United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 83-76: Reactor Trip Breaker Malfunctions (Undervoltage Trip Devices on GE Type AK-2-25 Breakers)

                                                            SSINS No.: 6835 
                                                            IN 83-76       

                                UNITED STATES
                           WASHINGTON, D.C. 20555
                              November 2, 1983

Information Notice No. 83-76:   REACTOR TRIP BREAKER MALFUNCTIONS  
                                   (UNDERVOLTAGE TRIP DEVICES ON GE TYPE 
                                   AK-2-25 BREAKERS) 


All nuclear power reactor facilities holding an operating license (OL) or 
construction permit (CP). 


To advise licensees of malfunctions of the undervoltage trip attachments in 
General Electric Type AK-2-25 breakers which are used in safety-related 
systems. Although no specific action is being required by the NRC at this 
time, it is expected that licensees will review the general problem 
described for applicability to their facilities and take appropriate action.

Description of Circumstances: 

Five malfunctions of the undervoltage (UV) trip device used on General 
Electric Type AK-2-25 reactor trip breakers (RTB) occurred at the San Onofre
Nuclear Generating Station, Units 2 and 3. On October 28, 1983, with Unit 3 
in Mode 3 (Hot Standby), while routine monthly surveillance was being 
performed on the reactor protection system, the undervoltage armatures for 
RTBs #5 and #8 were observed to be in a midposition rather than fully down 
and in contact with the air gap adjusting screw (See Figure 1). The RTBs 
were reset, observed to operate properly, and the undervoltage armatures 
were observed to be properly positioned at that time. 

On October 31, 1983, with both Units 2 and 3 in Mode 1 (Power Operation), 
the positions of all the undervoltage armatures of the RTBs were visually 
inspected. This inspection revealed that undervoltage armatures of RTB #4 on
Unit 2 and RTBs #5 and #8 on Unit 3 were not properly positioned. It has 
been established that the Unit 3 breakers had been tripped and reset 
subsequent to the October 28, 1983 event without further UV armature 
position verification. These RTBs were reset, observed to operate properly 
and the undervoltage armatures remained properly positioned. 

Southern California Edison Company, the licensee, has indicated that these 
malfunctions (i.e., the undervoltage armature in midposition rather than in 
contact with the air gap adjusting screw) could result in the RTB failing to
trip within the specified criteria of the undervoltage trip device. Southern
California Edison Company's preliminary conclusion is that the undervoltage 
armature can remain in a midposition as a result of interference (vertical) 


                                                           IN 83-76        
                                                           November 2, 1983 
                                                           Page 2 of 2     

between the undervoltage armature and the copper shading ring around the 
core of the coil (See Figure 1) 

No action or written response to this notice is required; however, licensees
using AK-2 type breakers with undervoltage trip devices may find it prudent 
to visually inspect each undervoltage armature to assure it is in its proper
position after each operation. If the UV armature were to be found in an 
improper position, the NRC would consider the RTB to be inoperable. If you 
have any questions regarding this notice, please contact the Regional 
Administrator of the appropriate NRC Regional Office, or a Technical Contact
listed below. 

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

Technical Contacts: I. Villalva, IE
                    (301) 492-9635

                    J. T. Beard, NRR
                    (301) 492-7465

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