ML20099G292

Forwards Info Re Miscellaneous Steel Verification Program Requested by NRC During 920707-08 Visit.Phase II Walkdown Procedure Encl

ML20099G292
Person / Time
Site:	Brunswick
Issue date:	08/07/1992
From:	Mccarthy D CAROLINA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20099G296	List: ML20099G292 ML20099G310
References
NLS-92-224, NUDOCS 9208140192
Download: ML20099G292 (11)

Text

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y o' CP&L CaroHns Power & Light Company AUG 0 71992 SERIAL: NLS 92 224 l

l United States Nuclear Regulatory Commission ATTENTION: Document Control Desk Washington, DC 20555 BRUNSWICK STEAM ELECTRIC PLANT, UNIT NOS.1 AND 2 l l

DOCKET NOS. 50-325 & 50-324/ LICENSE NOS. DPR 71 & DPR-02 MISCELLANEOUS STEEL VERIFICATION PROGRAM j Gentlemen:

On July 7 8,1992, representatives of the Nuclear Regulatory Commission staff visited the Brunswick Steam Electric Plant to discuss the miscellaneous steel design basis documentation program. During the meeting, Carolina Power & Light Company agreed to provide the information requested by the staff in two submittals. The company's initial response was submitted by letter dated July 27,1992 (Serial: NLS 92 203). Enclosure 1 provides a listing summariring the information being provided in this submittal. Enclosure 2 provides the information requesttid by the staff.

~ Please refer any questions regarding this submittal to Mr. W, R. Murray at (919) 546 4661.

Yours very truly, w -

D. C. McCarthy

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M Manager

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Nuclear Licensing Section WRM/wrm (steel 2.WPF)

Enr.'osurec cc: Mr. S. D. Ebneter Mr. R. H. Lo Mr. R. L. Prevatte

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ENCLOSURE 1 BRUNSWICK STEAM ELECTPIC PLANT UNITS 1 AND 2 NRC DOCKET NOS. 50-325 & 50 324 OPERATING LICENSE NOS. DPR 71 & DPR 62 MISCELLANEOUS STEEL VERIFICATION PROGRAM The miscellaneous steel programmatic and technical issues listed below have been identified for inclusion in CP&L's August 7,1992 response:

PROGRAMMATIC

1. Discuss the root causes.

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2. Provide the Phase ll proceduro.

3. Address miscellaneous steelin other Category I structures.

TECilNICAL

1. Compare long term acceptance c>iteria with Updated FSAR and provide justification for any deviations (includo usa of AISC 8'" edition),

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2. Provide justification for not considering tornado loads.

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ENCLOSURE 2 BRUNSWICK STEAM ELECTRIC PLANT, UNITS 1 AND 2 NRC DOCKET NOS. 50 325 & 50-324 i OPERATING LICENSE NOS. DPR 71 & DPR 62 1 MISCELLANEGUS STEEL VERIFICATION PROGRAM l

PROGRAMMATIC ISSUES l ITEM 1:  !

Discuss the root coutes.

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RESPONSE

Carolina Power & Light Company is currently working with United Engineers & Constructors and Brown & Root to prepare a formal root cause assessment. However, additional information is being received from the walkdowns and must be reviewed prior to finatiring a formal root causo.

Although the root cause assessment is stillin progress, preliminary assessmen" point to initial safety classification and construction practice as causal factors.

ITEM 2:

Provide the Phase il procedure.

RESPONSE

The Phase 11 Procedure is included as Attachment 2.

ITEM 3:

Address miscellaneous stect in other Category I structures.

RESPONSE

The initial effort of the Misceuaneous Steel Verification Program is to concentrate on the rniscellaneous steel in the reactor buildings and drywells for several reasons:

a. The verification.i .Je was initiated because of concerns related to the design and construction of reactor building structural steel.

h b. . The major portion of the miscellaneous steel is located in th0 reactor buildings and L drywells. Although some miscellaneous steel can be found in some of the other

i. Category I buildings, the quantity'is relatively small, as compared with the reactor l building and drywell.

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c. Although the miscellaneous steel may perform irnportant functions in other Category I structures, in general, the more critical functions for the miscellaneous steel are in the reactor buildings and the drywells. ,

However, the results from the verification of the miscellaneous steelin the reactor buildings and drywells will be evaluated to identify issues which are generic in nature. An engineering walkdown will be conducted in other Category ! structures to the extent neeessary to ev61oato the effect that the generic issues inay have on the performance of the miscellaneous t,teelin those structuras.

TECHNICAL ISSUES ITEM 1:

Compare long-term r,cceptance criteria with Updated FSAR and provide justification for any deviations (include use of AISC 8* editionb RESPONSE

• The design of the steelincluded in the Miscellaneous Steel Verification Program was based on the 6th Edition of the AISC Specification for Design, Fabrication and Erection of Structural Steel for Buildings. According to original FSAR commitments, the allowable streases included in that Specification can be mereased by 1.5 when considering the Design 3asir Earthquake. No detailed licting of specific load cases are included. The Updated FSAR imposes the same critoria with the following exceptions:

1. Specific load casos are identified, and ineluded in Attachment 1 for easy reference.

These load cases do not alter original FSAR commitments. Rather, they provide more specificity.

2. The use of 8th Edition of the AiSC Specificationfor Design, Fabrication and Erection ol Structural Steel for Buildings is allowed for current work.

In summary, th'e only difference between the long-term critoria and the original FSAR commitments is the use of a more recent version of the AISC Specification. Attachmant 1 provides additional input regarding justification for some of the more significant changes,  ;

ITEM 2:

Provide justification for not considering tornado loadu.

RESPONSE

The Miscellaneous Steet Verification Program for.the reactor building is limited to steel below the 117 foot elevation. Below this elevation, the structure consists of reinforced concrete exterior walls designed to resist the effects of tornado winds. .The portion of the structure above the-117 foot elention, which is not part of the Miscellaneous Steel Verification Program, has external

. steel siding. This siding is designed to remain attached to the structure on the windward side E2 2

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- during a totnado, but is allowed to be blown away on the other sides. Blowout panels are pmvided i in the concrete slab at th6117 foot elevation to relieve excess internal pressure due to the l depressurlaation of air surrounding the structure. Stairways, hatches, and other openings are used J to vent interior spar:es. Ukewiw, concrete slabs at the 80 foot, 50 foot, and 20 foot elevations j also have stairways, hatches, and other openings which relieve pressure from depressurization.

The Miscel!aneous Steel Verification Program for the reactor buildings consists of two distinct classes of steel. The miscellaneous steel outside the drywells, and the datforms inside the drywells. The miscellaneous steel outside the drywells consists primarily of optn horizontal members separated by several feet at various elevations which,in general, provides no defined <

b rrier to forrn an internal ecmpartment. Therefore, no defined mechanism exists to create a

- measurable differential pressure. Because the lower portion of the reactor buildings are vented from above (117 foot elevation), any amount of differential pressure that would be imposed on the beams would result in a net upward pressure, which will reduce the dead load.

The effects of wind or depressurization are factors precluded for the drywell platforms by the derign nf the drywell, which is sealed for pressures much higher than 3 psl.

In general the miscellaneous steel consists of open sections, thus precluding any differential pressure within the member. if tubular sections are ider tified, they will be checked to assure either venting capability exists or the member is sufficiently strong to withstand the postulated differential pressure along with other necessary loads, in summary, tornado loads are not a factor for the verification of the miscellaneous steel in the reactor buildings and drywells below the 117 foot elevation.

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ATTACHMENT 1 ygg[MSC_Snggliingii.pn_for the Dnian, Fabrication and Erection oLS1wrigral Steellar._Buildinaji ine basic philosophy of the Specification is that the primary load carrying mechanism of the structural steel (i.e. beams) is, in general, through bending. This is particularly true for structural components such as those included in the Miscellaneous Steel Verification Program. Therefore, it is appropriate that the stresses associatcd with bending establish the basic margins of safety in a structure. A basic allewable stress of 0.6 Fy (where Fy is tho minimum specified yield strength) is selected which results in a minimum f actor of safety of 5/3 - 1.67 against a collapse load. This factor of safety accounts for various unknown or unquantified factors, such as variations in loading, environmental effects, f atigue, deflection and limitations in design, analysis and construction procedures. All other stress considerations, such as cornpression, shear and stresses associated with connections and other discontinuities are generally given a highur factor of safety (Reference 1). These higher factors of safety are y arranted either because of the nature of the failure associated with that particular stret.s conipenent, limitations in commonly utilized stress analysis or construction techniques, or by the ecunomics of the issue.

The use of the 1970 Specification has been accepted for general use by the NRC staff as specified

'n the Standard Review Plan (SRP), Section 3.8.3 and has commonly been used on plants licensed since it was issued. Many more plants have used the 1970 Specification, which has allowable stresses sirnilar to those of the 1978 version for fillet welds and weak axis bending. In geneta' the design of these plants are based on the load combinatic'is included in the SRP Section 3.8.3 which are similar, and in some cases are slightly less conservativo than those imoosed on the Miscellaneous Steel Verification Program.

There ere three differences between the 1963 and 1978 Specification that are of primary interest and will have the greatest effect of the miscellaneous steel verification effort. These include the following:

• Fillet Welds - As discussed in the Commentary to the 1970 AISC Specification, I Section 1.5.3, "In earlier editions of the AISC Specification, working stresses were not given for fillet welds made with electrodes stronger than the E70 classification.

The stresses that were given were known to be overly conservative for their j

recommended use with an E70 classification. Based upon tests (Reference 2), the l

allowable stress on fillet welds, deposited on ' matching' base metal or steel having mechanical properties higher than those specified for such base metal, is now given in terms of the specified tensile strength of the base .tietal?

l As indicated in the commentary, there was no change specified in the design l procedure, material specification or construction techniques and practices to utilize these higher values, just the recognition that " overly conservative" allowable stresses existed in the earlier specification which was corrected in later editions.

An indication of the conservatism that exists for fillet welds based ei the 1978

! AISC Specification albwable stresses,is shown in the attached Figure 1, taken from the Steel Manual,8th Edition, Page 4 73. This figure represents the results from a series of tests. As shown, the 1978 Specification fillet weld allowable stresses have a minimum factor of safety, as compared with the minimum yield

( value, of approximately two (2). Compared to the basic factor of safety for I

structural steel of 1.67, included in both the 1963 and 1978 Specifications, the i 1978 Specification maintains excess safety margins for fillet welds. The higher l

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fillet weld allowable strasses will not control the overall margin of safety of the lower drywell platforms.

• Bolting As discussed in the Comrnentary to the AISC Specification for Structural Joints, Section C4, included in the 8th Edition of the Steel Construction Manual: "

in the current Edition of this Specification, significant increases have been made in the recommended working stresses for proportioning connections which function by i

resisting the transfer of shear between the connected parts in friction or bearing.

While the research which supports the new provisions has been published from time to time in individual papers (some of it more than a decado ago), it was felt that the updating of working stresses, unchanged since initial adoption, should not be Diocemeal. Therefore, a review looking toward a systematic presentation of the accumulated information within a single volume was initiated in 1970, under the direction of the Council. In restudying the research reported during the past two decades, the cornpteted publication (Reference 3) has had as its goal the more reliable prediction of the behavior of various bolted connections under various kinds of loading."

I "With the weal *h of available data at hand, it has been possible, through statistical analyses, to adjust allowable working stresses to provide uniform reliability for all loat"ng and joint types. The design of connections stillis more conservative than that of the connected members of buildings and bridges by a substantial margin, in the Jense that failure load of the fasteners is substantially in excess of the maximum serviceability limit (yield) of the connected material."

The allowable stresses included in the Specification for Structural Joints are consistent with those included in the 1978 AISC Specification for the Design.

Fabdcation and Erection of Structural Steel for Buildings. As indicated in the Commentary, this increase in allowabte stresses does not require any change to the design approach, material specifications, or construction techniques and/or practices that would have boon used for designs made to the 6th Edition Steel Manual. Figure 2 shows test data (taken from Reference 3) indicating that, based upon the 1978 Specification, the Factors of Safety for the bolting continues to exceed the allowable factor of safety for major exis bending. Therefore, increases in bolting allowable stresses through use of the 1978 Specification will not reduce l the controlling margins of safety.

• Weak Axis Bending of Doubly-symmetrical Compact Sections A concise l

i explanation for this increase is included in the Commentary of the 1970 Specification which is worth repeating:

"The 25% increase in allowable bending stress for compact sections and solid rectangular bars bent about their weak axis, as well ac for square and rectangular bars,is based upon the favorable shape factor present when these sections are bent

about their weaker axis, and ti.e fact that, in this position, they are not subject to lateral torsional buckling." Thus the applicdtion of a consistent increase factor to this load takes into account the added strength of the section due to the favorable

! shape factor and as a result does not reduce the effective margins specified in the i

Final Safety Analysis Report.

Other differences between the 1963 and 1978 specifications have been reviewed and found to be of much less significance. Justification for these changes are generally included in the Commentary to the 1978 AISC specification.

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in summary, overall margins are not adverself affected by the use of the 1973 AISC Specification for Design, Fabrication and Erection of Structural Steel for Buildings.

BaleLeucs.r 1 fitrustygt _ Steel Desian, Beedle, et al, The Ronald Press,1964

2. Higgens, T. R. and Preece, R. R. Procosed Workina Stresses for Fillet W.clWi_10 fiw! din.n.ConstLVG'jQn, Wolding Journal Research Supplement, Oct.,1968

3. Kulak, G. L., Fisher, J. W., and J. H. A. Struik, Guide to Desian Qiteria for Bolled and Riveted Joints,2nd Edition, John Wiley & Sons, Now York,1987 M

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