Ceramic Nuclear Waste Forms for Actinides and Lanthanides

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Ceramic Nuclear Waste Forms for Actinides and
Lanthanides
G.R. Lumpkin, E. Artacho, S.E. Ashbrook, M.T.
Dove, I. Farnan, E.R. Harvey, M. Pruneda, S.A.T.
Redfern, S. Rios, K.R. Whittle, M. Zhang
Department of Earth Sciences University of
Cambridge Downing Street, Cambridge, CB2 3EQ, UK
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Which Materials?

• Zirconolite (Ca,Ac,MLn)(Zr,Hf)(Ti,Nb,Fe,Al)2O7
  Perovskite (Ca,LLn,Sr,Ba)(Ti,Zr,Nb)O3 Pyrochlore
  (Ca,Ac,Ln,Sr)2(Ti,Zr,Hf,Nb,W)2O7
• Chrictonite (Ca,Ln,Ac)2-x(Ti,Mg,Al,Fe,Tr)21O38
• Monazite (LLn,Ac,Ca,Sr)(P,Si)O4
• Zircon (Zr,Ac,HLn)SiO4
• Fluorite - defect fluorite (Ca,Ln,Ac,Zr,Hf)O2-x
• Murataite (Na,Ca,Ac,Ln)6(Fe,Tr)5Ti12O36
• Garnet (Ca,Ln,Ac)3(Zr,Hf,Ti)2(Al,Fe,Si)3O12

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Partitioning
PW
JW, K2O substituted for Na2O
JW or PW 0.5 wtNa2O
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Partitioning
PW
JW REE2O3
Eu anomaly - effect of reduced valence
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Crystal Chemistry
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Chemistry - Pyrochlore
8-2nA2-m6B24X64-2mY1-npH2O
n 0.0-1.0
p 0-2
m - 0.0-1.7
A Na Ca Ln Th U .. B Ti Nb Ta Sb ... X O
.. Y O OH F ...
Sr Sb Ba Pb Bi H2O Mn Fe Zr Hf Sn W OH K Cs H2O
Role of Si in defect pyrochlore (with Sr, Ba, Pb,
U)?
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Pyrochlore Structure
As derived
Relaxed
x 0.3750
x 0.4375
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Pyrochlore Structure Field Map
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Nd2 Zr2-xTixO7 Cubic - Monoclinic
E.R. Harvey POLARIS Data
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Nd2 Zr2-xTixO7
Linear decrease indicates solid solution to about
Nd2Zr0.8Ti1.2O7 Cubic phase cannot accommodate
increased Ti monoclinic phase forms
E.R. Harvey POLARIS Data
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Backscattered SEM and EDS - Nd2Zr2-xTixO7
Nd2Zr0.4Ti1.6O7 Zr and Ti rich phases (cubic and
monoclinic), 5050 proportions
Nd2Ti2O7 More uniform, some zoning, but no
difference in EDS spectra
10 µm
10 µm
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Defect Pyrochlores - Neutron Data
Chalk River
K,R. Whittle
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Ti0.5 Ti0.25Zr0.25
Zr0.4
Defect Pyrochlores Structural Data Cs NMR
Hf0.4
K.R. Whittle, S.E. Ashbrook
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Chemistry - Zirconolite
M8CaM7ZrM5,6Ti2O7
lt 0.1 Vacancies pfu Minor hydration in natural
samples Polytypes 2M, 4M, pyrochlore, 3T, 3O
M8 Ca MLn Th U... M7 Zr Ti. M6 Ti Zr
Nb Ta Fe... M5 Ti Nb Ta Fe O O .
Na Mn Y HLn U Th Mg Al Mn Ti3 Zn W Al Ti3? OH?
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Zirconolite Polytypes
010
100
010
2M C2/c
3T P3121
4M C2/c
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Zirconolite Systems - UZr
Series CaZr1-xUxTi2O7
0 lt x lt 0.15
0.15 lt x lt 0.25
2M
2M 4Md
E.R. Vance, G.R. Lumpkin et al.
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Zirconolite Systems - UZr
Series CaZr1-xUxTi2O7
0.25 lt x lt 0.35
0.35 lt x lt 0.50
4M
4Md Pyrochlore
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Microstructure
Pu Bearing (35 wt) LLNL Pyrochlore type
Pyrochlore
20 nm
(111)P
Zirconolite-4M
(001)Z
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Zirconolite - CaZrTi2-2xNbxFexO7
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b0
a0
b
c0
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Cation Ordering - HTB Layer
Results of fixed test models CaZrNbFeO7
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x 0.2
x 0.4
x 0.6
x 0.8
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Site Fe Nb
M1 0.39 0.61 M2 0.42 0.08 M3 0.19 0.31
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Radiation Damage
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SAED of Irradiated Gd2Ti2O7
110 zone axis
0.0 Dc
0.2 Dc
0.4 Dc
0.6 Dc
(111) systematic row
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SAED of Irradiated Gd2Ti2O7
Note (111) lost in region of increased small
angle scattering, but (333) still apparent
0.6 Dc
111 222 333 444
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Ti L2,3 ELNES
L3 L2
3 eV
Gd2Ti2O7 0.0 Dc
O K
532 ev
2 eV
Gd2Ti2O7 1.0 Dc
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Coordination Fingerprinting
6Ti4
Gd2Ti2O7 1.0 Dc
5Ti4
Brydson and coworkers
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2004 IVEM Results - Pyrochlores
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Radiation Tolerance Pyrochlore
LaM Trend consistent with Models, K. Trachenko,
M. Pruneda
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Statistical Analysis Pyrochlore
Empirical models Tc versus structure, bonding,
disorder energy terms, N 19
Results Tc vs Cation Radii
Monoclinic
Best Model

• Tc - 29738.6 (x48f)
• 8457.7 (a0)
• 1148.8 (END)
• 939.7 (Edis)
• R2 0.991
• SD 82.2 K

Defect Fluorite
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Radiation Effects The Big Picture
Waste Storage Period
Dc 300
Dc RT
Natural Pyrochlore
ACT doped Pyrochlore
Ion Irradiation Experiments
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Aqueous Durability
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Leach Rates vs pH
Zirconate - REEs Cubic zirconia - REEs
Perovskite - Ca
Log Ri (g/m2/d
Monazite - REEs
Ansto, PNNL, Poitrasson data
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Pb Irradiated Zirconolite - XTEM
Unleached
Leached
Ansto - CEA - C3i collaboration
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Dissolution of Zirconolite
Ca0.8Nd0.2ZrTi1.8Al0.2O7
Ti data T 90 C pH 2
Smith et al., ANSTO - PNNL
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Conclusions

• Zirconolite and Ti pyrochlore systems as
  promising actinide host phases (5 vol bulk
  swelling, amorphization)
• Bonus radiation resistance in Zr pyrochlore,
  defect fluorite, fluorite (reduced crystal
  chemical flexibility)
• Promising results for Monazite, Zircon (large
  volume expansion), Garnet (needs work)
• Dissolution mechanisms need work
• Radiation effects on bulk samples, kinetics

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SrTiO3
La2/3TiO3
Radiation Damage in Perovskite
Ansto - C3i
Pm3m
Cmmm
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Crystal Structures and Ion Irradiation Response
Perovskite Sr1-1.5xLax?0.5xTiO3
Domains
TEM
Structural Data
Irradiation Data
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Domain Structures Observed by TEM
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Ion Irradiation Sr1-1.5xLaxTiO3
1.0 MeV Kr - HVEM
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Radiation Damage Kinetics
Basic Equation - S. Wang (Michigan)
Basic Equations - W.J. Weber (PNNL)
Tc Ea / k ln(sr /sa) irradiation assisted
Tc Ea / k ln(n /sa f) thermal recovery
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Sr-La Perovskite 1.0 MeV Kr Results
x Dc0 Ea1(eV) Ea2(eV) Tc (K)
0.00 5.1 0.054 0.86 394 0.10 8.3 0.080 0.68 308 0.
20 7.7 0.038 0.60 275 0.30 6.5 0.026 0.80 364 0.60
2.4 0.039 1.60 750 0.67 2.6 0.29 1.85 865
1014 ions cm-2
s 1-4 x 10-15 cm2 10-40 Å2