ML20085K378

Provides Responses to Generic Ltr 91-06, Resolution of Generic Issue A-30, 'Adequacy of Safety-Related DC Power Supplies.'

ML20085K378
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	10/25/1991
From:	Pelletier J VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-GTECI-A-30, REF-GTECI-EL, TASK-A-30, TASK-OR BVY-91-98, GL-91-06, GL-91-6, NUDOCS 9110310052
Download: ML20085K378 (11)

Text

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' ' -V'ERMONT YANKEE NUct ' EAR POWER CORPORATION

. W:, s Ferry Road. Brattieboro. VT 05301 7002 y

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[NGINEERING OFFICE MQ MAIN STHf fi BO L10'4 t/ A O t ?d(?

e' 906,1?)6:311 October 25,1991 1 United States Nuclear Regulatory Commission BVY 9198 1 A'ITN: Decument Control Desk '

Washington, DC 20555

References:

a. License No. DPR 28 (Docket No. 50-271) b, Letier, USNRC to [ All 1.icensees], NVY 91-83, dated April 29,1991 (Generic Letier 9106).

Subject:

Response to Generic Letter 91-06," Resolution of Generic Letter A 30, l Adequacy of Safety Related DC Power Supplies, Pursuant to 10CFR50.54(f).  !

Dear Sir:

In Reference (b), USNRC requested all licensees to provide, pursuant to Section 182 of the Atomic Energy Act of 1954 and 10CFR50.54(f), written responses to the questions in Enclosure 1 within 180 days.

Please find as Enclosure 1 Vermont Yankee's response to Reference (b), signed under oath and affirmation. Should you have any further questions or comments regarding the enclosed

. information, please contact this office.

Very truly yours, VERMONT Y ANKEE NUCLEAR POWER CORIORATION Eh _

ames P. Pelletier cc: USNRC Region I . Administrator USNRC Resident inspector- VYNPS USNRC Project Manager- VYNPS STATE OF VERMONT - -) i WINDHAM COUNTY _

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Then personally appeared before me, James P. Pelletier, who, being duly aworn. did state t V '

President' Engineering of Vermont Yankee Nuclear Power Corporation, that he is duly nuttoriiet . c Se the foregaing document in the name and on the behalf of Vermont Yankee Nuclear Power Co n and that t statementi therein are true to the best of his knowledge and belief. ,

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Enclosure 1 Q1. Name the Unit.

Response

The Unit is Vermcnt Yankee Nuclear Power Corporation.

Q2a. How m$ny independent redundant divisions of Class lE or rafety related de power exist at this unit. (Include any separate Class IE or safety related dc, such as any dc dedicated to the diesel generetors.)

Response

There e.re 'cwo independent trains of safety related DC power at Vert,;ont Yankee.

Division SI consists of 125V DC battery A, its associated bus DC-1 and charger CA-1; and 24V DC battery A, its associated bus A and charger A. The 125V DC battery A serves the major DC loads including control power for the diesel generator while 24V bus A serves certain ECCS instrumentation loads.

Division SII consists of 125V DC battery B, its associated bus DC-2 and charger CB-1; 125V DC battery AS-2 and its associated bus DC-2AS and charger CAS-2; and 24V battery L, its associated bus B and charger B. Loads connected to division SII are similar to those connected to division SI except r. hat the electric switchgear loads are normally connected to battery B and can be alternately connected to Lattery AS-2. The 'A' diesel generator is also connected to the AS-2 battery.

Q2b. How many functional safety-related divisions of de power are necessary to attain safe shutdown of this unit.

Response

The DC supply in divisions SI and S1I can each separately supply de power to the necessary emergency loads to attain safe shutdown of the plant.

Q3. Does the control room at this unit have the following separate, independently annunciated alarms and indications for each division of de power?

a. Alarms

1. Battery disconnect or circuit breaker open?

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Responset There is no annunciator to alert operators of a battery disconnect of the 125V DC batteries A and B, the AS-2 batteries and the ECCS 24V DC batteries A and B.

2. Battery charger disconnect or circuit breaker open (both input ac and output dc)?

Responset An annunciator in the control room alerts operators when there is a disconnect in the 12SV DC battery A charger supply breaker to the DC-1 bus. There are no other annunciators to alert operators of a battery charger disconnect (both input ac and output de) in division SI.

Similarly, there is an annunciator to warn operators of a disconnect in the 125V DC battery B charger supply breake r to the DC-2 bus. There is an annunciator to alert operators of a disconnect in the output DC breakor of charger CAS-2 of battery AS-2. There are no other annunciators to alert operators of a battery charger djsconnect (both input ac and output dc) in division 911.

Howeve r, proper operation of the chargers of the batteries of divisions SI and SII are ensured by an auxiliary operator verifying that the chargers are on during each shift. (3 shifts per day)

3. dc system ground?

tiesponse:

There is no specific alarm that alerts operators of a ground on the respective buses in divisions SI and SII _

of the de system.

However,.DC-1, the 125V DC bus in division SI, has a ground detection indicator'in the control room. The indicators are checked by the operators at the beginning of each shift. Therefore, the longest time the ground will remain undetected will be eight hours.

The operators may be alerted to a possible ground by the Battery Voltage Lo alarm depending on the severity of the ground.- The indicator specifies the actual

. problem. The ECCS 24V DC Bus A Failure alarm-alerts operators in the control room when there is a ground on Bus A of division SI. The operator determines the presence of a bus bus failure alarm. ground locally when responding to the The grounds on the buses in division SII are detected similarly by operators in the control room.

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4. dc bus undervoltage?

-Response:

A common Battery. Voltage Lo annunc! stor alarms in the control room when the voltage of DC-1 in division SI or DC-2 in division SII drops. T; 9 ECCS 24V DC Bus A failure annunciator in the control room alerts operators when there is a low bus voltage on Bus A of division SI.

The operstor res voltage locally, ponds to this alarm and verifies low f

Operators are warned similarly when there is a low voltage on the buses in division SII.

5. de bus overvoltage?

Rehponse:

The 125V DC bus in division SI does not have an alarm to alert operators of a bus overvoltage. The ECCS 24V DC Bus A Failure annunciator in the control room alerts operators when there is an overvoltage on Bus A. The operator responds to this alarm and verifies high voltage locally.

Similarly, the 125V DC bus in division SII does not have an alarm to alert operators of a bus overvoltage.

Similarly, DC-2AS of division SII does not have an alarm to alert operators of a bus overvoltage. The ECCS 24V DC Bus B Failure annunciator in the control room alerts operators when there is an overvoltage on Bus B.

6. Battery charger failure?

Response

There are annunciators in the control room that alert operators when there is a battery charger failure for the chargers in division SI.

Similarly there are annunciators for the battery chargers in division SII.

It should be noted that the-annunciators pertaining to the battery chargers of the ECCS 24V DC batteries A, B and AS-2 do not specify failure, but indicate trouble.

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Also, a standby-battery charger is available to substitute for either A-1 or B-1 normal battery chargers in_the event of normal charger failure or maintenanca. This charger is of.the same capacity as the normal battery chargers. A standby-battery charger is also available to substitute for battery charger AS-2 in the event of normal charger failure or maintenance. This battery charger is of the same capacity as the normal battery charger. A standby battery charger is available to substitute for either battery A or B of the ECCS 24VDC normal battery chargers in the event of normal- charger failure or maintenance. A spare battery charger is being purchased by Vermont Yankee and will be kept in storage in the event that the standby battery charger of the ECCS 24VDC system fails to operate.

7. Battery discharge Response: '

There is no specific battery discharge alarm available in the control room. The state of battery char determined by using the other available alarms,ge is local and remote indication, operator rounds and periodic surveillance,

b. Indications

1. Battery _ float charge current?

Response

There is no indication in the control room to inform operators of the float charge currents of the individual batteries in both divisions SI and SII.

However, batteries A-1 and A of division SI have locally mounted ammeters for battery current indication.

Similarly, batteries B-1, B and AS-2 of division SII have locally mounted ammeters for battery float charge current indication.

2. Battery circuit output current?

Response

There is no indication in the control room to inform operators of the battery circuit output currents of the individual batteries in both divisions SI and SII.

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However, batteries A-1 and A of division SI have locally mounted ammeters for battery current indication.

Similarly, batteries B-1, B and AS-2 of division SII have locally mounted ammeters for battery current indication.

3. Battery discharge?

Response

There is no battery discharge indication in the control room. However, the state of battery discharge is determined by using the other available alarms, local and remote indication, operator rounds and periodic surveillance.

4. Bus voltage?

Responset There is no control room indication for the bus voltage of the 125V DC bus DC-1 of division SI. However, the battery voltage of DC-1 is recorded on the computer and can be obtained in the control room. The ECCS 24V DC Bus A of divisicn SI has control room indication of the bus voltage.

Similarly, there is no control room indication of the bus voltage of the 125V DC bus DC-2 of division SII except for the computer indication of the battery voltage. The ECCS 24V DO Bus B and 125V DC bus DC-2AS have control room indication of the bus voltage.

However, locally mounted voltmeters exist on each of the DC buses corresponding to each division of the DC system, i.e. a locally mounted voltmeter exists for DC-1, DC-2, DC-2AS, ECCS 24V DC buses A and B.

c. Does the unit have written procedures for response to the above alarms and indications?

Response

Vermont Yankee maintains a written procedure for response to all the annunciators listed in Q3. The combination of alarms, alarm response procedures, plant procedures and operator training programs provides the operators with adeguate steps to respond to the indicators listed in Q3.

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9 Q4. Does this unit have indication of bypassed and inoperable status of circuit breakers or other devices that can be used to disconnect the battery and battery charger from its de bus and the battery charger from its ac power source during maintenance or testing?

Response

This unit does have an annunciator in the control room that alerts operators when certain of the DC-1 or DC-2 breakers are open. This annunciator provides indication of bypass and inoperable status of the battery charger circuit breakers.

Q5. If the answer to any part of question 3 or 4 is no then provide information justifying the existing design, features of the facility's safety related de systems.

Response

As-stated in the response to Q3 and Q4, Vermont Yankee may not have all the specific alarms or indicators listed in the questions but through alternate indications and alarm or the combination of alarms provided, existing alarm response procedures, plant procedures, operator training programs, the indication and alarms provided are adequate.

Q6. (1) Have.you conducted a review of maintenance and testing activities-to minimize the potential for human error causing more than one de division to be unavailable?

(2) Do plant procedures prohibit maintenance or testing on redundant de divisions at the same time?

Response

(1) Procedures generated at Vermont Yankee are written by professionals familiar with the operation of the plant and safety issues surrounding it end therefore steps to minimize human error are inherently introduced in the text. Vermont Yankee has a Procedures Writer's Guide which is used when writing procedures. Inherent to this document is information that helps the writer tc write a procedure that minimizes human errors. As part of this process, a procedure walkthrough is performed by someone familiar with the task to be performed. In addition, after generation, the procedure has to go through a review cycle where the Operations Department personnel who are familiar with the various plant conditions and violations can flag any potential problems. The procedure also has to be approved by the Plant Operations Review Committee (PORC). PORC has to ensure that all safety issues have been addressed-by the procedure.

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(2) Plant procedures-do not explicitly prohibit maintenance or testing on redundant de divisions at the same time.

However, prior to performing battery performance and service discharge tests, it is necessary to determine that the plant is in a mode that permits the inoperability-of 'h- unrociated battery. Also prior to any maintenance activity on a battery, has to be granted by the Shift Supervisor.The perm [ssion Shift Supervisor is familiar with the status of the plant and the various pieces of equipment that can be rendered inoperable at a given time.

Q7. Are maintenance, surveillance and test procedures regarding station batteries conducted routinely at this plant?

Specifically:

a. At least once per 7 days are the R 11owing verified to be within acceptable limits:

1. Pilot cell electrolyte level?

Response: Yes

2. Specific gravity or charging current?

Response Yes

3. Float voltage?

Response: Yes

4. Total bus voltage on float charge?

Response: Yes

5. Physical condition of all cells?

Response: Yes

b. At least once per 92 days, or within 7 days after a battery discharge, overcharge, or if the pilot cell readings are outside the 7-day surveillance requirements are the following verified to be within acceptable limits:

1. Electrolyte level of each cell?

Response: Yes

2. The average specific gravity of all cells?

Response: Yes 7

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3. The specific gravity of each cell?

Response: Yes t

4. The average electrolyte temperature of a representative number of cells?

Response

Instead of measuring the average electrolyte temperature of a representative number of cell, the temperature of each cell is measured.

5. The float voltage of each cell?

Response: Yes

6. Visually inspect or measure resistance of terminals and connectors (including the connectors

-at the de bus)?

Response Yes

c. At least every 18 months are the following verified:

1. Low resistance of each connection (by test)?

Response Yes

2. Physical condition of the battery?

. Response: Yes

3. Battery charger capability to deliver rated ampere outpilt to the de bus?'

Response

Vermont Yankee is currently revising its battery charger test procedure to include meas cing the load current of the battery chargers. The .evised procedure is scheduled for implementation during the next refueling outage.

4.- The capability of the battery to deliver its design duty cycle to the de bus?

Response

Yes, except every 60 months when the capacity of each battery is verified by a performance discharge test.

This test is then performed in lieu of the design duty test.

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5. Each individual cell. voltage is within acceptable limits during the service test?

Response Yes

d. At least every 60 months, is the capacity of each battery verified by performance of a discharge test?

Response Yes

e. At least annually, is the battery capacity verified by performance discharge test, if the battery shows signs of degradation or has reached 85% of the expected service life?

Response

Vermont Yankee procedures meet the intent of IEEE 450 for performance discharge testing. For batteries AS-2 and ECCS 24V DC batteries A and B, the performance discharge test will be performed once each cycle (every eighteen months) when the capacity has reached 90%.

For the 125V DC batteries A-1 and B-1, when the battery capacity reaches 90%, plant procedures require that an engineering evaluation is made to determine whether an immediate replacement is necessary or whether the replacement can be delayed to the next refueling outage.

08. Does the plant have operational features such that following loss of one safety related dc power supply or bust

a. Capability is maintained for ensuring continued and adequate. reactor cooling?

'b. Reactor coolant system integrity and isolation capability are maintained?

c. Operating procedures, instrumentation (including indicators and annunciators), and control functions are

-adequate to initiate-systems as required to maintain adequate core cooling?

Response

The safety related DC distribution system is divided into divisions SI and SII. Each division providing separate and redundant power to the emergency loeds required under postulated design-basis-accident conditions. Therefore, the failure of any one safety related dc power supply will.not jeopardize:

a. The capability to taaintain continued and adequate reactor-cooling.

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b. Reactor coolant system integrity and isolation capability. (Note: As ptrt of its IPE effort Vermont Yan1.co is analyzing the offects of lecing a DC bus.

The analysis will help verify that continued and adequate reactor cooling is maintained and that reactor coolant system integrity and isolation capability is maintained.)

c. Existing operating procedures, instrumentation and control functions are adequate to initiate systems required to maintain adequate cote cooling following the loss of one safety related de power supply or bus.

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