ML15133A131

South Texas, Unit 1 - LTR-PAFM- 15-27-NP, Technical Justification to Support Extended Volumetric Examination Interval for South Texas, Unit 1, Reactor Vessel Inlet Nozzle to Safe End Dissimilar Metal Welds (Non-Proprietary)

ML15133A131
Person / Time
Site:	South Texas
Issue date:	04/24/2015
From:	Glunt N L, McFadden J L, Udyawar A Westinghouse
To:	Document Control Desk, Office of Nuclear Reactor Regulation
Shared Package
ML15133A119	List: ML15133A130 NOC-AE-15003250, LTR-PAFM- 15-27-NP, Technical Justification to Support Extended Volumetric Examination Interval for South Texas, Unit 1, Reactor Vessel Inlet Nozzle to Safe End Dissimilar Metal Welds (Non-Proprietary)
References
CAW-15-4167, NOC-AE-15003250, RR-ENG-3-17, STI: 34114282 LTR-PAFM-15-27-NP
Download: ML15133A131 (23)

Text

Attachment 1NOC-AE-15003250Attachment 1LTR-PAFM-15-27-NP, Technical Justification to Support Extended Volumetric Examination Intervalfor South Texas Unit 1 Reactor Vessel Inlet Nozzle to Safe End Dissimilar Metal Welds, April 2015(Non-Proprietary). NOC-AE-1 5003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NPTechnical Justification to Support Extended VolumetricExamination Interval for South Texas Unit 1 Reactor VesselInlet Nozzle to Safe End Dissimilar Metal WeldsApril 2015Author: N. L. Glunt*, Piping Analysis and Fracture MechanicsVerifier:A. Udyawar*, Piping Analysis and Fracture MechanicsApproved: J. L. McFadden*, Manager, Piping Analysis and Fracture Mechanics*Electronically approved records are authenticated in the electronic document management system.© 2015 Westinghouse Electric Company LLCAll Rights Reserved* Westinghouse NOC-AE-1 5003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NPFOREWORDThis document contains Westinghouse Electric Company LLC proprietary information and datawhich has been identified by brackets. Coding (ac,e) associated with the brackets sets forth thebasis on which the information is considered proprietary. These codes are listed with theirmeanings in WCAP-7211 Revision 6 (March 2015), "Proprietary Information and IntellectualProperty Management Policies and Procedures."The proprietary information and data contained in this report were obtained at considerableWestinghouse expense and its release could seriously affect our competitive position. Thisinformation is to be withheld from public disclosure in accordance with the Rules of PracticeIOCFR2.390 and the information presented herein is to be safeguarded in accordance with1OCFR2.903. Withholding of this information does not adversely affect the public interest.This information has been provided for your internal use only and should not be released topersons or organizations outside the Directorate of Regulation and the ACRS without the expresswritten approval of Westinghouse Electric Company LLC. Should it become necessary to releasethis information to such persons as part of the review procedure, please contact WestinghouseElectric Company LLC, which will make the necessary arrangements required to protect theCompany's proprietary interests.The proprietary information in the brackets has been deleted in this report, the deletedinformation is provided in the proprietary version of this report (LTR-PAFM-15-27-P Revision0).Page 2 of 22 NOC-AE-1 5003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NP1.0 IntroductionService induced cracking of the nickel-base alloy components and weldments have beenoccurring more and more frequently in recent years, resulting in the need to repair and/or replacethese components. Such cracking and leakage have been observed in the reactor vessel upper andbottom head penetration nozzles as well as the dissimilar metal (DM) butt welds of thepressurizer and reactor vessel nozzles exposed to the high reactor coolant temperatures. ThesePressurized Water Reactor (PWR) power plant field experiences and the potential for PrimaryWater Stress Corrosion Cracking (PWSCC) require reassessment of the examination frequency aswell as the overall examination strategy for nickel-base alloy components and weldments. CodeCase N-770-1 (Reference 1) provides the visual and volumetric inspection guidelines for theprimary system piping DM butt welds to augment the current inspection requirements.In accordance with Code Case N-770-1 guidelines, volumetric examinations are required for theunmitigated DM butt welds at the Reactor Vessel (RV) inlet nozzles every second inspectionperiod not exceeding 7 years. A volumetric examination was previously performed for the SouthTexas Unit 1 reactor vessel inlet nozzle to safe end DM butt welds during the Fall 2009 Re-Fueling Outage (RFO). The next required volumetric examination for the Reactor Vessel inletnozzle DM welds will be during the Fall 2015 RFO in accordance with Code Case N-770- 1. Thisevaluation will determine the impact of performing the volumetric examination on South TexasUnit I during the Spring 2017 RFO. The time interval between the previous Unit I examinationduring the Fall 2009 RFO and the planned examination during the Spring 2017 RFO is 7.5 years,rather than the 7 years allowed by Code Case N-770-1. Therefore, South Texas is seekingrelaxation from the ASME Code Case N-770-1 examination requirement to be able to defer thevolumetric examination to the Spring 2017 RFO. The technical justification to support this reliefrequest is developed in this report based on a flaw tolerance analysis. The objective of the flawtolerance analysis is to determine the largest initial axial and circumferential flaw sizes that couldbe left behind in service and remain acceptable until the next planned inspection. This maximumallowable initial flaw size can then be compared to a flaw size which would have been detectedduring the Fall 2009 RFO inlet nozzle DM weld examination based on the inspection detectioncapability.The following sections provide a discussion of the methodology, geometry, loading and the flawtolerance analyses performed to develop the technical justification for deviating from thevolumetric examination requirements of Code Case N-770-1.Page 3 of 22 NOC-AE-15003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NP2.0 MethodologyIn order to support the technical justification for deferring the volumetric examination from theFall 2015 to Spring 2017 RFO for South Texas Unit 1, it is necessary to demonstrate thestructural integrity of the RV inlet nozzle DM welds subjected to the PWSCC crack growthmechanism. To demonstrate the structural integrity of the DM welds, it is essential to determinethe maximum allowable initial flaw size that would be acceptable in the DM welds for theduration between examinations. This maximum allowable initial flaw size would be the largestflaw size that would remain acceptable until the Spring 2017 RFO. The maximum allowableinitial flaw size for a given plant operation duration can be determined by subtracting the PWSCCcrack growth for that plant operation duration from the maximum allowable end-of-evaluationperiod flaw size, which is determined in accordance with ASME Code Section XI (Reference 2).To determine the maximum allowable end-of-evaluation period flaw sizes and the crack tip stressintensity factors used for the PWSCC analysis, it is necessary to establish the stresses, crackgeometry and the material properties at the locations of interest. The applicable loadings whichmust be considered consist of piping reaction loads acting at the DM weld regions and thewelding residual stresses which exist in the region of interest.The latest piping loads at the reactor vessel inlet nozzle DM weld locations are based on WCAP-9135 (Reference 3). In addition to the piping loads, the effects of welding residual stresses arealso considered. For PWSCC, the crack growth model for the DM weld material is based on thatgiven in MRP-1 15 for Alloy 182 weld material (Reference 4). The nozzle geometry and pipingloads used in the fracture mechanics analysis are shown in Section 3.0. A discussion of the plantspecific welding residual stress distributions used for the DM welds is provided in Section 4.0.The determination of the maximum allowable end-of-evaluation period flaw sizes is discussed inSection 5.0.The maximum allowable initial flaw size will be determined based on the crack growth due to thePWSCC growth mechanism at the RV inlet nozzle DM weld. The PWSCC crack growth iscalculated based on the normal operating temperature and the crack tip stress intensity factorsresulting from the normal operating steady state piping loads and welding residual stresses asdiscussed in Section 6.0. Section 7.0 provides the crack growth curves used in developing thetechnical justification to deviate from the Code Case N-770-1 guidelines by deferring thevolumetric inspection of the RV inlet nozzle DM welds from the Fall 2015 to Spring 2017 RFO.Page 4 of 22 NOC-AE-15003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NP3.0 Nozzle Geometry and LoadsThe DM weld geometry for the South Texas Unit I Reactor Vessel inlet nozzles is based on thenozzle detail drawings (Reference 5). The operating temperature of the reactor vessel inletnozzles is based on customer correspondence. The RV inlet nozzle geometry and normaloperating temperature used in the analysis are summarized in Table 3-1.The piping reaction loads at the RV inlet nozzle DM weld locations are based on WCAP-9135(Reference 3) and are summarized in Table 3-2. These loads are used in determining themaximum allowable end-of-evaluation period flaw sizes and the PWSCC growth.Table 3-1South Texas Unit 1 Reactor Vessel Inlet Nozzle Geometry and Normal OperatingTemperatureDimensionOutside Diameter (in.) 33.05Inside Diameter (in.) 27.47Thickness* (in.) 2.79RV Inlet Nozzle Normal Operating Temperature = 563'F EllNote:El The actual plant operating temperature is in the range of 560-561'F.Table 3-2South Texas Unit 1 Reactor Vessel Inlet Nozzle Piping LoadsForces MomentsLoading (kips) (in-kips)Fx Mx My Mz(Axial) (Torsion) (Bending) (Bending)Deadweight -0.2 -151.1 38.9 -371.2Normal Thermal 20.1 -3253.0 -862.0 -8436.7Upset Thermal 204.5 -4174.3 -2113.9 -9258.8OBE (Operational Basis Earthquake) 326.1 1226.1 2326.2 1802.5SSE (Safe Shutdown Earthquake) 535.6 2688.7 5674.6 5114.7Maximum Pipe Break 1300.2 984.0 12351.1 2387.1Page 5 of 22 NOC-AE-15003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NP4.0 Dissimilar Metal Weld Residual Stress DistributionThe welding residual stresses used in the PWSCC crack growth analysis are determined from thefinite element stress analysis (FEA) in Reference 6 based on the South Texas Unit 1 ReactorVessel inlet nozzle DM weld specific configuration. Figure 4-1 shows a sketch of the SouthTexas inlet nozzle DM weld configuration. The FEA in Reference 6 is based on a two-dimensional axisymmetric model of the inlet nozzle DM weld region. The FEA model geometryincludes a portion of the low alloy steel nozzle, the stainless steel safe end, a portion of thestainless steel piping, the DM weld attaching the nozzle to the safe end, and the stainless steelweld attaching the safe end to the piping. The FEA model also assumes a 3600 inside surfaceweld repair with a repair depth of 50% through the DM weld thickness, which is consistent withMRP-287 guidance (Reference 7). The following fabrication sequence was simulated in the FEAand matches the information provided in the reactor vessel nozzle details drawings (Reference 5):* The inlet nozzle was buttered with weld-deposited Alloy 82/182 material. Nozzle andbuttering are post weld heat treated (PWHT) at 1,100'F." The inlet nozzle was welded to the safe end ring forging using an Alloy 82/182 weld. Theinner diameter of the dissimilar metal weld is machined to finished size." An assumed 50% inside surface weld repair 3600 around the circumference wasconservatively simulated in the Alloy 82/182 weld, which is consistent with MRP-287(Reference 7)." Shop hydrostatic test was then performed at a pressure of 3110 psig and a temperature of3000F." The safe end was then machined for the piping side weld preparation.* The machined safe end was welded to a long segment of stainless steel piping using astainless steel weld.* A plant hydrostatic test was performed at 2485 psig pressure with a temperature of 300'F.* After the plant hydrostatic test, normal operating temperature and pressure was uniformlyapplied three times to consider any shakedown effects, after which the model was set tonormal operating conditions.Based on the FEA model, residual stresses at three different paths (centerline of the DM weld,nozzle side of the DM weld, and safe-end side of the DM weld) in the DM weld were obtained.Additionally, a recommended path was provided, which is a representation of the limiting stressfrom all three paths through the DM weld. This recommended stress axial and hoop stressprofiles were used in the generation of the crack growth charts to determine the maximumallowable initial flaw sizes (Section 7.0). The hoop and axial welding residual stresses for therecommended stress profiles are shown in Figure 4-2.Page 6 of 22 Westinghouse Non-Proprietary Class 3Attachment 1NOC-AE-1 5003250LTR-PAFM- 15-27-NPDDissimilar Metal WeldButterFigure 4-1: South Texas Unit 1 Reactor Vessel Inlet Nozzle DM Weld ConfigurationPage 7 of 22 NOC-AE-15003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NPa,c,eFigure 4-2: Reactor Vessel Nozzle DM Weld Through-Wall Residual Recommended StressProfiles Through DM Weld with 50% Inside Surface Weld RepairPage 8 of 22 NOC-AE-15003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NP5.0 Maximum Allowable End-of-Evaluation Period Flaw SizeDeterminationIn order to develop the technical justification to defer the volumetric examination of the RV inletnozzle DM welds from the Fall 2015 to Spring 2017 RFO, the first step is the determination ofthe maximum allowable end-of-evaluation period flaw sizes. The maximum allowable end-of-evaluation period flaw size is the size to which an indication is allowed to grow to until the nextinspection or evaluation period. This particular flaw size is determined based on the piping loads,geometry and the material properties of the component. The evaluation guidelines andprocedures for calculating the maximum allowable end-of-evaluation period flaw sizes aredescribed in paragraph IWB-3640 and Appendix C of the ASME Section XI Code (Reference 2).Rapid, nonductile failure is possible for ferritic materials at low temperatures, but is notapplicable to the nickel-base alloy material. In nickel-base alloy material, the higher ductilityleads to two possible modes of failure, plastic collapse or unstable ductile tearing. The secondmechanism can occur when the applied J integral exceeds the J~c fracture toughness, and somestable tearing occurs prior to failure. If this mode of failure is dominant, then the load-carryingcapacity is less than that predicted by the plastic collapse mechanism. The maximum allowableend-of-evaluation period flaw sizes of paragraph IWB-3640 for the high toughness materials aredetermined based on the assumption that plastic collapse would be achieved and would be thedominant mode of failure. However, due to the reduced toughness of the DM welds, it is possiblethat crack extension and unstable ductile tearing could occur and be the dominant mode of failure.To account for this effect, penalty factors called "Z factors" were developed in ASME CodeSection XI, which are to be multiplied by the loadings at these welds. In the current analysis forSouth Texas, Z factors based on Reference 8 are used in the analysis to provide a morerepresentative approximation of the effects of the DM welds. The use of Z factors in effectreduces the maximum allowable end-of-evaluation period flaw sizes for flux welds and thus hasbeen incorporated directly into the evaluation performed in accordance with the procedure andacceptance criteria given in IWB-3640 and Appendix C of ASME Code Section XI. It should benoted that the maximum allowable end-of-evaluation period flaw sizes are limited to only 75% ofthe wall thickness in accordance with the requirements of ASME Section XI paragraph IWB-3640 (Reference 2).The maximum allowable end-of-evaluation period flaw sizes determined for both axial andcircumferential flaws have incorporated the relevant material properties, pipe loadings andgeometry. Loadings under normal, upset, emergency and faulted conditions are considered inconjunction with the applicable safety factors for the corresponding service conditions required inthe ASME Section XI Code. For circumferential flaws, axial stress due to the pressure,deadweight, thermal expansion, seismic and pipe break loads are considered in the evaluation.As for the axial flaws, hoop stress resulting from pressure loading is used.The maximum allowable end-of-evaluation period flaw sizes for the axial and circumferentialflaws at the RV inlet nozzle DM welds are provided in Table 5-1. The maximum allowable end-of-evaluation period axial flaw size was calculated with an assumed aspect ratio (flaw length/flawdepth) of 2. The aspect ratio of 2 is reasonable because the axial flaw growth due to PWSCC islimited to the width of the DM weld configuration. For the circumferential flaw, a conservativeaspect ratio of 10 is used.Page 9 of 22 NOC-AE-15003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NPIt should be noted that the resulting maximum allowable end-of-evaluation period flaw sizes werelimited by the ASME Code limit of 75% of the weld thickness for both flaw configurations.Table 5-1Maximum End-of-Evaluation Period Allowable Flaw Sizes(Flaw Depth/Wall Thickness Ratio -a/t)Axial Flaw Circumferential Flaw(Aspect Ratio = 2) (Aspect Ratio = 10)0.75 0.75Page 10 of 22 NOC-AE-15003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NP6.0 PWSCC Crack Growth AnalysisA PWSCC crack growth analysis was performed to determine the maximum allowable initialflaw size that would be acceptable based on ASME Section XI acceptance criteria (Reference 2)for the operating duration from the Fall 2009 to the Spring 2017 RFOs. The maximum allowableinitial flaw size for the given plant operation duration is determined by subtracting the crackgrowth due to PWSCC for the specific plant operation duration from the maximum allowableend-of-evaluation period flaw size shown in Table 5-1.Crack growth due to PWSCC is calculated for both axial and circumferential flaws using thenormal operating condition steady-state stresses. For axial flaws, the stresses included pressureand residual stresses, while for circumferential flaws, the stresses considered are pressure, 100%power normal thermal expansion, deadweight and residual stresses. The input required for thecrack growth analysis is basically the information necessary to calculate the crack tip stressintensity factor (K), which depends on the geometry of the crack, its surrounding structure andthe applied stresses. The geometry and loadings for the nozzles of interest are discussed inSection 3.0 and the applicable residual stresses used are discussed in Section 4.0. Once K, iscalculated, PWSCC growth can be calculated using the applicable crack growth rate for thenickel-base alloy material (Alloy 182) from MRP- 115 (Reference 4). For all inside surface flaws,the governing crack growth mechanism for the RV inlet nozzle is PWSCC.Using the applicable stresses at the DM welds, the crack tip stress intensity factors can bedetermined based on the stress intensity factor expressions from API-579 (Reference 9). Thethrough-wall stress distribution profile is represented by a 4th order polynomial:a = o0+ GC (x/t)+ 02(x/t)2+ 03 (X/t)3+ o4(X/t)4Where:CO, ay, , 2, a3, and 04 are the stress profile curve fitting coefficients;x is the distance from the wall surface where the crack initiates;t is the wall thickness; anda is the stress perpendicular to the plane of the crack.The stress intensity factor calculations for semi-elliptical inside surface axial and circumferentialflaws are expressed in the general form as follows:4KI= Gj (a/c, a/t, t/R,(D)aj (t)jj=oWhere:a = Crack depthc = Half crack length along surfacet = Thickness of cylinderPage 11 of 22 NOC-AE-15003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NPR = Inside radius= Angular position of a point on the crack frontGj = Gj is influence coefficient for jh stress distribution on crack surface (i.e., Go, G1,G2, G3, G4)Q = The shape factor of an elliptical crack is approximated by:Q = 1 + 1.464(a/c)165 for a/c < I or Q = 1 + 1.464(c/a)1.65 for a/c > 1The influence coefficients at various points on the crack front can be obtained by using aninterpolation method. Once the crack tip stress intensity factors are determined, PWSCC crackgrowth calculations can be performed using the crack growth rate below with the applicablenormal operating temperature.The PWSCC crack growth rate used in the crack growth analysis is based on the EPRIrecommended crack growth curve for Alloy 182 material (Reference 4):d-"=exp [ Q " G r- -(K)IP=ep R kT Tref)IWhere:dad = Crack growth rate in m/sec (in/hr)dtQg = Thermal activation energy for crack growth = 130 kJ/mole (31.0kcal/mole)R Universal gas constant = 8.314 x 10s kJ/mole-K (1.103 x 10s kcal/mole-OR)T = Absolute operating temperature at the location of crack, K (OR)Tref = Absolute reference temperature used to normalize data = 598.15 K(1076.67°R)a = Crack growth amplitude= 1.50 x 10-12 at 3250C (2.47 x 10-7 at 6170F)= Exponent = 1.6K = Crack tip stress intensity factor (ksi4in)The normal operating temperature used in the crack growth analysis is 5630F at the RV inletnozzle. It should be noted that the fatigue crack growth mechanism is not considered in the crackgrowth analysis as it is considered to be small when compared to that due to the PWSCC crackgrowth mechanism at the reactor vessel inlet nozzle for the duration of interest. This isdemonstrated by the low fatigue usage factor of 0.00973 at the inlet nozzle location of interest inthe reactor vessel analytical report CENC-1302 (Reference 10). Therefore, it is not necessary toconsider fatigue crack growth in the evaluation.Page 12 of 22 NOC-AE-15003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NPThe PWSCC crack growth rate is highly dependent on the temperature at the location of the flaw,furthermore, the crack growth rate increases as the temperature increases. Therefore, duringperiods when the plant is not in operation, such as refueling outages or shutdowns, thetemperature at the reactor vessel nozzles is low such that crack growth due to PWSCC isinsignificant. Therefore, PWSCC crack growth calculation should be determined for the timeinterval when the plant is operating at full power. The amount of time when the plant is operatingat full power is determined based on previous plant operation data and the anticipated outagesscheduled until the next inspections. This operation duration at full power is referred to asEffective Full Power Days (EFPD), or Effective Full Power Years (EFPY). Plant operation dataand projected future outage dates and durations were provided for South Texas Unit I and areused to estimate the EFPD, or EFPY, between the Fall 2009 to the Spring 2017 RFOs.The determination of the EFPY based on plant operating data is shown in Table 6-1 for SouthTexas Unit 1. It should be noted that the EFPD calculation for future outages conservativelyincludes startup and coast down days. Therefore, based on Table 6-1, for the time intervalbetween the Fall 2009 RFO and Spring 2017 RFO, South Texas Unit I is estimated to operate atfull power for 6.7 EFPY. The values in Table 6-1 are rounded for reporting purposes; the impactof rounding on PWSCC growth is insignificant. The calculated EFPY values will be used in thedetermination of the maximum allowable initial flaw sizes in Section 7.0.Table 6-1Effective Full Power Year Estimation for South Texas Unit 1Cycle Operation Start Operation End EFPD16 11/19/2009 (Fall 2009 RFO) 4/1/2011 486*17 5/9/2011 10/19/2012 528*18 11/28/2012 3/14/2014 443*19 6/2/2014 10/16/2015 501"*20 11/17/2015 1 3/17/2017 (Spring 2017 RFO) 486**Cumulative EFPD 1 2444Cumulative EFPY 1 6.7Notes: *Based on plant operation data.**Estimated based on anticipated outages. Conservatively include startup and coast down days.Page 13 of 22 NOC-AE-15003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NP7.0 Technical Justification for Deferring the Volumetric ExaminationIn accordance with ASME Code Case N-770-1 (Reference 1), the volumetric examinationinterval for the unmitigated reactor vessel inlet nozzle to safe end DM welds must not exceed 7years. South Texas Unit 1 is seeking relaxation from the ASME Code Case N-770-1 requirementin order to defer the volumetric examination of the reactor vessel inlet nozzle to safe end DMwelds from the Fall 2015 to Spring 2017 RFO. Technical justification can be developed tosupport deferring the volumetric examination by calculating the maximum allowable initial flawsize that could be left behind in service and remain acceptable between the inspections. Thismaximum allowable initial flaw size can then be compared to a flaw size which would have beendetected during the Fall 2009 RFO inlet nozzle DM weld examination based on the inspectiondetection capability.The maximum allowable initial flaw depth is determined by subtracting the PWSCC crackgrowth for a plant operation duration of 6.7 EFPY from the maximum allowable end-of-evaluation period flaw depth shown in Table 5-1. The end-of-evaluation period flaw depth iscalculated based on the guidelines given in paragraph IWB-3640 and Appendix C of the ASMESection XI Code (Reference 2). The PWSCC crack growth at the Alloy 82/182 weld is calculatedbased on the normal operating condition, piping loads, and the welding residual stresses at theDM weld as well as the crack growth model in MRP-1 15 (Reference 4). The maximumallowable initial flaw depth was calculated for an axial flaw with an assumed aspect ratio of 2.An aspect ratio of 2 is reasonable for the axial flaw due to the DM weld configuration since anyPWSCC axial flaw growth is limited to the width of the weld. For the circumferential flaw, aconservative aspect ratio of 10 is used in the crack growth analysis.The PWSCC crack growth analysis of the circumferential flaws considered two cases: normaloperating piping loads with residual stresses from the recommended profile (shown in Figure 4-2)and normal operating piping loads without residual stresses in order to obtain the most limitingcrack growth results since a portion of the axial residual stress profile is compressive. It wasdetermined that the case which included only piping loads and no residual stresses was limitingfor circumferential flaws. The exclusion of residual stresses in the evaluation is conservative forthe circumferential flaw evaluation.The PWSCC crack growth curves and the maximum allowable initial flaw sizes for an axial flawand a circumferential flaw are shown in Figures 7-1 and 7-2, respectively. The horizontal axisdisplays service life in Effective Full Power Years, and the vertical axis shows the flaw depth towall thickness ratio (a/t). The maximum allowable end-of-evaluation period flaw sizes are alsoshown in these figures for the respective flaw configurations. Based on the crack growth resultsfrom Figures 7-1 and 7-2, the maximum allowable initial flaw sizes for the axial andcircumferential flaws are tabulated in Table 7-1.Page 14 of 22 NOC-AE-15003250Westinghouse Non-Proprietary Class 3LTR-PAFM-15-27-NPTable 7-1South Texas Unit 1 Maximum Allowable Initial Flaw SizesAxial Flaw Circumferential Flaw(Aspect Ratio = 2) (Aspect Ratio = 10)Maximum Allowable Initial FlawSie(/)0.064 0.376Size (a/t)Flaw Depth (inches) 0.178 1.049Flaw Length (inches) 0.356 10.49The flaw sizes shown in Table 7-1 are the largest axial and circumferential flaw sizes that couldbe left behind in service and remain acceptable from the Fall 2009 to Spring 2017 RFO for SouthTexas Unit 1. In accordance with the Ultrasonic Testing (UT) detection and sizing requirementsin ASME Section XI Appendix VIII, Supplement 10 (Reference 2), the minimum requireddetectable flaw depth is 10% of the wall thickness. Therefore, the maximum allowable initialcircumferential flaw size is above the minimum flaw depth requirement per the UT detectioncapabilities, and thus would have been reasonably detected at the previous inspection of the DMwelds.In addition to the required baseline volumetric UT examination of the RV inlet nozzle DM weld,South Texas also conducted Eddy Current Testing (ET) on the RV inlet nozzle DM welds. TheET examination is an additional means to detecting surface breaking indications on the insidesurface of the DM weld. The South Texas qualification process for the ET procedure is thesame as that of the qualification procedures used for ET used at Farley, which followed thedetails discussed in Reference 11. Per Reference 11, the qualification process and practical trialfor the ET procedure is in accordance with European Network for Inspection Qualification(ENIQ) guidelines. More details are provided in Reference 11, which is a NRC RAI responseprovided by Farley for justification of their ET procedure. Based on the qualification guidelinesas discussed in Reference 11, the Eddy Current examination is capable of detecting fatigue andintergranular stress corrosion cracking (IGSCC)/ interdendritic stress corrosion cracking (IDSCC)cracks as small as 0.04" deep by 0.24" long.The South Texas ET inspection procedure (Reference 13) from Fall 2009 required that anindication with a depth of 0.08" and length of 0.28" or more be recorded. For South Texas Unit1, the maximum initial axial flaw depth is 0.178" and flaw length is 0.356" from Table 7-1, theseparticular flaw dimensions are greater than the South Texas ET flaw depth of 0.08" and flawlength of 0.28". As a result, the calculated maximum allowable initial axial flaw size is largeenough to have been detected during the last Fall 2009 RFO examination of the RV inlet nozzleDM welds at South Texas Unit 1. Similar justification was used in the J.M. Farley Units 1 and 2RV inlet nozzle DM weld alternate inservice inspection relief request for axial initial flaw depthless than 10% of the through-wall thickness. Furthermore, the NRC staff in its response to theFarley relief request (Reference 12) accepted the use of the licensee's ET. qualification processto justify the acceptability for initial flaw sizes less than 10% of the through-wall thickness whensupplemented with volumetric examinations performed by UT as required by the ASME CodeCase N-770- 1.Page 15 of 22 NOC-AE-15003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NPTherefore, the maximum allowable initial axial and circumferential flaw sizes in Table 7-1 wouldhave been detected during the Fall 2009 RFO inlet nozzle DM weld examination. Since, therewere no indications found during the Fall 2009 RFO for the inlet nozzle DM weld, the technicaljustification developed in this letter report can be used to defer the volumetric examination for theSouth Texas Unit I RV inlet nozzle DM welds from the Fall 2015 RFO to the Spring 2017 RFO.Page 16 of 22 Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NP0.80.70.60.50.40.30.20.100 1 2 3 4 5 6 7 8 9 10 11 12Service Life (EFPY)Figure 7-1: PWSCC Crack Growth Curve for South Texas Unit 1 Inlet Nozzle Axial Flaw (DM weld), Aspect Ratio = 2Z0a1~Page 17 of 22 Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NPI.-U0.4JU0.80.70.60.50.40.30.20.100 2 4 6 8 10 12 14 16 18 20 22 24Service Life (EFPY)Figure 7-2: PWSCC Crack Growth Curve for South Texas Unit 1 Inlet Nozzle Circumferential Flaw (DM weld), Aspect Ratio = 10z00CAK) :Page 18 of 22 NOC-AE-15003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NP8.0 Summary and ConclusionsA volumetric examination of the reactor vessel inlet nozzle to safe end DM butt welds wasperformed during the Fall 2009 RFO at South Texas Unit 1. The next required volumetricexamination will be during the Fall 2015 RFO in accordance with Code Case N-770-1. However,the volumetric examination will be deferred to the Spring 2017 RFO for the Reactor Vessel inletnozzle DM welds. Since the time interval between the previous examination and the plannedexamination exceeds 7 years, which deviates from the Code Case N-770-1 inspection intervalrequirements, a relief request will be submitted to the Nuclear Regulatory Commission (NRC)seeking relaxation from the ASME Code Case N-770-1 examination requirement to defer thevolumetric examination of the inlet nozzle DM welds.This letter report provides technical justification to support the relaxation request by performing aflaw tolerance analysis to determine the largest initial axial and circumferential flaws that couldbe left behind in service and remain acceptable between the planned examinations. Thismaximum allowable initial flaw size can then be compared to any flaw size which would havebeen detected during the previous inlet nozzle DM weld examinations.Based on the PWSCC crack growth analysis results from Section 7.0, the maximum allowableinitial flaw sizes for the reactor vessel inlet nozzle DM welds are tabulated in Table 8-1 for SouthTexas Unit 1. These allowable initial axial and circumferential flaw sizes have been shown to beacceptable in accordance with the ASME Section XI IWB-3640 acceptance criteria through theSpring 2017 RFO for Unit 1 taking into account of potential PWSCC crack growth since the lastvolumetric and surface examinations.In accordance with the Ultrasonic Testing (UT) detection and sizing requirements in ASMESection XI Appendix VIII, Supplement 10 (Reference 2), the minimum required detectable flawdepth is 10% of the wall thickness. In addition to the UT examination of the RV inlet nozzle DMweld, supplemental Eddy Current Testing (ET) was performed on the RV inlet nozzle DM weldsfor South Texas Unit 1. Based on the qualification.guidelines as discussed in Reference 11, theEddy Current examination is capable of detecting fatigue and IGSCC/IDSCC cracks as small as0.04" deep by 0.24" long. The South Texas ET inspection procedure (Reference 13) in Fall 2009required that an indication with a depth of 0.08" and a length of 0.28" or more be recorded.Based on the South Texas Unit I results in Table 8-1, the calculated maximum allowable initialaxial flaw size is large enough to have been detected during the last Fall 2009 RFO examinationof the RV inlet nozzle DM welds. Similar justification was used in the J.M. Farley Units 1 and 2RV inlet nozzle DM weld alternate inservice inspection relief request for axial initial flaw sizesless than 10% of the through-wall thickness. Furthermore, the NRC staff in its response to theFarley relief request (Reference 12) accepted the use of the licensee's ET qualification processto justify the acceptability for initial flaw sizes less than 10% of the through-wall thickness whensupplemented with volumetric examinations performed by UT as required by the ASME CodeCase N-770-1. Therefore, deferring the volumetric examination for the South Texas Unit I RVinlet nozzle DM welds from the Fall 2015 RFO allowed by Code Case N-770-1 to the Spring2017 RFO is technically justified.Page 19 of 22 NOC-AE-15003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NPTable 8-1Maximum Allowable Initial Flaw SizesSouth Texas Unit 1Axial Flaw Circumferential Flaw(Aspect Ratio = 2) (Aspect Ratio = 10)Maximum Allowable InitialFlaw Size (a/t)Flaw Depth (inches) 0.178 1.049Flaw Length (inches) 0.356 10.49Note: Aspect ratio = flaw length/flaw depthPage 20 of 22 NOC-AE-15003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NP9.0 References1. ASME Code Case N-770-1,Section XI Division 1. "Alternative Examination Requirementsand Acceptance Standards for Class I PWR Piping and Vessel Nozzle Butt Welds Fabricatedwith UNS N06082 or UNS W86182 Weld Filler Material With or Without Application ofListed Mitigation Activities." Approval Date December 25, 2009.2. ASME Boiler & Pressure Vessel Code, 2004,Section XI, Rules for Inservice Inspection ofNuclear Power Plant Components.3. Westinghouse Report WCAP-9135, Volume 1, Rev. 4, "Structural Analysis of the ReactorCoolant Loop for the South Texas Project Units 1 and 2 Volume I Analysis of the ReactorCoolant Loop Piping (Units I & 2 RSG)," January 2003.4. Materials Reliability Program: Crack Growth Rates for Evaluating Primary Water StressCorrosion Cracking (PWSCC) of Alloy 82, 182, and 132 Welds (MRP-1 15), EPRI, PaloAlto, CA: 2004. 1006696.5. Drawings for South Texas Unit I RV inlet nozzles:a. Combustion Engineering, Inc. Drawing D-11073-128-002, Rev. 0, "Inlet NozzleCladding and Machining."b. Combustion Engineering, Inc. Drawing C-11073-131-001, Rev. 0, "Nozzle SafeEnds."c. Combustion Engineering, Inc. Drawing, E-11073-161-001, Rev. 3, "MaterialIdentification Vessel."d. Combustion Engineering, Inc. Drawing, E- 11073-121-003, Rev. 2, "Upper VesselMachining."6. Dominion Engineering, Inc. Document C-8891-00-01, Rev. 0, "Welding Residual StressCalculation for South Texas Project Units 1 and 2 RPV Inlet Nozzle DMW."7. Materials Reliability Program: Primary Water Stress Corrosion Cracking (PWSCC) FlawEvaluation Guidance (MRP-287), EPRI, Palo Alto, CA: 2010, 1021023.8. Materials Reliability Program: Advanced FEA Evaluation of Growth of PostulatedCircumferential PWSCC Flaws in Pressurizer Nozzle Dissimilar Metal Welds (MRP-216,Rev. 1): Evaluations Specific to Nine Subject Plants. EPRI, Palo Alto, CA: 2007. 1015400.9. American Petroleum Institute, API 579-1/ASME FFS-I (API 579 Second Edition), "Fitness-For-Service," June 2007.10. Combustion Engineering, Inc. Report CENC-1302, "Analytical Report for South TexasProject No. 1 Houston Lighting and Power Company," October 1977.11. Southern Nuclear Company, Inc. Letter NL-14-1193, "Joseph M. Farley Nuclear PlantResponse to Request for Additional Information Regarding Proposed Alternative to InserviceInspection Requirements of ASME Code Case N-770-1," Docket Nos. 50-348 and 50-364,Dated August 1, 2014. (ADAMS Accession Number ML14213A484)Page 21 of 22 NOC-AE-1 5003250Westinghouse Non-Proprietary Class 3LTR-PAFM- 15-27-NP12. United States Nuclear Regulatory Commission Letter Dated December 5, 2014, "Joseph M.Farley, Units 1 and 2, (FNP-ISI-ALT-15, Version 1) Alternative to Inservice InspectionRegarding Reactor Pressure Vessel Cold-Leg Nozzle Dissimilar Metal Welds (TAC Nos. MF3687 and MF3688)." (ADAMS Accession Number ML14262A317)13. WesDyne WDI-STD-146, Rev. 9. "ET Examination of Reactor Vessel Pipe Welds InsideSurface," December 2008.Page 22 of 22