*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. It was assumed to be hydrogen explosion.
- At 3:37 pm on March 25, 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.
As we observed reduction of the water injection rate to the Reactor, at
10:13 am on December 9, adjusted the water injection rate from the feed
water system from approx 4.2m3/h to approx 4.5m3/h. The current water
injection volume is approx 4.5 m3/h from the reactor feed water system.
- We commenced injection of nitrogen gas into Primary Containment Vessel
at 1:31 am on April 7.
- At 11:22 am on August 10, 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, 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, we started operation to inject nitrogen into
the reactor pressure vessel.
On December 7, as a part of installation work of the Primary Containment
Vessel Gas Management System in the Unit 1 reactor building, we
conducted nitrogen substitution in order to eliminate hydrogen in the
existing pipe arrangement to be used in the system. At 10:29 am on
December 8, we activated an exhaust fan in the Primary Containment
Vessel Gas Management System and started test operation of the system.
Unit 2 (Shut down)
- At approximately 6:00 am on March 15, an abnormal noise began emanating
from nearby Pressure Suppression Chamber and the pressure within the
chamber decreased.
- At 10:10 am on March 26, 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, we started injecting water to the reactor
through core spray system water injection piping arrangement in addition
to the water injection through reactor feed water system piping
arrangement.
As we observed reduction of the water injection rate to the Reactor, at
10:13 am on December 9, adjusted the water injection rate from the core
spray facility from approx 4.2m3/h to approx 4.5m3/h (from feed water
system remains at approx 3.0m3/h).
Water is currently injected at approx. 3m3/h through reactor feed water
system piping arrangement, and at approx. 4.5m3/h through core spray
system water injection piping arrangement.
- At 5:21 pm on May 31, 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, we started injecting nitrogen gas into the
Primary Containment Vessel.
At 4:15 pm on December 8, as it is considered that there would be
sufficient time before hydrogen reach the flammability limit in the
Primary Containment Vessel, the nitrogen injection amount into the PCV
was decreased from 20 Nm3/h to 16.5 Nm3/h.
- From 6:00 pm on October 28, we put the gas management system of the
reactor containment vessel in operation.
- At 11:04 am on November 6, we started operation of radioactive material
decontamination instrument of spent fuel pool. On December 5, the
facilities finished its operation.
- At 10:46 am on December 1, we started the nitrogen injection to the
Reactor Pressure Vessel.
At 4:15 pm on December 8, in order to secure the sufficient time before
hydrogen reaching the flammability limit in case the nitrogen injection
facilities stop its operation in the Unit 2 Reactor Pressure Vessel,
nitrogen injection amount into the RPV was increased from 13 Nm3/h to
14.5 Nm3/h.
- At 4:17 am on December. 7, on the alternative Spent Fuel Pool cooling
system of Unit 2, the alarm indicating that the difference of flow rates
between at the entering and at the exit of the primary pump is big went
off, and the system stopped automatically. At 4:41 on the same day,
after field investigation, no defect such as leakage was confirmed.
Currently the cause is under investigation,. At 4:00 am, the temperature
of Spent Fuel Pool was 18.4 degree C, the assumed increase of
temperature is 0.3 degree C/h, from the viewpoint of Spent Fuel Pool
temperature, and there is still enough allowance, so that there is no
problem.
Unit 3 (Shut down)
- Explosive sound and white smoke were confirmed at approximately 11:01 am
on March 14. It was assumed to be hydrogen explosion.
- At 6:02 pm on March 25, 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, we started water injection by core spray
system in addition to water injection by the reactor feed water system
piping arrangement. As we observed reduction of the water injection rate
to the Reactor, at 10:13 am on December 9, adjusted the water injection
rate from the feed water system from approx 2.0m3/h to approx 2.2m3/h,
from the core spray facility from approx 6.2m3/h to approx 6.1m3/h.
Water is currently injected at approx. 2.2m3/h through reactor feed
water system piping arrangement, and at approx. 6.1m3/h through core
spray system water injection piping arrangement.
- At 7:47 pm on June 30, 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, injection of nitrogen gas into the Primary
Containment Vessel started.
- At 4:26 pm on November 30, 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, 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, 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, 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, we started the Residual Heat Removal System Pump
in order to cool the spent fuel pool.
- At 2:30 pm on March 20, the reactor achieved cold shutdown.
- At 2:45 pm on July 15, we started the operation of the original Residual
Heat Removal System (System B) by its original seawater pump.
- 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, we started the Residual Heat Removal System
Pump of Unit 6 to cool down Spent Fuel Pool.
- At 7:27 pm on March 20, the reactor achieved cold shutdown.
- At 2:33 pm on September 15, 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.
- As we observed reduction of flow rate at the residual heat removal
seawater system pump (C) of Unit 6, At 10:32 am on December 9, we
stopped cooling the Reactor by the residual heat removal system (A) and
stopped the residual heat removal seawater system pump (C). After that,
we restarted the residual heat removal seawater system pump (C) and
confirmed that the performance of that pump returned to almost normal
level. At 11:18 am on the same day, we resumed cooling the Reactor by
the residual heat removal system (A). With this stop, Reactor water
temperature temporarily increased from 26.6 Celsius to 27.5 Celsius.
Others
- At around 10 am on June 13, 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, 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, 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, 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, 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 6:03 pm on November 30, we started transfer of the accumulated water
from the basement of Unit 2 turbine building to Centralized Radiation
Waste Treatment Facility High Temperature Incinerator Building.
- On December 4, workers of partner companies found that there was puddle
water inside the barrier around the evaporative condensation apparatus.
Afterwards we stopped the apparatus, and workers made visual inspection
of the apparatus and confirmed the leakage have stopped. After
conducting investigation, we found a crack in the concrete barrier, and
water leaking from this crack to the gutter (surface dose rate of leaked
water: beta ray 110 mSv/h, gamma ray 1.8 mSv/h). We also found water
leaking from between the barrier and the base concrete. We are
considering measures to stop this leakage to outside of the barrier. We
confirmed that the leakage had stopped by piling up sandbags between the
barrier and base concrete, and in the gutter. We sent the leaked water
remaining in the barrier to the waste water RO supply tank with a water
pump (approx. 15 m3).
Since the gutter led to the generally used channel of the power plant,
we have taken sea water from the channel around the water desalinations
(evaporative concentration apparatus) and the south drain (drain for the
generally used channel) and have conducted a nuclide analysis, and we
judged that the leaked water has been discharged into the sea from the
exit of generally used channel. It was estimated that approx. 150 liter
out of leakage water has flew in the channel, and assumed that it has
been discharged into the sea through the generally used channel. As a
result, the whole amount of radioactivity was approx. 2.6 x 1010 Bq
(temporary). As the impact of the discharge water into the sea, in the
assumption that we eat fish and seaweeds around the discharge channel
every day, the effective zone for an adult is approx. 0.0037 mSv / year,
that equals to approx. 1/600 of annual dose from nature for general
public (2.4 mSv), so that we evaluate there is almost no impact
- We plan to establish the system injecting water into the reactor in Unit
1 to 3 using the condensate storage tank of Unit 3. In preparation of
such establishment, the stored water in the tank was transferred to the
basement of turbine building of Unit 3 from 10:22 am on November 21 to
9:45 am on November 24. As the calibration of water level gauge is
required if all the water is transferred, approx. 200 ton was left in
the tank. During the measurement of salt concentration in the left water,
it turned out that concentration was high. In order to secure the space
for additional water injection to decrease such concentration, at 10:00
am on December 6, the left water was transferred from the tank to the
basement of the turbine building of Unit 3.
At 8:54 on December 7, we stopped transferring, and at approx. 9:19 am
on the same day, we started filling water in the tank, but afterwards,
we confirmed water leakage (approx. 5 liter) at the joint section of
hose connecting to the tank, at approx. 9:52 am, we stopped filling
water and confirmed the leakage has stopped. We plan to consider such
measures as repair etc. in future. The leaked water was treated as to be
free of radioactive materials and desalinated. At 9:05 am on December 9,
we restarted filling the water in the tank after completing the
replacement of the transfer hose.
- At 10:00 am on December 8, we started transferring accumulated water
from the Unit 6 turbine building to the temporary tank.
- At 9:28 am on December 9, the operation of facilities to cool the common
spent fuel pool was suspended in order to implement the replacement work
of power source for such facilities. The pool temperature at that time
was 18.8 degree C and expected increase would be 0.25 degree C/h. As
there exist enough buffers, there would be no major issue rising from
this operation. On the same day, with completion of change work of the
power board, at 11:58 am, we resumed cooling (the water temperature of
the common spent fuel pool at that time: approx 19.1 degree Celsius).
