Information Notice No. 88-44:Mechanical Binding of Spring Release Device in Westinghouse Type DS-416 Circuit Breakers
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
June 24, 1988
Information Notice No. 88-44: MECHANICAL BINDING OF SPRING RELEASE DEVICE
IN WESTINGHOUSE TYPE DS-416 CIRCUIT
All holders of operating licenses or construction permits for nuclear power
This information notice is being provided to alert addressees to potential
problems resulting from the mechanical binding of the spring release device
(SRD) in Westinghouse type DS-416 metal clad circuit breakers. It is expected
that recipients will review the information for applicability to their facili-
ties 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
Description of Circumstances:
On May 25, 1988, the South Texas Project Unit 1 (STP-1 or licensee) performed
a loss-of-offsite power test. During this test, two Class 1E electrical
circuit breakers failed to reclose as required during load sequencing.
Subsequent investigation by the licensee identified the failed breakers as
Westinghouse type DS-416 metal clad breakers. These DS-416 electrical
breakers are located in main 480-Vac load centers and are tie and feeder
breakers for 480-Vac components.
The breaker has an SRD that initiates the sequence for the breaker closing.
The SRD is attached to the breaker housing and is comprised of a coil housing
that is attached to the breaker casing, a closing coil, and a lever that is
attached to the coil housing. The lever travels up and down through a window
(a punched out opening) in the breaker casing. When the breaker is signaled
to close, the coil is energized and the lever is designed to move up and make
contact with the spring release latch that mechanically releases the breaker
closing springs. These SRDs also are used in Westinghouse type DS-420 and
DS-206 circuit breakers.
The licensee's preliminary investigation indicates that the breakers failed to
reclose because the closing coils had overheated and burned out. The licensee
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June 24, 1988
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believes that the coils burned out as a result of mechanical binding between
the lever and the edge of the breaker casing window. The licensee physically
inspected and electrically tested 28 other DS-416 breakers installed in Unit 1
and 18 breakers installed in Unit 2 as of June 16, 1988, and identified 10 ad-
ditional cases where the lever and the edge of the breaker casing window were
Although the root cause of the binding has not been determined, the licensee
has taken several steps to alleviate the problem. The licensee has replaced
the SRD in the STP-1 breakers that indicated signs of possible binding and has
verified that the clearances between the lever and the casing are sufficient
to preclude further binding. In addition, the licensee has extensively
briefed the STP control room personnel on this binding problem. It should be
noted that although the SRD may bind, it is still possible to manually trip
the breaker closing springs by pushing the "CLOSE" button located at the
The licensee has contacted Westinghouse for assistance in determining the root
cause of the binding. The NRC will remain cognizant of any new developments
and await the results of the South Texas and Westinghouse investigation. The
NRC will issue a further generic communication if warranted by the
availability of additional information or if additional regulatory action is
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact one of the techni-
cal contacts listed below or the Regional Administrator of the appropriate
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: Kamal Naidu, NRR
Jaime Guillen, NRR
Attachment: List of Recently Issued NRC Information Notices
June 24, 1988
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to________
88-43 Solenoid Valve Problems 6/23/88 All holders of OLs
or CPs for nuclear
88-42 Circuit Breaker Failures 6/23/88 All holders of OLs
Due to Loose Charging or CPs for nuclear
Spring Motor Mounting Bolts power reactors.
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
OL = Operating License
CP = Construction Permit
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