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. The scale of the retrieval will then be expanded in stages.

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.
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: Sampling

Sampling will be carried out to determine the state of the fuel debris.

Step 3: Retrieval of small amount of fuel debris

Based on information obtained in the surveys inside the containment vessel and from sampling, first of all a small amount of fuel debris will be retrieved.

Step 4: Retrieval of large amount of fuel debris

Based on the success with small-scale fuel debris retrieval and other factors, gradually larger amounts will be retrieved.

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.

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