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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 NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT 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) Addressees: All nuclear power reactor facilities holding an operating license (OL) or construction permit (CP). Purpose: 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) 8308310076 . 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 Attachment: 1. Figure 1 2. List of Recently Issued IE Information Notices .
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