05000374/LER-2012-001
| Lasalle County Station | |
| Event date: | 08-31-2012 |
|---|---|
| Report date: | 10-30-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| Initial Reporting | |
| 3742012001R00 - NRC Website | |
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:
Unit(s): 2 Event Date: August 31, 2012� Event Time: 09:40 CDT Reactor Mode(s): 1 Mode(s) Name: Run� Power Level: 100 percent
B. DESCRIPTION OF EVENT:
On August 31, 2012, at 09:40 CDT, while blowing down the 2B Diesel Generator (DG)[EK] A train Starting Air (DG)[LC] receiver for preventative maintenance, the receiver pressure decreased below the minimum 165 psig required for DG operability per Technical Specification (TS) 3.8.3, Condition D. The 2B DG provides emergency AC power to Division 3, which supplies the High Pressure Core Spray System (HPCS)[BG]. The 2B DG was declared inoperable in accordance with TS 3.8.3 Required Action E.1.
At 10:22 CDT, the A air start train was re-pressurized to greater than 165 psig, and the 2B DG was declared operable. The 2B DG was inoperable for approximately 42 minutes.
Because the 2B DG provides emergency power to HPCS, which is a single train system, this occurrence 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 structures or systems that are needed to mitigate the consequences of an accident. The NRC was notified of this occurrence via ENS# 48263 at 16:50 CDT on August 31, 2012.
C. CAUSE OF EVENT:
The cause of the loss of air pressure in the 'A' air start train receiver was degradation of the receiver drain valve. The drain valve was very difficult to operate, which resulted in the receiver air pressure decreasing more than expected when the operator opened it to blow down the receiver.
D. SAFETY ANALYSIS:
The safety significance of this event was minimal. The normal power supply to HPCS remained operable throughout the event. The B train air start system for the 2B DG remained greater than 165 psig and would have started the 2B DG if required.
Additionally, the Reactor Core Isolation Cooling System, Automatic Depressurization System, and the Low Pressure Emergency Core Cooling Systems were operable throughout the event.
E. CORRECTIVE ACTIONS:
- The receiver drain valve was fully closed, and the A train starting air compressor repressurized the A system receiver.
- The receiver drain valve was replaced on September 14, 2012.
F. PREVIOUS OCCURRENCES:
A search of the LER database going back 10 years found no previous occurrences where low starting air pressure caused the 2B DG to be declared inoperable.
G. COMPONENT FAILURE DATA:
3/4 inch, 2-way ball valve, Pittsburgh Brass MFG, Part # SPE-D5Q-G