United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 92-27, Supplement 1: 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.  20555-0001

                                March 21, 1997 


NRC INFORMATION NOTICE 92-27, Supplement 1:  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 thermally
accelerated aging of relays manufactured by the ITE/Gould Manufacturing
Company (currently Telemecanique).  The accelerated aging could lead to relay
coil failure, potentially rendering portions of 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.

Background

In Information Notice (IN) 92-27, "Thermally Induced Accelerated Aging and
Failure of ITE/GOULD A.C. Relays Used in Safety-Related Applications," dated
April 3, 1992, the NRC staff informed licensees of the failure of three
safety-related relays at the Millstone Nuclear Power Station, Unit 3.  The
relays were installed in the control circuits of three safety-related motor-
operated valves (MOVs).  These relays provided control power alarms and
thermal overload protection for the MOVs. 

The relays, which had been in service for about 7 years, were model J10 relays
with J20M magnet block assemblies and standard G10JA126, 120V, 60 cycle coil
assemblies manufactured by ITE/Gould.  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.  The failed relays were mounted shoulder-to-shoulder in a
horizontal "ganged" arrangement on a universal mounting strip supplied by the
manufacturer.  They were originally qualified, individually, for the life of
the plant.  


9703190139.                                                            IN 92-27, Supp. 1  
                                                            March 21, 1997 
                                                            Page 2 of 3 


Description of Circumstances

On October 11, 1996, Duquesne Light Company determined that J12 relays with
J20M magnet block assemblies and standard G10JA116, 110V, 60 cycle coil
assemblies manufactured by ITE/Gould and installed at Beaver Valley Unit 2
were susceptible to thermally induced premature aging.  (Licensee Event Report
No. 96-005-00, November 11, 1996, NRC Accession No. 9611210045.)  These relays
provide alarms, "Bypass Inoperable Status Indication," and thermal overload
protection for various MOVs, fans, and pumps.  Systems potentially affected
included safety injection, component cooling, charging, instrument air, quench
spray, recirculation spray, service water, and emergency diesel generators. 

Four of the J12 relays failed during routine outage testing.  In each case,
the normally energized relays had been deenergized for several days during 
electrical bus maintenance.  When the relays were reenergized, two contact
pairs on the relays failed to pick up.  This mode of failure would have
prevented manual operation of the safety-related valve that the relay
controlled, but did not affect the automatic engineered safety features (ESF)
actuation function.  The ESF portion of the circuit bypasses the failed
thermal overload relay and contacts.

The relays had been installed for 9 years.  Thermal aging had caused the
magnetic yoke assembly retainer and the movable plastic armature carrier,
which surrounds the core and coil, to become discolored, deformed, brittle,
and cracked.  The deformation of the armature carrier was sufficient to
interfere with free movement of the armature assembly and prevented pickup of
the contacts.  Following each of the four J12 relay failures at Beaver Valley,
the power supply circuit breaker was opened and reclosed.  The relay contacts
then made up as expected following this cycling of the power supply breaker.  
The relay degradation may have remained unknown if the licensee had not
investigated the anomaly further.  

The licensee postulated that the failures of the contact pairs to pick up on
the four J12 relays may be a precursor to coil failure and loss of control
power similar to that reported in IN 92-27.  The licensee determined that the
J20M armature assembly was also installed in J10, J11, J13, and J14 class
relays.  The licensee stated that only the J10, J12, and J13 relays were
normally energized and, therefore, susceptible to thermally induced
accelerated aging.

There are 223 J12 relays installed at Beaver Valley Unit 2.  None have been
identified at Beaver Valley Unit 1.  Before transitioning from mode 4 to mode
3 operation, the licensee replaced all J-class relays that were deemed
susceptible to thermally induced accelerated aging.

Discussion

The J12 relay is one of a family of J-class relays currently manufactured by 
Telemecanique as commercial-grade items.  Although the NRC staff is aware of
failures of .                                                            IN 92-27, Supp. 1 
                                                            March 21, 1997 
                                                            Page 3 of 3 


J-class relays at other facilities, most of the failures occurred during
surveillance testing and were attributed to "normal aging."  The NRC staff is
not aware of any analyses performed to determine the root cause for the
failures at these other facilities.  In analyzing the failure mode of the
relays at Beaver Valley, the licensee determined that if the relay remains
energized, the contacts remain shut, the armature field remains steady, and,
therefore, there is no excessive current to cause insulation breakdown and
circuit failure.  However, because the relay is continuously energized, the
resultant high temperature causes the plastic carriage material to deform. 
When the relay is deenergized, the spring-loaded armature assembly separates
the two magnet halves.  This creates the armature gap.  When the relay is
reenergized, the deformed plastic carriage restricts motion of the armature
assembly, which, in turn, maintains the large armature gap.  With the large
gap, the circuit current is greater than normal.  The higher current causes
increased heat to be generated, eventually resulting in the breakdown of coil
insulation and the development of a short circuit in the coil of the relay. 
The short circuit could cause the fuse in the control power circuit for the
component to open, rendering the component inoperable.    

Information Notice 92-27 focused on the importance of the thermal effects
resulting from ganged mounting of J10 relays.  The information notice may not
have adequately emphasized that the problem could exist with different
mounting configurations and with other J-class relays.  

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. 


                                          signed by M.M. Slosson

                                       Thomas T. Martin, Director
                                       Division of Reactor Program Management
                                       Office of Nuclear Reactor Regulation

Technical contacts:  D. Kern, Region I       
                     (412) 643-2000          
                     Email:  dmk@nrc.gov        

                     N. Fields, NRR
                     (301) 415-1173
                     Email:  enf@nrc.gov
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