NDF Forum July 2–3, 2017, Iwaki Japan

Fuel debris characterization
for Decommisiioning of Fukushima Daiichi NPS
Tadahiro WASHIYA
July 3, 2017

Collaborative Laboratories for Advanced Decommissioning Science (CLADS),

Japan Atomic Energy Agency (JAEA)International Research Institute for Nuclear Decommissioning (IRID)
This paper includes part of the results obtained under the research program entrusted to International Research Institute for Nuclear Decommissioning (IRID)
including Japan Atomic Energy Agency (JAEA) by the Agency for Natural Resources and Energy, Ministry of Economy, Trade and Industry (METI) of Japan.

0Introduction
 JAEA has been studied characterization of fuel debris
and MCCI product for Fukushima Daiichi NPP (1F).
 Obtained fundamental data by simulated fuel debris and TMI-2 sample
with considering 1F distinctive reactions
 Estimated 1F debris properties as mechanical and chemical Created the “ Estimated properties list ” of the 1F debris⇒ Contribute to preparation and planning for 1F decommissioning.

 1F debris sampling will be performed in the near future,and JAEA is conducting preparation of the analysis.
 To consider purpose of sample analysis
 To confirm debris properties by 1F sample analysis
 To confirm damaged condition in 1F reactor core by the results
 International cooperation will be effective⇒ The 1F’ debris sample will more specifically contribute to the defueling,storage, conditioning and disposal, and also to study on SA research andaccident management.

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1F Decommissioning Schedule
Mid-and-Long Term Roadmap
Now
Removal of spent fuelfor Unit 1~4

Phase 1

Phase 2 (within 10 yrs.)

Start debris removal (2021)

Phase 3 (after30-40yrs.)

Removal of spent fuel(Unit 1～4)

Decontamination,
investigation, preparation, etc.
Removal of fuel debris(Unit 1~3)

Casks forspentfuelRemoval of fuel debris(Unit 1~3)

Examination of appropriate measuresfor decommissioning, prepare for R&D

Development oftreatment technology andscenario study

Demolition &Disposal

Storage
Process or Disposal ?
Decision on fuel debris
processing / disposal methods

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Purpose of debris characterization
Decommissioning
Defueling

Debris’ property

ex. Submerged
defueling

Decision ofTools & Methods

Mechanical property
Hardness, Fracture toughness,
etc.

caskc

Thermal property

Storageex. Wet storagecanister

Consideration ofPre-treatment

Thermal conductivity, Melting
temperature, etc.

Physical property
Density, Drying characteristic,etc.

cask

Treatment

ex. U/Pu recovery
and vitrification

Consideration ofTreatment

Chemical property
DisposalAcid-solubility, antioxidant
property, etc.
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Specific effects on 1F debris property

The 1F debris, 1F specifically conditions are considered as following.

• Effect of sea water (alternative coolant) 〜salt deposition on the debris surface？
• Effect of B4C as control rod material 〜 boride’ chemical form and distribution in the debris• Effect of concrete interaction (MCCI)• Other effects: Pu, Gd（BP）, leaching,
FP chemical form and etc.

Sea water(Temporarily fedas cooling water)

Salt depo.？

Debris fine？

The property is estimated by simulated debris

B4C（Solid phase, Components, Mixing rate,
Mechanical and thermal proierties)
Concrete

Contribute to debris defueling (tool design,criticality safety control, storage andmanagement)

Typical perspective view of 1F reactor

4Fabrication of sim. fuel debris(1) Sintering(2) Arc dissolution

yUO2 + (1-y)ZrO2 → (UyZr1-y)O2• Entire uniform heating• Same as fuel pellet fabrication• Required metal richconditions• Mixture, Crush, Pelletize,Sintering （Ar, ~1730℃）• Additive: Gd2O3, Fe2O3, CaO• With control oxygen potential• Simulated Core Debris ,MCCI product• 〜5 g / sample(3) Heating by light collection• Concentrating light as heat soce
• Erosion under thermal gradientconditions• Various atmosphere gas• Small scale MCCI: Melting of(U,Zr)O2

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Effect of cooling rate on (U,Zr,Fe)O2
Sim. debris

Upper crustTMI-2 debris

Upper crust（Rapid cooling）
20 µm

Rapid coolingfrom molten state

20 µm

Cubicle single phase

Sinteringat 1600℃
Melting pool（Annealed）

Melting pool

10 µm

1010µmµm

Mixture of U-rich Cubicle and Zr-rich Tetragonal

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Sea salt and B4C effect on simulated debris(1) (U0.4,Zr0.6)O2－Sea water reaction in high temp.
Aluminum crucible
USalt filling

MgO(+NaCl)deposit

Zr(Ca,Na)-U-OUCa

Elemental profile

Mg
Zr

U-Zr-O(Matrixof pellet)

Na40µmCa

SEM images on the (U0.4Zr0.6) O2 pellet Heat-treated with salt at 1275K for 12h under air flow.

(1) B4C reaction in high temp.
(Fe,Cr,Ni)2Zr

ZrB2 ZrC

1: ZrB2
2: (Fe,Cr,Ni)2B

3: Fe-Cr-Ni
4: Fe-Cr-Ni-(Zr,U)

Mixture of
B4C/SS/Zr/(U,Zr)O2

Alloy+Borid

B4C/SS/Zr Mixture

B4C/SUS/Zr/(U,Zr)O2 Mixture

Simulated debris
pellet(U,Zr)O2Arc
melting

Controlrod

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Molten corium and metal reaction
Collaboration with Toshiba and National Nuclear Center of the Republic of Kazakhstan (NNC)
Presser Vessel

ElectricFurnaceSlow-cooling conditions
After test

After powdery debris
Part where removed

2070mmstainlesssteel plate
has melted“Fuel debris”(Solidified melt)

Fragmented material

Cross section
Powdery/Granularshaped solidification
Rock-shaped
solidification

Non melted
Metal

Ingot
0Residue from the plates
Trap

SUS 316L

SUS 304

50

Contour of plate
100

Test SectionTrap (Concrete)

100mm

Solidified metal

150mm

Molten corium
SS plate
ステンレス鋼板

WaterVessel

Water-cooling conditions
After test
Stainless steel plate

After powdery debris
has removed
Solidified melt

Water Stainless steer plateDebris

Cross section
Powdery/ Granularshaped solidification

SUS316L

100mm

Fixed ring

“Fuel debris”(Powdery/Granularshaped solidification)

Weight ratioof solidification

Rock-shapedsolidification

mm8mm

MCCI effects on pedestal concrete
Image of the sedimentof MCCI product

Fe-Cr-Ni- Zr -U-(Si-Mo-B-C) melt
U-Zr-O melt

Mixture of SS/Zr/(U,Zr)O2

Solidified surface
ConcretecomponentCore component (1)(2)

Concrete

Thermally-degradedconcrete (Low strength)

Molten concrete(Vitrified)Pyrolysis gas(Mainly H2O)Light-concentrating
heatingSilicate glass (containing 3-4 wt%-U)+(U, Zr, Ca) O2 precipitation
20 μm

Estimated reachedtemperature (K)Silicate glass
containing U
Silicate glass (no U)+SiO2
Thermally-degradedconcrete

Layered-structure
image(Dehydration andembrittlement)
Cross section after melting reaction(Concrete piece with a diameter of 25 mm)

Intact part9

MCCI product in engineering scale test
Collaboration with JAEA and French Atomic Energy and Alternative Energies Commission (CEA)
Image of cross section of MCCI
Calculation resultsby TOLBIAC-ICB

Upper crust
CavityCorium oxideArc Plasma furnace

Metallic extraction（For Oxide melt）

Metallic Layer
Lower Crust
Thermally-degradedconcrete
Intact Concreate
Oxide phasewith Si richConcrete rich
area

MCCI sample
High frequencyfurnace（for Metallic melt）

Oxide phasewith Zr rich

Metal grain

Mixture of corium
and Concreate

Coriumrich area

1mmEngineering scale MCCI Test Facility ：VULCANO @CEA

SEM/EDS analysis

Oxide phasewith U rich

Metallic phasewith Fe rich

10Chemical alternation of LFCM/Che-NPP
Collaboration with JAEA and Institute for Safety Problems of Nuclear Power Plants of NASU (ISP-NPP)
Chernobyl’s experience Chemical alteration of debris• Chernobyl’s “LFCM：Lava-like Fuel-Containing
Materials” is still leaving in the reactor area, hence
LFCM slowly react with moisture and air. 1)• Secondary chemical species are generated on thesurface, including dissolvable uranium.

Na3H(CO3)2・2H2O
UO3・2H2O
Na4(UO2)(CO3)3
Na2CO3・2H2O
UO4・4H2O
UO2CO3

 Aerosol generation• Aerosol is generated on the surface of LFCM
continuously. 2)• Major radio nuclides are 137Cs/241Am, 241Am/154Eu,
137Cs/154EuUranyl- phases generated on thesurface of Chernobyl’s ”Lava”

Concerning for Fukushima Daiichi NPP• Potential of similar alteration on the fuel debris ＆MCCI production in 1F conditions.
• Treatment of the aerosol generated by the fueldebris ＆ MCCI production.
Aerosol generated from LFCM
1) B. Burakov “Material Study of Chernobyl “Lava”and“Hot”Particles”, International Experts’Meeting on Decommissioning andRemediation after a Nuclear Accident ,Vienna,Austria,28 January-1 February 2013.

2) http://www.jsme.or.jp/pes/Research/A-TS08-08/index02.html

11Purpose of debris analysis and examination
 Contribution to decommissioning To understanding the damaged state inside
the reactors; quantity, shape, composition, etc.

Decommissioning To understanding the contamination;
radiation, nuclides, chemical form, etc.
 To understanding the safety; criticality,hydrogen, corrosion, etc.
 To examining the defueling; criticality, tools,method, etc.
 To storing and storage

Analysis and examination
using fuel debris and othercore materials

 To reatment and disposal

 Contribution to SA and AM
 To investigating the accident progression;
in/ex-vessel phenomena, containment failure,
fission product behavior, and source term, etc.
 To investigating the system reliability;
coolability , containment, corrosion and erosion, etc.

S.A. and A.M.
ResearchInternational Joint Research Project “Preparatory Study on Analysis of Fuel Debris (PreADES)”
will be launched by OECD/NEA/CNSI

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Image of 1F core conditions and analysis purpose
Region A : Upper Structure

Region E : RPV Lower Head(Purpose)
Surface contamination survey, Radiation
estimation, Study of decontamination
method(Purpose)
Evaluation of Residual volume,
Residual form, Homogeneity and safety

Region B : Shroud

Region F : Control Rod(Purpose)
Surface contamination survey, Radiation
estimation, Study of decontamination
method(Purpose)
Evaluation of Residual volume,
Residual form, Homogeneity and safety

Region C : Core part residue

Region G : Pedestal Floor(Purpose)
Evaluation of Residual volume, Residualform, Homogeneity and safety(Purpose)
Evaluation of Residual volume,
Residual form, Homogeneity and safety

Region D : Control Rod Guide
Tube(CRGT)

Region H : D/W Floor(Purpose)
Evaluation of Residual volume,
Residual form, Homogeneity and safety(Purpose)
Evaluation of Residual volume,
Residual form, Homogeneity and safety13Analytical technology for fuel debris• The analysis workflow considered to enable the efficient debris analysis.
• In this workflow, values of sample with unknown components are roughly analyzed by
the non-destructive method and then the overall analyses is created.
Receiving debris sample

Debris is :• hardly dissoluble material• Alkaline fusion method is being
examined as a pre-analysis
processing method.

(in the Transfer cask)

Non-destructive measurement(X-ray, CT, etc.)

Fundamental property(segregation)
Test piece preparation(Solid sample)

Dissolution(Liquid sample)

Surface analysis(SEM/WDX, etc.)

Mechanicalproperty(Hardness, etc.)

Nuclide analysis(Gamma spectrometry)

Thermal analysis(thermal conductivity,thermal expansion
etc.)

Elemental
quantitativeanalysis(ICP-AES, TIMS, etc.)

Debris dissolution(by Alkaline fusion method)

Nuclide analysis(Alpha spectrometry)(Liquid scintillation, etc.)

Overall debris analysis workflow plan14

The X-ray CT technology development
The X-ray CT test apparatus has been developed as a non-destructive
examination device for examining the internal condition of subassembly (Budle
Duct Interaction, etc) and for reflecting to soudness confirmation and fuel-lifeestimation, and installed in the extension facility of Fuel Monitoring Facility (FMF)
Density： 密度：低low ⇔high⇔ 高--：デブリ領域抽出

Intensity
強度

Density analysis ：Fuel clad tube （Red） 、 Fuel （Yellow）
A：空孔
B：ジルカロイ、C：燃料
A:Pore
B:Zry C:FuelA

B

C

Fuel element
密度

Density
1㎜
模擬デブリのFPs fromSFRadioactive
nuclide fromstructure

Structural materials

X-ray
CT ofX線CT画像
Simulated debri

Density histogram in thefuel debris area

Cross sectional of gamma tomography

 Construction of quantitative evaluation method of porosity due to pore, etc.
 Construction of fuel debris component identification method
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Conclusion
 Characterization on fuel debris• For 1F decommission, estimated debris properties is essential
 Fundamental data has been measured using simulated debris , etc..
 Density, Mechanical properties (Hardness, Elastic modulus, Fracture toughness),
and thermophysical properties (Thermal conductivity, Specific heat, Melting point).
• 1F’s specifically conditions are investigated Seawater, B4C as control rod material, Pu and concreate interaction wasexamined experimentally.
 Chemical alteration on the debris at various conditions needs to be investigating.

 Preparation of 1F debris analysis• Debris analysis will contribute to 1F decommissioning and SA research etc.
 Sample analysis help for understanding the damaged reactors core, for
implementing the decommissioning work, for investigating the accident
progression, and for safety analysis.

• Debris analysis needs to be discussed internationally The 1F debris analysis can be used as expanding the knowledge and expertiseon the severe accident internationally.
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Thank you for your attention

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