ML20092A694

Forwards 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.'

ML20092A694
Person / Time
Site:	Fort Calhoun
Issue date:	02/03/1992
From:	Gates W OMAHA PUBLIC POWER DISTRICT
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, LIC-92-013R, LIC-92-13R, NUDOCS 9202100241
Download: ML20092A694 (6)

Text

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+ e Omaha Public Power District 441 South 1 tit 4 Strert M311 Ornaha. Nesta$a (6102 2247 3 1992 40# **

februarbl3k LIC 92-U. S. Nuclear Regulatory Commission A11N: Document Control Desk Mail Station Pl-137 Washington, DC 20555

References:

1. Do(ket No. 50 285

2. Letter from NRC (J. G. Partlow) dated July 18, 1991 (Generic Letter 91-11)

Gentiemen:

SUBJEC1: Response to Generic Letter 91-11 Attached is the Omaha Public Power District (d under oath in response to theOPPD) respon (GL) 91-11. lhis document is being submitte requirements of GL 91-11.

The two issues which GL 91 11 address are as follows:

1. Generic issue 48 LCOs for Class lE Vital Instrument Buses

2. Generic lesue 49 Interlocks and LCOs far Class lE Tie Breakers As shown in the attachment, OPPD meets the requirements of GL 91-11 through existing design features, procedures and the Technical Specifici.tions.

If you should have any questions, please contact I c Sincerely, 4(/,A5 A 'N W. G. Gates Division Manager Nuclear Operations WGG/sel Attachment c: LeBoeuf, Lamb, teiby & MacRae R. D. Martin, NRC Regional Administrator, Region IV D. L. Wigginton, NRC Senior Project Manager R. P. Mullikin, NRC Senior Resident inspector S. D, Bloom NRC Project Engineer 9202100241 920203 //

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UN11[D STATES Of AMERICA NVCLEAR REGULA10RY COMMISSION in the Matter of ;l i

Omaha Public Power District h Docket No. 50 205 i

.(fortCalhounStation S Unit No. 1) )

AfflDAV11 W. G. Gates, being duly sworn, hereby deposes and says that he is the 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 the response to Generic Letter 9111 dated february 3 *192 concerning Generic issues 48 and 49; that he is familiar with the content thereof t and that the matters set forth therein are true and correct to the best of his knowledge, information, and belief, i

AV. /l. /h4*

W. G. Gates Division Manager Nuclear Operations STATE OF NEBRASKA ss COUNTY OF DOUGLAS Subscribed and sworn to before rge, a Notary Public in and for the State of Nebraska on this h L day of 4 2 [ w e( , 1992.

(l L:/~ Notary A&m Publ

....-a J T GLEASON d h tema tsa.My M laN

r T At t achmer.t t.lC-92 013R page 1 ESf0ME 10 GIEMC LET1FR 91-J1 A simplified one-line electrical distribution diagram for fort Calhoun Station (FCS) is provided as figure 1 of this tachment for reference.

GtuttiL11ML46 Generic issue 48 concerns administrative controls governing operational restrictions for Class lE,120 volt AC vital instrument buses and associated inverters. Fort Calhoun Station TCS instrument buses normally fed by a (dedi)cated instrument inverter for each bus. utilizes four Each of the four buses has an alternate power source supplied by a " bypass transformer" which is fed from the 480 VAC safety related buses. Control Room annunciation is , rovided when the instrument bus is fed from the alternate source.

Generic issue 48 discusses ensuring that plant procedures include time limitations and surveillance requirements for vital instrument buses and inverters. At fort Calhoun Station, the possibilities for abnormal alignment are as follows:

o Vital inst rument bus fed from the alternate supply (bypass transformer) o One inverter and bypass transformer out of service and the associated instrument bus crosstied to another instrument bus in the same electrical division is in both of invoked whichthese abnormal states 'One ofalignments, the four a c Technical instrument Specification buses may be 2.7(2)b(3) inopera le for 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> 3rovided tbe reactor protective and engineered safeguards systems instrumen; channels supplied by the remaining three buses are all operable". In the event the instrument bus is not returned to the normal cor. figuration within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> Technical Specification 2.7(2) requires that the reactor must be placed in a ho,t shutdown condition within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and if normal alignment is not met within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, the reactor must be placed in a cold shutdown condition within an additional 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Therefore, the requirements of the Technical Specifications provide adequate guidance to ensure that appropriate time limitations exist- for the vital instrument buses. In the event that abnormal alignment of the vital instrument buses is necessary for maintenance activities, provides the necessary procedure surveillance01-EE-4, "120 Volt requirements AC System to ensure Normal Operation"d all tie breakers an switching are returned to the correct, normal alignment, t -

1 Attachment LIC 92-013R

-Page 2 During outage conditans, when the neactor Coolant System is maintained below 300 degrees f, abnormal vital instrument bus alignment is allowed. When returning the station to power operation, and before exceeding 300 degrees f in the Reactor Coolant System, start up checklists are performed which provide the necessary verification of the tie breakers and switchesProcedure to ensure OP the 1, vital 'Haster instrument Checklist buses are aligned to their normal position.

for Start-up or Trip Recovery" requires the >erformance of the check lists contained in procedure Ol fE 4. Based on tie ICS Technical Specification .

I requirements and procedural guidance noted above, Generic Issue 48 is satisfied for FCS.

Asneric_blu1LH The concern of Generic issue 49 is that manually actuated tie breakers which can connect normally independent redundant Class 10 AC or DC buses could be inadvertently left closed and, compromise the independence of the buses.

The fort Calhoun Station safety related ele:trical system configuration is:

o Two safety related 4160 volt buses, lA3 and 1A4, and two non safety related 4160 volt buses, lAl and 1 A2. Buses IAI and 1A2 are normally fed from the 22 KV system and buses lA3 and 1A4 are normally fed from 161 KV off site power. Each of these buses have electrical Interlocks that ensures the redundant, Class IE buses cannot be connected outside the design basis for fort Calhoun Station, which meets the intent of GL 91 11.

o Nine 480 volt safety related buses consisting of two divisions fed from the 4160 volt buses. lA3 and 1A4. These buses are IB3A, IB4A, IB3A 4A (island bus that can be fed from either IB3A p.t IB4A but electrically interlocked so that the independent 4160 volt buses 1038, 1B48, 1838 4B island bus that can be fed cannot be crosstied),184B, from either 1830 9,t but electricall(y interlocked 50 that the independent 4160 volt buses cannot be crosstied),183C,184C, and  !

1830-4C (island bus that can be fed from either 183C g_t 1B40 but electrically interlocked so that the independent 4160 volt buses cannot be crosstied),

o Two-12S VDC safety related buses, EE 8f and CE 8G.

The 4160 volt buses may all be fed from either the 161kV off-site power :.ystem or the Station 22 KV system. However, automatic interlocks are provided that isolate the buses in the event of a loss of off-site power and ensure that diesel generator DG-1 feeds only bus lA3 and diesel generator DG-2 feeds only bus lA4.

Therefore, the separation criteria is maintained. Surveillance of these breakers is provided by indication and annunciation in the Control Room. The automatic operation of the system, regardless of alignment, assures t,us separation in the event of a loss of off-site power (both the 161kV and the 345kV systcms).

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Attachment

-LIC 92 013R Page 3 i The 480 volt buses are interlocked in such a manner that divisional separation at the 4160 volt level is maintained, i.e., it is not possible to connect (

redundant 480 volt buses to both 4160 volt divisions at the same timn. In the event an island bus is altaned in any manner other than normal procedure 01-[E+2, '480 Volt AC System iformal Operation', procedure OI EE 2B, 'd80 Volt Hot Bus Transfers', and Abnormal Operating Procedure A0p 32, " Loss of 4160 Volt or re 480 Volt Bus requires plantPower"down.

shut quireprovides This entry intothe Technical Specification time limit required by2.0.1, which GL 91-11.

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lhese buses and associated tie breakers are properly lined up arior to start up using the guidance contained in procedure OP 1, " Master Check List for Start up i

or Trip Recovery". This, coupled with the procedural guidance stated above on returning an abnormal lineup to normal, provides the necessary surveillance for the 480 volt system required by Generic issue 49.

The 125 volt DC buses are supplied with one tie breaker for each bus which allows a swing battery charger to be placed on either bus, The tie breakers are interlocked with a Kirk Key operated mechanical system that-allows only one of the breakers to be closed at a time. Therefore, the two 125 volt DC buses cannot be tied together without violating the interlock. Because of this design feature, no time limit specification is required. Proper lineup of the system is assured prior to returning the plant to operation by the requirements of procedure 0)-1, " Master Check list for Start up or 1 rip Recovery". lhis procedure provides adequate surveillance of the 125 VDC system.

Based on the above noted design features, Technical Specification requirements, and procedures, Generic Issue 49 is satisfied for FCS.

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