Information Notice No. 84-13:Potential Deficiency in Motor-Operated Valve Control Circuits and Annunciation
SSINS No.: 6835
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
February 28, 1984
Information Notice No. 84-13: POTENTIAL DEFICIENCY IN MOTOR-OPERATED VALVE
CONTROL CIRCUITS AND ANNUNCIATION
All holders of a nuclear power reactor operating license (OL) or
construction permit (CP).
This information notice is provided to alert licensees to a specific design
in the circuitry used for control and annunciation of certain safety-related
electric motor-operated valves (MOVs). This design may, under thermal
overload (TOL) bypass condition, preclude timely detection of a failure of a
safety-related motor. Affected licensees may elect to modify their design to
provide continuous TOL trip annunciation and indication. No specific action
or response to this notice is required.
Description of Circumstances:
On September 2, 1983, Pennsylvania Power and Light Company's (PP&L's)
Susquehanna Steam Electric Station reported a condition related to a failed
MOV which supplies cooling water to the barometric condenser of the high
pressure coolant injection (HPCI) turbine and to the HPCI lube oil cooler
pump. The TOL had tripped when the valve torque switch malfunctioned. This
condition was not indicated or annunciated to the control room operator.
Investigation into the valve failure found a burned out electric motor. This
condition went undetected for approximately three weeks. PP&L identified
seven previous MOV failures involving overloads, electric motors, and/or
valve torque switches. The present control circuit design at Susquehanna
does not annunciate a motor overload condition or a burned out motor if the
key lock bypass switch is in a "bypass" position.
The purpose of the bypass feature around the TOL device is to avoid spurious
trips of MOVs under accident demand situations. One of the positions in
Regulatory Guide 1.106 is that the TOL should not preclude completion of the
safety function. At Susquehanna, the key lock bypass switch is normally kept
in the bypass position. This continuous bypass of the TOL during normal
operation is one means of complying with Regulatory Guide 1.106 since a
tripped TOL will not inhibit operation of the MOV.
February 28, 1984
Page 2 of 2
However, with the Susquehanna design, with the key lock in the bypass
position, there is no indication of a tripped TOL. In such designs, emphasis
is placed on assuring operability of the safety function rather than on
protecting individual components from damage. However, good engineering
practice would retain the TOL protection for normal or test functions of the
MOV. Such a design would permit the TOL protection for the motor to be
reinstated under test conditions.
Corrective Action Taken by Licensee:
1. Following the discovery of this situation, PP&L inspected all AC and DC
motors of the MOVs and found them satisfactory.
2. Shift supervisors were instructed that the key lock bypass switch
should remain in the "open" (test) position for at least thirty (30)
seconds following a valve closing operation, before the switch was
placed back to the "normal" (bypass) position. This would assure
indication in the control room if the overload relay actuated to
protect the motor of the MOV against a TOL condition.
3. As an interim measure PP&L implemented a surveillance testing program,
and is presently evaluating the bypass circuit design and possible
changes to provide for continuous annunciation and indication of TOL
trip conditions. Other licensees may elect to provide similar
If you have any questions regarding this matter, please contact the Regional
Administrator of the appropriate NRC Regional Office, or this office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: W. Laudan, IE
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