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 
                           WASHINGTON, D.C. 20555 

                               March 21, 1985 

                                  VALVES RESULTING FROM INCORRECT 
                                  INSTALLATION OF PINION GEAR 


All nuclear power reactor facilities holding an operating license (OL) or a 
construction permit (CP). 


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 

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. 


                                                           IN 85-22 
                                                           March 21, 1985 
                                                           Page 2 of 3  


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 

6.  Providing training on proper pinion gear installation and the failure 
    mode for Limitorque valve operators to all responsible crafts personnel,
    including electricians. 

                                                           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 

                                   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 Thursday, August 20, 2020