ML20009A621
| ML20009A621 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 07/07/1981 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | Counsil W NORTHEAST NUCLEAR ENERGY CO. |
| References | |
| TASK-08-04, TASK-8-4, TASK-RR LSO5-81-07-011, LSO5-81-7-11, NUDOCS 8107130388 | |
| Download: ML20009A621 (12) | |
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/s li Docket No. 50-245 h ' JUL 10199g n LS05 07-011 n
\\ -> u ' >m Mr. W.G. Counsil, Vice President
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tiuclear Engineering and Operations Northeast Nuclear Energy Company
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Post Office Box 270 m
Hartford, Connecticut 06101
Dear Mr. Counsil:
SUBJECT:
SEP TOPIC VIII-4. ELECTRICAL PEllETRATIG S OF REACTOR CONTAIriMENT SAFETY EVALUATION REPORT (MILLST0tlE fiUCLEAR POWER STATI0fl UNIT 1) is the staff's safety ev4M+. ion report for SEP Topic VIII-4.
The basis for Enclosure 1 is given in Enclosure 2. is our contractor's technical evaluation that has been revised by the additional information and comments provided in your letter of May 20, 1981. is the staff's position with regard to the acceptability of the electrical penetrations for your facility. The staff has concluded that your facility meets current licensing criteria.
Sincerely, Dennis M. Crutchfield, Chief Operating Reactors Branch #5 Division of Licensing
Enclosure:
As stated cc w/ enclosure:
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NRCFORM 318110,80) NRCM O240 3FFICIAL RECORD COPY
ENCLOSURE 1 SEP TOPIC VIII-4 ELECTRICAL PENETRATIONS OF REACTOR CONTAINMENT I.
INTRODUCTION The safety objective of Topic VIII-4, " Electrical Penetrations of Reactor Containment," is to assure that all eletrical penetrations in the contain-ment structure are designed not to fail from electrical faults during a high energy line break.
As part of the Systematic Evaluation Program (SEP) the NRC staff performed an audit, comparing sample containment electrir.a1 penetrations in SEP facilities with current licensing criteria for protection against fault and overload currents following a postulated accident.
II.
REVIEW CRITERIA The review criteria are presented in Section 2.0 of EG&G Report 0105J,
" Electrical Penetrations of the Reactor Containment."
In addition, in licensing new plants, the staff requires compliance with the recommendations of Regulatory Guide 1.63 or an acceptable alternative method.
For each containment electrical penetration, the protective systens should provide primary and tickup circuit protect-ion-devices to prevent a single failure in conjunction with a circuit overload from impairing containment integrity.
The primary and backup protection cevices nLst have trip time vs. current response characteristics which assure protection against penetration failure.
The protectio-devices are to be periodically tested to verify trip setpoints anu adequacy of response.
No single failure should allow excessive currents in the penetration conductors that will degrade the penetration seals.
Where external control power is used for actuating the protection systems the power for primary and backup breakers should be derived from separate sources.
Overcurrent signals for tripping primary and backup system devices should be electrically independent and physically separated.
,--,v m.,.
III.
RELATED SAFETY TOPIC 5 AND INTERFACES The scope of review for this topic was limited to avoid duplication of effort since some aspects of the review were performed under the related topic III-12, Environmental Qualification.
The related topic report contains the acceptance criteria and review guidance'for its subject
- metter, e
w Theoretically, there are no safety topics that are dependent on the present topic information for thqir completion, however the results of the present topic have a definite impact upon the capability of equip-ment inside of containment to funttion af ter a high energy line break.
IV.
REVIEW GUIDELINES The review guidelines are presented in Section 3.0 of EG&G Report 0105J.
V.
EVALUATION As noted in the EG&G Report on this topic with a LOCA environment inside containment, the penetrations conform to the currert licensing criteria.
VI.
CONCLUSIONS As a result of our review we have concluded t' hat, with a LOCA environnent inside containment, the penetrations conform to the current licensing criteria and are, therefore, acceptable.
0105J i
ENCLOSURE 2 i
SEP TECHNICAL EVALUATION REPORT i
ELECTRICAL PENETRATIONS OF REACTOR COMPARTMENT FINAL DRAFT 1
MILLSTONE NUCLEAR STATION, UNIT NO. I Northeast Utilities June 1981 S. E. Mays i
l
.I 6-9-81 i
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CONTENTS
1.0 INTRODUCTION
I 2.0 CRITERIA.....
1 3.0 DISCUSSION AND EVALUATION 2
3.1 Typical Low Voltage (0-1000 V) Penetrations...........
4 3.1.1 Low Voltage Penetration Evaldation...........
4 3.2 Typical Medium Voltage (F1000 V) fenetratiori 5
e 3.2.1 Medium Voltage Penetr,ation Evaluation 5
3.3 Typical DC Penetrations....................
6 3.3.1 DC Fenetration Evaluation 6
4 SUM. MARY 6
5.
REFERENCES.........,,..................
7 O
ii
SEP TECHNICAL EVALUATION REPORT ELECTRICAL PENETRATIONS OF REACTOR COMPARTMENT MILLSTONE NUCLEAR STATION, UNIT NO. 1 1
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 fault current resulting from single random failures of circuit overload protection devices.
l General Design Criterion 50, " Containment Design Basis" of Appendix A,
" General Design Criteria for Nuclea-Power Plants" to 10 CFR Part 50 requires that penetrations be designed so that the containment structure can, witnout exceeding the design leakage rate, accommodate the cliculated 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 Guice 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 faults prior to exceeding the penetration design ratings under LOCA temperatures.
2.0 CRITIRIA 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" l
J 1
provides the basis acceptable to the NRC staff.
The following criteria are used in this report to determine compliance with current licP sing require-ments:
i 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 tem-perature of the conductors" exceeding their short circuit i
design limit with all other. conductors in the assembly 1
carrying their rated continuous current under the spe-cificd normal environmental conditions."
This paragraph is augmented by Regulatory Guide 1.63,
.)
Paragraph C "The electric penetration assembly i
should be designed to withstand, without loss of mechanical integrity, the maximum possible fault cur-rent versus time conditions that could occur given single random failures of circuit overload protection devices."
2.
IEEE Standarc 317, Paragraph 4.2.5 -
"The ratad maxi-mum duration of rated short circuit current shall 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, dur-ing whicn the electrical integrity may be lost, but for wnich the penetration asseacly snall maintain contain-l ment integrity."
~
3.
IEEE Standard 31/, paragrapn 6.4.14 -- "The maximum duration of rated short circu*.. shall be verified by the test.
The test shall be conductec at maximum post-ulated design bases event temperature and pressure and i
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
+.0 func-tion."
i i
i 3.0 DISC'JSSION AND EVALUATION i
I a
In this evaluation, the results of typical containment penetrations being at LOCA temperature initially concurrent with a random failure of the circuit protective devices will be analyzed.
i 2
. - _._.._.._. _ _ _ _._ -._.,. _ _ _. _ _ _ _ _ -.. _ _.. ~. _. _. _ _ _. _ _..
Northeast Utilities (NU) provided information (Reference 1) on typical penetrations.
No evaluation of the data was provided.
A temperature limit of 352 F (177 C) before seal failure for the three penetrations has been establisned based on testing done by Oyster Creek Nuclear Station for identical type connectors (Reference 2) in lieu of docketed data from NU cescribing tests or analysis to specify a temperature limit.
Maxim'.m short circuit current available (I
) was provided by North-east Utilities for a three-phase bolted fault.
Rated current (I ) for r
each penetration was also provided.
Since NU has not docketed any testing per IEEE Std 317 to verify the ability of the penetration to withstand a LOCA environment, the following f ormula (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
7
.0297 log (Formula 1) t=
Tg234 where time in seconds t
=
current in amperes I
=
concuctor area in circular mils A
=
l T) initial temperature (138 C, LOCA condition)
=
T2 maximum penetration temoerature before failure.
=
This is based on the heating effect of the short circuit current on I
the cenouctor and dces not take into accotnt heat losses of the conductor.
For times less than several seconds, this heat loss is negligible.
l In evaluating the capability of the penetration to withstand a LOCA temperature with a short circuit current, Formula 1 was used to calculate the time required to heat the conductor from the LOCA temperature to pene-tration f ailure temperature for currents from rated current to maximum i
3 i
short circuit current in 20% increments.
Times for the primary and secon-odary overcurrent devices to interupt these fault curren+s 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 hasidentifieapenetrationX-105D(GEgypeNSO4)asbeingtypicaloflow voltage penetrations.
This penetratTon provices 480 V ac power to motor-cperated valve 1-IC-1.
e 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 '600 amps.
A temperature limit of 352 F (177*C) before seal failure has been determined based on testing. At the maximum short circuit current (1600 aT.ps), overtemperature will be reached in 0.64 second from LOCA temperature initially.
From LOCA temperature initially, the secondary breaker will not operate to clear any f ault currents before penetration seal limiting temperature is attained.
However, NU has determined that the outboard seal of this pene-tration. sill have an intitial temperature of r.ot more than 90'E.
From this temperature initially, the secordary creaker will still not operate to clear the fault before the conductor reaches 177 C.
However the =10 A"G cable external to the penetration will fuse before this temperature is reached.
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.
Hcwever, NU verifies continuity upon penetration installation.
3.1.1 Low Voltage Penetration Evaluation.
With an initial pene-l tration temperature of 138 C (LOCA),
penetration X-105D does not meet l
current requirements of RG 1.63 and IEEE Std. 317 for any short circuit fault with a failure of the primary breaker.
However for an initial temperature of 90 C at the outboard seal the external cable will fuse prior l
to reaching the 177 C temperature limit on that seal.
The penetration does 4
l l
meet current requirements for short circuit faults if the primary breaker operates as designed provided that both cables in the penetration are operable.
3.2 Typical Medium voltage (_>1000 V) Penetration.
Northeast Utili-ties has identified penetration X-101A (GE type NS03) as being typical of medium voltage penetrations.
This penetration provides 4160 V ac power to Reactor Recirculation Pump 1.
This penetration uses two 500 MCM cables in parallel and nas a contin-uous 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) has been established based on testing.
At the maxi-mum short circuit current (1700 amps), overtemperature will be reached in 440 seconds from LOCA temperature initially.
Overcurrent protection is 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 winoings.
At >156 amos of current difference between the output of the generator and the input to tne motor, tne dif-ferential relay will cause a trip of the mctor 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 seconc or less.
The line overcurrent relay will operate to clear all fault currents in excess of 780 amps prior to reacning the penetration seal temperature limit f rom LOCA temperature initially.
For fault currents less than 1100 amps, the conductors will carry less than their rated cc ;inuous current (550 amps) provided both conductors nave ccntinuity.
If one conductor is open, tne overcurrent device will not operate for faults between 550 and 780 amps and penetration overheatirig may occur.
There are no Technical Specifications requiring continuity of the conductors to be checked. How-ever, cor tinuity is verified during installation of the penetration.
3.2.1 Medium Voltace Penetration Evaluation.
At LOCA tempera-ture, penetration X-101A meets current requirements of RG 1.63 and IEEE 5
Std. 317 for short circuit faults with a failure of the line overcurrent relay since the differential relay will operate to clear thh fault prior to reaching the penetration seal temperature limit. With a failure of the differential current relay at LOCA temperature, the penetration meets cur-rent requirements for all fault currents provided that both conductors in the penetration are operable.
3.3 Tyoical Direct Current Penetra'ti n.
Northeast Utilities has
~
identified penetration X-100A (GE jype NSO4) as being typical of DC pene-trations.
This penetration provide,s 125 V dc power to the solenoid valve on main steam isolation valve 203-1A.
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 reachec in 2.38 seconas from LOCA temperature initially.
At LOCA temoerature, both the primary and secondary fuses will operate to clear all fault currents before the senetration seal temoerature limit is reacnec.
3.3.1 DC Penetration Evaluation.
At LOCA temperature, penetra-tion X-100A meets current recuirements of RG 1.63 and IEEE Std. 317 for all f ault currents with a f ailure of the primary protective cevice.
4.0
SUMMARY
l At LOCA temperature, penetration X-105D does not meet cerrent require-ments of RG 1.63 and IEEE Std. 317 for any fault current with a failure of.
the primary protective device.
However, based on NU's evaluation that the outboard seal will have an initial temperature less than 90 C, the external l
cable will fuse before the limiting temperature of 177 C is reached.
If the primary device functions as designed, penetrations X-105D and X-101A meet current requirements provided that both of the conductors in the penetration l
6 l
T-are operable.
There are no Technical Specification requirements to verify continuity of both conductors in penetrations using two parallel conductors Der chase, but continuity is verified during penetration installation.
At LOCA temperature, penetration X-100A meets current requirements of RG 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 Description and Safety Analysis Report, Oyster Creek Nuclear Station, Ammendment 62 (Docket No. 50-219-102).
3.
IPC&A Publication P-32-382, "Short Circuit Characteristics of Insulated Cable."
Northeast Utilities letter (Counsil) to NRC (Crutchfield) dated l
August 29, 1980.
5.
Northeast Utilities letter (Counsil) to NRC (Crutchfield) dated January 29, 1981.
6.
Ncrtheast Utilities letter (Ccunsil) to NRC (Crutcnfielc) datea lay 20, 1981.
7.
'iilstone Nuclear Pov.er Station Control Wiring Diagram 5-187613, Sheet a34 (25205-31001) 7
_.