05000374/LER-2005-002
| Lasalle County Station, Unit 2 | |
| Event date: | |
|---|---|
| Report date: | |
| 3742005002R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor, 3489 Megawatts Thermal Rated Core Power
A. CONDITION PRIOR TO EVENT
� Unit(s): 2 Event Date: 03/12/2005� Event Time: 1830 CST � Reactor Mode(s): 4 Power Level(s): 00 Mode(s) Name: Cold Shutdown
B. DESCRIPTION OF EVENT
On March 12, 2005, during a VT-2 examination of the reactor coolant pressure boundary in accordance with LaSalle County Station procedure LOP-NB-01, "Reactor Vessel System Leakage Test," pressure boundary leakage was identified upstream of a drain valve (2B21-F067D) in the Main Steam (MS)[SB] system. The leakage source was the weld joint between the body of Main Steam Isolation Valve (MSIV) (2B21- F028D) and the drain line (2MS2OAD-2"). The leakage was characterized as a "steady stream" from a single pinhole location in the weld.
Pressure boundary leakage was determined to be reportable under 10 CFR 50.72(b)(3)(ii)(A) as a condition that resulted in the condition of the nuclear power plant, including its principle safety barriers, being seriously degraded.
An Emergency Notification System call was made on March 12, 2005, at 2318 hours0.0268 days <br />0.644 hours <br />0.00383 weeks <br />8.81999e-4 months <br /> CST (Event# 41487).
The weld was repaired and was inspected successfully within acceptance criteria on March 14, 2005.
C. CAUSE OF EVENT
A review of prior work orders identified that repair work had been, performed on this same weld location in 1995. The 1995 work involved replacing the drain line (2MS2OAD-2") between the outboard MSIV (2B21-F028D) and the 2" x 1-1/2" reducer leading to an adjoining pipe (2MS20BD-1-1/2").
The apparent cause of the event is a weld inclusion or defect from the 1995 weld.
It is believed that the pinhole flaw in the weld was due to internal porosity.
The flaw likely developed directly below the surface and therefore was not initially detected using liquid dye penetrant surface examination. For Class 1 socket welds of this type, only surface examinations are required in accordance with the ASME Code and LaSalle County Station procedural requirements.
D. SAFETY ANALYSIS
The safety significance of this event was low. The pinhole leak was discovered during hydrostatic testing while Unit 2 was shutdown in Mode 4. There was no evidence of corrosion in the area, indicating that the leak was new. No leakage was found when the previous hydrostatic test was performed on Unit 2 in 2003.
The condition did not result in a safety system functional failure.
CORRECTIVE ACTIONS E.�
- The weld was repaired and inspected using liquid dye penetrant testing. The hydrostatic test was re-performed in accordance with LaSalle County Station procedure LOP-NB-01, and the VT-2 examination was successful within acceptance criteria. (Complete)
- The subject weld will receive another VT-2 examination during the next refueling outage on Unit 2 that will provide further confidence that the repair was successful. (AT# 311917-10).
F. PREVIOUS OCCURRENCES
A search of LaSalle Licensee Event Reports from the last 10 years found no similar occurrences.
G. COMPONENT FAILURE DATA
No components failed in this event.