ML20085D112

Ro:On 730620,during Test on Turbine Redundant Overspeed Trip Sys,Turbine Trip Inadvertently Initiated.Caused by Turbine Stop Valve Limit Switch Failure.Switch Adjusted

ML20085D112
Person / Time
Site:	Robinson
Issue date:	06/27/1973
From:	Utley E CAROLINA POWER & LIGHT CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085D103	List: ML20085D105 ML20085D109 ML20085D112
References
NG-73-126, NUDOCS 8307200443
Download: ML20085D112 (2)

Text

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Ca,rolJna Power & Light Company June 27, 1973

'5 0 3.6 r File: NG 5212 NG-73-126 0, m' 8

Mr. John F. O'Imary Directorate of Reactor Licensing k

U. S. Atomic Energy Comission S. RECENED 3 Washington, D. C. 20545 2 1973 g-JUL6

Dear Mr. O'Icary:

{ us. 5 -2 g ,;. Myt H. B. ROBINSON UNIT NO. 2 -

wi Mm" J LICENSE DPR-23 .

FAILURE OF REACTOR TRIP FROM TURBINE TRIP I #x \

In accordance with Paragraph 6.6.2.A, Technical Specifications, it is reported that on June 20, 1973, while operating at approximately 92*/., a turbine trip occurred which did not directly trip the reactor.

While performing a periodic test on the turbine redundant overspeed trip system (TROTS), a turbine trip was inadvertently initiated at 1454 hours0.0168 days <br />0.404 hours <br />0.0024 weeks <br />5.53247e-4 months <br />.

Approximately seven seconds later a reactor trip was initiated by high pressurizer pressure, as indicated by first out annunciation and the plant computer. The plant tripped to the hot shutdown condition.

The reactor failed to trip, as a result of a turbine trip, due to a failure of one turbine stop valve limit switch. The only reactor trip function from TROTS trip is via both stop valve closure limit switches; therefore, the failure of this switch prevented a direct reactor trip from being initiated. Since the other reactor protection systems performed properly, the lack of an immediate reactor trip did not adversely affect the safety of the reactor.

The following corrective actions were initiated: l l

1) The turbine stop valve limit switches were checked and the right stop valve switch was found to operate marginally. This switch had last been satisfactorily tested on June 10, 1973.

The switch was adjusted and test operated satisfactorily prior

-to power operation.

cb' B307200443 730628 PDR ADOCK 05000261 4

COPY SENT REGION 336 Fayetteviue Street . P. O. Box 1551. Raleigh, N. C. 27602 U ,Yh

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. O O Mr. John F. O'Ieary June 27, 1973

2) An investigation is in progress to evaluate a separate input from the TROTS to the reactor trip logic rather than depending solely on stop valve closure.

The Plant Nuclear Safety Committee reviewed this incident on June 21, 1973, and it was reported to Mr. W. C. Siedic of Directorate of Regulatory Operations, Region II, by telephone and to Mr. Norman C. Moseley of the same office by telegraph on the same date.

Yours very truly,

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E. . Ut e Vice-President Bulk Power Supply WC:NBB:mp cc: Mr. C. D. Barhau Nr..N. B. Bessac Mr. B. J. Furr Mr. D. V. Menscer Mr. N. C. Moseley Mr. D. B. Waters 2-0-4-a A

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