ML20082R756

Ro:On 831015-16,standby Bus 2 Deenergized to Verify Emergency Power Path & CT-3 Startup Transformer Locked Out. Caused by Failure of Two Insulators Causing Short to Ground. Info Supersedes 831101 Rept

ML20082R756
Person / Time
Site:	Oconee
Issue date:	12/02/1983
From:	Tucker H DUKE POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
NUDOCS 8312130288
Download: ML20082R756 (3)

Text

.. ,t e.

DuxE PowEn GOMPANY P.O. BOX 33180 CHARLOTTE, N.C. 28242 HAL B. TUCKER TELEPHONE vwa essesman (704) 373-4531

= = = = - December 2, 1983

-Mr. James P. O'Reilly, Regional Administrator U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30303

~Re: Oconee Nuclear, tion Docket Nos. 5 269 -270, -287

Dear Mr. O'Reilly:

By my letter dated November 1,1983, you were sent a Special 5-Day Report concerning the deenergization of one of Oconee's standby buses to allow for operability verification of the underground emergency power path, with Keowee Unit 1 out of service. Please find attached a Special 5-Day Report which supersedes the Special 5-Day Report provided by my November 1, 1983 letter. The attached report is submitted pursuant to Oconee Nuclear Station

. Technical Specification 3.7.9 and describes an incident which is considered to be of no significance with respect to its effect on the health and safety of the public.

Very truly yours, O& VM Hal B. Tucker PFG/php Attachment cc: Document Control Desk U. S. Nuclear Regulatory Commission l Washington, D. C. 20555 INPO Records Center Suite 1500 1100 Circle 75 Parkway Atlanta, Georgia 30339 Mr. J. C. Bryant OFFICI AL COPY NRC Resident inspector J, b g

~

Oconee Nuclear Station Mr. John F. Suermann fj i

! Office of Nuclear Reactor Regulation [

!- U. S. Nuclear Regulatory Commission Washington, D. C. 20555 8312130288 831202

PDR ADOCK 05000269 i S PDR l'

JP0/HBT/PFG

• December 2, 1983 Duke Power Company Oconee Nuclear Station Special Report Deenergization of Oconee Standby Bus 2 to Allow for Operability Verification of the Underground Emergency Power Path While Keowee Unit 1 Was Out of Service On October 15 and 16, 1983, with Keowee Unit 1 out of service for planned maintenance and Keowee Unit 2 available, Lee "6C" Gas Turbine was being used to energize both Oconee 4160V Standby Buses as required by Technical Specifica-tion 3.7.4. At 1449 and 2156 hours0.025 days <br />0.599 hours <br />0.00356 weeks <br />8.20358e-4 months <br /> on October 15, and 0545 hours0.00631 days <br />0.151 hours <br />9.011243e-4 weeks <br />2.073725e-4 months <br /> on October 16, Standby Bus 2 was deenergized to allow operability verification of the under-ground emergency power path in accordance with Technical Specification 3.7.2.

-At 1349 hours0.0156 days <br />0.375 hours <br />0.00223 weeks <br />5.132945e-4 months <br /> on October 15, 1983 CT-3 (Unit 3 Startup Transformer) underwent a lockout as a result of an electrical ground fault. This made the overhead emergency power path from Keowee to Unit 3 unavailable. At the time of the incident Keowee Unit 1 had been unavailable for greater than 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> for maintenance. (Technical Specification 3.7.4 applicable), oconee Unit 3 was at 100% full power, and CT-3 was not in use. This incident is reportable to the Nuclear Regulatory Commission in accordance with Technical Specification 3.7.9 because Unit 3 was operating in a degraded mode beyond that allowed by Technical Specification 3.7.4 (c) . Technical Specification 3.7.4(c) requires the overhead emergency power path to be available even though it cannot be automatically energized because the remaining operable Keowee unit is already connected to the underground emergency power path.

The apparent cause of the CT-3 lockout was the failure of two insulators which caused a short to ground. .The location of these insulators prohibited the use of CT-2 (Unit 2 Startup Transformer) as a backup power source to the Unit 3 4160 volt Main Feeder Buses. Since the 6900 volt bus on Unit 3 was undamaged, a backup power source to the Unit 3 Reactor Coolant Pump motors was provided via connection to CT-2.

At 1430 hours0.0166 days <br />0.397 hours <br />0.00236 weeks <br />5.44115e-4 months <br /> Operations verified operable the underground emergency power path by starting Keowee Unit 2 and energizing CT-4 (Standby Transformer from Keowee). A Compliance Section representative was notified of the incident and conservatively determined that the requirements of Technical Specification 3.7.2(a) should be followed. This required the entire underground emergency power path including one standby bus to be energized from the operable Keowee unit within one hour and every eight hours thereafter. This required that the chosen standby bus would first have to be deenergized from a Lee gas turbine placing the operating Oconee units (Unit 1 and Unit 3) in a degraded mode of operation beyond that allowed by Technical Specification 3.7.4(a). Therefore, a safety evaluation as required by Technical Specification 3.7.9 was performed and determined that a shutdown or power reduction of the operating Oconee units was not necessary since power would always be available from several sources.

These sources included the following:

..: .,y

- .- JPO/HBT/PFG Decetbar 2, 1983

~

-1., Auxiliary Transformer on operating units c2. Off-site power via Startup Transformers (not available to Unit 3)

3. Lee gas turbine via Standby Busl#1

.4. Lde gas _ turbine via Standby Bus #2 '(except for 'during power path verification)

--5. JKeowee~ Unit 2 via underground emergency power path

6. Keowee Unit 2 via overhead emergency power path (not available to Unit 3)

Standby Bus' #2 was intentionally deenergized from Lee at- 1449 and 2156 hours0.025 days <br />0.599 hours <br />0.00356 weeks <br />8.20358e-4 months <br /> on October 15, 1983'and at 0545 hours0.00631 days <br />0.151 hours <br />9.011243e-4 weeks <br />2.073725e-4 months <br /> on October: 16, 1983. The total time that

=the bus was not energized by a Lee gas turbine was less than 4 minutes. The bad insulators were-replaced and CT-3 was returned to operable status at 2335 hours0.027 days <br />0.649 hours <br />0.00386 weeks <br />8.884675e-4 months <br /> on October 16, 1983.

.In summary, this report covers two incidents that are reportable in accordance with. Technical Specification 3.7.9.. The first was the loss of.the overhead emergency power path to Unit 3 which placed Unit 3 in a degraded mode beyond that allowed by _ Technical Specification 3.7.4(c) for nearly 34 hours3.935185e-4 days <br />0.00944 hours <br />5.621693e-5 weeks <br />1.2937e-5 months <br />. The second was-the_deenergization of Standby Bus #2 from Lee three times which' placed Unit 1 and Unit 3 in a degraded mode beyond that allowed by Technical

-Specification 3.7.4(a) for less than 4 minutes. These incidents are considered

~

to be of no significance with respect to their effect on the health and safety Jof the public since several sources of power were always~available.