Current Status and Challenges of R&D for
Decommissioning of Fukushima Daiichi
Nuclear Power Station
福島第一原子力発電所廃炉
研究開発の現状と課題
NICC
Tokyo Institute of Technology
July 31, 2024
Senior Manager Planning and Administration Department

International Research Institute for Nuclear Decommissioning (IRID)

Naoaki Okuzumi
The results are obtained under the Subsidy Project of Decommissioning and Contaminated Water Management granted by
the Ministry of Economy, Trade and Industry.
Unauthorized copy and技術研究組合
reproduction prohibited.
無断複製・転載禁止
国際廃炉研究開発機構©International
Research
Institute
NuclearDecommissioning
Decommissioning©International
Research
InstituteforforNuclear

Self Introduction
Naoaki Okuzumi
July 2016- current Senior Manager, Planning and Adoministration Department,International Research Institute for Nuclear Decommissioning(IRID)

June 2016Retired Toshiba Corporation

2000-2016

General Manager, Corporate Communications Division etc.,
Toshiba Head Quarters(Dec.1990-Jan.1992: Liaison Manager in GE Nuclear Energy at San Jose CA, U.S.A.)
1979-2000

System Engineering Department of Nuclear Energy Division etc.,
System Engineer for BWR Nuclear System, Toshiba Corporation

Apr.1979

Joined Toshiba Corporation

Mar.1979

Graduated from Faculty of Mechanical Engineering,
the University of Tokyo

June 1956

Born in Tokyo

2©International Research Institute for Nuclear Decommissioning

Contents
1. Introduction
2. Development of Remotely Operation Equipment for
Dose Reduction
3. Development of Repairing Technology for PCV
4. Development of Investigation Technology for inside
PCV
5. Development of Technology for Fuel Debris
Retrieval
6. Nuclear Safety Enhancement
PCV: primary containment vessel

3©International Research Institute for Nuclear Decommissioning

Contents
1. Introduction
2. Development of Remotely Operation Equipment for
Dose Reduction
3. Development of Repairing Technology for PCV
4. Development of Investigation Technology for inside
PCV
5. Development of Technology for Fuel Debris
Retrieval
6. Nuclear Safety Enhancement
PCV : Primary containment vessel

4©International Research Institute for Nuclear DecommissioningVideo: Introduction of IRID

5

©International Research Institute for Nuclear Decommissioning

■Boiling Water Reactor (BWR)

BWR : Boiling Water Reactor

The reactor heats water, which turns to steam and drives asteam turbine.

RPV
Steam

Water

Fuel

Reactor Operating
Pressure :7Mpa

Generator

Turbine

Water
Condenser
Control
rods

Water

Re-circulation
pump

Water
Circulationwater pump

Suppression pool

Discharged water
Cooling water(seawater)

Feedwater pump

*Reference: The Nuclear Consensus 2014, issued by Federation ofElectric Power Companies■Pressurized Water Reactor (PWR)
The heated and high pressure water flows to a steam
generator. Then the steam drives turbines.

PWR : Pressurized Water Reactor

Pressurizer

Reactor Operating Pressure :30Mpa

Steam

Control
rods

Water

Fuel

Coolantpump

Steamgenerator

Water

TurbineGenerator

Condenser
Water

RPV

Circulationwater pump

Discharged water
Cooling water(seawater)

Feedwater pump

Steam
Generator*Reference: The Nuclear Consensus 2014, issued by Federation ofElectric Power Companies©International Research Institute for Nuclear Decommissioning

Boiling Water Reactor (BWR)
Reactor Building

46m

SpringExternal
Fuelspring

Approx.10mm
Approx.
10mm

Steam dryer
Steam outlet
nozzleassemblies

RPV

3F

Channel
box
Tie
plate

5.5m

A-A’ Cross section

11m

Pedestal

Dry Well
(D/W)

Fuel
assemblies
Water rod
Control rod

2F

Reactor Pressure
Vessel (RPV)

Channelbox

20m

Approx.14cm

Bent Pipe

Fuel Assembly

1F

PCV: PrimaryContainment
Vessel

Torus
Room

Fuel
cladding(Zirconium
alloy
PelletDS pit34m

Recirculation
system outlet

4F

Spent
Fuel
Pool
(SFP)
21m

46m

Fuel assemblies

PelletSupportgrid

Operation Floor (5/F)

Steam separator

Control rod

Fuel assemblies

Handle9m

Suppression
Chamber
(S/C)

38m

7

©International Research Institute for Nuclear Decommissioning

Appearance of Primary Containment Vessel (PCV) (Photo of
PCV under construction)
Dry well (D/W): Upper part of PCV
above the S/C

PCV penetration：Penetrations ofpiping and electric wiring, etc.
Unit 1: Approx. 150 penetrations
Unit 2: Approx. 200 penetrations
Unit 3: Approx. 190 penetrations
Equipment hatch: Carry-in/out port oflarge equipment
Vent pipe: Connection pipe between
D/W and S/C
Suppression Chamber (S/C): The
S/C condenses water vapors
generated when an accident occurs
to suppress the increase of pressurein PCV.

Air lock: Entrance and exit
for humans“Browns Ferry Unit 1 under construction 1966.Sep.”
Tennessee Valley Authority – TVA’s 75th Anniversary webpa

88©International Research Institute for Nuclear Decommissioning

Outline of IRID

1. NameInternational Research Institute for Nuclear Decommissioning(IRID)
https://irid.or.jp/en/

R&D
2. Date of Establishment
August 1, 2013

IRID
3. Membership (19 organizations)
2 research institutes
International
JAEA etc.
Entities
4 manufacturers
Toshiba ESS, Hitachi-GE,MHI etc.
12 electric utilities, etc.
TEPCO Holdings etc.
9

HRD

©International Research Institute for Nuclear Decommissioning

Introduction: R&D projects conducted by IRID
1. R&D for fuel removal from spent fuel pool
Evaluation of Long-term Structural Integrity ofFuel Assemblies Removed from Spent Fuel Pool

2 R&D for Fuel Debris Retrieval
Technology for
Decontamination and Dose
Reduction
Remotely Operated
Decontamination
Technology in R/B
Completed in March 2016

3 R&D for Radioactive Wastes
Completed in
March 2016

Treatment andTechnology for Proceeding
Disposal of Solid
Process Methods of Radioactive
Radioactive
WastesWastesCompleted in March 2019

Fuel Debris Retrieval Technology
Retrieval Technology for Fuel Debris and Internal Structure:
Criticality Control/Fundamental Technology/ Small Neutron Detector

Completed in March 2019
Development of Retrieval Dust collection System Technology for
Containment,
Technology and Method
for Retrieval ofTransfer
For Fuel debris and Internal
Fuel debris and
And Storage ofStructures
Internal structures

Development of Safety
System for fuelDebris retrieval

Fuel Debris

Technology for Environmental
Improvement<Ensuring of the stable state>
Corrosion Control Technology
in RPV/PCVCompleted in March2018
Full-scale test for Repair
Technology for PCV Leak Points
Completed in March 2018
Full-scale Test for Water Circulation
Technology in PCV

Completed in March 2019

Investigation and Analysis Technology＜Direct Investigation＞＜Indirect Investigation＞
Fuel debris detection Technology
for RPV
Completed in March2018
Upgrading for Identifying Conditions
Technology for Detailed Investigation
Insides the Reactor
Inside PCVCompleted in March 2018
Investigation
Technology
Inside the RPV

Completed in March 2019

PCV detailed
Fuel Debris
PCV Detailed
Investigation:
Fuel Debris Sampling Technology/
Investigation: Characterization
Demonstration/Increase ofDemonstration
Through
Scale
and Analysis©International ResearchInstitute for NuclearRetrieval
Decommissioning
X-6 penetration of Sediments
for Fuel Debris

Contents
1. Introduction
2. Development of Remotely Operation Equipment for
Dose Reduction
3. Development of Repairing Technology for PCV
4. Development of Investigation Technology for inside
PCV
5. Development of Technology for Fuel Debris
Retrieval
6. Nuclear Safety Enhancement
PCV : primary containment vessel

11

12

Remote Decontamination Technology
Needs for technologicaldevelopment

For low places (floors andlower partRadiationof walls) dose in R/B
(1st
floor
of Unit 1)For
highplaces*As of March 22, 2013

Humans cannot access the R/B
because radiation levels arehigh in the R/B. It is necessary
to improve work
environments (dose
reduction).

1.2
1.9

4.5
2.0
4.5
X100B

3.0
2.5

Suction and blast

Spent
fuel
pool

3.5 3.5

arm Upper

22.0
7.0

3.5

4.0

Reactor building (R/B)

8.0

Upper

100

50

Upper

1700

X40B surface

MAX 23

X49 surface

Rotation arm

MAX800

4.5

11.4

9.0
1200

3.5

7.0

3.5

20
3.0
Extended
1.５

High5.0
pressure
3.5
Near the
water
floor
injection
4.0

2100
100
230
5.0
5.0
6.0
Dry7.0ice 20
4.5
40
blast
7.5 15
6.5 7.095
6.5 7.0 8.0
54
120
90
5.0

6.0

Decontamination ofwork and moving
RPVareas

PCV

For upper floors
100m

15Compressor
cart
60

40m

Less than 3mSv/h

Above funnel

2200

Floor
penetration

4700

247 300 220 1100

1280

290 800 1820
290
138
Decontamination
unit
cart
26
600
127
48
Work cart

20m

3mSv/h ～10mSv/h

20mSv/h ～50mSv/hMore than 50mSv/h

10mSv/h ～20mSv/h13

Remote Decontamination Technology
Site application (Unit 3)

Suction and dry ice blast
decontamination was
performed on 1st floor of the Unit
3 R/B from January 2016 to
February 2016.
：Suction：Dry ice blast

Photos of transporting decontaminationequipment from a container

Power panel

Decontamination equipment
for high places
Decontamination cart for
low places

Cable tray

Support cart for
low placesWest side wall
Entry route

Upper wall of elevator

Photo of decontamination equipment
moving to the Unit 3 R/B

Contents
1. Introduction
2. Development of Remotely Operation Equipment for
Dose Reduction

3. Development of Repairing Technology for PCV
4. Development of Investigation Technology for inside
PCV
5. Development of Technology for Fuel Debris
Retrieval
6. Nuclear Safety Enhancement
PCV : primary containment vessel

14

Repair Technology to Stop Water Leaks from PrimaryContainment Vessel (PCV)
Test for stopping waterleaks from vent pipe

：Repair area to stop
water leaks

Full-scale
mock-up test
楢葉遠隔技術センターでの実規模試験
Full-scale mock-up test facility (1/8 sector)
Vent pipe

Suppression
chamber (S/C)

Vent pipe

Downcomer
QuencherWater stop performance wasverified by using the 1/2 scale
test facility (in factory).

Test for stopping water
leaks

Built in Naraha Center for Remote Control
Technology Development

Stop leaking
vent pipeWork floor

Remote manipulator

Approx.
13m

Material to stop
leakageTorusroom wall

Vent pipe
Material to stop
leakageTest
facility

Water stop performance of thematerial was verified by using the fullscale test facility (outdoor).

15

Confirmation of Procedures for Full-scale Test Facility (JAEA Naraha
Center for Remote Control Technology Development)
Purpose⚫ Creating of procedure manual byusing a full-scale test facility
considering actual onsite work to
determine the applicability of
the actual equipment.

Major work
⚫ The procedures of the following
three methods for water stops
are tested to verify workability
and performance of concrete
placing.
① Stop water leaks from ventpipes
② Stop water leaks in the S/C
by injecting filling③ Strengthen the S/C support
columnTest period
Nov. 2016 – March 2018

Appearance of test facility

Inside of the test facility (in theS/C) ）

７m

10.5m

3.8m

Verification test of workability tostrengthen the S/C support column

16

Remotemanipulator

Contents
1. Introduction
2. Development of Remotely Operation Equipment for
Dose Reduction
3. Development of Repairing Technology for PCV
4. Development of Investigation Technology for inside
PCV
5. Development of Technology for Fuel Debris
Retrieval
6. Nuclear Safety Enhancement
PCV : primary containment vessel

17Muon Transmission Measurement◼

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)

Spent fuel pool
（SFP）
North

South

Estimated reactor
core region

West

Turbinebuilding
Measurement equipment

East

Measurement equipment
Illustration of measuring muons passing through the reactor
Illustration of measuring muons passing through the reactor buildingbuilding(horizontal cross section)(vertical cross section)<Measurement principle of the muon transmission method(illustration)>

Panel①Panel②X axisTwo panel detectors (plastic scintillator) that are placed in themeasurement equipment can detect muons falling from spaceand calculate their trace on where they have passed throughfrom the coordinates (X and Y axes) on the panel.

X axisMuon
Y axis

Y axisPanel interval approx. 50cm

Quoted from a material of TEOCO Holdings, Inc. website

18©International Research Institute for Nuclear Decommissioning

Measurement Result of the Muon Transmission Method for Unit 3
Length of density（g/cc・m）(As of September 8, 2017)

Height（OP）[m]Reactor wall (main steam isolation valve)
ReactorPressure Vessel(RPV)
Reactor core region

Spent fuelpool

PCV surrounding
concrete

Mountain side hill

Horizontal

South

North

Quoted from report released from the TEPCO Holding Inc. website.

19©International Research Institute for Nuclear Decommissioning

Robot Investigation of the PCV interiors
Investigation of inside the pedestal (Unit 2)

Investigation of outside the pedestal (Unit 1)○ Remote-operated crawler robot for investigation
CrawlerDuring investigation
Additional
lighting

Winch

Back camera andlighting
Camera for travellingthrough guide pipe

Duringinvestigation

Type Ⅰ(when travellingthrough guide pipe)

Crawler

Front camera and lighting

Camera for travelling

CRD rail○Suspension type
investigation equipment (A2’
investigation)

Winch confirmation
camera (inside)

Investigation of inside the pedestal (Unit 3)

Sensor unit measuring
cameraThruster for up-and-down

U-shape type (when travellingon the floor)

Front camera

Taper

Thruster for
driving
Light

Radiation
dosimetry○Submersible Crawling Robot

Measuringcamera20©International Research Institute for Nuclear Decommissioning

Unit 1 investigation: Radiation dose and visual images
Investigation target
and points (2D)

March 18(Sat)Ｄ３March 19 (Sun)

Ｄ２

Ｄ３

Ｄ２

Ｄ１

Ｄ２

Ｄ１

Ｄ１

ＢＧ

Ｄ０

ＢＧ

Ｄ０
Measuring dose ata point where fueldebris may notremain.

Confirming
spreading offuel debris
from trench

TrenchPiping thatrobots go
throughConfirming
spreading offuel debris
from opening

Opening
Ｄ３

Ｄ０

7.8Sv/h

BG

3.8Sv/hMarch 21 (Tue)March 20 (Mon)

Ｄ３

Ｄ０

Ｄ2

12Sv/h

Ｄ３

Ｄ２

Ｄ１

ＢＧ

March 22 (Wed)

Confirming
spreading offuel debris
from opening
ＢＧ

Ｄ３ 10Sv/h

Ｄ０

Ｄ1①8.4Sv/h②8.2Sv/h③9.2Sv/h

Ｄ２

Ｄ１

Confirming
spreading offuel debris
from opening
ＢＧ

Ｄ２

Ｄ０

9.3Sv/h

Ｄ０

1/F

Investigation
results(cross-section)

Approx.
１ｍ
Basement
Water↓
surface

1.5Sv/h（Approx.1mfrom thebottom）

Approx.
2.5ｍ

11Sv/h（Approx.0.3m
from thebottom）

6.3Sv/h（Approx.
1m from thebottom）

Investigation
point

Investigation
route

3.0Sv/h（Approx.1.6
m from thebottom）

Bottom of
PCV

Images of fuel debris
spreading (simulation
examples)①6.3Sv/h②5.9Sv/h③7.4Sv/h（Approx.0.9m
from thebottom）①6.7Sv/h②3.6Sv/h①1.6Sv/h（Approx.0.6m
from thebottom）

9.4Sv/h（Approx.0.9
m from thebottom）②5.4Sv/h（Approx.0.3
m from thebottom）

①

②

①

③

②

* Radiation at the site boundary remains unchanged in approx. 0.5～2µSv/h during investigation. No
effect on surrounding environment.
* Radiation dose and distance from the bottom will be evaluated.
* Radiation dose on 1/F is almost same dose as the previous measurement (4.1～9.7Sv/h in April 2015).

21©International Research Institute for Nuclear Decommissioning

Investigation of the Unit 2 upper pedestal interior(A2 investigation: January – February 2017)【Investigation method】⚫ Photographing by camera【Implementation period】⚫ Jan. – Feb. 2017
1. Pre-confirmation system
Guide pipe

Pre-confirmation for the
penetration interior

Investigation procedure

1.Pre-confirmation for the pedestalinterior
Conducted on 30 Jan. 2017

2. Removal of deposition on the
rail
Conducted on 9 Feb. 2017

2. Deposition removal
equipment

3. A2 investigationequipment
Back camera andlight

CameraPan-tilt camera
and light

3. A2
investigation
Conducted on
16 Feb. 2017

Cleaning
nozzleFront camera andlight

Pan-tilt
cameraScraper plate

Crawler
CRD housing

Telescopic
mechanismX-6
penetration

CRD rail
CRD platform
Pedestal

22©International Research Institute for Nuclear Decommissioning

Investigation of the Unit 2 upper pedestal interior(A2 investigation: January – February 2017)

Upper pedestal interior (after image processing)23

Investigation of the lower pedestal interior(A2’ investigation in January 2018)■ Purpose of investigation
Confirmation of the state below the platform■ Investigation procedure①Inserting a guide pipe ⇒ ②Extending a pipe ⇒③Suspending a pan-tilt camera ⇒ ④Investigation
PCV
Operation unit forbending the guide pipe
end

Isolation
valve

Guide pipe
（Φ110mm）

Pedestal①

Extension pipe②

PCV penetration(X-6 penetration)
Platform
Cable drum

Control rod driving
mechanism

AlternativeshieldCable
Cable feedingmechanism③

Bird’s eye view camera
Dosimeter,
thermometer

Pan-tilt camera, exterior
lighting
Overview of the guide pipe end
mounted camera©International Research Institute for Nuclear Decommissioning

Unit 2 investigation: Pedestal Floor

Pedestal floor and wall
Fuel debris? and a fuel assembly handle

Photographing
place

Bottom of the Unit 2 PCV(An overhead image)

25

25©International Research Institute for Nuclear Decommissioning

Investigation of the Lower Pedestal Interior(A2’ investigation in February 2019)
Pedestal opening
Telescopic
investigationequipment

Direction to
the pedestal
center

CRD housing
Platform

CRD exchanger
CRD replacement
rail
Upper platform surface

Worker access
portWork platform
Pedestal bottom

Cable tray

*Investigation point is tentative.
Pedestal floor

Investigation area (A photo taken in Jan. 2018)

Before touching deposition

Touching deposition

After touching deposition

無断複製・転載禁止 東京電力ホールディングス株式会社

Source: TEPCO Holding Inc. website

26

Investigation of the Unit 2 Lower Pedestal Interior(A2’ investigation in February 2019)
Video: Unit #2 deposition at the lower pedestal area

27

©International Research Institute for Nuclear DecommissioningSubmersible Remote Operated Vehicle (ROV)(mockup vehicle)
Thruster for driving
Thruster for up-and-downFront camera

Light

Neutral buoyancy cable
Items

Specifications

Outer size

Outer diameter：φ125mm
Overall length：Approx.300mm

WeightApprox. 2000g (in air)Radiation
resistance

200Gy

Back camera
Light

28

©International Research Institute for Nuclear Decommissioning

Results of investigation for the Unit 3 PCV
2. Investigation results
2.3. The lower pedestal
Access opening forworkers

Platform
frame

Area C5 where a photo was taken<Camera position: Lower>

Photo area C1
Rotation rail bracket

Photo area C5
Photo area C3
Area C1 where a photo was taken<Camera position: Lower>
Grating

Deposition (pebble-like) Photo area C4

Photo area C2

Fallen object
Massive form
deposition

Deposition
Direction of access opening
for workers

Massive form
deposition
Deposition(sandy form)
Area C2 where a photo was taken<Camera position: Horizontal>

Area C3 where a photo was taken Area C4 where a photo was taken<Camera position: Upper><Camera position: Lower>◼ The investigation has revealed that deposition in sandy, pebble-like and massive form has
accumulated.
◼ The access opening for workers was not confirmed visually (deposition was visually seen
* Reference: Investigation result of the廃炉・汚染水対策チーム会合／事務局会議（第48回）報告資料）」より抜粋
Unit 3 PCV interior (report of the 48th Team Meeting and Countermeasures「3号機原子炉格納容器内部調査について（2017年11月30日
nearby). for Decommissioning and Contaminated
Water Treatment Conference on Nov. 30, 2017)29©International Research Institute for Nuclear Decommissioning

Boat Type Access Equipment◼ Boat type access equipment which can move on a wide range of thewater surface in the primary containment vessel (PCV) was developed.
Guide ring

Water level during B
investigation

Estimated maximum water level2

A clockwise basic route

Example: Guide ring installation• Diameter: φ25cm• Length: Approx. 1.1ｍ
• Thrust: Over 25N

Boat

Above ground floor path

Guide
ring

Appearance of the boat type accessequipment

Travelling line of the equipment

30©International Research Institute for Nuclear Decommissioning

Boat Type Access Equipment (Video)©International Research Institute for Nuclear Decommissioning

Boat Type Access Equipment (Investigation inside PCV through X-2 penetration)◼ Six kinds of boat type access and investigation equipment with submersible functions will be prepared foreach function.
Installation items
Work flow (image flow)
Install equipment
Seal box equipment

Access/investigationequipment

Guide ring installation

Installation
cable

Water
level

Installation for cableentanglement prevention

Guide ring

Deposit

Visual observation
Confirmation of PCV conditions
by pan-tilt camera

Deposit three-dimensional
shape measurement

Fuel debris*

Stabilizing
anchorThree-dimensional shape ofdeposition was measured by ascanning ultrasonic range finder.

Measured by scanning
ultrasonic range finder

Deposit thickness
measurement
Measured by high output
ultrasonic sensor

Neutron flux measurement
Deposit surface
measurement by detector

Small amount of deposit
sampling
Removal of install equipment
and seal box

The thickness ofdeposition wasmeasured by a highoutput ultrasonic sensor.

Collected bydeposit collection
equipment*Thickness and existence of deposition and fuel debris are uncertain. The above figures are image descriptions.

32©International Research Institute for Nuclear DecommissioningReport of the 107th study committee of specific nuclear facility monitoring and evaluation on April 14, 2023.

【Reference】Panoramic photo images taken from the pedestal opening

⑦

⑧

⑨

⑩

⑪

⑫

⑬

無断複製・転載禁止 東京電力ホールディングス株式会社

Image processing by TEPCO Holding, Inc.

33

Report of the 107th study committee of specific nuclear facility monitoring and evaluation on April 14, 2023.

【Reference】Concrete remains of the right pedestal opening (1/2)◼

Tokyo Electric Power Company (TEPCO) Holdings, Inc. investigated theUnit 1 pedestal to confirm the concrete that likely remain outside thepedestal (Bolts that were installed before the accident were confirmed to be
fixed). The investigation on March 2023 confirmed the inside of thepedestal wall.

◼

TEPCO assumes that the lost concrete of the pedestal outer wall opening
in right side would be limited.

◼

The investigation found that reinforcing steels of the outside pedestal haveremained 7 pieces in the right opening part and 11 pieces in the left side.
The earthquake resistance should be evaluated based on 64° that isequivalent to the angle in accordnce with the opening angle.

Inner skirt

Photo 1

Photo 2

Opening

ROV frame

Remains ofconcrete walls ?

Photo 1: Concrete remains can be seen from the pedestal opening
無断複製・転載禁止
東京電力ホールディングス株式会社
Photo 2: Concrete
remains can be seen from the pedestal opening

Photos processed by TEPCO Holdings Inc.

34

Report of the 107th study committee of specific nuclear facility monitoring and evaluation on April 14, 2023.

【Reference】Concrete remains of the right pedestal opening (2/2)
Inner skirt

First reinforcing
steel

Shown theROV frame*The brightness of the original image is increased by 50%.

Photo taken fromdifferent angle*The brightness of theoriginal image isincreased by 50%.

Photo of left red-circled part taken from different angle*The brightness of the original image isincreased by 30%.

Secondreinforcing steel

Figure 2: Visual image taken from different angle of the remains
無断複製・転載禁止 東京電力ホールディングス株式会社
Figure 1: Remains of the pedestal outer wall of the right
opening
Photos processed by TEPCO Holdings Inc.

35

Arm Type Access Equipment◼ The arm type access equipment was manufactured which can accesson a wide range through the PCV penetration for maintenance ofcontrol rod drive mechanism.
⚫
⚫

Total length of the arm: Approx. 22m
Investigation equipment up to 10kg can be loaded.

トロリ
Trolley

Boom
ブーム

Telescopic
テレスコアームarm

Tiltmechanism
チルト機構

Two-axis
joint
2軸関節

Wand*
ワンド※

Mounted sensor
at the tip of the arm
アーム先端にセンサを搭載※代わりにツールの搭載も可能*The
wand can be replaced an alternative tool.

Arm type access equipment
36©International Research Institute for Nuclear DecommissioningConfiguration of Access Equipment

Access and investigation equipment
X-6 penetration

Arm enclosure

Arm (withsensor)

PCV©International Research Institute for Nuclear Decommissioning

37

Arm Type Access Equipment (video)38©International Research Institute for Nuclear Decommissioning

Mock-up Test Preparation(JAEA NARREC: Naraha Center for Remote Control Technology Development)

CRD

X-6 penetration+
X-6 penetration
connecting structure+
Extension pipe

Approx.
7.7m

CRD inclined rail
Approx.
5.5m

Approx.
15.8m

State of the pedestal interior
Approx.
5.1m
Approx.
7.5m

X-6 penetration

Extension pipe
X-6 penetration
connection
structure

PedestalAppearance of the X-6 penetration(connection structure + extension pipe)©International Research Institute for Nuclear Decommissioning

39

Contents
1. Introduction
2. Development of Remotely Operation Equipment for
Dose Reduction
3. Development of Repairing Technology for PCV
4. Development of Investigation Technology for inside
PCV
5. Development of Technology for Fuel Debris
Retrieval
6. Nuclear Safety Enhancement
PCV : primary containment vessel

40

Development of the Large Scale Fuel Debris Retrieval Method
To increase the retrieval scale, large-scale apparatus was installed.
➢

Secondary boundary
Removalequipment

Fuel debris retrieval methods are being developed:
Connecting routeAdditional building

Three side-access retrieval methods and two top-access methods.
➢

The retrieval amount of fuel debris will be gradually increased to

Double lid
Connecting sleeve

Transport
cart

up to 300 kg per day.
➢Container fortransportation

NDF assessed that Unit 3 is an appropriate unit to start fueldebris retrieval (by side-access method).
➢The obtained technology, know-how, organization structure, experiences Carry-out and removal of the whole structure
and lesson-learnt will be expected to be utilized for design, procurement,
construction and operation.
A concept of jet pump
A concept of separator removal
removalDismantlingequipment

増設建屋
Additionalbuilding

Fuel搬入セル
debris carry-in cell

Waste
廃棄物
搬出セル
transport
cell

燃料デブリ
Fuel debris
取り出しセルretrieval cell

Dismantlingequipment

保守セル
Maintenancecell

Auxiliarybase(installed shroudupper
flange)PCV

Fueldebris
燃料デブリ
搬出セル cellcarry-out

Cutting
manipulator

通路(アクセストンネル)
Accessroute (accesstunnel)The access rail method

The access tunnel method

41

Separator

Temporaryrack (carryout for each
rack)

Jet
pump

Development of the removal method
for the reactor internal structure©International Research Institute for Nuclear Decommissioning

Fuel Debris Retrieval Technology
Equipment cell
Equipment transfer cartNew
opening
Biological shieldwall (BSW)

Wastes transfer cartNew
opening
Seal with BSW-PCV
Equipment
transfer system

X-6 penetration

Example of robot arm

PCV
Sealing with the shielding wall
(BSW) and the primarycontainment vessel (PCV).

Wastes transfer
systemPedestalPedestal opening

Example of cutting
technology (Chisel)

Example of the side access method (illustration)
Unauthorized copy and reproduction prohibited.
©International Research Institute for Nuclear Decommissioning42

Animation of the Fuel Debris Retrieval Method: From Opening a Hole to Sealing
Installation
Example of Horizontal Access Route and Debris Retrieval©International Research Institute for Nuclear Decommissioning

43

Access Tunnel Method◼ The access tunnel method is required to connect a heavy-lift tunnel(approximately 800 ton) with the primary containment vessel (PCV) fromoutside the reactor building through the precise position control system.
◼ Delivery technology for curved heavy-lift tunnel in narrow spaces has
been developed with applied heavy delivery technology experienced in bridge
constructions.
Carry-in cell

Waste carry-out cell

Fuel debris retrieval cell

Maintenance cell

Fuel debris
carry-out cell

PCV

Access tunnel
A layout image of the access tunnel method
Unauthorized copy and reproduction prohibited.
©International Research Institute for Nuclear Decommissioning

44Element test of tunnel building technology

Out of R/B

Example of the delivery method
DeliverysystemPositioning
systemApprox.5000mm

R/B wallApprox.300mm

R/B wallApprox.100mm

Inside of R/B

Illustration of work in narrow areas
Positioning equipment
Illustration of element testing©International Research Institute for Nuclear Decommissioning

45*R/B: Reactor building

【Example of the top-access method】: Methods for Removing andTransporting the Entire Structures
Secondaryboundary
Connecting
routeConnecting
sleeveRemovalequipment
Additionalbuilding

Double lid
Transport
cart

Container fortransportation46

Technology for Containing, Transferring and Storing Fuel Debris
Design of canister⚫
⚫
⚫

⇒Responding to issues specific to the Fukushima Daiichi

High-burnup and the enrichment→ High reactivity
Molten products mixed with concrete→ Hydrogen generation caused by radiolysis of moisture
containing concrete
Molten products with sea water injected and instrumental cables,etc. → Impact of salt andcontamination of impurities

Transport method (Ex. Partial submersion side-access method
Reactor building

Maintenancecell

Fuel debris
storage cell

Carry-out
port(expanded)

Transport cell

Fuel debris
transport building

Canister handlingcell

Storagefacility

Unit canRetrieve fueldebrisCollect fueldebris incanisterCanisterTransport cart

Clean
canisters

Transport container

Store canisters intransport containers

Trailer

Carry outtransport
containers©International Research Institute for Nuclear
Decommissioning

Contents
1. Introduction
2. Development of Remotely Operation Equipment for
Dose Reduction
3. Development of Repairing Technology for PCV
4. Development of Investigation Technology for inside
PCV
5. Development of Technology for Fuel Debris
Retrieval
6. Nuclear Safety Enhancement
PCV : primary containment vessel48

Ensuring the Safety When Retrieving Fuel Debris
Risks necessary to be considered

1. Cooling・・・Decay heat has decreased over a long time after the accident,
however it must be cooled for a certain period of time. There is a risk oflosing its functions.

1. Confinement
・・・There is a risk of releasing dust to be generated when cutting andchipping debris.
2. Fire and explosion (inactivation)
・・・There is a risk of fire and hydrogen explosion when cutting andchipping debris.
3. Criticality
・・・There is a risk of criticality caused by changing the shape of debris
during fuel debris retrieval.
49©International Research Institute for Nuclear
DecommissioningEnsuring the Safety When Retrieving Fuel Debris
Necessary safety functions
1. Cooling
2. Confinement (negative pressure and water level
control of the torus room)
3. Inactivation (fire and explosion prevention)
4. Sub-criticality②Nitrogen supply and gas emission
processing apparatus
Nitrogen supply system((RPV inactivation)

PCV gas control system

Cleaning

Negative pressure control,hydrogen scavenging)

tower

Reactor building gas
control system
Mitigation of radioactive
release at ordinary times: Primary boundary①Circulation cooling and criticality control
apparatus
Circulation coolingsystemWater
treatment
equipment
Boric acidconcentration
adjustingequipment

Cell

P

Undergroundwater

Debris

Debris cooling and radioactive
concentration reduction

P

Underground water level reverse
prevention, radioactive concentration
reduction, criticality prevention (boric
acid concentration)③Ventilation for the building and cells
Air exhaustion system
for the building andcellP(negative pressure control andcontrol air exhaustion)P

Air supply system forthe building

Stop water leaks in the building: Secondary boundary(gas)

Torus room discharge
water system: Secondary boundary(liquid)50

In the auxiliary building(to maintain work
environments)©International Research Institute for Nuclear
Decommissioning

Concepts of Study: Procedures and Feasibility of System Design⚫
⚫

On the basis of the safety requirement setting (tentative), functional requirements from thethroughput will be added.
The safety requirements should be basically unchangeable, however potential current risks anwork risks (i.e. work dose of radioactivity) may be reviewed depending on estimated work andevaluation.
Review
Safetyrequirements

Functional
requirements

Study of systems andmethods

Review

Detailed flow

Study ofequipment

Feasibility
confirmation：Specific toFukushima Daiichi

Output from other R&D projects

Study of systems andmethods

Input condition setting

Review

Outline system model
setting
Exposure evaluation at
ordinary time

Study ofequipment

Study of system
Study of retrieval steps andconfigurations andequipment
equipment
Study of design criteria
accident

Exposure evaluation at
the accident

Review: Current progress status
無断複製・転載禁止 技術研究組合 国際廃炉研究開発機構

51

Feasibility confirmation of systems
and methods©International Research Institute for Nuclear
Decommissioning

Concepts of Defense in Depth (proposed) (1/2)◼ Regardless five levels of defense in depth for the light water reactor, an
additional defense level was newly determined for fuel debris retrieval.
◼ Specifically, three defense levels, “Prevention of abnormal operation,”“Control of abnormal operation and termination of failures” and“Impact mitigation of accidents of the public” were determined andorganized depending on the safety functions.
Defense in depth for duel deris retrieval (proposed)

Protection level
NormaloperationEventoccurrence

Abnormaloperation

Accident

Level 1

Level 2

Level 3

Level 4Control of abnormal
operation andtermination of
failures:Detection of failures
and prevention of the
progression of theaccidents.

Impact mitigationof accidents(Protection of the
public)Mitigation of
releases ofradioactive materials
at the accidents.

Disasterprevention*

Prevention ofabnormal operation:Minimizing deviationfrom normal operating
conditions (Preventing
the progression of theconsequences of
events).

52*Study of disasterprevention for theentire site
including resident
evacuation.

©International Research Institute for Nuclear Decommissioning

Concepts of Defense in Depth (proposed) (2/2)◼ The decommissioning of the Fukushima Daiichi differs from the one of normal plants.
Considering a special circumstance of the Fukushima Daiichi that the decommissioningof the accident plant (work in high radiation environments) will maintain for a long
period of time and has a potential hazard of the final level. The following items wereconsidered to establish the defense in depth.

【Exposure of workers】➢ The effects of worker’s exposure associated with installation work
should be also considered in addition to effects of the exposure during
fuel debris retrieval and exposure reduction of the public. The purpose of
exposure reduction is to totally reduce exposure for the public andworkers.
【Event progression 】➢ At the time of functional loss, existing facilities will respond to events that
rapidly progress. Transportable equipment will also be utilized forslow-progression-events.
【Robustness of existing facilities 】➢ The robustness of the facility is required for events that rapidly progress
and its function is expected to be used. In case that the function is
expected to be used for only normal time and is not significant eventhough it takes time to restore the function at the time of functionalloss, the robustness will not be required.

53©International Research Institute for Nuclear Decommissioning

Summary➢ In the development of debris retrieval work technology, detailed
on-site surveys are important for ensuring safety and earlier
decommissioning work.
➢ Preparations for detailed investigation in the containment vessel
and the taking out of small amounts of debris are underway.
➢ Risk assessment and defense in depth have been examined, andthe conceptual design of debris retrieval systems has been
advanced.
➢ Technology development concerning nuclear safety such as
criticality control and hydrogen generation control are also being
advanced.

54

54©International Research Institute for Nuclear Decommissioning

End of presentation©International Research Institute for Nuclear Decommissioning

55