United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 92-70: Westinghouse Motor-Operated Valve Performance Data Supplied To Nuclear Power Plant Licensees

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                            WASHINGTON, D.C.  20555

                              September 25, 1992



All holders of operating licenses or construction permits for nuclear power


The U.S. Nuclear Regulatory Commission is issuing this information notice to
alert addressees to the possibility of overestimating the thrust capability of
motor-operated valve (MOV) actuators when using performance data from valve
manufacturers.  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.


Many nuclear power plant licensees have concluded that more thrust than was
originally predicted is often required to open or close many valves under
differential pressure and flow conditions.  They have made this conclusion
upon receiving plant experience and analyses associated with the activities
for resolving the issues discussed in Generic Letter 89-10 (June 28, 1989),
"Safety-Related Motor-Operated Valve Testing and Surveillance," and its
supplements.  Licensees have also found that in many cases the Limitorque
Corporation's typical guidelines indicate that the MOV actuator would not be
able to produce the required thrust.

Description of Circumstances

To overcome these calculated thrust deficiencies, some licensees are
attempting to use less conservative stall thrust data to justify MOV
capability.  For example, the Wolf Creek Nuclear Operating Corporation, the
licensee of the Wolf Creek Generating Station, used stall thrust data provided
by the Westinghouse Electric Corporation.  However, the MOVs were later found
to be unable to deliver the stated thrust.

On July 7 to 9, 1992, the NRC Vendor Inspection Branch conducted an inspection
at Westinghouse to review the basis for the MOV thrust data given to the
nuclear industry.  During this inspection, the team determined that 


                                                           IN 92-70
                                                           September 25, 1992
                                                           Page 2 of 3

Westinghouse has supplied licensees with stall thrust data based on tests
performed for Westinghouse by Limitorque as part of the procurement process. 
As noted in NRC Inspection Report 99900404/92-01 (August 14, 1992) the NRC
team found a number of factors that can reduce the thrust delivered by the
actuator that were not addressed in the testing for Westinghouse.  Examples
that the staff found included:

1.    Limitorque performed the tests of actuator thrust capability under
      static (no load) conditions.  Therefore, the actuator thrust output did
      not reflect load sensitive behavior (also referred to as the rate of
      loading effect) which has been observed to reduce the thrust delivered
      by an actuator when the valve is operated against differential pressure
      and flow conditions.

2.    In testing the actuator, Limitorque did not determine the stem friction
      coefficient, which must be considered in calculating the conversion of
      torque produced by an actuator to the thrust delivered in operating the
      valve.  If the actual stem friction coefficient for an MOV installed in
      a nuclear power plant is greater than the stem friction coefficient
      during the Limitorque tests, the actuator would produce less thrust when
      installed than claimed by the valve supplier.  Stem lubrication
      conditions can significantly affect the stem friction coefficient. 
      During the Limitorque testing, valve stem lubrication was not

3.    In its documentation of the actuator tests, Limitorque did not discuss
      the inaccuracies of the test equipment or uncertainties in reading test

4.    Limitorque conducted the actuator tests under mild ambient conditions
      and did not address the degree to which the thrust output might be
      reduced if the MOV is located in a high temperature environment.


Stall thrust testing during procurement of an actuator does not address all of
the factors that may affect the capability of the actuator to operate its
valve when installed in a nuclear power plant.  Licensees may overestimate the
capability of actuators to operate valves if the licensees use stall test
data, such as those supplied by Westinghouse, without considering all factors
affecting operability.  Overestimation of the capability of an actuator can
lead to incorrectly concluding that an MOV is operable and capable of
performing its safety function.

Related Generic Communications

The NRC has issued other generic communications describing information or
actions by vendors and suppliers that, unless adequately verified by
licensees, can affect the operability of MOVs in nuclear power plants.  For
example, the NRC issued Information Notices 91-61 (September 30, 1991),
"Preliminary Results of Validation Testing of Motor-Operated Valve Diagnostic
Equipment," and IN 92-23 (March 27, 1992), "Results of Validation Testing of
Motor-Operated Valve Diagnostic Equipment," to alert licensees to the results.

                                                           IN 92-70
                                                           September 25, 1992
                                                           Page 3 of 3

of a testing program by the MOV Users Group of nuclear power plant licensees
that revealed that certain MOV diagnostic equipment did not meet the accuracy
claims of its vendors.

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

                                      ORIGINAL SIGNED BY

                                   Charles E. Rossi, Director
                                   Division of Operational Events Assessment
                                   Office of Nuclear Reactor Regulation

Technical contacts:  Jeffrey B. Jacobson, NRR
                     (301) 504-2996

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

                     Dr. P. K. Eapen, RI
                     (215) 337-5150

                     Michael F. Runyan, RIV
                     (817) 860-8142

Attachment:  List of Recently Issued NRC Information Notices

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