ML20085L006

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Forwards Response to Generic Ltr 91-06, Resolution of Generic Issue A-30, 'Adequacy of Safety-Related DC Power Supplies.'
ML20085L006
Person / Time
Site: Fort Calhoun Omaha Public Power District icon.png
Issue date: 10/25/1991
From: Gates W
OMAHA PUBLIC POWER DISTRICT
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-GTECI-A-30, REF-GTECI-EL, TASK-A-30, TASK-OR GL-91-06, GL-91-6, LIC-91-263R, NUDOCS 9111010186
Download: ML20085L006 (11)


Text

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u Omaha Public Power District 444 South 161h Stn et MA Omaha, Nebratk:i 68102 2247 October 25, 1991 402/636 20C0 LIC-91-263R U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Station PI-137 Washington, DC 20555

References:

1. Docket No. 50 285
2. Generic letter (CL) 91-06 dated April 29, 1991 Gentlemen:

SVEJECT: Response to GL 91-06, " Adequacy of Safety-Related DC Power Supplies" As requested in Reference 2, the attachment to this letter provides the Omaha Public Power District (0 PPD) responses as required by GL 91-06.

This response is being submitted under oath in accordance with the requirements of GL 91-06.

If you should have any questions, please contact me.

Sincerely, i

l 1 W.G.

DivisionGates Ma ager [#.

Nuclear Operations WGG/sel Attachments c: LeBoeuf, Lamb, Leiby & MacRae R. D. Martin, NRC Regional Administrator, kegion IV W. C. Walker, NRC Project Manager R. P. Mullikin, NRC Senior Resident inspector

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UtilTED STATES Of t.MERICA NUCLEAR REGULATORY COMMISS10fl In the Matter of )

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Omaha Public Power District ) Docket No. 50-283 (Fort Calhoun Station )

Unit No. 1) )

eLElDM11 J. K. Gasper, being duly sworn, hereby deposes and says that he is the Acting Division Manager - Nuclear Operations of the Omaha Public Power District; that as such he is duly authorized to sign and file with the Nuclear Regulatory Commission the attached information concerning response to Generic letter 91 06; that he is familiar with the content thereof; and that the matters set forth therein are true and correct to the best of his knowledge, information, and belief.

./ G,H $$

y.K.'GasperActingnager Division Ma/

fluclear Operations STATE Of NEBRASKA)

) ss C00!1TY OF DOUGLAS)

Subscribed and sworn to before me, a Notary Public in and for the State of Nebraska on this afrs day of October, 1991.

Mdkn Notary Fublic GutiML 10RRT4 tate et Irketa

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i Attachment LIC-91-263R QuntinDLB Answers 10 Gl. 91-05

1. Unit <

Fort Calhoun Nuclear Station. License Number DPR-40. Docket 50-285.  !

2.a. The ntunber ofIndependent redundant divisions of Class IE or safety related DC power for this plant h . (include any separate Class IE or safety related DC, such as any DC dedicated to the diesel generators.)

The DC distri'vution systern is arranged into two independent and redundant (Class IIVSafety Related) 125 VI;C trains (divisions), with each train consisting of a 58 cell battery. dedicated battery charger, main distribution panel with protective devices and threa branch distribution panels with protective devices.

Additionally, a spare battery charg;r that is powered from the A train of 480-VAC is furnished which can be connected to either D" distribution train.

2.b. The number of functional safety related disislons of DC power necessary to attain safe shutdoun for this unit is .

One division of safety related DC power is required to attain safe shutdown.

The electrical system [ including Station 11atteries] equipment is arranged so that no single failure can render engineered safeguards totally inoperable tojeopardize the plant safety.

3. Does the control rootn at this unit have the following separate, independently annunciated alarms and Indications for each division of DC power?

3.a. Alarms 3.a.l. llattery disconnect or circuit breaker open?

No Two interrupting devices appear instream between the battery and the main 125 Vdc bus; a 1600 amp. Gould-Shawmut fuse, and an ITI! non-auto disconnect switch.

Neither the fuse nor the disconnect switch alarm the control room on an open circuit condition.

Attachment LIC-91-263R However, administrative controls have been implemented which directly prevent the inadvertent opening of the fuse (for other than fault clearing action or internal fuse failure)  !

or the disconnect switch. Specifically, the station tagging requirements mandated by Star. ling Order 0-20 disallow fuse removal and the opening / closing of switches or components without proper tagging and shift supervisor clearances which requires a review of conformance to technical specifications. Additionally, the disconnect switch is key-locked closed and the key is kept by the Shif t Supervisor as delineated by Operating Instruction OI-EE 3.

3.a.2. Ilattery charger disconnect or circuit breaker osa (both input AC and output DC)?

Yes 3.a.3.1C System Ground Yes 3.a.4. DC lius Undenoltage Yes 3.a.5. DC Ilus 05ervoltage?

Yes 3.a.6. Ilattery Charger Failure?

Yes

I Attachment LIC-91-263R 3.a.7. llattery Discharge?

An alarm fo.- battery discharge is not provided, licwever, each main DC bus is provided with an alarm for low voltage via abc connected battery charger. This low voltage alarm (which is connected to the output of the battery charger and is described in questions 3.a.2 and 3.a.4) has a setpoint of 125 VDC as verified by procedures EM-RR-EE-0810, CSI1, 0812 - Maintenance of Battery ,

Charger No.1, 2, and 3. Should a fault internal to the ~

battery (short between plates or terminals) occur requiring current from the charger in excess of what the charger is capable of supplying, the charger (and ultimately the DC bus) output voltage would drop from typical float output of 130 VDC to less than 125 VDC resulting in an alarm on A-15, CB-20.

Should a high impedance type fault internal to the battery occur, requiring currents capable of being supplied by the charger, detection would be via the monthly surveillance testing (Procedures EM-ST-EE-0001,0002). The monthly surveillance tests monitor those parameters identified in question 7.a, and provide trending data for individual cell voltages and battery charging currents. A variance in either of these parameters would initiate investigation and identification of the failure. .

3.b. h!dkatimts 3.b.l. llattery float charge current?

Yes 3.b.2. Battery circuit outpd curreut?

Yes 3.b.3. Battery discharge?

Yes

i Attachment LIC-91 263R 3.b.4. Ihis voltage?

Yes 3.c. Does the unit hase written procedures it response to the above alarms and indications?

Yes

4. Does this unit have indication of b 3passed and inoperable status of circuit breakers or other devices that can be used to disconnect the battery and battery charger from its DC bus and the battery charger from its AC power source during maintenance or testing?

No.

Control and status are maintained administratively as discussed below:

+ As described in question 3.a.1, neither the 1600 amp fuse nor the battery disconnect switch (DC-B1 for battery 1, DC-B2 for battery 2) alarm in the control roorn when opened. Since the k> cal and control room panels (Al-41 A & B) battery voltmeters and ammeters are located downstream of the fuse, indication could identify a disconnected fuse, it should be noted, however, that maintenance procedures specify the opening of a disconnect switch to isolate the battery from the bus.

+ Since the control room has no alarm or indication of an open battery disconnect switch (DC-BI, DC-B2), procedural controls have been implemented for test / maintenance activities which require the switch to be opened, in addition to the tagging requirements highlighted in question 3.a.1 and the key-lock control highlighted in the answer to question 3.a.1, applicable test and maintenance procedures require caution tags to be hung on the control switches for all 4160 Volt feeder circuits and emergency diesel generator associated with the train of battery taken out of service.

These tags provide the necessary indication to the control room that the battery has been removed from service.

+ As discussed in question 3.a.2, control room alarms are provided for the battery chargers when they are disconnected from the 125 Vdc bus or from the AC power source. When a charger is removed from the bus for testing and/or maintenance, the spare charger (Battery Charger No. 3) is placed on the bus as required by the testing and maintenance procedure.

Attachment LIC-91-263R in summary, the control room das have indication of bypassed and inoperable status of battery (by way of administrative control), and battery charger disconnect devices.

5. 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.

Justifications are provided with the questions as applicable.

6. (1) llave you conducted a review of maintenance and testing activities to minimize the potential for human error causing more than one DC division to be unavailable? J) Do plant procedures prohibit mnintenance or testing on redundant DC divisions at the same time?

Yes (1) Safety-related maintenance and testing procedures, including those procedures specifically related to the DC system, have undergone a procedure upgrade process in accordance with S0-G-73 Station Writers Guide. S0-G-73 was written as a guideline for procedure writers regarding matters such as content, format, human factors considerations, composition, and vocabulary in accordance with Regulatory Guide 1.33, and INPO Good Practice 85-026.

All upgraded procedures were evaluated for safety impact / significance among other requirements. All procedures were technically verified and validated for accuracy and useability. Maintenance and testing activities identify and adhere to the applicable Tech Specs for the activity, and require Operations (specifically, the Shift Supervisor) concurrence and approval of the activity prior to performance. Through this interactive upgrade process, potential for human error causing more than one DC division to be unavailable ha; been minimized, with the Shift Supervisor providing the fmal layer of defense in terms of compliance with the Tech Specs and safety impact.

(2) Yes. See response to previous question.

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

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l Attachment 1.lC-91-263R 7.a. At least once per 7 days are the following verlfled to be within acceptable limits:

1. Pilot cell electrolyte level?
2. Specific gravity or charging current?
3. Float voltage?
4. Total bus voltage on float charge?
5. Physical condition of all cells?

No.

The above 5 parameters are not measured and evaluated on a weekly basis, rather, they are documented on a monthly basis via surveillance tests EM ST-EE-0001 (battery No.1), and EM ST-EE-002 (battery No. 2). Fort Calhoun Station Technical Specifications require the above 5 parameters to be measured and evaluated once per month for each battery, which is in agreement with the manufacturer's recommended periodicity, as well as the recommendations satted by IEEE-450-1987, paragraph 4.3.1.

The monthly surveillance procedures include the following verifications:

1. Float terminal voltage (bus).
2. Battery charging current.
3. Individual cell voltages (all cells).
4. Individual cell electrolyte temperatures (all cells),
5. Electrolyte levels (all cells).
6. Specific gravity of pilot cells.
7. Visual inspections of all cells.

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Attachment LIC-91-263R 7.b. At least once per 92 da3s, 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 verilled to be within acceptable limits:

1. Electrolyte level of each cell?
2. The average specific gravity of all cells?
3. The specific gruity of each cell?
4. The average electrolyte temperature of a representative number of cells?
5. The float voltage of each cell?
6. Visually inspect or measure resistance of terminals and connectors (including the connects at tiie de bus)?

Yes 7.c. At least every 18 months are the following verified:

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

Yes 7.c.2. Physical condition of the battery?

Ycs 7.c.3. Ilattery charger capability to deliver rated ampere output to the DC bus? 3 No There currently are no procedures or requirements for testing the battery chargers to rated output current. Open Item #20, SDBD-EE-202, regarding battery charger rated output testing was initiated during the FCS Design Ilasis Reconstitution. The open item is classified as a Category 3 item. Category 3 items address safety-related equipment or components that do not perform an active function in satisfying plant system operational requirements as specified in the Technical Specifications, and do not meet the reportability criteria Category 3 open items have a commitment to be resolved after category 1 and 2 resolutions, which are currently in progress.

I Attachment LIC-91-263R However, i a battery equ;dizing charge performed annually by procedure Eht-ET-EE-0901, output currents from the charger can be adjusted as high as 300 amperes.

As the battery charges, the charging current drops and output voltage is regulated accordingly. Also, during battery capacity discharge tests, Procedures Eht-ST-EE-0005 (Battery No.1) and Eht-ST-EE-0006 (llattery No. 2),

charger outputs to recharge the battery are adjusted to 190-200 amperes. Although the chargers are not periodically tested to rated capability (400 Amperes), the annual requirement for the chargers to provide as much as 300 Amperes during an equalizing charge provides adequate assurance that they can perform their intended design function.

The load drawn from the battery chargers by the 125 VDC buses during normal plant operations is typically 150 amperes. Approximately 40+ amperes of spare charger capacity for float charge and transients during normal plant operations are considered adequate.

7.c.4. The capability of the battery to delivery its design duty cycle to the DC bus?

Yes 7.c.5. Each individual cell voltage is within acceptable limits duriag the service test?

Yes 7.d. At least every 60 months, is capacity of each battery verified by performance of a discharge test?

Yes 7.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?

Yes

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Attachment LIC-91-263R 1 Capacity tests are performed every 54 months. The results of these capacity tests are reviewed by engineering, and forwarded to j the battery manufacturer for review. Should these capacity tests ever indicate a degradation of battery capacity and service life of 85 % expected, an engineering analysis would be performed based -j on the recommendations of IEEE-450, and the battery manufacturer. This analysis would adjust the capacity testing schedule accordingly.

8. Does this plant have operational features such that following loss of one safety-related de power supply or bus:
a. Capability is maintained for ensuring continued and adequate reactor cooling?

Yes i l

b. Reactor coolant systern integrity and isolation capability are maintained?

Yes

c. Operating procedures, lustrumentation (including indicators and annunciators), and control functions are adequate to initiate systems as required to msniain adequate core cooling?

Yes

9. If the answer to any part of question 6,7 or 8 is no, then piovide your basis . for not performing the maintenance, surveillance and test ,

-procedures described and/or the bases for not including the operational features ched.

Justifications are included with the questions as applicable.

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