ML20004C348

Forwards LER 81-004/03L-0

ML20004C348
Person / Time
Site:	Cooper
Issue date:	04/02/1981
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20004C349	List: ML20004C348 ML20004C350
References
CNSS810165, NUDOCS 8106030228
Download: ML20004C348 (3)

Text

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F COOPER NUCLEAR STATaoN l

( Nebraska Public Power District " * ?'A*E,2WM;"'s'."M"

" I CNSS810165 Dh

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\[J 4* Q0 ml a-Mr. K. V. Seyfrit, Director .'yA U.S. Nuclear Regulatory Commission \ , ., '/

Office of Inspection and Enforcement d

Region IV I3 611 Ryan Plaza Drive 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 tht.c was discovered on March 6, 1981. A licensee event report form is also enclosed.

Report No.: 50-298-81-04 Report Date: April 2, 1981 Occurrence Date: March 6,1981 Facility: Cooper Nuclear Station Brownville, Nebraska 68321 Identification of Occurrence:

A condition which could lead to operation in a degraded mode per-mitted by the limiting condition for operation established in Section 3.5.F.1 of the Technical Specifications.

Conditions Prior to Occurrence:

The reactor was operating at a steady state power level approx-imately 93% of rated thermal power.

Description of Occurrence:

During modification of circuits for relay 27X3/lG, the relay was found deenergized.

Designation of Apparent Cause of Occurrence:

The relay coil failed. No abnormal conditions were found and no f 1 i

specific cause could be determined.

II l

! 8106030.2 N 8

lir. K. V. Seyfrit April'2, 1981 Page 2.

{r Analysis of Gccurrence: '

Time delay relay 2713/1G provides a permissive interlock for che' closing of' diesel generator #2 output breaker EG2. During normal operation this relay is energized and its' contact is open. When-

- voltage on .4160V Bus 1G is lost, relay 2713/1G doenergizes.

-Closing of its contact is delayed for five seconds to assure that

, tall puso breakers are tripped before diesel generator number 2 out-Pat brealar EG-2 is closed. Inoperative relay-27X3/1G nullified the five second delay interlock in breaker EG2 closing circuit.

Diesel generator #2 suppl.es emergency power to 4160 Bus 1G through-breaker EG2 and 1GE. The normal and backupLpower source for Bus lG is supplied from Bus 1B through breaker 1BG and 1GB respectively.

Bus 1G is also supplied off site emergency power from the emergency transformer through breaker 1GS. The power source to Bus 1B is from the start up transformer or the normal station service trans-former. If DG #2 was running with output breaker EG 2 open and a

• loss of voltage on 4160V Bus G was' sustained due to an opening of breaker 1BG or 1GB, and the eubject time delay relay was inoper-ative, DG output breaker EG 2 and Emergency Transformer bresker 1GS would have attempted to close simultaneously. This simultaneous breaker closing could have overlodded DG #2 and/or the Emergency Transformer due'to the fact that the station load on Bus G had not been strip-ped and/or the two power sources were out of phase.

Should the loss of 4160V Bus 10 voltage occur with DG #2 not ,

running, breaker 1GS would have closed instantly. DG #2 would have started and remained running. In this case, the failure of time delay relay 27X3/1G would have had no effect on operation of DG #2  !

or closing of EG 2. Bus 1G would have been energized by the Emer-gency Transformer. However, if the power source from the Emergency Transformer had been lost, 'then the same sequence of events as previously described (i.e. , loss of Bus 1G voltage with DG running) would have occurred.

Redundant systems were available and operable. This occurrence presented no adverse potential consequences from the standpoint of '

public health and safety.

Corrective Action.

Relay 27X3/1G was immediately replaced with a spare relay. The new relay was bench tested and its correct operation verified. The corresponding relay 27X3/1F associated with DG #1 cutput breaker i

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Mr. K.~V. Seyfrit April 2. 1981, Page.3.

• EG1 was checked and found to be operable.- In the future, operation

. of these two relays will be verified per S.P. 6.3.4.3 during each refueling outage.

Sincerely,

^

- L. C. Lessor Station Superintendc.t Cooper Nuclear Station LCL:cg Attach.

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