Project Research
Project 5PR5Studies on Actinides and Fission Products Performed at the KURRI Hot Laboratory

T. Fujii

lavas (N. Hirano et al.).
ARS-19 Behavior of fission products in soil samples (S.
Fukutani et al.).

Research Reactor Institute, Kyoto University
1. Objectives and Allotted Research Subjects
Studies on actinide and fission product nuclides withcareful management are being more important for reprocessing, disposal, partitioning, and transmutation processes in the nuclear fuel cycle. Hot laboratory of KURRI is one of core facilities in Japan, in which various
nuclides can be handled. This project enhances utilizationof the KURRI hot laboratory by opening for fundamental
and application studies related to radiochemistry, nuclear
chemistry, environmental chemistry, geochemistry, andso on. Allotted research subjects are;
ARS-1 Complexation of actinides with organic substances (T. Sasaki et al.).
ARS-2 Solubility of actinide compounds in aqueous
media (T. Kobayashi et al.).
ARS-3 Leaching of actinides and FPs from fuel debris(N. Sato et al.).
ARS-4 Neutron irradiation damage of vitrified waste
matrices (T. Nagai et al.).
ARS-5 Ligand exchange reaction of actinides in molten
salts (A. Uehara et al.).
ARS-6 Electrochemical behavior of uranium in pyroreprocessing system (Y. Sakamura et al.).
ARS-7 Structural study of f-elements in molten halides(H. Matsuura et al.).
ARS-8 Molecular dynamics simulation of uranyl ion in
molten salts (N. Ohtori et al.)．
ARS-9 Fundamental study of fission products fortrans-actinide chemistry (Y. Kasamatsu et al.).
ARS-10 Isotope separation by using microreactor (R.
Hazama et al.).
ARS-11 Optical properties of molten aluminum halides(T. Goto et al.).
ARS-12 Precipitation of f-element oxides in molten halides (H. Sekimoto et al.).
ARS-13 Uptake of radiocesium and radiopotassium inplants (T. Ohta et al.).
ARS-14 Quantitative analysis of radionuclides in seawater (T. Kubota et al.).
ARS-15 Isotopic composition of radionuclides in environmental samples (Y. Shibahara et al.).
ARS-16 Noble gas mass spectrometry of neutron irradiated geological samples (H. Sumino et al.).
ARS-17 40Ar/39Ar dating of neutron irradiated minerals
and glasses (O. Ishizuka et al).
ARS-18 Radiometric Ar-Ar dating of neutron irradiated

2. Main Results and Contents
ARS-1, 2, 3, and 4 were performed in order to deepen theknowledge of nuclear waste management issues. In
ARS-1, for understanding the randomly cross-linked heterogeneous and macromolecule properties of humic substances (HSs), the complexation of actinides with HS
was studied. The HS samples irradiated by Co-60 gamma-ray source at KURRI were characterized by NMR
measurement, and the dependence of dose rate on thechemical structure was clarified. ARS-2 studied on thesolid phase transformation of Th(OH)4(am: amorphous)at 363 K. The apparent solubility and particle size of thesolid phase after aging were evaluated. ARS-5, 6, 7, 8,
and 12 were performed with the viewpoint of pyrochemistry. In ARS-5, the solubility of uranium in various molten alkali chlorides was determined. It was found that thesolubility of uranium does not depend on the melting
point of molten salts but increases with ionic diameter ofsolvent alkali metal ion. ARS-6 studied on the behaviorof Al3+ in LiCl-KCl eutectic melt in order to develop the
separation technique of Al from Al-actinides intermetallic compounds. It was found that Al can be separated
from U by using a Cu electrode in LiCl-KCl melts. In
ARS-7, the electrochemical measurement of zircomium
in molten LiCl-KCl has been carried out for the first stepof the elucidation of electrochemical behavior containing
zircomium. The results suggested that zirconium would
be difficult to be selectively electoreduced in molten
LiCl-KCl depending on the concentration of zircomium.
In ARS-8, the Helmholtz free energy changes for the
successive additional processes of chloride ion to uranyl
ion in aqueous solutions of LiCl with various concentrations have been evaluated. The stability of uranyl ion in
hydrate melts was then discussed. ARS-12 studied on theformation of Nd(II), Dy(II) and Pr(II) in CaCl2-LiCl eutectic molten salt with the combination of the absorption
spectroscopy and the galvanostatic electrolysis method.
The results showed that Nd(II) was decomposed throughthe disproportionation reaction. ARS-10 studied isotope
fractionation of Ca. A possible fractionation of 48Ca/40Ca
was found. ARS-13, 14, 15, 16, 17, and 18 focus on environmental chemistry and geochemistry by using KUR.
3. Summaries of the achievements
New and characteristic chemical, kinetic, structural, andthermodynamic data for actinides and fission products
were obtained. These new information encompass solid
chemistry, molten salt and solution chemistry, as well as
nuclear reactions of f-elements and FPs. Restart of the
KUR operation is strongly awaited.

27P5- 24 -

PR5-1

Study on Chemical Property of Gamma-irradiated Natural Organic Matters

T. Sasaki, T. Kobayashi, S. Nishikawa, R. Goto,
A. Uehara1, T. Fujii1 and T. Saito1
Graduate School of Engineering, Kyoto University
Research Reactor Institute, Kyoto University

1

INTRODUCTION: Due to the randomly cross-linked
heterogeneous and macromolecule properties of humic
substances (HSs) as natural organic matter, in soils, sediments, and natural waters, the apparent formation constant of actinides with HS changes depending on the solution conditions such as pH, metal and HS concentrations, and ionic strength. When the HS in undergroundwater contacts with a radioactive waste package at repository site, the chemical property of HS should be alteredby gamma-irradiation and the ability of complex formation may be decreased. The HS samples irradiated by
Co-60 gamma-ray source at KURRI were characterized
by NMR measurement, and the dependence of dose rateon the chemical structure was discussed.
EXPERIMENTS: The Eliot soil humic acid (SHA,
1S102H) and Suwannee river fulvic acid (SFA, 1S101F)
were purchased from International Humic Substance Society (IHSS). The proton dissociation constants havebeen reported. The brownish aqueous solution samples
for Co-60 gamma-irradiation were prepared to be 10-3
eq/dm3 at a given alkaline pH condition. The irradiationdose were 10, 100 and 500 kGy by controlling the time of
exposure. 1H NMR spectrum was obtained at 600.17
MHz (JEOL JNM-ECA600 FT NMR spectrometer) withacquisition time of 1.45 sec, pulse delay time of 5 sec,
and accumulation of 1000 scans, and 13C NMR spectrum
was obtained at 600.17 MHz with acquisition time of
0.69 sec, pulse delay time of 10 sec, and accumulation of
24000 scans.
RESULTS: The blackish precipitation was observed in
the SHA solution after 500 kGy irradiation, and the same
irradiation achromatized the SFA solution, suggesting a
different degradation process. As shown in Fig. 1, theproton NMR spectra of HS have broad peaks at the entire
chemical shift range and are different from that of generaland commercially available reagents such as acetic acidand EDTA. Based on the previous studies about naturalhydrocarbon compounds [1-4], these peaks of 1H wereassigned to be some kinds of functional groups. The integrated intensity of peaks is summarized in Table 1. The
fragment of aliphatic hydrocarbon Hγ increased after 10
kGy irradiation, while that of the aromatic protons HArdecreased. Meanwhile, the S/N ratio of 13C NMR spectra
was significant low even in longer acquisition time. For
better understanding of chemical property, a higher performance of NMR would need for further study.

Fig. 1. 1H NMR spectra of un-irradiated Eliot soil
humic acid (1S102H). (600.17MHz, Number of transients:1000 ) The upper spectrum of Inogashira-HS
is obtained from ref [5] for comparison.
Table 1. Distribution% of protons in SHA based on the1
H peak area at each range of chemical shift.
Proton assigned (δ, ppm)
Dose
(kGy)

Hγ
(00.9)

Hβ(0.91.6)Hα(1.63.0)

HO-C(3.04.3)

HAr(6.09.0)

0

7.8

16.7

23.3

33.3

18.9

10

10.8

16.9

22.9

32.5

16.9

REFERENCES:[1] H. Oka et al. Nenryo Kyokaishi (J. Jpn. Fuel Soc.), 48(1969) 295-302.
[2] K. Yonebayashi and T. Hattori, Soil Sci. Plant Nutr.,
35 (1989) 383-392.
[3] R.D. Malcolm, Anal. Chem. Acta, 232 (1990) 19-30.
[4] M. Kawahigashi et al., Soil Sci. Plant Nutr., 42 (1996)
355- 360.
[5] A. Watanabe, K. Tsutsuki, S. Kuwatsuka, Sci. Total
Environm., 81/82 (1989) 195-200.

27P5-1- 25 -

Effect of Solid Phase Transformationon the Solubility Product of Thorium Hydrous Oxide at 363 K

T. Kobayashi, H. Mizukoshi, T. Sasaki, A. Uehara1 andT. Fujii1
Graduate School of Engineering, Kyoto University
Research Reactor Institute, Kyoto University

1

INTRODUCTION: In the repository systems forhigh-level wastes or spent nuclear fuels, decay heat emissions are transferred to the groundwater aquifers surrounding the waste packages. Although the actual operating temperature depends on the structure of the repository system, temperature conditions greater than 333 K
are thought to simulate results of temperature evolution
up to a thousand years [1]. For evaluating the effects ofthe possible temperature on tetravalent actinide (An(IV))
migration behavior under certain scenarios, such as early
failure of the waste package, it is necessary to determine
the temperature effect on An(IV) solubility.
Under geological disposal conditions, An(IV) solubility is
primarily controlled by amorphous hydroxide solid phase(An(OH)4(am)). However, An(OH)4(am) is thermodynamically meta-stable, and it is converted to stable crystalline oxides (AnO2(cr)) by heating and calcination. A
transformation of An(OH)4(am) into a solid phase withhigher crystallinity has also been shown to occur inaqueous solutions at high temperatures [2]. These observations indicate that the thermodynamic description ofAn(IV) solubility under elevated temperatures requires
clarification of a possible transformation of An(OH)4(am)as a solubility-limiting solid phase.
In the present study, we focused on the solid phase transformation of Th(OH)4(am) at 363 K. Sample solutions incontact with Th(OH)4(am) were stored in a chamber controlled at the aging temperature of 363 K. The apparent
solubility and particle size of the solid phase after aging
at 363 K were then investigated.
EXPERIMENTS: A 0.3 M 232Th stock solution diluted
to obtain sample solutions, and pH value was adjusted by
HClO4/NaOH. The sample solutions were kept in an oven
controlled at 363 K for given periods. After aging, thesample solutions cooled down to 298 K and the pH values measured. The apparent solubility was measured byinductively coupled plasma mass spectroscopy (ICP-MS;
HP4500, Hewlett Packard) after ultrafiltration (3k - 100k
Da filter, Millipore), and the solubility product was determined. The detection limit for ICP-MS was about 10−8
M. The solid phases after aging at 363 K were separated,
and then investigated using XRD (RINT 2000, RIGAKU).
The Scherrer equation was applied to the XRD patterns todetermine the particle size of the solid phases.
RESULTS: Th(IV) solubility after heating at 363 K for 7
days started to decrease and the values after 41 days wereapproximately 3 orders of magnitude lower than those ofTh(OH)4(am). In the XRD spectra of the solid phases
kept at 363 K, broad peaks corresponding to ThO2(cr)were observed, indicating a progress of the crystallizationof initial Th(OH)4(am).
In Figure 1, trends of the solubility product for different
Th solid phases are shown as a function of particle size[3]. A dotted line represents an estimated solubility product according to the Schindler equation [4]. The solubility
product value obtained in this study seems to be consistent with general trends of the data, but is much lower
than the values for Th(OH)4(am,fresh) andTh(OH)4(am,dried), in spite of similar particle sizes. The
observed difference might be explained by considering
the higher sensitivity of the solubility value on the size ofthe smaller solid particles, and by considering possible
differences in the size distributions of solid particles prepared by different experimental methods-46－46.7±0.9
Th(OH)4(am,fresh)－47.8±0.8
Th(OH)4(am,dried)-48

log Kºsp

PR5-2

-50
－51.6±0.5 (present work)
Th(OH)4(s,363 K)-52－54.2±1.1
ThO2(cr)-54－53.5±0.5
ThO2(microcryst.)

-56
1

10

100

Particle size (nm)Fig. 1. The effect of particle size on the solubility
product of Th(OH)4(s,363) compared with the different
solid phases and predicted curves from the Schindler
equation [3].
REFERENCES:[1] 2nd progress report on research and development for
the geological disposal of HLW in Japan, JNC Report
TN1410 2000-001, JNC, Tokai, Japan.
[2] D. Rai et al. Radiochim. Acta 88, (2000) 297.
[3] T. Kobayashi et al., J. Nucl. Sci. Technol. In press.
(2016).
[4] M. Rand et al. Chemical Thermodynamics of Thorium. Elsevier, Amsterdam; 2009.

27P5-2- 26 -

PR5-3

Solubility of Uranium (VI) Oxides
in High Temperature Molten Alikali Chlorides

A. Uehara, T. Nagai1 and T. Fujii
Research Reactor Institute, Kyoto University
Nuclear Fuel Cycle Engineering Lab., Japan Atomic
Energy Agency

1
2

INTRODUCTION:

In the non-aqueous reprocessing process of spent nuclear fuels by the pyrometallurgical and the electrowinning methods, a spent fuel is dissolved into
molten alkali metal chloride eutectic and uranium andplutonium ions are recovered as metal or oxide. In thepresent study, the solubility of uranium ions in various
kinds of molten alkali chlorides was measured.
EXPERIMENTAL:

Uranium oxides were converted to U3O8 by heating at
1023 K for 4 hours before use. Chlorination experiments were carried out at 973 K under an argon atmosphere, in which humidity and oxygen impurity
were continuously kept less than 1 ppm. Chlorine gas
was purged for half an hour after U3O8 addition to thechloride melts. The solution phase was separated fromundissolving solid phase by using a glass filter which
was attached at the end of the tube. Argon gas waspurged to exchange chlorine gas dissolving in molten
salt phase before the phase separation. Uranium concentration in molten salt phase was measured by hydrogen peroxide process. Molten salts used were LiCl,
CsCl, RbCl, LiCl-KCl, LiCl-RbCl, NaCl-KCl,
NaCl-RbCl, NaCl-KCl, and NaCl-CsCl eutectics.

U3O8 was oxidized and dissolved into molten salt
phase by chlorine gas as Eq. (1).
U3O8 + 3 Cl2 → 3 UO2Cl2 + O2
(1)
In order to analyse the valence of the uranium ions inthe salts, UV-Vis absorption spectrum [1] was measured after the dilution of the salt by LiCl-KCl eutectic(Fig. 1). Absorption peak at 370 nm corresponding to
UO2+ as well as the peak at < 330 nm corresponding to
UO22+ were observed. The concentration of UO2+
formed was calculated to be < 5% of total uranium
concentration. It is suggested that UO22+ was partiallyreduced by Ar gas due to the shift of the equilibrium
potential in the melt as Eq. (2).
(2)
UO2Cl2 → UO2Cl + 1/2 Cl2Concentration of uranium ion in molten salt phase
was measured by hydrogen peroxide method. The
solubility of uranium in various molten salt was plotted as a function of melting point of the salts as shownin Fig. 2. The solubility of uranium in LiCl-KCl eutectic was 15.3 mol%, which was rather lower than that in
NaCl-CsCl eutectic (37 mol%), RbCl melt (34 mol%).
It was found that the solubility in CsCl was the highest
in the molten salt tested. It is suggested that the solubility of uranium was not depended on the melting
point of the molten salts but increased with increase ofionic diameter of alkali metal ion.

UO2Cl2 solubility (mol%)

50

RESULTS:

After 3.0 g U3O8 was putted into 3.1g LiCl-KCl eutectic melt at 973 K, chlorine gas was purged through themelts for over 1 hour at 20 ml/min.
0.6

abs (a.u.)

UO22+

40
RbCl

30

NaCl-KCl equ.

LiCl

10

LiCl-KCl eut.

0
UO2+

NaCl-RbCl eut.

LiCl-RbCl eut.

20

500

0.4

CsCl

NaCl-CsCl eut.

600

700

Chlorination
at 700℃
923K
chlorination at
800

900

1000

melting point of melt (K)

1100

0.2

Fig. 2. Solubility of UO22+ depended on the melting pointof the alkali chlorides.

0

REFERENCES[1] Nagai, et al., J. Nucl. Sci. Techol. 41(2004) 690–695.

300

350

400

450

500

550

600

wavelength (nm)Fig. １. UV-Vis absorption spectra of uranium samples
used in chlorination experimental (concentration depencence).

27P5-5- 27 -

PR5-4

A Study on the Separation of Aluminum from Actinides in LiCl-KCl Eutectic Melt

Al 3+ concentration (mol%)Y. Sakamura, M. Iizuka, K. Uozumi, A. Uehara1 and T. Fujii1 tential of Al/Al3+ on the W electrode is consistent with
the CV of Al metal previously obtained in a LiCl-KClCentral Research Institute of Electric Power Industry
UCl3 melt [2]. There is no other distinct peak, which in2
dicates that W hardly forms alloys with Al under the conResearch Reactor Institute, Kyoto University
dition of this measurement. The deposition behaviors of
Al on Ta and Fe were similar to that of W.
The CV of Cu has a cathodic peak at -0.90 V and an
INTRODUCTION:
Electrorefining
inmolten anodic peak at -0.75 V, which correspond to the forLiCl-KCl eutectic-based salts is the key separation step in mation and decomposition of an Al-Cu alloy, respectively.
the pyrochemical treatment of spent nuclear fuels. It has The anodic peak at -0.65 V might be due to a different
been reported that the Al cathode is suitable for collecting Al-Cu alloy with less Al activity. The anodic current risactinides in the form of intermetallic compounds with a ing at -0.40 V is due to the dissolution of Cu into the melthigh separation factor against rare-earth fission products in the form of Cu+ ion. It is suggested that Al can be sep[1]. However, how to separate actinides from Al becomes arated from U by using a Cu electrode in LiCl-KCl melts
problematic because U cannot be separated from Al by containing Al3+ and U3+ because of the underpotential
the anodic dissolution of U-Al alloy [2]. In this study, the deposition of Al. The CV of Ni has an anodic peak at
behavior of Al3+ in LiCl-KCl eutectic melt was investi- -0.45 V, which corresponds to the decomposition of angated to develop the separation technique of Al from Al-Ni alloy. Since the cathodic current for the
Al-actinides intermetallic compounds.
underpotential deposition of Al is small, the formation
reaction of Al-Ni alloy might proceed slowly though the
EXPERIMENTS:
LiCl-KCl eutectic melt was con- Al-Ni alloy is thermodynamically more stable than thetained by a high-purity Al2O3 crucible in the temperature Al-Cu alloy.
range 723-773 K, where a working electrode of W, Ta, Fe,
0.20
Ni or Cu wire (1 mm diameter), a counter electrode of Al
rod (3 mm diameter), a Ag/AgCl reference electrode and a
0.15
type-K thermocouple were placed. The Ag/AgCl elec-trode723 K
consisted of a Ag wire immersed in a LiCl-KCl eutectic
salt mixture with 1 wt% AgCl, which was con-tained in a
0.10
closed-end Pyrex tube. The potential of the Ag/AgCl
773 K
electrode was 2.410 V against a Li metal elec-trodeposited
0.05
on a Ni wire. The concentration of Al3+ in the melt waschanged by adding KAlCl4 (APL Engi-neered Materials,
0.00
99.9% purity). The Al3+ concentration was determined by
0
20
40
60
80
100
Duration (h)taking samples from the melt fol-lowed by ICP-AES
Fig. 1 Decrease in Al3+ concentration in melt with time.
analysis. All the measurements were conducted in a highpurity Ar atmosphere glove box (H2O, O2 < 1 ppm).
20

Current (mA)RESULTS: It is known that aluminum chloride hasWCuhigh vapor pressure. Figure 1 shows that the Al3+ concentration gradually decreased with time, which is probably
10
due to the evaporation of AlCl3 or Al2Cl6 from the melt.
Ni
The evaporation rates of Al at 773 and 723 K were evalu-5-52ated to be 5 x 10 and 1 x 10 g/cm /h, respectively0when the Al3+ concentration was 0.15 mol%. Hence, Al3+
can be spontaneously removed from LiCl-KCl melts
containing actinide chlorides. It is necessary to examine
how long it takes to reduce the Al3+ concentration to a
-10
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
sufficiently low level.
Potential ( V vs Ag/AgCl)
Cyclic voltammograms (CVs) of various metal wire
electrodes (W, Ta, Fe, Cu and Ni) were measured in Fig. 2 CVs of W (1x5 mm), Ni (1x5 mm) and Cu (1x7 mm)
electrodes in LiCl-KCl-KAlC l4 (0.099 mol%-Al) with
LiCl-KCl eutectic melts with dissolved KAlCl4 to invesscan rate of 0.1 V/s at 724 K.
tigate deposition behaviors of Al at the cathode. On the
W electrode, as shown in Fig. 2, a cathodic current rises at REFERENCES:
about -1.0 V, which corresponds to the deposition of pure [1] P. Soucek et al., Proc. Int. Conf. Global 2009, pp.
Al metal. The sharp anodic peak at -0.95 V is due to the 1156, Paris, France, Sept. 6-11, 2009.
dissolution of the deposited Al metal. The redox po[2] Y. Sakamura et al., KURRI Progress Report 2012, pp.
100.

27P5-6- 28 -Electrochemical Behavior of Zirconium in Molten Alkali Chlorides

H. Matsuura, T. Emori, K. Nakamura, T. Uchiyama,
T. Fujii1 and A. Uehara1
Faculty of Engineering,Tokyo City University
Research Reactor Institute, Kyoto University

1

INTRODUCTION: After the Fukushima Daiichi Nuclear Power Plant Accident, the reactor core has been
experienced by high temperature from strong decay
heat and leaded to fuel debris. The fuel debris may be
expected to be the mixture of nuclear fuel, zircalloy
theath, austenite stainless steel vessel, B4C control blade
and cement stuctural material. Especially, fuel material
fisrt has contacted to zircalloy and resulted in uranium –zirocnium oxide solid solution (corium). For the completion of decomissioning process, these heavily fuel contaminated materials should be properly treated and stablized in some ways. One of ideal options is pyrometallurgical process, which has simplicity and compactness feature. Our proposed process consists to fluorination andmolten salt electrolysis. In this process, uranium is expected to be selectively fluorinated, dissolved into molten
salts and electro-reduced into metallic form. However,the behavior of zirconium in solid solution is unpredictable in each process, thus fluorination behavior of uranium - zircomium oxide has been firstly investigated [1].
Here, the electrochemical measurement of zircomium in
molten LiCl-KCl has been carried out for the first step ofthe elucidation of electrochemical behavior containing
zircomium.

negatively shifted but electrooxidation potential of zirconium is almost independent to the sweep rate. This
trend is typical semi-reversible reaction, which also implies difficulty of selective reduction of zircomium in
LiCl-KCl.
In the next step, to be widen the reduction potential difference between zirconium and one of the elements ofbath, two direction have been proposed, 1) to change thealternative molten chloride bath (NaCl-KCl and
NaCl-2CsCl) or 2) to add small amount of fluoride in
LiCl-KCl bath.
0.025

Potential Region Until:-1.10[V]Potential Region Until:-1.14[V]Potential Region Until:-1.18[V]
Potential Region Until:-1.22[V]Potential Region Until:-1.26[V]Potential Region Until:-1.30[V]

0.02

0.015
Current Density[A/cm 2]

PR5-5

0.01

0.005

0

-0.005-0.01-0.015
-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

Potential[V]Fig.
1.
Cyclicvoltammograms
LiCl-KCl-ZrF4(0.5w/o). Sweep rate: 100 mV/s

of

0.06

EXPERIMENTAL: The molten salt was prepared by
the mixing LiCl – KCl eutectic and ZrCl4 powder(0.5w/o) (AAPL) in a quartz cell. Three electrodes wereused for electrochemical measurement; working electrode: a tungsten wire in 1mm, counter electrode: a pyrographite rod in 3mm and reference electrode: a silver
wire dipped to LiCl – KCl - AgCl molten salt in borosilicate glass. To avoid from the contamination of oxygenand moisture, all electrochemical measurements havebeen performed in an argon circulated glove box(Mbraun) and electroanalyser (Hokuto Denko). In thisyear, cyclic voltammetry has been carried out at 550 oC.

Current Density[A/cm 2 ]

0.04

0.02

0

-0.02

-0.06
-1.4

RESULTS and DISCUSSION: Figure 1 shows variated cyclic voltammograms depending on voltage sweep
region. As shown in Fig. 1, large reduction current at-1.13 V vs. Ag+/Ag is attributed to reduction to zirconium
metal, which is relatively close to the decomposition ofmolten LiCl-KCl bath (it starts at ca. -1.25 V). This fact
implies that zirconium would be difficult to selectively
electoreduced in molten LiCl-KCl depending on the concentration of zircomium. Figure 2 shows sweep rate dependence of cyclic voltammograms. With increasing
sweep rate, elecroreduction potential of zirconium is

Sweep Rate:500[mV/s]
Sweep Rate:200[mV/s]
Sweep Rate:100[mV/s]
Sweep Rate:50[mV/s]
Sweep Rate:20[mV/s]
Sweep Rate:10[mV/s]

-0.04

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

Potential[V]Fig. 2. Sweep rate dependence of cyclic voltammograms of LiCl-KCl-ZrF4(0.5w/o).
This study is financially aided by the JSPS KAKENHI(15K0665).
REFERENCES:[1] H. Matsuura et al., NuMat2014, Clearwater beach,
Florida, USA

27P5-7- 29 -

PR5-6

Stability of Uranyl Ion in Aqueous Solutions of LiCl

N. Ohtori, N. Sato1, Y. Ishii1, A. Uehara2, T. Fujii2

Table 1 Number of particles included the simulation cellfor aqueous solutions of LiCl containing uranyl ion andthe density of the simulated systems.

Department of Chemistry, Niigata University
Graduate School of Science and Technology, Niigata
University
2
Research Reactor Institute, Kyoto University
1[Cl–] /
mol dm–3

d / kg cm–3

14
8
3
0

1.301
1.173
1.067
1.001

INTRODUCTION: Recently, hydrate melts such asconcentrated alkali halide aqueous solutions attract someattention as one of the novel candidates for solvents useful for reprocessing of spent nuclear fuels[1]. We performed molecular dynamics (MD) simulation of LiClaqueous solutions containing uranyl ion and reported
some results such as diffusion coefficients and average
local structure around uranyl ion in the previous report[2].
Furthermore, we have analyzed coordination structurearound uranyl ions in 14 M LiCl aqueous solution in
more detail and compared the results with experimental
results[3]. In this work, in order to discuss the stability ofuranyl ion in hydrate melts, we have evaluated theHelmholtz free energy changes for the successive additional processes of chloride ion to uranyl ion in aqueous
solutions of LiCl with various concentrations.

2+

−

+

+ Cl → UO2Cl ・・・R1
UO2
UO2Cl+ + Cl− → UO2Cl2 ・・・R2
UO2Cl2 + Cl− → UO2Cl3− ・・・R3
UO2Cl3− + Cl− → UO2Cl42− ・・・R4

1
1
1
1

280
158
58
2

F(R) [kJ/mol]

FEP
TI

20

10

0

R1 14M

-10
3

4

5

6

7

R [Å]
Fig.1 Free energy change for the additional processof Cl− to UO22+ (R1) as a function of the coordination distance.
0

R1

-10

R2

-20

R3

: 14M
: 8M
: 3M
: 1M

-30
-40
0

RESULTS: Figure 1 shows the free energy change as afunction of distance between uranyl ion and chloride ion,
which compares the results from both the results. First ofall, we can see both the methods give the same results
within the statistical errors. The minimum around 3-3.5Å
means the most stable position within the first coordination shell. The maximum around 4-4.5Å means the energetic barrier caused by the first coordination shell.
Figure 2 shows free energy changes for the successive
additional processes from R1 to R4, which suggests thatthe most stable ionic species including uranyl ion is
UO2Cl42−, regardless of the concentrations.

782
926
1044
1000

30

F0→N [kJ/mol]

CALCULATION: MD calculation has been performed
under NVE ensemble. The SPC/E model was used forwater molecule. The other parameters were taken fromthe references cited in [3]. The water and uranyl molecules were constrained by SHAKE algorithm. The number of particles included in the simulation cell is shown in
Table 1. Time step was 1.0 fs. The Helmholtz free energychanges have been evaluated by both free energy perturbation (FEP) method and thermodynamic integration (TI)
method. The successive additional processes denoted by
R1, R2, R3, and R4 are as follows:

Number of unit
H2O
UO22+Cl–2
Li+ Cl–1

R4
2

N( Cl- )3

4

Fig.2 Free energy change for the successive additional processes of Cl− to uranyl ion as a function of
the coordination number of Cl− by TI method.
REFERENCES:[1] A. Uehara, O. Shirai, T. Fujii, T. Nagai and H. Yamana, J. Appl. Electrochem., 42, 455(2012).
[2] N. Ohtori, Y. Ishii, Y. Nagata, A. Uehara, T. Fujii, H.
Yamana, K. Minato and Y. Okamoto, KURRI Progress Report 2012, PR2-1(2013).
[3] N. Ohtori, Y. Ishii, A. Uehara, T. Fujii, H. Yamana,
and Y. Okamoto, KURRI Progress Report 2013,
PR1-12(2014)

27P5-8- 30 -

PR5-7 Study of Isotope Separation of Strontium and Calcium via Chemical Exchange Reaction
R. Hazama, Y. Sakuma1, T. Yoshimoto, T. Fujii2, S. Fukutani2 and Y. Shibahara2
Graduate School of Human Environment, Osaka Sangyo
University
1
Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology,
2
Research Reactor Institute, Kyoto University
INTRODUCTION: Calcium is congener of strontium
and easy to handle to check the isotope effects. By utilizing chemical separation method for calcium isotope eﬀect
in liquid-liquid extraction, we can evaluate the ratios between the ﬁeld shift eﬀect to the mass eﬀect.
EXPERIMENTS: Isotopic enrichment occurs
according to the following chemical exchange reaction:40
Ca2+(aq) +48CaL2+(org)48Ca2+(aq) +40CaL2+(org) (1) where
L represents macrocyclic polyether(18-crown-6).
Method and system
Temp.
Ref.
ε/△M
-5
(℃)
[×10 ]
51~17
(Sr)

0.31
(Sr)
0.29
(Sr)
0.10
(Sr)
100
(Ca)
0.5~0.4
(Ca)

3.7
(Ca)
5.3
(Ca)
11
(Ca)
51
(Ca)

Liquid-liquid extraction(LLE) with dicyclohexano-18-crown-6(DC18C6).
2.3M-0.5M Sr in aqueous phase.
Cation-exchange chromatography with Sr lactate.
Cation-exchange chromatography with Sr acetate.
Cation-exchange chromatography with Sr
chloride.
LLE with DC18C6.
0.07M CHCl3
Solid-liquid chromatography(SLC)with ion exchange
resin(Dowex50B)
SLC with ion exchange
resin (Dowex1,50).
SLC with ion exchange
resin (Dowex50W).
SLC with ion exchange
resin (Dowex) with NH4α-hydroxyisobutyrate
SLC with ion exchange
resin (ANKB-50) with

20±0.5[1]25±0.2[2]25±0.225±0.2

25

[3]

―(Not
specified)

[4]

―

[5]

―

[6]

―

[7]

―

[8]

iminodiacetate
SLC with ion exchange
24-82
[9]
resin (PK-1) with counter-current
2~5.2
SLC with ion exchange
25
[10]
(Ca)
resin (Asahi LS-6)12
SLC with ion exchange
25
[11]
(Ca)
resin (AG50WX4)
88
SLC with crown-ether
88
[12]
(Ca)
resin (18C6, dimethylsulfoxide)45
SLC with crown-ether
35(Ca)
resin (benzo-18C6).
[13]
9M HCl (0.8mmφ,1m)
38
SLC with crown-ether
35(Ca)
resin (benzo-18C6).
9M HCl (0.8mmφ,200m)
75
SLC with crown-ether
25
[14]
(Ca)
resin (benzo-18C6).
Methanol48
SLC with crown-ether
40
[15]
(Ca)
resin (benzo-18C6).
Ethanol/HCl mixed
13~24
Ion Exchange Elec- 20,25,
[16]
(Ca)
tromigration
40
150 *LLE with DC18C6
20
This
(Ca)
0.07M CHCl3
work
175 *
LLE with DC18C6
2
This
(Ca)
0.07M CHCl3
work
Table 1. Unit mass enrichment factors of Sr and Ca
isotope separation.*: Preliminary
RESULTS: Unit mass enrichment factors of Sr and Ca
isotope separation are summarized in Table 1. In general,a crown ether gives a large separation factor with morethan ten times, compared with an ion exchange method
and has an applicable ability of separation in reality.
REFERENCES:[1]K.Nishizawa et al.,J.Nucl.Sci.Technol., 32(1995)1230.
[2] T. Oi et al., Sep. Sci. Technol., 27 (1992) 631.
[3]B.E. Jepson et al., J. Inorg. Nucl. Chem.38(1976)1175.
[4]G.D. Klinskii et al., Russ.J.Phys.Chem. 48(1974) 659.
[5]D.A. Lee, J. Inorg. Nucl. Chem. 38(1976) 161.
[6]W.A. Russell et al., Anal. Chem. 50(1978)1151.
[7]J. Aaltonen, J. Suomen Kemi B44(1971)1.
[8]V.V.Gutsykov et al., Russ.J.Phys.Chem.55(1981)1667.
[9]N. Kobayashi, J. Chromatogr. 252(1982)121.
[10] T. Oi et al., Sep. Sci. Technol., 28 (1993) 1971.
[11]B.E.Jepson et al., Sep. Sci. Technol., 22 (1984) 1029.
[12]B.E.Jepson et al., Sep. Sci. Technol., 28(1993) 507.
[13]S.Umehara et al.,Prog.Theor.Exp.Phys.2015,053C03.
[14]S.Nemoto et al.,Isotopes Envir.Heal.Stu.49(2013)257[15]S. Okumura et al., J. Chromatogr. A1415(2015)67.
[16]Y. Fujii et al.,Z. Natureforsch, 40a (1985) 843.
13~87
(Ca)

27P5-10- 31 -

PR5-8Disproportionation Reaction of RE(II) (RE = Nd, Dy, Pr) in
CaCl2-LiCl Eutectic Molten Salt

H. Sekimoto, A. Uehara1 and T. Fujii1

indicates that Nd(II) decomposed through the disproportionation reaction.

Faculty of Engineering, Iwate University
Research Reactor Institute, Kyoto University

1

(a)

2.1

RESULTS: The cathodic potential during the galvanostatic electrolysis was as follows; -1.67 V for the
NdCl3-CaCl2-LiCl molten salt, -1.50 V for the
DyCl3-CaCl2-LiCl molten salt and -1.80 V for the
PrCl3-CaCl2-LiCl system. The absorption spectra shownin Fig. 1 (a) and (b) indicates that Nd(II) and Dy(II)formed during the galvanostatic electrolysis in the
NdCl3-CaCl2-LiCl molten salt and DyCl3-CaCl2-LiClmolten salt, respectively. On the other hand, the existenceof Pr(II) was not confirmed in the absorption spectra
shown in Fig.1 (c). Consequently, the following reactions
proceeded during the galvanostatic electrolysis.
Nd(III) + e  Nd(II)
Dy(III) + e  Dy(II)Pr(III) + 3e  Pr

Absorbance, A

1.5

Absorption of Nd(II)

1.2
0.9

during electrolysis

0.6
after electrolysis

0.3
0.0

before electrolysis

300

400

500

600

700

800

900

Wavelength,  /nm

(b)

2.5
Absorption of Dy(II)2.0Absorbance, A

EXPERIMENTS:
Regents of CaCl2, LiCl, NdCl3,
DyCl3, and PrCl3 was weighed and inserted into a opticalcell attached with a cylindrical quartz tube and melted at
700 °C to form RECl3(RE = Nd, Dy, Pr)-CaCl2-LiClmolten salt. The galvanostatic electrolysis at -10 mA
was conducted with 3 electrodes; the working electrode
was a tungsten wire of 1 mm diameter, the counterelectrode and the reference electrode was a silver wire of
0.5 mm diameter
which
was
immersedin
1 mol%AgCl-CaCl2-LiCl molten salt held in a cylindricalpyrex glass tube. The counter electrode and the referenceelectrode was electrically contacted with the RECl3-CaCl2LiCl molten salt through the thin pyrex glass film. All
potentials in this paper were measured against the Ag/
AgCl(1 mol%) electrode.
Theabsorption
spectraofthe RECl3-CaCl2-LiCl molten salt wasmeasured by UV-Vis absorption spectrometer with thereported procedure [2].

Absorption of Nd(III)

1.8

1.5

after electrolysis
Absorption of Dy(III)

1.0
0.5

during electrolysis

0.0

before electrolysis

400

600

800

1000

1200

1400

1600

1800

Wavelength,  / nm

(c)

2.4
2.1
1.8
Absorbance, A

INTRODUCTION: Mutual separation of Nd, Dy andPr is essentially important for the recycling of the neodymium magnet. Uehara et al. reported on the mutual
separation of La and Nd utilizing the disproportionation
reaction of Nd(II) to metallic Nd and Nd(III) in
LiCl-KCl molten salt [1]. This technique seems quite
attractive comparing with the conventional processes
such as the ion exchange process and the solvent extraction process in terms of the environmental load. In thisstudy, the formation of Nd(II), Dy(II) and Pr(II) in
CaCl2-LiCl eutectic molten salt was investigated with the
combination of the absorption spectroscopy and the galvanostatic electrolysis method.

after electrolysis (1 min.)

1.5
1.2

after electrolysis (10 min.)Absorption of Pr(III)

0.9
0.6

during electrolysis

0.3
0.0
400

before electrolysis

600

800

1000

1200

1400

1600

1800

Wavelength,  / nm

Fig. 1. Absorption spectra before, during and after
the galvanostatic electrolysis at -10 mA for (a)NdCl3-CaCl2-LiCl molten salt, (b) DyCl3-CaCl2-LiClmolten salt and (c) PrCl3-CaCl2-LiCl molten salt.
REFERENCES:[1] A. Uehara, K. Fukasawa, T. Nagai, T. Fujii, and H. Yamana,

(1)
(2)
(3)

J. Nuclear Mater., 414, 336 (2011).

[2] H. Sekimoto, A. Uehara, T. Fujii, H. Yamana, KURRI Progress report, (2014).

As shown in Fig. 1 (a), the absorption peak attributing
Nd(II) diminished in 10 min. after the electrolysis, which

27P5-12- 32-