United States Nuclear Regulatory Commission - Protecting People and the Environment

Morning Report for December 15, 1999

                       Headquarters Daily Report

                         DECEMBER 15, 1999

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PRIORITY ATTENTION REQUIRED  MORNING REPORT - HEADQUARTERS DEC. 15, 1999

Licensee/Facility:                     Notification:

Part 21 Database                       MR Number: H-99-0111
Abb Combustion Engineering Nuc Pwr     Date: 12/15/99
Windsor,Connecticut

Subject: Part 21 - ABB 4-kV Vacuum Circuit Breakers Fail to Close
         on Demand


Discussion:

In 1999, ABB/CENP supplied Model VHK-R 4-kV retrofit vacuum circuit
breakers to Baltimore Gas and Electric's (BG&E) Calvert Cliffs Nuclear
Power Plant to replace existing GE Magne-Blast horizontal draw-out
circuit breakers. The vacuum breakers were manufactured by ABB Power T&D
Company, in Florence, South Carolina. The truck assemblies (to which the
vacuum interrupter is attached, so that it fits in the GE switchgear)
were designed and built by ABB Service Company's Product Development
Group (PDG), in Cleveland, Ohio. ABB/CENP dedicated these
commercial-grade retrofit breakers for safety-related applications.

In March 1999, during pre-installation testing at the Calvert Cliffs
site, some of the breakers would intermittently go trip free when
attempting to close. One of the breakers was returned to the PDG facility
in Cleveland, Ohio, for evaluation. Without performing a detailed root
cause analysis, the vendor determined that the most probable cause of the
problem was interference between a guide pin and the extension trip rod
(part of the rack-out interlock mechanism). Since the guide pin was
designed to act as a guide for the trip rods in larger 13.8-kV breakers,
and was not needed for the 4-kV breakers, the vendor removed the guide
pin to prevent interference with the extension trip rod. After
successfully testing several modified retrofit breakers at the ABB's
Cleveland shop, they were shipped to Calvert Cliffs. During
pre-installation testing, three of them experienced intermittent trip
free operations.

The breakers were returned to PDG . An extensive root cause analysis was
performed to determine the cause of the trip free operations, and several
contributing factors that affected the extension trip rod performance
were identified. The vendor modified the extension trip rod and its
mounting assembly to preclude further interference with the trip latch.

BG&E is the first nuclear customer to order ABB horizontal draw-out
retrofit vacuum circuit breakers to replace GE Magne-Blast breakers.
Therefore, the NRC does not consider this issue to be a generic concern
for other licensees. Additional details concerning this issue will be
documented in the upcoming NRC Inspection Report 99900401/1999202.

Contacts:   Dave Skeen, NRR             Stephen Alexander, NRR
            301-415-1174                301-415-2995
            E-mail: dls@nrc.gov         E-mail: sda@nrc.gov

            Kamal Naidu, NRR
            301-415-2980
            E-mail: krn@nrc.gov

HEADQUARTERS      MORNING REPORT     PAGE  2          DEC. 15, 1999
MR Number: H-99-0111 (cont.)

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