Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
February 4, 1991
Information Notice No. 91-07: MAINTENANCE DEFICIENCY ASSOCIATED WITH
GENERAL ELECTRIC HORIZONTAL CUSTOM 8000
INDUCTION MOTORS
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is to alert addressees to a possible problem
resulting from improper maintenance that may affect the operability of
Horizontal Custom 8000 induction motors manufactured by the General Electric
Company (GE). The problem relates to inadequate tightening of the bolts
securing the air deflectors to the motor-end shield. 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:
On August 24, 1990, Northeast Utilities (NU), the licensee for the Millstone
Nuclear Power Station, Unit 3, notified the U.S. Nuclear Regulatory
Commission (NRC) that the lower fan shroud on the inboard side of one of the
reactor plant component cooling water pump (RPCCW) motors had come loose and
impacted the motor rotor causing a loud noise during its operation. The
licensee inspected the motor and determined that the protective glass tape
on the end turns of the drive-end winding had sustained damage; however, the
mica insulation was not damaged. Additional observations indicated that the
drive-end lower air deflector was loose and damaged with minor tears and
cracks. The licensee evaluated the available evidence and determined that
the cause of failure was the loosening of the clamps of the drive-end lower
air deflector. The licensee believes that excessive vibration caused the
clamping bolt to loosen and that a reduction in the metal contact grip of
the clamps and the air deflector (because metal had been worn away at the
corner) permitted the air deflector to loosen. GE repaired the damaged
motor by welding the lower shroud clamping bracket. A licensee inspection
of the other two RPCCW pump motors and additional motors of similar size and
model identified loosened shrouds on six motors and one with cracked upper
shrouds. The licensee tightened the loose bolts and repaired the cracks by
welding.
9101290149
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IN 91-07
February 4, 1991
Page 2 of 3
Discussion:
Typically, the GE Horizontal Custom 8000 series motor models are assembled
with split air deflectors at both ends of the motor. The circular air
deflectors are cut through the center into two halves, and each half is
secured to the motor-end shield with clamps, hex-head machine screws, and
star-lock washers at the circumference of the air deflectors. Similar
vertical motors are equipped with upper and lower air deflectors
(constructed from one piece, instead of two halves). In both designs, the
air deflectors direct incoming air to shaft-driven fans and cool the motor
and stator. In the vertical motor, the upper deflector is mounted directly
over the fan and is supported either by brackets or by 1/4-20 hex-head
machine screws. If a bracket or screw(s) fails, it could fall into the
rotating fan and be propelled into the winding end-turn, causing failure of
the motor.
In General Electric Nuclear Energy (GENE) Service Information Letter (SIL)
No. 484 of March 29, 1989, GENE discussed problems with air deflectors
installed in vertical motors. This SIL summarized several other specific
experiences and lessons learned from the use of similar GE alternating
current (AC) induction motors in various applications in boiling water
reactors (BWRs). In paragraph 8 of this SIL, GENE (1) described the purpose
of air deflectors in vertical motors, (2) discussed the damage that may
result if a bracket or screw loosens and falls into the rotating fan, (3)
recommended that owners ensure that their procedures for motor disassembly
and overhaul should include a provision to visually inspect the air
deflector fasteners, and (4) recommended that the 1/4-20 hex-head screws
securing the air deflector be replaced during each reassembly. On October
5, 1990, GENE issued Supplement 1 to SIL No. 484, which discussed several
additional lessons learned from the application of the AC induction motors.
In Paragraph 2 of this SIL, GENE discussed its experience with loose air
deflectors on Horizontal Custom 8000 Motors and recommended that users
ensure that the screws securing the air deflectors were tightened and
maintained at the required torque. The SIL requested users to contact the
GENE local representative for information pertaining to a design
modification to prevent bolt loosening for some motor models.
Because the issues discussed in the SILs only reflected BWR experience, GENE
only issued the SILs to BWR owners. Therefore, the NRC is concerned that
non-BWR owners may not have received all of the information on these
problems. Although GE normally sends service advisory letters (SALs) to
other equipment manufacturers and non-BWR owners to communicate problems
identified in GE products, GENE has informed the NRC that it had not issued
SALs on this matter because the GE facility that manufactured these types of
motors ceased to exist. Therefore, a copy of GENE SIL No. 484 and Supplement
1 to SIL 484 has been enclosed with this information notice for the benefit
of non-BWR addressees.
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IN 91-07
February 4, 1991
Page 3 of 3
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: Kamal R. Naidu, NRR
(301) 492-0980
Attachments:
1. SIL No. 484, March 29, 1989
2. Supplement 1 to SIL No. 484, October 5, 1990
3. List of Recently Issued NRC Information Notices
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