ML19320D041
| ML19320D041 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 07/01/1980 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | Kay J YANKEE ATOMIC ELECTRIC CO. |
| References | |
| TASK-08-04, TASK-8-4, TASK-RR NUDOCS 8007180466 | |
| Download: ML19320D041 (13) | |
Text
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- 4 UNITED STATES
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NUCLEAR REGULATORY COMMISSION
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. j WASHINGTON, D. C. 20555 e
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G July 1, 1980 Docket No. 50-29 Mr.. James A. Kay Senior Engineer-Licensing Yankee Atomic Electric Comany 25 Research Drive Kestborough, Massachusetts 01581
Dear Mr. Kay:
RE: SEP TOPIC VIII-4 ELECTRICAL PENETRATIONS OF REACTOR CONTAINMENT (Yank ee-Rowe)
Enclosed is a copy of our evaluation of Systematic Evaluation Program Topic VIII-4, Electrical Penetrations of Reactor Containment.
This assessment compares your facility, as described in Docket No. 50-29 with the criteria currently used by the regulatory staff for licensing new facilities. Please inform us if your as-built facility differs from the licensing basis assumed in our assessment within 60 days of receipt of this letter.
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 are modified before the integrated assessment is co@leted.
Si erely,
. y Dennis M. Crutchfield, ief Operating Reactors Branch #5 Division of Licensing
Enclosure:
Cogleted SEP l
Topic VIII-4 l
cc w/ enclosure:
See next page I
l 8007180 tlt,6
Mr. Janes A. Kay July 1, 1980 cc w/ enclosure:
Mr. Janes E. Tribble, President l
Yankee Atomic Electric Company 25 Research Drive Westborough, Massachusetts 01581 Greenfield Community College 1 College Drive Greenfield, Massachusetts 01301 Chairman Board of Selectmen Town of Rowe Rowe, Massachusetts 01367 Energy Facilities Siting Council 14th Floor One Ashburton Place j
Boston, Massachusetts 02108 Director, Technical Assessment Division Office of Radiation Programs (AW-459)
U. S. Environmental Protection Agency Crystal Mall #2 Arlington, Virginia 20460 U. S. Environmental Protection Agency Region I Office ATTN: EIS C0ORDINATOR JFK Federal Building Boston, Massachusetts 02203 Mr. Richard E. Schaffstall KMC, Incorporated 1747 Pennsylvania Avenue, NW Washington, D. C.
20006
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j SEP TECHNICAL EVALUATION i
TOPIC VIII-4 j
ELECTRICAL PENETRATIONS OF REACTOR CONTALNNENT YANKEE ROWE NUCLEAR STATION 2
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Yankee Atomic Electric Company Docket No. 50-29 4
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DATE:
July 1,~1980 I.
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CONTENTS
1.0 INTRODUCTION
1 2.0 CRITERIA.
2 3.0 DISCUSSION AND EVALUAIION 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 Penetration Evaluation 6
3.3 Typical Direct Current Penetration 6
3.3.1 Direct Current Penetration Evaluation 7
4.
SUMMARY
7 5.
REFERENCES.
8
SEP TECHNICAL EVALUATION TOPIC VIII-4 ELECTRICAL ?ENETRATIONS OF REACTOR CONTAINMENT YANKEI ROWE NUCLEAR STATION
1.0 INTRODUCTION
This review is part of the Systematic Evaluation Program (SEP),
Topic VIII-4. Yankee Atomic Electric Company (YAEC) has provided information (Reference 1) describing typical penetrations, typical in-containment loads, and fault currents. They did not provide an analysis of their suitability in Reference 1.
The objective of this review is eo determine the capability of overcurrent devices to prevent exceeding the design racing of the electrical penetrations through the reactor containment during short circuit conditions at LOCA temperatures.
General Design Criterion 50, " Containment Design Basis" of Appen-dix 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 leakege rate, accommodate the calculated pressure, temperature, and other environmental condi-tions 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 Regulatory Guide 1.63, provides a basis of electrical penetrations acceptable to the staff.
Specifically, this review will examine the protection of typical electrical penetrations in the containment structure to determine the
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ability of these protective devices to clear the circuit during a short circuic condition prior to exceeding the :entainment electrical pene-tration test or design racing 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 l y Nuclear Regulatory Commission Regulatory Guide 1.63, " Electric Penetra-tion Assemblies in Containment Structures for Light 'w'ater-Cooled Nuc-lear 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 cir-cuit current and duration shall be the maxi =um 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) following continuous operation at raced 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."
a This paragraph is augmented by Regulatory Guide 1.63, Para-graph C "The electric penetration assembly should be designed to withstand, without loss of mechanical integrity, the maximum possible fault current versus time conditions that could occur given single randem 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 conductort 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."
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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 cir-cuit protective devices will be analy:ed.
YAEC has provided information (Reference 1) on typical penetra-tions. All were field manufactured. Ne short circuit test data is available for these penetrations. YAEC has established a qualification temperature limit for each penetration below which damage to the her-metic seal of the penetration does not occur. The initial steady state temperatures of the containment environment is up to 120 F (49 C).
Under accident conditions, a peak temperature of 248 F (120 C) is expected. YAEC used the Insulated Power Cable tagineers Association publication, P-32-382, entitled "Short Circuit Characteristics of Insulated Cable" to determine limiting factors on the conductors of the pene ration.
In supplying the value of the maximum short circuit current avail-able (I
), YAEC supplied values for a three phase (on a three phase system) bolted fault; this type being able to supply the most heat into the penetration. The I value includes in the symmetrical AC compo-nent contributions by other connected induction motors. YAEC assumed a maximum operating temperature to allow for all other penetration con-ductors carrying their maximum reced current.
The following formula (Reference 6) was used to determine the time allowed for a short circuit before the penetration temperature would exceed its limiting value.
72 "T2 + 234 ~
7 e = 0.0297 log 7I 34 _
t = 0.0297 A 1 8 T1 + 234 -
2 (For=ula 1) 2 I se 3
I
where Time allowed for the short circuit seconds t
=
I Short cir:uit current amperes
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se A
Conductor area circular mils
=
T g Maximum operating temperature (120 C, LOCA
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condition)
T Maximum short circuit temperature (YAEC sup-
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2 lied limiting factor for a given penetration).
This is based upon the heating effect of the short circuit c'rrent u
on the conductors.
It should be noted that the short circuit temperature-time limits of the conductors in this report vary from the values calculated by YAEC (Reference 1) even though the same methods are used. YAEC calcu-laced an silowable current, given a temperature rise and time, where this report uses the YAEC supplied fault current magnitude and a smal-1er temperature rise to calculate the matimum time allowed to clear a fault condition. Also in this report, a pre-fault penetration conduc-tor temperature equal to the peak LOCA containment atmosphere tempera-ture is assigned, thus simplifying while accounting for an elevated condector temperature caused by pre existing current flow and above normal ambient temperature.
3.1 Tveical Lov Voltage (0-1000 VAC) Penetration. YAEC has pro-vided information on a penetration that is a part of a typical 480 VAC motor operated valve circuit. This penetration has a three conductor
- 8 mineral insulated copper sheathed cable. A brass compression seal ring is used at each end of the penetration to provide hermetic sealing.
These seal rings would be damaged at a lower temperature (900 C) than any other component of the hermetic seal. The temperature limit of the hermetic seal of the mineral cable is 1080 C as supplied by YAEC 4
(Reference 1).
The maximum I, available at this penetration is 1350 ras zmperes-symetrical.
It is calculated that, with the 900 temperature limit of the brass seal ring, this short circuit current can be carried by the 4
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penetration for 2.25 seconds before the penetration conductors exceed 900'C in the LOCA environment.
t The primary 30-ampere circuit breaker will clear this fault in
.015 second. The secondary, switch gear type circuit breaker, being between the short time and long time characteristics at this fault current level, will clear the fxel: in between.28 and 16 seconds.
Assuming that some asymstrical fault current component exists, it would set to clear the fault in less time. At lower values of fault current, the same results occur. The secondary breaker takes longer to clear the fault current than is deemed advisable.
3.1.1 Low Voltare Penetration Evaluation. With an initial pene-tration temperature of 120 C (the LOCA containment temperature),
the containment electrical penetration design for this low voltage penetration is not in conformance with the criteria described in Section 2.0 of this report for a three phase fault.
3.2 Tvvica13edium Voltare (>1000 VAC) Penetration. TAEC has 1
provided information on penetrations used to power the 2400 VAC main coolant pump, P-14-2.
Each penetration consists of three 5/8 inch diameter tinned copper rods insulated with buna rubber. Two panetra-tions are used per pump. These are held in place with silicone rubber seal rings at each end of the penetration. The temperature limited element of the hermetic seal of the penetration identified by TAEC is the buna rubber which melts at 200*C.
The maximum I,c available due to a bolted fault at the penetration is 25,260 ras symetrical amperes. YAEC did not supply the asymetrical fault current but, at this volcage, it is typically 1.6 times the symetrical current or 40,416 rms equivalent amperes.
It is noted that a portion of I, is supplied by induction motors (4550 rms amperes) which do not pass through the secondary protective device.
It is calculated that 2.51 seconds elapse af ter a 25,260-ampere fault occurs at a penetration temperature of 120'C (LOCA contai= ment temperature) before the conductors exceed 200 C.
It is also assumed 5
o that the silicone rubber seal ring does not fill any voids presented by the melting buna rubber insulation.
The instantaneous trip fault clearing ti=e of the primary air circuit breaker (ACS) is approximately.17 second per IEEE Standard 242-1975, Table 33, irregardless of the assymetrical fault current. The secondary ACS will clear the f ault current within.51 second crediting only the symetrical component. At lower values of fault current, in all cases, both the primary and the secondary circuit breakers clear the fault quicker than the time limit imposed by Formula 1 at the same current magnitude.
3.2.1 Medium Voltage Penetration Evaluation. With an inicial penetration temperature of 120 C (the LOCA containment tempera-ture), this medium voltage penetratiot conforms to the criteria described in Section 2.0 of this report, and provides reasonabla assurance that containment integrity wil1 be maintained upon a random failure of a circuit protective device should a three phase fault occur.
While parallel conductors are recognized and allowed by the National Electric Code, it is n'ot advisable with these penetra-tions. Should a line break occur without faulting, the single remaining penetration ~dois's ndt' ~confo'_rm to tFe-~cdteria'TescVibid-in
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Seetion 2.0 of this'~refort with th~e'. piimpTuIl-load current going
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through it.
3.3 Tveical Direct Current Penetrations. YAEC has provided information for the penetration used with the solenoid pressurizer relief valve, PR-SOV-90.
The penetration construction is identical to that discu'ssed in Section 3.1 except that a seven conductor #12 mineral insulated cable is used. The temperature limit of the hermetic seal identified by YAEC is the melting point of the brass seal ring (900 C).
The maximum I available at this penetration is 555 amperes.
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It is calculated that the maximum I, can be carried by this penetration for 2.08 seconds before the conductor temperature reaches 900 C.
No time lag is allowed for the heat to pass from the conductor to the seal ring.
The fuse curves supplir: by YAEC show that the primary fuse will clear this fault in.01 second and that the secondary fuse will indepen-dently clear this fault in less than 11 seconds. At all values of fault current less than 555 amperes, the primary fuse always cleared the fault within the time allowed by Formula 1, while the secondary fuse did not.
3.3.1 Virect Current Penetration Evaluation. With an initial penetration temperature of 120 C (the LOCA containment tempera-ture), this direct current penetration does not conform to trae criteria described in Section 2.0 of this report upon failure of the pr cmary fuse to clear a line-to-line fault.
4.0
SUMMARY
This evaluation looks at the capability of the protective devices to prevent exceeding the design or test racings of the selected pene-trations in the event of (a) a LOCA event, (b) a fault current through the penetration and simultaneously (c) a random failure of the circuit protective 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 conductor to other conductors and the containment Liner. To account for initial full-rated current in the penetration conductors, an ini-tial 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 penetration conforms to the specified criteria which 7
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assumes a short citauit fault and a single randem failure of the cir-cuit protective devices. Under the same circumstances, it is expected that the temperature of the hermetic seals of the low voltage AC and the DC genetrations would exceed their respective limiting ta=peratures.
Should one penetration of the penetration pair used with the pri-mary coolant pump have an open circuit in one of its three conductors, the normal operating current for the RCP would cause the remaining penetration to exceed the conductor temperature limit within 1.1 hours1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> at an initial penetration temperature of 60 C.
This condition occurs because the breaker protective setpoints disregard the fact that the use of one feeder to supply the RCP will cause conductor and penetration overheating and there is no provision to monitor the integrity of the parallel conductors.
The review of Topic III-12, " Environmental Qualification," may result in changes to the electrical penetration design and therefore, the resolution of the subject SEP topic will be deferred to the inte-grated assessment, at which time, any requi.ements imposed as a result of this review will take into consideration design changes resulting from other topics.
5.0 REFERENCES
1.
Robert H. Groce, Systematic Evaluation Program (SEP), WYR 79-32, March 14, 1979, YAEC letter.
2.
General Design Criterion 16, " Containment Design" of Appendix A,
" General Design Criteria of Nuclear Power Plants," 10 CTR Part 50,
" Domestic Licensing n /roduction and Utilization Facilities."
3.
Nuclear Regulatory Commission S tandard Reviev /lan, Section 8.3.1, "AC Power Systems (Onsite)."
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s 4.
Regulatory Guide 1.63, Revision 2, " Electrical Penetration Assemblies in Containment Structures for Light-Water-Cooled l
Nuclear Power Plants."
5.,
IEEE Standard 317-1976, "IEEE Standard for Electric Penetratice Assemblies in Containment Structures for Nuclear Power Generating Staticas."
6.
IPCEA Publicatien P-32-382, "Short Circuit Characteristics of Insulated Cable."
7.
IEEE Standard 242-1975, "IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems."
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