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| Entered date | Event description | |
|---|---|---|
| ENS 48541 | 28 November 2012 02:38:00 | The control room ventilation system (CRVS) pressurization mode is required to be actuated by a safety injection signal, control room radiation atmosphere air intake, and operator manual actuation in accordance with Technical Specification (TS) 3.3.7. On November 27, 2012 at 2038 hrs. PST, Pacific Gas and Electric Company (PG&E) identified that none of the CRVS four pressurization fans would operate continuously if they started in response to a safety injection or control room radiation atmosphere intake actuation signal. All of the pressurization fans remain capable of continuous operation via manual actuation. At 2050 PST the Unit 2 CRVS was manually placed in pressurization mode in accordance with TS 3.3.7, ACTION B.1.1. This was determined to be caused by a recent flow balancing of the CRVS that raised the static air pressure. The increased system static pressure actuates the fan-run pressure switches for each of the four associated pressurization fans, when only a single pressurization fan is operated. This results in the system logic securing all pressurization fans started by the CRVS automatic actuation signals. If all pressure switches actuate, automatically started pressurization fans will be secured until air pressure decays below the fan-run switch setpoint, at which time the pressurization fan would restart. This would result in cyclic operation of the pressurization fan. The fan-run pressure switches are not part of the manual actuation circuitry for the pressurization fans. Diablo Canyon (DCPP) is making this 8-hour, non-emergency notification under 10 CFR 50.72(b)(3)(v)(D). Plant personnel notified the NRC Resident Inspector. |
| ENS 47564 | 31 December 2011 11:53:00 | On December 31, 2011 at 0200 PST, a plant employee indentified the fire barrier material in each unit was potentially not qualified as a 3 hour rated fire barrier as specified by the Diablo Canyon power plant fire protection program. The fire barrier material in question is installed between the block wall portion of the barrier and the door frames in the walls separating three of the 480 Volt switchgear buses and separating the three vital instrument AC inverters. The condition was discovered by a plant employee who questioned the configuration while performing a routine tour of that area. Operators confirmed existing fire watches were in place and established additional fire watches as compensatory measures as required by the Diablo Canyon fire protection program. A review of the Appendix R fire protection analysis is in progress to confirm the rating of the installed configuration. The licensee has notified the NRC Resident Inspector.
This is an update to EN 47564 reported on 12/31/11 where it was reported that plant personnel had identified rated fire barriers were not qualified as a three hour rated barrier as required by the DCPP Fire Protection Program. On 1/3/12 plant personnel provided barrier design drawings to the manufacturer of the DCPP fireproofing material. The manufacturer reviewed the design detail and confirmed that the barrier design depicted on the drawing is qualified as a 3 hour barrier. Therefore no unanalyzed condition that significantly degraded plant safety existed. This event is being retracted. The licensee notified the NRC Resident Inspector. Notified R4DO (Vasquez). |
| ENS 42822 | 31 August 2006 18:42:00 | On August 31, 2006, licensed plant operators identified that Technical Specification 3.4.13 was not met due to a one to two gallon per minute unidentified reactor coolant system (RCS) leak. Plant Operators initiated a ramp of reactor power to take Unit 2 to mode 3, Hot Standby, at 1409 PDT. A containment entry has been initiated to identify the source of the RCS leak. The estimated restart date is preliminary, pending investigation of the leakage location. The Unit is currently ramping off line at 4-5 MW/min. Current reactor power level is 90% and 937 MW electric. The licensee stated that the suspected source of the leak is the seal table room where radiation levels have risen consistent with the containment leakage. Current unidentified leak rate is 1.3 gpm. The TS limit is 1 gpm. Current coolant activity is 1.88 microCi/ml. A press release is planned to be issued on 9/1/2006. The licensee notified the NRC Resident Inspector.
This is a follow up to the 4 hour notification that was initiated due to initiating a Technical Specification (TS) required shutdown when Technical Specification 3.4.13 was not met. Plant Operators entered containment and identified RCS leakage from one of the thimble tubes in the seal table 10 path. At 1622 on 8/31/06 the leakage was classified as identified leakage. The TS required shut down was stopped at 1623 as the leak rate is less than the TS leak rate limit for identified leakage. Operators have isolated the 10 path by closing the valve and the RCS leakage has stopped. Notified R4DO (Cain), NRR EO (McGinty) via e-mail, IRD MOC (Leach) via e-mail. |