05000446/LER-2003-004
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| 4462003004R00 - NRC Website | |
I. DESCRIPTION OF REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
Any operation or condition prohibited by the plant's Technical Specifications.
B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT
On November 5, 2003, Comanche Peak Steam Electric Station (CPSES) Unit 2 was in Mode 1, Power Operation, operating at approximately 99 percent power following the Unit 2 seventh refueling outage.
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 November 5, 2003, CPSES Unit 2 was in Mode 1, Power Operation, operating at approximately 99 percent power following the Unit 2 seventh refueling outage. During routine control board [EIIS:(NA)(MCBD)1 observations, Operators (utility, licensed) in the Unit 2 Control Room noted that one of the four Engineered Safety Feature Actuation System (ESFAS) intermediate range containment pressure channels (channel 2-P-0935) MILS :(JE )(CHA)] was reading approximately 0.7 prig low with respect to the other channels. At 0950, the channel was declared inoperable per Technical Specification (TS) 3.3.2. This TS requires that the inoperable channel be placed in bypass or trip within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> or the affected Unit must be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and Mode 4 within 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br />. Review of the plant computer data indicated that the affected channel had been inoperable from 0530 on November 3, 2003 to 1042 on November 5, 2003, for a total of 53 hours6.134259e-4 days <br />0.0147 hours <br />8.763227e-5 weeks <br />2.01665e-5 months <br /> and 12 minutes. This exceeded the TS completion time of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> to be in Mode 3. Therefore, a reportable violation of Technical Specifications occurred.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM
FAILURE, OR PROCEDURAL OR PERSONNEL ERROR
Operations personnel (utility, licensed) discovered during routine control board observations and review of plant computer data that intermediate range containment pressure channel 2-P-0935 was inoperable.
H. COMPONENT OR SYSTEM FAILURES
A. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED
COMPONENT
Intermediate range containment pressure channel 2-P-0935 failed reading low (approximately 0.7 psig).
B. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE
Intermediate range containment pressure channel 2-P-0935 failed reading low due to a degraded power supply circuit card. The failure of the power supply circuit card was determined to be a random electronic component failure.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY
FAILURE OF COMPONENTS WITH MULTIPLE FUNCTIONS
Failure of intermediate range containment pressure channel 2-P-0935 affects the Safety Injection (SI), Containment Spray (CI), and Main Steam Line Isolation (MSLI) ESFAS functions.
D. FAILED COMPONENT INFORMATION
Manufacturer — Westinghouse Model — NLP Card Group 2, serial number 803561 configuration, these channels are highly reliable with little history of failure. In addition, the SI or MSLI actuations could have been initiated from other diverse indications, such as low pressurizer pressure or low compensated steam line pressure.
If a parameter is used only for input to the protection circuits, three channels with a 2 out of 3 logic are sufficient to provide the required reliability and redundancy. If one channel fails in a direction that would not result in a partial function trip, the function is still operable with a 2 out of 2 logic. Therefore, the CT function would still have been satisfied with a 2 out of 3 logic, including the potential for a single failure of one channel.
As discussed above, no event requiring a SI, MSLI, or CT actuation actually occurred.
The SI and MSLI functions are backed up by other diverse indications that would have initiated equivalent mitigative functions. Finally, it is highly likely that any required SI, MSLI, and CT actuations would still have occurred, even with the inoperable channel.
Therefore, no safety system functional failures occurred.
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
TXU Energy believes that this event was caused by a random electronic failure in a power supply circuit card for an ESEAS intermediate range containment pressure channel. Once per shift, the maximum deviation between operable intermediate range containment pressure channels is verified to be without the failed channel being discovered. This was due to the design of the indicating gauge on the Main Control Board not providing a large amount of resolution in the negative pressure region. This lack of resolution contributed to the failure to detect that the failed channel was reading approximately 0.7 psig low.
V. CORRECTIVE ACTIONS
The failed power supply circuit card was replaced. As a part of the CPSES Corrective Action Program, Engineering will add a computer alarm for channel deviation between the four intermediate range pressure loops. This alarm will allow Operators to more easily identify this type of channel failure.
VI. PREVIOUS SIMILAR EVENTS
There have been no previous similar events in the last three years.
NEC MEM 366A (1-M01)