05000269/LER-2016-001, Regarding RPS Actuation - Unit 1 Reactor Trip Initiated by a Generator Lockout/Turbine Trip
| ML16139A840 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 05/05/2016 |
| From: | Batson S Duke Energy Carolinas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| ONS-2016-038 LER 16-001-00 | |
| Download: ML16139A840 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 2692016001R00 - NRC Website | |
text
ef_~DUKE
~ ENERGY ONS-2016-038 May 5, 2016 Attn: Document Control Desk U.S. Nuclear Regulatory Commission 11555 Rockville Pike Rockville, MD 20852-2746 Duke Energy Carolinas, LLC (Duke Energy)
Oconee Nuclear Station Unit 1 Docket No. 50-269 Renewed License Number DPR-38 10 CFR 50.73 Scott L. Batson Vice President Oconee Nuclear Station Duke Energy ON01 VP / 7800 Rochester Hwy Seneca, SC 29672 o: 864.873.3274 t. 864.873. 4208 Scott.Batson@duke-energy.com Subject: Licensee Event Report 269/2016-001, Revision 0 - Reactor Trip - System Aduation The enclosed Licensee Event Report (LER) describes the March 6, 2016, reactor trip at Oconee Nuclear Station (ONS), Unit 1. A Turbine Trip/Reactor Trip was initiated by an electrical failure on the high side bushing of Unit 1 Main Step-up Transformer. The actuation of the Reactor Protection System (RPS) for the reactor trip requires an LER to be submitted per 1 O CFR
- 50. 73( a)(2)(iv)(A).
There are no regulatory commitments associated with this LER.
If there are questions, or further information is needed, contact David Haile in ONS Regulatory Affairs at (864) 873-4742.
Sincerely,
~Y:!&s-Scott L. Batson Vice President Oconee Nuclear Site Enclosure LER: RPS Actuation - Unit 1 Reactor Trip initiated by a Generator Lockout/Turbine Trip
NRC Document Control Desk May 5, 2016 Page 2 cc:
Ms. Catherine. Haney Administrator Region II U.S. Nuclear Regulatory Commission Marquis One Tower 245 Peachtree Center Ave., NE, Suite 1200 Atlanta, Georgia 30303-1257 Mr. James R. Hall, Project Manager (ONS)
(by electronic mail only)
U.S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop 0-881 Rockville, MD 20852 Mr. Jeffery Whited, Project Manager (by electronic mail only)
U.S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop 0-881A Rockville, MD 20852 Mr. Eddy Crowe NRC Senior Resident Inspector Oconee Nuclear Station INPO (Word File via E-mail)
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 (11-2015)
, the NRG may not conduct or sponsor, and a person is not (See Paqe 2 of form 366 for reauired number of diqits/characters for each block) required to respond to, the information collection.
- 3. PAGE Oconee Nuclear Station, Unit 1 05000269 1 of 3
- 4. TITLE RPS Actuation - Unit 1 Reactor Trip Initiated by a Generator Lockout!Turbine Trip
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR ISEQUENTIALIREV MONTH DAY YEAR FACILITY NAME DOCKET NUMBER NUMBER NO.
NA 5000 03 06 2016 2016 -
001 00 05 05 2016 FACILITY NAME DOCKET NUMBER NA 5000
- 9. OPERATING MODE 11. THIS REPORT IS SUBMITIED 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)(ii)(A)
D 50.73(a)(2)(viii)(A) 1 D 20.2201 (d)
D 20.2203(a)(3)(ii)
D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
D 20.2203(a)(1)
D 20.2203(a)(4)
D 50.73(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1 )(i)(A)
~ 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. POWER LEVEL D 20.2203(a)(2)(ii)
D 50.36(c)(1 )(ii)(A)
D 50.73(a)(2)(v)(A)
D 73.71 (a)(4)
D 20.2203(a)(2)(iii)
D 50.36(c)(2)
D 50.73(a)(2)(v)(B)
D 73.71 (a)(5)
D 20.2203(a)(2)(iv)
D 50-46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73.77(a)(1) 100 D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(D)
D 73.77(a)(2)(i)
D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(ii)
... D 50.73(a)(2)(i)(C)
D OTHER Specify in Abstract below or in emergency classification to be upgraded to an "Alert" condition. The fire was declared to be completely extinguished at 1708 and the plant exited all Emergency declarations at 2016.
Other than entry into the Technical Specifications associated with the fire's impact on one emergency power path, there was no impact to systems required for safe operation and shutdown of the plant during the NOUE and Alert. The second emergency power path and multiple offsite sources remained operable and had no impact on the operational response to the reactor trip or recovery for the emergency declarations. Units 2 and 3 continued to operate at 100% power throughout the event.
CAUSAL FACTORS The cause of this Reactor Trip was determined to be an electrical failure of a transformer bushing (the transformer connection point for a conductor going to the 230KV switchyard). The electrical fault initiated a generator lockout and turbine trip which prompted a reactor trip.
CORRECTIVE ACTIONS
- 1. The 230KV bus was restored.
- 2. A replacement step-up transformer was tested and installed on Unit 1.
SAFETY ANALYSIS
The Unit 1 Main Step-up transformer's bushing failure caused a generator lockout/turbine trip, that initiated a RPS anticipatory reactor trip. The unit's system response was in line with a loss of electrical load reactor trip. Steam generator pressure control responded as expected and Main Steam Relief Valves (MSRVs) lifted and reseated within specifications. Steam generator level was controlled to appropriate post trip levels without an Emergency Feedwater actuation. RCS pressure, temperature and inventory (i.e., pressurizer level) was also controlled appropriately. All reactor coolant pumps operated throughout the event and no Emergency Core Cooling System (ECCS) or Engineering Safeguards (ES) actuation.
conditions were met. Thus, the controlled nature of the plant response to the reactor trip did not result in a significant risk to the public.
The transformer fire was contained and controlled without injury, and did not present any radiological safety challenges. The fire affected one out of two emergency power paths during post trip recovery. No other nuclear related plant systems were impacted. The loss of the emergency power path was within the safety allowances provided by Technical Specification actions.
ADDITIONAL INFORMATION
Energy Industry Identification System (EllS) codes are identified in the text as [XX].
There were no releases of radioactive materials or radiation exposures in excess of limits associated with this event.
SIMILAR EVENTS
A search of the Oconee Corrective Action Program (CAP) database was conducted for the preceding three year period. No other LERs were found related to reactor trips caused by secondary electrical load issues.
NRG FORM 366 (11-2015)
ef_~DUKE
~ ENERGY ONS-2016-038 May 5, 2016 Attn: Document Control Desk U.S. Nuclear Regulatory Commission 11555 Rockville Pike Rockville, MD 20852-2746 Duke Energy Carolinas, LLC (Duke Energy)
Oconee Nuclear Station Unit 1 Docket No. 50-269 Renewed License Number DPR-38 10 CFR 50.73 Scott L. Batson Vice President Oconee Nuclear Station Duke Energy ON01 VP / 7800 Rochester Hwy Seneca, SC 29672 o: 864.873.3274 t. 864.873. 4208 Scott.Batson@duke-energy.com Subject: Licensee Event Report 269/2016-001, Revision 0 - Reactor Trip - System Aduation The enclosed Licensee Event Report (LER) describes the March 6, 2016, reactor trip at Oconee Nuclear Station (ONS), Unit 1. A Turbine Trip/Reactor Trip was initiated by an electrical failure on the high side bushing of Unit 1 Main Step-up Transformer. The actuation of the Reactor Protection System (RPS) for the reactor trip requires an LER to be submitted per 1 O CFR
- 50. 73( a)(2)(iv)(A).
There are no regulatory commitments associated with this LER.
If there are questions, or further information is needed, contact David Haile in ONS Regulatory Affairs at (864) 873-4742.
Sincerely,
~Y:!&s-Scott L. Batson Vice President Oconee Nuclear Site Enclosure LER: RPS Actuation - Unit 1 Reactor Trip initiated by a Generator Lockout/Turbine Trip
NRC Document Control Desk May 5, 2016 Page 2 cc:
Ms. Catherine. Haney Administrator Region II U.S. Nuclear Regulatory Commission Marquis One Tower 245 Peachtree Center Ave., NE, Suite 1200 Atlanta, Georgia 30303-1257 Mr. James R. Hall, Project Manager (ONS)
(by electronic mail only)
U.S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop 0-881 Rockville, MD 20852 Mr. Jeffery Whited, Project Manager (by electronic mail only)
U.S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop 0-881A Rockville, MD 20852 Mr. Eddy Crowe NRC Senior Resident Inspector Oconee Nuclear Station INPO (Word File via E-mail)
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 (11-2015)
, the NRG may not conduct or sponsor, and a person is not (See Paqe 2 of form 366 for reauired number of diqits/characters for each block) required to respond to, the information collection.
- 3. PAGE Oconee Nuclear Station, Unit 1 05000269 1 of 3
- 4. TITLE RPS Actuation - Unit 1 Reactor Trip Initiated by a Generator Lockout!Turbine Trip
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR ISEQUENTIALIREV MONTH DAY YEAR FACILITY NAME DOCKET NUMBER NUMBER NO.
NA 5000 03 06 2016 2016 -
001 00 05 05 2016 FACILITY NAME DOCKET NUMBER NA 5000
- 9. OPERATING MODE 11. THIS REPORT IS SUBMITIED 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)(ii)(A)
D 50.73(a)(2)(viii)(A) 1 D 20.2201 (d)
D 20.2203(a)(3)(ii)
D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
D 20.2203(a)(1)
D 20.2203(a)(4)
D 50.73(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1 )(i)(A)
~ 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. POWER LEVEL D 20.2203(a)(2)(ii)
D 50.36(c)(1 )(ii)(A)
D 50.73(a)(2)(v)(A)
D 73.71 (a)(4)
D 20.2203(a)(2)(iii)
D 50.36(c)(2)
D 50.73(a)(2)(v)(B)
D 73.71 (a)(5)
D 20.2203(a)(2)(iv)
D 50-46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73.77(a)(1) 100 D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(D)
D 73.77(a)(2)(i)
D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(ii)
... D 50.73(a)(2)(i)(C)
D OTHER Specify in Abstract below or in EXPIRES 10/31/2018
- 3. PAGE 2
OF 3
This event is reportable per 1 O CFR 50.73(a)(2)(iv)(A) as an actuation of the Reactor Protection System (RPS) [JC]. When the reactor trip occurred, Oconee Nuclear Station (ONS) Units 1, 2 and 3, were operating in MODE 1 at approximately 100% power. No significant structures, systems or components were out of service such that they contributed to this event.
The 19KV output of the unit 1 generator is fed to a Main Step-Up (MSU) transformer where voltage is increased to 230KV. The MSU Transformer is located beside the Turbine Building and feeds the generator's power output to the switchyard.
The ONS electrical power system design credits two Keowee Hydroelectric Units (KHUs) [EK] within the owner controlled area of the station as its emergency power sources. Upon a loss of power, emergency power is supplied from both KHU units through two separate and independent routes, an overhead and underground emergency power path.
The ONS Limiting Condition for Operation (LCO) for Technical Specification (TS) 3.8.1 "AC Power Sources" contains the following:
. The following AC electrical power sources shall be OPERABLE:
- 1. Two offsite sources on separate towers connected to the 230 KV switchyard to a unit startup transformer and capable of automatically supplying power to one main feeder bus; and
- 2. Two Keowee Hydro Units (KHUs) with one capable of automatically providing power through the underground emergency power path to both main feeder buses and the other capable of automatically providing power through the overhead emergency power path to both main feeder buses.
EVENT DESCRIPTION
At approximately 1512 on March 6, 2016, a fault occurred on one of the bushings for the Unit 1 - Main Step-Up (MSU) transformer [EL], which resulted in a Generator [TB] Lockout/Turbine Trip which in turn prompted a reactor trip. At the time of these occurrences a security officer stationed in proximity of the MSU transformer heard a loud noise and observed smoke and flames coming from the MSU transformer and reported it to the Control Room.
This reactor trip is an anticipatory design feature of RPS which trips the reactor based on an "at power turbine trip," prior to Reactor Coolant System (RCS) [RC] parameters (pressure, temperature, level, flow, or reactor power) reaching their reactor trip setpoints.
Reactor trip breaker operation and control rod insertion all occurred as expected and within acceptable time responses. RCS and Secondary plant parameters were maintained such that no safety system actuation occurred.
With regard to nuclear safety systems, operational and plant system response to the Reactor Trip was evaluated as being normal/acceptable.
The reactor trip (RPS actuation) is the reportable attribute of this LER per 10 CFR 50.73(a)(2)(iv)(A).
A "Notification of Unusual Event" (NOUE) was declared at 1520 due to a transformer fire that was started by an electrical fault of one of its bushings. The transformer deluge system activation along with the response of onsite and offsite fire teams promptly contained the fire. The fire eventually caused a transformer overhead conductor to fail and fall to the ground, which triggered a switchyard bus lockout.
Due to the ONS electrical distribution design, the lockout also constitutes a loss of one emergency power path to the site. At 1658, the discovery that the fire had affected a safety system, led the NRG FORM 366 (11*2015)
emergency classification to be upgraded to an "Alert" condition. The fire was declared to be completely extinguished at 1708 and the plant exited all Emergency declarations at 2016.
Other than entry into the Technical Specifications associated with the fire's impact on one emergency power path, there was no impact to systems required for safe operation and shutdown of the plant during the NOUE and Alert. The second emergency power path and multiple offsite sources remained operable and had no impact on the operational response to the reactor trip or recovery for the emergency declarations. Units 2 and 3 continued to operate at 100% power throughout the event.
CAUSAL FACTORS The cause of this Reactor Trip was determined to be an electrical failure of a transformer bushing (the transformer connection point for a conductor going to the 230KV switchyard). The electrical fault initiated a generator lockout and turbine trip which prompted a reactor trip.
CORRECTIVE ACTIONS
- 1. The 230KV bus was restored.
- 2. A replacement step-up transformer was tested and installed on Unit 1.
SAFETY ANALYSIS
The Unit 1 Main Step-up transformer's bushing failure caused a generator lockout/turbine trip, that initiated a RPS anticipatory reactor trip. The unit's system response was in line with a loss of electrical load reactor trip. Steam generator pressure control responded as expected and Main Steam Relief Valves (MSRVs) lifted and reseated within specifications. Steam generator level was controlled to appropriate post trip levels without an Emergency Feedwater actuation. RCS pressure, temperature and inventory (i.e., pressurizer level) was also controlled appropriately. All reactor coolant pumps operated throughout the event and no Emergency Core Cooling System (ECCS) or Engineering Safeguards (ES) actuation.
conditions were met. Thus, the controlled nature of the plant response to the reactor trip did not result in a significant risk to the public.
The transformer fire was contained and controlled without injury, and did not present any radiological safety challenges. The fire affected one out of two emergency power paths during post trip recovery. No other nuclear related plant systems were impacted. The loss of the emergency power path was within the safety allowances provided by Technical Specification actions.
ADDITIONAL INFORMATION
Energy Industry Identification System (EllS) codes are identified in the text as [XX].
There were no releases of radioactive materials or radiation exposures in excess of limits associated with this event.
SIMILAR EVENTS
A search of the Oconee Corrective Action Program (CAP) database was conducted for the preceding three year period. No other LERs were found related to reactor trips caused by secondary electrical load issues.
NRG FORM 366 (11-2015)