IE Circular No. 78-16, Limitorque Valve Actuators


                               UNITED STATES 
                          WASHINGTON, D.C. 20555 

                              July 21, 1978 

MEMORANDUM FOR:     B. H. Grier, Director, Region I 
                    J. P. O'Reilly, Director, Region II 
                    J. G. Keppler, Director, Region III 
                    K. V. Seyfrit, Director, Region IV 
                    R. H. Engelken, Director, Region V 

FROM:               Norman C. Moseley, Director, ROI, IE 


The subject document is transmitted for issuance on July 26, 1978. The 
Circular should be issued to all power reactor facilities with an operating 
license or a construction permit. Also enclosed is a draft copy of the 
transmittal letter. 

                                   Norman C. Moseley, Director 
                                   Division of Reactor Operations 
                                   Office of Inspection and Enforcement 

1.  IE CircUlar No. 78-16 
2.  Draft Transmittal Letter 

CONTACT:  H. A. Wilber, IE 

(Draft letter to all pow er reactor facilities with an operating license or 
a construction permit) 

                                                         IE Circular 78-16 

The enclosed Circular 78-16 is forwarded to you for information. If there 
are any questions related to your understanding of the suggested actions, 
please contact this office. 

                                   (Regional Director) 

1.  IE Circular 78-16 
2.  List of IE Circulars 
      Issued in 1978 

                             UNITED STATES 
                         WASHINGTON, D. C. 20555 

                              July 26, 1978 

                                                         IE Circular 78-16 


Description of Circumstances: 

At Rancho Seco, a Limitorque Type SMB-2 motor-driven valve actuator in a 
safety feature system failed to function. The failure resulted from clutch 
wear which was due to manual operation of the valve and improper heat 
treatment of the clutch parts. Other SMB valve actuators at Rancho Seco had 
been subjected to undue clutch wear but were still operable. Based on 
information obtained from the licensee and from Limitorque Corporation, 
undue wear appears to be limited to Type SMB-0, 1, 2, and 3 valve actuators 
equipped with 3600 rpm motors. 

The type SMB valve actuator is provided with a handwheel so that the valve 
can be actuated manually in the event that power is unavailable. To shift 
from motor drive to handwheel drive, the operator must manually position a 
clutch so that the motor is disengaged from the drive train and the 
handwheel is engaged. The clutch latches into this position and cannot be 
manually repositioned. The next time that the motor is energized, the latch 
releases automatically and a spring repositions the clutch so that the motor 
engages the drive train. 

When the clutch is repositioned, a pair of lugs on the motor-side of the 
clutch engages a pair of lugs on the valve-side. At the instant the lugs 
engage, the lugs on the motor-side are being accelerated to full speed and 
the lugs on the valve-side are stationary. Before the motor is energized, 
the relative position of the lugs is random. This initial position 
determines the depth of engagement or bite at the instant the lugs make 
contact. When a full bite occurs, no damage is caused to the lugs. When a 
grazing bite occurs, the edges of the lugs are chipped or upset. After the 
edges are sufficiently rounded, the clutch will not engage and hold for 
motor actuation. 

                                  1 of 2 

July 21, 1978                                              IE Circular 78-16

The licensee estimated that the failure of the Type SMB-2 valve actuator 
occurred after it had been clutched 25 to 100 times. The valve which failed 
to function at Rancho Seco (SFV-25003) is operated by the actuator and is a 
safety features valve in a line connecting the borated water storage tank to
a high pressure safety injection pump and a decay heat removal (low head 
safety injection) pump. The valve actuator is wired so that the valve which 
it controls will drive to the fully open or fully closed position once the 
motor is energized. 

SFV-25003 is used for various routine operations during refueling, e.g. 
adding borated water to the primary cooling system. In these instances, the 
operator uses SFV-25003 as a throttle valve. To do this, the valve must be 
actuated manually, giving rise to the potential damage to the lugs as 
described above. This would not occur with the type of valve actuator that 
is clutched with the motor at rest. Likewise, a separate throttle valve for 
supplying borated water during routine operation would preclude the need for
manual operation of the subject valve actuator. 

Limitorque Corporation has a test program in progress for determining the 
clutch life of Type SMB 0, 1, 2, and 3 valve actuators. Results to date are 
inconclusive. Pending other resolution of the problem, the licensee has 
stated that the valve will be stroked with the motor drive to ensure that 
the clutch has engaged the motor following manual actuation of the valve. 

All licensee and construction permit holders should consider: 

     For Limitorque Type SMB-0, 1, 2, and 3 valve actuators with 3600 rpm 
     motors which are used or will be used in engineered safety systems; 

     1)   The potential for failure of the actuators resulting from manual 

     2)   Means for minimizing manual operation and, 

     3)   Procedures for verifying that the actuator is operable with the 
          motor after manual operation. 

No written response to this Circular is required. If you require additional 
information regarding this matter, contact the Director of the appropriate 
NRC Regional Office. 

                                  2 of 2 

Page Last Reviewed/Updated Thursday, March 25, 2021