Information Notice 2017-05, : 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 |
| Revision: | 0 |
| From: | McGinty T J, Christopher 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) | |
ML17311A081 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 rul
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 breaker The design of the breaker results in a susceptibility to internal binding in certain circumstances that can prevent the breaker from closing on deman The NRC expects that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problem Suggestions contained in this IN are not NRC requirement Therefore, no specific action or written response is require This revision supersedes IN 2017-05 in its entiret 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 generato Because of unrelated issues that prevented the other three chillers from starting, this resulted in a loss of control room coolin 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 implemente The technical specification limit is 104 degrees Fahrenhei The failure of chiller 1C to restart was the result of mechanical internal binding of a 480-volt alternating current (Vac) Masterpact NT circuit breake 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 failure 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 positio 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 interlock-a feature designed to prevent the circuit breaker from cycling between closing and openin 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 locall The licensee identified susceptible breakers and reconfigured the circuitry so the breakers would no longer be subject to a standing close signa 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 mechanis 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 spring 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 signa 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 cooler 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 signa The affected breakers could be manually operated to start or stop their associated equipment, if necessary for operatio The licensee identified compensatory measures for each impacted breaker to restore system operability until further modifications could be mad 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 condition This manual action would clear the binding condition if it occurred and allow the breaker to close if a subsequent close signal was receive The NRC chartered a special inspection to review the events surrounding the loss of control room coolin 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 rese 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 closin 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 resul 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 desig The Masterpact breakers used at River Bend Station and at several other sites are a modification from the original General Electric AKR electrically-operated breaker The original breakers used an electrical anti-pump interlock featur The change from the electrical anti-pump interlock to a mechanical anti-pump interlock feature introduces mechanical binding as a potential failure mod 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 operation (2) An anti-pump condition is presen (3) The breaker receives a command to open electrically before or at the same time as the close command is initiate (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 cycl (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 cycl 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 documen This modification replaces the normal XF (closing) coil in the breaker with an XFCOM coi 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-applie With the closing coil plunger retracted, this modification is designed to eliminate the potential for mechanical binding from the anti-pump featur The closing springs are electrically recharged automatically each time the breaker close 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 bindin 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 vulnerabilit However, this situation could occur during a design-basis scenario involving a loss of offsite power concurrent with a loss-of-coolant acciden These breakers may be installed for years with no noted issues, but still be vulnerable to a self-revealing failur 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 even IN 2017-05, Rev. 1
CONTACT
This IN requires no specific action or written respons 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 manage /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 Librar IN 2017-05, Rev. 1 NRC INFORMATION NOTICE 2017-05, "POTENTIAL BINDING OF SCHNEIDER ELECTRIC/SQUARE-D MASTERPACT NT AND NW 480VAC CIRCUIT BREAKER ANTI-PUMP FEATURE," DATE: December 13, 2017
ADAMS Accession No.: 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 OFFICIAL RECORD COPY