05000336/LER-2013-003, Regarding Postulated DC Ammeter Circuit Hot Shorts

Regarding Postulated DC Ammeter Circuit Hot Shorts

ML14023A595
Person / Time
Site:	Millstone
Issue date:	12/18/2013
From:	Scace S Dominion, Dominion Nuclear Connecticut
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
13-646 LER 13-003-00
Download: ML14023A595 (6)

LER-2013-003, Regarding Postulated DC Ammeter Circuit Hot Shorts

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
LER closed by
IR 05000245/2016008 (4 January 2017)
3362013003R00 - NRC Website

text

Dominion Dominion Nuclear Connecticut, Inc.

Rope Ferry Rd., Warerford, CT 06385 Mailing Address: PO. Box 128 Waterford, CT 06385 dom.com DEC 18 2013 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Serial No.

MPS Lic/LES Docket No.

License No.13-646 RO 50-336 DPR-65 DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 2 LICENSEE EVENT REPORT 2013-003-00 POSTULATED DC AMMETER CIRCUIT HOT SHORTS This letter forwards Licensee Event Report (LER) 2013-003-00 documenting a condition discovered at Millstone Power Station Unit 2 on October 30, 2013. This LER is being submitted pursuant to 10 CFR 50.73(a)(2)(ii)(B).

If you have any questions or require additional information, please contact Mr. William D. Bartron at (860) 444-4301.

Sincerely,

/Ste"ph rl'E.Scace Site Vice President - Millstone Attachments: 1 Commitments made in this letter: None

Serial No.13-646 Docket No. 50-336 Licensee Event Report 2013-003-00 Page 2 of 2 cc:

U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd, Suite 100 King of Prussia, PA 19406-2713 J. S. Kim Project Manager - Millstone Power Station U.S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 08 C2A Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station

Serial No.13-646 Docket No. 50-336 Licensee Event Report 2013-003-00 ATTACHMENT LICENSEE EVENT REPORT 2013-003-00 MILLSTONE POWER STATION UNIT 2 DOMINION NUCLEAR CONNECTICUT, INC.

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2016 (10/2010)

, the NRC may not conduct or sponsor.

digits/characters for each block) and a person is not required to respond to, the information collection.

3. PAGE Millstone Power Station - Unit 2 05000336 1 OF 3

4. TITLE Postulated DC Ammeter Circuit Hot Shorts

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED S

FACILITY NAME DOCKET NUMBER SEQUENTIAL REV MONTH DAY YEAR 05000 MONTH DAY YEAR YEAR NUMBER NO.

10 30 2013 2013-003-00 12 18 2013 05000

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR :.Check all that apply)

9. OPERATING MODE 20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(i)(C) 50.73(a)(2)(vii) 20.2201(d) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 20.2203(a)(1) 20.2203(a)(4)

X 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i) 50.36(c)(1 )(i)(A) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A) 20.2203(a)(2)(ii) 50.36(c)(1)(ii)(A) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x)

10. POWER LEVEL 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(A) 73.71 (a)(4) 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(B) 73.71 (a)(5) 100 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C)

OTHER 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D)

Specify in Abstract below or in

1.

EVENT DESCRIPTION

While Millstone Power Station Unit 2 (MPS2) was operating at 100 percent power in Mode 1 on October 30, 2013, operations determined that a concern identified by Engineering as a result of recent industry operating experience could result in an unanalyzed condition. Engineering's review of the impact of unfused direct current (DC) ammeter [11] circuits in the Control Room determined the described condition to be applicable to MPS2. It is postulated that a fire could cause one of the DC ammeter wires to hot short to ground. Concurrently, the fire causes another DC wire from the opposite polarity on the same battery to also short to ground. This would cause a current path through the unfused ammeter cable. The original plant wiring design and associated circuitry analysis for the batteries' control room ampere indications do not include overcurrent protection features to limit the fault current in this scenario.

The following MPS2 components have the vulnerability identified, i.e., DC current measuring circuits connected to a 125VDC power [El] source without a protective device.

• Inverters #1 through #6

• DC1 "A" Battery Charger [BYC] to Battery Bus [BU] 201A

• DC2 "B" Battery Charger to Battery Bus 201 B

• DC4 125 VOLT DC Turbine [MT] Battery Charger

• 201A DC Battery Bus 201A (D01)

• 201B DC Battery Bus 201B (D02)

• 201D Turbine Battery Bus (D03)

Fire areas affected because of the postulated hot shorts in DC circuits with ammeters are the battery rooms, the DC switchgear rooms, the turbine battery room located in the 31' 6" elevation of the turbine building, the 25' elevation cable vault, the old and new computer rooms, the plant equipment operator (PEO) meeting area, the west 480V switchgear room, and the control room.

This condition is reportable pursuant to 10 CFR 50.73(a)(2)(ii)(B) as an unanalyzed condition that significantly degraded plant safety. A prompt notification per EN49487 was submitted to the NRC on October 30, 2013.

2.

CAUSE

The cause of the condition was a latent design error that was made during plant construction.

3.

ASSESSMENT OF SAFETY CONSEQUENCES

Fire areas affected because of the postulated hot shorts in DC circuits with ammeters in the equipment listed above are the battery rooms, the DC switchgear rooms, the turbine battery room located in the 31' 6" elevation of the turbine building, the 25' elevation cable vault, the old and new computer rooms, the plant equipment operator (PEO) meeting area, the west 480V switchgear room, and the control room.

The zones where the initial fire occurs that could lead to a secondary fire are the west 480V and DC switchgear rooms, the 31'6" elevation of the turbine building, and the PEO meeting area.

A reportable condition' would only occur if a secondary fire occurs which affects the opposite train equipment. This could only occur if the secondary fire occurs in the control room or the 25' cable vault.

In order for this low probability occurrence to result in a secondary fire, the opposite pole short must develop, and it must not be mitigated by other circuitry protection schemes, such as fuses present in the

affected cables. Furthermore, if multiple faults were to occur, they would be limited in number, small in magnitude, and short in duration.

The majority of these fire areas have fire detection installed and several have reliable automatic fire suppression systems. The control room is constantly manned by personnel who are trained to extinguish fires. Therefore, any low energy secondary fire will be quickly detected and extinguished. On this basis, the safety consequences of these postulated secondary fires is considered low.

4.

CORRECTIVE ACTION

Compensatory measures, i.e., fire watches, have been implemented for affected areas of the plant. Plant modifications are planned that will protect or isolate the affected circuits leaving the initial fire area.

Additional corrective actions are being taken in accordance with the Station's corrective action program.

5.

PREVIOUS OCCURRENCES

No previous similar occurrences.

Energy Industry Identification System (EIIS) codes are identified in the text as [XX].

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