United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9411070265

TVA

Tennessee Valley Authority, Post Office Box 2000, 
Spring City, Tennessee 37381


OCT 31 1994

CFR-50-390, 391/94-10                              10 CFR 50.55(e)

U.S. Nuclear Regulatory Commission
ATTN:  Document Control Desk
Washington, D.C.  20555

Gentlemen:

In the Matter of the Application of      )    Docket Nos. 50-390
Tennessee Valley Authority               )                50-391

WATTS BAR NUCLEAR PLANT (WBN) - UNITS 1 AND 2 - GENERAL ELECTRIC (GE)
MAGNE-BLAST CIRCUIT BREAKERS - CONSTRUCTION DEFICIENCY REPORT (CDR)
50-
390, 391/94-10 - SUPPLEMENT REPORT


The subject deficiency was initially reported to NRC Operations Center on
July 12, 1994, in accordance with 10 CFR 50.55(e) as Problem Evaluation
Report (PER) WBPER940262.  An initial report was submitted on August 6,
1994.  A supplement report is provided in the enclosure.

If there are any questions, please telephone P. L. Pace at (615) 365-1824.

Sincerely,


Dwight E. Nunn
Vice President
New Plant Completion
Watts Bar Nuclear Plant

Enclosure
cc:   See page 2


U.S. Nuclear Regulatory Commission
Page 2

OCT 31 1994

cc (Enclosure):

      INPO Record Center
      700 Galleria Parkway
      Atlanta, Georgia  30339

      NRC Resident Inspector
      Watts Bar Nuclear Plant
      Rt. 2, Box 700
      Spring City, Tennessee  37381

      Mr. P. S. Tam, Senior Project Manager
      U.S. Nuclear Regulatory Commission
      One White Flint North:
      11555 Rockville Pike
      Rockville, Maryland 20852

      U.S. Nuclear Regulatory Commission
      Region II
      101 Marietta Street, NW, Suite 2900
      Atlanta, Georgia  30323


                                ENCLOSURE

                  WATTS BAR NUCLEAR PLANT UNITS 1 AND 2
              GENERAL ELECTRIC MAGNE-BLAST CIRCUIT BREAKERS
                  PROBLEM EVALUATION REPORT WBPER940262
                   10 CFR 50.55(e) SUPPLEMENTAL REPORT
                          CDR 50-390, 391/94-10

DESCRIPTION OF DEFICIENCY:

On May 9, 1994, smoke was observed coming from a 6.9 KV breaker
compartment.  Further investigation revealed a General Electric Magne-
Blast circuit breaker, Serial Number 256A4604-027, inoperable.  The pin
connecting the trip coil link to the crank had separated from the
adjoining weld and had fallen out.  Without the pin, the breaker failed
to open after receiving a trip signal.  As a result, the trip coil
remained energized and eventually overheated and also failed.  Preliminary
inspection of the surface area along the pin weld may indicate that the
weld surface was shaved too thinly during the finishing process.  The
depth of the weld material remaining on the pin surface was estimated to
be only 1/32 of an inch deep along the side of the pin. The weld was
separated along the pin surface and not along the adjoining surface of the
special weld cavity.  The cause of the pin failure appears to be the
result of insufficient weldment between the pin and the crank.

On June 26, 1994 while performing an unrelated inspection, a similar pin
was found under the Normal Feeder Breaker of a 6.9 KV Unit Board, Serial
Number 256A4608-023.

In November of 1985, a similar deficiency was documented in nonconformance
report (NCR) W-312-P.  At that time, the manufacturer considered the
failure to be isolated to one batch of welded pins associated with Serial
Number 256A4603.


Additional Information:

GE Magne-Blast 6.9 KV circuit breakers are used in 206 applications
involving the Unit Boards, Common Boards, Shutdown Boards, Start Boards,
and Reactor Coolant Pump Boards:


SAFETY IMPLICATIONS:

The subject breakers are used in various safety-related applications such
as the feed for the 480 Volt Shutdown Board Transformers and on the 6.9
KV Shutdown Board as the feed for the Emergency Raw Cooling Water pump
motors.  Thus, failures as described above could compromise the plant's
capability to mitigate the consequences of postulated accidents.

                                   E-1


CORRECTIVE ACTIONS:

TVA developed an inspection plan and acceptance criteria in conjunction
with GE.  GE has indicated that breakers procured prior to 1988 are
suspect.  After 1988, the crank assemblies were manufactured with an
improved design.

TVA has inspected 191 crank assemblies of the previous design on 6.9 KV
Magne-Blast circuit breakers installed in the plant.  The remaining
breakers will be inspected by December 5, 1994.  Approximately 50 percent
of inspected breakers have exhibited defects.  The results have been
discussed with GE.  The crank was visually inspected by viewing the flat
surface of the crank at the point where the pin penetrates the crank.  Any
indications at the interface between the crank and the 3/8 inch diameter
pin was considered cause for replacing the part, for example:

                     a:   voids in the weldment,
                     b:   hairline cracks around the pin,
                     c:   and other flaws in the weldment.

Defective breakers have been taken out of service.  Tags have been placed
on the breakers which prohibit their use without further actions to
resolve the subject deficiency.

TVA has procured new snap rings (94NH-111946) and trip coil cranks (94N3H-
112108) for crank assembly replacements.  Crank assembly parts of the
previous design have been removed from inventory and scrapped.

Maintenance Instruction (MI)-57.001, "6900 Volt Circuit Breaker
Inspection," has been revised to require future inspections of the crank
pin weldment area.

Four suspect breakers were being held in warehouse stock. Inspection of
these breakers revealed two defective pin weldments.  These two have been
tagged as nonconforming which prohibits their use without further actions
to resolve the subject deficiency.  The two circuit breakers, which were
determined to have acceptable pin weldments, have been made available for
issue to the plant.


Additional Information:

GE is currently experiencing difficulty passing its own in-house
acceptance criteria for crank assemblies from its subsupplier.  TVA
engineering is investigating the manufacturing process and design
alternatives.  The results are expected to be available by November 15,
1994.

                                   E-2


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