ML19321A412
| ML19321A412 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 07/01/1980 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19321A267 | List: |
| References | |
| TASK-08-04, TASK-8-4, TASK-RR NUDOCS 8007230324 | |
| Download: ML19321A412 (9) | |
Text
._______
g'""*>
O,'
SEP TECHNICAL EVALUATION TOPIC VIII-4 ELECTRICAL PENETRATIONS OF REACTOR CONTAINMENT MILLSTONE NUCLEAR STATION, UNIT NO. 1 Northeast Utilities Docket No. 50-245 DATE: July 1, 1980 80 07230 3 z4
CONTENTS
1.0 INTRODUCTION
1 2.0 CRITERIA.
1 3.0 DISCUSSION AND EVALUATION 3
3.1 Typical Low Voltage (0-1000 V) Penetrations 4
3.1.1 Low Voltage Penetration Evaluation..
4 3.2 Typical Medium Voltage (>1000 V) Penetration 5
3.2.1 Medium Voltage Penetration Evaluation 6
3.3 Typical DC Penetrations.
6 3.3.1 DC Penetration Evaluation 6
4.
SL1{KARY 7
5.
REFERENCES..
7 0
il i
t' i
i I
(
i SEP TECHNICAL EVALUATION TOPIC VIII-4 ELECTRICAL PENETRATIONS OF REACTOR CONTAINMENT MILLSTONE NL* CLEAR STA!!ON, UNIT NO. I
1.0 INTRODUCTION
This review is part of the Systematic Evaluation Program (SEP),
Topic VIII-4.
The objective of this review is to determine the capa-bility of the electrical penetrations of the reactor contninmentco withstand short circuit conditions of the worst expected transient fault current resulting from single random failures of circuit overload protection devices.
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 leakage race, 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 ability of the protective devices to clear faults prior to exceeding the penetration design ratings under LOCA temperatures.
~ 2. 0 CRITERLA IEEE Standard 317, " Electric Penetration Assemblies in Containment Structures for Nuclear Power Generating Stations" as supplemented by 1
Nuclear Regulatory Commission Regulatory Guide 1.53, " Electric Penetra-tion Assemblies in Containment Structures for Light-Water-Cooled Nuc-lear Power Plants" provides the basis acceptable to the :TRC 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 raced short cir-cuit 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 temperature of the conductors exceeding their short circuit design limic with 411 other conductors in the assembly carrying their rated continuous current under the specified normal environmental conditions."
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 random failures of circuit overload protection devices."
(2) IEZZ 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 which the penetration assembly shall maintain containment integrity."
2
3.0 DISCUSSION AND EVALUATION In this evaluation, the results of typical contain=ent penetra-tions being at LOCA temperature initially concurrent with a random failure of the circuit protective devices will be analyzed.
Northeast Utilities (NU) provided information (References 1 and 2) 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 established based on testing done by Oyster Creek Nuclear Station for identical type connectors (Reference 2).
Maximum short circuit current available (Isc) was pr vided by Northeast Utilities for a three phase bolted fault. Rated current (I ) for each penetration was also provided.
The following formula (Reference 3) was used to determine the time allowed before a short circuit would cause the penetration to heat up to the temperature limit.
2*
c=A
.0297 log (Formula 1) 7 T +234 I
L 9here time in seconds t
=
current in amperes I
=
A conductor area in circular mils
=
Ti initial temperature (1380C, LOCA condition)
=
T2 maximum penetration temperature before failure.
=
l i
This is based on the heating effect of the short circuit current on the' conductor and does not take into account heat losses of the 1
i 3
conductor. For times less than several seconds, this heat loss is negligible.
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 temper-acure to penetration failure temperature for currents from rated cur-rent to maximum short circuit current in 20% increments. Times for the primary and secondary overcurrent devices to inter [upt these fault cur-rents were calculated. Where breaker ratings provided by the licensee indicated minimum and maximum f ault clearing times, the maximum time was used for conservatism.
3.1 Typical Lov Voltage (0-1000V) Penetrations. Northeast Util-ities has identified penetration X-105D (GE type NSO4) as being typical of low voltage penetrations. This penetration provides 480 V ac power to motor-operated valve 1-IC-1.
This penetration uses #8 AWG cable and has a continuous current racing of 20 amps. The maximum available short circuit current has been determined by NU to be 1600 amps. A temperature limit of 352*F (177 C) before seal failure has been determined based on testing. At the maximum short circuit current (1600 amps), overtemperature will be reached in 0.14 second from LCCA temperature initially.
From LOCA temperature initially, neither the primary nor secondar7 breaker will.. operate to clear any fault currents before penetration seal limiting temperature is attained.
3.1.1 Low Voltage Penetration Evaluation. With an initial penetration temperature of 138 C (LOCA),
penetration X-105D does not meet current requirements of RG 1.63 and IEEE Std. 317 for any short circuit fault with a failure of the primary breaker. Furthermore, it does not meet current requirements for short circuit faults even if the primary breaker operates as designed.
4
O 3.2 Typical Medium voltage (>1000 V) Penetration. Northeast Utilities has identified penetration X-101A (GZ cype NS03) as being typical of medium voltage penetrations. This penetration provides 4160 V ac power to Reactor Recirculation Pump 1.
This penetration uses 500 MCM cable and has a continuous current racing of 550 amps. 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 maximum short circuit current (1700 amps), overtemperature will be reached in 110 seconds from LOCA temperature initially.
There are no circuit protective devices located between the motor generator and the reactor recirculation pump. Overcurrent pro caccion is provided by a differential current sensing relay and a line over-sensing relay, each of which will operate to trip the motor current ger.erator by securing power to the motor generator motor and opening the generator field windings. At 2156 amps of current difference between phases, the differential relay will cause a trip of the motor generator in 0.133 second or less. At line current in excess of.
780 amps, the overcurrent relay will cause a trip of the motor gener-4 ator in 0.18 second or less.
4 For a three phase shcrt circuit condition, it cannot be assumed that sufficient current differences will exist to cause the differen-tial relay to operate and trip the motor generator. Therefore, oper-ation of this relay cannot be expected to clear fault currents prior to exceeding the penetration seal temperature limit of 177 C.
For fault currents producing current differences between phases in excess of 156 amps, this relay will, operate to trip the motor generator prior to reaching the penetration seal temperature limit.
The line overcurrent relay will operate to clear all fault cur-rents in excess of 780 amps prior to reaching the penetration seal 5
camperature limit from LOCA temperature initially. For fault currents less than 780 ampe, this relay will not ope ate to trip the motor generator.
3.2.1 Medium Voltage Penetration Evaluation. At LCCA tem-perature, penetration X-101A does not meet current require-ments of RG 1.63 and IEEE Std. 317 for short circuit faults with a failure of the line overcurrent relay since the dif-ferential relay cannot be assumed to operate for a three phase short circuit. With a failure of the differential current relay at LOCA temperature, the penetration does not meet current requirements for fault currents less than 780 amps.
3.3 Typical Direct current Penetration. Northeast Utilities has identified penetration X-100A (GE type NSO4) as being typical of DC penetrations. This penetration provides 125 V de power to the solenoid valve on main steam isolation valve 203-1A.
This penetration uses #14 AWG cable and hr. a continuous current racing of 10 amps. The maximum available short circuit current has been determined by NU to be 95 amps. A temperature limit of 352 7 (177 C) before seal failure has been determined based on testing.
At the maximum short circuit current (95 amps), overtemperature will be reached in 2.38 seconds from LOCA temperature initially.
At LOCA temperature, both the primary and secondary fuses will operate to clear all fault currents before the penetration seal tem-perature limit is reached.
3.3.1 DC Penetration Evaluation. At LOCA temperature, pene-tration 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.
6
/
x r
4.0 3U$tARY e,
At LOCA temperature, penetrations X-105D and X-101A do not meet current requirements of RG 1.63 and IEEE Std. 317 for any f ault current with a failure of the primary protective device. Further= ore, penetra-tion X-105D 'does not meet current requirements even if the primary breaker operates as designed.
Penetration X-101A does not meet current requirements with a failure of the line overcurrent relay at LOCA ten-perature with a short circuit.
If the line overcurrent relay operates as designed under these conditions, the penetration still does not meet current requirements for fault currents less than 780 amps.
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.
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 requirements imposed as a result of this review will take into consideration design changes resulting from other topics.
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, "Shor: Circuit Characteristics of Insulated Cable."
O
_. _