Recent Examination Results From Fukushima Dai-ichiForensics of the Fukushima Dai-ichi Accident at...

©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.

Forensics of the Fukushima Dai-ichi Accident

at RIC 2018

Recent Examination Results From Fukushima Dai-ichi

Takashi Hara

Deputy General Manager

Tokyo Electric Power Company Holdings, Washington Office

March 15,2018

©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.1

Fukushima Daiichi D&D roadmap phase definition

current statusTarget：commencement

of fuel debris retrieval


Six Technical Programs at Fukushima Daiichi D&D

Pool Fuel Removal Fuel Debris Retrieval

Contaminated Water Management

Waste Management

On-site land management& Work environment

improvement

Urgent issue Long term issue

Complemental issue

Intermediate targetImmediate target

Waste generation, Fuel Debris storage

Fuel storage

Secondary waste(Sludge, Adsorbent,Storage tank, etc.)

On-site Dose and Dust Control, Area Management

Basic step

Unit 5,6 Decommission

Today’s Presentation Focus Area


3

Unit 3: Investigation inside the Primary Containment (July.2017)

The investigation inside the pedestal was conducted using a submersible remotely

operated vehicle in July 2017.

Diagram of the investigation

Basement

Submersible ROV

Control Rod Drive (CRD)replacement rail

Pedestal opening

Platform

Control RodDrive (CRD)housing

Opening (slot)

PCV penetration pipewhere submersibleROV was inserted(X-53 penetration)

PCV accumulatedwater level

Access hatchfor workers

PCV wall surface

Propulsion thruster

Light

Cable

Rear camera

Light

Up and down thruster

Front Camera


[Ref.] Structures/Components inside Reactor Building


5

Unit3: Investigation inside the Primary Containment (July.2017)

A structure that is assumed to be the CR guide tube was found near the CRD housing.

Melted objects solidified and are attached to the CRD housing brackets.

Photograph area A3 <Camera angle：Upward＞ Photograph area A4 ＜Camera angle：Horizontal

RPV center

Platform

Pedestal

180°

Photograph area A3

90°

CRD railCylindrical structure（assumed to be CR guide tube）

Melted objects that have solidified.

0°

270°

Photograph area A4

CRD housing bracket support bar.

CRD housing flange

＜Camera angle：All Upward＞

CRD housing brackets before the accident（Unit 3）

CRD housing bracketsupport bar

PIP cable

CRD housing brackethangar rod


[Ref.] Structures/Components inside Reactor Pressure Vessel

CR guide tubes

PedestalCRD housing

Control Rods

Reactor Pressure Vessel


7


Disturbances on the water surface at ①~④ suggest the possibility that there is damage

on the periphery of the RPV as well as at the center of the bottom of the RPV.

①

③

②

①

③②

0°

90°

270°

④

Pedestal

180°

④

Platform

CRD rail

Assumed damage at the bottom of the RPV


8


Deposits resembling sand, pebbles and clumps were found.

Access hatch was not visible. (Deposits were found nearby)

Lower part inside pedestal

Deposit（granular）

Photograph area C1<Camera angle：Downward＞

Photograph area C2＜Camera angle：Horizontal＞

Photograph area C4＜Camera angle：Downward＞

Fallen object 0°

Photograph area C3＜Camera angle：Upward＞

Clump deposit Direction toward the Access hatch for workers

DepositClump deposit

Photograph

area C5

Photograph area C4

Photograph area C2

Photograph area C1

Deposit（pebble form）

90°

Access hatch for workers

180°

270°

Circling rail bracket

Platform frame

Photograph area C5 ＜Camera angle：Downward＞

Grating

Photograph

area C3


9

Photograph area C2＜Camera angle：Horizontal＞

Fallen object

Grating

[Ref.] Control rod falling speed limiter

This fallen object could not be identified for certain since the unique umbrella-

shaped part of the structure could not be found.

However some characteristics shape and estimated dimension are very similar to

control rod falling speed limiter.

Slit

Rollershape

Assumed to be a socket

・Control rod falling speed limiter

In case of an accident involving a control rod drop, this part generates resistance thereby slowing the

increase in speed of the fall and preventing drastic reactivity level changes inside the reactor.

Deposit

CR falling speed limiter

Slit

RollerControl Rod

Direction of the core＝CR insertion direction

Directionof falling CR


The area underneath the platform, where fuel debris may exist, was investigated.

Telescopic device , which has a hanging mechanism with camera, dosimeter and

thermometer, was used.

ＣＲＤ

X-6Opening

CRD replacement

railOpening of Pedestal

ＰＣＶ

ＲＰＶ

Pedestal

X-6Opening

10

Area whereequipment waslowered duringthis investigation

PlatformAlternative

shield

Isolation

valvePedestal

Control Rod Drive

Extendableconcentriccylinders withdifferentdiameters

Tip bendcontrol box

Guide pipe

（Φ110mm）

Cabledrum

PCV penetration

pipe (X-6

penetration)

Lower part of CRD

Cable Feed Machinery Cable

OverheadCamera

Investigate Unit

Pan Tilt Camera ,Light

Telescopic investigation device

Platform

Unit2: Investigation inside the Primary Containment (Jan.2018)


Worker access

opening

Bottom of

pedestal

垂直断面図

Telescoping

investigation device

CRD housing

Fallen

grating ①

Fallen

grating②(no holes)

CRD rails

No holes

Middle work

platform

Cable tray

CRD replacement

mechanism

Platform

Area that the

investigation unit

accessed during

this investigation

[Ref.] PCV Internal investigation location


12

Fuel assemblycomponent


Photos provided by: IRID

Platform

CRD housing

Fallengrating①

CRD rails

Worker access openingBottom of the pedestal

Cable tray

No Holes

Middle work platform


No Holes

Fallengrating②

CRD replacementmechanism

The entire bottom of the pedestal was found

to be covered with sandy and clay-like

deposits.

Some fuel assembly components have fallen

to the bottom of the pedestal and deposits

thought to be fuel debris were found in the

vicinity of these fallen components.

Affixed deposits.

Fallen Object

Deposits.

Inner wall of pedestal.

Sandy deposits.

Tie Plate


13


Platform

CRD housing

Fallengrating①

CRD rails

Worker access openingBottom of the pedestal

Cable tray

No Holes

Middle work platform


No Holes

Fallengrating②

CRD replacementmechanism

Inner wall of pedestal

No significant damage was seen on the

inner wall of pedestal.

No significant damage was seen to existing

structures inside the pedestal (CRD

replacement mechanism).

Near the worker access opening (estimated)

CRD replacement mechanism

CRD housing support fitting support bar

CRD housing support fitting hanger rod

PIP cable

Photos provided by :IRID


14


Worker access opening

Bottom of pedestal

垂直断面図

Telescoping investigation device

CRD housing

CRD rails

Middleworkplatform

Cabletray

CRDreplacement mechanism

Platform

Measurement point ａ

Measurement point ｂ

Measurement point ｃ

Measurement point ｄ

Approx. 0.3m

Approx. 0.4m

Approx. 1.0m

Approx. 0.6m

Platformtop

Bottom surface ofpedestal

Approx. 3.2m

Fallen grating①

Fallen grating②

Dose and temperature were

approximately the same regardless

of the height at which measurements

were taken.

And, dose rates tended to be higher

outside the pedestal than inside.

Measurement

point

Dose rate*1,2

(Gy/h)

Temp.*2

（℃）

a 7 21.0

b 8 21.0

c 8 21.0

d 8 21.0

【Reference ; Outside the pedestal*3】

Dose rate: Max. 42 [Gy/h]

Temp.:Max. 21.1[℃]

※1：Calibrated with Cs-137 radiation source※2：Error: Dosimeter: ±7%

Temp. Gauge: ±0.5℃※3：Reference value because the measurement

equipment is housed inside the survey unit


15

[Ref.] Reference dose rate measurement locations

Reference measurement location (this investigation) ※1

2017 investigation measurement location (estimated from camera screen static)

2017 investigation measurement location (calculated usingintegral dosimeter

19Gy/h

Measurement location (this investigation) ※1：Reference value because the measurementequipment is housed inside the survey unit

Less than approx. 10Gy/h

ScaffoldingApprox. 70Gy/h

Approx. 80Gy/h

Approx. 70Gy/h

Less than approx. 10Gy/h

PCV

X-6 penetration

Approx. 0.7m

CRD rails

Pedestal

Platform

Lifting beam

7Gy/h (Measurement

point ａ)

7Gy/h(Fallen grating ① top)

7Gy/h(Fallen grating ② top)

CRD housing

15Gy/h

Approx. 6.8m

Approx. 0.9m Approx. 0.9m

28Gy/h42Gy/h

Approx. 2.6m Approx. 1.2m

Approx. 0.4m

20Gy/h

Dose rates tended to be higher

outside the pedestal than

inside.


16

[Ref.] Data/Information obtained (Reactor Building) (1/2)

Data／Information obtained through D&D

activities (R／B)

Potential insights

1 Photos/videos of damaged walls and structures

(1F1,1F3 and 1F4)

Seismic integrity, Characteristic

of hydrogen explosion

2 Radiation dose surveys in Reactor Bldg. (1F1,

1F2, and 1F3)

Characteristic of contamination,

FP transport into Bldg, Potential

leakage path e.g. pipe

penetration seal or containment

top head seal. Potential damage

by exposure to harsh

environment.

3 Radiation dose surveys around DW Concrete

Shield in Refueling floor. (1F1, 1F2, and 1F3)

4 Isotopic evaluations of obtained samples from

Reactor Bldg. e.g. floor concrete, building

debris, etc. (1F1,2,3)

5 Observations of water leakage and

Photos/videos at appropriate locations near

identified leakage points (1F1,2,3)

e.g. 1F1 (vacuum breaker, sand cushion drain),

1F3 PCV leakage points (bellows of Main

Steam pipe penetrations)


17

[Ref.] Data/Information obtained (Reactor Building) (2/2)


activities (R／B)

Potential insights

6 Photos/videos and radiation dose surveys on

containment hardpipe venting pathway,

standby gas treatment system and associated

reactor building ventilation system

(1F1-4)

Behavior of wetwell venting gas

flow, back flow via SGTS, inter-

unit back flow via shared

exhaust stack.

7 Examinations of 1F1 RCW (Closed Cooling

Water system) surge tank; water level and

radiation dose measurements.

FP transport via RCW line due to

molten core interaction in the

sump in DW floor.


18

[Ref.] Data/Information obtained (PCV)


activities (PCV)

Potential insights

1 Ex-vessel inspections and operability

assessments of in-vessel and ex-vessel

sensors and sensor support structures (1F1-3)

Sensor availability under harsh

environment during Severe

Accident and post-SA

monitoring strategy.

2 Photos/videos of PC coatings (1F1-3, so far

only DW inside wall)

Characteristic of PC coating

exposed to harsh environment.

3 Radiation dose surveys in PCV (1F1-3) Characteristic of contamination,

FP transport in PCV.

4 Photos/videos of TIP tubes and SRV/IRM

tubes outside the RPV (so far 1F2, 3)

In-vessel and Ex-vessel core

melt progression.

5 Isotopic evaluations of samples of water, mud,

sand from DW, as well as water samples from

outside of PCV (1F1-3)

Characteristic of FP transport in

PCV. Long term FP and water

chemistry.


19

[Ref.] Data/Information obtained (RPV)


activities (RPV)

Potential insights

1 Remote mapping of core through shroud wall

from annular gap region (muon tomography)

(1F1-3)

Rough image of fuel debris

distribution.


20

[Ref.] Links of Data/Information from TEPCO and Japan webpages

TEPCO Holdings Webpages

Decommissioning Plan of Fukushima Daiichi Nuclear Plant (main Fukushima Daiichi D&D

website, photos and video)

http://www.tepco.co.jp/en/decommision/index-e.html

TEPCO’s News Room (prompt reports, handouts at press conferences)

http://www.tepco.co.jp/en/decommision/news/index-e.html

The Council for the Decommissioning of TEPCO's Fukushima Daiichi Nuclear Power

Plant(updated monthly)

http://www.tepco.co.jp/en/nu/fukushima-np/roadmap/conference-e.html

Progress Report on the Investigation and Examination of Unconfirmed and Unresolved Issues on

the Development Mechanism of the Fukushima Daiichi Nuclear Accident (last update; coming

soon: Update No. 5 in English)

http://www.tepco.co.jp/en/press/corp-com/release/2015/1264602_6844.html

Other Japan Webpages

The Mid and Long Term Roadmap towards the Decommissioning of TEPCO's Fukushima Daiichi

Nuclear Power Station (updated non-regularly)

http://www.meti.go.jp/english/earthquake/nuclear/decommissioning/pdf/20170926_01a.pdf

Technical Strategic Plan 2017 for Decommissioning of the Fukushima Daiichi Nuclear Power

Station of Tokyo Electric Power Company Holdings, Inc (updated annually)

http://www.dd.ndf.go.jp/en/strategic-plan/index2017.html

http://www.tepco.co.jp/en/decommision/index-e.html

http://www.tepco.co.jp/en/decommision/news/index-e.html

http://www.tepco.co.jp/en/nu/fukushima-np/roadmap/conference-e.html

http://www.tepco.co.jp/en/press/corp-com/release/2015/1264602_6844.html

http://www.meti.go.jp/english/earthquake/nuclear/decommissioning/pdf/20170926_01a.pdf

http://www.dd.ndf.go.jp/en/strategic-plan/index2017.html


Thank you for your

kind attention

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