Regulatory Guide 1.61

Damping Values for Seismic Design of Nuclear Power Plants

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Structures, systems, and components of a nuclear power plant that are designated as Seismic Category I are designed1to withstand the effects of the safe shutdown earthquake (SSE) and remain functional, see Regulatory Guide 1.29,"Seismic Design Classification."Appendix S to 10 CFR Part 50 applies to applicants for a design certification or combined license pursuant to210 CFR Part 52, "Early Site Permits; Standard Design Certifications; and Combined Licenses for Nuclear Power Plants,"or a construction permit or operating license pursuant to 10 CFR Part 50 after January 10, 199 However, for eitheran operating license applicant or holder whose construction permit was issued before January 10, 1997, the earthquakeengineering criteria in Section VI of Appendix A to 10 CFR Part 100 continue to apply.The U.S. Nuclear Regulatory Commission (NRC) issues regulatory guides to describe and make available to the public methods that the NRC staffconsiders acceptable for use in implementing specific parts of the agency's regulations, techniques that the staff uses in evaluating specific problemsor postulated accidents, and data that the staff need in reviewing applications for permits and license Regulatory guides are not substitutesfor regulations, and compliance with them is not require Methods and solutions that differ from those set forth in regulatory guides will be deemedacceptable if they provide a basis for the findings required for the issuance or continuance of a permit or license by the Commission.This guide was issued after consideration of comments received from the publi The NRC staff encourages and welcomes comments and suggestionsin connection with improvements to published regulatory guides, as well as items for inclusion in regulatory guides that are currently being developed. The NRC staff will revise existing guides, as appropriate, to accommodate comments and to reflect new information or experienc Written commentsmay be submitted to the Rules and Directives Branch, Office of Administration, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001.Regulatory guides are issued in 10 broad divisions: 1, Power Reactors; 2, Research and Test Reactors; 3, Fuels and Materials Facilities;4, Environmental and Siting; 5, Materials and Plant Protection; 6, Products; 7, Transportation; 8, Occupational Health; 9, Antitrust and Financial Review;and 10, General.Requests for single copies of draft or active regulatory guides (which may be reproduced) should be made to the U.S. Nuclear Regulatory Commission,Washington, DC 20555, Attention: Reproduction and Distribution Services Section, or by fax to (301) 415-2289; or by email to Distribution@nrc.gov. Electronic copies of this guide and other recently issued guides are available through the NRC's public Web site under the Regulatory Guides documentcollection of the NRC's Electronic Reading Room at http://www.nrc.gov/reading-rm/doc-collections/ and through the NRC's Agencywide DocumentsAccess and Management System (ADAMS) at http://www.nrc.gov/reading-rm/adams.html, under Accession No. ML070260029.U.S. NUCLEAR REGULATORY COMMISSION March 2007Revision 1REGULATORY GUIDEOFFICE OF NUCLEAR REGULATORY RESEARCHREGULATORY GUIDE 1.61(Draft was issued as DG-1157, dated October 2006)DAMPING VALUES FOR SEISMIC DESIGNOF NUCLEAR POWER PLANT

S. INTRODUCTION

This regulatory guide is being revised to update the guidance for applicants and licenseesregarding the acceptable damping values that the U.S. Nuclear Regulatory Commission (NRC) staff usedin the seismic response analysis of Seismic Category I nuclear power plant structures, systems,1and components (SSCs) in accordance with Title 10, Part 50, of the Code of Federal Regulations(10 CFR Part 50), "Domestic Licensing of Production and Utilization Facilities" [Ref. 1].Specifically, General Design Criterion 2, "Design Bases for Protection Against Natural Phenomena,"of Appendix A, "General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50 requires thatSSCs important to safety be designed to withstand the effects of natural phenomena such as earthquakeswithout losing the ability to perform their safety function Such SSCs must also be designedto accommodate the effects of and be compatible with the environmental conditions associated withnormal operation and postulated accident Appendix S, "Earthquake Engineering Criteria for NuclearPower Plants," to 10 CFR Part 50 specifies the requirements for the implementation of General DesignCriterion 2 with respect to earthquake Rev. 1 of RG 1.61, Page 2This regulatory guide specifies the damping values that the NRC staff considers acceptablefor complying with the agency's regulations and guidance for seismic analysi The specified dampingvalues are intended for elastic modal dynamic seismic analysis where energy dissipation is accounted forby viscous damping (i.e., the damping force is proportional to the velocity).This regulatory guide contains information collections that are covered by the requirementsof 10 CFR Part 50, which the Office of Management and Budget (OMB) approved under OMB controlnumber 3150-001 The NRC may neither conduct nor sponsor, and a person is not required to respond to,an information collection request or requirement unless the requesting document displays a currentlyvalid OMB control numbe DISCUSSIONBackgroundDamping is a measure of the energy dissipation of a material or structural system as it responds todynamic excitatio It is a term used to assist in mathematically modeling and solving dynamic equationsof motion for a vibratory system in which energy is dissipate When performing an elastic dynamicseismic analysis, one can account for the energy dissipated by specifying the amount of viscous damping(i.e., damping force proportional to the velocity) in the analytical model.Current NRC guidance on damping values to be used in the elastic design of nuclear power plantsis presented in this regulatory guide, which was first issued in October 1973 [Ref. 2]. Like the originalversion of this guide, this revision specifies equivalent viscous modal damping values as a percentageof critical damping for Seismic Category I SSC However, the staff based the original damping valueson limited data, expert opinion, and other information available in 197 Since that time, the NRCand industry have been involved in various studies, research work, and testing to predict and estimatedamping values of SSC In view of the available data, the damping values provided in the originalversion of Regulatory Guide 1.61 may not reflect realistic damping values for SSC Also, it is recognizedthat additional guidance is needed to address issues, such as correlation between damping and structuresstress level, and damping values for materials not included in the original version of Regulatory Guide 1.61(e.g., electrical distribution systems and reinforced masonry structures).Over the past three decades, the nuclear industry has proposed damping values and discussedthese values during various meetings and reviews of licensing issue Nuclear industry groups and licenseeshave suggested that the NRC ought to accept more realistic damping values for seismic design and analysisof SSCs, in place of the damping values provided in the original Regulatory Guide 1.61.Structural DampingIn 1993, the NRC completed an investigation of the adequacy of original Regulatory Guide 1.61structure damping values and other recommendations, and reported the results in NUREG/CR-6011 [Ref. 3]. Data were analyzed to identify the parameters that significantly influenced structure dampin Based onthat study, the NRC determined that the original Regulatory Guide 1.61 damping values for structure designwere adequate but required one significant revisio Specifically, Regulatory Guide 1.61 should distinguishbetween "friction-bolted" and "bearing-bolted" connections for steel structure Friction-bolted connectionsare also referred to as "slip-critical" connection In these connections, the bolt preload is high enoughto ensure that friction is not overcome, and the bolt does not experience shear loadin RegulatoryPosition 1 in Section C of this revised guide provides the updated structural damping value Rev. 1 of RG 1.61, Page 3Piping DampingIn 1986, the American Society of Mechanical Engineers (ASME) established Code Case N-411,"Alternative Damping Values for Response Spectra Analysis of Class 1, 2, and 3 Piping," in Section III,Division 1, of the ASME Boiler and Pressure Vessel Code [Ref. 4]. The NRC staff used Code Case N-411,with certain limitations specified in Regulatory Guide 1.84 [Ref. 5], to review operating reactor issuesuntil Code Case N-411 expired in 200 The staff also approved the use of alternate damping valuesfor the General Electric Advanced Boiling Water Reactor Design in 1994 [Ref. 6], Combustion EngineeringSystem 80+ Design in 1992 [Ref. 7], and Westinghouse AP600 Design in 1998 [Ref. 8]. RegulatoryPosition 2 in Section C of this revised guide provides the piping damping values that resulted fromthe staff's experience with ASME Code Case N-411 and application reviews of new reactor designs.Electrical Distribution System DampingRegulatory Guide 1.61 did not originally provide damping values for cable tray or conduit systems. Historically, the nuclear power industry used the damping values for bolted steel structures for seismicdesign of cable tray and conduit system In the late 1980s, however, the NRC staff reviewed the resultsof the cable tray test at the Comanche Peak Steam Electrical Station [Ref. 9]. Regulatory Position 3in Section C of this revised guide provides the damping values that resulted from the staff's reviewof data from the Comanche Peak test [Ref. 10] and two safety evaluation reports [Refs. 9, 11].Heating Ventilation and Air Conditioning Duct DampingThe damping values for heating ventilation and air conditioning (HVAC) systems are consistentwith the guidance provided for bolted steel structure Because no tests of welded duct constructionhave been identified, the damping values are the same as for welded steel structures, and RegulatoryPosition 4 in Section C of this revised guide provides these same damping value In addition, the NRCprovides related information on HVAC duct damping in NUREG/CR-6919, "Recommendationsfor Revision of Seismic Damping Values in Regulatory Guide 1.61" [Ref. 12].Mechanical and Electrical Component DampingNUREG/CR-6919 [Ref. 12] considers guidance in American Society of Civil Engineers (ASCE)Standard 43-05, "Seismic Design Criteria for Structures, Systems, and Components in Nuclear Facilities"[Ref. 13], and Non-Mandatory Appendix N, "Dynamic Analysis Methods," to Section III, Division 1,of the ASME Boiler & Pressure Vessels Code [Ref. 14]. In addition, NUREG/CR-6919 [Ref. 12]provides recommendations and commentary on damping values for (1) containment structures,containment internal structures, and other Seismic Category I structures; (2) piping; (3) electricaldistribution systems (i.e., cable tray or conduit systems); (4) HVAC; and (5) mechanical and electricalcomponent Regulatory Position 5 in Section C of this revised guide provides the damping valuesthat resulted from the staff's review of this industry guidanc Rev. 1 of RG 1.61, Page 4 REGULATORY POSITIONThe following regulatory positions provide acceptable damping values to be used in the elasticdynamic seismic analysis and design of SSCs, where energy dissipation is approximated by viscous dampingunless otherwise specifie Damping values higher than those provided may be used if documentedtest data support the higher value Damping values associated with soil-structure interaction analysisare not within the scope of this regulatory guide.1.

Structural Damping1.1 Acceptable Structural Damping Values for Containment Structures,Containment Internal Structures, and Other Seismic Category I Structures1.1.1 Safe-Shutdown Earthquake (SSE)Table 1 provides acceptable damping values for the SSE analysis.Table SSE Damping ValuesStructural Material Damping (% of Critical Damping)Reinforced Concrete 7%Reinforced Masonry 7%Prestressed Concrete 5%Welded Steel or Bolted Steel with Friction Connections 4%Bolted Steel with Bearing Connections 7%Note:

For steel structures with a combination of different connection types, use the lowest specified damping value, or asan alternative, use a "weighted average" damping value based on the number of each type present in the structure.1.1.2 Operating-Basis Earthquake (OBE)If the design-basis OBE ground acceleration is selected to be less than or equal to one-thirdof the design-basis SSE ground acceleration, then a separate OBE analysis is not require However,if the design-basis OBE ground acceleration is selected to be greater than one-third of the design-basisSSE ground acceleration, then a separate OBE analysis should be conducte Table 2 provides acceptabledamping values for the OBE analysis.Table 2. OBE Damping ValuesStructural Material Damping (% of Critical Damping)Reinforced Concrete 4%Reinforced Masonry 4%Prestressed Concrete 3%Welded Steel or Bolted Steel with Friction Connections 3%Bolted Steel with Bearing Connections 5%

Rev. 1 of RG 1.61, Page 51.2 Special Consideration for In-Structure Response Spectra GenerationThe SSE damping values specified in Table 1 for linear dynamic analysis of structureshave been selected based on the expectation that the structural response attributed to load combinationsthat include SSE will be close to applicable code stress limits, as defined in Section 3.8 of NUREG-0800[Ref. 15].However, there may be cases where the predicted structural response to load combinationsthat include SSE is significantly below the applicable code stress limit Because equivalent viscousdamping ratios have been shown to be dependent on the structural response level, it is necessaryto consider that the SSE damping values specified in Table 1 may be inconsistent with the predictedstructural response level.For structural evaluation, this is not a concern, because the stresses resulting from the useof damping-compatible structural response will still be less than the applicable code stress limits,as defined in Section 3.8 of NUREG-0800 [Ref. 15].However, for in-structure response spectra generation, it is necessary to use the damping-compatiblestructural respons Consequently, the following additional guidance is provided for analyses usedto determine in-structure response spectra:(1)

Use the OBE damping values specified in Table 2, which are acceptable to the staffwithout further review.(2)

Submit a plant-specific technical basis for use of damping values higher than the OBE dampingvalues specified in Table 2, but not greater than the SSE damping values specified in Table 1(e.g., see NUREG/CR-6919, Section 3.2.3), subject to staff review on a case-by-case basis.In general, for certified standard plant designs where the design-basis in-structure response spectrarepresent the envelope of the in-structure responses obtained from multiple analyses conductedto consider a range of expected site soil conditions, it is not necessary for combined license applicantsto address this issu However, if plant-specific seismic analyses are conducted for Category I structuresand/or structures not included as part of the standard plant design, then the applicant is expectedto address this issue accordingl Rev. 1 of RG 1.61, Page 62.

Piping DampingTable 3 presents the constant damping values specified for SSE and OBE (where required)analyses of piping system These values are applicable to time-history, response spectra,and equivalent static analysis procedures for structural qualification.Table Damping Values for Piping SystemsCategoryDamping ValueSSEOBE > SSE/3Piping Systems4%3%As an alternative for response spectrum analyses using an envelope of the SSE or OBE responsespectra at all support points (uniform support motion), frequency-dependent damping values shownin Figure 1 may be used, subject to the following restrictions:*

Frequency-dependent damping should be used completely and consistently, if at all. (Damping values specified in Regulatory Guide 1.61 are to be used for equipmentother than piping.)*

Use of the specified damping values is limited only to response spectral analyses. Acceptance of the use of the specified damping values with other types of dynamic analyses(e.g., time-history analyses or independent support motion method) requires further justification.*

When used for reconciliation or support optimization of existing designs, the effects of increasedmotion on existing clearances and online mounted equipment should be checked.*

Frequency-dependent damping is not appropriate for analyzing the dynamic response of pipingsystems using supports designed to dissipate energy by yielding.*

Frequency-dependent damping is not applicable to piping in which stress corrosion crackinghas occurred, unless a case-specific evaluation is provided and reviewed and found acceptableby the NRC staf Rev. 1 of RG 1.61, Page 73.

Electrical Distribution System DampingTable 4 presents the constant damping values specified for SSE and OBE (where required)analyses of cable tray and conduit system These values are applicable to response spectraand equivalent static analysis procedures for structural qualificatio The damping values specifiedin Table 4 are applicable to all types of supports, including welded support The use of higher dampingvalues for cable trays with flexible support systems (e.g., rod-hung trapeze systems, strut-hung trapezesystems, and strut-type cantilever and braced cantilever support systems) is permissible, subject toobtaining NRC review for acceptance on a case-by-case basis.The analysis methodology should consider the flexibility of supports in determining the systemresponse to seismic excitatio Rev. 1 of RG 1.61, Page 8Table Damping Values for Electrical Distribution SystemsCategoryDamping ValueSSEOBE > SSE/3Cable Tray System4Maximum Cable Loading1Empty2Sprayed-on Fire Retardant or othercable-restraining mechanism310%7%7%7%5%5%Conduit Systems4Maximum Cable fill1Empty27%5%5%3%Notes:1.

Maximum cable loadings, in accordance with the plant design specification, are to be utilizedin conjunction with these damping values.2.

Spare cable tray and conduit, initially empty, may be analyzed with zero cable load and these dampingvalue (Note: Re-analysis is expected when put into service.)3.

Restraint of the free relative movement of the cables inside a tray reduces the system damping.4.

When cable loadings of less-than maximum are specified for design calculations, the applicantor licensee is expected to justify the selected damping values and obtain NRC review for acceptanceon a case-by-case basis.4.

Heating, Ventilation, and Air Conditioning Duct DampingTable 5 presents the constant damping values specified for SSE and OBE (when required)analyses of HVAC duct system These values are applicable to response spectra and equivalentstatic analysis procedures for structural qualification.The analysis methodology must consider the flexibility of supports in determining systemresponse to seismic excitation.Table Damping Values for HVAC Duct SystemsType of Duct ConstructionDamping ValueSSEOBE > SSE/3Pocket Lock10%7%Companion Angle7%5%Welded4%3%

Rev. 1 of RG 1.61, Page 95.

Mechanical and Electrical Component DampingTable 6 presents the damping values for mechanical and electrical components, which areapplicable to passive subcomponents that can be seismically qualified by analysi Active subcomponentsdo not readily lend themselves to seismic qualification by analysis, and require qualification by test,as described in Section 3.10 of NUREG-0800 [Ref. 15].Table Damping Values for Mechanical and Electrical ComponentsComponent TypeDamping ValueSSEOBE > SSE/3Motor, Fan, and Compressor Housings(protection, structural support)3%2%Pressure Vessels, Heat Exchangers,and Pump and Valve Bodies (pressure boundary)3%2%Welded Instrument Racks(structural support)3%2%Electrical Cabinets, Panels, and MotorControl Centers (MCCs)(protection, structural support)3%2%Metal Atmospheric Storage Tanks(containment, protection) - Impulsive Mode - Sloshing Mode3%0.5%2%0.5%

Rev. 1 of RG 1.61, Page 10 IMPLEMENTATIONThe purpose of this section is to provide information to applicants and licensees regardingthe NRC staff's plans for using this regulatory guid No backfitting is intended or approved inconnection with the issuance of this guide.Except in those cases in which an applicant or licensee proposes or has previously establishedan acceptable alternative method for complying with specified portions of the NRC's regulations,the NRC staff will use the methods described in this guide to evaluate (1) submittals in connection withapplications for construction permits, standard plant design certifications, operating licenses,early site permits, and combined licenses; and (2) submittals from operating reactor licenseeswho voluntarily propose to initiate system modifications if there is a clear nexus between the proposedmodifications and the subject for which guidance is provided herein.REGULATORY ANALYSIS / BACKFIT ANALYSISThe regulatory analysis and backfit analysis for this regulatory guide are available inDraft Regulatory Guide DG-1157, "Damping Values for Seismic Design of Nuclear Power Plants"(Ref. 16). The NRC issued DG-1157 in October 2006 to solicit public comment on the draft of thisRevision 1 of Regulatory Guide 1.6 All NRC regulations listed herein are available electronically through the Electronic Reading Room on the NRC's3public Web site, at http://www.nrc.gov/reading-rm/doc-collections/cfr/part05 Copies are also available for inspectionor copying for a fee from the NRC's Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDR'smailing address is USNRC PDR, Washington, DC 20555; telephone (301) 415-4737 or (800) 397-4209; fax (301)415-3548; email PDR@nrc.gov.All regulatory guides listed herein were published by the U.S. Nuclear Regulatory Commission or its predecessor,4the U.S. Atomic Energy Commissio Most are available electronically through the Electronic Reading Roomon the NRC's public Web site, at http://www.nrc.gov/reading-rm/doc-collections/reg-guides/. Single copies ofregulatory guides may also be obtained free of charge by writing the Reproduction and Distribution Services Section,ADM, USNRC, Washington, DC 20555-0001, by fax to (301) 415-2289, or by email to DISTRIBUTION@nrc.gov. Active guides may also be purchased from the National Technical Information Service (NTIS). Details may beobtained by contacting NTIS at 5285 Port Royal Road, Springfield, Virginia 22161, online at http://www.ntis.gov,by telephone at (800) 553-NTIS (6847) or (703) 605-6000, or by fax to (703) 605-690 Copies are also available forinspection or copying for a fee from the NRC's Public Document Room (PDR), which is located at 11555 RockvillePike, Rockville, Maryland; the PDR's mailing address is USNRC PDR, Washington, DC 20555-000 The PDRcan also be reached by telephone at (301) 415-4737 or (800) 397-4209, by fax at (301) 415-3548, and by emailto PDR@nrc.gov.All NUREG-series reports listed herein were published by the U.S. Nuclear Regulatory Commissio Copies are5available for inspection or copying for a fee from the NRC's Public Document Room at 11555 Rockville Pike,Rockville, MD; the PDR's mailing address is USNRC PDR, Washington, DC 20555; telephone (301) 415-4737or (800) 397-4209; fax (301) 415-3548; email PDR@nrc.go Copies are also available at current rates fromthe U.S. Government Printing Office, P.O. Box 37082, Washington, DC 20402-9328, telephone (202) 512-1800;or from the National Technical Information Service (NTIS) at 5285 Port Royal Road, Springfield, Virginia 22161,online at http://www.ntis.gov, by telephone at (800) 553-NTIS (6847) or (703) 605-6000, or by fax to (703) 605-6900. NUREG-0800 and NUREG/CR-6919 are also available electronically through the Electronic Reading Roomon the NRC's public Web site, at http://www.nrc.gov/ reading-rm/doc-collections/nuregs/.Copies may be obtained from the American Society of Mechanical Engineers, Three Park Avenue, New York, NY610016-599 Phone (212)591-8500; fax (212)591-8501; www.asme.org.Rev. 1 of RG 1.61, Page 11REFERENCES1.

U.S. Code of Federal Regulations, Title 10, Part 50, "Domestic Licensing of Productionand Utilization Facilities," U.S. Nuclear Regulatory Commission, Washington, DC.32.

Regulatory Guide 1.61, "Damping Values for Seismic Design of Nuclear Power Plants,"U.S. Atomic Energy Commission, Washington, DC, October 1973.43.

NUREG/CR-6011, "Review of Structure Damping Values for Elastic Seismic Analysis ofNuclear Power Plants," U.S. Nuclear Regulatory Commission, Washington, DC, March 1993.54.

"ASME Boiler and Pressure Vessel Code, Code Case N-411-1, Alternative Damping Valuesfor Response Spectra Analysis of Class 1, 2 and 3 Piping,"Section III, Division 1,American Society of Mechanical Engineers, New York, New York, February 20, 1986.65.

Regulatory Guide 1.84, "Design, Fabrication, and Materials Code Case Acceptability -ASME Section III," U.S. Nuclear Regulatory Commission, Washington, DC.36.

NUREG-1503, "Final Safety Evaluation Report Related to the Certification of the AdvancedBoiling-Water Reactor," U.S. Nuclear Regulatory Commission, Washington, DC, July 199 Copies are available for inspection or copying for a fee from the NRC's Public Document Room at 11555 Rockville Pike,7Rockville, MD; the PDR's mailing address is USNRC PDR, Washington, DC 20555 (telephone: 301-415-4737or 800-397-4209; fax: 301-415-3548; email: PDR@nrc.gov).Copies may be purchased from the American Society for Civil Engineers (ASCE), 1801 Alexander Bell Drive,8Reston, VA 20190 [phone: (800) 548-ASCE (2723)]. Purchase information is available through the ASCE Web siteat http://www.pubs.asce.org.Draft Regulatory Guide DG-1157 is available electronically under Accession #ML062680189 in the NRC's9Agencywide Documents Access and Management System (ADAMS) at http://www.nrc.gov/reading-rm/adams.html. Copies are also available for inspection or copying for a fee from the NRC's Public Document Room (PDR), which islocated at 11555 Rockville Pike, Rockville Maryland; the PDR's mailing address is USNRC PDR, Washington, DC20555-000 The PDR can also be reached by telephone at (301) 415-4737 or (800) 397-4209 by faxat (301) 415-3548, and by email to PDR@nrc.gov.Rev. 1 of RG 1.61, Page 127.

NUREG-1462, "Draft Safety Evaluation Report related to the Design Certification of the System 80+Design," U.S. Nuclear Regulatory Commission, Washington, DC, September 1992.48.

NUREG-1512, "Final Safety Evaluation Report related to Certification of the AP600 StandardDesign," U.S. Nuclear Regulatory Commission, Washington, DC, September 1998.49.

NUREG-0797, "Safety Evaluation Report Related to the Operation of Comanche Peak SteamElectric Station, Units 1 and 2," Supplement No. 16, U.S. Nuclear Regulatory Commission,Washington, DC, July 1988.410.

Ware, A.G., and C.B. Slaughterbeck, "A Survey of Cable Tray and Conduit Damping Research,"Idaho National Engineering Laboratory, Report No. EGG-EA-7346, Rev. 1, prepared forthe U.S. Nuclear Regulatory Commission, Washington, DC, August 1986.711.

NUREG-0847, "Safety Evaluation Report for Watts Bar Nuclear Plant, Units 1 and 2,"Supplement No. 8, U.S. Nuclear Regulatory Commission, Washington, DC, January 1992.412.

NUREG/CR-6919, "Recommendations for Revision of Seismic Damping Values for the SeismicDamping Values in Regulatory Guide 1.61," U.S. Nuclear Regulatory Commission, Washington,DC, November 2006.413.

American Society of Civil Engineers, ASCE Standard 43-05, "Seismic Design Criteriafor Structures, Systems, and Components in Nuclear Facilities," Reston, VA, 2005.814.

American Society of Mechanical Engineers, "Boiler and Pressure Vessel Code,"Section III,Division 1, Non-Mandatory Appendix N, "Dynamic Analysis Methods," New York, New York,2004.515.

NUREG-0800, "Standard Review Plan for the Review of Safety Analysis Reports for NuclearPower Plants," U.S. Nuclear Regulatory Commission, Washington, DC.416.

Draft Regulatory Guide DG-1157, "Damping Values for Seismic Design of Nuclear PowerPlants," U.S. Nuclear Regulatory Commission, Washington, DC.9