ML13142A032

San Onofre Nuclear Generating Station, Unit 2, Supplement to Response to Request for Additional Information (RAI 70) Regarding Confirmatory Action Letter

ML13142A032
Person / Time
Site:	San Onofre
Issue date:	05/20/2013
From:	St.Onge R J Southern California Edison Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC ME9727
Download: ML13142A032 (12)

Text

SOUTHERN CALIFORNIA Richard 1. St. OngeEDISObNJ Director, Nuclear Regulatory Affairs andL.. ON Emergency PlanningAn EDISON INTERNATIONAL CompanyMay 20, 201310 CFR 50.4U.S. Nuclear Regulatory CommissionATTN: Document Control DeskWashington, DC 20555-0001Subject: Docket No.50-361Supplement to Response to Request for Additional Information (RAI 70)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 24. Email from Mr. James R. Hall (USNRC) to Mr. Ryan Treadway (SCE), datedMarch 15, 2013, Request for Additional Information (RAIs 68-72) RegardingResponse to Confirmatory Action Letter, San Onofre Nuclear GeneratingStation, Unit 25. Letter from Mr. Richard J. St. Onge (SCE) to Document Control Desk(USNRC), dated April 1, 2013, Response to Request for Additional Information(RAIs 68, 69, 70 and RAI 2 Revision 1) Regarding Confirmatory Action LetterResponse, San Onofre Nuclear Generating Station, 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 e-mail dated March 15, 2013 (Reference 3), the NRC issued Requests for AdditionalInformation (RAIs) regarding the CAL response. SCE provided the response to RAIs 68, 69, 70,and RAI 2 Revision 1, in a letter dated April 1, 2013 (Reference 4). Enclosure 1 of this letterprovides a supplement to the RAI 70 response.P.O. Box 128San Clemente, CA 92672 Document Control Desk-2-May 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.Enclosure:1. Supplement to RAI 70 responsecc:A. T. Howell IIl, 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 EDISONSUPPLEMENT TO THE RESPONSE TO REQUEST FOR ADDITIONALINFORMATIONREGARDING RESPONSE TO CONFIRMATORY ACTION LETTERDOCKET NO. 50-361TAC NO. ME 9727Supplement to RAI 70 Response RAI 70Reference 1, Response to RAI 2 -It is unclear to the staff how TTW initiation times werecalculated (see description on pages 4 and 5 (of 18)). Describe each individual step, insequential order, to calculating TTVV initiation time for a given tube, for a given trial. Provide (orreference) in figure form all distributions that were sampled.RESPONSE SUPPLEMENTNote: RAI Reference 1 is SCE's "Response to Request for Additional Information (RAIs 2, 3,and 4) Regarding Confirmatory Action Letter Response," dated February 25, 2013. SCEresponded to RAI 70 via letter "Request for Additional Information (RAI 70) RegardingConfirmatory Action Letter Response," dated April 1, 2013. This response supplementdemonstrates the process explained in the response to RAI 70.Single Trial Calculation of Initiation Time for Tube R92 C84 in 3E-088The purpose of this discussion is to provide further details into how the initiation time iscalculated using a bi-linear wear index model, which represents the tube conditions before andafter in-plane instability. It presents an example calculation in the context of the analyticalprocedure given in RAI 70 response. Also discussed is the determination of the anti-vibrationbar (AVB) wear rates at tube contact locations.Figure 1 shows the calculation of tINIT for a single trial. Tube R92 C84 in 3E-088 was chosen toshow the calculation procedure. The analysis variables are shown to aid in the description ofthe probabilistic solution for TTW initiation time and the numerical calculations. The importantpoints on the wear index lines are labeled A through E.Governing EquationsThe equation that defines the initiation time isMP-U -WIR2 tcYcWIR1 -WIR2Where: EOP is the end of the operating period for Unit 3, andtINIT is the initiation time (Figure 1 Point B)MOP-US is the wear index at EOP from AVB wear in the upper supports (Figure 1Point D)WIR1is the growth rate in the WIAVB-US prior to initiation (slope of Line AB in Figure 1)Page 2 of 10 WIR2 is the growth rate in the WIAvE-us after initiation (slope of Line BD in Figure 1)tcyc is the length of the operating period (0.926 years at power)Equation 1 is the solution for the intersection of the two lines (AC and ED) and defines the timein the operating period when the change in the upper support wear index slope due to in-planeinstability occurs. Point B in Figure 1 represents the calculated initiation time as determined bythe model.The growth in the wear indices in the AVB upper supports before in-plane instability (WIR1) andafter in-plane instability (WIR2) are calculated from the following:... [WRAB-us]i (2)WIR2 E=1 AN=N r' AIRPOstWIR2... AVB-[us]i (3)AIPr e adI~swhere ....AB-US and rAVBus are the cumulative distribution functions (CDF) for the AVBwear rates derived from wear depth data for tubes without TTW and with TTW. The variable N1is the number of AVB upper-support locations in the tube before in-plane instability. Theparameter N2 is the number of AVB upper-support locations with detected wear in the tube after0.926 years at power.Analysis InputFor Tube R92 C84 in 3E-088, the following input data are known from the Cycle 16 inspectionresults and used in the simulation to determine Line ED in Figure 1.1) Total number of AVB upper support locations having detected wear after 0.926 yearsat power is seven, N2 = 7.2) Wear index due to AVB wear in upper supports after 0.926 years at power,WEOPUS = 82% TW (Figure 1 Point D).The following variables that are treated statistically and used to determine Line AC:1) Number of AVB upper support locations before in-plane instability (N1) is randomlypicked from Poisson distribution in Figure 2 based on tubes with no TTW.2) AVB wear rates before and after in-plane instability are randomly selected from thedistributions in Figure 3.AVB Wear RatesThe AVB wear rates for the upper supports (B03 through B10) were determined by dividing theAVB wear depths by the 0.926 years at power. The technical basis for using the full operatinginterval of 0.926 years at power to establish the AVB wear rates was discussed in the responseto RAI 2 with supporting data given in RAI 68. As shown in Figure 4, the AVB upper supportPage 3 of 10 wear depths in tubes are not significantly dependent on whether in-plane instability hadoccurred or not. Final AVB wear depths for tubes with TTW are similar to the final wear depthsfor tubes without TTW including the upper extreme values. The average wear depth for tubeswith TTW is 10.1% TW with a maximum depth of 37% TW. For tubes without TTW, the averagedepth is 8.9% TW and the maximum is 36% TW. This indicates that the wear rates at individualtube/AVB contact points before in-plane instability are not significantly elevated after TTW hasinitiated.It is appropriate to use 0.926 years at power to develop AVB wear rates for conditions prior toin-plane instability (tubes without TTW) since it is reasonable to assume that AVB wear in thesetubes began at the start of Cycle 16. Since the AVB depths in tubes with TTW include AVBlocations that existed before in-stability, it is also reasonable to assume that these locationsmake up the upper tail for the distribution of wear rates shown in Figure 4. Given the depthdistribution comparison shown in Figure 4, the interval 0.926 years at power was used todetermine the CDF for AVB wear rates for conditions following in-plane instability. The post-initiation curve was used to calculate the wear index rate WIR2 since this will result in a steeperslope for Line BD and a longer initiation time to be calculated in the simulation.Procedure to Calculate TTW Initiation TimeFor the example trial, the following calculations were performed for Tube R92 C84:1.0 Determination of N11.1 At the start of a trial, the number of AVBs is selected by a random pick from thePoisson distribution developed from the number of affected AVBs observed in tubeswithout TTW. This CDF is given in Figure 2. Both Unit 3 steam generators havesimilar distributions and these data were combined to obtain the mean parameter forthe Poisson distribution.1.2 For this trial for Tube R92 C84, a random pick from the CDF in Figure 2 gave fourAVBs in the upper supports as having wear commencing at the start of Cycle 16.Therefore, N1 = 4 which meets the criteria that 0 < N1 < N2.2.0 Determination of WIR,2.1 The wear index growth rate before instability is calculated by summing the individualAVB wear rates from the upper supports using Eq. 2. The AVB wear rates aredetermined by N1 random selections from the AVB wear rate distribution in Figure 3(pre-initiation curve). For N, = 4, the growth in the wear index before tube instability(WIRj) isWIal 4 [Wi PreWR E= [WAvBUS]iPage 4 of 10 Four random selections from the AVB wear rate CDF in Figure 3, pre-initiation curvegives,WIR1 = 12.2 + 8.8 + 6.6 + 16.8 = 44.4% TW per years at powerThe equation for Line AC is WIAVB-US = 44.4 t.3.0 Determination of WIR23.1 The wear index growth rate after instability is calculated by summing the individualAVB wear rates using Eq. 3. The AVB wear rates are determined by N2 randomselections from the AVB wear rate distribution in Figure 3 (post-initiation curve).3.2 Since N2 = 7 for Tube R92 C84, the growth in the wear index after tube instability(WIR2) isn7 DPost 1WIR2 i=1 JiSeven random selections from the AVB wear rate in Figure 3, post-initiation curvegivesWIR2 = 14.8 + 9.8 + 7.6 + 16.8 + 14.2 + 12.6 + 20.7 == 96.5 %TW per years at power3.3 The intercept point (Figure 1 Point E) is calculated from the expressionPointE ..AVB-us -WIR2 tcYc = 82%TW -96.5 (0.926) = -7.36 %TW3.4 Point E for this trial meets the criterion that the intercept is less than zero. Thisrequirement ensures the slope for Line ED is always greater than or equal to theslope for Line AD (WIR2 > WIRj). If Point E > 0, the AVB growth rates would be re-sampled and WIR2 recalculated from Eq. 3 to satisfy this constraint.The equation for Line ED is WIAVB-US = 96.5 t -7.36Page 5 of 10 4.0 Calculation of Initiation TimeFrom Eq. 1, the initiation time for this trial for Tube R92 C84 istINIT 82-96.5(0.926) -7.36 =0.141 years at power44.4-96.5 -52.1The above calculation is repeated 1000 times for 1000 trials per tube. The 1000 initiationtimes (tINIT) are ranked in ascending order and the median value (500th in ranking) isrecorded.Page 6 of 10 Variable Initiation-Time Trial For Tube R92 C84 in 3E-088140ca0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Operation Time, t (Years at Power)Figure 1 -TTW Initiation-Time Calculation Example for One TrialPage 7 of 10 Unit 3 AVB Distribution for Tubes without TTW10008 0 =Cumulative Distribution800700600C)500-0 400300200100000 1 2 3 4 5 6 7 8 9 10 11 12Number of AVBs1.00.90.8U-0.7 0CF0.6 .2.00.40.5000.4 >0.3 E0.20.10.0Figure 2 -Distribution of Affected AVBs in Unit 3 for Determining N,Page 8 of 10 Unit 3 AVB Wear RatesU-I.2CU-CE..6Q°UEC.,1.00.90.80.70.60.50.40.30.20.10.00 5 10 15 20 25 30AVB Wear Rate, %TW per Years at Power35 40Figure 3 -Log-Normal AVB Upper Support Wear Rate Distributions for Unit 3Page 9 of 10 Unit 3 AVB Wear Depths -Upper SupportsL-a0dU.a0EUJ1.00.90.80.70.60.50.40.30.20.10.00 5 10 15 20 25 30 35 40NDE Depth, (%TW)Figure 4 -Wear Depths for Tube/AVB Contacts at the Upper Supportsafter 0.926 Years at PowerPage 10 of 10