Information Notice 2006-05, Possible Defect in Bussman KWN-R and KTN-R Fuses
| ML060330540 | |
| Person / Time | |
|---|---|
| Issue date: | 03/03/2006 |
| From: | Grimes C I NRC/NRR/ADRA/DPR |
| To: | |
| Tabatabai O, NRR/DIRS/IOEB, 415-6616 | |
| References | |
| IN-06-005 | |
| Download: ML060330540 (5) | |
March 3, 2006
NRC INFORMATION NOTICE 2006-05: POSSIBLE DEFECT IN BUSSMANN KWN-R ANDKTN-R FUSES
ADDRESSEES
All holders of operating licensees for nuclear power reactors, except those who havepermanently ceased operations and have certified that fuel has been permanently removed from the reactor vessel.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to informaddressees of a possible defect in Bussmann KWN-R and KTN-R fuse Recipients are expected to review the information for applicability to their facilities and consider actions toavoid similar problem However, the suggestions in this information notice are not NRC requirements; therefore, no specific action or written response is required.
DESCRIPTION OF CIRCUMSTANCES
A customer of Wyle Laboratories reported that a KWN-R fuse lost its electrical continuity whilein servic The customer 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 fus According to the customer, the fuse had been in service from March 31, 2005 to August 4, 2005, carrying 2 to 3 amperes, and there had been no overcurrent events to cause the fuse to ope The customer returned the fuse to Wyle for failure analysi Wyle forwarded the fuse to Bussmann (the fuse manufacturer) for evaluatio Bussmann found a poor solder connection on the rejection ca Apparently the cap did not get hot enough to reflow solderduring the manufacturing proces Bussmann stated that the issue might extend to other fusesdue to a manufacturing process problem. Wyle Laboratories indicated to the NRC that the only two nuclear power plants that purchasedthe susceptible KWN-R fuses from Wyle are Hatch Electric Generating Plant and Pilgrim Nuclear Power Statio Wyle has contacted the two customers that have purchased KWN-Rfuses from Wyle Laboratorie Since these fuses might have been sold to other nuclear power plants by different vendors, this problem may be generi Some nuclear power plants have contacted Bussmann and Wyle with inquiries since a Part 21 report was posted on the NRC Web-site.
DISCUSSION
The only KWN-R fuses affected are fuses rated less than or equal to 30 ampere To date,poor solder joints have been found in 3, 6, and 10 ampere KWN-R fuses with date codes L05, M37, and M1 Poor solder connections have also been found in fuses with date codes L11, L19, M07, M20, and M4 KTN-R fuses with ratings less than or equal to 30 ampereswere later added to the potentially defective fuse list since these fuses are manufactured using the same process as the KWN-R fuse Poor solder connections have been found in 3, 4, 5, and 15 amperes KTN-R fuses of 1987-1991 vintage (there are no date codes on these fuses). On one KWN-R-10 fuse that was in service, Bussmann found no solder connection on therejection ca It appeared the cap did not get hot enough to reflow the solder to the tab on theelemen There were no signs of solder on the connecting tab of the bridge/element assembly.
The lack of solder and corrosion in the cap caused an open circuit conditio Bussmann identified that the manufacturer's personnel have failed to follow process instructio They are supposed to pull on the bridge assembly of every fuse to determine that a junction has been obtained between the bridge tab and ca The design of the bridge and cap attachment iscommon to the KWN-R and KTN-R fuses rated at 1 through 30 amperes. Bussmann has taken corrective actions to prevent the potential defect in these fuse It hasadded a mechanical test to the KWN-R and KTN-R manufacturing proces The test consists of checking the resistance of each fuse and then mechanically impacting it and checking the resistance agai If the resistance readings differ, the fuse is segregated for dispositio The mechanical impact is produced by dropping the fuse at least 3 feet (93 centimeter) onto the plain cap end through a tube with an internal diameter of about 5/8 inch (1.6 centimeters).
Bussmann also tests each production lot at 110 percent of the rated current for the KWN-R product. As a screening test to ensure a good solder connection, the manufacturer recommendsperforming a current-carrying test for 30 minutes at 110 percent of the rated current after warmup at 100 percent of the rated curren This will avoid blowing the fus When performing themechanical impact test, if the resistance readings differ by more than +/- 10 percent or fall outside the manufacturers' specifications, the fuse should be rejecte Only KWN-R and KTN-
R fuses that pass the mechanical impact test and the 110 percent current-carrying capacity test are qualifie IN 2006-05