ML17258A224

SEP Topic VIII-4,Electrical Penetrations of Reactor Containment,Re Ginna Nuclear Station,Unit 1, Informal Rept

ML17258A224
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Site:	Ginna
Issue date:	09/30/1981
From:	Udy A EG&G, INC.
To:	Scholl R Office of Nuclear Reactor Regulation
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ML17258A223	List: ML17258A224
References
CON-FIN-A-6425, TASK-08-04, TASK-8-4, TASK-RR EGG-EA-5565, NUDOCS 8110140351
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Enclosure 2 EGG-EA-5565 SEPTEMBER 1981 SYSTEMATIC EVALUATION PROGRAM TOPIC VIII-4, ELECTRICAL PENETRATIONS OF REACTOR CONTAINMENT, R. E. GINNA NUCLEAR STATION, UNIT NO. 1

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A. C. Udy

.U.S. Department of Energy.

Idaho Operations Office ~ Idaho National Engineering Laboratory

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Prepared for the U.S. Nuclear Regulatory Commission Under DOE Contract No. DE-AC07-76ID01570 FIN No. A6425 n+SCIZ&ldaha PDR ADQCK i

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(Rev, 11 79)

INTERIM REPORT Accession No.

Report No. EGG"EA"5565 Contract Program or Project

Title:

Electrical, Instrumentation, and Control Systems Support for the Systematic Evaluation Program (II)

Subject of this Document:

Systematic Evaluation Program Topic VI II-4, Electrical Penetrations of. Reactor Containment, R. E. Ginna Nuclear Station, Unit No. 1 Type of Document:

Informal Report

'uthor(s):

A. C. Udy Date of Document:

September 1981 Responsible NRC individual and NRC Office or Division:

Ray F. Scholl, Jr., Division of Licensing This document was prepared primarily for preliminary or internal use. It has not received full review and approval. Since there may be substantive changes, this document should not be considered final.

EG8 G Idaho, Inc.

Idaho Falls, Idaho 83415 Prepared for the U.S. Nuclear Regulatory Commission Washington, D.C.

Under DOE Contract No. DE-AC07-76ID01570 NRC FIN No A6425 INTERIM REPORT

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• SYSTEMATIC EVALUATION PROGRAM TOPIC VIII-4 ELECTRICAL PENETRATIONS OF REACTOR CONTAINMENT R.E. GINNA NUCLEAR STATION, UNIT NO. 1

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Docket No. 50-244 s ~ '" ~ ~ '

September 1981.

. A. C. Udy Reliability an'd Statist'ics Branch Engineering Analysis Division Idaho, Inc." 'GEG 9-9-81

ABSTRACT This SEP technical evaluation, for..the R. E. Ginna Nuclear Station, Unit No. 1 reviews the capability of the overcurrent protection devices to protect the electrical penetr ations of the reactor containment for postu-lated fault conditions concurrent with an accident condition.

FOREWORD This report is supplied as part of the "Electrical, Instrumentation, and Control Systems Support for the Systematic Evaluation Program (II) "

being conducted for the U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation,"Division of Licensing by EGEST Idaho, Inc.,

Reliability E Statistics Branch.

The U.S. Nuclear Regulatory Commission funded the work under the authorization BER 20-10-02-05 FIN A6425.

CONTENTS

1.0 INTRODUCTION

.....:..... '........ -....-......."...- .. '- -. ~ ~ ~ ~ ~ . ~

2.0 CRITERIA ..............:... ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 2 3-0 DISCUSSION AND EVALUATION . ~ ~ ~ ~ ~ ~ ~ ~ ~ t ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

3.1 Typical Low'oltage (0-1000 VAC) Penetrations ......-....;-..

3.1.1 Penetration Number AE-6 .....*..........'.. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 5 3.1.2 Penetration Number AE-5 ................. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 5

3. 1.3 Penetration Number CE-21 ................ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 6 3.1.4 Low Voltage Penetration Evaluation ...... ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 6 3.2 Typical Nedium Voltage (>1000 VAC) Penetrations ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

3.2.1 Nedium Voltage Penetration. Evaluation ... ~ ~ 0 ~ ~ ~ ~ ~ ~ ~ ~ 7 ~

3.3 Typical Direct Current Penetrations ....;....... ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

3.3.1 Penetration Number CE-18 ............ 'I

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 8 3.3.2 Penetration Number CE-17 ........,... ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 8 3.3.3 Penetration Number CE-23 ........... ~ ~ ~ ~ ~ ~ ~ ~ 0 ~ ~ ~ ~ ~ ~ ~ 9 3.3.4 . Direct Current Penetration Evalutati on io ~ ~ o ~ ~ ~ ~ ~ ~ ~ ~ 9 3.4 Other Penetrations;............................-..........'.

CI INMIIDv

4. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ V~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 10 E ERENCES REFER ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~ ~~ ~~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

SYSTEMATIC EVALUATION PROGRAM TOPIC VIII-4 ELECTRICAL PENETRATIONS Of REACTOR CONTAINMENT-R.E. GINNA NUCLEAR STATION, UNIT NO. 1

1.0 INTRODUCTION

This review is part of the Systematic Evaluation Program .(SEP), Topic VIII-4. The evaluation provided by Rochester Gas and Electric (RGE) has demonstrated the adequacy of the penetrations and the circuit protective devices during normal operation. A letter of July 21, 1980 provides

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additional information on the penetration designs. The objective of this review is to determine the capability of the overcurrent pro'tective devices to prevent exceeding the design rating of the electrical penetrations .

through the reactor containment during short circuit conditions at LOCA temperatures.

General Design Criterion 50, "Containment Design Basis" of Appendix A, "General Design Criteria for Nuclear Power Plants" to 10 CFR Part 50 requires tnat 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 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 with initial assumed LOCA temperatures.

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2.0 ., CRITERIA

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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" Penetration Assem-blies 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 require-ments:

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 tne operating time of the primary overcurrent protective device'or apparatus of the circuit) following continuous operation at rated'continuous current without the tem-perature of the conductors exceeding their short circuit design limit with all other conductors in the assembly carrying their rated cont'inuous current under the speci-fied normal environmental conditions."

Tnis paragraph is augmented by Regulatory Guide 1.63, Paragraph C-1--"The electric penetration assembly snould be designed to withstand, without loss of mechanical integrity, the maximum possible fault current versus 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 snail be the maximum time that the conductors of a circuit can carry rated snort 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 contain-ment integrity."

'I Additional clarification of these criteria was provided to RGE on 3

Mar.ch 30, 1981.

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 wi 1 1 be analyzed.

RGE has 'n provided information 1,2 typical penetrations. Additional 4

material, submitted as a result of this review was provided on June 9, 1981 and July 14, 1981. All penetrations but one were manufactured by Crouse- ~

Hinds, who no longer makes these penetrations. Crouse Hinds:supplied RGE with test data, where- available, and calculated data with a 10x safety factor where test data was not available.

h RGE has established that before damage to the hermetic seal of the penetration occurs, melting of the solder in the hermetic seal of the pene-trations must occur (361'..F, 180'.C).- A silver braze is used for penetrations CE-21, CE-25 and CE-27 instead of solder (1100'F, 600'C). This temperature is used because'it is the lowest temperature that affects the penetration seal. Other materials, while affecting the strain relief of the penetration at lower temperatures, do not affect the hermetic seal. Tne limiting temperature is determined by the analysis of the construction of the penetrations rather than testing. The Ginna 1 Technical Specifica-tion allows for initial steady.'tate temperatures of tne penetration envi-ronment up to 120'F (49'C). Under accident conditions, a peak temperature of 285'F (140'C) is expected.

.In those penetrations with conductors larger than 82 copper, the limit was not heat input but mechanical forces generated by electromagnetic coup-ling, and the limits put on these was determined by tests, with no mechani-cal failure of the penetration. Smaller penetration conductors are not subject to =failure by mechanical forces when used within their maximum current rating.

RGE also used the Insulated Power Cable Engineers Association publica-tion, P-32-382, entitled "Short Circuit Characteristics of Insulated Cable" 3

to determine separate limiting factors on the conductors of the penetration.

Where. these figures were more conservative tnan the Grouse-Hind figures,'hey were used instead.

'" 'n 7 supplying the value of the maximum short circui't current-available (I. ), RGE supplied values for a three-phase (on a three-phase system) bolted fault; this type being'able to supply the most heat into the penetra-tion. The I value supplied by RGE takes both the symmetrical AC compon- 'c ent and the peak OC offset component. In the RGE analysi's,.the'I 'was held to the maximum value for all phases when only one phase can have the full initial offset, and despite the fact that the DC'component decays.

This provides an additional safety factor in their calculations. RGE did not assume that all other penetration conductors were carrying .their maximum rated current, but applied the normal operating current.

The following formula 6 was used to determine the time allowed for before the penetration conductor temperature would exceed. the a..'nort-circuit melting point of solder..

I 2 T2 + 234 t = 0.0297 log T + 234 (Formula 1)

'where Time allowed for the snort circuit seconds Short circuit .current amperes sc Conductor area circular mi ls Maximum operating temperature ( 140 C, LOCA condition)

T2 Maximum short circuit temperature (180 C, tem-perature for melting solder).

This is based upon tie neating effect of the snort,c cuit current 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 RGE 1 even tnough the same methods are used. RGE has utilized an in.itial temper-ature of 40'C while tnis review uses an initial temperature of 140'C (LOCA condition) for the penetration. A pre-fault penetration conductor temper.-

ature equal to the peak LOCA containment atmosphere temperature is assigned, thus simplifying while accounting for an elevated conductor temperature

. caused by pre-existing current flow and above-normal ambient temperature.

3.1 Ty ical Low Volta e 0-1000 VAC) Penetrations. RGE has provided information on three typical low-voltage AC penetrations.

3.1.1 Penetration Number AE-6. This penetration has b2 AWG con-ductors and was type-tested to 37,400 amperes for 3 cycles by the manufac-turer, Crouse-Hinds. The I available on the identified 480-V circuit is 9600 amperes. Using Formula 1, tnis current can be carried for 0.06 sec-ond Defore the penetration conductor temperature exceeds the melting point of solder while under a LOCA environment. The primary circuit breaker responds within this time (.018 second). The secondary circuit breaker does not. For smaller fault currents, both the allowable time before the hermetic seal is damaged increases and the fault clearing time increases.

At all fault current levels, the primary breaker cleared, while the secon-dary breaker did not clear the fault within the allowable time.

As a result of this review, RGE has'roposed to install a 70 ampere backup circuit breaker in series with the primary circuit oreaker. RGE has'hown that the response of this new circuit breaker is properly coordinated to protect the AE-6 penetration under any postulated fault conditio~.

3.1.2 Penetration Number AE-5. This penetration has 8'8 AWG conductors and is calculated by the manufacturer to be able to withstand 1400 amperes for 0.54 second (including the Grouse-Hinds-supplied 10x 5

safety factor). RGE does no expect mechanical damage at less than 4662 amperes (this is equal to 1400 x 3.33 or 1/3 of the original safety factor). The identified 480 VAC circuit is capable of supplying a maximum I of 3500 amperes into the penetration. The primary breaker can clear sc this fault in 0.018 second, while the secondary fuse clears the fault in 0.002 second. The backup device will clear the fault before the primary protective device at this level of fault current.

It is calculated that the maximum I can be carr'ied by this penetra-tion in a LOCA environment for 0.029 second before the penetration conductor

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temperature exceeds the melting point of solder. Both protective devices will clear the fault within this time. At lower levels of fault current, both devices clear the fault in time to prevent solder melting.

3. 1.3 Penetration Number CE-21. This penetration has 500 NCM conductors and was type'-tested by the 'manufacturer and extrapolated by RGE to withstand 44,000 amperes for 10 cycles. The 480 VAC circuit identified by RGE as typical can supply a 'maximum I sc. of 20,000 amperes. Both the primary and secondary breakers will clear the postulated fault within 0.45 and 0.50 second, respectively.

It is calculated that the 20,000-ampere fault current can be carried by this penetration in a LOCA environment for 6.46 seconds before the pene-tration conductor temperature exceeds the melting point of the silver braze.

8oth the primary and the secondary circuit breaKer will act in time to pre- .

vent damage to the hermetic seal of this penetration at this current level.

Both circuit breakers respond faster than the penetration heat build-up limit for all current levels.

Since all in-containment components of this identified circuit are environmentally qualified for class 1E service, HRC position 2 can be applied. This position requires only a single class lE circuit breaker for penetration protection where all components served by that penetration are qualified to class 1E requirements.

3. 1.4 Low-Volta e Penetration Evaluation. With the initial temperature of the penetr ations at 140'C (LOCA), penetrations AE-5 and

CE-21 are designed and o

utilized within e

the criteria described in Sec-tion 2.0 of this report. The protective devices for penetration AE-6, while. not designed and utilized within the criteria describ'ed in Sec-tion 2.0 of tnis report, supply power for class lE components, and therefore, are acc'eptable per NRC position 2.

A 3.2 Typical Medium Volta e (~1000 VAC) Pe>>etration. Penetration numbers CE-25 and CE-27 have been identified by RGE as typical of medium-voltage (4160 V) penetrations. These. penetrations are used in parallel to supply power to one 6000 horsepower (HP) reactor coolant pump (RCP). These pumps are the only medium-voltage load within containment.

Construction of these penetrations is of the same materials and methods as discussed in Section 3.0. The hermetic seal is silver brazed (T2 = 600'C). Each penetration', containing three 750,000-MCN conductors, vas type-tested by the manufacturer and found to have no damage at 80,000 amperes for 10 cycles (0.167 second).

The maximum Isc available (including that available from the source and from the subtransient and transient response of the 6000 HP motor fed oack through the single remaining penetration and cable) is 46,000 asym-metrical/36,800 symmetrical amperes. The primary breaker overcurrent relay trips in 0.018 second, and the. oackup 'breaker overcurrent relay trips in 0.17 second should the primary oreaker not clear the fault (both values based on 36,800 amperes).

It is calculated that the available 46,000-ampere asymmetrical, fault current can oe carried by this penetration for 2.75 second before penetra-tion seal failure would occur. Using the time-current characteristics, assuming 46,000 amperes is constant tnroughout the clearing time, the pri-mary breaker overcurrent will clear the fault in 0.018 second while the secondary breaker overcurrent will clear the fault in 0.17 second.

3.2.1 Medium Volta e Penetration Evaluation. Penetrations CE-25 and CE-27 are designed and utilized within the criteria described in Sec-tion 2.0 of this report.

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Additionally, RGE has committed to improve the protect nn characteris-4 tics for low magnitude faul~urrents. This will be acco ished by installing a redundant set of overcurrent relays between the primary pro-tective relays and the penetration. This set of relays will actuate the-ba'ckup breaker. RGE has shown that with this additional set of relays, the respo'nse of the circuit protective devices is properly coordinated to pro-.

tect the CE-25 and CE-27 penetrations under any postulated fault conditions; 3.3 Typical Direct Current Penetrations. RGE has provided information of three typical direct-current power penetrations. These penetrations are of the same construction as in SectiOn 3.0, and the same methods of determining the limiting heating factors were- used.

3.3. 1 Penetration Number CE-18. This penetration, constructed with number 2 conductors, provides 125 V DC power to the lift coil and was type-tested to be able to withstand a current in excess of 30,000 amperes for'3 cycles with no mechanical damage. The maximum I sc available to this penetration is identified as 270. amperes. At this 270-ampere current, the two primary (both + and - leads) 50-ampere. fuses will clear the line-to-line fault in 0.18 second or, should these fuses fail, the secondary 150-ampere fuse will clear the fault in 0.576 second. ~

It is calculated that the 270-ampere fault current can be carried by this penetration for 79.2 seconds before damage to the hermetic seal of the penetration occurs. The primary and secondary fuses will clear this fault and all faults of less magnitude before the penetration temperature exceeds its qualification limit.

3.3.2 Penetration Number CE-17. This penetration, constructed with numoer 8 conductors, provides 125 V DC power for the rod drive circuit, and. is calculated to be able to withstand 1400 amperes for 0.54 second.

The maximum I available to this, penetration 'is 260 amperes.. At this current, the primary fuse will clear the line-to-line fault in,0.0004 second or, snould this fuse fail, the secondary fuse will clear the fault in 0.0043 second.

It is calculated tha e 260-ampere fault current c ve carried by this penetration for 5.28 seconds before damage to the hermetic seal of the penetration occurs. Both the primary and the secondary fuses will clear tl~is fault and all faults of less=magnitude before the,-penetration temper-,

ature exceeds its qualification limit.

3.3.3 Penetration Number CE-23. Tnis penetration, constructed with 010 conductors, provides 125 V DC control power and is calculated to be able to withstand 1250 amperes for 0.27 second. The maximum I available at the penetration is 600 amperes. At this'current,.the primary fuse will clear the fault in 0.014 second. The secondary fuse will not melt in time to prevent damage to the penetration ( 700 seconds operating time at 600 amperes).

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It is calculated that the-600-ampere. fault current can be carried by this penetration for 0.39 second. Tne primary fuse will, and the secondary

'use will not, clear this fault and all faults of less magnitude before the temperature. of the penetration will exceed the melting point of solder.

As a result of this review, RGE has proposed to install a new. primary fuse (25A) . 4 The existing primary fuse (30A) will then be the secondary fuse. The two fuses will oe in series with penetration number CE-23. AGE nas snown that the response times for these two fuses are properly coor-dinated to protect the CE-23 penetration under any postulated fault condi-tion.

3.3.4 Direct Current Penetration Evaluation. With the initial temperature of tne penetrations at 140'C as expected with a LOCA, penetra-tions CE-17, CE-18 and CE-23 are designed and utilized within the criteria described in Section 2.0 of this report.

3.4 Other Penetrations. RGE also provided information on penetration 1

numbers AE-10, CE-1, and CE-8. Penetration numbers AE-10 and CE-1 are part of instrumentation ( 10-50 mADC) current loops. The transmitters of these are current-limited to 50 milliamperes while each penetration conduc-tor is rated at 12 amperes continuous. Penetration number CE-19 is triaxial

L instrumentation signals,. an the circuit descrioed is equipi ent-limited to less than 200 watts (i.e., the source of the signal would fail before 200 watts output is reached). A maximum I sc of ampere would be carried 1

on a penetration conductor rated at 10 amperes continuous. No mechanical fai lures are postulated for these penetrations (construction and materials-siioi lar to the power penetr ations previously described) even under accident conditions within containment.

A recent modification installed a low-voltage power, control, and instrumentation penetration that is IEEE-Standard-317-1972-qua'lified for an in-containment television-monitor system. This penetr at,ion, for which application data was not submitted, is none the less qualified to IEEE Stan-dard 317-1972, assuming it is being used within specification limits.

4.0 SUHiiiARY This evaluation looks at the- capability of the protective devices to prevent exceeding the design ratings of:the selected penetrations 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 tne suoject of SEP Topic III-12.

'The penetrations identified with power-limited instrumentation circuits are deemed suitable under all postulated conditions.

After tne proposed modifications to the circuit protective devices are complet d, with a LOCA environment inside containment all penetrations are designed and utilized within the criteri a described in Section 2.0 of tnis repori: which assumes a snort circuit and random failure of circuit protec-tive devices.

AGE is .investigating improvements for the protection of other penetra-tion circuits as a result of this SEP topic. No completion date has been estaolished, but, any modifications are expected to be similar to those discussed in this report and in reference 4.

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4 The review of Topic -12, "Environmental gualifica on" may resolt in changes to the electrical penetration design and therefore, the resolu-tion of the subject SEP topic will be deferred to the integrated assessment, at which time, any requirements imposed as a result of this review will take into consideration design cnanges resulting from other topics.

5.0 'REFERENCES

1. RGE letter, Harry G. Saddock, Systematic Evaluation Progr am Topic VIII-4, "Electrical Penetrations of Reactor Containment",

R.E. Ginna Nuclear Power Plant, Unit No. 1, Docket No. 50-244, April 12, 1979.

2. RGE letter, C. D. White, Jr., to Director of Nuclear Reactor Regula-tion, U.S. NRC, "SEP Topic VII-4--Electrical Penetration of Reactor Containment," July 21, 1980.

3. NRC letter to RGE, "SEP Topic VIII-4," March 30, 1981.

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4. RGK letter, J. E. Maier to Director of Nuclear Reactor Regulation, NRC, "SEP Topic VIII-4, Electrical Penetrations," June 9, 1981.

5. RGE letter, J. E. Maier to Director of Nuclear Reactor Regulation, NRC, "SEP Topic VIII-4, Electrical Penetrations," July 14, 1981.

6. IPCEA Publication P-32-382, "Short Circuit Characteristics of Insu'lated Cabl e."

7. General Design Criterion 16, "Containment Design" of Appendix A, "General Design Criteria of Nuclear Power Plants," 10 CFR Part 50, "Domestic Licensing of Production and Utilization Facilsties."

8. Nuclear Regulatory Commission Standard Review Plan, Section 8.3.1, "AC Power Systems (Onsite)."

9. Regulatory Guide 1.63, Revision 2, "Electrical Penetration Assemolies in Containment Structures for Light-Nater-Cooled Nuclear Power.'Plants."

10. IEEE Standard 317- 1976, " IEEE Standard for Electric Penetration Assem-blies in Containment Structures for Nuclear Power Generating Stations."