Electrochemical behaviors of U, Th in fluoride molten salts
Dewu Long, Wei Huang, Qingnuan Li
Shanghai Institute of Applied Physics (SINAP), Chinese Academy of Sciences(CAS)
INTERNATIONAL PYROPROCESSING RESEARCH CONFERENCE 2014 IDAHO FALLS, IDAHO, OCT. 19-23, 2014
TMSR Project at SINAP (CHINA)
Fluorides coolant
Homogenous fuel
Thorium breeding
On-line fuel treatment
Background
Features
3
Conceptual flowsheet of TMSR Fuel Processing
Fluorination Reactor Th,U,Pa,FPs
LiF-BeF2
UF6
Th,Pa,FPs LiF,BeF2
Storage 233Pa 233U
FPs Distillation
Fuel reconstitution
LiF BeF2
U,Th LiF-BeF2-UF4-ThF4
Waste proper to later disposal
Hydrofluoric acid dissolution LiF BeF2
Pyrohydrolysis
Modified Thorex
Th,Pa,FPs LiF,BeF2
Fluorides Oxides
Electrochemical separation
Electrochemical separation
2014-10-20 reprocessing and recycling Off-line reprocessing
U in FLiBe or in FLiNaK
Th and U in FLiNaK or in LiCl-KCl
Background
4
Background
Fluoride-based molten salt medium. One or more steps of the
electrochemical separation in TMSR fuel processing have to
be conducted in fluoride electrolyte, e.g. LiF-BeF2.
Fundamental database unavailable. The lack of reliable and
systematic database of Ans and Lns in fluoride molten salt.
The feasibility for recovering of U or Th and the efficiency of
the separation process. The applicability of electrochemical
separation method in TMSR fuel processing and the recovery
efficient should be evaluated.
Challenges for the implementation of electrochemical separation technology in TMSR
Due to the toxicity of LiF-BeF2, LiF-NaF-KF (46.5- 11.5- 42.0 mol%, FLiNaK, m. p. 454℃) is initially adopted as the medium.
FLiBe (7LiF-BeF2
66-34 mol%, m. p. 460 ℃)
Molten salts used in TMSR
The R&D of electrochemical technology in TMSR
Fundamental data acquisition Electrochemical measurement method Electrochemical deposition
Thermal stability Low vapor pressure Manageable melting point Low neutron cross section Radiation resistance Dissolvable media for Ans and Lns Toxicity and poison High cost for Li-7
Background
Ni wire
BN tube
Inner salt
Ion Channal
Potential shifting (< 5 mV)
Performance of as-prepared RE Over 50 hrs stability,shifting less
than 10mV Excellent repeatability, potential
deviation less than 5mV Suitable for experimental
requirement
Fabrication and Performance of Reference Electrode
performance of reference electrode is essential .
Non-commercial electrode available.
Illustration of reference electrode
Progress
7
On mechanism understanding the performance of an reference Electrode
Performance of an RE exhibits strong Ni2+ speciation dependence of the inner electrode couple.
20 wt%
40 wt%
70 wt%
Progress
K2NiF4
KNiF3 Li2NiF4
KNiF3 Li2NiF4
Ni2++2e-→Ni0
NiF2
NiF2
NiF2
~
-2.0 -1.5 -1.0 -0.5-0.02
0.00
0.02
Curre
nt /A
Potential/V
U3+→U0
U0→U3+
U3+→U4+
U4+→U3+
FLiNaK
Reaction Redox potential(V)vs. NiF2/Ni D/cm2 s-1 Separation
Gd3++3e→Gd0 -2.02/-1.68 3.2×10-4 Y Y3++3e→Y0 -1.96/-1.91 5.4×10-6 Y
Sm3++e→Sm2+ -1.65/-1.53 7.4×10-6 N Eu3++e→Eu2+ -1.07/-0.89 1.3×10-5 N Nd3++3e→Nd0 -1.95/-1.88 1.1×10-5 Y Zr4++4e→Zr0 -1.86/-1.50 2.5×10-6 Y Th4++4e→Th0 -1.91/-1.66 8.4×10-7 Y
U4++e→U3+ U3++3e→U0
-1.42/-1.24 -1.83/-1.69 1.3×10-6 Y
Determination the parameters of key elements
FLiBe LiCl-KCl
U4+→U3+
U3+→U0
U3+→U0 U4+→U3+
Progress
9
CV of U 4+ and U3+ in FLiNaK
Progress
FLiNaK, 823K D(U4+) = (4.7±0.9)× 10-6 cm2 s-1 D(U3+) =(2.6±0.2) × 10-6 cm2 s-1
ip=0.44(nF)3/2AC0U4+D1/2v1/2(RT)-1/2
Reduction sequence and electro-deposition of U
U deposition
Deposition product
Product after removal of salt Ni Electrode
U %~ 30%
U %~ 3% C0
U in MS
CU in product
20 40 60 80 100
Inte
nsity
/Cou
nts
2θ/°
♦--UO2
∇--KF• --LiF♠--Martix
♦
♦♦ ♦
♦♦♦ ♦ ♦
∇
∇
∇ ∇∇ ∇•
•
•
♠
♠
Progress
11
0 500 1000 1500
-1.85
-1.80
-1.75
-1.70
-1.65
-1.60
-10 0 10 20 30 40 50 60 70
-200
-150
-100
-50
0
50
i/mA
time/s
-200mA
-40mA
30mA0mA
1s
60s
3s
3s
Pote
ntia
l/V
time/s
Advanced method for electro-deposition of U
Current pulse electrolysis
Pre-concentration
deposition
dissolving
Post-stabilization
Progress
12
Electro-deposition of Th in LiCl-KCl
Progress
Deposited product
In molten salt
ICP-AES
XRD
Product
13
High performance reference electrode has been fabricated and the influence
of Ni2+ speciation on the performance of the electrode is evaluated.
Electrochemical behaviors of U and Th in various molten salts have been
investigated and preliminary deposition of U and Th was conducted. The
feasibility of recovery of U and Th was confirmed.
Future work would be focused on
Improve the reliability of the measurement of fundamental data in fluoride
salt.
Develop in-situ electrochemical method for process monitoring and TMSR
salt chemistry controlling (U4+/U3+ ratio represent the redox chemistry).
R&D of electro-chemical separation technique for TMSR fuel cycle as well
as designing of large-scale apparatus.
Summary & future work