Information Notice No. 86-71: Recent Identified Problems with Limitorque Motor Operators
SSINS NO.: 6835
IN 86-71
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
August 19, 1986
Information Notice No. 86-71: RECENT IDENTIFIED PROBLEMS WITH
LIMITORQUE MOTOR OPERATORS
Addressees:
All nuclear power reactor facilities holding an operating license or a
construction permit.
Purpose:
This notice is provided to alert recipients of two potential problems
discovered with Limitorque motor operators. It is expected that recipients
will review this information for applicability to their facilities and
consider actions, if appropriate, to preclude a similar problem from
occurring at their facilities. However, suggestions contained in this notice
do not constitute NRC requirements; therefore, no specific action or written
response is required.
Past Related Documents:
Information Notice No. 86-03 "Potential Deficiencies in Environmental
Qualification of Limitorque Motor Valve Operator Wiring," January 14, 1986.
Description of Circumstances - Burn Damage to Internal Wiring
On November 8, 1985 Georgia Power Company submitted a preliminary report to
the NRC indicating that it had discovered burn damage to internal wiring in
several Limitorque motor operators installed in their Vogtle Unit 1 Power
Plant. Evidence suggested the burn damage had been caused by electric heater
elements installed in the limit switch compartment for storage purposes
within certain types of Limitorque motor operators.
On March 20, 1986 Georgia Power Company submitted a final report to the NRC
which suggested that the burn damage was a generic problem applicable to all
Limitorque motor operators. This assumption was based on a sampling
inspection of 104 Limitorque motor operators installed in Vogtle Unit 1.
Forty-six of the motor operators examined were Limitorque type SMB-000, and
six of these were found to have burnt internal wiring. Out of the 58
operators other than type SMB-000 which were inspected, 5 were found to
contain wires deemed susceptible to damage because of their close proximity
to the heater elements (less than 1/2 inch).
8608150010
.
IN 86-71
August 19, 1986
Page 2 of 3
On May 20, 1986 an NRC inspector, along with Limitorque, Georgia Power, and
Bechtel personnel, performed a random inspection on four type SMB-000
operators installed in Vogtle Unit 2. Three of the four operators were found
to contain burnt internal wiring. One type SMB-00 operator also was
inspected and was found to contain wiring susceptible to damage.
Discussion:
The wiring in question is Limitorque installed internal wiring located in
the operator limit switch compartment. The wiring is being burnt as a result
of its close proximity to, or contact with, the installed limit switch
compartment electric heater element or heater bracket. The wiring is not
properly routed and is not restrained from contacting the heater or heater
bracket. Although the heater is not a seismically or environmentally
qualified part and is intended for use only during storage, its use has been
shown to cause serious degradation of environmentally qualified internal
wiring.
The burnt wiring has been discovered only in Limitorque type SMB-000 motor
operators that contain previously energized heaters, although any Limitorque
operator that contains a previously energized heater could possibly exhibit
a similar problem.
Description of Circumstances - Cracked Limit Switch Rotors
Several licensees have submitted reports to the NRC concerning a problem
with cracked limit switch rotors on Limitorque motor operators installed
inside and outside of containment. The limit switches are used for control
of the motor operator and also provide indication of valve position in the
control room.
The cracks have been found on white melamine limit switch rotors. Most of
these cracks were found in the area where the limit switch rotors are pinned
to the pinion shafts. Some cracks have been found to extend halfway through
the melamine rotors, weakening them to the extent that they are easily
broken.
Discussion:
In its letter dated February 21, 1984 to the Westinghouse Electric
Corporation, Electro Mechanical Division, Cheswick, Pennsylvania Limitorque
recommended that any white limit switch components which are found with
cracks should be replaced with components manufactured with a later design,
brown colored material. Violations of 10 CFR Part 21 have been issued to
Limitorque for failure to report and for failure to evaluate defects
discovered in their motor operators. Licensees are reminded of their
responsibility to ensure that procurement documents include a contractual
requirement that the provisions of 10 CFR Part 21 apply (when applicable)
and that Criterion VII of 10 CFR Part 50 Appendix B requires that purchased
material, equipment, and services conform to the requirements of the
procurement documents.
.
IN 86-71
August 19, 1986
Page 3 of 3
No specific action or written response is required by this information
notice. If you have any questions about this matter, please contact the
Regional Administrator of the appropriate NRC regional office or this
office.
Edward L. Jordan Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: Jeffrey Jacobson, IE
(301) 492-8845
Attachment: List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Tuesday, March 09, 2021