Morning Report for October 5, 2005

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Part 21 2005-0037-00 - Existence of a Possible Defect In Bussmann KWN-R Fuses



License No:

MR Number: H-2005-0026
Date: 09/27/2005


Part 21 2005-0037-00 - Existence of a Possible Defect In Bussmann KWN-R Fuses

On September 27, 2005 Wyle Laboratories informed NRC of a possible defect in Bussmann KWN-R fuses. The defect is a poor solder connection of the fuse link assembly to the rejection ferrule. The defect applies potentially to all KWN-R fuses. As a screening test to ensure a good soldered connection, the manufacturer recommends performing a Current Carrying Capacity Test for 30 minutes at 110% of rated current after warm up at 100% of rated current. Only KWN-R fuses that pass the 110% Current Carrying Capacity Test are qualified.

To the best of vendor's knowledge, only Hatch and Pilgrim nuclear power plants have purchased Bussmann KWN-R fuses.

In September 2005, Pilgrim reported to Wyle Laboratories that the fuse lost electrical continuity while in service. Pilgrim technicians cut the fuse open and found the fuse element intact and a lack of electrical continuity across the soldered connection of the element to the rejection ferrule of the fuse. The fuse had been in service since 3/31/05 carrying 2 - 3 amperes, and there were no overcurrent events which caused the fuse to open. In another instance, in September 2002, Pilgrim nuclear power plant declared its High-Pressure Coolant Injection System inoperable due to a failed Bussmann KWN-R fuse (Licensee Event Report 2002-001-00, dated September 4, 2002, ADAMS Accession No.: ML022550439).

The manufacturer of Bussmann fuses will test each production lot at 110% of rated capacity. Wyle Laboratories will also revise its quality plan to increase the Acceptable Quality Level (AQL) and will perform impact test on fuses.

Accession Numbers:

Accession No Accession Date
ML052720334 09/27/2005


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