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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 . 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. . 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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