05000446/LER-2003-005
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4462003005R00 - NRC Website | |
I. DESCRIPTION OF REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
Any event or condition that resulted in manual or automatic actuation of the Reactor Protection System (RPS) including reactor trip or reactor scram.
B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT
was in Mode 1, Power Operation, operating at 99.5 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 contributed to the event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND
APPROXIMATE TIMES
was in Mode 1 operating at 99.5 percent power. At 0827 hours0.00957 days <br />0.23 hours <br />0.00137 weeks <br />3.146735e-4 months <br />, a Meter and Relay Technician (utility, non-licensed) entered the Main Generator exciter house [EIIS:
(TB)(IX)(ENCL)] to collect monthly voltage and current data readings from the operating 2-01 Main Generator rotor shaft. This activity requires a technician to use a hand-held probe for making contact with the Main Generator rotor shaft. The probe is constructed from a wooden dowel approximately four feet long with a metallic contact and meter leads affixed to one end. Following procedure instructions, the technician contacted the shaft with the probe and successfully acquired the voltage and current data.
Upon completing the task, the technician turned to exit the exciter house. As he turned he inadvertently struck the "A" stroboscope assembly with the probe. The "A" stroboscope is located on the rotating rectifier wheel [EIIS: (TB)(RECT)] air guide cover directly adjacent to the position from which the data is acquired. When the stroboscope assembly was struck, the lamp reflector separated from the stroboscope assembly, falling approximately eighteen inches and into the "A" (negative) rectifier wheel.
Contact between the lamp reflector, exposed circuit elements (fuses, diodes, and diode leads) of the rectifier wheel, and the rectifier wheel casing resulted in sparks and phase-to-phase faults. The phase-to-phase faults in the Main Generator exciter resulted in a Main Turbine trip followed by an automatic reactor trip on a "Turbine Trip >50% Power" signal. All control rods fully inserted, all Auxiliary Feedwater pumps [EIIS: (BA)(P)] automatically started as expected, and the unit was stabilized in Mode 3.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM
FAILURE, OR PROCEDURAL OR PERSONNEL ERROR
Operators (utility, licensed) in the Unit 2 Control Room received a "Turbine Trip >50% Power" alarm.
H. 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
The Reactor Protection System and The Auxiliary Feedwater System actuated during the event. The Unit 2 reactor automatically tripped on a "Turbine Trip >50% Power" signal, and all three Auxiliary Feedwater pumps automatically started on "Steam Generator Lo-Lo water level" signals.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
Not applicable -- No safety system train was rendered inoperable.
C. SAFETY CONSEQUENCES AND IMPLICATIONS
This event is specifically bounded by the Final Safety Analysis Report (FSAR) accident analysis of the turbine trip presented in Section 15.2.3 of the CPSES FSAR. The analysis uses conservative assumptions to demonstrate the capability of pressure relieving devices and to demonstrate core protection margins. The event of December 22, 2003, occurred at 99.5 percent reactor power, and all safety related systems and components functioned as designed. There were no safety system functional failures associated with this event.
Based on the above, it is concluded that the event of December 22, 2003, did not adversely affect the safe operation of CPSES Unit 2 or the health and safety of the public.
IV. CAUSE OF THE EVENT
TXU Energy believes that the cause of the event was improper reassembly of the stroboscope. The stroboscope lamp reflector is mounted to the rotating rectifier wheel air guide cover using four cap screws and retaining clips. Inspection of the "A" stroboscope assembly after this event revealed that all of the cap screws and retaining clips for the lamp reflector were loose, and the retaining clips were not oriented in their normal/design position. The personnel who reassembled the stroboscope did not ensure that the retaining clips were sufficiently tight and oriented as required.
The work instructions for disassembly/reassembly of the stroboscope are generic and nondescript in nature. TXU Energy believes that this vagueness contributed to the personnel error which resulted in the stroboscope being reassembled incorrectly.
V. CORRECTIVE ACTIONS
Access to the Unit 1 and Unit 2 Main Generator exciter houses and monthly collection of rotor voltage and current data on the Unit 1 and Unit 2 Main Generator were suspended.
The damaged components in the Unit 2 rectifier wheel were repaired/replaced and the "A" stroboscope assembly was reassembled correctly. The "B" stroboscope assembly was also found to be incorrectly assembled and it was subsequently assembled correctly. Both Unit 1 stroboscopes were inspected and found to be correctly assembled.
As a part of the CPSES corrective action program, the following actions will be taken to prevent recurrence:
1. The work instructions for disassembly and reassembly of stroboscopes will be enhanced.
2. Other turbine work instructions that may have a similar potential to cause a reactor trip will be reviewed, and enhancements will be implemented as appropriate.
3. To heighten awareness of this event, a Lessons Learned will be issued on this event to all personnel that are regularly involved in Main Generator work.
VI. PREVIOUS SIMILAR EVENTS
There have been other events which resulted in a turbine trip followed by an automatic reactor trip. However, the causes of those events were sufficiently different such that the previous corrective actions could not have prevented this event.