Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No: 6835
IN 86-02
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
January 6, 1986
Information Notice No. NO 86-02: FAILURE OF VALVE OPERATOR MOTOR DURING
ENVIRONMENTAL QUALIFICATION TESTING
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP)
Purpose:
This notice is to alert recipients of a potentially significant problem
involving the failure of Reliance Motor Corporation magnesium motors during
environmental qualification (EQ) testing of Limitorque valve operators for
River Bend and Nine Mile Point 2 nuclear power stations It is expected that
recipients will review this information for applicability to their
facilities and consider actions, if appropriate, to preclude a similar
problem occurring at their facilities However, suggestions contained in
this notice do not constitute NRC requirements; therefore, no specific
action or written response is required
Description of Circumstances:
On August 30, 1985, the General Electric Company (GE) reported to the NRC
that they had experienced test anomalies of the Reliance, class RH, ac
motors during EQ testing of a Limitorque fast-acting SMB-3-150 valve motor
operator for its Gulf States Utilities (River Bend) and Niagara Mohawk (Nine
Mile Point 2) BWR customers These motors have magnesium rotors Magnesium
rotor motors have previously undergone EQ testing by Limitorque (PWR
Qualification - Project 600456A) without failures However, during the
current testing, three motors failed during the 100-day design-basis-event
(DBE) test The first motor had been subjected to the 40-year qualification
series of radiation, thermal, mechanical, and dynamic aging before the
loss-of-coolant-accident (LOCA) testing This motor had been exposed for 7
days to a steam environment with temperatures as high as 355F when the
rotor bar at the interface with the end ring had corroded, causing
separation of the end ring from the conducting bars A second (unaged) motor
was then substituted into the test; after 14 days in the steam environment,
with a maximum temperature of 245F, it experienced the same failure as
the first motor A third (unaged) motor experienced the same failure
following 43 days with a maximum temperature of 223F
8512310466
IN 86-02
January 6, 1986
Page 2 of 2
Discussion:
Limitorque Corporation has used Reliance medium and large (180 frame and
larger) ac motors, with magnesium alloy as a standard rotor material, in its
operators for many years Although all specific applications and affected
power plants could not be identified, Limitorque has concluded that all
domestic nuclear power facilities, using Limitorque actuators, would have
several motors in 180-frame size and larger containing magnesium alloy
rotors The magnesium alloy rotors have been primarily used where high
torque, high horsepower, fast-acting motors are required Reliance Motor
Corporation has stated that, while they are reviewing possible design
changes to prevent corrosion of the rotor in high temperature steam
environments, there are no existing rotors available to replace the
magnesium alloy components and retain the same motor characteristics
General Electric has reviewed the BWR applications and has provided
recommended action via Service Information Letter No 425 (July 17, 1985)
In summary, GE recommends that licensees determine the plant-specific
applications of magnesium motors subject to harsh environment, the adequacy
of long-term cooling could be evaluated assuming failure of the magnesium
rotor MOVs a few days after the DBE Some systems may allow for the operator
to position the valve to its safety position immediately following the DBE
instead of waiting for automatic actuation, while other systems may require
realignment to a standby mode after initial core cooling In addition to
operator training, it may be prudent to disconnect some of the valve
actuation logic following safety positioning to prevent valve realignment
without operator initiation Other corrective actions may be appropriate for
specific applications
PWR owners may wish to review their Limitorque MOV qualification packages in
light of this new information If the review determines that the equipment
may not be qualified for its intended use then they may wish to consider
taking action, as recommended by GE for BWRs and as described above, to
mitigate the potential for long-term core cooling problems caused by
motor-operated valve (MOV) failures in the days following a DBE
No specific action or written response is required by this information
notice If you have any questions about this matter, please contact the
Regional Administrator of the appropriate regional office or this office
Edward L Jordan Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: James E Stewart
(301) 492-9061
Attachment:
List of Recently Issued IE Information Notices
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