05000263/LER-2013-002, Regarding Essential Bus Transfer During 2R Transformer Testing

Regarding Essential Bus Transfer During 2R Transformer Testing

ML13204A306
Person / Time
Site:	Monticello
Issue date:	07/23/2013
From:	Schimmel M Xcel Energy, Northern States Power Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
L-MT-13-067 LER 13-002-00
Download: ML13204A306 (4)

LER-2013-002, Regarding Essential Bus Transfer During 2R Transformer Testing

Event date:
Report date:
Reporting criterion:	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) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 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
2632013002R00 - NRC Website

text

Xcel Energy@

July 23, 2013 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Monticello Nuclear Generating Plant Docket 50-263 Renewed Facility Operating License No. DPR-22 Monticello Nuclear Generating Plant 2807 W County Road 75 Monticello, MN 55362 L-MT-13-067 10 CFR 50.73 LER 2013-002 "Essential Bus Transfer during 2R Transformer Testing" A Licensee Event Report (LER) for this occurrence is attached.

Summary of Commitments This letter contains no new commitments and no revisions to existing commitments.

" Mark A. Schimmel Site Vice-President, Monticello Nuclear Generating Plant Northern States Power Company-Minnesota Enclosure cc:

Regional Administrator, Region III, USNRC Project Manager, Monticello Nuclear Generating Plant, USNRC Resident Inspector, Monticello Nuclear Generating Plant, USNRC

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150*0104 EXPIRES 10/31/2013 (10-2010)

, the NRC may not conduct or sponsor, and a person is no required to respond to, the information collection.

3. PAGE Monticello Nuclear Generating Plant 05000 - 263 1 OF 3

4. TITLE Essential Bus Transfer Durinq 2R Transformer Testinq

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED YEAR I SEQUENTIAL I REV t-AGILII Y NAME DOGKET NUMBER MONTH DAY YEAR NUMBER NO MONTH DAY YEAR FAGILITY NAME DOCKET NUMBER 05 24 13 2013 - 002 - 00 7

23 2013

9. OPERATING MODE

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

D 20.2201 (b)

D 20.2203(a)(3)(i)

D 50.73(a)(2)(i)(C)

D 50.73(a)(2)(vii) 5 D 20.2201 (d)

D 20.2203(a)(3)(ii)

D 50.73(a)(2)(ii)(A)

D 50.73(a)(2)(vlli)(A)

D 20.2203(a)(1)

D 20.2203(a)(4)

D 50.73(a)(2)(ii)(B)

D 50.73(a)(2)(viii)(B)

D 20.2203(a)(2)(i)

D 50.36(c)(1)(i)(A)

D 50.73(a)(2)(lIi)

D 50.73(a)(2)(ix)(A)

10. POWER LEVEL D 20.2203(a)(2)(ii)

D 50.36(c)(1)(ii)(A)

IZI 50.73(a)(2)(iv)(A)

D 50.73(a)(2)(x)

D 20.2203(a)(2)(iii)

D 50.36(c)(2)

D 50.73(a)(2)(v)(A)

D 73.71(a)(4) 0%

D 20.2203(a)(2)(iv)

D 50.46(a)(3)(II)

D 50.73(a)(2)(v)(B)

D 73.71 (a)(5)

D 20.2203(a)(2)(v)

D 50.73(a)(2)(i)(A)

D 50.73(a)(2)(v)(C)

D OTHER Specify in Abstract below or in D 20.2203(a)(2)(vi)

D 50.73(a)(2)(I)(B)

D 50.73(a)(2)(v)(D)

EVENT DESCRIPTION

On May 24, 2013, prior to the event, the Monticello Nuclear Generating Plant (MNGP) was in Mode 5 at approximately 0% power. Operations was performing 4kV load testing on the new 2R Transformer when they were unable to observe red-light indication for a 4kV breaker [BRK] either in the control room or locally. Lack of red-light indication with the breaker closed indicates that the breaker cannot be electrically tripped.

Operators took action to trip the breaker manually using the mechanical trip button as directed by procedures.

As a result, at 0334 MNPG experienced a loss of power to the Bus-15 (Division 1-4kV Essential Bus) [BU]

which initiated an Essential Bus Transfer of Bus-15 and automatic start of 12-Emergency Diesel Generator (EDG) [DG]. 11-EDG was in pull-to-Iock as directed by the test plan and therefore did not start. At the time, all credited safety systems were lined up to Bus-16 (Division 2-4kV Essential Bus) which was not affected by the event, as a defense-in-depth measure. Bus-15 was automatically re-powered from the 1AR-Reserve Transformer [XFMR] as designed. During the event all systems responded as expected to the Essential Bus Transfer.

EVENT ANALYSIS

This event is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A) System Actuation for the valid actuation of the 12-EDG. This event was not considered a safety system functional failure.

SAFETY SIGNIFICANCE

Bus-15 automatically transferred to the 1AR-Reserve Transformer and 12-EDG auto started but did not load as expected due to the availability of normal off-site power to Bus-16. All safety systems credited with decay heat removal were aligned to Bus-16 during the event which was not affected. During the evolution all critical safety functions remained available and responded as expected to the Essential Bus Transfer.

CAUSE

During the MNGP refueling outage, extensive modifications to the electrical distribution system were performed which resulted in the need to remove five normally installed circuit breakers from the Lower 4kV Room. The number of breakers that required temporary storage exceeded normal storage capacity in the 4kV rooms; the remaining breakers were stored outside the 4kV rooms out of the path of travel and with foreign material exclusion covers. Troubleshooting immediately following the event determined the cause of the lack of red light indication was a damaged secondary disconnect pin. The damage misaligned the pin so that it could not make contact with the secondary disconnect rail.

The apparent cause of the damage to the breaker, which ultimately resulted in an Essential Bus transfer, was inadequate protection provided for the breaker during temporary storage.

CORRECTIVE ACTION

A spare breaker was successfully tested and installed. Other breakers in temporary storage were inspected for potential damage. The long term corrective action is to revise the operations manual to provide additional guidance regarding the appropriate storage of breakEJrs and to specify items requiring inspection prior to installation into switchgear cubicles.

PREVIOUS S'IMILAR EVENTS There were no previous similar licensee event reports in the past three years.

ADDITIONAL INFORMATION

Energy industry identification system (EllS) codes are identified in the text within brackets [xx]. 3. PAGE 3 OF 3