ML20058H358

Special Rept:On 901010,diesel Generator (DG) 2B Tripped W/No Alarms Due to Water Leakage Into Control Panel,Causing Short Circuit.On 901011,DG 2B Tripped Due to Lightning Strike

ML20058H358
Person / Time
Site:	Mcguire
Issue date:	11/09/1990
From:	Tuckman M DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9011150206
Download: ML20058H358 (2)

Text

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Duke her Crimporry (TNtt13 4011

, Nuclear Pn.dvawn Department TO Bm- litoi

• Chiiriotte, NC 2k:01-Mii DUKE POWER

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November 9, 1990 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555

Subject:

McGuire Nuclear Station, Unit 2 Docket Number 50-370 Diesel Generator Failure Special Report Attached is a Special Report, as required by "'ochnical Specifications '

4.8.1.1.3 and 6.9.2, regarding a valid failure of diesel generator 2B at McGuiro Nuclear Station.

If you require any additional information, please call Scott Gewehr at (704) 373-7581.

Very truly yours, p

p,v,'[L J o

M. S. Tuckman, Vice President Nuclear Operations SAG /242/1cs xc Mr.'S, D. Ebneter, Regional Administrator U. S. Nuclear Regulatory Commission Region II. 101 Marietta St., NW, Suite 2900 Atlanta, Georgia 30329 Mr. Tim Reed, Project Manager Office of Nuclear Reactor Regulation U. S Nuclear Regulatory Commission One White Flint North, Mail Stop 9H3 Washington, D.C. 20555 Mr. P. K. Vanboorn NRC Resident Inspector McGuire Nuclear Station 901115020 {$},l(47g PDR ADO PDC S . .y f622

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DUKE POWER COMPANY McGUIRE NUCLEAR STATION Diesel Generator Special Report On October 10, 1990 at 1652, diesel generator (DG) 2B was started (attempt No. 851) to perform the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> run surveillance test. Unit 2 was in No Mode. Two hours and 30 minutes into the run, DG 2B tripped with no alarms.

At the time of the trip, water was observed Acaking into the DG control panel. The water was due to a heavy rain storm and entered the DG room by being sucked into the intake air plenum. The leakage occurred around the plenum drain connection which was fastened by rivets but was not water tight. The control panel doors had previously been removed for case of testing and troubleshooting during the post DG outage runs. Watered splattered octo electrical components through the door opening and a small amount 1 caked in through the top of the control panel. It is thought that the water led to a short circuit which caused the trip. Since the actus1 contact that opened up in the start circuit. to cause the trip could not be ident.lfied, this start is conservatively classified as a VALID FAILURE.

This was the first Valid Failure in the last 20 Valid Tests and the 9th Valid Failure in the last 100 Valid Tests for DG 2B. On a unit basis, this is the 6th Valid Failure in the last 100 Valid Tests of DG 2A and 2B combined. Surveillance testing remains on a weekly frequency.

Work Request No. 143291 was initiated to investigate the failure. The control panel was covered with plastic to prevent further water entry, dried, the top of the panel scaled and door put in place. The entire start circuit was checked at about 0900 on October 11, 1990.- No evidence as to which relay and contact.. caused the f ailure could be found. Start No. 852 at 1101 on October 11, 1990 was successful. Work Request No. 89415 was initiated to seal the plenum drain connection and SPR No. 3776 was written and approved to modify the roof ~ drainage such that water will not be sucked into the plenum while t.he IX) is running (this modification will apply to all HNS DGs).

On October 11, 1990 at 2130, DG 2B was again started to perform the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> run surveillance test (Attempt No. 853). Heavy lightning was noted in the area and at 1125 on October 12, 1990 the DG breaker tripped due to a lightning st.rike that ran into t.he 4160V switchgear and picked up relay 50 DGT (overcurrent). This condition would not have occurred during emergency operation because the DG would not have been tied to the utility grid

-(i.e., the incoming breaker to the 4160V switchgear would be open). Also, relay 50 DGT is bypassed during emergency operation. Therefore, this start is classifled as an INVALID TEST FAILURE. The failure statistics remain the same as discussed previously. Unit 2 was in No Mode at. the time of this failure. Relay-50 DGT was reset. Start No. 654 was made at 1505 on October 12, 1990. This was a Valid success. No further action is planr.id.

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