ML20101B087

Revises 920129 Response to Generic Ltr 91-11, Resolution of Generic Issues 48, 'Lcos for Class 1E Vital Instrument Buses' & 49, 'Interlocks & LCOs for Class 1E Tie Breakers.'

ML20101B087
Person / Time
Site:	Prairie Island
Issue date:	05/01/1992
From:	Parker T NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-GTECI-048, REF-GTECI-049, REF-GTECI-NI, TASK-048, TASK-049, TASK-48, TASK-49, TASK-OR GL-91-11, NUDOCS 9205050316
Download: ML20101B087 (5)

Text

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Northem States Power Company 414 Nicollet Mall Minneapolis, Minnesota 55401-1927 Telephone (612) 330-5500 May 1, 1992 10 CFR Part 50 Section 50.54(f)

U S Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PLGT Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 1

! Revised Response to Generic Letter 91-11 " Resolution of Generic Issues 48, 'LCOs for Class 1E Vital Instrument Buses', and 49, ' Interlocks and LCOs for Class 1E Tie Breakers' Pursuant to 10 CFR 50.54(f)"

Refennee : Letter from Thomas M Parker, Northern States Power, to U S Nuclear Regulatory Commission dated January 29, 1992 titled " Response to Generic Letter 91-11, ' Resolution of Generic Issues 48, "LCOs for Class lE Vital Instrument Buses", and 49, " Interlocks and LCOs for Class 1E Tie Brtaxers' Pursuant tc 10 CFR 50.54(f)'"

This letter provides a revised response to Generic Letter 91-11, " Resolution of Generic Issues 48, 'LCOs for Class 1E Vital Instrument Buses', and 49,

' Interlocks and LCOs for Class lE Tie Breakers' Pursuant to 10 CFR 50.54(f)".

Questions from Mr Om Chopra of the NRC staff have prompted us to revise our I response for clarity.

As recommended by Enclosure 1 to the Generic Letter, a review was conducted of the Prairie Island Nuclear Generating Plant vital instrument buses, their power supplies, and'their associated procedures and instructions. A revised summary of the results of this review is provided as Attachment 1 to this le tt er.

Please contact us if you have ny questions related to our response.

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• thomas M Parker

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Manager Nuclear Support Servicer l

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1 Ie Northern States Power Company

. -U $ NRC May 1, 1992 Page-2 of 2 l c: Regional Adininistrator - Region III, NRC Senior Resident Inspector, NRC I NRR Project Manager, NRC J E Silberg At tachraents : Affidavit: to the US Nuclear Regulatory Commission Attachrnent 1 - Generic Letter 91-11 Response

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UNITED STATES NUCLEAR REGUIATORY COMMISSION

- NORTHERN STATES P0fJER COMPANY PRAIRIE ISLAND NUG?IAR GENERATING PIANT DOCKET NO. 50-282

.50-306 Revised Response to Generic Letter 91 11, " Resolution of Generic Issues-48, 'LCOs for Class 1E Vital Instrument Buses', anc' 49, ' Interlocks

-and LCOs for Class lE Tie Breakers' Pursuant to:10 CFR 50.54(f)"

-Northern States Power Company, a Minnesota corporation, with this letter is submitting information requested by NRC Generic Letter 91-11.

This-letter contains no restricted or other defense information.

NORTHERN S ATES VER' COMPANY

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/ 2s By # Diomas M Parker Manager -Nuclear Support Services On this day of .

M h efore me a notary public in and for_said County,; personally'appe y d Thomas M Parker, Manager, Nuclear Support Services,-and being'first duly sworn acknowledged that he is authorized to ey.ecute this document on behalf of Northern States-Power Company, that he' knows the contents 1 thereof, and that to the best of his knowledge, information, and' belief the statements made in it are true and that it is not -

interposed-for. delay.

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_@ WARCIA K bCORE NOTARY PUBUC-MINNESOTA HENNEPIN COUNTY My Commesion bpues Sept 24,1993 g h_

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- Attachment 1 RESPONSE TO NRC GENERIC LETTER 91-11 The -results of our review of the recommendations contained in Enclosure 1 to Generic Letter 91-11'are sammarized below:

Generic ^ Letter 91-11 Recommended Action Ensure that your plant has procedures that include time limitations and surveillance requirements for:

1. Vital instrument huses (typically 120V ac buses),

Results of Review:

a. Time Limitations - Prairie Island Tech Specs allow r.a more than one vital instrument bus to be powered by an alternate source or its associated instrument inverter bypass source.

b. Surveillance Requirements - Weekly surveillance procedures have been-implemented- to verify the operability and correct configuration of _ the vital instrument buses.

2. Inverters or other onsite power sources to the vital instrument buses, and Eggqlts of Review:

a. Time Limitations - New adminstrative controls limit the maximum time an instrument inverter should be out of service (while the associated unit is above cold shutdown) to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Only one instrument inverter should be out of' service at a time, ^

cecend byt}opy pypyQ$fyinverter_upplyingavitalinstrumentbusmaybepowered from an inverter bypass source for 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.

b'. Surveillance Requirements - Weekly surveillance procedures have been L , implemented to verify the operability and correct configuration of the i

inverters and instrument buses.

3. Tie breakers that can connect redundanc class 1E buses at one unit or that can connect class IE buses between units at the same site.

Results of Review:

I L 120VAC and DC Hpses The 120VAC at.d DC buses at Prairie Island are not configured with bus ties.

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480V Busea li L Bus ties at-the 480V lovel are between the opposite trains of the same l unit and normally only used during cold shutdown. ,

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• At tactwent 1 May 1,1W2 Page 2 of 2 The 480VAC bus ties will be eliminated when the Station Black Out /

Electrical Safeguards Upgrade (SB0/ESU) modification is complete inL1994.

a. Time Limitations - Prairie Island administrative controls specifies an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> limit on 480V bus tio closed time when the unit is above 200*F.

b. Surveillance Requirements Weekly surveillance procedures have been implemented to ensure correct breaker alignment and indicated voltage on the 480V buses.

Other 480V Concerns Group B pressurizer heaters' sources are switchable between a safeguards bus and a non-safeguards bus, Procedure C20.6 requires both breakers -il supplying the group B pressurize

• heaters be opened before a transfer is made. Therefore, the transfer of the heaters is an administrative break-before-make transfer.

The supply breakers to motor control centers IT1-and IT2 can be switched  !

from one unit to the other. These breakers are interlocked to only allow a break before make transfer. The break-before-make configuration prevents these load breakers from becoming a bus tie.

4.16 KV Buses 4.16 KV bus ties exist between the same trains of the opposite units and are used in the automatic voltage rastoration scheme. This conf _guration has been evaltated by the Updated Safety Analysis Report section 8.3 which states that "In the extremely _ remote case of a bus tie breaker failure resulting in loss of the two associated buses, the engineered safety features on the remaining buses are sufficient for safe shutdown of either unit. " - - ThisisdnfiguistiloiG1FTptFssiitiffneEsisiiff7hodsiidVtEEFe EafsTiSnis twf6dstje h6%fdie seliSe66r$tdrs$hibhlafe f shared ibitweSts Nhel t061 uhits$j

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a. Time Limitations - There are no time limitations per the Updated Safety Analysis Report discussion reference above.

' b. Surveillance Requirements - Weekly surveillance procedures will be implemented _by April 30, 1992. to ensure-correct breaker alignment and indicated voltage on the 4.16 KV buses.

Af ter the SB0/ESU modification ((which] adds [.tQofs;ddi.tionh1[tijaFrgsncy[diessl gebergtorsJ, the 4.16 KV bus ties will be manually operated only (no longer closed as part of the voltage restoration scheme), and under-adminiscrative control. In addition, there will be two breakers per bus tie.

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