ML20150D348

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Forwards LER 78-031/03L-0
ML20150D348
Person / Time
Site: Cooper Entergy icon.png
Issue date: 09/28/1978
From: Lessor L
NEBRASKA PUBLIC POWER DISTRICT
To: Seyfrit K
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20150D351 List:
References
NUDOCS 7812050166
Download: ML20150D348 (2)


Text

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COOPER NUCLEAR ST ATioN P.o. DoX 98, D ROWN VILLE, NE BR ASKA 68 321

_ Nebraska Publ=c Power D. tr ct i is i ret o ~oNe s u m s.u n a; u n=ma= = == = .= == - -- == - -- - -. - - -

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tember 28, 1978 Mr. K. V. Seyfrit U.S. Nuclear Regulatory Commission Of fice of Inspection and Enforcement Region IV 611 Ryan Plaza Suite 1000 Arlington, Texas 76011

Dear Sir:

This report is submitted in accordance with Section 6.7.2.B.2 of the Technical Specifications for Cooper Nuclear Station and discusses a reportable occurrence that was discovered on September 12, 1978. A licensee eve.: report form is also enclosed.

Report No.: 50-298-78-31 Report Date: September 28, 1978 Occurrence Date: September 12, 1978 Facility: Cooper Nuclear Station Brownville, Nebraska 68321 Identification of Occurrence:

A condition which resulted in operation in a degraded mode per-mitted by a limiting condition for operation established in Section 3.9.B.3 of the Technical Specifications.

Conditions Prior to Occurrence:

The reactor power was at steady state at approximately 84% of rated thermal power.

Description of Occurrence:

During performance of Surveillance Procedure 6.3.12.1, diesel generator number 2 tripped apor ximately one minute af ter reaching rated speed.

Designation of Apparent Cause of Occurrence:

The diesel generator trip was initiated by the bearing detector which sensed high temperature in the number 10 main crankshaft bearing.

4 78120501GG 9l J l

Mr. K. V. Seyfrit September 28, 1978 Page 2.

Analysis'of Occurrence:

The diesel generator is equipped with numerous protective devices.

Among them are temperature detectors on the main bearings. During normal operating conditions and surveillance tests any of these detectors can initiate a trip if a bearing temperature increases above a safe level. The subject temperature detector sensed a high temperature and initiated a diesel generator trip. During emerg-ency conditions the tripping due to bearing high temperature is locked out. The main bearing number 10 apparently became hot due to minimum oil flow and/or foreign material in the lube oil. Upon bearing removal, indications of unusual wear and rubbing were noted. It is believed that a minimal oil flow may occur at the number 10 bearing af ter the engine is tripped during engine coast-down. Secondly, there was some evidence of bearing damage which could have been caused by foreign material. The lube oil is routinely sampled on a quarterly frequency and a review of the records indicated that all previous samples on DG #1 and 2 had'been satisfactory. This occurrence presented no adverse consequences with respect to public health and safety.

Corrective Action:

Following the trip of DG #2, DG #1 was demonstrated operable in accordance with Surveillance Procedure 6.3.12.1 and no abnormal parameters were noted. The number 10 main bearing was removed and the crankshaf t jour. sal was inspected and verified to be undamaged.

A new main bearing was installed. Proper bearing clearance and oil flow were verified. Procedures 6.3.12.1 and 2.2.20 have been revised to specify manual operation of the electric lube oil pump prior to and after engine operation. All oil was removed from the crankcase and the crankcase was cleaned and refilled with clean oil.

DG #1 is scheduled for annual inspection in October and the crank-case will be c1 caned and refilled with new oil. In addition, bearing oil flow will be verified.

Sincerely, e

L. C. Lessor Station Superintendent Cooper Nuclear Station LCL:cg Attach.

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