ML13190A030

Cooper - Response to Request for Additional Information Regarding Core Plate Hold Down Bolt Stress Analysis

ML13190A030
Person / Time
Site:	Cooper
Issue date:	07/03/2013
From:	Limpias O A Nebraska Public Power District (NPPD)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NLS2013065, TAC ME9550
Download: ML13190A030 (15)

Text

{{#Wiki_filter:Nebraska Public Power DistrictAlways there when you need us50.90NLS2013065July 3, 2013U.S. Nuclear Regulatory CommissionAttn: Document Control DeskWashington, D.C. 20555-0001

Subject:

Response to Request for Additional Information Regarding Core Plate HoldDown Bolt Stress AnalysisCooper Nuclear Station, Docket No. 50-298, DPR-46

Reference:

1. Letter from Lynnea E. Wilkins, U.S. Nuclear Regulatory Commission, toOscar A. Limpias, Nebraska Public Power District, dated May 24, 2013,"Cooper Nuclear Station -Request for Additional Information Re: Core PlateHold Down Bolt Stress Analysis (TAC No. ME9550)"2. Letter from David W. Van Der Kamp, Nebraska Public Power District, toU.S. Nuclear Regulatory Commission, dated January 16, 2012, "Completionof License Renewal Commitment NLS2009100-1 (Revision 1)"(NLS2012002)

Dear Sir or Madam:

The purpose of this letter is for the Nebraska Public Power District (NPPD) to respond to thesubject Nuclear Regulatory Conmmission (NRC) Request for Additional Information (RAI)(Reference 1). These RAIs were issued in regards to the Core Plate Rim Bolt Analysis providedin Reference 2. Attachment 1 provides the proprietary responses, and Attachment 2 provides anon-proprietary version of the RAI responses. On behalf of General Electric Hitachi (GEH),NPPD requests that Attachment I be withheld from public disclosure in accordance with 10 CFR2.390. The address for GEH is:3901 Castle Hayne RoadWilmington, NC 28401There are no commitments made in this submittal.Should you have any questions concerning this matter, please contact Dave Bremer, CooperNuclear Station (CNS) License Renewal Implementation Project Manager, at (402) 825-5673.COOPER NUCLEAR STATIONP.O. Box 98 / Brownville, NE 68321-0098Telephone: (402) 825-3811 / Fax: (402) 825-5211www.nppd.com A0 NLS2013065Page 2 of 2I declare under penalty of perjury that the foregoing is true and correct.Executedon c7 o03/p2,(Date)Sincerel('\Os ar~ kLimppiasVice President -N Lclear andChief Nuclear OfficerOAL/wvAttachments: 1. Response to Request for Additional Information Regarding Core Plate HoldDown Bolt Stress Analysis (Proprietary)2. Response to Request for Additional Information Regarding Core Plate HoldDown Bolt Stress Analysis (Non-Proprietary)

Enclosure:

Proprietary Affidavit for RAI Responsescc: Regional Administrator w/ Attachment 2 and EnclosureUSNRC -Region IVCooper Project Manager w/ Attachments and EnclosureUSNRC -NRR Project Directorate IV-ISenior Resident Inspector w/ Attachment 2 and EnclosureUSNRC -CNSNPG Distribution w/o Attachments or EnclosureCNS Records w/ Attachments and Enclosure NLS2013065Attachment 2Page 1 of 9Attachment 2Response to Request for Additional Information RegardingCore Plate Hold Down Bolt Stress Analysis (Non-Proprietary)The Nuclear Regulatory Commission (NRC) request for additional information (RAI) containedtwo sets of questions, one non-proprietary and one proprietary regarding the Cooper nuclearStation (CNS) Core Plate Hold Down Bolt Stress Analysis. Both sets are responded to in thisattachment. To distinguish the question numbering, the non-proprietary RAIs will be given an"NP-" designator, and the proprietary RAIs will be given a "P-" designator. The questions areshown in italics. The Nebraska Public Power District (NPPD) response to the supplementalrequest is shown in block font. Redacted information is denoted by double brackets ([[ ]]).NRC Request -Question NP-1The example stress analysis provided in the Boiling Water Reactor Vessel and Internals Project(B WR VIP)-25, "B WR Core Plate Inspection and Flaw Evaluation Guidelines," is based on anelastic finite element analysis of the core plate and core plate hold down bolts. The informationprovided in NEDC-33674P, Revision 0, does not state what type of analysis was performed todemonstrate that the CNS core plate hold down bolts (core plate bolts) will remain structurallyadequate throughout the PEO, considering a potential loss ofpreload. Please confirm that thestress analyses performed in NEDC-33674P are consistent with the approach assumed inB WR VIP-25 (i.e., elastic finite element analysis).NPPD ResponseThe stress analysis performed in NEDC-33674P was not based on finite element analysis (asexplained in the subsequent RAI responses), but is still consistent with the approach used inBWRVIP-25, Appendix A, (differences are listed in Section 8.1 of the report) and uses linearelastic calculations.NRC Request -Question NP-2Section 2.0 of NEDC-33674P notes that a portion of the CNS plant-specific data was notavailable for this analysis and, subsequently, scaled data from Appendix A ofBWRVIP-25 wasused in lieu ofplant-specific data. Please state what CNSplant-specific data was not availableand what corresponding data was used from BWRVIP-25. Further, please provide a technicaljustification demonstrating that the alternative data provides a sound basis for determining thatthe core plate bolts will remain structurally adequate during the PEO.NPPD ResponseScaling was only performed for initial calculations and qualitative comparisons. All CNS-specific data required for the evaluation (and creation of Table 8-1) were available and the NLS2013065Attachment 2Page 2 of 9results do not depend on any scaled data. Details regarding the scaling that was performed forcomparison calculations are described below.In BWRVIP-25, Appendix A, Scenario 2, the force exerted on the highest-loaded aligner pin wasdetermined from Finite Element Analysis (FEA) and the pure shear was calculated for thisaligner pin (see the Question NP-4 Response for additional detail). From this, one can calculatethe percentage that this aligner pin resists compared to the total horizontal load (the other pinstaking the remainder).The CNS evaluation did not utilize a plant-specific finite element model (it was not necessary).Therefore, it was not possible to obtain the force on the highest-loaded aligner pin in the samemanner as the BWRVIP-25, Appendix A, example. For comparison purposes only, the CNSevaluation initially utilized the same percentage as the Appendix A example to determine theforce on the highest-loaded pin. However, because of the difference in aligner pin geometry andits questionable effect on the validity of FEA-scaling, the calculation was updated as described inSection 7.2.2 of the evaluation (and the Question NP-4 Response below). This was moreconservative and did not depend on scaled results. Therefore, the results of the CNS evaluationdo not depend on scaling, which was only used during initial calculations and qualitativecomparisons.NRC Request -Question NP-3Section 7.1 of NEDC-33674P discusses the preload which was accounted for in the CNS coreplate bolt stress analyses. This section notes that the original preload for each bolt was 300 plusor minus 25foot-pound force (ft-lbJ). However, no references are provided regarding the basisfor this value. Please provide the basis for the value of the preload assumed in this analysis.NPPD ResponseThe reference for the value of preload is from Note 5 in General Electric Hitachi (GEH) drawing(197R576, Revision 9). Both the minimum and maximum values of preload were used duringthe analysis, reduced by fluence and thermal relaxation as described in Sections 6.7 and 6.8 ofthe report.NRC Request -Question NP-4Section 8.1 of NEDC-33674P notes that the analysis performed for CNS core plate boltscalculate the shear loads on the core plate aligner pins using a different method than that usedin B WR VIP-25 due to the variance in aligner pin configurations. Please describe the methodused to calculate the shear loads for the CNS core plate aligner pins and provide a technicaljustification for this deviation from B WR VIP-25, which demonstrates that the alternative methodprovides an accurate means to evaluate the shear stresses imposed on the aligner pins. NLS2013065Attachment 2Page 3 of 9NPPD ResponseThe aligner pin configuration of CNS (Figures NP-4.1 and NP-4.2) is different than the plantused in the BWRVIP-25, Appendix A, example (Figure NP-4.3). Both include four assembliesand resist load mainly in shear. However, the CNS aligner pins are horizontal instead of vertical.For both configurations, the most limiting direction of applied horizontal load will engage atleast three of the four aligner pin assemblies (in Scenario 2, all the horizontal load is assumed tobe taken by the aligner pins).In the BWRVIP-25, Appendix A, calculation, the maximum horizontal load on a single pin was[[ ]] (by FEA calculation) out of approximately [[ ]] total horizontal load. The ratio of worstpin load to the total horizontal load is [[ ]]. The aligner pin diameter of that example was [[]]. The maximum pure shear of one pin was calculated, E[ ]]. The three remaining pinsresisted the rest of the load.For CNS, the horizontal load is [[ ]]. Using the same ratio of pin load to total load as theBWRVIP-25, Appendix A, calculation [[ ]] resulted in a shear stress of [[ ]]. However, dueto the difference in aligner pin configuration, it was ultimately decided to use non-scaled results.Therefore, a more conservative calculation was performed E[ ]], as shown in Table 8-1 ofNEDC-33674P. NLS2013065Attachment 2Page 4 of 9Figure NP-4.1[[l NLS2013065Attachment 2Page 5 of 9Figure NP-4.2: CNS Aligner Pin Lug ConfigurationFdFigure NP-4.3: BWRVIP-25, Appendix A, Aligner Pin ConfigurationEr NLS2013065Attachment 2Page 6 of 9NRC Request -Question NP-5Section 8.1 of NEDC-33674P provides the results of the stress analyses of the CNS core platebolts for three distinct scenarios. For each scenario, the bolt stress levels were comparedagainst applicable allowable stress values prescribed by the American Society of MechanicalEngineers Boiler and Pressure Vessel Code (ASME Code), depending on the service levelconsidered (i.e., Normal, Upset, Emergency or Faulted). The construction of the core plateresults in an uneven distribution of the resultant horizontal and vertical loads supported by thecore plate bolts. However, the results presented in Section 8.1 of NEDC-33674P do not specifywhether these results apply to the limiting CNS core plate bolt(s). Please confirm that the resultspresented in this section of NEDC-33674P correspond to the limiting core plate bolt(s) (i. e.,those which support the greatest horizontal and/or vertical loads) and demonstrate that theselimiting core plate bolt(s) meet the applicable ASME Code allowable stress values. If the resultspresented in NEDC-33674P do not correspond to the limiting core plate bolts, please present theresults of the stress analyses for the limiting core plate bolt(s) which demonstrate that thestresses induced in the limiting core plate bolts meet the applicable ASME Code allowable stressvalues.NPPD ResponseThe evaluation supporting NEDC-33674P did not calculate individual core plate bolt stresses,which would have required the development of a finite element model or very detailed handcalculations. This detail was unnecessary. Rather, a conservative alternative approach was usedthat determined the average stress values, consistent with the example presented in BWRVIP-25,Appendix A, and also consistent with industry practice when demonstrating ASME Codecompliance for linear elastic analyses. Using the BWRVIP-25, Appendix A, approach providedconservative results which bounded the individual bolt stresses, assuring the actual individualbolt stresses are below the ASME Code allowable stress values. This approach providesreasonable and conservative assurance that all bolts will meet all postulated design basis loadingconditions. The CNS evaluation applied the same methodology as BWRVIP-25, Appendix A,by using the average stress for the core plate bolt analysis. This is explained in more detail in thefollowing paragraphs.Figure A-3 in BWRVIP-25, Appendix A, shows a specious variation in core plate bolt force.Variation does exist [[ ]]. However, this figure only depicts forces from externally-appliedvertical loads. The total load in a core plate bolt is the fluence- and thermally-relaxed preloadplus only a portion of the external loads. Figure A-3 does not include the internal force due topreload and assumes the entirety of the external load is carried by the bolts. If the example's [[]] internal force due to preload were added to the bolts, the [[ ]] maximum variation in boltvertical force as compared to the average would be reduced by more than half. This, however,still assumes all of the external load transfers to the bolts.Joint-to-fastener participation effects were not included in Figure A-3 [[ ]] Realistically, themajority of the externally-applied vertical load will go into reducing the clamping force on theclamped components (the core plate rim in this case) with a smaller portion going into increasing NLS2013065Attachment 2Page 7 of 9the force in the fastener (the core plate bolt). [[ ]] Therefore, the already-reduced variationdiscussed in the above paragraph will be further reduced. This will bring the variation of boltforce for the BWRVIP-25, Appendix A, example down [[ ]], such that the total bolt force islower than that used in the Pm calculation. For CNS, the variation is even smaller because [[ ]]Ergo, in Scenarios 1 and 3, the average bolt force used in the BWRVIP-25, Appendix A,example and in the CNS evaluation is greater than the realistic maximum (including the locationvariation) total bolt force when participation effects are considered.NRC Request -Question P-1[[ ]1NPPD ResponseA fast neutron fluence evaluation was performed by TransWare Enterprises, Inc. for CNS usingthe BWRVIP Radiation Analysis Modeling Application (RAMA) methodology. The analysiswas accepted by NPPD via NEDC 07-033, Revision IC I (Note: NEDC 07-032 referenced in theGEH analysis is a typographical error that should have stated NEDC 07-033). The RAMAmethodology has been reviewed by the NRC and subsequently given generic approval fordetermining fast neutron fluence in BWR pressure vessels' and vessel internal components thatinclude the core shroud and top guide2.An axial fluence profile for the peak core support platerim bolt was calculated for energy >1 MeV at the end of the CNS extended design life of 54Effective Full Power Years.The peak rim bolt was determined to reside at the 37.5-degree location. The rim bolt has aheight of about 25.5 inches, extending from approximately 177.59 inches to 203.09 inchesrelative to vessel zero. The evaluation predicted the fluence to range from a value of 1.63E+20n/cm2 near the top of the bolt (closest to the fuel) to 1.1 5E+l 7 n/cm2 near the bottom of the bolt(farthest from the fuel).NRC Request -Question P-2[[ 11See letter from William H. Bateman (NRC) to Bill Eaton (BWRVIP), dated May 13, 2005,regarding the Safety Evaluation of BWRVIP- 114, -115, -117, and -121, and TWE-PSE-001 -R-001.2 See letter from Matthew A. Mitchell (NRC) to Rick Libra (BWRVIP), dated February 7, 2008,regarding the Safety Evaluation of BWRVIP- 145. NLS2013065Attachment 2Page 8 of 9NPPD ResponseThe fluence range on which the BWRVIP-25 loss of preload range was based is 0 nlcm2 (allrelaxation due to thermal effects) to 8E 19 n/cm2 (E> 1 MeV).NRC Request -Question P-3[[ 1NPPD ResponseNPPD performed Visual Test (VT)-3 examinations in Reload (RE) 19 (Spring 2000) from the topside of the bolts on forty-eight (48) bolts with no recordable indications.In 2010, the BWRVIP issued revised interim guidance to the BWR fleet requiring plants todevelop and submit a technical justification in the form of a Deviation Disposition to theBWRVIP since the inspection guidance of BWRVIP-25 could not be met. No techniques arecurrently available to perform an Ultrasonic Test (UT) volumetric examination of the boltingabove the core plate. It was also determined that the enhanced VT-I visual examination belowthe core plate would not provide meaningful results since the bolt threads would not be visiblefor inspection. Performing examinations from below the core plate would require disassembly ofreactor vessel internals. Section 3.2.5 of BWRVIP-47-A, "BWR Vessel and Internals ProjectBWR Lower Plenum Inspection and Flaw Evaluation Guidelines," states that removing ordismantling of internal components for the purpose of performing inspections is not warranted toassure safe operation. However, in accordance with BWRVIP-47-A, NPPD performsinspections to the extent practical below the core plate if access is made available due tomaintenance activities not part of normal refueling activities. Results of those inspections areprovided to the BWRVIP and are then forwarded by the BWRVIP to the NRC.NPPD provided a Deviation Disposition to the BWRVIP in March 2011 using a generic templatedeveloped by the BWRVIP that provided the technical justification and included interiminspection guidance. The technical justification demonstrates that the core plate bolts have arelatively low susceptibility to cracking based on field experience and fabrication practices. Inaddition, should some cracking occur in some bolts, the consequences are mitigated byredundancy in the bolting and associated alignment hardware. The interim guidance requiredplants such as CNS to perform VT-3 examinations on 25% of the bolts from the top side by2015. The BWRVIP stated examinations completed back to 2005 could also be credited towardsmeeting the 25% minimum. VT-3 examinations from the top side are considered reasonable todetect loosened and rotated bolts due to a combination of vibration and failure of the welds onthe locking device, which should be obvious by visual VT-3 examination.Based on the interim guidance, CNS credited five (5) VT-3 examinations performed in RE25(Fall 2009) from the top side of five (5) bolts and three (3) bolt examinations performed in RE27(Fall 2012). No recordable indications were reported, providing reasonable assurance that thebolting is intact after nearly thirty-eight (38) years of operation. NLS2013065Attachment 2Page 9 of 9NPPD has scheduled ten (10) additional VT-3 bolting examinations from the top side of thebolting in the next refueling outage in RE28 (Fall 2014) in accordance to the interim guidanceprovided by the BWRVIP. The BWRVIP interim guidance effectively requires 25% of thebolting to be examined over a ten (10) year interval. In a letter dated April 20, 2011, NPPDnotified the NRC that CNS was not able to fully inspect 50% of the core plate bolts inaccordance to BWRVIP-25. The BWRVIP is currently working on revised guidance for the coreplate bolts and expects to complete that work, including gaining NRC approval of the revisedguidance, by 2015. Until such time as new guidance is provided, NPPD will be performing VT-3 inspections on 25% of core plate bolts on the top side on a periodic basis consistent with theinterim guidance (i.e., 25% each 10 year interval after 2015 or until such time the BWRVIPprovides alternative guidance as approved by the NRC). Given the low likelihood that thefunction of the core plate will be compromised by bolting failures, the VT-3 examinationsconstitute an acceptable interim inspection strategy until the BWRVIP develops revisedguidance.NRC Request -Question P-4[1 1]NPPD ResponseSee response to Question P-3. NLS2013065EnclosurePage 1 of 4EnclosureProprietary Affidavit for Request for Additional Information Responses GE-Hitachi Nuclear Energy Americas LLCAFFIDAVITI, Linda C. Dolan, state as follows:(1) 1 am the Manager of Regulatory Compliance, of GE-Hitachi Nuclear Energy Americas LLC("GEH"), and have been delegated the function of reviewing the information described inparagraph (2) which is sought to be withheld, and have been authorized to apply for itswithholding.(2) The information sought to be withheld is contained in Enclosure I of GEH letter, 7491-317703-HPI-I, "GEH Responses to CNS Core Plate Hold Down Bolt Stress RAIs," datedJune 18, 2013. The GEH proprietary information in Enclosure I, which is entitled "GEHResponses to CNS Core Plate Hold Down Bolt Stress RAIs," is identified by a dottedunderline inside double square brackets. Th~is..sentence is an examppl.e..3'1 Figures areidentified with double square brackets before and after the object. In each case, thesuperscript notation 13: refers to Paragraph (3) of this affidavit, which provides the basis forthe proprietary determination.(3) In making this application for withholding of proprietary information of which it is theowner or licensee, GEH relies upon the exemption from disclosure set forth in the Freedomof Information Act ("FOIA"), 5 U.S.C. Sec. 552(b)(4), and the Trade Secrets Act, 18 U.S.C.Sec. 1905, and NRC regulations 10 CFR 9.17(a)(4), and 2.390(a)(4) for trade secrets(Exemption 4). The material for which exemption from disclosure is here sought alsoqualifies under the narrower definition of trade secret, within the meanings assigned tothose terms for purposes of FOIA Exemption 4 in, respectively, Critical Mass EnergyProject v. Nuclear Regulatory Commission. 975 F.2d 871 (D.C. Cir. 1992), and PublicCitizen Health Research Group v. FDA, 704 F.2d 1280 (D.C. Cir. 1983).(4) The information sought to be withheld is considered to be proprietary for the reasons setforth in paragraphs (4)a. and (4)b. Some examples of categories of information that fit intothe definition of proprietary information are:a. Information that discloses a process, method, or apparatus, including supporting dataand analyses, where prevention of its use by GEH's competitors without license fromGEH constitutes a competitive economic advantage over other companies;b. Information that, if used by a competitor, would reduce their expenditure of resourcesor improve their competitive position in the design, manufacture, shipment,installation, assurance of quality, or licensing of a similar product;c. Information that reveals aspects of past, present, or future GEH customer-fundeddevelopment .plans and programs, resulting in potential products to GEH;d. Information that discloses trade secret or potentially patentable subject matter forwhich it may be desirable to obtain patent protection.Affidavit for Enclosure I of 7491-317703-HPI-I Page l of 3 GE-Hitachi Nuclear Energy Americas LLC(5) To address 10 CFR 2.390(b)(4), the information sought to be withheld is being submitted toNRC in confidence. The information is of a sort customarily held in confidence by GEH,and is in fact so held. The information sought to be withheld has, to the best of myknowledge and belief, consistently been held in confidence by GEH, not been disclosedpublicly, and not been made available in public sources. All disclosures to third parties,including any required transmittals to the NRC, have been made, or must be made, pursuantto regulatory provisions or proprietary or confidentiality agreements that provide formaintaining the information in confidence. The initial designation of this information asproprietary information, and the subsequent steps taken to prevent its unauthorizeddisclosure, are as set forth in the following paragraphs (6) and (7).(6) Initial approval of proprietary treatment of a document is made by the manager of theoriginating component, who is the person most likely to be acquainted with the value andsensitivity of the information in relation to industry knowledge, or who is the person mostlikely to be subject to the terms under which it was licensed to GEH. Access to suchdocuments within GEN is limited to a "need to know" basis.(7) The procedure for approval of external release of such a document typically requires reviewby the staff manager, project manager, principal scientist, or other equivalent authority fortechnical content, competitive effect, and determination of the accuracy of the proprietary-designation. Disclosures outside GEH are limited to regulatory bodies, customers, andpotential customers, and their agents, suppliers, and licensees, and others with a legitimateneed for the information, and then only in accordance with appropriate regulatoryprovisions or proprietary or confidentiality agreements.(8) The information identified in paragraph (2), above, is classified as proprietary because itcontains the detailed GEH methodology for core plate hold down bolt stress analysis for theGEH Boiling Water Reactor (BWR). These methods, techniques, and data along with theirapplication to the design, and analyses associated with the core plate hold down bolt stresswere achieved at a significant cost to GEH.The development of the evaluation processes along with the interpretation and applicationof the analytical results is derived from the extensive experience databases that constitute amajor GEH asset.(9) Public disclosure of the information sought to be withheld is likely to cause substantialharm to GEH's competitive position and foreclose or reduce the availability of profit-making opportunities. The information is part of GEH's comprehensive BWR safety andtechnology base, and its commercial value extends beyond the original development cost.The value of the technology base goes beyond the extensive physical database andanalytical methodology and includes development of the expertise to determine and applythe appropriate evaluation process. In addition, the technology base includes the valuederived from providing analyses done with NRC-approved methods.The research, development, engineering, analytical and NRC review costs comprise asubstantial investment of time and money by GEH. The precise value of the expertise toAffidavit for Enclosure I of 7491-317703-HPI-I Page 2 of 3 GE-Hitachi Nuclear Energy Americas LLCdevise an evaluation process and apply the correct analytical methodology is difficult toquantify, but it clearly is substantial. GEH's competitive advantage will be lost if itscompetitors are able to use the results of the GEH experience to normalize or verify theirown process or if they are able to claim an equivalent understanding by demonstrating thatthey can arrive at the same or similar conclusions.The value of this information to GEH would be lost if the information were disclosed to thepublic. Making such information available to competitors without their having beenrequired to undertake a similar expenditure of resources would unfairly provide competitorswith a windfall, and deprive GEH of the opportunity to exercise its competitive advantageto seek an adequate return on its large investment in developing and obtaining these veryvaluable analytical tools.I declare tinder penalty of perjury that the foregoing affidavit and the matters stated therein aretrue and correct to the best of my knowledge, information, and belief.Executed on this 18th day of June 2013.Linda C. DolanManager, Regulatory ComplianceGE-Hitachi Nuclear Energy Americas LLC3901 Castle Hayne Rd.Wilmington, NC 28401Linda.Dolan@ge.comAffidavit for Enclosure I of 7491-317703-HPI-1 Page 3 of 3 }}