Closeout of IE Bulletin 79-11: Faulty Overcurrent Trip Device in Circuit Breakers for Engineered Safety Systems.

摘要

IE Bulletin 79-11 was issued May 22, 1979 as a result of information received in April 1979 from Westinghouse and an NRC licensee relating to the potential failure of a circuit breaker in an engineered safety system of a nuclear power plant. The defect of concern was a small hairline crack in the dashpot end cap of one of the three overcurrent trip devices of a Type DB-75 breaker. The Bulletin was also applicable to Type DB-50 breakers, because they use the same type of dashpot end cap. The defective end cap had been installed in 1973 as a replacement, in compliance with IE Bulletin 73-1. Westinghouse Technical Bulletin NSD-TB-79-02 was issued April 17, 1979 to alert utilities to the potential problem, to provide background information, to recommend review of calibration test data and retesting of erratic breakers, to advise visual examination of end caps for cracks and to call for replacement of cracked end caps.