05000446/LER-2005-002
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| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4462005002R00 - NRC Website | |
I.�DESCRIPTION OF REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
An event or condition that resulted in valid actuation of any of the systems listed in 10CFR50.73(a)(2)(iv)(A). Specifically, the Unit 2 AFW System automatically started.
Pursuant to 10 CFR 50.72(b)(3)(iv)(A), TXU Power made notification of this event to the NRC Headquarters Operations Officer on February 23, 2005 (reference ENS # 41432).
B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT
On February 23, 2005, CPSES Unit 2 was in Mode 1 operating at 100 percent 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 were inoperable at the start of the event that contributed to the event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND
APPROXIMATE TIMES
On February 23, 2005, CPSES Unit 2 was in Mode 1 operating at 100 percent power. During the evening hours on February 23, thunderstorms with lightning were occurring in the area around CPSES. At 0153 hours0.00177 days <br />0.0425 hours <br />2.529762e-4 weeks <br />5.82165e-5 months <br />, a momentary interruption of power to the 138kV switchyard [EIIS: (FK)] occurred which caused the Unit 2 6.9kV safeguards buses to transfer to their alternate power source. This resulted in actuation of both trains of the Unit 2 BOS followed by an actuation, as expected, of the Unit 2 AFW System [EIIS: (BA)]. All three (two motor driven and one turbine driven) AFW pumps started as designed. Unit 2 turbine load was reduced from 1195MWe to 1100MWe in response to the AFW actuation to maintain reactor power below 100 percent. At 0227 hours0.00263 days <br />0.0631 hours <br />3.753307e-4 weeks <br />8.63735e-5 months <br /> all three AFW pumps were secured.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM
FAILURE, OR PROCEDURAL OR PERSONNEL ERROR
During investigation into the cause of this event, TXU Electric Delivery personnel (utility, non-licensed) discovered a misconfigured jumper in the power line communication equipment located in the switchyard of another TXU Power generating plant (DeCordova Steam Electric Station).
II. COMPONENT OR SYSTEM FAILURES
A. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED
COMPONENT
Not applicable — No component or system failures were identified during this event.
B. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE
Not applicable — No component or system 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 or system failures were identified during this event.
D. FAILED COMPONENT INFORMATION
Not applicable — No component or system failures were identified during this event.
III. ANALYSIS OF THE EVENT
A. SAFETY SYSTEM RESPONSES THAT OCCURRED
Both trains of the Unit 2 BOS actuated during this event resulting in actuation of the Unit 2 AFW motor driven and turbine driven pumps. Control Room HVAC shifted to emergency recirculation and both Unit 2 Centrifugal Charging pumps started as designed; however, no ECCS actuation occurred.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
Not applicable -- No safety system was rendered inoperable.
C. SAFETY CONSEQUENCES AND IMPLICATIONS
The actuation of the Unit 2 Auxiliary Feedwater System is specifically bounded by the accident analysis in section 15.1.2 of the CPSES Final Safety Analysis Report.
During this event, power to the safeguards busses was always available and the transfer from one power source to the other functioned as designed. Also, there was no disruption in the non-safeguards loads required for normal plant operation because these loads are unaffected by a loss of the 138kV switchyard.
There were no safety system functional failures associated with this event. Based on this analysis, it was concluded that this event did not adversely affect the safe operation of CPSES Unit 2 or the health and safety of the public.
IV. CAUSE OF THE EVENT
During this event, it is believed that a lightning strike occurred somewhere on the Stephenville to CPSES 138kV power line. Breakers 7050 (138kV Stephenville feeder breaker) and 4060 (138kV CPSES feeder breaker from Stephenville) tripped and automatically closed as expected to clear the fault. However, breaker 4460 (138kV CPSES feeder breaker from DeCordova) unexpectedly tripped. This event resulted in a 6.9kV safeguards buses to transfer to their alternate power source.
Breaker 4460 was not expected to open for a fault on the Stephenville line. During investigation into the cause of this event, TXU Electric Delivery personnel discovered that the power line communication equipment in the switchyard of the DeCordova Steam Electric Station had an improper jumper setting. The power line communication equipment is intended to prevent remote breakers from operating when it is not necessary to clear a sensed fault. With the incorrect jumper setting, a "permissive" signal was present when an "inhibit" signal should have been present, resulting in an inappropriate trip of breaker 4460.
The improper jumper setting occurred during a 2004 modification that replaced the electro mechanical relays with microprocessor relay packages in the power line communication equipment at the CPSES, DeCordova Steam Electric Station, and Stephenville switchyards.
The improper jumper setting caused the unexpected trip of breaker 4460 and the momentary interruption of power to the 138kV switchyard which lead to an actuation of the Unit 2 BOS with an actuation, as expected, of the Unit 2 AFW System.
V. CORRECTIVE ACTIONS
The misconfigured jumper in the DeCordova Steam Electric Station power line communication equipment was corrected. Jumper settings associated with the 2004 microprocessor relay package modification were operationally checked on the relay terminals in the CPSES, DeCordova Steam Electric Station and Stephenville switchyards.
As a part of the CPSES corrective action program, TXU Energy Delivery has agreed to physically verify the proper switchyard jumper configurations.
VI. PREVIOUS SIMILAR EVENTS
There have been other reportable events involving actuation of the AFW system in the last three years. However, the details/causes are sufficiently different from the event described in this LER such that the previous corrective actions could not have prevented this event.