ML20084A302
| 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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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of the valve disclosed that its dowr.itream seat protruded from the valve body such that if the valve disc was fully withdrawn from the guides, as allowed by itt backscating ring, the disc could catch the " lip" of the seat ring when reinserting.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
.O Mr. John F. O' Leary 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 in the downstream seat could not be fully lapped out during the repair.
Accordingly, a manual valve was added to the system downstream of IMov-1299 to back up the root valve.
IMOV-1299 thereby remains effective and operable as a remotely Valve 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 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 the valve was fully open ard backscated.
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 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.
valves are never operated during normal pressurized and power These 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 427 is to close 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 icolation valves.
Valve IMOV-427 was investigated during a Unit 1 shut-down on October 13, fully close remotely.1973, af ter it was reported that it would not 1973, had shown that at approximately one-half shut andManual ber 28, again just prior to closing, Tests were conducted at that time to verify that 1Mov-427 wasthe valve oper capable of performing its primary function of initiating an iso-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 isoletion valves.
Measurements indicated that the discs of 1MOV-427 when e
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o O ctober 29, 1973 O
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l open *o simi-backscated cleared the seat rings and icft the va veInspection showed lar problems as experienced in 1MOV-1299.
i of the upper damage to valve IMOV-427 other than a slight mark ng Before d in 1MOV-1299.
edge of the seat ring, similar to that founclosing up the v unded to aid in 5/16" less than the maximum back-guiding the discs down between 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 IMOV-270B was At the disc hangup.
manually with no evidence of stickiness or 13, 1973, it was completion of repair of IMOV-427, on October erience and tele-concluded frem measurements taken, opercting exp that, indeed, a phone discussions with the valve manufacturer, dimensi t locations With these confirmations, investigation on a sche-i twelve valves of this type would requ re on the stem.
l dule commensurate with the plant operating schedu es.
ill be 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 conven eNew valve stens with back-will not permit lowing the receipt of a new valve.
l seats located so that full opening of the va ve have been ordered t
the discs to lose the guide effect of the sea sand will o onvenient shut-The service of the 598, the stems of these that it is not considered necessary to change downs.*
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 Mr. James G. Keppler cc:
Regional DirectorDirectorate of Regulatory Operations, Region III 4
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