ML20244D928

Review of Licensee Responses to SEP Topic III-7.B, Design Codes,Design Criteria & Loading Combinations,Dresden Unit 2, Final Supplementary Rept

ML20244D928
Person / Time
Site:	Dresden
Issue date:	06/03/1986
From:	Stilwell T CALSPAN CORP.
To:	NRC
Shared Package
ML17202G550	List: ML17202G549 ML20244D928
References
CON-NRC-03-81-130, CON-NRC-3-81-130, TASK-03-07.B, TASK-3-7.B, TASK-RR TER-C5506-425, NUDOCS 8606050031
Download: ML20244D928 (35)

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{{#Wiki_filter:,__ _ . n, [. a [* ENCLOSilRE (* L TECHNICAL EVALUATION REPORT NRC DOCKET NO.50[ FRC PROJECT C6606 l NRC TAC NO. -- FRC AS$1GNMENTIB NRC CONTRACT NO. NRG 0441130 FRCTASK 425 FINAL SUPPLEMDITARY REPORT REVIEW OF LICENSEE RESPONSES TO SEP TOPIC III-7.B DESIGN CODES, DESIGN CRITERIA, AND IDADING COMBINATIONS COMMONhT.ALTH EDISON COPJANY DRESDEN NUCLEA : POhT.R STATION UNIT 2 TER-C5506-425 Preparedfor Nuclear Regulatory Commission FRC Group Leader: T. Stilwell Washington, D.C. 20555 NRC Lead Engineer: P. Y. Chen June 3, 1986 This report was prepared as an account of work sponsored by an spency of the United States Government. Neither the United States Government nor any agency thereof, or any of their employees, makes any warranty, expressed or implied, or assumes any legal hability or responsibility for any third party's use, or the results of such use, of any information, appe-ratus, product or process disclosed in this report, or represents that its use by such third party would not infringe privatefy owned rights. Prepared by: Reviewed by: Approved by: T(,dd bk O

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r~.: ^ I' V :- TER-C5506-425 l; CONTENTS Section Title Pace 1 INTRODUCTION 1 2 DESIGN CODE CHAN3ES DESIGNATED SCALE A. 2 2.1 Shear Connectors for Composite Beams 2 2.2 Composite Beams or Girders with Formed Steel Deck. 3 2.3 Tiange Strecs in Hybrid Girders 3 2.4 Stresses in Unstiffened Compression Elements 4 2.5 Maximum Load in Riveted or Bolted Tensile Members. 4 2.6 Shear Load in Coped Beams. 6 2.7 Column Web Stiffeners at Frame Joints. 6 2.8 Lateral Support Spacing in Trames. 7 2.9 Brackets and Corbels 8 2.10 Special Provision for Walls 8 2.11 Elements Loaded in Shear with No Diagonal Tension. 9 2.12 Elements Subject to Temperature Variations. 9 2.13 Columns with Spliced Reinforcing IV 2.14 Dmbedments. 10 2.15 Ductile Response to Intpulse Loads. 11 2.16 Tangential Shear (Containments) 11 2.17 Areas of Containment Shell Subject to Peripheral Shear. 12 0 2.18 Areas of Containment Shell Subject to Torsion. 12 2.19 Thernal Loads. 12 2.20 Areas of Containment Shell Subject to Biaxial Tension. 13 2.21 Brackets and Corbels (on the Containment Shell) 13 lii

T TER-C5506-425 CONTENTS (Cont.) Section Title Pace 3 REVIEW METHOD AND TABULAR PRESENTATIONS. 14 3.1 Review Documents-14 3.2 Review Presentation 14 4 TABULAR SLWARY OF TINDINGS OF LICENSEE COMPLIANCE STATUS CONCERNING IMPLEMENTATION OF SEP TOPIC III-7.B IMPACT OF DESIGN CODE CHANGES 16 5 LOADS AND LOAD COMBINATIONS 26 6

SUMMARY

OF REVIEW FINDINGS. 26 6.1 Items'Not Addressed 2B 6.2 Items Which Were Addressed by the Licensee Using a 28 Sampling Philosophy 6.3 Items Requiring Further Clarification. 29 7 CONCLUSIONS. 30 8 REFERENCES. 31 i 9 iv

TER-C5506-425 i FOREWORD This Technical Evaluation Report was prepared by Franklin Research Center under a contract with the U.S. Nuclear Regulatory Conrnission (Office of Nuclear Reactor Regulation, Division of Operating Reactors) for technical Essistance in support of NRC operating reactor licensing actions. The technical evaluation was conducted in accordance with criteria established by the NRC. 9 Y

= -. t TER-C5506-425 1. INTRODUCTION . Current design criteria for nuclear power plant structuras contain requirements that were not in effect when older plants were designed and licensed. Consequently, one aspect (designated Topic III-7.8) of the - implementation of NRC's Systematic Evaluation Program requires licensees to review changes that have occurred in structural design criteria since their plant was built and also to review the Joads and load combinations used for design of plant structures by comparing them with the loads and load combinations now specified for current construction. The licensen's objective is to assess the impact that these changes may have on margins of safety of Seismic Category I structures as they were originally perceived and as they would be perceived under current criteria. Upon completion of this work, licensees report their findings to the NRC. To assist in this review, the NRC provided licensees with plant-specific Technical Evaluation Reports (TERs) concerning these issues (e.g., Reference 1). The TERs listed design code changes and, on a building-by-building basis, the load and loading combination changes to be addressed in the licensee review. The items listed were ones judged to have the greatest potential to degrade the originally perceived margins of safety. In May 1983, under contract NRC-03-81-130, the NRC retained the Franklin Research Center (TRC) to assist in its review of licensee findings. This report describes the review for the Dresden Nuclear Power Station Unit 2 and runanarises Commonwealth Edison Company's compliance status with respect to the b implementation of SEP Topic III-7.E,.

~ . 7, TER-C5506-425 2. DESIGN CODE CHANGES DESIGNATED SCALE A Current structural design codes contain provisions that differ from, or 1 did not appear in, the codes to which older plants were designed and con-structed. Changes that were judged to have the potential to significantly affect perceived nargins of safety have been designated as Scale A. For reference, changes in ACI-63 and AISC-63 designated Scale A are l briefly discusced in this section of the report. Although all such changes were considered in the Topic III-7.B assessment of all plants constructed to these codes, not all appear among the issues the Licensee was requested to address. On & plant-specific basis, some were eliminated as not applicable to the type of construction employed. When this was done, the eliminated code changes were listed (together with the reason they were considered inapplica-ble) in Appendix A of Reference 1, and the Licensee was requested to confirm I the validity of Appendix A. 2.1 SHEAR CONNECTORS FOR COMPOSITE BEAMS Four major modifications to the 1963 AISC Code [2] related to the type, distribution, and spacing of shear connectors for composite beams occur in the 1980 Code [3). These modifications are: a. Permission to use lightweight structural concrete (concrete made with C330 aggregates) in composite designs b. Allowance of design for composite act;on in the negative moment region of continuoas beams and provision of design guidance for including the longitudinal reinforcing steel in the negative moment resisting section c. Design requirements for the minimum number of shear connectors in regions of concentrated load d. Maximum and minimum spacing requirements in terms of stud diameters. The first two modifications will not affect old designs because they were not allowed by the previous code. The new provisions concerning the number of studs in the region near concentrated loads and the new limits concerning - _ _

TER-C5506-425 spacing of studs may adversely affect the margin of safety in older designs when checked against the new code provisions. These new requirements are of special concern in the case of composite beams subject to large concentrated loads, such as those associated with extreme environmental or critical accident conditions. 2.2 00MPOSITE BE W.S OR GIRDERS WITH TORMED STEEL DECK The 1980 AISC Code [3] contains a new section covering stay-in-place formed steel deck when used in a composite design. These provisions for formed steel decking, depending on the rib geometry and the direction of the ribs relative to the beam, may affect the load capacity of the shear studs st.d the effective flange width of the assumed concrete compression flange. They provide for reduction factors, to be applied to the shear stud allowable capacity, which account for the structural irregularity introduced into the composite slab. Composite beams with formed steel decks that were designed to the previous code could have less conservative margins of safety when compared to l present requirements, especially in cases where extreme loadings are to be cransidered. 2.3 FIJRGE STRESS IN HYBRID GIRDERS The AISC Code section covering reduction of bending stress in the compression flange was modified in the 1980 Code. The original flange stress redu: tion formula in the old code was needed to account for stress transfer which may occur in ordinary beam webs if the compression region should deflect Ir.terally, thereby changing the bending capacity of the cross section. In hybrid girders, the amount of the loss of bending resistance resulting from this phenomenon will vary depending on the relative properties of the web and flange steel. A reduced bending stress formula reflecting this interaction was introduced. In order to keep the formulation relatively simple, the reduced bending stress was made applicable f to both flanges of the hybrid member. i Where the ratio of web yield stress to flange yield stress is less than l 0.45 and the ratio of the web area to flange area is low, beams or girders 1 _ - _ _ _ _ _ _ _ _ _ _

1.' TER-C5506-425 fabricated from plate where the flange and web steels are different could have lower margins of safety under the new code than were thought to exist under older code requirements. 2.4 STRESSES IN UNSTIITINED COMPRESSION ELEMENTS New requirements provide stress reduction factors ior unstiffened elements subject to compression with one edge - an edge parallel to the compressive stress - free. Previous code provisions allowed the designer to neglect a portion of the area of such elements. The new code requirements provide equations for var-ious elements based on the critical buckling stress for plates. The new analytical approach is more conservative for the stems of tees and less conservative for all other cases. Where structural tees are used as main members and the tee stem is in compression, the mergin of safety for older designs (if checked under the new code) could be significantly less than was thought under prior code requirements. Since buckling is a non-duct!.= type failure, these new requirements are of special concern in the case of tee shapes subjected to the extreme environmental or critical accident conditions. A 2.5 MAXIMUM LOAD IN RIVLTED OR BOLTED TENSILE MEMBERS The 1980 AISC Code [3] introduces codes changes which affect the naximum load permitted in tensile members. Two interacting code changes are involved in establishing this limit, and e the mutual effects of both must be considered in assessing the impact of the new code upon the perception of margins of safety in tension members. The two provisions involved concern: 1. the tensile area permitted to be used in establishing load carrying capacities 2. the allowable stresses to be used in conjunction with these areas. Both effects are taken into account in ranking this change. The potential magnitude of the mutual effects of the two changes is discussed below. c._

lJ TDR-C5506-425 The 1980 AISC Specification definition of 'Tffective Net Area introduces a reduction coefficient which is to be applied to the traditional definition of net area. This essentially changes the design capacity of a tension member when compared to older versions of these specifications. First consider only the effect of the critical area used for the design of a tension member as defined,in the new code compared to the critical area used for the design of the same member as defined in the old code. Clearly, if all other factors are equal, the new code is more conservative. However, all other factors are not the same. The changes in allowable tensile stress (on the gross area and on the effective net area), which were introduced simultaneously with the new ~ definition of effective net area, modify the above conclusion. In addition, the traditional upper limit on the critical net area of 85% of the gross area (a requirement of the old code) is no longer a requirement of the new code. Both of these changes interact with the new effective net area requirement. A valid assessment of the effect of these changes is best accomplished by a comparison of the allowable load each code permits in tension members. If one considers the allowable load on the effective net area, the value based on the new code is a function of three variables: the new reduction coefficient, the net area,* and the ultimate tensile strength of the steel. The allowable load based on the old code is a function of only two variables: the net area and the yield strength of the steel. First, form the load ratio of the allowable load defined by the new code criteria to the allowable load defined by the old code criteria. Next, consider the ranges of all of the parameters mentioned above, this ratio will have defined upper and lower limits which are a function of the ratio of the net areas, the new code net area reduction factor, and the ratio of the steel ultimate strength to the yield strength. For all the steels allowed under the new code, this load ratio ranges from 1.5 to 0.69. For all the steels allowed under the old code, this load ratio ranges from 1.6 to 0.88. It is apparent that, for those steels with reduced load ratios, the new code is less conservative than the old. The margin of safety of some older designs therefore could be significantly lower when checked against the new code requirements.

• In making this comparison, one must be careful to note that the net area is not always the same under the old and new codes.

TER-C5506-425 f 2.6 SHEAR LOAD IN COPED BEAMS ithe 1980 AISC Code [3] introduces additional control over the shear load permitted at beam end connections where the top flange has been coped. Web shear control in older coder did not distinguish between coped and uncoped beams or between shear allowed at connections and over the free span (except'for requiring reinforcement of thin webs at connections). The shear load allowed was given by: allowable shear load = 0.4 (yield strength) (gross web section). The 1980 Code retains this limit, but introduces an additional requirement to protect against a failure mode associated with coped beams. For coped beams (and similar situations), a portion of the web may sever, failing along the perimeter of the connection holes. In perticular, coped beam web connections where the fastener holes lie close to the butt end of the beam may be prone to such failures. This web " tear out" failure is actually a combination of shear failure through the line of fasteners together with tensile failure acrons the shortest path to the beam end. The failure surh ee turna a corner with shear failure along a line trending upward through the noles, combined with tensile failure across a more or less horizontal line running out to the beam end. The newly introduced shear limit is given as A function of the minimum net failure surface and the steel ultimate strength. Thus, the new requirements may or may not control a coped beam's alle.vable capacity in shear. Whether or not it does depends on both the connection geccetry and the ~ type of steel used. When this requirement is controlling, coped beams designed by previous rules may be found, if checked against the new criteria, to have significantly smaller margins of safety than previously thought. 2.7 COLUMN WEB STIITENERS AT FRAME JOINTS The more recent editions of the AISC code u.andate which columns must be stiffened at locations where beams of girders are rigidly attached to the column flan;e and also establish requirements for the geometry of such web - _ _ _______-_-

TER-C5506-425 stiffeners. These requirements are introduced to preclude local crippling at such frame joints. No such guidance was provided by AISC-63 [2]. Older codes (such as AISC-63) left such matters to the designer's discretion. Consequently, there is no assurance that all such columns are adequately stiffened for current accident and faulted loadings. 2.8 IATERAL SUPPORT SPACING IN FRAMES (PI.ASTIC DESIGN METHOD) The 1980 AISC Code contains changed spacing requirements for lateral supports in portions of members in frames where failure mechanisms are expected to form at ultimate load. Members of such frames must not only be capable of developing a plastic hinge, but must also be stable enough to sustain moments larger than those computed on an elastic-perfect-plastic theory (because real steels work-harden at strains expected to occur at hinge locations). Previous lateral bracing requirements were developed for a limited range of steels. Research on high-strength steels has shown that, for certain ranges of slenderness ratio of the compression flange of such frame members, sider specification bracing requirements were not sufficiently conservative. The new specification requirements rake the slenderness ratio limits a function of the steel yield strength and the member curvature (as expressed by the ratio of the lesser bending soment at the ends of the unbraced segment to the pitstic soment). The new specifications are more conservative for (ll'any segment bent in douole curvature regardless of its steel specification and (2) very high-strength steel members. The adequacy of frame members bent in single curvature and constructed of steels whose yield strength exceeds 36 ksi should be examined on a case-by-case basis. The new requirements may reduce the a rgins of safety thought to exist in: 1. structures designed under the plastic requirements of older codes 2. elastica 11y designed structures sized to carry a smaller maximum load than is now required by current accident and faulted load _ _ _ _ _ _ _ _ -

r ' f TER-C5506-425 combinations. In this case, plastic logic may have to be invoked to justify the adequacy of exisiting structures. Nonconformance with current bracing requirements may substantir.11y restrict the capability of frame members to carry code-acceptable overloads. 2.9 BRACKETS AND CORBI:LS ACI 349-76 [4), Section 11.13 contains design requirements for short brackets and corbels which are considered primary load-carrying members; no comparable requirements are provided in ACI 318-63 [5). The requirements apply to brackets and corbels having a shear span-to-depth ratio of unity or less. They provide minimum and maximum limits on tension and shear reinforcement, limits on ultimate shear stress in concrete. and constraints on member geometry and location of reinforcement. Brackets and corbels designed under earlier codes may or may not satisfy the newly imposed limits. If they do not, they may be prone to non-ductile failure (which occurs suddenly and without warning) and may exhibit smaller margins of safety than those currently required. 2.10 SPECIAL PROVISIONS FOR WALLS 2.10.1 Shear Walls ACI 349-76, Sections 11.15.1 through 11.15.6 specify requirements for reinforcing and permissible shear stresses for in-plane shear loads on walls. The ACI 318-63 Code had no specific requirements for in-plane shear on shear walls. 2.10.2 Punching Shear ACI 349-76, Section 11.15.7 specifies permissible punching shear stresses for walls. ACI 318-63 had no specific provisions for walls for these stresses. Punching loads are caused by relatively concentrated lateral loads on the walls. These loads may be from pipe styports, equipment supports, duct supports, conduit supports, or any other component producing a lateral load on a wall, i .g-

? TER-C5506-425 2.11 ELEMDJTS LOADED IN SHEAR WITH NO DIAGONAL TD;SION (SHEAR TRICTION) The provisions for shear friction given in ACI 349-76 did not exist in ACI 318-63. These provisiens specify reinforcing and stress requirements for situations where it is inappropriate to consider shear as a measure of diagonal tension. 2.12 ELEMENTS SUBJECT TO TEMPERATURE VARIATIONS The ACI 349-76, Appendix A requirements for thermal considerations in nuclear safety-related, reinforced concrete strucutres do not have a comparable counterpart in ACI 318-63. The new provisions give guidan e in the form of general design require-ments and limiting concrete temperatures. New design provisions require that the effects of temperature gradients and the effects of the difference between mean temperature and base temperature during normal operation of accident conditions be considered. Also, thermal stresses are to be evaluated considering the stiffness and rigidity of members and the degree of restraint of the structures. Concrete temperature limits are specified, both for normal operation or other long-term periods and for accident or other short-term periods. In addition, special temperature limits are provided for localized conditions such as around penetrations and from steam or water jets that might strike concrete structures as a result of postulated pipe breaks. All requirements of the older codes are a result of experience and research with reinforced concreta at temperatures primarily related to nornal weather conditions. Consequently, the older code. did not reflect major effects of high-temperature exposures. Research into the effects of temperature on mechanical properties of concrete reveals that generally both strength and stiffness degrade significantly with high temperature beginning at about 120* to 150*F. Both properties are reduced as a result of a combination of mechanisms. Above these temperatures, microcracking (which results from differential expansion of aggregate and the cement paste matrix) and paste dehydration are significant contributors to loss of strength and stiffness. l l

,y< TER-C5506-425 The new requirements may reduce the margins of safety previously thought to exist in older designs if the newly specified general design requirements were not'given appropriate consideration or if current temperature limits are exceeded. In additien, the new code provides specific guidance for thermal stress analysis in cases where thermal gradients exist and defines (in the ccamentary to Appendix A)'three acceptable approaches to the analysis. It is possible, that the structural analysis of some plants designed to earlier codes may not have fully taken into account stresses from thermal loadings. Where this is true, the computed margins of safety may overstate the actual , structural integrity. 2.13 COLUMNS WITH SPLICED REINFORCING' The ACI 349-76, Section 7.10.3 requirements for columns with spliced reinforcing did not exist in the ACI 318-63 Code. The ACI 349-76 Code requires that splices in each face of a column, where the design load stress in the longitudinal bars' varies from f in compression to 1/2 f in y tension, be developed to provide at least twice the calculated tension in that face of the column (splices in combination with unsp'. iced bars can provide this if applicable). This code change requires that a minimum of 1/4 of the yield capacity of the bars in each face of the column br developed by both spliced and unspliced bars in that face of the column. 2.14 EMBEDMENTS Appendix B cf ACI 349-80 provides rules for the design of steel embedments in concrete; the design of embedments is not specifically addressed in ACI 318-63. Current requirements of Appendix B are based upon ultimate strength design using factored loads. The anchorage design is controlled by the ultimate strength of the embedmont steel. Ductile failure (i.e., steel yields before concrete fails) is postulated. Under the provisions of ACI 318-63, the design of embedments was left to the discretion of the designer. Working stress design methods were widely used. _ _ _ _ - - - _ _ _ _ _ _ _ _ - _ _

t i-TER-C5506-425 I Consequently, it is likely that original embedment designs do not fully l conform to current criteria. Review of such designs to determine the implications with respect to margins of safety is therefore judged a desirable precaution. 2.15 DUCTILE RESPONSE TO IMPULSE LOADS Appendix C to ACI 349-76 (4) contains design rules for structures which I may be subjected to impulse or impact loads; no such provisions occur in ACI 318-63 [5). The rules of Appendix C are intended to foster ductile response (i.e., ' steel yields prior to concrete failure) of nuclear structures if and when they experience impulse or impact loads. For structures built to codes not containing such provisions, there is no assurance that sufficient design effort was directed toward proportioning members to provide energy absorbtion (,apability. Consequently, such structures might be prone to non-ductile, sudden failure should they ever experience postulated accident loadings such as jet impingement, pipe whip, compartment depressurization, or tornado missiles. 2.16 TANGENTIAL SHEAR (CONTAINMENTS) Paragraph CC-3421.5, Tangential Shear, of Section III, Division 2 of the ASME Boiler and pressure Vessel Code (6) addresses the capacity of reinforced l concrete containments to carry horizontal shear load. It provides code-acceptable levels of horizontal shear stress that the designer may credit to the concrete. No specific guidance in this matter exists in ACI 318-63. The provisions associate the allowable concrete stress in horizontal shear with the concrete properties, the manner in which lateral loads are imposed on the structure, and tha presence of sufficient reinforcement to assure that the assumed shear capacity of concrete can be developed. Sufficient diagonal reinforcement (or its demonstrated equivalent) is te be supplied to carry, without excessive strain, shear in excess of that permitted in 6.he concrete. A major consideration here is the preservation of the structural integrity of the liner. l __ _ _ _ _

,6 TER-C5506-425 In containments constructed to older codes, such matters were left to the discretion of the designer, who may or may not have provided the horizontal shear capacity at controlled strains that the code currently requires. 2.17 AREAS OF CONTAINMDC SHELL SUBJECT TO PERII"H:RAL SHEAR Concrete containment design is currently governed by the ASME Boiler and Pressure Vessel Code, Section III, Division 2, 1980 [6). The provisions for peripheral (punching) shear appear in code Section CC-3421.6. These provisions are similar to the ACI 318-63 Code [5] provisions for slabs and footings, except that the allowable punching shear stress in CC-3421.6 includes the effect of shell membrane stresses. For membrane tension, the allowable concrete pur-hing shear stress in the ASME Code is less than that allowed by ACI 318-63. 2.18 AREAS OF CONTAINMDC SHELL SUBJECT TO TORSION Concrete containment design is currently governed by the ASME Boiler and Pressure Vessel Code, Section III, Division 2, IS80. Section CC-3421.7 of the code contains provisions for the allowable torsional shear stre-in the concrete. Such provisions were not contained in the ACI 318-b3 Code. The present allowable torsional shear stress includes the effects of the membrane stresses in the containment shell and is based on a criterion that liri.ts the principal membrane tension stress in the concrete. 2.19 THERMR., LOADS ACI 349-76 Appendix A and ASME B&PV Code, Section III, Div. 2, CC-3440 contains requirements for consideration of temperature variations in concrete that are not contained in ACI 318-63. The new provisions require consideration of the effects of thermal gradients and of the effects depending on the mean temperature distribution and the base temperature distribution during normal operation or accident conditions. The new provisions also require that thermal stresses be eval-usted considering the stiffness and rigidity of members and the degree of restraint of the structure. 7______-._,_ r >. TER-C5506-425 9-En assessment is to be made of the analytical methods used to determine thermal stresses as compared to current code-acceptable practices, e.g., those discussed in ACI 349.1R-80 and the commentary to ACI 349R-80. If the methods used for design produce stress results which are signifi-cantly different from those current procedures generate, perceived margins of safety could be affected. 2.20 AREAS OF CONTAINMENT SHELL SUB.TECT TO BIAXIAL TENSION Increased tensile development lengths are required by Section CC-3532.1.2 . of Reference 6 for reinforcing steel bars terminated in areas of reinforced concrete containment structures which may experience biaxial tension. For biaxial tension loading, bar development lengths, including both straight embedment lengths and equivalent straight length for stant'.ard hooks, are required to be increased by 25% over the standard development lengths required for uniaxial loading. Nominal temperature reinforcement is excluded from these special provisions. ACI 318-63 had no requirements related to this increase in development length. 2.21 BRACKEIS AND COREELS (ON THE CONTAINMENT SHELL) The ACI 318-63 Code did not specify requirements for brackets and corbels. Provisions for these components are included in the ASME Boiler and Pressure Vessel Code, Section III, Division 2, Section CC-3421.8. These provisions apply to brackets and corbels having a shear-span-to-depth ratio of unity or less. The provisions specify minimum and maximum limits for tension and shear reinforcing, limits on shear stresses, and constraints on the member geometry and placement of reinforcing within the member. - _ _ _ _ _

3 TER-C5506-425 ,,O ) 1 3. REVIEW METHOD AND TABULAR PRESENTATIONS 3.1 ' REVIEW DOCUMENTS The information relating to SEP Topic III-7.B which was supplied to the NRC by Consweer.lth Idison Company and made available for this review is contained in t se Allowing document and its numerous attachments: 1. T. J. Rausch, Nuclear Licensing Administrator, Boiling Water Reactors [ Letter to P. W. O'Connor, Project Manager, Operating Reactor Branch No. 5, USNRC

Subject:

Dresden Unit 2, SEP Topic III-7.B, Design Codes, Design Criteria, and Imading Combinations, Docket No. 50-237 ^ ~ Augus t 't, 1982 2. Consonwealth Edison (CECO) Letter to the Nuclear Regulatory Commission

Subject:

Clarifications of CECO Response to SEP Task III-7.B Items Concerning the Dresden Unit 2 Nuclear Power Station, July 11, 1984 3.2 REVIEW PRESENTATION Before undertaking licensee report reviews, FRC prepared tabular forms to be used as a working tool during the review process and also to document the review work and its findings. These' tables are intended to: 1. establish a systematic and comprehensive review procedure 2. standardize, as much as possible, the review process for all licensees 3. present a relatively compact overview of each licensee's SEP Topic III-7.B compliance status. TM form sheets summarise key information reported in licensee responses. Certain items (such as descriptions of Scale A code changes, conclusions, and comments) frequently are not adaptable to abbreviated summary. For such items, the form sheets refer the reader either to sections of this TER where the matter is developed more fully or to an extended note ' list compiled on separate sheets. The note list, although detached from the main table in order to allow a fuller discussion, should be regarded as an integral part of it. The form sheet consists of four major columnar sections which: -

. ll TER-C5506-425 y 1. identify each Scale A item 2. state the action tnat the licensee took or the logic that the licensee presented to resolve the item 3. provide an assessment of engineering conclusions that shay be reasonably drawn (Tom the evidence provided

4.. summarize the Licensee's compliance status with respect to the item.

Items listed on the tables are design code changes designated Scale A. This list is drawn directly from TER-C5257-324, the previ us Technical Evaluation Report on this topic [1]. Form sheets summarizing the review findings concerning the Licensee's compliance statur with respect to the implementation of SEP Topic III-7.B aspects related to design code changes follow in Section 4. A discussion of the review findings concerning the Licensee's compliance status with respect to load and load combination changes is presented in Section 5. l l

,h, i 2-TER-C5506-425 4. TABULAR

SUMMARY

OF REVID7 FINDINGS OF LICENSEE COMPLIANCE STATUS CCNCERNING IMPLEMENTATION OF SEP TOPIC III-7.B IMPACT OF DESIGN CODE CHANGES Form sheets sumarizing the review findings concerning technical aspects with respect to the implementation of SEP Topic III-7.B as related to design code changet follow. 'O e Y _ _ _ - _ _ _ _ _ _ _ - _ - _ _ _ _ _ _ _ _ _ _

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E'. j l[ TER-C5506-425 l NOTES: I I In the following notes, the Licensee's conclusion is presented first, followed by the reviewer's comments, if any, in brackets. C-4. The Licensee affirms: { " Original design configurations excluded the use of the structural-T ( i as a compression member." (The only standard structural shape affected by this code change is the structural-T.] C-5. The Licensee affirms: " primary tension members for Category I structures have been reviewed and do not fall within any additional limitations of this AISC section." C-6. The results of previous work under other reassessment programs are cited as supporting plant-wide acceptability of all as-built stru:tures where coded beams are used. [The results from these reassessment programs are relevant to the issue and furnish documentary evidence of substantial areas where structure is known to be now acceptable under current criteria. However, the extrapolation of this evidence to acceptability of all structures of like character throughout the plant does not seem to immediately follow. First, the evidence supplied may be restricted to a certain class of applications and thus not be truly representative of all applications throughout the plant. Secondly, even if the evidence supplied is taken as representative of general practice, it must be regarded as sample data. In the descriptions of the reassessment programs cited, there are references to structural modifications which were (in some instances) provided to meet current code criteria. O Consequently, the Licensee should be asked to supply the following data for coped beams: a. The number of structures (incorporating such details) reassessed in the programs described. b. The number of these found to meet current structural criteria outright. The number which were qualified without modification on grounds c. ~ other than (b) above. d. The number which required modification. - _ _ _ _ _ _ _ - _ _ _ _ -

b y '* '6 y ~... 5 - TER-C5506-425 e. The total number (or estimated total number) of applications throughout the plant.] C.7 The lateral load resisting system is generally not made up of restrained frame members. Moment connections have been used only for crib house (B-58) and lightly loaded gallory supports. [The crib house design was subsequently reviewed and found adeguato.] l C.io.1 The Licensee stated: " Shear walls have been shown to be adequate.per the report by the Senior Seismic Review Team, NUREG/CR-0891, Section 4.5.1." [It is the understanding of the SEP Topic II-7.B reviewers that this was the judgment of NUREG/CR-0891 with respect to earthquake loading.] C.10.2' With respect to current' requirements governing design of walls to withstand punching shear, the Licenses states: "During the course of review of all additional loading imposed on the various structures, as noted in Section I of this document, a punching shear check has been performed as part of the review of structural integrity. Due to the extent of the review involved, Ceco /S&L considers this to be sufficient cause to say that i Section 11.15.7 requirements have been satisfied." [The Licensee.should be requested to clarify the extent to which Section 11.15.7 requirements are considered to have been shown to be satisfied. For example, it is FRC's understanding that Seismic Category I mason.y walls were considered under IE Bulletin 80-11;- that some of these walls support pipe or other attachments which generate punching shear loads; that punching shear was considered in this reassessment; but that the loads and loading combinations used in this program are those of the Dresden Unit 2 FSAR (which are not necessarily identical to those to be considered under Topic III-7.B). The status of Seismic Category I building walls with respect to current punching shear requirements would be considerably clarified by a table showing (actual or estimated) data for: a. The number of walls subjected to punching shear in each program. b. The loading ecosidered and the code taken as governing in each program. The number of walls found acceptable as-built on purely structural c. grounds. d. The number of walls qualifying as-built on grounds other than (c). The number of walls or supports requiring modifications in order to a. qualify..

~~ t 7 C ~ y TER-C5506-425 f. The total number of walls plant-wide subject to loadings involving punching shear.] C.12 The Licensee cites the satisfactory performance of all concrete structures under the thernal loadings they have experienced throughout the plant life as evidence.that the intent of Appendix A is met. We concur that performance under normal and operational L thermal loadings has been proven. [The cor.cern of Topic III-7.B centers strongly on the potential structural effects of accident conditions and the thermal. transients associated with them. To date, Dresden structures have been subject only to operational' thermal transients. The effect of these must be compared to the effect of postulated accident transients before the cited argument can be accepted as valid.) C.13 The Licensee states that columns do not experience load reversals because of the heavy dead loads they carry and that this code previsions therefore not applicable. [This section of the. code addreses stress reversals in columns, not load reversals only. Stress reversals in columns may arise if (under severe loadings such as a safe shutdown earthquake [5SE)) the column is called upon to support a moment of magnitude sufficient to relieve one face from normal compression and put it into tension. The Licensee should examine critical columns under the most severe loadings they must carry. If stress reversal is found, and the provisions.of this section are applicable, the adeguacy of the existing splice should be established.) C.14 The Licensee cites investigations made (using current design code criteria) under other reevaluation programs, such as evaluations made for the IE 79-14 program, and the plant's current status of compliance with such programs as sample evidence indicating plant-wide acceptability of all embedments. [The comments provided under C-6 apply here also. Is the sample studied representative? Was any retrofitting required? How do results project when statistically extended to the number of plant-wide applications?) -

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f TER-C5506-425 5.

LOADS AND LOAD COMBINATIONS An important aspect of current criteria is the loading combinations for which Seismic Category I structures must be designed. One objective of TER-C5257-321 [1] was to assemble technical information to assist the hTC in making safety evaluations concerning the structural integrity of Dresden Unit 2 Seismic Category I plant structures, based on a comparison of loading combinations actually used for design with the loading combinations currently required. Section 10.4 of TER-C5257-321 provides tables, one for each Seismic Category I structure, which are intended to give an overview of this comparison as it relates to Dresden Unit 2. The tables show: 1. The generalized loading combinations currently specified (in NRC's Standard Review Plan) as appropriate for the structure. 2. The appropriate structure-specific loading combinations. These are obtained Gom the generalized loading combinations by stricking off loads believed to be inapplicable or negligible. 3. The loading combinations actually used for design. These were obtained from the FSAR or other relevant documentation made available to the reviewers. Loads actually combined are indicated by encircling (in the appropriate load combinations) each load used in the summation considered for design. Licensees were requested to review there tables to ensure their accuracy. Disparities between the load combinations actually used for design and those currently specified are readily apparent on these tables. If the load combinations used were in complete accord with the present criteria, each load symbol in the table would appear as either struck or encircled. Ioad combinations not considered and loads ceitted from the loading combinations stand out as unencircled items. When discrepancies were found to exist, a limited number of loading i combinations (usually two) were designated Scale A. Licensees were asked to review Sea.le A loading combinations and provide documented evidence of structural adequacy under these loading combinations as currently specified. 1 l

o. .i ' TER-C5506-425 4 In general, the information furnished in References 8 and 9 appears to be insufficient to provide a basis upon which to form engineering judgments on the ability of Dresden Unit 2 Seismic Category I building structures to meet j currently speelfied loading combination criteria with margins adequate to satisfy the intent of current licansing requirements. l l This statement is not intended to imply that the existing structures may not have adequate safety margins under currently specified loading combina-tion criteria, but only that the information furnished in References B and 9 is not developed in sufficient detail to demonstrate that they do. In a number of instances, detailed investigations made for other SEP topics are relevant in assessing the effects that certain of the loads making up the load combinations have on the structure. In general, results from such SEP topics are.neither cited nor appraised in conjunction with the effects of other simultaneous loads in the loading combination. In particular, from the information furnished, it appears that for Dresden Unit 2, loads due to SSE and loads due to LOCA have been considered in the design of plant building structures, but have been independently considered. Current desigr 1 cad combinations for Seismic Category I buildings require that wherever plant structures can experienet these loads individually, the effects of simulatneous application must be considered. For all Dresden Unit 2 structures of co.)cern, this loading combination was designated Scale A in Reference 1. In addition, no analyses or other appraisals were found in the information submitted addressing the tbility of Dresden Unit 2 buildings to safeguard Seismic Category I equipment houses within them in the event that building roofs experience the extreme environmental snow loads identified in SEP Topic II-2.A. - _ -

^ . p TER-C5506-425 6.

SUMMARY

OF REVIIM TINDINGS This section suramarised SEP Topic III-7.B items considered not fully resolved by the Licensee's submittal either be:ause they were not addressed, or not fully addressed, or because the response requires clarification. These fall in,:.hree broad categories:

1. ' Items not addressed 2.

Items addressed on a sample basis 3. Items requiring further clarification. Each category is discussed in turn below. The items falling within cach category are identified. 6.1 ITEMS NOT ADDRESSED Two items fall within the category. Both concern the ability of buildings, when subject to extreme loadings, to protect Seismic Category I systems and components housed within them. The loading cases not treated are: a. The extreme environmental snow load identified in SEP Topic II-2.A. b. Simultaneous SSE and LOCA, a load combinations currently required to be in the design or of Seismic Category I structures. 6.2 ITDiS WHICH WERE ADDRESSED BY THE LICENSEE USING A SAMPLING PHILOSOPHY Some changes in the structural design codes apply to the design of a large number of structural components comonly used in the construction of Seismic Category I buildings. Individual assessment of the effects of code change on every member affected is precluded by the magnitude of the undertaking. Consequently, for the SEP review, investigation on a sample basis is considered acceptable, f The Licensee had previously performed analyses of a number of structural components using current design criteria. Thess analyses were made to ascertain Dresden Unit 2 cornpliance with several structural reassessment and retrofit programs, such as those undertaken in conjunction with IE Bulletin -2B-j L-

. i. pp,,* \\ e. TER-C5506-425 ,t 79-14. The current state of compliance with such programs is offered as evidence of plantwide acceptability (under current design codes) of the l following types of components: l a. Coped beams b. Walls subject to punching shear c. Embedments. It is noted that this is essentially a sampling approach. Compliance does document substantial areas where structures now meet current code criteria, but does not necessarily support a conclusion of plantwide acceptability. More information is required before such a conclusion can be said to be justified; for example: a. How many components of a given type were actually analyzed? b. Are the samples analyzed typical of all similar components plantwide? c. How many were found acceptable outright? How many required retrofit? d. What is total aumber of similar components throughout the plant? 6.3 ITEMS REQUIRING FURTHER CLARIFICATION The Licensee's responses to two items need clarifications. These are: Adequacy of spliced reinforced columns (see comment C-13 for details). a. b. Adequacy of concrete regions subject to accident temperatures and thernal transients (see comment C-12). _ _ _ _ _ _ - _ _ _ _ _ _ _ - -

a. j : TER-C5506-425 7. CONCLUSIONS Commonwealth Edison Company has submitted its appraisal of SEP Topic III-7.B issues as they relate to the Dresden Unit 2 Nuclear Power Station. The Licensee's submittals have been reviewed and, based on the assurances provided therein, sany of the issues of concern relating to SEP Topic III-7.B L may be considered resolved. However, the submittals do not provide sufficient information to fully resolve a',1 issues. As discussed individually in Section 6, these issues remain open: Code Changes AISC 1.5.1.2.2 - Coped beam connections AISC 11.15.7 - Walls subject to punching shear (SEP load combinations) ACI 7.10.3 - Column splices where stress reversal may occur ACI Appendix A - Transient thermal loads ACI Appendix B - Design of embedments. Ioads and Load Combinations o Accident load cases requiring simultaneous consideration of SSE and LOCA o Extreme environmental snow loads on roofs.

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,p -e f TER-C3506-425 8. REFERENCES ) 1. Franklin Research Center, Technical Evaluation Report Design Codes, Design Criteria, and Loading Combinations (SEP Topic III.7.B), Connonwealth Edison Company, Dresden Nuclear Power Station Unit 2, TER-C5257-321 May 17, 1982 2. " Specification for Design, Fabrication, and Erection of Structural Steel for Buildings," Sixth Edition American Institute of Steel Construction, Inc. New York, NY 1963 3. " Specification fcr Design, Fabrication, and Erection of Structural Steel for Buildings," Eighth Editior. American Institute of Steel Construction, Inc. New York, NY 1980 4. " Code Requirements for Nuclear Safety Related Concrete Structures" (ACI 349-76) American Concrete Institute, Detroit, MI 5. " Building Code Requirements for Reinforced Concrete" (ACI 318-63) American 0,oncrete Institute, Detroit, MI 6. ASME Boiler and Pressure Vessel Code, Section III, Division 2 " Code for Concrete Reactor Vessels and Containments" New York, NY 1980 7. ASME Boiler and Pressure Vessel Code, Section III, Division 2 " Code for Concrete Reactor Vessels and Containments" New York, NY 1962 8. T. J. Rausch, Nuclear Licensing Administrator, Boiling Water Reactors Letter to P. N. O'Connor, Project Manager, Operating Reactor Branch No. 5, USNRC

Subject:

Dresden Unit 2, SEP Topic III-7.B, Design Codes, Design Criteria, and Ioading Combinations, Docket No. 50-237 August 2, 1982 9. Connonwealth Edison (CECO) Letter to the Nuclear Regulatory Commission

Subject:

Clarifications of CICO Response to SEP Task III-7.B Items Concerning the Dresden Unit 2 Nuclear Power Station, July 11, 1984 __--___--____________a}}