VIII-Ⅱ-1. Project Research
Project 9

Application Studies on Effective Use of F-Elements

PR9
H. Yamana

Research Reactor Institute, Kyoto University
1. Objectives and Allotted Research Subjects
Studies on actinide nuclides with careful management are
being more important for reprocessing, disposal,
partitioning, and transmutation processes in the nuclear
fuel cycle. Hot laboratory of KURRI is one of corefacilities in Japan, in which actinides especiallytransuranic elements (Pu, Am, Cm, and so on) can betreated. In our series of past research projects, separation,
purification, and synthesis procedures were found to beeffective for other elements, for example, rare metal
refining. In this context, the actinide studies are expanded
for fundamental and application studies on f-elements.
Allotted research subjects are as the followings.
ARS-1 Molecular dynamics simulation of molten salts
containing f-elements (N. Ohtori et al.)ARS-2 Assessment study on chemical properties ofactinides in molten salts (M. Myochin et al.).
ARS-3 Absorption spectrophotometric study ontitanium in molten salts. (T. Uda et al.)
ARS-4 Study on complexation of actinides in aqueous
solutions (T. Sasaki et al.).
ARS-5 Spectroelectrochemical analysis of actinide ionsin molten salts and hydrate melts (A. Uehara etal.)
ARS-6 Study on chemical isotope effect of actinides andfission product elements (T. Fujii et al.).
ARS-7 Systematic study on bonding characteristics oftrivalent actinides with ligands (A. Shinohara etal.).
ARS-8 Electrochemical

study

of

uraniuminpyrochemical reprocessing system (Y. Sakamura
et al.).
ARS-9 XAFS analysis on halogenides containing
actinides and FP elements (H. Matsuura et al.).
ARS-10 Fundamental and application studies on effective
use of f-elements (Y. Ikeda et al.).
ARS-11 Fundamental
study
on

electrolytic

formation/dissolution of f-element compounds inmolten salts (T. Goto et al.).
ARS-12 Study on neutron capture cross sections oflong-lived nuclides by activation method (S.
Nakamura et al.).

2. Main Results and Contents
ARS-1, 2, 3, 8, 9, and 11 studied the chemical behaviorof actinides, lanthanides, FP elements, and structural
material elements in molten salts, the results of which are
to be dedicated to the development of nuclear fuel cycle
or general industrial use. MD calculations of LiCl-KCl
containing small amount of TbCl3 was performed in
ARS-1 and the structural information around Tb ions was
obtained. In ARS-2, reduction from UO22+ to UO2+ or U4+
in alkali chloride melts was studied. An applicability oftungsten as a reductant was confirmed. ARS-3 studied theeffect of fluoride ion and oxide ion on the Ti3+ dissolvedin chloride molten salt using the method for developmentof coherent electrodeposition of Ti0. ARS-8 studied the
reduction rate of UO2 in LiCl and discussed the reduction
mechanism of UO2 using an one-dimensional diffusion
layer model. In ARS-9, the local structure of Nd ions inmolten chlorides was studied by extended X-ray
absorption fine structure (EXAFS). All the samples wereprepared at KURRI and XAFS analysis was performed at
BL11XU, SPring-8. ARS-11 studied electrochemical
behavior of Al ion in molten LiCl-KCl and
LiCl-KCl-CsCl. The diffusion coefficient of Al(III) was
determined. ARS-5 and 10 studied the U chemistry in
low temperature or room temperature melts. Coordination
circumstance and redox reaction of U ions in Ca chloride
hydrate melt was clarified in ARS-5 by spectroscopic andelectrochemical methods. In ARS-10, the electrochemical
behaviorof(EMI)2UO2Cl4(EMI:
1-ethyl-3-methylimidazoliun), in the mixture of EMICland EMIBF4 was studied and the basic electrochemical
data were obtained. ARS-4, 6, and 7 studied aqueous
chemistry of actinides and FP elements. ARS-4 studied
Th solubility in the presence of humic substances.
Dependence of the Th solubility on pHc was clarified.
ARS-6 studied Sr complexation by ab initio method.
Optimized geometries of hydrated Sr species were
calculated. ARS-7 studied precipitation properties of thehydroxide complexes of various FP elements. A
multitracer produced at KURRI using UO2 was supplied
for ARS-7. Nuclear physical properties of TRUs were
investigated in the study, ARS-12. By activation method
using KUR, the thermal-neutron capture cross section of237
Np was newly evaluated.
3. Summaries of the achievements
In this research, by using various unique facilities of
KURRI for f-element research, new and characteristic
chemical and nuclear physical data were obtained. These
new information encompass solid chemistry, molten salt
and solution chemistry, as well as nuclear reactions of
f-elements. The results are useful either for scientificpurpose or for technological purpose for nuclear scienceand general industry.

採択課題番号 23P9
ｆ－元素の有効利用に関わる基礎及び応用研究（京大・原子炉）山名 元

プロジェクトPR9-1

Molecular Dynamics Simulation of Molten (Li-K)Cl Containing TbCl3

Department of Chemistry, Niigata University
Research Reactor Institute, Kyoto University
2
Department of Materials, Oxford University
1

INTRODUCTION: Molten salts are hopeful solventsfor lanthanides and actinides in reprocessing of nuclear
fuel. However, knowledge of chemical stability of ionicspecies in melts is still inadequate to maximize theirpotential abilities. Information on local structure aroundionic species in melts may provide useful measures fortheir stability in melts. Molecular dynamics (MD)simulation is a powerful tool to elucidate such thestructures microscopically. In particular, recent MD
simulations with polarizable ionic model (PIM)[1-4] havebrought much progress in understanding of structure inionic melts: they have successfully revealed more reliable
pictures of local structures in UCl3[2] and LaCl3[3] melts
and molten alkali chlorides containing LaCl3[4] which
are comparable with those from XRD and EXAFS
studies. In this work, we have performed MD
calculations of molten mixtures of lithium and potassium
chlorides containing small amount of TbCl3 in order toobtain the structural information around Tb ions.
CALCULATIONS: All the MD calculations havebeen carried out by using NVT condition[5]. The total ion
numbers N were about 1700 in the cell volume V
determined from the experimental density[6] at simulated
temperature, T = 973 K. The ratios of LiCl to KCl in
simulated melts were set at 25:75, 50:50, and 75:25 in
mol%. Each melt was added with 1 mol% TbCl3. as asolute. The potential parameters used in the present
works were taken from the ref. [7].
14
12

g (r)

10

Tb-Cl
Tb-Li
Tb-K

8
6
4

RESULTS:
Figure 1 shows the obtained radial
distribution functions between Tb and the other ions at
the ratio of LiCl:KCl = 50:50 mol%. The first peak was
observed at 2.64 Å in that for Tb and Cl pair. Although
the peak position didn’t depend on the composition ofsolvent melts, the angular distribution function clearlysuggests that the first coordinated shell around Tb ion by
Cl ions may become more regular octahedron withincreasing KCl ratio as illustrated in Fig. 2.
0.04

25:75
50:50
75:25

0.03

P (θ )

N. Ohtori, Y. Ishii, K. Fukasawa1, A. Uehara1, T. Fujii1, H.
Yamana1 and P. A. Madden2

0.02

0.01

0.00

0

50

100

150

200

θ / degree

Fig. 2. The calculated angular distribution functionof Cl-Tb-Cl in the first coordinated shell around Tb
ion in molten (Li-K)Cl at 973 K.
REFERENCES:[1] P. A. Madden, R. Heaton, A. Aguado and S. Jahn, J.
Mol. Struct.:THEOCHEM, 771 (2006) 9-18.
[2] Y. Okamoto, P. A. Madden and K. Minato, J. Nucl.
Mater. 344 (2005) 109-114.
[3] Y. Okamoto and P. A. Madden J. Phys. Chem. Solids.,
66 (2005) 448–451.
[4] Y. Okamoto, S. Suzuki,H. Shiwaku, A. Ikeda-Ohno, T.
Yaita and P. A. Madden, J. Phys. Chem. A, 114 (2010)
4664–4671.
[5] M. P. Allen and D. J. Tildesley, in Computer
Simulation of Liquids, (Clarendon, Oxford, 1997).
[6] G. J. Janz, in NIST Molten Salts Database, Ver. 2.0,
(NIST SRD 27, 1992).
[7] M. Salanne, C. Simon, P. Turq and P. A. Madden, J.
Phys. Chem. B, 112 (2008) 1177-1183.

2
0

0

2

4

6

8

10

-10

r / 10 m
Fig. 1. Radial distribution function, obtained by the
MD simulation, between Tb and the other ions inmolten (Li-K)Cl at 973 K.

採択課題番号 23P9-1 融体中での f-元素の分子動力学計算と実験系の照合研究
プロジェクト
（新潟大・理）大鳥範和、石井良樹（京大・原子炉）深澤一仁、上原章寛、藤井俊行、山名 元（オックスフォード大学）Paul A. Madden

Reduction from UO22+ to UO2+ or U4+ in Alkali Chloride Melts by using Tungsten

T. Nagai, A. Uehara1, T. Uda2, K. Fukasawa2, T. Fujii1, M.
Myochin and H. Yamana1
Japan Atomic Energy Agency (JAEA)
1
Research Reactor Institute, Kyoto University
2
Graduate School of Engineering, Kyoto University
INTRODUCTION: In the pyro-metallurgical method
for reprocessing spent oxide fuels, it is necessary to once
reduce from those oxides to metallic state. The currently proposed reduction process is electro-reduction
technique, which electrolytically reduces UO2 and PuO2
to their metallic states, and those product metals are dissolved into melt. However, this dissolution is likely tocause appreciable amount of un-reduced oxides, whichleads to the formation of actinyl ions dissolved in themelt. Therefore, the reduction of actinyl ions to lower
valence states, such as trivalent and tetravalent ions, isdesired before the refining operation. In this study, we
made researches on the reduction from UO22+ to UO2+
or U4+ in alkali chloride melts by using tungsten as a
reductant.
EXPERIMENAL: All operations were carried out in a
glove box filled with dry Ar gas. An anhydrous reagentof LiClKCl eutectic was purchased from Aldrich-APL
L.L.C. and was used without further treatment. The
uranyl source material containing UO22+ was prepared bydissolving the U3O8 powder with purging dry Cl2 gas into
the LiClKCl eutectic melt. In the spectrum measurements, the reagent of LiClKCl eutectic was put into thequartz tube which had a welded optical measurement cellat the bottom of tube. After measuring the backgroundabsorption spectrum of the pure melt, a portion of theuranyl source material was added into the melt and thespectrum of UO22+ was measured. And the tungsten
mesh was immersed into the melt, and the valencechange of uranyl ions was monitored until the spectrum
was steady and the changed spectrum was recorded.
After then, dry Cl2 gas was purged into the melt in presence of the tungsten mesh, and the spectrum was measured after the remaining Cl2 in the melt was removed by
dry Ar gas purging.
RESULTS: In this experiment before the reductive
operation, the absorption spectrum of the initial sample
of UO22+ in LiClKCl eutectic at 500 °C was observed asshown in Fig. 1(a). When the tungsten mesh was immersed into the melt, the spectrum changed and otherpeaks were observed in the wavenumber range below
23000 cm1 and small absorptions at 12500 and 15500
cm1 as shown in Fig. 1(b). This spectrum is agreed
with that of UO2+ in LiClKCl eutectic.[1] This indicates that UO22+ reduced to UO2+ by using the tungsten.
However, in the spectrum in Fig. 1(b), the absorption
peak of U4+ at 8500 cm1 was slightly observed. In aword, there is a little possibility of the reduction from
UO22+ to U4+. By Cl2 purging into the melt in presenceof the tungsten mesh, the absorption peaks of UO 22+ andUO2+ decreased and another peaks appeared at 15000,
8500 and 5000 cm1 as shown in Fig. 1(c). This spectrum was a good agreement with that of U4+ in LiClKCleutectic.[2]To identify the reductions from UO22+ to U4+, thesereaction paths were examined. When the tungsten was
immersed into the melt, the reduction of UO22+ to UO2+
was observed. This reduction of UO22+ to UO2+ proceeded by the oxidation of tungsten, and can be given byfollowing reaction 1. In the spectrum in Fig. 1(b) which
can be slightly observed the peak of U4+ at 9000 cm1,
the absorption of the produced WCl2 by this reaction 1
was not observed. It is thought that the product of WCl2
reacted as following reaction 2. The WOCl4 could not
be observed in the melt, and seemed to vaporize easily
from the melt without remaining. We observed that thevolatile compound was coagulated as red powder on theupper area of the cell. After then, purging Cl2 into themelt in presence of the tungsten mesh, this coagulated
powder grew to be needle-shape crystals on the upperarea of the cell. The growth of these crystals wasproved to proceed with increasing the amount of WOCl4
by the reductions of UO2+ and UO22+ to U4+ by following
reactions 3 and 4, respectively.
2UO2Cl2 + W → 2UO2Cl + WCl2
(1)
7UO2Cl2 + 2WCl2 → 6UO2Cl + UCl4 + 2WOCl4↑ (2)2UO2Cl + 4W + 11Cl2 → 2UCl4 + 4WOCl4↑(3)
UO2Cl2 + 2W + 5Cl2 → UCl4 + 2WOCl4↑
(4)
0.8

(a)
0.6

(c)

(b)

absorbance

PR9-2

(c)
0.4

(b)
0.2

0

(a)

(c)

25

(b)

20

15

wavenumber (×103 cm1)

10

5

Fig.1. Absorption spectra of uranium ions before tungsten mesh immersion: (a), after tungsten mesh immersion: (b), and after additional dry Cl2 gas purging: (c) in LiClKCl eutectic at 500 °C.
REFERENCES:[1] D. A. Wenz, et al., Inorg. Chem., 3 (1964) 989-992.
[2] G. Landresse, Anal. Chim. Acta, 56 (1971) 29-37.

採択課題番号 23P9-2 アクチニド元素の溶融塩中での化学的性質の評価研究 プロジェクト（原子力機構）小藤博英、永井崇之、岡本芳浩、明珍宗孝（京大・原子炉）上原章寛、藤井俊行

Caracterization of Dissoved Titanium Ion in Chloride Molten Salt

EXPERIMENTS:
We measured the absorbance of TiCl3 dissolved in
NaCl-KCl equimolar molten salt to obtain the absorption
spectrum of Ti3+. And then, we investigated the effect ofF- and O2- on Ti3+ by repeating measurement of absorance
and addition of NaF and Na2O, respectively. The samples
used in this study were mixtures of NaCl, KCl, NaF,
Na2O and TiCl3 which were prepared by melting the reagents in a closed stainless container. The titanium
trichloride (TiCl3) was synthesized by the reported technique [2].
RESULTS:
Figure 1 shows the absorption spectra of the trivalenttitanium ion in NaCl-KCl equimolar molten salt at 700
C. The chloride complex of Ti3+ has an absorption peakat around 786 nm. We confirmed that the shape of thespectrum was drastically changed by adding F- as shownin Fig. 1 (a). This change gradually proceeded by adding
NaF until the ratio of the concentration of F- to that of
Ti3+ (CF- / CO2-) was over about 6. These results indicatethat Ti3+ dissolved in NaCl-KCl molten salt reacted with
F- to form fluoride complex with 6 coordinate ions(TiF63-), which may be more stable than chloride complexof Ti3+. On the other hand, by adding O2-, the shape of thespectrum of Ti3+ was not changed but the spectrum was(a)Wave length (nm)20001500
1000
16
T = 700 C
14

500
CF- / CTi3+ = 6

CF- / CTi3+ = 0

12

-1

-1

Molar absorbance (cm mol L)

INTRODUCTION:
The information on dissolved ions in molten salt is important for development and optimization of materials
processing using molten salt electrolysis. The valence
number of electrode active ions is an essential parameter.
If active ions are complex ion, the structure of ions (forexample, the kind of coordinating ion and its number) is
also important. Nagai and his co-workers developed amethod for in-situ measurement of absorption spectrumof dissolved ion in high temperature molten salt and applied it to some actinides for development of recycling
process for nuclear fuels [1]. This method is useful toinvestigate the valence number and the complex of dissolved ions in molten salt. In this study, we investigatedthe effect of fluoride ion and oxide ion on the trivalenttitanium ion dissolved in chloride molten salt using themethod for development of coherent electrodeposition of
metallic titanium.

CF- / CTi3+ = 3

10
8

CF- / CTi3+ = 1

6
4
2
0
5000

10000

15000

20000

25000

-1

Wave number (cm )(b)Wave length (nm)-1

Department of Materials Science and Engineering, Iwate
University
1
Department of Materials Science and Engineering,
Kyoto University
2
Research Reactor Institute, Kyoto University

slightly shifted upward as shown in Fig. 1 (b). We considered that this increase of absorbance is due to the decrease of the dissolved Ti3+ because the molar absorbanceshown in Fig. 1 (b) is an apparent value obtained by division of the nominal mole of Ti3+ by the volume of themolten salt. We also confirmed that black particles weresuspended in the molten salt after adding O2-. The particles were identified to be TiOCl by XRD. Therefore, we
considered that when O2- is introduced to the NaCl-KCl
molten salt containing Ti3+, Ti3+ reacts with O2- and Cl- toform TiOCl.

20001500
1000
16
T = 700 C
14

500
CO2- / CTi3+ = 0
CO2- / CTi3+ = 0.6

12-1

H. Sekimoto, T. Uda1, Y. Nose1, A. Uehara2, T. Fujii2 andH. Yamana2

Molar absorbance (cm mol L)

PR9-3

10
8
6
4
2
0
5000

10000

15000

20000

25000

-1

Wavenumber (cm )Fig. 1. Absorption spectra of Ti3+ in NaCl-KCl equimolar
molten salt. Solid line attributes the absorption by chloride complex of Ti3+. The broken lines corresponds theabsorption spectra after adding anion, (a) F- and (b) O2-.
REFERENCES:[1] T. Nagai, T. Fujii, O. Shirai and H. Yamana, J. Nuc.
Sci. Tech., 41 (2004) 690-695.
[2] H. Sekimoto, Y. Nose, T. Uda, H. Sugimura, High
Temp. Mater. Proc., 30 (2012) 435-440.

採択課題番号 23P9-3 溶融塩中の吸収分光測定を用いたチタン製錬に関する研究 プロジェクト（京大院・工）宇田 哲也、野瀬 嘉太郎（岩手大・工）関本 英弘（京大原子炉）上原 章寛、藤井 俊行、山名 元

PR9-4

Thorium Solubility in the Presence of Humic Substances

T. Sasaki, Y. Matsuura, T. Kobayashi, K. Date, H. Moriyama1, T. Fujii1 and H. Yamana1
Department of Nuclear Engineering, Kyoto University
1
Research Reactor Institute, Kyoto University
INTRODUCTION: The amount of radionuclide potentially mobilized in radioactive waste repository system
is related to its solubility in groundwater. For tetravalentactinide, the solubility under relevant geological condition is rather limited because of strong hydrolysis reaction. However, in the presence of inorganic and organic
complexing ligands, the ‘apparent’ solubility of tetravalent actinide may be influenced by forming complexes
and compounds. For the reliable assessment of their migration behaviour, it is important to clarify dominant species and evaluate the solubility of tetravalent actinide
quantitatively. Among various kinds of complexing ligands, humic acid (HA) prevails in groundwater and hasstrong complexation capability. HA consists of aromaticrings and hydrocarbon chains, has negatively charged
functional groups, such as carboxyl and phenolic groups,
and would strongly coordinate with tetravalent actinide
with these functional groups. In the present study, weinvestigate the solubility of thorium(IV) in the presenceof HA under different pH and ionic strength conditions toevaluate the impact of HA to the solubility of thorium(IV).
EXPERIMENTAL: A stock solution of thorium perchlorate was prepared from Th(NO3)4·4H2O and a stock
solution of purified humic acid (Aldrich HA) was obtained after purification. The initial Th concentration ofsample solutions was set to be 10-6 mol/dm3 (M) and theinitial concentrations of humic acid were set to be from
5.28·10-6 to 5.28·10-3 eq/L. The hydrogen ion concentration (pHc) was adjusted from 4 to 12 with HClO4/NaOH
and the ionic strength (I) was adjusted to be 0.1 and 1.0
by adding appropreate amount of NaClO4. The sample
solutions were kept in an Ar glove box. After given periods, the pHc of each sample solution was measured using
combination glass electrodes (9611-10D Horiba Ltd.) andthe supernatant was filtrated through 0.45 µm syringe
filter and 3k Da ultrafiltration membranes (ca. 2 nm poresize). Th concentrations after each filtration were determined by ICP-MS (HP4500, Hewlett Packard). The detection limit was around 10-10 M.
RESULTS: Th solubility in the presence of HA after
144 days is shown in Fig. 1. A dashed curve represents
the solubilituy of Th(OH)4(am) in the absence of HA [1].
In the presence of 5.28·10-3 eq/L HA, the solubility values after filtration through 0.45 µm remain initial Th
concentration level, while those after filtration through3k Da show considerably low values. This trend is ingood agreement with the size distribution of purified HA
itself, and rather different from the size distribution of Thhydrolysis species. Therefore, it is considered that Th
forms a complex with HA and the complex was filteredout by 3k Da membranes. In the presence of 5.28·10-5
eq/L HA, similar trend is shown. In the acidic pHc, thesolubility values after filtration through 0.45 µm membranes are slightly lower than those in neutral and alkaline pHc. Under acidic pHc condition, HA is considered
to release less protons and agglomerate to form larger
species. The Th-HA complex may agglomerate in a similar manner and filtered out even by 0.45 µm. The trend
is observed under the condition of I = 1.0 more clearly,
suggesting that co-existing cation (Na+) may affect theagglomeration of HA. Thus, we confirmed that HA
coordicate with tetravalent Th to change the ‘apparent’solubility of Th(OH)4(am). It is also indicated that size
distribution of the Th-HA complex is highly important,since Th-HA complex is thought to increase in size andfiltered out by small size filters such as 3k Da membranes under certain condition. For the quantitative discussion of Th solubility in the presence of HA, and evaluation using thermodynamic data, further investigation isneeded.

Fig. 1. Th solubility in the presence of 5.28·10-3 eq/L
HA (upper) and 5.28·10-5 eq/L HA (lower) after filtration
through 0.45 µm (□) and 3k Da(◇). The initial Th concentration is 10-6 M, and a dashed curve represents thesolubility of Th(OH)4(am) in the absence of HA [1].
REFERENCES:[1] Kobayashi, T., Sasaki, T., Takagi, I., Moriyama, H., J. Nucl.
Sci. Technol. 48 (2011) 993–1003.

採択課題番号 23P9-4
アクチニド元素の水溶液内錯生成反応に関する研究
プロジェクト(京大院･工)佐々木隆之,松浦由佳,小林大志,伊達海斗 (京大･原子炉)森山裕丈,藤井俊行,山名 元Electrochemical Characteristics of Uranium Ions in Calcium Chloride Hydrate Melts1

Research Reactor Institute, Kyoto University
Nuclear Fuel Cycle Engineering Lab., Japan Atomic
Energy Agency
2
Graduate School of Agriculture, Kyoto University
3
Institute of Multidisciplinary Research for Advanced
Materials, Tohoku University
1

INTRODUCTION:
The calcium chloride hexahydrate, CaCl2·6H2O, and similar hydrate melts are of considerable interest as solventswith properties intermediate between those of aqueous
solution and molten salts. In view of the activity coefficients, viscosity and structural property, it is consideredthat water molecules in CaCl2·6H2O melts are strongly
coordinated to the calcium ion and there are no free watermolecules to dissociate to form H+ and OH-. As a result,
this material has advantages such as inorganic-based melt
and low melting temperature. In the present study, coordination circumstance and redox reaction of uranium ionssuch as U4+ and UO22+ in CaCl2·nH2O hydrate melt (n = 6– 10) have been investigated by spectroscopic and electrochemical methods. The chemical behavior of uranium
ion in the hydrate melt was compared with that in theother solvents such as high temperature [1] or room temperature [2] molten salts, organic solvents [3] and relatively low concentration solution of hydrochloric acid
[4].
EXPERIMENTAL:
For the electrochemical measurements, a three-electrodesystem was used. A pyro-graphite carbon (Toyo Tanso Co.
Ltd.) of 3 mm diameter was used as a working electrode,and the silver|silver chloride (Ag|AgCl) electrode wasused as a reference electrode. This reference electrode, inwhich was put an aqueous solution containing 1 M LiClalong with a Ag wire of 1 mm diameter coated by AgCl.
For voltammetric operation, the platinum mesh electrodewas employed as a counter electrode. Electrochemicalmeasurement systems, Hz-5000 (Hokuto Denko Co.)
were used for the cyclic voltammetry and the linear
sweep voltammetry. Controlled-potential electrolysis was
carried out in order to identify the electrode reaction. In
this experiment, a rotating carbon electrode was employed as a working electrode to enhance the efficiencyof the electrolysis. The counter electrode was also a platinum mesh electrode, and the counter phase was separated by glass filter membrane from the objective phase to
avoid cyclic redox reaction. After the electrolysis, absorption spectra were measured. A self-registering spectrophotometer UV-1000 (Shimadzu Co.) was used for themeasurements over the wavelength from 400 to 900 nm.
These measurements were carried out at 300 ± 2 K.

採択課題番号 23P9-5

RESULTS:
Influences of the water content on chemical status of
UO22+ and U4+ in CaCl2·nH2O were also studied by electrochemical and spectroscopic methods. Visible absorption spectra of U4+ in CaCl2·nH2O changed drasticallyalong with the water content. This suggested the strong
influence of water content on the coordination status of
U4+ in the melt. Cyclic voltammograms of U4+ in
CaCl2·nH2O indicated that the U4+/U3+ redox couple wasquasi-reversible reaction and that the formal redox potential for the U4+/U3+ couple was almost independent of thehydration number n to be 0.790 ± 0.010 V vs. Ag|AgCl
reference electrode (1M LiCl) at 298 K. Diffusion coefficients of U4+ depended not only on the hydration number
n but also on the temperature in the melts. The oxidation
peaks of voltammogram were attributed to the oxidationof U4+ to uranyl ions by the water molecules. The resultsof the cyclic voltammogram of UO22+ in CaCl2·nH2O
showed that there are various reductions from UO22+ tolower valence states including the formation of UO2+ andsolid UO2. The UO2+ formed in CaCl2·6H2O was identified spectrophotometrically after the controlled potential
electrolysis. On the other hand, it is reported that UO2+
formed electrochemically in diluted acidic solutions suchas 0.1M HCl disproportionates spontaneously to form U4+and UO22+. These results indicate that the UO2+ in
CaCl2·6H2O was more stable than that in the acidic solutions. It was also found that UO2+ disproportionated toform UO22+ and UO2 in CaCl2·6H2O.
1.0
0.5
-2

A. Uehara, T. Nagai1, T. Fujii, O. Shirai2, N. Sato3 and H.
YamanaI / mA cm

PR9-5

0.0
-0.5
-1.0
-1.5
-2.0
-1.0

-0.5

0.0

0.5

1.0

E / V vs. SSE

Fig. 1. Cyclic voltammogram of U4+ in CaCl2·6H2O containing 0.05 M UCl4. Potential scanning rate is 0.02 V
s–1.
REFERENCES:[1] T. Nagai, A. Uehara, T. Fujii, O. Shirai, N. Sato, H.
Yamana, J. Nucl. Sci. Technol., 42 (2005) 1025.
[2] P. Giridhar, KA. Venkatesan, TG. Srinivasan, PR.
Vasudeva Rao, Electrochim. Acta, 52 (2007) 3006.
[3] L. Martinot, D. Laeckmann, L. Lopes, T. Materne, V.
Muller, J. Alloys Compd., 185 (1992) 151.
[4] WE. Harris, IM. Kolthoff, J. Am. Chem. Soc., 69(1947) 446.

溶融塩及び水和物溶融体中におけるプロジェクトアクチノイドイオンの分光電気化学的研究（京大・原子炉）上原章寛、藤井俊行、森山裕丈、山名 元 （原子力機構）永井崇之（京大院工）深澤一仁、宇多健詞

PR9-6

Chemical Isotope Effect of Actinides and Fission Product Elements

T. Fujii, S. Fukutani and H. Yamana,
Research Reactor Institute, Kyoto University
INTRODUCTION: Strontium 90 (90Sr) is known as oneof fission products, and it has a large fission yield. Inorder to know the chemical behavior of Sr complexes, westudy the highly precise isotopic analysis of Sr [1]. The
analytical technique will be helpful to understand thefractionation mechanism of Sr isotopes in environmental
samples and so on. In parallel with the analytical studies,
quantum chemical calculations are performed to checkthe validity of analytical results. The equilibrium constantof the isotope exchange reaction can be theoretically obtained as the reduced partition function ratio (RPFR) of
isotopologues. The RPFR value is usually calculated
through harmonic vibration analysis. In this study, we
report some ab initio calculations of hydrated Sr2+ complexes.
COMPUTATIONAL DATAILS: The orbital geometries
and vibrational frequencies of hydrated Sr(II) complexes
were calculated by using the conventional Hartree-Fock(HF) approximation and the density functional theory(DFT) as implemented by the Gaussian03 code [2]. The
DFT method employed here is a hybrid density functional consisting of Becke’s three-parameter non-local hybrid
exchange potential (B3) with Lee-Yang-and Parr (LYP)
non-local functionals (B3LYP). The 6-31++G** basis set
was chosen for H and O, and LanL2DZ was chosen for Sr.
The former is an all-electron basis, while the latter is aneffective core potential (ECP) basis.
RESULTS: The hydrated Sr2+ species is generally
thought to be present as eight-coordinated Sr(H2O)82+.
The structure was converged to be the square antiprismwith 2.69 Å Sr-O bond length [3]. This agreed with literature data determined by a combination of the extended
X-ray absorption fine structure (EXAFS) spectrometry
and molecular dynamics (MD) [4]. Isotope fractionationof a Sr carbonate complex shown in Fig. 1 was estimatedin the present study. The coordination number was set tobe eight. Carbonate ion was treated as a bidentate ligand.
This model complex was unstable and deformed into
[SrCO3(H2O)5]H2O with the 6th water molecule moving
out of the inner coordination shell.
The isotope enrichment factor due to the intramolecularvibrations can be evaluated from RPFR [5], (s/s’)f,ln (s/s’)f = [ln b(ui’)  ln b(ui)]
(1)
where
ln b(ui) = ln ui + ui/2 + ln (1  eui)(2)andui = hi/kT(3)
 stands for vibrational frequency. The subscript i stands
for the ith molecular vibrational level with primed variables referring to the light isotopologue. The isotope en-richment factor due to the molecular vibration can beevaluated from the frequencies () summed over all thedifferent modes.
The ln(s/s’)f values of hydrated Sr(II) species were estimated by quantum chemical calculations. The results areshown in Table 1. Carbonate showed larger ln(s/s’)f value
compared with that of the hydrated Sr ion. This suggeststhat heavier Sr isotopes enrich in carbonate. These values
may be useful to estimate the degree of isotope fractionation.

Fig. 1.

Equilibrium geometry of SrCO3(H2O)6.

Table 1ln(s/s’)f (‰) of hydrated Sr2+ species for an
isotope pair, 86Sr-88Sr.
HF
B3LYP
Sr(H2O)82+
1.424
1.416
SrCO3(H2O)6
1.640
1.507

REFERENCES:[1] T. Fujii et al., KURRI Prog. Rep. 2007 (2008)
93-93.
[2] M. J. Frisch et al., Gaussian 03 Revision B.05,
Gaussian Inc., Pittsburgh PA, 2003.
[3] T. Fujii et al., KURRI Prog. Rep. 2008 (2009)99-99.
[4] L. X. Dang et al., J. Phys. Chem., 107 (2003)
14119-14123.
[5] J. Bigeleisen and M. G. Mayer, J. Chem. Phys., 15(1947) 261-267.

採択課題番号 23P9-6 アクチニド元素及び FP 元素の化学同位体効果に関する研究（京大・原子炉）藤井俊行、福谷 哲、山名 元

プロジェクトPR9-7

Investigation on the Properties of Hydroxide Precipitation Using KUR Multitracer

Y. Kasamatsu, N. Shiohara, T. Yokokita, Y. Komori, T.
Yoshimura, N. Takahashi, K. Takamiya1, and A. Shinohara
Graduate School of Science, Osaka University
Research Reactor Institute, Kyoto University

1

INTRODUCTION: Chemistry researches on actinide
and transactinide elements at the uppermost end of theperiodic table are very important in inorganic chemistry.
It is because the chemical properties of these elements
would be unique, which is caused by strong relativistic
effect on the shell electrons. It is, however, difficult toperform chemical experiment with heavy actinide andtransactinide elements because these must be produced ataccelerators using heavy-ion induced nuclear reactions
with low production rates. Furthermore, these elements
have short half-lives. Thus, we need to establish new experimental methods or apparatuses specified for theseelements and test them using the elements whose chemical properties are known.
We have ever developed the preparation method of a coprecipitate sample with Sm which has high energy resolution in the α spectrometry by using membrane filters[1]. In this work, precipitation properties of the hydroxide
complexes of various elements were studied by thismethod using multitracer produced with Kyoto University Reactor (KUR) aiming at the precipitation experimentof heavy actinide and transactinide elements.
EXPERIMENTS: The KUR multitracer sample wasprepared by irradiating thermal neutrons on UO2 powderwhich is mixed with NaCl at KUR [2]. Fission products
implanted in NaCl were dissolved in 0.01 M HCl andwere separated from the UO2 powder by a suction filtration. A portion of the sample was subjected to γ-ray
measurement by a Ge detector, and count rates of γ-ray
peaks and their time dependences were measured.
In the precipitation experiment, 200 µL of water and 20µL (20 µg) of Sm standard solution (1 M HNO3) wereadded into 20–40 µL of the multitracer solution. After
mixing it, 2 mL of basic solution was added to generatehydroxide precipitate. In the present experiment, we used
dilute NH3 solution, concentrated NH3 solution, 0.1, 1, 6,
and 12 M NaOH solutions as the basic solutions to observe the dependence of the precipitation yield on thecomponent of the basic solution. Subsequently, the solution was stirred for 10 s and was soon filtrated with apolypropylene membrane filter. To check the complete
precipitation of the samples, precipitate samples withstirring for 5 min in water bath after adding the basic solutions were also prepared. The samples were then driedon heater at 100 degree C and were assayed for γ-ray

measurements. Supernatant solutions were evaporated todryness and were also subjected to measurements. The
precipitation yields were determined from the results ofthe γ-ray measurements.
RESULTS: Main nuclides identified from the γ-ray
energies and their half-lives were 24Na, 91Sr, 95,97Zr, 99Mo,
103
Ru, 105Rh, 131m,132Te, 131,133I, 140Ba, 140La, 141,143Ce, and151
Pm. To obtain correct precipitation yields, we exclude
the nuclides whose decays are affected by their parent ordaughter nuclide from determining the yields.
The precipitation yield for each nuclide is shown in Table
1. The yields of alkaline metal element were almost 0 %,and those of lanthanide elements were almost 100 %. It
would indicate that chemical properties which are inherent in each element influence the coprecipitation yields
with Sm. For some elements such as Zr and Ru, interesting dependences of the yields on the component of thebasic solution were observed. For further discussion, precipitation properties of these elements, not coprecipitation properties, should be studied.
Table 1. Precipitation yields of multitracer.

REFERENCES:[1] H. Kikunaga et al., Appl. Radiat. Isot., 67 (2009)539-543.
[2] K. Takamiya et al., J. Nucl. Radiochem. Sci., 1 (2000)
81-82.

採択課題番号 23P9-7３価アクチノイドと配位分子との化学結合性の系統的研究
プロジェクト（阪大院・理）笠松良崇、塩原直也、横北卓也、小森有希子、吉村 崇、高橋成人、篠原 厚、（京大炉）高宮幸一

PR9-8Mechanism of Electrolytic Reduction of UO2 Pellet in Molten LiCl and LiCl-KCl

Y. Sakamura, M. Iizuka, T. Fujii1, A. Uehara1 and H.
Yamana1

Then, the following equation can be derived from themass balance of O2- ions.

Central Research Institute of Electric Power Industry
1
Research Reactor Institute, Kyoto University (KURRI)
INTRODUCTION: The electrolytic reduction processof actinide oxides in molten LiCl salt bath at 923 K has
been developed for the nuclear fuel reprocessing. UO2and MOX can be reduced to the metallic form by thefollowing cathode reaction:
MO2 + 4 e-  M + 2 O2- , (M = U and Pu).

(1)

Since salt-soluble FPs of alkali and alkaline-earth metals
accumulate in the LiCl, their effect on UO 2 reduction was
experimentally studied at KURRI [1]. UO2 pellets werereduced by potential-controlled electrolysis in various
LiCl salt baths containing up to 30 mol% of KCl. The
reduction progressed from the outside toward the centerof the UO2 pellet. It was found that the reduction rate wasremarkably decreased after the additions of KCl, which
was attributed to the decrease in the solubility of Li2O inthe salt bath with increasing the KCl concentration [2]. In
this study, the reduction mechanism of UO2 was discussed using an one-dimensional diffusion layer model.

C1-C2
C -C
C -C
i
C -C
= D12 0 1 = D02
= D01 2 3 = D0 3 4 (2)
2F
L1
2
1
L-L1-2

Here, i is the current density, F is the Faraday constantand Ci is the concentration of O2- at each interface.
RESULTS AND DISCUSSION: The relationship between the thickness of U metal layer and square root of
the electrolysis time was calculated for LiCl and
LiCl-10mol% KCl systems using Eq. (2) and the valuesof parameters appropriately determined considering theliterature [1, 2]. Fig. 2 shows the calculated results alongwith the experimental results [1]. The values of D0 for
LiCl-10mol%KCl,1 and 2 were mainly adjusted to best
fit the experimental results. The negative deviation fromthe parabolic relation was reproduced by assuming boththe shrinkage of outer U metal layer and the smaller diffusion coefficient of O2- in a high concentration range.
For improving the simulation, it is strongly desired toclarify the dependence of diffusion coefficient of O2- on
KCl and O2- concentrations as well as the configurationof pore in U metal products.
U metal layer
L
PorousDense

UO2
Thicknessof layerC0 (solubility)

採択課題番号 23P9-8

L2

L1

1

C1
C2

2

Effective porosity
O2- diffusion
coefficientC3

O2- concentration
profileC4 (bulk salt)

1

D1

D0

Fig. 1. Schematic view of one-dimensional diffusion
layer model for electrolytic reduction of an UO2 pellet.
0.6

Thickness of U metal layer (mm)

CALCULATION MODEL: The reduction mechanismof UO2 pellets is considered as follows. The diffusion of
O2- ions from the inside of UO2 pellet to the bulk salt
determined the reduction rate. At first, the surface of UO2pellet is reduced to metal. The reduced U metal layer has
gaps because the density of UO2 is about 60% that of U
metal, and the molten salt then permeates into the gaps.
The O2- ionized at the U metal/UO2 interface is discharged to the bulk salt through the molten salt pass bydiffusion. The O2- concentration seems to be the solubility limit at the vicinity of the U metal/UO2 interface sincecharge transfer of Eq. (1) is fast at high temperature.
Therefore, the O2- solubility to determine the driving
force of diffusion strongly affects the reduction rate.
To simulate how the reduction progresses, an
one-dimensional diffusion layer model was designed asshown in Fig. 1. The assumptions are as follows.
a) The cathode potential is negative enough to reduce
UO2 to U metal and charge transfer is fast. Thus, the diffusion of O2- through the salt is the rate determining step.
b) The U metal formed in the beginning of electrolysis
shrinks to give a dense outer layer, L1 [1]. Inside thedense outer layer, the volume shrinkage of U metal does
not occur to give a porous inner layer, L2. 1 and 2 areeffective porosities of L1 and L2, respectively.
c) In the 2 layer next to the UO2/U metal interface, thevalue of diffusion coefficient of O2-, D1, might be smaller
than the value at a low concentration, D0, because theviscosity would increase with increasing the O2- concentration. There is a diffusion layer, 1, outside of L1.

2

Salt

0.5

LiCl

0.4
0.3
LiCl-10mol%KCl

0.2
0.1
0.0

0

20
40
60
80
100
Square root of electrolysis time (sec1/2)

120

Fig. 2. Dependence of thickness of U metal layer onelectrolysis time: comparison of calculated results(solid lines) with experimental values [1].
REFERENCES:[1] Y. Sakamura, J. Nucl. Mater., 412 (2011) 177.
[2] Y. Sakamura, J. Electrochem. Soc., 157 (2010) E135.

溶融塩化物中でのウランの酸化還元挙動に関する
プロジェクト
乾式再処理基礎研究（電中研）坂村義治、飯塚政利、魚住浩一（京大・原子炉）山名 元、藤井俊之、上原章寛

Local Structural Analysis of Neodymium Cation in Molten Various Chlorides

Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology
1
Kansai Photon Institute, JAEA
2
Research Reactor Institute, Kyoto University

INTRODUCTION: It is very essential to grasp thechemical behaviour of fuel elements and fission products
in each step of processes in order to make realization of
pyrochemical reprocessing of nuclear fuel. Neodymim
is one of the fission products as well as the rare earth
element having divalent cation through the electrochemical reaction[1]. It seems to be existing the simple
relationship between the structural model and electrochemical properties of molten salts, however, even thevariation of redox potential depending on various electrolytes has not been well explained scientifically. To
obtain the information on the local structure of neodymium cation in various molten electrolytes, the systematiccharacterization using extended X-ray absorption finestructure (EXAFS) has been carried out.

LiCl, those with K and Ca do not so much variated butthat with Cs gets shorten and that with Ba gets expanded.
These tendencies are partly following to the structural
information obtained for rare earth trichlorides in various
alkali cationic chlorides[5,6]. Although the structural
information obtained by EXAFS is limited to the 1st coordination sphere around neodymium cation, it is foundthat even in such diluted solution of neodymium, the local structure has been influenced by the cation existing in
2nd coordination sphere from neodymium. The tendency
observed in the melts containing Ba2+ which has larger
cationic size is one of the useful informations to explain
the anomalous tendencies observed in UV-Vis spectroscopy and electrochemical behaviour[7,8].
2.9
R [Å]

H. Matsuura, A. Nezu, T. Yaita1, H. Shiwaku1, H. Yamana2, T. Fujii2, K. Fukasawa2, T. Uda2 and A. Uehara2

2.85
2.8
2.75
0.03

σ2 [Å2]

PR9-9

0.025
0.02
0.015
0.003

Fig. 1. structure parameters obtained by curve fitting analysis for neodymium in various melts.

RESULTS and DISCUSSION: By utilization of X-ray
from an undulator beamline, even such as highly diluted
solution with the highly X-ray absorbing element, i.e.
NdCl3-BaCl2-LiCl (1:10:89), could be measured within 5
minutes to obtain decent quality of spectrum. It is
epoque making that the similar concentration of the electrolytes will be able to evaluated by EXAFS. Various
structural parameters obtained by assuming 6-coodinatedstructure for the mixtures of 1 mol % of neodymium in
10 mol % of LiCl exchanged with KCl, CsCl, CaCl2, and
BaCl2 are shown in Fig. 1. With reference to the inter-ionic distance between Nd3+ and Cl- in molten pure

REFERENCES:[1] H. Yamana et al., J. Alloys Compd., 408-412 (2006)
66.
[2] H. Matsuura et al., J. Alloys Compd., 408-412 (2006)
80.
[3] T. Ressler, J. Synchrotr. Rad., 5 (1998) 118.
[4] A. L. Ankudinov et al., Phys. Rev. B. 58 (1998) 7565.
[5] Y. Okamoto et al, J. Synchrotr. Rad., 8 (2001) 1191.
[6] Y. Okamoto et al, J. Phys. Chem. A, 114 (2010) 4664.
[7] K. Fukasawa et al., J. Nucl. Mater., 414 (2011) 265.
[8] K. Fukasawa et al., J. Alloys Compd., 509 (2011)5112.

C3 [Å3]

EXPERIMENTS: Since the concentration of neodymium in electrolytes is 1 to 5 molar %, the EXAFS
measurements have been carried out using high enegy
X-ray generated at BL11XU, SPring-8, Japan. The samples of mixture melts have been molten in a quartz vessel
kept in an argon circulated glove box and sealed in thequartz cells in a funnel or a rectangular type (X-ray path:
1.5 mm or 10 mm, respectively) under vacuum condition.
EXAFS spectra of neodymium K- Edge (43.571 keV) of
these samples heated at 923 K by an electric furnace[2]on the beamline have been obtained by a quick scan oftransmission mode. The data analyses have been doneusing WinXAS 3.0[3] and FEFF 8.01[4] and the curve
fitting analyses introduced 3rd and 4th cumulants havebeen performed since anharmonic oscillation effect cannot be ignored on the spectra at high temperature.

0.002
0.001

C4 [Å4]0.00040.00030.00020.00010

NdCl3 +CsCl +KCl +BaCl2 +CaCl2

採択課題番号 23P9-9アクチニド元素及び FP 元素含有ハロゲン化物の XAFS 構造解析 プロジェクト（東工大・原子炉研）松浦治明、赤塚 洋、根津 篤（京大・原子炉）上原章寛、山名 元、藤井俊行

PR9-10

Electrochemical and Spectroelectrochemical Studies on [UO2Cl4]2- in
1-Ethyl-3-methylimidazolium Based Ionic Liquids- Identification of Uranyl(V) Species -T. Ogura and Y. Ikeda
Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology
INTRODUCTION: Room temperature ionic liquids(ILs) are expected to be useful media for recovering uranium from spent nuclear fuels and solid wastes contaminated with uranium[1], e.g., as media for extraction andelectrolytic deposition. Hence, the extraction behavior of
uranyl species from aqueous to IL phase, the electrochemical behavior of uranyl species in ILs, and so on
have been studied[2-5]. In the present study, we haveexamined the electrochemical behavior of uranyl(VI)species, (EMI)2UO2Cl4, in the mixture of EMICl and
EMIBF4 (EMI = 1-ethyl-3-methylimidazoliun) to obtain
the basic data for evaluating application of ILs to pyro-reprocessing process. We used the mixture of EMICland EMIBF4 as the reaction media, because this mixture
is liquid at room temperature.
EXPERIMENTS: 1-Ethyl-3-methylimidazolium chloride and EMIBF4 were commercially available from
Kanto Chemical Co., Inc. The former was repeatedly (atleast 4 times) treated with activated charcoal in acetonitrile, followed by filtration and vacuum evaporation, andthe latter was used without further purification. The[EMI]2[UO2Cl4] was prepared by the similar method
reported previously. UV-visible absorption spectra ofsolutions prepared by dissolving [EMI]2[UO2Cl4] into
EMIBF4/Cl ([Cl-] = [BF4-] = 3.54 x 10-1 M) were measured by using SHIMADZU UV-3150 spectrophotometer.
Cyclic voltammetric (CV) measurements of sample solutions were carried out at 25 ºC under a dry Ar atmosphereusing BAS ALS660B. A conventional three-electrodesystem was utilized, i.e., a Pt disc working electrode(surface area (S): 0.020 cm2), a Pt wire counter electrodeand an Ag/Ag+ reference electrode (0.01 M AgNO3, 0.1
M tetra-n-butylammonium perchlorate in acetonitrile)connected to the sample solution through a glass frit
filled with the solvent ionic liquid. The Fc/Fc + couple
was used as the reference redox system. All potentials
reported here are versus Fc/Fc+. Dissolved O2 in thesample solutions was removed by passing Ar gas throughfor at least 10 min prior to starting the CV measurements.
The ohmic drop in this experiment was compensated bysubtracting the cyclic voltammogram of the blank
EMIBF4/Cl solution from that of [UO2Cl4]2– in the same
solvent.
RESULTS: The cyclic voltammograms of the EMICland EMIBF4 mixture dissolved [EMI]2[UO2Cl4] (6.06 x
10-2 M ) were measured. One redox couple is observed
around -1.0 V vs. Fc/Fc+. It was found that the values of(Epc + Epa)/2 (Epc and Epa are peak potentials for cathodic
and anodic peaks, respectively) are constant (-0.989 V vs.
Fc/Fc+) regardless of the scan rates, and that a plot of ipc(the peak currents of cathodic peaks) against v1/2 gives alinear relationship with slope of 8.21. Furthermore, weestimated the standard rate constant (k0) based on the
kinetic parameter () proposed by Nicholson. The k0
value was estimated as (2.7~2.8) x 10-4 cm/s in the rangeof scan rates from 50 to 300 mV/s. The estimated value
is in the range of the k0 value ((4.0 ~ 9.9) x 10-3 > ko >(2.7 ~ 6.6) x 10-7) for the quasi-reversible reaction on thebasis of the reversibility factor () of Matsuda andAyabe. These results suggest that the electrochemical
reaction of [UO2Cl4]2-ocuurs quasi- reversibly. In order
to examine the reduction product, we carried out
spectroelectrochemical studies using optically transparent thin layer electrode (OTTLE) cell in the range from 0
to -1.306 V. The isosbestic point is found to be observed
around 350 nm. In addition, from the Nernstian plot, theelectron stoichiometry (n-value) and the formal potential
were evaluated as 0.99 and -0.99 V, respectively. These
results indicate that [UVIO2Cl4]2- is reduced to [UVO2Cl4]in the mixture of EMICl and EMIBF4 and the resulting[UVO2Cl4]- species are relatively stable.
REFERENCES:[1] V.A. Cocalia, K.E. Gutowslki, and R.D. Rogers,
Coord. Chem. Rev., 250, 755 (2006).
[2] K. Binnemans, Chem. Rev., 107, 2592 (2007).
[3] Y. Ikeda, K. Hiroe, N. Asanuma, and A. Shirai, J.
Nucl. Sci.Technol., 46, 158 (2009).
[4] Y. Ohashi, N. Asanuma, M. Harada, Y. Wada, T.
Matsubara, and Y. Ikeda, J. Nucl. Sci. Technol., 46,
771 (2009).
[5] T.J. Bell and Y. Ikeda, Dalton Trans.,40, 10125(2011).

採択課題番号 23P9-10
f-元素の有効利用に関わる基礎及び応用研究（東工大・原子炉研）小倉逸也、池田泰久

プロジェクトPR9-11

Electrochemical Behavior of f-elements Compound

T. Goto and K. Hachiya1
Department of Environmental Systems Science, Facultyof Science and Engineering, Doshisha University
1
Department of Fundamental Energy Science, Graduate
School of Energy Science, Kyoto University
INTRODUCTION: Molten salts are promising media
for separation and recovery of the spent nuclear fuel. To
realize the process, clarifying the physicochemical properties of f-elements in molten salts is required. Althoughcesium is known as an important fission product, little
has been reported about its effect on the molten salts.
From the background, we have examined the influencethat the existence of the cesium ion gave to other multivalence ions in molten LiCl-KCl. In this report, aluminum ion was selected as model of a multi valence cation(f-elements) and electrochemical behavior of aluminumion in molten LiCl-KCl and LiCl-KCl-CsCl were investigated.
EXPERIMENTS:
The LiCl-KCl-CsCl eutectic(LiCl-KCl-CsCl=57.5:13.3:29.2 mol %) was used as anelectrolyte. AlCl3 was directly added to the melt as an
Al(Ⅲ) ion source. A Chromel-Alumel thermocouples
were used for temperature measurement. The temperature was maintained within 1±K by a temperature control
unit. All experiments were conducted in an argon atmosphere with a continuous gas refining instrument. A tungsten wire electrode covered with a high purity alumina
tube was used as a working electrode for investigating
electrochemical behavior of aluminum ions. The reference electrode was a silver wire immersed in
LiCl-KCl-CsCl containing 1 mol% of AgCl, placed in a
Pyrex glass tube with a thin bottom to maintain electricalcontact with the melt. The potential of this referenceelectrode was calibrated with reference to that of a Li+/Li
electrode, which was prepared by electrodepositing Li
metal on W wire. All potentials are given in reference to
Li+/Li electrode potential. A potentio/galvanostat wasused for electrochemical measurement. Diffusion coefficient of aluminum ions was determined by means ofelectrochemical measurement. Micro Raman measurement was performed for analyzing the liquid structure
and coordination of aluminum ion in molten salts.
RESULTS:
Figure 1 shows a typical cyclic
voltammograms (CV) obtained at 0.1 Vs-1 in the eutectic
LiCl-KCl-CsCl melt containing Al(Ⅲ) ions on a tungsten
electrode. The peaks A and A’ are attributed to the reduc-

採択課題番号 23P9-11

tion of Al(Ⅲ) to Al and the oxidation of Al to Al(Ⅲ)
respectively.
(1)
Al(Ⅲ)+3e-→Al
Al→Al(Ⅲ)+3e(2)Detail analysis of the voltammogram CV was performedby using the convolutional analysis as shown in Fig.1. By
analyzing the convoluted curves, it can be observed thatthe direct and reverse scans are not identical. This indicated that the reduction of Al(Ⅲ) on a tungsten electrodewas not reversible reaction and the electrochemical couple of Al(Ⅲ)/Al was typically characteristic of a soluble-insoluble exchange.
According to the theory of convolution, the diffusion
coefficient is calculated using the equation(3):m* = nFCD0.5(3)where m* is the limiting current of the convoluted curveof the corresponding cyclic voltammogram. The diffusion coefficient of Al(Ⅲ) in LiCl-KCl-CsCl at 603 K was
estimated to be 4.0×10-8 cm2 s-1. The diffusion coefficient was 3 orders lower than that in LiCl-KCl. This implied the coordination of aluminum ion in the molten
salts was affected by the existence of the cesium ion.
These results were also supported by the Raman spectraof aluminum ion which largely changed greatly by thepresence of cesium ions.

REFERENCES:[1] Patrick Masset et al., Journal of Nuclear Materials,
344, pp.173-179 (2005)

溶融塩中における f-元素化合物の電気化学的形成・溶解に関する基礎研究（同志社大・理工）後藤琢也（京大院・エネ科）蜂谷 寛

プロジェクトPR9-12

Measurements of Neutron Capture Cross Sections for Radioactive Nuclei

S. Nakamura, F. Kitatani, H. Harada
T. Fujii1, A. Uehara1 and H. Yamana1

1

Japan Atomic Energy Agency
Research Reactor Institute, Kyoto University

INTRODUCTION: As a part of the research projects,
a series of cross-section measurements has been carriedout for minor actinides to obtain basic data for studies on
nuclear-fuel cycles and nuclear transmutation. Neptunium-237 is one of important isotopes because it contributes to the long-term radiotoxicity of nuclear wastes.
However, there still exist large discrepancies among reported data of the thermal-neutron capture cross section(σ0) as shown in Figure 1. Then, the present work reports the measurement for the thermal-neutron capture
cross-section of 237Np.

ANALYSIS AND DISCUSSION: The reaction ratesof 237Np samples were calculated with γ-ray yields, efficiencies, decay data and γ-ray emission probabilities.
However, there are still discrepancies among the data ofthe γ-ray emission probabilities (Iγ). The data of theemission probability for984-keV γ-ray emitted from238
Np have been reported as shown in Table 1. These
data are in good agreement with each other.
Table 1 984-keV γ-ray emission probability
AuthorYear
984-keV Iγ (%)
Harada et al.
2006
25.2±0.5
Rengan et al.
2006
25.2±0.5
Chang et al.
1990
25.19±0.21
Lederer
1981
27.8
Winter et al.
1972
25.4
On the other hand, there are still discrepancies among
reported data of Iγ for 984-keV γ-ray emitted from 233Pa
as listed in Table 2.
Table 2. 312-keV γ-ray emission probability
AuthorYear
312-keV Iγ (%)
Harada et al.
2006
41.6±0.9
Singh and Tuli2005
38.5±0.4
Schukin et al.
2004
37.5±0.24
Lucva et al.
2000
37.8±0.6
Woods et al.
2000
38.7±0.4
Gehrke et al.
1979
38.6±0.5

Fig.1. Situation of the reported data of σ0 for 237Np
Np
EXPERIMENT: A standardized solutions of(200Bq) were irradiated together with neutron monitors
in the pneumatic tube (Pn-2) of the KUR in the latter halfof 2010. The reactor power was 1 MW. The 237Np samples were irradiated for 600sec, and another one together
with a Gd shield (25µm in thickness) for 300 sec. Afterthe irradiations, induced activities of samples were
measured with a high purity Ge detector. Figure 1 shows
the neutron fluxes
obtained from themeasurements oftheirradiatedneutron monitors.
The thermal neutron flux was
4.4x1012 n/cm2sec
at the irradiation
position of thePn-2.
Fig.2. neutron flux components at Pn-2
237

Then, when the combinations of Iγ data were changed,
their influences on the σ0 were examined. When the influences were examined about the data by Kobayashi and
Katoh, their results are modified as shown in Table 3.
Table 3. influences on the σ0 by the Iγ data
Pa: 38.6%
41.6
38.5
Author
Np: 27.8%
25.2
25.2
This Work
198±8
183±7
Katoh(‘03)
141.7±5.4
169±6
156±6
Kobayashi(‘94)
158±3
196±4
181±3
The present work is in good agreement with the data
by Kobayashi. From reviewing data, the discrepancies
among the σ0 of 237Np would be caused by the Iγ data
used for the analyses. The data of the σ0 should be settled
by experimental further check on the Iγ data.

採択課題番号 23P9-12放射化法による長寿命核種の中性子断面積研究（原子力機構） 中村詔司、北谷文人、原田秀郎（京大・原子炉）藤井俊行、上原章寛、山名 元

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