United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 92-44: Problems with Westinghouse DS-206 and DSL-206 Type Circuit Breakers

                              UNITED STATES
                         WASHINGTON, D.C. 20555

                              June 18, 1992

                               DSL-206 TYPE CIRCUIT BREAKERS


All holders of operating licenses or construction permits for nuclear
power reactors.


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to a problem with DS-206 and DSL-206 type
circuit breakers manufactured by the Westinghouse Electric Corporation
(Westinghouse) which could cause these breakers to fail to open when
required.  It is expected that recipients will review the information for
applicability to their facilities and consider actions, as appropriate,
to avoid similar problems.  However, suggestions contained in this
information notice are not NRC requirements; therefore, no specific action
or written response is required.

Description of Circumstances

The following describes three Westinghouse DS-206 circuit breaker

On September 3, 1990, the Commonwealth Edison Company, licensee for the
Byron Nuclear Power Station (Byron), reported that while performing a
surveillance test, the 2C reactor containment fan cooler low speed fan
circuit breaker failed to open.  Attempts to manually open the circuit
breaker failed.  The licensee replaced the failed circuit breaker and sent
it to Westinghouse for a failure analysis.

On November 30, 1990, operators at the South Texas Project Electric
Generating Station (STPEGS), Unit 1, were unable to open the electrical
auxiliary building Supply Fan 11B breaker from the control room, by the
local hand switch, or by the manual trip pushbutton; eventually, they
opened it using an insulated push rod within the breaker cubicle.    

On March 31, 1992, the Arizona Public Service Company, licensee for the
Palo Verde Nuclear Generating Station, reported that during a surveillance
test, when an operator tripped a Unit 3 reactor trip breaker (RTB) from
the control room, it remained in an intermediate position with its "A" and
"C" poles connected and the "B" pole disconnected.


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Westinghouse examined the DS-206 circuit breaker that failed to open at
Byron and determined that the probable cause of the failure was the
improper adjustment of its contacts.  Westinghouse issued Technical
Bulletin NSD-TB-91-06-RO, "DS-206 and DSL-206 Breakers - Mechanical
Friction Of Main Contact Assemblies," (Attachment 1), advising its
customers that if the contact adjustment procedures in the technical
bulletin were not followed, the breaker might only partially open because
of excessive friction in the main contact assemblies.

STPEGS personnel could not duplicate the malfunction which had occurred
on the DS-206 type electrical auxiliary building supply fan breaker and
did not immediately perform a root cause analysis.

Licensee and Westinghouse personnel inspected the DS-206 type reactor trip 
breaker that failed to open at Palo Verde and determined that its main 
contacts in the "A" and "C" poles were misaligned.  They observed the
mechanical alignment of the arcing contacts to be outside the tolerances
in Westinghouse's specification.  The "B" pole insulating link was twisted
and was binding on the poleshaft lever.  These misalignments cause
inadequate compression of the main contact springs and reduce the opening
force.  They also determined that the pivot blocks in the moving contacts
had not been lubricated as recommended in the Westinghouse technical
bulletin.  An additional significant contributing factor was that the
reset spring on the poleshaft (which assists in completing the opening
sequence) was found to be elongated and weakened, probably the result of
repeatedly detaching and attaching the springs before performing
undervoltage trip attachment surveillance tests in a manner not
recommended by Westinghouse.  Therefore, this failure could have resulted
from the combined effect of the misalignments, the weakened reset spring
and incorrect lubrication.  They also determined that Palo Verde personnel
had not incorporated the recommendations contained in NSD-TB-91-06-RO into
their maintenance procedures. 

In the technical bulletin, Westinghouse provided detailed steps on how to
inspect and adjust the stationary and moving (main and auxiliary) contacts
without causing the insulating links to twist and bind and on how to
verify clearances in the stationary contacts and specified lubricating
pivot blocks.  The Westinghouse cover letter for the bulletin advised that
if contact adjustment procedures given in the bulletin are not followed,
then the potential exists for the DS- and DSL-206 breakers to partially
open due to excessive friction in the main contact assemblies.  However,
the technical bulletin advised performing these steps upon finding
difficulty in electrically opening the breaker.  NRC staff discussions
with Westinghouse personnel indicate that the inspection recommendations
are applicable to all DS- or DSL-206 type circuit breakers, even if no
difficulties have been experienced, and in particular, if the licensee has
replaced the poleshaft or performed other maintenance activities involving
replacement of major components, such as contacts (main or arcing), on

NRC Generic Letters 83-28, "Required Actions Based on Generic Implications
of Salem ATWS Events," and 90-03, "Relaxation of Staff Position in GL 83-
28, Item.

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2.2 of Part 2, `Vendor Interface for Safety Related Components'," address
the need for licensees to obtain and incorporate vendor technical
information that applies to their facilities into plant procedures to
ensure that safety-related equipment is operated and maintained properly. 

This information notice requires no specific action or written response. 
If you have any questions about the information in this notice, please
contact one of the technical contacts listed below or the appropriate
Office of Nuclear Reactor Regulation (NRR) project manager.

                              Charles E. Rossi, Director              
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation

Technical contacts:  Thomas Koshy, NRR 
                     (301) 504-1176
                     Kamalakar Naidu, NRR 
                     (301) 504-2980
                     Stephen Alexander, NRR 
                     (301) 504-2995 

1.  Westinghouse Technical Bulletin NSD-TB-91-06-RO
2.  List of Recently Issued NRC Information Notices

Page Last Reviewed/Updated Tuesday, November 12, 2013