ML17037C098

Nine Mile Point Unit 1 - Letter Regarding a Problem with the Electromagnetic Relief Valves Disclosed During the Annual Inspection Outage

ML17037C098
Person / Time
Site:	Nine Mile Point
Issue date:	06/02/1972
From:	Burt P A Niagara Mohawk Power Corp
To:	Skovholt D J US Atomic Energy Commission (AEC)
References
Download: ML17037C098 (8)

Text

AEC DISTRIBUTION FOR PART 0 DOCKET MATERIAL TEMPORARY FORM CONTROL No: FROM: Niagara Mohawk Plex, Corporation

~Syracuse~N.Y.13202 P.Allister Burt 6-2<<2 6-8-2 DATE OF DOC: DATE REC'D MEMO TO 0 Mr.S ovholt ORIG'C SENT AEC PDR SENT LOCAL PDR CLASS'PROP INFO No CYS REC'D DOCKET No: DESCRIPTION:

Ltr reporting an incident on 6-2-72, regarcLin alproblem with the electromatic relief valves 8e trans the following:

PLANT NAMES: Nine Mile Point ENCLOSURES:

Consolidated.

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NIAGARA MOHAWK POWER CORPORATION

~~)$)lil&., NIAGARA', MOHAWK Nine Mile Point Nuclear Station Post Office Box 32 Lycoming, New York 13093 June 2, 1972 Mr.Donald J.Skovholt Assistant Director for Reactor Operations Division of Reactor Licensing United States Atomic Energy Commission Washington, D.C;20545

Dear Mr.Skovholt:

Re: Provisional Operating License: DPR-17 Docket No.: 50-220 O During the annual inspection outage of Nine Mile Point Unit¹1, which will terminate tomorrow, June 3, 1972, a problem with the electromatic relief valves was disclosed.

There'are three 6" Consolidated Electromatic Relief Valves, Type 1525-VX, installed on each of the two steam lines within the drywell for a total of six.Three are required for depressurization on loss of coolant accident and five are required to maintain pressure margin between peak transient pressure and lowest safety valve setting on turbine trip without bypass.On one valve, the locking screw, Part¹8 on enclosed drawing, had become unscrewed allowing lock retainer Plate¹7 to fall free (both parts were recovered in the turbine stop valve strainer basket).This permitted the disc retainer, Part¹6, to completely back-out falling to the bottom of the valve body.In this condition, it would be impossible to bleed enough steam from Chamber"C" to open the valve as it would be wide open to Chamber"A" and would not have the benefit of the restricting orifice in the retainer plate.One other valve was found with the locking screw, Part¹8, backed out 1/16" but the lock retainer plate and disc retainer had not moved, therefore the valve was operable.Tie-wires holding the locking screws were broken on all six valves.

O.r Mr.Dceald J.Skovholt June 2, 1972 Repair was effected to all six valves by removing the locking screw, Part¹8, and lock retainer plate, Part¹7.In their place, four 1/4" V grooves, 1" long, were cut in the joint between the disc retainer and the valve body insert.These were stitch welded together, Future maintenance may be accomplished by grinding out the stitch weld.In this manner, there can be no loose parts on the valves to drop into the steam lines and dependability of valve operation is increased.

Very truly yours, P.Allister Burt General Superintendent Nuclear Generation PAB:pw Enclosure I I J 21 22 20 IS 23 18 17 16 15 14 PORT F 12 ll tIew Stitch Weld 4 Places E 25 26 27 9 28 CONSOLIDATED ELECTROMATIC RELIEF VALVE 6"-TYPE 1525-VX Effected Parts¹4 Valve Disc.¹6 Disc Retainer¹7 Lock Retainer Plate¹8 Locking Screw When normally closed, steam pressure is equal in Chambers"A","B" and"C".Disc 4 is held to seat by greater force in"C" over"B" (difference in projected areas)and spring.Valve operates when pressure in"C" is decreased by opening of pilot valve.Higher total force in"B" then pushes Disc 4 away from seat allowing steam to discharge.

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