05000373/LER-2013-005
| Lasalle County Station, Unit 1 | |
| Event date: | 04-27-2013 |
|---|---|
| Report date: | 06-26-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded |
| Initial Reporting | |
| 3732013005R00 - NRC Website | |
LaSalle County Station Unit 1 is a General Electric Company Boiling Water Reactor with 3546 Megawatts Rated Core Thermal Power.
A. CONDITION PRIOR TO EVENT:
B. DESCRIPTION OF EVENT:
On April 27, 2013, LaSalle Unit 1 was in Mode 2 (Startup) following a forced outage. At 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br /> CDT, during a walk down 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 (1 E51-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 2124 hours0.0246 days <br />0.59 hours <br />0.00351 weeks <br />8.08182e-4 months <br /> CDT the leak was classified as reactor coolant pressure boundary leakage, and Technical Specification (TS) 3.4.5 Condition C was entered. TS 3.4.5 Required Actions 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 />.
Unit 1 entered Mode 4 at 0841 hours0.00973 days <br />0.234 hours <br />0.00139 weeks <br />3.200005e-4 months <br /> on April 28, 2013, as required by TS 3.4.5 to allow for repair of the leak on 1E51-F076.
The event is reportable under 10 CFR 50.73(a)(2)(i)(A) as a completion of a nuclear plant shutdown required by the plant's TS, and 10 CFR 50.73(a)(2)(ii)(A) as an event or condition that resulted in the condition of the nuclear power plant, including its principle barriers, being seriously degraded. An ENS call (EN# 48977) was made at 2348 hours0.0272 days <br />0.652 hours <br />0.00388 weeks <br />8.93414e-4 months <br /> CDT on April 27, 2013, pursuant to 10 CFR 50.72(b)(2)(i) and 10 CFR 50.72(b)(3)(ii)(A).
C. CAUSE OF EVENT:
In February 2011, a similar steam leak was seen on the same valve in the same area. The small weld repair to fix the steam leak was QC and MT inspected and passed both tests before the Unit was placed back online.
The valve was walked down again in the February 2012 refueling outage, and was found to be in good condition with no leaks.
The leak seen in the April 2013 event was on each end of the weld repair performed in 2011. The apparent cause was a weld defect or discontinuity introduced at the time of 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:
- The entirety of the original weld was ground out, including the previous weld repair, and was replaced with new weld covering the entire radius of the affected joint.
- Actions to identify and order the correct replacement valve are in-progress. There is currently no spare, and the original valve manufacturer no longer exists.
F. PREVIOUS OCCURRENCES:
On February 9, 2011, LaSalle Unit 1 was in Mode 2 (Startup) following a forced outage. During a walk down 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 Actions 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 />.
Corrective actions were to grind-out the defect and perform a code weld repair of the affected area. The corrective action from the most current event was to grind out the entirety of the original weld, including the previous weld repair, and to replace it with new weld covering the entire radius of the affected joint.
G. COMPONENT FAILURE DATA:
Manufacturer: Anderson Greenwood Company (A415) Model Number: NO3-6498-510 LaSalle County Station, Unit 1 05000373