*The 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.
The current water injection amount from the reactor feed water system is
approx.4.5 m3/h and that from the core spray system is approx. 1.9 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.
-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
feed water system, we started water injection from piping of core spray
system to the reactor.
Because the tendency of temperature rise at the bottom of PCV had been
accelerated since February 2, we increased the amount of water injected
to the reactor and continued monitoring the tendency of the temperature
fluctuation. Since the temperature increased slightly, at 10:45 pm on
February 11, 2012, we changed the water injection amount through the
reactor feed water system from approx. 6.8m3/h to 7.8m3/h (the water
injection amount through the core spray system is kept at approx. 6.8m3/h).
On February 12, 2012, we conducted a sampling of gas in the gas management
system in the Primary Containment Vessel of Unit 2 and the result is that
around the entry of the system, Xe-135 was below the detection limit
(9.5 x 10-2 Bq/cm3). As it is below 1 Bq/cm3, the criterion to judge
re-criticality, we have confirmed that it has not reached re-criticality.
After that, we continued monitoring the tendency of the temperature
fluctuation, and then found that the temperature at the bottom of PCV
tended to be still high. Therefore, in order to avoid a chance of the
re-criticality due to the increase of water density in the PCV by sudden
cold water injection, from 11:38 am to 1:50 pm on February 12, before
starting water flow rate change, we injected boric acid into the reactor
for the safety measures. Then, from 2:10 pm on the same day, although we
increased the water injection rate, the indicated temperature of the
bottom of PCV was confirmed to be 82°C beyond 80°C so that, At 2:20 pm,
we judged that it was not satisfied "the temperature is below 80°C at
the bottom of PCV *1", which is stipulated in "the Reactor Facility
safety Regulation *2" as one of the "Conditions of operation". Thereafter,
we continued the increased water injection, and changed the water flow
rate from approx. 7.2m3/h to 7.5m3/h through the reactor feed water
system, and from approx. 6.9m3/h to 9.9m3/h through the core spray system.
Currently, the temperature is approx. 79.2°C as of 3:00 pm on February
12 for reference. We continue to monitor the tendency of the temperature.
The current water injection amount from the reactor feed water system is
approx. 7.5 m3/h and that from the core spray system is approx. 9.9 m3/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-scale 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. 2.9 m3/h and that from the core spray system is approx. 6.1 m3/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.
Since 9:50 am on February 10, we have conducted the work to add
flowmeters to the nitrogen injection line at the side of Primary
Containment Vessel of Unit 3 in order to improve the reliability of
nitrogen injection activity. During this period, due to this work, we
suspended the nitrogen injection task temporarily.
-At 4:26 pm on November 30, 2011, we started operation to inject nitrogen
into the reactor pressure vessel.
-At 3:18 pm on January 14, we started operation of the radioactive
material removal instrument for the spent fuel pool in Unit 3.
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.
-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 10:00 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.
-As accumulated water containing radioactive materials was found in the
trench between Process Main Building and Miscellaneous Solid Waste Volume
Reduction Treatment Building (High Temperature Incinerator Building) in
Centralized Radiation Waste Treatment Facility (December 18, 2011),
inspection of other trenches in the site was commenced from January 11.
-At 9:18 am on January 31, we started transfer of Sub-drain Water of Unit
6 to the temporary tank. We will conduct transferring to the temporary
tank appropriately.
-At 2:43 pm on February 10, we started to transfer accumulated water from
underground floor of turbine building of Unit 2 to centralized radiation
waste treatment facility (Miscellaneous Solid Waste Volume Reduction
Treatment Building [High Temperature Incinerator Building]).
-At 9:57 am on February 12, we started to transfer accumulated water in
the underground of turbine building of Unit 3 to the Centralized Radiation
Waste Treatment Facility (Process Main Building).
*1) 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.*2) Based on the management of facilities stipulated at the Article 12
"Mid-term safety securing" of Act of the Regulation of Nuclear Source
Material, Nuclear Fuel Material and Reactors, it provides "Operational
Limit" and "measures required in the case that does not satisfy the
Operational Limit", it is required to respond based on the measures
required in the case that does not satisfy the Operational Limit. In
our case, in order to implement the preservation work, it was shifted
to outside of operational limit condition as planned (from 1:55 pm on
February 12), we change the water injection amount into the reactor of
Unit 2. At 2:20 pm, we judged that it was not satisfied "the
temperature is below 80 °C at the bottom of PCV ", which is stipulated
in "the Reactor Facility safety Regulation" as one of the "Conditions
of operation". as the indicated temperature was 82 °C beyond 80 °C. We
continue to change the water injection amount accordingly.
