Semantic search
| Entered date | Event description | |
|---|---|---|
| ENS 49634 | 14 December 2013 19:32:00 | At 1503 PST on December 14, 2013, Pacific Gas and Electric Company identified that, if atmospheric conditions were to develop that had both sustained high winds exceeding 60 miles per hour from the NW to NNE direction, and ambient air temperature exceeding 97 degrees Fahrenheit, the combination of these conditions could result in inadequate heat removal to support continuous operation of the Unit 1 emergency diesel generators. Upon identification of this condition, shift orders were issued requiring implementation of existing procedural guidance to open plant doors to allow additional air flow that would provide adequate emergency diesel generator cooling to support continuous operation of the U1 emergency diesel generators. This report addresses a condition as described in 10 CFR 50.72(b)(3)(ii)(B). The NRC Resident Inspector has been notified of this condition. This condition was discovered during a license basis verification review. |
| ENS 49184 | 10 July 2013 16:13:00 | On July 10, 2013, at 0950 PDT, the Diablo Canyon Power Plant Unit 2 500kV line differential relay actuated. This action tripped the turbine and opened the generator output breakers to isolate the generator. With the turbine tripped and Unit 2 operating above the P-9 50% power permissive, a reactor trip was initiated from the reactor protection system. All plant equipment responded as designed. All three Unit 2 Auxiliary Feedwater pumps started, the Containment Fan Cooling units started and ran in slow speed, and the standby Auxiliary Saltwater train started, all as expected. Unit 2 is stable at normal operating temperature and pressure. All power transferred to the plant startup source without incident. Condenser vacuum was maintained. The preliminary cause of the differential relay actuation was a flashover of Phase A 500 kV to ground across the Phase A lightning arrestor during maintenance activities to wash the 500 kV insulators. NRC Resident Inspector has been informed of this event. A press release is planned for local media. Decay heat is being removed by steam dumps to the condenser. No relief valves lifted during the transient. The steam generators are being supplied by the auxiliary feedwater pumps. There were no injuries to personnel. Unit 1 was not affected. |
| ENS 48819 | 13 March 2013 00:58:00 | On March 12, 2013, at 1706 PDT, with the reactor coolant system not intact, plant operators identified (an) unexpected increase in nuclear reactivity count rate as indicated by source range instrumentation channel N-32. This increase was NOT indicated on redundant wide range instrumentation channels N-51 and N-52. Operators identified that technicians working in the area of the N-32 cable routing had bumped the cabling, resulting in the false increase in the count rate. The source range channel N-32 was subsequently declared inoperable. Prior to this event the other source range channel N-31 had been declared inoperable. The above event resulted in loss of control room audible indication required by DCPP (Diablo Canyon Power Plant) technical specification to monitor the core reactivity condition and consequently caused loss of the monitoring system. Operators retained capability of monitoring core reactivity conditions through use of the two wide range nuclear instrumentation channels N-51 and N-52. In response to this concern, plant operators verified all core alterations were suspended, verified boron concentration was within acceptable limits for current conditions, suspended operations that could dilute the boron concentration, verified reactor trip breakers were open and control rods incapable of withdrawal, and initiated actions to restore to service one of the source range instrumentation channels with its associated control room audible count rate indication. NRC Resident Inspectors have been notified.
This is an update to EN #48819 reported on March 12, 2013 at 2158 PDT. This update informs the NRC that PG&E, in accordance with provisions of TS 3.0.4b, will be restoring the source range instrumentation channel N-32 to service in Mode 5, maintaining the availability and monitoring of the wide range instrumentation channels while in Mode 5 until the source range channel is returned to service. The licensee has notified the NRC Resident Inspector. Notified R4DO (Powers). |
| ENS 48400 | 11 October 2012 18:44:00 | On October 11, 2012, at 1208 PDT, the Diablo Canyon Power Plant Unit 2 500kV line differential relay actuated, resulting in a unit trip. The unit trip actuated the turbine trip. With the turbine tripped and Unit 2 operating above the P-9 50% power permissive, a reactor trip was initiated from the reactor protection system. All plant equipment responded as designed. Unit 2 is stable at normal operating temperature and pressure. All power transferred to the plant startup source without incident. Condenser vacuum was maintained. The cause of the differential relay actuation is under investigation. Based on personnel observation it appears to have been initiated due to a flashover to ground across the phase 'A' main bank transformer capacitive coupled voltage transformer. PG&E will issue a press release regarding the Unit 2 trip. NRC Resident Inspectors have been informed of this event.
This update to clarify the status of the auxiliary feedwater system during the above noted transient. Both motor driven pumps and the steam driven pump automatically started as expected. In addition, on October 11, 2012, at 12:26 PDT, the Diablo Canyon Power Plant Unit 2 turbine driven auxiliary feedwater pump was secured by plant operators manually closing the steam supply valve to the pump turbine. This action was performed in accordance with plant operating procedures after the operators had verified that the indicated steam generator levels were greater than the procedural requirement of 16%. However, because the steam generator low level bistables associated with the auxiliary feedwater actuation circuits had not yet cleared, the emergency safeguards actuation signal drove the steam supply valve back open, restarting the turbine driven auxiliary feedwater pump. Operators increased steam generator levels to clear the bistables and successfully reclosed the steam supply valve. The NRC Resident Inspector has been informed of this event. Notified R4DO (Hagar). |
| ENS 48002 | 7 June 2012 11:56:00 | 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. |
| ENS 47733 | 12 March 2012 11:51:00 | At 0742 PDT on March 12, 2012, a non-work related on-site fatality occurred at the Diablo Canyon Power Plant. The fatality was not related to the health and safety of the public or on-site personnel. Specifically, a contractor for Pacific Gas and Electric (PG&E) was found in the Engineering Offices before work hours with no pulse or life signs. The individual was promptly attended to by Diablo Canyon Industrial Fire Officers and a transfer to a local hospital by ambulance was completed. The individual was pronounced dead at the hospital. The individual was outside of the Radiological Controlled Area and no radioactive material or contamination was involved . The work location was outside of the Protected Area. PG&E has not observed any heightened public, media, or government concern as a result of the fatality. Because the fatality is unrelated to Diablo Canyon Power Plant industrial or radiological health and safety, no news release is planned. Because the fatality was not work-related, nor the result of an accident, no notification to other government agencies was made at the time. However, PG&E may make a notification to the California Occupational Safety and Health Administration due to a cardiac arrest on-site. Thus this ENS notification is in response to a notification to another government agency in accordance with 10CFR50.72(b)(2)(xi). The deceased person worked for Enercon Services. The licensee notified the NRC Resident Inspector. |
| ENS 47580 | 9 January 2012 23:44:00 | On January 9, 2012, at 1405 (PST), plant personnel notified the Diablo Canyon shift manager that a nut on a hold-down stud on an Independent Spent Fuel Storage Installation(ISFSI) HISTORM spent fuel storage cask was loose to the touch. Plant personnel hand tightened the nut and verified that none of the other 16 casks in the facility had nuts that were loose to the touch. The Diablo Canyon ISFSI design requires that each spent fuel storage cask be installed with the cask compressed against the embedment plate using 16, two-inch diameter, anchor studs. Each stud is pre-loaded to approximately 157,000 lbf. This design ensures the cask will remain stable during a seismic event. A manufacturer's analysis of the stability of the cask with all of the 16 hold down stud nuts installed with no pre-load concluded that the cask would maintain its stability during a seismic event. PG&E has contracted the vendor to re-tension the stud and expect(s) completion (by) 1/13/2012. PG&E will assess the need to verify tension of the remaining studs based on the extent of condition evaluation. Cause of the loose nut has not yet been determined. The NRC Senior Resident Inspector has been informed.
On January 11, 2012, at 1325 PDT, plant personnel notified the Diablo Canyon shift manager that two additional nuts on hold-down studs for other ISFSI HISTORM spent fuel storage casks were discovered to be loose. The two additional nuts (one per cask) were discovered when the full effort of two hands was used on the nuts while performing an extent-of-condition evaluation. All 16 nuts on all 16 casks were tested for tightness using the full effort of two hands (i.e., no pre-load). NRC senior resident inspector has been informed. Notified the R4DO (Powers), NRR EO (Cheok), and NMSS EO (Mohseni).
On February 29, 2012, at 1610 PST, plant personnel notified the Diablo Canyon shift manager that cause analysis of loose nuts on hold-down studs of ISFSI HISTORM spent fuel storage casks determined the cause is not a defect and this occurrence is not reportable. Accordingly, the reporting criteria for Event Notification 47580 is changed from '72.75(c)(1) Non-emergency condition' to 'Voluntary Report.' Pacific Gas and Electric (PG&E) plans to submit a voluntary, written report (licensee event report) to the NRC. PG&E personnel informed the NRC resident inspector. Notified R4DO (Lantz), NRR EO (Lee), and NMSS EO (Rubenstone). |