Information Notice No. 88-98: Electrical Relay Degradation Caused by Oxidation of Contact Surfaces
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
December 19, 1988
Information Notice No. 88-98: ELECTRICAL RELAY DEGRADATION CAUSED BY
OXIDATION OF CONTACT SURFACES
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
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.
Background:
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).
Discussion:
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.
8812130028
. IN 88-98
December 19, 1988
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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
licensees.
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
distribute
industrial nuclear
gauges.
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit
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