*Updates 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 volume is approx. 4.8 m3/h from the reactor feed
water system and approx. 2 m3/h from the core spray system.
-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.
-On October 28, 2011, we completed installation of the cover for the
Reactor Building in order to contain dispersion of radioactive
substances.
-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
water feeding system, we started water injection from piping of core
spray system to the reactor.
Current water injection amount is approx.2 m3/h in feed water system and
approx.7 m3/h in corer spray system
-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, we put the gas management system of the
reactor containment vessel in operation.
-At 10:46 am on December 1, 2011, we started the nitrogen injection to the
Reactor Pressure Vessel.
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 volume is approx 2.9 m3/h from the reactor
feed water system and approx. 6 m3/h from the core spray system.
-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.
Since inlet pressure of the primary circulation pump in the alternative
cooling system of the spent fuel pool frequently tended to decrease due
to the effect of clogging of the inlet strainer of the pump, the pump was
stopped at each time in order to flush the strainer. However, since this
tendency is supposed to continue and the temperature of the spent fuel
pool is sufficiently low, which is approx. 13.0°C, and there is enough
margin from the operational limit value (upper limit) by the safety
regulation, which is 65.0°C, we determined to stop the pump by January 4
of 2012 and temporary stop the cooling of spent fuel pool, considering
the exposure dose during the flushing.
At 4:54 pm on December 30, 2011, the pump was stopped. (Temperature of
the spent fuel pool was approx. 13.3°C at the time of shutdown.) It is
valuated that the temperature rise of the spent fuel pool due to the
shutdown of the pump is approx. 5 to 6 degrees for a day. And it is
planned that this pump operates for one time in a day to check the
temperature of the spent fuel pool during this temporary operation, since
December 31, 2011.
-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.
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 approx. 5:30 pm on January 1, 2012, we observed approx. 240 mm
decrease in the water level of the skimmer surge tank*1 of Unit 4 spent
fuel pool in the three hours between 2:00 pm to 5:00 pm (According to the
operation record so far, there had been an approx. 50 mm decrease.). As a
result of the site investigation later, we did not observe any leakage
around the Unit 4 reactor building, connecting points of primary system
pipes of Unit 4 spent fuel pool alternative cooling system, or its
installation space. The water temperature of Unit 4 spent fuel pool as of
5:00 pm on January 1 is 23°C (22°C as of 5:00 am on January 2). The spent
fuel pool alternative cooling system is still in operation and there is
no problem in cooling the reactor. Though the water level of the spent
fuel pool is kept stable without any problem, the water level in the
skimmer surge tank continues decreasing. Therefore, from 10:27 pm to
11:13 pm on January 1, we filled water in the skimmer surge tank. At
present, the water level in the skimmer surge tank keeps decreasing
approx. 90mm/hour. We will strengthen surveillance on observation of the
water level in the skimmer surge tank, increasing the frequency to once
in an hour from once in three hours. At the same time, we will continue
examination of the causes of the decrease in the water level, such as
site investigations based on such possibilities as the water may flow
into the reactor well*2 from the spent fuel pool.
At present, no leakage is observed outside the building. No significant
change is observed in the water level of the accumulated water in the
building.
*1 The tank installed in order to receive the water overflows from the
spent fuel pool. The water in the spent fuel pool is overflowed into
the skimmer surge tank in order to cool the fuel assembly and remove
impurities in the water. The water returns to the spent fuel pool after
passing through the heat exchanger and the filter.
*2 The reactor well is the space which contains the reactor pressure
vessel and the lid of the reactor containment vessel. During the
periodical inspections, the space filled with water and the fuel is
changed.
-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 this moment, we don't think there is any reactor coolant leakage
inside the primary containment vessel.
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.
-At this moment, we do not think there is any reactor coolant leakage
inside PCV.
Others
-At around 10 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 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.
-Since December 22, 2011, the atmospheric temperatures at point C of Unit
1 Primary Containment Vessel (PCV) monitored by the Containment
Atmospheric Monitoring System had risen (the atmospheric temperature of
the PCV on December 22 was approx. 38°C, at 7 pm on December 27 was
approx. 49°C). The other temperatures had not risen, so we conducted a
survey checking the reliability of the meters from 9 am to 10 am on
December 28, and we confirmed that there are no problems. From 11:00am
to 12:15pm on the same day, we adjusted the volume of Nitrogen injection,
from approx. 8 m3/h to approx.18 m3/h, and emission of the gas
management system, from approx. 23 m3/h to approx.30 m3/h, in order to
identify the cause by monitoring the system with the same injection and
emission volume as before December 22. The temperature went up to approx.
54.6°C at 6:00 pm on December 28 at its maximum and fell to approx.
43.5°C at 5:00 am on January 2, 2012. Temperatures at other two points
also indicated slight increases but are currently in the stable status.
Point D: (Maximum) approx. 35.8°C at 5:00 pm on December 29, 2011 →
approx. 32.7°C at 5:00 am on January 2, 2012.
Point E: (Maximum) approx. 40.0°C at 5:00 pm on December 29, 2011 →
approx. 35.8°C at 5:00 am on January 2, 2012.
We will continuously conduct the survey for the cause of temperature
increase and surveillance of the plant.
-At 3:22 pm on December 28, 2011, we started to transfer accumulated water
from the basement of turbine building of Unit 2 to the Centralized
Radiation Waste Treatment Facility (Miscellaneous Solid Waste Volume
Reduction Treatment Building [High Temperature Incinerator Building] and
the Process Main Building).
-From 2:37 pm on December 30 to 9:58 am on December 31, 2011, we
transferred the accumulated water from the basement of turbine building
of Unit 3 to the Centralized Radiation Waste Treatment Facility (the
Miscellaneous Solid Waste Volume Reduction Treatment Building [High
Temperature Incinerator Building] and the Process Main Building).
