Innovation for Fukushima-Daiichi
Decommissioning
Future Challenges and Expectations

Toyoaki Yamauchi, President of IRID
International Research Institute for Nuclear Decommissioning (IRID)

Roles of Organizations in Decommissioning of Fukushima Daiichi
International Research Institute for Decommissioning(IRID)
・Established : Aug 1 2013
・Partnership organization : 19 corporations
・Number of IRID : 766 people
・PJ cost : 12～17 billion Yen/year

Reference: The Agency of Natural Resources Energy, Ministryof Economy, Trade and Industry of Japan website

Muontransmission measurement to identify fuel debris
Muons are secondary cosmic rays, which generate when radiation from space collides with the atmosphere of the

Earth. The cosmic ray muons are high-energy particles and can pass through materials.
Muon tomography can measure the number of muons that pass through the reactor building to image the density ofmaterials such as X-ray. It can be used to image the distribution of fuel debris in the reactor pressure vessel (RPV).
(Smaller number of muons will pass through high density regions so higher density regions show dark shadow).
Reactorbuilding(R/B)

Estimated reactor
core region

WestReactor wall
(main steam isolation valve)
ReactorSpent fuelpoolTurbine
building

Pressure
Reactor core region
Vessel(RPV)

PCV
surrounding
concrete

EastMeasurement
equipment

Illustration of measuring muons passing through the reactor building(horizontal cross section)

Mountainside hill<Measurement principle of the muon transmission method >Panel②X axisSouthPanel①
X axisLength of density（g/cc・m）(As of September 8, 2017)

Height（OP）[m]

Horizontal

North

Measurement image of inside the unit 3Muon
Y axis

Y axisReference: The TEOCO Holdings, Inc. website

3©International Research Institute for Nuclear Decommissioning

Robots Developed for Investigation of PCV Interiors

Investigation results of inside the PCV (2017-2023)
 The investigation robot was developed based on a method of accessing thePCV. The robot investigated the inside of the Units 1-3 PCVs by using cameras.
 There are large differences in state of the damaged reactor cores depending oneach Unit.
 The severity of damage is estimated in order of No. 1, No. 3 and No. 2.
 In Unit 2, part of fuel assembly ( a handle) that has fallen on the floor outside of
写真の視野
the reactor was observed.

Before touching deposits

Photo: Near the pedestal inner wall at the Unit 2PCV bottom
Reference: The TEPCO Holding Inc. website.

Touching deposits

Photo: Touching pebble-like deposits by tool atthe Unit 2 PCV bottom

5©International Research Institute for Nuclear Decommissioning

Investigation results of the Unit 1 pedestal (2023)
We confirmed the Unit 1 pedestal wall on inner andopening were damaged and remained only iron rebar.

We assumes that the lost concrete area of the pedestal
inner wall (only rebar remains) is approximately 1meter inheight and 50cm in depth.

The lost of the pedestal outer wall opening would be limited.

インナースカート
Inner skirt

Photo 1

Photo 2

開口部
Opening

Remains ofconcretewalls ?

A ROV frame can be seen,

Photo 1: Concrete wall seen from the pedestal opening
Photo 2: Concrete wall seen from the pedestal outside

無断複製・転載禁止 東京電力ホールディングス株式会社

Reference: Study committee of monitoring and evaluating specific nuclear facilities (the 107th), April 14, 2023

6

Photos processed by TEPCO Holdings Inc.

Development and Demonstration of the Robot Arm・A long cantilever arm with 22 meter in length and 4.6 ton inweight is designed to pass through a narrow X-6 penetration(55 cm in inner diameter and some deposits haveaccumulated inside the X-6 penetration).
・Fuel debris which is located on the pedestal floor 5 and 10
meters below the X-6 penetration end can be retrieved byusing a tool operated with the program control system.
・Collected fuel debris will be stored in a container designed for
Fuel debris, which is remotely operated in the enclosure.

 The arm type access equipment was manufactured
which can access on a wide range through the PCV
penetration for maintenance of a control rod drive
mechanism.
 Total length of the arm: Approx. 22m
 Investigation equipment up to 10kg can be loaded.

Preparation for Fuel Debris retrieval from Unit 2
Demonstration test at the JAEA Naraha Center for Remote Technology Development
Mock-up steel X-6
penetration

LightCamera
Pedestal

Robot arm
AWJ tool

Reference: Report of the preparation status of investigation inside the Unit 2 PCV and trial retrieval of fuel debris issued by the Team Meeting and Countermeasures forDecommissioning and Contaminated Water Treatment Conference (the 115th).

Installation work of the connecting part at the Unit 2 site
Isolation room: Confirmation ofperformance for carry-in, assembly andcarry-out.

Assembled isolation
room

Imaging view of carrying to
an isolation room

8

©International Research Institute for Nuclear Decommissioning

Summary of the Investigation Results (Unit 1)
・ The Unit 1 reactor core was damaged about eight
hours after the loss of power.
・ Unit 1 has almost no fuel in the RPV, and deposits
have spread outside the pedestal. The inner walls ofthe pedestal were also damaged.

Summary of the Investigation Results (Unit 2)
・ The Unit 2 reactor core was damaged about
3 days after the loss of power.
・ Unit 2 has a lot of fuel left in the reactor
pressure vessel (RPV). Although there is
1 meter-deposit on the pedestal floor. The RPV
substructure retains its original form.

Summary of the Investigation Results (Unit 3)
・ The Unit 3 reactor core was damaged about one
and half day after the loss of power.
・ Unit 3 have some fuel left in the RPV. There is 2-3
meters of deposits on the pedestal floor.

Future Challenges and Expectations•IRID has been conducting research and development for the investigation of inside thePCVs. The results of R&D revealed that the situation of inside the PCVs was clarified byphotography taken by camera.
•Further investigation and clarification of the accident occurrence are needed to develop
the future plan and to proceed with engineering for the decommissioning.
•We will continue working together for the decommissioning of the Fukushima Daiichi bysharing knowledge and experience with relevant parties from Japan and overseas.
• Elucidation of the accident phenomenon will be useful not only for Fukushima
decommissioning, but also for accident operation procedures for operating reactors
and for designing safety measures for new reactors. We will continue sharing theseuseful information with the world to contribute the safety of the nuclear power plant.