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Efforts to Decommission the TEPCO
Fukushima Daiichi Nuclear Power Station

By Nuclear Accident Response Office, Agency for Natural Resources & Energy, Ministry of Economy, Trade & Industry

IntroductionMore than seven years have passed since the accident at theTEPCO Fukushima Daiichi Nuclear Power Station. Having emerged
from the initial post-accident emergency response, efforts todecommission the power station and manage contaminated water
are moving forward safely and steadily based on the Mid-to-LongTerm Roadmap Towards the Decommissioning of TEPCO Fukushima
Daiichi Nuclear Power Station. This paper presents an overview ofthe schedule for decommissioning the power station, including adescription of measures taken to date since the accident, their effect,
and future efforts.

Schedule for Decommissioning the Fukushima
Daiichi Nuclear Power Station
The Japanese government drew up its first Mid-and-Long-Term
Roadmap for decommissioning the Fukushima Daiichi Nuclear
Power Station in December 2011. As a result of the accident, themeltdown of fuel in the reactor pressure vessels (RPVs) at the power
station was accompanied by the generation of hydrogen, which led
to hydrogen explosions. Currently, a solidified mixture of melted fueland surrounding structural material (“fuel debris”) remains in the
primary containment vessels (PCVs) at Units 1–3, and there is aneed to move forward with the processing of radioactive waste andcontaminated water.
The Mid-and-Long-Term Roadmap lays out a target schedule foreach step in the decommissioning work. It is divided into threephases; we are currently in Phase 2.

CHART 1

Phases of the Mid-and-Long-Term
Roadmap
Dec. 2011

Nov. 2013

Today

Dec. 2021

30–40 years later

Phase 1

Phase 2Phase 3

Until the startof fuelremoval fromthe SFP(within
2 years)

Until the start of fueldebris removal(within 10 years)

Until completion of
decommissioning(30–40 years later)

We would like now to explain the difficultly of decommissioning
work at the Fukushima Daiichi Nuclear Power Station. Highconcentrations of radioactive material within the reactor buildings
make it difficult for people to enter to work and difficult to accurately
ascertain the details about conditions inside. Undertaken in thisenvironment, the decommissioning of the power station isunprecedented anywhere in the world for its difficulty and, relative toordinary construction projects for which conditions can be fully
ascertained, can be described as a project with inherent
uncertainties.
Even amid such uncertainty, however, there is a need to move
forward safely and surely in a way that enables coping with unlikely
events, proceeding carefully in order to minimize the burden placedon those working on site.
The Mid-and-Long-Term Roadmap has been revised from time totime to optimize it for changing conditions by reflecting newunderstandings of the conditions in the field as well as the latest
knowledge and the results of research and development, with thefourth revision undertaken in September 2017 (Chart 1).

Current Conditions
Each measure will be addressed in turn in the next section, while
this section describes the overall situation today at the Fukushima
Daiichi Nuclear Power Station.

● Condition of the Fuel
The melted-down fuel debris at Units 1–3 is being kept stable, andthe temperature inside the reactors kept low, through a continuous
injection of water. Decay heat from the fuel in the Spent Fuel Pool
(SFP) has decreased significantly with the passage of more thanseven years since the accident. In fact, when the water temperature
was checked after cooling of the pool was suspended for one monthunder severe midsummer conditions, the water temperature wasconfirmed to remain below the limit (65°C) due to natural heatradiation (Image 1).
Given these stable conditions, the likelihood of another accident isextremely low. Nevertheless, steps are being taken to prepare for theunlikely, including facilities to suppress recriticality and measures toaddress and train for earthquakes and tsunami.

Source: Agency for Natural Resources and Energy

44 Japan SPOTLIGHT • September / October 2018https://www.jef.or.jp/journal/

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IMAGE 1

PHOTO 1

Reactor building (schematic)
Pressure vessel

Photo: Tokyo Electric Power Company Holdings, Inc. (TEPCO)

Area where protective clothing is required
Area where duties can be executed wearing
ordinary work clothing (96%)

Spent Fuel Pool
(SFP)

Primary containment
vessel (PCV)

Injected water
Fuel debris

Source: Agency for Natural Resources and Energy
Area where duties can be executed wearing ordinary work clothing.

● Condition of the Site and the Surrounding Area
Monitoring posts and dust monitors installed around the perimeterof the power station site keep watch around the clock, andconditions remain stable. The concentration of radioactive material in
the seawater in the sea surrounding the power station (outside theharbor), for example, is low enough to ensure public safety, evencompared to global water quality standards for drinking water, andan assessment by an international organization has concluded thatthe marine environment is stable (Chart 2).
The working environment has also greatly improved. Althoughprotective clothing was required throughout almost the entire area
immediately after the accident, measures to reduce radiation doses
from the natural environment through decontamination and facing

work have made it possible for workers to now carry out their duties
in ordinary work clothes at around 96% of the site. In addition,measures have been implemented to bolster medical readiness intime of emergency such as stationing emergency physicians on sitearound the clock and installing a heliport to reduce the time required
for transport. A large rest house has also been constructed thatincorporates a restaurant, shops, and shower rooms, canaccommodate 1,200 people at a time, and serves hot, delicious,
locally-prepared meals.
Efforts will continue to be made to provide a safe and improved
working environment in order to move steadily forward withdecommissioning over the long term (Photo 1).

CHART 2Concentration of radioactive material (Cesium-137) near the south
discharge channel (monthly average)(Bq/L)
100,000
10,000Cesium-137

1,000

Guidance level in the WHO guidelines fordrinking-water quality (10Bq/L)

100
10
1
0.1
0.01

2012

2013

2014

2015

2016

2017

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2011

Source: Agency for Natural Resources and Energy

Japan SPOTLIGHT • September / October 201845

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PHOTO 2

Photo: Tokyo Electric Power Company Holdings, Inc. (TEPCO)

The presence of part of a fuel assembly (marked in yellow) suggests that the surrounding deposits
are fuel debris.

Progress of Each Measure & Future Efforts(1) Efforts Leading to Fuel Debris Retrieval(i) A Fourth Revision of the Mid-and-Long-Term Roadmap
As described above, the Mid-and-Long-Term Roadmap
underwent a fourth revision in September 2017. One of the
key points in this revision was the determination of the policy
on fuel debris retrieval. Safely completing this retrieval is amajor target on the schedule leading to decommissioning. The
determination of the policy on the retrieval in the revision in2017 came about as the result of various research andanalysis that revealed previously unverifiable details about thesituation inside of Units 1–3.
(ii) Investigation Towards Fuel Debris Retrieval
Investigation environments that people could not enter
directly required both existing techniques and bringing
together wisdom from Japan and overseas to conduct
computer analyses as well as research utilizing a variety of
cutting-edge technologies.
1 Development of Robots Adapted to Conditions Inside theReactors
Conditions inside the reactors are severe, with highradioactivity and almost no light. In addition, approach
routes are difficult to navigate, being narrow with many
obstacles and other unexpected impediments.
Investigations, then, were conducted using robots in aneffort to gather a variety of data in order to grasp conditions
insider the reactor building that could not be observed
directly by people, such as radiation levels and the state ofdamage. Previously, a number of robots optimized to various
conditions were developed for remote-control investigations,
including robots that changed shape in accordance with theirroute or that could swim under water. The surveys made it
possible to image conditions inside the reactors and to
46 Japan SPOTLIGHT • September / October 2018confirm the presence of deposits thought to be fuel debris. It
was also possible to confirm whether there was space towork toward retrieval of the fuel debris (Photo 2).
2 Investigations Using Cosmic-ray Muons
In investigating the inside of the PCVs, muons — a kindof cosmic ray that rains down from space — were used tovisualize the situation inside the reactors.
Muons pass through nearly all kinds of material but are
unable to pass through high-density material such as fuelthat has melted and solidified. Taking advantage of thischaracteristic, it is possible to analyze the volume ofmaterial in substances along the path that is traced by flying
particles and, seeing inside the reactor as if looking at an
x-ray, to determine whether or not the fuel is in the reactor
core.
The findings revealed that almost no fuel remained in thereactor core of RPV at Unit 1, and the possibility that some
fuel debris remained in the bottom of the RPVs at Units 2
and 3.
(iii) Determination on the Policy on Fuel Debris Retrieval
The fuel debris is currently being cooled and kept stable.
Nevertheless, from a mid-to-long-term risk management
perspective, it is impossible to remove all uncertainty oruneasiness so there is a need to retrieve the fuel debris assoon as possible and transport it to a safe place for stablestorage.
As previously described, investigations to date using avariety of methods have revealed important information about
the inside of the reactors, including information on the
distribution of fuel debris, information needed to confirm
access routes to fuel debris, and information to help evaluate
work safety.
As a result, the following retrieval policies have been
determined in the revision in 2017:• A step-by-step approach should be adopted, beginningwith small-scale tasks and then expanding gradually tolarger-scale tasks while confirming the situation andflexibly reviewing methods based on the information
thereby obtained.
• With regard to retrieval policies, given the technologicaldifficulty of the “full submersion method” of completely
filling the reactor containment vessel with water, emphasisshould be placed on retrieval of fuel debris from the vesselusing “partial submersion methods”.
• Primary emphasis should be placed on retrieving fueldebris at the bottom of the containment vessel using aside-access method.
Given the above policies, deliberations leading to debris
retrieval are now underway, with further interior investigations
and technological developments moving forward toward theretrieval of fuel debris beginning in 2021.
In addition, in order to ascertain the feasibility of the work,
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will move forward in deliberating engineering aspects toensure a smooth transition to the actual work of retrieval.

(2) Management of Contaminated Water
In the reactor buildings, the reactors are kept stable at low
temperature by cooling them with water, but this water mixes withgroundwater flowing into the buildings, generating new
contaminated water every day. Multilayered prevention measures,
therefore, are being taken in line with the three basic principles of (i)isolating water from sources of contamination, (ii) preventing
leakage of contaminated water, and (iii) removing sources ofcontamination.
(i) Isolation Measures
Measures to isolate water from sources of contamination
are aimed at reducing the volume of contaminated water
generated, with a combination of various measures taken to
constrain the flow of groundwater into the buildings.
Specific measures taken include a groundwater bypass thatdraws groundwater from the mountain side of the buildings
and discharges it into the ocean, sub-drains and groundwater
bypasses nearer the buildings that draw groundwater anddischarge it into the ocean after purification, a land-side
impermeable wall made of frozen soil and groundwater, andwide-area paving of the site to prevent rainwater from seeping
into the soil. These measures have greatly reduced the volume
of contaminated water generated. (Before measures: approx.
540m3/day; FY 2017 average: approx. 220m3/day)(ii) Measures to Prevent Leakage
Measures to prevent leakage of contaminated water are
aimed at reducing the risk of radioactive material outflowing to
the sea. In October 2015, construction was completed on the
installation of a 30-meter-deep, 780-meter-long wall of steel
pilings on the ocean side of the buildings (the sea-side
impermeable wall). This has greatly reduced the volume ofradioactive material outflowing into the harbor and the water
quality in the harbor is confirmed to be gradually improving.
Furthermore, in addition to proceeding with new installationsof high-reliability welded storage tanks, and the replacementof flange-type storage tanks made of bolted steel plates withsuch welded tanks, preventative measures are also being
taken to prepare for any unexpected leakage such as doublediking in the areas surrounding the tanks and installing
waterproof seals on the lateral flanges, as well as multiple
patrols each day (Chart 3).
(iii) Removal Measures
Measures to remove sources of contamination include
purifying contaminated water using multiple purification
facilities including multi-nuclide removal equipment (ALPS:
Advanced Liquid Processing System) and then storing it intanks. In particular, processing of the highly contaminatedwater that was problematic after the accident concluded in
May 2015; today, it is purified water that is being stored intanks. Highly contaminated water also collected in the

CHART 3

Changes in the concentration ofradioactive material in seawater
within the harbor (before and after completionof the sea-side impermeable wall)(Bq/L)
140

140

Strontium-90
Cesium-137

120
100

Oct. 26, 2015
Completion of sea-side
impermeable wall

80
60
40
20
0

16

0.4

2.6

After completion(Oct. 26–30)

Before completion(Sept. 15–19)

Source: Agency for Natural Resources and Energy

underground tunnel on the sea-side of the reactor buildings(seawater piping trench), posing a large risk in the event of
unexpected leakage. This contaminated water, therefore, waspumped out and the trench interior filled in and blocked off,with the removal of contaminated water and filling in of thetrench completed by December 2015, which greatly reducedrisk.
Due to these multilayered preventative efforts, great progress has
been made in managing contaminated water. In order to bring final
resolution to the issue of contaminated water, however, continued
efforts are being made for subsequent measures throughdeliberation by a committee of experts.

(3) Removal of Fuel from the SFP
The removal of fuel on the way to decommissioning means theremoval of an enormous risk; transporting the fuel from thedamaged buildings to a sound building will enable storing andmanaging it in a safer place.
(i) Completion of Fuel Removal from the SFP at Unit 4
Removal of fuel from the SFP at Unit 4, considered among
the highest priority issues at hand, was completed in
December 2014. All of the 1,535 fuel assemblies weretransferred to a common SFP.
(ii) Fuel Removal from the SFPs at Units 1–3
At Unit 1, removal of the reactor building cover has been
completed, and windbreak fencing and work platforms
installed. Work is underway to remove rubble from the northside of the operating floor. At Unit 2, which avoided explosion,an opening has been installed on the west side of the building
and surveys of the operating floor are being conducted. Fuelremoval at Units 1 and 2 is scheduled to begin in FY 2023. At
Unit 3, installation of a cover in preparation for fuel removal
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PHOTO 3

Unit 1

At time of accident

Today

Unit 3

Today

Unit 2

At time of accident

Photo: Tokyo Electric Power Company Holdings, Inc. (TEPCO)

Today

Unit 4Current status at the Fukushima Daiichi Nuclear Power Station

has been completed and fuel removal is schedule to begin
around mid-FY 2018.
Furthermore, to ensure that radioactive material does not
scatter during these operations, thorough protective measures
such as the spraying of anti-scattering agents are being
undertaken and the concentration of radioactive materials atwork sites is being strictly monitored (Photo 3).

(4) Waste Management
The safe storage of radioactive waste generated in the process of
decommissioning is of primary importance. The solid radioactive
waste that is generated will be categorized by surface dose rate andstored appropriately at the solid waste storage building or at outdoor
facilities. Efforts are also being made to secure sufficient storage
space based on estimates of the volume that will be generated going
forward.
Solid radioactive waste from the Fukushima Daiichi Nuclear Power
Station where the accident occurred has characteristics that differ
from the radioactive waste normally generated at a nuclear power
PHOTO 4 & IMAGE 2

No. 9 Solid waste storage building(completed February 2018)

Photo & Image: Tokyo Electric Power Company Holdings, Inc. (TEPCO)

48 Japan SPOTLIGHT • September / October 2018

station, so research and development leading to processing anddisposal is underway while ascertaining these properties (Photo 4 &Image 2).

Conclusion
Above, we have described the decommissioning schedule for the
Fukushima Daiichi Nuclear Power Station and the progress made todate. The working environment at the power station remains difficult,however, because the task is unprecedented and there are many
places on site where doses are high. Going forward, therefore, it will
be necessary to review matters flexibly to address new information,
possibly including additional safely measures or altering the natureof the work to be done.
In addition, there is a need to broadly communicate theprocedures for decommissioning as a whole and its individual steps
both to local residents and to those concerned in Japan andoverseas.
For the sake of Fukushima reconstruction, the work ofdecommissioning must be accomplished no matter what it takes.
Work will continue over the mid to long term. Bringing together thecapabilities of the world as well as Japan and making safety thehighest priority, the national government will stand at the fore and do
everything in its power to move the project forward.