United States Nuclear Regulatory Commission - Protecting People and the Environment

LICENSEE: EATON CUTLER-HAMMER
SITE: EATON CUTLER-HAMMER EN NUMBER: 36429
DOCKET: EVENT DATE: 11-12-99
RX TYPE: EVENT TIME:
VENDORS: NOTIFY DATE: 11-12-99
EMERGENCY CLASS: N/A REGION: 0 STATE: TIME: 10:09
OPS OFFICER: DICK JOLLIFFE
10 CFR SECTION: CDEG DEFECTS/NONCOMPLIANCE

10 CFR PART 21 REPORT -

Eaton Cutler-Hammer personnel identified a potential safety concern involving the potential for the malfunction of the Eaton Cutler-Hammer DS and DSL Class 1E circuit breakers due to the application of incorrect torque values during breaker reconditioning.

Previous industry DS Circuit Breaker Maintenance Guidance originally published by Westinghouse Nuclear Services Division in June 1993 and subsequently revised in March 1999 contained incorrect torque specifications for DS circuit breaker arc chute mounting bolts. Specifically, this guidance as originally published, was in error by a factor of at least 2 (two) regarding the DS 206 and by a factor of at least 3 (three) for the DS 416 when compared to the torque values identified in the Manufacturing Instructions utilized by the OEM (Cutler-Hammer) factory during the manufacturing process. The current revision information while being closer to the proper values is still incorrect. Multiple instances of longitudinal cracks have been observed in the mounting bolt block portion of the arc chute case. In addition, the "O" rings used as a retaining or capture device for the arc chute mounting bolts have been damaged.

Pieces of the "O" rings have been found laying around the inside of circuit breakers. The failure of the arc chute case to maintain its design integrity due to cracking and the potential for the total separation of pieces during a seismic event or normal operation and their subsequent infiltration of the breaker operating assembly could cause the failure of the breaker to perform its design function. Likewise, "O" ring failure could result in the same final effect.

The installed base of the DS style circuit breakers is spread throughout the nuclear industry. However, it is unknown to Eaton Cutler-Hammer specifically which utilities may have incorporated this erroneous information into their maintenance programs.

Eaton Cutler-Hammer recommends that a thorough inspection be conducted with the arc chutes properly torqued into place on the circuit breaker. Please note that the cracks may not be visible once the arc chutes have been removed from the breaker. A second inspection should be conducted of the "O" rings following removal of the arc chute from the breaker.

See the Eaton Cutler-Hammer Part 21 report for additional details.

Page Last Reviewed/Updated Thursday, March 29, 2012