ENS 43992
ENS Event | |
|---|---|
06:20 Feb 18, 2008 | |
| Title | Unanalyzed Condition Due to #2 Turbine Bypass Valve Failure |
| Event Description | Unit two reduced power to 90% to perform monthly turbine testing surveillance on 2/18/08. All tests were completed satisfactorily with the exception of the main turbine #2 Bypass Valve (BPV). At 0120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br />, the #2 BPV stroked fully open per procedure, but the last 10% of travel to full open did not yield the expected response of BPV fast open from 90% to 100%. The fast acting solenoid did indicate expected state change to 'energized' at 90% valve open, but the BPV did not indicate fast open. Therefore the Main Turbine Bypass System has been declared inoperable and associated actions of Tech Spec 3.7.7 have been invoked. This spec requires compliance with LCO 3 .2.2 MINIMUM CRITICAL POWER RATIO (MCPR) limits for an inoperable main turbine bypass system as specified in the COLR (Core Operating Limit Report), are made applicable (within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />) or reduce THERMAL POWER to <24% RTP within the following 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. The MCPR limits were calculated by reactor engineering and installed in the process computer at 0347 hours0.00402 days <br />0.0964 hours <br />5.737434e-4 weeks <br />1.320335e-4 months <br />. A decrease in reactor power was not required once the MCPR limit was installed.
The COLR (ref.: TRM Appendix A) states Unit Two can be operated with EITHER the End- of- Cycle Recirc Pump Trips (EOC-RPTs) out of service OR the Turbine Bypass Valves inoperable, but not both. The EOC-RPTs were already out of service as allowed for current conditions of the operating cycle. Upon discovery of the inoperable Bypass Valve, it was recognized that this placed Unit Two in an unanalyzed condition for fuel thermal limit. The shift crew took immediate actions to confirm the surveillance was current for EOC-RPTs and placed them in service per approved plant procedures. This was accomplished at 0315 hours0.00365 days <br />0.0875 hours <br />5.208333e-4 weeks <br />1.198575e-4 months <br />, which returned the unit to an analyzed condition. The licensee notified the NRC Resident Inspector.
During the surveillance testing of the main turbine bypass valves, one of the three main turbine bypass valves did not function as expected. The function of the main turbine bypass system was degraded but not lost. Upon discovery the required action statement (RAS) in Technical Specifications 3.7.7 and 3.2.2 were properly entered, and the required actions were taken within the allowed out of service time of two hours. Based on the initial review of the condition and the fact that the core operating limits report (COLR) described operation in the condition with the EOC-RPT out of service concurrent with loss of the main turbine bypass capability as an unanalyzed condition, a notification was made in accordance with the following reporting requirement: '10 CFR 50.72 (b)(3)(ii)(B) The nuclear power plant being in an unanalyzed condition that significantly degrades plant safety.' The initial notification was a conservative action taken shortly after the condition was discovered. The condition was immediately identified during surveillance testing of the main turbine bypass valves, the required Technical Specifications RAS was entered and the actions completed within the allowed two hour time frame of 0120 - 0315 EST on 2/28/08. This prompt action prevented continued operation with EOC-RPT out of service and main turbine bypass inoperable and eliminated this potential to be in a condition where the design basis may not have been met. A more detailed review was subsequently performed which determined that the minimum critical power ratio thermal limit for having EOC-RPT out of service and main turbine bypass inoperable as calculated during the reload analysis was 1.42. At the time of the event the actual MCPR at that point in core life was 1.57. Even though prompt actions were taken as required, there was actual margin to the calculated MCPR limit of 1.42. Had a design basis transient occurred, the MCPR Safety Limit would not have been exceeded. Based on this information the determination has been made that the unit was not in an unanalyzed condition that significantly degraded plant safety. This notification serves to retract the previous event notification 43992 made on 2/18/2008 at 0508 EST. The licensee notified the NRC Resident Inspector. |
| Where | |
|---|---|
Hatch  Georgia (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+-1.2 h-0.05 days <br />-0.00714 weeks <br />-0.00164 months <br />) | |
| Opened: | Edwin Urqhart 05:08 Feb 18, 2008 |
| NRC Officer: | Jason Kozal |
| Last Updated: | Mar 20, 2008 |
| 43992 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (89 %) |
| After | Power Operation (89 %) |
WEEKMONTHYEARENS 526502017-03-30T13:22:00030 March 2017 13:22:00
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