ML20058K713

AO 263/74-22:on 740806,during Daily Surveillance Test of HPCI Auxiliary Oil Pump,Hpci Turbine Stop Valve Observed to Partially Open & Close.Tension of Overspeed Trip Piston Spring Increased & Oil Sys Vented

ML20058K713
Person / Time
Site:	Monticello
Issue date:	08/16/1974
From:	Mayer L NORTHERN STATES POWER CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
AO-263-74-22, NUDOCS 9102130529
Download: ML20058K713 (4)

Text

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1 NORTHERN STATES POWER COMPANY g M I N N E A PO LI S. M I N N E S OTA 58401 fb.N $ y  !

Mr. J F O' Leary, Director ' f'%' ' '

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Directorate of Licensing s Office of Regulation ~ -

cn 9 s August 6, 1974. N J ^

5. Conditions Prior to the Occurrence: .

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Steady State Power - The plant was operating at 83.97. rated pow r. {ll ' .t j gc . ~

6. Description of Occurrence: M

. ','h At 2300, August 6,1974, during the daily surveillance test of the HPCI Aux'iiiary oil Pump, the HPCI Turbine Stop Valve was observed to partially open and then close. After repeated attempts the valve functioned normally.

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7. Designation of Apparent Cause of Occurrence:

Component Failure - Because of the intermittent nature of the proolem it was not possible to determine a definite cause. However, it ,

is postulated that the turbine overspeed trip reset spring (see Figure One) relaxed so that slight pressure surges in the oil syste:s were sufficient to lift the trip piston and vent control : 4 1 pressure. It is believed that air trapped in the oil sysh a contributed to propagation of pressure surges into the overspeed trip mechanism. The above conclusions were based on the following considerations:

1. An inspection of the oil system (including the over-speed trip mechanism) revealed that internal surfaces 03130 M63CF and orifices did not contaiu significant deposits of dirt and scale. As a preventive me.asure, the control oil system was flushed. During subsequent testing the

. i NORTHERN CTATED POWER COMPANY l

stop valve failed to open on two occasions. It is therefore unlikely that deposits of dirt caused the initial failure of the stop valve to open.

2. Inspection revealed that the condition of the pilot valve (see Figure Two) plug, seat, piston rings and cylinder surface was satisfactory. The possibility of a defective pilot valve was therefore ruled out.

3. Discussions with a representative of the General Electric Company revealed that a similar HPCI Stop Valve failure had occurred at an overseas Bk'R facility. The cause of that failure was attributed to a relaxed trip reset spring and trapped air in the oil syste=.

8. Analysis of Occurrence:

Although failure of the stop valve to open caused the HPCI system to become inoperable, operability of LPCI, RCIS and Core Spray was demonstrated as required by the Technical Specifications.

9. Corrective Action:

The tension of the overspeed trip piston spring was increased and the oil system was vented. Leaking pipe fittings were located and tightened. Until it is i determined that the problem has been satisfactorily resolved, surveillance of the auxiliary oil pump will be performed at times when operation of the stop valve and associated oil system controls can be closely observed.

It is planned to replace or retension the trip reset spring on a regular basis in the future.

10. Failure Data:

The failure of the HPCI Turbine Stop Valve to open is the first such occurrence at the Monticello Kuclear Generating Plant. The stop valve is a 10-inch Schutte and Koerting, M67 05774-V, Serial K67438. The overspeed trip mechanism is manu-factured by the Terry Steam Turbine Company.

L'O Mayer, PE / I Director of Nuclear Support Services LOM/kn cc: J G Keppler G Charnoff Minnesota Pollution Control Agency Attn. E A Pryzina' attachments

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