Unit 3

On March 11, 2011, the major tsunami caused the loss of most power supply, water injection, and heat removal functionality. As a result, following the damage to Unit 1, on March 14, Unit 3 also experienced a hydrogen explosion and the building was damaged. Currently, there are 566 fuel rod assemblies remaining in the spent fuel pool. As part of the decommissioning efforts, removal of the remaining fuel rods eliminates a major risk. In addition, transferring the fuel from the damaged building to a structurally sound building allows much safer storage and management.

Progress of fuel removal

  • Fuel removal started in April,2019.

  • Number of fuel assemblies having been transported to the common pool7/566
    (As of April 25, 2019)

  • Breakdown of transferred assemblies by type
    Spent fuel: 0 / 514
    Unirradiated (New) fuel: 7 / 52

※The common pool keeps fuel removed from the Unit 4 and others.

Steps for fuel removal

  • (1)

    Fuel assemblies stored in the spent fuel pool are put into a transport container (cask) one by one in the water using a fuel handling machine.

  • (2)

    Lid is attached to the cask, which is then cleaned. After that it is lowered to the ground floor using a crane and loaded onto a trailer.

  • (3)

    The cask is transported to the common pool located on-site.

  • (4) Fuel in the cask is stored in the common pool.

Main Work Procedure

Decontamination and Shielding

Decontamination and shielding are necessary due to the high levels of radiation on the top floor of the building that houses the fuel handling machine. Starting with decontamination and shielding work, the removal of fuel is an effort on an unprecedented scale. Since the conditions made it difficult for people to carry out on-site work, a crane was redesigned to allow remote operation so that decontamination work and shielding installation could be completed.

Removal of Debris (From the Spent Fuel Pool)

As large pieces of debris and other objects were present in the spent fuel pool, a detailed removal plan was devised based on an underwater camera pre-investigation and 3D model simulations. Other measures were also devised such as the development of new removal tools. On August 2, removal of the largest pieces of debris (fuel handling machine) was completed.

Installation of Fuel Removal Cover and Fuel Handling Machine

For the installation of the required fuel removal cover, much emphasis was placed on improving construction safety and reducing worker radiation exposure. Therefore, partial assembly was first carried out in Onahama, Iwaki City, around 60 km from the Fukushima Daiichi Nuclear Power Station. After removing the debris, installation work for the fuel removal cover commenced in January 2017. Installation of the fuel handling machine was completed in November 2017, followed by the successful installation of the dome roof in February 2018.

Removal of Fuel

Removal of 566 fuel rod assemblies after installation of the new fuel handling machine. In order to carry out work with the utmost care, repeated training exercises will be carried out on the actual equipment to be used for on- site work such as removal of debris and fuel. Fuel removal from the spent fuel pool started in April,2019.

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