United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9611040126

CHARLES H. CRUSE                   Baltimore Gas and Electric Company
Vice President                     Calvert Cliffs Nuclear Power Plant
Nuclear Energy                     1650 Calvert Cliffs Parkway
                                   Lusby, Maryland 20657
                                   410 495-4455

                            October 25, 1996
BGE

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
               Failures of General Electric Type AMH-4.76-250
               Circuit Breakers

Calvert Cliffs has experienced two failures of the General Electric type
AMH-4.76-250 circuit breaker.  Investigation to date has revealed the
breaker's manual trip paddles had bent, thus preventing proper automatic
or manual closure of the breaker.  This problem is being conservatively
reported in accordance with 10 CFR 21.21 (a)(2) as an interim
notification.  Although a defect or noncompliance has not been positively
identified, these failures represent a potential challenge to the
reliability of safety-related components to perform their intended safety
function.  We do not yet know exactly why these failures have occurred
but the investigation is continuing.

Should you have questions regarding this matter, we will be pleased to
discuss them with you.

                                   Very truly yours,

                                        for
                                   C. H. Cruse
                              Vice President - Nuclear Energy

CHC/CDS/bjd

Attachment


cc:  D. A. Brune, Esquire                    H. J. Miller, NRC
     J. E. Silberg, Esquire                  Resident Inspector, NRC
     Director, Project Directorate I-1, NRC  R. I. McLean, DNR
     A. W. Dromerick, NRC                    J. H. Walter, PSC

                             ATTACHMENT (1)

                      10 CFR PART 21 INTERIM REPORT
                 CONCERNING BENT MANUAL TRIP PADDLES IN
           GENERAL ELECTRIC MAGNE BLAST 4-kV CIRCUIT BREAKERS

Calvert Cliffs Nuclear Power Plant, Units 1 and 2

Docket Nos.: 50-317 and 50-318

(i)       Name and Address of Individual Making Notification

          C. H. Cruse, 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:

          General Electric Magne Blast Circuit Breakers Type AMH-4.76-250

(iii)     Firm Supplying Components:

          General Electric Nuclear Energy
          6901 Elmwood Avenue
          Philadelphia, PA 19142

(iv)      Nature of the Potential Defect

          During surveillance testing in June and July, 1996, the plant
          found two problems with General Electric type AMH-4.76-250
          circuit breakers.  In June, a Low Pressure Safety Injection
          (LPSI) pump breaker failed to close during testing.
          Investigation revealed that there was no gap between the manual
          trip rod and the manual trip lever.  The trip lever had been
          bent.  The bent trip lever had prevented the trip latch from
          fully rotating onto the stop pin; thus, there was a smaller
          than normal trip latch "wipe" (i.e., area of contact).  With
          this reduced wipe, there is no guarantee of breaker closure.
          The trip lever was replaced.

          The function of the manual trip lever is to transmit the forces
          from the manual trip rod to the trip shaft and facilitate
          manual tripping of the breaker.  The function of the manual
          trip rod is to transmit forces from the breakers manual trip
          push button to the manual trip lever.

          In July, another LPSI pump breaker failed to close during
          testing.  In this case, investigation revealed that a support
          "L" bracket attached to the manual trip lever had broken and
          the trip lever was bent, with the same effect as in the first
          event.  The "L" bracket serves to provide additional support
          and stiffness to the manual trip lever.  As the breaker trips,
          the manual trip lever quickly rotates until it comes in contact
          with the breaker frame creating a momentary bending stress in
          the manual trip lever and the "L" bracket.  The breaker was
          replaced with a spare breaker.  The

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                             ATTACHMENT (1)

                      10 CFR PART 21 INTERIM REPORT
                 CONCERNING BENT MANUAL TRIP PADDLES IN
           GENERAL ELECTRIC MAGNE BLAST 4-kV CIRCUIT BREAKERS

          broken parts were removed from the breaker and sent to the
          Baltimore Gas and Electric Company metallurgical laboratory for
          analysis.

          We conducted metallurgical analyses of the broken "L" bracket
          and bent trip levers.  Each of these parts is made of low
          carbon steel.  They appear to have failed due to "strain-aging
          embrittlement," a phenomenon that affects hot-rolled low carbon
          steel parts fabricated by cold bending.  However, we currently
          do not feel this is the cause of the trip lever bending and "L"
          bracket failure we have experienced.  More probably, the
          cracking and bending are a symptom of another problem that is
          overstressing these components.

          As a result of the second failure, an inspection program was
          initiated for all 4 kV safety-related breakers to look for the
          broken "L" bracket problem.  Just prior to the start of this
          inspection program, cracks were found in the "L" brackets in
          two other breakers.  The inspection program was accelerated and
          all breakers were checked for the cracking identified on the
          "L" brackets.  During this inspection, two other breakers were
          found with no gap between the manual trip lever and the manual
          trip shaft (one was the breaker which had failed in June; its
          replacement lever had also bent).  A method was developed to
          verify operability of the safety-related breakers by insuring a
          gap existed between the manual trip lever and the manual trip
          rod after each breaker operation.

          These breakers have no difficulty in opening.  The problem is
          that they could lose their closing ability.  Since Calvert
          Cliffs uses many of these breakers in safety-related
          applications, this could challenge the reliability of safety-
          related components to perform as designed.

(v)       Date on Which Potential Defect Was Identified

          We determined on August 27, 1996 that this breaker problem
          could potentially represent a challenge to the reliability of
          safety-related components to perform their intended safety
          function.  We do not yet know exactly why these failures have
          occurred but the investigation is continuing.

(vi)      Number and Location of Components

          Calvert Cliffs has approximately 120 of the General Electric
          type AMH-4.76-250 circuit breakers on site in safety-related
          and non-safety-related applications.

(vii)     Corrective Actions Taken

          At this time, a definitive explanation for the breaker failures
          has not been confirmed.  We are continuing our investigation
          into the possible causes of the problem.  A team was
          established to evaluate the problem and determine possible
          causes.  A list of possible causes was established and
          inspections and troubleshooting are currently in progress to
          validate them.

                                    2

                             ATTACHMENT (1)

                      10 CFR PART 21 INTERIM REPORT
                 CONCERNING BENT MANUAL TRIP PADDLES IN
           GENERAL ELECTRIC MAGNE BLAST 4-kV CIRCUIT BREAKERS

Based on the metallurgical evaluation results, an operability evaluation
was performed for the rest of the breakers.

We have sent the breaker from July LPSI pump failure to the breaker
manufacturer for a more complete failure analysis.

The vendor has recommended a modification to the breakers to prevent
additional cases of trip lever bending and "L" bracket failures.  We are
currently in the process of implementing this recommended modification on
the plants General Electric Magne Blast 4 kV breakers.  They include
replacing the trip paddles, support bracket and the spring discharge
link.  The trip lever material will change from AISI 1005 Carbon Steel to
AISI 1018 Carbon Steel.  The "L" brackets will change from AISI 1005
steel to aluminum.  In addition, the configuration of the parts will be
changed.

Additional corrective actions will be implemented as needed after the
final results of the root cause analysis are finalized.  This report will
be supplemented after the root cause is complete and a complete set of
corrective action is in place.

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