05000528/LER-2005-004
| Palo Verde Nuclear Generating Station | |
| Event date: | 08-12-2005 |
|---|---|
| Report date: | 10-07-2005 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| Initial Reporting | |
| ENS 41913 | 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown |
| 5282005004R00 - NRC Website | |
1. REPORTING REQUIREMENT(S):
This LER (50-528/2005-004-00) is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(A), to report the completion of a reactor shutdown required by Technical Specifications. Specifically, on August 12, 2005 Control Room personnel completed a reactor shutdown to avoid exceeding the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> required action completion time associated with Technical Specification Limiting Condition for Operation (LCO) 3.8.1 condition "B". LCO 3.8.1 condition "B" requires two Emergency Diesel Generators (EDG) (EIIS code: EK, DG), each capable of supplying one train of the onsite class lE alternating current (ac) power distribution system, be operable. On August 12, 2005 at 0026 a 4-hour NRC notification was made per 10 CFR 50.72 to report a plant shutdown required by Technical Specifications (re: ENS 41913).
2. DESCRIPTION OF STRUCTURE(S), SYSTEM(S) AND COMPONENT(S):
The standby power supply (EIIS code: EK) for each safety-related load group consists of one EDG, complete with its accessories and fuel storage and transfer systems. The standby power supply functions as a source of alternating current (ac) power for safe plant shutdown in the event of loss of preferred power and for post-accident operation of engineered safety feature (ESF) loads.
3. INITIAL PLANT CONDITIONS:
On August 12, 2005 Palo Verde Unit 1 was in Mode 1 (Power Operations), operating at approximately 94 percent power. At the start of the event EDG "B" was inoperable. No other major structures, systems, or components were inoperable that contributed to the event.
4. EVENT DESCRIPTION:
Prior to the event, on August 9, 2005, voltage anomalies (steady state voltage fluctuations) were observed immediately after EDG "B" was started for a routine monthly surveillance. At 0420 on August 9, Control Room personnel declared EDG "B" inoperable and entered Technical Specification 3.8.1 condition "B." EDG "B" was quarantined and a work mechanism was initiated to troubleshoot the voltage anomalies.
Technical Specification 3.8.1 condition "B" requires the following actions to be completed with one EDG inoperable:
B.1� Perform SR 3.8.1.1 for the operable required offsite circuit(s) within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter and, B.2 Declare required feature(s) supported by the inoperable DG inoperable when its redundant required feature(s) is inoperable within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> from discovery of condition B concurrent with inoperability of redundant required feature(s) and, B.3.1 Determine OPERABLE DG is not inoperable due to common cause failure within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> (or) B.3.2 Perform SR 3.8.1.2 for OPERABLE DG within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and, B.4 Restore DG to OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and within 6 days from discovery of failure to meet LCO.
Engineering and Maintenance personnel developed an action plan to troubleshoot EDG "B" and correct the voltage anomalies but were not successful in identifying the cause of the problem within the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> required action completion time allowed by Technical Specification 3.8.1. Unable to restore EDG "B" to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, at 0019 on August 12, 2005 Control Room personnel entered LCO 3.8.1 condition "H" and commenced a normal reactor shutdown. LCO 3.8.1 condition "H" requires Unit 1 to be in Mode 3 (Hot Standby) within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and Mode 5 (Cold Shutdown) within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.
At 0216 on August 12, 2005, Control Room personnel performed a manual reactor trip from 23 percent reactor power. At 0217, Unit 1 entered Mode 3. On August 12, 2005, at 2237, Unit 1 entered Mode 5 and exited LCO 3.8.1.
5. ASSESSMENT OF SAFETY CONSEQUENCES:
With one EDG inoperable, the remaining operable EDG and offsite circuits are adequate to supply electrical power to the onsite class lE ac power distribution system.
The 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> required action completion time takes into account the capacity and capability of the remaining ac sources, a reasonable time for repairs, and the low probability of a Design Basis Accident.
The event did not result in any challenges to the fission product barriers or result in the release of radioactive materials. Therefore, there were no adverse safety consequences or implications as a result of this event and the event did not adversely affect the safe operation of the plant or health and safety of the public.
The event did not result in a transient more severe than those analyzed in the updated Final Safety Evaluation Report Chapters 6 and 15. The event did not have any nuclear safety consequences or personnel safety impact.
The condition would not have prevented the fulfillment of any safety function and did not result in a safety system functional failure as defined by 10 CFR 50.73(a)(2)(v).
6. CAUSE OF THE EVENT:
The cause of the event was the inability to return EDG "B" to operable status within the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> required action completion time allowed by LCO 3.8.1 condition "B.
The root cause of the EDG "B" voltage anomalies was a failed Automatic Voltage Regulator (AVR) (EIIS code: EK, DG, RG). The AVR manufacturer is NEI Peebles/Portec, model number 72-08300-100.
The engineering action plan to troubleshoot the voltage anomalies attempted to first rule out possible causes not associated with the AVR in part because replacement of the AVR would require post maintenance load rejection surveillance testing in accordance with Technical Specification Surveillance Requirement (SR) 3.8.1.9. Performance of this surveillance is prohibited in Modes 1 through 4.
7. CORRECTIVE ACTIONS:
On August 12, 2005 the reactor was manually shutdown. The AVR on EDG "B" was replaced and all retests were completed satisfactorily. On August 14, 2005, at 1232, EDG "B" was returned to operable status.
A significant investigation into the EDG "B" voltage anomalies is currently in progress. If results from the significant investigation identify substantial information that would change the reader's perception of the event or corrective actions described in this LER, a supplemental LER will be submitted.
8. PREVIOUS SIMILAR EVENTS:
In the past three years, Palo Verde reported reactor shutdowns required by Technical Specifications but none associated with the same root cause.