- forces and moments for the stress and 4
fatigue analysis of the surge line and nossles. The line-was then
< evaluated in accordance with the 1984 Edition of the ASME Code NB-3600. Based on this evaluation, B&WoG concluded that the surge 3
line satisfied all code ntress and fatigue limits. However, upon review of the analysis, used to determine stresses in the elbows.SNL questioned the analytical methodologyI secondary stress index and the peak stressB&W had redefined the !
index based on an elastic-plastic B&W finite element analysis. BNL disagreed with the !
interpretation of secondary stress versus peak stress in an '
elbow indices and suggested given that the elbows be reevaluated using the stress in NB-3600. !
However, when the Code indices were applied, the surge line elbows did not satisfy the code limits for l expansion stress or fatique usage. As a result, B&W . performed another analysis based on the alternate ASME Code criteria given in NB-3228.4.
)
Using an elastic-plastic model of the surge line, B&W demonstrated that shakedown will occur-after a few cycles of the most severe thermal stratification loading with an acceptably small amount of accumulated strain. The fatigue evaluation based on this analysis demonstrated that the usage factor for the bounding plant is below the code allowable. Thus the revised analysis showed that all Codelowered of each requirements loop plant.are satisfied for the forty year design life 4
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4.0 HISTORY OF REVIEW PROCESS NRC Bulletin 88-11 was issued on December 20, 1988. The bulletin addressed stratification in the pressurizar technical surge concerns line andassociated required all with PWRtherm licensees to structural establish integrity _ of and the implement surge line. a program to ensure the subsequently formed The a Thermal Stratification Working GroupB&W. Owners and developed the bulletin. a comprehensive program to address the requirements of' l staff on September A portion of the program was' presented to the NRC Bulletin Action 1.b, 29, 1988 and April 7, 1989.
In accordance with j an interia evaluation was documented in B&W report BAW-2085 dated May 1989 (Ref. 4).
performed and That report provided the operation for all of the operating B&W plants. staff with a justification for near ters The NRC staff ,
been provided to justify near term operation for B&W p the fincl report could be completed.
reportThe final results of the B&WoG program were documented in B&W BAW-2127 dated December 1990 (Ref. 2 .
This report-summarized loop plants. the generic analysis and evaluation o)f the B&W lowered It included the development of revised design basis !
well as the structural reevaluation to demonstrate that integrity will be maintained over the forty year design life. The-report was reviewed by BNL under contract to the NRC staff. BNL generatedthe complete a list of questions review (Ref. 5). and additional information needed to BNL then participated in an NRC I staff audit provided personnel at B&W offices res in February 1991 in which B&W technical detailed calculations.ponses and additional information including Following a more detailed review of the information, an audit trip report was issued which summarized the BNL findings and recommendations (Ref. ' 4) .
B& Woo program was comprehensive and addressed BNL concluded all of thethat the issues described in Bulletin 88-11. The technical personnel involved in the program were well' qualified and produced high quality' work.
However, the stressthere evaluation. was one significant unresolved issue which-impacted BKL disagreed _ with the method in which B&W calculated the secondary and peak stresses in the surge line elbows.
Evaluation Report-(Ref. 7) as an open itaa.This issue was incorpora surge In order to resolve the BER open item, R& Woo reevaluated the line elbows using elastic-plastic analysis methods and demonstrated Code compliance in 'accordance with the alternate criteria given in ASME Code Section_III Subsection NB-3224.4.. The methodology was presented and discussed during meetings-held at B&W offices in October 1991 and January 1992. The discussions were summarized in audit trip reports (Ref. 8 and 9) . The final results were (Ref.documented 3). in B&W report RAW-2127 Supplement 2 dated May 1992 reevaluation is presented in this TER.The BNL evaluation of the B&WOG pr 5
. . ._ _ . _ __. _ _ - .. .._ __ ~ . _ .
$.0 TECHNICAL EVALUATION OF B&WOG PROGRAM was divided into two basic sections:The B&WOG Program for evalua analysis. thermal-hydraulics and stress of surge line Thedesign thermal-hydraulics portion developed a revised set basis transients stratification and thermal striping.that account for thermal It involved the instrumentation and monitoring of surge line temperature and displacement data from a representative plant (Oconee Unit It 1) included an assessment historical plant data from all B&W plants.of operating procedures and review of portion of the surgeinvolved line the anddevelopment of structural mathematical modelsTh associated equipment.
basis.
analysis was performed using the revised thermal-hydraulic designS Stress and fatigue evaluations were performed in accordance with the 1986 Edition of the ASME Code Section III requirements.
The major areas of review and evaluation are summarized below .
5.1 Generic Application B&W reviewed the factors affecting surge line stratification to determine if the B&WOG plants can be evaluated thermal generically.
the plant specific The assessment operating considered procedures.both the piping design and summarized below. The findings are 5.1.1 Pressurizar Surge Line Design A review of the surge line piping for all B&W plants showed '
that all lowered loop plants have the same nominal dimensions and configuration.
inch are lines diameter insulated schedule 140 austenitic stainless steel' The pipe similar characteristics.with a reflective / mirror insulation having the hot leg and to the pressuriser.The and nossles connect the surge line to run, a one inch diameter nossle made of austenitic stainless steelIn the connects TMI-1, a drain line to the surge line.
snubbers are used as seismic restraints.With the exception of does not contain any seismic anubbers, restraints The TMI-1 line or supports.
The supports. Crystal River plant uses' variable spring hangers,as dead weight free hanging.The surge lines in all other lowered loop plants are free travel of the snubbers and spring hangers, these suppo -
have in theasurge negligible line. effect on thermal stratification-induced stresses 5.1.2 Plant Operations B&W reviewed the plant operational aspects which affect the magnitude surge line. and number of thermal cycles applied to the pressurizar procedures and data, as well as interviews of plant operators.T . The 6
operational RCS review concentrated pressurization phases, on the heatup/cooldown and initial since the highest potential for significantThey phases. thermal stratification concluded that all conditions of . ' the B&W exists.during these I i
operate in a similar fashion with some minor differences. plants basically .I During !
power operating conditions and during operating conditions where-the RCS temperature is near " Hot Standby", all of the plants operate inisarelatively potential similar fashion small. and the thermal stratification events, During design basis transient identical for all of the lowered. loop plants.the transients imposed o ;
t B&W noted that the reactor vessel oporttional P/T limits, in accordance surge linewiththermal-10CFR50 Appendix G, provide the upper limit of the l stratification- potential during the
- heatup/cooldown and initial pressurizatirm phases,-and that these i limits are operation. a function of the effective full power years (EFPY) of i The magnitude of the thermal stratification-gradients l as well as the actual number of heatup/cooldown cycles were grouped on the basis of the periods of the applicable' Appendix G limits.
Actual plant data was reviewed to confirm that the B&W plants have .
operated below the reactor vessel P/T limits. Based on the plant :
data and surge line,the measured data from the instrumented Oconee Unit 1.
thermal stratification cycles for the generic design basis.-B&W Based wa on cooldowns,the P/T path taken by each of the plants during past heatups and the magnitude of future thermal stratification cycles was fatigue. developed to form the basis for evaluating future surge line 5.1.3 BNL Evaluation Based on a review of the information provided by B&W, BNL concluded that the -lowered loop plant configuration and plant operations were sufficiently similar to justify the development of a L generic design basis transients as well as a generic structural and fatigue evaluation..
l The evaluation of the revised-design basis transients development and of the stress and fatigue evaluation is I presented in the following sections.
5.2 Revised Design Basis Transients The development of the revised design basis transients involved the monitoring development of _ surge line thermal of surge line data at-oconee Unit 1, the stratification and thermal striping correlations, the review of operational histories, and the formulation of revised transients.
5.2.1 Monitoring Program and Stratification Correlations l line Based plants, on comparisone of dimensions of the lowered loop surge 4
B&WoG ccocluded that a single plant could be 9
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instrumented to provide typical thermal Oconee stratification data.
and 14 Unit I was selected and instrumented with 54 thermocouples lines. displacement instruments affixed . to various parts of the January 1989 The instrumentation refueling outage.package was installed during the Temperature measurements were ;
recorded. at cooldown, either and 20 second various power or one minute operation intervals during heatup,
. conditions. The measured data was processed and used to develop correlations to predict surge line temperature versus time based on global plant conditions i including pressurizer and hot leg temperature, surge line flow rate, and reactor coolant pump and spray valve-status. prediction correlations were developed for stratification temperatures in the horizontal piping as well as for temperatures at the nossles. The :
stratification correlations were used in conjunction with the !
i synthesized use in the stress plantanalysis.transients to develop temperature profiles for .
t 5.2.2 Development of Thermal Striping correlations B&W developed thermal striping correlations experimentally observed striping data. Based on a review based on of the i literature on striping experiments, B&W found that experiments I performed in the HDR facility at Battelle Institute, Karlsruhe, FRG !
- were conducted under the pressurizer surgeconditions lines. The that most closely matched those of large-diameter (15.6 inch), insulated HDR tests were performed in a typical fluid conditions. metal _ pipe using plant-The pipe was extensively instrumented .
with fast-response thermocoupl,es. B&W obtained the complete. set of measurements processed from the "PWRa subseries of tests. The data was to determine I striping frequencies and amplitudes. interface characteristics as well as !
B&W used the ordered overall range method to count striping cycles and to develop distributions of cumulative frequencies of occurrence versus striping amplitude.
The maximum striping amplitude for each test . was compared and correlated with the governing fluid conditions. The maximum striping amplitudes of the final correlation were increased by 10%
to allow for uncertainties.
5.2.3 Development of Revised Design. Transients In . developing the revised design basis transients, considered past operational information. An information baseB&W of plant operating. data, operating procedures, surveillance procedures, B&W records. and operational limits was collected from utility.and Discussions with plant operators provided additional information.
based on theThe revised surge line design basis transients were
-original design basis transients with some modifications and additions. For all transients, the surge line conditions were redefined to include stratification and striping.
The most significant transients which produce the largest top to bottom temperature difference and contribute most to the cumulative fatigue in the surge line are, plant heatup and cooldown. These .
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e 5.3.1 Model Development and Analysis sathematical piping sodel of the pressurizer surge line.The included the pressuriser, surge line, hot leg, reactor vessel The model steam generator.
correct anchor movements The attached equipment was included soethat and component and correctly simulated. flexibility would be~
capability to analyzeThe ANSYS program was chosen because of its a piping system with a top-to-botton ,
i can only be applied-linearly, however, B&W develo linear temperatura indicated by plant asasurements.profiles" to represent the nonlinear profiles Nonlinearity coefficients were give the same pipe cross-section rotation.as the non i The nonlinearity botton temperatures coefficient and fluid was found toelevation.
interface be a function of top and l of these variables.a mathematical formula for nonlinearity coefficient as a funct -
t the nonlinearity coefficients for the Oconee data, a ver run was performed. 1 model and displacasantsThe measured temperatures were applied to the were determined. The comparison a( .i calculated to measured displacements showed very good agreement .
B&W statedcorrection nonlinearity that this verified method.the accuracy of the model and the B&W used this model to analyse the three most critical thermal stratification transient. conditions that occur during the most severe heatup and 3 8 6'F. Top-to-bottom temperature differences were 397'F, 393*F, i
. Additional analyses were performed for seven other thermal stratification conditions plus the unstratified 100% power condition. +
With these 11 sets of internal forces and moments, B&W !
was able to set up an interpolation scheme to~ determine internal forces and moments everywhere in the surge line for all temperature conditions. '
5.3.2-stress Analysis and code Evaluation '
Reevaluation of the surge line for thermal t involved satisfying ASME Code Section III NB-3600 allowable stressstratification limits for primary plus secondary stress intensity range (Equetion rangeand
- 10) (E cumulative fatigue usage: limits for peak stress intenalty cycles, quation the Equation 11). For the acet
- 10. stress' limitcritical of 38thermal stratificar.lon was exceeded. As.an alternative, the code permits a simplified e,lastic-plastic fatigue analysis by. applying a penalty factor, K to the peak stress (Equation 14) provided that the load sets meet , the stress limits of Equationof equation 12NS-3653.7.
and -13 of NB-3653.6 and the thermal stress ratcheting Equation 13 B&W was able to demonstrato compliance with (primary plus secondary stress intensity excluding 10 '
thermal to aset expansion) the Equation and12thermal stress ratcheting, but was'not able (secondary -stress range due to thermal expansion) and limit ofgiven stress indices 3N ininthe theelbows Code. using the simplified formulas B&w then attempted to remove and y stress element analysis.indices for the surge line elbows based on fini The computer program ABAQUS was used to generate an elastic-plastic plane and out-of-plane finitebending element model of the elbows and apply in-moments. Using the definitions of recondary and peak stresses and taking the higher of the two loading conditions, B&W defined generic stress indices of C, = 1.58 and y = 1.47 compared to values of C, = 2.33 and 5 = 1.0 from formulas given in Table NB-3685.1-2 of the code, i
Using the internal forces and soments from the most severe thermal stratification conditions and the redefined generic elbow the Equation 12 three stress-indices, of the four surge line elbows still exceeded stress allowable. B&W then applied these forces' directly to the elastic-plastic finite element model and used the i l
same method generate the Cto calculate maximum secondary stress as was used to !
stress index. ';
stresses were .s,hown to be less than the 38, allowable.The resulting calculat 5.3.3 Fatigue Analysis and Code Evaluation For the ASME Code fatigue evaluation, B&W considered the stresses due to stratification induced soment loadings as well as localized peak stresses induced by through-wall temperature gradients DT, and DT,profiles.
nonlinear temperature due to fluid flow, thermal striping, and Peak stresses due to thermal 1
striping were determined in the design from the striping temperature data given basis transients. The temperature distribution through the wall thickness was determined from an ANSYS finite element model.
as a The time-dependent wall temperature was simulated
" cut-sawtooth" wave. From the experimental data, B&W determined seconds. that the fluctuations have a period of approximately 1.0 To cover a range of periods which could. be expected, thermal 4.0 seconds.
analyses were performed with periods of 0.5, 1.0, 2.0 and were determined and For each period, the - extreme temperature profiles
'the linear and nonlinear through-wall tamparature gradients were calculated, leading to the maximum peak stress intensity range.
Peak stresses due to the nonlinearity of the temperature !
profile are the result of the difference between the actual nonlinear and the " equivalent linear" temperature profiles used in the structural loading analysis. B&W referred to this temperature difference es DT4 . An ABAQUS finite element analysis was performed for the two most severe asasured profiles. top-to-botton_ temperature The analyses indicated that the maximum peak ' stress intensity occurs at the inside radius of the pipe cross section. .,
From these results, B&W developed a correlation to calculate DT. as j 11
,..~c
- a. function of top-to-bottom temperature difference and fluid interface elevation, and give the maximum peak stress intensity in andpipe the fluidas a function interface of DT., top-to-bottom temperature difference elevation.
B&W performed a fatigue analysis in accordance with the 1986 l
Edition of ASME Section III NB-3600 as required by Bulletin 88-11.
Since all plantswas reconciliation hadperformed. been designed to earlier Code Editions, a Code .
The findings indicated that for the' 'j 1986 Code 1) indices, 2) more sophisticated formulas are used for stress allowables allowables, 3) the fatigue curves go up are equal to or smaller than.the earlier {
to 10" c j earlier curves which only went up to 10,. cycles. ycles compared to i 1
B&W calculated the " main fatigue usage" which they defined as the usage factor due to all thermal stratification conditions which are characterized by a top-to-bottom temperature difference. The absolute values contributions were of added: the peak stress ranges from the following 1.
Moment loading range due to thermal stratification.
2.
Moment loading range for the 30 occurrences of OBE.
3.
Internal pressure range.
4.
Additional localized peak stress due to nonlinearity of the top-to-bottom temperature profile (DT.) .
5.
Maximum stress between the - peak stress due to thermal striping and the one due to fluid flow: (through-wall temperature gradients DT, and DT ) .
valuesB&W performed a sort of all the total paak-stress intensity .
and built a selection table for the combination of the thermal that stress stratification ranges werepeaks and valleys into pairs in such a way maximized.
For each pair of conditions, the-alternating stress intensity was calculated as a function of the peak. stress secondary stress intensity intensity range range. and of the Equation 10 primary plus each alternating stress intensity The usage factor associated with-value was calculat accordance in 10" cycles).with Thethesummation 1986 ASME of Code extended fatigue curves ed (up to the' total
- amin fatigue usage."all usage factors for each pair gave In addition to the main .. usage factor, B&W evaluated the additional striping ranges fatigue contributions due to.the highly cyclic thermal stratification, ,and the additional OBE ranges not associated with the additional fluid flow conditions not associated with stratification.
flow were found to be very small. Contributions due to OBE and fluid Fatigue usage due to thermal striping was found to be in the rangte of 0.10 and 0.15 depending on 12
_ - - - . . . - - - - . - . . - . . _ . _ . _ - . _ _ . = . - - . . . . - . . - .
.s the specific plant.
additional fatigue B&W combined the main usage factor with' the '
usage contributions to calculate the total cumulative plants. The values were for each of the six B&W lowered loop usage factor different for each plant because -the number is unique oftooccurrences each plant.of the events in the design basis transients usage factors were below their allowable of 1.0.The results showed that all f actor was 0.82 and occurred in the vertical elbow at the bottom ofThe highest the su.cge line riser to the hot leg in oconee Unit 2.
5.3.4 Nozzle Evaluation In addition to the piping analysis, stress analyses of the pressuriser and hot leg nozzles.R&W performed detailed nozzles, axisynsetric thermal and thermal stress analyses . Forwere both performed using the - ANSYS finite element computer code. The loadings piping external consisted of _ thermal gradients, internaF pressure, and loads.
there were no significant' thermal stratification loads.Since leg. nozzle is The hot the pressu horizontal and is subject to . direct thermal stratification gradients.
which produces circumferential ,
temperature l the use of the ANSYS harmonic element STIF 25 which can h .
axisymmetric were evaluatedstructure with nonaxisymmetric loading. The nozzles in accordance with. the requirements for class 1 components of the ASME Code,Section III, 194C Edition. For both nozzles thethe exceeded linearized 35, limit.primary-plus-secondary stress intensities-However, the Code requirements were satisfied by defined in NS-3228.5.performing a " simplified elastic-plastic analysis" as Cumulative calculated for each plant. All plants met the fatigue usage factors ' were both nozzles. The highest usage factors in the pressurizer 1.0 allowable for was 0.41 in oconee Unita 2 and 3. nozzle In the hot leg nozzle, the highest and ANOusage Unit 1.factor was 0.62 in TMI "
Unit 1, Crystal River Unit 3, 5.3.5 BNL Evaluation '
BNL reviewed the stress analysis and Code methodology and results described in the BAW-2127 report evaluation and raised a number audit. of questions which were discussed during the February 1991-piping B&W provided copies of the detailed calculations on the and nossle stress analyses for review. BNL reviewed selected portions of.the piping stress analysis in detail. Based on the review, BNL comprehensive found the B&W stress reevaluation effort to be and complete. . Thermal stratification effects including global bending ' stresses, local stresses due to the nonlinear striping were temperature considered. profiles, and cyclic stresses due to-thermal well organized. Assumptions Calculations were found to. be clear and were reasonable- and conservative. The accuracy of the mathematical piping model generally was checked against data taken at oconee and showed good agreement in 13 d
-,w y --
predicting displacements.
intensity as well asranges due to other cyclic all global design loads. and local stratification loadsThe stresses due to different Absolute values of peak assuming pipe that maximum cross-section. stresses occur at the same location on disagreed Therewith was, however, one significant issue of concern. -BNL stress index for thethe B&W surgemethodology line elbows. for calculating a revised C, The discussed with B&W during the February 1991 audit and calculationsmethodology were - further reviewed in detail. The analysis involved . the application of in-plane and out-of-plane bending acaents to ABAQUs elastic and elastic-plastic finite element models of the surge line elbows.
indices were calculated as follows: Based on the results of these analyses, new For peak stress:
qc, =
Maximum stress anywhere in the elbow divided by the nominal (straight pipe) stress at the surface.
For secondary stress:
c, = Maximum stress at mid-thickness divided by the correspondin nominal in' the elbow pipe) stress at ald-thickness.g (straight-The K C, value was based on an elastic analysis while the C value was , based on an elastic-plastic analysis with a correction, factor for displacement-controlled loading. 04W took the. larger of
=the in plane 1.58, K and out-of-plane stress index values and obtained C, values wou.C, = 2.33 (or K, = 1. 4 7 ) . Using A:JME Code tables, these ld be C = 2.33 and K 1.0. The v>&W indices, therefore, would predict sig,nificantly lower secondary stresses but the same peak (equation 11) stresses. In differentiating between secondary and peak stresses, B&W referred to the Code definition of peak stress to the(NB-3213.ll) primary plus as "that increment of stress which is additive secondary stresses by reason of local discontinuities or local thermal stress including the effect of stress concentrations. The basic characteristic of a-peak stress-is that it does not cause any noticeable distortion and is objectionable only as a possible source of a fatigue crack." B&W ;
l also noted that Figure NS-3222-1 defines a " secondary" expansion !
stress of free end -intensity P as " stresses which result from the constraint displacement. !
not local stress concentration." Considers effects of discontinuities but t i B&W argued .that the maximum stress in the elbow has.all. the concentration. Their review of the stress analysis characteristics of a' local stress results around the circumference and through the elbow thickness indicated that !
I the highest stress intensity was highly localized. B&W also stated i
that the elbow behaved in a linear fashion after the highest l
l 14 l
j
stressed loc". cions entered the plastic domain and that these stresses had a negligible impact on elbow distortion. B&W therefore felt stresses and the average throu justified in treating surface stresses as peak stresses) as secondary stresses. gh-wall stresses (mid-thickness With the redefined " generic" C stress index, three of the four elbows still did not meet the e,quation.12 stress allowable.
B&W performed additional elastic-plastic finite element analyses ;
for the the critical loading expansion stress case to demonstrate that the elbows meet intensity limit. These analyses took advantage and torsionof(1.0) the lower stress indices for in-plane bending (1.30) and demonstrated acceptable results. .However, as discussed above. of secondary and peak stresses were the same the basic definitions on mid-thickness stress. Secondary expansion stress intensity was based secondary BNL disagreed and peak stress with the in an B&Welbow. interpretation of the definition of t The Code (NB-3682) defines the C stress index as the maximum stress intensity due to load L divided by the nominal stress intensity due to load L. This presumably means maximum stress intensity anywhere in the cross-section, not a mid-thickness stress intensity. The B&W definition of secondary stresses that stress develop concletely in an elbow. neglects the circumferential bending only as peak stresses by B&W. These stresses are considered It does not appear that the circumferential considered peak bending stresses. stressas in the elbow walla should be Peak stresses are generally associated with localized geometric or material discontinuities that effect the stress distribution through a fractional part of . the wall thickness or with local thermal stresses that produce no significant distortion. In the case"of elbows, the circumferential bending stresses affect the entire wall thickness and produce distortion (ovalization) of the elbow cross-section. NS-3222.3 i defines expansion stress intensity as "the highest value of stress, !
neglecting local structural discontinuities, produced at any noint across the thickness of a section by the loadings that result from restraint of free and displacement." The code stress index tables i (NB-3681(a)-1 and NS-3685.1-2) provide further evidence that the l maximum The C elbow stresses should be treated as secondary stresses. i value of 2.33 computed from the table ~ formulas agrees exactl,y with the B&W finite element model maximum stress ' at the l
elbow surface. The X value of 1.0 indicates that no stress l
concentration peak stress. factor nee,ds to be applied to elbows for determining-stress The use of indices codehave~a would stress indices si instead of the redefined B&W' stress and fatigue evaluation. gnificant If Code impact stress on,the indices ASME were Code used,.
for the most severe thermal stratification load conditions, .the range(Equation limit of 4ernal 12).expansion stress intensity would exceed' the 35, The higher Code C, stress indices would also 15 j
L L.
i-increase the primary plus secondary l calculated in Equation 10. strean intensity value simplified elastic-plastic For severe load sets, which require the analysis. method of NB-3653.6, the penalty factor, K increase. which This .,will result in is based on Equation 10 stress will l
larger alternating stresses (Equation the 1.0~ allowable. 14) and higher fatigue usage with potential for exceeding -
In order to assess the consequences.of this issue, BNL also consulted with ASME code piping expert, Everett Rodabaugh.
indicated that the Equation 12 38 He
' margin because various tests have, allowable may have. significant have substantial Nevertheless, fatigue since meeting capacity the 38even if Equation 12 is not met.shown expansion stress limit is a currentinquiry code code requirement, to determine BNLwhether recomm, ended the that B&W initiate an ASME B&W interpretation . of allowable is permissible for this application. the Equation 12ci stress index is acceptable or whether not meeting BNL and Mr. Rodabaugh agreed that the fatigue usage allowable of 1.0 for the life of the plant must be met. BNL therefore table stress indices. recommended that B&W reevaluate the fatigue usage using the If the allowable was exceeded, B&W should investigate and justify alternate approaches to demonstrate that code requirements for fatigue and expansion stress are met.
5.4 Structural Reevaluation of Surge Line Elbows
\
analysis In order to address the BNL concern, B&W performed additional '
to reevaluate. the surge .line elbows. The revised methodology was presented and discussed during meetings. held at B&W -
offices in October 1991 and in January 1992. As expected, B&W 3 found that when the code stress indices were used for:the elbows, !
the fatigue usaga factor exceeded the 1.0 allowable. Therefore B&W proposed an alternate approach based on elastic-plastic analysis. ,
The methodology the overall approach was presented was reached. at the first meeting and agreement on l l
At. the second meeting, B&W presented results. additional details of the analysis and preliminary !
BAW-2127 The final results of the wasreevaluation issued in Maywere 1992.documented in Supplement 2'which l i
the reevaluation methodology and the BNL evaluation is given'below.A summary of !
5.4.1 Reevaluation Methodology and Results The B&W reevaluation was based on the alternate ASME code criteria given Plastic Analysis". in section III subsection NB-3224, " Applications of In this subsection, the Code provides some relaxation of the basic stress limits if Subsection NB-3224.4," Shakedown Analysis' plastic-analysis
, specifically_ is used.
states that the limits 'of thermal stress ratchet (NB-3222.5), progressive distortion (NB-3227.3), local membrane stress (NB-3221.2), and primary plus secondary stress intensity (NB-3222.2) need not be i 16 e i l
satisfied at a specific location if a plastic analysis demonstrates that shakedown shakedown do not occurs exceed and the deformations specified limits. In which occur prior to for comparison with fatigue allowables, the evaluating stresses which occurs after shakedown shall be multiplied by one-half thetotal strain r modulus of elasticity of the material at the mean temperature value.
In order to demonstrate shakedown, .
, finite element model of the surge line piping which was identicalB&W de pipe elbow elements.to the original ANSYS model except for the use of elastic-p steel at different temperatures Stress-strain werecurves generatedfor austenitic to match the stainless ASME code yield relationship. and tensile values using an exponential stress-strain-were used as input Piecewise linear curves approximating these curves to the analysis.
assumed for the loading / unloading behavior. Kinematic strain hardening was verified The ABAQUS model.was by comparison to the ANSYS mathematical model. . B&W identified the most severe thermal stratification stress loading.
severe that range loadwas seenwas range in the previous fatigue evaluation. Tnis applied in combination with expansion, deadweight and internal pressure for a totalthermal cycles. of 13 lowered loop plants.The 13 cycles envelope the number of occurrences for.all-According to B&W, the results of the elastio-plastic analysis demonstrated that for the most severe ranges of thermal stratification conditions, shakedown was achieved in four cycles.
critical elbowThe maximum location. accumulated local strain was 1.07% at the most The total cumulative fatigue usage in the elbows was recalculated based on the elastic-plastic analysis. As in the original analysis, B&W considered both the " main fatigue usage" due to all stratification conditions and the " additional fatigue usage" associated with thermal striping, OBE stresses not associated with stratification, and non-stratified fluid flow conditions (as discussed in Section 5.3.3 above) . Only the main' fatigue usage for cycles with Equation 10 stress range intensity. greater than the.
Code 35, limit needed to be recalculated for this analysis. For these cycles, fatigue was recalculated using the cyclic strain range as a function of the moment and pressure terms along with a strain of that based cycle.penalty factor applied to the additional peak stresses B&W used detailed elbow models to develop-correlation tables for the calculation of the highest strain range anywhere moment in theand range elbow as a function of the elastically-calculated-of the internal pressure in the elbow.
correlation tables were also developed for the plastic penalty ,
factor to be applied to the additional peak stresses. For each thermal stratification cycle, the strain' range and the plastic.
penalty factor were calculated through a conservative linear interpolation between values in the correlation tables to determine the the a)ternating stresses for fatigue evaluation. The results of fatigue analysis showed that the highest cumulative usage i 17 4
, 1
, . - _ ~ . __ _ _ ___ _ _ _ _ . __
factor for the lowered loop plants was 0.50 for the vertical albow at
- 2. the bottom of the surge line riser to the hot leg in oconee Unit of Based on the results of the original evaluation and the results the elbow Bulletin 88-11reevaluation,were satisfied. B&W concluded that requirements of l
5.4.2 BNL Evaluation determined During the October 1991 and January 1992 B&W meetings, BNL that the elbow reevaluation approach - was acceptable provided that specific concerns regarding implementation of the
" analysis were adequately addressed. The major concerns and their resolution are summarized below.
The shakedown analysis did not apply an actual load history corresponding to - the normal sequence of heatups, cooldowns and other anticipated operating transients. Instead B&W identified and applied the loads corresponding to the most severe peaks and valleys of thermal-stratification conditions. They identified PV4 (a peak associated with a heatup) and PV402 ~ a valley associated with fatigue a cooldown) evaluation. as the most severe loading ran(ge from the original applied in the shakedown Thirteen analysis.cycles of this load range were BNL pointed out that since the strains the in the plastic application of analysis are nonlinear and path dependent, an actual load history would. be more appropriate. B&W was requested to provide additional justification to ensure that the loads that were applied in the shakedown analysis were indeed bounding.
the use of a Bree diagram.'
B&W agreed to verify this through evaluation were reported in BAW-2127 TheSupplement results of2.this additional A Bree diagram was strain.
built for the surge line location undergoing the largest on this diagram, the most severe thermal stratification loads (analyzed in the elastic-plastic shakedown analysis) were shown to be the controlling conditions for shakedown when compared to other conditions during the same heatup transient. In addition all of the stress points corresponding to the peaks were shown to be acceptable.
concern. This additional information resolved the BNL In. addition.to demonstrating shakedown, ASME Subsection NB-3228.4 requires that the deformations which occur prior to shakedown do not exceed specified limits. The B&W shakedown analysis showed that the maximum accumulated . local strain (resulting in permanent. deformation) that occurred due-to the application of the thirteen bounding load cycles was 1.074. BNL requested that R&W provide a basis for acceptability of this strain -
-value. In response, B&W noted that ASME Code Cases N-47 and'N-196 permit a maximum allowable accumulated local strain of 54. Code Casa N-47 provides rules for Class 1 components in elevated temperature service and code Case N-196 provides relief from the shakedown requirements of NB-3228. Although these code cases were not being specifically applied to qualify the surge line, BNL 18
- , .- - . - . . . - - - -. .-. = -. -.
l l
agreed that they provided l.07% calculated strain. a reasonable basis for acceptance of the 1
\
In the surge line elbow reevaluation, B&W still could not '
demonstrate that the thermal expansion stress limit of 3B, given in NB-3653.6 (Equation 12) as well as in NB'3222.2 was met. The requirements of NB-3228.4 did not provide relief from this limit.
Based on further discussions with B&W and with Mr. Rodabaugh, BNL agreed that demonstrating shakedown appeared to satisfy the intent of this stress limit. However, as a confirmatory iten, B&W was asked to initiate an ASME Code inquiry to confirm this. B&W complied with this request and obtained a response'from the Code Committee on March 26, 1992, (see Appendix A) . The response confirmed that when shakedown is demonstrated in accordance with NB-3228.4 (b), the expansion stress criterion of NB-3222.3 does not need to be satisfied. This resolved the issue.
Based on the review of the additional structural analysis and reevaluation of the surge line elbows, BNL concluded that the B&W analysis adequately demonstrated the. structural integrity of.the lowered loop plant surge lines for the 40 year design lives.of the plants with proper consideration given to the effects of thermal stratification. In order to provide additional confidence BNL recommends that licensees perform augmented volumetric inspec,tions of surge line elbows in order to ensure that the most highly stressed damage. areas (albow bodies as well as welds) have not sustained 5.5 Plant' Specific Applicability of B&WOG Analysis The BAW-2127 report identified the conditions upon which the generation of the revised design basis transients and the thermal stratification fatigue stress analysis of the surge line were based. . These conditions and the licensee actions needed to' verify that the conditions are applicable on a plant specific basis are summarized below.
I 5.5.1 Applicability of Revised Design Basis Transients The generation of the~ revised design basis transients- for future events was based on the incorporation of operational guidelines which: '
o limit the pressuriser to RCS temperature difference '
during plant heatups and cooldowns (imposed- with pressure / temperature limits), and o prevent surveillance tests that cause rapid additions of ,
water to the RCS from being performed with pressurizer to '
RCS tamperature difference greater than 220'F.
19
'l i
,, , , . . , ,, , _ _ - - _- -__________.___--____i-_--___.
-. . ~ . - . - - - - . .. - . - . - . -
Pressurizer operations were / temperature limits for future heatup and cooldown ,
included as Figure 8-1 of BAW-2127. In order to meet the pressure limit specified for heatup in the 70*F to 150'F temperature range, B&W recommended preheating the RCS. For heatups involving. pressurization i at lower RCS restrictive. limit was
- included in Figuretemperatures, 8-1. The a- less fatigue evaluation was based on the assumption that 85% of the heatups for path CDEN of Figure 8-1,the remainder of plant life meet the recommen restrictive path ABEN. and 15% of future heatups meet the less _
5.5.2 Applicability of Fatigue Analysis '
following Theassumptions:
thermal stratification fatigue analysis was based on the no inte arence of the surge line with any other o
surge line movement within the travel snubber, range of each i
l j
o surge line hanger, novament within the travel range of each I 1
. : l o
branch within moments their at the surge line drain nozzle connection respective maximum 1
allowables (for !
deadweight, OBE and thermal stratificacion).
5.5.3 BNL Evaluation j
The conditions representatives at theofB&W applicability audits. were discussed with licensee The licensees agreed that the B&W proposed operational guidelines will be followed.
procedures will have to be revised to reflect these limits. Operating addition, licensees will review the maximum surge In line displacements to ensure that there are no interferences and that travel limits on hangers and snubbers are not e:tceeded. Each licensee the drainwill linebepipingresponsible and nossle. for reevaluating the pipe supports and will evaluate them on a plant specific basis. Plants with welded attachments conditions are met, the licensees will be able When to useallthe of B&W these generic analysis as the basis for verifying the -
integrity of the surge line. structural-20 1
6.O CONCLUSIONS in the B&W reports, . BAW-2127 and BAW-2127and suppleme the additional information provided during the February 1991,. October 1991 *and Jattuary 1992 audits, BNL concludes that the B&WoG prograa has adequately demonstrated that the bounding surge. line and nozzles forty year meet design ASME Code stress and fatigue requirements for the life with consideration of the thermal-stratification and thermal striping phenomena.
The results of the B&WoG analysis may be used as the basis for licensees to update their plant-specific Code stress reports to demonstrate compliance with applicable Code requirements as requested in Bulletin as-11..
following Thesix generic B&M lowered analysis loopand results are applicable to the plants:
Arkansas Nuclear One Unit 1 Crystal River Unit 3 oconee Units 1, 2, 3 Three Mile Island Unit 1 Licensees are responsible- fout verifying plant-opecific applicability of the B&WoG program and results. This will include verification of analysis assumptions, qualification of supports and attached piping, and revision of operating procedures as indicated in BAW-2127 and summarized in Section 5.5 of this report.
In order to provide additional. confidence in the structural integrity of the surge lines, BNL recommends that licensees perform volumetric inspections . of critical elbow components as part of future ASME Code Section XI in-service inspections. ' Inspections of elbow bodies as well as elbow welds should be performed to ensure that the most highly stresses areas have not sustained damage.
I 21 MO OO
-w .
.- _, , . . , u - , - - - , .-,r .- a r+
7.0 REFERENCES
- 1. NRC . Bulletin No. 88-11, " Pressurizer Surge Line Thermal Stratification", December 20, 1988.
2.
B&W Report BAW-2127, " Final Submittal for Nuclear Regulatory Commission Bulletin 88-11, Pressurizer Surge Line Thermal Stratification", December 1990.
- 3. B&W Report BAW-2127 Supplement 2, " Pressurizer Surge Line-Thermal Stratification for the B&W 177-FA Nuclear Plants,.
Summary Report, Fatigue Stress Analysis of the Surge Line Elbows", May 1992.
4.
B&W Report BAW-2085, " Submittal in Response to NRC Bulletin 88-11, 1989. Pressurizer Surge Line Thermal Stratification", Nay 4
- 5. BNL IAtter, G. DeGrassi to S. Hou, " Request for Additional Information on B&W Report BAW-2127, Final Submittal for NRC Bulletin 88-11, Pressurizer Surge Line Thermal Stratification, (FIN A-3869, Task 48)", February 13, 1991.
- 6. BNL Letter, G. DeGrassi to S. Hou, " Audit of Babcock and Wilcox Owners Group (B&WOG) Pressuriser . Surge Line Thermal Stratification Generic Detailed Analysis (FIN ' A-3869, Task 48)", June 13, 1991.
7.
NRC Letter, J. W. Shea to J. A. Taylor, "NRC Bulletin 88-11, Pressurizer Surge Line Thermal Stratification, Safety Evaluation Report", July 24, 1991.
Pressurizer surge Line Final Audit Trip Report (FIN A-3869, Task 60)", March 11, 1992. *
- 9. BNL Letter, G. DeGrassi to H. Shaw, "B&W owners Group Pressurizer Surge Line Final Audit Trip Report (FIN A-3869, Task 61)", September 25, 1992.
22 1
9 APPENDIX A ASME CODE INQUIRY AND RESPONSE
A so m e p. uso s a .
manne semes== samens un smee amena
= ww . man.c u rm aun.eas etM me a s hus(FHg m 7sse December 30, 1991' 7549-2
.N.
Secretary ASME Boiler asd Pressure Yessel Committee 345 East 47th Street New York, NY 10017 Sub3ect: Technical Inquiry - ASM BPVC Section !!!
Gentlemen:
The writer be considered byrespectfully Section !!!. requests that the attached Technical Inquiry.
Very truly yours, M ELJu DFL/tmo Attachment i
I l
l e
A
Secretary'
. ASME Seiler and Pressure Vessel Coanittee 754g l' Attachment 4
Additional guidance is requested regarding paragraph NS-3228.4 !
Shakedown Analysis (19 Edition with Addendus). !
8ACKERtM S .
The structura,1 integrity of a pressurizer. surge line undergoing thermal loading (in'cluding -expansion bending soments and forces) as a:
result of flow stratification has been demonstrated by performing a Shakedown Analysis in accordance with N8-3228.4 kinematic hardening. Shakedown occurred in a few cycles conservatively and a cumulative usin usage factor of < 1.0 over. the design life was calculated. The j deformations prior to shakedown are well within specified limits. 1 Subparagraph (b) of N8-3228.4 recognizes- that the following limits have I been satisfied by the Shakedown Analysis:
N8 3221.2 - Local Membrane Stress Intensity M8-3222.2 - Primary Plus Secondary Stress Intensity N8-3222.5 - Thermal Stress Ratchet NS-3227.3 - Progressive Distortion of Nonintegral Connections However, sattsfaction of N8 3222.3 Expansion Stress Intensity is' not specifically. exempted even though in satisfying M8 3222.2 for piping. l loadings categorized as expansion must be included.
llDLLE la demonstrating Shakedown in accordance with N8-3228.4(b). are the-expansion stress criterien of MS-3222.3 satisfied?
RESPORSES Yes, as long as the range of strain calculated on a plastic basis:
includes the effect of all cyclic loads which. lead to distortion..
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