ML20084A090

Ao:On 730915,following Investigation of Excess Letdown Line Leak,Valve 1MOV-1299 Downstream Seat Protruded from Valve Body & Crack Discovered in Upper Portion of Downstream Seat Ring.Cause Unknown.Vendor Notified of Valve Problem

ML20084A090
Person / Time
Site:	Point Beach, 05000000
Issue date:	10/29/1973
From:	Burstein S WISCONSIN ELECTRIC POWER CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20083R894	List: ML20084A027 ML20084A090
References
NUDOCS 8304050091
Download: ML20084A090 (3)

Text

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231 WEST MICHIGAN, MILWAUKEE. WISCONSIN 53201 ,

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October 29, 1973 Mr. John F. O' Leary, Director ,

Directorate of Licensing U. S. Atomic Energy Commission ,

Washiagton, D. C. 20545

Dear Mr. O' Leary:

DOCKET NOS. 50-2G6 AND 50-301

, FACILITY OPERATING LICENSE NOS. DPR-24 AND DPR-27 POINT BEACH NUCLEAR PLANT BACKSEATING DISC MISLOCATION PROBLEM ON 2" DARLING VALVES In accordance with Section 15.6.6.A.3.b of the Technical Specifications for Point Beach Nuclear Plant (Facility Operating License Nos. DPR-24 and DPR-27) , this report describes a possible generic problem with a category of 2" gate valves in-stalled at Point Beach Nuclear Plant. The valves in question are 2", No. S-350 WDD welding end, outside screw and yoke, double disc gate valves with lip seals, and are manufactured by the Darling Valve and Manuf acturing . Company. The valves used at Point Beach Nuclear Plant are safety class I, ASA series 1500 ,

e c lb. valves.

An investigation of excess letdown line leakage on September 15, 1973, lead to an inspection and subsequent repair of valve 1MOV-1299 on Unit 1 (excess letdown system root valve) on Septereber 26, 1973. Inspection of the valve disclosed that its downstream seat protruded from the valve body such that if the. valve disc was fully withdrawn from the guides, as allowed by its backscating ring, the disc Four could marks catch on the t'he " lip" of the lip of the down-seat ring when reinserting.

stream seat' ring indicated that the disc had caught there during previous valve closings. Internal damage to the valve consisted of a fine vertical crack at the 12 o' clock position in the upper portion of the downstream seat ring. Two locating pins between the upstream and downstream discs of the split disc valve were found to be slightly bent also and some facial scratches to the down-stream disc were evident. There was no metal loss involved in the damage.

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Mr. John,F. O' Leary -

October.29, 1973 l

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Repair of the valve involved rounding the lip of the seat ring to prevent future hangups of the disc. The thin ver-I tical crack in the downstream seat could not be fully lapped out during the repair. Accordingly, a manual valve was added.to the s'ystem downstream of 1MOV-1299 to back up the root valve. Valve

1MOV-1299 thereby remains effective and operable as a remotely

controlled root shutoff valve, but is considered not totally capable of effecting completely tight shutoff without some t ,

through-leakage.

At the time, measurements-indicated-that the location of the backseating ring on the valve stem was too low but this

! could not be assuredly determined. If such was the case, this would allow the split discs to fully clear the seat rings when

.l the valve was fully open and backseated. The tendency for inter-ference to occur between the downstream disc and seat during l , valve closing could be expected to increase if there was flow I through the valve, creating a diff6rential pressure which could

swing the loose hanging disc onto the lip of the seat.

There are six similar 2" Darling valves in each unit at Point Beach Nuclear Plant. In addition to the above mentioned 1299 valve, valves 270A & B (normally open) are installed on the reactor coolant pump seal return lines. These valves are, rarely

, operated in the life of the plant. Also, valves 598 and 599 on the reactor coolant system drain line are of this type. These valves are never operated during normal pressurized and power.

operation. The sixth similar valve on each unit is MOV-427 on the normal letdown line. The function of valve 427 is to c2ose-1 in the event of low pressurizer level and, in closing, cause the~

closure'of the containment isolation valves 200 A, B and C, via an interlock. None of the Darling valves described in this-re-port are containment isolation valves.

Valve IMOV-427 was investigated during a Unit 1 shut-

, down on October 13, 1973, af ter it was reported that it would not i ful.ly close remotely. Manual manipulation of the valve on Septem-i ber 28, 1973, had shown that at approximately one-half shut and again just prior to closing, the valve operation became-sticky.

Tests were c6nducted at that time to verify that IMOV-427 was*

capable of performing its primary function of initiating an. iso-i j lation signal for the letdown line. The slightest movement of the valve off its backseat was found to be' sufficient to activate the interlocks and close the AOV-200 letdown isolation' valves. -

I 8 Measurements indicated that the discs of.lMOV-427 when G

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October 29, 1972 backseated cleared the seat rings and lef t the valve open to sini-lar problems as experienced in 1MOV-1299. Inspection showed no damage to valve IMOV-427 other than a slight marking of the uppa

edge of the seat ring, similar to that found in 1MOV-1299. Eeferc closing up the valve, the seat ring edges were rounded to aid in guiding the discs down between the seats. The " valve open" limit switch was then set for 2-1/4", 5/16" less than the maximum back-seating position of 2-9/16". Valve cycling tests were then con-ducted satisfactorily.

During the same shutiown, valve IMOV-270B was cycled

manually with_no_.evidencecofistickiness or disc -hangup. At the

' completion of repair of 1MOV-427, on October 13, 1973, it was -

concluded frcm measurements taken, operating experience and tele-phone discussions with the valve manufacturer, that, indeed, a-dimension error could exist with respect to backseat locations on the stem. With these confirmations, it was concluded that all i , twelve valves of this type would recuire investigation on a sche-dule commensurate with the plant Operating schedules.

Valves IMOV-1299, 2MOV-1299 and 2MOV-427 will be

< electrically limited.similarly to IMOV-427. Valve IMOV .'299 will be completely changed out during a convenient shutdown fol-

lowing the receipt of a new valve. New valve stems with back-seats located so that full opening of the valve will not permit

the discs to lose the guide effect of the seats have been ordersi

• and will be fitted in the remaining valves at convenient shut-i downs. The service of the 598, 599 and 270A & B valves is such that it is not considered necessary to change the stems of these i valves until the next refueling shutdown of each unit.

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The nuclear steam supply system supplier has been in-

formed about the problems encountered with these valves.

Very.truly yours, l -

Sol Burstei'n Senior Vice President i

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cc: Mr. James G. Keppler ,

i Regional Director Directorate of Regulatory Operations, -

Region III . .

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Jersey Central Power & Light company i Attantion: Mr. I. R. Finfrock, Jr. hehmt Noe 50-219

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! Vice President - Generation Madison Avenue at Punch Bowl Road Morristown, New Jersey 07960 Goatlement he emelosed Directorate of Regulatory operations-Bulletin No. 74-1, 4

involving two valve problems is sent to you to provida you with tu-

! formation we recently reenived frcs the Philadelphia Electric Company and the Wisconsin Electric Power Conspany. Thd problems involved

~ ~'defief==-4=a identified at the Peach Bottem/Unita 2 and 3 and the Point Beach reactors. h is information may relate to the performance b of certain equipment at your facilities. /The Bu11stia also requests certain action on your part in this matter.

i Sincerely,

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James P. O'Reilly Director

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i Enclosures

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