05000445/LER-2010-001
| Document Numbersequential Revmonth Day Year Year Month Day Year N/A 05000Number No. | |
| Event date: | 01-09-2010 |
|---|---|
| Report date: | 03-03-2010 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4452010001R00 - NRC Website | |
I. DESCRIPTION OF THE REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION:
10CFR50.73(a)(2)(iv)(A) "Any event or condition that resulted in a manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B).
B.PLANT CONDITION PRIOR TO EVENT:
On January 9, 2010, CPNPP Unit 1 was in Mode 1, operating at 100% power.
C. STATUS OF STRUCTURES, SYSTEMS, OR COMPONENTS THAT WERE INOPERABLE AT
THE START OF THE EVENT AND THAT CONTRIBUTED TO THE EVENT
There were no inoperable structures, systems, or components that contributed to the event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES:
On January 9, 2010, CPNPP Unit 1 was in Mode 1 operating at 100% power. At 1028 hours0.0119 days <br />0.286 hours <br />0.0017 weeks <br />3.91154e-4 months <br />, the Unit 1 Main Turbine tripped due to a pressure relay [EIIS: (RLY)] actuation on the Unit 1 Main Transformer 01 [EIIS: (XFMR)] and the Main Turbine Trip caused an automatic reactor trip. All control rods fully inserted and all three Auxiliary Feedwater pumps [EIIS: (BA)(P)] started as expected as a result of the reactor trip. All systems responded normally during and following the event. There were no safety consequences impacting plant or public safety as a result of this event.
In the Control Room (CR), the following alarms were received at 1028 (in order): 72 Generator
- Lockout Relay 82-2/1G Trip, 70 Generator Lockout Relay 86-1/1G Trip, 98 Generator Off the Line- Load Rejection Protection, 24 Turbine Trip & P9 Reactor Trip, 97 Turbine trip, and 92 CRDS Breakers 52/RTA & RTB open. These alarms were followed by a normal plant trip response.
The Unit 1 Main Transformer 01 is an ABB transformer and is one of two Unit 1 main generator output transformers designed to step-up the three-phase, 22-thousand volts (kV) output by the generator to 345kV for power transmission to the electric power grid. The other Unit 1 Main Transformer 02 is also manufactured by ABB.
Immediate corrective actions included isolating the Main Transformer 01 from Unit 1 and the other Main Transformer 02. On January 11, 2010, Unit 1 was synchronized to the grid at 0011 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br /> and reached a 640 megawatt output by 2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br />.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE, OR
PROCEDURAL PERSONNEL ERROR
Operators (utility, licensed) in the Unit 1 CR received a Unit 1 Main Transformer 01 pressure alarm.
�
II. COMPONENT OR SYSTEM FAILURES
A. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE
There was an internal phase to ground fault on Unit 1 Main Transformer 01 that could not be rectified. The exact cause of the fault could not be determined.
B. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED COMPONENT
The Unit 1 Main Turbine tripped due to a pressure relay actuation on the Unit 1 Main Transformer 01 and the Main Turbine Trip caused an automatic reactor trip.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT.WERE AFFECTED BY FAILURE OF
COMPONENTS WITH MULTIPLE FUNCTIONS
Not applicable - The component that failed did not have any multiple functions.
D. FAILED COMPONENT INFORMATION
Manufactured by ABB POWER T&D CO 20.9/345kV, Three phase, Main Transformer
III. ANALYSIS OF THE EVENT
A. SAFETY SYSTEM RESPONSES THAT OCCURRED
Both Motor Driven Auxiliary Feedwater Pumps and the Turbine Driven Auxiliary Feedwater Pump started as expected as a result of the reactor trip.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
Not applicable - there was no safety system train inoperability that resulted from this event.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT
This event is bounded by the CPNPP Final Safety Analysis Report (FSAR) accident analysis which assumes conservative initial conditions which bound the plant operating range and other assumptions which could reduce the capability of safety systems to mitigate the consequences of the transient.
This event is bounded by the analysis of the Turbine trip presented in Section 15.2.3 of the CPNPP FSAR. The analysis uses a conservative assumption to demonstrate the capability of pressure relieving devices and to demonstrate core protection margins. The event of January 9, 2010, occurred at 100% reactor power, and all systems and components functioned as designed.
� Based on the above, it is concluded that the health and safety of the public were unaffected by this condition and this event has been evaluated to not meet the definition of a,safety system functional failure per 10CFR50.73(a)(2)(v).
IV. CAUSE OF THE EVENT
On January 9, 2010, CPNPP Unit 1 was in Mode 1 operating at 100% power. At 1028 hours0.0119 days <br />0.286 hours <br />0.0017 weeks <br />3.91154e-4 months <br />, the Unit 1 Main Turbine tripped due to a pressure relay actuation on the Unit 1 Main Transformer 01 and the Main Turbine Trip caused an automatic reactor trip.
Internal inspection of the transformer showed that the relay actuation resulted from an internal failure of the transformer that could not be rectified. The specific cause could not be determined.
Subsequent oil testing revealed high levels of gasses. Since the transformer was shell form, the windings are horizontal and only the top half was visible. There was also evidence of movement in the H1 and H2 windings, the insulating material was distorted, the blocks were broken loose, and carbon had covered the windings and visible structures. There was no evidence of a problem with the lead assemblies or bushings.
V. CORRECTIVE ACTIONS
Immediate corrective actions included isolating Main Transformer 01 from Unit 1 and the other Main Transformer 02. On January 11, 2010, Unit 1 was synchronized to the grid at 0011 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br /> and reached a 640 megawatt output by 2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br />.
was synchronized to the grid on January 21, 2010 at 2326 hours0.0269 days <br />0.646 hours <br />0.00385 weeks <br />8.85043e-4 months <br /> and reached 100% power the next day at 1341 hours0.0155 days <br />0.373 hours <br />0.00222 weeks <br />5.102505e-4 months <br />.
VI. PREVIOUS SIMILAR EVENTS
There have been no previous similar reportable events at CPNPP in the last three years.