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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July 2, 1987
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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
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