*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 strengthened 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 present, no leakage is observed
outside the building. No significant change is observed in the water
level of the accumulated water in the building.
By further investigation, we confirmed that amount of water that is
equivalent to decreased water level of the skimmer surge tank and amount
of water that is equivalent to increased water level of the reactor
well*2 are almost the same and the water level at reactor well is lower
than that of the spent fuel pool. With these facts, we estimate that
situation of gate between the reactor well and the spent fuel pool
changed and water flow from the spent fuel pool to the reactor well
increased made decrease in water flow from the spent fuel pool to the
skimmer surge tank, and so decrease in water level at the skimmer surge
tank was more than usual. To decrease the difference between the water
level of the reactor well and that of the spent fuel pool, we put water
into the reactor well from 11:50 am to 11:59 am on January 2. As of 4:00
pm, we can not find decrease in the water level of the skimmer surge
tank. We will continue surveillance the water level of the skimmer tank.
*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 Nm3/h to approx.18 Nm3/h, and emission of the gas
management system, from approx. 23 Nm3/h to approx.30 Nm3/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. 43.3°C at 11:00 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. 32.6°C at 11:00 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 11:00 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).
