Information Notice No. 84-20: Service Life of Relays in Safety-Related Systems

                                                           SSINS No.:  6835 
                                                           IN 84-20        

                               UNITED STATES 
                           WASHINGTON, D.C. 20555 

                               March 21, 1984 



All holders of a nuclear power reactor operating license (OL) or 
construction permit (CP). 


This information notice is provided as a notification of potentially 
significant problems pertaining to the service life of relays in 
safety-related systems.  These problems are similar to those discussed in IE
Bulletin No. 84-02, and the general concerns associated with the HFA relay 
failures discussed in that bulletin apply to the problems described below. 
It is expected that recipients will 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 information notice do not constitute NRC requirements and, 
therefore, no specific action or written response is required. 

Description of Circumstances: 

Agastat GP Series Relays Agastat GP series relays manufactured by Amerace 
Corporation are used in the reactor protection system and other 
safety-related systems for logic actuation in instrumentation and control 
circuits at certain plants. Earlier than anticipated end-of-service-life 
failures of Agastat GP series relays were reported by Mississippi Power and 
Light Company on October 17, 1983 under the provisions of 10 CFR Part 21 for
the Grand Gulf Nuclear Station. It has been determined that undetected 
cumulative relay failures could result in a substantial safety problem. 

During the performance of 18-month-surveillance tests at Grand Gulf Unit 1 
twelve (out of approximately 1700) inoperable Agastat GP series relays, 
manufactured before August 1977, were identified. These relay failures 
precluded the automatic operation of standby service water system valves, 
main steam isolation valves, and components in the control room ventilation 
system, combustible gas control system, reactor core isolation cooling 
system, residual heat removal system, and high pressure core spray system. 


                                                           IN 84-20        
                                                           March 21, 1984  
                                                           Page 2 of 3     

On September 2, 1983, Mississippi Power and Light Company, General Electric,
and Amerace Corporation began a combined effort to determine the failure 
mechanism. During a preliminary examination, the failures of the relays to 
operate properly were determined to be a result of the nylon movable contact
arm coming in contact with the barrier strip on the melamine phenol plastic 
relay base. This mechanical interference consequently prevented one of four 
sets of contacts in the relay from changing state. 

After additional testing by General Electric and Amerace, it was determined 
that the failures were end-of-service-life failures resulting from service 
aging of energized relays in combination with the mechanical configuration 
and tolerances of the internal parts specific to the pre-August 1977 Agastat
GP series relays. Although, as discussed in the following paragraph, a 
design change has been made to correct the mechanical configuration and 
tolerance problems, it is not yet apparent that this will extend the service 
life of the relay. The current qualified service life, on the basis of 
General Electric test data, for all Agastat GP series relays (GP, FGP, and 
EGP series) operated in the energized state is stated to be 4.5 years. The 
service life for all Agastat GP series relays operated in the de-energized 
state is currently stated by Amerace to be 10 years. Amerace Corporation is 
in the process of developing a test program which may establish a qualified 
life for the EGP relays in the energized state in excess of the currently 
stated 4.5 years. 

The mechanical interference problem with Agastat GP series relays 
manufactured prior to August 1977 appears to be caused by casing shrinkage 
following assembly as the melamine phenol plastic base cures. This 
phenomenon is called post-mold plastic shrinkage. The post-mold plastic 
shrinkage causes a reduction in clearances and, in some assemblies, causes 
mechanical interference between the moving relay contact arm and the 
stationary base of the relay case. In August 1977, Amerace Corporation 
introduced a design change modifying the relay base by cutting a notch in 
the barrier strip to provide additional clearances which would preclude 
mechanical interference resulting from post-mold plastic shrinkage. 
Subsequent operational experience has shown that this design change 
precludes failures related to post-mold shrinkage; however, there is no 
evidence that the notched base design extends the service life of the 
normally energized relays. 

GTE Sylvania AC Relays 

On August 27, 1983, at Three Mile Island Unit 1, smoke was observed coming 
from a relay room. On further investigation it was discovered that the smoke
was coming from a normally energized engineered safeguards actuation system 
(ESAS) relay coil. An electrician de-energized the relay coil and the 
smoking stopped immediately. 

The relay coil was manufactured by GTE Sylvania and this was the fourth such
failure in the last year. All four GTE Sylvania coil failures occurred while
the relays were energized. The licensee has begun an investigation of the 
GTE Sylvania relays in an attempt to determine the exact cause of the coil 
failures. Preliminary findings indicate that the failures may result from 

                                                           IN 84-20        
                                                           March 21, 1984  
                                                           Page 3 of 3     

end-of-life thermal aging, but the licensee is continuing to investigate and
is replacing the coils in all GTE Sylvania relays. 

The GTE Sylvania relay coils that failed were model numbers TB113-61 and 
TB130-1 and wore used in model #X5U, Type PM 7305 Sylvania AC relays. These 
relays were in service for approximately eight to ten years. The 
manufacturer has not specified the exact service life of these normally 
energized GTE Sylvania relays and relay coils. 


In general, the service life of all relays in the normally energized state 
is significantly shorter than when used in a cycled or normally de-energized
application. It is believed that the shorter service life of the normally 
energized relays can be attributed to accelerated thermal aging of relay 
components. Furthermore, even relays used only in a cycled or normally 
deenergized application may have a service life considerably shorter than 
the plant life. Generic Letter 83-28, dated July 8, 1983, requests licensees 
to maintain a program that includes specifications on the qualification 
testing for expected safety service conditions to support the limits of life
recommended by the suppliers of components in safety-related systems. 

We advise all recipients of this notice to review their safety-related 
systems to ascertain whether Agastat GP series relays (especially those 
manufactured before August 1977) and GTE Sylvania AC relays have been 
installed or are being held as spare parts. Preventative maintenance 
programs should recognize the application-dependent (energized/de-energized) 
service life of these relays and the service life of relays supplied by 
other manufacturers. In addition, in systems where the current surveillance 
interval is not small in comparison with the service life of relays used in 
those systems, it may be prudent to increase the frequency of surveillance 
activities. For example, an 18-month-surveillance interval for a component 
with only a 4.5 year service life may not be appropriate. 

It is expected that this notice will be useful in responding to the reviews 
requested in IE Bulletin No. 84-02, particularly the first unnumbered 
paragraph on page 5 of that document. If you have any questions regarding 
these matters 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: M. Virgilio, NRR              P. Farron, IE 
                    (301) 492-9454                (301) 492-4766 

List of Recently Issued IE Information Notices

Page Last Reviewed/Updated Wednesday, March 24, 2021