ML19309F388
| ML19309F388 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 04/25/1980 |
| From: | Justin Fuller PUBLIC SERVICE CO. OF COLORADO |
| To: | Stello V NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| References | |
| IEB-79-27, NUDOCS 8004290390 | |
| Download: ML19309F388 (6) | |
Text
8004290 3 %
- i puniie ervice company ce cdlende 12015 East 46th Avenue, Suite 440; Denver, CO 80239 April 25, 1980 Fort St. Vrain
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Unit No. 1 P-80087 Mr. Victor Stello, Jr., Director Nuclear Regulatory Commission Office of Inspection and Enforcement Washington, DC 20555
Subject:
Class 1E and Non-Class 1E 120 VAC Instrument Buses
References:
IE Bulletin 79-27 and P-80032 Swart to Seyfrit February 28, 1980
Dear Mr. Seyfrit:
Per our February 27, 1980 letter (P-80032), the following is our response to IE Bulletin 79-27.
The Fort St. Vrain (FSV) Station has three Class 1E Buses, all of which are non-interruptible:
Instrument Bus #1 Instrument Bus #2 Instrument Bus #3 FSV also has one Non-Class 1E interruptible Instrument Bus:
Interruptible Bus #3 Item #1 from IE-79-27 NRC Position:
" Review the Class IE 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:"
"la) Identify and review the alarm and/or indication provided in the control room to alert the operator of the loss of power to the bus."
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fir. Victor Stello, Jr.
April 25,1980 Page 2 PSC Reply:
Loss of instrument bus voltage is alarmed in the control room (all buses) and voltmeters are provided (all buses) for additional verification.
NRC Position:
"lb) 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."
PSC Reply:
Extensive load identification and evaluation studies have been completed.
No problems that would prohibit the ability to achieve.a cold shutdown were identified.
Several minor concerns were identified and are available at the Denver Engineering Office for NRC review.
The evaluation ha's identified one area of concern.
The valves required for placing the Helium Circulator Water Turbines into service are nomally of a fail open nature and/or are powered from two buses (multiple solenoids). The four Helium Circulator Water Turbine Speed Valves are an exception.
The Loop #1 speed valves fail closed and are powered from bus #2.
The reverse situation is true for the Loop #2 speed valves.
This is not a desirable situation since, in general, the Helium Circulator auxiliaries for Loop #1 are powered from bus #1 and bus #2 for Loop #2.
The water turbines are a backup to the normal steam turbine mode of circulator operation and are required to operate during certain accident conditions. All of the water turbine speed valves in question above have manual override capability which can be used to open the valves when required within approximately 5 minutes.
No single failure mode exists that would require immediate operation of these speed valves for safe shutdown cooling.
It must be stressed that while this is an undesirable situation, it should not be considered a situation that will endanger the safety and health of the public.
This condition is currently under engineering evaluation and will be resolved by August 1,1980.
The loss of power to one bus will result in the normal shutdown of one cooling loop.
Depending on plant conditions, this could also result in a turbine trip and reactor scram.
Otherwise, the plant would be manually shutdown to reestablish cooling to both loops before power operation is resumed.
Mr. Victor Stello, Jr.
April 25,1980 Page 3 NRC Position:
"Ic) Describe any proposed design modifications resulting from these reviews and evaluations and your proposed schedule for implementing those modifications."
PSC Reply:
The existing undervoltage alarms are " sensed" at the bus for non-interruptible buses # 1 and 2 and interruptible bus #3.
Under voltage for non-interruptible bus #3 is sensed at the inverter / charger unit.
To provide a true " bus" voltage alarm when non-interruptible bus #3 is fed from its backup source an under voltage relay will be added to the bus. Modification will be complete by November 1,1980.
NRC Position:
"2) Prepare emergency procedures or review existing ones that will be used by control room operators, including procedures required to dchieve a cold shutdown condition, upon loss of power to each Class 1E and Non-Class 1E bus supplying power to safety related and non-safety related instrument and control systems.
The Emergency Procedures should include:
a)
The diagnostics / alarms / indicators / Symptoms resulting from the review and evaluation conducted per Item 1 above, b)
The use of alternate indication and/or control ciricuits which may be powered from other Non-Class 1E 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."
PSC Reply:
The Emergency Procedures were reviewed and were found to be adequate.
Certain Design Modifications to tne 120 VAC instrument buses have been under consideration for some time.
These modifications were being pursued independently of IE-79-27.
These modifications will improve the reliability / operability of the instrument buses, therefore, the changes will be discussed at this time.
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fir. Victor Stello, Jr.
April 25,1980 Page 4 The modification under consideration is to provide backup power to non-interruptible bus #1 and non-interruptible bus #2 from two new instrument power transformers.
This would also allow the implementation of automatic transfers via contactors to the backup power sources for non-interruptible buses #1, #2 and #3 and interruptible bus #3.
All transfers with the existing system are done manually.
These modifications will be completed by flovember 1,1980.
flRC Position:
"3) Review IE Circular flo. 79-02, Failure of 120 Volt Vital AC Power Supplies, dated January 11, 1979, to include both Class 1E and fion-Class 1E Safety Related power supply inverters.
Based on a review of operating experience and your re-review of IE Circular flo. 79-02, describe any proposed design modifications or administrative controls to be implemented as a result of the re-review."
NRC Positions From I&E Circular 79-02:
"All holders of operating licenses should be aware of the potential problems of the types noted above.
It is recommended that the following items be considered in your review of this matter:
1.
Determine whether or not time delay circuitry is used in your inverter units.
If so, have they been adjusted to the appropriate setpoint as required by equipment and the integrated system designs?"
PSC Reply:
The FSV instrument bus configuration is entirely different than the bus configuration from IE Circular 79-02.
The question does not readily apply to our Instrument Power System.
The following is provided on our inverters.
fion-interruptible buses #1&2 have exide inverters. These inverters have time delay fuses in the input circuits.
Low voltage on the DC input (less than approximately 105 volts) will result in sufficient current to cause the fuse to operate and interrupt the circuit in accordance with its time delay characteristic. There is no adjustment to this time delay. fion-interruptible bus #3 has a Deltec Inverter.
This inverter has no time delay circuitry. Low or high DC input voltage will cause the inverter input breaker to trip instantaneously. Each inverter is supplied from a different 125 volt DC battery.
FSV does not have the problem outlined by question #1 above.
flRC Position:
"2) Determine if the AC input voltage and transformer tap settings are optimized to prevent exceeding the inverter component nameplate maximum rated DC input voltage in the event of a high AC input voltage transient."
Mr. Victor Stello, Jr.
April 25,1980 Page 5 PSC Reply:
The IE Circular 79-02 Instrument Power System is entirely different than the FSV System.
Battery chargers normally supply the inverters and station batteries.
If the charger fails the batteries are immediately available as backup. There are no transformers with the FSV configuration.
The charger does have tap settings but these are strictly for optimizing station battery float charge.
FSV does not have any problems as outlined in Question #2 above.
"3)
If an alternate 120 volt source is used in your design, detennine if the protection transfer circuitry of the inverter has been optimized within design limits to ensure maximum possible availability of the inverter system during transient loading conditions. An operating history of inexplicable transfers may be indicative of the above."
PSC Reply:
FSV does not utilize automatic transfers on any of its inverters. All bus transfers are manual at this time.
Care will be taken on the implementation of the proposed design from Item 2 (IE Bulletin 79-27) to insure that the protection transfer circuitry is optimized.
4)
Determine if the administrative controls employed by your facility ensures operability of safety systems after its subcomponents (e.g., time delay relays, switches, etc.) have been subjected to maintenance or testing.
PSC Reply:
The administrative controls have been reviewed and were found to be acceptable.
Very truly yours, J./l K. Fuller, Vice President Engineering and Planning Pa
STATE OF COLORADO
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ss.
CITY AND COUNTY OF DENVER)
J.K. Fuller, being first duly sworn, deposes and says; That he is Vice President of Engineering and Planning of Public Service Company of Colorado, the Licensee herein; that he has read the accompanying material and knows the contents thereof, and that the statements and matters set forth therein are true and correct to the best of his knowledge, information and belief.
J Fuller' Subscribed and sworn to before me this 25th day of April,1980.
Witness my hand and official seal.
My commission expires:!!/JC:r..::::r._:3:0 7.;:. ', L:'
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n v<r e Notary Public