05000373/LER-2011-002
| Lasalle County Station Unit 1 | |
| Event date: | 02-09-2011 |
|---|---|
| Report date: | 04-01-2011 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown |
| Initial Reporting | |
| 3732011002R00 - NRC Website | |
LaSalle County Station (LSCS) Unit 1 is a General Electric Boling Water Reactor with 3546 Megawatts Thermal Rated Core Power.
A. CONDITION PRIOR TO EVENT:
On February 9, 2011, LaSalle Unit 1 was in Mode 2 (Startup) following a forced outage. During a walkdown of the drywell, a steam leak was observed coming from the Reactor Core Isolation Cooling (RI)[BN] Steam Supply Inboard Isolation Bypass/Warm up Valve (1E51-F076), a normally-closed, one inch, motor operated valve. The leak was determined to be on the valve bonnet extension-to-bonnet upper seal weld. At 1804 hours0.0209 days <br />0.501 hours <br />0.00298 weeks <br />6.86422e-4 months <br />, the leak was classified as Pressure Boundary Leakage, and Technical Specifications (TS) 3.4.5 Condition C was entered. TS 3.4.5 Required Action C.1 and C.2 require that the unit 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 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.
On February 9, 2011, at 1830 hours0.0212 days <br />0.508 hours <br />0.00303 weeks <br />6.96315e-4 months <br />, a plant shutdown of Unit 1 commenced. The unit entered Mode 3 at 2258 hours0.0261 days <br />0.627 hours <br />0.00373 weeks <br />8.59169e-4 months <br /> on February 9, and reached Mode 4 at 0353 hours0.00409 days <br />0.0981 hours <br />5.83664e-4 weeks <br />1.343165e-4 months <br /> on February 10, 2011.
The event was reportable under 10 CFR 50.72(b)(2)(i) as an initiation of a nuclear plant shutdown required by TS. An ENS call (EN# 46605) was made at 1859 CST on February 9, 2011. The event is also reportable under 10 CFR 50.73(a)(2)(i)(A), as the completion of a nuclear plant shutdown required by TS.
C. CAUSE OF EVENT:
The equipment apparent cause evaluation determined that the cause was due to a weld defect or discontinuity from the original weld construction (i.e., manufacturing, installation/construction errors, etc.) of the upper seal weld that propagated through wall as a result of system loading and conditions (i.e., high pressure steam) during normal plant operations.
D. SAFETY ANALYSIS:
The safety significance of the event was minimal. Makeup capability was adequate to compensate for the leak. All Emergency Core Cooling Systems (ECCS) were operable and capable of fulfilling their intended safety functions during the period of excessive leakage. The event did not constitute a safety system functional failure.
E. CORRECTIVE ACTIONS:
Corrective Actions:
e The defective upper seal weld area was successfully repaired in a timely manner
- An extent of condition review was performed to identify similar valves Corrective Action to Prevent Recurrence:
- Options will be explored to procure a new and more robust replacement valve to ensure long term reliability
F. PREVIOUS OCCURRENCES:
On October 11, 2009, at 2333 CDT, an unidentified leakage on LaSalle Unit 2 exceeded the TS Limiting Condition for Operation 3.4.5.d limit of less than or equal to a two-gallon per minute increase in the previous 24-hour period while in Mode 1. A plant shutdown was commenced at 0300 hours0.00347 days <br />0.0833 hours <br />4.960317e-4 weeks <br />1.1415e-4 months <br /> on October 12, 2009, and Mode 4 was reached at 0005 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> on October 13, 2009. The unidentified leakage was determined to be from a packing leak on the Inboard Main Steam Isolation Valve Drain Line Isolation Valve (2B21-F016). The packing leak was repaired and the unit was restarted on October 14, 2009. Corrective actions to prevent recurrence included training maintenance personnel on the different types of gaskets used on pressure seal valves, and revisions to the subject maintenance procedures.
G. COMPONENT FAILURE DATA:
Manufacturer: Anderson Greenwood Company (A415) Model Number: NO3-6498-510