ML20039C010
| ML20039C010 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 12/13/1981 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | Counsil W CONNECTICUT YANKEE ATOMIC POWER CO. |
| References | |
| TASK-08-04, TASK-8-4, TASK-RR 811223-01, 811223-1, LSO5-81-12-073, LSO5-81-12-73, NUDOCS 8112280307 | |
| Download: ML20039C010 (19) | |
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December 23, 1981 D
Docket No. 50-213 s
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DEC2419815 Mr. W. G. Counsil. Vice President g,.
,, 4 Nuclear Engineering and Operations w.a m44 u Air Connecticut Yankee Atomic Power Company M
Post Office Box 270
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Hartford, Connecticut 061 01
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Dear Mr. Counsil:
RE: SEP TOPIC VIII-4, ELECTRICAL PENETRATIONS OF REACTOR CONTAINMENT
, is our contractor's technical evaluation of SEP Topic VIII-4 l
for Haddam Neck. This assessment compares your facility with the criteria currently used by the regulatory staff for licensing new facilities. The enclosed report concludes that low voltage penetrations do not meet current criteria.
I Draft Technical Evaluation Reports (TER) on Topic VIII-4 have been prepared and forwarded to all SEP Licensees for comment.
Comments from some licensees (e.g., Northeast Utilities letters dated August 29, 1980 and January 29, 1981) indicated concern with the model used and assumptions made in the initial conditions and material properties. Unfortunately, most respondents have not i
provided sufficient technical information nor detailed schematics to support their comments.
Our audit calculations failed to establish that the fault current protection for containment electrical penetrations in SEP facilities is generally ade-i i
quate. This does not necessarily mean that the protection is inadequate.
Our calculations were simplified and conservative so that there is room to improve the result by using more realistic models.
In addition, licensee consents have indicated that there may be some errors in our calculations.
Nevertheless, our audit did not put the matter to rest and, thus, you are requested to evaluate the adequacy of all electrical penetrations in your facility in accordance with the enclosed position (Enclosure 2).
Generally, where needed, our position calls for more realistic calculations than were used in our audit.
In relation to current licensing criteria, it i
provides relief from the need for redundant circuit protective devices in certain instances and specifically provides for using fuses as an alterna-i tive to circuit breakers. Other straightforward alternatives such as deen-l ergizing circuits are also provided for.
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-2 ff any instances arise where your calculations cannot denonstrate circuit protection in accordsnce with our position, you are requested to infom us of your intended correction actions.
4 In order to complete our evaluation of Topic VIII-4, please provide a report describing the calculations perfomed and criteria for evaluating the pene-trations for the specific circuits identified in the staff's previous report within 30 days of receipt of this letter.
l The report as a minimum should address backup protection for your low voltage penetrations like those used for 480 volt motor operated valves.
The requested infomation will be used to revise our topic Safety Evaluation Report and will be used in the preparation of the integrated assessment for your plant.
The reporting and/or recordkeeping requiremer,ts contained in this letter affect fewer than ten respondents; therefore, OMB clearance is not required under P.L.96-511.
Sincerely, J
Dennis M. Crutchfield, Chief Operating Reactors Branch No. 5 Division of Licensing
Enclosures:
As stated cc w/ enclosures:
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December 23, 1981 Y...../
Docket No. 50-213 LS05 12-073 Mr. W. G. Counsil, Vice President Nuclear Engineering and Operations
- Connecticut Yankee Atomic Power Company Post Office Box 270 Hartford, Connecticut 061 01
Dear Mr. Counsil:
RE: SEP TOPIC VIII a, ELECTRICAL PENETRATIONS OF REACTOR CONTAINMENT is our contractor's technical evaluation of SEP Topic VIII-4 for Haddam Neck. This assessment compares your facility with the criteria currently used by the regulatory staff for licensing new facilities. The enclosed report concludes that low voltage penetrations do not meet current criteria.
Draft Technical Evaluation Reports (TER) on Topic VIII-4 have been prepared and forwarded to all SEP Licensees for comment.
Comments from some licensees (e.g., Northeast Utilities letters dated August 29, 1980 and January 29, 1981) indicated concern with the model used and assumptions made in the initial conditions and material properties.
Unfortunately, most respondents have not provided sufficient technical information nor detailed schematics to support their comments.
Our audit calculations failed to establish that the fault current protection for containment electrical penetrations in SEP facilities is generally ade-quate. This does not necessarily mean that the protection is inadequate.
Our calculations were simplified and conservative so that there is room to improve the result by using more realistic models.
In addition, licensee comments have indicated that there may be some errors.in our calculations.
Nevertheless, our audit did not put the matter to rest and, thus, you are requested to evaluate the adequacy of all electrical penetrations in your facility in accordance with the enclosed position (Enclosure 2).
Generally, where needed, our position calls for more realistic calculations than were used in our audit.
In relation to current licensing criteria, it provides relief from'the need for redundant circuit protective devices in certain instances and specifically provides for using fuses as an alterna-tive to circuit breakers. Other straightforward alternatives such as deen-ergizing circuits are also provided for.
. If any instances arise where your calculations cannot demonstrate circuit protection in accordance with our position, you are requested to inform us of your intended correction actions.
In order to complete our evaluation of Topic VIII-4, please provide a report describing the calculations performed and criteria for evaluating the pene-trations for the specific circuits identified in the staff's previous report within 30 days of receipt of this letter.
The report as a minimum should address backup protection for your low voltage penetrations like those used for 480 volt motor operated valves.
The requested information will be used to revise our topic Safety Evaluation Report and will be used in the preparation of the integrated assessment for your plant.
The reporting and/or recordkeeping requirements contained in this letter affect fewer than ten respondents; therefore, OMB clearance is not required under P.L.96-511.
Sincerely,
] [1 Dennis M. Crutchfield, Chief Operating Reactors Branch tio. 5 Division of Licensir.g
Enclosures:
As stated cc w/ enclosures:
See next page I
I i
c Mr..W. G. Counsil t
Cc Day, Berry a.Howard Counselors at Law One Constitution Plaza Hartford, Connecticut 06103 Superintendent Haddam Neck Plant
'RFD #1 Post Office Box 127E East Hampton, Connecticut 06424 Mr. Richard R. Laudenat Manager, Generation Facilities Licensing Northeast Utilities Service Company P. O. Box 270 Hartford, Connecticut 06101 Russell Library 119' Broad Street Middletown, Connecticut 06457 Board of Selectmen Town Hall Haddam, Connecticut 06103 Connecticut Energy Agency ATTN: Assistant Director Research and Policy Development Department of Planning and-Energy Policy 20 Grand Street Hartford, Connecticut 06106 U. S. Environmental Protection Agency Region I Office ATTN: Regional Radiation Representative JFK Federal Building Boston, Massachusetts 02203 Resident Inspector Haddam Neck N1 clear Power Station c/o U. S. NRC East Haddam Post Office East Haddam, Connecticut 06423 O
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. SYSTEMATIC EVAltATION PROGRAM TOPIC VIII-4 ELECTRICAL PENETRATIONS OF REACTOR CONTAINMENT HADDAM NECK NUCLEAR STATION Docket No. 50-213 November 1981 A. C. Udy EG&G Idaho, Inc.
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9 ABSTRACT This SEP technical evaluation, for the Haddam Neck Nuclear Station, reviews the capability of the overcurrent protection devices to protect the electrical penetrations of the reactor containment for postulated fault conditions concurrent with an accident condition.
FOREKGRD-
.This report is supplied as part of the " Electrical, Instrumentation, and Control Systems Support for the Systematic Evaluation Progran (II) being conducted for the U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation, Division of Licensing by EG&G Idaho, Inc.,
Reliability & Statistics Branch.
The U.S. Nuclear Regulatory Commission funded the work under the
- authorization B&R 20-10-02-05, FIN A6425.
)
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CONTENTS
1.0 INTRODUCTION
1 2.0 CRITERIA........................................................
2 3.0 DISCUSSION AND EVALUATION.......................................
3 3.1 Typical Low Voltage (0-1000 VAC) Penetration..............
4 3.1.1 Low Voltage Penetration Evaluation................
5 3.2-Typical Medium Voltage (>1000 VAC) Penetration............
5 3.2.1 Medium Voltage Pei.atration Evaluation.............
3.3 Typical Direct Current Penetration........................
6 3.3.1 Direct Current Penetration Evaluation.............
6 4.0 SultMARY.........................................................
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5.0 REFERENCES
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SYSTLn% TIC EVALUATION PROGRAM TOPIC VIII-4 ELECTRICAL PENETRATIONS OF REACTOR CONTAINMENT HADDAM NECK NUCLEAR STATION
1.0 INTRODUCTION
This review is part of the Systematic Evaluation Program (SEP), Topic VIII-4. Connecticut Yankee Atomic Power Company (CYAPCO) has provided l
information describing typical penetrations, typical in-containment loads, and fault currents. As new penetrations have becn installed, CYAPCo has provided information on these penetrations.
The objective of this review is to determine the capability of the overcurrent protective devices to prevent exceeding the design rating of the electrical penetrations-through the reactor containment during short circuit conditions at LOCA' te peratures.
General Design Criterion 50, " Containment Design Basis" of Appendix A,
" General Design Criteria for Nuclear Power Flants" to 10 CFR Part 50 requires that penetrations be designed so that the containment structure can, without exceeding the design leakage rate, acccmmodate the calculated pressure, temperature, and other environmental conditions resulting from any loss-of-coolant accident (LOCA).
IEEE Standard 317, " Electric Penetration Assemblies in Containment Structures for Nuclear Power Generating Stations", as. augmented by Regula-tory Guide 1.63, provides a basis of electrical penetrations acceptable to the staff.
Specifically, this review will examine the protection of typical elec-trical penetrations in the containment structure to determine the ability of the protective devices to clear the circuit during a short circuit con-dition prior to exceeding the containment electrical penetration test or design ratings under LOCA temperatures.
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2.0 CRITERIA IEEE Standard 317, " Electric Penetration Assemblies in Containment Structures for Nuclear Power Generating Stations" as supplemented by Nuclear Regulatory Commission Regulatory Guide 1.63, " Electric Penetrat' ion Assemblies in Containment Structures for Light-Water-Cooled Nuclear Power Plants" provides the basis acceptable to the NRC staff.
The following criteria are used in this report to determine compliance with current licensing requirements:
(1)
IEEE Standard 317, Paragraph 4.2.4 -
"The rated short circuit current and duration shall be the maximum short circuit current in amperes that the conductors of a circuit can carry for a specified duration (based on the operating time of the primary overcurrent protective device or apparatus of the circuit) fol-lowing contincous operation attrated continuous current without the temperature of the conductors exceeding their short-circuit design limit with all other conductors in the assembly carrying their rated continuous current under the specified normal environmental conditions."
This paragraph is-augmented by Regulatory Guide 1.63, Para-graph C "The electric penetration assembly should be designed to withstand, without loss of mechar,ical integrity, the maximum possible fault current versut time conditions that could occur given single random failures of circuit overload protection devices."
(2)
IEEE Standard 317, Paragraph 4.2.5 -
"The rated maximum duration of rated short circuit current shall be the maximum time that the conductors of a circuit can carry rated short circuit current based on the operating time of the backup protective device or apparatus, during which the electrical integrity may be lost, but for which the penetration assembly shall maintain containment integrity."
2
3.0 DISCUSSION'AND EVALUATION In this evaluation, the results of typical containment penetrations being at LOCA temperatures concurrent with a random failure of the circuit protective devices will be analyzed.
CYAPC0 has provided information on the newly installed penetrations.2
- All were manufactured by Conax Corporation, which also performed tests and reported to CYAPC0 the test qualification data.
In supplying the value of the maximum short circuit current available (Isc), CYAPC0 supplied values for a three-phase (on a three-phase system) bolted fault, this type of fault being able to supply the most heat into the penetration. The I value includes in the symmetrical AC component g
cor)tributions by other connected induction motors.
Under accident conditions, a peak containment temperature of 260*F (127'C) is expected.
The following formula was used to determine the time allowed for a snort circuit before the penetration temperature would exceed its limiting value.7 2
T2 + 234 7
7 t = 0.0297 log
+ 234 2+
t = 0.0297 A IO9 (Formula 1) 2 TI + 234 I sc where Time allowed for the short circuit - seconds t
=
Short circuit current - amperes I
=
sc Conductor area - circular mils A
=
T)
Maximum operating tempe.rature (127'C, LOCA
=
condition, to account for current in other penetration conductors) 3 vn
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Maximum short circuit temperature (limiting T
=
2 factor for a given penetration determined from qualification test data).
This formula is based upon the heating effect of the short circuit current on the conductors, and assumes that the penetration seal heats uniformly with the penetration conductors.
In this report, a pre-fault penetration conductor temperature that is equal to the peak LOCA contain-ment atmosphere temperature is assigned, thus simplifying, while accounting for, an elevated conductor temperature caused by a pre-existing current flow and an above normal ambient temperature.
3.1 Typical Low Voltaae (0-1000 VAC) Penetration. CYAPC0 has pro-vided information on a penetration that is.a part of a typical 480-VAC motor operated valve circuit. This penetration has ten feedthru ports, and presently uses five of these, with a total of 95 #10 AWG conductors. The current capacity is rated at 16.4 amperes (13.6 amperes for an accident condition). The test data was extrapolated by Conax Corporation to give a conductor temperature limit of 372*C for short circuit conditions.
The maximum I available for this circuit is 750 amperes rms sym-ge metrical.
It is calculated that, with the 372* temperature limit of the penetration conductors, this short circuit current can be carried by the penetration for 1.28 second before the temperature limit penetration conductors is exceeded, when the. initial temperature is 127 C (peak LOCA in-containment temperature).
No crecit for heat transfer lag from the conductor to the penetration is taken.
The primary 40-ampere circuit breaker will clear this fault in
.65 second. The secondary switch-gear-type circuit breaker will clear the fault in between 12 and 32 seconds. At all levels of current between the rated continuous current of the penetration conductors and the 40 ampere primary circuit breaker, both circuit breakers failed to clear the overload current before the conductor temperature limit is exceeded.
Should the primary breaker fail, at current levels above the primary circuit breaker rating, the secondary breaker will not react in sufficient time to prevent the conductor from exceeding its qualification temperature.
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3.1.1 Low Voltage Penetration Evaluation. With an initial pene-tration temperature of 127*C (the LOCA containment temperature),
the containment electrical penetration design for this low volt-age penetration is not in conformance with the criteria described in Section 2.0 of this report for a three-phase fault.
3.2 Typical Medium Voltage (>1000 VAC) Penetration. CYAPC0 has provided information on a penetrations used to power the reactor coolant pump, P-17-2.
Each penetration consists of three 1500 MCM conductors that have Kerite" insulation.
These have been tested for short circuit con-ditions, to 255*C.10 The maximum I available at the penetration is 21,625 rms symmetri-sc cal amperes.
CYAPC0 did not suppl'y the asymmetrical fault current, saying it.is insignificant.
It is calculated that 18.8 seconds elapse after this f ault occurs at a penetration temperature of 127*C (LOCA containment temper-ature) before the conductors exceed the temperature limit of the conductors.
The instantaneous trip fault clearing time of the primary air circuit breaker (ACB) is approximately.17 second per IEEE Standard 242-1975, Table 33, regardless of the asymmetrical fault current. This circuit breaker can also be tripped by differential current relays.
The secondary ACB will clear the fault current within 2.03 seconds crediting only the syar.ctrical component. At all levels of current greater than the rated continuous ~ current of the penetration conductors, both circuit protective devices clear the fault before the conductor temperature exceeds the temperature limit of the penetration.
3.2.1 Medium Voltage Penetration Evaluation. With an initial penetration temperature of 127 C (the LOCA containment tempera-ture), the containment' electrical penetration design for this medium voltage penetration is in conformance with the criteria described in Section 2.0 of this report.
5
It can be seen that the asymmetrical component is, indeed, insignificant. Using an asymmetrical / symmetrical current ratio of 1.6, the asymmetrical component, lasting less than three 6
2 cy'cles, supplies no more than 8.42 x 10 amperes -second to 8
2 heat the penetration conductors versus 9.5 x 10 amperes -second over the entire clearing time of the secondary circuit breaker.
Thus, the asymmetrical heat generated would be less than 0.9% of the total heat generated in the penetration.
3.3 Typical Direct Current Penetration. CYAPC0 has provided infor-mation for tne penetration used with a 125-V DC stationary gripper coil on control rod #24. The penetration construction is identical to that discus-sed in Section 3.1 except that there are ten feedthru ports, each with nine
- 6 AWG conductors (a total of 90 conductors). The current capacity is rated at 27.1 amperes (22.5 amperes for an accident condition). The test data also shows a conductor temperature limit of 372*C for~short circuit'condi-tions.9 The maximum I available for this circuit is 890 amperes DC.
It is sc calculated that the maximum I can be carried by this penetration for 5.81 seconds before the conductor temperature reaches its limiting temper-ature.
The fuse curves supplied by CYAPC0 show that both the primary fuse and the secondary fuse will clear this fault in less than.01 second. At all current levels above the 30-ampere rating of the fuse, the clearing time is adequate to prevent damage to the penetration seal.
3.3.1 Direct Current Penetration Evaluation. With an initial penetration temperature of 127 C (the LOCA containment tempera-ture), this direct current penetration conforms to the criteria described in Section 2.0 of this report and provides reasonable assurance that containment integrity will be maintained upon a random failure of a circuit protective device should a fault occur. However, the 30-ampere fuse rating is in excess of the 22.5-ampere continuous current rating (at LOCA conditions) of the 6
penetration conductor.
It is recommended that these fuses be resized as applicable.
4.0
SUMMARY
This evaluation looks at the capability of the circuit protective devices to prevent exceeding the design ratings of the selected penetra-tions in the event of (a) a LOCA event, (b) a' fault current through the penetration and simultaneously, (c) a random failure of,the circuit protec-tive devices to clear the fault. The environmental qualification tests of the penetrations is the subject of SEP Topic III-12.
This assessment neglects any heat transfer from the penetration to the containment liner.
To account for rated current in the penetration con-ductors, an initial penetration temperature equal to the peak LOCA in-containment temperature was assigned.
With a LOCA environment inside containment, the protection of the medium voltage AC and the DC penetrations conforms to the specified cri-teria which assumes a short circuit fault and a single random failure of the circuit protective devices. Under the same circumstances, it is expected that the temperature of the low voltage AC penetration will exceed the temperature limit of the hermetic seal of the penetration.
Moreover, as pointed out in Sections 3.1.1 and 3.3.1 of this report, there are conditions upon which the' low voltage penetrations could fail.
CYAPC0 should investigate alternative means of protecting these low voltage penetrations and similiar penetrations durino overcurrent conditions (i.e.--protection immediately above the current rating for accident conditions).
The review of Topic III-12 " Environmental Qualification," may result in changes to the electrical penetration design and therefore, the resolu-tion of the subject SEP topic will be deferred to the integrated assess-ment, at which time, any requirements imposed as a result of this review will take into consideration design changes resulting from other topics.
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5.0 REFERENCES
1.
CYAPC0 letter, W. G. Counsil, Haddam Neck Plant, " Systematic Evalua-tion Program (SEP), Topic VIII-4, Electrical Penetrations," Docket No. 50-213, March 23, 1979.
2.
CYAPC0 letter, W. G. Counsil to Director of Nuclear Reactor Regula-tion, NRC, "SEP Topic VIII-4, Electrical Penetrations," September 30, 1981, A01811.
3.
General Design Criterion 16 " Containment Design" of Appendix A, " Gen-eral Design Criteria of Nuclear Power Plants," 10 CFR Part 50,
" Domestic Licensing of Production and Utilization Facilities."
4 Nuclear Regulatory Commission Standard Review Plan, Section 8.3.1, "AC Power Systems (Onsite)."
5.
Regulatory Guide 1.63, Revision 2, " Electrical Penetration Assemblies in Containment Structures for Light-Water-Cooled Nuclear Power Plants."
6.
IEEE Standard 317-1976, "IEEE Standard for Electric Penetration Assem-blies in Containment Structures for Nuclear Power Generating Stations."
7.
IPCEA Publication P-32-382, "Short Circuit Characteristics of Insulated Cable."
8.
IEEE Standard 242-1975, "IEEE Recommended Practice for Protection and
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Coordination of Industrial and Commercial Power Systems."
9.
" Design Qualification Report of Low Voltage Power and Control Penetra-tion Assemblies for Connecticut Yankee Nuclear Power Station for North-east Utilities Service Company," IPS-434.1, Revision 1, May 23, 1980, Conax Corporation.
10.
" Design Qualification Report of Medium Voltage Dower Penetration Assemblies for Connecticut Yankee Nuclear Power Station for Northeast Utilities Service Company," 1P5-434.3, Revision B, August 12, 1980, Conax Corporation.
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e ENCLOSURI 2
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POSITION ON PROTECT 3DN OF CONTAlk'iENT ELECTRICAL PENETRATIORS AGATs51 ITTLuR1TCAusED et FAuti _Aso OvERLOO CURREN15 FOR SEP PLANii introduction As part of the Systematic Evaluation Program (SEP) the WRC staff performed un audit, conparing sample containment electrical penetrations in SEP facilities with current licensing criteria for protection against fault and overload currents following a postulated accident. The simplified and conservative model used did not shw that the SEP facilitics meet current licensins criteria nor did it shc= the existing circuit protection to be adequate. Accordingly, the SEP licensees are requested to deronstrate, using rore realistic calcula-tions where necessary, that the circuit protection is adequate in accordance with the position described belom.
Backerotmd In licensing new plants, the staff reacires compliance with the recomendations of Regulatory Guide 1.63 or an acceptable-alternative method.
For each containment electrical penetratien, the arctective systems provide C
primary and backup circuit protection devices to prevent a single failure in con-junction with a circuit overload from impairing containment integrity. The pri:cy and backup protection devices have trip time vs. current response charac-
.teristics which assure protection against penetration failure.
The protection devices are periodically tested to verify trip setpoints and adequacy of response.
No single failure allows excessive currents in the penetration conductors which will degrade the penetration seals. Where external control power is used for actuating the protection systems the power for primary and backup breakers are derived from separate sources.
Overcurrent signals for tripping primary and backup system devices are electrically independent and physically separated.
Staff Audit The safety objective of SEP Topic VIII-4,
- Electrical Penetrations of Reactor Containment," is to assure that all electrical penetrations in the containment structure are designed not to fail from electrical faults durinF a high energy line break (LOCA or secondary system line break).
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2-We have perforted preliminary evaluations, on a conservative basis, of th: <sult current protection for three samle containrent electrical penetrations for each of the eleven SEP plants. The entire penetration was assumed to be initially at the peak calculated LOM temerature. Then, for a given fault current, the tire to heat the wire to the limiting raterial temerature (usually the reiting point of the seal raterial) was calculated. This time was comared to the tice for the protective device (s) to interrupt the fault current.
On this basis, several penetrations exceed limiting temeratures if the prirary protection device f ails.
Others do so without postulating pricary device failure.
Two of the samle penetrations even have reiting temeratures less than the peak LOM temerature and thus exceed the limits of this model 'even if there is no f ault current.
(References 1 through 11)
This does not necessarily rean that the penetrations would actually fail.
The analysis was conservative, particularly in assuming that the penetration was initially at the pe2L calculated containrent te.perature. The penetrations would not reach such a temerature following an accident.
In addition, licensee coments have indicated that there ray be so e errors in the calculations.
(For exagle, Northeast Utilities letter dated August 29,19D, D9:Lc ho. 50-245.
providing coments on the staff calculations for Millstone, Unit 1). Neverthclass, this audit clearly did not put the ratter to rest.
Position
{
Each SEP licensee is requested to evaluate the adequacy of the existing fault current prote: tion for contain.ent electrical penetrations in a:cercan:e with the position discussed ir, rcre detail belt
- and to propose re edies where neeoed in order to reet the position.
1.
The basic requirement of' Regulatory Guide 1.63 that all penetration circuits, Class IE or non-Class IE, be provided with overcurrent protection in conferren:e with the redundan:y an: testability requirements of IEEE Std 279-1971 should be met; 2.
A single circuit breaker to protect a penetration serving a Clas:; It circuit or l
r a non safety circuit containing only components that are qualified to Class IE requirements is acceptable provided that each component of such circuit is qualified to the accident environment; and l
3.
A circuit whose lo'ds inside containment are not required to mitigate the a
consequences of accidents may be automatically disconnected from its power l
source on receipt of an accident signal or it may be maintained deenergized by positive means such as those outliend in Branch Technical Position ICSB l
18 (PSB) of Appendix 8A to the Standard Revicw Plan whenever cuntainment l
integrity is required.
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0- Notes For the purpose of evaluating the adequacy of protection for contain.ent protection, faults should be postuisted up to a bolt,ed cable fault inside containment at the penetratien (a bolted three phase fault for thret phase circuits).
The primary protection device should have a trip time vs. current response characteristic that assures against penetration failure under all fault conditions.
Circuit breakers should be tested periodically to verify their trip setting value and response titre.
Breakers should be designed to ini,errupt the seximm possible fault current for the circuit or backup protection fast response current limiting fuses should be provided.
In addition, fuses may be used Un lieu of circuit breakers as protective devices.
Where fuses are used, documentati.on of their response characteristics derived f rom prodsttion testing should be available for audit.
It' is acceptable to use less conservative rodels than were used in our preliminary evaluations provided that they address fault currents up to bolted f aults and still provide reasonable assurance that the penetration vill not fail.
For exarple, a rore realistic initial terperature of the
(
containmnt penetration could be determined rather than assuming the penetration has reached the peak calculated containrent atmosphere terp-e rat ure.
Circuits may be codified to reduce the shert circuit current to acceptable values by the use of current limiting devices (such as resistors, isolation transformers, and chancing transformer taps) external to the Containment.
,-