Information Notice No. 85-22: Failure of Limitorque Motor-operated Valves Resulting from Incorrect Installation of Pinion Gear
SSINS No.: 6835
IN 85-22
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
March 21, 1985
Information Notice No. 85-22: FAILURE OF LIMITORQUE MOTOR-OPERATED
VALVES RESULTING FROM INCORRECT
INSTALLATION OF PINION GEAR
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP).
Purpose:
This information notice is provided to alert recipients of a potentially
significant problem pertaining to the incorrect installation of pinion gears
in Limitorque motor-operated valves. It is expected that recipients will
review the information for applicability to their facilities and consider
actions, if appropriate, to preclude a similar problem occurring at their
facilities. However, suggestions contained in this notice do not constitute
NRC requirements; therefore, no specific action or written response is
required.
Description of Circumstances:
On December 21, 1984 and February 20, 1985, the Tennessee Valley Authority
reported [Licensee Event Report (LER) 84-013] failure of the outboard high
pressure coolant injection (HPCI) valve to open at the Browns Ferry Nuclear
Power Station Unit 3. Operators observed the failure while attempting to
perform an operability surveillance on the HPCI system.
An inspection of the Limitorque operator revealed that the pinion gear had
been installed in a reversed position. This reversed installation resulted
in only about one third of the normal gear mesh surface and the complete
wearing away of the portion of the pinion gear teeth that were in contact
with the shaft (drive) gear. With the pinion gear teeth worn away, the motor
could no longer operate the valve. This inspection also revealed that the DC
shunt field for the operator had failed. With the shunt field open, the
valve travel speed was limited only by load. A review of completed
surveillances since 1980 revealed that the travel time for the valve had
been about 8 seconds. This is approximately one half of the normal travel
time of 16 seconds and may have accelerated the gear tooth erosion.
8503190659
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IN 85-22
March 21, 1985
Page 2 of 3
Discussion:
A similar problem was found at Browns Ferry Nuclear Power Station Unit 1
(LER 79-035 reported January 2 and March 11, 1980, and February 12, 1981)
and at Unit 2 (LER 80-2 reported March 11, 1980).
Several factors contribute to the potential for the reverse installation of
the pinion gear, including the following: (1) the reverse installation is
relatively easy and not readily detected by observation, (2) the reverse
installation is not revealed in postmaintenance testing (except for Limi-
torque operator Types SMB 00 and SMB 000), and (3) the pinion is installed
in one direction in certain types of Limitorque operators while in others it
is properly reversed 180". Because Limitorque valve operators are used for
many safety-related valve applications, the unexpected failure of a valve to
operate electrically could be very significant.
Corrective actions initiated by the licensee include:
1. Conducting a sampling of accessible safety-related Limitorque valve
operators to ensure correct pinion gear installation. Should the
sampling give a positive indication that other safety-related
Limitorque valve operators are suspect, develop a program for their
inspection to precede corrective action 4 below.
2. Adding a requirement for independent verification of the correct instal-
lation of pinion gear to applicable maintenance procedures.
3. Adding a caution statement to applicable maintenance and electrical pro-
cedures to ensure that personnel verify the correct Limitorque valve
operator model, and to warn that incorrect installation cannot be
detected in postmaintenance testing and can lead to unexpected failure
of the valve.
4. Adding inspection of the pinion gear installation and gear tooth wear to
the preventive maintenance program for Limitorque valve operators.
5. Adding the inspection of the shunt field for primary containment isola-
tion valve dc operators to the Limitorque valve operator inspection
program.
6. Providing training on proper pinion gear installation and the failure
mode for Limitorque valve operators to all responsible crafts personnel,
including electricians.
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IN 85-22
March 21, 1985
Page 3 of 3
No specific action or written response is required by this information
notice. If you have any question 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 Contacts: Silas David Stadler, RII
(404) 221-5600
Richard J. Kiessel, IE
(301) 492-8119
Attachment: List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Tuesday, March 09, 2021