ML20086D782
| ML20086D782 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 03/13/1973 |
| From: | Heider L VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 8312050109 | |
| Download: ML20086D782 (4) | |
Text
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G VERMONT YANKEE NUCLEAR POWER CORPORATION SEVENTY SEVEN OROVE STREET RuTr.AND, VEMMONT 05701 REPLY TO:
ENGINEERING OFFICE TURNPIKE ROAD WEST 80RO, MASSACHUSETTS ot581 TELEPHONE G17 3GS 900 9 March 13, 1973 t-
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np United States Atomic Energy Commincion 7d j
Washington, D. C.
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Attention: Directorate of Licensing
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Reference:
a) License No. DPR-28 (Docket No. 50-271)
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b) USAEC letter dated January 15, 1973
Dear Sir:
With reference to your letter dated January 15, 1973 relative to a review of control circuits for safety related equipment at the plant, Vermont Yankee Nuclear Power Corporation offers the following:
h160 VOLT COMPONENTS 1.
Station Service Water Pumps.
In the case of h160 volt safety related components, no instance was found in which a safety related component was affected by the disabling of another component by plaaing its breaker in the racked
,g out position. One situation was found where the testing of a circuit
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Jk breaker could have an effect on a component through interlock p
circuitry. As shown on FSAR Figure 8.1-3, Station Service Water Pumps "B" and "D" are connected to bl60 volt bus 3.
Under normal operating Y I.
conditions, either one or both of these pumps are in service, depending
[f on water temperature conditions. In event of a loss of normal power o&
(LNP) condition with both pumps running, the "B" pump breaker tript>;
but the "D" pump breaker does not trip and the pump will restart as I
soon as the diesel generator is connected to the bus. During one-pump operation with either pump, the pump breaker does not trip under J
LNP conditions. Under the following combination of conditions:
(1) the "B" pump is running, (2) the "D" pump breaker is in the racked out position,
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(3) the "D" pump breaker is being tested and is in the closed position, and (4) a LNP condition occurs; the "B" pump control circuitry will assume that the "D" pump is running 8312050109 730313 1*go*
PDR ADOCK 05000271 P
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o United States Atomic Energy Commission March 13, 1973 Attn: Directorate of Licensing Page Two and will trip on bus undervoltage.
If the "D" breaker is still in the test close position when bus voltage is restored, the "B" pump will not restart automatically. The pump can be started manually from the main control board. This situation does not enist in the case where the "D" pump is running with the "B" pump breaker in the test close position, because the "D" pump breaker does not trip under LNP conditions.
The control circuits for the redundant set of pumps, "A" and "C",
on h160 volt bus h arc similarly connected. There are no control circuit intercennections between the pumps on bus 3 and the pumps on bus h.
This situation only exists when either the "C" or "D" pump breaker is in the test close pcsition. Since h160 volt breakers are usually tested when the plant is shutdown, this situation vould only occur during plant operation if treaker maintenance was necessary and subsequent testing of closing action was required. Administrative procedures vill be written and the "C" and "D" pump breakers will be marked to insure that the breakers are not tested unless the plant is in the chutdown condition.
If testing cheuld be necessary during breaker maintenance when the plant is in power operation, a special procedure vill be written requiring permission from higher authority, operational monitoring during the test period, and a minimum time of testing in the close position.
2.
Diesel Generator Breakers.
A similar situation involving the test closing of bl60 volt circuit breakers was fcund in the diesel generator circuit breaker and LUP circuit. As shown on FSAR Figure 8.1-3, breakers 3Tl and 3V are source breakers for bus 3 Under LUP conditions, the control circuit for the diesel generator breaker checks the pocition of breakers 3T1 and 3V to assure they are tripped before the diesel generator breaker is allowed to close automatically to the dead bus. Under normal operating conditione, 3T1 is closed and 3V is open. Under LNP conditions, 3Tl trips ana 3v remains open.
If breaker 3V vere in the test close position and LUP conditions occurred, the control circuitry would assume that 3V waa closed and would prevent the diesel generator breaker from closing automatica1]y. This situation would not prevent manual closure from the main control board. Since breakers 3T1 and 3V are not tested during plant operation, it is unlikely that this situation could occur. These breakers vill be included in the administrative controls applied to the Station Service Water Pump breakerc "C" and "D".
Breakers hT2 and kV on bus k are similarly connected and vill receive similar administrative control.
h80 VOLT COMPONENTS 1.
480 Volt Buses.
On the h80 volt level, no instance was found in which a safety l
related component was affected by the disabling of another component 1
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United States Atomic Energy Commission March 13, 1973 Attn: Directorate of Licensing Page Three by placing its breaker in the racked out position. One situation was found whereby a circuit breaker could be prevented frem closing if a second circuit breaker were racked out and then placed in the test close position, or if the second breaker were completely withdrawn from the cubicle. Figure 8.1-5a in the FSAR shows the two sources of power to bus 8.
The normal source in through Station Service Transformer T-8 and breaker 88, which is manually operated and normally closed. The other source is from bus 9 through tie breakers 9T8 and 8T9 Tie breakers 8T9 and 9T8 are both manually operated and normally open. Breaker 88 is interlocked with tie breaker 8T9 and can be closed only when breaker 8T9 is open. Breaker 8T9 is interlocked with source breakers 88 and 99, and cannot be closed when both 88 and 99 are closed.
Similar interlocks are provided for breakers 99 and 9T8.
These interlocks are designed to prevent tying the two bl60 volt emergency buses 3 and 4 together through the 480 volt buses. When any of the four breakers is placed in the test close position or is completely withdrawn from the cubicle, the interlock intelligence from'that breaker indicates that the brecker is closed, placing its interlock into effect.
Because of this design the manual switching operations in re-energizing either dead bus must be properly sequenced. Should operating personnel test close or completely remove one of thece breakers before attempting to energize the dead bus, it will be immediately apparent that the proper procedural sequence had not been followed, as the breaker vill not close and the bus will not become energized. As long as the bus is energized before the given breaker is placed in the test close or fully withdrawn position, the closed breaker position indication from that breaker has no effort.
2.
480 Volt Motor Control Centers and Contactors In the case of 480 volt motor control centers, no situation was found where a compcnent which is disabled by placing its breaker in the racked out position adversely affects another component. However, if the analysis is carried one step further to include a racked out breaker and the physical disconnection of wires to the contactor assembly (motor starter), the following situations were found to result.
The Standby Liquid Pumps were the only components found that affect a redundant train when their contactor assemblies are disconnected from the motor control center. The effect of disconnecting the contactor assembly of the train A Standby Liquid Pump is to prohibit the starting of the train B Standby Liquid Pump. This happer only when it is necessary to do maintenance on the contactor assembly. A similar situation occurs if the train B Standby Liquid Pump contactor assembly is disconnected. In order to prevent thic situation from occurring, the maintenance procedures for these pumps require bypassing the _ inter-lock contact in the motor control center cabinet from which the contactor assembly has been disconnected. This allows the redundant-pump to operate if required.
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United States Atomic Energy Commission March 13, 1973 Attn: Directorate of Licensing Page Four The discharge damper for the control room air conditioner supply ran is contrclled by a normally closed contact in the fan motor contactor assembly. The discharge damper is open when the fan is running, and closed when the fan is not running. When the fan motor breaker is placed in the racked out position, the damper remains closed.
If the wires are then disconnected from the contactor assembly for maintenance purposes, the damper opens. A similar situation occurs with the control room air conditioner standby fan, in that when the standby fan motor breaker is racked out and its contactor assembly wires are disconnected, both its inlet and outlet dampers open. The control circuits for these dampers will be changed to make the dampers close under this maintenance condition. A complete description of these modifications will be sent to you within thirty days.
When train A standby gas treatment exhaust fan motor breuker is racked out and the wiring of the contactor assembly is disconnected, a component in the same train is affected. A one kilowatt heater is used to keep moisture out of the charcoal filter when the standby gas treat-ment exhaust fan is in service but not running.
This heater is prevented from operation when the fan motor contactor assembly is disconnected as described above. When the fan is inoperable, the train is out of service and the heater is not required. When the train is restored to service, the heater vill operate as required. The removal of the fan in train A from service has no effect on the components in train B.
Plant procedures are currently being reviewed to ensure that when a redundant system is removed from service the remaining system is functionally tested before and after loss of redundancy. Revisions to plant procedures and/or new procedures shall be prepared and approved to insure the above.
We trust you vill find this information satisfactory; however, should you desire additional information feel free to contact us.
Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION HAL L. H. Heider Manager of Operations GCA/kg
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