ML20024B824

Forwards Response to Structural Engineering Branch Question 220.22(b) Re Damping Value for Electrical Raceway Sys. Response Will Be Incorporated Into FSAR Rev 23 Scheduled for Aug 1983

ML20024B824
Person / Time
Site:	Limerick
Issue date:	07/07/1983
From:	Bradley E PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Schwencer A Office of Nuclear Reactor Regulation
References
NUDOCS 8307110459
Download: ML20024B824 (6)

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PHILADELPHIA ELECTRIC COMPANY 23O1 M ARKET STREET P.O. BOX 8699 PHILADELPHI A. PA.19101 EDW ARD G. B AU ER, J R.

(215)841-4000 a oemme ab CoynsEh ttuGENE J. BR ADLEY assocants sansmak counsa6 DON ALD BLANKEN CUDOLPH A. CHILLEMI E. C. KI R K H ALL T. H. M AM ER CORNELL PAUL AUERBACH Assistant osmanAL counset 3DW ARD J. CULLEN. J R.

July 7, 1983 THOM AS H. MILLER. J R.

IREME A. McKEN N A assrevant counssk Docket Nos. 50-352 50-353 Mr. A. Schwencer, Chief Licensing Branch No. 2 Division of Licensing U.S. Nuclear Regulatory Commission

Subject:

Limerick Generating Station (LGS) - Units 162 Response to Structural Engineering (220)

Question No. 220.22(b)

Reference:

Letter from J. S. Kemper (PECO) to A. Schwencer dated June 21, 1983 File:

GOVT (1-1) FSAR

Dear Mr. Schwancer:

Attached please find our response to Structural Engineering Question No. 220.22(b). This response will appear in revision 23 (August 1983) to the FSAR.

The attached completes our response to Question 220.22, part (a) of which was responded to in the referenced letter.

Very truly yours, Attachment Copy to: See Service List 8307110459 830707 l

PDR ADOCK 05000352 g

A PDR

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. cc: Judge Lawrence Brenner (w/o enclosure)

Judge Richard F. Cole (w/o enclosure)

Judge Peter A. Morris (w/o enclosure)

Troy B. Conner, Jr., Esq.

(w/o enclosure)

Ann P. Hodgdon (w/o enclosure)

Mr.. Frank R. Romano (w/o enclosure)

Mr. Robert L. Anthony (w/o enclosure)

Mr. Marvin I. Lewis (w/o enclosure)

Judith A. Dorsey, Esq.

(w/o enclosure)

Charles W. Elliott, Esq.

(w/o enclosure)

Jacqueline I. Ruttenberg (w/o enclosure)

Thomas Y. Au, Esq.

(w/o enclosure)

Mr. Thomas Gerusky (w/o enclosure)

Director, Pennsylvania Emergency Management Agency (w/o enclosure)

'Mr. Steven P. Hershey (w/o enclosure)

Donald S. Bronstein, Esq.

- (w/o enclosure)

Mr. Joseph H. White, III (w/o enclosure)

David Wersan, Esq.

(w/o enclosure)

Robert J. Sugarman, Esq.

(w/o enclosure)

Martha W. Bush, Esq.

(w/o enclosure)

Spence W. Perry, Esq.

(w/o enclosure) i Atomic Safety and Licensing Appeal Board (w/o enclosure)

Atomic Safety and Licensing Board Panel (w/o enclosure)

Docket and Service Section (w/o enclosure) l 9

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Pesponse to:

Question 220.22 (b) (DAR)

For the normal load condition, involving Steam Relief Valve (SRV) discharge loading, a danping value equal to 3% of critical is used for all raceway systms. The SRV load is considered similar to an Operating Basis Earthquake (OBE) load; therefore, a 3% damping value is considered conservative since 4% damping is recamended by Regulatory Guide (R. G.)

1.61 for bolted steel structures for the OBE loading.

For the abnormal / extreme load condition, the following damping values are used: 1) 10% of critical for cable tray support system design; 2) 7% damping for conduit and wireway gutter trapeze type support systems; and 3) 5% damping for conduit and wireway gutter non-trapeze type support systems. These damping values are based on the results of the " Cable Tray and Conduit Raceway Seismic Test Program" (IGS Design Assessment Report Reference 7.1-11).

The cable tray system damping is substantially greater than that of bolted steel structures due to the cable notion within the trays. The test program demonstrated that cable tray system damping is, in general, nuch higher than 10%, and damping values up to 50% were reported. The damping values reemnended in Reference 7.1-12, and shown in Figure 220.22-1, are based on the lower bound values developed frm the test program. An unloaded tray will have an associated lower bound damping value of about 7% as shown in the Figure.

Analysis using 10% damping for a fully loaded tray system under the abnormal /extrene load conditions is conservative and will envelop an analysis of an unloaded tray with a 7% damping ratio for the following reason:

The frequency shift resulting from reduced mass in a relatively unloaded tray may result in either higher or lower response, depending on the individual response spectrum. However, when the cmbined effects of frequency shift, reduced damping, and lower weights are considered, the end result will be a more conservative design. For exanple, consider the cmparison of accelerations, weights, and resulting seismic forces for fully loaded and unloaded trays shown in Table 220.22 (b)-1. As shown, a fully loaded tray typically weighs approximately eight tines more than an empty tray.

The maximum acceleration for the unloaded tray case (at 7% damping) is four tines that for the fully loaded tray case (at 10% damping) assuming that frequency shift, due to the reduced mass of the unloaded tray, which results in the maximum increase in acceleration.

In calculating the resulting seismic forces for both cases, it is apparent that the loaded tray case yields the higher seismic load.

' Further, based on a randem sanpling of cable tray supports and conservatively assunung a fully loaded tray and peak acceleration approximately 75% of the sanpled members have a stress margin of 30% or nore. The rmaining 25% of the members are within allowable stress limits.

Limerick cable tray systems are similar to those tested in Ref.

7.1-12, i.e., the trays are of the same material and of similar construction, and the hangers and installation are similar in construction and design. Therefore, the dynamic behavior of Limerick tray systems will parallel the dynamic behavior of the tested tray systems.

For conduit systems, the test program demonstrates that, at the abnormal /extrene load condition, the danping value equals 7% of critical. This danping value is consistent with Reg. Guide 1.61 recmmended values for bolted steel structures. Therefore, 7% danping is used for conduit with trapeze type support systems, and a more conservative 5% damping is used for conduit with non-trapcze type support systems.

Wireway gutters were not tested; however, the manner in which they are constructed - with more bolted connections and more cables than conduit - provides nore danping mechanism than those present in conduit systms. Therefore, it is conservative to use the conduit system

<b ~ing value.

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Fully imaml Tray Dtpty Tray (10% Danping)

(7% Danping)

Acceleration a

4a Weight 8w w

Seismic Force 8aw 4aw

(= Acceleration X Weight)

Exanple Caparison of Seismic Forces Acting On Fully Emdul 4

and Dipty Cable Trays Table 220.22 (b) - 1 i

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24 50% TO Full.Y LOADED TRAY j

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j UN(0ADED TRAY,& CONDulT n

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4 0.1 0.2 0.3 0.4 0.5 - 0.8 0.7 0.8 0.9 1.0 INPUT FLODR SPECTRUM ZPA N g Figure 220.22 Allowable Danping Values for Electrical Raceway System Design (Source - DAR Reference 7.1-12) i Y

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