United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 92-59: Horizontally-Installed Motor-Operated Gate Valves

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

                                August 18, 1992

                               GATE VALVES


All holders of operating licenses or construction permits for nuclear power


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to problems with the performance of motor-operated
gate valves that are installed in a horizontal position.  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.

Description of Circumstances

Three licensees recently informed the NRC staff that they had problems testing
motor-operated valves (MOVs) that had been installed with the valve disc
oriented horizontally. 

On March 13, 1992, the Southern California Edison Company, licensee for the
San Onofre Nuclear Generating Station, informed the NRC that two of four
4-inch gate MOVs in the high pressure coolant injection/low pressure coolant
injection (HPCI/LPCI) combined miniflow line at Unit 3 failed to close during
design-basis differential pressure and flow testing performed in response to
Generic Letter (GL) 89-10, "Safety-Related Motor-Operated Valve Testing and
Surveillance."  The licensee adjusted the MOVs in the Unit 3 miniflow line to
satisfy the thrust requirements demonstrated by the tests.  Before testing the
Unit 3 MOVs, the licensee had added new spring packs and provided higher gear
ratios in these MOVs as part of its GL 89-10 program.  However, the licensee
did not modify the motor operators for the Unit 2 HPCI/LPCI miniflow MOVs,
which remained sized and setup under the old assumptions of the licensee's
program in response to NRC Bulletin 85-03, "Motor-Operated Valve Common Mode
Failures During Plant Transients Due to Improper Switch Settings."  Therefore,
the licensee shut down Unit 2 as a safety precaution because of the concern
that the Unit 2 miniflow MOVs would not be able to perform their safety
function.  The licensee then improved the Unit 2 miniflow MOVs with new spring


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packs and higher gear ratios to allow the MOVs to satisfy the higher thrust 
requirements.  The licensee tested the improved Unit 2 miniflow valves under
design-basis differential pressure and flow conditions, and they performed 
satisfactorily.  The licensee evaluated the Unit 2 test data and determined
that its decision to shut down Unit 2 was appropriate because the test results
revealed that the Unit 2 miniflow MOVs could not have operated in their old
configuration under design-basis conditions.  The licensee believed that the
higher thrust requirements for these MOVs resulted from their horizontal
orientation, which caused additional sliding friction on the valve discs.  

During a midcycle outage in October 1991 at the Crystal River Plant, the
Florida Power Corporation, the licensee, tested emergency feedwater (EFW)
MOV EFV-14 from EFW pump EFP-1 to the "A" steam generator under differential
pressure and flow conditions as part of its program in response to GL 89-10. 
During the test, the valve did not close electrically under the design-basis
differential pressure conditions calculated by the Babcock & Wilcox Company
(B&W) for Crystal River.  The EFW system at Crystal River has four discharge
isolation valves, one in each of the EFW supply lines to the once-through
steam generators (OTSGs).  The MOVs are required to close during a high-energy
line break to isolate flow to the damaged OTSG thereby only supplying the
undamaged OTSG.  At that time, the licensee believed that the differential
pressure calculated for EFV-14 by B&W was greater than the actual design-basis
differential pressure.  On April 28, 1992, the licensee notified the NRC staff
that it had determined that the differential pressure calculated for EFV-14
was actually greater than the value calculated by B&W.  Thus, the October 1991
test failure had properly revealed that EFV-14 could not perform its safety
function to close under design-basis differential pressure.  In its April 28
notification, the licensee indicated that it had closed EFV-14 and the
parallel EFV-11 from EFP-2 to the "A" steam generator because of its similar
design to EFV-14.  The licensee reviewed the results of previous testing and
concluded that the EFW control logic could open these MOVs if needed.  Before
the failed test, the licensee had set EFV-14 using assumptions more
conservative than those of some other licensees, but EFV-14 nevertheless
failed to operate under design-basis differential pressure conditions.  After
April 28, the licensee conducted differential pressure tests on the other
three EFW MOVs (including EFV-11) and found those MOVs also to be incapable of
closing under design-basis differential pressure and flow.  All four of these
MOVs are installed horizontally.  The licensee attributed the failure of the
EFW MOVs to their horizontal orientation.  The licensee has modified the four
EFW MOVs and successfully tested them under design-basis differential pressure

On April 14, 1992, the Power Authority of the State of New York, the licensee
of the James A. FitzPatrick Nuclear Power Plant, notified the NRC staff that
the double disc gate valves 10 MOV-16A and 10 MOV-16B in residual heat
removal/low pressure coolant injection pump minimum flow lines might not be
able to fully seat during closure because they do not include wedge springs. .

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After conducting MOV tests, the licensee had noted unusual valve behavior
reviewing diagnostic traces and requested the valve manufacturer
Anchor/Darling to explain the behavior of these valves.  Anchor/Darling
informed the licensee that it did not include "wedge springs" and "disc
retainers" in its double disc gate valves manufactured before 1975 (such as 
10 MOV-16A&B) when it believed that the valves were to be installed with the
valve stem vertical and pointing upward.  The wedge spring allows the valve to
be installed in any orientation by maintaining separation of the discs and
preventing wedging before the disc contacts the valve seat.  The disc
retainers improve performance during valve closure by limiting disc wobble. 

Because 10 MOV-16A and 10 MOV-16B are installed horizontally, the licensee
determined that premature wedging could prevent these valves from closing when
required for containment isolation.  The licensee has installed wedge springs
in the valves to correct the problem.  


Many nuclear power plant licensees have begun testing MOVs as part of their
programs in response to GL 89-10.  Some licensees have found that the thrust
required to operate MOVs under differential pressure and flow conditions is
greater than predicted by the valve vendor using the industry's standard
equations and valve factors.  Some licensees have believed that the higher
thrust would be required only under blowdown conditions.  However, licensees
have found more thrust than predicted is required to operate some MOVs under
pumped flow conditions.  Although higher-than-predicted thrust requirements
have been observed for MOVs in various installed orientations, MOVs in
horizontal positions may be especially susceptible to performance problems,
including higher thrust requirements.

Installing an MOV in a horizontal orientation can also lead to maintenance and
performance problems other than those caused by the friction or binding of the
disc.  For example, either the actuator spring pack or motor is at the lowest
point of an MOV in a horizontal orientation.  If the spring pack is at the
lowest point, excessive grease in the spring pack might cause hydraulic lock,
which would prevent the torque switch from tripping and might overstress the
MOV or cause the motor to burn out.  If the motor is at the lowest point, the
gasket between the motor and actuator might allow grease to fill the motor and
cause it to fail..

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

                     Mckenzie Thomas, RII
                     (404) 331-5599

                     Christopher Myers, RV
                     (510) 975-0260

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