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 (BNL) technical review and evaluation of the Babcock and Wilcox owners Group (B&WOG) program to reevaluate the integrity of the pressurizer surge line considering the effects of thermal stratification.
NRC Bulletin 88-11 identified the potential for thermal stratification in surge lines and requested all PWR licensees to establish and implement a program to verify the structural integrity of these lines.
The NRC Bulletin requested a number of specific actions including conducting visual inspections of the surge lines and supports for indications of structural damage 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 the Bulletin, the B&WOG established a program to address the concerns for all B&W plants.
Based on similarities in plant design and operation, B&WOG demonstrated that a generic evaluation could be performed for the following six B&W lowered loop plants:
Arkansas Nuclear One Unit 1 Crystal River Unit 3 Oconee Units 1, 2,
3 Three Mile Island Unit 1 Davis-Beese Unit 1, the only B&W raised loop plant required plant-specific evaluation.
The B&WOG program consisted of a
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 loop plant surge lines for the remainder of their Corty year design lives.
BNL reviewed the report and raised several questions and concerns.
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 (SER) issued in July 1991.
The reevaluation methodology was found to be acceptable with one l
111
l exception.
BNL disagreed with the B&W interpretation of stress indices used to calculate stresses in elbows.
qualification of the elbows as an open item.
This left the code B&WoG subsequently proposed another approach to qualify the elbows.
BNL participated in followup NRC staff meetings to discuss the proposed alternate analysis methods.
The issue was resolved when B&WOG performed an elastic-plastic analysis which demonstrated that the surge line elbows meet the alternate requirements of ASME Code Section III Subsection NB-3228.4.
surge line was shown to shake down after a few cycles of severe The thermal stratification loads with an acceptable amount of accumulated local strain and a maximum elbow cumulative fatigue usage factor of less than 1.0.
The revised methodology and results were documented in B&W report BAW-2127 Supplement 2.
Based on the additional information presented in the final report, BNL concluded that the 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.
To provide additional confidence, BNL also recommended that licensees perform volumetric inspections of critical surge line elbows as part of future ASME Code Section XI in-service inspections.
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TABL2 OF CONTENTS
1.0 INTRODUCTION
1 2.0 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.
6 5.1.2 Plant Operations 6
5.1.3 BNL Evaluation
.7 5.2 Revised Design Basis Transients.
7 5.2.1 Monitoring Program and Stratification Correlations 7
5.2.2 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 10 5.3.2 Stress Analysis and Code Evaluation.
10 5.3.3 Fatigue Analysis and Code Eval Nozzle Evaluation...... uation 11 5.3.4 13 5.3.5 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
7.0 REFERENCES
22 APPENDIX A ASME Code Inquiry and Response V
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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 surge lines in U.S. plants was first identified at thestratifica Trojan plant when unexpected pipe movements were observed.
Licensee investigations determined that the movements were caused by thermal stratification in the line.
The stratification was found to be most severe during heatup' and cooldown when temperature differences existed between the pressuriser and the hotlarge i
leg.
part of the. pipe was heated to a higher temperature than part.
The difforential thermal expansion of the -pipe ~ metal resulted in significant pipe deflections.
This phenomenon was not considered in the original piping design.
The NRC staff's concern.
was that the additional bending acaents and loads introduced by this condition may invalidate the analyses supporting the integrity.
of the surge line.
NRC Bulletin 88-11 requested all PWR licensees to take a-series of actions to verify the integrity of their surge lines.
These actions included conducting visual' inspections for-analyses to justify continued operation, establishing programs to obtain plant specific data on stratification, and updating stress 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 program were published in B&WOG report BAN-2127 in - December 1990 (Ref. 2 t
the repo)rt and prepared a request"for additional informa needed to complete the review.
Meetings with B&W were subsequently held to discuss that RAI responses and to review: the program in greater detail.
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, their methodology and reevaluated the elbows.
B&W revised 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 of operating PWR's were requested to take the following actions:
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.
2
3.0
SUMMARY
or B&WoG PROGRAM The B&W owners Group Materials Committee-developed a
comprehensive program to address all technical concerns identified in NRC bulletin 88-11.
Based on similarities in design and operation, B&WoG was able to perform a generic evaluation for all j
lowered loop plants.
They include the following six plants:
i Arkansas Nuclear.One Unit 1 Crystal River Unit 3 oconee Units 1,2,3 '
Three Mile Island Unit 1 j
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The B&WoG determined that Davis-Besse Unit 1, 'which is the only B&W raised loop plant, differed significantly and required a-plant-specific evaluation.
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 investigatud the thermal hydraulic phenomena occurring in the surge lines.
The goal of the. first part of the program was the development of revised design basis thermal transients which J
appropriately account for the effects of thermal stratification and -
thermal striping. -
This effort included the instrumentation and l
monitoring of the oconee Unit 1
surge line -to determine 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 of historical plant data from all lowered loop B&W plants.
Upper limits 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.
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
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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 fatigue analysis of the surge line and nossles.
The line-was then 4
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 methodology B&W had redefined the secondary stress index and the peak stress index based on an elastic-plastic finite element analysis.
BNL disagreed with the B&W interpretation of secondary stress versus peak stress in an elbow and suggested that the elbows be reevaluated using the stress indices given in NB-3600.
However, when the Code indices were applied, the surge line elbows did not satisfy the code limits for 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 Code requirements are satisfied for the forty year design life of each lowered loop plant.
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4.0 HISTORY OF REVIEW PROCESS NRC Bulletin 88-11 was issued on December 20, 1988.
The bulletin addressed technical concerns associated with therm stratification in the pressurizar surge line and required all PWR licensees to establish and implement a program to ensure the structural integrity _ of the surge line.
The subsequently formed a Thermal Stratification Working GroupB&W. Owners developed a comprehensive program to address the requirements of' and the bulletin.
A portion of the program was' presented to the NRC l
staff on September 29, 1988 and April 7, 1989.
In accordance with j
Bulletin Action 1.b, an interia evaluation was performed and documented in B&W report BAW-2085 dated May 1989 (Ref. 4).
That report provided the staff with a justification for near ters operation for all of the operating B&W plants.
been provided to justify near term operation for B&W p The NRC staff the fincl report could be completed.
The final results of the B&WoG program were documented in B&W report BAW-2127 dated December 1990 (Ref.
2 This report-summarized the generic analysis and evaluation o)f the B&W lowered loop plants.
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.
report was reviewed by BNL under contract to the NRC staff.
The-generated a list of questions and additional information needed to BNL complete the review (Ref. 5).
BNL then participated in an NRC staff audit at B&W offices in February 1991 in which B&W technical personnel provided res 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).
BNL concluded that the B& Woo program was comprehensive and addressed all of the issues described in Bulletin 88-11.
The technical personnel involved in the program were well' qualified and produced high quality' work.
However, there was one significant unresolved issue which-impacted the stress evaluation.
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 In order to resolve the BER open item, R& Woo reevaluated the line elbows using elastic-plastic analysis methods and surge demonstrated Code compliance in 'accordance with the alternate criteria given in ASME Code Section_III Subsection NB-3224.4..
methodology was presented and discussed during meetings-held at B&W The offices in October 1991 and January 1992.
The discussions were summarized in audit trip reports (Ref. 8 and 9). The final results were documented in B&W report RAW-2127 Supplement 2 dated May 1992 (Ref. 3).
reevaluation is presented in this TER.The BNL evaluation of the B&WOG p 5
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$.0 TECHNICAL EVALUATION OF B&WOG PROGRAM was divided into two basic sections:The B&WOG Program for evalua thermal-hydraulics and stress analysis.
The thermal-hydraulics portion developed a revised set of surge line design basis transients that stratification and thermal striping.
It involved the account for thermal instrumentation and monitoring of surge line temperature and displacement data from a representative plant (Oconee Unit 1) included an assessment of operating procedures and review of It historical plant data from all B&W plants.
portion involved the development of structural mathematical modelsTh of the surge line and associated equipment.
analysis was performed using the revised thermal-hydraulic designS basis.
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 thermal stratification to determine if the B&WOG plants can be evaluated generically.
The assessment considered both the piping design and the plant specific operating procedures.
The findings are summarized below.
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 diameter schedule 140 austenitic stainless steel' pipe lines are insulated The 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 a drain line to the surge line.
snubbers are used as seismic restraints.With the exception of TMI-1, does not contain any seismic anubbers, The TMI-1 line restraints or supports.
The Crystal River plant uses' variable spring hangers,as dead weight supports.
free hanging.The surge lines in all other lowered loop plants are free travel of the snubbers and spring hangers, these suppo have a negligible effect on thermal stratification-induced stresses in the surge line.
5.1.2 Plant Operations B&W reviewed the plant operational aspects which affect the magnitude and number of thermal cycles applied to the pressurizar surge line.
procedures and data, as well as interviews of plant operators.T
. The 6
operational review concentrated on the heatup/cooldown and initial RCS pressurization
- phases, since the highest potential for significant thermal stratification conditions exists.during these i
I phases.
They concluded that all of. ' the B&W 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 in a similar fashion and the thermal stratification potential is relatively small.
During design basis transient
- events, 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 with 10CFR50 Appendix G, provide the upper limit of the surge line thermal-stratification-potential during the i
heatup/cooldown and initial pressurizatirm phases,-and that these limits are a function of the effective full power years (EFPY) of i
operation.
The magnitude of the thermal stratification-gradients 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 the measured data from the instrumented Oconee Unit 1.
surge line, thermal stratification cycles for the generic design basis.-B&W wa Based on the P/T path taken by each of the plants during past heatups and cooldowns, the magnitude of future thermal stratification cycles was developed to form the basis for evaluating future surge line fatigue.
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
generic design basis transients as well as a generic structural and L
fatigue evaluation..
The evaluation of the revised-design basis transients development and of the stress and fatigue evaluation is presented in the following sections.
5.2 Revised Design Basis Transients The development of the revised design basis transients involved the monitoring of surge line data at-oconee Unit 1, the development of _ surge line thermal stratification and thermal striping correlations, the review of operational histories, and the formulation of revised transients.
5.2.1 Monitoring Program and Stratification Correlations Based on comparisone of dimensions of the lowered loop surge l
line
- plants, B&WoG ccocluded that a
single plant could be 4
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instrumented to provide typical thermal stratification data.
Oconee Unit I was selected and instrumented with 54 thermocouples displacement instruments affixed. to various parts of the and 14 lines.
The instrumentation package was installed during the January 1989 refueling outage.
Temperature measurements were recorded. at either 20 second or one minute intervals during heatup, cooldown, and various power operation. 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 synthesized plant transients to develop temperature profiles for use in the stress analysis.
t 5.2.2 Development of Thermal Striping correlations B&W developed thermal striping correlations based on experimentally observed striping data.
Based on a review of the literature on striping experiments, B&W found that experiments performed in the HDR facility at Battelle Institute, Karlsruhe, FRG were conducted under conditions that most closely matched those of the pressurizer surge lines.
The HDR tests were performed in a large-diameter (15.6 inch),
insulated metal _ pipe using plant-typical fluid conditions.
The pipe was extensively instrumented with fast-response thermocoupl,es. B&W obtained the complete. set of measurements from the "PWRa subseries of tests.
The data was processed to determine interface characteristics as well as striping frequencies and amplitudes.
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, B&W considered past operational information.
An information base of plant operating.
- data, operating procedures, surveillance procedures, and operational limits was collected from utility.and B&W records.
Discussions with plant operators provided additional information.
The revised surge line design basis transients were based on the -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 8
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e 5.3.1 Model Development and Analysis sathematical piping sodel of the pressurizer surge line.Th included the pressuriser, surge line, hot leg, reactor vessel The model steam generator.
The attached equipment was included so that e and correct anchor movements and correctly simulated.
component flexibility would be~
The ANSYS program was chosen because of its capability to analyze a piping system with a top-to-botton i
can only be applied-linearly, however, B&W develo linear temperatura profiles" to represent the nonlinear profiles indicated by plant asasurements.
Nonlinearity coefficients were give the same pipe cross-section rotation.as the non i
The nonlinearity coefficient was found to be a function of top and botton temperatures and fluid interface elevation.
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.
model and displacasantsThe measured temperatures were applied to the 1
were determined.
The comparison a(
.i calculated to measured displacements showed very good agreement B&W stated that this verified the accuracy of the model and the nonlinearity correction method.
B&W used this model to analyse the three most critical thermal stratification conditions that occur during the most severe heatup transient.
Top-to-bottom temperature differences were 397'F, 393*F, and 3 8 6'F.. Additional analyses were performed for seven other i
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
- 10) and cumulative fatigue usage: limits for peak stress intenalty range (E cycles, quation 11).
For the acet critical thermal stratificar.lon the Equation 10. stress' limit of 38 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 me,et the stress limits of Equation 12 and -13 of NB-3653.6 and the thermal stress ratcheting equation of NS-3653.7.
B&W was able to demonstrato compliance with Equation 13 (primary plus secondary stress intensity excluding 10
thermal expansion) and thermal stress ratcheting, but was'not able to aset the Equation 12 (secondary -stress range due to thermal expansion) limit of 3N in the elbows using the simplified formulas and stress indices given in the Code.
B&w then attempted to remove and y stress indices for the surge line elbows based on fini element analysis.
The computer program ABAQUS was used to generate an elastic-plastic finite element model of the elbows and apply in-plane and out-of-plane bending 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 thermal stratification conditions and the redefined generic elbow severe stress-indices, three of the four surge line elbows still exceeded the Equation 12 stress allowable.
B&W then applied these forces' directly to the elastic-plastic finite element model and used the i
same method to calculate maximum secondary stress as was used to stress index.
generate the C 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, due to fluid flow, thermal striping, and nonlinear temperature profiles.
Peak stresses due to thermal striping were determined from the striping temperature data given in the design basis transients.
The temperature distribution 1
through the wall thickness was determined from an ANSYS finite element model.
The time-dependent wall temperature was simulated as a
" cut-sawtooth" wave.
From the experimental data, B&W determined that the fluctuations have a period of approximately 1.0 seconds.
To cover a range of periods which could. be expected, thermal analyses were performed with periods of 0.5, 1.0, 2.0 and 4.0 seconds.
For each period, the - extreme temperature profiles were determined and '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 DT.
An ABAQUS finite element analysis was performed 4
for the two most severe asasured top-to-botton_ temperature profiles.
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
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- a. function of top-to-bottom temperature difference and fluid interface elevation, and give the maximum peak stress intensity in the pipe as a function of DT., top-to-bottom temperature difference and fluid interface elevation.
B&W performed a fatigue analysis in accordance with the 1986 Edition of ASME Section III NB-3600 as required by Bulletin 88-11.
Since all plants had been designed to earlier Code Editions, a Code.
reconciliation was performed.
The findings indicated that for the'
'j 1986 Code 1) more sophisticated formulas are used for stress indices, 2) allowables are equal to or smaller than.the earlier
{
allowables, 3) the fatigue curves go up 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.
absolute values of the peak stress ranges from the following The contributions were added:
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 ).
B&W performed a sort of all the total paak-stress intensity.
values and built a selection table for the combination of thermal stratification peaks and valleys into pairs in such a way the that stress ranges were maximized.
For each pair of conditions, the-alternating stress intensity was calculated as a function of the peak. stress intensity range and of the Equation 10 primary plus secondary stress intensity range.
The usage factor associated with-each alternating stress intensity value was calculat in accordance with the 1986 ASME Code extended fatigue curves ed 10" cycles). The summation of (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 fatigue contributions due to.the highly cyclic thermal striping ranges the additional OBE stratification,,and 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.
B&W combined the main usage factor with' the additional fatigue usage contributions to calculate the total cumulative usage factor for each of the six B&W lowered loop plants.
The values were different for each plant because -the number of occurrences of the events in the design basis transients is unique to each plant.
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 were
. For both performed using the - ANSYS finite element computer code.
The loadings consisted of _ thermal gradients, internaF pressure, and external piping loads.
there were no significant' thermal stratification loads.Since the pressu leg. nozzle is horizontal and is subject to. direct thermal The hot stratification which produces circumferential temperature gradients.
the use of the ANSYS harmonic element STIF 25 which can h axisymmetric structure with nonaxisymmetric loading.
The nozzles were evaluated in accordance with. the requirements for class 1 components of the ASME Code,Section III, 194C Edition.
For both nozzles the linearized primary-plus-secondary stress intensities-exceeded the 35, limit.
However, the Code requirements were satisfied by performing a " simplified elastic-plastic analysis" as defined in NS-3228.5.
Cumulative fatigue usage factors ' were calculated for each plant.
All plants met the 1.0 allowable for both nozzles.
The highest usage factors in the pressurizer nozzle was 0.41 in oconee Unita 2 and 3.
In the hot leg nozzle, the highest usage factor was 0.62 in TMI Unit 1, Crystal River Unit 3, and ANO Unit 1.
5.3.5 BNL Evaluation BNL reviewed the stress analysis and Code evaluation methodology and results described in the BAW-2127 report and raised a number of questions which were discussed during the February 1991-audit.
B&W provided copies of the detailed calculations on the piping and nossle stress analyses for review.
BNL reviewed selected portions of.the piping stress analysis in detail.
Based on the review, BNL found the B&W stress reevaluation effort to be comprehensive and complete..
Thermal stratification effects including global bending ' stresses, local stresses due to the nonlinear temperature profiles, and cyclic stresses due to-thermal striping were considered.
Calculations were found to. be clear and well organized.
Assumptions were reasonable-and generally conservative.
The accuracy of the mathematical piping model was checked against data taken at oconee and showed good agreement in 13 d
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predicting displacements.
intensity ranges due to all global and local stratification loadsThe as well as other cyclic design loads.
stresses due to different Absolute values of peak assuming that maximum stresses occur at the same location on pipe cross-section.
There was, however, one significant issue of concern.
disagreed with
-BNL stress index for thethe B&W methodology for calculating a revised C, surge line elbows.
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 in' the elbow
=
divided by the correspondin nominal (straight-pipe) stress at ald-thickness.g 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 and out-of-plane stress index values and obtained C,
= 1.58, K (or K, = 1. 4 7 ).
Using A:JME Code tables, these values wou.C, = 2.33 ld be C = 2.33 and K v
would predict sig,nificantly lo 1.0.
The >&W indices, therefore, wer 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 (NB-3213.ll) as "that increment of stress which is additive to the primary plus 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 also noted that Figure NS-3222-1 defines a " secondary" expansion stress -intensity P as " stresses which result from the constraint of free end displacement.
Considers effects of discontinuities but t
not local stress concentration."
B&W argued.that the maximum i
stress in the elbow has.all. the characteristics of a' local stress concentration.
Their review of the stress analysis results around the circumference and through the elbow thickness indicated that the highest stress intensity was highly localized.
B&W also stated I
that the elbow behaved in a linear fashion after the highest i
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 justified in treating surface stresses as peak stresses and the average throu stresses (mid-thickness stresses) as secondary stresses. gh-wall 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 critical loading case to demonstrate that the elbows meet the expansion stress intensity limit.
These analyses took advantage of the lower stress indices for in-plane bending (1.30) and torsion (1.0) and demonstrated acceptable results..However, the basic definitions of secondary and peak stresses were the same as discussed above.
on mid-thickness stress. Secondary expansion stress intensity was based BNL disagreed with the B&W interpretation of the definition of t
secondary and peak stress in an elbow.
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 stress concletely neglects the circumferential bending stresses that develop in an elbow.
These stresses are considered only as peak stresses by B&W.
It does not appear that the circumferential bending stressas in the elbow walla should be considered peak stresses.
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 i
distortion (ovalization) of the elbow cross-section.
NS-3222.3 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 (NB-3681(a)-1 and NS-3685.1-2) provide further evidence that the maximum elbow stresses should be treated as secondary stresses.
The C 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 concentration factor nee,ds to be applied to elbows for determining-l peak stress.
The use of code stress indices instead of the redefined B&W' stress indices would have~a si stress and fatigue evaluation. gnificant impact on,the ASME Code If Code stress indices were used,.
for the most severe thermal stratification load conditions,.the range of 4ernal expansion stress intensity would exceed' the 35, limit (Equation 12).
The higher Code C, stress indices would also 15 j
LL.
i-increase the primary plus secondary strean intensity value calculated in Equation 10.
For severe load sets, which require the l
simplified elastic-plastic analysis. method of NB-3653.6, the penalty factor, K which is based on Equation 10 stress will increase.
This.,will result in larger alternating stresses l
(Equation 14) and higher fatigue usage with potential for exceeding -
the 1.0~ allowable.
In order to assess the consequences.of this issue, consulted with ASME code piping expert, BNL also indicated that the Equation 12 38 Everett Rodabaugh.
He margin because various tests have, allowable may have. significant have substantial fatigue capacity even if Equation 12 is not met.shown Nevertheless, since meeting the 38 expansion stress limit is a current code requirement, BNL recomm, ended that B&W initiate an ASME code inquiry to determine whether the B&W interpretation. of stress index is acceptable or whether not meeting the Equation 12ci allowable is permissible for this application.
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
\\
In order to address the BNL concern, B&W performed additional analysis 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 was presented at the first meeting and agreement on the overall approach was reached.
At. the second meeting, B&W presented additional details of the analysis and preliminary results.
The final results of the reevaluation were documented in BAW-2127 Supplement 2'which was issued in May 1992.
the reevaluation methodology and the BNL evaluation is given'below.A summary of i
5.4.1 Reevaluation Methodology and Results The B&W reevaluation was based on the alternate ASME code criteria given in section III subsection NB-3224, " Applications of Plastic Analysis".
In this subsection, the Code provides some relaxation of the basic stress limits if Subsection NB-3224.4," Shakedown Analysis' plastic-analysis is used.
, specifically_ states that the limits 'of thermal stress ratchet (NB-3222.5), progressive distortion (NB-3227.3), local membrane stress (NB-3221.2),
and i
primary plus secondary stress intensity (NB-3222.2) need not be 16 e
i l
satisfied at a specific location if a plastic analysis demonstrates that shakedown occurs and the deformations which occur prior to shakedown do not exceed specified limits.
In evaluating stresses for comparison with fatigue allowables, the 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 Stress-strain curves for austenitic stainless steel at different temperatures were generated to match the ASME code yield and tensile values using an exponential stress-strain-relationship.
Piecewise linear curves approximating these curves were used as input to the analysis.
assumed for the loading / unloading behavior. Kinematic strain hardening was The ABAQUS model.was verified by comparison to the ANSYS mathematical model.. B&W identified the most severe thermal stratification stress loading.
range that was seen in the previous fatigue evaluation.
Tnis severe load range was applied in combination with thermal expansion, deadweight and internal pressure for a total of 13 cycles.
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.
The maximum accumulated local strain was 1.07% at the most critical elbow location.
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.
these cycles, fatigue was recalculated using the cyclic strain For range as a function of the moment and pressure terms along with a strain based penalty factor applied to the additional peak stresses of that cycle.
B&W used detailed elbow models to develop-correlation tables for the calculation of the highest strain range anywhere in the elbow as a function of the elastically-calculated-moment range and 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 a)ternating stresses for fatigue evaluation.
The results of the fatigue analysis showed that the highest cumulative usage i
17 4
,. - _ ~
factor for the lowered loop plants was 0.50 for the vertical albow at the bottom of the surge line riser to the hot leg in oconee Unit 2.
Based on the results of the original evaluation and the results of the elbow reevaluation, B&W concluded that requirements of Bulletin 88-11 were satisfied.
l 5.4.2 BNL Evaluation During the October 1991 and January 1992 B&W meetings, BNL determined 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 a cooldown) as the most severe loading ran(ge from the original fatigue evaluation.
Thirteen cycles of this load range were applied in the shakedown analysis.
BNL pointed out that since the strains in the plastic analysis are nonlinear and path dependent, the application of 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.
B&W agreed to verify this through the use of a Bree diagram.'
The results of this additional evaluation were reported in BAW-2127 Supplement 2.
A Bree diagram was built for the surge line location undergoing the largest strain.
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.
This additional information resolved the BNL concern.
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 being specifically applied to qualify the surge line, BNL not 18
.-. =
l agreed that they provided a reasonable basis for acceptance of the l.07% calculated strain.
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 areas (albow bodies as well as welds) have not sustained damage.
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.
5.5.1 Applicability of Revised Design Basis Transients I
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 prevent surveillance tests that cause rapid additions of o
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.
meet the pressure limit specified for heatup in the 70*F to 150'F In order to temperature range, B&W recommended preheating the RCS.
i involving. pressurization at lower RCS temperatures, a-less For heatups restrictive. limit was
- included in Figure 8-1.
The 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 The thermal stratification fatigue analysis was based on the following assumptions:
no inte arence of the surge line with any other i
o surge line movement within the travel
- snubber, range of each j
o surge line novament within the travel range of each I
- hanger, branch moments at the surge line drain nozzle connection o
within their respective maximum allowables (for 1
deadweight, OBE and thermal stratificacion).
5.5.3 BNL Evaluation j
The conditions of applicability were discussed with licensee representatives at the B&W audits.
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 line In displacements to ensure that there are no interferences and that travel limits on hangers and snubbers are not e:tceeded.
Each licensee will be responsible for reevaluating the pipe supports and the drain line piping and nossle.
will evaluate them on a plant specific basis. Plants with welded attachments When all of these conditions are met, the licensees will be able to use the B&W generic analysis as the basis for verifying the structural-integrity of the surge line.
20 1
6.O CONCLUSIONS in the B&W reports,. BAW-2127 and BAW-2127 suppleme additional information provided during the February 1991,. October and the 1991 *and Jattuary 1992 audits, BNL concludes that the B&WoG prograa has adequately demonstrated that the bounding surge. line and nozzles meet ASME Code stress and fatigue requirements for the forty year design 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..
The generic analysis and results are applicable to the following six B&M lowered loop 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
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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, Pressurizer Surge Line Thermal Stratification", Nay 1989.
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.
8.
BNL Intter, G.
DeGrassi to H.
- Shaw, "B&W owners Group 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 respectfully requests that the attached Technical Inquiry.
be considered by Section !!!.
Very truly yours, M ELJu DFL/tmo Attachment i
I 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 conservatively usin kinematic hardening.
Shakedown occurred in a few cycles and a cumulative 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 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.
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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