05000247/LER-2002-002
| Docket Number | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i) |
| 2472002002R00 - NRC Website | |
DOCKET
Indian Point, Unit 2 05000247 LER NUMBER) 6)
SEQUENT REVISI
IAL � ON
PLANT AND SYSTEM IDENTIFICATION
Westinghouse 4-Loop Pressurized Water Reactor
EVENT IDENTIFICATION
Restoration of Previously Isolated Portion of Weld Channel and Containment Penetration Pressurization System
EVENT DATE
June 8, 2002
REFERENCES
Condition Reporting System Number: 200205704, 200001335
PAST SIMILAR EVENTS
EVENT DESCRIPTION
On June 8, 2002, at approximately 0530 hours0.00613 days <br />0.147 hours <br />8.763227e-4 weeks <br />2.01665e-4 months <br />, a previously determined inoperable and retired portion of the Weld Channel and Containment Penetration Pressurization System (WCCPPS)(EIIS:BD], Zone W-11, was determined to be operable following the completion of an engineering investigation. The WCCPPS provides a means for determining the leak tightness of the containment by continuously pressurizing the positive pressure zones incorporated into the containment penetrations, the channels over the welds in the steel liner, and certain containment isolation valves. Indian Point 2 Technical Specification 3.3.D.2.c. states, "With the portion of the weld channel pressurization system inoperable, and it is determined that it is not repairable by any practicable means, then that portion may be disconnected from the system.
On February 29, 2000 operations personnel observed an increase in the flow rate indication for weld channel Zone 3 from 0.32 scfm to 4.2 scfm, as read on FIT-1126-3A. The flow rate for weld channel Zone 3 represents a total flow to several wall and bottom zones fed from two (2) WCCPPS supply racks, Rack No.
16 and 17. Zone W-11 is a wall channel zone located below the floor elevation 46' of the vapor containment building, and is fed via Rack No. 17. The Fix It Now (FIN) team was assigned to locate and repair the source of the leakage.
All of the carbon steel tubing from Rack No. 17 (Elev. 68 ft.) downstream of valve PCV-1101-W11B to the floor penetration (Elev. 46 ft.) was checked visually for leakage using a liquid leak detector with the zone pressurized to its normal operating pressure of 52 psig.
DOCKET
FACILITY NAME (1) NUMBER (2) LER NUMBER 6) PAGE (3 ) SEQUENT � REVISI ) AL � ON � NIIMR EVENT DESCRIPTION (Continued) Similarly the tubing that exits the floor penetration area (Elev. 46 Ft.) was checked up to the vent isolation valve (Elev. 68 Ft.). No visible evidence of leakage was detected. Consequently it was determined that the source of the leakage was most likely located below the concrete floor, as had been seen in previously isolated zone leaks. A modification consisting of cutting and capping of the supply tubing to zone W-11 at Rack No. 17 was performed. Zone W-11 was subsequently disconnected from the WCCPPS on March 28, 2000.
On June 7, 2002, while conducting investigation activities associated with the containment integrated leakage rate test, it was determined that the previously retired portion of the WCCPPS was not leaking. A visual inspection of all exposed tubing from Rack No. 17 (Elev. 68 Ft.) to the floor penetration area (Elev. 46 Ft.) was performed. A similar inspection was performed for the tubing between the floor penetration area (Elev. 46 Ft.) and the vent-thru- test station (Elev. 68 Ft.). An air pressure test was performed on the previously abandoned zone by pressurizing the zone to its normal operating pressure of 52 psig with service air. A test rig consisting of flexible hose, a pressure regulator, a 0-16 scfm flow meter, and an isolation valve were connected to the supply tubing feeding zone W-11. Upon the completion of the zone pressurization the flow meter indicated 0 scfm. Flow was established through the zone at approximately 7 scfm by opening the appropriate test valve to verify the validity of the tested zone and flow meter. Liquid leak detector was used on all accessible tubing to look for visible leakage. No leakage was identified.
EVENT ANALYSIS
Analysis of this event indicates that the high flow condition reported on February 29, 2000 was not confirmed by alternate means during the diagnostic and investigation phase following its immediate discovery. Zone W-11 had been identified as the leaking zone responsible for the high flow indication (flow increase from 0.32 scfm to 4.2 scfm); however, it had not been verified by an independent flow rate method. Potential sources for leakage of accessible tubing in the containment were checked and determined to be acceptable. Based upon this investigation, the source of the excessive flow was assumed to be below the floor and embedded in concrete. This conclusion was attributed predominantly to past historical WCCPPS zone leaks. The recent inspection results indicate virtually no leakage in zone W-11. Thus, the cause for this event was human performance related and is attributed to a failure to perform an independent verification of the increased flow rate indication.
Independent verification using alternate flow indication would have confirmed the magnitude of leakage and whether Zone 3 was indeed leaking. The lack of a questioning attitude by the FIN team initially assigned to locate and repair the source of the leakage was a contributing cause for this event.
FACILITY NAME (1)
DOCKET
(1
SEQUENT REVISI
IAL � ON PAGE (3 ) LER NUMBER6) This report is being made pursuant to 10 CFR 50.73 (a)(2)(i)(B), which requires that "Any operation or condition which was prohibited by the plant's Technical Specification except when 1) The Technical Specification is administrative in nature; 2) The event consisted solely of a case of a late surveillance test where the oversight was corrected, the test was performed, and the equipment was found to be capable of performing its specified safety functions; or 3) The Technical Specification was revised prior to discovery of the event such that the operation or condition was no longer prohibited at the time of discovery of the event.
EVENT SAFETY SIGNIFICANCE
This event resulted in the retirement of an operable zone of the WCCPPS.
Indian Point 2 Technical Specification 3.3.D.2.a. states, "Any one zone of the WC & PPS may be inoperable for a period not to exceed seven consecutive days.
Further, 3.3.D.2.c. states, "With the portion of the weld channel pressurization system inoperable, and it is determined that it is not repairable by any practicable means, then that portion may be disconnected from the system." During the February 2000 investigation, the exact location of the leakage from zone W-11 was not verified. Therefore, corrective actions to repair zone W-11 were not deemed impractical. The criteria for determining impracticability include the following considerations:
1. The source of the WCCPPS inoperability is inaccessible for repair. Some of WCCPPS and air supply piping is embedded in concrete and is therefore inaccessible for conventional repairs. Some portions of the WCCPPS and air supply piping are inaccessible for repair either because of the high radiation exposure involved or the location of existing plant equipment.
2. The repair itself would require destructive intrusion to the containment structure or other components. Some portions of the WCCPPS are located on the sections of the liner on the base mat of the containment.
Repairs to these portions of the WCCPPS could involve removing some portion of the containment structure, including concrete and rebar.
Other repairs might require the relocation of equipment (e.g., cable trays, accumulator tanks, etc.) within the containment in order to gain access to containment floor concrete before excavation could begin to gain access to the WCCPPS and air supply piping.
During the period from March 2000 through June 2002, zone W-11 was isolated from the containment atmosphere by physically capping the zone supply tubing.
During this isolation period no events potentially representing a challenge to the integrity of the containment liner welds were noted. Nor were there any mechanisms noted, which could lead to potential corrosion of the liner welds.
The concrete containment wall structure fully encloses the exterior surfaces of containment liner welds. Interior liner weld surfaces are protected from corrosion by the WCCPPS channels, which are further embedded in concrete.
While in the retired state, zone W-11 contained air at atmospheric pressure with moisture content no greater than normal containment relative humidity.
This would not be expected to sustain corrosion of the liner welds. Based upon the above, this event has been determined to be of minimal safety significance.
CORRECTIVE ACTIONS
Immediate corrective action was taken to restore WCCPPS zone W-11 to operable status. On June 8, 2002, following the reconnection of zone W-11 at Rack No.
17, the affected WCCPPS section was declared operable.
Prior to the discovery of this event, Entergy Nuclear Operations Inc. (ENO), the new owner and licensee for IP-2 recognized the need to address weaknesses in human performance. Elements of ENO's plan to address human performance were identified in its Fundamental Improvement Plan, submitted to the NRC on January 25, 2002. Specifically, a human performance training program, and continuous coaching program were initiated to provide additional skills training, and to monitor the performance of daily work activities.
PREVIOUS OCCURRENCES
A review of previous occurrences that involved the same underlying concern or reason as this event was performed. One event was identified, and reported to the NRC in the following LER:
an engineering review of instrumentation setpoints associated with the Overpressure Protection System (OPS), it was determined that there were past occasions during which Indian Point 2 may have operated in a condition prohibited by the plant's Technical Specifications.