Part 21 Report - 1995-106
ACCESSION #: 9505150034
CHARLES H. CRUSE Baltimore Gas and Electric Company
Plant General Manager Calvert Cliffs Nuclear Power Plant
Calvert Cliffs Nuclear Power 1650 Calvert Cliffs Parkway
Plant Lusby, Maryland 20657
410 586-2200 Ext. 4101 Local
410 260-4101 Baltimore
BGE
May 8, 1995
U. S. Nuclear Regulatory Commission
Washington, DC 20555
ATTENTION: Document Control Desk
SUBJECT: Calvert Cliffs Nuclear Power Plant
Unit Nos. 1 & 2; Docket Nos. 50-317 & 50-318
10 CFR Part 21 Interim Report Concerning Failures of
Gould-Shawmut Fuses
Please find attached a 10 CFR Part 21 notification concerning a recently
discovered failure mechanism for Gould-Shawmut A25X 10-15 ampere fuses.
The A25X 10-15 ampere fuses have experienced a higher than expected
failure rate over the last five months. Investigation into the problem
has revealed a certain percentage of these fuses have developed cracks in
their fuse elements. As the cracks propagate, the fuse fails to carry
current, creating the appearance of a blown fuse.
This failure mechanism has not been verified to have created a
substantial safety hazard at Calvert Cliffs. An evaluation to determine
the cause of the cracking is continuing. This interim report is being
submitted in accordance with 10 CFR 21.21(a)(2) and a supplemental report
will be issued after ongoing metallurgical analyses of the fuse elements
are completed.
Should you have questions regarding this matter, we will be pleased to
discuss them with you.
Very truly yours,
CHC/CDS/bjd
Attachment
cc: D. A. Brune, Esquire T. T. Martin, NRC
J. E. Silberg, Esquire P. R. Wilson, NRC
L. B. Marsh, NRC R. I. McLean, DNR
D. G. McDonald, Jr., NRC J. H. Walter, PSC
ATTACHMENT (1)
10 CFR PART 21 REPORT CONCERNING FAILURES OF
GOULD-SHAWMUT A25X 10-15 AMPERE FUSES DUE
THE CRACKING OF THE FUSE ELEMENT
Calvert Cliffs Nuclear Power Plant, Units 1 and 2
Docket Nos: 50-317 and 50-318
(i) Name and address of individual making notification:
R. E. Denton, Vice President-Nuclear Energy
Baltimore Gas and Electric Company
Calvert Cliffs Nuclear Power Plant
1650 Calvert Cliffs Parkway
Lusby, MD 20657
(ii) Basic Component Affected:
Gould-Shawmut A25X (10-15 ampere) fuses
(iii) Firm Supplying Component:
Gould Electronics Incorporated
374 Merrimac Street
Newburyport, MA 01950-1998
Telephone: (508) 462-3131
(iv) Nature of Defect:
Between November 1994 and March 1995 Calvert Cliffs Units 1 and
2 experienced five failures of Gould-Shawmut A25X 10-15 ampere
fuses. When tested with an ohmmeter the fuses read open but
with pressure exerted on the ends of the barrel, causing the
barrel ends to be pushed together, the fuses read in the 100-
1000 ohm range. Based on the high failure rate and unusual
failure characteristics, a root cause investigation was
initiated.
Gould-Shawmut provided information indicating that a possible
cause of the cracking was an old manufacturing process. Prior
to January 1993, this type of fuse was manufactured utilizing
an external soldering process on the fuse barrel end to attach
the zinc fuse element to the fuse barrel. The process utilized
an acid core flux. If the soldering process was not hot
enough, the acid core flux did not completely burn away and a
semi-corrosive flux residue was left on the zinc element. In
time, this semi-corrosive flux residue may have led to the
development of cracks at the residue line on the zinc element.
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ATTACHMENT (1)
10 CFR PART 21 REPORT CONCERNING FAILURES OF
GOULD-SHAWMUT A25X 10-15 AMPERE FUSES DUE
THE CRACKING OF THE FUSE ELEMENT
The old soldering process was used at least as far back as the
early 1980's according to the Gould-Shawmut. In January 1993
Gould-Shawmut changed the soldering process and solder to
improve the yield of the fuse manufacturing process. The
soldering flux was changed from the acid core flux to a non-
corrosive paste.
It should be noted that we have not yet verified that the
manufacturing process described above is the actual cause of
the failures. We are currently performing our own
metallurgical analysis on the fuses. Our analysis to date has
found the thin and flat fuse elements cracked all the way
through the element thickness and half way through the element
width. The cracking does not occur in all A25X fuses, only in
a certain as yet undetermined percentage of the total
population.
The fuses are not manufactured as safety-related but are bought
commercial grade and dedicated as safety-related.
(v) Date on Which Defect was Identified:
On March 7, 1995 an Issue Report was prepared documenting that
five Gould-Shawmut A25X 10-15 ampere fuses had failed since
November 1994. Presently it is unclear if these fuses could
have failed in a manner that would have rendered redundant
trains of safety-related equipment inoperable and created a
substantial safety hazard at Calvert Cliffs. However, since we
strongly suspect the fuses would fail during a design basis
seismic event or certain electrical transients, this interim
report is being submitted as a potential defect under 10 CFR
Part 21(a)(2).
(vi) Number and Locations of Components:
This problem has been found in only a certain percentage of
fuses that have been examined. Therefore, it is not known
exactly how many defective fuses were in the plant at the time
this defect was discovered. Each Calvert Cliffs Unit has 240
A25X 10-15 ampere fuses installed in circuits associated with
the Vital AC busses.
(vii) Corrective Actions Taken:
We have communicated the problem to Gould-Shawmut, who informed
us of the manufacturing process change. Gould-Shawmut also
indicated that they have had no previous indication of this
fuse failure mechanism from their customers.
Prior to the current Unit 2 refueling outage, all 240 A25X 10-
15 ampere fuses in the Unit 1 vital AC busses were replaced
with new fuses with the exception of spares. During the
current Unit 2 refueling outage all 240 of the A25X 10-15
ampere fuses were replaced with new fuses. All spares will
replaced with new fuses after the current Unit 2 refueling
outage.
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ATTACHMENT (1)
10 CFR PART 21 REPORT CONCERNING FAILURES OF
GOULD-SHAWMUT A25X 10-15 AMPERE FUSES DUE
THE CRACKING OF THE FUSE ELEMENT
A metallurgical analysis of some of the failed fuses has been
initiated by our Materials Engineering and Inspection Unit.
This analysis is expected to be completed by May 31, 1995.
Additional information concerning the results of this analysis
will be provided in a supplement to this interim report.
An INPO Nuclear NETWORK message has been issued to make other
industry personnel aware of this potential problem.
(viii) Other Advice Related to Purchasers or Licensees:
Although the Manufacturer changed the manufacturing process in
January 1993, the older type fuses are still being received
from fuse suppliers. A new non-corrosive type flux and solder
is now used and the method of soldering has changed. The new
generation fuses may be distinguished from the old by observing
the barrel end. The new fuses have no trace of solder puddles
or grinding marks. Please be advised however, that the old
manufacturing process has not been verified as the actual cause
of the cracking.
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