ML20215B270

Forwards Supplemental Response to NRC 860828 Technical Info Request Re Restart Criteria for Cable Tray Supports.Response Suppls 860818 & 0904 Submittals

ML20215B270
Person / Time
Site:	Sequoyah
Issue date:	09/24/1986
From:	Gridley R TENNESSEE VALLEY AUTHORITY
To:	Youngblood B Office of Nuclear Reactor Regulation
References
NUDOCS 8610060460
Download: ML20215B270 (7)

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TENNESSEE VALLEY AUTHORITY CHATTANOOGA. TENNESSEE 374o1 SN 157B Lookout Place SEP 241986 Director of Nuclear Reactor Regulation Attention: Mr. B. Youngblood, Project Director PWR Project Directorate No. 4 Division of Pressurized Water Reactors (PWR)

Licensing A U. S. Nuclear Regulatory Connission Washington, D.C. 20555

Dear Mr. Youngblood:

In the Matter of ) Docket Nos. 50-327 Tennessee Valley Authority ) 50-328 Your letter dated August 28, 1986 forwarded several questions on cable tray

- supports which, although generic in nature, were to be addressed specific to the Sequoyah Nuclear Plant interim acceptance program. These technical information requests (TIRs) are in addition to those previously responded to by TVA submittals dated August 18, 1986 and September 4, 1986.

Enclosed is TVA's response to these 14 additional cable tray support TIRs.

If you have any questions, please get in touch with M. R. Harding at 615/870-6422.

Very truly yours, TENNESSEE VALLEY AUTHORITY R. Gridley, rector Nuclear Safe y and Licensing Enclosure cc: See Page 2 ptAooaBes!8883lig7 p/iI An Equal Opportunity Employer

i Director of Nuclear Reactor Regulation SEP 24 syg5 cc (Enclosure):

U.S. Nuclear Regulatory Commission Region II Attn: Dr. J. Nelson Grace, Regional Administrator 101 Marietta Street, NW Suite 2900 Atlanta, Georgia 30323 Mr. Carl Stahle, Sequoyah Project Manager U.S. Nuclear Regulatory Commission 7920 Norfolk Avenue Bethesda, Maryland 20814 Mr. G. G. Zech Director, TVA Projects U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW Suite 2900 Atlanta, Georgia 30323

SEQUOYAH NUCLEAR PLANT NRC Request For Additional Information On i

Restart criteria For Cable Tray Supports Ouestion No. 1 l State if field installation requirements may produce connections outside the range of anchor bolt tolerances provided by the design and/or specified by the manufacturer.

TVA Resoonse The original design calculations for cable tray (C.T.) supports did not specifically consider construction tolerances. Our design procedures now require the consideration of construction tolerances in the design and evaluation of anchorages.

The C.T. support re-evaluation that is being performed for restart is based on the as-built configuration of the baseplate and anchors. Therefore, in these eas:: the :ch:llt safi.gurations were considered. Where as-built configuration was no't determined, the " worst case" effects of tolerances were

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considared in the re-evaluatio,n for restart. The Phase II (after restart) 2Y*1t s!!en 9f t he M.T. tutre .i lor long-term operation will consider either inplace configuration 62 " worst case" construction tolerance effects.

Question No. 2 Indicate if rotation of the base connections has been accounted for in the determination of the resulting tensile forces on the anchor bolt. ,

Due's Ln Gii M0. 3 T4vsd.ify if a pryjng factor is considered in the design of the cable tray supports fue anther toits and embecded plates. If used, indicate the respective values and related justification. -

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TVA Resoonse To Ouestions 2 and 3 i l The C.T. support re-evaluation for restart has considered the effects,of-l baseplate flexibility on the loads in the concrete ancnors. Our design procedures require the consideration of baseplate flexibility for all baseplates that do not meet specific rigidity requirements. The analyses have been performed using a finite element computer program (BASEPLATE II). The computer program used also considers the effects of prying on anchor loads.

l Therefore, an additional " prying factor" is not required.

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Ouestien No. 4 As applicable, identify and justify the safety factors used for the different loading conditions of the anchor bolt designs.

'TVA Response Our design procedures provide the factors of safety to be used for both interim and long-term operation. For cable tray supports, the factor of safety for expansion anchors for interim operation is required to be at least 2 for all loading conditions. This factor of safety is based on the NRC OIE Bulletin 79-02. This Bulletin, which applies specifically to Category I pipe supports, allows a factor of safety of 2 for interim operation. This criteria is also appropriate for C.T. supports. .

The long-term factors of safety will be those used for the original design.

The original design basis provided for a factor of safety of 4.5 for self-drilling anchors and 4.0 for wedge bolt anchors for service or normal load conditions. Up to a 60 percent increase in stress is allowed for abnormal conditions (FS = 2.8 and 2.5, respectively).

Question No. 5 Identify if any anchor bolts have or will be installed in core bored holes.

State and justify the related effect on the design safety factors. '

TVA Response TVA uses core drilled holes for undercut anehors, through-bolts, and grouted anchors. Core drilled holes are not used for expansion anchors.

Undercut anchors and through-bolts do not depend on friction or bond of the anchor to the sides of the hole. Therefore, the capacity of these anchors is not affected by core-drilling. For grouted anchor bolts, the core-drilled nole could reduce the capacity of the grout " plug" to pullout. However, TVA's Construction specifications have always required core-drilled holes for grouted anchors to be roughened, thereby resulting in load capacities equivalent to cast in-place anchors.

Question No. 6 _

As applicable, identify and justify the use of the dynamic amplification .

factors in the evaluation of the cable tray systems.

IVA Response . . .

The dynamic amplification factors used for cable tray support design vary with the type of analysis. Some supports were designed using accelerations of 1.5 times the peak of the response spectrum, which results in amplification factors of as much as five tc ten. Other supports are analyzed by response spectrum modal analysis in the GTSTRUDL computer program, in which case the dynamic amplification factors vary on a mode-by-mode basis.

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. :e Question No. 7 State if the effects of the seismic responses are evaluated per requirements

. of Regulatory Guide 1.92. Identify any deviations from the provisions of the guide and provide justification for the deviations.

TVA Response Regulatory Guide (R.G.) 1.92 was issued in 1975 after many of the SQN cable tray supports had been designed, fabricated, and installed. There are two separate aspects to be addressed in defining the conformance to R.G.1.92:

the combination of directional effects and the combination of modal responses.

1. Directional effects are combined by taking the absolute sum of the response due to the vertical seismic component and the responses due to each of the two horizontal components separately. This combination method can sometimes be more or less conservative than a square-root-of-the-sum-of-the-squares (SRSS) of the three directional components as prescribed by R.G. 1.92. This directional combination method has been previously reviewed by NRC and documented in the SQN FSAR.

2. The SQN cable tray supports have been seismically analyzed using an SRSS modal combination method, which did not utilize absolute summation of closely-spaced modes. Re-examination of some of these supports using the Ten Percent Method (TPM) defined in Section 1.2.2 of the Regulatory Position of R.G. 1.92 shows preliminary results of increases in the stress interaction factors for the governing members ranging from zero (when there are no closely-spaced modes) to a maximum of 14 percent. The percent difference is affected by the complexity of the structure and the modeling technique utilized. While these parameters can result in larger differences than described above, they would be isolated. These variances are well within the accuracy of the dynamic analyses and do not necessitate reanalysis of supports by the TPM.

Question No. 8 Indicate how longitudinal support is provided for the cable tray systems.

Also, describe the assumptions used in determining the longitudinal forces for various cable tray configurations.

TVA Response .

The longitudinal loads in the cable trays are carried by each individual .

support. The cable trays are modeled on each support as tributary masses based on span lengths to adjacent supports. In addition, for some of the supports on the Steel Containment Vessel (SCV), the cable trays themselves were also modeled along with the supports. The longitudinal forces which each support must restrain are generated from a response spectra analysis or an equivalent static method.

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. s-Question No. 9 State if the weight of the trays and frames are considered in the evaluation -

of supports. Discuss the mannee in which the weight of the trays and support frames are modeled in their analysis.

TVA Response The weight of the trays and the supports are considered and included in the analyses of cable tray supports. The computer program GTSTRUDL includes the dead weight of the structure in the response spectra model or equivalent static analysis. The weight of the trays and supports is modeled either as lumped masses on the support member to which the tray is attached, or the trays themselves are included as part of the model. _

Ouestion No. 10 Indicate if the reduction of structural member's section properties due to bolt holes is considered in the evaluation of these structural members.

TVA Response The use of bolted connections in the cable tray system is limited to the s attachment of the cable tray to a structural angle which is welded to the support structure. The bolted connections-are designed to transfer the loads, 2

and the net section of the structural angle is adequate for these design loads.

Question No. 11 State if you have accounted for in your analysis the effects of deviation

, between center of cable trays's mass points and relevant brace connection points.

TVA Response For the trays attached to the steel containment vessel which are subjected to both DBA and seismic loads, a model which included the offsets of the mass from the centerline of the brackets was used.

Other analyses lumped the mass of the trays at the centerline of the brackets to which they are attached. This is consistent with the level of detail of .

the model and the level of accuracy inherent in the seismic design process.

Question No. 12 ff If tray clamps are used, indicate how they are assumed to provide out-of-plane bracing to the tray supports in order to prevent buckling of the support members and to prevent rotation of the support frame.

TVA Response The support frames are designed as free standing structures and do not rely on the capability of the cable tray connections to provide additional out-of-plane support.

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• .c Question No. 13 Indicate if you have conducted a program that verifies that there is

- compliance between the design / construction drawings and the field installed configurations. Provide the results of this program, otherwise indicate why this validation program is not needed.

TVA Response Compatibility between design and construction drawings and the field installed configuration was performed commensurate with the identified conditions. The specific walkdown procedures and parameters examined are described in our Interim Acceptance Criteria transmittal dated August 18, 1986.

The walkdown program has identified some differences with the drawings, and these differences are being accounted for in the reevaluation of the supports.

Question No. 14 Address the generic design controls utilized as per the requirements of Appendix B to CFR Part 50 and identify any resulting deficiencies and related resolutions.

TVA Response This issue was addressed for all systems, including cable trays, in TVA's September 4, 1986 letter in response to an August 7, 1986 letter from NRC's B. J. Youngblood.

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