United States Nuclear Regulatory Commission - Protecting People and the Environment

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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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, July 23, 2013