ML20196H459
| ML20196H459 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 06/24/1988 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| NUDOCS 8807060173 | |
| Download: ML20196H459 (11) | |
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TENNESSEE VALLEY AUTHORITY CHATTANOOGA TEN JESSEE 37408 5N 1578 Lookout Place WUN 241988
(
U.S. Nuclear Regulatory Commission ATIN: Document Control Desk Washington, D.C.
20555 Gentlemen:
I1 the Matter of
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Docket Nos. 50-259 Tennessee Valley Authority
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50-260 50-296 BR0HNS FERRY NUCLEAR PLANT (BFN) - AMPACITY EVALUATION PROGRAM PLAN -
REVISION 1 The purpose of this letter is to transmit BFN's ampacity evaluation program plan, revision 1, which supersedes revision 0 submitted January 25, 1988.
Revision 1 incorporates the results of the April 26 meeting with TVA and NRC at BFN.
Specifically, the program plan was updated and presently reflects a 40 year full life, as opposed to reduced life of unit 2 safety-related cables and describes-a modified approach to verification of.the V3.. cables. A summary statement of commitments contained in this submittal is provided.
Since this item is schedule sensitive, TVA is proceeding with its l
implementation, concurrent with your preparation of the safety evaluation report.
TVA will be glad to discuss this matter with you.
Should you have any questions, please telephone M. J. May at (205) 729-3570.
Very truly yours, TENNESSEE EY AUTHORITY l
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ridley,DJrector Nuclear Licerfsing and Regulatory Affairs Enclosures cc:
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U.Sl Nuclear Regulatory Commission g g jggg cc (Enclosures)*
Mr. K. P. Barr, Acting ~ Assistant Director
. for Inspection Programs
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.TVA Projects Division U.S. Nuclear Regulatory Commission Region II.
101 Marietta Street, NH, Suite 2900 Atlanta, Georgia 30323 Ms. S. C.' Black, Assistant Director for Projects TVA Projects Division U.S. Nuclear Regulatory Commission One White Flint,. North 11555 Rockville Pike' Rockville, Maryland 20852.
Browns Ferry Resident Inspector Browns Ferry Nuclear Plant Route 12, P.O. Box 637 Athens, Alabama 35611 4
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41 II ENCLOSURE
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.e AMPACITY EVALUATION PROGRAM PLAN
. REVISION 1
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SUMMARY
STATEMENTS OF COMMITMENTS
- 1) ' Safety-related cables not having a remaining life of 26 years operation after restart will be replaced before restart of unit 2.
2)
Safety-related cable will not operate greater than.its qualified maximum temperature rating (if an EQ cable) or its manufacturer's g
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rating.
3)
TVA will ensure the raceway configuration bv a maintenance program.
- 4)
The Browns Ferry Nuclear Nuclear Performance Plan and the 1989 Final Safety Analysis Report update will be revised to reflect the program described.
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AMPACITY EVALUATION PROGRAM PLAN REVISION 1 4
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2 AMPACITY EVALUATION PROGRAM PLAN REVISION 1 Prepared Approved Concurred r-
l AMPACITY EVALUATION PROGRAM PLAN REVISION 1
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L TABLE OF CONTENTS i
1.0 INTRODUCTION
2.0~ OBJECTIVE 3.0 SCOPE
4.0 DESCRIPTION
OF PROGRAM 4.1 IDENTIFY CABLES REQUIRING EVALUATION 4.2 IMPLEMENTATION OF 5AMPLING PLAN 4.3 VERIFICATION OF CABLE INSTALLED CONFIGURATION 4.4 EVALUATE CABLES AND CONDUCT 100 PERCENT REVIEW IN AREAS OF COMMON CAUSE DEcICIENCIES 4.5. PERFORMANCE OF CALCULATIONS 4.6 DETERMINATION OF EXPENDED AND REMAINING LIFE 4.7 CABLE REPLACEMENT 4.8 CABLE INSTALLATION RESTRICTIONS 4.9 TEST PROGRAMS 4.10 PROGRAM INTERFACES 5.0 PROGRAM IMPLEMENTATION 6.0 PROGRAM DOCUMENTATION l
7.0 CONCLUSION
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AMPACITY EVALUATION PROGRAM PLAN REVISION 1
1.0 INTRODUCTION
An INPO finding on Bellefonte Nuclear Plant concerning the lack of design calculations to show the adequacy of cable ampacities resulted In a Problem Identification Report (PIR GENEEB8605) covering all TVA nuclear plants. A detailed review determined that TVA design standards DS-E12.1.1 through DS-E12.1.4 were incomplete and did not properly account for the. effects of environment and raceway configuration on ampacity.
Since these standards were used for initial design, the potential exists for undersizing of safety-related cable in Browns Ferry Nuclear Plant (BFN).
A new electrical design standard (DS-E12.6.3) based on various industry standards and test reports was subsequer.tly developed which corrects the identified deficiencies. A program to determine the extent of conformance to that standard has been developed and is being implemented at BFN.
This program meets or exceeds the Sequoyah Nuclear Plant (SQN) ampacity program (See attachment 1).
2.0 OBJECTIVE The objective is to fully substantiate a 40 year design life, i.e., a remaining 26 years or more continued operation of unit 2 auxiliary and control power safety-related cables after removing any sizing conservatism which resulted in a loss of operating life.
Safety-related cables not having a remaining life of 26 years after restart will be replaced before unit 2 restart.
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3.0 SCOPE L
The scope is to verify the adequacy of safety-related auxiliary and l
control power cables in voltage levels V3, V4, and V5, (as defined by l
DS-E12.6.3) designed before the issuance of DS-E12.6,3 R0.
The l
evaluation shall be accomplished, in part, by applying a single or maltisampling plan based upon the Nuclear Construction Issues Group (NCIG) sampling plan which has been accepted for visual reinspection of welds.
4.0 DESCRIPTION
OF PROGRAM l
The program plan is to 1) identify cables reautring evaluation; 2) l implement a sampling plan; 3) verify raceway configuration; I
- 4) evaluate and conduct 100 percent review it, areas of common cause deficiencies; 5) perform calculations; 6) determine life expended and remaining operating life; 7) impose installation restrictions; l
- 8) implement test programs and, 9) implement program interfaces.
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2 4.1 IDENTIFY CABLES _ REQUIRING EVALUATION Voltage level V3, V4, and V5 safety-related cables are being evaluated as well as-nonsafety related cables routed in safety-related raceways. -Safety-related cables are identified from the BFN Q-List which is the minimum set of st ucture, systems, and components necessary to prevent or mitigate the consequences of Final Safety Analysis Report (FSAR), Chapter 14, design basis events and to safely shut down the plant following such events.
Environmentally qualified cables are identified by the BFN 10 CFR 50.49 list.
4.2 IMPLEMENTATION OF SAMPLING PLAN A sampling plan using inspection lots similar to SQN's nine (9) inspection lots for V3, V4, V5 cables has been implemented at 8FN as follows:
V4, V5 Sampling Approach A NCIG sample site and allowable discrepant items established a minimum of 95 percent confidence and a 95 percent reliability level.
A discrepant item (or failure) is considered to be a cable whose 40 year design life allowable ampacity (which takes into consideration the derating requirements DS-E12.6.3) is less than the required actual load with margin to account for reduced voltage, service factor, etc.
V3 Approach As done for SQN, the V3 voltage level has been divided into two subcategories:
- 1) "control power cables" that require evaluation and
- 2) "control function cables" that are used for controlling the operating status of equipment and do not require evaluation.
Based on the SQN results, it is anticipated that the total population of BFN control power cables is small and as a result, TVA will review 100 percent of this subcategory. V3 Q-List control power cables which serve as primary feeds to panels and miscellaneous devices are being identified by review of BFN ac/dc voltage drop calculations for safety-related equipment.
In addittoa, panels whose total load current exceeds 6 amps are being reviewed to identify cables leaving the panels that carry greater than 6 amps (the minimum size for a control cable is a #14 and that size is allow 4 to carry up to 6 amps before being designated as control power).
In addition, identified control power cables are being evaluated for ampacity.
Cables carrying this load are being reviewed against the load vs conductor size criteria in DS-E12.6.3 for classification as "control power" or control function.
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3 4.3 VERIFICATION OF RACEHAY CONFIGURATION To determine ampacity, cable routing, insulation temperature, and raceway configuration must be known.
Route and raceway configuration, i.e., conduit and tray fill, tray covers and bottoms, thickness of flame retardant coatings, fire wrap, fire stops, pressure seals,'and environment (mild or harsh) are being determined from the BFN As-Constructed Cable and Conduit Schedule (CCS), As-Designed Cable and Conduit Schedule when the As-Constructed CCS is not available and field walkdowns. As trays are walked-down, information identifying conduits entering and leaving trays along with any cables which leave tray by air is compared against the CCS to confirm its accuracy.
If no discrepancy is found.the cable route given in the schedule is considered to be correct and verified by review.
Where discrepancies exist between the cable schedule and the walkdown data, further investigation is being conducted to resolve the discrepancy.
Where required; signal tracing is being performed to determine the route.
4.4 EVALUATE CABLES AND CONDUCT 100 PERCENT REVIEW IN AREAS OF COMMON CAUSE DEFICIENCIES Based upon SQN's results, it is anticipated that upon completion of the sampling program at BFN there will be no failures of V3 cables in tray or conduit and minimum failures of V4 and V5 cables in conduit.
It is anticipated that failures may exist for 10 CFR 50.49 cables in V4 and V5 conduit which may also require 100 percent review.
- However, common cause deficiencies would be expected in V4 and V5 tray inspection lots of the sampling program which would require 100 percent review in V4 and V5 trays.
Hence, 100 percent walkdown and evaluation is being performed for the cables in these inspection lots.
4.5 PERFORMANCE OF CALCULATIONS Cables are being evaluated by calculations progressively performed in three phases designated as Phase I, Phase II, and Phase III as follows:
Phase I evaluates cables conservatively using design standard DS-E12.6.3.
l Phase II takes a closer look at the conservatism in DS-E12.6.3 and permits higher cable ampacity when actual load current, adjusted load multipliers, and actual cable depth of fill are considered.
Phase II also determines the operating temperature of cables in tray by evaluating load diversity provided no hotspot exists in the tray.
Load diversity analysis evaluates the difference between worst case heat intensity (i.e., all fully loaded cables) and an actual average heat intensity for caues in the tray.
A portion of this difference l
is applied, with margin, to selected cables that would otherwise be I
considered overloaded. At the same time, the ampacity of other cables l
In the tray is lowered accordingly.
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PhaseIIIincludesamoredetailedreviewoftheequipmentloabsfor those cables which do not pass Phase I and Phase II. Operating modes of the cable (e.g., normal, shutdown and test modes) and loading cycling (e.g., time diversity of loads sharing a raceway) are considered.
4.6 DETERMINATION OF EXPENDED AND REMAINING LIFE Cables which.are initially identified as operating above their 40 year life temperature based upon actual load current and present raceway configuration are being further analyzed to ensure a remaining life of 26 years minimum.
In this analysis, the duration of each cable's maximum past and future operating temperatures (both in its loaded and nonloaded state) is determined based upon the installed configuration, its duty cycle loading'(1.e., intermittent or continuous) and the duty cycle of cables surrounding it (i.e., tray diversity loading). Once the operating temperatures and durations are known, remaining life can be predicted by utilizing the Arrhenius methodology as commonly applied for insulation materials encountered throughout the nuclear industry.
This methodology features the use of empirical test data to form the basis for each life prediction.
In no case will safety-related cable, in its future operation, exceed its qualified maximum temperature rating (if an EQ cable) or its manufacturer's rating during any period of time.
4.7
. CABLE REPLACEMENT Those safe'y-related cables that do not have 26 years remaining t
operating life after restart (for a total of 40 years life) will be replaced before the restari of BFN unit 2.
The BFN design criteria BFN-50-758 is the governing document with regard to these cable replacements.
4.8 CABLE INSTALLATION RESTRICTIONS In order to ensure the raceway configuration used in the cable evaluations is not altered by additional cables, tray covers, flamemastic, fire wrap, etc., without assessing the impact to cables, TVA is developing a cable maintenance program.
4.9 TEST PROGRAMS To provide additional information for the ampacity analysis, flamemastic (fire retardant coating) derating research is planned.
Tests are underway to increase the presently reduced temperature ratings of 10 CFR 50.49 cable.
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5 4.10 PROGRAM INTERFACES Coordination with other BFN design review programs, such as voltage drop analysis, cable short circuit and coordination-analysis, EQ, and any other program which may be dependent on cable temperature, is d
being performed to ensure those analyses are not invalidated.
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5.0 PROGRAM IMPLEMENTATION:
TVA is performing the ampacity evaluation and is providing design modification changes for replacement cables.
Evaluation, design and modification is being performed in accordance with TVA procedures and practices.
Key TVA personnel involved in the SQN ampacity calculation evaluation ensures consistency between the BFN and SQN programs.
6.0 PROGRAM DOCUMENTATION The sampling program for V3, V4, and V5 safety-related cables is being performed by approved project instructions and calculations (TI-E110-01).
Calculations are performed and documented in accordance with TVA's Nuclear Engineering Procedure (NEP) 3.1.
Walkdown data is of a QA level that it may be used as input to calculations.
Cables not sized in accordance with OS-E12.6.3 are identified on Conditions Adverse to Quality Reports (CAQR) and are being further evaluated or replaced. Cables which are found acceptable for 26 years or more, but which are not sized in accordance with OS-E12.6.3 will be identified on an exception request to design criteria BFN-50-758.
Program completion is being documented by installation of replacement cables, approval of design criteria exception request and closure of existing BFN.CAQR's regarding the ampacity issue.,
The BFN Nuclear Performance Plan (NPP) and FSAR are being revised at the next update to reflect the prcgre ie r ribed herein.
7.0 CONCLUSION
The BFN Ampacity Evaluation Program implements an evaluation program similar to SQN. As result of the experience at SQN, BFN has elected to bypass initial sampling of V4 and VS cable sizing in trays and perform a 110 percent ve.ification.
In addition, field walkdowns and i
signal tracing are being used to verify the V4/V5 portions of the BFN cab:e schedules. Cable failure and replacement is determined by cable remaining life. Cables determined to have a remaining operating life of less than 26 years after restart are being replaced before BFN unit 2 restart.
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