05000245/LER-1997-027-01, :on 970423,inadequate Current Interrupt Capability of Molded Case Circuit Breakers in Safety Related MCC Compartments Was Found.Caused by Inadequate Work & Design Control Practices.Revised Design Change Manual

:on 970423,inadequate Current Interrupt Capability of Molded Case Circuit Breakers in Safety Related MCC Compartments Was Found.Caused by Inadequate Work & Design Control Practices.Revised Design Change Manual

ML20141J910
Person / Time
Site:	Millstone
Issue date:	05/23/1997
From:	Robert Walpole NORTHEAST NUCLEAR ENERGY CO.
To:
Shared Package
ML20141J875	List: 05000245/LER-1997-027, Forwards LER 97-027-00 Per 10CFR50.73(a)(2)(ii).Commitments Made within Ltr 05000245/LER-1997-027-01, :on 970423,inadequate Current Interrupt Capability of Molded Case Circuit Breakers in Safety Related MCC Compartments Was Found.Caused by Inadequate Work & Design Control Practices.Revised Design Change Manual
References
LER-97-027-01, LER-97-27-1, NUDOCS 9705280258
Download: ML20141J910 (3)

LER-1997-027, on 970423,inadequate Current Interrupt Capability of Molded Case Circuit Breakers in Safety Related MCC Compartments Was Found.Caused by Inadequate Work & Design Control Practices.Revised Design Change Manual

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)
2451997027R01 - NRC Website

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NRf FORM 360 U.S. NUCLEAR REGULATORY CO4 AISSION APPROVED BY OM8 NO. 31bo-0104 EXP1REs 04/30/98 (4-95)

'J,'ot"r#"R"/c'1"J51.TS'sl A "%is* Ten"o^"iM80 L'M"%^%2?ti "'" anal'os! s" i"?s'a ^%MR LICENSEE EVENT REPORT (LER)

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FCCiUTY NAME nl DOCKfT NUMSER (2)

PAGE (3)

Millstone Nuclear Power Station Unit 1 05000245 1 of 3 TITLE 14)

Inadequate Current Interrupt Capability of Molded Case Circuit Breakers in Safety Related MCC Compartments EVENT DATE (5)

LER NUMBER (6)

REPORT DATE (7)

OTHER FACIL(TIES INVOLVED (8)

MONTH DAY YEAR YEAR SEQUENTIAL REVISION MONTH DAY YEAR FACluTY NAME DOCKET NUMBER NUMBER 04 23 97 97 027 00 05 23 97 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR i: (Check one or more) (11)

MODE (9)

N 20.2201(b) 20.2203(a)(2)(v) 50.73(an2)(i) 50.73(a)(2)(viii)

POWER 20.2203(a)(1) 20.2203(a)(3)(i)

X 50.73(a)(2)(ii) 50.73(a)(2)(x)

LEVEL (10) 000 20.2203(a)(2Hi) 20.2203(aH3Hii) 50.73(a)(2)(iii) 73.71 20.2203(a)(2Hii) 20.2203(aH4) 50.73(a)(2)(iv)

OTHER 20.2203(aH2)(iii) 50.36(c)(1) 50.73(a)(2)(V)

Specify in Abstract below x

or en NRC Form 366A

~

20.2203(a)(2Hiv) 50.36(cH2) 50.73(aH2)(vii)

LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER Unclude Area Codel j

Robert W. Walpole, MP1 Nuclear Licensing Manager (860)440-2191 j

COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE

SYST EM COMPONENT MANUF ACTURER REPORTABLE

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE TO NPRDS To NPRDs SUPPLEMENTAL REPORT EXPECTED (14)

EXPECTED Mowm DAY YEAR SUBMISSION f

YES NO

~~

(if yes, complete EXPECTED SUBMISSION DATE).

ABSTRACT (Lemit to 1400 spaces, Le., approximately 15 single-spaced typewritten lines) (16)

On April 23,1997, with the plant shutdown, the reactor in the COLD SHUTDOWN, and the fuel off-loaded, it was found that some molded case circuit breakers in safety related Motor Control Center (MCC) compartments do not have adequate current interruption capability. The breakers in the MCC compartments are sized to protect the cable downstream of the MCC by being able to interrupt the currents from short circuits occurring within or downstream of the motor control center. This event was prompt reported on April 23, 1997, pursuant to 10CFR50.72(b)(1)(ii)(B) as a condition that is outside the design basis of the plant.

l No safety consequences have resulted from this event. A review has been completed to identify all circuit breakers requiring a design review. A design review will document the current interrupting capability of the enisting safety related MCC breakers, compare the interrupting current with the calculated short circuit current of the MCC for each breaker, and identify those breakers that are not correctly sized. The non-conforming breakers identified in the design review will be replaced.

i 9705280258 970523 PDR ADOCK 05000245 S

PDR WRC FORM 366 (4 95)

NRC FOR'M 3:6A U.S. NUCLEAR REGULAloRY CoMMisSloN wh UCENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3)

YEAR SEOuENTIAL REVISION Millstone Nuclear Power Station Unit 1 05000245 NUMBER NUMBER.

2 of 3 97 027 00 TEXT fit more space is required, use additional copies of NRC Form 366A) (17) 1.

Descriotion of Event On April 23,1997, with the plant in cold shutdown and fuel off-loaded, a walkdown of the molded case circuit breakers in the MCC's showed that some safety related MCC compartments in E2, ES E6A, F1, F2, F3, F4, F5, end FE3 have breakers with lower current interrupting capacity than the short circuit current calculated for that MCC. A short circuit carrying currents close to the calculated maximum short circuit current may not be interrupted by the breaker, resulting in over-tripping of the upstream MCC feeder breaker, or other breakers in the MCC, and causing electrical damage or a loss of power.

There were no automatic or manually initiated safety system responses as a result of this event. This event was reported, pursuant to 10CFR 50.72(b)(1)(ii)(B) as a condition that n; outside the design basis of the plant.

II.

Cause of Even.1 The cause of this event was determined to be inadequate work control and design control practices. Historically, breakers have been changed without close attention to the MCC's short circuit currents during the design change process.

111. Analysis of Event The molded case circuit breakers in the MCC's are designed to protect the cable and downstream equipment in the circuit from the excessive currents that may be generated due to short circuits or abnormal behaviors of the motor. The calculation of the short circuit currents is based on the impedance's between the source of current and a bolted 3 phase f ault at the MCC location. Each machine in the circuit could contribute to the short circuit current and the machine, device, or line impedances are the short circuit current limiting factors. In a conservative short circuit calculation, the location of the short is selected to be close to the current source and no contact resistance (circuit breaker contact, relay contact, or heater resistance in thermal overload relays, etc.) is considered. The breaker current interruption capability determines the limit of the current that the breaker can safely interrupt without damaging itself, in a worst case short circuit on the MCC cable immediately downstream of the breaker, the breaker may not be able to clear the fault immediately, resulting in a trip of the upstream breaker which may take the whole MCC out of service. No immediate safety concern resulted from this event.

The fault currents at the MCC level are calculated in a conservative fashion, meaning that no contact resistance on the breaker or the motor starter is taken into consideration, if quantified, the inclusion of the contact resistance may reduce the short circuit currents to levels below the circuit breaker capabilities.

IV. Corrective Action

The design change manual and the work control process procedures have been revised to properly control changes to the facility. A review has been completed to identify all circuit breakers requiring a design review. As a result of this event and the subsequent investigation, the following corrective actions will be taken.

1.

A design review will document the mis-coordination of the existing safety related MCC breakers. The review will compare the interrupting current with the calculated short circuit current of the MCC for each breaker, and identify those safety related breakers that are not correctly sized prior to fuel load for operating cycle 16.

- _,. = _.

.. _ _ _.., _ _ _ -. _ _. _.. _. _.. _.. - -. _ _ - ~ _ _. _ _. _. -.. -. _ _ _ _.. _ _.. -

NRC IOR'M 361A U.S. NUCLEAR REGULATORY COMMISSION 14fM l

LICENSEE EVENT REPORT (LER) l TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3) l YEAR SEQUENTIAL REVISION i

Millstone Nuclear Power Station Unit 1 05000245 NUMBER NUMBER 3 of 3 97 027 00 l

t TEXT (11 more space is required, use additiorral copies of NRC form 366A) (17) l

' 2.

The non-conforming breakers identified in the design review will be replaced prior to fuel load for operating l

cycle 16.

l f

V.

Additional information

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None.

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Similar Events

i LER 94-029 00, "MCC Circuit Breaker Not properly Coordinated" Manufacturer Data None.

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f4RC FORM 366A (4 95)