Information Notice No. 88-42: Circuit Breaker Failures due to Loose Charging Spring Motor Mounting
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
June 23, 1988
Information Notice No. 88-42: CIRCUIT BREAKER FAILURES DUE TO LOOSE
CHARGING SPRING MOTOR MOUNTING BOLTS
All holders of operating licenses or construction permits for nuclear power
Information Notice No. 87-41, "Failures of Certain Brown Boveri Electric
Circuit Breakers" was issued August 31, 1987. This information notice is
being provided to alert recipients of additional information regarding circuit
breaker failures due to loose charging spring motor mounting bolts. 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
Description of Circumstances:
There are two emergency diesel generators (EDGs) at North Anna Unit 2 ("H" and
"J"). On May 18, 1988, with the unit at power, the licensee removed the "J"
EDG from service for scheduled preventive maintenance. On May 19, 1988, fol-
lowing completion of the scheduled preventive maintenance, the "J" EDG failed
to pick up and carry the required load during preoperational testing. The
licensee then shut down the "J" EDG and performed unplanned corrective mainte-
nance. The licensee's technical specifications require that the operable EDG
be tested within 24 hours if the inoperable EDG is inoperable due to any cause
other than preplanned preventive maintenance or testing; thus, because of the
unplanned maintenance on the "J" EDG the licensee tested the "H" EDG. During
this test, the "H" EDG output circuit breaker (ITE Type 5HK) failed to close.
The licensee's investigation determined that the "H" EDG output breaker
closing spring had not been charged because the charging spring motor mounting
bolts had become loose, allowing the motor to become detached from the frame.
The output breaker for the "H" EDG had been successfully closed on May 6,
1988; however, procedures did not require verification that the closing spring
had successfully charged. Thus, both EDGs were inoperable for approximately
A similar occurrence was previously reported in accordance with the
requirements of 10 CFR 50.55(e) by Philadelphia Electric Company (the Limerick
Units 1 and 2 licensee) on August 27, 1984. During an EDG preoperational
test, the charging
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June 23, 1988
Page 2 of 2
spring motor of a BBC Brown Boveri, Inc. 5HK breaker failed to perform its
intended function. The licensee determined that three out of the four hori-
zontal charging spring motor mounting bolts had loosened, allowing the
charging spring motor to rotate. Subsequent inspections identified a similar
breaker with loose charging spring motor mounting bolts. The licensee
indicated that the charging spring motor mounting bolts had not been
sufficiently torqued by the vendor (e.g., measured torque values were 3 to 4
foot-pounds). Although the vendor recommends inspections of all accessible
bolts after 1000 breaker operations, the breaker failure occurred after only
several hundred operations. The licensee indicated that charging spring motor
mounting bolts in similar breakers would be removed, cleaned, coated with
Locktite, and torqued to 12 foot-pounds.
Failure of a circuit breaker to perform its intended function can result in
the loss of a power supply (such as a vital bus or an EDG). The occurrence of
these events, including the event at River Bend previously discussed in
Information Notice 87-41, indicates that loose charging spring motor mounting
bolts may be a generic concern. In addition, because of changes in corporate
name, mergers, etc., circuit breakers similar to those discussed above may
indicate manufacture by ITE, ITE Imperial, Gould, Brown Boveri, or a
combination thereof. Recipients may need to be cognizant of this when
determining whether they utilize similar equipment.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical
contact listed below or the Regional Administrator of the appropriate regional
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact: Jack Ramsey, NRR
Attachment: List of Recently Issued NRC Information Notices
June 23, 1988
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to________
88-41 Physical Protection 6/22/88 All holders of OLs
Weaknesses Identified or CPs for nuclear
Through Regulatory Ef- power reactors.
fectiveness Reviews (RERs)
88-40 Examiners' Handbook for 6/22/88 All holders of OLs
Developing Operator or CPs for nuclear
Licensing Examinations power reactors.
88-39 LaSalle Unit 2 Loss of 6/15/88 All holders of OLs
Recirculation Pumps With or CPs for BWRs.
Power Oscillation Event
88-38 Failure of Undervoltage 6/15/88 All holders of OLs
Trip Attachment on General or CPs for nuclear
Electric Circuit Breakers power reactors.
88-37 Flow Blockage of Cooling 6/14/88 All holders of OLs
Water to Safety System or CPs for nuclear
Components power reactors.
88-36 Possible Sudden Loss of RCS 6/8/88 All holders of OLs
Inventory During Low Coolant or CPs for PWRs.
88-35 Inadequate Licensee Performed 6/3/88 All holders of OLs
Vendor Audits or CPs for nuclear
88-34 Nuclear Material Control 5/31/88 All holders of OLs
and Accountability of or CPs for nuclear
Non-Fuel Special Nuclear power reactors.
Material at Power Reactors
87-61, Failure of Westinghouse 5/31/88 All holders of OLs
Supplement 1 W-2-Type Circuit Breaker or CPs for nuclear
Cell Switches power reactors.
OL = Operating License
CP = Construction Permit
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