Bulletin 88-01: Defects in Westinghouse Circuit Breakers
OMB No.: 31500011
NRCB 88-01
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
February 5, 1988
NRC BULLETIN NO. 88-01: DEFECTS IN WESTINGHOUSE CIRCUIT BREAKERS
Addressees:
For Action - All holders of operating licenses or construction permits for
nuclear power reactors.
Purpose:
The purpose of this bulletin is to provide information on Westinghouse series
DS circuit breakers and safety concerns associated with their use and to
request that addressees using these breakers in Class 1E service perform and
document inspection of the welds on the pole shafts and inspection of the
alignment in the breaker closing mechanism.
Description of Circumstances:
The following occurrences have raised concerns about the use of these circuit
breakers:
McGuire 2: On July 2, 1987, a DS-416 reactor trip breaker (RTB) failed to
open in response to manual trip demands from the control room. The RTB had
bound mechanically in the closed position because the main roller had become
wedged between a raised segment of the close cam and the nearby side frame
plate. Excessive lateral movement of the main drive link and a broken center
pole lever to pole shaft weld permitted the binding to occur. The failure was
reproduced once by the licensee during bench tests of the RTB at McGuire and
several times during detailed laboratory investigations performed by
Westinghouse. Substandard welding during fabrication (i.e., porosity, lack of
fusion, inadequate extent of welding) caused the weld to break. Details of
this failure mode are given in Information Notice No. 87-35, Supplement 1,
dated December 16, 1987.
The licensee visually inspected the remaining pole shaft welds of the
defective McGuire breaker and the other McGuire RTBs and found indications of
lack of fusion (i.e., lack of characteristic weld bead ripple, notches at the
edges of the weld beads, and small evidence of base metal melting).
Catawba 1 and 2: The licensee inspected all DS-416 RTBs and found a pole
shaft with a crack about 1/4 inch long at the finish end of the antibounce
lever weld. The licensee also observed lack of fusion at the start ends of
the center pole
8802020034
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lever and antibounce lever welds. Subsequent examination under magnification
of the Catawba pole shaft in the laboratory of an NRC contractor revealed two
additional cracks, one at each end of the center pole lever weld. After the
cracks from the center pole lever weld were removed, about half (i.e., 67
degrees of weld arc) of the original 120 degrees of weld arc remained.
Similarly, 86 degrees of weld arc remained after the antibounce lever weld
defects were removed. The licensee's inspection of the RTBs included checking
the alignment of the main roller on the close cam surface. Two RTBs were
found with excessive lateral tolerance, allowing the roller to strike the side
frame plates located adjacent to the close cam, even though the pole shaft
welds were observed to be intact. The licensee also noted that some pole
shaft welds of this type of circuit breaker used in its hydroelectric plants
had failed several years ago but that they have performed satisfactorily since
they were repaired by additional welding on the opposite sides of the levers.
Sequoyah 2: In April 1987, two fillet welds broke on the pole shaft assembly
of a DS-416 circuit breaker that energizes the emergency fire protection
pumps. The weld failures apparently freed the center moving contact assembly
(i.e., the Y-phase contact assembly), allowing it to move independently of the
pole shaft that drives the other two moving contact assemblies, as evidenced
by an electrical phasing problem and erratic operation of the fire pump. The
two failed welds joined adjacent levers (the center pole lever and the
antibounce lever) to the pole shaft. The two levers are connected by a pin.
On the basis of engineering analysis, the licensee concluded that the center
pole lever weld failed first because of excessive porosity; the antibounce
lever weld then failed because it was inadequately sized and could not
accommodate the load normally supported by the center pole lever weld that was
thrust upon it through the connecting pin.
Calvert Cliffs 1: In September 1986, a broken weld connecting the center pole
lever to the pole shaft in a DS-206 circuit breaker used in Class 1E service
for the control room habitability system was detected during routine mainte-
nance surveillance. No adverse effect on breaker performance had been noted;
the weld for the adjacent antibounce lever was observed to be intact and car-
rying the load of the broken weld. The licensee's measurements showed that
the leg size on the pole shaft side was 0.3 inch and the leg size on the lever
arm side was 0.1 inch. On the basis of analysis, the licensee concluded that
the failure was due to extensive lack of fusion of the weld to the lever as a
result of improper weld technique. The licensee examined an additional 10
welds on this pole shaft and another pole shaft and found that the start ends
of the welds in general were not fused properly to the levers and that the
weld legs generally exhibited mismatches. Cracks were detected in the start
ends of 2 of the 10 welds.
Westinghouse: Both commercial grade and Class 1E circuit breakers of the DS
series use similar pole shafts or possess features associated with the
observed binding and electrical phasing problems. Specifically, Model Nos.
DS-206, DSL-206, DS-416, DSL-416, and DS-420 are susceptible to these types of
failures. The welds of these pole shafts were randomly inspected during
manufacture. However, no documentation confirms either that in-process
inspections were performed
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when the pole levers were welded to the pole shafts or that inspections were
performed during the dedication of the commercial grade breakers to Class 1E
service.
Discussion:
As a result of the operating experiences and observations discussed above,
there is a question concerning the operability of RTBs and other Class 1E
circuit breakers of the Westinghouse DS series. Some DS series circuit
breakers may not have been fabricated in compliance with General Design
Criterion (GDC) 1 and Appendix B, 10 CFR 50, and have inadequate welds joining
levers to pole shafts. Excessive misalignment of the main rollers on the
close cam also can occur. GDC 1 and Appendix B require, in part, that
components important to safety be fabricated to quality standards commensurate
with the importance of the safety functions to be performed. Consequently,
licensees should take action to confirm compliance with GDC 1 and 10 CFR 50
Appendix B and to inspect all relevant welds and roller clearances according
to the manufacturer's specifications and to take appropriate remedial actions
to correct deficiencies.
On December 1, 1987, Westinghouse issued Technical Bulletin NSID-TB-87-11
(Attachment 1) as a result of its investigation of the McGuire 2 RTB failure.
It recommended inspection of the pole shaft welds and of the alignment in the
breaker closing mechanism according to specific criteria and provided guidance
for corrective actions if required, including a procedure for the removal and
installation of pole shafts. The NRC has reviewed the Westinghouse technical
bulletin and finds that it adequately addresses the NRC concerns subject to
certain changes discussed below. Specifically, the NRC has concluded that
RTBs should be inspected expeditiously, that in view of the Sequoyah 2 weld
failures welds should be inspected for porosity, and that a bypass breaker not
meeting the weld criteria in the Westinghouse technical bulletin should be
removed from service.
Actions Requested:
The phrases "short-term inspection" and "long-term inspection" used in this
NRC Bulletin are consistent with the phrases as used in the Westinghouse
technical bulletin. Specifically, short-term inspections refer to inspections
of the three main pole levers (the left pole lever, the center pole lever, and
the right pole lever). These short-term inspections should be performed on
breakers at the next available opportunity (e.g., a maintenance outage) or
during the next surveillance test for the breaker, whichever is earlier.
Long-term inspections refer to inspections of the four remaining welds on the
pole shaft and to the direct check of the alignment of the breaker closing
mechanism. These long-term inspections should be performed on the breaker
prior to restart following the next refueling outage. However, for plants
that have not yet received an operating license, the implementation periods
for the short-term and long-term inspections are modified by this NRC bulletin
to mean before fuel loading.
As used in this NRC bulletin, the phrase "replacement pole shaft" may include
a repaired pole shaft. However, since welding of a pole shaft lever may cause
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February 5, 1988
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distortion and misalignment of the lever, such repairs should be attempted
only after consultation with Westinghouse. Any repaired pole shaft weld
should meet the criteria in Section 6.1.1 of the Westinghouse technical
bulletin, as supplemented below.
Addressees using Westinghouse DS-206, DSL-206, DS-416, DSL-416, and DS-420
circuit breakers in Class 1E applications, including RTBs, are requested to
perform short-term and long-term inspections in accordance with the
Westinghouse technical bulletin, except that the following changes should be
made to the following sections:
6.0 Add the following:
However, inspection of the 3 main pole shaft welds for all RTBs
(both main and bypass) should be completed within 30 days of receipt
of this NRC bulletin.
6.1.1, 6.1.2, and 7.1 Add the following:
e) porosity - surface pin holes with cumulative diameters
less than 1/16 inch in each inch of weld
6.2.4 Delete this section and the reference to it in Section
6.2.3.
With regard to Section 6.2.4, any RTB with a pole shaft that does not meet the
criteria in Section 6.1.2 should be deemed inoperable and should not be used
in the operating or bypass breaker position in the reactor trip switchgear.
Such pole shafts should be removed from service and a replacement pole shaft
installed in the breaker before returning it to service. The replacement pole
shaft should meet the criteria in Section 6.1.1.
Reporting Requirements:
If addressees cannot meet this suggested schedule for short-term and long-term
inspections, they should justify to the NRC their proposed alternative
schedules.
Records of inspections and corrective actions in response to this NRC bulletin
shall be documented and maintained in accordance with plant procedures for
Class 1E equipment. Any addressee who does not have circuit breakers subject
to this bulletin shall provide a letter to the NRC stating this fact within 60
days of receipt of this bulletin. Addressees who do have circuit breakers
subject to this bulletin shall provide letters of confirmation to the NRC of
the completion of the inspections. These letters shall include the number of
breakers of each type inspected, the number of breakers of each type requiring
corrective actions due to pole shaft welds not meeting the acceptance criteria
and the number of breakers of each type requiring corrective actions due to
mechanism alignments not meeting the acceptance criteria. These letters of
confirmation shall be submitted to the NRC within (1) 30 days of completion of
the short-term inspections and (2) 30 days of completion of the long-term
inspections.
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Since inspection of the three main pole shaft welds for all RTBs should be
completed within 30 days of receipt of this bulletin, a letter of confirmation
of completion of these inspections including the above information is
requested within 60 days of receipt of this bulletin.
The letter of confirmation shall be submitted to the appropriate Regional
Administrator under oath or affirmation under the provisions of Section 182a,
Atomic Energy Act of 1954, as amended. In addition, the original copy of the
cover letter and a copy of any attachment shall be transmitted to the U. S.
Nuclear Regulatory Commission, Document Control Desk, Washington D.C. 20555,
for reproduction and distribution. For purposes of NRC accounting, all corre-
spondence associated with this bulletin, including the letter of confirmation,
should bear the identifying number TACS 65955/65956.
This request for information was approved by the Office of Management and
Budget under blanket clearance number 31500011. Comments on burden and
duplication should be directed to the Office of Management and Budget, Reports
Management, Room 3208, New Executive Office Building, Washington D.C. 20503.
Although no specific request or requirement is intended, the following
information would be helpful to the NRC in evaluating the cost of complying
with this bulletin:
(1) staff time to perform requested inspections, corrective actions, and
associated operability testing
(2) staff time to prepare requested documentation
(3) additional cost incurred as a result of the inspection findings (e.g.,
costs of corrective actions, costs of down time)
If you have any questions about this matter, please contact one of the
technical contacts listed below or the Regional Administrator of the
appropriate regional office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: Darl S. Hood, NRR K. R. Naidu, NRR
(301) 492-1442 (301) 492-0980
C. Vernon Hodge, NRR C. D. Sellers, NRR
(301) 492-1169 (301) 492-0930
Attachments:
1. Westinghouse Technical Bulletin NSID-TB-87-11, December 1, 1987
2. List of Recently Issued NRC Bulletins
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021