05000446/LER-2010-001
| Document Numbersequential Revmonth Day Year Year Month Day Year Cpnpp Unit 1 05000 445Number No. | |
| Event date: | 04-12-2010 |
|---|---|
| Report date: | 06-07-2010 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4462010001R00 - NRC Website | |
Comanche. Peak Nuclear Power Plant Unit 2 05000 - 446 YEAR I SEQUENTIAL I� REV NUMBER� NO.
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 April 12, 2010, Comanche Peak Nuclear Power Plant (CPNPP) Unit 1 was de-fueled as part of the 1RF14 refueling outage and CPNPP Unit 2 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 April 12, 2010, Comanche Peak Nuclear Power Plant (CPNPP) Unit 1 was de-fueled as part of the 1RF14 refueling outage and CPNPP Unit 2 was in Mode 1 operating at 100% power. At 0720, CPNPP experienced a loss of power to startup transformer XST1 [EIIS: (XFMR)] which is the preferred offsite power source to the Unit 2 Class 1 E buses and the alternate power source for Unit 1. The Control Room (CR) Operators (Utility, Licensed) entered Technical Specification (TS) 3.8.1 Limiting Condition for Operation (LCO), Condition A for one required source of offsite power inoperable.
Unit 2 momentarily lost power to the Trains A and B safeguards buses during the automatic transfer to the alternate offsite power source. The loss of power to XST1 caused a signal to be sent to the engineered safety feature equipment, including both motor-driven Auxiliary Feedwater (AFW) pumps [EIIS: (BA)] and the Turbine-Driven AFW pump [EIIS: (BA)]. CR Operators (Utility, Licensed) responded and reduced the Unit 2 output power by 50 mega-watts electric. Furthermore, the Spent Fuel Pool (SPF) cooling pumps [EIIS: (DA)] which are common to both Units 1 and 2 were automatically load shed by the BOS as designed.
The SFP pumps are common to both Units and were shutdown as designed. At that time, the Unit 1 core was off loaded into the SPF with a time to boil of 6.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. The SFP cooling pumps were restored by procedure within six minutes.
During this event, CPNPP equipment operators (Utility, Non-Licensed) were observing the satisfactory starts on various safeguard equipment; however, the equipment operators reported vapor in the vicinity of the outboard pump shaft packing in the area of the Unit 2, Train A, motor-driven AFW pump. Not knowing the exact condition of the motor-driven AFW pump, the CR Operators (Utility, Licensed) conservatively entered TS LCO 3.7.5, Condition B for one Train of AFW inoperable.
�NRC FORM 366A (9-2007) PRINTED ON RECYCLED PAPER Per 10CFR50.72(b)(3)(iv)(A), CR Operators (Utility, Licensed) made an eight hour notification to the Nuclear Regulatory Commission (NRC) to make them aware of the plant condition as it was known at that time.
An engineering evaluation was performed on the Unit 2 motor-driven AFW pump with vendor input and determined that the vapor was steam and it was not detrimental to the packing or the pump.
The motor-driven AFW pump was then tested and no abnormalities were found. The motor-driven AFW pump was declared OPERABLE and the LCO exited at 1539 the same day.
The XST1 transformer was lost when switchyard breakers 7030 and 7040 opened due to a phase to ground fault across a transmission tower insulator between the 138kV (kilo-volt) switchyard and XST1. Approximately eight hours later, the insulator was replaced and XST1 was restored as the preferred offsite power source to Unit 2 and the alternate offsite power source for the Unit 1 Class 1E Buses.
The system response of Unit 1 and Unit 2 and the operator actions were consistent with plant design and the supporting analyses presented in the CPNPP Final Safety Analysis Report (FSAR).
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE, OR
PROCEDURAL PERSONNEL ERROR
Control board indications and alarms alerted the reactor operators (Utility, Licensed) in both Units that XST1 was de-energized, and in Unit 2 that the blackout sequencers actuated and the motor driven feedwater pumps and turbine-driven auxiliary feedwater water pump automatically started.
II. COMPONENT OR SYSTEM FAILURES
A. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE
Not applicable — No component or system failures were identified during this event.
B. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED COMPONENT
Not applicable — No component failures were identified during this event.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE OF
COMPONENTS WITH MULTIPLE FUNCTIONS
Not applicable — No component failures were identified during this event.
D.FAILED COMPONENT INFORMATION Not applicable — No component failures were identified during this event.
III. ANALYSIS OF THE EVENT
A. SAFETY SYSTEM RESPONSES THAT OCCURRED
On Unit 2, both motor-driven Auxiliary Feedwater Pumps and the Turbine-Driven Auxiliary Feedwater Pump started as expected.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
The Unit 2, Train A motor-driven AFW pump was removed from service when unusual indications (steam) were noticed coming from the outboard bearing area after the pump start. Conservatively, the pump was disabled and Technical Specification 3.7.5 was entered until the indications could be understood. The pump was then restored eight hours and nine minutes later.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT
Unit 2 momentarily lost power to the Trains A and B safeguards buses during the automatic transfer to the alternate offsite power source. The loss of power to XST1 caused a signal to be sent to the Unit 2 Trains A and BOSs. The BOSs then started the Unit 2 engineered safety feature equipment, including both motor-driven Auxiliary Feedwater pumps and the Turbine-Driven AFW pump. There was no disruption in the non-safeguards loads required for normal plant operations because normal plant operations are unaffected by the loss of the 138 kV switchyard. This event involved an increase in heat removal by the AFW system and is bounded by the CPNPP Final Safety Analysis Report (FSAR) section 15.1, "Increase in Heat. Removal by the Secondary System.
The Spent Fuel Pool (SPF) cooling pumps, common to both Units, were automatically load shed by the BOSs as designed and then restored within 6 minutes by procedure. At the time the SFP pumps were shutdown, the Unit 1 core was off loaded into the SPF with a time to boil of 6.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
The temperatures in SPF pools 1 and 2 increased by 1.4 and 1.0 degree Fahrenheit, respectively, and thus, there was minimal impact on SFP temperature.
Approximately 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> later, the transmission insulator was replaced and XST1 was restored as the preferred offsite power source to Unit 2 and the alternate offsite power source for the Unit 1 Class 1E Buses.
All safety systems responded 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).
� NRC FORM 366A (9-2007) PRINTED ON RECYCLED PAPER IV.CAUSE OF THE EVENT Investigation determined that the phase B insulator on a 138kV transmission tower between XST1 and the 138kV switchyard had black marks and foreign material hanging down on the north side of the insulator. The foreign material turned out to be' a vine that contacted the top and bottom skirt of the insulator, precipitating the fault. The vine was brought to the insulator's mounting adaptor by a bird for nest building. The design of the mounting adapter used as a connection mechanism between the under-slung insulators and tower pedestal allows birds to use the mounting adapter openings as sites for nest building. The nest building material came in contact with the top and bottom skirt of the phase B insulator on the 138kV line.
V. CORRECTIVE ACTIONS
Immediate actions included replacement of the insulator and restoration of XST1 as the preferred offsite power source to the Unit 2 Class lE buses. The insulator mounting adapters will be modified to reduce the probability of nest building.
VI. PREVIOUS SIMILAR EVENTS
There have been no previous similar reportable events at CPNPP in the last three years.
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