United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 92-27: Thermally Induced Accelerated Aging and Failure of ITE/Gould A.C. Relays used in Safety-Related Applications

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF NUCLEAR REACTOR REGULATION 
                          WASHINGTON, D.C.  20555 

                               April 3, 1992 


NRC INFORMATION NOTICE 92-27:  THERMALLY INDUCED ACCELERATED AGING AND 
                               FAILURE OF ITE/GOULD A.C. RELAYS USED
                               IN SAFETY-RELATED APPLICATIONS


Addressees

All holders of operating licenses or construction permits for nuclear power 
reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information 
notice to alert addressees to problems resulting from the accelerated aging 
and failure of 120V ac relays manufactured by the ITE/Gould Manufacturing 
Company (currently Telemecanique).  The relay failures rendered portions of 
the associated safety-related systems inoperable.  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 are not NRC requirements; 
therefore, no specific action or written response is required.

Description of Circumstances

On November 23, 1991, while performing an eighteen month engineered safety 
features operability test, the licensee for the Millstone Nuclear Power 
Station, Unit 3, noted that control power was interrupted to three safety-
related motor operated valves (MOVs).  The valves were located in the 
charging, component cooling water, and steam generator atmospheric dump 
systems.  The licensee inspected the valves' control power circuitry and 
determined that three normally energized auxiliary relays had failed.  These 
relays provided control power alarms and thermal overload protection for the 
MOVs.  The relay failures rendered each valve inoperable.

The relays, which had been in service for about seven years, were class J10 
relays with J20M magnet block assemblies and standard G10JA126, 120V, 60 
cycle coil assemblies manufactured by the ITE/Gould Manufacturing Company.  
Inspection of the relays revealed that the movable plastic armature carrier, 
which surrounds the core and coil, and the retainer for the magnet yoke 
assembly were discolored, brittle and severely cracked.  Insulation 
degradation was severe, allowing electrical shorts to develop within the 
coils.  The licensee concluded that the failures resulted from the thermal 
aging of the coil assemblies and plastic parts near the coil assemblies.     



9203270157 
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The failed relays were mounted shoulder to shoulder in a horizontal "ganged" 
arrangement on a universal mounting strip supplied by the manufacturer.  The 
three relays that failed were each mounted in the middle of a ganged relay 
cluster.  The relays were originally qualified, individually, for the life 
of the plant.  However, the qualification process did not account for the 
use of the relays in the ganged arrangement.  The licensee stated that the 
potential heat induced degradation of "weak-link" materials such as the 
plastic armature carrier was not considered in the qualification test 
report.

The licensee inspected relays in other safety and nonsafety systems and 
found similar discoloration and embrittlement caused by overheating, but 
found no additional failures.  The Millstone licensee has replaced 
approximately 260 relays with identical components from spare motor control 
centers.  Long term corrective actions include periodic monitoring and 
replacement and/or physical separation of ganged relays.  

During the period April 1987 through August 1987, the licensee for the 
Seabrook Generating Station experienced similar failures of ITE/Gould J-10 
relays.  Following those failures, Telemecanique submitted a report to the 
NRC under Title 10 of the Code of Federal Regulations (10 CFR), Part 21 
(Part 21 report)  describing the failures at Seabrook.  The report 
attributed the overheating failures to the special low voltage coils in the 
J10 relays that were supplied to the Seabrook Nuclear Station.  Telemec- 
anique stated that the relays supplied to Seabrook were equipped with a 
non-standard magnet coil (identified as 816 with 50 ohms resistance) and, 
therefore, the failure mode would not be experienced at any other facility.  
The licensee for the Seabrook Station submitted a Licensee Event Report 
(LER) to the NRC under 10 CFR Part 50.73 describing the relay failures and 
their root cause analysis.  The licensee stated in the LER that, "...It was 
originally believed that excessive temperature resulted from the close 
proximity of six normally energized relays...Subsequent investigation led to 
the identification of relays not in close proximity with other energized 
components that showed slight discoloration."  However, the Seabrook 
licensee accepted the Telemecanique Part 21 report conclusions that the 
failures were due to the heat generated by the energized, non-standard coil.

The recent failures at Millstone suggest that the Seabrook licensee's 
original conclusion may have been accurate.  The gang mounting ("close 
proximity") of these relays was likely a major contributor to the 
accelerated aging with the condition being exacerbated by the additional 
heat generated by the continuously energized coil.

The J10 relay is one of a family of J-class relays currently manufactured by 
Telemecanique as commercial grade items.  Although the NRC staff is not 
aware of the failure of any of the other J-class relays, these relays could 
be susceptible to similar heat induced degradation when gang mounted.  

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                                                            IN 92-27 
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This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
one of the technical contacts listed below or the appropriate Office of 
Nuclear Reactor Regulation (NRR) project manager. 



                                   Charles E. Rossi, Director
                                   Division of Operational Events Assessment
                                   Office of Nuclear Reactor Regulation

Technical contacts:  N. Fields, NRR
                     (301) 504-1173

                     K. Naidu, NRR
                     (301) 504-2980

                     R. Spence, AEOD
                     (301) 492-8609

Attachment:  List of Recently Issued NRC Information Notices






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