ML20002B300
| ML20002B300 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 10/30/1980 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | Counsil W NORTHEAST NUCLEAR ENERGY CO. |
| References | |
| TASK-08-04, TASK-8-4, TASK-RR NUDOCS 8012110290 | |
| Download: ML20002B300 (17) | |
Text
g,,-.,k UNITED STATES NUCLEAR REGULATORY COMMISSION
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Docket No. 50-245 s
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< :s Mr. W. G. Counsil, Vice President E. "
U ll5 Nuclear Engineering and Operations 5
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-'S Northeast Nuclear Energy Company M
a Post Office Box 270 os Hartford, Connecticut 06101
Dear Mr. Counsil:
RE: SEP TOPIC VIII ELECTRICAL PENETRATIONS OF REACTOR COMPARTMENT (Millstone Station Unit 1)
Enclosed is a copy of our evaluation of Systematic Evaluation Program Topic VIII-4, Electrical Peretrations of Reactor Compartment. This assessment compares your facility, as described in Docket No. 50-245, with the criteria currently used by the regulatory staff for licensing new facilities. Please infom us if your as-built facility differs from the licensing basis assumed in our assessment.
This evaluation will be a basic input to the integrated safety assessment for your facility unless you identify changes needed to reflect the as-built conditions at your facility. This topic assessment may be revised in the future if your facility design is changed or if NRC criteria relating to this topic is modified before the integrated assessment is completed.
Sincerely, s
ge!Y nnis M. Crutchfield, Chief Operating Reactors Branch #
Division of Licensing
Enclosure:
Completed SEP Topic VIII-4 cc w/ enclosure:
See next page l
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Mr. W. G. Counsil October 30, 1980 cc William H. Cuddy, squire Connecticut Energy Agenpy Day, Berry & Howard ATTN: Assistant Director Counselors at Law Research and Policy One Constitution Plaza Development Hartford, Connecticut 06103 Department of Planning and Energy Policy Board of Selectmen 20 Grand Street Town' Hall Hartford, Connecticut 06106 Haddam, Connecticut 06103 Director, Technical Assessment Division Northeast Nuclear Energy Coapany Office of Radiation Programs ATTN: Superintendent (AW-459)
Millstone Plant U. S. Environmental Protection P. O. Box 128 Agency Waterford, Connecticut 06385 Crystal Mall #2 Arlington, Virginia 20460 Mr. James R. Himmelwright Northeast Utilities Service Company U. S. Environmental Protection P. O. Box 270 Agency Hartford, Connecticut 06101 Region I Office ATTN: EIS COORDINATOR Resident Inspector JFK Federal Building c/o U. S. NRC Boston, Massachusetts 02203 P. O. Box Drawer KK Niantic, Connecticut 06357 Superintendent Haddam Neck Flcnt Water :ord Public Library RfD #1 Rope ferry Road, Route 156 Post Office Box 127E Waterford, Connecticut 06385 East Hamptnn, Connecticut 06424 First Selectman of the Town Resident Inspector of Waterford Haddam Neck Nuclear Power Station Hall of Recerds c/o U.S. NRC 200 Boston Post Road East Haddam Post Office Waterford, Connecticut 06385 East Haddam, Connecticut 06423 John F. Opeka Systens Superintendent Northeast Utilities Service Company P. O. Box 270 I
/
Hartford, Connecticut G6101 hatural Resources Defense Council 91715th Street, N. W.
Washington, D. C.
20005
f SEP TECHNICAL EVALUATIOE TOPIC VIII-4 ELECTRICAL PENETRATIONS OF REACTOR COMPARTMENT MILLSTONE NUCLEAR STATION, UNIT NO. 1 Northeast Utilities Docket No. 50-245 t
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CONTENTS
1.0 INTRODUCTION
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2.0 CRITERIA.
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3.0 DISCUSSION AND EVALUATION 2
3.1 Typical Low Voltage (0-1000 V) Penetraticas 4
3.1.1 Low Voltage Penetration Evaluation......
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3.2 Typical Medium Vo1tage ( 1000 V) Penetration 4
l 3.2.1 Medium Voltage Penetration Evaluation 6
4 3.3 Typical DC Penetrations 6
l 3.3.1 DC Penetration Evaluation 6
4.
SUKMARY 6
5.
REFERENCES.
7 APPENDIX A--RESPONSE TO NORTHEAST UTILITIES LETIER OF
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AUCUST 29, 1980 CONCERNING SEP TOPIC VIII-4, 8
j ELECTRICAL PENETRATIONS i
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SEP TECHNICAL EVALUATION TOPIC VIII-4 ELECTRICAL PENETRATIONS OF REACTOR COMPARTHENT MILLSTONE NUCLEAR STATION, UNIT NO. I
1.0 INTRODUCTION
This review is part of the Systematic Evaluation Program (SEP), Topic VIII-4. The objective of this review is to determine the capability of the electrical penetrations of the reactor compartment to withstand short cir-cuit conditions of the worst expected transient f ault current resulting from single random failures of circuit overload protection devices.
General Design Criterion 50, " Containment Design Basis" of Appendix A,
" General Design Criteria for Nuclear Power Plants" to 10 CFR Part 50 requires that penetrations be designed so that the containment structure can, without exceeding the design leakage rate, accommodate the calculated pressure, temperature, and other environmental conditions resulting from any loss-of-coolant accident (LOCA).
IEEE Standard 317, " Electric Penetration Assemblics 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.
l Specifically, this review will examine the protection of typical elec-trical penetrations in t'e containment structure to determine the ability n
of the protective devices to clear faults prior to exceeding the penetra-L tion design ratings under LOCA temperatures.
l 2.0 CRITERIA l
IEEE Standard 317, " Electric Penetration Assemblies in Containment Structures for Nuclear Power Generating Stations" as supplemented by Nuclear Regulatory Commission Fegulatory Guide 1.63, " Electric Penetration Assem-blies in Containment Structures for Light-Water-Cooled Nuclear Power Plants" 1
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1 provides the basis acceptable to the NRC staff. The following criteria are I
used in this report to determine compliance with current licensing requirements:
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1.
IEEE Standard 317, Paragraph 4.2.4 - "The rated short i
circuit current and duration shall be the maximum short circuit current in amperes that the conductors of a l
circuit can carry for a specified duration (based on the operating time of the primary overcurrent protec-tive device or apparatus of the circuit) following j
continuous operation at rated continuous current with-
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out the temperature of the conductors exceeding their j
short circuit design limit with all other conductors in j
ene assembly carrying their rated continuous current under the specified normal environmental conditions."
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This paragraph is augmente: by Regulatory Guide 1.63, Paragrapn C "The eleewric penetration assembly l
should be designed to withstand, without loss of =ech-anical integrity, the maximum possible fault current versus time conditions that could occur given single random failures of circuit overload protection devices."
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2.
IEEE Standard 317, Paragraph 4.7.5 - "The rated maxi-mum duration of rated short circuit current shall be the maximum time that the conductors of a circuit can I
carry rated short circuit current based on the opera-i ting time of the bLckup protective device or apparatus, l
during which the electrical integrity may be lost, but for which the penetration assembly shall maintain con-t tainment integrity."
3.
IEEE Standard 317, paragraph 6.4.14 - "The maximum
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duration of rated short circuit shall be verified by the test.
The test shall be conducted at maximum pos-tulated design bases event temperature and pressure and relative humidity. The test current and duration shall be in accordance with Section 4.2.5 plus margin. The test duration shall be not less than the time required for the backup overcurrent protection device to function."
3.0 DISCUSSION AND EVALUATION In this evaluation, the results of typical containment penetrations being at LOCA temperature initially concurrent with a random failure of the i
circuit protective devices will be analyzed.
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4 Northeast Utilities (NU) provided information (Reference 1) on typical penetrations. No evaluation of the data was provided. A temperature limit l
of 352 F (177 C) before seal failure for the three penetrations has t
been established based on testing done by Oyster Creek Nuclear Station for identical type connectors (Reference 2) in lieu of docketed data from NU l
j describing tests or analysis to specify a temperature limit.
J Maximum short circuit current available (Isc) W88 Provided by North-east Utilities for a three phase bolted fault. Rated current (I )
r each penetration was also provided.
To evaluate the ability of the penetration to withstand a LOCA envi-ronment, the following formula (Reference 3) was used to determine the time allowed before a short circuit would cause the penetration to heat up to the temperature limit.
2 T +234 2
t=A
.0297 log (Formula 1) 7 T +234 I
1 where time in seconds t
=
current in amperes I
=
conductor area in circular mils A
=
T1 initial temperature (13800, LOCA condition)
=
T2 maximum penetration temperature before failure.
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This is based on the heating effect of the short circuit current on the conductor and /ses not take into account heat losses of the conductor.
For times less t'an several seconds, this heat loss is negligible.
In evaluating the capability of tne penetration to withstand a LOCA temperature with a short circuit current, Formula 1 was used to calculate the time required to heat cne conductor from the LOCA temperature to pene-tration failure temperature for current = from rated current to maximum 3
short circuit current in 20*. increments. Times for the primary and second-ary overcurrent devices to interupt these fault currents were calculated.
Where breaker ratings provided by the licensee indicated minimum and maxi-mum fault clearing times, the maximum time was used for conservatism.
3.1 Typical Low voltage (0-1000V) Penetrations. Northeast Utilities has identified penetration X-105D (CE type NSO4) as being typical of los voltage penetrations. This penetea. ion provides 480 V a: power to motor-operated valve 1-IC-1.
This penetration uses two #8 AWG cables in parallel and has a contin-uous current rating of 20 amps per conductor. The maximum available short circuit current has been determined by NU to be 1600 amps. A temperature limit of 352 F (177 C) before seal failure has been dete mined based on testing. At the maximum short circuit current (1600 amps), overtemperature will be reached in 0.64 second f rom LOCA temperature initially.
From LOCA temperature initially, the secondary breaker will not operate to clear any fault currents before penetration seal limiting temperature is attained. The primary breaker will clear the fault currents before seal limiting temperature is attained provided that both conductors are intact.
There are no Technical Specification requirements to verify that both con-ductors have continuity.
3.1.1 Low voltage Penetration Evaluation. With an initial pene-tration temperature of 138 C (LOCA),
penetration X-105D does not meet j
requirements of RG 1.63 and IEEE Std. 317 for any short circuit current i
fault with a failure of the primary breaker.
It does meet current require-ments for short circuit faults if the primary breaker operates as designed 1
providad that both cables in the penetration are operable.
3.4
. Medium Voltage (>1000 V) Penetration. Northeast Utili-ties has identified penetration X-101A (GE type NS03) as being typical of l
medium voltage penetrations. This penetration provides 4160 V ac power to 1
Reactor Recirculation Pamp 1.
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This penetration uses two 500 MCM cables in parallel and has a contin-t uoes current rating of 550 amps per conductor. The maximum available short circuit current has been determined by NU to be 1700 amps. A temperature limit of 352 F (177 C) nas been estaolished based on testing. At the 1
maximum short circuit current (1700 smps), overtemperature will be reached in 440 seconds from LOCA temperature initially.
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There are no circuit protective devices located between the motor generator and the reactor recirculation pump. Overcurrent protection is j
provided by a differential current sensing relay and a line overcurrent sensing relay, each of which will operate to trip the motor generator by securing power to the motor generator motor and opening the generator field windings. At 2156 amps of current difference between phases, the dif fer-ential relay will cause a trip of the motor generator in 0.133 second or less. At line current in excess of 780 amps, the overcurrent relay will cause a trip of the motor generator in 0.18 second or less.
For a three phase short circuit condition, it cannot be assumed that sufficient current differences will exist to cause the differential relay to operate and trip the motor generator. Therefore, operation of this relay cannot be expected to clear fault currents prior to exceeding the penetration seal temperature limit of 177 C.
For fault currents producing current differences between phases in excess of 156 amps, this relay will I
l operate to trip the motor generator prior to reaching the penetration seal temperature limit.
The line overcurrent relay will operate to clear all fault currents in excess of 780 amps prior to reaching the penetration seal temperature limit from LOCA temperature initially. For fault currents less than 1100 amps, the conductors will carry less than their rated continuous current (550 amps) provided both conductors hade continuity. If one conductor is l
open, the overcurrent device will not cperate for faults between 550 and l
780 amps and penetration overheating may occur. There are no Technical 1
Specifications requiring continuity of the conductors to be checked.
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3.2.1 Medium Voltage Penetration Evaluation. At LOCA tempera-ture, penetration X-101A does not meet current requirements of RG 1.63 and IEEE Std. 317 for short circuit faults with a failure of the line overcur-rent relay since the differential relay cannot be assumed to operato for a three-phase short circuit. With a failure of the differential current relay at LOCA temperature, the penetration meets current requirements for all fault currents provided that both conductors in the penetration are operable.
3.3 Typical Direct Current Penetration. Northeast Utilities'has identified penetration X-100A (GE type NSO4) as being typical of DC pene-
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trations. This penetration provides 125 V de power to the solenoid valve on main steam isolation valve 203-1A.
2 This penetration uses #14 AWG cable and has a continuous' current rating' of 10 amps. The maximum available short circuit current has been determined by NU to be 95 amps. A temperature limit of 352 F (177 C) before seal failure has been determined based on testing. At the maximum short circuit current (95 amps), overtemperature will be reached in 2.38 seconds from LOCA temperature initially.
At LOCA temperature, both the primary and secondary fuses will operate
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to clear all fault currents before the penetration seal temperature limit is reached.
3.3.1 DC Penetration Evaluation. At LOCA temperature, penetra-tion X-100A meets carrent requirements at RG 1.63 and IEEE Std. 317 for all f anit currents with a failure of the primary protective device.
4.0
SUMMARY
At LOCA temperature, penetrations X-105D and X-101A do not meet current requirements of RG 1.63 and IEEE Std. 317 for any fault current with a failure of the primary protective device. They do not meet current require-ments if one of the two conductors in the penetration is inoperable even if
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the primary protective device operates as designed under these conditions.
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There are no Technical Specification requirements to verify continuity of both conductors in penetrations using two parallel conductors per phase.
I At LOCA temperature, penetration X-100A meets current requirements of RC 1.63 and IEEE Std. 317 for all fault currents with a failure of the primary protective device.
5.0 REFERENCES
1.
Northeast Utilities letter (Counsil) to NRC (Ziemann) dated March 14, 1979.
2.
Final rescription and Safety Analysis Report, Oyster Creek Nuclear i
Station, Anunendment 62 (Docket No. 50-219-102).
3.
IPC&A Publication P-32-382, "Short Circuit Characteristics of Insula-ted Cable."
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a Aph NDIX A L
i RESPOiWE TJ NORTHEAST UTILI;IES LCTTCR OF ALGUST 29, 1980 C0NCE.RAING SEP TOPIC VI!! +, ELECTRICAL PENETRATIONS i
4 1980, res'onded to the Nortneast Utiltties (NU) letter
>f August 29, p
l NRC staf f evaluati 'a of SEP Topic VIII-4, Electrical Penetrations of Reactor Containac F tor Millstone 1.
Several areas of disagreement were i
noted. This appendi t responds to those areas of disagreement.
4 1.
Northeast Utilities asserts that the Oyster Creek FSAR, Ammend-j ment 62. was not' docketed by NU.
f This discrepancy has been corrected in thi,s revised report.
However, the penetrations are identical to those described in Ammendment 62.
This information aas used in liea of any docketed information by NU to determine temperature limits for the pene-f trations.
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2.
NU questions the use of 352 F as che temperature limit for use in calculsting the time to penetration overtemperature since the Ammenlment 62 tests resulted in no leakage at that temperature.
i NU states than no allowance for leakage was specified in the i
l initial evsluation and that no temperature / leakage rate refer-en:es were made.
I The 332 F. limit was chosen since it represents the highest value to which these types of peneti ations had been successfully l
tested (oased on available docketed.afornation). Leakage rates were not addressed since RG 1.63 requires that the penetrations l
withstand the specified conditions, "without loss of mechanical 1
integrity" (see Section 2.0 of this revised report). Further-more, no docketed information was available giving leakage rates / temperatures for these penetrations. Therefore, :he most successful docketed tent uss used
,s the basis for the evalu-ation. Should other docketed information beceme available, this evaluatian will be reconsidered.
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NU qua*tions the use of the LOCA temperature of 138 C as the initial temperature for the conductor for determining the time to reach one limiting temperature using the formula in Section 3.0 of thts report. They also question the lack of consideration for i
the temperature dif ference between the inboard and outboard seals (both must fail to breach containment).
I IEEE Standard 317, paragraph 6.4.14, stipulates that the penetra-l 1
tions be tested at LOCA temperature, pressure, and humidity at the maximum f au'tt current for the time required for the backup overprotection device to function. This paragraph is quoted in Section 2.0 of this revised report to clarify the rationale for using LOCA temperature for T in the calculations.
g 4.
NU questions the validity of the equaticn in Section 3.0 of this report for use in determining time to penetration failure, since this equation is normally used in calculating protection set-points for preventing cable damage.
1 The equation of Section 3.0 was used te calculate the time for the conductor to reach a specified temperature from an initial f
temperature for various fault currents. Tnis equation is valid for that purpose. As noted in Section 3.0, it was assumed that i
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there was no heat loss from the conductor to ambient. Section 3.0 further states tnut the times were calculated for the conductor to reach the penetration limiting temperature.
In the absence of a detailed heat transfer evaluation from the conductor to the seal, this is considered to be conservative and justified.
5.
NU asserts that the times calculated for the 1)w voltage and i
medium voltage. penetrations did not accoint for the presence of two conductors per pnase to carry the fault current.
This error has b"en carrected in this revised report. However, it has been notec that no Technical Specifications exist to 5
verify that bath conda: tors have continuity. It is loubtful l
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lb tnat. if me conductor wera a,en,.mc tuJication of the problem woull appear prior to seat f+tlure.i t currents as low as 20 to 330 r ps tar the low voltag-n3nerretion and 550 to 780 amps for the m.:lium voltage penetrat i u.
6.
NU as :rts tast the los voltage p inot ratian will be protected from r crtemperature even if tne primary breaker fails, since the
!/10 Aih vire external to tne penetration will fuse at 1600 amps in abrit une second and a #8 AWG wire with 800 amps (1/2 fault curret.t} will fuse in about s:ne woonds.
rais in!3rmation yields no change in the evaluation. For 800 amps per v3 N..G conductor, the tenper u t re will rise from LOCA temper-tture to 177 C (tne temperature ! t rai t s previously described) in 0.33 sc>: ends, which is before fus..ng of tae f*10 AWG external conduct;r would occur.
7.
NU claims tnat the dif ferential ri.iays used for protection on the medium valtage penetration circuit are capaole of detecting a tnree p nse bolted f ault since tae.urrent transformers for detecting phase current are located at botn the motor and the generator.
Tne basic assumption of the taree pnase bolted fault is that the current in each phase is equal. Location of the cts to measure tne paase current should nave no af tect oa differential relay operation unless the cts for each phase are located in different positions with respect to the cts in other phases.
It is not apparent that tne differential relays for this circuit are cap-aale of detecting a three pnase oolted fault oefore the conductor reacnes the penetration temperature limit. Further justification oy NU is necessary to support this claim.
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NU asserts that, for fault currents leas than 780 amps (390 amps
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per conductor) on the medium voltage penetration circuit, pene-tration overtemperature will not occur since each 500 McM conduc-I
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tor is rated at 550 amps continuous current.
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This assertion is correct provided thte both conductors are oper-able. As notad in this revised report and in Number 5 of this appendix, there are no Technical Specifications requiring verifi-
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cation of continuity of both conductors. This revised report t
reflects these points.
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