Information Notice 2006-05, Possible Defect in Bussman KWN-R and KTN-R Fuses
| ML060330540 | |
| Person / Time | |
|---|---|
| Issue date: | 03/03/2006 |
| From: | Charemagne Grimes NRC/NRR/ADRA/DPR |
| To: | |
| Tabatabai O, NRR/DIRS/IOEB, 415-6616 | |
| References | |
| IN-06-005 | |
| Download: ML060330540 (5) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001 March 3, 2006 NRC INFORMATION NOTICE 2006-05: POSSIBLE DEFECT IN BUSSMANN KWN-R AND
KTN-R FUSES
ADDRESSEES
All holders of operating licensees for nuclear power reactors, except those who have
permanently 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 inform
addressees of a possible defect in Bussmann KWN-R and KTN-R fuses. Recipients are
expected to review the information for applicability to their facilities and consider actions to
avoid similar problems. 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 while
in service. 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
fuse. 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 open. The customer returned the fuse to Wyle for failure analysis. Wyle forwarded
the fuse to Bussmann (the fuse manufacturer) for evaluation. Bussmann found a poor solder
connection on the rejection cap. Apparently the cap did not get hot enough to reflow solder
during the manufacturing process. Bussmann stated that the issue might extend to other fuses
due to a manufacturing process problem.
Wyle Laboratories indicated to the NRC that the only two nuclear power plants that purchased
the susceptible KWN-R fuses from Wyle are Hatch Electric Generating Plant and Pilgrim
Nuclear Power Station. Wyle has contacted the two customers that have purchased KWN-R
fuses from Wyle Laboratories. Since these fuses might have been sold to other nuclear power
plants by different vendors, this problem may be generic. 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 amperes. To date, poor solder joints have been found in 3, 6, and 10 ampere KWN-R fuses with date codes L05, M37, and M17. Poor solder connections have also been found in fuses with date codes
L11, L19, M07, M20, and M40. KTN-R fuses with ratings less than or equal to 30 amperes
were later added to the potentially defective fuse list since these fuses are manufactured using
the same process as the KWN-R fuses. 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 the
rejection cap. It appeared the cap did not get hot enough to reflow the solder to the tab on the
element. 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 condition. Bussmann
identified that the manufacturers personnel have failed to follow process instruction. 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 cap. The design of the bridge and cap attachment is
common 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 fuses. It has
added a mechanical test to the KWN-R and KTN-R manufacturing process. The test consists
of checking the resistance of each fuse and then mechanically impacting it and checking the
resistance again. If the resistance readings differ, the fuse is segregated for disposition. 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 recommends
performing a current-carrying test for 30 minutes at 110 percent of the rated current after warm
up at 100 percent of the rated current. This will avoid blowing the fuse. When performing the
mechanical impact test, if the resistance readings differ by more than +/- 10 percent or fall
outside the manufacturers specifications, the fuse should be rejected. Only KWN-R and KTN-
R fuses that pass the mechanical impact test and the 110 percent current-carrying capacity test
are qualified.
CONTACT
This information notice requires no specific action or written response. Please direct any
questions about this matter to the technical contact listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
/RA/
Christopher I. Grimes, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contact:
Duc Nguyen, NRR/DE/EEEB
301-415-3202 E-mail: dtn1@nrc.gov
Omid Tabatabai, NRR/DIRS/IOEB
301-415-6616 E-mail: oty@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
ML060330540 *previous concurrence
OFFICE NRR/DE/EEEB Tech Editor BC/DE/EEEB NRR/DIRS/IOEB TL:NRR/DIRS/IQEB
NAME DNguyen* PKleene* EABrown* OTabatabai* EJBenner*
DATE 02/08/2006 02/06/2006 02/09/2006 02/13/2006 02/13/2006 OFFICE DPR:PGCB:LA DPR:PGCB DPR:PGCB:BC DPR:D
NAME CHawes* DBeaulieu* CJackson* CIGrimes*
DATE 02/02/2006 02/28/2006 03/03/2006 03/03/2006