*The updates from the previous press release are underlined.
All 6 units of Fukushima Daiichi Nuclear Power Station have been shut down.
Unit 1 (Shut down)
- Explosive sound and white smoke were confirmed after a big quake occurred at 3:36 pm on March 12, 2011. It was assumed to be hydrogen explosion.
- At 3:37 pm on March 25, 2011, we started injecting freshwater to the reactor and are now injecting fresh water by a motor driven pump powered by the off-site transmission line.
- At 10:11 am on December 10, 2011, in addition to water injection from water feeding system, we started water injection from piping of core spray system to the reactor.
The current amount of water injection from the feed water system is approx. 4.8 m3/h and that from the reactor core spray system is approx. 2 m3/h.
- At 1:31 am on April 7, 2011, we commenced injection of nitrogen gas into Primary Containment Vessel.
- At 11:22 am on August 10, 2011, we started cyclic cooling for the water in the spent fuel pool by an alternative cooling equipment of the Fuel Pool Cooling and Filtering System.
- At 4:04 pm on November 30, 2011, we started operation to inject nitrogen into the reactor pressure vessel.
- At 6:00 pm on December 19, 2011, a full-scale operation of the PCV gas management system started.
- At approx. 11:00 am on March 29, 2012, we confirmed that the indicators for reactor water level (fuel range)B, pressure of PCV and pressure of suppression chamber were disabled. Afterwards, we reset the power of the indicators. At 12:56 pm on the same day, we confirmed that the indicators recovered normal condition. Now, the cause is under investigation. While data monitoring was disabled, the key parameters in terms of safety were continued to be monitored using other indicators. Because we confirmed that there has been no significant fluctuation of the parameters, we concluded that there is no problem in terms of safety.
Unit 2 (Shut down)
- At approximately 6:00 am on March 15, 2011, an abnormal noise began emanating from nearby Pressure Suppression Chamber and the pressure within the chamber decreased.
- At 10:10 am on March 26, 2011, we started injecting freshwater to the reactor and are now injecting fresh water by a motor driven pump powered by the off-site transmission line.
- At 2:59 pm on September 14, 2011, in addition to water injection from feed water system, we started water injection from piping of core spray system to the reactor.
The current water injection amount from the reactor feed water system is approx. 2.8 m3/h and that from the core spray system is approx. 6m3/h.
- At 5:21 pm on May 31, 2011, we started cyclic cooling for the water in the spent fuel pool by an alternative cooling equipment of the Fuel Pool Cooling and Filtering System.
- At 8:06 pm on June 28, 2011, we started injecting nitrogen gas into the Primary Containment Vessel.
- At 6:00 pm on October 28, 2011, a full operation of the PCV gas control system started.
- At 10:46 am on December 1, 2011, we started the nitrogen injection to the Reactor Pressure Vessel.
- At 11:50 am on January 19, 2012, we started the operation of the spent fuel pool desalting facility.
Unit 3 (Shut down)
- Explosive sound and white smoke were confirmed at approximately 11:01 am on March 14, 2011. It was assumed to be hydrogen explosion.
- At 6:02 pm on March 25, 2011, we started injecting fresh water to the reactor and are now injecting fresh water by a motor driven pump powered by the off-site transmission line.
- At 2:58 pm on September 1, 2011, we started water injection by core spray system in addition to water injection by the reactor feed water system piping arrangement.
The current water injection amount from the reactor feed water system is approx 1.8m3/h and that from the core spray system is approx. 4.9m3/h.
- At 7:47 pm on June 30, 2011, we started cyclic cooling for the water in the spent fuel pool by an alternative cooling equipment of the Fuel Pool Cooling and Filtering System.
- At 8:01 pm on July 14, 2011, injection of nitrogen gas into the Primary Containment Vessel started.
- At 4:26 pm on November 30, 2011, we started operation to inject nitrogen into the reactor pressure vessel.
- At 7:00 pm on March 14, 2012, the regular operation of the PCV gas control system started.
Unit 4 (Outage due to regular inspection)
- At around 6 am on March 15, 2011, we confirmed an explosive sound and the sustained damage around the 5th floor rooftop area of Reactor Building.
- At 12:44 pm on July 31, 2011, we started cyclic cooling for the water in the spent fuel pool by an alternative cooling equipment of the Fuel Pool Cooling and Filtering System.(At 1:26 pm on March 29, 2012, we started hydrazine injection.)
- From 2:00 pm to 4:40 pm on March 27, Hydrazine injection into the Unit 4 reactor well through the instrument pipes inside the reactor was conducted.
- At 10:58 am on November 29, 2011, in order to decrease more salinity, we installed Ion exchange equipment and started the operation of such equipment.
- At 5:41 am on March 27, the cooling of the spent fuel pool of Unit 4 was stopped (water temperature at the time of stoppage: approx. 24 ℃) in order to implement the replacement of flexible hose in the primary coolant system and pump inlet strainer in the secondary coolant system. Stoppage is scheduled to continue till March 28. The increasing rate of the water temperature is estimated to be approx. 0.5 ℃/h, therefore no material issue in the management of the pool temperature is expected. At 4:35 pm on March 28, we restarted the cooling of the spent fuel pool the since we finished the replacement. (The water temperature of the spent fuel pool was approx. 33 ℃ when we restarted the cooling)
- At this moment, we don't think there is any reactor coolant leakage inside the primary containment vessel.
Unit 5 (Outage due to regular inspection)
- Sufficient level of reactor coolant to ensure safety is maintained.
- At 5:00 am on March 19, 2011, we started the Residual Heat Removal System Pump in order to cool the spent fuel pool.
- At 2:45 pm on July 15, 2011, we started the operation of the original Residual Heat Removal System (System B) by its original seawater pump.
- At 10:11 am on December 22, 2011, since we finished the recovery work of seawater pump (System B) of equipment water cooling system, we made a trial run. At 11:25 am on the same day, we confirmed no abnormalities and restarted the operation.
- At 7:05 am on March 28, 2012, we stopped Shutdown Cooling System due to suspension of power supply for construction work regarding power supply cars installation in case of outage of AC power source of Unit 5 and 6. Due to this work, cooling the reactor stopped (water temperature of the reactor when stopped: approx. 32.3℃ ). At 2:56 pm on the same day, we restarted Shutdown Cooling System and re-started cooling the reactor. (water temperature of the reactor when restarted: approx. 38.2℃)
Unit 6 (Outage due to regular inspection)
- Sufficient level of reactor coolant to ensure safety is maintained.
- At 10:14 pm on March 19, 2011, we started the Residual Heat Removal System Pump of Unit 6 to cool down Spent Fuel Pool.
- At 2:33 pm on September 15, 2011, we started separately cooling the reactor through the Residual Heat Removal System and the spent fuel pool through Equipment Cooling Water System and Fuel Pool Cooling System.
Others
- At around 10:00 am on June 13, 2011, we started the operation of the circulating seawater purification facility installed at the screen area of Unit 2 and 3.
- At 8:00 pm on June 17, 2011, we started operation of Water Treatment Facility against the accumulated water. At 6:00 pm on July 2, we started the circulating injection cooling to inject the water, which was treated by the accumulated water treatment system, to the reactors through the buffer tank.
- At 7:41 pm on August 19, 2011, we started treatment of accumulated water by parallel operation of one line from the cesium adsorption instrument to the decontamination instrument and the other treatment line of the cesium adsorption instrument No.2.
- At 2:06 pm on October 7, 2011, we started to spray purified accumulated water brought from Unit 5 and 6 continually in order to prevent dust scattering and potential fire outbreaks from the cut down trees.
- On October 28, 2011, we started installation of the water proof wall at the sea side, in front of the existing shore protection, Units 1-4, in order to contain marine pollution by underground water.
- At 12:25 pm on December 13, 2011, we started the re-circulating operation of desalination facility (reverse osmosis membrane) for the purpose of suppression of condensed water after desalination treatment.
- From 10:00 am to 4:00 pm on March 28,2012, we transferred accumulated water from the basement of Unit 6 T/B to the temporary tank. At 10:00 am on March 29, we restarted the transfer.
- At 9:08 am on March 29, 2012, as for the Centralized Radiation Waste Treatment Facility, we started to transfer accumulated water from the On-site Bunker Building to Process Main Building.
- At 10:30 am on March 29, 2012, we started the trial run of the station common diesel generator (A). At 1:00 pm on the same day, we confirmed no abnormalities and completed the restoration of the station common diesel generator (A).
