*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.
The current water injection volume is approx 4.4m3/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.
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.
Water is currently injected at approx. 3.1m3/h through reactor feed water
system piping arrangement, and at approx. 4.4 m3/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.
- 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.
* As of 5:00 pm on November 26, the indicator of the gas temperature of
Suppression Chamber read 52.7°C, but at 11:00 pm on the day we confirmed
that it read "Overscaled" (digital recorder). Then, as of 5:00 am on
November 27, it read 102.6°C. Though the readings were not stable, as
there were no significant changes or variations in the temperatures of
the same types of 2 thermometers and the pool water in Suppression
Chamber, we have been investigating the causes for this event including
the possibility of malfunction of the measuring instruments.
Later, we inspected the measuring instruments and estimated that the
readings were overscaled due to certain impacts on the signal detection
line seeing that signal from the temperature detector is not stable. We
will keep monitoring readings of this instrument and also monitor the
temperature using instruments close to it.
* The indicator for the inside of the Primary Containment Vessel (Drywell)
of Unit 2 (base line temperature of the air conditioning unit, local
cooling equipment) read 78.2°C as of 5:00 am on November 27 but at 6:50
am on the day it was confirmed that it read approximately 84°C,
increasing in a staircase pattern. On the other hand, it was also
confirmed that the temperature changes of the bottom of the Reactor
Pressure Vessel and the water in the pool of the Suppression Chamber were
smaller than that of the inside of the Primary Containment Vessel
(Drywell) and that there was no significant change in the temperature.
Now we have been decreasing the flow rate of water injection as stated
below and therefore it is expected that the temperature inside the
Primary Containment Vessel will rise, but, as the line temperature of
which rose in a staircase pattern was only one line of the five lines
and the rest of the lines did not show the same changes, we have been
investigating the causes for this event, including the possibility of
malfunction of the measuring instruments.
Later we inspected the instrument but got no data indicating malfunction,
and the readings after the inspection are not different from those before.
Therefore, we estimated that the signal detection line was somehow
affected, which raised the temperature indicated. We will keep monitoring
this instrument and also monitor the temperature using instruments close
to it.
· At 7:11 pm on November 24, we adjusted the flow rate of water
injection from Core Spray System from approx. 7.2 m3/h to approx.
5.6m3/h (for feed water system, the flow rate is kept at 2.9 m3/h).
· On November 26 (from 10:18 am to 11:02 am), we adjusted the flow rate
from Core Spray System from approx. 5.5 m3/h to approx. 4.5m3/h (for
feed water system, the flow rate is kept at 3.0 m3/h).
At 9:12 am on November 28, the alarm telling that the difference of flow
rates between at the entering and at the exit of the primary pump at the
alternative cooling system for the spent fuel pool went off, and the
system automatically stopped. At 9:16 am on the same day we checked the
site and no leakage was confirmed. We are investigating the cause. 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.
Water is currently injected at approx. 1.9 m3/h through reactor feed
water system piping arrangement, and at approx. 6.0 m3/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.
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 11:34 am on August 20, we started an operation of desalination
equipment in the spent fuel pool.
- 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.
- For the purpose of the cleaning starting on November 28 to avoid the
performance deterioration of pumps by sucking up sands etc. accumulated
at the bottom of the inlet canal pump room, we stopped the pump (D) of
the residual heat removal system thus suspended cooling the reactor, and
also stopped the pump (C) of the cooling water system thus suspended
cooling the spent fuel pool. When each pump was stopped, the temperatures
of the water in the reactor and the spent fuel pool were 25.7°C and 20.4°C
respectively. The planned suspension of cooling is between 7:00 am to
5:00 pm everyday, and the temperature increases of the water in the
reactor and the spent fuel pool due to the suspension will be approx.
17°C and approx. 4°C per day respectively (we plan to do the cleaning
work for approx. 1 week).
- 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.
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 9:10 am on November 10, we started transfer of accumulated water from
the basement of Unit 2 turbine building to Centralized Radiation Waste
Treatment Facility High Temperature Incinerator Building.
- At 9:25 am on November 15, we started transfer of accumulated water from
basement of Unit 3 turbine building to Centralized Radiation Waste
Treatment Facility Building.
