United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 89-88: Recent NRC-Sponsored Testing Of Motor-Operated Valves

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

                              December 26, 1989


Information Notice No. 89-88:  RECENT NRC-SPONSORED TESTING OF 
                                   MOTOR-OPERATED VALVES 

Addressees:

All holders of operating licenses or construction permits for nuclear power 
reactors.

Purpose:

This information notice is intended to alert addressees to potential 
problems identified as a result of recent NRC-sponsored testing of 
motor-operated valves (MOVs).  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 do not constitute NRC requirements; therefore, no 
specific action or written response is required.

Description of Circumstances:

The NRC-sponsored blowdown testing of six motor-operated, flexible wedge 
gate valves was recently completed.  The test results are generally 
applicable to any MOV that must open or close in a high flow, a high 
differential pressure, or a low subcooling situation.

The tests were sponsored by the NRC and conducted by the Idaho National 
Engineering Laboratory (INEL) at the Kraftwerk Union (KWU) facility in the 
Federal Republic of Germany.  The test results substantiated and expanded 
the concerns that were previously identified with the operational capability 
of MOVs in high flow, high differential, or low subcooling applications.  
These previous concerns were identified by INEL testing of two MOVs at the 
Wyle Labs facility in Huntsville, Alabama, and were reported in 
NUREG/CR-5406, "BWR Reactor Water Cleanup System Flexible Wedge Gate 
Isolation Valve Qualification and High Energy Flow Interruption Test."  The 
expanded concerns now include (1) valves supplied by four different 
manufacturers; (2) valves of two different sizes (i.e., 6- and 10-inch 
valves); (3) water conditions, including several different subcoolings and 
pressures; and (4) saturated steam conditions at several different 
pressures.

Using experience gained from the Wyle tests, INEL adjusted the torque 
switches to obtain higher stem thrust values than would have been required 
using the standard industry design formula.  This was done to assure 
isolation of the 




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                                                       IN 89-88 
                                                       December 26, 1989 
                                                       Page 2 of 3 


vast majority of flow through each valve during each blowdown.  However, 
these adjustments may have resulted in the stem thrust available during the 
blowdown tests being above that currently being used (and possibly also 
above the mechanical and electrical capabilities) for some currently 
installed valve and motor operator assemblies.  Even with the high settings 
used during the KWU tests, several blowdowns resulted in closure of the flow 
area but did not achieve full seating of the valve.  During one such test, 
there was considerable leakage through the valve after the valve stopped its 
closure stroke.

The KWU test results confirm the concern raised by the Wyle testing.  The 
KWU test data has not been fully evaluated at this time, but preliminary 
review indicates that

1.   The valves required stem thrusts well in excess of those predicted by 
     the industry design formula in use at the time of their design and 
     manufacture.

2.   The required stem thrust of the valves was not linearly dependent on 
     the differential pressure across the valve at the time of closure.  
     This circumstance precludes determination of the required stem thrust 
     from data that could be obtained under normal plant operating 
     conditions.

3.   The thrust at which torque switch trip occurs was not constant with 
     respect to the loading history of the valve.  Many within the industry 
     refer to this as the "rate of loading" phenomenon.  However, the 
     testing indicates that there may be more involved than variations of 
     the torque switch spring pack's response time.

4.   The stem factor (i.e., the ratio of the motor operator's output torque 
     to the valve's stem thrust) appears to be dependent on direction and 
     magnitude of the load being applied to the stem.

5.   Several of the valves significantly damaged themselves during closure.

NRC plans to hold an information meeting to present the KWU test results for 
industry peer review.  The meeting and a data report are planned for the 
early part of 1990.

Related Generic Communications:

The general concern about the ability of MOVs to function properly when 
subjected to design-basis loadings has been previously addressed in NRC 
Bulletins 81-02, "Failure of Gate-Type Valves to Close Against Differential 
Pressure," and 85-03, "Motor-Operated Valve Common Mode Failures During 
Plant Transients Due to Improper Switch Settings"; NRC Circular 77-01, 
"Malfunctions of Limitorque Valve Operators"; and 
NRC Information Notices 81-31, "Failure of Safety Injection Valves to 
Operate Against Differential Pressure," 85-50, "Complete Loss of Main and 
Auxiliary Feedwater at a PWR Designed by Babcock & Wilcox," and 89-61, 
"Failure of Borg-Warner Gate Valves to Close Against Differential Pressure."
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                                                       IN 89-88 
                                                       December 26, 1989 
                                                       Page 3 of 3 


In addition, Generic Letter 89-10, "Safety-Related Motor-Operated Valve 
Testing and Surveillance," requested all addressees to develop a program for 
the testing, inspection, and maintenance of MOVs so as to provide the 
necessary assurance that the MOVs will function when subjected to the 
design-basis conditions that are to be considered during both normal 
operation and abnormal events in the design basis of the plant.  

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 contacts listed below or the appropriate NRR project manager.




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


Technical Contacts:  Hugh W. Woods, RES
                     (301) 492-3908

                     Richard J. Kiessel, NRR
                     (301) 492-1154


Attachment:  List of Recently Issued NRC Information Notices

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