ML20136F607

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Forwards Resolution of Open Items from Cygna Hearings.Items Should Be Deleted from Sser 5.Review Team Should Review Items 10 & 12
ML20136F607
Person / Time
Site: Comanche Peak  Luminant icon.png
Issue date: 12/19/1984
From: Knight J
Office of Nuclear Reactor Regulation
To: Noonan V
NRC
Shared Package
ML17198A292 List: ... further results
References
FOIA-85-59 NUDOCS 8412310140
Download: ML20136F607 (5)
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Text

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NUCLEAR REGULATORY COMidlSSION

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r. ASHING TO N, D. C. 20555

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DEC 191984 MEMORANDUM FOR: Vince S. Noonan, Project Director Comanche Peak Technical Review Team FROM:

James P. Knight, Assistant Director for Components and Structures Engineering Division of Engineering

SUBJECT:

CCMANCHE PEAK STEAM ELECTRIC STATIONS 1 & 2 -

RESOLUTION OF OPEN ITEMS FROM CYGMA HEARINGS

References:

1.

Menorandum from V. S. Noonan to J. Zudans et. al.

dated December 7, 1984.

2.

Mercrandum from J. P. Knight to T. M. Novak dated August 21, 1984.

Eased on the applicant submittal of October 26, 1984, the Structural and Geotechnical Engineering Branch has resolved three stru tural engineering concerns related to CYGNA's Independent Assessment Program (IAP) on the RHR Cable Tray System. These items were identified as open issues during the CPSES hearings on CYGNA IAP and were not addressed by CYGNA.

These items were previously addressed in the draft SSER #5 and should now be deleted from the SSER #5. These items should now be addressed as part of the SSER being developed by the TRT Civil / Structural group as delireated in Reference 1 above.

Furthermore, Action Item 10 icentified in Reference 1 above has already been addressed in the staff supplemental testimony on CYGNA (Reference 2 above).

It is therefore suggested that the TRT review this item for incorporation ir.to its SSER. Action Item 11 is addressed in the attachment to this transmittal. Action Item 12 has not been addressed by the staff to dcte and should be addressed by the TRT under its scope of responsibility (See Transcript at pages 13479-13483}.

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James P. Knight,-

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I ENCLOSURE COMANCHE PEAK NPP

,ASLB HEARING ISSUES l

L The ::tsff has reviewed all structural questions raised by the

-intervenor CASE and the responses provided by Cygna, both in writing and at the ASLB hearings.

In order to resolve the concerns and clear the record'with regard to the Independent Assessment Program (IAP),

the steff requested additional information on the following specific issues and provides related summaries:

1.= In one of the CASE Questions of February 22, 1984 to Cygna (Question-Walsh5),CASEpointedoutthatthedampingvalue t

of 4f used for designing the cable tray supports was not consistent i

uith the FSAR and Reculatory Guide 1.61 which recommend damping values for the operating basis earthquakes of 2% for welded structures and 4 damping for bolted structures.

Cygna based its acceptance on two arguments:

a) in cable tra dissipating energy, and b) y systems there are many mechanisms for published literature on testing cable tray l

system behavior under seismic excitation illustrates that these systems l

exhibit damping values greater than 4%. Cygna referred to ANCO's l

test results report on " Seismic Testing of Electric Cable Support

' Systems." This report provides good engineering test results i

l related to allowable damping values to be used in the design of cable trays and their supports. Also, the staff has used the l

results of this report as a basis for accepting design demping l

values greater than the values identified in NRC Regulatory Guide

  • 1.61. We acknowledge the fact that the cable trays can be designed l

to higher damping values than those identified in Regulatory Guide l

1.61. We requested of the applicant that the FSAR be revised to address the variation with the guidelines of Regulatory Guide 1.61 l

related to the use of the 4% damping for welded cable tray components.

1 The applicant has amended the FSAR to indicate that the, l

configuration of the trays and support systems consist of tray segments with bolted splice connections, trays attached to their respective support by bolted connections and supports attached to the concrete super-structures generally by bolted connections.

i Welded connections are used for the latter if embedded plates are available. The supports consists of various relatively light weight i

structural steel shapes welded together so as to provide a ttauctural element to support the cable tray raceway. The total i

Q stem configuration consists of structural eierents connected

, p tber with er.";' t @ ed cenrections which indicates thet the system i

perforecnce in respense to earthquake ccnditions would be that of a-tolted steel structure.

Damping values used in cable tray / support l

design are based or damping values no higher than 4%'and 7% for Operating Basis Earthquake (OBE) and Safe Shutdown {arthquake (SSE) l respectively.

I I

, Based on justificatiens provided by Cygna and the applicant, and the licensing egerience related to numerous test results of cable tray systens containing welded and bolted ccnnections yielding damping values much larger than 4%, the staff accepts the values proposed by the applicant of 4% for OBE and 7% for SSE for all structural components related to the cable tray systems.

2.

Related to the same Question - Walsh 5, Cygna identified a safety factor of at least three (3) for the SSE condition as related to Hilti expansion anchors, while providing a safety factor of four (4) for the OBE condition.

Cygna determined that the design is acceptable since they find acceptable a safety factor of three (3) for the SSE load condition by staff draft document M5129-4.

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 puide has not been finalized and recommends a safety factor lower than the manufacturer's recommended safety factor of four, the staff requested the applicant to justify the basis for accepting a safety factor of three (3) for the SSE condition and to 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).

Cygna justifies the lower safety factor of 3 for.the SSE case based on the lower occurrence of the SSE vs. OBE, the great flexibility of the cable tray systems as generally documented by the ANCO test results, the non-catastrophic consequences of failure of one support, and the guidance provided by NRC draft document MS 129-4.

Cygna has stated, at the request of the staff, that this condition applies only at the top elevations (top two floors) of the related buildings, that these elevations have a very small percentage of cable tray supports, and that the number of cable trays that can be effected by a safety factor lower than four but higher than three are between 5 and 10 percent of the total. The applicant makes similar justifications on this subject matter. The staff will provide additional discussion on the adequacy of the lower safety factor in staff testinony i

to Walsh Ouestion #8.

Based on the limited numbers'and locations of affected cable tray supports, and the staff evaluation related to the adequacy of the lower safety factor of three, the staff has resolved their concerns on this issue.

3.

In response to t. rteff cuestion at the ASLB heering of Pay 3, l

..J ',Tr. p.p : 12".2 ISM), Cygnt. witnesses sttted that ure'er ISE load conditions, the yield strength might be exceeded for certain l

corponents.

At the same time, it was en.phasized that the design l

1s considered elastic and the use of the 1.6 factor in conjunction With some of the code allowable stress values brings the condition i

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where the yield strength of certain cetponents miy'be exceeded fer the SSE lcac ctabinatiens.

The staff asked the applicant and Cygna to identify all of the cases in the design of the cable tray l

supports where this condition occurs and provide detailed explanations for each controlling case.

Cygna discussed this issue (FSRI Tr. 80-82) during the July 3, 1934, meeting and indicated, "that when one takes a further lonk at that, there were no examples of where it exceed.9Fy....

There is a letter by Gibus and Hill attesting to that." Cygna stated that this informat'on will be documented in Phase IV of the Cygna's IAP. The applicant has indicated that the increase in stresses due to SSE loading conditions would be of an order of magnitude of 5 to 23 percent over the OBE stress levels. The allowable stress levels for SSE loading conditions are permitted to be increased to a value equivalent to 1.6 times the allowable stress levels for the OBE loading ecmbinations. Also, the American Institute of Steel Construction (AISC) Manual of Steel Construction accepts an allowable stres's in bearing for the projected area of bolted connection to reach a limit of 1.35 times the yield value of the material.

For this latter condition there exists the possibility that the yield value of the material may be acteally exceeded.

However, based on a numerical evaluation of actual stress levels in the applicable bolts, the applicant concludes that there are no conditions under SSE loading ccmbinations that would exceed the yield of the materials even without the use of the load factor of 1.6 specified in the FSAR and the SRP.

In conclusion, the SSE load condition for the subject cable tray systems meets the requirements set in the FSAR and staff SRP 3.8.4, and is acceptable to the staff.

MRC Staff Conclusions Rased on its review of the draft Cygna report dated November 5, 1983, its audit of February 9 and 10, 1984, at the Gibbs & Hill offices, the site visit of April 25, 1984, and Cygna's testimony at the ASLB hearings, the NRC staff concludes:

1.

Additional confirmatory information should be provided regarding the verification by Cygna of the correct use of the standard cable tray suppert design orawings in the preparation of construction drawings f:r the supports.

Additieral confirratorj infer.ation sheuld be provided en the justificatien cf exceedence of yield strength used for cable tray supports under the

!!! loading ccmbination.

Cygna has committed to provide this information in Phnso IV of the Cygna IAP.

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