Information Notice 1994-24, Inadequate Maintenance of Uninterruptible Power Supplies & Inverters
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UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C.
20555
March 24, 1994
INADEQUATE MAINTENANCE OF UNINTERRUPTIBLE POWER
SUPPLIES AND INVERTERS
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purnose
-
The U.S. Nuclear Regulatory Commission (NRC) Is issuing this information
notice to alert addressees to potential failures of uninterruptible power
supplies and inverters because of inadequate maintenance. 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
Nine Mile Point Nuclear Station Unit 2 (NMP-2)
On August 13, 1991, an internal failure in the main transformer caused a
degraded voltage which resulted in the simultaneous loss of power outputs from
five uninterruptible power supplies. The power outputs from the five power
supplies were lost because of a combination of a wiring problem and the
failure of the internal batteries to supply control power. The five power
supplies provide power to the main control room annunciator system and to
other systems important to safety.
On March 26, 1992, a non-safety-related power supply failed to provide power
to a radiation monitoring cabinet, causing an engineered safety features
actuation. The licensee determined that an output breaker from the power
supply failed to close because grease in the breaker had dried out and
solidified.
Susquehanna Steam Electric Station Unit 1 (SSES-1)
On July 31, 1991, a relay in the switchyard was operated incorrectly, causing
the loss of one of the offsite power sources to the plant. The loss of this
power source, coupled with the failure of one uninterruptible power supply to
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transfer to its backup power supply, resulted in a loss of power to some ac
instrument panels. The power supply failed to transfer because of problems
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IN 94-24 March 24, 1994 with the internal batteries. The loss of power to the instrument panels
caused the loss of numerous instruments and control room indications, as well
as some plant support equipment.
Discussion
Uninterruptible power supply units are designed to supply reliable ac power to
their loads. Designs for such power supplies use an inverter to convert dc
power from a battery to ac power.
Some designs also provide a rectifier in
combination with the inverter as one unit. The rectifier converts station
power from ac to dc. The inverter then converts either the output of the
rectifier (normal) or power from a battery (backup) from dc to ac. Offsite ac
backs up the inverter ac output through a power transfer device. Direct
current control power for the power supply is developed internally using power
from external power sources. In some designs, back-up control power is
provided by an internal battery bank.
Major contributing factors for the power supply failures at NMP-2 on
August 13, 1991, and March 26, 1992, were inadequate maintenance of the
batteries which supply power to the control logic and inadequate maintenance
of the power supply output breakers respectively. The cause of the failure at
Susquehanna was three failed cells in the power supply battery bank.
The NRC Office for Analysis and Evaluation of Operational Data (AEOD) recently
prepared engineering evaluation AEOD/E93-03, "Electrical Inverter Operating
Experience - 1985 to 1992," December 1993, to assess inverter operating
experience in the nuclear industry over the last 74 years. In the report, the
staff concludes that the number of inverter failures has decreased, but some
problems still warrant attention. Significant findings in the report are as
follows:
(1) Inverter failures are still causing a large number of inadvertent
engineered safety features actuations, reactor trips, and turbine
runbacks.
(2) Component failures are still the predominant root cause of the failures, followed by human error.
(3) The components that failed most frequently were electrolytic capacitors, followed by transformers, silicon-controlled rectifiers, and transfer
switches.
The staff concluded in this report that, based on a review of licensee event
reports, some licensees obtained a marked decrease in the frequency of
electrical inverter failures by (1) providing the inverter units with adequate
cooling and (2) implementing a preventive maintenance program for the inverter
units that periodically replaced selected components. The staff also
concluded that the proper implementation of vendor recommendations for minor
and major maintenance activities would reduce the number of failures because
licensees would frequently identify and replace degraded components before
they failed.
March 24, 1994 Related Generic Communications
The NRC has issued the following related generic communications:
Information
Notice (IN) 93-26, "Grease Solidification Causes Molded-Case Circuit Breaker
Failure to Close,* April 7, 1993, and Supplement 1 to IN 93-26, January 31, 1994; IN 91-64, wSite Area Emergency Resulting From a Loss of Non- Class 1E Uninterruptible Power Supplies," October 9, 1991, and Supplement 1 to
IN 91-64, October 7, 1992; IN 88-57, "Potential Loss of Safe Shutdown
Equipment Due to Premature Silicone Controlled Rectifier Failure,"
August 8, 1988; and IN 87-24, "Operational Experience Involving Losses of
Electrical Inverters," June 4, 1987.
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.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contacts: J. G. Ibarra, AEOD
(301) 492-4441
F. S. Ashe, NRR
(301) 504-2785 Attachment:
List of Recently Issued NRC Information Notices
Al
Attachment
March 24, 1994 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
94-23
94-22
94-20
Guidance to Hazardous,
Radioactive and Mixed
Waste Generators on the
Elements of a Waste
Minimization Program
Fire Endurance and
Ampacity Derating Test
Results for 3-Hour Fire- Rated Thermo-Lag 330-1
Fire Barriers
Regulatory Requirements
when No Operations are
being Performed
Common-Cause Failures
due to Inadequate
Design Control and
Emergency Diesel
Generator Vulnerability
to Failure from Cold
Fuel Oil
Accuracy of Motor- Operated Valve Diag- nostic Equipment
(Responses to Sup- plement 5 to Generic
Letter 89-10)
Strontium-90 Eye Appli- cators: Submission of
Quality Management Plan
(QMP), Calibration, and
Use
02/22/94
03/16/94
03/18/94
03/17/94
03/16/94
03/16/94
03/11/94 All NRC Licensees.
All holders of OLs or CPs
for nuclear power reactors.
All fuel cycle and materials
licensees.
All holders of OLs or CPs
for nuclear power reactors.
All holders of OLs or CPs
for nuclear power reactors.
All holders of OLs or CPs
for nuclear power reactors.
All U.S. Nuclear Regulatory
Commission Medical Use
Licensees.
94-19
94-18
94-17 OL - Operating License
CP - Construction Permit
March 24, 1994 Related Generic Communications
The NRC has issued the following related generic communications:
Information
Notice (IN) 93-26, "Grease Solidification Causes Molded-Case Circuit Breaker
Failure to Close," April 7, 1993, and Supplement 1 to IN 93-26, January 31, 1994; IN 91-64, "Site Area Emergency Resulting From a Loss of Non- Class lE Uninterruptible Power Supplies," October 9, 1991, and Supplement 1 to
IN 91-64, October 7, 1992; IN 88-57, "Potential Loss of Safe Shutdown
Equipment Due to Premature Silicone Controlled Rectifier Failure,"
August 8, 1988; and IN 87-24, "Operational Experience Involving Losses of
Electrical Inverters," June 4, 1987.
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.
Originalsigned by
Bran K. Grimes
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contacts:
J. G. Ibarra, AEOD
(301) 492-4441 F. S.
(301)
Ashe, NRR
504-2785 Attachment:
List of Recently Issued NRC Information Notices
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ROAB:AEOD*
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NAME
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AJKugler
GLanik
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DATE
01/04/94
01/06/94
01/21/94
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OFFICE
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03/04/94 O3//Z/94 DOCUMENT NAME:
94-24. IN
V,_ IN 94-XX
March XX, 1994 The manuals provided by manufacturers give
for particular UPS and inverter equipment.
able to give licensees new information that
manuals were issued, that licensees can use
maintenance of inverters and UPSs, and thus
specific maintenance requirements
In addition, manufacturers may be
- has been developed since the
a to improve the design and
- reduce the number of failures.
Related Generic Communications
The NRC has issued the following related generic communications: Information
Notice (IN) 93-26, 'Grease Solidification Causes Molded-Case Circuit Breaker
Failure to Close,' April 7, 1993 and Supplement 1 to IN 93-26, January 31, 1994; IN 91-64, "Site Area Emergency Resulting From a Loss of Non- Class lE Uninterruptible Power Supplies," October 9, 1991 and Supplement 1 to
IN 91-64, October 7, 1992; IN 88-57, 'Potential Loss of Safe Shutdown
Equipment Due to Premature Silicone Controlled Rectifier Failure,'
August 8, 1988; and IN 87-24, "Operational Experience Involving Losses of
Electrical Inverters,w June 4, 1987.
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.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contact(s):
J. G. Ibarra, AEOD
(301) 492-4441 F. S.
(301)
Ashe, NRR
504-2785 Attachment:
List of Recently Issued NRC Information Notices
SEE PREVIOUS CONCURRENCES
OFFICE
RPB:ADM*
OGCB:NRR*
ROAB:AEOD*
C/ROAB:AEOD*
D/DSP:AEOD*
KAME
TechEd
AJKugler
GLanik
JRosenthal
GHolalan
DATE
01/04/94
01/06/94
01/21/94
01/21/94
01/24/94 OFFICE
EELB:NRR*
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DATE
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02/22/94
02/24/94
03/94N/94
03/
/94 DOCUMEN -AM:-----LK
DOCUMENT NAME:
INVEKIEK.IN
IN 94-XX
February XX, 1994 The manuals provided by manufacturers give specific maintenance requirements
for particular pieces of equipment. The manufacturers may also be able to
give licensees new information that has been developed since the manuals were
issued, in order to improve the design and maintenance of inverters and UPSs, and thus reduce the number of failures.
Related Generic Communications
The NRC has issued other generic communications related to this subject.
These generic communications included Information Notice (IN) 93-26, "Grease
Solidification Causes Molded-Case Circuit Breaker Failure to Close,' April 7,
1993 and Supplement 1 to IN 93-26, January 31, 1994; IN 91-64, 'Site Area
Emergency Resulting From a Loss of Non-Class lE Uninterruptible Power
Supplies," October 9, 1991 and Supplement 1 to IN 91-64, October 7, 1992;
IN 88-57, Potential Loss of Safe Shutdown Equipment Due to Premature Silicone
Controlled Rectifier Failure," August 8, 1988; and IN 87-24, "Operational
Experience Involving Losses of Electrical Inverters," June 4, 1987.
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.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contact(s):
Jose Ibarra, AEOD
(301) 492-4441
F. S. Ashe, NRR
(301) 504-2785 Attachment:
List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCES
OFFICE
RPB:ADM*
OGCB:NRR*
ROAB:AEOD*
C/ROAB:AEOD*
D/DSP:AEOD*
NME
TechEd
AJKugler
GLanik
JRosenthal
GHolalan
DATE
01/04/94
01/06/94
01/21/94
01/21/94
01/24/94 OFFICE
EELB:NRR*
C/A LWR A
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AC/OGCB:NRR
D/DORS:NRR
NAME
EWeiss
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BKGrimes
DATE
01/27/94
02/2Z/94
02/94
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02/
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lr4LKIL. ir
WOCUMMN NAME:
INVLK ItK .IN
y_ < IN 94-XX
February XX, 1994 The manuals provided by the manufacturer give the specific maintenance
requirements for a particular piece of equipment. The manufacturer may also
be able to give the licensees new information that has been developed since
the manuals were issued, in order to improve the design and maintenance of the
inverters and reduce the number of maintenance-related failures.
Related Generic Communications
The NRC has issued other generic communications related to this subject.
These generic communications included Information Notice (IN) 91-64, *Site
Area Emergency Resulting From a Loss of Non-Class IE Uninterruptible Power
Supplies,3 October 9, 1991 and Supplement 1 to IN 91-64, October 7, 1992;
IN 88-57, 'Potential Loss of Safe Shutdown Equipment Due to Premature Silicone
Controlled Rectifier Failure," August 8, 1988; and IN 87-24, "Operational
Experience Involving Losses of Electrical Inverters,' June 4, 1987.
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.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contact(s):
Jose Ibarra, AEOD
(301) 492-4441
E. W. Weiss, NRR
(301) 504-3264 Attachment: List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCES
OFFICE
RPB:ADM*
OGCB:NRR
ROAB:AEOD
C/DD:EOD
TechEd
AJKuler
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GLanik
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DATE
01/04/94
01/06/94
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01/11/94 O1/Z't94 OFFICE
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DATE
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02/
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02/
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INVtK I K. IN
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IN 94-XX
February XX, 1994 The manuals provided by the manufacturer give the specific maintenance
requirements for a particular piece of equipment. The manufacturer may also
be able to provide the licensees with new information that has been developed
since the manuals were issued to improve the design and maintenance of the
inverters and reduce the number of maintenance-related failures.
Related Generic Communications
The NRC has previously issued the following generic communications on this
subject:
Information Notice 91-64, Supplement 1, 'Site Area Emergency Resulting From A
Loss of Non-Class IE Uninterruptible Power Supplies," issued October 7, 1992 Information Notice 91-64, "Site Area Emergency Resulting From A Loss Of Non- Class IE Uninterruptible Power Supplies," issued October 9, 1992 Information Notice 88-57, "Potential Loss of Safe Shutdown Equipment Due to
Premature Silicone Controlled Rectifier Failure," issued August 8, 1988 Information Notice 87-24, Operational Experience Involving Losses of
Electrical Inverters," issued June 4, 1987 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.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contact(s):
Jose Ibarra, AEOD
(301) 492-4441
, NRR
(301) 504- Attachment: List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCES
OFFICE
RPB:ADM
OGCB:NRR
ROAB:AEOD
C/ROAB:AEOD
D/DSP:AEOD
NAME
TechEd k
AJKugler
GLanik
JRosenthal
GHolalan
DATE
01/ ff94
01/ /94 O1/ /94
01/ /94
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EELB:NRR
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D/DE:NRR
C/OGCB:NRR
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