*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 12th. It was assumed to be hydrogen
explosion.
-At approximately 2:30 am on March 23rd, seawater injection to the nuclear
reactor through the feed water system was initiated.
-From 3:37 pm on March 25th, we started injecting freshwater and are now
injecting fresh water by a motor driven pump powered by the off-site
transmission line.
-As it is suspected that hydrogen gas is accumulated inside reactor
containment vessel, we commenced the valve opening operation concerning
injection of nitrogen gas into the reactor container vessel at 10:30 pm
April 6th and commenced injection at 1:31am April 7th.
Unit 2(Shut down)
-At approximately 6:00 am on March 15th, an abnormal noise began emanating
from nearby Pressure Suppression Chamber and the pressure within the
chamber decreased.
-From 10:10 am on March 26th, 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.
-From 7:35 pm on April 12th, we started transferring the high level
radioactive accumulated water in the trench of the turbine building to
the condenser by an underwater pump. At 5:04pm on April 13th, the
scheduled transfer was completed.
Unit 3(Shut down)
-Explosive sound and white smoke were confirmed at approximately 11:01am
on March 14th. It was assumed to be hydrogen explosion.
-From 6:02 pm on March 25th, 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.
Unit 4(outage due to regular inspection)
-At approximately 6:00 am on March 15th, we confirmed the explosive sound
and the sustained damage around the 5th floor rooftop area of the Nuclear
Reactor Building.
-At this moment, we do not consider any reactor coolant leakage inside the
reactor happened.
Unit 5(outage due to regular inspection)
-Sufficient level of reactor coolant to ensure safety is maintained.
-At 5:00 am on March 19th, we started the Residual Heat Removal System
Pump (C) in order to cool the spent fuel pool.
-At 2:30 pm on March 20th, the reactor achieved reactor cold shutdown. At
around 5:24 pm on March 23rd, when we switched the temporary Residual
Heat Removal System Seawater Pump, it has stopped automatically. At
around 4:14 pm on March 24th we replaced the pump, and restarted cooling
of reactor at around 4:35 pm.
-At this moment, we do not consider any reactor coolant leakage inside the
reactor happened.
Unit 6(outage due to regular inspection)
-Sufficient level of reactor coolant to ensure safety is maintained.
-At 10:14 pm on March 19th, we started the Residual Heat Removal System
Pump (B) of Unit 6 in order to cool the spent fuel pool.
-At 7:27 pm on March 20th, the reactor achieved reactor cold shutdown.
-In relation to the two seawater side pumps of the Residual Heat Removal
System, we switched the power source from temporary to permanent at 3:38
pm and 3:42 pm, Mar 25 respectively.
-At this moment, we do not consider any reactor coolant leakage inside the
reactor happened.
Operation for cooling the spent fuel pools
-From 5:39pm to 9:22 pm on April 17th, we have sprayed water to Unit 4 by
a concrete pump vehicle.
-From 2:17pm to 3:02 pm on April 18th, we have sprayed water to Unit 3 by
a concrete pump vehicle.
-We will conduct further water spray depending on the conditions of spent
fuel pools, if needed.
Others
-The national government has instructed evacuation for those local
residents within 20km radius of the periphery and evacuation to inside
for those residents from 20km to 30km radius of the periphery, because it
is possible that radioactive materials are discharged.
-From 7:03 pm on April 4th to 5:40 pm, April 10th, we discharged to the
sea approximately 9,070 tons of the accumulated low level radioactive
water stored in the Centralized Radiation Waste Disposal Facility. Also
from 9:00 pm on April 4th to 6:52 pm, April 9th, we discharged to the
ocean approximately 1,323 tons of the low level radioactive subsurface
water stored in the sub drain pits of Unit 5 and 6.
Regarding radioactive concentrations at measuring points including those
adjacent to the power station due to the discharge of the low level
radioactive stored water to the ocean, no significant change has been
found, though we compared them with the transition of concentrations for
a week before the discharge.
The total amount of emitted radioactivity is approximately 1.5 x 1011
Becquerel. We evaluate approximately 0.6 mSv of effective radioactive
doses per year per an adult as the impact on the discharge of the low
radioactive stored water to the ocean if an adult eats adjacent fish and
seaweeds every day. The amount (0.6 mSv of effective radioactive doses
per year) is one-forth of annual radioactive dose (2.4 mSv) to which the
general public is exposed from nature and equivalent to that when we
evaluated before discharging the water to the ocean.
-From 2:30 pm to 3:45 pm on April 15th, we installed 3 sandbags containing
zeolite (as an absorbent material) between the screen pump rooms of the
Unit 3 and Unit 4.
Also, from 9:00am to 11:15am, we threw in two sandbags between the screen
pump rooms of Unit 1 and 2, and five sandbags between the screen pump
rooms of Unit 2 and 3.
-From 10:19 am to 5:00 pm on April 15th, we transferred distribution
panels of the pumps to inject water to the reactors of Units 1 to 3 as a
countermeasure against tsunami.
-At 2:34pm on April 17th, power supplies to a common spent fuel pool was
temporarily stopped because a breaker at the upstream side was released
due to an electrical short circuit which was caused by an insufficient
treatment of the end of the unused cable which was connected to the power
source of the common spent fuel in parallel. However, after removal of
the cable and checkups, at 5:30pm, the power supplies to the common spent
fuel pool was restored.
-From 11:30am to 2:00pm, we opened and closed the double doors and
conducted surveys of the situation of the inside of the nuclear reactor
building of Unit 3 and measured a dose of radiation, etc. by a remote
control robot. Also, from 4:00pm to 5:30pm, we did the same kind of work
on Unit 1. From 1:42pm to 2:33pm on April 18th, we opened and closed the
double doors, measured a dose of radiation and so on, and conducted
surveys of the situation of the inside of the nuclear reactor building of
Unit 2, by a remote control robot.
-From 11:50am to 1:05pm on April 18th, we suspended operations injecting
water to the reactor of Unit 1 to 3, and replaced hoses for injecting
water, to the brand new ones.
-We will continue to take all measures to ensure the safety and to
continue monitoring the surrounding environment around the power station.