Information Notice 1994-10, Failure of Motor-Operated Valve Electric Power Train Due to Sheared or Dislodged Motor Pinion Gear Key

Failure of Motor-Operated Valve Electric Power Train Due to Sheared or Dislodged Motor Pinion Gear Key
	ML031060635
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	02/04/1994
From:	Grimes B; Office of Nuclear Reactor Regulation
To:	;
References
	IN-94-010, NUDOCS 9402010052
	Download: ML031060635 (10)
	v • d • e

4

1

, . I 11 W

I

V .-S_ -1, .7 .- I

. . - 1. I .

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 February 4, 1994 NRC INFORMATION NOTICE 94-10: FAILURE OF MOTOR-OPERATED VALVE ELECTRIC POWER

TRAIN DUE TO SHEARED OR DISLODGED MOTOR PINION

GEAR KEY

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information

notice to alert addressees to the potential for motor-operated valve (MOV)

electric power train failures caused by structural failure or improper

installation of the motor pinion gear key. It is expected that recipients

will review the information for applicability to their facilities and consider

actions, as appropriate, to avoid similar problems. However, suggestions

contained in this information notice are not NRC requirements; therefore, no

specific action or written response is required.

Background

The motor pinion gear is located on the shaft of the electric motor and

transmits motor torque to the worm shaft gear. The motor pinion gear is

connected to the motor shaft by means of a key which transfers rotary force

from the motor shaft to the gear. A set screw is used to prevent axial

movement of the motor pinion gear on the motor shaft.

In 1989, Limitorque Corporation issued Maintenance Update 89-1 which made

recommendations for securing the motor pinion gear key when replacing the

motor or the gears. The update stated that some users had not adequately

secured the key, permitting it to subsequently slide out of the keyway and

decouple the motor from the actuator. The update gave a procedure for staking

the motor shaft at the open end of the keyway to mechanically lock the key in

place.

In 1992, Limitorque issued Matntenance Update 92-2 which stated that the

material for motor pinion keys supplied with SMB-000 through -2 actuators had

recently been changed from American Iron and Steel Institute (AISI) 1018 to

AISI 4140 steel because of customer requests for the higher strength material.

Limitorque stated that all SMB-3 through -5 actuators with motors rated in

excess of 13.8 kg-m [100 ft-lbsJ and serial numbers greater than 12160 were

supplied with motor pinion keys of AISI 4140 steel. In the maintenance

' 9402010052 PDt 94-010 chqotpOL

WAPE & 1>'

/ 0 -;e - I/C

ll

94-10

K" Aruary 4, 1994 update, Limitorque recommended that, if not already done, the motor pinion key

be replaced with AISI 4140 steel for SMB-3 through -5 actuators with motors

rated in excess of 13.8 kg-m [100 ft-lbs].

Description of Circumstances

On August 30, 1993, the high-pressure coolant injection system pump discharge

isolation valve at the Cooper Nuclear Station failed to open during the

performance of a surveillance procedure, causing the valve to be declared

inoperable. Subsequent investigation revealed that the SB-3 Limitorque

actuator motor pinion gear key had migrated out of its keyway, allowing the

motor shaft to spin without transferring torque to the motor pinion gear. The

cause of this event was attributed to the failure to stake the motor shaft

keyway following a motor replacement in 1990.

The licensee for Cooper Nuclear Station incorporated the recommendations of

Limitorque Maintenance Update 89-1 in a 1991 revision to its MOV maintenance

procedures. However, at that time, the licensee did not investigate the

potential consequences of maintenance activities that had been performed

before the procedure was revised. During that time, staking of the motor

shaft had not been a requirement. Based on vendor contacts and independent

sampling, the licensee determined that the particular actuators at Cooper

initially procured from Limitorque were properly staked. Therefore, the

potential extent of the condition at Cooper was limited to actuators that had

received onsite maintenance (affecting the motor pinion gear set) before the

procedures were revised. The licensee further narrowed the scope of its

investigation based on a Limitorque assertion and industry information that

only larger size actuators (SMB/SB-0 and above) are susceptible to this

problem.

On October 8, 1993, the licensee of the Waterford Steam Electric Generating

Station, Unit 3, notified the NRC that the motor pinion keys in both MOVs used

for isolating the shutdown cooling system suction line were not staked to the

motor shaft. The actuators were size SMB-0.

On October 8, 1993, the licensee of the Clinton Power Station, Unit 1, notified the NRC that the SB-3 Limitorque actuator motor pinion key to the

high-pressure core spray injection MOV had sheared. The actuator was attached

to a motor rated at 11 kg-m [80 ft-lbs]. The licensee determined that the key

material was AISI 1018 steel. This motor was rated lower than the threshold

for replacement recommended by Limotorque Maintenance Update 92-2 and is a

different actuator type.

Discussion

The NRC staff has reviewed information suggesting that a small, but not

inconsequential, number of MOV motor shaft keyways may be unstaked at various

nuclear power plants. Although a low incidence of motor pinion gear key

dislodgements has been observed, it is possible that an extended time period

may be necessary for axial migration of the key in a horizontally mounted

motor, suggesting the potential for additional failures of this type.

94-10

February 4, 1994 K. The incidence of motor pinion key failures may be increased as a result of the

higher thrust and torque found to be necessary to operate some valves under

dynamic conditions.

Related Generic Communications

NRC has issued other generic communications on MOV motor pinion keys, including NRC Office of Inspection and Enforcement Information Notices (INs)

81-08, 'Repetitive Failures of Limitorque Operator SMB-4 Motor-to-Shaft Key";

85-22, 'Failure of Limitorque Motor-Operated Valves Resulting From Incorrect

Installation of Pinion Gear'; and 85-67, "Valve-Shaft-to-Actuator Key May Fall

Out of Place When Mounted Below Horizontal Axis"; and NRC INs 88-84, Defective Motor Shaft Keys in Limitorque Motor Actuators"; and 90-37,

'Sheared Pinion Gear-to-Shaft Keys in Limitorque Motor Actuators.'

This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: Thomas F. Westerman, RIV Thomas G. Scarbrough, NRR

(817) 860-8145 (301) 504-2794 John M. Jacobson, RIII

(708) 829-9736 Attachment:

List of Recently Issued NRC Information Notices

IN 94-10

"\-vFebruary 4, 1994 The incidence of motor pinion key failures may be increased as a result of the

higher thrust and torque found to be necessary to operate some valves under

dynamic conditions.

Related Generic Communications

NRC has issued other generic communications on MOV motor pinion keys, including NRC Office of Inspection and Enforcement Information Notices (INs)

81-08, "Repetitive Failures of Limitorque Operator SMB-4 Motor-to-Shaft Key";

85-22, "Failure of Limitorque Motor-Operated Valves Resulting From Incorrect

Installation of Pinion Gear"; and 85-67, "Valve-Shaft-to-Actuator Key May Fall

Out of Place When Mounted Below Horizontal Axis"; and NRC INs 88-84,

"Defective Motor Shaft Keys in Limitorque Motor Actuators"; and 90-37,

"Sheared Pinion Gear-to-Shaft Keys in Limitorque Motor Actuators."

This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager. Original signedly

Brian K. Grimel

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: Thomas F. Westerman, RIV John M. Jacobson, RIII

(817) 860-8145 (708) 829-9736 Thomas G. Scarbrough, NRR

(301) 504-2794 Attachment:

List of Recently Issued NRC Information Notices

see orevious concurrence

OFFICE [*EMEB/DE/NRR [*EMEB/DE/NRR *C:EMEB/DE/NRR D:DE/NRR

NAME TGScarbrough GJohnson JANorberg JTWiggins

DATE 11/30/93 11/30/93 11/30/93 12/ /93 OFFICE *OGCB/DORS/NRR *Tech Ed *EB/DRS/R3 *C:EB/DRS/R3 NAME RJKiessel RSanders JMJacobson GCWright

DATE 12/ 9/93 12/10/93 _ 12/16/93 12/22/93 OFFICE *D:DRS/R3 *DRS/R4 *D:DRS/R4 C:OGCB/DORS/NRR

NAME GEGrant TFWesterman SJCollins *GHMarcus

DATE 12/22i93 I 12/15/93 12/16/93 01/10/94 OFFICE D_ _ _ ___

NAME 4B E _I

DATE '02/1 /94 _

Document Name: 94-10.IN

\,_IN 93-xx

December xx, 1993 The instances of motor pinion key failures might be increased as a result of

the higher thrust and torque found to be necessary to operate some valves

under dynamic conditions.