05000395/LER-2007-003
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | 10-04-2007 |
|---|---|
| Report date: | 03-06-2008 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3952007003R01 - NRC Website | |
PLANT IDENTIFICATION
Westinghouse - Pressurized Water Reactor
EQUIPMENT IDENTIFICATION
IFS01900A RBCU Drain Flow Switch IFS01900B RBCU Drain Flow Switch
IDENTIFICATION OF EVENT
On October 4, 2007, during an as-found functional flow test of the V. C. Summer Nuclear Station (VCSNS) Reactor Building Cooling Unit (RBCU) drain flow switch IFS01900A, the required alarm failed to initiate. IFS01900A was declared inoperable.
Boroscope investigation of the bottom of the 6 inch P-trap of the RBCU drain line revealed debris plugging the 1 inch line tapping off the P-trap. An engineering review of plant operating records completed on November 14, 2007, found multiple occasions over the last three years where the more restrictive six hour portion of Technical Specification 3.4.6.1 Action Statement should have been entered due to other leakage detection systems being declared inoperable.
Condition Reports CR-07-02167 and CR-07-03332 were initiated to address this event.
EVENT DATE
10/04/2007
REPORT DATE
12/03/2007 03/06/08
CONDITIONS PRIOR TO EVENT
Mode 1, 100% Power
DESCRIPTION OF EVENT
A concern was raised regarding the adequacy of testing and maintenance of the RBCU drain flow switches. The surveillance test procedure did not flow water from the RBCU to the flow switch; instead, the procedure utilized a tap near the flow switch and thus bypassed the 6 inch drain piping, the P-trap and the inlet point to the sensor piping. As a result of this test configuration, there is no assurance that the P-trap or the inlet pipe is not blocked with trash or debris.
On 10/4/07 during a Reactor Building entry at power, an as-found functional flow test that included the previously bypassed drain piping was conducted on RBCU drain flow switch IFS01900A. During the test, IFS01900A failed to alarm. Visual inspection revealed a small trickle of flow through the 1 inch piping for the flow switch. Based on the similarity of design and previous testing, VCSNS conservatively declared both trains (IFS01900A and B) of RBCU drain flow switches inoperable.
DESCRIPTION OF EVENT (CONTINUED) Boroscope inspection of the 6 inch P-trap was evaluated as clean. Further inspection revealed that the 1 inch line tapping off the bottom of the P-trap was plugged. Various cleaning techniques were employed until all debris was removed. IFS01900A was tested satisfactorily and declared operable on October 11, 2007.
IFS01900B will remain inoperable until plant conditions allow for inspection and testing.
Technical Specification 3.4.6.1 requires the following Reactor Coolant System leakage detection systems to be operable: reactor building atmosphere particulate radioactivity monitoring system, a reactor building sump level, and either the reactor building cooling unit condensate flow rate or a reactor building atmosphere gaseous radioactivity monitoring system. With only two of the above required leakage detection systems operable, operation may continue for up to thirty days provided grab samples are periodically obtained and analyzed when the radioactivity monitoring system is inoperable, otherwise the plant must be placed in hot shutdown within six hours and cold shutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.
An engineering evaluation was conducted to determine past operability and TS compliance for the Leakage Detection System as identified in TS 3.4.6.1. The evaluation, completed on November 14, 2007, reviewed plant records over the last three years. The evaluation determined that while the reactor building sump level leakage detection systems remained operable in Modes 1 through 4 during the last three years, there were multiple times when reactor building atmosphere particulate and gaseous radioactivity monitoring system was unavailable while in Modes 1 through 4 for a period greater than six hours. Had the station known the RBCU drain flow switches were inoperable, the plant would have entered the more restrictive six hour portion of Technical Specification 3.4.6.1 Action Statement requiring a plant shutdown. In addition on November 30, 2006, the reactor building atmospheric gaseous radioactivity monitoring system was declared inoperable for this LCO only, since it may not have been able to detect Reactor Coolant System (RCS) leakage due to low RCS activity levels. Had the station known the RBCU drain flow switches were inoperable, the plant would have entered a 30-day action and would have either restored the switch to operable status or would have conducted a plant shutdown.
With the RBCU leak detection switches inoperable, VCSNS failed to comply with TS 3.4.6.1 action statements on multiple occasions. The failure to comply with the plant's Technical Specifications is reportable to the NRC in accordance with the requirements of 10CFR50.73(a)(2)(i)(B).
CAUSE OF EVENT
The cause of the inoperable RBCU drain flow switches and subsequent technical specification violation was foreign material introduced through the drain piping during RBCU cleaning, and an inadequate Surveillance Test Procedure (STP). STP 342.003 tested the flow switches only, instead of verifying that condensate flow from the RBCU's would actuate the flow switches.
ANALYSIS OF EVENT
As discussed in bases of TS 3.4.6.1, the RCS Leakage Detection System monitors and detects leakage from the Reactor Coolant Pressure Boundary. With the RBCU drain flow alarms inoperable, detection of RCS leakage was provided by the reactor building sump level leakage detection system and the reactor building atmosphere particulate and gaseous radioactivity monitoring system. During the last three years the reactor building atmosphere particulate and gaseous radioactivity monitoring system was unavailable while in Modes 1 through 4 for a period greater than six hours, 14 times for a total time of approximately 500 hours0.00579 days <br />0.139 hours <br />8.267196e-4 weeks <br />1.9025e-4 months <br />.
Although, the Technical Specification design bases function was not met, this event was determined to have very low safety significance because at least one method of RCS leakage was available at all times. With reactor building sump level indication and Technical Specification required RCS water balance surveillances, even a small RCS leak would have been easily detected.
CORRECTIVE ACTIONS
IFS01900A was cleared of the blockage via a 6 inch blind flange downstream of the P-trap, was functionally checked to ensure water draining from the RBCU would actuate the switch, and was declared operable. IFS01900B will remain inoperable until plant conditions allow for inspection and testing. Corrective actions will be developed to ensure foreign material will not affect the P-trap and associated piping for IFS01900A and IFS01900B. The surveillance test method for the RBCU drain flow switches will be revised to ensure the RCS leakage function is met.
In addition, l&C procedures will be reviewed for instrumentation that is required by technical specifications or supports a Maintenance Rule Risk Significant Function to ensure the procedures test all components involved in the process measurement.
PRIOR OCCURRENCES
There have been no other instances of Technical Specification violations related to leak detection systems in containment in the past three years.