05000348/LER-2012-005
| Joseph M Farley Nuclear Plant-Unit 1 | |
| Event date: | 07-26-2012 |
|---|---|
| Report date: | 09-24-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown |
| Initial Reporting | |
| ENS 48140 | 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown |
| 3482012005R00 - NRC Website | |
A. REQUIREMENT FOR REPORT
This report is required per 10 CFR 50.73(a)(2)(i)(A) due to the completion of a plant shutdown pursuant to Technical Specifications 3.8.1, "AC Sources — Operating".
B. UNIT STATUS AT TIME OF EVENT
At the time of this event, Unit 1 was in Mode 1 at approximately 100 percent rated thermal power.
C. DESCRIPTION OF EVENT
On July 26, 2012 at 2151 hours0.0249 days <br />0.598 hours <br />0.00356 weeks <br />8.184555e-4 months <br /> CDT, with Unit 1 operating in Mode 1 at approximately 100 percent rated thermal power, the Unit operators commenced a reactor shutdown in accordance with Condition H of Limiting Condition for Operation (LCO) 3.8.1 following expiration of the Completion Time allowed for compliance with Condition B.4 of that LCO. The Unit was subsequently stabilized in Mode 5 pending necessary repairs to EDG 1B and its return to operability.
In accordance with 10 CFR 50.72(b)(2)(i) which specifies the reporting requirement for a Technical Specification required shutdown, a 4-hour non-emergency notification was made on July 26, 2012, at 2224 CDT for Unit 1 (Event Notification 48140).
D. CAUSE OF EVENT
On July 16, 2012, at approximately 2152 CDT, Technical Specification LCO 3.8.1 was voluntarily entered on Plant Farley Unit 1 and EDG 1B was removed from service for the purpose of performing the planned 24-month maintenance activities. Five days into the Required Action Statement (RAS), the maintenance was completed and EDG 1B began a post-maintenance operation evaluation run. Approximately two hours into the evaluation run, soon after reaching a fully loaded condition, oscillations were noted to occur for certain EDG parameters (such as load, output amps and power, scavenging air pressure, and governor position). Subsequently, within a few minutes, EDG 1B unexpectedly shutdown. The initial investigation included an examination of all cylinders which led to the discovery of a damaged piston and cylinder liner on the #12 cylinder.
Subsequent investigation determined that the immediate cause of the EDG 1B shutdown was a high crankcase pressure trip; the underlying cause of the engine shutdown was the malfunction of the engine's intercooler thermostatic bypass valve (Q1R43V0561) due to the failure of one of three thermal actuating devices. The malfunction of the thermostatic bypass valve prevented adequate cooling of the intercooler system that in turn led to EDG overheating and cylinder/piston breakdown.
The extent of repairs required to return EDG 1B to operability required a period of time that exceeded the Completion Time allowed by Condition H of LCO 3.8.1, and the Unit was shut down and placed in Mode 5 pursuant to the associated Required Action.
The underlying failure of the engine's intercooler thermostatic bypass valve to provide adequate cooling of the EDG's intercooler system (that is, the EDG's water jacket) was concluded to be due to the failure of one of three thermal actuating devices (commonly termed "power pill"). The power pill is a device (a subcomponent of the thermostatic bypass valve) which contains a temperature sensitive wax that expands with increasing temperature and provides the motive force to lift the controlling valve element off of its seat allowing intercooler fluid to flow to remove heat from the supported load. Industry experience with such thermostatic valve elements has shown that a failure mechanism of the power pill may exist which appears to be related to the device's time-in-service (Reference INPO OE 34938).
Contributing causes were determined to be inadequate monitoring of the intercooler inlet and outlet water temperatures during EDG runs and the inadequate preventative maintenance replacement frequency of Robertshaw power pill elements in the subject thermostatic bypass valve.
E. SAFETY ASSESSMENT
The safety significance of this event is considered minimal. Power from EDGs 1-2A and 1C remained available to supply the redundant Train "A" safety-related equipment. Further, offsite power circuits were available and adequate to supply electrical power to the onsite Class 1 E distribution system. The plant was stabilized in Mode 5 within the allowed time limits. The Unit remained within Technical Specification limits at all times.
Based upon these considerations, there was no adverse effect on plant safety or on the health and safety of the public as a result of this event.
F. CORRECTIVE ACTION
1. The corrective actions were to:
- Replace all three power pills in the intercooler thermostatic valve poppet assembly for EDG 1B;
- Institute more robust monitoring of the cooling system during EDG runs: and
- Revise preventative maintenance frequency for the Robertshaw power pills.
G. ADDITIONAL INFORMATION
2) � Previous Similar Events:
There have been no failures of the subject power pill at Plant Farley in the previous three years, See Industry experience identified in section H below.
3) Energy Industry Identification System Code:
EDG 1 - EK Thermostatic Control Valve - FCO 4) Commitment Information:
This report does not create any new permanent licensing commitments.
H. PREVIOUS INDUSTRY OPERATING EXPERIENCE:
1) 0E18813 - Failure of Diesel Generator Jacket Water Temperature Control Valve (July 2004) 2) 0E34938 - High Emergency Diesel Generator Jacket Water Temperature Due to Failed Temperature Regulator (November 2011)