Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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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IN 92-27
April 3, 1992
Page 2 of 3
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
April 3, 1992
Page 3 of 3
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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