05000445/LER-2004-003
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4452004003R00 - NRC Website | |
I. DESCRIPTION OF REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
Any operation or condition which was prohibited by the plant's Technical Specifications.
B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT
On July 26, 2004, Comanche Peak Steam Electric Station (CPSES) Unit 1 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 contributed to the event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND
APPROXIMATE TIMES
On June 11, 2004, Operations personnel (utility, licensed) observed that the containment sump flow counter [EIIS:(CTR)] did not indicate flow when containment sump pump 4 ran to pump down containment sump 2. At CPSES, containment leakage is collected in containment sump 1, containment sump 2, or the reactor cavity sump [EIIS:(WK)(SUMP)] and is pumped via a common discharge header to a floor drain tank [EIIS:(WK)(TK)] or a waste hold-up tank [EIIS:(WK)(TK)]. The common discharge header contains a flow totalizer [EIIS:(FQI)] that measures flow and facilitates the recording of this total flow in the control room. Additionally, a run time counter [EIIS:(CTR)] records the run time of each pump. When the water level in the sump reaches a low level, the sump pumps [EIIS:(NH)(SUMP)(P)] are designed to shutoff.
Subsequent troubleshooting revealed that system elevation differences were causing the drain header to siphon intermittently to the floor drain tank leaving a void in the piping. When the sump pump was subsequently run, the water would fill the piping resulting in minimal flow registering on the flow totalizer. The siphoning condition would occur after the pump was secured from the normal pump run resulting in the flow totalizer continuing to indicate flow.
At 2350 hours0.0272 days <br />0.653 hours <br />0.00389 weeks <br />8.94175e-4 months <br /> on June 11, 2004, the Containment Sump Level and Flow Monitoring System [EIIS:(IJ)(MON)] was declared inoperable. At 2300 hours0.0266 days <br />0.639 hours <br />0.0038 weeks <br />8.7515e-4 months <br /> on June 25, 2004, vacuum breakers [EIIS:(VACB)] were installed in the discharge piping and the Unit 1 Containment Sump Level and Flow Monitoring System was restored to operable status.
A review was performed to determine if the Unit 1 Containment Sump Level and Flow Monitoring system had been inoperable in the past for a time period greater than allowed by TS 3.4.15. Condition A of TS 3.4.15 requires that if the Containment Sump Level and Flow Monitoring System is inoperable, a Reactor Coolant System [EIIS: (AB)] water inventory balance must be performed within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> (Condition A.1) and the Containment Sump Level and Flow Monitoring System must be restored to operable status within 30 days (Condition A.2). If Condition A is not met, Condition D.1 applies which requires the plant to be in Mode 3 within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
At 1449 hours0.0168 days <br />0.403 hours <br />0.0024 weeks <br />5.513445e-4 months <br /> on July 26, 2004, Engineering personnel (utility, non-licensed) concluded that the Unit 1 Containment Sump Level and Flow Monitoring system had been inoperable on December 15, 2003, for approximately 31 hours3.587963e-4 days <br />0.00861 hours <br />5.125661e-5 weeks <br />1.17955e-5 months <br />. Since the required Reactor Coolant System water inventory balance was not performed and Unit 1 was not placed in Mode 3 within 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> (24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for condition A.1 plus 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> for Condition D.1) on December 15, 2003, as required by TS 3.4.15, this condition is reportable as a condition prohibited by TS.
The Containment Sump Level and Flow Monitoring system at CPSES uses a series of level switches, a timer, and an alarm. To be considered operable per TS, the system must be capable of detecting a one gallon per minute (gpm) leakage increase within one hour. Engineering's review determined that the system is capable of detecting a one gpm leakage increase within one hour provided that the sump water level is not within an approximate 1/2 inch band above the Timer Start set point. When the sump water level was within the V2 inch band, the estimated time to detect a one gpm leakage increase was approximately 64 minutes. At all other water levels the system is operable because it would have detected a one gpm leakage increase within one hour. Therefore, the Unit 1 Containment Sump Level and Flow Monitoring system has not been inoperable continuously since initial licensing, rather, it has only been inoperable at intermittent periods in the past as described above.
TXU Power believes that the higher amount of containment leakage in the past contributed to masking the siphoning condition, and that recent measures taken to reduce containment leakage facilitated observing the siphoning condition.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM
FAILURE, OR PROCEDURAL OR PERSONNEL ERROR
At 1449 hours0.0168 days <br />0.403 hours <br />0.0024 weeks <br />5.513445e-4 months <br /> on July 26, 2004, Engineering personnel (utility, non-licensed) determined that the Containment Sump Level and Flow Monitoring System had been inoperable on December 15, 2003, for approximately 31 hours3.587963e-4 days <br />0.00861 hours <br />5.125661e-5 weeks <br />1.17955e-5 months <br />.
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
The Unit 1 Containment Sump Level and Flow Monitoring system was determined to have been inoperable per TS on December 15, 2003, for approximately 31 hours3.587963e-4 days <br />0.00861 hours <br />5.125661e-5 weeks <br />1.17955e-5 months <br />. The Unit 1 Containment Sump Level and Flow Monitoring system could have also been inoperable at other times in the past due to the siphoning condition which existed since initial Unit 1 licensing in 1990.
C. SAFETY CONSEQUENCES AND IMPLICATIONS
Section 5.2.5.2.2 of the Final Safety Analysis Report (FSAR) describes the primary detection of unidentified leakage to the Containment atmosphere as being provided by air particulate monitors, containment sump flow monitors, and the condensate flow rate measuring system. These systems provide an early indication of reactor coolant pressure boundary degradation as soon after occurrence as practical to minimize the potential for a gross pressure boundary failure which would result in a loss of coolant accident. The leakage detection system is credited in the CPSES safety analyses for General Design Criteria 4 (GDC-4) Leak Before Break to detect leaks and allow an orderly shutdown prior to a LOCA. This event involved the inoperability of one of the means of Reactor Coolant System leak detection, namely the containment sump flow monitors.
Had all means of detecting unidentified leakage been unavailable, early detection of a pressure boundary breach would have been compromised. However, a loss of coolant accident is fully bounded by Section 15.6.5 of the FSAR. Because the Containment Sump Level and Flow Monitoring system does not perform a nuclear safety function, 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 1 or the health and safety of the public.
IV. CAUSE OF THE EVENT
TXU Power has determined that the cause of this event was a siphoning condition that was inherent in the original design of the Unit 1 Containment Sump Level and Flow Monitoring system.
V. CORRECTIVE ACTIONS
To correct the siphoning condition, vacuum breakers were installed in the Unit 1 sump discharge piping. Unit 2 was not believed to be affected by this condition. However, vacuum breakers were also installed in Unit 2 sump discharge piping as a precautionary measure.
VI. PREVIOUS SIMILAR EVENTS
There has been one other reportable event in the last three years involving an original design condition (see LER 02-001-00 for Units 1 and 2). However, details/causes are sufficiently different from the event described in this LER such that the previous corrective actions could not have prevented this event.