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 Entered dateSiteScramRegionReactor typeEvent description
ENS 537641 December 2018 16:56:00Diablo CanyonAutomatic ScramNRC Region 4At 1006 (PST), on December 1, 2018, with Unit 2 at 100 percent power, the reactor automatically tripped due to a load rejection from the 500 kV offsite electrical system. Operations responded and stabilized the plant. Decay heat is being removed by the Main Steam system to the main condenser using the steam dump valves. The cause of the load rejection is currently under investigation. Due to the Reactor Protection System actuation while critical, this event is being reported as a four-hour, non-emergency notification per 10 CFR 50.72(b)(2)(iv)(B). Additionally, due to the actuation of the Auxiliary Feedwater System, as expected, this event is being reported per 10 CFR 50.72(b)(3)(iv)(A). There was no impact on the health and safety of the public or plant personnel. The NRC Senior Resident Inspector was notified. A press release is planned for this event. All control rods fully inserted and the trip was uncomplicated. There was no effect on Unit 1.
ENS 4840011 October 2012 18:44:00Diablo CanyonAutomatic ScramNRC Region 4Westinghouse PWR 4-Loop

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.

  • * * UPDATE FROM DAN STERMER TO DONG PARK AT 2259 EDT ON 10/11/12 * * *

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 4839510 October 2012 00:32:00Diablo CanyonManual ScramNRC Region 4Westinghouse PWR 4-Loop

On 10/9/12, at 16:30 PDT control room operators were questioned whether recently identified fire protection program deficiencies should have been reported to the NRC. On October 3 and October 8, 2012, DCPP (Diablo Canyon Power Plant) staff reviewing NFPA 805 Nuclear Safety Capability Assessment (NSCA) Variance From Deterministic Requirements (VFDRs) identified fire areas that neither conformed to Appendix R requirements nor had established, proceduralized and practiced compensatory measures in place. The issues were identified in the DCPP corrective action program and compensatory measures were established in accordance with the DCPP fire protection program requirements. Event: 10/3/12 Fire areas containing cables associated with startup transformers 1-2 and 2-2 could result in loss of startup power and also prevent the emergency diesels from performing their Appendix R safe shutdown function. Event: 10/8/12 Fire areas containing reactor coolant pump (RCP) breakers could result in loss of RCP seal cooling and prevent the credited local manual trip of the RCPs, contrary to the specified method of performing the Appendix R safe shutdown function. Event: 10/8/12 Fire areas containing cables for the ventilation systems of the 480V switchgear, DC panels, and battery chargers could require unproceduralized use of portable fans to maintain adequate cooling of the electrical equipment necessary to perform the Appendix R safe shutdown function. Operators established fire watches as compensatory measures as required by the DCPP fire protection program requirements. The above late notification of discovery of the unanalyzed conditions has been entered into the DCPP corrective action program. NRC Resident Inspector has been notified.

          • UPDATE AT 0028 EDT ON 11/01/12 FROM GLENN GOELZER TO S. SANDIN*****

This is an update to EN #48395 reported on October 10, 2012, at 0032 EDT. During the NRC's Fire Protection Triennial Inspection the NRC identified that several Alternate Compensatory Measures (ACMs) were not in the current post-fire procedure CP M-10. The ACMs address potential Appendix R non-conformance issues identified via the initiative to convert the DCPP fire protection program to NFPA 805. PG&E has established compensatory measures for all the identified areas in accordance with the DCPP fire protection program requirements. (The) NRC Resident Inspector has been notified. Notified R4DO (Deese).

  • * * UPDATE FROM D. BAHNER TO V. KLCO ON 11/30/12 AT 1618 EST * * *

This is an update to EN #48395 reported on October 9, 2012, at 2132 PST. During the ongoing evaluation of the issues previously identified in this event notification, PG&E (Pacific Gas & Electric) has concluded that a fire in the fire areas containing cables associated with startup transformers 1-2 and 2-2 would not result in loss of startup power or prevent the emergency diesels from performing their Appendix R safe shutdown function. This issue was reported as an unanalyzed condition. However, it is analyzed and controlled in plant procedure CP M-10, 'Fire Protection of Safe Shutdown Equipment.' PG&E retracts the initial event documented on October 3, 2012, thus making the date on which the first unanalyzed condition was discovered October 8, 2012. Therefore, PG&E will submit the 60-day Licensee Event Report by December 7, 2012. The NRC Resident Inspector has been notified. Notified the R4DO(Whitten).

  • * * UPDATE AT 1944 EST ON 1/30/13 FROM KLINE TO TEAL* * *

This is an update to EN #48395 reported on October 9, 2012, at 2132 PDT. On October 31, 2012, at 2128 PDT, PG&E provided an update to this event notification identifying that several alternate compensatory measures (ACMs) were not in plant procedure, CP M-10, 'Fire Protection of Safe Shutdown Equipment.' PG&E has evaluated this further and concluded that ACMs had been adequately implemented in CP M-10, and therefore retracts the EN update of (November 1, 2012 at 0028 EDT). NRC resident inspector has been notified. Notified R4DO (Walker).

ENS 4670126 March 2011 21:10:00Diablo CanyonManual ScramNRC Region 4Westinghouse PWR 4-LoopThis notification provides the 4-hour non-emergency event report for the manual reactor trip of Diablo Canyon Power Plant Unit 2 in accordance with 10 CFR 50.72(b)(2)(iv)(B) 'RPS Actuation (scram)'. Additionally, this notification provides the 8-hour non-emergency event report of the automatic actuation of the auxiliary feedwater system as a result of the reactor trip in accordance with 10 CFR 50.72(b)(3)(iv)(A) 'Specified System Actuation'. On March 26, 2011 at 1449 PDT operators at Diablo Canyon Power Plant Unit 2 manually initiated a reactor trip in response to loss of main feedwater pump 2-1. The main feedwater pump is believed to have tripped due to non-radioactive water spray on its control console. The water spray was caused by leakage from the flange of the relief valve on the feedwater heater 2-1A condenser dump valve line. Emergency plan activation was not required. The unit is stable in mode 3 (Hot Standby) with offsite power being supplied to all buses via the 230 kV startup circuit. Diesel generators 2-1 and 2-2 remain OPERABLE in standby. Diesel generator 2-3 remains unavailable due to pre-planned maintenance. All rods fully inserted on the reactor trip. The reactor is being cooled by the auxiliary feedwater system with the condenser in service. All systems performed as designed with no unexpected pressure or level transients. ECCS actuation was not required. Automatic main feedwater isolation, auxiliary feedwater actuation, and steam generator blowdown isolation occurred as expected. Unit 1 was unaffected by this event and remains at 100% power. The licensee has notified the NRC Resident Inspector, San Luis Obispo County, and the State of California.
ENS 4517830 June 2009 21:49:00Diablo CanyonManual ScramNRC Region 4Westinghouse PWR 4-LoopOn 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 4458822 October 2008 01:44:00Diablo CanyonManual ScramNRC Region 4Westinghouse PWR 4-Loop

On October 21, 2008, with both units operating at 100% power, Operators manually actuated the Unit 2 reactor protection system (RPS/reactor trip) due to high differential pressure (DP) across the circulating water pumps' intake traveling screens. The high DP resulted from a rapid influx of jellyfish. All systems responded as designed. All control rods fully inserted. Auxiliary feedwater actuated as designed. The grid is stable with power being supplied by 230 Kv startup power. Diesel generator (DG) 2-2 and 2-3 are operable in standby. DG 2-1 is inoperable due to scheduled maintenance. The traveling screens for the safety-related auxiliary saltwater system (ASW) are not degraded and are managing the influx of jellyfish with no significantly elevated DP. Unit 2 is stable in Mode 3 at normal operating temperature and pressure. This event is being reported in accordance with 10 CFR 50.72(b)(2)(iv)(B), 'RPS actuation,' and 50.72(b)(3)(iv)(A), 'Specified System Actuation.' Operators reduced power on Unit 1 in response to the potential loss of normal flow to the condenser due to the jellyfish influx on the traveling screens. Currently, the traveling screens are maintaining DP within limits and the unit is stable at 50% power. Unit 2 decay heat removal is being performed by Auxiliary Feed Water to four steam generators blowing down via the 10% steam dumps to atmosphere. No other safety related equipment was out of service at the time of the trip. The licensee notified the NRC Resident Inspector.

  • * * UPDATE PROVIDED BY JOHN WHESTLER TO JASON KOZAL ON 10/22/08 AT 0726 * * *

The licensee issued a press release regarding this issue. Notified R4DO (Deese).

ENS 4441917 August 2008 03:37:00Diablo CanyonAutomatic ScramNRC Region 4Westinghouse PWR 4-Loop

At 0012 the licensee declared a Notice of Unusual Event due to a fire in Main Bank Transformer. The licensee is fighting the fire along with offsite assistance from CAL FIRE. The unit is shutdown and stable in mode 3. All control rods fully inserted on the trip. Decay heat is being removed via auxiliary feedwater to the steam generators steaming to the main condenser via the main condenser steam dumps. Emergency buses remain powered via offsite power with emergency diesel generators available if required. The licensee will notify the NRC Resident Inspector. Notified DHS (Barnes), FEMA (Blankenship).

* * * UPDATE FROM J. DILLIS TO J. KOZAL AT 0501 EDT ON 8/17/08 * * * 

The fire is out. Plant personnel are assessing the damage in the main transformer area. The plant is stable in mode 3. The licensee will notify the NRC Resident Inspector.

* * * UPDATE FROM J. DILLIS TO P. SNYDER AT 0542 EDT ON 8/17/08 * * * 

The licensee has terminated the Notice of Unusual Event at 0231 PDT due to the fact that the fire was out and no reflash occurred. The plant remains stable in mode 3. The licensee will notify the NRC Resident Inspector. Notified R4DO (Lantz), IRD (McMurtray), NRR EO (Wermiel), R4 (Collins), NRR (Grobe), DHS (Wallace), FEMA (Biscoe).

  • * * UPDATE FROM M. KENNEDY TO J. KOZAL AT 1038 EDT ON 8/17/08 * * *

This is an update of the Notification of Unusual Event due to Fire in the 'C' phase of the main bank transformer, and Automatic Reactor Trip. This update is to report automatic actuation of the auxiliary feedwater system (AFW) and is being reported as an 8-hour non-emergency event in accordance with 10 CFR 50.72(b)(3)(iv)(A) 'System Actuation.' The unit is stable in mode 3 (Hot Standby) with offsite power being supplied to all buses via the 230 Kv startup circuit. All rods fully inserted on the reactor trip. All systems performed as designed. Operators are preparing to place the unit in Mode 5, while preparing to assess the damage to the 500 Kv transformer. All emergency diesel generators remain operable in standby. Unit 1 was unaffected by this event and remains at 100% power. This notification also constitutes a late 4 hour notification for the RPS actuation. To summarize, on August 16, 2008, at 2356 PDT, the 'C' phase 500 Kv transformer failed resulting in a fire and an automatic reactor trip, and automatic actuation of AFW. An unusual event was declared on August 17, 2008, at 0012 PDT due to the fire. Cal Fire was called to assist and support the on-site fire brigade. The fire was extinguished and the NUE was downgraded at 0231 PDT. The NRC Resident Inspector has been notified as well as State and local government agencies. The licensee intends to issue a press release. R4DO (Lantz) notified.

ENS 4339127 May 2007 18:08:00Diablo CanyonManual ScramNRC Region 4Westinghouse PWR 4-Loop

On May 27, 2007, at 11:17 PDT, with Diablo Canyon Power Plant (DCPP) Unit 1 in Mode 3 (Hot Standby) during day 28 of refueling outage 14, operators manually actuated the reactor protection system. All rods fully inserted. Operators were performing Surveillance Test Procedure (STP) R-1 C 'Digital Rod Position Indictor Functional Test'. While control bank C was being re-inserted, at 42 steps withdrawn, rod N-13 indicated position changed to 24 steps withdrawn. In response to this 18 step deviation, and in accordance with STP R-1C, operators opened the reactor trip breakers. At the time of the event, the reactor coolant system remained at normal operating temperature and pressure, and all other shutdown and control rod banks remained fully inserted. This event is being reported as an 8-hour non-emergency event in accordance with 10 CFR 50.72(b)(3)(iv)(A) for a valid actuation of the reactor protection system. Unit-1 is maintaining temperature with atmospheric steam dumps and aux feed water. Electrical power is from 500 KV backfeed (normal electrical shutdown lineup). Control rod N-13 was being tested along with seven other control rods. The licensee notified the NRC Resident Inspector.

  • * * UPDATE ON 05/27/07 AT 2301 EDT BY JOY SKAGGS TO MACKINNON * * *

(STP) R-1C 'Digital Position Indicator Functional Test' was re-performed on control bank C to obtain additional information. At 1706 hours, while control bank C was being re-inserted, at 138 steps withdrawn, rod N-13 indication dropped to 126 steps withdrawn. Rod motion was stopped to gather data. All other shutdown and control banks remained fully inserted. At 1725 hours, operators manually actuated a reactor trip to fully insert all control bank C rods. All rods fully inserted. (STP) R-1C 'Digital Rod Position Indicator Functional Test' was re-performed on control bank C for further evaluation. At 1838 hours, while control bank C was being re-inserted, at 168 steps withdrawn, rod N-13 indication dropped to 150 steps withdrawn. Rod motion was stopped to gather data. All other shutdown and control banks remained fully inserted. At 1840 hours, operators manually actuated a reactor trip to fully insert all control bank C rods. All rods fully inserted. At the time of the event, the reactor coolant system remained at normal operating temperature and pressure, and all other shutdown and control rod banks remained fully inserted." R4DO (C. Johnson) notified. The licensee will notify the NRC Resident Inspector.

  • * * UPDATE PROVIDED BY LARRY PARKER TO JEFF ROTTON AT 0951 EDT ON 05/31/07 * * *

On May 27, 2007, in response to the initial occurrence of Rod N-13 slipping at 11:17 PDT, PG&E contacted the vendor and researched operating experience to develop a troubleshooting plan. Management approved a plan based on the vendor recommendations, which consisted of exercising all rods successfully five cycles. It was acknowledged that additional slipping events could occur requiring mitigation by opening the reactor trip breakers. Upon implementation of this plan, two similar events occurred and are described in the update above (provided on 05/27 at 2301 EDT). Following these events, Rod N-13 was successfully cycled five times without any deviation. Reactor startup was then allowed to proceed and there have been no further rod position deviation events. The licensee notified the NRC Resident Inspector. Notified R4DO (C. Cain)

ENS 4304712 December 2006 16:59:00Diablo CanyonAutomatic ScramNRC Region 4Westinghouse PWR 4-Loop

On December 12, 2006, at 1322 PST, while conducting power ascension operations with Unit 2 at approximately 25 percent power, an electrical failure occurred in the Unit 2 circulating water pump motor enclosure (CWP) 2-1. A loud bang and explosion was reported to the Unit 2 control room. At 1322 PST, an electrical transient was experienced on Unit 2 12-Kv non-vital bus 'D' which in turn caused reactor coolant pump (RCP) 2-2 and RCP 2-4 motor breakers to trip on 12kV non-vital bus 'D' undervoltage, initiating an automatic reactor trip. The reactor trip signal was initiated when 2 out of 4 RCP motor breakers opened. All control rods fully inserted in response to the reactor trip and all plant systems functioned as required. The auxiliary feedwater system for Unit 2 was manually actuated per plant procedures, before an auto-start signal for this system was generated. At 1356 PST, DCPP Fire Department first responders reported that the fire was out. At 1340 the licensee declared a Notice of Unusual Event (NUE), number 23, 'Confirmed Explosion Onsite'. Decay heat is being removed via auxiliary feedwater to the steam generators steaming to the atmospheric dump valves. Emergency power is being supplied via offsite power. The NRC resident inspector has been informed and was onsite at the time of the Unit 2 reactor trip. Diablo Canyon Power Plant (DCPP) Unit 2 is presently in Mode 3. There were no injuries associated with this event. Investigations into the electrical transient are ongoing. DCPP Unit 2 will remain in Mode 3 pending the results of this investigation. An estimated restart of DCPP Unit 2 is not known at this time. DCPP Unit 1 is unaffected and remains in Mode 1 at 100% power.

* * * UPDATE AT 1730 EST ON 12/12/06 FROM T. CHITWOOD TO P. SNYDER * * *

The licensee terminated the Unusual Event at 1430 PST. The Notice of Unusual Event was terminated due to the fact the licensee assessed the damage to the circulating water pump and determined that the explosion was caused by a breaker in the local area. The licensee fire brigade was satisfied that the fire was extinguished and that the damage was confined to the local area of circulating water pump 2-1. The licensee notified the NRC Resident Inspector. Notified the R4DO (Smith), NRR EO (Highland), IRD (Wilson), DHS (Inzer), and FEMA (Discoe).

* * * UPDATE AT 1841 EST ON 12/12/06 FROM T. CHITWOOD TO J. ROTTON * * *

The licensee provided an update to make the formal 4 hour notification pursuant to 10 CFR 50.72 (b)(2)(iv)(B) due to the RPS actuation while critical, and the formal 8 hour notification pursuant to 10 CFR 50.72 (b)(3)(iv)(A) due to the actuation of the auxiliary feedwater system. The licensee notified the NRC Resident Inspector. Notified the R4DO (Smith), and NRR EO (Highland).

ENS 4304211 December 2006 00:31:00Diablo CanyonManual ScramNRC Region 4Westinghouse PWR 4-Loop

On December 10, 2006, at 1608 PST, operators manually tripped the reactor while it was subcritical. This is an 8 hour notification per 10 CFR 50.72(b)(3)(iv)(A) for actuation of the reactor protection system while subcritical. On December 10, 2006, with Unit 2 operating in Mode 1 at 100% power, operators initiated an unplanned reactor shutdown due to indications of increasing stator temperature on reactor coolant pump 2-2. In accordance with plant procedures, when the reactor coolant pump stator temperature reached 300 degrees Fahrenheit, operators manually tripped the reactor and tripped the coolant pump 2-2. The reactor was subcritical at the time of the reactor trip but all rods had not been fully inserted. All control rods fully inserted in response to the reactor trip and all systems functioned as required. The auxiliary feedwater system was already in service as part of the shutdown. The grid is stable and with the exception of RCP 2-2, all major equipment including the 3 emergency diesel generators remain operable. Unit 2 electrical loads are being supplied by the normal startup power. The other 3 RCPs are maintaining forced circulation of the reactor coolant system. Investigations into the high RCP stator temperature are ongoing, the unit will remain in Mode 3 pending the results of these investigations. An estimated restart date is not known at this time. The NRC Resident Inspector has been informed and was onsite at the time of the trip. Unit 1 is unaffected and remains in Mode 1. The licensee stated that a press release related to this event is likely.

  • * * UPDATE TO HUFFMAN DURING PLANT STATUS ON 12/11/06 AT 0419 EST * * *

Licensee believes the cause of the high RCP stator temperature was due to a failed RTD.

  • * * UPDATE FROM L. PARKER TO P. SNYDER AT 1531 ON 12/14/06 * * *

Unit 2 was in Mode 3 (Hot Standby) at 0 percent power at the time of the manual trip. At the time of the Initial notification, all procedural requirements for declaring Mode 3 had not been met, but upon further review, PG&E has verified K effective was less than 0.99. The licensee notified the NRC Resident Inspector. Notified R4DO (Proulx). The original report was modified by this change. The 'RX Crit' field was changed from 'Y' to 'N'. The 'Init Power' field was changed from '5' to '0'. The 'Curr Power' field was changed from 'Startup' to 'Hot Standby'.