ML20090D494
| ML20090D494 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point, 05000000 |
| Issue date: | 06/02/1972 |
| From: | Burt P NIAGARA MOHAWK POWER CORP. |
| To: | Skovholt D US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20090D471 | List: |
| References | |
| NUDOCS 8303010358 | |
| Download: ML20090D494 (3) | |
Text
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NI AGARA MOH AWK POWER CORPORATION HlAGARA MOHAWK Nine Mile Point Nuclear Station Post Office Box 32 1.ycoming, New York 13093 June 2, 1972 Mr. Donald J. Skovholt Assistant Director for Reactor Operations Division of Reactor 1.icensing United States Atomic Energy Commission Washington, D. C.
20545
Dear Mr. Skovholt:
Re:
Provisional Operating License: DPR-17 Docket No.:
50-220 During the annual inspection outage of Nine Mile Point Unit #1, 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, Part #8 on enclosed drawing, had become unscrewed allowing lock retainer Plate #7 to fall free (both parts were recovered in the turbine stop valve strainer basket). This permitted the disc retainer, Part #6, 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 wa Id not have the benefit of the restricting orifice in the retainer plate.
One other valve was found with the locking screw, Part #8, backed out 1/16" but the lock retainer plate and disc retainer had not moved, therefore the valve was operable. Tic-wires holding the locking screws were broken on all six valves.
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8303010358 721212 PDR ADOCK 05000220
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Str. Donald J. Skovholt June 2, 1972 Repair was effected to alI six valves by removing the locking screw, Part #S, and lock retainer plate, Part #7.
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.
I'uture 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 stean. 1ines and dependability of valve operation is increased.
Very truly yours, P. Allister Burt General Superintendent Nuclear Generation PAB:pw Enclosure c
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4 Places 28 CONSOLIDATED ELECTR0MATIC RELIEF VALVE 6" - TYPE 1525-VX Effected Parts
- 4 Valve Disc.
- 6 Disc Retainer
- 7 Lock Retainer Plate
- 8 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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