ML021910490

Draft Regulatory Guide DG-1099, Anchoring Components and Structural Supports in Concrete

ML021910490
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Issue date:	07/31/2002
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1 Appendix S to 10 CFR Part 50 applies to applicants for a design certification or combined license pursuant to10 CFR Part 52 or a construction permit or operating license pursuant to 10 CFR Part 50 on or after January 10, 1997. However, for either an operating license applicant or holder whose construction permit was issued before January 10, 1997, the earthquak eengineering criteria in Section VI of Appendix A to 10 CFR Part 100 continue to apply.This regulatory guide is being issued in draft form to involve the public in the early stages of the development of a regulatory position in thisarea. It has not received complete staff review and does not represent an official NRC staff position.Public comments are being solicited on the draft guide (including any implementation schedule) and its associated regulatory analysis orvalue/impact statement. Comments should be accompanied by appropriate supporting data. Written comments may be submitted to the Rulesand Directives Branch, Office of Administration, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001. Comments may b esubmitted electronically or downloaded through the NRC's interactive web site at <

WWW.NRC.GOV> through Rulemaking. Copies ofcomments received may also be examined at the NRC Public Document Room, 11555 Rockville Pike, Rockville, MD. Comments will be mosthelpful if received by October 25, 2002.Requests for single copies of draft or active regulatory guides (which may be reproduced) or for placement on an automatic distribution list forsingle copies of future draft guides in specific divisions should be made in writing to the U.S. Nuclear Regulatory Commission, Washington, DC20555, Attention: Reproduction and Distribution Services Section, or by fax to (301)415-2289; or by email to DISTRIBUTION@NRC.GOV.

Electronic copies of this draft guide are available through NRC's interactive web site (see above), on the NRC's web site <www.nrc.gov> in theRegulatory Guides, and in NRC's Public Electronic Reading Room at the same web site, under Accession Number ML021910490.

U.S. NUCLEAR REGULATORY COMMISSIONJuly 2002 OFFICE OF NUCLEAR REGULATORY RESEARCHDivision 1Draft DG-1099 DRAFT REGULATORY GUIDEContact: H.L. Graves (301)415-5880DRAFT REGULATORY GUIDE DG-1099ANCHORING COMPONENTS AND STRUCTURAL SUPPORTS IN CONCRETEA. INTRODUCTIONThis draft regulatory guide is being issued to provide guidance to licensees and applicantson methods acceptable to the NRC staff for complying with the NRC's regulations in the design, evaluation, and quality assurance of anchors (steel embedments) used for component and structural supports on concrete structures.General Design Criterion (GDC) 1, "Quality Standards and Records," of Appendix A,"General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50, "Domestic Licensing of Production and Utilization Facilities," requires, in part, that structures, systems, and components (SSCs) important to safety be designed, fabricated, erected, and tested to quality standards commensurate with the importance of the safety functions to be performed. In addition, GDC 2, "Design Bases for Protection Against Natural Phenomena," and GDC 4, "Environmental and Dynamic Effects Design Bases," require, in part, that such SSCs be designed to withstand the effects of natural phenomena and to accommodate the effects of and be compatible with the environmental conditions associated with normal operation and postulated accidents. Appendix B, "Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants," to 10CFR Part 50 establishes overall quality assurance for SSCs important to safety. Appendix S, "Earthquake Engineering Criteria For Nuclear Power Plants," to 10 CFR Part 50, states, in part,requirements for the implementation of GDC 2 with respect to earthquakes.

1 Licensees and applicants may propose means other than those specified by theprovisions of the Regulatory Position of this guide for meeting applicable regulations. No new 2standards are being imposed by this regulatory guide. Implementation of this guidance bylicensees will be on a strictly voluntary basis.Regulatory guides are issued to describe to the public methods acceptable to theNRC staff for implementing specific parts of the NRC

's regulations, to explain techniquesused by the staff in evaluating specific problems or postulated accidents, and to provide guidance to applicants. Regulatory guides are not substitutes for regulations, and compliance with regulatory guides is not required. Regulatory guides are issued in draft form for public comment to involve the public in developing regulatory positions. Draft regulatory guides have not received complete staff review or approval; they therefore do not represent official NRC staff positions.The information collections contained in this draft regulatory guide are covered bythe requirements of 10 CFR Part 50, which were approved by the Office of Management and Budget (OMB), approval number 3150-3011. The NRC may not conduct or sponsor, and a person is not required to respond to, a request for information or an information collection requirement unless the requesting document displays a currently valid OMB control number.B. DISCUSSION Component and structural supports are fastened to the concrete building structureby anchors (steel embedments) that transmit forces to the concrete building structure by bearing, shear, tension, or a combination thereof. Structural failure of piping supports for safety systems and questions concerning the performance of one type of steel embedment, the expansion anchor bolt, led to the issuance of Inspection and Enforcement Bulletin (IEB) 79-02, "Pipe Support Base Plate Designs Using Concrete Expansion Anchor Bolts," in March of 1979. Review of reports required by IEB 79-02 revealed that industry practices varied. No consistency existed in the design and installation of such anchors as grouted anchors, embedded plates, or inserts. Utilities and anchor manufacturers were prompted by these inconsistencies to conduct research to answer questions raised by IEB 79-02. In October 1980, the American Concrete Institute released Appendix B, "Steel Embedments," to ACI 349-80, "Code Requirements forNuclear Safety Related Concrete Structures.

" The design methodology and codestandards in Appendix B to ACI 349-80 were based on a limited amount of available test data.In December 1980, the NRC designated "Seismic Qualification of Equipment inOperating Plants" as Unresolved Safety Issue (USI) A-46. The objective of USI A-46 was to develop alternative seismic qualification methods and acceptance criteria that could be used to assess the capability of mechanical and electrical equipment in operating nuclear power plants to perform their intended safety functions. Since equipment is usually anchored to the concrete structure through steel embedments, it was necessary to ensure that the embedments were capable of resisting seismic loads. In March 1988, in accordance with the provisions of 10 CFR Part 21, it wasreported that tests of some expansion anchor bolts had disclosed that the previously recommended minimum edge distance from an unsupported edge of five times the anchor bolt diameter might be insufficient to develop 100% of the recommended anchor capacity.

The issue of minimum edge distance was incorporated into USI A-46.

3The Seismic Qualification Utility Group (SQUG) developed a GenericImplementation Plan (GIP), including criteria and walkdown procedures, that was used to resolve the concerns of USI A-46. Following NRC approval of the GIP, each utility conducted a walkdown of its nuclear facilities using the GIP criteria and procedures.The criteria and procedures specified for anchorage walkdown in the GIPcontained specific information related to bolt strength. The GIP, including criteria and walkdown procedures, has been reviewed and accepted by the NRC.Since the release of Appendix B to ACI 349-80 in 1980 and the resolution of USIA-46, extensive work has been done by ACI 349 code committee and others in the industry (EPRI NP-5228). Recent testing sponsored by industry groups in the United States and Europe and by the NRC has increased the amount and type of test data available to code committees (ASCE, NUREG/CR-5434, NUREG/CR-2999, NUREG/CR-5563, and SP-130).As a result of extensive studies and tests performed since the late 1980s,questions were raised regarding the design methodology used in Appendix B to ACI 349-

80. These questions were on the shape of the anchor pullout cone under tensile loads, behavior of bolt groups, and edge conditions. Traditionally, the pullout cone has been assumed to be a 45 cone initiating at the bearing edge of the anchor (anchor head) andradiating toward the free surface of the concrete member. However, later research and test results have shown the pullout cone to be closer to a 35 cone and has also shownthat the concrete breakout failures for anchor bolt groups and edge conditions were different. Based on these latest findings, a new methodology, the Concrete Capacity or "CC-Method," was proposed to the ACI 349 code committee by independent researchers (Fuchs, Eligehausen, and Breen). After an extensive review of all available test data, in February 2001 the ACI 349 code committee issued a revision to Appendix B that was based, in part, on the CC-Method.Anchors used in nuclear power plants may need to withstand stress for longperiods of time and may need to compensate for additional transient-imposed stresses as a result of environmental effects. Thus, it is necessary to carefully evaluate anchor performance, taking into consideration the environment to which the anchors are subjected (ACI 355). This Draft Regulatory Guide DG-1099 generally endorses Appendix B (February 2001) to ACI 349-01, with exceptions in the area of load combinations. In addition, the guide has supplementary recommendations in the areas of materials, installation, inservice inspection, and the use of anchors in masonry walls.Discussion of Regulatory PositionsThis regulatory guide sets forth Regulatory Positions on the New Appendix B toACI 349-01. The reasons for each of these regulatory positions are as follows.Regulatory Position 1 endorses Appendix B to ACI 349-01. The notations anddefinitions in Sections B.0, "Notation," and B.1, "Definitions," are acceptable to the NRCstaff because they reflect the latest industry practices. However, clarification is needed in Section B.2.2 as to what type of grouted embedments are excluded from the code. Regulatory Position 1.2 supplements Section B.3, "General Requirements," ofAppendix B in three areas: load combinations, testing, and materials. It is recommended 4that load combinations outlined in Section 9.2 of ACI 349-01 and specified in SectionB.3.2 of Appendix B be changed as discussed in Regulatory Position 1.3. Section B.3.3 requires testing post-installed anchors in cracked concrete under seismic loads. The NRC staff agrees with the requirement of Section B.3.3, but also recommends that ASTM E488-96, "Standard Test Methods for Strength of Anchors in Concrete and MasonryElements," be used as a guide for establishing a test program because ASTM E488-96 isa recent standard based on industry consensus. ACI Code Committee 355, Anchorage to Concrete, developed a document on a test method for evaluating the performance of post-installed mechanical anchors in concrete, which was published in ACI 355.2-01, effective January 2002.Section B.3.7 states that material standards should be specified by the Engineer sothat embedment design is compatible with the attachment. In general, specifications require that metal anchors be made of a material that is resistant to corrosive conditions or coated with a protective material. In the case of metal anchors, the material must be stable in the concrete of the support structure and not cause any chemical reactions that could adversely affect the concrete or any reinforcement that may be present.Regulatory Position 1.3 endorses Section B.4, "General Requirements for Strengthof Structural Anchors," of ACI 349-01. However, the staff disagrees with Section B.4.4,which provides that the load combinations of Section 9.2 of ACI 349-01 should be used.

The staff agrees with the strength reduction factors given in Section B.4.4, but recommends that load factors consistent with SRP Section 3.8.4, "Other SeismicCategory I Structures," be applied to the load combinations given in Section 9.2 of ACI349-01.Regulatory Position 1.4 endorses Section B.5, "Design Requirements for TensileLoading," and Section B.6, "Design Requirements for Shear Loading," of Appendix B. The NRC staff endorses Sections B.5 and B.6 because they are based on extensive test data and incorporate the latest knowledge on the subject.Regulatory Position 1.5 endorses Section B.7, "Interaction of Tensile and ShearForces," and B.8, "Required Edge Distances, Spacings, and Thicknesses to PrecludeSplitting Failure," of Appendix B. The NRC staff endorses Sections B.7 and B.8 becausethey are based on test data and incorporate the latest knowledge on the subject.Regulatory Position 1.6 endorses and supplements Section B.9, "Installation ofAnchors." Tests have shown that the proper installation of anchors is of prime importancein ensuring good anchor performance. The intentions of the guide are not to specify a detailed program for anchor installation but to ensure that the factors important for good anchor performance are considered before the anchor is installed. In addition, it is necessary to provide a sufficient preload to expansion anchors to set the anchor mechanism, limit the initial slip of the anchor, and aid in withstanding cyclic loads. Regulatory Position 1.7 endorses Section B.10, "Structural Plates, Shapes, andSpecialty Inserts," and Section B.11, "Shear Capacity of Embedded Plates and ShearLugs," because they are based on test data and incorporate the latest knowledge on thesubject. For Section B.12, "Grouted Embedments," the NRC staff recommends that coderequirements be followed.

5Section B.9 of Appendix B states that the Engineer should specify an anchorinspection program. Therefore, Regulatory Position 2 recommends the creation of guidelines to help ensure that anchors are properly installed and provide satisfactory service throughout the life of the structure. An anchor inspection program is to cover the installation and inservice conditions of anchors. An inspection of anchors during the installation stage will verify that they are of the specified size and type and that thread stripping has not occurred. Items recommended for inspection during and after the installation stage include the items discussed in Regulatory Positions 1.6 and 2 of this guide. Appendix B to ACI 349-01 does not include masonry in its scope; thereforeRegulatory Position 7 offers guidance on the use of anchors in masonry. The extensive use of anchors (expansion and others) has led to considerable concern over the behavior of anchors in concrete masonry. Manufacturers generally indicate only the load capacities for anchors tested in cast-in-place concrete and do not recommend expansion anchors for use in concrete masonry. Until recently, the use of anchors in masonry was not subject to licensing review. Even though most standards and architect/engineer

'sspecifications prohibit the use of anchors in concrete masonry units (CMUs), a review of

licensees' responses to IEB 79-02 indicated the use of anchors in CMUs.

Licensees' use of anchors in CMUs was limited in most cases to a small number ofpiping supports for Seismic Category I piping in a few plants, which raised questions about the anchors' performance and capabilities in concrete block walls. The limited amount of data available on static tests performed on anchor bolts installed in concrete block walls indicates that the ultimate capacity of bolts in concrete block walls is lower than that of the same type and size anchors in cast-in-place concrete. It is also expected that, under dynamic loading, the ultimate capacity of anchors will be further reduced.

Until standards address anchoring in masonry are developed, the use of anchors in block walls is not recommended.

C. REGULATORY POSITION The following Regulatory Positions describe minimum recommendations to qualify,design, install, and inspect steel embedments installed in concrete to support components and structures.

1.The procedures and standards of Appendix B to ACI 349-01 are acceptableto the NRC staff as described and supplemented below. The recommendations areapplicable to the types of anchors discussed in Section B.1, "Definitions," and B.2, "Scope," of Appendix B to ACI 349-01. 1.1The notations and definitions given in Sections B.0 and B.1 of Appendix B toACI 349-01 are acceptable to the NRC staff. The position on grouted anchors is inRegulatory Position 1.7. 1.2 The position on load combinations is given in Regulatory Position 1.3. Inaddition to the guidance of Section B.3.3 of Appendix B, the testing recommendationsdefined in ASTM E488-96, "Strength of Anchors in Concrete and Masonry Elements," areacceptable to the NRC staff as a guide for establishing a testing program. Test methods not covered by ASTM E488-96 (e.g., combined tension and shear, cracked concrete) 6should be established and executed using good engineering judgment. ACI 355.2-01,"Evaluating the Performance of Post-Installed Anchors in Concrete," provides guidanceacceptable to the NRC staff for determining whether post-installed mechanical anchors are acceptable for use in uncracked as well as cracked concrete. For materials consideration, the NRC staff recommends, as a minimum, that anchors be designed, manufactured, and tested to be compatible with the load application, environment, and installation conditions. 1.3 The load factors used in Section 9.2.1 of ACI 349-01 are acceptable to theNRC staff except for the following:1.3.1. In load combinations 9, 10, and 11, 1.2T o should be used in place of l.05T o.1.3.2. In load combination 6, 1.5P a should be used in place of 1.25P a.1.3.3. In load combination 7, 1.25P a should be used in place of 1.15P a.1.4The design standards given in Sections B.5, "Design Requirements forTensile Loading," and B.6, "Design Requirements for Shear Forces," are acceptable to thestaff.1.5 The design standards given in Sections B.7, "Interaction of Tensile andShear Forces," and B. 8, "Required Edge Distances, Spacing, and Thickness To PrecludeFailure," are acceptable to the staff.1.6 Checks to be considered in the installation of expansion anchor bolts are:Correct hole diameterProper embedment depthDrill hole angularity is within established limitsEdge distance and spacing of anchors are to specified valuesAnchor is threaded properlyPlate thickness meets specified size and thickness valuesPlate bolt-hole size is within established limitsAnchor has been correctly preloadedCorrect bolt diameter and length are usedBolt hole has been cleared of drill dustConcrete is sound (free of voids)Grout has been mixed and installed to specifications.1.7 The design standards given in Sections B.10, "Structural Plates, Shapes,and Specialty Inserts," and B.11, "Shear Capacity of Embedded Plates and Shear Lugs," are acceptable to the NRC staff. When grouting is the only option, it is recommended that tests be performed in accordance with Sections B.12.3 and B.12.4 of Appendix B.

2. All anchors should be inspected to verify that they are of the specified sizeand type. Installation standards should be consistent with accepted industry-specifiedtolerances. Anchor systems that are external to the concrete surface should be inspected regularly during the life of the structure. In addition to the requirements in Section B.9.2 of Appendix B, the NRC staff recommends the following minimum post-installed 6-step inspection program to verify the proper installation of post-installed anchors.

71.Are the nut and anchor bolt tight

? This step will detect certain types ofinstallation defects: oversized holes, total lack of preload, loose nuts, damagedsubsurface concrete, and missing plug (for shell type). To implement this step, it is necessary to place a wrench on the bolt head or nut and to apply a torque. A well-installed bolt should not rotate under the torque applied equal to about 20% of the normal installation torque.2.Are there washers between the equipment base and the anchor bolt nut or bolt head? Washers are required for all bolts. Oversize washers arerecommended for thin equipment bases. Lock washers are recommended whereeven low-level vibration exists.3.Is the bolt spacing in accordance with the anchorage design

?4.Is the distance between the bolt and any free concrete surface in accordance with the anchorage design

?5.Is the concrete sound and uncracked

? This inspection element will detectgross defects in the concrete that could affect the holding power of expansionanchor bolts. Hairline shrinkage cracks in the vicinity of an expansion bolt are not a matter of concern so long as the design strength is based upon cracked concrete.

If cracks in the vicinity exceed about 0.01 inch (0.3mm), the design strength should be appropriately reduced.6.Is there a significant gap between the equipment base and the concrete surface? This inspection element will identify situations where the equipment baseis raised. This detail causes concern because shear forces result in flexuralstresses in the anchor bolt. A gap of less than about 1/4 inch is not significant and should be ignored. Anchorages with gaps larger than about 1/4 inch should be evaluated in more detail.For maximum assurance of adequacy, all six of these steps should be performedfor all bolts. However, adequate assurance can be achieved by a less extensive inspection program. Inspection steps 2 through 6, which are simple and mainly visual, should be applied to each bolt. However, a sampling approach might be used for the tightness check in step 1. A sampling program for expansion anchor bolts used in pipe support base plates was recommended in Appendix A of NRC IE Bulletin 79-02. The essential features of this program may be adopted for equipment anchorage as shown in Appendix A of this draft guide.

3.All quality assurance standards of ASME NQA-2,1983, "Quality AssuranceProgram Requirements for Nuclear Facilities," are applicable to load-bearing steelembedments and other load-bearing components of component and structural supports.

4.The concrete constituents and embedded materials should be compatiblewith the anticipated environmental conditions to which they will be subjected during thelife of the plant.

8 5.Loads and forces on embedments should be properly evaluated to accountfor baseplate flexibility and eccentricity of connections and the dynamic (strain rate andlow-cycle fatigue) effects of loads and forces.

6.The hardness, materials, and heat treatment of high-strength anchor boltsand studs (Fy > 110 ksi) should be carefully controlled to prevent environmental andstress-corrosion cracking.

7. Because anchors are not generally specified for masonry, the NRC staffdoes not recommend the use of any type of anchor discussed in this guide to attachSeismic Category I components or systems to concrete block walls that are seismically qualified, except for extremely low load applications. In locations where it is impossible to avoid the use of anchors, the staff recommends bolting through the block wall.D. IMPLEMENTATIONThe purpose of this section is to provide information to licensees and applicantsregarding the NRC staff

's plans for using this regulatory guide. This proposed revision has been released to encourage public participation in itsdevelopment. Except in those cases in which the applicant or licensee proposes an acceptable alternative method for complying with specified portions of the NRC

'sregulations, the method to be described in the active guide reflecting public comments will be used in the evaluation of anchors (steel embedments) used for component and structural supports on concrete structures.

1 Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 RockvillePike (first floor), Rockville, MD; the PDR

's mailing address is USNRC PDR, Washington, DC 20555; telephone(301)415-4737 or 1-(800)397-4209; fax (301)415-3548; e-mail <PDR@NRC.GOV>.

9 REFERENCESACI 349-01 and 349R-01, "Code Requirements for Nuclear Safety Related ConcreteStructures," with Appendix B, "Steel Embedments," (ACI 349-01) and Commentary (ACI349R-01) American Concrete Institute, Farmington Hills, Michigan, 2001. Appendix B,"Anchoring to Concrete," to ACI 349-01, "Code Requirements for Nuclear Safety RelatedConcrete Structures.

" ACI 349-97, "Code Requirements for Nuclear Safety Related Concrete Structures," withAppendix B, "Steel Embedments," American Concrete Institute Detroit, Michigan, 1997.ACI 349-80, "Code Requirements for Nuclear Safety Related Concrete Structures," withAppendix B, "Steel Embedments," American Concrete Institute, Detroit, Michigan, 1980.ACI 355.2-01/ACI 355.2R-01, "Evaluating the Performance of Post-Installed MechanicalAnchors in Concrete

" (ACI 355.2-01) and "Commentary

" (ACI 355.2R-01), AmericanConcrete Institute, Farmington Hills, MI, 2001.ASCE Task Group on Steel Embedments, "State-of-the-Art Report on SteelEmbedments," Vol. 2, p. 1080, in Proceedings of the Conference: Structural Engineering inNuclear Facilities, Raleigh, North Carolina, American Society of Civil Engineers, September1984. ASTM E 488-96, "Standard Test Methods for Strength of Anchors in Concrete andMasonry Elements," American Society for Testing and Materials, West Conshohocken,PA, 1996.EPRI NP-5228, "Seismic Verification of Nuclear Plant Equipment Anchorage," Volumes 1and 2, May 1987.Fuchs, W., R. Eligehausen, and J.E. Breen, "Concrete Capacity Design (CCD) Approachfor Fastening to Concrete," ACI Structural Journal, Volume 92, No. 1, January-February 1995.GIP, Memo from J.G. Partlow, USNRC, to All USI A-46 Plant Licensees Who AreMembers of the Seismic Qualification Utility Group (SQUG), May 22, 1992. (NUDOCSAccession Number 9205190366) 1IEB 79-02, "Pipe Support Base Plate Designs Using Concrete Expansion Anchor Bolts," Inspection and Enforcement Bulletin, USNRC, Revision 2, November 1979. (NUDOCSAccession Number 7908220136) 1NUREG-0800, "Standard Review Plan for the Review of Safety Analysis Reports forNuclear Power Plants," Section 3.8.4, "Other Seismic Category I Structures," Revision 1,USNRC, 1981.

1 2 Copies are available at current rates from the U.S. Government Printing Office, P.O. Box 37082, Washington, DC20402-9328 (telephone (202)512-1800); or from the National Technical Information Service by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161; (telephone (703)487-4650; <http://www.ntis.gov/ordernow>. Copies areavailable for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDR

's mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or(800)397-4209; fax (301)415-3548; email is PDR@NRC.GOV.

10NUREG/CR-2999, M.R. Lindquist, "Final Report on USNRC Anchor Bolt Study DataSurvey and Dynamic Testing," USNRC (HEDL-MISC-7246), December 1982.

2NUREG/CR-5434, R. Klingner et al., "Anchor Bolt Behavior and Strength DuringEarthquakes," USNRC, August 1998.NUREG/CR-5563, R. Klingner et al., "A Technical Basis for Revision to AnchorageCriteria," USNRC, March 1999.SP-130, "Anchors in Concrete: Design and Behavior," G.A. Senkiw and H.B. Lancelot,Editors, SP-103, American Concrete Institute, Farmington Hills, MI, 1991.

1Adapted from: EPRI-NP-5228, May 1987.

11APPENDIX ASampling Program for Anchor BoltsThis sampling program for expansion anchor bolts used in pipe support base plates wasrecommended in Appendix A of NRC IE Bulletin 79-02. The essential features of this program may be adopted for equipment anchorage.Perform inspection step 1 in Regulatory Position 2 on at least 25% of the bolts in everyequipment anchorage. If the selected bolts do not pass the inspection, perform step 1 on all bolts in the anchorage. ORPerform inspection step 1 on a randomly selected statistical sample of bolts. The size ofthe sample and the number of nonconformances should be such that there is a 95%

confidence of no more than 5% nonconforming bolts. This can be determined as follows:RRZ n N-nN-1R(1-R)1/21/2 where: R' = Upper limit of the true defect rate at a specified confidence level (R

' =0.05 in this application) R = Defect rate observed in sampleZ = Confidence coefficient for a normally distributed statistical model of testdata. For a 95% confidence level, Z= 1.65.n = Test sample size N = Total population from which test sample was selectedTable 1 gives the allowable number of nonconforming bolts as a function of the populationsize N and the test sample size n.

1When the failure rate for this check exceeds the limitations corresponding to 95%

confidence of no more than 5% nonconforming bolts, the installation procedure should be considered to be unacceptable.

12Table 1ALLOWABLE NUMBER OF NONCONFORMING ANCHORSAllowable Number of Nonconforming Anchors for Test Sample Size, nTotal Populati onSize, N4060801001502002503003504004505001001235------------------------2001123610------------------3001123571015------------

4001123579121520------

50011235791214172025 60011235791114161922 70011234791113161821 80011234691113161821 90011234681113151820 1,00011234681113151720 13REGULATORY ANALYSIS1.STATEMENT OF THE PROBLEMStructural failure of piping supports for safety systems and questions concerningthe performance of expansion anchors led to the issuance of Inspection and Enforcement Bulletin (IEB) 79-02, "Pipe Support Base Plate Designs Using Concrete Expansion Anchor Bolts," in March of 1979. Review of reports required by IEB 79-02 revealed that industry practices varied. No consistency existed in the design and installation of such anchors as grouted anchors, embedded plates or inserts. Utilities and anchor manufacturers were prompted by these inconsistencies to conduct research to answer questions raised by IEB 79-02. Industry codes and standards writing groups began to address the anchorage issue in seminars and reports. In October 1980, the American Concrete Institute released Appendix B, "Steel Embedments," to ACI 349-80, "CodeRequirements for Nuclear Safety Related Concrete Structures.

" Appendix B designmethodology and code standards was based on a limited amount of available test data.In December 1980, the NRC designated "Seismic Qualification of Equipment inOperating Plants" as Unresolved Safety Issue (USI) A-46. The objective of USI A-46 was to develop alternative seismic qualification methods and acceptance criteria that could be used to assess the capability of mechanical and electrical equipment in operating nuclear power plants to perform their intended safety functions. Since equipment is usually anchored to the concrete structure through anchor bolts, it was necessary to ensure that the bolts were capable of resisting seismic loads.The Seismic Qualification Utility Group (SQUG) developed a GenericImplementation Plan (GIP), including criteria and walkdown procedures that were used to resolve the concerns of USI A-46. Following NRC approval of the GIP, each utility conducted a walkdown of its nuclear facilities using the GIP criteria and procedures.The criteria and procedures specified for anchorage walkdown in the GIPcontained specific information related to bolt strength under dynamic conditions. The GIP, including criteria and walkdown procedures, has been reviewed and accepted by the

NRC.Since the release of Appendix B to ACI 349-80 and the resolution of USI A-46,extensive work has been done by ACI code committee 349 and others in the industry.

Recent testing sponsored by industry groups in the United States and Europe and by the NRC has increased the amount and type of test data available to code committees.As a result of extensive studies and tests performed since the late 1980s,questions were raised regarding the design methodology (shape of the anchor pullout cone under tensile loads) used in Appendix B to ACI 349-80. Traditionally the pullout cone has been assumed to be a 45 cone initiating at the bearing edge of the anchor(anchor head) and radiating toward the free surface of the concrete member. However, later research and test results have shown the cone to be closer to a 35 cone. Based onthese latest findings, a new methodology, the Concrete Capacity, or "CC-Method," was proposed to ACI 349 code committee by European researchers. After an extensive 14review of all available test data, in May 2000 the ACI 349 code committee issued arevised Appendix B that is based, in part, on the CC-Method.Based on the developments discussed above, the staff maintains thatendorsement of the latest version of Appendix B to ACI 349, supplemented with lessons learned from the resolution of USI A46, will result in better review guidance for the evaluation of steel embedments used to anchor component and structural supports to concrete.2.OBJECTIVESThe objective of the regulatory action is to update NRC guidance on the design,analysis, and inspection of steel embedments used to anchor components and structural supports to concrete.3. ALTERNATIVES AND CONSEQUENCES OF PROPOSED ACTION3.1Alternative 1 - Do not issue guidance on the design, analysis, and inspectionof steel embedments used to anchor components and structural supports to concrete.Under this alternative, guidance would not be issued and licensees would continueto rely on the criteria of IEB 79-02 and those used in the resolution of USI A-46. The staff acknowledges that, although the NRC has not formally endorsed Appendix B to ACI 349, licensees have submitted anchorage modifications with appropriate testing for review based on more recent editions of Appendix B. This alternative is considered the baselineor no action alternative.3.2Alternative 2 - Issue guidance on the design, analysis, and inspection ofsteel embedments used to anchor components and structural supports to concrete.The staff has identified the following consequences associated with adoptingAlternative 2.3.2.1Guidance will help to ensure that licensees will use the latest consensusstandards available, thereby resulting in improved design, evaluation, and qualityassurance of steel embedments used to anchor component and structural supports to concrete. For example, past seismic Probabilistic Risk Analysis (PRA) studies have often reported the anchorage of safety-related components to concrete as the controlling weak link that defined the seismic fragility of the component. In fact, anchorage was the controlling weak link used to define the seismic fragility for more than 50% of the passive components (cabinets, tanks, etc.) considered in past seismic PRA studies. Anchorage controlled the seismic fragility for several reasons: (1) variations in seismic design criteria used to design anchorages led to varying degrees of conservatism, (2) anchorage design criteria were based on a more limited amount of test data than now exists, (3) anchors were not designed with the same degree of seismic margin as the component being 15anchored, and (4) the as-built anchorage has sometimes differed in a detrimental mannerfrom the as-designed anchorage.The adoption and use of the proposed Appendix B anchorage provisions wouldsubstantially reduce the percentage of cases where anchorage controls seismic fragility, as a result of the first three of the above reasons. The fourth reason is expected to be controlled by improved quality assurance of anchorage in the installation and inspection of anchorages.Appendix B anchorage provisions are based on a careful study of over 3000anchorage tests. The proposed anchorage capacity formulas fit this test data with a lower coefficient of variation (COV) than do prior anchorage capacity formulas. This COV is typically about 0.2 or less, which is consistent with the COV obtained for other well defined concrete or steel failure mode capacities. Therefore, the level of conservatism introduced into the anchorage design is more uniformly controlled over a wide variety of cases. The net result would be a reduction in the likelihood that anchorage is the controlling weak link in the capacity of an anchored component.The staff views the latest standard as improved because it is based on extensivetest data and incorporates the latest technology and knowledge on the subject.3.2.2Guidance would promote regulatory efficiency by reducing uncertainty as towhat is acceptable and by encouraging consistency in the design, evaluation, and qualityassurance of steel embedments used to anchor component and structural supports to concrete. To the extent this occurs, it will result in potential benefits to both the NRC and industry. Published guidance should facilitate NRC review because licensee submittals should be more predictable and consistent analytically. Similarly, licensee

's adherence tolatest consensus standards should benefit licensees by reducing the likelihood for follow-up questions and possible revisions to licensees

' plans.3.2.3Published guidance could result in cost savings to both the NRC and theindustry. From the NRC

's perspective, relative to the baseline, NRC would incur one-timeincremental costs to develop the guidance for public comment and to finalize a regulatory guide. However, the NRC should also realize cost savings associated with the review of licensee submittals. In the staff

's view, the continuous and on-going cost savingsassociated with these reviews should more than offset this one-time cost.Similarly, on balance, it is expected that industry would realize a net savings as itsone time incremental cost to review and comment on a regulatory guide would be more than compensated for by the efficiencies (e.g., reduced follow-up questions and revisions) associated with each licensee submittal.3.2.4The use of industry consensus standards, which are already being used bylicensees, would enhance the continued use of the guidance contained in Appendix B,thereby avoiding costs related to a "new" agency-prepared standard. This approachwould also comply with the Commission

's directive that standards developed by 16consensus bodies be utilized per Public Law 104-113, "National Technology and TransferAct of 1995.

"4.CONCLUSIONBased on this regulatory analysis, it is recommended that the NRC develop andissue guidance. The NRC staff concludes that the proposed action would reduce unnecessary burden on the part of both the NRC and its licensees, and it would result in an improved process for the design, evaluation, and quality assurance of steel embedments used to anchor component and structural supports to concrete. The staff sees no adverse effects associated with issuing guidance.BACKFIT ANALYSISThe regulatory guide does not require a backfit analysis as described in 10 CFR50.109(c) because it does not impose a new or amended provision in the Commission

'srules or a regulatory staff position interpreting the Commission

's rules that is either new ordifferent from a previous applicable staff position. In addition, this regulatory guide does not require the modification or addition to systems, structures, components, or design of a facility or the procedures or organization required to design, construct, or operate a facility. Rather, a licensee or applicant can select a preferred method for achieving compliance with a license or the rules or the orders of the Commission as described in 10 CFR 50.109(a)(7). This regulatory guide provides an opportunity to use industry-developed standards, if that is a licensee

's or applicant

's preferred method.