“1F” is the abbreviation for the Fukushima Daiichi Nuclear Power Station used by workers on site.

The Great East Japan Earthquake, which occurred at 2:46pm on March 11, 2011, triggered an automatic scram of Units 1~3 which were in operation at the Fukushima Daiichi Nuclear Power Station (1F), and the cooling of fuel began. The cooling of fuel, for which power was needed, continued using onsite emergency power sources after external power supply was cut off by the earthquake. However, these auxiliary power sources were ultimately rendered inoperable by the tsunami that struck the site following the earthquake, thereby resulting in a loss of cooling functions.

After fuel cooling functions were lost, the temperature of the fuel rose causing a melt-down and a significant volume of hydrogen was generated due to the chemical reaction that ensued. In Units 1 and 3, hydrogen leaking from the Primary Containment Vessel accumulated in the Reactor Building and caused explosions. An explosion also occurred at Unit 4, which was undergoing periodic inspection, due to hydrogen that flowed into the building from Unit 3 through pipes.

Please click here for more details.
https://www7.tepco.co.jp/responsibility/decommissioning/accident-e.html

At Unit 1, the top part of the reactor building was severely damaged during the accident by a hydrogen explosion and rubble from that time still remains at the top of the building.
This rubble must be cleared away to remove fuel from the spent fuel pool, so that is the task in which we are currently engaged.
Going forward, we plan to complete construction of a large cover by the summer of 2025 in order to prevent the dispersion of dust and will continue to remove rubble from underneath it.

Preparations are underway to remove fuel from the Unit 2 spent fuel pool using a method that is even safer and further prevents the dispersion of dust.
Ground improvement work is currently underway toward installing a platform to remove fuel.

During the accident a hydrogen explosion occurred at Unit 3. Rubble generated during this explosion that was on the uppermost floor of the reactor building has already been removed, and the removal of fuel from the spent fuel pool began in April, 2019.
On February 28, 2021, the removal of all 566 fuel assemblies from the spent fuel pool was completed.
These tasks were conducted remotely, and the fuel assemblies are stored safely in the common pool on the premises.
We commenced the removal of control rods, etc. that have high dose and remain in the spent fuel pool in March 2023, and have been conducting the work.

This is a cover installed to remove fuel from the spent fuel pool.
Installation was completed in February 2018.
The large cover, which is 53.5m high and 56.9m long, weighs 1,250t and was designed to prevent loads from being transferred to the damaged reactor building.

During the accident, hydrogen generated at Unit 3 flowed through pipes into Unit 4 and caused a hydrogen explosion.
Since the reactor had been shut down for periodic inspection, all the reactor fuel was in the spent fuel pool.
Removal of the 1,535 fuel assemblies stored in the spent fuel pool was completed in 2014.

It is a cover installed to aid with the removal of fuel from Unit 4. The frame is made from strong steel beams that support the overhead crane required for removal.
Approximately 4,000t of steel beams in total was used for the structure. That’s the same amount that was used for Tokyo Tower.
This frame was designed to prevent loads from being transferred to the damaged reactor building.

They are taken to the common pool, etc. located on-site and stored appropriately in water.

Unit 5 is being used to deliberate fuel debris retrieval methods because its Primary Containment Vessel (PCV) is similar in structure to Units 2~4.

6,799 fuel assemblies can be stored at cool temperatures in the common pool but the common pool is not big enough to store all the fuel.
So, fuel which has dropped in temperature is transferred in dry casks to an air-cooled storage facility. Fuel is thus stored in two ways.

Storing all the spent fuel together in the common pool reduces risk compared with keeping it in the fuel pools of each reactor.
That’s why we are gradually relocating it to the common pool.

This is a fuel storage rack.
Fuel is stored in racks so it can be easily moved in and out, and to make it easier to keep track of quantity.

Investigations of the Primary Containment Vessel (PCV) were conducted in preparation for fuel debris retrieval.
During these investigations we utilized robots, small drones and muons (a type of cosmic ray) to take footage inside the primary containment vessel and measure dose levels.

PCV Internal Investigation(Non‐submerged area)
Photo from PCV Internal Investigation(Non‐submerged area)

Submersible investigation

In February 2018, an investigation of the inside of the Primary Containment Vessel (PCV) was conducted in preparation for fuel debris retrieval.
We successfully took footage from immediately below the Reactor Pressure Vessel (RPV), where it is assumed that fuel debris exists.
Some of this footage showed deposits that are assumed to be fuel debris. The investigation also showed that water is dripping from above and keeping the fuel debris at the bottom cool and stable.
The following year in February 2019, we conducted a “contact investigation” for the first time during which we touched deposits in order to examine hardness and brittleness.
We grabbed deposits that had accumulated at the bottom of the PCV to examine their shape and size, and we also confirmed that the deposits could be moved.
We opened a penetration hatch of the primary containment vessel in October 2023 and commenced deposit removal work inside the penetration in January 2024 for fuel debris trial retrieval.

Between September and November 2024, we conducted trial fuel debris retrieval at Unit 2. This marked the first time that fuel debris was retrieved from the primary containment vessel at the Fukushima Daiichi Nuclear Power Station.
The trial retrieval device(telescopic type) was used to reach down to the floor of the pedestal and grasp fuel debris with a sampling device affixed to its end.
The dose and weight of the retrieved fuel debris was measured on site. With taking measures to prevent contamination, it was loaded into a transport container after taking steps to prevent the spread of contamination and transported to a Japan Atomic Energy Agency (JAEA) research facility in Ibaraki Prefecture for attribute and condition analysis.
Analysis results will be used to deliberate methods for preventing fuel from reaching criticality during retrieval and reducing worker exposure.
The analysis should take anywhere from several months to one year.

Deposit contact investigation

Grabbing fuel debris with the sampling device

In order to remove fuel debris, in July 2017, the inside of the Primary Containment Vessel (PCV), which contained 6.4m of stagnant water, was investigated and an underwater robot was used to take footage on the inside.
The footage from directly below the RPV, where fuel debris probably exists, revealed structures and deposits that are assumed to have melted and fallen.

The freezer room is a facility for lowering the temperature for coolant used to create an ice wall (land-side impermeable wall) to -30°C.The coolant passes through pipes that enclose Units 1~4.
This underground ice wall, which is 1,500m long in total and extends 30m below the surface, was created to block the flow of groundwater.

Land-side impermeable wall
Cross-section of ground

About -10°C.

No, it doesn’t, because the ice wall is underground, which is less affected by the external air.
And, coolant temperature is maintained 24/7.

Pipes that encompass Units 1~4 under the ground are used to circulate coolant.

For example, groundwater flowing down from the mountains is pumped up using wells that comprise a groundwater bypass and discharged outside the port.
Groundwater flowing near the buildings is pumped up and discharged into the port using sub-drain wells.
And, ground surfaces are being paved or faced to prevent rainwater falling on-site from seeping into the ground and becoming groundwater.

This is a facility that houses purification equipment to remove the radioactive materials contained in contaminated water.
By passing contaminated water through special filters, this equipment can reduce the concentrations of 62 types of radioactive substances present in contaminated water. Click here for more information on the “treated water*” resulting from the purification of contaminated water.

Note on “Water treated with multi-nuclide removal equipment, etc. (ALPS treated water)” is notated.
"ALPS treated water" refers to water that has been purified with multi-nuclide removal equipment (ALPS), etc. until the concentrations of radioactive substances, excluding tritium, meet the government’s regulatory standards (The sum of the ratio of legally required concentrations, excluding tritium, being less than 1).
Water that has been purified with multi-nuclide removal equipment (ALPS), etc., but has yet to fulfill the government’s regulatory standards (The sum of the ratio of legally required concentrations, excluding tritium, being 1 or higher) is referred to as, "treated water to be re-purified". When referring to both of the aforementioned types of treated water collectively, "ALPS treated water, etc." is used.

Tritium is a relative of hydrogen that bonds with oxygen just like other hydrogen and exists as a liquid that has almost the same qualities as water.
The energy of radiation emitted by tritium is extremely weak and can travel only approximately 5mm through the air. It can be shielded with a single sheet of paper.
Tritium occurs naturally in the environment when radiation from space falls to the Earth in the form of "cosmic rays" and mixes with our atmosphere.

Tritium is also generated through the process of nuclear fission at nuclear facilities in Japan and overseas. Tritium is present in rain water, seawater, and tap water, and can be found inside the bodies of humans and animals. Click here for more information on tritium.

*Tritium generated at nuclear power facilities is regulated and managed in accordance with each country's requirements and discharged into the sea and atmosphere, etc.

This is an area for treating contaminated water so workers wear protective clothing and full-face masks.

The entire multi-nuclide removal equipment can treat a maximum of approximately 2,000 tons of contaminated water per day.

These tanks contain ALPS treated water, etc. that has been treated with multi-nuclide removal equipment (ALPS), etc. and Sr removed water.

Note on “Water treated with multi-nuclide removal equipment, etc. (ALPS treated water)” is notated.
"ALPS treated water" refers to water that has been purified with multi-nuclide removal equipment (ALPS), etc. until the concentrations of radioactive substances, excluding tritium, meet the government’s regulatory standards (The sum of the ratio of legally required concentrations, excluding tritium, being less than 1).
Water that has been purified with multi-nuclide removal equipment (ALPS), etc., but has yet to fulfill the government’s regulatory standards (The sum of the ratio of legally required concentrations, excluding tritium, being 1 or higher) is referred to as, "treated water to be re-purified". When referring to both of the aforementioned types of treated water collectively, "ALPS treated water, etc." is used.

There are many types of tanks. A standard tank can hold approximately 1,000m³of water.

As of January 2025, there are more than 1,000 tanks on site with a capacity of approximately 1.37 million m³ of water such as ALPS treated water.
See the Treated Water Portal Site for more details.

Note on “Water treated with multi-nuclide removal equipment, etc. (ALPS treated water)” is notated.
"ALPS treated water" refers to water that has been purified with multi-nuclide removal equipment (ALPS), etc. until the concentrations of radioactive substances, excluding tritium, meet the government’s regulatory standards (The sum of the ratio of legally required concentrations, excluding tritium, being less than 1).
Water that has been purified with multi-nuclide removal equipment (ALPS), etc., but has yet to fulfill the government’s regulatory standards (The sum of the ratio of legally required concentrations, excluding tritium, being 1 or higher) is referred to as, "treated water to be re-purified". When referring to both of the aforementioned types of treated water collectively, "ALPS treated water, etc." is used.

These tents have been set up to prevent rainwater from entering leak prevention dikes.
In the slight chance that a tank did leak, this would enable us to accurately measure and analyze the amount of water that leaked.

The various tank manufacturers use different colors.
There is no difference in performance.

Since August 24, 2023, we have commenced the discharge of ALPS treated water into the sea. This water was stored in tanks, and confirmed prior the discharge that the concentrations of radioactive substances, excluding tritium, meet the government’s regulatory standards after the purification by multi-nuclide removal equipment (ALPS), etc.

Therefore, the amount of water being stored in these tanks will gradually decrease over time.
See the Treated Water Portal Site for information on the future handling of treated water*.

Note on “Water treated with multi-nuclide removal equipment, etc. (ALPS treated water)” is notated.
"ALPS treated water" refers to water that has been purified with multi-nuclide removal equipment (ALPS), etc. until the concentrations of radioactive substances, excluding tritium, meet the government’s regulatory standards (The sum of the ratio of legally required concentrations, excluding tritium, being less than 1).
Water that has been purified with multi-nuclide removal equipment (ALPS), etc., but has yet to fulfill the government’s regulatory standards (The sum of the ratio of legally required concentrations, excluding tritium, being 1 or higher) is referred to as, "treated water to be re-purified". When referring to both of the aforementioned types of treated water collectively, "ALPS treated water, etc." is used.

Site areas are color-coded based on the level of contamination. The three zone colors are the same as a traffic light: G (for Green), Y (for Yellow) and R (for Red)

G zone

Workers may wear simple dust masks and regular uniforms

Y zone

Workers must wear protective clothing and a full or half-face mask

R zone

Workers must wear protective clothing and a full-face mask

From here into the PCV is a Y zone because the reactor was in operation prior to the accident and dust containing radioactive materials that still remain in the PCV may cling to clothing.

96% of the entire site. The map has been color-coded to show zone demarcations in accordance with radioactive substance contamination conditions.

By law, workers must be registered as radiation workers before working on site.
Each of these workers wears a dosimeter to strictly manage daily radiation exposure doses.
Total exposure dose must be less than 50 mSv during a single year, and less than 100 mSv over five years.
Currently, work plans are created to reduce exposure doses, and the average exposure dose of workers is sufficiently lower than legal limits. The health of personnel engaged in radiation work is also managed through periodic checkups.

After being sorted by type and dose level, rubble and other waste is stored in waste storage buildings and other facilities located on-site.

Used equipment is stored appropriately as waste. In order to reduce volume it will be incinerated step-by-step, and ashes generated will be stored.

Facilities to incinerate, compact and store waste. Approximately 770,000㎥ of waste is estimated to be generated over the next decade.
The volume will be reduced to approximately 260,000㎥ by incineration and crushing after which the waste will be appropriately stored and managed.

The Miscellaneous Solid Waste Incineration Facility, Volume Reduction Equipment and Solid Waste Storage Vault building 10(2 out of 3 buildings) have already been put into use.
The other facilities will be put into use one-by-one as preparations are completed.

The facilities will be built in an area approximately 14ha in size.

Radiation is like a strong ray of light.
If we use a flashlight as an analogy, radioactive material is the flashlight and the radiation is the light emitted by the flashlight.
“Radioactivity” refers to the ability of a substance to emit radiation, which is analogous to the ability of a flashlight to emit light.

During a tour each visitor is provided with a dosimeter to attach to their clothing.
The tour route has been set to limit the maximum total radiation exposure dose to 0.1mSv or less, which is lower than the exposure dose received during a roundtrip flight from Tokyo and New York.

Dose level monitors (dosimeters) at approximatel 90 locations on site measure air dose rates in real time.
The dose levels shown at the bottom of the screen indicate the levels measured by these monitors or measurements taken with portable dosimeters depending on the location.
※Displayed data was taken between January 2021 and November 2024.

Six workers were confirmed to have been exposed to more than 250mSv, which is the dose limit for workers responding to an emergency.
All of these workers were either operators monitoring instruments or electricians/instrument system engineers in the main control room.
The average annual dose at the Fukushima Daiichi NPS before the accident was 1.4mSv/yr (FY2009).

It is an exhaust stack which was used before the accident as part of the reactor building’s air-conditioning system to vent air outside. The exhaust stack is no longer in use.
The seismic resistance of this exhaust stack exceeds requirements, but to eliminate the risk of it falling over the top 60m of the stack was dismantled in cooperation with a local contractor. This task was completed on May 1, 2020.

This is called an anticum and was constructed to investigate the roof of the reactor building.
The anticum prevents dust, etc. that contains radioactive materials from being dispersed into the environment when boring holes in the wall of the reactor building.
The anticum is 30m high, 38m long and 16m wide.

No. The decision has already been made to decommission Units 5 and 6.

This is a simplified diagram of the Unit 1~5 reactor buildings.
Fuel rods are put inside the pressure vessel, and the heat generated by them is used to produce electricity.
The spent fuel pools are used to store unused fuel and also to cool spent fuel that continues to generate heat.

In nuclear power generation, water in the reactor is boiled using the thermal energy generated from the nuclear fission of Uranium.
The high temperature and highly pressurized steam that is produced turns a turbine that generates electricity.
In Unit 5, steam pressure was approximately 7Mpa and steam temperature was approximately 286 degrees Celsius in the Reactor Pressure Vessel (RPV) when generating electricity.

This facility was originally used to monitor and operate the reactors and turbines, and also control radiation.
It is currently not in use.

It is a platform used for the removal of spent fuel.

ALPS treated water which has been confirmed that the concentrations of radioactive substances, excluding tritium, meet the government’s regulatory standards for discharge into the environment is transferred to the dilution facility located close to the sea through transfer pipes designed to reduce the risk of leaks.

In the dilution facility, ALPS treated water is mixed with a large volume of seawater taken in from outside the port.

ALPS treated water has been diluted with seawater more than 100 times, and then transferred to the discharge vertical shaft. After that, it passes through a discharge tunnel and is discharged from a discharge outlet approximately 1km offshore.
During discharge, we confirm that there are no safety issues by monitoring tritium concentrations calculated from the dilution ratio continuously and measuring the concentrations in discharging water daily. Furthermore, we will measure the tritium concentration in water in the vertical shaft prior to discharge once a year.

Flow meters are continually used to monitor ALPS treated water and seawater, and if an abnormality is detected emergency isolation valves will automatically close thereby terminating sea discharge.
Emergency isolation valves have been installed in two locations just in case one does not work.

Furthermore, one of the emergency isolation valves has been installed inside of the seawall so that sea discharge can be stopped even in the event of a large tsunami.

In order to examine the radioactive impact of radioactive substances on the environment from the Fukushima Daiichi Nuclear Power Station, we measure the concentrations of radioactive substances in seawater and marine products.

Monitoring is also implemented by TEPCO, Fukushima Prefecture, the Ministry of the Environment, the Nuclear Regulation Authority and the Fisheries Agency. The results are being disclosed and disseminated on our website “Overarching Radiation-monitoring data Browsing System”.