United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 87-30: Cracking of Surge Ring Brackets in Large General Electric Company Electric Motors

                                                 SSINS No.: 6835 
                                                     IN 87-30 

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                      OFFICE OF NUCLEAR REACTOR REGULATION
                                WASHINGTON, D.C.

                                  July 2, 1987


Information Notice No. 87-30:  CRACKING OF SURGE RING BRACKETS IN LARGE 
                                   GENERAL ELECTRIC COMPANY ELECTRIC MOTORS


Addressees:     

All nuclear power reactor facilities holding an operating license or a con-
struction permit. 

Purpose: 

This notice is provided to alert recipients to a potentially significant 
safety problem that could result in the loss of safety-related equipment, such 
as residual heat removal (RHR), core spray, and high-pressure pumps that are 
driven by large, vertical electric motors manufactured by General Electric 
Company (GE).  It is expected that recipients will review this information for 
applicability and consider actions, as appropriate, to preclude a similar 
problem at their facilities.  However, suggestions contained in this notice do 
not constitute NRC requirements; therefore, no specific action or written 
response is required. 

Background: 

Felt blocks are used in large electric motors to keep the windings separated 
where they loop back at the end of the stator.  The blocks are attached to a 
surge ring that is held in place by L-shaped surge ring brackets welded to the 
surge ring and bolted to the motor casing.  Failure of these surge ring brack-
ets and cracking of the felt blocks allows movement and wear of the end-turns, 
leading to a reduction in insulation resistance and possible motor failure.  
In addition, broken pieces of the surge ring bracket may enter the space 
between the stator and the rotor, resulting in electrical or mechanical motor 
degradation.  

Description of Circumstances: 

During the 1985 outage at Peach Bottom Atomic Power Station, Unit 3, broken 
surge ring brackets were discovered in a 2000-horsepower (hp) RHR pump motor 







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and a 600-hp core spray pump motor.  Attempts to repair the brackets by 
welding were unsuccessful, and they were removed from the motors at GE's 
suggestion.  The licensee for Peach Bottom is reevaluating the motor design 
and the need to replace the brackets.

During the week of November 10, 1986, the licensee for Cooper Nuclear Station 
inspected its 1000-hp RHR pump motors and discovered that three of four motors 
had broken lower surge ring brackets and cracked upper and lower end-turn felt 
blocks.  In the B motor, five of six lower brackets were fractured.  Repairs 
were made and periodic visual inspections are being conducted. 

GE informed the NRC on March 24, 1987 that the equipment affected in BWR 
plants includes the RHR, core spray, and high-pressure core spray system 
electric motors.  GE recommended that annual inspections be performed until 
operating experience indicates that this is no longer necessary.  At plants 
where the support brackets have been removed, GE stated that restoration 
actions should be taken as soon as possible.  Although GE notified BWR 
licensees of the Cooper Station event, it did not notify PWR licensees.  A 
list, which was provided to the NRC by GE, of PWR facilities that have 
received large, vertical electric motors from GE is attached.  It should be 
noted that other plants could have similar motors. 

Discussion: 

The surge ring bracket, a 1-inch-wide by 1/8-inch-thick L-shaped piece of 
carbon steel, has been breaking at the sharp bend.  After the bracket breaks, 
a 1-inch-long portion remains attached to the surge ring by a double fillet 
weld.  If this weld fails, the 1-inch by 1-inch by 1/8-inch piece of steel may 
move inside the motor.  Although tests conducted at Cooper Station showed 
significant cyclic loading of the bracket when the motor was started, the 
bracket also was shown to be subject to vibration during steady-state 
operation. 

At Cooper Nuclear Station, surge ring brackets of an improved design, which 
incorporated a larger bend radius, were installed and the motor insulation 
system was revarnished to fill and bond the cracks in the felt blocks.  The 
licensee is visually inspecting the brackets on a regular basis.  This 
examination is conducted without disassembling the pump motor, using either a 
boroscope or a mirror inserted through the existing air vents.  GE has recom-
mended a complete disassembly and inspection at 10-year intervals to ensure 
the continued qualification of these motors. 

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                                                                 Page 3 of 3


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. 




                              Charles E. Rossi, Director 
                              Division of Operational Events Assessment 
                              Office of Nuclear Reactor Regulation 


Technical Contact:  Paul Cortland, OSP 
                    (301) 492-7190 


Attachments:   
1.  List of PWR Facilities Known to Have Received 
      Large, Vertical Electric Motors from General Electric Company 
2.  List of Recently Issued NRC Information Notices
.                                                                 Attachment 1
                                                                 IN 87-30
                                                                 July 2, 1987
                                                                 Page 1 of 1


              LIST OF PWR FACILITIES KNOWN TO HAVE RECEIVED LARGE,
             VERTICAL ELECTRIC MOTORS FROM GENERAL ELECTRIC COMPANY


The plant numbers were not identified for multi-unit facilities. 

     PLANT                                   MOTOR SIZE IN HORSEPOWER 

     Arkansas Nuclear One                         800 
     Bellefonte Nuclear Plant                     900
     Farley Nuclear Plant                         600
     Harris Nuclear Power Plant                   1300 
     Indian Point Station                         400
     Millstone Nuclear Power Station              500, 600, 700 
     North Anna Power Station                     400
     Palo Verde Nuclear Station                   600 
     Salem Nuclear Generating Station             1000 
     Seabrook Nuclear Station                     600, 800 
     Sequoyah Nuclear Plant                       700
     SNUPPS                                       1750 
     St. Lucie Plant                              500, 600 
     Turkey Point Plant                           500
     Vogtle Nuclear Plant                         700 

Page Last Reviewed/Updated Tuesday, November 12, 2013