05000446/LER-2004-003
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4462004003R00 - 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 23, 2004, at the time of discovery for this reportable event, Comanche Peak Steam Electric Station (CPSES) Unit 2 was in Mode 1, Power Operation, operating at approximately 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 contributed to the event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND
APPROXIMATE TIMES
On August 5, 2004, CPSES Unit 2 was in Mode 1, Power Operation, operating at approximately 100 percent power. At 0755 hours0.00874 days <br />0.21 hours <br />0.00125 weeks <br />2.872775e-4 months <br />, Operators in the Unit 2 Control Room received a computer point deviation alarm on one of the four Engineered Safety Feature Actuation System (ESFAS) intermediate range containment pressure channels (channel 2-P-0935) [EIIS:(JE)(CHA)]. At that time, the channel was found to be reading approximately 2.0 psig low with respect to the other channels. Over the next 25 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br />, channel 2-P-0935 acted erratically and failed to track the other three containment pressure channels. The channel deviations during this time ranged from approximately 5.0 psig low to approximately 1.0 psig low.
On August 6, 2004, at 0900 hours0.0104 days <br />0.25 hours <br />0.00149 weeks <br />3.4245e-4 months <br /> Engineering was contacted for assistance in troubleshooting the deviation problem with channel 2-P-0935. At that time, Engineering suggested that a Channel Operational Test (COT) be performed to ascertain the channel's operability. The COT established that the bistable set points for the High 1, High 2, and High 3 activations were well within the calibration range. However, upon restoration of the loop from the COT, channel 2-P-0935 did not return to a normal reading when compared to the other containment pressure channels. At 1030 hours0.0119 days <br />0.286 hours <br />0.0017 weeks <br />3.91915e-4 months <br />, the channel was left in bypass and Technical Specification (TS) 3.3.2. Condition D was entered. This TS requires that an 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 />.
Troubleshooting activities by Maintenance personnel on August 6, 2004 lead to the discovery of a grounded shield wire condition in the junction box associated with the pressure transmitter [EIIS:(JE)(CHAXPT)]. At 1506 hours0.0174 days <br />0.418 hours <br />0.00249 weeks <br />5.73033e-4 months <br /> this condition was corrected and the loop was restored to service, with normal containment pressure indications.
On August 10, 2004, Engineering began an evaluation to determine if channel 2-P 0935 had been inoperable while the grounded shield wire condition existed. On November 23, 2004, Engineering completed the evaluation and determined that channel 2-P-0935 had been inoperable from 0755 on August 5, 2004 to 1506 on August 6, 2004, for a total of 31 hours3.587963e-4 days <br />0.00861 hours <br />5.125661e-5 weeks <br />1.17955e-5 months <br /> and 11 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
Engineering personnel (utility, non-licensed) determined that channel 2-P-0935 had been inoperable for longer than allowed by TS.
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
Not applicable — No safety system responses occurred as a result of this event.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
Engineering determined that intermediate range containment pressure channel 2-P 0935 was inoperable from 0755 hours0.00874 days <br />0.21 hours <br />0.00125 weeks <br />2.872775e-4 months <br /> on August 5, 2004, until 1506 hours0.0174 days <br />0.418 hours <br />0.00249 weeks <br />5.73033e-4 months <br /> on August 6, 2004 (a total of 31 hours3.587963e-4 days <br />0.00861 hours <br />5.125661e-5 weeks <br />1.17955e-5 months <br /> and 11 minutes).
C. SAFETY CONSEQUENCES AND IMPLICATIONS
The containment pressure sensing channels are necessary for the Safety Injection (SI), Main Steam Line Isolation (MSLI), and Containment Spray (CT) ESFAS functions. For the SI and MSLI functions, three of the channels are used with a 2 out of 3 logic. For the CT function, four channels are employed with a 2 out of 4 logic. The additional redundancy is added for system reliability due to the CT function being an "energize to trip” design.
During the 31 hours3.587963e-4 days <br />0.00861 hours <br />5.125661e-5 weeks <br />1.17955e-5 months <br /> and 11 minutes that channel 2-P-0935 was inoperable, no event occurred that required the SI or MSLI actuations on high containment pressure. Had the SI and MSLI actuations been necessary, it is highly likely that the 2 out of 2 logic would have been satisfied. Even though the trip function is not single failure proof in this 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 Power believes that this event was caused by a secondary ground in the junction box associated with the pressure transmitter. The expansion anchors, securing the junction box to the reactor building wall, were found to be exuding a white, mineral-rich liquid from the concrete. This liquid had over time dripped on the cable shield at the bottom of the junction box. The built up mineral deposits produced a current path to ground, essentially causing the shield for one of the cables to be grounded at both ends. This caused a grounding loop, which lead to the intermittent erroneous indications.
V. CORRECTIVE ACTIONS
This condition was corrected and the loop was restored to service, with normal containment pressure indications. Per the CPSES Corrective Action Program, Engineering will review other potential locations where this condition may exist and inspect those locations for the existence of this condition as appropriate.
VI. PREVIOUS SIMILAR EVENTS
There has been one other reportable event in the last three years involving channel 2-P 0935 being inoperable (see Unit 2 LER 2003-004-00). However, the cause of that event (random electronic failure) was sufficiently different from the event described in this LER such that the previous corrective actions could not have prevented this event.