United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 97-32: Defective Worm Shaft Clutch Gears in Limitorque Motor-Operated Valve Actuators

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF NUCLEAR REACTOR REGULATION
                         WASHINGTON, D.C.  20555-0001

                                 June 10, 1997


NRC INFORMATION NOTICE 97-32:  DEFECTIVE WORM SHAFT CLUTCH GEARS IN            
                               LIMITORQUE MOTOR-OPERATED VALVE ACTUATORS       


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 a recent discovery of a defective worm shaft
clutch gear in a Limitorque SMB Size 1 motor-operated valve actuator.  The
defective gear was not made by Limitorque, the original equipment manufacturer
(OEM).  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.  

Description of Circumstances

On October 8, 1996, personnel at General Public Utilities Nuclear
Corporation's Oyster Creek facility discovered that a nonsafety-related
Limitorque valve actuator in the circulating water system failed to operate
from the control room switch.  The licensee determined that the actuator
failed to operate because the tripper pin had fallen out of the worm shaft
clutch gear.  The actuator was sent to the original vendor, Limitorque
Corporation in Lynchburg, Virginia, for root cause analysis.

Discussion

The Oyster Creek licensee procured several surplus or refurbished Limitorque
actuators from a third party company (non-OEM supplier) for use in nonsafety-
related applications.  Two of the actuators failed to operate electrically
because of problems with the worm shaft clutch gear.  One gear was replaced
with an original Limitorque worm shaft clutch gear and operated satisfactor-
ily.  However, in the second actuator, the worm shaft clutch gear was replaced
with a non-OEM part.  Subsequently, the Oyster Creek licensee determined that
the third party supplier had replaced the original OEM worm shaft clutch gears
in the actuators with gears produced by a non-OEM replicator.


9706040318.                                                            IN 97-32
                                                            June 10, 1997
                                                            Page 2 of 3


When the actuator was electrically operated from the control room, the worm
shaft clutch gear tripper pin fell out because it was not securely fastened
onto the worm shaft clutch gear.  Consequently, the actuator tripper fingers
were not separated as the gear rotated, and the actuator would not operate
electrically.  Manual actuator operation with the hand wheel is not affected
by the loss of the tripper pin.

Limitorque examined the worm shaft clutch gear and found several examples of
failure to meet required specifications:

.    The tripper pin was not staked to the worm shaft clutch gear. 

.    The worm shaft clutch gear lugs were not heat treated.

.    The gear teeth were inappropriately shaped and not shaved.

.    Other non-serious dimensional differences were also identified.

On the basis of this information, Limitorque determined that it had not
manufactured the gear and informed the NRC in a letter dated January 23, 1997. 
Limitorque informed the NRC that it had discovered the non-OEM component
installed in the SMB Size 1 nonsafety-related actuator that was received from
Oyster Creek for root cause analysis.  The letter also stated that Limitorque
informed its nuclear customers of record about the defective component.

When compared side by side, some of the differences in the non-OEM and OEM
gear can be readily identified.  However, if such a comparison is not
available to the customer, the non-OEM part may be harder to detect. 
Licensees may not have sufficient information to detect and recognize a
defective worm shaft clutch gear during receipt inspection or dedication for
safety-related use.

Failure of the nonsafety-related Limitorque actuator at Oyster Creek was
caused by the tripper pin being inadequately fastened to the worm shaft clutch
gear.  The potential exists for use of non-OEM parts in Limitorque actuators
in safety-related applications.  This information notice is intended to alert
licensees that problems can result from use of non-OEM parts, if those parts
are not manufactured to the same specifications as the OEM parts.
.                                                            IN 97-32
                                                            June 10, 1997
                                                            Page 3 of 3


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.


                                            signed by S.H. Weiss for

                                       Marylee M. Slosson, Acting Director
                                       Division of Reactor Program Management
                                       Office of Nuclear Reactor Regulation

Technical contacts:  K. Naidu, NRR
                     301-415-2980
                     E-mail:  krn@nrc.gov

                     T. Scarbrough, NRR
                     301-415-2794
                     E-mail:  tgs@nrc.gov

                     D. Skeen, NRR
                     301-415-1174
                     E-mail:  dls@nrc.gov
Page Last Reviewed/Updated Tuesday, December 03, 2013