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PHYSICO-CHEMICAL PROPERTIES OF THORIUM FUELS
O. Beneš, R. J. M. Konings, J. Somers, D.Staicu, D. Manara
European Commission – Joint Research Centre Institute for Transuranium Elements (ITU), Karlsruhe, Germany
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Institute for Transuranium Elements
One of the 7 research institutes
of the European Commission‘s
Joint Research Centre
~ 300 staff members
Location: Germany, Karlsruhe
6 Scientific Units
4 pillars of the ITU work programme:
- Basic actinide science and application
- Safety of the nuclear fuel cycle
- Safeguards and nuclear forensics
- Education and user facilities
http://itu.jrc.ec.europa.eu/
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Th-containing fuel
2 main research lines at ITU
solid oxide fuels
(Th-U)O2, Th-MOX
molten salt fuels
F-, Cl- salts
- basic actinide research
- better understanding of physico-chemical properties
to increase the safety of neclear reactors.
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solid oxide fuels
Systematic study of the Th-U-Pu-O system
(possibly Am addition)
5
solid oxide fuels
Heat capacity determination - by drop calorimetry, PPMS, adiabatic calorimetry
- 0.5 – 1800 K
Melting temperature determination - using a laser flash technique
- self-containing method – above 4000 K
Vapour pressure measurements - Knudsen cell coupled with MS
- up to 2800 K
Thermal conductivity measurements
- laser flash technique
- up to 3000 K (tungsten heater)
Irradiated fuel investigation (hot cells, γ-tight GB)
- fuel synthesis and fabrication
- P-C properties, topography
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solid oxide fuels
1. Heat capacity determination
drop calorimeter
400 - 1800 K
dH measured first Cp
automatic
motor
dropping tube
crucible
crucible
28 TCs
Al2O3 tube
heating element
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solid oxide fuels
Heat capacity determination of (Th,U,Pu)O2 mixtures
heat capacity functions obtained by derivation
Enthalpy increments measurments
ThO2-PuO2 system: 3%, 15%, 30% of Pu
ThO2-UO2 system: 20%, 40%, 60%, 80% of Pu
UO2-PuO2 system: 25%, 50%, 75% of Pu
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solid oxide fuels
2. Melting temperature determination
Experimental set-up of laser flash method
Advantages:
• Fast experiments (from ms to s)
• Containerless conditions (no contact between liquid sample holders)
Disadvantages
• Emissivity needs to be known
• Thermal stresses
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solid oxide fuels
Melting temperature determination
0 20 40 60 80 100
2000
2400
2800
3200
3600
Solidification point
Te
mp
era
ture
/ K
Time / ms
RLS first derivative
Fast pyrometer thermogram (= 0.83)
0
500
1000
1500
2000
2500
3000
Laser power
La
se
r P
ow
er
/ W
0,15 0,16 0,17 0,18 0,19
2600
2800
3000
3200
3400
3600
0,150 0,155 0,160 0,165
2940
3000
3060
Lyon et al.Riley
Kato et al.
Peak laser power
630 W
675 W
720 W
Tem
pe
ratu
re / K
time / s
This work
(3017 28) K
Melting temperature measurement of PuO2
Measurement of PuO2 and NpO2 performed recently at ITU observed melting points significantly higher than
reported in the literature.
Measurement of ThO2 confirmed the literature value
It is planned to make systematic study of solidus-liquidus equilibria in the ThO2-UO2 and ThO2-PuO2 systems
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solid oxide fuels
3. Vapour pressure determination
scheme of Knudsen cell with MS
Knudsen cell glove box
W/Ir set-up – up to 2800 K
contained in shielded glove box
- fundamental studies of An-containing
systems
- studies of fission product release at
high temperatures of irradiated fuels
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solid oxide fuels
Ionization potential determination of UOx
8.0
8.3
0.5
+
+
+
+
UO
10.8
5.92
7.85
7.81
U U
UO
UO2 UO2
UO3 UO3
5.4
5.6
6.15
11.3
19.3
13.9
13.4
21.7
27.6
21.6
15.7
units in eV
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solid oxide fuels
Vapour pressure determination of PuO2
PuO2 (g)
PuO (g)
Pu (g)
1 2 3
Ordinary fuel
structure Rim
structure
Cladding+corrosion
products
500 1000 1500 2000 2500 3000
0.0
0.2
0.4
0.6
0.8
1.0
3
2
136 X
e A
bso
lute
rele
ase n
orm
alised
Temperature (K)
1
Low
Tirr
High
Tirr
136Xe release from irradiated fuel
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solid oxide fuels
4. Thermal conductivity determination
ΔTmax
t1/2
α = 0.13885 L2/t1/2
Parker‘s model
scheme of laser flash technique
Experimental set-up
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solid oxide fuels
Thermal conductivity determination of (Th,Pu)O2 solid solution
Cozzo C., et al. J. Nucl. Mater. 416 (2011)135
ThO2 and PuO2 pure compounds measured
(Th0.97Pu0.03)O2, (Th0.92Pu0.08)O2 and
(Th0.7Pu0.3)O2 compositions measured for
500 – 1500 K
at low temperatures the addition of Pu into
the ThO2 matrix influence significantly (almost
by one half) the thermal diffusivity
at higher temperatures this influence is of
much lower order – due to increase of phonon-
phonon scattering mechanism, becoming
predominant compared to lattice strains.
(Th,U)O2 system is planned to be investigated
synthesis of Th80%, Th60%, Th40% and Th20%
is being performed now.
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molten salt fuels
Reference system: LiF – ThF4 – UF4 (AlkF (Alk=Na, K, Rb),
BeF2, AnF3(An=Pu,MA))
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molten salt fuels
Work carried out at ITU
Experimental part Thermodynamic modelling
Heat capacity determination
- pure solid compounds
- liquid solutions (systematic study)
Equilibrium data determination (phase diagram)
- melting temperatures
- solidus, liquidus points
Heats of transition and fusion determination
Enthalpy of mixing of liquid solutions
extremely strong tool to predict behaviour
of any multi-component system
ITU‘s molten salt database (2002-2011)
contanining 39 binary systems
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Calorimetry at ITU Total temperature range covered from 0.5 K to 1750 K
2 low temperature adiabatic calorimeters (Cp determination)
(4.2 K – 350 K, from 0.5 K coupled with PPMS)
2 Drop calorimeters (Cp and fusion
enthalpy determin.)
(400 K – 1750 K)
1 DSC (equilibrium data
fusion enthalpy)
(400 K – 1650 K)
molten salt fuels
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molten salt fuels
Low temperature heat capacity measurement of UF3
S298 = 126.8 J.K-1.mol-1
TC = 1.59 K
Benes O., et al. Inorg. Chem. doi.org/10.1021/ic2010453
further measurements of Cp in
magnetic field and magnetization
confirmed ferromagetic nature
of the transition.
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molten salt fuels
High temperature studies
Encapsulation necessary to avoid F- vapour release
Drop calorimetry
nickel crucible
emergency button
optical scope
laser inlet
vacuum pump
turning device
moveable platform
vacuum chamber
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molten salt fuels
High temperature studies
Encapsulation necessary to avoid F- vapour release
Differential Scanning Calorimetry (DSC)
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molten salt fuels
High temperature heat capacity measurement of molten salts
systematic study of LiF-AlkF systems: LiF-NaF, LiF-KF, LiF-RbF and LiF-CsF
will be followed by An-containing systems, LiF-ThF4, UF4-ThF4 ...
Very important observation as untill now all
assessed systems were treated ideally in terms
of the heat capacity behaviour.
X (LiF)
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molten salt fuels
Phase diagram investigation of molten salt systems
NaNO3-KNO3, RbF-CsF measured as first systems (also to proof the encapsulation technique)
Th-containing systems: CaF2-ThF4, LiF-ThF4, UF4-ThF4 (next planned)
CaF2-ThF4 system
preliminary version
LiF-ThF4 system
(purification of ThF4 was required)
- our data
- ORNL data
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molten salt fuels
Heats of transition of fluoride salts
from DSC and Drop technique: ∆fusH of CsF recently evaluated
by DSC by Drop
∆fusH = 22,190 J.mol-1 ∆fusH = 21,550 J.mol-1
Literature: ∆fusH (Dworkin et al.) = 21,700 J.mol-1
∆fusH (Macleod) = 14,850 J.mol-1
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molten salt fuels
Future plans:
To establish a suitable technique to measure the thermal conductivity of MS
requires encapsulation – more complex model necessary
To set-up the Raman spectroscopy to high temperatures
- To determine the structure of these liquids
- what clusters are formed
- to couple these results with MD studies (UPMC collaboration)
- improve ITU‘s thermodynamic database which considers cluster formation
- To determine solubilities of AnFx in various fluoride matrixes
- e.g. PuF3 solubility in LiF-ThF4 melt/eutectic (EVOL project)
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furnace
sample inside
laser generator
detector
2 methods:
- Macro line
higher sensitivity
- Superhead
more flexible for
manipulation,
easier focusing
microscope
Raman - molten salt fuels
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molten salt fuels
Thermodynamic modelling as a tool to
optimize a fuel composition of the MSR
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MSFR reactor concept (French concept) (Molten Salt Fast Reactor) (considered in EVOL EU-project) Initial MSFR fuel composition: X(LiF) = 77.45 mol% X(ThF4) = 20 mol% (LiF-ThF4 eutectic) X(UF4) = 2.55 mol%
Criteria:
X (ThF4) = ~20 mol%
X (UF4) = 2.55 mol%
Temperature low as possible
(to avoid freezing)
MSFR pre-conceptual design,
GIF Annual Report 2009: (MSR)
molten salt fuels
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7LiF – NaF – ThF4 – UF4
Matrix components
Fertile material Fissile material
Fuel for Molten Salt Fast Breeder Reactor (MSFR)
232Th + 1n 233Th 233Pa 233U
fertile fissile
β- decay β- decay
22 min 27 days
Th / U fuel cycle
molten salt fuels
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The aim: to make a full thermodynamic decription of a molten salt
reactor fuel (LiF-NaF-ThF4-UF4) optimize the MSR
fuel composition
The way: 1. TD assessment of all binary sub-systems
LiF – NaF LiF – ThF4 LiF – UF4
NaF – ThF4 NaF – UF4 ThF4 – UF4
2. extrapolation to higher order systems
molten salt fuels
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X (ThF4)
T /
K
0.0 0.2 0.4 0.6 0.8 1.0
400
600
800
1000
1200
1400
LiF - NaF LiF – ThF4 LiF – UF4
NaF – ThF4 NaF – UF4 ThF4 – UF4
X UF4
T(K
)
0.0 0.2 0.4 0.6 0.8 1.0
400
600
800
1000
1200
1400
X (ThF4)
T /
K
0.0 0.2 0.4 0.6 0.8 1.0
400
600
800
1000
1200
1400
X (NaF)
T /
K
0 .2 .4 .6 .8 1
600
700
800
900
1000
1100
1200
1300
X (UF4)
T /
K
0.0 0.2 0.4 0.6 0.8 1.0
400
600
800
1000
1200
1400
X (UF4)T
/ K
0.0 0.2 0.4 0.6 0.8 1.0
1200
1240
1280
1320
1360
1400
molten salt fuels
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Lowest eutectic:
T = 775 K (502 °C)
x (ThF4) = 0.221
x (UF4) = 0.0255
x (LiF) = 0.521
x (NaF) = 0.23
Tinlet = 825 K (552 °C)
12 Invariant eq.:
2 Eutectics
9 Quasi-peritectics
1 Peritectic
Criteria:
X (ThF4) = ~20 mol%
X (UF4) = 2.55 mol%
Temperature low as possible
(to avoid freezing)
molten salt fuels
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