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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 54417 | 30 November 2019 19:00:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Both Trains of Containment Spray Removed from Service | On November 30, 2019, at 1100 PST, with Unit 2 in Mode 4, Operations identified that both trains of containment spray had been removed from service earlier at approximately 0217 hours as part of preparations for a planned Mode 5 entry. The containment spray pumps are required to be operable (along with the containment fan cooler units) in Modes 1 through 4 in accordance with Technical Specification 3.6.6. With both containment spray pumps inoperable, TS 3.6.6 Action F requires the Unit to be shut down in accordance with TS 3.0.3. At 1125 hours, both trains of containment spray were returned to operable and the required actions of TS 3.6.6 and TS 3.0.3 were exited. The five containment fan cooler units remained operable for the duration of the occurrence. This notification is being made in accordance with the requirement of 10 CFR 50.72(b)(3)(v) as an event or condition that could have prevented fulfillment of a safety function, and 10 CFR 50.72(b)(3)(ii) as an event or condition that may have resulted in the plant being in an unanalyzed condition. The NRC Senior Resident Inspector has been notified. | Containment Spray | |
| ENS 50711 | 31 December 2014 18:05:00 | 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Through Wall Seepage Affecting Rhr System | At 1105 PST, plant personnel identified through-wall seepage in a Diablo Canyon Power Plant Unit 1 socket weld inside containment that provides a flow path to a relief valve protecting a common portion of both trains of the Residual Heat Removal (RHR) System. The as-found condition falls under the requirements of the ASME acceptance criteria. Unit 1 was already in Mode 3, or offline, due to a planned maintenance outage. PG&E accordingly declared both Unit 1 trains of RHR inoperable and has initiated a transition from Mode 3 to Mode 4 in accordance with requirements of Technical Specification 3.0.3. The licensee notified the NRC Resident Inspector. | Residual Heat Removal | 05000275/LER-2015-001 Both Trains of Residual Heat Removal Inoperable Due to Circumferential Crack on a Socket Weld |
| ENS 49663 | 19 December 2013 15:52:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Two of Three Emergencey Diesel Generators Inoperable at the Same Time | On 12/19/13 Unit 1 Emergency Diesel Generator (EDG) 1-2 was inoperable for scheduled maintenance. During an operational walk-down of the Unit 1 EDG 1-3, the associated fuel oil priming pump discharge fitting and pump housing were inadvertently damaged. Pacific Gas and Electric Company declared EDG 1-3 inoperable on 12/19/13 at 0752 PST. Since both Unit 1 EDGs were inoperable at the same time, this condition is reportable in accordance with 10 CFR 50.72(b)(3)(ii)(B) and 10 CFR 50.72(b)(3)(v)(D). The NRC Senior Resident Inspector has been notified. | Emergency Diesel Generator | |
| ENS 49148 | 26 June 2013 04:58:00 | 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown | Plant Shutdown Required Due to Rhr System Socket Weld Leak | At 2158 PDT, plant personnel identified a through-wall leak in a Diablo Canyon Power Plant Unit 1 socket weld inside containment that provides a flow path to a relief valve that protects a common portion of both trains of the Residual heat Removal (RHR) system. The as-found condition did not comply with the requirements of equipment control guideline 7.6 and the ASME acceptance criteria. PG&E accordingly declared both Unit 1 trains of RHR inoperable and initiated plant shutdown at 2237 PDT in accordance with requirements of Technical Specification 3.0.3. PG&E will complete shutdown to Mode 4 and will perform repairs to restore compliance with ASME code requirements. The licensee notified the NRC Resident Inspector. * * * UPDATE AT 1303 EDT ON 6/26/13 FROM WESLEY FIANT TO PETE SNYDER * * * Pacific Gas and Electric Company is submitting an update based on a press release issued at 0915 PDT detailing the above information to local television, newspaper, and radio media outlets. San Luis Obispo County and State of California Offices of Emergency Services have already been notified. The licensee notified the NRC Resident Inspector. Notified R4DO (Pick). | Residual Heat Removal | |
| ENS 48541 | 28 November 2012 04:38:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Control Room Ventilation System Will Not Automatically Start in Pressurization Mode | 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 48246 | 29 August 2012 00:00:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Mitigating Actions Implemented for Inoperable Control Room Envelope | On August 28, 2012, 17:00 PDT, Pacific Gas and Electric Company (PG&E) identified additional release pathways that could affect the control room (CR) operator dose following a Large-Break Loss-of-Coolant Accident (LBLOCA). Consequently, PG&E declared the control room envelope (CRE) inoperable and is establishing mitigative actions in accordance with TS 3.7.10, Action B.1, 'Initiate action to implement mitigating actions' immediately, and Action B.2, 'Verify mitigating actions ensure CRE occupant exposures to radiological hazards will not exceed limits, and CRE occupants are protected from smoke and chemical hazards' within 24 hours. PG&E is establishing mitigative actions in accordance with TS 3.7.10 and RG 1.196. These mitigative actions are for operations control room personnel to administer potassium iodide and don self-contained breathing apparatus equipment in a timely fashion should a LBLOCA occur. They will be communicated and controlled by a standing order to the control room staff. PG&E previously established controls on other release pathways that offset the potential increases to the maximum predicted offsite dose due to the new release pathways. No increase in maximum predicted offsite dose is expected from the new release pathways. Diablo Canyon (DCPP) is making this 8-hour, non-emergency notification under 10 CFR 50.72(b)(3)(ii)(B) and 10 CFR 50.72(b)(3)(v)(D). Plant personnel notified the NRC Resident Inspector. * * * UPDATE AT 1600 EDT ON 9/8/12 FROM GLEN GOELZER TO PETE SNYDER * * * PG&E is retracting EN 48246, based on the results from a new dose analysis coupled with compensatory measures implemented to ensure that the analysis input parameters and assumption will not be inadvertently exceeded. The analysis concluded that the CRE was operable and that CR doses remained below regulatory limits. Plant personnel notified the NRC resident inspector. Notified R4DO (Gaddy). | Control Room Envelope | |
| ENS 48002 | 7 June 2012 08:29:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Both Trains of Low Temperature Overpressure System Inoperable | On June 7, 2012, at 0129 PDT, both trains of the low temperature overpressure (LTOP) system were rendered inoperable when the vital 120 VAC panel PY-13 was de-energized due to a human performance error. DCPP Unit 1 was in Mode 5, reactor coolant system loops not filled. Technicians were troubleshooting an existing de-energized vital 120 VAC panel PY-14 that had resulted from the supply breaker tripping open. The technician incorrectly opened the supply breaker to panel PY-13 instead of PY-14. With PY-14 de-energized, one train of LTOP was inoperable due to loss of signal from Reactor Coolant System (RCS) wide range pressure transmitter PT-405A. With PY-13 de-energized, the second train of LTOP was rendered inoperable due to loss of signal from RCS wide range pressure transmitter PT-403A. Operations immediately recognized the error and had the technician reclose the PY-13 supply breaker, thereby re-energizing panel PY-13, returning one train of LTOP back to its operable condition. Plant personnel notified the NRC Resident Inspector. | Reactor Coolant System | |
| ENS 46531 | 10 January 2011 21:21:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Both Trains of Auxiliary Building Ventilation Became Inoperable | On January 10, 2011, at 1321 PST, Diablo Canyon Power Plant, Unit 2, entered Technical Specification Limiting Condition of Operation (TS LCO) 3.0.3, when both trains of Auxiliary Building Ventilation System (ABVS) became inoperable following closure of damper M-4 and the ensuing loss of both exhaust fans E-1 and E-2. TS LCO 3.0.3 was exited on January 10, 2011, at 1342 following a status reset and selection of fan E-2. This provided a ventilation flowpath and use of both exhaust fans in the Safeguards mode. Both trains of Auxiliary Building Ventilation are operable. This 8-hour non-emergency report is made pursuant to 10 CFR 50.72(b)(3)(v)(D). The unit is not in a TS LCO. All 3 unit EDG's are operable and offsite power is in the normal lineup. The NRC Resident Inspector has been notified.
On January 13, 2011, at 1603 PST, engineering determined that a single failure design vulnerability exists at Diablo Canyon Power Plant Units 1 and 2. Engineering review of the control logic of the ABVS determined that while in Buildings Only (non-safeguards) alignment or during system realignment from Safeguards Only to Buildings Only alignment, failure of damper M-4A or M-4B (series dampers) could result in the control logic securing both ABVS exhaust fans. This would prevent ABVS actuation on receipt of a valid safeguards actuation signal. When this occurs, a control room alarm is actuated, which requires the operators to reset the control logic from the control room, thereby re-enabling the capability of the ABVS to respond to a safeguards actuation signal. The Unit 2 event on January 10, 2011, at 1321, occurred due to this single failure vulnerability when the control system attempted to restore the ABVS alignment from Safeguards Only to the Buildings Only alignment. This design vulnerability is currently mitigated by maintaining the ABVS in either of the two safeguards alignments (Safeguards Only or Buildings and Safeguards). This single failure design vulnerability is an 8-hour non-emergency report made pursuant to 10CFR50.72(b)(3)(ii)(B) for an event that resulted in the nuclear power plant being in an unanalyzed condition for both Unit 1 and Unit 2. The licensee will notify the NRC Resident Inspector. Notified R4DO (Hagar). | 05000275/LER-2011-002 | |
| ENS 44287 | 11 June 2008 21:05:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Identification of a Potential Issue with Accumulator Drain Valves | On June 11, 2008 at 1405 PDT, licensed plant operators entered Technical Specification (TS) 3.0.3 on Units 1 and 2 due to identification of a potential ASCO solenoid valve failure that could initiate draining if the safety injection system accumulators following a small break Loss-of-Coolant-Accident (LOCA). ASCO Model 8316 and 8321 pilot-operated solenoid valves over 12 years old are susceptible to a potential shuttle ('insert' per vendor documentation) malfunction. The malfunction is that with greater than 12 years of service and a loss of minimum operating pressure differential (MPOD), the shuttle (or insert) could reposition and fail to return to the desired position. This MPOD related reposition could result following instrument air pressure loss and subsequent restoration to containment following a postulated small break LOCA. Diablo Canyon Power Plant (DCPP) Units 1 and 2 each have four susceptible ASCO solenoid valve locations used as drain valves for each of the four safety injection system accumulators per unit. DCPP is reviewing the performance of the ASCO solenoids based on a plant problem report and subsequent discussion with the vendor. The safety significance of this event is low as there was no actual accumulator drain valve failure. Although PG&E is still evaluating the potential degradation mechanism and failure mode of these valves, TS 3.03 was conservatively entered base on the potential for malfunction of these valves. On June 11, 2008, at 1610 PDT licensed plant operators exited TS 3.0.3 following isolation of the suspect accumulator drain lines. A licensee event report will be issued for this event. The NRC Resident Inspector has been notified. | 05000275/LER-2008-001 |