ML20023B261

Suppl to Final Deficiency Rept Re Structural Steel Beam to Column Connection Design.Initially Reported on 800924. Bechtel Method of Analysis & Design in Final Phase Summarized

ML20023B261
Person / Time
Site:	South Texas
Issue date:	12/16/1982
From:	Oprea G HOUSTON LIGHTING & POWER CO.
To:	Jay Collins NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
10CFR-050.55E, 10CFR-50.55E, ST-HL-AE-915, NUDOCS 8212270172
Download: ML20023B261 (10)

Text

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The Light Company m,

,iusi%mm m m,xivoo ii ,,,ciwx s77ooi (7 3,m,2ii l Deceriber 16, 1982 ST-HL-AE-915 SFN: V-0530 PFN: G12.75 Mr. John T. Collins Regional Administrator, Region IV Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 1000 Arlington, Texas 76012

Dear Mr. Collins:

South Texas Project Units 1 & 2 Docket Nos. STN 50-498, STN 50-499 Supplement to the Final Report Concerning Eeam to Column Connection Design in the Reactor Containment Building On September 24, 1980 pursuant to 10CFR50.55(e), Houston Lighting &

Power Company (HL&P) notified your office of an item concerning the structural steel bean to column connection design in the Reactor Containment Buildir](RCB). A ':nal report was submitted to your office by letter dated September 8, 1981.

By letter dated October 26, 1981 your Mr. W. C. Seidle requested that a supplement to the final report be submitted to further address this iten. In response to that request, please find attached a supplenent to the final report providing acditional information to close this iten.

If you should have any questions concerning this iten, please contact Mr. Michael E. Powell at (713) 877-3281.

Very truly yours, Yk ehh N -#rr

(

.- y' G. W. Oprea , Jr. '

Executive Vice President MEP/syt Attachment OKo!hohdhg PDR

jI Houston Lighting & Power Compuy

! cc: G. W. Oprea, Jr. ST-HL-AE-915 J. H. Goldberg File Number: G12.75 J. G. Dewease Page 2 J. D. Parsons D. G. Barker M. R. Wisenburg R. A. Frazar J. W. Williams R. J. Maroni J. E. Geiger H. A. Walker S. M. Dew J. T. Collins (NRC)

D. E. Sells (NRC)

W. M. Hill, Jr. (NRC)

M. D. Schwarz (Baker & Botts)

R. Gordon Gooch (Baker & Botts)

J. R. Newman (Lowenstein, Newman, Reis, & Axelrad)

STP RMS ,

Director, Office of Inspection & Enforcement Nuclear Regulatory Commission Washington, D. C. 20555 G. W. Muench/R. L. Range Charles Bechhoefer, Esquire Central Power & Light Company Chairman, Atomi. Safety & Licensing Board P. O. Box 2121 U. S. Nuclear Regulatory Commission Corpus Christi, Texas 78403 Washington, D. C. 20555 H. L. Peterson/G. Pokorr.y Dr. James C. Lamb, III City of Austin 313 Woodhaven Road P. O. Box 1088 Chapel Hill, North Carolina 27514 Austin, Texas 78767 J. B. Poston/A. vonRosenberg Mr. Ernest E. Hill City Public Service Board Lawrence Livermore Laboratory P. O. Box 1771 University of California San Antonio, Texas 78296 P. O. Bcx 808, L-46 Livermore, California 94550 Brian E. Berwick, Esquire William S. Jordan, III Assistant Attorney General Harmon & Weiss for the State of Texas 1725 I Street, N. W.

P. 0, Box 12548 Suite 506 Capitol Station Washington, D. C. 20006 Austin, Texas 78711 Lanny Sinkin Citizens for Equitable Utilities, Inc. I Citizens Concerned About Nuclear Power c/o Ms. Peggy Buchorn 5106 Case Oro Route 1, Box 1684 San Antonio, Texas 78233 Brazoria, Texas 77422 Jay Gutierrez, Esquire Hearing Attorney Office of the Executive Legal Director U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Revision Date 10-18-82

4 Supplement to the Final Report Concerning Beam to Column Connection Design in the Reactor Containment Building I. Summary The design of the structural steel inside the Reactor Containment Building (RCB) has been determined to be reportable pursuant to 10CFR50.55(e). Although a substantial safety hazard has not been identified, Bechtel has initiated reanalysis of the RCB internal steel structura. As of this date, the reanalysis is approximately eighty percent (80%) complete with a forecast completion date of March, 1983.

II. Description of the Incident A detailed description of the incident was previously provided in our final report which was submitted by letter dated September 8, 1981 (reference ST-HL-AE-722).

III. Corrective Action To correct the deficiencies found in the original calculations, Brown & Root, Inc. (B&R) started the structural steel verification program. The program was completed in July 1982 leaving a few open items for Bechtel to resolve. After reviewing the B&P calculations for methodology and assumptions, Bechtel concluded that although these were generally acceptable and in compliance with industry standards, except for minor corrections.

The modification scheme suggested, however, did not represent an optimized solution and could be improved to gain economy and ease of construction. As a resul; of this conclusion, a totally new analysis and partial redesign was implemented to reduce the impact of modifications and ensure the structural adequacy of the system.

A comprehensive list of all the problems that may have been contained in the original design calculations has not been developed. Such a list and evaluation is not deemed helpful or relevant since Bechtel has reassessed the internal steel structure using a different analysis concept for lateral load transfer and considered all the mpplicable loads in proper loading combinations with the corresponding allowable stresses.

The method of analysis and design adopted by Bechtel in this final ,

phase is summarized as follows: l

1) Computer Program In the final analysis, Bechtel standard computer program BSAP was used for modal response spectrum analysis and static frame analysis.

2) Design Input

- . ~ .  :: .- . . . . . - . . .

The following load input was used in the analysis:

Operating Floors Other Floors Dead Load 300 psf 300 psf

• Live Load 1000 psf 500 psf

• Operating Temperature 120 F 120 F 0

A: cider.t Temperature 286 F 286 F Pipe Rupture l'orces Actual Load Actual Load Seismic Load response from dynamic analyses of whole steel frime-work by modal response spectrum

, , analysis.

• In some areas the actual dead load and live load are input.

The major change in the analysis by Bechtel is the utilization of modal response spectrum analysis (MRS) for the seismic analysis of the steel framing and incorporation of expansion joints located at midpoints rather than at attachment points of the steel-framed floors.

3) Scope of Reanalysis and Design Modifications a) Floor Areas with Metal Grating Bechtel utilized B&R existing layout but relocated the expansion joints to the middle of the grating sector.

MRS analyses of the integrated floor framing systems were used for the evaluation of seisniic loads for design of beams and connections. This is a more rigorous analysis that results in lower seismic design loads for individual elements than the B&R analysis which was based upon the upper-bound acceleration generally applied to all beams.

The relocation of the expansion joints and the use of MRS resulted in significant reduction of design loads and fewer expansion joints positioned at more effective locations. Without the modification of the enhanced analysis, core drilling to install rock anchor bolts and vertical stiffeners would have been required to strengthen the embedded plates at several locations on the secondary shield walls.

It is to be noted that for the MRS analysis the response spectra from both the finite element method ar.J the elastic half-space method were incorporated.

b) Concrete Slabs B&R designed the concrete skbs to act compositely with the supporting beams encased within the slabs. The partially embedded beams were considered as composite beams although no shear studs were provided.

The fully embedded beams in mid-thickness of the slabs are inefficient for the heavy out-cf-plane pipe whip / jet impingement loads. B&R indicated in its design reverification that seven beams needed to be replaced with heavier sections. Bechtel

' determined that the desired effect of such a design modification could be achieved by other means. Accordingly, in the Bechtel redesign calculation the inefficiency of the beam is recognized and the loads are assigned, instead, to the reinforced concrete slab disregarding the encased beams. The reinforcement of the slaL is then designed to develop one-way flexural action to resist all the pipe whip or jet impingement loads. The reactions of the slabs are transferred to the secondary shield wall through the connections of the radial steel beams. For thermal loads, cracked-section analyses are incorporated for the Design Basis Accident Temperotuna loading condition, thus recognizing tl.e relaxation of thermal stresses that occurs in reinforced concrete members.

As a result of the Bechtel redesign considerations described above, additional reinforcing bars are prescribed fo,- the slabs and changes in the beams are unnecessary. That is, the addition of ret.1 forcing bars results in elimination of the need to increase the beam size for the already erected beams. These beams will still be encased in the slabs for which additional reinforcement has been added. For the slabs with partially er.. bedded beams, the beam connection modifications proposed by the B&R reverification program are eliminated, c) RCFC Ducts and Support Structures The B&R reverification calculation package was

U -

4 verified for methodology and assumptions. It was found that the ducts are adequately designed and no further investigation is required. The locations of the expansion joints of the ring ducts were modified to be consistent with the revised arrangement of the thermal expansion i joints of the supporting structure and to reduce the thermal toads; however, these modifications were not necessary to assure the functionality of the ring ducts.

The return air riser supports were found to be ,

inadequate. Redesign of the supports was '

perfonned to provide appropriate support for the return air riser duct by adding beams at each support. l

4) Results The reanalysis by Bechtel has resulted in significant reduction in seismic forces compared to the B&R design  !

at the connections, especially at the secondary shield j wall. Bechtel has also analyzed all the connections of j floor beams to the secondary shield wall. The j introduction of the thermal expansion jdints at the  !

center portion of grating sectors has reduced the anchorage forces at the secondary shield wall and the local design of the areas where the steel beams are connected are considered adequate for the following reasons: i l

a) The dead weight of the floor decks was included in <

the lumped mass model of the internal structure for seismic analysis. Therefore, the overall design of the secondary shield wall has adequately considered the effects of seismic forces, b) The reduction in seismic forces and thermal stresses makes the effects of both insignificant in the wall design.

c) All connections to the secondary shield wall have been reanalyzed. lhdifications were made to the connec'; ion design where needed.

Adequate safety margins for the structural steel are prov ded in the design. A typical floor deck sector at i

elevation 68'-0" is shown in Figure 1 of Attachment I. The results for principal structural members are shown in Tables 1 and 2 of Attachment I. The last column in these tables gives the combined stress ratio which is the ratio of actual to allowable stress. As can be observed in these tables, the stresses are below allowables except in the last two entries of Table 2, where they are equal to the allowable.

IV. Recurrence Control A recurrence control program is not necessary as this situation is unique. Bechtel generic and project specific procedural controls in place are considered sufficient to preve: 1 recurrence.  !

l V. Safety Evaluation '

No detailed calculations have been performed by Bechtel to l determine the adequacy of the original RCB Internal Steel Framing system design or the proposed reverification program. B&R's analysis of the worst case conditions failed to produce total structural failure in the original structure. Based on engineering judgement and on the checks performed during their review of the turnover documentation and available B&R calculations, Bechtel supports the conclusions reached by B&R. Bechtel's position is based on the following:

1) The thermal load is self limiting in nature. The original RCB internal steel frames would have accommodated the thermal loads by limited localized yielding of the connections.

2) The horizontal seismic loads were confirmed by MRS analysis to be insignificant.

3) Although the actual pipe break loads were not included in the initial design, the steel framing would have been capable of supporting these loads after some local reinforcing.

Instead of going through detailed verification calculations in an attempt to establish the adequacy of the original design, Bechtel has performed an independent analysis and design for the entire structure, modifying the conceptual design of the system and introducing the necessary nodifications to the connections where the new design required them. The RCB internal steel is considered structurally adequate after the modifications described in this report.

. _ - _ - __ _ . _ . . _ . - ~ .-

ATTACH!!ENT I TABLE 1 CONTAINfENT INTERNAL STRUCTURES SUll!!ARY OF GOVERNING COMBINED STRESS RATIOS FROM THE BEAM /COLUl!N INTERACTION EQUATI,0N FOR PRINCIPAL STRUCTURAL STEEL MEl1BERS Governing Load - Combined Description of Location of Combination Stress Prin'cipal Members Principal Mcmbers Number

• _ Ratio (4,1.0)

W27 x 160 Beam El 68'-0" between Az 180* - 206.5' 1 . 0.95 W33 x 240 Beam El 68'-0" 9 Az 355' 9 0.6 W33 x 240 Beam El 68'-0" O Az 322.5' 1 0.58 W27 x 160 Beam El 68'-0" between Az 5' - 25.5' 1 0.68 W27 x 160 Beam El 68'-0" between Az 334.5' - 355' 1 0.72 W30 x 190 Beam El 68'-0" between Az 106.56 - 159.5' 5 0.97 h24 x 100 Beam El 68'-0" between Az 127.0* - 132.0* 1 0.87 W33 x 240 Beam El 68'-0" O Az 139' 5 0.85

• For load combinations referred to by these numbers, see FSAR Table 3.8.3-2.

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. ATTACR1ENT I TABLE 2 CONTAIN!!ENT INTERNAL STRUCTURES SUM!!ARY OF GOVERNING COMBINED STRESS RATIOS FROM THE BEAll/COLUf1N INTERACTION EQUATION FOR.

PRINCIPAL STRUCTURAL STEEL llEl:BERS .

Governing Load Combined Destription of Location of Combination Stress Principal ikmbers Princip31 Members Number

• Ratio (dil.0)  ;

W24 x 120 Beam El 37'-3" 9 Az 78* 9 0.88 l W24 x 110 Beam El 37'-3" between at 42.5* to 62.0* 1 0.66

. W33 x 200 Beam El 37'-3" G.Az 139' 5 0.70 El 37'-3" 9 270*

W33 x 200 Beam 3 0.68 W24 x 110 Bea.m El 37'-3" 9 Az 247.5* 9 0.88 i W33 x 200 Beam El 37'-3" 9 Az 227.0* 9 -

0.76 l W24 x 110/WT8 x 48 El 37'-3" between Az 247.5' to 270* 1 1.00**

k'24 x 84/PL l' x 8" El 37'-3" between Az 270' to 284.5* 1 1.00**

l 0For load combinations referred to by these numbers, see FSAR Table 3.8,3-2.  !

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