Information Notice 1987-24, Operational Experience Involving Losses of Electrical Inverters
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SSINS No.: 6835 ItN 87-24
UIN ITED STATES
FUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
VASHINGTON,
D.C.
20555
June A, l9R7
NRC INFORMATION NOTICE NO. 87-24: OPERATIONAL EXPERIENCE INVOLVING LOSSES
OF ELECTRICAL INVERTERS
Addressees
j
All nuclear power reactor facilities holding an operating license or a con- struction permit.
Purpose
This notice is provided to alert recipients of potential problems involving
electrical inverter losses that have led to unplanned plant transients and/or
inoperability or improper functioning of safety-related and other important
plant equipment. It is expected that recipients will review this information
for applicability to their facilities and consider actions, as appropriate, to
preclude similar problems from occurring at their facilities. However, sugges- tions contained in this notice do not constitute NRC requirements; therefore, no specific action or written response is required.
Past Related Correspondence:
IE Information Notice 84-80, "Plant Transients Induced By Failure of
Non-Nuclear Instrumentation Power," November 8, 1984 IE Bulletin 79-27, 'Loss of Non-Class lE Instrumentation and Control Power
System BUS During Operation,' November 30, 1979 IE Information Notice 79-29, "Loss of Nonsafety-Related Reactor Coolant
System !nstrumentation During Operation," November 16, 1979 IE Circular 79-02, "Failure of 120 Volt Vital AC Power Supplies,"
January 11, 1979
Background
Inverters in nuclear power plants provide "uninterruptible" vital ac electrical
power to safety- and non-safety-related instrumentation and control systems.
Generally, loss of this function results in some type of undesirable system
condition and/or plant transient, including unnecessary actuation of safety
systems such as reactor protection and engineered safeguards systems; loss of
indicators that provide plant status information; system disturbances,
87052
IN 87-2A
June 4, 1987 including reactor coolant system transients; improper response of the feedwater
and steam generator water level control systems; loss of safety-related elec- trical equipment functions; damage to mechanical equipment; and challenges to
operators and the remaining functional equipment. Such conditions and/or
transients clearly have significant safety implications since they result 4n
challenges to safety equipment and plant operations and/or a degradation of
plant equipment.
The NRC case study report, AEOD/C605 dated December 1986, "Operational Experi- ence Involving Losses of Electrical Inverters," includes the review of 94 licensee event reports (LERs), totaling 107 events %nvolving inverter losses
that occurred during 1982 through 1984. The study includes 35 additional
events from the Nuclear Plant Reliability Data System (NPRDS) that occurred in
the same timeframe. These 142 events occurred at 51 distinct plants: 26 designed by Westinghouse, 11 by General Electric, 9 by Combustion Engineering,
4 by Babcock & Wilcox, and 1 by General Atomic. The total number of events
included in the study for each of the 3 years along with the number of reactor
units which were operating during each of those years is summarized below.
Parameter
1982
1983
1984 Operating Reactor Units
72
74
82 Inverter Loss Events
34
51
57 Losses/Operating Reactor
.47
.69
.70
As indicated above, the NRC has issued information on inverter losses since
1979; and industry groups have issued approximately 14 reports related to this
issue.
Description of Circumstances
The NRC case study report identified three potential failure mechanisms for
inverters. One of these involves relatively high ambient temperature and/or
humidity within inverter enclosures. This condition appears to result in
accelerated aging of components that form a part of the inverter circuitry
causing a significant reduction in component life expectancy and inverter loss.
Another mechanism for inverter failure involves the electrical interconnecting
and physical arrangements for the inverter circuitry components. In some
installations, these arrangements are such that when certain components fail, other components also may fail or degrade.
The third failure mechanism involves voltage spikes and perturbations. Many of
the electrical loads in a plant have inductive characteristics. During plant
operations that involve energizing and deenergizing these loads, voltage spikes
and perturbations are generated. The solid-state devices in the inverter cir- cuitry are sensitive to these voltage spikes, and this has resulted in component
failure, blown fuses, and inverter losses. Additionally, secondary voltage per- turbations caused by lightning strikes or switching surges can have an adverse
effect on inverter operation.
IN 87-24 June 4, 1987 Discussion:
The NRC case study report indicates that the failure mechanisms involving
service condition parameters (e.g., ambient temperature and/or humidity and
voltage spikes and perturbations) have common-cause implications. However, none of the events reviewed and evaluated in the report involved the simulta- neous loss of redundant inverter-powered buses.
The dominant cause of inverter losses was attributed to component failures.
Such components include diodes, fuses, silicon controlled rectifiers, capacitors, transistors, resistors, printed circuit boards, transformers and inductors. It
also appears that major contributing factors for the occurrence of component
failure events are high ambient temperature and/or humidity within inverter
enclosures and electrical disturbances at the Inverter input/output terminals.
In addition, incorrectly operating circuit breakers, improperly setting up test
equipment, removing the wrong inverter unit from service, and improperly
transferring power sources for a bus are some personnel actions that make them
the second largest contributor to inverter losses.
It is suggested that licensees consider monitoring of temperature and/or humidity
internal to inverter enclosures and evaluating input and output voltages of the
inverter unit during steady-state and transient conditions to assure that manu- facturer's recommendations are being considered. Additionally, to minimize the
number of inverter loss events resulting from personnel actions, licensees might
consider reviewing related maintenance and testing procedures and practices for
inverters. Further, specialized training and practice sessions with involved
plant personnel and verification of appropriate sequence of'steps to achieve
desired related maintenance and testing activities also may be considered.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the Regional
Administrator of the appropriate regional office or this office.
Rhar
es .ossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
Vincent D. Thomas, NRR
(301)492-4414 Attachment:
List of Recently Issued NRC Information Notices
IN 87-24 June 4, 1987 Discussion:
The NRC case study report indicates that the failure mechanisms involving
service condition parameters (e.g., ambient temperature and/or humidity and
voltage spikes and perturbations) have common-cause implications. However, none of the events reviewed and evaluated in the report involved the simulta- neous loss of redundant inverter-powered buses.
The dominant cause of inverter losses was attributed to component failures.
Such components include diodes, fuses, silicon controlled rectifiers, capacitors, transistors, resistors, printed circuit boards, transformers and inductors. It
also appears that major contributing factors for the occurrence of component
failure events are high ambient temperature and/or humidity within inverter
enclosures and electrical disturbances at the inverter input/output terminals.
In addition, incorrectly operating circuit breakers, improperly setting up test
equipment, removing the wrong inverter unit from service, and improperly
transferring power sources for a bus are some personnel actions that make them
the second largest contributor to inverter losses.
It is suggested that licensees consider monitoring of temperature and/or humidity
internal to inverter enclosures and evaluating input and output voltages of the
inverter unit during steady-state and transient conditions to assure that manu- facturer's recommendations are being considered. Additionally, to minimize the
number of inverter loss events resulting from personnel actions, licensees might
consider reviewing related maintenance and testing procedures and practices for
inverters. Further, specialized training and practice sessions with involved
plant personnel and verification of appropriate sequence of steps to achieve
desired related maintenance and testing activities also may be considered.
No specific action or written response Is required by this information notice.
If you have any questions about this matter, please contact the Regional
Administrator of the appropriate regional office or this office.
Original Signed by
Charles E Ross
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
Vincent D. Thomas, NRR
(301)492-4414 Attachment: List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCES
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- C/OGCB:DOEA:NRR
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CHBerlinger
05
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05/27/87
- DEPER:IE
- ROAB:AEOD
- DEPER:IE
WMARM
- DEPER:IE
VDThomas
AWDromerick
Tech Ed
RLBaer
2/13/87
2/13/87
2/13/87
05/24/87
2/25/87
IN 87-XX
May xx, 1987 No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the Regional
Administrator of the appropriate regional office or this office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
Vincent D. Thomas, NRR
(301)492-4414 Attachment:
List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCES
D/DOEA:NRR
CERossi
05/ /87 APPMB:ARM
Tech Ed
05/24/87 C/OGCB:DOEA:NRR
CHBerlinger
05/97/87
- DEPER:IE
RLBaer
2/25/87
- DEPER:IE
VDThomas
2/13/87
- ROAB:AEOD
2/13/87
- DEPER: IE
AWDromerick
2/13/87
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IN 87-XX
February , 1987 No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the Regional
Administrator of the appropriate regional office or this office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contacts:
Vincent D. Thomas, IE
(301)492-4755
Frank Ashe, AEOD
(301)492-4442
List of Recently Issued IE Information Notices
Attachment:
- SEE PREVIOUS CONCURRENCES
- DEPER: IE
VDThomas
2/13/87
- ROAB:AEOD
2/13/87
- DEPER:IE
AWDromerick
2/13/87 P B
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2/2h/87
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IN 87-XX
February , 1987 No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the Regional
Administrator of the appropriate regional office or this office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contacts:
Vincent D. Thomas, IE
(301)492-4755
Frank Ashe, AEOD
(301)492-4442 Attachment:
List of Recently Issued IE Information Notices
- SEE PREVIOUS CONCURRENCES
- DEPER:IE
VDThomas
2/13/87
- ROAB:AEOD
2/13/87
- DEPEF)IE
e4 rick
' 0i3 8 PSB:I E
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2/ /87 D:DEPER: IE
ELJordan
2/ /87 DEPER:IE
RLBaer
2/ /87 DD:DEPER:IE
SASchwartz
2/ /87 DEPER:IE
JERosent~hal
2/ /87"
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IN 87-XX
February , 1987 No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the Regional
Administrator of the appropriate regional office or this office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contacts:
Vincent D. Thomas, IE
(301)492-4755
Frank Ashe, AEOD
(301)492-4442 Attachment:
List of Recently Issued IE Information Notices
DEPER:IE
VDThomas Kf
2//1/87 ROAB:AEOD
FAshe roer
2/13/87 h9a
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2$ /87 D:DEPER:IE
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2/ /87 DEPER:IE
RLBaer
2/ /87 DD:DEPER:IE
SASchwartz
2/ /87- DEPER:IE
JERosenthal
2/ /87 PSB:IE
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2/ /87
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Document Name: i-'
INFO NOTICE - V THOMAS
Requestor's ID:
WERTMAN
Author's Name:
Vince Thomas
Document Comments:
FIO Operational Experience Involving Losses of Inverters