ML20210G992
| ML20210G992 | |
| Person / Time | |
|---|---|
| Site: | Millstone, Hatch, Monticello, Salem, Oconee, Nine Mile Point, Indian Point, Fermi, Wolf Creek, Oyster Creek, Sequoyah, Pilgrim, Brunswick, Limerick, River Bend, Crystal River, Callaway, Duane Arnold, Yankee Rowe, 05000000, Crane |
| Issue date: | 08/13/1985 |
| From: | Denham F LIMITORQUE CORP. |
| To: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| References | |
| REF-PT21-85 NUDOCS 8702110363 | |
| Download: ML20210G992 (6) | |
Text
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' *g Limitorque Corporation B590 Automated Volve Actuotors ond Jacks for Industry 5114 Woodoll flood P.O. Box 11318 Lynchburg. VA 24506-1318 s
Telephone-804-528-4400 = Telex-82-9448 O
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=>d August 13, 1985 c.-.
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Office of the Director
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,a p g Nuclear Regulatory Commission s
Incoection & Enforcement Wasnington, DC 20555 1
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Subject:
Limitorque Actuator Size 2 Type SMB, SB, and SBD Potential Worm Shaft Gear Failure Gentlemen:
The conclusion of our extensive investigation of isolated worm shaft gear failures at Calloway (Union Electric) and Wolf Creek (Kansas Gas and Electric) is that this component is prone to failure when certain critical speeds are combined with repetitive transfer of the actuator clutch mechanism from the manual
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(handwheel) to the motor drive mode.
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This difficulty has been identified to be limited only to the Size 2 Limitorque actuator (Type SMB, SB, and SBD) and only when it is combined with a two-pole AC motor (3600 rpm, 60 hertz or 3000 rpm, 50 hertz) or a DC motor using an actuator ratio less than 55.84:1.
All other variations of motor and ratio combinations in the Size 2 actuator are not at risk in this regard nor are any other smaller or larger size actuators with any combination of motor speed or ratio.
Failure of this worm shaft gear (a component in the power gear drive) would prevent the actuator from properly positioning the valve in the motor drive mode.
Auxiliary handwheel operation would, however, still be available.
l l
l Our testing identifies the source of the problem to be the I
impact loads associated with the clutch mechanism returning from manual operation to motor operation in isolated, high-speed situations.
The clutch (piece # 50),
reference pages 22 and 24 of the enclosed Instruccion and Maintenance Manual, engages l
the worm shaft gear (piece # 41) in motor operation and the j
handwheel pinion (piece # 42) in manual operation --the clutch is normally in the motor operation mode.
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Limitorque Corporation 8/13/85 When the declutch lever (piece # 60) is depressed, the clutch (piece # 50) moves along the worm shaft so as to -disengage from the worm shaft-gear and engage the handwheel pinion (piece
- 42).
The clutch trippers (piece # 32 and 33) then latch the declutch fork (piece # 12) and clutch in the manual mode.
The actuator will' remain in this manual mode until the motor is energized and - rotation of the motor pinion and worm shaf t gear release. the clutch trippers and the clutch return spring (piece # 58) drives the clutch into engagement with the rotating worm shaft gear.
The clutch and worm shaft gear engage at high, rotative speeds creating high inertia impact loads.
We recommend two possible solutions to avoid potential failure of this worm shaft gear component on the Size 2 Limitorque actuator as follows:
1.
Increase the actuator ratio to the minimum of 55.84:1 which which has been established by our test program as the lower limit of the safe range.
This can be accomplished by a change of the motor helical gear set (motor pinion and worm shaft gear) to achieve the higher ratio.
This change of ratio would proportionately increase the valve operating time.(i.e.
New Ratio x
Closing Time = New Closing Time)
Existing Ratio 2.
As an alternate to a change of ratio, the clutch trippers which latch the clutch in the manual mode can be removed.
This will eliminate engagement of the clutch under high speed - high inertia conditions as the clutch would always be. in the motor drive mode except when the actuator is being manually orrated.
With the clutch trippers removed, it will be necessary to hold the declutch lever in the depressed position while turning the handwheel.
When the declutch lever is released, the clutch will return to its normal motor drive position automatically without experiencing high inertia impact.
This alternative does not otherwise modify the performance of existing actuators.
A complete search of our historical record on safety related actuators shipped to the nuclear industry reveals the attached list of candidates for further evaluation and the specific nuclear plant locations defined by our records.
Each of these actuators contain the combination of motor speed and ratio identified as a potential problem in our evaluation test program.
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Limitorque Corporation 8/13/85 We wish to emphasize that our reported failure experience represents only approximately four precent (4
%)
of the identified candidate quantity of 107 actuators shipped over the last 12 years.
Failure of this worm shaft gear component is by no means certain as our test program could only duplicate, the few reported failures by introducing unusually severe circumstances of high
- speeds, stalled motor stress
- levels, and a
repetitive sequential series of clutching operations
-- all in combination.
This combination is abnormal to the average in-servce actuator.
We have written to each of the above utilities / customers and provided them a list of the actuator t.erial n. umbers and other identification information contained in our records to allow them to make a judgment on the course of action appropriate to their operating experience to date.
A sample of this notification letter and a summary of this data is attached.
An information copy of this correspondence has also been sent f;
to the various architect / engineer firms involved in the various N
,/
facilities identified.
Should you have any question on the above, we would be happy to discuss this matter further with you.
Yours very truly, V(
o F. K. Denham Executive Vice President FKD/ecm cc:
T. Mignogna W. Denkowski D. Warsing l
P. McQuillan J. Drab l
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August :13, \\~~d' LIMITORQUE CORPORATION QUANTITY FACILITY / CUSTOMER UTILITY 4
Duane Arnold Iowa Electic Light and Power 2
Nine Mile Point # 1 Niagara Mohawk Power Company 3
Pilgrim Boston Edison Company 1
Yankee Atomic Yankee Atomic Company 7
Sequoyah T. V. A.
2 Millstone Northeast Utilities 4
Monticello North States Power 6
Oconee Duke Power Company 1
Limerick Philadelphia Electric Company 6
Fermi # 2 Detroit Edison 10 Brunswick Carolina Power and Light 10 E.
I. Hatch Georgia Power 4
Crystal River # 3 Florida Power Corporation 1
Indian Point # 3 New York Power Authority 6
River Bend # 1 Gulf States Utilities 5
Oyster Creek GPU Nuclear Corp.
1 Three Mile Island GPU Nucler. Corp.
1 Salem Public Service Electric & Gas Co.
4 Atwood & Morrill Company)
(Not presently identified 29 Westinghouse)
(as to facility. location 107 I
'@g Limitorque Corporation Automoted Volve Actuators and Jacks for Industry 5114 Woodoll Rood P.O. Box 11318 Lynchburg[VA 24506-1318 Telephone-804-528-4400
- Telex-82-9448 a>0 August 13, 1985
.E
-U Duke Power Company
[h Oconee Nuclear Station b
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P. O.
Box 1175 Seneca, South Carolina 29678 g
Attention:
Quality Assurance Manager
Subject:
Limitorque Actuator Size 2 Type SMB, SB, and SBD Potential Worm Shaft Gear Failure Gentlemen:
The enclosed notification letter August 13, 1985 to the Nuclear Regulatory Commission is self-explanatory and we also include a copy of the Instruction and Maintenance Manual referred to
[-)/
therein.
G The attached chart documents those Size 2 Limitorque Actuators (Type SMB, SB or SBD) shown by our records to be located in or purchased by your facility.
Each of these actuators contain the combination of ratio less than 55.84 to 1 and high speed motor referred to in our letter to the NRC and are candidates for your evaluation.
Should you require further assistance in ordering replacement motor helical gear sets or instructions on removal of the clutch l
trippers, please contact either your local Limitorque Corporation Sales Representative or Mr.
Joseph Drab at Limitorque Corporation, 5114 Woodall Road, P.
O.
Box 11318, Lynchburg, VA
- 24506, Phone (804) 528-4400.
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Yours Very Truly,
' N-
,D F. K. Denham Executive Vice President V'
FKD/ecm cc:
Mr. G. Cusak, Charlotte Office
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INSTALLATION: ~[
Oconee Nuclear Unit Unit Limitorque Actuator S/N Ratio Type 0/N Valve Tag Information Remarks
-361180 & 181 26.24 SB-2 3J3096A ILP21 & ILP22 (See Note 1) 361324 & 325 26.24 SB-2' 3J30968 2LP21 & 2LP22 366900 & 901 26.24 SB-2 3J3096C 3LP21 & 3LP22 Note 1: These units purchased from Limitorque Corporation on Mill Power Supply Purchase Order J17672-73, Add 2.
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