In Units 1 to 3, the fuel and the metal cladding that forms the outer jacket of the fuel rods melted, then re-solidified as fuel debris. To reduce the risk from this fuel debris, preparations are under way for retrieving it from the reactors. The current aim is to begin retrieval from the first unit (Unit 2) in 2021, and to gradually enlarge the scale of the retrieval. The retrieved fuel debris will be stored in the new storage facility that will be constructed within the site.

What Is Fuel Debris?

At the time of the accident, Units 1 to 3 were operating and had fuel rods loaded in the reactors. After the accident occurred, the loss of emergency power prevented further cooling of the cores, resulting in overheating and melting of the fuel. Fuel debris refers to this melted fuel and other substances after they cooled and re-solidified.
Currently the state inside the containment vessel is being confirmed, and various kinds of surveys are being conducted prior to retrieval of the debris.

Estimated Distribution of Core and Containment Vessel Fuel Debris in Each Unit

Approach to Retrieving Fuel Debris

Policy1 A step-by-step approach As the retrieval is being carried out, the approach will be adjusted flexibly based on information obtained gradually over the course of the operation.
Policy2 Optimization of the overall reactor workflow A comprehensive plan will be studied, aimed at overall optimization, from the preparatory phase to fuel debris retrieval work, transport, processing, storage, and cleanup.
Policy 3 Combination of multiple methods A combination of engineering methods will be studied, optimal for the location of the fuel debris, built on the basic approach of accessing the bottom of the containment vessel from the side and accessing the pressure vessel from above.
Policy4 Emphasis on aerial methods Since the submersion method for filling the reactor containment vessels with water is technically of high difficulty, the emphasis of the efforts will be on aerial work methods.
Policy5
Starting with fuel debris retrieval involving side access to the bottom of the containment vessel
From the standpoint of quickly reducing fuel debris risk, first of all the debris at the bottom of the reactor containment vessel will be retrieved from the side.

Fuel Debris Retrieval Steps

Step 1: Surveys inside containment vessels

Surveys using robots and other means will be conducted to obtain information about the state inside the containment vessels.

Step 2: Fuel Debris Retrieval

Fuel debris retrieval will be carried out on an experimental bases and the conditions of the fuel debris will be analyzed. Furthermore, the scale of the fuel debris retrieval will be enlarged based on the obtained information from Primary Containment Vessel internal investigations and experimental retrieval.

Step 3: Storage

The retrieved fuel debris will be transported with the specially designed container to the new storage facility that will be constructed within the site.

Status of Each Unit

Surveys will be conducted in the containment vessels of each unit, to confirm the status of fuel debris and the structures around the debris.

The status of progress on the mid- to long-term roadmap (decommissioning and contaminated water measures team meetings/secretariat conferences) is updated in monthly progress reports and other materials.
See the Fuel Debris Retrieval material for details.

Efforts of Primary Containment Vessel Internal investigation (chronology)

Unit1 Unit2 Unit3
2012

October (1st)

January (1st)

March (2nd)

2013

August (3rd)

2014
2015

April (2nd)

October (1st)

2016
2017

March (3rd)

January to February (4th)

July (2nd)

2018

January (5th)

2019

February (6th)

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