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Information Notice No. 92-44: Problems with Westinghouse DS-206 and DSL-206 Type Circuit Breakers
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 June 18, 1992 NRC INFORMATION NOTICE 92-44: PROBLEMS WITH WESTINGHOUSE DS-206 AND DSL-206 TYPE CIRCUIT BREAKERS Addressees All holders of operating licenses or construction permits for nuclear power reactors. Purpose The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert addressees to a problem with DS-206 and DSL-206 type circuit breakers manufactured by the Westinghouse Electric Corporation (Westinghouse) which could cause these breakers to fail to open when required. 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 are not NRC requirements; therefore, no specific action or written response is required. Description of Circumstances The following describes three Westinghouse DS-206 circuit breaker failures. On September 3, 1990, the Commonwealth Edison Company, licensee for the Byron Nuclear Power Station (Byron), reported that while performing a surveillance test, the 2C reactor containment fan cooler low speed fan circuit breaker failed to open. Attempts to manually open the circuit breaker failed. The licensee replaced the failed circuit breaker and sent it to Westinghouse for a failure analysis. On November 30, 1990, operators at the South Texas Project Electric Generating Station (STPEGS), Unit 1, were unable to open the electrical auxiliary building Supply Fan 11B breaker from the control room, by the local hand switch, or by the manual trip pushbutton; eventually, they opened it using an insulated push rod within the breaker cubicle. On March 31, 1992, the Arizona Public Service Company, licensee for the Palo Verde Nuclear Generating Station, reported that during a surveillance test, when an operator tripped a Unit 3 reactor trip breaker (RTB) from the control room, it remained in an intermediate position with its "A" and "C" poles connected and the "B" pole disconnected. 9206120270. IN 92-44 June 18, 1992 Page 2 of 3 Discussion Westinghouse examined the DS-206 circuit breaker that failed to open at Byron and determined that the probable cause of the failure was the improper adjustment of its contacts. Westinghouse issued Technical Bulletin NSD-TB-91-06-RO, "DS-206 and DSL-206 Breakers - Mechanical Friction Of Main Contact Assemblies," (Attachment 1), advising its customers that if the contact adjustment procedures in the technical bulletin were not followed, the breaker might only partially open because of excessive friction in the main contact assemblies. STPEGS personnel could not duplicate the malfunction which had occurred on the DS-206 type electrical auxiliary building supply fan breaker and did not immediately perform a root cause analysis. Licensee and Westinghouse personnel inspected the DS-206 type reactor trip breaker that failed to open at Palo Verde and determined that its main contacts in the "A" and "C" poles were misaligned. They observed the mechanical alignment of the arcing contacts to be outside the tolerances in Westinghouse's specification. The "B" pole insulating link was twisted and was binding on the poleshaft lever. These misalignments cause inadequate compression of the main contact springs and reduce the opening force. They also determined that the pivot blocks in the moving contacts had not been lubricated as recommended in the Westinghouse technical bulletin. An additional significant contributing factor was that the reset spring on the poleshaft (which assists in completing the opening sequence) was found to be elongated and weakened, probably the result of repeatedly detaching and attaching the springs before performing undervoltage trip attachment surveillance tests in a manner not recommended by Westinghouse. Therefore, this failure could have resulted from the combined effect of the misalignments, the weakened reset spring and incorrect lubrication. They also determined that Palo Verde personnel had not incorporated the recommendations contained in NSD-TB-91-06-RO into their maintenance procedures. In the technical bulletin, Westinghouse provided detailed steps on how to inspect and adjust the stationary and moving (main and auxiliary) contacts without causing the insulating links to twist and bind and on how to verify clearances in the stationary contacts and specified lubricating pivot blocks. The Westinghouse cover letter for the bulletin advised that if contact adjustment procedures given in the bulletin are not followed, then the potential exists for the DS- and DSL-206 breakers to partially open due to excessive friction in the main contact assemblies. However, the technical bulletin advised performing these steps upon finding difficulty in electrically opening the breaker. NRC staff discussions with Westinghouse personnel indicate that the inspection recommendations are applicable to all DS- or DSL-206 type circuit breakers, even if no difficulties have been experienced, and in particular, if the licensee has replaced the poleshaft or performed other maintenance activities involving replacement of major components, such as contacts (main or arcing), on site. NRC Generic Letters 83-28, "Required Actions Based on Generic Implications of Salem ATWS Events," and 90-03, "Relaxation of Staff Position in GL 83- 28, Item. IN 92-44 June 18, 1992 Page 3 of 3 2.2 of Part 2, `Vendor Interface for Safety Related Components'," address the need for licensees to obtain and incorporate vendor technical information that applies to their facilities into plant procedures to ensure that safety-related equipment is operated and maintained properly. This information notice requires no specific action or written response. If you have any questions about the information in this notice, please contact one of the technical contacts listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager. Charles E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical contacts: Thomas Koshy, NRR (301) 504-1176 Kamalakar Naidu, NRR (301) 504-2980 Stephen Alexander, NRR (301) 504-2995 Attachments: 1. Westinghouse Technical Bulletin NSD-TB-91-06-RO 2. List of Recently Issued NRC Information Notices .
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