ML20248F475
| ML20248F475 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood, 05000000 |
| Issue date: | 03/29/1989 |
| From: | Chrzanowski R COMMONWEALTH EDISON CO. |
| To: | Murley T Office of Nuclear Reactor Regulation |
| References | |
| 0058T, NUDOCS 8904130078 | |
| Download: ML20248F475 (8) | |
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.,Os C:mmonwealth ' Edison
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..k ' O[N) Ons First National Plala, Chicago, Illinois Address Reply to: Post Office Box 767-
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March 29, 1989' g
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Dr. Thomas E. Murley, Director' Office of Nuclear' Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555 ATTN: ' ' Document Control Desk
Subject:
Byron Station Units 1 and 2 Braidwood Station Units 1 and 2
-Use of Fuses for Electrical Isolation NRC Docket Nos. 50-454/455 and 50-456L451.
Dear Dr. Murley:
A teleconference was held between Commonwealth Edison and members of your staff on March 23, 1989, to discuss the use of fuses for electrical isolation of non-class 1E DC power systems. Attachment A contains a description of the proposed modification and UFSAR revisions that are required-to utilize two fuses in series for electrical isolation. Approval-is not normally requested for modification, however, this type of electrical isolation
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is unique at Byron and Braidwood. Therefore, to ensure future acceptance of l
the 10 CFR 50.59 reviews, Commonwealth Edison is requesting approval of the design. To allow installation of the proposed modification during the Fall and Winter outages, we are requesting the review and approval be completed by j
August 1, 1989.
If any questions arise, please direct them to this office.
Very truly yours, GtWALl/
1 R.A. Chrzanowski Nuclear Licensing Administrator j
1m cc:
Byron Resident Inspector Braidwood Resident Inspector L.N. Olshan - NRR N. Trehan 0058T 890413007s 890329 DR ADoCK 05000454 li h
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SARGENT & LUNDY ENGINEERS CHICAGO December 2, 1988 i
ATTACHMENT "A" Commonwealth Edison Company _
Byron /Braidwood Stations - Units
& 2 Use of Fuses for Electrical Isolation of Mon-Class lE
~
Loads / Circuits from Class lE DC Power Systems This document provides a technical justification (and identifies the required FSAR changes) for accepting fuses (that are qualified to Class lE requirements, properly applied, sized, and coordinated for the application) as isolation devices between non-Class lE and Class lE dc power circuits.
IEEE Std. 384-1981 (Section 7.1.2) identifies three acceptable power circuit isolation devices - " Circuit Breaker Tripped by Fault Current," " Circuit Breaker Tripped by Accident Signal," and
" Input Current Limiters."
IEEE Std. 384-1981 also includes (Section 7.2.2. 3) fuses as an acceptable isolation device for
" Instrumentation and Control Circuits," but omits fuses for isolation of power circuits.
However, it is the consensus of the IEEE Std. 384 Working Group (NPEC SC-6. 5), that fuses qualified to Class lE requirements, properly applied, sized, and I
coordinated for the application, are acceptable isolation devices in de power circuits.
It is the intent of the Working Group to revise IEEE Std. 384-1981, accordingly (see Attachment 1).
Furthermore, Commonwealth Edison Company (CECO) believes that such a fuse will provide power circuit isolation reliability which may well be higher than that for a circuit breaker tripped by fault current.
This belief is supported by the data on fuses and breakers in IEEE Std. 500-1977 (relative to probability of failure upon demand) which indicates that a fuse (low voltage, up to 1,000V) will probably have ten failures (maximum) per million cycles, whereas a circuit breaker will probably have 1,841 failures (maximum) per million cycles.
Based on the above, CECO would like to implement a modification to the 125 Vdc system (at both Byron and Braidwood Stations) that utilizes fuses for isolation of the non-Class lE loads from the Class lE buses.
Figure 1 illustrates the 125 Vdc system as presently designed; Figure 2 shows it as it would be following implementation of the proposed modification.
In the existing i
125 Vdc design (Figure 1) Breakers No. 2 and 3 provide the two l
Class lE interrupting devices (in series) necessary to comply with the present FSAR commitment.
These breakers must be (a)
Class lE qualified, (b) coordinated with their upstream interrupting device (i.e., Breaker No. 1), and (c) periodically tested to verify coordination. In the proposed modification I
(Figure 2), two fuses (in series) will be connected in parallel with the main feed breaker to the 125 Vdc distribution panel l
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I servicing the non-safety-related loads (i.e., Breaker No. 2).
This main feed breaker (No. 2) would'then be normally operated in the open (N.0.)
. position.
This operation of Breaker No. 2 would be controlled by administrative procedures allowing.it to be closed only.when necessary for. maintenance, inspection, replacement of the fuses.. The incentive for this modification is the elimination of the periodic testing required to verify coordination of Breaker Nos. 2 and 3 with Breaker No. l.. contains marked copies of UFSAR pages-.A1.75-1 and -2, indicating the changes that will be required.
He believe that the application of fuses as isolation devices in de power circuits is based on a sound technical justification.
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7 ATTAClIMENT l' IEEE POWER ENGINEERING SOCIETY i
NUCLEAR POWER ENGINEERING COMMITTEE a
Cl a.omon Voc e Cl.a.oman Standards Coord norar Se c re t or y j
J. T. Bever N. 5. Po ter J. E. Tloomos A. R. Roby i
General Atom e s washington Public Pe.e, Supply Syoem Duk e Po.e, Company Northeast Unioie s Sen.ce P.O. Bon 85608 P.0, Bo 968 M.S. 981C P.O. Bos 33189 P.O. Bon 270 Room Ih. 32 l
Son Diego. C A 92138 Richland, W A 99352-Charlotte, NC 28242 Hertford. CT 0614 tM70 l
4619) 455 4487 (509) 377 8640 (704) 373-4612 (203) 665-3157 PAST CHAIRMAN 1
R. E. Allen 1215) 422 3734 o, an0 September 7, 1988 SUBCOMMIT TEE. CHAIRMEN SC.1, Adminiorative J. T. Bov
Reference:
1/11/84 letter, B. G. Treece to T. S. Killen SC 2, Qualificanon G. K. Henry Gulf States Utilihe s Company River Bend 5tation 5A Mr. B. G. Treece, Chairman P.O. Bon ??O (N)'EN
DC Auxiliary Power Working Group, Nuclear Power Subcommittee SC 3, Operooons.
Sargent & Lundy Svoveillance & Tesong 55 East Monroe Street D. C. Lemie" Common =eoith Edison Company Chicago, Illinois 60603 P.O. Bos 767 Rm. 35 FN West Chicago, IL 60690 (312) 294 2830
Dear Mr. Treece:
N' #",',$Y This letter confirms that ^: h e Institute of Electrical and Ebosco 5erv'ce s, Inc.
Electronics Engineers (IEEs)/ Nuclear Power Engineering i
"' N','d ['ede c'""'
Committee (NPEC) Subcommittee SC-6.5 Working Group ar,rces 9;
w Nsw York, NY 10048 0752 that fuses qualified to Class 1E requirements. properly (2121 839 2210 applied, sized, and coordinated for the application, are SC-5, Reliability ac.aptable isolation devices in de power circuits.
It is wsIn the intent of the Working Group to revise IEEE 384-1981 se riec t,,c Corp.
Water Reactor Division accordingly.
However, it must be pointed out that this hhbv$hNA15230 represents work being done by an IEEE technical committee 4 12) 374 4211 airad at revising an IEEE standard.
It is furnished as SC 6,5afety Related 5ystems informational material only.
You are cautioned that this
- w. w. so..rs is not an IEEE-approved action and, therefore, cannot be Philadelphia Elecenc Co*
2301 Market Stree N21 presumed to reflect the position of the IEEE, nor of any Philadelphia, PA 19101 otber committee, group, or society associated with LEEE.
(215) 841 6471 SC.7, Human Factors &
Yours very truly, Control Focilities L. F. Hones fWg/)b
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O westinghouse Elecer c Corp.
M Research & Development Censer 1310 Beulah Rood Poisburgh, PA 15235 M. S. Zar, Chairman (412) 256-2682 SC-6.5 Working Group SC 8, Qualay Assurance MSZ rbmh j.
J. D. Lomo"'
l Gibert Common *eoith, Inc.
P.O. Bon 1498 Copies
- Reed.ng, PA 19603 J. T.,Bauer (215) 3271200 Est, 2073 l
g,
. Bo ers SC.9. E c sinom ec '
Mer,e rs, SC-6.5 Working Group R. E. Allen United E ngineers & -Consituciou s, lac.
P.O. Bon 8223 Philadelph.o. PA 19101 (215) 422 3734 or 3DO 1
SC.10. Ad.onc ed Conc ept s
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THE INSTITUTE OF EL ECTRICAL AND ELECTRONICS ENGINFFRS. INC j
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B/B-UFSAR REGULATORY GUIDE 1.75 Revision 2, September 1978 i
PHYSICAL INDEPENDENCE OF ELECTRIC SYSTEMS NSSS Scope The commitment to comply with the intent of the requirements of this guide by the Applicant is present in Subsections 7.1.2.2.1 and 7.1.2.2.2.
NonNSSS Scope physical independence of redundant electric systems is discussed in Subsections 8.1.14 and 8.3.1.4, respectively.
The Applicant compl.ies with the requirements of this guide with the exceptions P A/or clarifications to the regulatory positions identified and justified below:
Reculatory Position C1 Section 3, " Isolation Device" should be supplemented as follows:
"(Interrupting devitas actuated only by f ault current are not considered ti be isolation devices within the context of this document.)"
Applicant's Position l
Interrupting devices.ac.tuated only by fault current may,. ~ m m ~,
be used as isolation devices provided that the ccerdir. -reg l
ticr criteri of IEEE 384-1977/*Cccticr. 5.1.2)are met.
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Jng.tification of Apolicant's Position g--' = N o-Cl DSS.t.E fuse.s )
There is no technical justification \\fe:
ecluding the use of Class lE circuit breakerstactt4tse only by fault or overload current as X circuit intet. pting or isola-i tion device 5 (For further discussion of this subject, i
see S&L letter to the NRC dated December 21, 1978 and NRC's response dated March 28, 1979.)
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B/B-UFSAR Byron /Braidwood Design
-- or 90se!7 Although t h'e' % p p T 'i c a n t b e l i e v e s t h a t a s i n g l e c i r c u i t breaker &(actuated by fault current only) provides adequate isolation, the Byron /Braidwood design will incorporate the following additional features to further ensure isolation and thus satisfying NRC concerns.
The Applicant (where practical) will provide two interrupting devices (in series) actuated only by fault current.
These two interrupting devices will be:
- 1) Class 1E qualified 4/2) will be coordinated with their
(_rwr~s, upstream interrupting device;-ar.d 2)4will be periodically (dM31k,"O ~~ tested to verify coordination.+ Any remaining non-Class 1E loads (not utilizing two interrupting devices) will be tripped from the Class 1E buses with a Safety Injection coincident with loss of offsite power signal.
The cables See e
Ahachment which supply non-Class lE loads f rom redundant Class lE g
buses are routed through separate raceways.
Reculatory Position C2 Section 3,
" Raceway".
Interlocked armor enclosing cable should not be construed as a " raceway."
Applicant's Positinn Although not a " raceway" in the same sense as a conduit or cable tray, recognition of and design credit for the additional protec-tion provided by the metallic jacket of interlocked armored cable should be included in the regulatory guide.
Use of armored cable, in lieu of the separation distances stated in the regula-tory guide, should be permitted when justified by specific testing and/or analysis, as providing the required degree of protection for Class lE circuits against specific credible hazards.
Justification of Applicant's Positian There is no technical justification for precluding the use of armored cable, in lieu of separation distances, to provide adequate isolation between Class lE and non-Class IE circuits and between redundant Class lE circuits, when shown to be adequate by specific testing and/or analysis.
Reaulatory Position C6 Analyses performed in accordance with Sections 4.5(3), 4.6.2, and 5.1.1.2 should be submitted as part of the Safety Analysis Report and should identify those circuits installed in accordance with these sections.
A1.75-2
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