*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. 4.3 m3/h and that from the core spray system is approx. 1.7 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.
The current water injection amount from the reactor feed water system is
approx.7.7m3/h and that from the core spray system is approx.10 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.
- Because the tendency of temperature rise at the bottom of the PCV had
been accelerated since February 2 and it continued, we have increased
the amount of water injection to the reactor since 14:10 on February 12.*1
We confirmed that the meter indicated 82°C exceeding 80°C which is the
maximum temperature limit at the bottom of the PCV for the safety
operation defined in the safety regulation*2 and evaluated that it
violated the regulation at 14:20 on February 12. In order to satisfy the
limit of the safety operation, we increased the amount of water
injection. After the countermeasure was taken, the temperature continued
to rise and we conducted an investigation of the meter which monitors
the temperature at the bottom of the PCV. As a result of the
investigation, we evaluated that the thermocouple has been out of order
due to disconnection, because the DC resistance was higher than normal
level. After the inspection of the soundness of thermocouple, we
evaluated that it has been out of order. At 2:00 pm on February 17, we
evaluated that the temperature at the bottom of the PCV was not actually
risen and it didn't exceed the limit of the safety operation. Our
evaluation of violation of the safety operation was corrected
retroactive to February 12. The meter was deleted from the list of the
meters to monitor the temperature of the bottom of the PVC. The
temperature is monitored with the other meters.
*1) 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[the rate of the increase in
the water injection volume is less than 1.0m3/h in any 24 hour period]
as planned (from 1:55 pm on February 12), we changed the water
injection amount into the reactor of Unit 2. At 2:00 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". We continue to
change the water injection amount accordingly.
*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.
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.
At 11:33am on February 17, since the current amount of the water
injection has enough margin against the water injection for decay heat,
the water injection from the core spray system has been reduced from
approx. 6.0m3/h to approx. 5.0m3/h in order to alleviate transfer and
treatment of accumulated water increased by the water injection increase
into Unit 2. And we confirmed the change of the water injection. The
water from the reactor feed water system was adjusted from approx.
2.9m3/h to approx. 3.0m3/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. 5 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 flow
meters 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.
- In order to conduct inspection of the strainer changeover valve of the
pump of the reactor sea water system of Unit 6 from February 14 to
February 17, at 10:02 am on February 14, we stopped cooling of the spent
fuel pool by the spent fuel pool cooling system (B) and at 10:06 am on
the same day, we stopped the pump of the reactor sea water system (A)
(spent fuel pool water temperature during the stoppage: approx. 23°C).
Because the spent fuel pool cooling system isn't in operation during the
inspection, we conduct alternating cooling of the reactor and the spent
fuel pool by the residual heat removal system. At 2:07pm on February 17,
since the inspection was completed ,the auxiliary cooling seawater
system pump (A) was activated. At 2:53pm on the same day, we restarted
the cooling of the spent fuel pool by the spent fuel pool cooling system
(B) and the system was back to the normal operating condition. (The
maximum temperature during alternate cooling period :Reactor Water:
33.6°C, Spent Fuel Pool Water: 29°C).
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 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 8:46 am on February 17, since the treatment capacity of the 2nd
Cesium adsorption apparatus was declining gradually, we stopped it and
cleaned the filters. At 10:59 am on the same day, we started this
apparatus, at 11:05 am ,we confirmed steady flow quantity (36.4 m3/h).
- At 10:00 am on February 17, we started to transfer accumulated water
from underground floor of turbine building of Unit 6 to the temporary
tank.
