Information Notice No. 88-84: Defective Motor Shaft Keys in Limitorque Motor Actuators
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
October 20, 1988
Information Notice No. 88-84: DEFECTIVE MOTOR SHAFT KEYS IN LIMITORQUE
All holders of operating licenses or construction permits for nuclear power
This information notice is being provided to alert recipients to potential
problems from defective motor shaft keys installed in certain Limitorque
actuators. 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 do not constitute NRC requirements; therefore, no specific action or
written response is required.
Description of Circumstances:
On October 15, 1987, the NRC received a report from Houston Lighting and Power
Company concerning sheared motor shaft-to-pinion keys found in a Limitorque
actuator at its South Texas Project, Unit 2, nuclear plant. A similar key
failure also occurred in April 1987. The sheared key from one of the valves
was sent to a metallurgical laboratory which found that the properties of the
material were not consistent with those of American Iron and Steel Institute
(AISI) type 1018 steel. AISI type 1018 steel is the material designated by
Limitorque for these particular keys as specified in Limitorque design
In August 1987, three additional keys had been removed from similar actuators
and sent to the laboratory for analysis. One of the removed keys was split
and the other two showed signs of deformation. Laboratory analysis of these
keys revealed that the properties of the key material were not consistent with
those of AISI type 1018 steel. The metallurgical analysis revealed that the
keys had failed longitudinally along manganese sulfide inclusions and that the
key material was probably an AISI type 1118 or 1119 resulphurized steel.
Addi-tionally, on March 16, 1983, Westinghouse had submitted a 10 CFR Part 21
report to the NRC concerning its discovery of sheared keys on six actuators.
These keys were also analyzed and found to be made of other than AISI type
During an NRC inspection at Limitorque in May 1988, inspectors found that at
the time of the manufacture of the South Texas actuators, keys were purchased
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October 20, 1988
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from a commercial vendor without certificates of conformance for the material
type or properties. No checks were performed at Limitorque to verify that the
proper key material was received. Keys purchased today are still bought as
commercial grade; however, certified material test reports (CMTRs) are
received from the vendor. Limitorque also performs hardness and dimensional
checks of the keys upon receipt from the vendor.
In a letter to the NRC dated May 19, 1988, Limitorque provided additional in-
formation on this issue. Limitorque stated that the current material control
procedures for key procurement were fully implemented in September 1983. At
that time, the existing key inventory was scrapped and completely replaced
with keys purchased under the new controls. It is estimated that all
actuators from serial number 362735 onward were supplied with keys procured
under the upgraded material controls. Additionally, Limitorque determined
that only the following actuator-motor combinations could potentially
experience similar key failures due to improper material.
Unit Size Motor Size
SMB-00 25-ft.lb 1800 rpm
SMB-0 25-ft.lb 1800 rpm
25-ft.lb 3600 rpm
40-ft.lb 1800 rpm
SMB-1 60-ft.lb 1800 rpm
60-ft.lb 3600 rpm
SMB-2 80-ft.lb 3600 rpm
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical
contact listed below or the Regional Administrator of the appropriate regional
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact: Jeffrey B. Jacobson, NRR
Attachment: List of Recently Issued NRC Information Notice
October 20, 1988
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to________
88-83 Inadequate Testing of Relay 10/19/88 All holders of OLs
Contacts in Safety-Related or CPs for nuclear
Logic Systems power reactors.
88-82 Torus Shells with Corrosion 10/14/88 All holders of OLs
and Degraded Coatings in or CPs for BWRs.
88-81 Failure of Amp Window 10/7/88 All holders of OLs
Indent Kynar Splices or CPs for nuclear
and Thomas and Betts power, test, and
Nylon Wire Caps During research reactors.
88-80 Unexpected Piping Movement 10/7/88 All holders of OLs
Attributed to Thermal or CPs for PWRs.
88-79 Misuse of Flashing Lights l0/7/88 All holders of OLs
for High Radiation Area or CPs for nuclear
Controls power reactors.
88-69, Supp 1 Movable Contact Finger 9/29/88 All holders of OLs
Binding in HFA Relays or CPs for nuclear
Manufactured by General power reactors.
88-78 Implementation of Revised 9/22/88 All holders of OLs
NRC-Administered Requali- or CPs for nuclear
fication Examinations power reactors.
88-77 Inadvertent Reactor 9/22/88 All holders of OLs
Vessel Overfill or CPs for BWRs.
88-76 Recent Discovery of a 9/19/88 All holders of OLs
Phenomenon not Previously or CPs for nuclear
Considered in the Design power reactors.
of Secondary Containment
OL = Operating License
CP = Construction Permit
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