Information Notice No. 91-07: Maintenance Deficiency Associated with General Electric Horizontal Custom 8000 Induction Motors

                                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
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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
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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 
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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