United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-15: Loss of Offsite Power Caused by Problems in Fiber Optics Systems

                                                            SSINS No: 6835 
                                                            IN 86-15       

                                UNITED STATES
                           WASHINGTON, DC 20555

                               March 10, 1986

                                   IN FIBER OPTICS SYSTEMS 


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


This notice is to alert addressees to recent instances of loss of offsite 
power caused by problems with fiber optics systems used to control 
switchyard circuit breakers Recipients are expected to review the 
information for applicability to their facilities and consider actions, if 
appropriate, to preclude similar problems occurring at their facilities 
However, suggestions contained in this notice do not constitute NRC 
requirements; therefore, no specific action or written response is required

Description of Circumstances: 

Three recent instances of total loss of offsite power at nuclear power 
plants were caused by problems with fiber optics control systems Fiber 
optics systems are sometimes thought to be immune to radio frequency 
interference problems However, at least one of these instances was probably 
caused by interference from a hand-held radio in close proximity to the tone 
relaying trip receivers of the fiber optics system 

On October 3, 1985, the Palo Verde Unit 1 nuclear power plant tripped from 
52 percent power because of a total loss of offsite power The loss of 
offsite power was caused by the apparent malfunction of a multiplexer in the
fiber optics system that in turn controlled breakers in the plant 
switchyard The loss of offsite power caused the starting and loading of the 
emergency diesel generators that restored power to the engineered safety 
features buses 

On October 7, 1985, while shut down in Mode 3, Palo Verde Unit 1 again 
experienced a loss of offsite power apparently because of a failure of the 
multiplexer Although some failed components were identified, the ultimate 
cause of these failures of the fiber optics multiplexer was never 
determined As a corrective measure, control of the affected switchyard 
breakers was hardwired and the multiplexer control was bypassed 


                                                             IN 86-15      
                                                             March 10, 1986 
                                                             Page 2 of 2   

On January 1, 1986, the River Bend nuclear power station experienced a total
loss of offsite power caused by the tripping of the preferred station 
transformers A and C at 0941, and approximately 1 hour later, the tripping 
of the preferred station transformers B and D The plant was shut down at 
the time because of a reactor scram that occurred approximately 6 hours 
earlier for unrelated reasons 

Investigation indicated that the loss of offsite power event was not caused 
by a valid signal Testing did show that hand-held radios could have caused 
the loss of offsite power event Two hand-held radios, one 4 watts at 150 
MHz and the other 5 watts at 450 MHz, caused system trips when keyed within 
12 feet of the transmitters and receivers for the fiber optics system 
Mobile radios of greater power located outside the building containing the 
fiber optics system would not cause spurious trips 

At River Bend, the fiber optics transmitting and receiving equipment is 
located in the turbine building and the Fancy Point substation, a distance 
of about 08 miles The corrective measures adopted at River Bend include 
shielding of the fiber optics transmitters and receivers, posting signs that
prohibit use of radios near the fiber optics equipment, rewiring the 
equipment so that two channels instead of one are required for tripping, 
providing control room annunciation of system status, training personnel on 
restricted use of radios, installing a sequence-of-events recorder to 
diagnose any future events, and training personnel on resetting lockouts, 
including posting of operator aids 

Other problems caused by use of hand-held radios in nuclear power plants 
were discussed in Information Notice No. No 83-83, "Use of Portable Radio 
Transmitters Inside Nuclear Power Plants," published on December 19, 1983 

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

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

Technical Contact:  Eric Weiss, IE
                    (301) 492-9005

Attachment: List of Recently Issued IE Information Notices 

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