Text

Official Exhibit - ENT000687-00-BD01 - NRC, Safety Evaluation Report, Topical Report on ASME Section Iii Piping and Component Fatigue Analysis Utilizing the Westems Computer Code (WCAP-17577, Revision 2) (Undated)
	ML15334A284
Person / Time
Site:	Indian Point
Issue date:	08/10/2015
From:	; Entergy Nuclear Operations
To:	; Atomic Safety and Licensing Board Panel
	SECY RAS
References
	RAS 28138, ASLBP 07-858-03-LR-BD01, 50-247-LR, 50-286-LR
	Download: ML15334A284 (18)
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1 Safety Evaluation Report "Topical Report on ASME Section III Piping and Component Fatigue Analysis Utilizing the WESTEMSŽ Computer Code" (WCAP-17577, Revision 2)

1.0 Introduction

This safety evaluation report (SER) provides the U.S. Nuclear Regulatory Commission (NRC) staff's evaluation of the use of the Westinghouse Electric Company (Westinghouse) WESTEMSŽ computer code to perform the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (B&PV Code)Section III piping and component design process documented in the topical report (TR) numbered WCAP-17577, Revision 2, "Topical Report on ASME Section III Piping and Component Fatigue Analysis Utilizing the WESTEMSŽ Computer Code." The scope of this TR is limited to the ASME B&PV Code Section III, Subsections NB 3200 and NB 3600 design analysis modules of the WESTEMSŽ computer code for application to AP1000 ASME Class 1 piping and component design. The online monitoring module of WESTEMSŽ is not in the scope of the NRC staff's review of this TR.

To evaluate the technical process internal to the computer code information given in this TR, the NRC staff used the acceptance criteria and guidelines documented in NUREG 0800, "Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition,"

Section 3.9.1, "Special Topics for Mechanical Components," Revision 3 (Reference 1), to address ASME Section III NB 3200 and NB 3600 requirements. The staff also reviewed Westinghouse computer software requirements to ensure the software is in compliance with the ASME NQA 1 quality assurance standard.

The WESTEMSŽ computer code has the ability to compute a stress history for given piping and components from temperature, pressure, and moment transient input data. Fatigue usage is then evaluated from the stress history.

The WESTEMSŽ methodology to calculate stress and cumulative usage fatigue (CUF) involves developing transfer functions (stress tensors caused by unit pressure, unit moment, and unit temperature step load increase or decrease) to convert transient data to stress versus time for a given component to address NB 3200 requirements. WESTEMSŽ performs one dimensional heat transfer analysis to determine the temperature data for the piping cross section and range of average temperatures for gross structural or material discontinuities to be used in calculating the stress intensity ranges as described in the NB 3653 piping stress qualification.

Westinghouse submitted, by letter dated February 29, 2012, WCAP-17577, Revision 0, "Topical Report on ASME Section III Piping Fatigue Analysis Utilizing the WESTEMSŽ Computer Code" (Reference 4). The staff performed an acceptance review and identified specific gaps in the TR. After the NRC staff conveyed these information needs to Westinghouse, the applicant requested by letter dated May 9, 2012, "Withdrawal Request for WCAP-17577 P and -NP," (Reference 5), that Revision 0 of WCAP-17577 be withdrawn from NRC review. The NRC staff confirmed this withdrawal in a letter dated June 1, 2012 (Reference 6). In a letter dated September 28, 2012 (Reference 7), Westinghouse submitted Revision 1 of WCAP-17577 for NRC review. The NRC staff accepted Revision 1 of the TR for review by letter dated November 13, 2012 (Reference 8), identifying the NRC sta ff's need to understand the circumstances in which WESTEMSŽ requires user controlled modification. The staff issued several requests for 2 additional in formation (RAIs) to ask Westinghou se to address specif ic technical issues with this TR. To facilitate the staf f review and examine de tailed docu mentation not required t o be submitted for review, the NRC staff also completed audits in December 2 012 and April 2013 (audit report s, References 9 and 10) and held meetings with the applican t on April 25

, 2013, and June 3, 2013 (meeting summari es, References 11 and 12, respectively). Westinghouse addressed a ll RAIs (References 13 t hrough 16) and submitted an updat ed Revision 2 that reflected all RAI responses by letter dated June 17, 2013 (Reference 17

). 2.0 Regulatory Basis The applica ble regulator y requireme nts for computer codes f or piping an d component design are as follo ws:

Title 10 of th e Code of Federal Regulations (10 CFR) 50.55 a, "Codes and Standards,"

which incorp orates by reference the ASME Boiler and Pressure Vessel Code Section III, Division 1.

Appendix A, "General Design Criteria for Nuclea r Power Pla nts," to 10 CFR Part 50, "Domestic Licensing of P roduction an d Utilization Facilities," General Desi gn Criterion (GDC ) 1, which require s, in part, th at components important to safety be designed, fabricated, e rected, and t ested to qua lity standard s commensurate with the importance of the safety functions to be performed.

Appendix B to 10 CFR Part 50, "Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plant s," as it re lates to the qu ality of desig n control.

In addition, SRP Section 3.9.1 provides staff guidance in reviewing applications with respect to the require ments of 10 CFR Part 50

, Appendix B, and GDC 1. This guidance state s that application s should inclu de a list of computer programs to be used in analyses to determine stresses. To determine the applicability and validity of the codes, the NRC staff reviews information about the co des, incl uding the source

, version, and facility; a d escription of the code; the extent and limitation of the code's app lication; and t he solution s of test problems that are demonstrated to be substantially similar to solutions obtained from other specifie d sources (e.g., hand calculation s or benchmark problems).

For quality assurance (Q A) programs

, the Commi ssion's regulatory requirements are set forth in 10 CFR Part 50, Appendix B. Appen dix B establishes QA requirements for the design, fabrication, construction

, and testing of the structures, syste ms and components (SSCs) of the facility. The pertinent re quirements of Appendix B apply to all activities that affect the safety related funct ions of those SSCs and include de signing, purch asing, fabricating, handling,

shipping, storing, cleaning, erecting, installing, in specting, te sting, operat ing, maintaining, repairing, re fueling, and modifying.

Criterion II, "

Quality Assurance Program," of App endix B to 10 CFR Part 50 establish es QA program req uirements. It states, in part, that, "The program shall provide for indoctrin ation and training of p ersonnel per forming activities affecting quality as necessary to assure th at suitable proficiency is achieved and maintained."

3 3.0 Technical Evaluation 3.1 Introduction and Background Section 1, of WCAP-175 77 states th at the purpo se of this re port is to do cument the use of the WESTEMSŽ computer program for performing ASME Section III fatigue analysis on Class 1 piping and components for the AP1000 nuclear p ower plant, specifically t he applicat ion of the NB 3600 and NB 3200 modules of the program. Initially, the TR referred only to piping analyses; during a public meeting on April 25, 2013 (Reference 11), the NRC staff noted that ASME Section III NB 3200 can be a pplied to all components designed b y analysis and is not limited to piping only. In addition, it was initially unclear wh ether the scope of the T R included both the design analysis modules and the online monitoring module. In RAI WST M-011, dated April 25, 2013 (Reference 18), the NRC staff request ed that the applicant address this issue. In its respon se dated May 10, 2013 (Reference 16

), Westingh ouse stated that "[t]he re vised version of the [TR] will in clude a stat ement that specifica lly excludes the Online Monitoring Module from the scope o f this review. It will also clarify that t he scope for use of the p rogram is Class 1 piping and components." On the basis t hat NB 3200, "Design by Analysis," is applied to design analysis for all C lass 1 components and t hat the applicant provided clarificatio n to the review scope by excluding the online monitori ng module, the NRC staff determined that this response w as acceptable. The NRC staff confirmed that the change has been incor porated in WCAP-1757 7, Revision 2.

The WESTEMSŽ co mputer program performs stress time history calcu lations. The alternating stress in tensities can be calculat ed by pairing the stress pea ks and valle ys from the stress time history. The fatigue usa ge factor ca n be calcu lated using alt ernating stre ss intensity. However, the WESTEMSŽ co mputer code do es not inclu de algorithms to cover all possib le situations in peak and valley selectio

n. The computer code g enerates re dundant pea ks that may have to be eliminated t o reduce co nservatism. This redund ant peak elimination is t o be determined by the analysts' re asonable en gineering de cisions. However, witho ut proper procedural guidance, different ana lysts may make different engineering judgment in determining redundant peaks to eliminate. T herefore, Westinghouse developed a procedure associated with the use of WESTEMSŽ to ensure the validity and repeatability of the f atigue analysis resu lts. In TR Section 1.1, Westinghouse ind icated that t his compute r program is designed to be partially automatic, and user controls over the computer code process ar e needed.

The NRC staff's initial concern fro m when WESTEMSŽ was first d iscussed in the context of the AP1000 review (Ref erences 2 a nd 3), was that the non-automatic part of the user controls may not produce rep eatable resu lts for a spe cific input, limiting the code's ability to produce a valid solution to a physical pr oblem with user controls. User con trols are implemented in the selection of the peak times in the fatigue analysis process. W estinghouse states that t he WESTEMSŽ program i s designed t o provide qualified fat igue analysts t he necessar y tools to perform fatigue analyses commensurate with the degree of conservatism required to demonstrate qualifica tion to ASME Code limits.

This include s versatility i n inputs, availabili ty of intermediate and final ou tputs to und erstand the problem and support qua lification documentation, and efficiency of the iterative process that could be requir ed for more complex problems. As describe d in Section 3.2 below, user controlle d decision s for peak sele ction are documented and reviewed to justify the technica l decision made and ensure the validity and repeatability of the fatigu e analysis r esults. The evaluation of the software analysts' d ecision process is d ocumented in Section 3.

3 of this rep ort.

4 The TR emp hasizes the use of user controls in the applicat ion of WESTEMSŽ to ensure that ASME Code and regulat ory requirements are met. These controls inclu de QA policies for the developmen t and validation of softw are, proced ures for usin g the software and docu menting the analysis pro cess, training and qualification requir ements for individuals, a nd benchmarking of the analysis process.

The staff reviewed the QA policies and programs for the WESTEMSŽ computer code, as documented in Section 3

.3 of this rep ort. 3.2 Resolution of Regulatory Concerns with Fatigue Analysis Software and Process In NUREG 1 793, "Final Safety Evaluation Report Related to Certification of the AP1000 Standard Design," Supplement 2, Volume 1, dated September 2011, (Reference 19), the NRC staff documented initia l review and discussion o f the WESTEMSŽ computer code in the context of the AP1000 design certification review. The WESTEMSŽ computer code was la ter removed from the scope of the de sign certif ication. However, Sections 1.2 and 2.1 of the TR include those technical issues pr eviously identified by t he staff in it s initial review of the WESTEMSŽ computer code, as documented in NUREG-1793

. First, the N RC staff noted that the a lgebraic su mmation of t hree orthogonal momen t components is mathematically incorr ect and physically mean ingless an d requested th e applicant to provide technical ju stification for this option in se lecting pea k and valley times for the fatigue e valuation. This concern was not addressed at th at time because WESTEMSŽ was removed fro m the scope of the desig n certifica tion. In Sectio n 2.1 of WCAP-17577, Westinghou se indica tes that the user controlled o ption on pea k selection with algebraic summation of the three orthogonal moments ha s been eliminated and th e modified peak selection process, which is based o n stress ran ges using A SME Sectio n III equatio ns 10, 11, and 14 always uses the square root of the sum of the square s (SRSS) ra nged orthogonal moment co mponents. In audits perf ormed in the context of the review of WCAP-175 77, the NRC staff reviewed the user manual, software design specification, and validation package of WESTEMSŽ Version 4.5.6 to confir m the comp uter code ha s been revised to address this concern. On the basis t hat the peak selectio n option using SRSS of three moment component ranges to de termine the moment stre ss is consistent with the requirement in ASME Section III NB 3653, the NRC staff found this resolution acceptable.

Second, the NRC staff identified that the WESTEMSŽ option allowing the elimination of peak and valley points would necessitate review of configuration control and limitations of the program for this option.

This additio nal information would enable the staf f to conclud e that the process and results are valid and repeatable. In Section 2.1 of the TR, the applicant provided its resolut ion of this issu

e. The applicant identif ied that ther e are two primary aspects to this concern. Th e first is with respect to ASME's Quality Assurance Requirements for Nuclear Facility Appl ications (NQA 1)-requirements that t he results o f safety related computer software are valid and repeatable

. The secon d aspect focuses on qua lity control o f the analyst performing the fatigue e valuation with specific re gard to the editing of th e input peak and valley set in a rest art file.

The applica nt stated tha t the Westin ghouse soft ware develo pment process implemented in the developmen t and maintenance of the WESTEMSŽ co mputer program is fully in compliance with NQA 1 requirements, and valid ation and verification o f the WESTEMSŽ program show that the soft ware produces valid and repeatable results for a given set of inputs. The applicant considers W ESTEMSŽ fatigue analysis as a tw o phase pro cess. The f irst phase is an initial 5 analysis, in which the pr ogram performs stress h istory calculations, se lects peak and valley times, and calculates fatigue results f rom the parameters associated with initial pea k and valley times select ed. The second phase includes an optional ste p for editing of the input peak and valley set based on the identified co nservatisms. If the peak and valley set is modifie d to reduce conservatism, then the final analysis is p erformed in the second phase of the fatigue analysis. T he edited se t of stress p eaks is considered to be a new user input as provided in a restart file.

Each phase is an indepe ndent analysis that prod uces consistent output fo r a given set of inputs. The complete fatigue a nalysis-including inputs, methodology, results o f the initia l and final evaluation pha ses, and associated en gineering justification-is fully reviewed by an independent verifier. By this separat ion of the fatigue analysis process int o two distinct phases, Westinghou se indica tes that there is one set of in put for each phase, which does not constitute producing different outp ut for the sa me analysis inputs. The initial ana lysis has one set of inputs and always produces co nsistent and repeatable outputs. Th e final analy sis is based on initial analysis, but it also considers an inde pendent set of revised user inputs.

The applica nt states that the final analysis ph ase will al so produce co nservative and acceptab le results; the staff's evaluation of the accept ability of the results i s documented in Section 3.

5 of this rep ort. The second aspect of the NRC staff's concern focuses on quality control of the analyst performing fatigue evaluation with sp ecific regard to the editin g of the inpu t peak and valley set between the two phases of WESTEMSŽ e valuations. This is not an aspect of the software, and cannot be controlle d through so ftware specifications an d validation analyses.

Westinghou se developed a fatigue a nalysis procedure to ser ve as the quality control to ensure that decisio ns made by the analyst are justifie d, documented, verified, and repeatable. Both the procedure a nd user manual provide discussion o f the potential cause s for conservative (redundant) peaks and valleys that may be included in the initial analysis. The procedure also provides the analyst the guidelines for identifyin g instance s of these non controlling r edundant peak and valley times that are considered conse rvative and unnecessar

y. Westinghouse stated that all analysts who intend to use t he WESTEMSŽ co mputer program are required to review the procedu re and docu ment this review in a training record in accordance with the Westinghou se training p rocess. The NRC st aff noted that WESTEMSŽ TR is also applied to ASME Section III NB 3200 fatigue analysis, an d the NB 3200 analysis also require s user contr olled elimina tion of redun dant peaks/valleys. The staff issued an R AI (WSTM-0

06) to ask Westinghou se to provide an NB 3200 fatigue procedure.

In its respo nse dated March 4, 2013 (Reference 15), the applicant provided an additional N B 3200 fatig ue analysis procedure t o address th is RAI. The evaluation of this proce dure is docu mented in Section 3.4 of this report.

The NRC st aff reviewed the two phase procedur e documentation and user manual during an audit. The NRC staff determined that this approach is acceptable for yielding a result that is valid and repeatable. T he evaluation of the procedure and process is do cumented in Section 3.4 of this report

. 3.3 General So ftware Requirements In TR Section 3, Westing house provides its computer software development and validation process and requirements. The computer so ftware developed for safety related desig n and analysis must meet a series of requir ements defined in Westinghouse qu ality and procedure documents that ensure t he software is in complia nce with ASME NQA 1 QA standards. In line with the policies pertaining to software development are Westinghouse p olicies and procedures governing the design an d analysis p rocess for th e AP1000.

6 At Westingh ouse, the Quality Management Syst em (QMS) serves as a directive for a ll functio ns in establishing necessar y policies an d procedure s that comply with requirements of ISO 9001; and in addition, as applicable for saf ety related activities, Ap pendix B to 10 CFR Part 50, and ASME NQA

1. Software developme nt at Westin ghouse is p erformed in accordance with documented policie s and procedures that implement QMS an d conform to NQA 1. Th ese procedures explicitly apply to safety related soft ware, and software used in the design and analysis of safety related systems, structur es, and components (e.g., the WESTEMSŽ analysis software). As noted in NUREG 179 3, the NRC staff previously approved Revision 5 of the QMS in a letter dated September 13, 2002. Furthermore, the NRC staff concluded in Section 17.3.3 of NUREG 1 793 that the QMS, as described in the AP1000 design control document, Revision 17, meets the criteria of 10 CFR 52.63(a)(1)(vii) and Appendix B to 10 CFR Part 50 and is, therefore, acceptable.

The NRC st aff reviewed the software design spec ification and design specification changes from version 4.5 to version 4.5.6 during an audit in December 2012. The staff determined that all required documentation is availab le. The validation of the software for reliability and repeatability is evaluate d and docu mented in Section 3.5 of this report.

In Section 3.

2 of the TR, Westinghou se indica tes that regardless of the software and engineering tools used a nd the qualif ication of th e analyst, the analyst is required to satisfy all requirements identified in Westingho use policy NSNP 3.2.6 in performing and docu menting a design analysis. This is intended to ensure that t he design a nalysis meets all defined acceptance criteria. In a ddition, all calculation s performed wit h or without a computer code are independent ly verified in compliance with NSNP 3.3.7. In TR Section 3.3, Westi nghouse pro vided applicability limits of the WESTEMSŽ software. The staff reviewed these lim itations and focused on t he limits of t he automatic processin g of calculation input (i.e., user controlled activities).

This evaluat ion is do cumented in Section 3.4 of this report.

Quality Assurance Program Section 1.5, "Summary,"

of Chapter 1, "Introductio n," of WCAP-17577-P states, in part, that: The development of safety related com puter software and the requirements for performing design analysis are gover ned by Westinghouse quality policies and procedures t hat ensure compliance with NQA 1 q uality contro ls. Chapter 3, "General Software Requirements," notes that:

Computer s oftware developed for safety related design and analysis must meet a series of requirements defined in Westingh ouse quality policy and procedure d ocuments that ensure the software is in compliance with ASME NQA 1 quality assurance standards.

These docu ments identify the responsibilities for developing a computer code, valida ting the software functionality, maintainin g configuration control, d ocumenting errors and their resolution, and upd ating controlled software

. Section 3.1, "Developme nt and Valid ation of Computer Cod es," of the a bove sectio n further states that:

7 Activities aff ecting the q uality of ite ms and services are perf ormed at Westinghouse in accordance with the Quality Management Sy stem (QMS). T he QMS serves as a directive for all functions in establishing necessar y policies an d procedure s that comply with the requirements of ISO 9001; and in addition, as applicable for saf ety related activities, 10 CFR 50, Ap pendix B; ASME NQA 1. Software developmen t at Westinghou se is perfor med in acco rdance with documented policie s and procedures that implement the QMS and confo rm to NQA 1

. These pro cedures explicitly apply t o safety related software (e.g., plant o perational control), and software used in the de sign and analysis of safety related systems st ructures, and components (e.g., t he WESTEMS analysis soft ware). The staff not es that WCAP-17577-P, Revision 2, references t he Westingh ouse Quality Managemen t System (

QMS). By letter dated February 24, 2011 (Reference 20), the NRC staff found that Revision 6 to the Westing house QMS meets the requirements of Appendix B to 10 CFR Part 50 and is, t herefore, acceptable.

Training The staff issued RAI WSTM-010 on January 28, 2013, requesting that th e applicant specifically address ind octrination a nd training a nd requirements for the f atigue analysts that perf orm fatigue analyses to demonstrate qua lifications to ASME Code limits using the WESTEMSŽ computer code.

In a letter re sponse to W STM-010, d ated February 18, 2013, the applican t describe s how the Westinghou se Quality Program defines how the company meets custom er and regulatory requirements. The applicant provides additiona l details regar ding its tra ining program for the WESTEMSŽ analysis covering two areas: (1)

The level 3 WESTEMSŽ Fatigue Procedure PSDR QP 4.7 and (2) correct use of WESTEMSŽ version 4.5.6.

The applica nt notes that

The WESTEMSŽ trainin g consists of four training module presentations a nd completion of a test pro blem which is submitted for demonstration of und erstanding.

In addition, a mentoring relationship (on the job tr aining) is e stablished un til the analyst has demonstrated sufficient understanding by produc ing an acceptable analysis which h as been determined to be correct.

(-) Individual tr aining for ea ch analyst is documented in each an alyst's training records a nd is summarized in a qualification and training matrix, which is maintained by the group manager in accordance with Westin ghouse level 2 procedur e WEC 2.6, Training. T he qualificat ion matrix is used to determine who is qualified to perform fatigue analysis using WESTEMSŽ and who is qualif ied to verify the WESTEMSŽ fatigu e analysis.

The staff det ermined that users of the WESTEMSŽ software are required to be adequ ately trained in accordance with Westingh ouse's QA program. The staff found the applica nt's response meets the training require ments of Appendix B to 10 CFR Part

50.

8 3.4 Overview of WESTEMSŽ Fatigue Anal ysis The WESTEMSŽ desig n analysis module calculates the stre sses require d by ASME Section III, Subsections NB 3200 and NB 3600, and provides a comparison of the calculated re sults to those allowe d under the ASME Code

. Westingho use provided the general steps for t he fatigue analysis calculation a s follows: (1) Calculate primary plus secondary stress inten sity ranges.

(2) Calculate Simplified Elastic Plastic p enalty factors (Ke) for each stress ra nge pair.

(3) Calculate tot al stress int ensity ranges.

(4) Calculate alt ernating stre ss intensity (Sa) includin g Ke required by the code.

(5) Calculate fat igue usage f actors using the Sa value and corresponding cycles.

(6) Calculate th ermal stress ratchet req uirements.

The staff reviewed the calculation process and f ound that it meets the ASME Code requirements and that th e steps are in the right o rder. Accor dingly, the staff found this process acceptable.

3.4.1 NB 3600 An alysis Review NB 3600 thermal stress analyses ar e based on heat transfe r temperature solution s and stress formula. WESTEMSŽ uses a fin ite difference t echnique to calculate the temperature solution

s. The ASME Code stress intensity ra nge calculation is based upon the eff ect of chang es in mechanical or thermal loadings that t ake place a s the syste m goes from one load se t, such as pressure, te mperature, moment, an d force loading, to any other load set that follows it in time.

The process flowchart fo r this calcula tion is in Figure 4-1, the equations u sed to deter mine the stress in tensity ranges are in Figur e 4-3, and t he NB 3600 peak sele ction method is in Figures 4-2 and 4-4.

The NRC st aff reviewed the process flowchart and determined that WESTEMSŽ p rocess follows ASME Code stress inten sity range calcu lation for each pair, inclu ding the pea k and valley time s election. In addition, the NRC sta ff confirmed that WESTEMSŽ version 4.5.6 does address the previously identified alge braic summation of thre e orthogonal moments (a s mentioned above, this option has been eliminated by Westinghouse). Therefore, the NRC staff concludes t hat Figure 4

-3 is consist ent with ASME Section III, Subsection NB 3653, and that the methodology document ed in Figure s 4-2 and 4-3 is accepta ble. In addition, t he staff observed that Figure 4-1 and Section 4.

1.1 indicate that [

] (optionally) at the first step as an alternative to an enveloping momen t stress range. The applicant pr ovided clarification spe cific to this option in a teleconference o n June 25, 20 13, noting th at the details of this step are documented in the analysis pro cedure (Section 5.1

.2.2, as Figu re 4-6 notes) and user manual (Section 10.2 of Volume 2), both of which the st aff previously audited (References 9 and 10). These documents clarify th at the general app roach is to u se moment stress range s, but the an alyst may ch oose to use moment component histories in certain cases. The NRC staff observes that a thermal analysis would first need to be completed to develop the timing of temperature peaks ide ntified in the

9 procedure.

The piping moment co mponent histories are fu nctions of th e piping glo bal temperature histories.

If the moment component histories are used, the in put consider s the relative timing of temperature and pressure pea ks and valle ys to result in a conservative range of combined stress, and the calcu lation package documents the justification for and a dequacy of the input. The NRC staff concludes that this app roach is sufficient to provide conservative moment inp uts to the ca lculation.

TR Figure 4-4 shows th at a peak exclusion t ime constant ch eck is used to eliminate redundant peaks and valleys. The staff issued RAI WSTM-07 to ask th e applicant t o clearly def ine how the time consta nt is determined and provide clear ju stification for this elimin ation. In its respon se dated Fe bruary 18, 2013, the app licant st ated that the WESTEMSŽ [

] The staff asked a follow up question, RAI WSTM-007, to clarify the determination of the time constant value. In its re sponse date d May 10, 2 013, Westin ghouse upd ated part of the previous response as follows:

[

]

The staff reviewed the response. On the basis th at the time constant value can remove the identified re dundant pea k and that th e procedure requires review by the analyst and independent verifier to ensure that this process does not elim inate actual peaks, the NRC staff found this a cceptable.

TR Figure 4-4 shows that a stress filter check is used for the peak selection process.

The NRC staff issued RAI WSTM-009 to ask t he applicant to explain the process t o ensure the critical (maximum stress for pea k, minimum stress for va lley) points are retained for both NB 3600 and NB 3200. In its respon se dated Feb ruary 26, 2013, the applicant provided examples to explain the stress f ilter check pr ocess and a lso provided guidelines of the NB 3600 fatigue a nalysis procedure.

The applica nt stated tha t WESTEMSŽ always retains the maximum and minimum stress state s that contribute to the g reatest alter nating stress within a tr ansient and these values cannot be eliminated by the applicat ion of the st ress filter

. WESTEMSŽ procedural g uidelines require that the analyst and indepen dent verifier review peaks following t he applicat ion of the stress filter t o ensure tha t a peak is included for each sub cy cle load excursion. Because the critical values cannot be eliminated by the stre ss filter, the NRC staff found this acceptable.

In TR Figure 4-5, Westin ghouse presents a proce ss flowchart for WESTEMSŽ NB 3600 peak review and editing. The staff reviewed Figure 4-5 and identif ied two critical decision p oints in the flowchar t for which t he process f lowchart do es not provide justification or criteria

.

10

The process flowchart in dicates that "if peak doe s not correspond to a lo ad excursio n, eliminate this peak." Th e applicant did not provide technica l justification for why this peak is redu ndant.

The flowcha rt indicated t hat "if two or more peak times exist for the same load excursion, then eliminate redundant peak 'A' an d 'B'." The applicant d id not provide technica l justification f or the elimination.

The staff issued RAI WSTM-008 to ask Westin ghouse to addr ess this issu

e. In its response dated February 26, 2013, Westingho use provided examples in which pea ks occur due to stress phasing diff erences or d ue to small f luctuation of applied loa ding. The st aff reviewed the response an d determined that a follo wup questio n was needed to clarify the technica l justification f rom the exa mples. The example ind icated that if time points P1 and P2 are selected by the automated process and represe nt the same state, P2 may be deleted. The condition for eliminating P2 is under the flow path "Does peak correspon d to a load e xcursion? NO Eliminate con servative peak using the WESTEMSŽ peak editing tool." Th e staff asked whet her the same principle can be applie d to delete p eaks A and B. The staff asked the applicant to define which peaks corre spond to loa d excursion.

In its respon se dated May 10, 2013, Westinghou se stated:

The intent of the procedu re is to [

]. To better clarify the intent, t he wording "corresponding to a load excursion" will be chan ged in the fl ow chart in t he TR and procedure to be more exp licit, as shown in the topical r eport markup section of this respon se. In Revision 2 of the TR, the wording of this item was change d from "Doe s peak corre spond to a load excursion" to "Is pe ak a sub cycle peak due to [

]?

" On the basis that this would be a redundant peak that can be appr opriately eliminated, the NRC staff found this change acceptable and the issue re solved. TR Secti on 1.1 indicates tha t "[t]he effort to develop algorithms to cover all p ossible conceived problem dependencies is not p ractically justified compared to the effort fo r analysts to make reasonable engin eering decisions about t he inputs for known problems." The NRC staff issued RAI WSTM-005 to request the applicant to identify all reasonab le engineering decisio ns for the removal of the redundant pe aks with cor responding engineering criteria and t o clarify whether these a re all includ ed in the pro cedure. Specifica lly, the applican t was asked to address u nder what situation, if an y, the peak elimination process criteria could not be included in the procedure.

The NRC st aff observed that TR Section 4.1.2 stated that "[

i]n addition t o the peak selection controls, the an alyst has th e ability to r efine the fatigue analysis restart f ile to manually eliminate peak times justified to b e redundant and conservative and to per form fatigue reanalysis with the restar t file." The NRC staff asked the applicant to clarify this situation with examples.

In a letter da ted March 4, 2013 (Reference 15), th e applicant r esponded to the RAI and provided the potential so urces of the redundant peaks in WE STEMSŽ NB 3600 analysis with three scenar ios: (1) [

]

(2) [

]

11 (3) [

]

Redundant peaks cou ld occur in the NB 3200 analysis in two scenarios:

(1) [

]

(2) [

]

The response also state d that all tho se scenario s have been described in the user manual and procedure a nd there are no addition al situations presently kn own that can be describ ed. The staff found this acceptable. However, the NRC staff issued a supplemental question to RAI WSTM-005 requesting t hat the applicant revise t he sentence mentioned above that appeared to grant the an alyst the ability to manua lly eliminate peak times.

In its respo nse dated May 10, 2013, Westinghouse sta ted that it w ould revise t he TR to state that no ot her redundant peaks can be credited, aside fr om those defined in Sect ion 4.1.5 for NB 3600 analysis and in Section 4.2 for NB 3200 analysis, without prior NRC approval

. The NB 3600 and NB 3200 procedures will be revised, as nece ssary, to refl ect this change to the T R. The applicant also provided its TR markup for Sections 4.1.5 and 4.

2 to address this issue, a nd the staff confirmed that these changes were incorporat ed in Revision 2 of the TR. On the basis that th e applicant correctly addressed this concern an d limited the peak sele ction criteria to these five defined instances, the NRC staff found this acceptable.

3.4.2 NB 3200 Re view As noted in Section 1.1 of the TR, proper incorpo ration of the user controls for elimina tion of the redundant peaks and valleys has been the subject of previous interaction with the NRC staff.

To address t his concern, the applica nt proposed to use a fatigue analysis procedure.

WESTEMSŽ is also ap plied to NB 3200 fatigue analysis. On the basis t hat the NB 3200 fatigue analysis also req uires user controlled elimination of redundant pe aks and valleys, the NRC staff issued RAI WSTM 006 to request the applicant to provide the criteria and procedure for NB 3200 fatigue analysis. In its r esponse dat ed March 4, 2013, Westinghouse sta ted: The proced ure for NB 3200 fatigue analysis is b eing added as a new Section 8.1.13 in the WESTEMSŽ User Manual Volume 2 for De sign Analysi

s. The procedure will reference a n updated Section 8.1.1 3 in the manual that provides expanded criteria a nd guidelines for peak sele ction contro l and peak e diting in NB 3200 (ASN) analysis.

The applicant also provided the WESTEMSŽ User Manual Volume 2 markups. The NRC staff reviewed this information related to t he NB 3200 procedure a nd found tha t additional information was needed related to th e use of a time constant to eliminate peaks. The staff issued supplemental RAI s WSTM-006 and WSTM-007 to address this to pic. In it s response dated May 1 0, 2013, Westinghouse provided its response to RAI WSTM-006 as follo ws: (1) The wording in the NB 3200 user's manual markup, attache d to the RAI response, w ill be revised to change "n o greater than" to "less t han" in the last paragra ph before Figure 1 in t he section o n time const ant input. [

]

12 (2) [

]

(3) The TR defines redunda nt peaks as

[

]. In ad dition, conte xtual use of the term will be made to be consiste nt with the definition in the revised version of the TR." (4) Item 3 of the time consta nt input for t he NB 3200 procedure markup will be updated as follows: [

] The applica nt also provided its resp onse to RAI WSTM-007 as follows:

[

]

The applicant also provided its TR markups to incorporate the changes, and the NRC staff verified that these chang es were incorporated in Revision 2 of the TR. On the basis that the applicant clarified how to determine the time constant used in peak sele ction, as well as how to determine redundant peaks using this time cons tant, the NRC staff found this response acceptable.

As describe d above, the staff issued RAI WSTM-005 to request the applicant to ident ify all reasonable engineering decisions for the removal of the red undant peaks with corre sponding engineering criteria and clarify whether these are all included in the proce dure. The staff also issued RAI WSTM-009 to ask the a pplicant to e xplain the process to en sure the crit ical (maximum stress for pea k, minimum stress for va lley) points are retained for both NB 3600 and NB 3200. As documented in Sectio n 3.4.1 of this report for t he NB 3600 analysis, the staff 13 found the ap plicant's response acce ptable and considers th is issue closed with Revi sion 2 of the TR. 3.5 Validation of the Revised WESTEMSŽ Program Section 2.1 of the TR discusse s the applicant's r esolution of regulatory issues that w ere raised in previous NRC audits. Of note, in response to an original question in S RP Section 3.9.1 EMB 07 issued d uring the review of the AP1000 desig n certifica tion, discussed on Page 2-1 of the report, the application states that the WESTEMSŽ computer code consists of a two p hased fatigue analyses. The first phase w as performed to calcu late stress t ime history for each individual tr ansient, se lect peak an d valley time s, and calculate fatigue r esults from all transien t pairs asso ciated with the selected p eak and valley times. The second p hase inclu des a user's controlled modification of redundant peaks and valleys for in put to the re analysis.

The NRC st aff noted that the user's controlled modification is part of the application of the computer code as it is in cluded in th e program user's manual and that it is consid ered necessary b y Westinghouse for usin g WESTEMSŽ comput er program. It is noted t hat no user's con trolled modification will be required if th ere exist no redundant peaks from the computer run. As such, in RAI WSTM-001, the NRC staff requested that Westinghouse provide the root cau se of genera ting the redu ndant and a dditional pe aks and valleys that the program users need t o eliminate during the manual modification. The staff also re quested that Westinghou se confirm whether the additional re dundant times could be created because of deficiencies in certain pr ogram algorithms and whether there are transien t cases othe r than those stated in Section 4

.1.5. In its respon se dated Fe bruary 26, 2013 (Reference 14), the applicant att ributed the "

root cause" of re dundant pea ks to three p otential sour ces stated in Section 4.

1.5 of the to pical report (WCAP-175

77) for an NB 3600 fatig ue analysis in WESTEMSŽ:

(1) [

] (2) [

]

(3) [

]

The first "ro ot cause" of redundant peaks is attributed to tra nsient defin itions. The tr ansient definitions may inheren tly include r edundant extreme stress states, su ch that a final stress state for one transient may represent an initial stre ss state of anot her transient (e.g., heatu p and cooldown d esign transients in which cooldown begins at th e same state that heatu p ends and heatup begins at the sa me state that cooldown ends). The second "root cause" of redundant peaks is attributed to phasing of p rimary plus secondary stress (Sn) and total str ess (Sp) for a transient load excursion. ASME Code fatigue usage is based on alt ernating stre ss (Sa), which is determ ined from the total stress range and the Ke penalty factor. The Ke penalty factor is a funct ion of the Primary plus Secondary stress range.

Therefore, the [

14

]

[

] The applica nt asserted t hese potential redundant sources to be the only cases wher e the redundant peaks can be generated by WESTEMSŽ co mputer code.

The analysts will se lect redundant peaks for elimination only in the above three cases and docu ment the justification in the calcu lation notes.

Regarding the root causes related to computer programming algorithmic deficiencies, the applicant stated that the creation of r edundant pe aks is intentionally code d into WESTEMSŽ to conservatively account for all possible peaks, a nd that these are not th e result of a ny algorithmic deficiencies.

For instance, the opera tion of the pr ogram is to [

] for the thro ugh wall temperatures to return t o steady state condition

s. Also, the program operation will conservatively allow both times to be included in the initia l fatigue evaluation. This allows for any domina nt effects of Ke at the Sn peak time to produce a higher altern ating stress in the fatigue pair contribution s than that p roduced by the Sp peak time. If both times result in significant fa tigue pairs, t his is a conservative accounting of th e transient stress cycle, as illustrated below. The user is theref ore provided options to r educe this conservatism if necessary.

In addition t o the RAI response described above, the applicant revised Section 4.1.

5 of the TR to state that justificat ion for eliminatio n of conservative peak times is limited to the above three root causes. As a resu lt of its review, the NRC staff concludes that the applican t has adequ ately identified the "root cause" for r edundant pe aks, which, as stated above, were generated in an initial a ttempt to conservatively account for all possible peaks in the fatigue calculation.

Therefore, the RAI WST M-001 is resolved and closed.

The staff's a cceptance r eview letter dated Nove mber 13, 2012 (Reference 8), noted that the TR does not cle arly address the technical basis re garding how the WESTEMSŽ co mputer program requires use r controlled modification in some ca ses, and tha t further understanding would be necessary t o determine that WESTEMSŽ produ ces justifiable and conse rvative results.

Therefore, in RAI WST M-002, the NRC staff requested that the applicant compare peaks and valleys from hand calcu lations with t he results fr om WESTEMSŽ anal ysis and en sure that no real peaks a nd valleys are missed by WESTEMSŽ calculation. Alternatively, the applicant was asked to de monstrate that the hand calculated peaks and valleys are at least a subset of WESTEMSŽ output peaks and valleys.

In its respon se dated March 4, 2013 (Reference 15), the applicant provid ed an example to demonstrate WESTEMSŽ analysis would generate conservative results such that th e hand calculated peaks and valleys would be at least a subset of W ESTEMSŽ output peaks and valleys. The following calculation s are provided in the two part example:

15 (1) An NB 3600 fatigue analysis is perfo rmed using traditional manual (hand calculation) methods to select pea k and valley stress state

s. (2) The same NB 3600 mod el and loading is analyzed in WESTEMSŽ to demonstrate that the same set of manually selected p eaks is also identified by the software.

The exampl e consider s a represent ative NB 36 00 fatigue a nalysis of a standard co mponent (a 3 inch valve) with a thermal transient loads and enveloping moment stre ss ranges a pplied. The component also include s a structura l discontinuity. The thermal stress h istory inputs are used to select the peak and valley stress states (peak) using a tra ditional manual approach. Manual calculations are also use d to evaluate the fatigue pairs, inclu ding alternat ing stress, cycle consumptio n, and usag e factors. T he same fatigue analysis is then run in WESTEMSŽ and reviewed to demonstrate that all pea ks identified manually are also ident ified by the WESTEMSŽ peak sele ction proce ss. The response described the details o f the hand calculation, including the t emperature and pressure tra nsients, the associated thermal stress response s, the resultin g combinations of fatigue load pairs, and th e calcula tion of total CUF. The resp onse also d escribed the parallel calculation using the WE STEMSŽ computer code and the pe aks ident ified in this calculation.

The staff reviewed these calculat ion results. Wit h respect to the manual method stated above, the NRC staff concludes that the peak times set identified while performing the fatigue analysis by manual methods is a subset of t hese peak times identified by the WESTEMSŽ computer code. Ther efore, RAI WSTM-002 i s resolved a nd closed.

The NRC st aff's acceptance review letter also not ed that the TR does not address the technical criteria in pe rforming the user controlled modifica tion in which the redundant peaks ar e eliminated f or the reanalysis. Instea d, the TR focuses on pr ocedures for the user to perform each of the operations a nd to provide justificatio n in the analysis documentation to su pport the decisions made. To ensure that no real peaks ar e removed when performing the second phase analysis, the NRC staff requested in RAI WSTM-003 that the applicant pr ovide an example problem in which the initial run outp ut peaks are modified by users to red uce the resu lting CUF value and confirm that the final resu lts are corre ct by comparing the final results with the hand calculation. In its respon se dated March 4, 2013 (Reference 15), the applicant presen ted information using the example problems described in response to RAI WSTM-002. In this example pro blem, the WESTEMSŽ analysis also include d a number of additional peaks beyond those selected by manual met hods. Ther e were 11 WESTEMSŽ run output peaks that translate to 55 possible fatigue load pairs to be considered.

The total CUF from WESTEMSŽ a nalysis is 0.

782, comparison to 0.776 fro m the hand calculat ion. Following th e process fr om the Westinghouse pr ocedure flo wchart in Figure 4-5 of the TR, the example an alysis includ ed justification confirming which pea ks are redun dant based on one of the three ca uses of NB 3600 redundant peaks listed in Sect ion 4.1.5 of WCAP-1757

7. Redundant peaks are eliminated from the fatigue analysis fo llowing Reference 7 of th e TR (PSDR QP 4.7), "WESTEMSŽ NB 3600 Fatigu e Analysis a nd Verification Procedure."

Re analysis of the modified peak set is performed, and the results were co mpared with the hand calculation results pre sented in the r esponse to RAI WSTM-002. The fin al CUF from WESTEMSŽ analysis is reduced to 0.7757, which is co nsistent with 0.776 of the ha nd calculation. The staff reviewed this e xample and determined that the methodology and procedure will reduce C UF by elimin ating redund ant peaks fo r the reason s listed in 16 Section 4.1.

5 of the TR, and the resu lting reduce d CUF is consistent with the hand ca lculation.

Therefore, the NRC staff concludes that RAI WSTM-003 is resolved and closed.

It is noted th at for this example, the CUF calcula ted by WESTEMSŽ is less than 1, and further refinement (peak editing

) would not typically be necessary ba sed on the a cceptance criteria in Section 5.3.

1 of the procedure (PSDR QP 4.7).

Even thoug h the elimin ation of redu ndant peaks would not normally be d one for a calculation with this CUF result, the sa me example was used for both RAI responses f or simplicity.

The full pro cess was fo llowed to demonstrate the methodology as outline d in Section 4.1.5 of the TR to reduce the usage factor, and t o show that the adjusted WESTEMSŽ results ar e verified by the manual fatigue calculations whe n these conservatisms are removed.

On April 23 and 24, 2013 (Reference 10), the NRC staff conducted an audit to review the detailed ca lculations that supported t he Westingh ouse respon ses to RAIs WSTM-002 and 003.

The audit was conducted by a team of NRC sta ff members who are knowledgeable in various aspects of the piping an d component stress eval uation, fatig ue analysis, and computer program review. Duri ng this audit

, Westingho use present ed the respo nses to RAI WSTM-002 and 003 and walked through the analysis per formed and how it was performed in accordance with the procedure.

Westinghou se explaine d how this sample problem provides a sufficient demonstration of the pr ocess for re ducing con servatism by removing re dundant pea ks in accordance with the program documentation, when needed f or an analysis.

As a result o f the audit, Westinghou se is committed (1) to document the analyses pe rformed for these respo nses to RAI WSTM-002 and 003 and (2) to provide an explanation for ho w a change to the proce dure would impact the TR.

Regarding the first item, Westinghou se later com pleted a for mal calculation note CN-PAFM 29, "Sample NB-3600 Fatigue Analysis in Respo nse to RAIs Received on WESTEMSŽ Topical Report WCAP-17577," and discussed this calculation with the NRC staff in a closed meeting on June 3, 201

3. The staff found that th e results of t he spreadsh eet calcu lation and the WESTEMSŽ computer run match the response

. Therefore, the audit followup item is satisfied and closed.

Regarding the second it em, the NRC in WSTM-003, Supplement 1, requested that Westinghou se review the references to the topical report tha t refer to the NB 3600 procedure and ensure t hat all the key methodol ogies and cr iteria are included in the TR. In its re sponse dated May 1 0, 2013, the applicant in dicated that the revision numbers from the program documentation references in the TR will be removed in the next revision of the TR since the key methodology and criteria of the NB 3600 and NB 3200 analyses using WESTEMSŽ are included in the TR and considered a s the licensing basis for the use of th e program for AP1000.

The staff reviewed Revision 2 of the TR and found that the re vision number of the an alysis procedure PSDR QP 4.7 (Reference 7 of the TR) was remove

d. Base on this review, the NRC staff conclu des that the second audit followup ite m and associated RAI WSTM-003, Supplement 1, are also closed. 4.0 Conclusion On the basis of the NRC staff's evaluation documented in this report, the NRC staff determined that the analysis of ASME Section III piping and components using the W ESTEMSŽ code is consistent with the requir ements and guidance list ed in Sectio n 2 above and, therefore, acceptable.

17

5.0 REFERENCES

(1) NUREG-0800, "Standard Review Pl an for the Review of Saf ety Analysis Reports for Nuclear Power Plants: LWR Edition," Chapter 3, Section 3.9.

1, Revision 3, Special Topics for M echanical C omponents, March 2007.

(2) "Summary o f the AP1000 Design Certification-R egulatory on Site and Off-Site Revie ws of Open Items for the WESTEMS Computer Code," dated April 1, 201 1, (Agencywide Documents Access and Managemen t System (ADAMS) Accession No.

ML110250634).

(3) Regulatory Issue Summary 2011-14, "Metal Fatigue Analysis Performed by Co mputer Software," December 29, 2011, (ADAMS Accession No. ML1 1143A035).

(4) WCAP-1757 7, Revision 0, February 29, 2012, "Topical Repo rt on ASME Section III Piping Fatig ue Analysis Utilizing the WESTEMSŽ Compute r Code." (ADAMS Accession No. ML120610676).

(5) "Withdrawal Request for WCAP-1757 7-P and -NP," Ma y 9, 2012, (ADAMS Accession No. ML1213 2A367). (6) "Withdrawal Acknowledgement Letter for Topical Report on ASME Sectio n III Piping Fatigue Analysis Utilizin g the WESTEMSŽ Co mputer Code." Revision 0, June 1, 201 2, (ADAMS Ac cession No.

ML12151A2 21). (7) WCAP-1757 7, Revision 1, Septemb er 28, 2012, "Topical Re port on ASME Section III Piping Fatig ue Analysis Utilizing the WESTEMSŽ Compute r Code." (ADAMS Accession No. ML12275A115).

(8) Acceptance for Review L etter, Nove mber 13, 2012, WCAP-1 7577, Revision 1, "Topical Re port on ASME Section III Piping Fatig ue Analysis Utilizing the WESTEMSŽ Computer Code" (ADAMS Accession No. ML123 10A052).

(9) Audit Summary for Revi ew of WCAP-17577, Revision 1, December 2012, (ADAMS Ac cession No.

ML13017A1 25). (10) Audit Summary for Revi ew of WCAP-17577, Revision 1, April 2013, (A DAMS Accession No. ML1313 4A290). (11) Summary of Public and Closed Meeting with We stinghouse Electric Co mpany on Request for Additional In formation Responses fr om the Revi ew of WEST EMS Topical Rep ort WCAP-1 7577, April 25, 2013, (ADAMS Accession No. ML13122A282).

(12) Summary of Public and Closed Meeting with We stinghouse Electric Co mpany on Request for Additional In formation Responses fr om the Revi ew of WEST EMS Topical Rep ort WCAP-1 7577, June 3, 2013, (ADAMS Accession No. ML13156A078).

(13) Westinghou se Response to Requests for Additio nal Information on WCAP-17577, Revision 1, February 18, 2013, (ADAMS Accession No. ML13051A655).

(14) Westinghou se Response to Requests for Additio nal Information on WCAP-17577, Revision 1, February 26, 2013, (ADAMS Accession No. ML13063A163).

18 (15) Westinghou se Response to Requests for Additio nal Information on WCAP-17577, Revision 1, March 4, 2013, (ADAMS Accessio n No. ML1306 6A113). (16) Westinghou se Response to Requests for Additio nal Information on WCAP-17577, Revision 1, May 10, 201 3, (ADAMS Accession No. ML13134A475).

(17) WCAP-1757 7, Revision 2, June 17, 2013, "Topical Report on ASME Section III Piping and Compo nent Fatigue Analysis Utilizing the WESTEMSŽ Computer Code."

(ADAMS Ac cession No.

ML13170A0 25). (18) Supplemental Request f or Additional Information Letter No. 2, April 25, 20 13, (ADAMS Ac cession No.

ML13115A9 09). (19) NUREG-1793, "Final S afety Evalua tion Report Related to Certification of the AP1000 Standard Design," Sup plement 2, Volume 1, September 2011, (ADAMS Accession No. ML1129 3A087). (20) Letter Regarding Westin ghouse Electr ic Company Quality Management System, Revision 6, February 24, 2011, (ADAMS Accession No. ML110310088).