Information Notice No. 93-01: Accuracy of Motor-Operated Valve Diagnostic Equipment Manufactured by Liberty Technologies

                                UNITED STATES
                           WASHINGTON, D.C.  20555

                               January 4, 1993



All holders of operating licenses or construction permits for nuclear power


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice (IN) to alert addressees to new information on the accuracy of motor-
operated valve (MOV) diagnostic equipment manufactured by Liberty Technologies
when used to estimate the thrust delivered by a motor actuator in opening or
closing its valve.  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 are not NRC requirements; therefore, no specific action or written
response is required.


Most licensees rely on MOV diagnostic equipment to provide information on the
thrust delivered by the motor actuator in opening or closing its valve.  The
various types of MOV diagnostic equipment estimate valve stem thrust using
different parameters, such as displacement of the spring pack or strain in the
stem, mounting bolts, or yoke.  Liberty Technologies has developed MOV
diagnostic equipment, referred to as the Valve Operation Test and Evaluation
System (VOTES), that estimates the thrust needed to open or close a valve
based on strain of the valve yoke.  The VOTES equipment derives thrust from
yoke strain that has been calibrated to stem thrust using measured diametral
strain of the valve stem and nominal engineering material properties.

Many licensees make decisions regarding the operability of safety-related MOVs
that are based on diagnostic equipment thrust readings.  Therefore, the use of
MOV diagnostic equipment can have a significant effect on the safe operation
of a nuclear power plant.

Description of Circumstances

On October 2, 1992, Liberty Technologies notified the NRC, in accordance with
Part 21 of the Title 10 of the Code of Federal Regulations, that it had
determined that two new factors can affect the thrust values obtained with its


                                                           IN 93-01
                                                           January 4, 1993
                                                           Page 2 of 3

equipment.  Those factors involve (1) the possible use of improper stem
material constants and (2) the failure to account for a torque effect when the
VOTES equipment is calibrated by measuring strain in the threaded portion of
the valve stem.  In its October 2 submittal, Liberty Technologies states that
the factors mainly cause the thrust estimated by its equipment to be less than
the actual thrust.  Therefore, the factors will primarily relate to the
potential for the maximum allowable thrust limits of MOVs to be exceeded.  In
its October report, Liberty Technologies provided information on performing
manual calculations to address these factors and stated that its new software,
Version 2.3, assists in performing corrections to the thrust data.

During an inspection of the MOV program at the LaSalle Nuclear Power Station
in November 1992 (NRC Inspection Report 50-373/92-023 dated
December 16, 1992), the NRC found that the licensee had performed the manual
corrections of thrust data from MOV tests in accordance with guidance provided
by Liberty Technologies to address the stem material and torque effect issues. 
In certain instances, the licensee determined that the VOTES equipment had
underestimated by as much as 40 percent the thrust delivered by the motor
actuator in opening and closing its valve.  This underestimation of actual
thrust by the VOTES equipment raised questions regarding the effect of higher
thrust on the MOV assembly and the operation of the motor under degraded
voltage conditions for several MOVs.

Related Generic Communications

The NRC has issued other generic communications on the accuracy of MOV
diagnostic equipment and thrust limits.  Most recently, 

(1) On March 27, 1992, the NRC issued IN 92-23, "Results of Validation Test-
    ing of Motor-Operated Valve Diagnostic Equipment," to alert licensees to
    information regarding the accuracy of MOV diagnostic equipment
    manufactured by ITI-MOVATS and ASEA-Brown Boveri Impell.

(2) On December 17, 1992, the NRC issued IN 92-83, "Thrust Limits for
    Limitorque Actuators and Potential Overstressing of Motor-Operated
    Valves," to alert licensees to concerns identified in two programs used by
    licensees to increase thrust limits of Limitorque actuators.


                                                           IN 93-01
                                                           January 4, 1993
                                                           Page 3 of 3

This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.

                                     ORIGINAL SIGNED BY

                                  Brian K. Grimes, Director
                                  Division of Operating Reactor Support
                                  Office of Nuclear Reactor Regulation

Technical contact:  Thomas G. Scarbrough, NRR
                    (301) 504-2794

Attachment:  List of Recently Issued NRC Information Notices

Page Last Reviewed/Updated Thursday, March 25, 2021