Information Notice 2017-05, Potential Binding of Schneider Electric/Square-D Masterpact Nt and Nw 480-VAC Circuit Breaker Anti-Pump Feature: Difference between revisions

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{{#Wiki_filter:UNITED STATES
{{#Wiki_filter:ML17311A081 UNITED STATES


NUCLEAR REGULATORY COMMISSION
NUCLEAR REGULATORY COMMISSION
Line 20: Line 20:
OFFICE OF NUCLEAR REACTOR REGULATION
OFFICE OF NUCLEAR REACTOR REGULATION


WASHINGTON, DC 20555-0001 December 13, 2017 NRC INFORMATION NOTICE 2017-05, Revision 1: POTENTIAL BINDING OF SCHNEIDER
WASHINGTON, DC 20555-0001  
 
December 13, 2017  
 
NRC INFORMATION NOTICE 2017-05, Revision 1: POTENTIAL BINDING OF SCHNEIDER


ELECTRIC/SQUARE-D MASTERPACT
ELECTRIC/SQUARE-D MASTERPACT
Line 39: Line 43:
design approval, or manufacturing license under 10 CFR Part 52, Licenses, Certifications, and
design approval, or manufacturing license under 10 CFR Part 52, Licenses, Certifications, and


Approvals for Nuclear Power Plants. All applicants for a standard design certification, including
Approvals for Nuclear Power Plants. All applicants for a standard design certification, including


such applicants after initial issuance of a design certification rule.
such applicants after initial issuance of a design certification rule.


==PURPOSE==
==PURPOSE==
The U.S. Nuclear Regulatory Commission (NRC) is issuing this revised information notice (IN)
The U.S. Nuclear Regulatory Commission (NRC) is issuing this revised information notice (IN)  
to inform addressees about recent issues related to the operation of Schneider
to inform addressees about recent issues related to the operation of Schneider


Line 51: Line 55:
The design of the breaker results in a susceptibility to internal binding in certain circumstances
The design of the breaker results in a susceptibility to internal binding in certain circumstances


that can prevent the breaker from closing on demand. The NRC expects that recipients will
that can prevent the breaker from closing on demand. The NRC expects that recipients will


review the information for applicability to their facilities and consider actions, as appropriate, to
review the information for applicability to their facilities and consider actions, as appropriate, to


avoid similar problems. Suggestions contained in this IN are not NRC requirements. Therefore, no specific action or written response is required.
avoid similar problems. Suggestions contained in this IN are not NRC requirements. Therefore, no specific action or written response is required.


This revision supersedes IN 2017-05 in its entirety.
This revision supersedes IN 2017-05 in its entirety.
Line 68: Line 72:
Because of unrelated issues that prevented the other three chillers from starting, this resulted in
Because of unrelated issues that prevented the other three chillers from starting, this resulted in


a loss of control room cooling. Control room ventilation duct air temperatures rose from 18 degrees Celsius (64.5 degrees Fahrenheit) to 23.9 degrees Celsius (75 degrees Fahrenheit)
a loss of control room cooling. Control room ventilation duct air temperatures rose from 18 degrees Celsius (64.5 degrees Fahrenheit) to 23.9 degrees Celsius (75 degrees Fahrenheit)  
before compensatory measures were implemented. The technical specification limit is
before compensatory measures were implemented. The technical specification limit is


104 degrees Fahrenheit. The failure of chiller 1C to restart was the result of mechanical internal
104 degrees Fahrenheit. The failure of chiller 1C to restart was the result of mechanical internal


binding of a 480-volt alternating current (Vac) Masterpact NT circuit breaker. The licensee later
binding of a 480-volt alternating current (Vac) Masterpact NT circuit breaker. The licensee later


determined that this same condition had been responsible for nine breaker failures at the site
determined that this same condition had been responsible for nine breaker failures at the site


from 2007-2015 and may have been a factor in six additional breaker failures.
from 2007-2015 and may have been a factor in six additional breaker failures.
ML17311A081


IN 2017-05, Rev. 1 All of these breakers were installed at River Bend Station with a standing close signal, where
IN 2017-05, Rev. 1 All of these breakers were installed at River Bend Station with a standing close signal, where
Line 85: Line 87:
the closing coil of the breaker remained energized while the breaker was in its normal, closed
the closing coil of the breaker remained energized while the breaker was in its normal, closed


position. This circuit configuration set up a situation where any open signal, if received while
position. This circuit configuration set up a situation where any open signal, if received while


the breaker was also receiving a close signal, would activate the mechanical anti-pump
the breaker was also receiving a close signal, would activate the mechanical anti-pump
Line 91: Line 93:
interlocka feature designed to prevent the circuit breaker from cycling between closing and
interlocka feature designed to prevent the circuit breaker from cycling between closing and


opening. Testing performed by the breaker vendor and dedicating entity, AZZ/Nuclear
opening. Testing performed by the breaker vendor and dedicating entity, AZZ/Nuclear


Logistics, Inc. (AZZ/NLI), found that the anti-pump mechanism was susceptible to mechanical
Logistics, Inc. (AZZ/NLI), found that the anti-pump mechanism was susceptible to mechanical
Line 97: Line 99:
internal binding of the closing coil plunger, which would prevent the breaker from closing until
internal binding of the closing coil plunger, which would prevent the breaker from closing until


manual action was taken to operate the breaker locally. The licensee identified susceptible
manual action was taken to operate the breaker locally. The licensee identified susceptible


breakers and reconfigured the circuitry so the breakers would no longer be subject to a standing
breakers and reconfigured the circuitry so the breakers would no longer be subject to a standing
Line 107: Line 109:
that could lead to activation of the anti-pump interlock and potentially introduce the same failure
that could lead to activation of the anti-pump interlock and potentially introduce the same failure


mechanism. Specifically, AZZ/NLI determined that all Masterpact NT and NW style remote
mechanism. Specifically, AZZ/NLI determined that all Masterpact NT and NW style remote


electrically operated circuit breakers are susceptible to the mechanical internal binding of the
electrically operated circuit breakers are susceptible to the mechanical internal binding of the
Line 115: Line 117:
than 200 milliseconds during the approximately 4 seconds it takes for the spring charging motor
than 200 milliseconds during the approximately 4 seconds it takes for the spring charging motor


to recharge the closing springs. The licensee identified additional impacted breakers in multiple
to recharge the closing springs. The licensee identified additional impacted breakers in multiple


systems that had not been included in the original extent of condition checks because they were
systems that had not been included in the original extent of condition checks because they were


not subject to a standing close signal. They included breakers for the emergency ventilation
not subject to a standing close signal. They included breakers for the emergency ventilation


fans in the Division 1 and 2 emergency diesel generator rooms, and breakers supplying the
fans in the Division 1 and 2 emergency diesel generator rooms, and breakers supplying the
Line 125: Line 127:
Division 1 and 2 containment unit coolers and the Division 1 and 2 auxiliary building general
Division 1 and 2 containment unit coolers and the Division 1 and 2 auxiliary building general


area unit coolers. Subsequent notification from AZZ/NLI alerted the licensee to further potential
area unit coolers. Subsequent notification from AZZ/NLI alerted the licensee to further potential


problems with breakers that had already been modified to address the issue with the standing
problems with breakers that had already been modified to address the issue with the standing


close signal. The affected breakers could be manually operated to start or stop their associated
close signal. The affected breakers could be manually operated to start or stop their associated


equipment, if necessary for operation. The licensee identified compensatory measures for each
equipment, if necessary for operation. The licensee identified compensatory measures for each


impacted breaker to restore system operability until further modifications could be made. This
impacted breaker to restore system operability until further modifications could be made. This


included placing Division 1 systems in continuous run when possible to avoid susceptibility to
included placing Division 1 systems in continuous run when possible to avoid susceptibility to
Line 141: Line 143:
push to open button on the breaker after any remote opening during power operations or
push to open button on the breaker after any remote opening during power operations or


hot-shutdown conditions. This manual action would clear the binding condition if it occurred and
hot-shutdown conditions. This manual action would clear the binding condition if it occurred and


allow the breaker to close if a subsequent close signal was received.
allow the breaker to close if a subsequent close signal was received.
Line 147: Line 149:
The NRC chartered a special inspection to review the events surrounding the loss of control
The NRC chartered a special inspection to review the events surrounding the loss of control


room cooling. The results of the inspection are available in NRC Special Inspection Report
room cooling. The results of the inspection are available in NRC Special Inspection Report


05000458/2015010, dated February 16, 2016 (Agencywide Documents Access and
05000458/2015010, dated February 16, 2016 (Agencywide Documents Access and


Management System (ADAMS) Accession No. ML16047A268). Additional information is
Management System (ADAMS) Accession No. ML16047A268). Additional information is


available from the River Bend Licensee Event Reports 05000458/2016-005, dated
available from the River Bend Licensee Event Reports 05000458/2016-005, dated
Line 174: Line 176:
actuated anti-pump circuitry on the breakers that disabled the affected equipment until the
actuated anti-pump circuitry on the breakers that disabled the affected equipment until the


IN 2017-05, Rev. 1 anti-pump circuit was manually reset. In these historical cases, the design of the breaker
IN 2017-05, Rev. 1 anti-pump circuit was manually reset. In these historical cases, the design of the breaker


circuitry was such that the anti-pump circuit was sealed in under certain circumstances, preventing breakers from closing. The current issue involves a situation where the anti-pump
circuitry was such that the anti-pump circuit was sealed in under certain circumstances, preventing breakers from closing. The current issue involves a situation where the anti-pump


mechanism is not intended to remain sealed in, but becomes mechanically bound, with the
mechanism is not intended to remain sealed in, but becomes mechanically bound, with the
Line 187: Line 189:
Plants, to 10 CFR Part 50, Criterion III, Design Control, requires, in part, to subject design
Plants, to 10 CFR Part 50, Criterion III, Design Control, requires, in part, to subject design


changes to control measures commensurate with those applied to the original design. The
changes to control measures commensurate with those applied to the original design. The


Masterpact breakers used at River Bend Station and at several other sites are a modification
Masterpact breakers used at River Bend Station and at several other sites are a modification


from the original General Electric AKR electrically-operated breakers. The original breakers
from the original General Electric AKR electrically-operated breakers. The original breakers


used an electrical anti-pump interlock feature. The change from the electrical anti-pump
used an electrical anti-pump interlock feature. The change from the electrical anti-pump


interlock to a mechanical anti-pump interlock feature introduces mechanical binding as a
interlock to a mechanical anti-pump interlock feature introduces mechanical binding as a
Line 203: Line 205:
the circuit breaker could be more susceptible to the mechanical binding condition that would
the circuit breaker could be more susceptible to the mechanical binding condition that would


prevent the breaker from being able to reclose on command:
prevent the breaker from being able to reclose on command:  
(1)      The closing circuit is continually energized during charge and/or open operations.


(2)     An anti-pump condition is present.
(1)  
The closing circuit is continually energized during charge and/or open operations.


(3)     The breaker receives a command to open electrically before or at the same time as the
(2)
An anti-pump condition is present.
 
(3)  
The breaker receives a command to open electrically before or at the same time as the


close command is initiated.
close command is initiated.


(4)     The operator initiates a local or remote electrical closing action that may hold the close
(4)  
The operator initiates a local or remote electrical closing action that may hold the close


signal for longer than 200 milliseconds, which would extend into the closing spring
signal for longer than 200 milliseconds, which would extend into the closing spring


charging cycle.1
charging cycle.1  
(5)     The logic scheme has a component controlling the close circuit that would apply the
 
(5)  
The logic scheme has a component controlling the close circuit that would apply the


voltage to the close coil for longer than 200 milliseconds, extending into the closing
voltage to the close coil for longer than 200 milliseconds, extending into the closing


spring charging cycle.1 In Technical Bulletin TB-12-007, Revision 3, which is attached to the referenced 10 CFR Part 21 report (ADAMS Accession No. ML16278A471), AZZ/NLI provided a proposed modification to
spring charging cycle.1  


the breaker and an updated circuit diagram, shown in Figure 1 of this document. This
In Technical Bulletin TB-12-007, Revision 3, which is attached to the referenced 10 CFR Part 21 report (ADAMS Accession No. ML16278A471), AZZ/NLI provided a proposed modification to


modification replaces the normal XF (closing) coil in the breaker with an XFCOM coil. The
the breaker and an updated circuit diagram, shown in Figure 1 of this document.  This
 
modification replaces the normal XF (closing) coil in the breaker with an XFCOM coil. The


XFCOM coil acts as a oneshot and releases the close coil plunger immediately after the close
XFCOM coil acts as a oneshot and releases the close coil plunger immediately after the close
Line 231: Line 242:
signal is applied to the breaker and will not reactivate the close coil plunger unless power is first
signal is applied to the breaker and will not reactivate the close coil plunger unless power is first


removed from the operating order signal of the XFCOM and then re-applied. With the closing
removed from the operating order signal of the XFCOM and then re-applied. With the closing


coil plunger retracted, this modification is designed to eliminate the potential for mechanical
coil plunger retracted, this modification is designed to eliminate the potential for mechanical
Line 237: Line 248:
binding from the anti-pump feature.
binding from the anti-pump feature.


1 The closing springs are electrically recharged automatically each time the breaker closes.
1 The closing springs are electrically recharged automatically each time the breaker closes.


IN 2017-05, Rev. 1 Figure 1: The XF coil in the original logic is replaced by an XFCOM coil, which releases the close coil plunger as soon as the close signal is
IN 2017-05, Rev. 1 Figure 1: The XF coil in the original logic is replaced by an XFCOM coil, which releases the close coil plunger as soon as the close signal is


received, eliminating the potential for binding.
received, eliminating the potential for binding.
Line 247: Line 258:
wired with a standing close signal will receive a close and an open signal in quick enough
wired with a standing close signal will receive a close and an open signal in quick enough


succession to expose the breaker to this vulnerability. However, this situation could occur
succession to expose the breaker to this vulnerability. However, this situation could occur


during a design-basis scenario involving a loss of offsite power concurrent with a loss-of-coolant
during a design-basis scenario involving a loss of offsite power concurrent with a loss-of-coolant


accident. These breakers may be installed for years with no noted issues, but still be vulnerable
accident. These breakers may be installed for years with no noted issues, but still be vulnerable


to a self-revealing failure. Verification that this failure mechanism will not impact the safety
to a self-revealing failure. Verification that this failure mechanism will not impact the safety


function of these breakers can help to ensure that systems are able to respond as intended
function of these breakers can help to ensure that systems are able to respond as intended
Line 262: Line 273:


==CONTACT==
==CONTACT==
This IN requires no specific action or written response. Please direct any questions about this
This IN requires no specific action or written response. Please direct any questions about this


matter to the technical contact(s) listed below or the appropriate Office of Nuclear Reactor
matter to the technical contact(s) listed below or the appropriate Office of Nuclear Reactor
Line 268: Line 279:
Regulation or Office of New Reactors project manager.
Regulation or Office of New Reactors project manager.


/RA/(P. Krohn for)                             /RA/
/RA/(P. Krohn for)  
Timothy J. McGinty, Director                   Christopher G. Miller, Director
 
/RA/  
 
Timothy J. McGinty, Director
 
Christopher G. Miller, Director
 
Division of Construction Inspection


Division of Construction Inspection            Division of Inspector and Regional Support
Division of Inspector and Regional Support


and Operational Programs                     Office of Nuclear Reactor Regulation
and Operational Programs


===Office of New Reactors===
Office of Nuclear Reactor Regulation
Technical Contacts:    Rebecca Sigmon, NRR/DIRS


301-415-0895 E-mail: Rebecca.Sigmon@nrc.gov
Office of New Reactors
 
Technical Contacts: Rebecca Sigmon, NRR/DIRS
 
301-415-0895  
 
E-mail: Rebecca.Sigmon@nrc.gov


Samuel Graves, RIV/DRS
Samuel Graves, RIV/DRS


817-200-1102 E-mail: Samuel.Graves @nrc.gov
817-200-1102  
 
E-mail: Samuel.Graves @nrc.gov
 
Note:  NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Library.
 
ML17311A081
*concurred via e-mail
 
TAC No. MF9367 OFFICE
 
NRR/DPR/PGCB/LA* Tech Editor*
NRR/DIRS/IOEB*
RIV/DRS/EB2*
NRR/DE/EEEB/BC*
NAME
 
ELee
 
JDougherty
 
RSigmon
 
SGraves
 
JQuichocho
 
DATE
 
04/17/17
04/24/17
11/2/17
11/6/17
11/6/17 OFFICE
 
NRO/DCIP/QVIBI/BC* NRR/DIRS/IRGB/LA
 
NRR/DIRS/IRGB/PM
 
NRR/DIRS/IRGB/BC
 
NRO/DCIP/D
 
NAME
 
TJackson
 
ELee
 
TGovan
 
HChernoff
 
TMcGinty (PKrohn)
DATE
 
11/2/17
11/08/17
11/08/17
11/28/17
11/30/17 OFFICE


Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Library.
NRR/DIRS/D*


ML17311A081          *concurred via e-mail                TAC No. MF9367 OFFICE NRR/DPR/PGCB/LA* Tech Editor*        NRR/DIRS/IOEB*      RIV/DRS/EB2*      NRR/DE/EEEB/BC*
NAME
NAME   ELee              JDougherty        RSigmon              SGraves            JQuichocho


DATE  04/17/17          04/24/17          11/2/17              11/6/17            11/6/17 OFFICE NRO/DCIP/QVIBI/BC* NRR/DIRS/IRGB/LA NRR/DIRS/IRGB/PM      NRR/DIRS/IRGB/BC NRO/DCIP/D
CMiller


NAME  TJackson          ELee              TGovan              HChernoff          TMcGinty (PKrohn)
OFFICE
DATE  11/2/17            11/08/17          11/08/17            11/28/17          11/30/17 OFFICE NRR/DIRS/D*


===NAME  CMiller===
12/13/17}}
OFFICE 12/13/17}}


{{Information notice-Nav}}
{{Information notice-Nav}}

Revision as of 00:29, 8 January 2025

Potential Binding of Schneider Electric/Square-D Masterpact Nt and Nw 480-VAC Circuit Breaker Anti-Pump Feature
ML17311A081
Person / Time
Issue date: 12/13/2017
From: Mcginty T, Chris Miller
Division of Construction Inspection and Operational Programs, Division of Inspection and Regional Support
To:
Govan T
References
IN-17-005, Rev 1
Download: ML17311A081 (6)
v • d • e


ML17311A081 UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, DC 20555-0001

December 13, 2017

NRC INFORMATION NOTICE 2017-05, Revision 1: POTENTIAL BINDING OF SCHNEIDER

ELECTRIC/SQUARE-D MASTERPACT

NT AND NW 480-VAC CIRCUIT

BREAKER ANTI-PUMP FEATURE

ADDRESSEES

All holders of an operating license or construction permit for a nuclear power reactor under

Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Domestic Licensing of

Production and Utilization Facilities.

All holders of and applicants for a power reactor early site permit, combined license, standard

design approval, or manufacturing license under 10 CFR Part 52, Licenses, Certifications, and

Approvals for Nuclear Power Plants. All applicants for a standard design certification, including

such applicants after initial issuance of a design certification rule.

PURPOSE

The U.S. Nuclear Regulatory Commission (NRC) is issuing this revised information notice (IN)

to inform addressees about recent issues related to the operation of Schneider

Electric/Square-D Masterpact 480-volt alternating current (VAC) NT and NW circuit breakers.

The design of the breaker results in a susceptibility to internal binding in certain circumstances

that can prevent the breaker from closing on demand. The NRC expects that recipients will

review the information for applicability to their facilities and consider actions, as appropriate, to

avoid similar problems. Suggestions contained in this IN are not NRC requirements. Therefore, no specific action or written response is required.

This revision supersedes IN 2017-05 in its entirety.

DESCRIPTION OF CIRCUMSTANCES

On March 9, 2015, during Division I emergency core cooling system and loss-of-coolant

accident testing at River Bend Station, control building chiller 1C shed from the electrical bus as

expected, but then failed to restart and sequence onto the emergency diesel generator.

Because of unrelated issues that prevented the other three chillers from starting, this resulted in

a loss of control room cooling. Control room ventilation duct air temperatures rose from 18 degrees Celsius (64.5 degrees Fahrenheit) to 23.9 degrees Celsius (75 degrees Fahrenheit)

before compensatory measures were implemented. The technical specification limit is

104 degrees Fahrenheit. The failure of chiller 1C to restart was the result of mechanical internal

binding of a 480-volt alternating current (Vac) Masterpact NT circuit breaker. The licensee later

determined that this same condition had been responsible for nine breaker failures at the site

from 2007-2015 and may have been a factor in six additional breaker failures.

IN 2017-05, Rev. 1 All of these breakers were installed at River Bend Station with a standing close signal, where

the closing coil of the breaker remained energized while the breaker was in its normal, closed

position. This circuit configuration set up a situation where any open signal, if received while

the breaker was also receiving a close signal, would activate the mechanical anti-pump

interlocka feature designed to prevent the circuit breaker from cycling between closing and

opening. Testing performed by the breaker vendor and dedicating entity, AZZ/Nuclear

Logistics, Inc. (AZZ/NLI), found that the anti-pump mechanism was susceptible to mechanical

internal binding of the closing coil plunger, which would prevent the breaker from closing until

manual action was taken to operate the breaker locally. The licensee identified susceptible

breakers and reconfigured the circuitry so the breakers would no longer be subject to a standing

close signal.

Subsequently, the licensee reviewed notifications from AZZ/NLI of additional circuit alignments

that could lead to activation of the anti-pump interlock and potentially introduce the same failure

mechanism. Specifically, AZZ/NLI determined that all Masterpact NT and NW style remote

electrically operated circuit breakers are susceptible to the mechanical internal binding of the

anti-pump mechanism and the closing coil plunger if the breaker receives a start signal longer

than 200 milliseconds during the approximately 4 seconds it takes for the spring charging motor

to recharge the closing springs. The licensee identified additional impacted breakers in multiple

systems that had not been included in the original extent of condition checks because they were

not subject to a standing close signal. They included breakers for the emergency ventilation

fans in the Division 1 and 2 emergency diesel generator rooms, and breakers supplying the

Division 1 and 2 containment unit coolers and the Division 1 and 2 auxiliary building general

area unit coolers. Subsequent notification from AZZ/NLI alerted the licensee to further potential

problems with breakers that had already been modified to address the issue with the standing

close signal. The affected breakers could be manually operated to start or stop their associated

equipment, if necessary for operation. The licensee identified compensatory measures for each

impacted breaker to restore system operability until further modifications could be made. This

included placing Division 1 systems in continuous run when possible to avoid susceptibility to

the failure mechanism and implementing a standing order with dedicated operators to press the

push to open button on the breaker after any remote opening during power operations or

hot-shutdown conditions. This manual action would clear the binding condition if it occurred and

allow the breaker to close if a subsequent close signal was received.

The NRC chartered a special inspection to review the events surrounding the loss of control

room cooling. The results of the inspection are available in NRC Special Inspection Report 05000458/2015010, dated February 16, 2016 (Agencywide Documents Access and

Management System (ADAMS) Accession No. ML16047A268). Additional information is

available from the River Bend Licensee Event Reports 05000458/2016-005, dated

April 25, 2016 (ADAMS Accession No. ML16126A229), and 05000458/2016-006, dated

July 12, 2016 (ADAMS Accession No. ML16208A056), and from the 10 CFR Part 21, Reporting

of Defects and Noncompliance, report 2016-20-03 submitted by AZZ/NLI on

September 22, 2016 (ADAMS Accession No. ML16278A471).

BACKGROUND

The NRC IN 1988-75, Disabling of Diesel Generator Output Circuit Breakers by Anti-Pump

Circuitry, dated September 16, 1988 (ADAMS Accession No. ML031150110), and its

Supplement 1, dated April 17, 1989 (ADAMS Accession No. ML082970437), discuss the

circumstances in which simultaneous open and close signals for safety-related equipment

actuated anti-pump circuitry on the breakers that disabled the affected equipment until the

IN 2017-05, Rev. 1 anti-pump circuit was manually reset. In these historical cases, the design of the breaker

circuitry was such that the anti-pump circuit was sealed in under certain circumstances, preventing breakers from closing. The current issue involves a situation where the anti-pump

mechanism is not intended to remain sealed in, but becomes mechanically bound, with the

same end result.

DISCUSSION

Appendix B, Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing

Plants, to 10 CFR Part 50, Criterion III, Design Control, requires, in part, to subject design

changes to control measures commensurate with those applied to the original design. The

Masterpact breakers used at River Bend Station and at several other sites are a modification

from the original General Electric AKR electrically-operated breakers. The original breakers

used an electrical anti-pump interlock feature. The change from the electrical anti-pump

interlock to a mechanical anti-pump interlock feature introduces mechanical binding as a

potential failure mode.

Additional breaker testing by Schneider Electric identified the following five scenarios in which

the circuit breaker could be more susceptible to the mechanical binding condition that would

prevent the breaker from being able to reclose on command:

(1)

The closing circuit is continually energized during charge and/or open operations.

(2)

An anti-pump condition is present.

(3)

The breaker receives a command to open electrically before or at the same time as the

close command is initiated.

(4)

The operator initiates a local or remote electrical closing action that may hold the close

signal for longer than 200 milliseconds, which would extend into the closing spring

charging cycle.1

(5)

The logic scheme has a component controlling the close circuit that would apply the

voltage to the close coil for longer than 200 milliseconds, extending into the closing

spring charging cycle.1

In Technical Bulletin TB-12-007, Revision 3, which is attached to the referenced 10 CFR Part 21 report (ADAMS Accession No. ML16278A471), AZZ/NLI provided a proposed modification to

the breaker and an updated circuit diagram, shown in Figure 1 of this document. This

modification replaces the normal XF (closing) coil in the breaker with an XFCOM coil. The

XFCOM coil acts as a oneshot and releases the close coil plunger immediately after the close

signal is applied to the breaker and will not reactivate the close coil plunger unless power is first

removed from the operating order signal of the XFCOM and then re-applied. With the closing

coil plunger retracted, this modification is designed to eliminate the potential for mechanical

binding from the anti-pump feature.

1 The closing springs are electrically recharged automatically each time the breaker closes.

IN 2017-05, Rev. 1 Figure 1: The XF coil in the original logic is replaced by an XFCOM coil, which releases the close coil plunger as soon as the close signal is

received, eliminating the potential for binding.

The time periods involved, on the order of a few seconds, make it unlikely that a breaker not

wired with a standing close signal will receive a close and an open signal in quick enough

succession to expose the breaker to this vulnerability. However, this situation could occur

during a design-basis scenario involving a loss of offsite power concurrent with a loss-of-coolant

accident. These breakers may be installed for years with no noted issues, but still be vulnerable

to a self-revealing failure. Verification that this failure mechanism will not impact the safety

function of these breakers can help to ensure that systems are able to respond as intended

during a design basis event.

IN 2017-05, Rev. 1

CONTACT

This IN requires no specific action or written response. Please direct any questions about this

matter to the technical contact(s) listed below or the appropriate Office of Nuclear Reactor

Regulation or Office of New Reactors project manager.

/RA/(P. Krohn for)

/RA/

Timothy J. McGinty, Director

Christopher G. Miller, Director

Division of Construction Inspection

Division of Inspector and Regional Support

and Operational Programs

Office of Nuclear Reactor Regulation

Office of New Reactors

Technical Contacts: Rebecca Sigmon, NRR/DIRS

301-415-0895

E-mail: Rebecca.Sigmon@nrc.gov

Samuel Graves, RIV/DRS

817-200-1102

E-mail: Samuel.Graves @nrc.gov

Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Library.

ML17311A081

  • concurred via e-mail

TAC No. MF9367 OFFICE

NRR/DPR/PGCB/LA* Tech Editor*

NRR/DIRS/IOEB*

RIV/DRS/EB2*

NRR/DE/EEEB/BC*

NAME

ELee

JDougherty

RSigmon

SGraves

JQuichocho

DATE

04/17/17

04/24/17

11/2/17

11/6/17

11/6/17 OFFICE

NRO/DCIP/QVIBI/BC* NRR/DIRS/IRGB/LA

NRR/DIRS/IRGB/PM

NRR/DIRS/IRGB/BC

NRO/DCIP/D

NAME

TJackson

ELee

TGovan

HChernoff

TMcGinty (PKrohn)

DATE

11/2/17

11/08/17

11/08/17

11/28/17

11/30/17 OFFICE

NRR/DIRS/D*

NAME

CMiller

OFFICE

12/13/17


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