United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 87-12: Potential Problems with Metal Clad Circuit Breakers, General Electric Type AKF-2-25

                                                         SSINS No.: 6835 
                                                             IN 87-12 
                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555

                              February 13, 1987

Information Notice No. 87-12:  POTENTIAL PROBLEMS WITH METAL CLAD CIRCUIT 
                              BREAKERS, GENERAL ELECTRIC TYPE AKF-2-25 

Addressees: 

All nuclear power reactor facilities holding an operating license or a 
construction permit. 

Purpose: 

This notice is to alert recipients of potential problems with the General 
Electric Company (GE) AKF-2-25 type circuit breakers failing to fully open 
on demand. It is expected that recipients will review the information for 
applicability to their facilities and consider actions, if appropriate, to 
preclude similar problems. However, suggestions contained in this 
information notice do not constitute NRC requirements; therefore, no 
specific action or written response is required. 

Description of Circumstances: 

1.   Pilgrim Nuclear Power Station 

     On June 29, 1986, the "A" recirculation pump (RP) motor/generator (NG) 
     set field breaker (AKF-2-25) failed to trip while the MG was being 
     removed from service. Licensee investigation revealed that the breaker 
     was mechanically bound and could not be actuated by rotating the trip 
     shaft. Because the breaker had not fully opened, the breaker auxiliary 
     switch "a" contact, which is in series with the shunt trip coil (STC), 
     did not open the circuit to the STC, which then burned out. Improper 
     lubrication and misadjustment appeared to be the cause of binding. 

     On March 15, 1985, the turbine generator field breaker (AKF-2-25) 
     failed to open when it received a trip signal from its manual control 
     switch. Examination determined that there was insufficient lubrication 
     on the link and cam of the centerpole of the breaker and that the 
     eccentric cam bushing was improperly installed. 

     On February 9, 1985, the "A" RP MG-set field breaker (AKF-2-25) failed 
     to open on demand after the "A" RP motor tripped. The control/ATWS STC 
     was observed to be burned and open circuited. Additionally, the 
     auxiliary switch that was connected to the breaker trip shaft was 
     found to have loose mounting bolts and to be damaged. The licensee 
     determined that mechanical binding and/or auxiliary switch problems 
     caused the failure of the breaker to trip on demand. 

8702110132
.

                                                       IN 87-12 
                                                       February 13, 1987 
                                                       Page 2 of 4 

     On April 3, 1983, the "B" RP MG-set field breaker (AKF-2-25) failed to 
     open; consequently, the STC burned out when the "B" RP was secured by 
     the control room operators. The licensee maintenance personnel found 
     mechanical binding of the breaker unit, which required partial 
     disassembly to free the breaker. The licensee determined that the 
     shunt trip device rotated the trip shaft, thereby starting the trip 
     action; however, the cam arrangement failed to complete its intended 
     action and the trip action was interrupted. 

2.   Dresden Unit 3 

     On September 2, 1983, personnel could not open the "B" RP MG-set field 
     breaker (AKF-2-25) and found the STC burned out. The STC was replaced 
     and the breaker was cleaned and lubricated. 

     On March 1, 1982, while performing the ATWS surveillance, which 
     requires tripping and reclosing the field breaker, the plant personnel 
     found the field breaker inoperable. Plant personnel investigated and 
     found the operator arm disconnected from the auxiliary contacts. The 
     arm was reconnected and the surveillance was performed. 

Discussion: 

On February 21, 1980, the NRC issued an order requiring the installation of 
an ATWS RP trip function. Some licensees installed a second STC on the two 
RP MG-set field breakers and the necessary instrumentation/logic to cause a 
breaker trip when certain parameters are sensed. Pilgrim and Dresden have 
this arrangement. Other licensees installed the ATWS trip coils in the 4.16 
kV/6.9 kV circuit breakers that supply power to the two MG-sets. 

The AKF-2-25 circuit breaker is a field switch without overcurrent 
protection. It is a three-pole breaker with the center pole modified 
specifically to serve as a dc switch. In the ATWS RP trip function 
application, the AKF-2-25 field breaker is equipped with two STCs, one of 
which is dedicated to respond to an ATWS demand. Each STC is energized 
through a normally open "A" contact that is controlled by the breaker's 
moving contacts. The "A" contact is an auxiliary switch that opens when the 
breaker is fully open and closes when the breaker is closed (ON position). 
The "A" contact is in series with the STC. Thus, when the breaker is closed, 
the "A" contact is closed and the STC is ready to trip on receipt of a 
signal from the control room or the ATWS logic. The STC is not rated for 
continuous duty and will overheat and fail if subjected to full voltage for 
more than a few seconds. If a breaker does not fully open when demanded by 
an STC, the "A" contact will not open and the STC will overheat and fail. 
Therefore, if a subsequent ATWS trip signal is initiated, the safety 
function will not be performed. An STC failure can only be detected by 
testing; remote indication is not provided.
.

                                                       IN 87-12
                                                       February 13, 1987 
                                                       Page 3 of 4 

The most recent breaker failure at Pilgrim has been attributed to improper 
maintenance performed by GE service technicians, who at the time were 
unaware of special maintenance practices developed by the GE Atlanta Service 
Shop. The GE Atlanta facility disassembled the failed breaker and discovered 
that it was out of adjustment and that improper lubricants had apparently 
been used. GE has issued Service Information Letter Number 448 to address 
special maintenance practices developed for the entire AK type breaker 
series which includes AK, AKU, AKF, and AKR type circuit breakers. 

The ATWS trip function is required by 10 CFR 50.62(c)(5) and specific 
quality assurance guidance has been provided for non-safety-related AIVS 
equipment (NRC Generic Letter 85-06 dated April 16, 1985). 

The GE AKF type circuit breakers have been shown to be susceptible to 
failure as a result of binding within the breaker cam mechanism, unless 
proper maintenance procedures are developed and followed by individuals 
trained specifically to service the AKF breaker. GE has suggested that the 
following maintenance information be incorporated into licensee programs for 
GE AKF-type circuit breakers: 

(1)  Maintenance/inspection intervals of every 12 months or at each 
     refueling outage. A complete breaker overhaul every 5 years is 
     recommended to complement the annual cyclical maintenance. 

(2)  Only specified lubricants should be used on these circuit breakers. 
     Molykote BR2 Plus grease or equivalent for the slot in the circuit 
     breaker centerpole cam-link and GE Specification D50HD38 (Mobil 28) 
     for all other applications. The grease of GE Specifications D5OHl5 and 
     D5OH47 is no longer recommended for this breaker. 

NOTE:     D50HD38 lubricant should not be mixed with D5OHl5 and D5OH47 
lubricants. Before changing to D50HD38 lubricant, maintenance personnel 
should clean the circuit breaker thoroughly to remove all D5OHl5 and D5OH47 
lubricant from the circuit breaker. 

(3)  Because of the complexity and difficulty in properly making crucial 
     adjustments unique to GE AKF type circuit breakers, only qualified, 
     properly trained personnel should perform these maintenance 
     activities. 

(4)  For type AKF circuit breakers which have not yet been converted to 
     D50HD38 lubricant, cycle the breakers a few times between maintenance 
     and inspection events whenever plant conditions allow.
.

                                                       IN 87-12
                                                       February 13, 1987 
                                                       Page 4 of 4 

No specific action or written response is required by this notice. If you 
have any questions regarding this matter, please contact the Regional 
Administrator of the appropriate regional office or this office. 




                         Edward L. Jordan Director
                         Division of Emergency Preparedness
                           and Engineering Response
                         Office of Inspection and Enforcement 

Technical Contact:  K. R. Naidu, IE
                    (301) 492-4179

                    J. Jacobson, IE
                    (301) 492-8845

Attachment: List of Recently Issued Information Notices
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