Information Notice 1987-24, Operational Experience Involving Losses of Electrical Inverters

Operational Experience Involving Losses of Electrical Inverters

ML031150304
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Skagit, Marble Hill
Issue date:	06/04/1987
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-87-024, NUDOCS 8705290040
Download: ML031150304 (9)

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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 4 transients clearly have significant safety implications since they result n

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.

.ossi, Director

es Rhar

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

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

Vincent D. Thomas, NRR

(301)492-4414 Attachment: List of Recently Issued NRC Information Notices

• SEE PREVIOUS CONCURRENCES

Dlj' K *C/OGCB:DOEA:NRR

CEos'l 'V CHBerlinger

05 7 05/27/87

• DEPER:IE *ROAB:AEOD *DEPER:IE WMARM *DEPER:IE

VDThomas FAshe 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

Vincent D. Thomas, NRR

(301)492-4414 Attachment: List of Recently Issued NRC Information Notices

• SEE PREVIOUS CONCURRENCES

D/DOEA:NRR C/OGCB:DOEA:NRR

CERossi CHBerlinger

05/ /87 05/97/87

• DEPER:IE *ROAB:AEOD *DEPER: IE APPMB:ARM *DEPER:IE

VDThomas FAshe AWDromerick Tech Ed RLBaer

2/13/87 2/13/87 2/13/87 05/24/87 2/25/87

K) KJ 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

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2/13/87 2/13/87 2/13/87 2/2h/87 2>/--87

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

D:DEPER: IE DD:DEPER:IE

ELJordan SASchwartz

2/ /87 2/ /87

• DEPER:IE *ROAB:AEOD *DEPEF)IE PSB:I E DEPER:IE DEPER:IE

VDThomas FAshe e4 rick DGable RLBaer JERosent~hal

2/13/87 2/13/87 ' 0i3 8 2/ /87 2/ /87 2/ /87"

-IuiV 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

D:DEPER:IE DD:DEPER:IE

ELJordan SASchwartz

2/ /87 2/ /87- DEPER:IE ROAB:AEOD D IE PSB:IE DEPER:IE DEPER:IE

VDThomas Kf FAshe roer eri/ck DGable RLBaer JERosenthal

2//1/87 2/13/87 h9a 2$ /87 2/ /87 2/ /87 2/ /87

S . I 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