ML19309C172
| ML19309C172 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 03/10/1980 |
| From: | Groce R Maine Yankee |
| To: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| IEB-79-27, NUDOCS 8004080263 | |
| Download: ML19309C172 (8) | |
Text
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$ wT ENCINEERING OFFic5 WESTBORO, MASSACHUSETTS 01581 617-366-9011
.1:3lI B.4.1.1 WMY 80-47 March 10, 1980 United States Nuclear Regulatory Commission Region I 631 Park Avenue King of Prussia, Pennsylvania 19406 Attention: Office of Inspection and Enforcement Mr. Boyce H. Grier, Director
References:
(1) License No. DPR-36 (Docket No. 50-309)
(2) USNRC Letter to MYAPC dated November 30, 1979; IE Bulletin No. 79-27
Subject:
Response to IE Bulletin No. 79-27, " Loss of Non-Class IE Instrumentation and Control Power System Bus During Operation"
Dear Sir:
The following information is submitted in response to Reference (2):
Item 1:
" Review the Class lE and Non-Class IE buses supplying power to safety and non-safety related instrumentation and control systems which could affect the ability to achieve a cold shutdown condition using existing procedures or procedures developed under Item 2 below.
For each bus:"
Response
The Class IE and Non-Class IE instrumentation and control systems required to achieve a cold shutdown are fed by the following buses:
Class 1E Buses 125 volt de Bus 1 125 volt de Bus 2 125 volt de Bus 3 125 volt de Bus 4 120 volt ac Vital Bus 1 120 volt ac Vital Bus 2 120 volt ac Vital Bus 3 120 volt ac Vital Bus 4 Non-Class IE Buses 120 volt ac Instrument Bus DP/IAC s o 04 080' <5l(o[3
United States Nuclear Regulatory Commission March 10, 1980 Attention:
Mr. Boyce H. Grier Page 2 We have reviewed the loading of each of these buses and have determined that because of redundancy of information and controls available to the operator, failure of any single bus will not affect the ability to achieve a cold shutdown condition.
Item 1(a):
"ldentify and review the alarm and/or indication provided in the control room to alert the operator to the loss of power to the bus."
Response
The buses listed above are provided with the following alarms in the main control room:
Class 1E Buses 125 volt de Bus 1,2,3, & 4 Voltage Low (Common alarm for 125 V de Bus 1,2,3, & 4)
Voltage Critical Low (Common alarm for 125 V de Bus 1,2,3, & 4)
Loss of 480 volt ac to Battery Chargers (Common alarm for 125 V de Bus 1,2,3, & 4) 120 volt ac Vital Bus 1,2,3, & 4 Undervoltage (Common alarm for 120 V ac Vital Bus 1,2,3, & 4)
Non-Class IE Buses 120 volt ac Instrument Bus - DP/IAC No specific indication or alarm Item 1(b):
" Identify the Instrument and Control System Loads connected to the bus and evaluate the effects of loss of power to these loads including the ability to achieve a cold shutdown condition."
Response
Class IE 125 V de and 120 V ac (Vital) Buses A description and one line diagram of the 125 V de system and the 120 V ac vital bus system is contained in the attached FSAR pages 8-6, 8-7 and Figure 8-4 (Attachment A).
United States Nuclear Regulatory Commission March 10, 1980 Attention:
Mr. Boyce H. Grier Page 3 We have reviewed the loading of each of these buses and have determined that because of the redundancy of information and controls available to the operator, failure of any single bus will not affect the ability to achieve a cold shutdown condition.
Non-Class 1E 120 V ac Instrument Bus Power to the Non-Class IE 120 V ac Instrument Bus is supplied from either of two emergency Motor Control Centers (MCC-7A or MCC-8A) via a two position manual transfer switch. As either MCC 7A or 8A can accommodate system loading, initial positioning of the switch is arbitrary.
Although failure of this Non-Class IE 120 V ac Instrument Bus has never occured at Maine Yankee, we have postulated its total failure in accordance with the requirements of this bulletin. Assuming this postulated failure, a review was performed to determine the resultant affect on the instrument and control loads from this bus on the ability to achieve cold shutdown. The changes required as a result of this review are addressed in the response to Item 1(c) and Item 2.
Item 1(c):
" Describe any proposed design modifications resulting from these reviews and evaluations and your proposed schedule for 4
implementing those modifications."
Response
Class 1E 125 7 de and 120 V ac Class 1E (Vital) Buses No design modifications to these buses are required.
Non-Class 1E 120 V ac Instrument Bus The 120 V ac Instrument Bus will be provided with an undervoltage relay which will alarm in the main control room to indicate
" Instrument Bus Failure".
This alarm will be installed during March, 1980.
l Item 2:
" Prepare emergency procedures or review existing ones that will be used by control room operators, including procedures required to achieve a cold shutdown condition, upon loss of power to each Class 1E and Non-Class 1E bus supplying power to safety and non-safety related instrument and control systems.
The emergency procedures should include:
United States Nuclear Regulatory Commission March 10, 1980 Attention:
Mr. Boyce H. Grier Page 4 The diagnostics / alarms / indicators / symptoms resulting from a.
the review and evaluation conducted per Item 1 above.
b.
The use of alternate indication and/or control circuits which may be powered from other Non-Class IE or Class IE instrumentation and control buses.
c.
Methods for restoring power to the bus.
Describe any proposed design modification or administrative controls to be implemented resulting from these procedures, and your proposed schedule for implementing the changes."
Response
Class IE 125 V de and V ac Vital Buses Due to the redundancy noted in reply to Item 1(b) for all instrument and control systems on Class 1E Buses, and due to alarms provided on these buses as described in reply to Item 1(a), no additional modifications to design or procedures are deemed necessary to these systems to bring the plant to a required cold shutdown condition.
The methods to restore power to a failed bus are illustrated in Figure 8-4 of Attachment A.
Non-Class IE 120 V ac Instrument Bus For the 120 V ac Instrument Bus, an emergency procedure will be prepared to deal specifically with actions to be taken by the operators upon receipt of an " Instrument Bus Failure" alarm as described in our response to Item 1(c).
Alternate methods of obtaining needed indication and control to achieve cold shutdown will be addressed in this procedure. The methods of restoring power to this bus as noted in our response to Item 1(b) will also be included in this new procedure. The projected date for the implementation of this procedure is June 1, 1980.
Item 3:
"Re-review IE Circular No. 79-02, Failure to 120 Volt Vital AC Power Supplies, dated January 11, 1979, to include both Class IE and Non-Class IE safety related power supply inverters.
Based on a review of operating experience and your re-review of IE Circular No. 79-02, describe any proposed design modifications or administrative controls to be implemented as a result of the re-review."
United States Nuclear Regulatory Commission March 10, 1980 Attention:
Mr. Boyce H. Grier Page 5
Response
Class IE Power Supply Inverters Our re-review of IE Circular No. 79-02 indicates that the concerns expressed in the circular are not applicable to Maine Yankee's vital 120 V ac inverters for the following reasons:
1.
No time delay circuitry similar to the one described in the circular, is used in the inverters.
2.
The power fed to the inverters is from a de bus.
No alternate ac sources are used to feed the inverters.
3.
The inverter feed vital buses do not have any alternate ac source with automatic transfer capabilities.
Non-Class IE Power Supply Inverters The Non-Class 1E inverters at Maine Yankee are used to feed the station computer, which is not used for any control functions.
Based on the above analysis, we plan no design modifications or administrative controls.
We trust that you will find this information satisfactory; however, should you desire additional information, please contact us.
Very truly yours, MAINE YANKEE ATOMIC POWER COMPANY l
llAf R. H. Groce Senior Engineer-Licensing Attachment SFU/wpc
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i Trre-H ->1,,,g,enerator neutrals are not grounded as grounding is effected W =g,h e
the 4.16 kv bus D m.f!"3 ty.ansformers.
These g~di% uansformers limit the ground fault current en = 5 osia co M thus permit uninterrupted operation d ;.6 iaulty equipment with annunciation in thT'c"'odIivh 6
8.3.3 125 VOLT D-C SYSTDi The 125 volt d-c system shown in Figure 8-4 has a capacity to supply the plant with normal d-c requirements as well as emergency d-c power for a time deemed V adequate to restore normal a-c sources of power, 1
Four independent 125'v d-c, 2-wire, ungrounded systems are provided to supply d-c power and control requirements for the turbine-generator emergency auxill-aries, the switchgear, the annunciators, the emergency lighting, the vital bus inverters, the vital motor operated valves, the instrumentation, and the compu-ter inverter.
Each system consists of a battery, a battery charger, a distribution cabinet and a ground detector. The four systems and their d-c buses are designated by numbe rs 1, 2, 3, and 4.
To facilitate maintenance and still permit supply to all buses, buses 1 and 3 may be tied together.
A similar tie can interconnect buses 2 and 4 chen required.
Buses 1 and 3 serve power and control requirements for motors, switchgear, emergency lighting and inverters, and power for instrumentation.
Batteries 1 and 3, and battery chargers 1 and 3 are each sized to m rry the total load of both buses 1 and 3.
Buses 2 and 4 serve instrumentation and inverter requirements only.
Bat teries 2 and 4, and battery chargers 2 and 4 are each sized to carry the total load of both buses 2 and 4.
The ground detectors provided on each bus annunciate grounds in the control room.
In a manner similar to that used for distribution of loads on the 4.16 kv l
emergency buses, redundant equipment requiring d-c, whether for power, control, or instrumentation, is connected to separate d-c buses so that the overall I
degree of reliability and integrity of the redundant system is not jeopardized in any way.
Each battery is sized to supply the combined emergency load of the two buses to which it may be connected for two hours without charging and without its voltage per cell falling below 1.75 volts under this condition.
The batteries are mounted on protected corrosion resistant steel racks designed to withstand design basis seismic effects.
The batteries are housed in pairs,1 and 2 to-gether, and 3 and 4 together, in physically separated missile proof areas.
The battery chargers are supplied from the 480 v emergency buses. All the chargers and the distribution cabinets are located in one room separate from the batteries.
8.3.4 120 VOLT A-C VITAL INSTRUMENT POWER SYSTDi Four 120 v a-c, 60 Hz,1 phase vital instrument buses constitute a very reli-able and stable electrical supply system for critical control and instrumenta-i tion.
This system is designed to be the c:ost reliable power source available at the station.
8-6
Re'. 12/70 v
The source of power for each bus is from an inverter fed from a d-c bus (see Figure 8-4).
On failure of the a-c source for the charger, the inverter takes
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its power from the battery without interruption or disturbance to the vital bus voltage or frequency.
A synchronizing signal from the emergency 480 v bus maintains the phase and frequency of the inverter output in synchronism with the power line; however, on loss or deviation of this signal the inverter operates on its own internal frequency reference.-
Distribution' cabinets feed reactor protection and other vital instrument chan-nels.
Redundant equipment and channels requiring the 120 v a-c vital instru-ment power supply will be connected to separate vital buses so that the overall degree of reliability and integrity of the redundant system is not jeopardized in any way, d
The vital buses are ungrounded and a ground fault results in annunciation only.
During inverter maintenance, adjacent vital buses can be interconnected to pro-vide an alternate source for the dead bus.
.3.5 LIGHTING SYSTEM Norm lighting for the control room, turbine area, auxiliary building, fu buildi
, service building and office building is supplied from the 480 station it rvice system through single phase, 480-120/240 v dry-type tr s-formers.
hting for the reactor containment is supplied by 3 phas, 480-120/240 v d type transformers.
Emergency lighting for these ar s is pro-vided at all es ential control positions and access ways with i andescent units, which are ncinuously energized at 120 y a-c.
If the leernating
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current supply to t emergency lights should fail, the sup y will be auto-matically transferred o the station battery supply at 1 v d-c.
Normal lighting for remote areas is supplied through ocal transforners.
Emergency lighting for these reas is provided by ocal self-contained, battery-powered emergency ligh ng units.
1 8.3.6 COMMUNICATIONS SYSTEM 1
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Three independent wire-circuit communi tion systems are provided.
The first, leased from the telepho compan permits calls from the control
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room and selected administrativ offices to p nts outside the plant for system dispatching and other mmunication, as 11 as station-to-station i
intraplant communications.
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The,second is a four c nel intraplant communication d paging system i
comprised of handset and loudspeakers interconnecting a.
sections of the j
plant.
The third is system for maintenance use consisting of circuit and jacks for a sound owered telephone' system.
R Microva voice channels are also'available for communication between he plant nd the system dispatcher.
In addition, there is a base radio sta Ion in e control room to allow communication with the Maine State Police hea -
g' arters in Augusta.
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Bus 7 480 V-AC EMERGENCY BUSES i
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BATTERY I
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I BUSES I
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VITAL BUSES Y
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ONE LINE DIAGRAM-125-DC BUSES s
AND 120V-AC VITAL BUSES MAIN E YANKEE ATOMIC POWER COM PANY j
REVISED DECEMBER 1970
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