View source for Information Notice 2017-05, Potential Binding of Schneider Electric/Square-D Masterpact Nt and Nw 480-VAC Circuit Breaker Anti-Pump Feature

{{Adams
| number = ML17311A081
| issue date = 12/13/2017
| title = Potential Binding of Schneider Electric/Square-D Masterpact Nt and Nw 480-VAC Circuit Breaker Anti-Pump Feature
| author name = Mcginty T, Miller C
| author affiliation = NRC/NRO/DCIP, NRC/NRR/DIRS
| addressee name = 
| addressee affiliation = 
| docket = 
| license number = 
| contact person = Govan T
| document report number = IN-17-005, Rev 1
| document type = NRC Information Notice
| page count = 6
}}
{{#Wiki_filter: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.

ML17311A081

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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