ML17309A139

Forwards Evaluation of SEP Topic VIII-4, Electrical Penetrations of Reactor Containment. Requests Rept Describing Calculations Performed & Criteria for Evaluating Penetrations for Circuits within 30 Days

ML17309A139
Person / Time
Site:	Ginna
Issue date:	03/30/1981
From:	Crutchfield D Office of Nuclear Reactor Regulation
To:	Maier J ROCHESTER GAS & ELECTRIC CORP.
References
TASK-08-04, TASK-8-4, TASK-RR LSO5-81-03-072, LSO5-81-3-72, NUDOCS 8104010362
Download: ML17309A139 (30)

Text

MAR 80 1981 Docket No. 50-244 LS0581.-03-072 Mr. John E. Maier Vice President Electric and Steam Production Rochester Gas 5 Electric Corporation 89 East Avenue Rochester, New York 14649

Dear Mr. Maier:

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. ~~4@'wv SUBJECT,:

SEP TOPIC VIII-4, ELECTRICAL PENETRATIONS OF REACTOR CONTAINMENT (R.

E.

GINNA NUCLEAR POllER PLANT)

The staff's evaluation of SEP Topic VIII-4 for the--R; E. Ginna Nuclear Power Plant is enclosed.

This assessment compares your facility, as described in Docket No. 50-244, with the criteria currently used by the regulatory staff for licensing new facilities.

Th-is report<<

has-been revised to reflect the factual comments provided by your July 31, 1980 letter.

Draft Technical Evaluation Reports (TER) on Topic VIII-4 have been prepared and forwarded to all SEP Licensees for coment.

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 respondshts 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 adequate.

This does not necessarily mean that the protection is inadequate.

Our calcula-tions were simplified and conservative so that there is room to improve the result by using more realistic models.

In addition, licensee coments 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

. t3e adequacy of all electrical penetrations in your facility in accordance

>vith the enclosed position.

Generally, where needed, our position calls for more realistic calculations than were used in our audit.

In relation to currentllicensing criteria, it provides relief from the need for 1;edundant circuit protective devices in certain instances and specifically provides for using fuses as an alternative to circuit breakers.

Other straightforward alternatives such as deenergizing circuits are also provided for.

OFFICE)

SURNAME)

OATS J>

QP4010 F

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NRC FORM 318 RO/80) NRCM 0240 OFFICIAL R ECOR 0 COPY A USGP0 198~29 824

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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 penetrations 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 penetrations like AE-6, CE-21 and CE-23.

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.

Sincerely,

Enclosures:

As stated Dennis H. Crutchfield, Chief Operating Reactors Branch Ho.

5 Division of Licensing cc w/enclosures:

See next page OFFICEP SURNAME/

OATED S PB; 11:d SEPB':SL

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NRC FORM 318 (10/80) NRCM 0240 SE B:

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DL:PM OR OFFJClAL RECORD COPY A

SA:DL,"'nas...

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NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 Docket No. 50-244 LS05-81-03-072 MAR 30 1981 Mr. John E. Maier Vice President Electric and Steam Production Rochester Gas 8 Electric Corporation 89 East Avenue Rochester, New York 14649

SUBJECT:

SEP TOPIC VIII-4, ELECTRICAL PENETRATIONS OF REACTOR CONTAINMENT (R.

E.

GINNA NUCLEAR POWER PLANT)

The staff's evaluation of SEP Topic VIII-4 for the R.

E. Ginna Nuclear Power Plant is enclosed.

This assessment compares your facility, as described in Docket No. 50-244, with the criteria currently used by the regulatorv staff for licensing new facilities.

This report has been revised to reflect the

- factual comments provided by your July 21, 1980 letter.

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 adequate, This does not necessarily mean that the protection is inadequate, Our calcula-tions were simplified and conservative so that there is room to improve the result by using more realistic models.

In addition, licensee coranents have indicated that there may be some errors in our calculations.

Nevertheless,

'ur audit did not put the matter to.rest and, thus, yqu are requested to evaluate the adequacy of al'I e'lectrical penetrations in your facility in accordance with the enclosed position.

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 alternative to circuit breakers, Other straightforward alternatives such as deenergizing circuits are also provided for.

If any instances arise where your calculations cannot demonstrate circuit protection in accordance with cur 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 penetrations 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 penetrations like AE-6, CE-21 and CE-23.

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.

Sincerely, Dennis N. Crutchfield, C

ef Operating Reactors Branch No.

5 Division of Licensing

Enclosures:

As stated cc w/enclosures; See next page

Mr. John E. Maier CC Harry H. Voigt, Esquire

LeBoeuf, Lamb, Leiby and MacRae 1333 New Hampshire

Avenue, N.

W.

Suite 1100 Washington, D.

C.

20036 Mr. Michael Slade 12 Trailwood Circle Rochester, New York 14618 Ezra Bialik Assistant Attorney General Envi ronmenta 1

P rotect i on Bureau New York State Department of Law 2 World Trade Center New York, New York 10047 Jeffrey Cohen New York State Energy Office Swan Street Building Core 1, Second Floor Empire State Plaza

Albany, New York 12223 Director, Technical Development Programs State of New York Energy Office Agency Building 2 Empire State Plaza

Albany, New York 12223 Rochester Public Library 115 South Avenue Rochester, New York 14604 Supervisor of the Town of Ontari o 107 Ridge Road West

Ontario, New York 14519 Resident Inspector R. E. Ginna Plant c/o U. S.

NRC 1503 Cake Road

Ontario, New York 14519 Director, Criteria and Standards Division Office of Radiation Programs (ANR-460)

U. S. Environmental Protection Agency Washington, D. C.

20460 U. S.

E nvi ronment a 1 P rotect i on Agency Region II Office ATTN:

E I S COORDINATOR 26 Federal Plaza New York, New York 10007 Herbert Grossman, Esq.,

Chairman Atomic Safety and Licensing Board U. S. Nuclear Regulatory Commission Washington, D. C.

20555 Dr. Richard F, Cole Atomic Safety and Licens ing Board U.

S. Nuclear Regulatory Commission Washington, D.

C.

20555 Dr.

Emmeth A. Luebke Atomi c Sa fety and Licens ing Board U. S. Nuclear Regulatory Commission Washington, D. C.

20555 Mr. Thomas B. Cochran Natural Resources Defense Council, Inc.

1725 I Street, N.

W.

Suite 600 Washington, D. C.

20006 Ezra I. Bialik Assistant Attorney General Environmental Protection Bureau New York State Department of Law 2 World Trade Center New York, New York 10047

0065J SEP TECHNICAL EVALUATION TOPIC VIII-4 ELECTRICAL PENETRATIONS OF REACTOR CONTAINMENT FINAL DRAFT ROBERT ERAT GINNA UNIT NO.

1 Docket No. 50-244 November 1980 A. C. Udy 11-7-80

CONTENTS

.0 INTRODUCTION....ooo

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1 1.

~ 0 CRITERIA

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3.0 DISCUSSION AND EVALUATION..

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2 3.1 Typical Low Voltage (0-1000 VAC) Penetrations.................

4 3.1.1 3.1.2 3.1.3 3.1.4 Penetration Number AE-6 Penetration Number AE-5 Penetration Number CE-21 Low Voltage Penetration Evaluation

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5 3.2

'Typical Medium Voltage

(>1000 VAC) Penetrations

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6 3.2.1 Medium Voltage Penetration Evaluation..................

6 3.3 Typical Direct Current Penetrate.ons

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7 3.3.1 3.3.2 3.3.3 3.3.4 Penetration Number CE-18 Penetration Number CE-17 Penetration Number CE-23 Direct Current Penetration Evalutation

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8 3..4 Other Penetratxons............................................

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SUMMARY

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5 REFERENCES

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10

SEP TECHNICAL EVALUATION 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 1

demonstrated the adequacy of the penetrations and the circuit protective devices during normal operation.

A letter of July 21, 1980 provides 2

additional information on the penetration designs.

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 temperatures.

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 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'f 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.

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 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 requirements:

l.

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) following continuous operation at rated continuous. current without the temp-erature of the conductors exceeding their short circuit design limit with all other conductors in the assembly carrying their rated continuous current under the speci-fied normal environmental conditions."

This paragraph is augmented by Regulatory Guide 1.63, Paragraph C-1"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 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 wnich the penetration assembly shall maintain contain-ment integrity."

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.

?i l

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RGE has provided information 'n typical penetrations.

All but 1,2 one were manufactured oy Grouse-Hinds, who no longer makes these penetra-tions.

Grouse-Hinds supplied RGE with test data, where available, and calculated data with a 10x safety factor where test data was not available.

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 the 0

0 medium voltage penetrations instead of solder (1100 F, 600 C).

This 0

0 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.

The limiting temperature is determined by the analysis of the construction of the penetrations rather than testing.

The Ginna Technical Specifica-tion allows for initial steady state temperatures of the penetration envi-0 0

ronment up to 120 F (49 C).

Under accident conditions, a peak temper-ature 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

coupling, and the limits put on these was determined by tests, with no mecnanical 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" to determine separate limiting factors on the conductors of the penetration.

Where these figures were more conservative than the Grouse-Hind figures, they were used instead.

In supplying the value of the maximum short circuit current available (I

)

RGE supplied values for a three-phase (on a three-phase system) sc bolted fault; this type being able to supply the most heat into the pene-tration.

The I value supplied by RGE takes both the symmetrical AC sc component and the peak DC offset component.

In the RGE analysis, the Isc

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 was used to determine the time allowed for a short-circuit before the penetration conductor temperature would exceed the melting point of solder.

2 rT2 + 2341 0.0297 log l.T

+ 234~

1 0.0297 A

1 l 2

'"1 I

t-2 logLT

+234J 1

sc (Formula 1) where Time allowed for the short circuit seconds Isc Short circuit current amperes A

~

Conductor area circular mils Tl

=

Maximum operating temperature (140 C, LOCA condition)

T2

~

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

This is based upon the heating effect of the short circuit 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 even though the same methods are used.

RGE has utilized an initial temper-ature of 40 C while this review uses an initial temperature of 140 C

(LOCA condition) for the penetration.

A pre-fault penetration conductor temperature 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 T

ical Low Volta e (0-1000 VAC) Penetrations.

RGE has provided 1

information on three typical low-voltage AC penetrations.

3.1.1 Penetration Number AE-6.

This penetration has g2 AWG conductors and was type-tested to 37,400 amperes for 3 cycles by the manu-facturer Grouse-Hinds.

The I available on the identified 480-V circuit t

sc is 9600 amperes.

Using Formula 1, this current can be carried for 0.06 sec-ond before 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 At all fault current levels, the primary breaker cleared, dary breaker did not clear the fault within the allowable time increases.

while the secon-a time.

3.1.2 Penetration Number AE-5.

This penetration has 88 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 safety factor).

RGE does not 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.

a.

RGE suggested2 that instead of using the Formula 1 to establish the time for the penetration seal to overheat, that it be used to establish a derating factor to be applied to the test data value of I2t-.

This was done, and the results, as shown in this report, were verified.

Coordination of the secondary protection device to the penetration design needs to be improved" for a LOCA environment.

It is calculated that the maximum I can be carried by this pene-sc tration in a LOCA environment for 0.029 second before the penetration con-ductor 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 MCM 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 of 20,000 amperes.

Both the sc 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 0.82 second before the pene-tration conductor temperature exceeds the melting point of solder.

Both the primary and the secondary circuit breaker will act in time to prevent damage to the hermetic seal of this penetration at this current level.

The primary circuit breaker responds faster than the penetration heat build-up limit for all current levels.

The secondary circuit breaker will clear higher magnitude faults with sufficient speed to prevent

damage, but at some lower magnitude faults, the fault clearing time is long enough for the a

penetration to exceed the melting point of solder.

3.1.4 Low-Volta e Penetration Evaluation.

With the initial temperature of the penetrations at 140 C (LOCA),

penetration AE-5 is designed and utilized within the criteria described in Section 2.0 of this report.

Penetrations AE-6 and CE-21 are not designed and utilized within tne criteria described in Section 2.0 of this report.

a.

RGE suggested2 that instead of using the Formula 1 to establish the time for the penetration seal to overheat, that it be used to establish a derating factor to be applied to the test data value of I2t.

This was done, and the results, as shown in this report, were verified.

Coordination of the secondary protection device to the penetration design needs to be improved for a LOCA environment.

In all cases looked at, the secondary clearing device rating or nominal value exceeded the penetration continuous current rating supplied, thus relying on motor overload relays, for which no information was supplied, as secondary protective devices for the penetration.

3.2 T

ical Medium Volta e (>1000 VAC) Penetration.

Penetration numbers CE-25 and CE-27 nave 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 meth-ods as discussed in Section 3.0.

The hermetic seal is silver brazed (T

= 600 C).

Each penetration, containing three 750,000-MCM conduc-2

tors, was type-tested by the manufacturer and found to have no damage at 80,000 amperes for 10 cycles (0.167 second).

The maximum I available included that available from the source sc and the subtransient and transient response of the 6000 HP motor fed back through the single remaining penetration and cable.

46,000 asymetrical/

36 800 symetrical amperes I are available.

The primary breaker over-t sc current relay trips in 0.018 second, and the backup breaker overcurrent relay trips in 0.17 second should the primary breaker not clear the fault (both values based on 36,800 amperes).

It is calculated that the available 46,000-ampere asymetrical fault current can be 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 throughout the clearing time, the primary 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.

From the curves supplied, it could not be determined what effect motor overloads would have, as neither the primary nor the secondary switchgear protect at the penetration continuous rated current.

3.3 T

ical 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 available to sc 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 number 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 sc

current, the primary fuse will clear the line-to-line fault in 0.0004 second or, should this fuse fail, the secondary fuse will clear the fault in 0.0043 second.

It is calculated that the 260<<ampere fault current can be 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

this fault and all faults of less magnitude before the penetration temper>>

ature exceeds its qualification limit.

3.3.3 Penetration Number CE-23.

This penetration, constructed with 8'10 conductors, provides 125 V DC control power and is calculated to be able to withstand 1250 amperes for 0.27 second.

The maximum Isc 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).

It is calculated that the 600<<ampere fault current can be carried by this penetration for 0.39 second.

The primary fuse will, and the secondary fuse will not, clear this fault and all faults of less magnitude before the temperature of the penetration will exceed the melting point of solder.

3.3.4 Direct Current Penetration Evaluation.

With the initial temperature of the penetrations at 140 C as expected with a LOCA, pene-0 trations CE-18 and CE-17 are designed and utilized within the criteria described in Section 2.0 of this report.

However, penetration CE-23 is not utilized within the criteria described in Section 2.0 of this report, regardless of the initial penetration temperature.

3.4 Other Penetrations.

RGE also provided information on penetration 1

numbers AE-10, CE-l, 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 wnile each penetration conduc-tor is rated at 12 amperes continuous.

Penetration number CE-19 is triaxial instrumentation

signals, and the circuit described is equipment-limited to less than 200 watts (i.e.,

the source of the signal would fail before 200 watts output is reached).

A maximum I of 1 ampere would be carried sc on a penetration conductor rated at 10 amperes continuous.

No mechanical failures are postulated for these penetrations (construction and materials similar to the power penetrations previously described) even under accident conditions within containment.

A rec nt modification installed a low-voltage power, control, and instrumentation penetration that is IEEE-Standard-317-1972-qualified for an in-containment television monitor system.

This penetration, 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

SUMMARY

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 the subject of SEP Topic III-12.

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

With a LOCA environment inside containment, penetrations AE-5, CE-25 and -27, CE-17, and CE-18 are designed and utilized within the criteria described in Section 2.0 of this report which assumes a short circuit and random failure of circuit protective devices.

Penetration CE-21 is utilized within the criteria described in Sec-tion 2.0 of this report.

However, the secondary breaker does not adequately protect the penetration for faults of less than bolted fault magnitudes.

The secondary breaker for penetration AE-6 is not utilized within the criteria of Section 2.0 of this report.

At an'initial temperature of normal environment, this penetration is properly utilized.

The seal of penetration CE-23 could be voided with the failure of the primary fuse to clear the fault, as the operating time of the backup fuse will -not protect it from short circuits up to the maximum I supplied by sc RGE.

10

RGE is investigating improvements for penetrations CE-21, CE-23, CE-25 and -27, and AE-6 as a result of this SEP topic.

No completion date has been established.

The review of Topic III-12, "Environmental Qualification" may result in cnanges 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 changes resulting from other topics.

5.0 REFERENCES

1.

RGE letter, Harry G. Saddock, Systematic Evaluation Program 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-4Electrical Penetration of Reactor Containment," July 21, 1980.

3.

IPCEA Publication P-32-382, "Short Circuit Characteristics of Insulated Cable "

4.

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 Facilities."

5.

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

6.

Regulatory Guide 1.63, Revision 2, "Electrical Penetration Assemblies in Containment Structures for Light-Water-Cooled Nuclear Power Plants."

7.

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

ENCLOSURE POSITION ON PROTECTION OF CDNTAIIBENT ELECTRICAL PENETRATIONS AGAINST FAILURES CAUSED BY FAULT AND OVERLOAD CURRENTS FOR SEP PLANTS introduction As part of the Systematic Evaluation Program (SEP) the NRC staff performed an audit, coaqaring 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 sho that the SEP facilities eeet current licensing criteria nor did it shm the existing circuit protection to be adequate.

Accordingly, the SEP licensees are requested to demonstrate, using sere realistic calcula-tions where necessary, that the circuit protection is adequate in accordance arith the position described belm.

Bact around 7n licensing neN plants, the staff requires corn,liance ~ith the recoamendations of Regvlatory 6uide 1.63 or an acceptable alternative method.

For each containment electrical penetration, the protective systems provide primary and backup circuit protection devices to prevent a single failure in con-junction with a circuit overload from impairing containment integrity.

The primary and backup protection devices have trip time vs. current response charac-teristics which assure protection against penetration failure.

The protection devices are periodica'Ily 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.

Mhere external control power is used for actuating the protection systems the power for primary and backup breakers are derived from separate sovrces.

Overcvrrent 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 containmant structure are designed not to fail from electrical faults during a high energy line break (LOCA or secondary system line break).

Me have performed preliminary evaluations, on a conservative basis, of the <auld current protection for three sample containment electrical penetrat5ons ipr each of the eleven SEP plants.

The entire penetration was assumed to be initially at the peak calculated LOCA tetnperature.

Then, for a given fault current, the time to heat the wire to the limiting material tetnperature (usually the melting point of the seal material) was', calculated.

This tine was compared to the tom for the protective device(s) to interrupt the fault current.

On this basis, several penetrations exceed limiting tenperatures if the primary protection device fails.

Others do so without postulating primary device fai}urte.s Two of the sanqle penetrations even have melting temperatures less than the peak LOP tenqerature and thus e ceed the limits of this nodel even if there is no fault cuir rent.

(ReS'erences 1 through 11)

This does not necessarily mean that the penetrations would actually fail.

The analysis was conservative, particularly in assuming that the penetration

+as initially at the peak calculated containaant temperature.

The penetrations would not reach such a temperature folly ing ah accident.

In addition, licensee coments have indicated that there m'y be some errors in the calculations.

{Fpz-

example, Northeast Utilities letter dated August 29,

1980, Dock t No. 5D-245, providing conrnents on the staff calculations for Yillstoqe, Unit 1).

Nevertheless, this audit clearly did not put the matter to rest.

Position Each SEP licensee is requested to evaluate the adequacy of the existing fault current protection for contai'nni nt electrical penetrations in accordance with the position discussed in nore detail bein and to propose rem dies where needed in order to neet the position.

The basic requirem nt of Regulatory Guide 1.63 that all., penetration circuits, Class IE or non-Class IE, be provided with overcurrent'rotection in con ormance with the redundancy and testability requirements of IEEE Std 279-1971 should be met; 2.

A single ci.rcuit breaker to protect a penetration serving a Class IE circuit or a non-safety circuit contaTning only components that are qualified to Class IE requi.rements js acceptable provided that each component of such circuit is qualifi"d to the accident environment; and A circuit whose loads inside containmen't are not required to mitigate the consequences of accidents may be automatically disconnected from its powe'r source on recei:pt of an accident signal or it may be maiotained deenergized by positive means such as those outliend in Branch Technical Position ICSB 18 (PSB) of Appendix 8A to the Standard Review Plan whenever containment integrity is required.

Notes For the purpose of evaluating the adequacy of protection for containrent pro:ection, faults should be postulated up to a bolted cable fault inside containment at the penetration (a bolted three phase fault for three phase circuits).

The primary protection device should have a trip time vs. current response characteristic that assures against penetration failure under all fault conditions.

t Circuit breakers should be tested periodically to verify their trip setting value and response tim.

Breakers should be designed to in'errupt the maximum possible fault current for the circuit or backup protection fast response current limiting fuses should be provided.

In addition, fuses aey be used in lieu of circuit breakers as pro'.ective device.;-

l'here fuses are

used, docum ntation of their response characteristics derived frorproduction testing should be available for audit.

It is acceptable to use less conservative models than were used in our prelim'nary evaluations provided that they address fault currents up to bolted fa"its and s:ill provide reasonable assurance that the penetration will not fail.

For exarqle, a rare realistic initial tenqerature of the con.-ainrent penetration could be determined ra:her than assuming the pene:ration has reached the peak calculated containment atmosphere temp-erature.

Circuits may be mo"ified to reduce the short circuit current to acceptable values by the use of current limitino devices (such as resistors, isolation transformers, and changino transformer taps) external to the containment.

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