United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 94-33: Capacitor Failures in Westinghouse Eagle 21 Plant Protection Systems

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

May 9, 1994


NRC INFORMATION NOTICE 94-33:  CAPACITOR FAILURES IN WESTINGHOUSE EAGLE 21
 PLANT PROTECTION SYSTEMS


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 two different types of capacitor failures that
can cause loss of power to portions of Eagle 21 reactor protection systems
manufactured by Westinghouse Electric Corporation.  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

During the past year, Commonwealth Edison Company (CECo) experienced several
instances of partial loss of electrical power within the Westinghouse Eagle 21
plant protection system at Zion Station, Unit 1, during normal plant
operation.  Two types of failures were identified, and these were reported by
CECo under Part 21 of Title 10 of the Code of Federal Regulations (10 CFR) on
April 8, 1994.

One type of failure involved Series RS 300 and RT 300 dc power supplies
manufactured by ASTEC America, with Westinghouse part numbers 2D33574G07 and
2D33574G09.  Electrolytic capacitors C2 and C7 failed, causing complete loss
of dc power to the connected loads.  Unit 1 at Zion Station has 10 racks of
Eagle 21 equipment.  Each rack contains two power supplies.  One provides
power to the tester subsystem, which is not essential for performing the
system design safety function.  The other power supply provides power for the
loop processor subsystem, which includes reactor protection and engineered
safety features channels and logic, and may include some control room
indication channels.  On loss of power, a loop processor channel fails to the
de-energized state, which normally is the tripped state.  Containment spray,
however, is an energize-to-actuate function, and loss of power would prevent
the channel from tripping.  In certain racks, loss of power would also defeat
some control room indications required by Regulatory Guide 1.97.




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The other failure type involved type TDA40DM time delay relays manufactured by
Douglas-Randall, with Westinghouse part number PS12800H02.  Ceramic capacitor
C2 failed, causing either repetitive cycling or complete loss of ac power to
the connected loads.  The time delay relays are used in the Eagle 21 ac power
distribution panels to sequentially load the power supplies during protection
system startup.  The failure consequences are similar to those for the power
supply capacitors described above.

Discussion

The failed capacitors in the ASTEC America dc power supplies were type
SR65, Z5U manufactured by AVX Corporation.  The failed capacitors had date
codes from 9130 to 9136 where the first two digits of the date code indicate
the year of manufacture and the last two digits indicate the week within that
year.  The capacitors were used in power supplies manufactured in 1991, with
date codes 9134 through 9147.  Westinghouse determined that several capacitors
with the suspect date codes shorted or exhibited electrical leakage, and were
cracked or ruptured.  The Zion power supplies were returned to Westinghouse,
the capacitors with the suspect date codes were replaced, and the power
supplies were tested and returned to service.  The ASTEC America power
supplies are used in the following Westinghouse systems:

  Neutron flux monitoring system (NFMS)
  Auxiliary Shutdown Indication System (ASIS)
  Plant Safety Monitoring System (PSMS)
  Qualified Display Processing System (QDPS)
  Reactor Vessel Level Instrumentation System - 86 (RVLIS-86)
  Inadequate Core Cooling Monitor System (ICCM)
  ATWS Mitigating System Actuation Circuitry (AMSAC)
  Eagle 21

CECo and Westinghouse determined that the capacitors in the Douglas-Randall
time delay relays were failing prematurely because of excessive heat
dissipated in the epoxy potted module by nearby resistor R1.  The problem was
corrected by returning the relays to Westinghouse, where the resistors were
relocated outside the relay module.  The relays were tested and returned to
service.

The Zion failures were discussed at an Eagle 21 owners group meeting in
November 1993, but the causes had not been identified at that time.  Because
the failures are detectable and a Westinghouse failure analysis determined
that they are aging related and likely to be random rather than simultaneous,
Westinghouse elected not to submit a notification under 10 CFR Part 21.  For
the power supply failures, Westinghouse advised the NRC that it issued an
Infogram to all customers with Eagle 21 or other affected equipment on
April 29, 1994.  For the relay failures, only four of the five Eagle 21
customers are affected, since Sequoyah does not have the relays.  Zion is
fully aware of the concerns, and the hardware has been corrected.  The Diablo
Canyon system will be corrected before it is shipped to the site.
Westinghouse advised that it was preparing plant-specific followup letters to
Watts Bar, Turkey Point, and Diablo Canyon for issue on April 29, 1994.
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This information notice is being sent to all power reactor licensees because
AVX capacitors and Douglas-Randall time delay relays may be used in other
applications at nuclear power plants.

This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) Project Manager.

/S/'D BY BKGRIMES


Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation


Technical contact:  Richard C. Wilson, NRR
  (301) 504-3220

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