United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 92-23: Results of Validation Testing of Motor-Operated Valve Diagnostic Equipment

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                           WASHINGTON, D.C.  20555

                               March 27, 1992


NRC INFORMATION NOTICE 92-23:  RESULTS OF VALIDATION TESTING OF 
                               MOTOR-OPERATED VALVE DIAGNOSTIC EQUIPMENT


Addressees

All holders of operating licenses or construction permits for nuclear power 
reactors and all vendors of motor-operated valve (MOV) diagnostic equipment.  

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information 
notice to alert addressees to the final results of validation testing of MOV 
diagnostic equipment conducted for the MOV Users Group (MUG) of nuclear 
power plant licensees.  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.

Background

In 1990, the MUG initiated a program to conduct tests of MOV diagnostic 
equipment to validate the accuracy asserted by the equipment vendors.  The 
MUG requested the Idaho National Engineering Laboratory (INEL) to provide a 
test stand for the program.  The NRC Office of Nuclear Regulatory Research 
(RES) provided funds for INEL to participate, with the stipulation that the 
results of the testing would be made available to the NRC and the public.  
The MOV diagnostic equipment vendors participating in the MUG test program 
were ASEA-Brown Boveri (ABB) Impell, ITI-MOVATS, Liberty Technologies, 
Siemens/KWU, Teledyne, and Wyle Laboratories.  The INEL test stand included 
a Limitorque motor operator which pushes a valve stem into a water reservoir 
with a compressed air overcharge, providing various loading conditions on 
the valve stem.  INEL obtained accurate measurements of thrust using a 
stem-mounted load cell as a reference standard.  Each diagnostic equipment 
vendor installed and operated its own equipment to measure various 
parameters so as to obtain estimates of stem thrust.  

At a public meeting on July 30, 1991, the MUG released a progress report of 
its program to validate the accuracy of MOV diagnostic equipment.  During 
the meeting, the MUG stated that licensees and diagnostic equipment vendors 
should review the progress report for its applicability to MOVs installed in 
nuclear power plants.  The MUG also alerted licensees and diagnostic 
equipment vendors to their responsibilities under Part 21 of Title 10 of the 
Code of Federal Regulations (10 CFR Part 21).  The NRC issued Information 

9203230070 
.

                                                            IN 92-23
                                                            March 27, 1992
                                                            Page 2 of 3


Notice 91-61 (September 30, 1991), "Preliminary Results of Validation 
Testing of Motor-Operated Valve Diagnostic Equipment," to alert licensees to 
the issues raised by the MUG progress report.

Description of Circumstances

At a public meeting on February 3, 1992, the MUG released "Final Report - 
MUG Validation Testing as Performed at Idaho National Engineering 
Laboratories (Volume 1)."  The report has been placed in the NRC Public 
Document Room (PDR), 2120 L Street, N.W., Washington, D.C. 20555 (telephone 
(202) 634-3273).  Upon receiving the remaining three volumes, which will 
provide data traces, test documentation, and torque measurement information, 
the staff will place these volumes in the PDR.  On March 4, 1992, the NRC 
staff discussed the MUG final report with members of the MUG committee that 
conducted the validation program.  The MUG final report presents the 
findings of the validation program and specifies whether or not the tested 
diagnostic equipment provided the accuracy claimed by its vendors in 
predicting stem thrust.  The MUG final report indicates that the MOV 
diagnostic equipment that relied on spring pack displacement to estimate 
stem thrust did not meet the accuracy claims of its vendors.  MOV diagnostic 
equipment that relied on other parameters such as stem or yoke strain was 
shown, in general, to meet the applicable accuracy claims, although certain 
equipment did not meet the accuracy claims in certain individual tests.

ABB Impell and ITI-MOVATS are two MOV diagnostic equipment vendors that have 
equipment commercially available that relies on spring pack displacement to 
estimate stem thrust.  At the MUG meeting in February 1992, ABB Impell 
representatives stated that they would work with their two licensee 
customers to develop new accuracy values.  On March 2, 1992, the NRC staff 
held a public meeting with representatives of ITI-MOVATS to discuss the 
accuracy of the thrust measuring device (TMD) used by ITI-MOVATS to estimate 
stem thrust based on spring pack displacement.  During the meeting on March 
2, the representatives of ITI-MOVATS described the results of their own 
field validation program that had been initiated to address the preliminary 
concerns raised in the MUG progress report.  However, the ITI-MOVATS program 
addressed only the accuracy of the TMD under static (zero differential 
pressure and flow) conditions and not the accuracy of this equipment under 
differential pressure and flow conditions.  Nevertheless, the results of the 
field validation program showed that the inaccuracy of the TMD may be larger 
than assumed in some instances by licensees.  The ITI-MOVATS representatives 
also discussed the results of their efforts to resolve concerns regarding 
the fact that the TMD is calibrated in the valve opening direction, but is 
also used to predict the thrust delivered by the actuator in the valve 
closing direction.  Although this study of valve directional effect by 
ITI-MOVATS focused on static conditions, the study indicated that the effect 
of the direction that the valve moves could increase significantly the 
uncertainty of the TMD.  

Discussion

Many licensees rely on MOV diagnostic equipment to provide information on 
the thrust required to open or close the valve and on the thrust delivered 
by the motor actuator.  The various types of MOV diagnostic equipment 
estimate valve stem thrust using different parameters, such as the 
displacement of the spring 
.

                                                            IN 92-23
                                                            March 27, 1992
                                                            Page 3 of 3


pack or the strain in the stem, mounting bolts, or yoke.  Some licensees 
make decisions regarding the operability of safety-related MOVs based on the 
thrust information obtained from the diagnostic equipment.  Therefore, the 
use of MOV diagnostic equipment can affect significantly the safe operation 
of a nuclear power plant.

The MUG validation program indicated that the accuracy of MOV diagnostic 
equipment that relies on spring pack displacement has not been verified to 
be within its original stated accuracy under differential pressure and flow 
conditions.  Further, the field validation program and valve directional 
effect study by ITI-MOVATS have shown an increase in the uncertainty of this 
MOV diagnostic equipment under static conditions.  Therefore, licensees who 
use MOV diagnostic equipment that relies on spring pack displacement to make 
decisions regarding the capability of MOVs to operate under design-basis 
conditions may have overestimated the capability of those MOVs.  A 
particular concern arises where a licensee has lowered the torque switch 
settings of its MOVs below the settings recommended by the actuator 
manufacturer based on thrust estimates from diagnostic equipment during 
tests conducted under static or partial design-basis differential pressure 
conditions.  

The NRC will address each case individually for MOV diagnostic equipment 
that was not included in the MUG validation program.  For example, the 
concerns regarding the accuracy of MOV diagnostic equipment that relies on 
spring pack displacement apply to all commercial or plant-specific MOV 
diagnostic equipment that relies on spring pack displacement to estimate 
stem thrust.  Similar concerns might be present for other MOV diagnostic 
equipment that also predicts stem thrust by indirect means, such as spring 
pack force.

"Load-sensitive behavior" in an MOV has been shown to result in less thrust 
delivered by the actuator under differential pressure conditions than 
delivered under static conditions.  "Load-sensitive behavior" is independent 
of the type of MOV diagnostic equipment used and such behavior can lead 
licensees to overestimate the capability of their MOVs.

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.


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

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

                     Edmund J. Sullivan, Jr., NRR
                     (301) 504-3266

Attachment:  List of Recently Issued NRC Information Notices
.
Page Last Reviewed/Updated Tuesday, November 12, 2013