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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 45628 | 13 January 2010 19:25:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Wrong Train of Emergency Core Cooling System Removed from Service | On January 13, 2010, at about 1125 PST, Train A suction piping from the SONGS Unit 3 Refueling Water Storage Tank (RWST) was determined to be inoperable following detection of weld flaw indications during ultrasonic testing. Due to miscommunication, operators mistakenly declared the Train B Emergency Core Cooling System (ECCS) header inoperable at about 1125 and removed DC control power to the Train B ECCS pumps. This resulted in both trains of Unit 3 ECCS being inoperable and entry into the Technical Specification (TS) 3.0.3 one-hour shut down action. At 1140 PST, the DC control power was restored to the Train B ECCS pumps, Train B ECCS was declared operable, and TS 3.0.3 was exited. SCE is reporting this in accordance with 10 CFR 50.72(b)(3)(v) as an event that could have prevented the fulfillment of a safety function. SCE is further evaluating the indications found on Train A piping to determine if the piping is capable of performing its safety function. At the time of this occurrence, Unit 2 was in a Steam Generator Replacement Outage, and Unit 3 was at approximately 100% power. The licensee notified the NRC Resident Inspector.
On January 13, 2010, SCE reported that both trains of Unit 3 Emergency Core Cooling System were inoperable for approximately 15 minutes because Train B ECCS was mistakenly taken out of service when weld flaw indications were found on Train A ECCS piping. This resulted in a condition that could have prevented the fulfillment of a safety function. Consequently, both trains of ECCS in Unit 3 were declared inoperable and the unit entered into Technical Specification 3.0.3 at 1134 PST (Time of Discovery). At 1140 PST, Train B ECCS was declared operable and TS 3.0.3 was exited. Event Notification 45628 was conservatively made because, although Train A ECCS piping remained capable of performing its safety function, this was not yet formally documented at the time the 8-hour report was due. Subsequently, an engineering evaluation was completed at 2308 PST on January 13, 2010, that demonstrates the as-found condition of the Train A ECCS piping was operable because the flaw meets the evaluation criteria of ASME Boiler and Pressure Vessel Code Case N-513-2. Since Train A ECCS piping was operable, this event did not constitute a condition that could have prevented the fulfillment of a safety function and is not reportable under 10 CFR 50.72(b)(3)(v)(D). Consequently, SCE is retracting the phone report to the NRC on January 13, 2010. The NRC Resident Inspector will be informed of this report. Notified R4DO (Werner). | Steam Generator Emergency Core Cooling System | |
| ENS 44247 | 29 May 2008 18:36:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Offsite Power Below 59.7 Hz | On May 29, 2008, at approximately 1136 PDT, the offsite power grid connected to San Onofre experienced a momentary system disturbance. Control Room indicators alerted Operators that the grid frequency dipped to approximately 59.6 Hz. Because frequency dipped below 59.7 Hz, SCE is reporting this event in accordance with 10CFR50.72(b)(3)(v)(D). The frequency dip lasted approximately 10 seconds, reportedly due to a loss of generation in the Pacific Northwest. The grid is currently operating at nominal frequency. At the time of the event, San Onofre Unit 2 was operating in Mode 1 at approximately 99 percent power and Unit 3 was operating in Mode 1 at approximately 80 percent power. The NRC Resident Inspector has been notified of this event and will be provided a copy of this report. | ||
| ENS 44227 | 20 May 2008 20:10:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Offsite Power Grid Disturbance | On Tuesday, May 20, 2008, at approximately 1310 PDT, the offsite power grid connected to San Onofre experienced a momentary system disturbance. Control Room indicators alerted Operators that the grid frequency dipped to approximately 59.69 Hz. Because frequency dipped below 59.7 Hz, SCE is reporting this event in accordance with 10CFR50.72(b)(3)(v)(D). The frequency dip lasted approximately 10 seconds, reportedly due to a high voltage DC transmission line disturbance in Oregon. The grid is currently operating at nominal frequency. At the time of the event, San Onofre Unit 2 was operating in Mode 1 at approximately 99 percent power and Unit 3 was operating in Mode 1 at approximately 80 percent power. The NRC Senior Resident Inspector has been notified of this event and provided a copy of this report. | ||
| ENS 42310 | 4 February 2006 02:15:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Offsite Power Not within Specifications | On February 3, 2006, at about 1646 PST the Devers-Palo Verde line relayed. This required an evaluation of grid nomograms for San Onofre. At about 1815 PST, the Grid Control Center (GCC) notified San Onofre that the grid nomograms predicted offsite power would not be within limits if San Onofre Unit 3 were to trip (San Onofre Unit 2 is currently shutdown in a refueling outage and Unit 3 is operating at about 100 percent power). Plant Operators declared offsite power inoperable at about 1815 PST. At about 1843 PST, the GCC notified San Onofre that the grid operator added generation to the grid and that offsite power was within nomogram limits. Plant Operators declared offsite power operable at that time. Consistent with the guidance provided in NUREG-1022, Rev. 2, Southern California Edison is reporting this event in accordance with 10CFR50.72(b)(3)(v)(D). All four San Onofre diesel generators (two per Unit) remained operable during this event. The San Onofre Senior Resident Inspector has been notified of this event and will be provided with a copy of this report. | ||
| ENS 41798 | 26 June 2005 11:17:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Edg Inoperable Due to Loose Electrical Connection | On June 25, 2005, at about 1335 PDT, during a test of Unit 3 Emergency Diesel Generator (EDG) 3G003, Emergency Supply Fan 3A276 did not start. SCE's investigation found a loose electrical connection at the thermal overload auxiliary switch contact for that fan. A similar condition was found on Emergency Supply Fan 3A277. SCE declared 3G003 inoperable and initiated a common cause investigation required by the EDG Technical Specifications. SCE tightened the affected electrical connections and after successfully start testing 3G003, declared 3G003 operable at 0406 PDT on June 26, 2005. On June 26, 2005, at about 0417 PDT, SCE found similar loose connections for EDG 3G002. Components affected were the EDG radiator fan and an EDG Emergency Supply Fan. Because SCE could not conclusively determine if the loose connections would have caused 3G002 to be inoperable, SCE conservatively declared 3G002 inoperable. (SCE currently plans to start test the Unit 2 EDGs today to confirm the Unit 2 EDGs remain operable.) Because it appears that both Unit 3 EDGs could have been inoperable at the same time, SCE is reporting this occurrence in accordance with 10CFR50.72(b)(3)(v)(D) as an event or condition that could have prevented fulfillment of a safety function. At the time of this occurrence, Unit 2 was operating at about 99 percent power and Unit 3 was at about 100 percent power. SCE has notified the NRC Resident Inspectors about this occurrence and will provide them with a copy of this report.
On June 26, 2005, SCE reported to the NRC that both Unit 3 emergency Diesel Generators (EDGs) were conservatively declared inoperable at the same time. SCE reported that occurrence to the NRC in accordance with 10CFR50.72(b)(3)(v)(D) for the loss of a safety function. SCE has since determined that both EDGs were operable in the as found condition and that a report to the NRC was not required and SCE is retracting that report. For EDG 3G003, even though one of two emergency supply fans did not function, SCE confirmed by calculation that the remaining emergency supply fan was sufficient. That is, 3G003 was capable of performing its specified safety function with only one emergency supply fan operating. For EDG 3G002, the electrical connections that were reported to be 'loose' did not prevent circuit continuity and did not degrade the operability of the EDG. 3G002, therefore remained operable. Because the EDGs were operable, no report was required. SCE is retracting the June 26, 2005 report. SCE will, however, submit a voluntary licensee event report to document this event and inform the NRC of the corrective actions taken. At the time of this phone call, Unit 2 was operating at about 99 percent power and Unit 3 was at about 100 percent power. SCE has notified the NRC resident inspectors about this retraction and will provide them with a copy of this report. R4DO (Smith) was notified. | Emergency Diesel Generator | |
| ENS 40818 | 14 June 2004 14:41:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Licensee Declared Offsite Power Inoperable Due to Dip in Grid Frequency | On June 14, 2004 at 0741 PDT, the offsite power grid connected to San Onofre experienced a system disturbance. Grid frequency dipped to about 59.7 Hz or slightly lower, and then recovered about three minutes later. Plant Operators declared offsite power inoperable. Southern California Edison is conservatively reporting this event in accordance with 10 CFR 50.72(b)(3)(v)(D). The diesel generators for both Units 2 and 3 were operable during this event. At the time of this report, Units 2 and 3 continue to operate at about 100% power. The NRC Resident Inspector was notified. NOTE: see events 40814, 40815 and 40816 |