05000374/LER-2015-001
| Lasalle County Station Unit 2 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| Initial Reporting | |
| 3742015001R00 - NRC Website | |
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Unit(s): 2 Reactor Mode(s): 1 Event Date: December 29, 2014 Event Time: 2330 CST Mode(s) Name: Power Operation Power Level: 100% LaSalle County Station, Unit 2 05000374 LaSalle County Station Unit 2 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 December 29, 2014, Unit 2 was in Mode 1 at 100% power with a diesel generator (DG)[EK] operability test in progress on the 2B DG. During performance of the test, operators noticed a small leak of about one drop per second coming from the casing of the 2B High Pressure Core Spray (HPCS)[BG] DG cooling water pump[BI].
The 2B DG was declared inoperable at 2330 hours0.027 days <br />0.647 hours <br />0.00385 weeks <br />8.86565e-4 months <br /> CST on 12/29/2014, as was the supported HPCS system.
The Station entered Technical Specification 3.5.1 Required Actions B.1 to verify the Reactor Coolant Isolation Cooling (RCIC)[BN] System operable and B.2 to restore HPCS to operable status within 14 days.
This inoperability of HPCS is reportable under 10 CFR 50.73(a)(2)(v)(D) as an event or condition that could have prevented the fulfillment of the safety function of the structures or systems that are needed to mitigate the consequences of an accident. An ENS report was made to the NRC at 0351 hours0.00406 days <br />0.0975 hours <br />5.803571e-4 weeks <br />1.335555e-4 months <br /> EST (EN 50707) on December 30, 2014, pursuant to 10 CFR 50.72(b)(3)(v)(D).
This event constitutes a safety system functional failure.
C. CAUSE OF EVENT:
The apparent cause of the casing leak was determined to be erosion from impeller flow impingement.
D. SAFETY ANALYSIS:
The safety significance of this event was minimal. The extent of the degradation was a pin hole leak that was weeping water at approximately one drop per second. The surrounding area material appeared sound and the structural integrity of the pump casing was not compromised. The normal AC power supply to HPCS was operable throughout the event. HPCS remained available and capable of vessel injection if required to mitigate the consequences of an accident.
RCIC, the Automatic Depressurization System (ADS)[SB], and the Low Pressure Emergency Core Cooling Systems (Residual Heat Removal (RH)[B0] and Low Pressure Core Spray (LP)[BM]) were operable throughout the event.
E. CORRECTIVE ACTIONS:
The 2B DG cooling water pump was replaced and the system returned to service on January 3, 2015.
- The damaged pump was returned to the original equipment manufacturer for refurbishment.
F. PREVIOUS OCCURRENCES:
On April 18, 2013, Unit 2 was in Mode 3 following a scram and a loss of offsite power that had occurred on both LaSalle Units the previous day. At 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br /> CDT, three pinhole through-wall leaks in the U2 High Pressure Core Spray (HPCS) minimum flow line piping were discovered. The leaks were on the outside bend of the first elbow downstream of the minimum flow restricting orifice, and appeared to be leaking a total of approximately 0.5 gpm with the HPCS pump not running.
The direct cause of the event was a combination of cavitation and mechanical wear/erosion of the piping wall.
The apparent cause was procedural inconsistencies that allowed operation of the HPCS system in minimum- flow for extended periods. Corrective actions included replacing the leaking pipe elbow, and performing ultrasonic inspections of susceptible piping on both Units. HPCS operating procedures were reviewed and revised as required to provide consistent guidance for minimizing operation of HPCS in minimum flow mode.
These actions were directed at piping downstream of the pump, and would not have prevented the pump casing leakage that resulted in the current event.
G. COMPONENT FAILURE DATA:
Union Pump Company, Model 21A1776AB, 1000 GPM, 100 HP, Single-Stage Centrifugal Pump