ML20106J665

Forwards Revised Responses to NRC Questions 130.37,130.38 & 130.39 Re Structural Engineering Aspects of Cable Tray Supports

ML20106J665
Person / Time
Site:	Comanche Peak
Issue date:	10/26/1984
From:	George J TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	Youngblood B Office of Nuclear Reactor Regulation
References
NUDOCS 8411010302
Download: ML20106J665 (13)

Text

r TEXAS UTILITIES GENERATING COMi%NY P. O. BOX 1001 GI.EN ROSE. TEXAS 76043

• .1 October 26, 1984 Mr. B. J. Youngblood, Chief Director Of Nuclear Reactor Regulation Division of Licensing Licensing Branch No. 1 Office of Nuclear Regulatory Comission U.S. Nuclear Regulatory Comission Washington, D.C.

20555 SU8 JECT:

COMANCHE PEAK STEAM ELECTRIC STATION DOCKET NOS. 50-445 AND 50-446 CLARIFICATION TO SGEB ADDITIONAL QUESTION RESPONSES

Dear Mr. Youngblood:

Per our discussion last week, we hereby forward revised responses to NRC questions 130.37, 130.38, and 130.39.

Should you have any questions in this matter, please contact this office.

Sincer fj eor 6e)

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Vice President Project General Manager JBG/bh Attachment cc:

J.J. Stefano j-John Beck l

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9WESI1QN 130.37 1

In Cygna's reLponse to CASE's question Walsh #5 and

s during the ASLB hearing of May 1, 1984, Cygna identified a safety factor of three (3) for the SSE condition as related to Hilti expansion anchors.. As part of the justification Cygna referred to NRC Document MS 129-4.

This NRC document (MS 129-4) is in a draft' form, and has not been converted into a draft NRC Regulatory Guide and/or issued for public comments.

Since this guide has not been finalized and recommends a safety factor lower than the manufacturer's recommended safety factor of four, we request that you justify your-basis for accepting a safety factor of three.

Also, as part of this response you should identify the total number of Hilti expansion anchors used on cable tray supports and the number and locations of expansion anchors that have a safety factor of less than four (4).

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' RESPONSE 130.37-JUSTIFICATION FOR F.

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= 3.0 f

The. factor,of safety"on expansion anchors (Hilti

-Kwik-Bolts) used for Cable. Tray.. Supports has been established to be a minimum of 4 for Operating Basis Earthquake loading conditions (Maximum Working Load Conditions). 'These loading conditions.per the FSAR are considered to be severe environmental loads and will be encountered infrequently during the plant life.

Steel structures subject to this loading condition are designed based on elastic working stress design methods and meet the requirements of AISC working stress allowables. 'The expansion anchors which are-used with these steel structures have been designed inaccordance with

' the manufacturer's recommendation of a. minimum factor of safety'of 4 for the maximum working load conditions, OBE, (copy.cf Hilti Kwik-Bolt Technical 1Information, pg C3, attached).

.The/ factor of safety on expansion anchors used for Cable LTray Supports when' subjected to full Safe Shutdown Earthquake 4

(SSE) loading conditions is minimum of 3.

The SSE load per the'FSAR'is considered to be an extreme environmental load

'which is credible but highly improbable.

The steel structures which are subjected to this loading condition when designed

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using working stress' design methods are allowed to be stressed to a level of 1.6 times the stress of OBE loading conditions.

This~ increased allowable in stress levels is partly attributed to the high improbability of the occurrence of such SSE loading combinations.

This same rational is likewise applicable to the associated factor of safety of 3 for expansion anchors.

As provided within the Hilti Kwik-Bolt Technical Information sheet, actual factor of safety to be used depends on the application and should be selected by the designer on this basis.

Since the loading condition in question is one of extreme environmental conditions and highly improbcble, the lower factor of safety is applicable.

Other' technical information and Codes that support this Jecision are NRC IE Information Notice No. 79-14 and ACI 349, Appendix B.

As provided in the NRC IE Information Notice No. 79-14, Class IE electrical cable support systems should be designed to withstand the effects of SSE and remain functional.

Expansion anchors designed based on a factor of safety of 3 for SSE conditions will meet this requirement.

ACI 349, Appendix B, Section B.7.2 provides for a factor of safety of 3 for expansion anchors which do not meet the ductility requirements of Section B.7.1.

Based on the above, factor of safety of 3 for SSE loading combinations is acceptable for Hilti Kwik-Bolt expansion anchor use.

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- QUANITY ESTIMATE OF CABLE TRAY SUPPORTS HAVING FS < 4.0

,1 Estimation'of the number of cable tray' supports that

-would have a factor of safety less than-4 was determined by

the following' method.

7 Generic designs of cable tray supports were based on (accelerations of Ay = 1.67g's and Ax = A: =

2.67g's for OBE conditions.- 'This'would provide an approximate resultant acceleration affect based'on the following formula:

Resultant acceleration = 1.0 D.L.

+ SRSS ( Ax,y,z)

=~5.129 g's V

where, D.L.

= gravitational dead load Ax,y,: = OBE acceleration for.

-X,Y,Z directions

The estimation approach utilized this resultant acceleration for comparison purposes to the computed resultant accelerations associated with SSE conditions for damping factor of 7%.

The following are the building areas which g

would potentially have factor of safety less than 4.0 on expansion. anchors.

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5 BUILDING

. ELEVATIONS NO. CABLE TRAY SUPPORTS GENERIC SPECIALS REACTOR BLDG-ABOVE 860'-O" 92 193 l ELECTRICAL CONTROL. NONE-0 0

AUX BLDG ABOVE 873'-O" 147 81 SAFEGUARDS' ABOVE 831*-6" 335 243 FUEL' BUILDING NONE O

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. TOTAL NO. SUPTS-574 517 Estimated 80% use HKB---------

460 414 Estimated average-of 4 Bolts per support GENERICS 1840 SPECIALS 1656

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TOTAL BOLTS 3496 The total number of supports associated with cable tray raceway is approximately 13,500.

It is estimated that 80 %

(10,800) of these supports utilize expansion anchors.

At 4 bolts per supports, the total number of expanion anchors used

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. for. cable tray supports is 43,200.

Based on these approximate figures, supports utilizing expansion anchors at the above tabulated building elevations would represent 8.1 % of the supports utili=ing expansion anchors.

Additional SPECIAL supports at lower building

- mievations which are designed based on the-acceleration values

' for their respective' elevations may be involved.

These supports are estimated to be not more than the total number of supports identified above.

These supports added to the supports identified in the above tabulation would potentia 111y increase the number of bolts to approximately 7000.

This represents approximately 16.2 % of the expansion anchors used for cable tray supports that would have an associated factor of safety between 3.0 and 4.0.

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9WEEI19N 130.38 In response to a staff question at the ASLB hearing of May 3, 1984, (pages 13722-13725) Cygna witnesses stated that

-.under SSE load conditions, the yield strength might be exceeded for certain components.

At the same time, it was-emphasized that the design is considered elastic and the use of the 1.6 factor in conjunction with some of the code allowable stress values brings the condition where the yield strength of certain components may be exceeded for the SSE load combinations.

Identify all-of the cases in the design of the cable tray supports where.,this condition occurs and provide detailed explanations for each controlling case.

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RESPONSE 130.38 The design of cable tray supports is based on working-stress design methods.

By comparison of SSE accelerations to 1/2 SSE accelerations for each respective building floor elevation per the methodology as described in Response 130.37, increase in stresses due to GSE loading conditions would be of an order of magnitude of 5 to 23 percent.over 1/2 SSE stress levels.

Per the FSAR, allowable stress levels for SSE loading conditions are allowed to be increased to a value equivalent to 1.6 times the allowable

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stress levels for 1/2 SSE loading combinations.

This infers that allowables for 1/2 SSE conditions that are equal to or greater than.625 Fy when increased by the factor of 1.6 for equivalent allowables for SSE conditions, that the resultant SSE allowables would be equal to or exceed Fy of the materials used in fabrication.

By use of the acceleration comparison values, the actual stress levels of the supports for SSE conditions would be increased to a value equivalent to a maximum of 1.25 times the 1

actual stress levels for 1/2 SSE loading combinations.

For 1/2 SSE loading combinations, the allowable stress levels are those found in Appendix A of the American Institute of Steel Construction Inc.,

" MANUAL of STEEL CONSTRUCTION AISC.

s A review of the allowables provided in Appendix A of the

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P AISC' Manual'_when. increased'by-a factor of 1.25 results in the

.followingfareas"in which t'he. resultant.value would exceed-the-

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yield-(Ff) of.the materials used

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1.5.1.5: BEARING (on. contact area),

Bearing"on1 milled surfaces, including bearing stiffeners and

.- p ns lin reamed,' drilled or bored holes:

i Fp = 0.90 Fy

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1.5.2 RIVETS, BOLTS, AND THREADED PARTS, l Bearing on-projc=ted area of bolts in bearing-type connections and on rivets:

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Fp =.1.35 Fy For cable ' tray supports, there are no conditions in which A-the items identified.in (1) above are used; therefore, this provision (is not applicable to the design.

For item (2),. based on the structural shapes and bolting materialsiused in attachment of the tray to:-the support, 1/2.

?-4 SSE-maximum load on bolts actachingL the tray to the support is approximately '4.71 kips pa - bolt. 'With an increase of 25% in i

cload.from 1/21SSE to SSE, the SSE~ load-would be 5.875 kips.

Thickness of the support member at point ofiattachment is a Jminimum of 0.200 inches.

BAwed on-ASTM A325 5/8" diameter

.boltsfand A36 stee17 supports, the 1/2 SSE allowable bearing i."*.'9 s

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-' stress of 1.35 times Fy!for the support would be 48.6 ksi.

' For the connection,.the allowable bearing load would be equivalent to approximately 6.1 kips.

Therefore, the SSE' load condition,would meet'the allowable of AISC without the 1.6

. increase as provided for in the FSAR.

The conclusions of the above are that-there are no conditions under SSE-Icading combinations that would exceed

- the-yield of-the materials e1 cept as permitted by the AISC

. Specification..

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gyEEIlgN 130.39 In support of the damping values used for the design of cable trays and supports with welded conections, Cygna referred to ANCO's test results report on " Seismic Testing of Electric Cable Support Systems."

This report provides good engineering test results related to allowable damping values

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to be used in the. design.of cable-trays and their supports.

Also, the results of this report with accompanying Justifications have been accepted by the staff for accepting design damping values greater than the-values identified in

.NRC Regulatory Guide 1.61.

However, Cygna's answer.to Walsh's question does.not establish all of the specific ties (e.g.

configuration) with the ANCO's report.

We acknowledge the

' fact..that the cable trays may be acceptably designed to higher s

damping values than.those identifiou in RG 1.61, but good documentation and a clear determination of the applicability of-test results is a must.

Provide the necessary documentation and ~ justifications.

The FSAR should also be

= revised _to accurately reflect how the design of the cable tray supports conforms to-RG 1.61.

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.c RESPONSE130.I39-

-The _.desi gn. of the cableztray and' associated 'upport s

systems'are' based on.' damping factors as provided in NRC Regu1Atory Guide 1.61 for bolted ~ steel structures,.

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. configuration of the tray and support system consist of. tray isegments with bolted splice: connections, tray attachment-t'a 4_

'the. respective supports by bolted connections and support

- attachment.to'.the concrete super-structures generally by..

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' bolted _ connections byt may be by welded connection if embedded The~ supports consist of va'ri ous.

plates are available.-

relatively light weight structural steelEshapes, welded together such as.to provide a-structural element.to support the cable tray. raceway.

As indicated above,.the_ total spstem configuration consistEof1 structural elements connected

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via. bolted' connections'which indicates'that the-ttogether

system performance in1 response to earthquake conditions would' Jbe thatlofra bolted' steel structure.

Critical damping-values

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.used in1 cable-tray-/ support-design are based on damping

. values noJhigher than 4-% and 7 %'for Operating Basis

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Earthquake'and1 Safe Shut'down: Earthquake respectively.

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