05000425/LER-2014-001
| Vogtle Electric Generating Plant - Unit 2 | |
| Event date: | 04-08-2014 |
|---|---|
| Report date: | 05-30-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4252014001R00 - NRC Website | |
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A. REQUIREMENT FOR REPORT
This report is required per 10CFR 50.73(a)(2)(iv)(A) due to an unplanned automatic actuation of the Reactor Protection System (RPS) and automatic actuation of the Auxiliary Feedwater System (AFW) and Feedwater Isolation (FWI) Engineered Safety Features Actuation Systems (ESFAS).
B. UNIT STATUS AT TIME OF EVENT
Mode 1, 100 percent power
C. DESCRIPTION OF EVENT
While operating at 100 percent power, Unit 2 experienced a low-low level alarm in Steam Generator 3. This resulted in an automatic RPS actuation due to low-low level in Steam Generator 3. AFW actuated and Main Feedwater isolated following the RPS actuation, as expected. All rods inserted and the plant was stabilized in Mode 3. Decay Heat was discharged to the condenser and no complications were experienced during the trip as all systems responded as designed.
The source of the water intrusion into the primary MFRV positioner was the result of a small leak (3 drops per minute) approximately eighteen feet above the positioner conduit. The collection area of the water was not immediately identified and as a result of less than adequate installation of the flex conduit, water accumulated inside the positioner housing. Over time, the accumulation of water inside the positioner housing reached a level resulting in an electrical short circuit of the primary MFRV positioner. This resulted in erroneous feedback from the primary positioner to the digital control system. This condition existed until the Loop 3 MFRV suddenly closed.
D. CAUSE OF EVENT
The cause of the event was failure to maintain installation standards of non-safety related conduit for the MFRV digital control system resulting in primary positioner water intrusion.
E. SAFETY ASSESSMENT
When the reactor tripped, all rods fully inserted. As a result of the trip, a FWI occurred and the AFW system actuated as designed. The unit was stabilized in Mode 3 at normal temperature and pressure. Because the plant responded as designed and there were no complications with plant shutdown, there was no adverse effect on plant safety or the health and safety of the public.
F. CORRECTIVE ACTION
Immediate interim action to inspect and seal the flex conduit to the remaining MFRV positioners was completed for both Unit 1 and Unit 2. Quality Control inspections will be required for conduit installation on critical components to ensure design and installation standards are maintained.
G. ADDITIONAL INFORMATION
1) Failed Components:
MFRV Primary Positioner 2) Previous Similar Events:
IER 13-14-12 "Water Intrusion into Relay Box Causes Main Feedwater Isolation Valve Closure and Manual Scram" 3) Energy Industry Identification System Code:
[JB] -Feedwater/Steam Generator Water Level Control System [JC] -Reactor Protection System [BA] -Auxiliary Feedwater System