05000325/LER-2012-001, Regarding Manual Reactor Protection System Actuation in Anticipation of a Loss of Condenser Vacuum

Regarding Manual Reactor Protection System Actuation in Anticipation of a Loss of Condenser Vacuum

ML12124A271
Person / Time
Site:	Brunswick
Issue date:	04/21/2012
From:	Frisco J Progress Energy Carolinas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
BSEP 12-0045 LER 12-001-00
Download: ML12124A271 (6)

LER-2012-001, Regarding Manual Reactor Protection System Actuation in Anticipation of a Loss of Condenser Vacuum

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)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 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
3252012001R00 - NRC Website

text

Progress Energy APR 2 1 2012 SERIAL: BSEP 12-0045 10 CFR 50.73 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

Subject:

Brunswick Steam Electric Plant, Unit No. 1 Renewed Facility Operating License No. DPR-71 Docket No. 50-325 Licensee Event Report 1-2012-001 Ladies and Gentlemen:

In accordance with the Code of Federal Regulations, Title 10, Part 50.73, Carolina Power

& Light Company, now doing business as Progress Energy Carolinas, Inc., submits the enclosed Licensee Event Report (LER). This report fulfills the requirement for a written report within sixty (60) days of a reportable occurrence.

Please refer any questions regarding this submittal to Mr. Lee Grzeck, Acting Supervisor -

Licensing/Regulatory Programs, at (910) 457-2487.

Sincerely, Joseph M. Frisco, Jr.

Plant General Manager Brunswick Steam Electric Plant MAT/mat

Enclosure:

Licensee Event Report Progress Energy Carolinas, Inc.

Brunswick Nuclear Plant P.O. Box 10429 Southport, NC 28461

Document Control Desk BSEP 12-0045 / Page 2 cc (with enclosure):

U. S. Nuclear Regulatory Commission, Region II ATTN: Mr. Victor M. McCree, Regional Administrator 245 Peachtree Center Ave. N.E., Suite 1200 Atlanta, GA 30303-1257 U. S. Nuclear Regulatory Commission ATTN: Mr. Philip B. O'Bryan, NRC Senior Resident Inspector 8470 River Road Southport, NC 28461-8869 U. S. Nuclear Regulatory Commission (Electronic Copy Only)

ATTN: Mrs. Farideh E. Saba (Mail Stop OWFN 8G9A) 11555 Rockville Pike Rockville, MD 20852-2738 Chair - North Carolina Utilities Commission P.O. Box 29510 Raleigh, NC 27626-0510

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 not required to respond to, the information collection.

3. PAGE Brunswick Steam Electric Plant (BSEP), Unit 1 05000325 1 of 4

4. TITLE Manual Reactor Protection System Actuation in Anticipation of a Loss of Condenser Vacuum

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL I REV MONTH DAY YEAR FACILITY NAME DOCKET NUMBER NUMBER NO.

FACILITY NAME DOCKET NUMBER 02 22 2012 2012 - 001 - 00 04 21 2012

9. OPERATING MODE

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

[_1 20.2201(b)

El 20.2203(a)(3)(i)

El 50.73(a)(2)(i)(C)

Li 50.73(a)(2)(vii)

Li 20.2201(d)

Li 20.2203(a)(3)(ii)

El 50.73(a)(2)(ii)(A)

Li 50.73(a)(2)(viii)(A)

Li 20.2203(a)(1)

Li 20.2203(a)(4)

Li 50.73(a)(2)(ii)(B)

EL 50.73(a)(2)(viii)(B)

__ 20.2203(a)(2)(i)

EL 50.36(c)(1)(i)(A)

[I 50.73(a)(2)(iii)

El 50.73(a)(2)(ix)(A)

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

[I 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(iv)(A)

EL 50.73(a)(2)(x)

Li 20.2203(a)(2)(iii)

El 50.36(c)(2)

EL 50.73(a)(2)(v)(A)

EL 73.71(a)(4) 073 EL 20.2203(a)(2)(iv)

EL 50.46(a)(3)(ii)

[: 50.73(a)(2)(v)(B)

EL 73.71(a)(5)

[I 20.2203(a)(2)(v)

Li 50.73(a)(2)(i)(A)

Li 50.73(a)(2)(v)(C)

Li OTHER EL 20.2203(a)(2)(vi)

Li 50.73(a)(2)(i)(B)

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

Specify in Abstract below or in As a result of the Unit 1 manual RPS actuation, reactor water level reached the Reactor Vessel Water Level - Low Level 1 actuation set point and PCIS Groups 2 and 6 isolations occurred. Additionally, the MSIVs (i.e., PCIS Group 1) were manually closed prior to reaching the Condenser Vacuum - Low actuation set point. With the closure of the MSIVs, RCIC and HPCI were operated manually, as necessary, for Reactor Coolant System level and pressure control, respectively. No automatic RCIC or HPCI initiation signals were received. No Safety/Relief valves lifted or were manually operated in response to the Unit 1 manual RPS actuation.

Event Cause

The root cause of this event is inadequate preventive maintenance for the 4160/480 V transformer associated with the Common C BOP bus.

The direct cause of the loss of the Common C BOP bus was failure of its 4160/480 V transformer.

Investigation of the failed transformer identified that the X2 winding (i.e., center phase, low voltage) was faulted on the innermost windings against the core. Insulation resistance testing revealed short circuits from the winding to the core and the ground clamping structure. This was at least partially attributable to the fault, but the condition of the core ground strap indicated an unintentional ground may have existed for an extended time. An unintentional ground would have increased the temperature of the transformer. The insulation between the secondary winding and core was severely degraded. Heat damage and degradation was found throughout the windings and core of the transformer, including the non-faulted phases. Arcing over time has occurred between the steel core clamping plates and the innermost X3 winding (i.e., right phase, low voltage). The plates were warped from heating and were pushing into the winding.

Based on the above, it was concluded that the preventive maintenance associated with the 4160/480 V transformer was inadequate. Specifically, preventive maintenance procedure OPM-XMR001, "ITE Substation Transformers," does not include a core ground check or monitor for signs of overheating on the core clamping structure nor did the performance monitoring include a comparison to initial design data. As a result, deterioration was not detected before the transformer failed.

Safety Assessment

The safety significance of this event was minimal. Operators took appropriate actions in response to the Common C bus failure. The manual RPS actuation was initiated in advance of relying upon automatic design features. HPCI and RCIC were operated manually and operated per design for reactor coolant system pressure and level control, respectively.

Although use of low pressure ECCS was not required to respond to this event, the loss of Demineralized Water Transfer Pumps and loss of keepfill was evaluated to determine its impact on ECCS and RCIC systems. While low pressure ECCS systems were considered inoperable when low discharge pressure alarms were received, the systems were available and able to perform their intended safety function. Most scenarios requiring these systems to inject will cause the systems to start, either automatically or by operator action, within a matter of minutes. Excessive voiding in the injection lines would not occur in this timeframe. Evaluation of data from the February 22, 2012, event demonstrates that in the event of delayed system starts, the systems would reach equilibrium (i.e., negligible check valve backleakage) before causing voids that would prevent the system from performing its injection function.

Corrective Actions

The following corrective actions to prevent recurrence are planned.

Revise preventive maintenance procedure OPM-XMROOI, "ITE Substation Transformers," to require: (1) performance of core ground testing and (2) inspection for discoloration and signs of overheating on core clamping structure. This revision is currently scheduled to be completed by June 28, 2012.

Establish and implement ITE Substation Transformer monitoring which includes: (1) thresholds for temperature monitoring based on transformer loading using vendor data, theoretical knowledge, engineering judgment, and comparison to the entire population of the same transformers and (2) required actions once thresholds are reached or exceeded. This action is currently scheduled to be completed by June 28, 2012.

Previous Similar Events

A review of LERs and corrective action program condition reports for the past three years did not identify any similar previous occurrences.

Commitments

No regulatory commitments are contained in this report.