ML13080A406

San Onofre Nuclear Generating Station, Unit 2 - Response to Request for Additional Information (RAIs 39, 43, 44, 58 and 61) Regarding Confirmatory Action Letter, (TAC Me 9727)

ML13080A406
Person / Time
Site:	San Onofre
Issue date:	03/20/2013
From:	St.Onge R J Southern California Edison Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC ME9727
Download: ML13080A406 (11)

Text

SOUTHERN CALIFORNIAEDISONAn EDISON INTERNATIONAL CompanyRichard I. St. OngeDirector, Nuclear Regulatory Affairs andEmergency PlanningMarch 20, 201310 CFR 50.4U.S. Nuclear Regulatory CommissionATTN: Document Control DeskWashington, DC 20555-0001Subject:Docket No. 50-361Response to Request for Additional Information (RAIs 39, 43, 44, 58 and 61)Regarding Confirmatory Action Letter Response(TAC No. ME 9727)San Onofre Nuclear Generating Station, Unit 2References: 1.Letter from Mr. Elmo E. Collins (USNRC) to Mr. Peter T. Dietrich (SCE), datedMarch 27, 2012, Confirmatory Action Letter 4-12-001, San Onofre NuclearGenerating Station, Units 2 and 3, Commitments to Address Steam GeneratorTube Degradation2. Letter from Mr. Peter T. Dietrich (SCE) to Mr. Elmo E. Collins (USNRC), datedOctober 3, 2012, Confirmatory Action Letter -Actions to Address SteamGenerator Tube Degradation, San Onofre Nuclear Generating Station, Unit 23. Email from Mr. James R. Hall (USNRC) to Mr. Ryan Treadway (SCE), datedFebruary 20, 2013, Request for Additional Information (RAIs 38-52) RegardingResponse to Confirmatory Action Letter, San Onofre Nuclear GeneratingStation, Unit 24. Email from Mr. James R. Hall (USNRC) to Mr. Ryan Treadway (SCE), datedFebruary 21, 2013, Request for Additional Information (RAIs 53-67) RegardingResponse to Confirmatory Action Letter, San Onofre Nuclear GeneratingStation, Unit 2Dear Sir or Madam,On March 27, 2012, the Nuclear Regulatory Commission (NRC) issued a Confirmatory ActionLetter (CAL) (Reference 1) to Southern California Edison (SCE) describing actions that the NRCand SCE agreed would be completed to address issues identified in the steam generator tubesof San Onofre Nuclear Generating Station (SONGS) Units 2 and 3. In a letter to the NRC datedOctober 3, 2012 (Reference 2), SCE reported completion of the Unit 2 CAL actions andincluded a Return to Service Report (RTSR) that provided details of their completion.By emails dated February 20, 2013 (Reference 3) and February 21, 2013 (Reference 4), theNRC issued Requests for Additional Information (RAIs) regarding the CAL response.Enclosure 1 of this letter provides the response to RAIs 39, 43, 44, 58 and 61.P.O. Box 128San Clemente, CA 92672 Document Control Desk-2-March 20, 2013There are no new regulatory commitments contained in this letter. If you have any questions orrequire additional information, please call me at (949) 368-6240.Sincerely,Enclosure:1. Response to RAIs 39, 43, 44, 58 and 61cc: E. E. Collins, Regional Administrator, NRC Region IVJ. R. Hall, NRC Project Manager, SONGS Units 2 and 3G. G. Warnick, NRC Senior Resident Inspector, SONGS Units 2 and 3R. E. Lantz, Branch Chief, Division of Reactor Projects, NRC Region IV ENCLOSURE 1SOUTHERN CALIFORNIA EDISONRESPONSE TO REQUEST FOR ADDITIONAL INFORMATIONREGARDING RESPONSE TO CONFIRMATORY ACTION LETTERDOCKET NO. 50-361TAC NO. ME 9727Response to RAIs 39, 43, 44, 58 and 61 RAI 39In Reference 2, p. 36, Bottom of page, the term P is not defined. Please define the parameter, andexplain (1) how it is formulated, and (2) how it is related to the ATHOS computed nodal void fraction.RESPONSENote: RAI Reference 2 is "Evaluation of Stability Ratio for Return to Service," prepared by MHI,Document No. L5-04GA567, Revision 6.Define the parameter 13As used in RAI Reference 2, P is the homogeneous void fraction defined by the volumetric flowrates of the gas and liquid phases:V9 + VThe correlations used in the stability ratio evaluation depend, in part, on the homogeneous voidfraction. Experiments control void fraction by varying the volumetric flow rate of the two phases,so experimental data are correlated to homogeneous void fraction. Homogeneous void fractiondistribution along the tube length is not an ATHOS output. The homogeneous void fraction iscalculated by using the Smith correlation and nodal void fraction obtained from ATHOS outputas outlined below.1) Explain how 13 is formulatedThe homogeneous void fraction, P, is formulated in terms of quality (x, vapor mass flowfraction). The definition for quality is:,%Mrg + 1711The mass flow rate of each phase is defined as;=h pg -V1Substitute the definition for each mass phase into the expression for quality:X=-Th liui + Pv f V1The liquid volume flow fraction (11 -p)is derived from the homogeneous void fraction:1g +3 V, 1ýPage 2 of 9 Substitute in the quality expression:_' _ +_ , g + fl,PgPg

• _ g _ _Pgg+i~ 1I4 V, Pgfl3+PI-(1/l)Vg + i;' P~g V~+V9 I " Vg+ V,Solve for P3 as a function of quality, x:P 9f =p Pg f X + Pp X -P 'fl XP, "" X + Pg " -P9 " l " X = P" XPI .xP 'x + Pg (- x)2) Explain how P3 is related to the ATHOS computed nodal void fraction aHomogenous void fraction (P) is obtained from local void fraction (a) through the use of theSmith correlation and saturated density for liquid and vapor." ATHOS provides nodal void fraction (a) as a function of position along the tube.* Nodal void fraction (a) is converted to quality (x) by using the Smith correlation:Pa p1 x p1) -)P* Quality is used to calculate homogeneous void fraction (p3):Pi .xP 'X + Pg (1- x)Terminologya: Nodal Void Fractionp9: Vapor Densityfl: Homogeneous Void Fraction (vapor volume fraction)PI: Liquid Densitymg: Vapor Massmi: Liquid MassVg: Vapor VolumeV1: Liquid Volumex : Mixture Quality (vapor mass fraction)e: Entrainment Coefficient (ratio of the mass of liquid flowing in thehomogeneous mixture to the total mass of water flowing)Page 3 of 9 RAI 43In Reference 4, p. 15, Section 6.3, "Assumption," Item (1) "Fluid force," please explain the basisfor the statement, "The turbulent excitation force is evaluated and fluid force caused by FEI isnot taken into account..." It is not clear how the turbulent excitation force is used to determinewhen the friction force is adequate to assume that there is no in-plane motion at the subjectAVB intersection. Please clarify the statement, "When the friction force due to contact force issmaller than the turbulent excitation force at an AVB support point, a tube can slide in the in-plane direction."RESPONSENote: RAI Reference 4 is "Analytical Evaluations for Operational Assessment," prepared byMHI, Document No. L5-04GA585, Revision 2.It is important to note that the analysis in RAI Reference 4, Section 6, was ultimately not used inthe Operational Assessment (OA) contained in Return to Service Report Attachment 6,Appendix B. As explained in the response to RAI 35, an alternate analysis was developed andvalidated based on the observed performance of Unit 3 and Unit 2.Explain the basis for the statement "The turbulent excitation force is evaluated and fluidforce caused by FEI is not taken into account ..."The condition being evaluated is the design condition with no relative motion between the tubeand the AVB. In the design condition FEI is not occurring so the only driving force is fromturbulence.Please clarify the statement, "When the friction force due to contact force is smaller thanthe turbulent excitation force at an AVB support point, a tube can slide in the in-planedirection."The support effectiveness criterion developed in RAI Reference 4, Section 6, assumed only oneAVB support resists all the flow force along the U-bend tube. As long as the static resistingfriction force at an AVB intersection is greater than the driving force due to flow, the tube will notmove in the in-plane direction at the AVB intersection. For this support effectiveness criterion,the AVB intersection was considered to be an active support. As indicated above and asdiscussed in the response to RAI 35, this support effectiveness criterion was not used for theOA contained in Return to Service Report Attachment 6, Appendix B.Page 4 of 9 RAI 44In Reference 4, p. 15, Section 6.3, "Assumption," Item (1) "Fluid force," it is assumed there is noin-plane motion if the stability ratio (SR) is less than 1.0. How has MHI accounted for thepotential that in-plane tube motion may occur at a SR less than 1.0 and how is the analysisresult affected if a smaller value is used for this threshold?RESPONSENote: RAI Reference 4 is "Analytical Evaluations for Operational Assessment," prepared byMHI, Document No. L5-04GA585, Revision 2.RAI Reference 2 is "Evaluation of Stability Ratio for Return to Service," prepared by MHI,Document No. L5-04GA567, Revision 6.RAI Reference 4, p. 15, Section 6.3, "Assumption," Item (1) "Fluid force," does not assume thereis no in-plane tube motion when the SR is less than 1.0. The assumption is that no in-plane FEIoccurs when the SR is less than 1.0. This is consistent with the definition of FEI.How has MHI accounted for the potential that in-plane tube motion may occur at a SRless than 1.0?RAI Reference 4 does not address the potential that in-plane tube motion may occur at a SRless than 1.0. The in-plane motion that occurs at SR less than 1.0 is accounted for in RAIReference 2. The dynamic analysis model described in RAI Reference 2 allows for in-planemotion.How is the analysis result affected if a smaller value is used for this threshold?Stability analysis is performed subsequent to the calculation of required contact force. Thestability ratio threshold has no effect on the contact force analysis result. In the response toRAI 35, we have explained that this derivation of contact force was not used in the OperationalAssessment (OA) contained in Return to Service Report Attachment 6, Appendix B.Page 5 of 9 RAI 58In Reference 3, Appendix 9, Table 6.2-1, which parameters are sampled randomly at eachtube/AVB intersection? Why is this appropriate in lieu of assuming a functional relationship foreach given parameter from tube to tube in a given column of tubes? For parameters (e.g., AVBtwist) assumed to follow a functional relationship from tube to tube in the same column, providethe basis for the assumed relationship. For AVB twist, how does the assumed relationshiprelate to Figure 6.2-2?RESPONSENote: RAI Reference 3 is "Tube Wear of Unit-3 RSG -Technical Evaluation Report." preparedby MHI, Document No. L5-04GA564, Revision 9.Six parameters representing manufacturing variations were considered for the contact forceanalysis: tube ovality (G value), tube pitch, tube flatness, AVB thickness, AVB twist, and AVBflatness.Tube G valueTube pitch(True position of land)Tube FlatnessAVB thicknessI AVB twistAVB FlatnessThe input values were randomly sampled at each tube/AVB intersection for the first fourparameters. AVB twist was randomly sampled at each AVB and then varied at each tubeintersection along the AVB following a functional relationship. AVB flatness was not used incontact force analysis. The basis for using either random sampling or a functional relationshipfor each parameter follows:Page 6 of 9 Tube Ovality (G value):Tube ovality was randomly sampled at each tube/AVB intersection. The random distribution oftube ovality from tube-to-tube was based on actual tube manufacturing data which provide moreaccurate results than assuming a functional relationship.Tube Pitch (TSP hole variation from true position):The contact force model included the effect of tube pitch by using gap elements at TSP holes.The gap size was randomly sampled at each tube-to-TSP intersection at the top TSP from adistribution based on the fabrication tolerance for TSP hole pitch. Therefore, random samplingis more appropriate than assuming a functional relationship.Tube Flatness:Tube flatness was randomly sampled at each tube/AVB intersection from a distribution basedon the fabrication tolerance. Random sampling for this parameter is appropriate because actualflatness varies randomly both from tube-to-tube and along the tube length.AVB Thickness:AVB thickness was randomly sampled at each tube/AVB intersection. As Table 6.2-1 shows,separate AVB thickness distributions were sampled for Unit 2 and Unit 3 based onmeasurement results. Therefore, random sampling is appropriate.AVB Flatness:AVB flatness was not used in the contact force analysis. AVB flatness variations have anegligible effect on contact forces.Page 7 of 9 AVB Twist:AVB twist was randomly sampled as a property of each AVB, then varied systematically alongthe length of the AVB using a functional relationship. AVB twist is generated by bending astraight AVB bar during AVB manufacturing, as shown in the following figure. As a result of thisprocess, an unloaded AVB (i.e., before insertion in the tube bundle) has a uniform twist alongeach straight leg.bendingTwisted TwistedFigure 6.2-2 shows the functional form of the AVB twist factor that represents the variation oftorsional stiffness along the length of an AVB in the contact force model. Since the AVB hasuniform cross section, its torsional stiffness at each tube/AVB intersection along its length isinversely proportional to the distance of the intersection from the nose and retaining barendpoints of the AVB. This is the reason for the characteristic "bathtub" shape of the AVB twistfactor depicted in Figure 6.2-2. For more details regarding the basis for the AVB twist factor,please see the response to RAIs 64 through 66.Page 8 of 9 RAI 61Reference 3, Appendix 9, Attachment 9-3, Figure 4.1.2-3. Discuss the pedigree of the data inthis figure and how it differs from Reference 2, Figure 6-19 and 6-20. Please explain thedifferences between the Reference 3 versus the Reference 2 figures for dings exceeding 0.5volts?RESPONSENote: RAI Reference 3 is "Tube Wear of Unit-3 RSG -Technical Evaluation Report." preparedby MHI, Document No. L5-04GA564, Revision 9.RAI Reference 2 is "SONGS U2C1 7 Steam Generator Operational Assessment for Tube-to-Tube Wear," prepared by Areva NP Inc. Document No. 51-9187230-000, Revision 0.The data plotted in Figure 4.1.2-3 of Appendix 9, Attachment 9-3 in RAI Reference 3 and thosein Figures 6-19 and 6-20 in RAI Reference 2 use the same Pre-Service Inspection Eddy CurrentTesting (ECT) data. The ECT data were obtained under AREVA's 10 CFR 50 Appendix Bprogram for the Pre-Service Inspection and are retained under SONGS Steam GeneratorProgram.The differences between the figures in RAI References 2 and 3 are:" The figures in RAI Reference 2 cover the signals on the U-bend region, which includethe signals on freespan area and those at U-bend AVB locations but do not include thesignals at TSP locations. The plotted data cover the voltage range from 0.5 to 1.5 Volts." The figures in RAI Reference 3 cover the signals on the locations of structures, whichinclude the signals at U-bend AVB locations and those at TSP locations but do notinclude the signals on freespan area. The plotted data cover the full voltage range of thereported ding indications.RAI Reference 2 RAI Reference 3Figures 6-19 Figure 4.1.2-3and 6-20Pre-service ECT Inspection Data Yes YesU-bend Freespan Dings Yes NoTSP Dings No YesAVB Dings < 0.5 Volts No YesAVB Dings 0.5-1.5 Volts Yes YesAVB Dings > 1.5 Volts No YesDespite these differences, the figures support the comparison of the relative numbers of contactsignals in the upper bundle for Units 2 and 3 and demonstrate that contact forces are moresignificant in Unit 2 than in Unit 3.Page 9 of 9