ML20090M804

Ro:On 731217,during Routine Surveillance Testing,Number 12 DG Could Not Be Started Using Number 2 Starting Sys.Caused by Sticking Plunger Piston in Relay Valve.All Components Cleaned & Piston Relubricated

ML20090M804
Person / Time
Site:	Monticello
Issue date:	12/27/1973
From:	Mayer L NORTHERN STATES POWER CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9105090410
Download: ML20090M804 (3)

Text

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.MW NORTHERN STATES POWER COMPANY ,

Minneapolis, Minnesota 55201 f Jos 4lM)W December 27, 1973 1 'l -

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Dear Mr. O' Leary:

?ONTICELLO NUCLEAR GENERATING plat Docket No. 50-263 License No. DM-22 Inoperability of No. 2 Starting System of No.12 Diesel Generator A condition occurred at the hbnticello Nuclear Generating Plant which we are reporting to your office in accordance with Section 6.7.B.1, Abnormal Occurtencc Reports, of the TGehnical Specifications of Provisional Operating License DPR-22.

On December 17, 1973, during routine surveillance testing, the No. 12 diesel generator could not be started using the No. 2 starting system. Investigation revealed that the No. 2 starting system air relay valve was inoperative and thus preventing the main air valve from releasing the air supply to the starting motors.

The relay valve was disassembled and the plunger piston f:- nd to be sticking in the cylinder bore. The piston was excessively lubricated with a light oil which was slightly sticky; however, the remainder of the valve was in good condition. All components were cleaned and the piston relubricated with silicone grease. The engine was then successfully cranked six times by the No. 2 starting system; proper perfomance was verified in each instance.

The air relays in the No. 1 starting system of No. 12 diesel generator and both start-ing systems of No 11 diesel generator were disassembled and inspected; all were found to be in good operating condition with no excessive lubrication. The former lubricant was removed and the pistons relubricated with silicone grease. To insure reliable operation in the future, proper lubricant will be specified in the starting system preventive maintenance procedure.

This occurrence did not affect safe operation of the plant since the redundant No.1 starting system of the No.12 diesel generator was verified to be operable and would have started the engine in the event of an actual automatic initiation. Furthermore, the redundant #11 diesel generator was fully operable during the time the No. 2 start-ing system was inoperable.

9105090410 731227 POR ADOCK 05000263 S PDR '7

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2-There has been one previous failure of a diesel starting system due to an air relay malfunction. The cause of that malfunction was attributed to the presence of foreign particles in the air relay bleed orifice. Other previous air starting system malfunctions which have occurred at Monticello and other facilities have included plugging, stickint, or other malfunctions of screens, lubricators and air motors. Considering the redundancy of the diesels and air starting systems, the corrective actions (primarily additional or improved preventive maintenance) which were taken for these malfunctions should result in an extremely low probability fbr the simultaneous multiple failures which must occur to prevent the diesel generator systems from performing their safety functions. Nevertheless, as previously reported, a design review of the diesel starting systems has been conducted by an independent consultant. Modifications to the systems, including the addition of noisture removal equipment, installation of larger air supply piping and replacement of the air relays, are presently under consideration by NSP.

Yours very truly, W o.9 L. O. Mayer, P-Director of Nuclear Support Services I;Wkik cc: J G Keppler G Charnoff Minnesota Pollution Control Agency ATD4: E A Pryzina

AEC DIST; UTION FOR PART 50 DOCKET MATER

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PROM: DATE CF l>0C DATE REC'D LTR MEMO RPT OTHER Northern States Power Corgany Minnoxpolis, Minn. 55401

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XXX 40 30-263 DESCRIPTION: ENCLOSURES:

Ltr reporting an abnormal occurrence at the l'onticollo Nuclear Plant. . . . . concern the failure of the No. 12 Diesel generator to ,

stort using the No. 2 starting system.... "'

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