ML13038A010

San Onofre Nuclear Generating Station, Unit 2, Response to Request for Additional Information (RAI 8) Regarding Confirmatory Action Letter Response (TAC ME9727)

ML13038A010
Person / Time
Site:	San Onofre
Issue date:	02/04/2013
From:	St.Onge R J Southern California Edison Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC ME9727
Download: ML13038A010 (4)

Text

J j SOUTHERN CALIFORNIAA EDISONAAn EDISON INTERNATIONAL CompanyRichard J. St. OngeDirector, Nuclear Regulatory Affairs andEmergency PlanningFebruary 4, 201310 CFR 50.4U.S. Nuclear Regulatory CommissionATTN: Document Control DeskWashington, DC 20555-0001Subject:Docket No. 50-361Response to Request for Additional Information (RAI 8)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. Letter from Mr. James R. Hall (USNRC) to Mr. Peter T. Dietrich (SCE), datedDecember 26, 2012, Request for Additional Information Regarding Responseto Confirmatory Action Letter, 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 letter dated December 26, 2012 (Reference 3), the NRC issued Requests for AdditionalInformation (RAIs) regarding the CAL response. Enclosure 1 of this letter provides theresponse to RAI 8.P.O. Box 128San Clemente, CA 926726 -ýýýKk Document Control Desk-2-February 4, 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 RAI 8cc: 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 RAI 8Page 1 of 2 RAI 8It is stated in Reference 4, page 4-6, second paragraph that, "It has been observed that thenumber of AVB supports that develop wear in the second cycle of operation can increasedependent on the number of worn AVB indications at the beginning of the second cycle. Thesedata were used in the OA to add AVB locations at the start of Cycle 17 from a statisticalrepresentation of this data." Provide a more complete description of the model used to add AVBlocations that will develop wear during the second cycle. Confirm that this model applies to boththe 560 tubes with existing tube support wear and the 1350 NDD tubes.RESPONSENote: RAI Reference 4 is the "Operational Assessment for SONGS Unit 2 SG for Upper BundleTube-to-Tube Wear Degradation at End of Cycle 16," prepared by Intertek APTECH for Areva,Report No. AES 12068150-2Q-1, Revision 0, September 2012.The inspection results from a similar replacement steam generator (RSG) unit were used toestablish the probability of having new wear locations in a tube with prior anti-vibration bar(AVB) wear after completing the second (full) cycle of operation subsequent to generatorreplacement. The algorithm for SONGS Unit 2 conservatively assumes any new wear locationsinitiate at the start of the next cycle of operation, although in reality, new wear locations maydevelop at various times during the cycle.New tube to AVB wear locations are assigned using a statistical model. The data for the modelcame from a similar RSG two-loop design of comparable size with more than two operatingcycles. Because of the similar U-bend support structure, the data were considered applicable toSONGS. A difference between the two units is the number of AVB supports (eight versus 12bars for SONGS steam generators). Most support of the U-bend for SONGS comes from theinner eight AVBs. Little to no tube to AVB wear is observed in the outer support locations priorto TTW. Since the two units are similar in the number of active supports, normalizationbetween the two designs was not required for assigning new wear locations.The data defining the increase in the number of tube to AVB contact locations are wellrepresented by Poisson distribution functions. The parameters for the Poisson distribution weredeveloped by standard regression analysis. The Poisson distribution was selected because it isa single parameter function and is a good representation for distributions of integer variablessuch as the number of AVBs.Cumulative distribution functions (CDF) were developed from the fitted Poisson distributions.Each CDF is dependent on the number of wear locations that exist in a given tube at the end ofthe first cycle of operation. These CDFs were sampled at the start of the next cycle of operationfor each trial in the Monte Carlo simulation and new locations were added to each tubeaccordingly. The CDFs representing new wear sites are based on 100% power for thesimilar RSG over the full 2nd cycle of operation. No credit was taken for operation at 70%power for the five month operating interval when assigning new wear sites, making thisapproach conservative.This method was implemented for the 560 tubes with existing tube support wear. The group of1350 tubes with no detected wear used a different method for assigning wear locations at thestart of the next operating cycle as described in the response to RAIs 5 and 7.Page 2 of 2