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| Entered date | Event description | |
|---|---|---|
| ENS 48796 | 1 March 2013 04:00:00 | On February 28, 2013, at 2154 PST, Unit 2 4kV ESF Bus G deenergized while attempting a repair to the bus automatic transfer circuitry. The deenergization of 4kV ESF Bus G initiated a start signal to Diesel Generator 2-1, which supplies emergency power to 4kV ESF Bus G. Diesel Generator 2-1 did not start due to being placed in manual control to prevent starting automatically during the repair. However, a valid actuation signal was generated to start Diesel Generator 2-1. As the Diesel Generator was shut down and in manual control, no actuation occurred. This is reportable as a valid system actuation that was not part of a pre-planned sequence during testing. Unit 2 is currently defueled, with the core offloaded into the spent fuel pool. No loss of cooling occurred as spent fuel pool cooling equipment had been selected to unaffected buses. The NRC resident has been notified. |
| ENS 46900 | 27 May 2011 20:12:00 | On May 27, 2011, at 1212 PDT, Unit 1 startup power was lost due to actuation of startup transformer 1-1 overcurrent/differential relay 51-87UT11-1, which isolated the 12 kV feeder to startup bus. The loss of offsite startup power caused all Unit 1 emergency diesel generators (EDGs) to start in the standby mode. The EDGs started as designed with no issues observed. No vital loads were affected as a result of the 12 kV bus loss. On May 27, 2011, at 1241 PDT, all Unit 1 EDGs were shut down and returned to auto. Subsequently, startup transformers 1-1 and 1-2 were energized, followed by the 12 kV underground loop, and on May 27, 2011, at 1337 PDT, Unit 1 startup power was declared operable. The cause of the event was a human performance error while attempting to test the startup transformer 2-1 overcurrent/differential relay. The maintenance electrical worker inadvertently installed a jumper on the overcurrent/differential relay for startup transformer 1-1. Unit 2 startup power was cleared at this time and there was no effect on Unit 2. The NRC Resident Inspector was notified. |
| ENS 45260 | 13 August 2009 17:25:00 | On August 13, 2009, at 1304 PDT, Unit 2 was shut down in accordance with established plant procedures to perform more in-depth analysis of the main electrical transformer 'A' phase 500 kV bushing. Diablo Canyon Unit 2 was taken off line in a planned maintenance outage to investigate a power-factor condition currently identified by the 500 kV bushing monitoring instrumentation. The main electrical transformer 'A' phase 500 kV bushing will be replaced if warranted by the results of testing. The licensee notified the NRC Resident Inspector. |
| ENS 45178 | 30 June 2009 21:49:00 | On June 30, 2009, at 1513 PDT, Unit 2 commenced a ramp(-down) in accordance with the annunciator response guidance to enter Operating Procedure (OP) Abnormal Procedure AP-25 due to loss of forced cooling to main transformer bank (MTB) C-Phase transformer. At 1538, Unit 2 was separated from the grid in accordance with plant OP AP-25 initiation of a main generator unit trip. At 1554 PDT, the Reactor Trip Breakers (RTBs) were manually opened per OP AP-25 Step 24.j. (Reactor) power was being held in Mode 2 at about 3% reactor power per the procedure when the RTBs were opened. The investigation into the cause is continuing. This event is being reported in accordance with 10 CFR 50.72(b)(2)(xi), Offsite Notification, as Pacific Gas and Electric plans to make a news release regarding the event that may raise media interest. The licensee notified the NRC Resident Inspector. |
| ENS 40659 | 8 April 2004 17:02:00 | On April 08, 2004, during the Unit 1 twelfth refueling outage (1R12), analysis of eddy current data on (Steam Generator) SG 1-4 indicated that greater than one percent of the total tubes inspected in SG 1-4 were defective. Approximately ninety (90) defective tubes in SG 1-4 were detected and are being plugged. Most of the pluggable indications are due to circumferential primary water stress corrosion cracking in the Rows 5 to 8 U-bend region. Results of the SG tube inspection fall into Category C-3, which requires a four-hour non-emergency report in accordance with Technical Specification (TS) Table 5.5.9-2 and 10 CFR 50.72(b)(3)(ii) (an 8-hour requirement replacing the former (b)(2)(iii)(C), 4-hour requirement). An NRC teleconference in accordance with TS 5.6.10.d to report the results of the voltage-based repair criteria implemented for the tube support plate intersections is currently scheduled for Wednesday April 14, 2004, at 1300 EDT. A Special Report in accordance with TS 5.6.10.a and e will be submitted prior to returning Unit 1 to power operation. A Licensee Event Report in accordance with 10 CFR 50.73(a)(2)(v)(C) will be submitted within 60 days. The Licensee notified the NRC Resident Inspector. |