ML13028A475

San Onofre, Unit 2 - Response to Request for Additional Information (RAI 27) Regarding Confirmatory Action Letter

ML13028A475
Person / Time
Site:	San Onofre
Issue date:	01/25/2013
From:	St.Onge R J Southern California Edison Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC ME9727
Download: ML13028A475 (4)

Text

SOUTHERN CALIFORNIAEDISONAn EDISON INTERN4TIONA4L& CompanyRichard 1. St. OngeDirector, Nuclear Regulatory Affairs andEmergency PlanningJanuary 25, 201310 CFR 50.4U.S. Nuclear Regulatory CommissionATTN: Document Control DeskWashington, DC 20555-0001Subject:Docket No. 50-361Response to Request for Additional Information (RAI 27)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 27.P.O. Box 128San Clemente, CA 92672 Document Control Desk-2-January 25, 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,Enclosures:1. Response to RAI 27cc: E. E. Collins, Regional Administrator, NRC Region IVR. 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 27Page 1 of 2 RAI 27Reference 6, Appendix 8, "SG Tube Flowering Analysis", page 8-2 (307 of 474) -MHIconcludes, in part, that the tube-to-AVB gaps in the center columns increase due tohydrodynamic pressure by [ ... ] when the manufacturing tolerance dispersion is not taken intoaccount. MHI also concludes that the gap increase due to hydrodynamic pressure is smallwhen the manufacturing tolerance dispersion is taken into account. Discuss whether this latterfinding may simply reflect the hydrodynamic pressures acting to relieve the tube-to-AVB contactforces caused by the manufacturing tolerance dispersion, such that the gaps are relativelyunchanged relative to the case where the hydrodynamic pressure is not considered.Reference 6, Appendix 9, "Simulation of Manufacturing Dispersion for Unit-2/3," does not seemto make specific mention of whether the calculated tube-to-AVB contact forces directlyconsidered the effect of the hydrodynamic effect on tube-to-tube contact forces, but the staffunderstands that they did not. If the staffs understanding is correct, explain how the resultingcontact forces are conservative.RESPONSENote: RAI Reference 6 is MHI Document L5-04GA564, Tube Wear of Unit-3 RSG -TechnicalEvaluation Report, Revision 9, October 2012, prepared by Mitsubishi Heavy Industries, LTD.(ADAMS Accession Nos. ML12285A265, ML12285A266, and ML12285A267).The staffs understanding is correct: the contact force analysis contained in RAI Reference 6,Appendix 9 does not consider the effect of hydrodynamic forces. Since hydrodynamic forcesare very small in comparison to contact forces they were not included in the contact forceanalysis. To demonstrate this, a sensitivity study was performed in response to this RAI.This study compared the probability of occurrence of in-plane fluid-elastic instability (FEI) for twocases: (1) contact force distribution including hydrodynamic forces and manufacturingdispersion and (2) contact force distribution based on manufacturing dispersion alone. For the70% power condition, there was no statistically significant increase in the probability of in-planeFEI when hydrodynamic forces were included.The consideration of hydrodynamic forces results in a slight reduction of average contact forceat 70% power, but the tube-to-support gaps are relatively unchanged. Hydrodynamic forces arepostulated to have little effect on tube-to-support gaps due to their low estimated magnitude.The sensitivity study performed for this RAI response determined there is no statisticallysignificant increase in the probability of in-plane FEI when the effects of hydrodynamic forcesare included in the analysis.Page 2 of 2