ML20090L628

Submits Rept on MSIV Leakage & Closure Time

ML20090L628
Person / Time
Site:	Monticello
Issue date:	01/19/1976
From:	Mayer L NORTHERN STATES POWER CO.
To:	Stello V Office of Nuclear Reactor Regulation
References
595, NUDOCS 9102120464
Download: ML20090L628 (6)

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Mr Victor Stello, Director

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Dear Mr Stello:

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f MONTICELLO NUCLEAR GENERATING PLANT s

Docket No. 50-263 License No. DPR-22 Main Steam Isolation Valve Leakage and Closure Time This report is submitted in accordance with paragraph 6.7.C.5 of the Appendix A Technical Specifications for the Monticello Nuclear Generating Plant. Paragraph 6.7.C.5 requires a report of main steam isolation valve (MSIV) leakage and closure times to be made 90 days after completion of MSIV leakage tests.

l Table 1 is a summary of regularly scheduled m IV surveillance testing at Monticello since our last report. Tests of automatic closure, closure times, l

partial exercising, and leakage testing are tabulated giving the number of valve tests conducted and number of discrepancies experienced. Tabic 2 is a detailed i

listing of the results of MSIV leakage tests conducted during the 1975 autumn outage.

Leakage before and after maintenance is given nions with a summary of maintenance perfomed. Table 3 is a detailed listing of results of regularly scheduled MSIV timing tests at Monticello since our last report.

Main Steam Isolation Valve Leakage Measurements Three of the eight MSIV's tested during the 1975 autumn outage failed to meet the 11.5 scfh leakage limit established by the Monticello Technical Specifications.

An additional valve was close to the limit. As found Icakages were:

A0-2-80A 21.87 seni AO-2-86A 24.95 scfh A0-2-80C 10.85 scfh A0-2-86C 33.26 sefh Initial rotameter measurements showed the inboard "C" EIV, A0-2-80C, to be belov the acceptance criteria.

But these results were questionable since the outboard valve leaked excessively.

Therefore, A0-2-80C was also disassembled and repaired.

9102120464 760119 PDR ADOCK 05000263 f-595 P

PDR a

NO.

HERN CTATEO POWER C iPANY Mr Victor Stello Page 2 January 19, 1976 Upon disassembly of the valves, inspection revealed no apparent cause for the leakage though very small scratches were found on the pilot valve seats.

These scratches were probably caused by valve closure on scale accumulations on the seats.

The pilot and main poppet seats were cicaned and lapped.

The valve pairs were tested and each set was satisfactorily leak tested with essentially zero leakage.

In two of the four main steam lines, both of the isolation valves required repairs. Total steam line leakage, however, based upon the sum of the maximum possible Icakage through each of the four steam lines amounted to only 39.37 scfh.

This is less than the total leakage acceptance criteria of 46 scfh included in the Technical Specifications. Total leakage assuming the worst case single failure of an MSIV to close would have been less than 61.8 scfh (13.5% b ).

The leaking valves did not, therefore, pose a significant hazard r

to the health and safety of the public and would have performed their intended function in the event of a loss of coolant accident.

151V Closure and Exercise rests There we-c no failures experienced in FBIV exercise tests or closure timing tests during this period.

The modifications made to the MSIV ai r operators described in our report dated July 9, 1974 have corrected all problems initially experienced with the Automatic Valve Corporation air operators installed in 1973.

No further instances of yoke rod binding c-inadequcte dashpot oil have been enc ount e r ed.

In 1974 the operating assembly of MSIV 2-SOA was rotated about the shaft axis approximately 45 to align its guide rollers with the vertical.

This valve has performed satisfactorily.

FSIV 2-80D, which was also originally in-stalled canted along its axis, will be similarly rotated the next time it must be disassembled for maintenance.

A comprehensive formal preventive maintenance program has been placed into effect covering the FBIV's.

We believe that adherence to this program in combination with the modifications made during the 1973 and 1974 refueling outages have corrected previous problems with unreliable operation and closure time drif t.

Although progress has also been made in inproving FBIV leak tightness, maintenance will centinue to be required at regular intervals to meet the stringent leakage acceptance criterion.

Yours very truly, h.

L 0 Mayer, PE Manager of Nuclear Support Services LOM/DMM/ak cc: J G Keppler G Charnoff Funnesota Pollution Control Agercy Attn: J W Ferman Attachments

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e TABIE 1 Main Steam Isolation Valve Surveillance Testing Requirements and Sumary of Results (7/1/74 - 12/31/75)

No. of Valve Tests No. of Test Surveillance Test Frequency Performed Discrepancis MSIV Local Leak Rate Test Each Operating 8

3 (TS 4.7.A.2.e)

Cycle Test of simulated automatic Each Operating 8

0 closure Cycle (TS 4.7.D.1.a)

Trip test and measurement Quarterly 56 0

of closure tin.s (TS 4.7.D.1.c (2))

Partial closure and Weekly 656 0

reopening MSIV exercise (TS 4.7.D.2) 4 Manufacturer, Atwood and Morrill Company, Salem, Massachusetts Vendor Drawing No. 20786-H 18" "Y" Globe Valve Cast Carbon Steel - Body and Internals l

Butt Weld Ends Stellite Trim Air Operators: Automatic Valve Corporation C-5157 4

TABLE 2 Results of Main Steam Isolation Valve Leakage Tests Conducted During 1975 Autumn Outage Leak Rate (SCFil)

Sur. nary of Maintenance Performed 0 25 PSIG Valve Identification As Found As left to Improve Leak Tightness 2-80A 21.87 0

Main and pilot poppets cleaned and lapped.

2-86A 24.95 0

Main and,)ilot poppets cleaned and lapped.

4.45 4.45 None 2-80B 8.65 8.65 None 2-86B 10.85*

O Main and pilot poppets cleaned and 2-80C lapped.

33.26 0

Main and pilot poppets cleaned and 2-86C lapped.

2.20 2.20 None 2-80D 2-86D 9.98 9.98 None

• Although leakage was within acceptable limits, maintenance was performed to improve leak tightness.

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TABLE 3 Results of Main Steam Isolation Valve Quarterly Timing Tests (7/1/74 - 12/31/75)

Time to C'ose in Seconds (3-5 seconds acceptable)

Date 2-80A 2-80B f-80C 2-80D 2-86A 2-86B 2-86C 2-86D 8/30/74 4.3 3.8 3.9 4.1 4.3 3.9 4.1 4.2 11/8/74 4.0 3.8 3.8 3.7 4.5 4.9 3.8 4.0 2/7/75 4.0 4.0 4.0 4.0 4.0 3.9 4.2 3.9 5/15/75 4.4 4.0 4.4 4.5 4.4 4.4 4.8 4.5 8/17/75 4.2 4.4 4.2 4.2 4.8 4.6 4.8 4.4 9/11/75 4.0 3.9 4.1 3.9 4.2 4.1 4.5 3.9 11/19/75 4.3 4.2 4.2 4.2 4.2 4.2 4.4 4.2 i

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Ni DISTRIBilTION FOR PAftT 110 DOf T MATERI AL (TEMPOR ARY FORM)

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FROM: tiorthern States Pwr Co DATE OF DOC OATE REC'D LTR TWX RPT OTHER Minneapolis, Mn L 0 Mayer 1-19-76 1-21-76 xx TO:

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50-203

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DESCRIPTION:

ENCLOSURES:

Ltr trans the followinS:

Info concerning main steam isolation valve leakage

.....(40 cys encl rec'd) 4 PLANT NAME:

Monticello

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