ML20056B734

Ro:On 711113,MSIV Problems Reported.Main Spool Valve Disassembled & Found That Spool Would Not Travel Freely in Spool Sleeve.Investigation Conducted

ML20056B734
Person / Time
Site:	Monticello
Issue date:	11/26/1971
From:	Mayer L NORTHERN STATES POWER CO.
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9102080452
Download: ML20056B734 (2)

Text

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NORTHERN STATES POWER COMPANY flinneapolis, Minnesota 55401 i

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, \ h '- ,j November 26, 1971

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l G NOV2 91971 + '

u cu a, j Dr. Peter A. florris o

???M Division of Reactor Licensine 'O a

! United States Atomic Energy Commission Washington, D.C. 20545 ~ k'2.ifE$. ro

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Dear Dr. f/crris:

fONTICELLO IOCLEAR GEIERATIIG PLANT Docket No. 50-263 Li cense No. DPR-22 Report on Win Steam Isolation Valve Problems Conditions have occurred recently at the Monticello IJuclear Generating Plant which we are reporting in accordance with the reporting reqJirements of seClion 6.6.B of the Technical Sp ecifications. T he Reg i on l i l "Compl i an ce o f fi ce has been noti fied of these events.

On November 13, 1971, an ISIV Closure Time Surveillance Test was conducted.

The closure tires for two of the eight LSIV's were not within the Technical Sp ecification limi ts of > 3 seconds and i5 seconds. ISIV 2-80B closed in 20 seconds and ISI V 2-860 closed in 1.2 seconds.

Investication revealed the fast closure of fSIV 2-86C (located outside of the primary coniainment)was caused by leakage from the oil dashpot cylinder external I piping. The dashpot piping and fittings on all ISIV's have been tightened, l sealed, or replaced to eliminate cil leakage. The oil level in the dashpois has l been checked and oil added as necessary, i Investigation revealed that ISIV 2-80B would close slowly only if it was opened and irnediately re-closed,, i f the valve was allowed to stay open for approximately {

one minute, its closure time was approximately 3.5 seconds which is within the i Technical $peci fication limi ts. Since this was the only ISIV which exhibited this  ;

characteristic, the decision was made to de-inert the primary containment l (fSIV 2-80B is located inside the containment) and further investicate- this  ;

p robl em. On November 15, 1971, ii was found that the main spool valve for ISIV l

2-80B was not operating ~ properly.

i The main spool valve was dis-assembled and it was found that the spool would  !

not travel freely in the spool sleeve'. There was no evidence of any material on the spool. The spool was put on a lathe and an emery cloth was used to polish the spool piston. The main spool valve for fSIV 2-80B was exchanged with the test spool valve from ISIV 2-860 The troublesome spool valve was found to operate fy -

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properly when installed as the test spool val ve for LSIV 2-86C. LSI V 2-803 has been tested and found to operate properly.

On November 17 1971, while attempting to fill the reactor vessel with water to perform an opera,tional hydrostatic test on the primary system, i t was found that LSI V 2-86A was leaking. A local leek rate test was performed on November 18, 1971, by attempting to pressurize between the two mainsteam line A isolation valves 2-80A and 2-86A. The steamline could not be pressurized between the two valves indicatine that the isolation valve was leakinc greatly in excess of 11.5 SCFH as 1imitedb'y Techni cal Specifi cation 4.7. A.

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On November 22,1971, LSI V 2-86A was dis-assembled and the seats were inspecied.

There were no indications on either the main seat or the pilot valve seat. On Novembe r 23, 1971, an inspection of the enti re valve assembly was performed and it was found that one of the three main poppet guides showed excessive wear on the lower 1 inch of cuide material. There was also indication on the side of the main poppet of wear between the guide and the poppet. I t is believed that the worn cuide allowed the main valve poppet to seat improperly resulting in the high leakare.

An Atwood and Morrill Company representative has been notified of the problem and will be on site durine the week of November 29 to assist with the invesiipation and corrective action! ~

A follow-up report will be prepared when our investigation is complete. The Region t il Compliance offi ce will be noti fied of any signi fi cant developments.

Yours very truly M

L.O. L,aye r 0 Di rector of Nuclear Support Services LOM/GHJ/caf I

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