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| Entered date | Event description | |
|---|---|---|
| ENS 48600 | 18 December 2012 02:07:00 | This is a non-emergency notification. At 1804 PST on December 17, 2012, Diablo Canyon Unit 1 experienced a loss of plant vent continuous radiation monitors (RM) and redundant monitors 14/14R, 24/24R, 28/28R and 87. These radiation monitors are credited for Emergency Action Level (EAL) classification in the Diablo Canyon Emergency Plan. This event is reportable per 10 CFR 50.72(b)(3)(xiii) as described in NUREG-1022, Rev. 2. Compensatory measures of periodic sampling have been established in accordance with plant equipment control guidelines. Event classification can be performed by means of the sampling in accordance with plant procedures. Additionally, continuous radiation monitoring of the plant vent remains via high range radiation monitor RM-29. The cause of the loss of radiation monitors is not known at this time. This condition does not affect the health and safety of the public or the operation of the facility. The NRC Resident Inspector was informed.
The licensee determined that the flow element on the sampling pump for the radiation monitors had failed. At 0630 EST, the condition was repaired and the radiation monitors returned to service. R4DO (Whitten) notified. |
| ENS 47865 | 26 April 2012 04:20:00 | On April 25, 2012, at 2227 PDT, Diablo Canyon Power Plant (DCPP) U2 was manually taken offline and the reactor shut down due to an influx of sea salp - a small, jellyfish-like organism - in the intake structure. Operators manually started the auxiliary feedwater pumps in accordance with the plant operating procedures. PG&E will not restart Unit 2 until conditions improve at the intake structure. As previously announced, Unit 1 was safely shut down for a planned refueling and maintenance outage. All systems operated as designed and no unexpected equipment performance issues were noted. The licensee notified the NRC Resident Inspector. The licensee plans on issuing a press release. |
| ENS 47758 | 21 March 2012 13:53:00 | At 0749 PDT on March 21, 2012, during a training scenario in the plant simulator, plant personnel inadvertently issued an Alert notification for Diablo Canyon Power Plant (DCPP), Unit 1. This Alert should be disregarded. The Alert was issued as a loss of the Unit 1 fuel cladding barrier with no radioactive release. There is no Alert declaration at DCPP Units 1 or 2, and both units are operating normally. DCPP contacted notified parties to clarify that the Alert notification was inadvertent. DCPP is making this 4-hr, non-emergency notification under 10 CFR 50.72(b)(2)(xi) as a situation for which an (inadvertent) notification to other government agencies has been made. The licensee is investigating this inadvertent notification but believes that the notification system was still set up from the emergency plan drill which was conducted last week. The licensee notified the NRC Resident Inspector, San Luis Obispo County, and the State. |
| ENS 47414 | 3 November 2011 23:51:00 | On November 3, 2011, at 1550 PDT, operators determined that control room ventilation system (CRVS) contained a single failure vulnerability whereby unfiltered air supplied to the control room could exceed the flowrates used in the licensing basis analyses of design basis accident (DBA) consequences. This vulnerability was discovered during performance of control room inleakage testing required by TS SR 3.7.10.5. It was determined that the control room pressurization system airflow could bypass the supply filter if the CRVS booster fan in the associated train was not operating. This would allow as much as 800 cubic feet per minute of unfiltered air to be delivered to the control room following an accident that results in initiation of the CRVS pressurization mode. Operators would correct the condition approximately 10 minutes after a safety injection by manually selecting the train's redundant booster fan in accordance with existing proceduralized actions specified in the DCPP emergency procedure E-0 Appendix E. This period of unfiltered air supply to the control room due to a single failure of a CRVS booster fan had not been previously analyzed and could have potentially resulted in operator dose greater than contained in plant analyses. Plant staff verified that all components and redundant components in each ventilation train are currently OPERABLE. Plant staff has implemented additional compensatory measures by issuing a shift order to require that TS Action 3.7.10.A be entered for unavailability of either of the two CRVS booster fans in each CRVS train. Additionally, evaluation of the new unfiltered inleakage may result in more restrictive administrative controls to ensure operator doses are maintained less than the FSAR accident analyses. The licensee informed the NRC Resident Inspector. |