Information Notice No. 90-72: Testing of Parallel Disc Gate Valves in Europe

                                UNITED STATES
                           WASHINGTON, D.C.  20555

                              November 28, 1990

Information Notice No. 90-72:  TESTING OF PARALLEL DISC GATE VALVES 
                                   IN EUROPE


All holders of operating licenses or construction permits for nuclear power 


This information notice is intended to alert addressees to the results of 
tests of parallel disc gate valves by researchers from the United Kingdom 
(UK) and the Federal Republic of Germany (FRG).  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.


On October 15 to 19, 1990, members of the U.S. Nuclear Regulatory Commission 
(NRC) staff met with nuclear regulatory authorities and industry 
representatives in the UK and the FRG to discuss the performance of 
motor-operated valves (MOVs) at nuclear power plants.  During these 
discussions, researchers from both the UK and the FRG described tests of the 
operation of parallel disc gate valves under high differential pressure and 
flow conditions.  According to the UK and FRG researchers, the tests 
resulted in internal damage to the gate valves.  This damage included 
abrasion and galling of the disc and seat sliding surfaces.  Because of this 
damage, significantly more thrust was required to operate the valves than 
was predicted by the commonly-used equation.  In some instances, the 
increased thrust requirements could have exceeded the setting of the MOV 
torque switch or the capability of the motor operator.

During the meetings, the FRG representatives reported that an improved 
design for parallel disc gate valves had been developed.  This improved 
design has additional sliding surface area to eliminate the excessive thrust 
requirements for valve operation.  The FRG representatives reported that, as 
a result of their valve tests, the FRG valve vendors now typically assume a 
valve friction factor of 0.4 (plus or minus 0.1) in the commonly-used 
equation to estimate the thrust required to operate the improved valve 
design.  In the United States, a valve friction factor of 0.2 is typically 
assumed for all parallel disc gate 


                                                       IN 90-72
                                                       November 28, 1990
                                                       Page 2 of 2

valves even though little research has been conducted regarding the 
performance of these valves under conditions of high differential pressure 
and flow. 

A summary of the FRG parallel disc gate valve tests is provided in "Testing 
of Safety-Related Valves of PWR and BWR Power Plants," by U. Simon, N. 
Rauffmann, and H. Schafer, which is printed in The American Society of 
Mechanical Engineers, PVP - Volume 180, Pipeline Dynamics and Valves (1989).

The parallel disc gate valve tests performed by the UK and FRG researchers 
provided results similar to the results of the NRC-sponsored tests of 
flexible-wedge gate valves performed by researchers at the Idaho National 
Engineering Laboratory.  As with the tests of parallel disc gate valves 
performed by UK and FRG researchers, the NRC-sponsored tests revealed that 
internal damage may occur to the flexible-wedge gate valves when operated 
under conditions of high differential pressure and flow.  Because of this 
internal damage, the thrust required to operate the flexible-wedge gate 
valves exceeded the thrust predicted from the commonly-used equation and 
typical friction factors.  The NRC-sponsored test results were discussed at 
public meetings on February 1, 1989, and April 18, 1990, and are summarized 
in NRC Information Notice 90-40, "Results of NRC-Sponsored Testing of 
Motor-Operated Valves."

Licensees and construction permit holders may wish to consider the results 
of the UK and FRG tests when evaluating the capability of 
currently-installed parallel disc gate valves and when considering the 
adequacy of replacement valves.

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 NRR project manager.

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

Technical Contact:  Thomas G. Scarbrough, NRR
                    (301) 492-0794

Attachment:  List of Recently Issued NRC Information Notices

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