05000353/LER-2011-003
| Limerick Generating Station, Unit 2 | |
| Event date: | 05-23-2011 |
|---|---|
| Report date: | 06-22-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3532011003R01 - NRC Website | |
Unit Conditions Prior to the Event Unit 2 was in Operational Condition (OPCON) 1 (Power Operation) at approximately 100% power. There were no other structures, systems or components out of service that contributed to this event.
Description of the Event
On Monday, May 23, 2011, Limerick Unit 2 was operating at 100% power and an investigation regarding a loss of electric output was in progress. The troubleshooting plan involved performing verification that the feedwater (EIIS:SJ) long path flushing valves (EIIS:20) were full closed. During the activity the HV-041-209B valve was identified to have through seat leakage of approximately 570 gpm. The HV-041-210 valve was also identified to have through seat leakage of approximately 570 gpm since the valves are in series. When HV-041- 209B and HV-041-210 were fully closed the main generator load was increased by approximately 20 MWe.
The investigation determined that the HV-041-209B and HV-041-210 valves failed to fully close when securing feedwater long path flushing during the prior refueling outage (2R11) on Thursday, April 21, 2011. Initially the HV-041-210 failed to fully close as determined by both indicating lights (red and green) illuminated (dual indication). The HV-041-209A and HV-041-209B valves were then closed to terminate long path flushing flow. It was later determined that the HV-041-209B valve was actually not fully seated even though the indicating lights were indicating full closed (green illuminated and red extinguished). The HV-041-210 was then closed until the indicating lights indicated fully closed. However, the valve was not fully seated. This resulted in a partially open flow path from the "B" feedwater header to the main condenser.
The reactor core isolation cooling (RCIC) system (EIIS:BN) is rated at 600 gpm. The RCIC injection flow path to the reactor pressure vessel (RPV) is through the "B" feedwater header. The leakage from the "B" feedwater header to the condenser was approximately 570 gpm.
Therefore, RCIC was inoperable during the affected period due to potentially diverting the design flow from the reactor core.
Technical Specification (TS) 3.7.3 RCIC action "a" required restoration of RCIC within 14 days. This TS action allowance was exceeded.
RC FORM 366A (10-2010) The HV-041-209B valve is a primary containment isolation valve (PCIV).
Since the valve was not fully seated the PCIV was inoperable during the affected period. TS 3.6.3 PCIVs action "a.1" required restoring the PCIV to operable within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. Otherwise, be in at least Hot Shutdown within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and in Cold Shutdown within the following 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. This TS action allowance was exceeded.
During restart from refueling outage 2R11 this event resulted in an entry into an OPERATIONAL CONDITION when a Limiting Condition for Operation was not met which is a nonconformance with TS 3.0.4.
During restart from refueling outage 2R11, planned testing rendered the high pressure coolant injection system (HPCI) (EIIS:BJ) inoperable during the period when the RCIC system was also inoperable. TS 3.5.1 ECCS - Operating, action "c.1", does not apply when RCIC is inoperable; therefore, TS 3.0.3 was applicable. TS 3.0.3 required action within one hour to place the unit in Startup within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
However, the one hour action was not met which is a nonconformance with TS 3.0.3.
Therefore, this LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(i)(B). This event is not reportable under 10CFR50.73(a)(2)(v) as an event that could have prevented the fulfillment of the HPCI safety function because the HPCI testing performed during the affected period was a planned evolution.
Analysis of the Event
There were no actual safety consequences associated with this event.
The potential safety consequences of this event were minimal. There were no plant transients or accidents that required RCIC operation or primary containment during the affected period. High pressure coolant injection (HPCI) was inoperable during the affected period for less than seven hours during 2R11 restart testing. HPCI remained available during this period except for a period of less than one hour when test equipment was installed and removed during the test. Condensate and feedwater remained capable of injection to the RPV through the degraded feedwater header.
V RC FORM 366A (10-2010) The feedwater long path flush line is used during refuel outage restart to clean the condensate and feedwater lines. The flush also cleans up the hotwell until reactor water chemistry goals are achieved. The "A" and "B" feedwater headers are each equipped with a 16 inch long-path flush line near the feedwater line penetrations into primary containment. Each flush line is equipped with a 16 inch motor operated gate valve. The two flush lines merge into a single 16 inch line which returns to the main condenser. The single line is also equipped with a 16 inch motor operated gate valve.
During the refueling outage restart the indicating lights on the two affected motor operated valves indicated that the valves were fully seated. The green light was illuminated and the red light was extinguished on both valves. However, the valves were not fully seated which resulted in seat leakage back to the main condenser at a flow rate of approximately 570 gpm. The feed switches on the HV-041- 209A and HV-041-209B were locked open as required prior to entering Startup Mode (OPCON 2). It is normal for a motor operated valve red indicating light to extinguish as the valve enters the seat just prior to actuation of the torque switch which terminates the valve motion.
If the torque switch actuates before the valve is fully seated the red light may be extinguished with the valve slightly open.
Cause of the Event
The cause of the event was the HV-041-210 valve failed to isolate the feedwater long path recirculation line due to degradation of valve internals or stem lubrication degradation.
Corrective Action Completed The HV-041-110 and HV-041-210 valves preventive maintenance (PM) scope was revised to include performance of diagnostic testing and an actuator PM.
The procedure (506.5.A) for long path recirculation was revised to add steps which will ensure HV-041-109A, HV-041-109B, HV-041-209A and HV- 041-209B long path flushing valves are properly closed when securing long path flushing and verified as closed prior to restart.
Corrective Action Planned In-body maintenance and diagnostic testing will be performed on HV- 041-210 during the next refueling outage (2R12) which is currently scheduled for the spring of 2013.
V RC FORM 366A (10-2010) Previous Similar Occurrences There were no similar events involving conditions prohibited by TS for an inoperable RCIC system for the last 3 years.
Component data:
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Equipment:
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Reactor Core Isolation Cooling System 20-S212 T147 Terry Steam Turbine Co GS-2 TYP Feedwater Line Flushing PCIV HV-041-209B V085 Velan Valve Corp B20-07054P-02WN FIG V RC FORM 366A (10-2010)