ML18033A983

Forwards Details & Summary of Recently Completed Testing of Cable Tray Configurations,Summary of Scope & Results of Ampacity Evaluations & Radon Cable Fill within Tray,Per NRC 890710 Request

ML18033A983
Person / Time
Site:	Browns Ferry
Issue date:	10/06/1989
From:	Michael Ray TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
TAC-62260, NUDOCS 8910160094
Download: ML18033A983 (14)

Text

A,C CELE RATED D1S1BUTION DE M ONSTRON SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:8910160094 DOC.DATE: 89/10/06 NOTARIZED: NO DOCKET FACIL:50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee 05000260 AUTH. NAME AUTHOR AFFILIATION RAY,M.J. Tennessee Valley Authority RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)

SUBJECT:

Provides requested info re electrical cable'ampacity,per 890710 meeting.

DISTRIBUTION CODE: D030D COPIES RECEIVED:LTR ENCL SIZE:

TITLE: TVA Facilities Rout'ine Correspondence NOTES:1 Copy each to: S.Black,D.M.Crutchfield,B.D.Liaw, 05000260 R.Pierson,B.Wilson RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL LA 1' PD 1 1 GEARS,G 1 1 INTERNAL: ACRS 1 1 NUDOCS-ABSTRACT 1 1 OC/LEMB 1 0 OGC/HDS2 1 0 01 1 1 EXTERNAL: LPDR 1 1" NRC PDR 1 1 NSIC 1 1 NOTES 5 5 R

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TENNESSEE VALLEY AUTHORITY CHATTANOOGA. TENNESSEE 37401 5N 157B Lookout Place GOT its IBS U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Hashington, D.C. 20555 Gentlemen:

In the Matter of ) Docket No. 50-260 Tennessee Valley Authority )

BROGANS FERRY NUCLEAR PLANT (BFN) ELECTRICAL CABLE AMPACITY (TAC 62260)

This letter provides the information as requested, by NRC in the meeting at BFN on July 10, 1989.

The enclosure to this letter provides the details and summary of recently completed testing of cable tray configurations, a summary of scope and results of ampacity evaluations, and a discussion on the 'random cable fill within a tray. As discussed with the NRC staff subsequent to this meeting the information provided herein completes documentation of BFN's ampacity program and will provide the basis for NRC's safety evaluation of, this., issue:.

Please refer any questions concerning this submittal to Patrick P. Carier, BFN Site Licensing, (205) 729-3570.

Very truly yours, TENNESSEE VALLEY AUTHORITY Manage , Nuclear Licensing and Regulatory Affairs Enclosures cc: See page 2 p p9i006 PDR PDOCK 050002(0 o

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An Equal Opportunity Employer

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U.S, Nuclear Regulatory Commission cc (Enclosures):

Ms. S. C. Black, Assistant Director for Projects TVA Projects Division U.S. Nuclear Regulatory Commission One Nhite Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Mr. B. A. Nilson, Assistant Director for Inspection Programs TVA Projects Division U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NN, Suite 2900 Atlanta, Georgia 30323 NRC Resident Inspector Browns Ferry Nuclear Plant Route 12, Box 637 Athens, Alabama 35609-2000

ENCLOSURE

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acit Pro ram Evaluation and Results

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Reference:

1. TVA letter to NRC on July 7, 1988, "Ampacity Evaluation Program Plan Revision 1"

2. NRC letter to TVA on March 21, 1989, "Request for Additional Information Cable Ampacity Program Plan Tennessee Valley Authority, Browns Ferry Nuclear Plant, Unit 2 (TAC 62260)"

3. TVA letter to NRC on April 18,. 1989, "Electrical Cable Ampacity-Test Results Summary Report (TAC No. 62260)"

General The ampacity reevaluation program for safety-related power and control power cables (V3, V4, and V5) required for unit 2 in accordance with section 4.1 of the Ampacity Evaluation Program Plan, Revision 1 (reference 1) has been completed. Corrective actions are now being taken to address those cables considered to be program evaluation failures.

The following discussion provides the results by voltage levels.

V3 Control Power and Control Function Cables The more than 3500 V3 level cables were reviewed against the criteria set forth in the program plan (reference 1) to identify the cables of a size and load defined as control power. None were determined to be control power. These control function cables did not require evaluation due to their inherent low power levels and intermittent operation.

V4 V5 Low Volta e and Medium Volta e Cables Originally, the program plan called for a 100 percent review of cables in areas of anticipated and discovered common cause deficiencies (including tray routed cable) and a sampling program to provide 95/95 percent confidence/reliability in other areas of least anticipated failures (such as cables routed in dedicated conduit in mild environment areas). During the course of program implementation, a decision was made to review 100 percent of the V4, V5 cables in both dedicated conduit and tray, and no sampling was used in the final analysis.

The evaluations included provisions to ensure that fire retardant coatings, wraps, installation configuration, and association with nonsafety cables do not adversely affect the current carrying capability of the safety-related cables.

The ampaci ty evaluations for cables in dedicated conduit were performed using TVA Standard DS-E12.6.3 based on industry standards such as Insulated Cable Engineers Association (ICEA) P-46-426 and the National Fire Protection Association (NFPA) National Electrical Code. The analysis, which resulted in no failures, reviewed 263 safety-related V4/V5 cables'

Page 2 of 6 Original design and ampacities of power cables in trays were based on industry standards (such as ICEA P-46-426);, which predated publication of ICEA P-54-440 which incorporated the concept of uniform heating. The reevaluation of the safety-related cables for unit. 2 was based on ampacities from ICEA P-54-440 and a conservative method of quan+i'fyi ng diversity which was inherent to ICEA P-46-426 to ensure that"the cables were not affected by heating from adjacent cables...A total of 941 cables, including 194 safety-related cables, were analyzed through the review of 45 trays; 66 safety-related cables required corrective action.

As a result of an engineering review of the changes from revision 0 to revision of TVA's Q-List, three new cables were identified as needing 1

to be evaluated for ampacity. Subsequent to this review, calculation ED-Q2999-890047 R2 has been issued showing two of the cables do meet the ampacity criteria. The third cable is an IE suffix cable which has been upgraded to divisional. A drawing discrepancy generated as a result of the. Appendix R walkdown indicates that the cable is partially routed in a nondivisional tray. As a result of the upgrade, the cable does not meet the separation criteria. In lieu of performing an ampacity evaluation for this cable, the cable wi 11 be replaced end-to-end. ' Therefore, no calculation is required to document the existing cable acceptability for ampacity.

II. Summar of Ph sical Testin Performed on a Tra Model Com ared to the TVA Diversit Com uter Pro ram As described in our July 10, 1989 meeting with NRC at BFN, a test was performed by TVA's Central Laboratories Services Department which was a mockup of the case 1 computer model proposed to TVA by NRC (reference 2). Although a specific configuration was not defined by NRC and the TVA computer program does not model exact cable location within a tray segment, the test did require cable placements. The worst case configuration of a tightly bound single cable layer with two overloaded cables carrying 436 amps located in the center, two 100 percent loaded (248 amps) "safety cables" on either side of them, and the remaining 16 unloaded cables placed with eight each on either side on the outer portion of the cable layer, was tested in a 40'C ambient environment.

The results produced were conservative compared to those predicted by TVA's Diversity Program. Table 1 provides a comparison of temperatures, from the center of the tray outward (in one direction), of the test results to the Diversity prediction. The Diversity temperatures given for the tray center and ]acket interfaces are conservatively assumed for this comparison since the program calculates conductor temperatures only. The test temperatures shown are the greatest measured on either side of the symmetrical test model.

It is recognized that the tested model does not reflect actual installation practices. However, due to the conservatisms such as the tightly packed cables, the relatively large distance from the overloaded cables to the cooler unloaded cables, and no Flamemastic to more evenly spread the.,heat within the cable mass, the model represents a conservative challenge to the Diversity analysis. ;Comparing the test

TABLE l,-MODEL COMPARISON (DIVERSITY/HEATING6/TEST)

GABLE DIAMETER = .756 CABLE OR LOAD TRAY CENTER 85.5 108 NONSAFETY 105.7 105 JACKET 90 77.6 SAFETY 248.16 90 78.8 82 JACKET 90 63.2 SAFETY . 248.16 90 66.6 JACKET. 53.3 59 NONSAFETY 0 50.8 52 JACKET SAFETY CABLE 5 100% LOAD

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FIGURE i MODEL COMPARISON CABLE DIAMETER = .756 IN TEMPERATURE (DEG. C)

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80 60 40 CTR N/SAFETY JACKET SAFETY JACKET SAFETY JACKET N/SAFETY JACKET CABLE ClR JACKET INTERFACE DIVERSITY ~ HEATING6 ~ TEST

Page 5 of' results to a Diversity calculation as presented in Figure 1, Diversity bounds the test and again provides confidence in the conservatism of the TVA analytical methodology. Based on this test and previous evaluations of analytical and test results (reference 3), it -is concluded that the diversity evaluation is a sound engineering approach to quantj.fjjing the heat sharing capabilities within a tray system and conservatively determining a cable's temperature.

III. Discussion of Differences between HEATING6 Anal sis and Test Results The results from the HEATING6 analysis of the test configuration are provided in Table 1, and as shown, some seemingly significant differences from the test exist. Nhen charted, however, as in Figure 1, HEATING6 and the tested results for the conductors follow very closely with the major differences being at the jacket interfaces and the center of the tray.

The simplifying modeling techniques and assumptions used in the HEATING6 analysis contributed to these variations.

HEATING6 assumes a square cable and a rectangular cable mass with a maximum surface area available for heat transfer to the ambient of only one-quarter the perimeter (circumference) of the cables'urface open to the top and bottom or side. In the test, the cables are pressed together, but only a point contact between the cables exists which allows for nearly the full surface to be exposed to the ambient.

Also, the test is composed of discrete components; cables with copper conductors, insulation and jacket materials, specific locat'ions and loads. The HEATING6 calculation simplified this setup as described before by assuming a single homogenous mass with the different loads simulated as squares of'emperature dependent heat sources. HEATING6 uniformly distributes this heat throughout the mass giving an even temperature distribution. Since the model consists only of a single layer, the calculational differences tend to be accentuated due to influence of the jackets'hermal conductivity between the heat sources or conductors. Hith a greater mass and more cable layers, less surface area per cable would be available in a test for heat transfer to the ambient and the jacket conductivity would be less influential and the calculation would more closely approximate the test. Considering these minor modeling differences, HEATING6 has compared well to this test and to a number of test configurations considered previously.

IV. Discussion of Random Fill Typical of industry practice, cables are installed approximately at the same time that the end equipment is installed according to construction/

modification schedules. No 'design attempt was made to specifically locate cables or circuits in a particular position within the tray. The larger, heavier loaded feeder cables of sizes 2 ANG and greater are exclusively single conductors and after being installed, may or may not have been tied together but each allowed to snake through the tray and seek its own particular position. As later cable runs are installed, the new cables continue to seek their own position within a tray. Continued

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Page 6 of 6 installations would generally follow the:same pattern until a tray was considered filled to its maximum allowabl'e cross-sectional area and a uniform depth across the width of *the tray. Diverse cable entry and exit points throughout a tray system leads to further .location randomness within the tray.

At BFN, the use of Flamemastic cable coatings .has-,-in some cases, prevented a uniform depth of cable across the tray. As cables were coated and subsequent new cables installed, several mounds of cable and Flamemastic may occur within a tray segment. In a ladder backed tray, the separation of the cable mounds allows for air flow which would not be the case with a completely filled tray. In most cases the appropriate mound within the tray to assign a cable location is unknown. The TVA program does not take credit for this separation and conservatively assigns all cables to a particular mound where the combination of derating factors for cable depth and Flamemastic thickness is worst case. Hithin this mound, the cable is considered uniform in depth and random in placement.

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