Information Notice No. 88-98: Electrical Relay Degradation Caused by Oxidation of Contact Surfaces

                                   UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                            WASHINGTON, D.C.  20555 

                                December 19, 1988

                                   OXIDATION OF CONTACT SURFACES 


All holders of operating licenses or construction permits for nuclear power 


This information notice is being provided to alert addressees of potentially 
degraded electrical relay performance from oxidation of relay contact surfaces 
caused by low current applications.  It is expected that recipients will 
review the information for applicability to their facilities and consider 
actions, as appropriate, to avoid similar problems.  However, suggestions 
contained in this information notice do not constitute NRC requirements; 
therefore, no specific action or written response is required. 


The NRC staff was recently informed by the Clinton Power Station that a 
reactor scram on June 24, 1988, was caused by an electrical relay failure from 
oxide buildup on relay contact surfaces.  Other information on relay failure 
from contact oxidation indicates that this problem may be more prevalent than 
pre-viously thought.  For example, a July 17, 1988, 10 CFR Part 21 report from 
Palo Verde, Unit 2, reported relay failures from contact oxidation that were 
due to the low current application of the relays.  The relay contact surfaces 
in both of these examples are silver-nickel alloys, and both applications were 
for low current (i.e, milli-ampere current). 


Electrical relay contacts made of silver-nickel or silver-cadmium alloys will 
oxidize (tarnish) when used in low current applications because of the absence 
of contact surface sparking from the typical relay contact "making and break-
ing" functions.  The sparking in the contact surfaces promotes a self-cleaning 
mechanism that reduces the tarnish buildup on the silver-nickel or 
silver-cadmium contacts.  Discussions with one relay manufacturer revealed 
that the normal in-dustry practice for low current circuit applications is 
either to use a contact surface material that will not oxidize or to 
compensate for the oxidation by increased maintenance activities to ensure 
reliability.  The applied voltage may also influence contact oxidation.

.                                                            IN 88-98 
                                                            December 19, 1988 
                                                            Page 2 of 2 

Selection of the appropriate contact surface materials or preventive main-
tenance measures are important, integral parts of the activity to review 
electrical relay suitability for low current applications.

No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact one of the techni-
cal 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:  N. P. Kadambi, NRR 
                     (301) 492-1153 

                     J. J. Petrosino, NRR 
                     (301) 492-0979 

Attachment:  List of Recently Issued NRC Information Notices 

.                                                            Attachment 
                                                            IN 88-98 
                                                            December 19, 1988 
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                             NRC INFORMATION NOTICES
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to________

88-97          Potentially Substandard       12/16/88       All holders of OLs
               Valve Replacement Parts                      or CPs for nuclear
                                                            power reactors. 

88-96          Electrical Shock Fatalities   12/14/88       All holders of OLs
               at Nuclear Power Plants                      or CPs for nuclear
                                                            power reactors. 

88-95          Inadequate Procurement        12/8/88        All holders of OLs
               Requirements Imposed by                      or CPs for nuclear
               Licensees on Vendors                         power reactors. 

88-94          Potentially Undersized        12/2/88        All holders of OLs
               Valve Actuators                              or CPs for nuclear
                                                            power reactors. 

88-93          Teletherapy Events            12/2/88        All NRC medical 

88-92          Potential for Spent Fuel      11/22/88       All holders of OLs
               Pool Draindown                               or CPs for nuclear
                                                            power reactors. 

88-91          Improper Administration       11/22/88       All holders of OLs
               and Control of                               or CPs for nuclear
               Psychological Tests                          power reactors and
                                                            all fuel cycle 
                                                            facility licensees 
                                                            who possess, use, 
                                                            import, export, or 
                                                            transport formula 
                                                            quantities of 
                                                            strategic special 
                                                            nuclear material. 

88-90          Unauthorized Removal of       11/22/88       All NRC licensees 
               Industrial Nuclear Gauges                    authorized to 
                                                            possess, use, 
                                                            manufacture, or 
                                                            industrial nuclear 
OL = Operating License
CP = Construction Permit 

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