2023-12-14 ATFワークショップ
東大 武田ホール

ATF開発に向けた基礎研究とその展開

Development of Metal-Coated Zircaloy for Accident-Tolerant Fuels
Hiroaki ABE
The University of Tokyo
Collaborators:
The Univ Tokyo:

Tohoku Univ:
JAEA:
MHI (NDC):

K. Takanabe, A. Nakayama, S. Kano,
H.L. Yang (Shanghai Jiaotong University),
L.J. Cui (Chengdu Univ.), K.J. Wei, B.Li,
N. Nikolova, Z.Q. Wei, J.A. Jovellana
Y. Chen, T. Davey
M. Yamaguchi
K. Ogata, Y. Shinohara

謝辞：本研究は文部科学省原子力システム研究開発事業JPMXD02 2034500の助成を受けたものです1Contents
1. Background and Purpose
2. Structure of this project
3. Alloy design
4. Cr/Zircaloy bonding
5. Corrosion properties and surface reactions
6. Irradiation effects
7. Mechanical tests- A-EDC test
- in-situ tensile and bending test
8. Summary2

Accident Tolerant Fuels（ATFs）
OECD/NEA and AESJ

integrity
・modified zircaloymid
・Cr-coated Zr-alloy mid
・Zr-coated Mo-alloy ？
・FeAlCr、ODS
high
・SiC composite
very hightech levelhigh
low～highlow
low～mid
low

terms
short
short
mid～long？
midvery long

The Cr-coated Zr alloy incorporates the idea of suppressing reactions withother parts at high temperature. Since Zr alloys are practical materials forindustrial use, it is expected as the highest possible and near-term
introduction in commercial nuclear plants.

3Cr被覆ジルコニウム合金の課題
fuel pellet

cladding

coating

coolant water

material design
thermal expansion
creep down
reaction atinterfacehoop stressswelling
FP gas
PCMI

mechanicaldegradation

Hoop stressat the interface

physicaldegradation

effect ofinterface?

anti-corrosion
behaviors

embrittlement?
self-healing?

radiation damage

radiation hardening
radiation embrittlement

oxidationhydrogenabsorption?
diffusion barrier?

hydrogenembrittlement

reaction with water

knowledge none

atomic mixing
at interface

chemicaldegradation

IssuesCoating- materials design- radiation effects
Surface oxide- reaction- reaction with H2
Coating/zircaloyinterface- stability at HT- radiation effects- reaction with H2 4

structure of this project and roadmap

5

Contents
1. Background and Purpose
2. Structure of this project
3. 合金設計 Alloy design
4. 接合技術 Cr/Zircaloy bonding
5. 耐食性 Corrosion properties and surface reactions
6. 照射効果 Irradiation effects
7. 機械的性質 Mechanical tests- A-EDC test
- その場測定 in-situ tensile and bending test
8. Summary6合金設計 (DFT)Cr-X alloy as a coating material for ATF
Basic idea on searching elements by DFT calculations• X in bcc-Cr stable as solid solution (ΔEf: small)Cr-X• X in hcp-Zr stable as solid solution (ΔEf: small)• X in ZrCr2 destabilizes the Laves phase (ΔEf : large)• Small volume change due to doping to avoid strain and cracking• Low neutron absorption cross section: requirement for nuclear

X in hcp-Zr

Supercell 3x3x3 bcc cells (54 atoms)
doping concentration 1.85%

X in ZrCr2 (C15)Sn, Zn, Mg
ΔEf(C15)<ΔEf(Cr),most likely migrate to Laves phase,act as suppressing elements.
Alstable in both C15 and Cr, but
ΔEf(Cr)slightly<ΔEf(C15),
more like Al in bcc-Cr.
Mg+(Sn, Zn) in ZrCr2 (C15)

7

耐食性

8

Crー水反応

severe oxidation inzircaloy over 800℃

Retardation ofoxidation in Cr

9水素発生とその抑制
2.5kPa H2O / Ar

2.5kPa H2O / 20kPa O2 / Ar

Severe H2 formation
over 950℃

H2 generation
before oxidation

suppression ofH2 in Zry
Trivial H2 formation in Cr

H2 formation by catalytic reaction
without surface severe oxidationfor Zry
1
Mixture of O2 suppress H2 formation ≤10 10

残留酸素による水素発生の抑制

PO2 ↑H2 formation ↓PO2PO2lowhigh

H2 formation is limited at thebeginning of exposure→ suppression by Cr2O3 layer formation

Non H2 formation
at PO2 >15kPa

O2 gas in environment
suppresses H2 formation11水素発生に対するCr2O3表面酸素空孔の効果
Cr2O3a)d)c)adsorptionof Hb)
2OO-vacancy on surface assists
dissociation of H2O molecule

Cr2O3-x

O adatomDissociation of
H2O molecule
意外と高値？

O vacancy in the 2nd layer
moves to top surface.
adsorptionof H2O at O vacancy

Dissociation of
H2O molecule2H adatom
12Cr/zircaloy接合
Needs・joining in the α-phase of Zry→ Low temperature joining
Concept of exp steps
・diffusion bonding
β-phase → accidental condition of NPP→ Cr/Zry interface
α-phase → normal operation condition→ clarify the reaction
・application of pulsed laser deposition for low-T joining→ Developing fabrication concept
introducing excess vacancies to enhance diffusion/mixingnon-equilibrium phase formation to achieve recrystallization at low-T
13

接合実験
Composition (Wt. %)sample preparation
optical grade finish

laser ablation
deposition <100nmdiffusion bondingduration 4hat various Tanalysis
SEM/EDS
FIB/TEM14拡散接合によるCr/Zry界面反応：Laves相 Zr(Fe,Cr)2の形成
Cr

T=1023K × 4hrs

αZr

αT=1023K × 4hrs

Zr(Fe,Cr)2Zr

CrβFe

•
•
•
•

Preferential diffusion of Cr
Laves phase layer at interface
Segregation of Fe
Bonding at β-phase results in
the growth of Laves phase.
15パルスレーザー蒸着（PLD）法の応用
Cross section TEM ofCr deposited Zry at ambient temperature

Amorphous layer formation wasobserved at shorter or milder deposition.

Recrystallization temp
300～400℃

Nano crystalline layer formation
Recrystallization temp. >400℃

Idea
Employ amorphous layer as the buffer
layer at the Cr/Zry interface results in- lower bonding temperature AND- flatness improvement17

PLD法による低温拡散接合
Temp（K）

w/o PLD-Crw PLD-Cr

1073

○

○

1023

○

○

973

○

○

873

○

○

823

×773

×723

○××4hrs
The amorphous layer seems less effective to the formation of Laves phase.

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照射影響
HIT, The Univ. Tokyo

試料作製
arc melting + anneal.
照射後分析
GIXRD
SEM/EDS analysis
FIB and TEM analysis
nano-hardness+180keV-He
into Laves
615E d,Fe, Cr, Zr = 40 eV

ρ = 7.69 g/cm 3

4Incident angle : ~18.8°10250000.2

0.40.6
Depth (µm)

0.8He (at.%)Tandetron
accelerator

Displacement damage (dpa)

Ion irradiation (180 keV-He+ , 5.5 dpa @ peak)Temp.: RT, 473, 523, 573 K

19

Laves相 Zr(Cr,Fe)2 の照射誘起非晶質化
180keV He → Zr(Cr,Fe)2 5.5 dpa (peak)
ions

BF
0.0He

RT

DF

BF

473 K

DF

523 K
BF

DF573 K

BF

DFDoseDepth (µm)

0.2
0.4
0.60.8SAED

300 nm

300 nm

300 nm

300 nm20

Laves相 Zr(Cr,Fe)2 の非晶質化臨界線量

Displacment damage (dpa)

Tc ～548 K

BF, 180keV-He+ @ 523 K
SurfaceZr(CrFe)2180 keV-He+

6Shallow

Y. Li et.al.

(400 keV-Fe+)

4Amorphous

Crystal

AMORPHOUS

20Shallow

Deep CRYSTALLINE

Deep

0200
400600Temperature (K)

800

Dose
He

Governed by dose
200 nm21

2.8 MeV Fe2+
Dose rate 2.1×10-3 dpa/s
Irradiation flux 2×1012/cm2
Dose: 0.1 dpa, 3 dpa, 15 dpa
target: pure Cr
Temperature 550±2 ℃Radiation dose (dpa)

Irradiation → FIB and TEM

3800600

2400
1200

Implanted Fe (appm)

Crのイオン照射損傷

00
0

500

1000

1500

Depth (nm)

3 dpa

Raft

Nested loops

15 dpa23

機械試験 (Advanced Expansion Due to Compression (A-EDC) test)
35

IP testring-shaped
specimen
inner pellet(i.p.)

30
25Load (KN)

A-EDC

2010rigid body

50Ideal hoop uniaxial tensionEnergy consumed for thedeformation of the ring

15EDC test

0.00.5

1.0

1.5

2.0

2.5

3.0

3.5

Height Displacement (mm)24

水素吸収効果（Zircaloy-4）
1200

1200

1000

1000

800
600
400

400 ppm

1400

800
600
400

1000
800
600
400

200

200800 ppm

1200

Hoop Stress (Mpa)

1400

100 ppm

Hoop Stress (Mpa)

Hoop Stress (Mpa)

1400

200

00.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20

00.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20

00.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20

Hoop Strain

Hoop Strain

Hoop Strain

Hydrogencontent[ppm]
0100400800

Yield
Stress[MPa]899± 40801± 81010± 77
912±122σy increased due to H

• Multiple necking observed.
• Necking become shallower with increasing the with increasing
the hydrogen content.
• Fewer necking was evident in 800ppm.
Due to the texture structure of zry, platelet hydrides are formed
along hoop direction. Less effective to the hoop strength.
25

Cr被覆Zry-4の曲げ試験とその場測定

tensiledirection

High speed camera is set for in-situ obs. inbending/tensile.
AE sensors for detection of crack formation.
load

AE signals

displacement/mm

Crack formation and propagation on Cr side.
AE detected the formation.

26

まとめ、総合討論• Cr/Zry接合に成功した。界面反応による層状のLaves相形成を確認した。
• バッファ層として非晶質Crを用いることにより接合の低温化に成功した。
Crコートジルカロイ被覆管について、本研究成果より以下の提案がなされる。

• 製造工程においては界面に非晶質相を形成させることにより、より低温での接合性を期待することができる。
• ただし、熱処理温度次第でキャビティの形成（未説明）も観察されたことから、熱処理条件には注意が必要。
• 異常条件では、界面にLaves相が層状に形成されることから、その影響評価は必要である。これは、製造法によらない。
• Laves相形成は拡散律速であることから、これに対する照射加速影響も懸念され、今後の課題としている。
※東大HITの実験装置群は共同利用としてご利用いただけます。

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ご清聴ありがとうございました阿部弘亨
abe.hiroaki@n.t.u-tokyo.ac.jp
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