ML20084A302

Deficiency Rept Re Backseating Disc Mislocation Problem on Darling 2-inch Gate Valves.Downstream Seat Protruded from Valve Body Such That Fully Withdrawn Valve Disc Could Catch Lip of Seat Ring When Reinserting.Nsss Supplier Notified

ML20084A302
Person / Time
Site:	Point Beach
Issue date:	10/29/1973
From:	Burstein S WISCONSIN ELECTRIC POWER CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8304050155
Download: ML20084A302 (3)

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~ p l ,_ October 29, 1973 Mr. John F. O' Leary, Director ,

Directorate of Licensing U. S. Atomic Energy Ccmmission Washington, D. C. 20545

Dear Mr. O' Leary:

DOCKET NOS. 50-266 AND 50-301 FACILITY OPERATING LICENSE NOS. DPR-24 AND DPR-27 POINT BEACG 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. DDR-24 and DPR-27), this report describes a possibic generic probicm with a category of 2" gate valves in-stalled at Point Beach Nuclear Plant. The valves in question are 2", No. S-350 WDG welding end, outside screw and yoke, double disc gate valves with lip seals, and are manufactured by the l Darling Valve and Manufacturing Company. The valves used at Point Beach Nuclcar Plant are safety class I, ASA series 1500 ,

lb. valves.

• An investigation of excess letdown line leakage on September 15, 1973, lead to an inspection and subsequent repair of valve 11.OV-1299 on Unit 1 (excess letdown system root valve) on September 26, 1973. Inspection of the valve disclosed that its dowr.itream seat protruded from the valve body such that if the valve disc was fully withdrawn from the guides, as allowed by itt backscating ring, the disc could catch the " lip" of the seat ring when reinserting. Four marks on the lip of the down-stream seat ring indicated that the disc had caught there during previous valve closings. Internal damage to the valve consisted cf 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.

O Mr. John F. O' Leary

.O October 29, 1973 Repair of the valve involved rounding the lip of the seat ring to prevent future hangups of the disc. The thin ver-tical crack during in the downstream seat could not be fully lapped out the repair. Accordingly, a manual valve was added to the system downstream of IMov-1299 to back up the root valve. Valve IMOV-1299 thereby remains effective and operable as a remotely controlled root shutoff valve, but is considered not totally 1 capable of effceting completely tight shutoff without some through-leskage, j

At the time, measurements indicated that the location of the backseating could not be assuredly ringdetermined.

on the valve stem was too low but this If such was the case, this would the valve was fully open ard backscated. the seat rings when allow the split discs to fully clear The tendency for inter-forence to occur between the downstream disc and seat during i

l valve closing could be expected to increase if there was flow through the valve, creating a differential pressure which could swing the loose hrnging disc onto the lip of the seat.

at Point Beach Nuclear Plant.There are six similar 2" Darling valves in each unit 1299 valve, valves 270A & B (normally In addition to the open) areabove mentioned 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 normal letdown line.The sixth,similar valve on each unit is MOV-427 on '

in the event of low pressurizer level and,The function of valve in closing, 427 cause is to close the closure an of the containment isolation valves 200 A, B and C, via interlock.

port are containmentNone of the Darling icolation valves. valves described in this re-down on October Valve 13,IMOV-427 was investigated during a Unit 1 shut-fully close remotely.1973, af ter it was reported that it would not ber 28, 1973, had shown that at approximately one-half shut andManual again just prior to closing, Tests were conducted at that time to verify that 1Mov-427 wasthe valve oper capable lation signalof performing its primary for the letdown line. function of initiating an iso-The slightest movement of the valve off its backseat was found to be sufficient to activate the interlocks and close the AOV-200 letdown isoletion valves.

Measurements indicated that the discs of 1MOV-427 when e

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3-O ctober O 29, 1973 Mr. John F. O' Leary e

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l open *o simi-backscated cleared the seat rings and icft the va veInspection of the upper showed n lar problems as experienced in 1MOV-1299. i Before damage to valve IMOV-427 other thand ina 1MOV-1299. slight unded mark to aidngin edge of the seat ring, similar to that founclosing up the v guiding the discs down between5/16" less than the maximum back-the seats.

switch was then set for 2-1/4", Valve cycling tests were then con-seating position of 2-9/16".

ducted satisfactorily. cycled During the same shutdown, valve disc hangup. At IMOV-270B wasthe manually with no evidence of stickiness or 13,erience 1973, it was and tele-completion of repair of IMOV-427, on Octoberthat, indeed, a concluded frem measurements taken, opercting exp t locations phone discussions with the valve manufacturer, dimensi With these confirmations, investigation on a sche-on twelvethe stem.

valves of this type would requ re i

l dule commensurate with the plant operating schedu ill bees.

Valves IMOV-1299, 2MOV-1299 and 2MOV-427 wValve IMOV-1299 electrically limited similarly to IMOV-427. i nt shutdown fol-vill be completely changed out during a convenwill eNewnot valve permitstens with back-lowing the receipt of a new valve. l t have been ordered seats located so that full opening of the va ve onvenient shut-the discs to lose the guide effecttheofstems theofsea these sand will o downs.*

The service of the 598, that it is not considered necessary to change h unit.

valves until the next refueling shutdown of eac has been in-The nuclear steam supply system supplier l es.

formed about the probicms encountered with these va v Very truly yours,

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- # vt Senior Vice President Sol Burstein cc: Mr. James G. Keppler Regional DirectorDirectorate of Regulatory Operations, .

Region III -

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