ML20090D449

Ro:On 720919,unidentifiable Leakage Into Drywell Equipment Drain Tank 11 Increased.Caused by Faulty Pump Seals.Seals Repaired & Recirculation Sys Isolation Valves Repacked

ML20090D449
Person / Time
Site:	Nine Mile Point
Issue date:	11/03/1972
From:	Burt P NIAGARA MOHAWK POWER CORP.
To:	Skovholt D US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20090D451	List: ML20090D449
References
6247, NUDOCS 8303010142
Download: ML20090D449 (2)

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NIAGARA MOHAWK POWER CORPORATION NI AGAR A MOHAWK Nine Mile Point Nuclear Station P. O. Box 32 Lycoming, New York 13093 November 3, 1972

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m ~. m Mr. Donald J. Skovholt ['i'i)

Assistant Director for Reactor Operations ic- 3' _

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Division of Reactor Licensing {.]. ,. 1 United States Atomic Energy Commission s

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Dear Mr. Skovholt:

Ni Re: Provisional Operating License: DPR-17 Docket No. : 50-220 On September 19, 1972, with the Nine Mile Point Unit operating at 602 MW (c) the identifiable leakage into #11 drywell equipment drain tank started to slowly increase. The trend of this leakage closely followed previous trends resulting from recirculation system valve packing leakage into the drywell equipment drain tanks. The primary inputs to

1. 11 drywell equipment drain tanks consist of #11 and #12 reactor re-circulation pump suction and discharge valves and #13 reactor recirculation pump discharge valve. A planned program to discover the exact source of Icakage was undertaken. The unit load was reduced to S10 MW (e) and reactor recirculation pumps #11, #12 and #13 were individually isolated to determine the effect in total drywell leakage. Throughout this period accurate determination of leakage was obtained on a continuous basis. No substantial change in Icakage could be detected during the isolation attempts, however, the pressure on #11 reactor recirc pump low pressure ,

seals fluctuated during the time that the pump was isolated as seen in the control room indication.

On September 20, 1972, surveillance data revealed that leakage into #11 DWEDT was approaching the limiting condition for operation (25 gpm total) . At 1745 hours0.0202 days <br />0.485 hours <br />0.00289 weeks <br />6.639725e-4 months <br /> plant shutdown was initiated in order

, to repair the pump seal on #11 reactor recirculation pump and repack certain recirculation system isolation valves. Four hours after starting to shutdown, the leakage reversed its trend and began to decrease with power level . Cold shutdown was achieved at 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br /> on September 21, 1972 and recirculation system repairs were started.

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. . . . 3 - 2 (3 U Nsvemb3r 3,1972 Mr. Donald (s_.vholt 4%

U.S. Atomic Energy Commission .

During the repair to the #11 recirculation pump seal, the pump suction valve was closed manually as the motor operated actuator (Limitorque valve operator) could not close the valve. Following repairs to the pump seal, the suction valve was cycled to test the valve operator, however, the valve locked up in the open position.

Neither the motor operated or manual mode of operation could move the valve. The valve was jacked to the closed position and locked there.

Inspection of the valve operator revealed that extensive internal damage had occurred and immediate repairs could not be made. Damage to the valve operator was identified as a broken worm shaft in the drive assembly and a cracked case around the stem drive nut which damaged a thrust bearing assembly on the lower side of the drive nut.

A replacement valve operator was ordered. Until installation of the replacement valve operator, the plant output was limited to 80% as only four of the five recirculation loops were in service.

On the weekend of October 28, 1972, the limitorque SMA-1 valve operator was successfully replaced by an SMB-1 valve operator as the SMA-1 is no longer made. The replacement unit is larger than the original and has greater power transmission capabilities, however, the driver motor is the same size as on the original unit. During this outage, considerable packing maintenance was also accomplished on all of the reactor recirculation isol.ation valve packing. All work was completed by October 29, 1972 and the plant was started up with all five recirculation loops available for service.

l Very truly yours, b

P. Allister Burt General Superintendent l Nuc1 car Generation PAB/an u

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