United States Nuclear Regulatory Commission - Protecting People and the Environment

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

                              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,



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)

                GOULD-SHAWMUT A25X 10-15 AMPERE FUSES DUE

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

          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.


                             ATTACHMENT (1)

                GOULD-SHAWMUT A25X 10-15 AMPERE FUSES DUE

          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

          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


                             ATTACHMENT (1)

                GOULD-SHAWMUT A25X 10-15 AMPERE FUSES DUE

          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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