*
Updates from 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 the 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.
Current water injection amount from the reactor feed water system is approx. 4.7m3/h and that from the core spray system is approx. 1.6m3/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.
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.
At 9:45 am on March 19, we started increasing nitrogen injection to the reactor from approx. 2.5m3/h to 3.0m3/h due to preparation of investigation on the inside of Unit 2 reactor (The injection amount to core spray system is still approx. 6.0 m3/h).
The current water injection amount from the reactor feed water system is approx. 3 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 1:24 pm on March 19, we started injection of hydrazine to spent fuel pool of Unit 2 through the circulating cooling system. )
-At 8:06 pm on June 28, 2011, we started injecting nitrogen gas into the Primary Containment Vessel.
At 10:33 am on March 19, we started decreasing nitrogen injection to the reactor from approx. 10 m3/h to 5 m3/h due to preparation of investigation on the inside of Unit 2 reactor (There was no change in the injection amount to reactor pressure vessel).
-At 6:00 pm on October 28, 2011, a full operation of the PCV gas control system started. On March 14,
-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 1.9m3/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 9:38 am on March 18, 2012, such system and cooling of the pool was temporarily suspended in order to implement the disassemble inspection of valve in the primary coolant system (Temperature of the pool at the time of the operation stoppage: approx. 15.0°C). The operation is schedule to be under halt till March 21 and no major concern is expected for the temperature of the pool (The temperature of the pool is expected to increase approx 20°C during the stoppage).
-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 the 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 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 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.
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 type) for the purpose of suppression of condensed water after desalination treatment.
-At 10:13 am on March 18, 2012, we started transferring the accumulated water from the basement of Turbine Building of Unit 2 to the centralized radiation waste treatment facility process main building.
-In order to stop the offset power and change the station power supply with starting to operate the south switching station, at 5:12 am on March 19, we stopped the operation of reactor monitoring indicator of Unit 3 (the temperature of reactor pressure vessel)*1and the cooling operation of spent fuel pool. At 5:33 am, we stopped the cooling operation of common spent fuel pool. Regarding spent fuel pool of Unit 4, temperature of water in spent fuel pool when we stopped is approx. 28 °C and expected temperature increase rate is approx. 0.55 °C/h. Regarding common spent fuel pool, temperature of water is 21.3 °C and expected temperature increase rate is approx. 0.23 °C/h. The period of suspension of cooling is approx. 14 hours, but regarding the temperature of pool water there is no problem on cooling.
*1: During the suspension of operating power supply, it is not content with Article 138 and 143(limiting condition for operation*2) in Safety Regulation. Therefore, we apply the Article 136 (exemption of limiting condition for operation in order to conduct maintenance work). Using temporary generator, we can monitor the temperature. (At 5:56 am on March 19 temporary generator started to supply power.)
*2: Reactor Facility Safety Regulation provides necessary conditions such as the numbers of the permitted machines etc. or criteria of temperatures and pressures for securing multiple safety function for operating reactors and for keeping nuclear power stations stable and these are treated as conditions for operation. When there happen some malfunctions of equipment provided in the regulation and a nuclear power station can not clear the conditions temporarily, operators have to take required countermeasures.
-At 8:27 am on March 19, 2012, we started transferring the accumulated water from On-site Bunker Building to Process Main Building.
-From 8:41 am on March 19, we started transferring the accumulated water from the basement floor of the turbine building of Unit 3 to the centralized radiation waste treatment facility (Miscellaneous Solid Waste Volume Reduction Treatment Building [High Temperature Incinerator Building]).
