Information Notice No. 87-61, Supplement 1: Failure of Westinghouse W-2-type Circuit Breaker Cell Switches
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
May 31, 1988
All holders of operating licenses or construction permits for nuclear power reactors.
This information notice supplement is being provided to alert addressees to additional potential problems resulting from the failure of Westinghouse W-2-type circuit breaker cell switches. 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.
On October 16, 1987, Westinghouse Electric Corporation notified the Nuclear Regulatory Commission (NRC) staff, pursuant to the requirements of 10 CFR Part 21, of the failure of a modified Westinghouse W-2-type switch that was being utilized as a circuit breaker cell switch. The failure occurred at Indian Point Station, Unit 3. The output breaker for an emergency diesel generator (EDG) was prevented from re-energizing a 480-volt bus because of erroneous input to the EDG logic system. The licensee identified deformation of the spring retainer in the spring-return mechanism of the cell switch in the breaker cell as the root cause of the erroneous input. Spring retainer deformation allowed a loss of spring tension that rendered the cell switch unable to spring-return from the racked-in to the racked-out position. The spring is continuously under stress whenever the breaker is racked-in. Subsequent inspections by the licensee showed that 35 out of a total of 37 similar W-2-type switch spring retainers in the 480-volt system breakers exhibited some sign of deformation. The cell switches had been in service for close to 15 years.
NRC Information Notice (IN) 87-61 stated that, based on recommendations provided by Westinghouse, inspection or testing performed whenever the breaker is racked-out would determine if a failure has occurred. In addition, it stated that visible inspection could be used to verify cell switch operation. However, on March 23, 1988, Westinghouse provided a supplement to their October 16, 1987 notification, which indicated that the W-2 cell switch may give the physical appearance of being in the proper position when the contacts have not actually changed state. This information was based on information received from Indian Point Station, Unit 3, that an electrical continuity check was the only reliable method to determine the operability of the W-2 switch.
As a result of the new information in the Westinghouse March 23, 1988, supplement to the 10 CFR Part 21 notification on W-2 cell failure, Westinghouse now recommends that switch operability be determined by a continuity check of a spare set of contacts whenever the breaker is in its racked-out position. Proper operability of the safety-related contacts should also be verified as part of the normal surveillance program. These contacts are wired to a terminal block located at the rear of the circuit breaker cell. In addition, Westinghouse recommends that the spring retainers of switches with the spring under tension during normal operation be checked for deformation after approximately 10 years of service and that the complete switch or the spring retainer assembly be replaced if one of the spring retainer tabs is found to be deformed compared to the opposite tab of the retainer assembly.
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 technical contacts listed below or the Regional Administrator of the appropriate regional office.
|Charles E. Rossi, Director|
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
|Technical Contacts:||Jaime Guillen, NRR|
|Kamal Naidu, NRR|
|Attachment:||List of Recently Issued NRC Information Notices|
(NUDOCS Accession Number 8805240090)
IN 87-61, Supplement 1
May 31, 1988
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
|Information Notice No.||Subject||Date of Issuance||Issued to|
|88-33||Recent Problems Involving the Model Spec 2-T Radiographic Exposure Device||5/27/88||All Agreement States and NRC licensees authorized to manufacture, distribute or operate radiographic exposure devices and source changers.|
|88-32||Promptly Reporting to NRC of Significant Incidents Involving Radioactive Material||5/25/88||All NRC material licensees.|
|88-31||Steam Generator Tube Ruptube Analysis Deficiency||5/25/88||All holders of Ols or CPs for Westinghouse and Combustion Engineering-designed nuclear power plants.|
|88-30||Target Rock Two-Stage SRV Setpoint Drift Update||5/25/88||All holders of Ols or CPs for nuclear power reactors.|
|88-29||Deficiencies in Primary Containment Low-Voltage Electrical Penetration Assemblies||5/24/88||All holders of Ols or CPs for nuclear power reactors.|
|88-28||Potential for Loss of Post-LOCA Recirculation Capability Due to Insulation Debris Blockage||5/19/88||All holders of Ols or CPs for nuclear power reactors.|
|88-27||Deficient Electrical Terminations Identified in Safety-Related Components||5/18/88||All holders of Ols or CPs for nuclear power reactors.|
|85-35, Supplement 1||Failure of Air Check Valves to Seat||5/17/88||All holders of Ols or CPs for nuclear power reactors.|
OL = Operating License
CP = Construction Permit