I.

Project Research
Project 3

PR3

Studies on Actinides and Fission Products Performed at the KURRI Hot Laboratory

T. Fujii
Graduate School of Engineering, Osaka 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 Coordination behavior of actinides in ionicliquds (A. Uehara et al.).
ARS-6 Electrochemical behavior of uranium in pyroreprocessing system (Y. Sakamura et al.).
ARS-7 Molecular dynamics simulation of actinide andFP ions in melts (N. Ohtori et al.)．
ARS-8 Fundamental study of fission products fortrans-actinide chemistry (Y. Kasamatsu et al.).
ARS-9 Isotope fractionation of Sr and Ca by chemical
exchange method (R. Hazama et al.).
ARS-10 Thermochemical measurement of rare earth
complexes (H. Sekimoto et al.).
ARS-11 Migration behavior of radiocesium in plants (T.
Kubota et al.).
ARS-12 Isotopic composition of radionuclides in environmental samples (Y. Shibahara et al.).
ARS-13 Behavior of fission products in soil samples (S.
Fukutani et al.).
ARS-14 Noble gas mass spectrometry of neutron irradiated geological samples (H. Sumino et al.).
ARS-15 40Ar/39Ar dating of neutron irradiated minerals
and glasses (O. Ishizuka et al).

28P3

2. Main Results and Contents
ARS-1 and -2 were performed in order to deepen theknowledge of nuclear waste management issues. In
ARS-1, for further study on actinides, the formation constants of the Zr-isosaccharinic acid (ISA) complexes
were determined by the least squares fitting analysis of
the solubility data. Deprotonated Zr-ISA complexes were
found at high pH region. In ARS-2, Zr solubility in carbonate solutions was measured and discussed based on
the thermodynamic constant and existing activity correction model. The results were compared with Th complexes, and it was found that highly negatively charged
Zr carbonate complex was not stable at high ionicstrength. ARS-5, 6, 7, and 10 were performed with the
viewpoint of pyrochemistry. In ARS-5, the redox reactions of uranium ions in hydrate calcium chloride melts
were investigated by electrochemical methods. It was
found that the disproportionation of U(V) occurs after the
reduction of U(VI) via formation of UO2, which is notobserved in acidic HCl solutions. In ARS-6, the redox
mechanism of Se, a fission product element, in molten
salts was studied by UV-Vis spectrometry. The results
support the electrochemical data, which indicate thecomplexation of Se with Cu. In ARS-7, the MD simulation for concentrated aqueous LiCl solutions containing
La(III) ion. Specific radial distribution functions of O
and Cl around La were found. In ARS-10, mutual separation of Nd and Pr in Ca-Li chloride molten salts using
molten metallic tin cathode and graphite anode was performed. Reaction mechanisms of Nd and Pr with Sn wereclarified. ARS-9 studied isotope fractionation of Ca. A
possible fractionation of 48Ca/40Ca was found. In ARS-11,
Cs-134 and Cs-137 were produced via photonuclear reactions. The isotopic composition of Cs was measured bymass spectrometry and gamma-spectrometry. The effectiveness of this method for correcting the coincidence
sum effect was demonstrated. ARS-3, 4, 8, 12, 13, 14,and, 15, focus on environmental chemistry and geochemistry by using KUR, and hence restart of the KUR
operation is needed.
3. Summaries of the achievements
New and characteristic chemical, kinetic, structural, andthermodynamic data for actinides and fission products
were obtained. These new information encompass aqueous chemistry, pyrochemistry, and isotope chemistry off-elements and FPs.

PR3-1

Solubility of Tetravalent Metal Hydroxide in the Presence of Isosaccharinic Acid

T. Sasaki, T. Kobayashi, S. Nishikawa, R. Goto, T. Saito1
and A. Uehara1
Graduate School of Engineering, Kyoto University
1
Research Reactor Institute, Kyoto University
INTRODUCTION: For the safety assessment of radioactive waste disposal, it is very important to predict the solubility limit of M(IV) under relevant conditions. Isosaccharinic acid (ISA), a degradation product of cellulose
found in low- and intermediate-level radioactive waste, isknown to form strong complexes with radionuclides [1].
Under repository conditions, in the presence of the aforementioned organic acid, the solubility of radionuclides
could potentially be enhanced, which could affect thesafety assessment of radioactive waste disposal. Since thesolubility and complexation behavior of tetravalent actinide (An(IV)) is primarily controlled by the solubility ofthe sparingly soluble solid phase amorphous hydroxide(An(OH)4(am)) and concentration of complexing agent,respectively, it is necessary to quantify the impact of thecomplexation ability of the organic acid on the solubilityof An(OH)4(am). Although several reports have investigated the interaction of ISA with tetravalent actinides, thenumber of reported values of thermodynamic constants
such as complex formation constants were considerably
limited [1]. In the present study, we focused on the solubility of zirconium in the presence of ISA at a wide rangeof hydrogen ion concentrations (pHc). As a tetravalent ion,zirconium is considered to be a chemical analog oftetra-valent actinides (such as Pu(IV)), although different
chem-ical characteristics have also been observed.
Zirconium is a relevant element in the safety assessmentof radioactive waste disposal since it has a high yield in
uranium fission products and Zr metal is used as a fuelcladding material in light-water reactors. However, nothermodynamic data on Zr-ISA are available. The
formation constants of the Zr-ISA complexes were
determined by the least squares fit-ting analysis of thesolubility data.
EXPERIMENTS: Calcium isosaccharinate (Ca(ISA)2)
was synthesized from α-lactose and converted to NaISA
stock solution. An aliquot of NaISA stock solution and
HCl and/or NaOH solutions were added to polypropylene
tubes to prepare sample solutions at specific hydrogen ion
concentrations (pHc) and ISA concentrations. The ionicstrength (I) was fixed at I = 0.5 mol/dm3 (M) NaCl. A portion of freshly precipitated Zr(OH)4(am) solid phase wasthen added to the tubes. After aging for several weeks, supernatants were filtered through from 10 kDa to 0.45 µm
membranes and Zr concentrations were determined by
ICP-MS. The solid phases were investigated by XRD
within a range of 2θ = 10°−60°.

28P3-1RESULTS: Zr solubility after 14 weeks in the presence of
10−3–10−1 M ISA was measured in a pHc range of 8–12.5
after ultrafiltration through 10 kDa membranes. A steadystate was confirmed to be achieved within 10 weeks. In thepresence of ISA with a concentration higher than 10−2.5 M,
Zr solubility was found to be higher in comparison withsystems with an absence of ISA, depending on the pHc and
ISA concentration [2]. Zr solubility seemed to be almost
independent of pHc under weakly alkaline pH conditions
between pHc 8 and 10, indicating that four OH− ions are
involved in the Zr-ISA complex, provided that
Zr(OH)4(am) is in the solid phase. Zr solubility increased
with a slope of approximately 1 above pHc 10, suggestingthat one additional OH− was involved in the reaction in thispH region. This may be due to further coordination of one
OH− to the Zr-ISA complex or to deprotonation of the hydroxyl group on the main chain of ISA. The Zr solubility
at pHc 9.3 and 12.1 was shown as a function of the total
ISA concentration ([ISA]tot). The slope against the total
ISA concentration was approximately 2, indicating that
two ISA molecules were involved in the formation of a ZrISA complex. It was noted that no significant peak exceptthat of NaCl(cr) was observed in the XRD patterns of thesolid phase aged in the presence of 10−1 M ISA.
Zr4+ + 4OH– + 2ISA– ⇌ Zr(OH)4(ISA)22– (β142)
Zr4++5OH–+2ISA– ⇌ Zr(OH)4(ISA)(ISA-H)3–+H2O (β152)
Taking the isosaccharinate complex formation reactions,the deprotonation of the carboxylic group of ISA [3], thelactonization of ISA [3], and the hydrolysis reactions of Zr[4] into account, Zr solubility ([Zr]) and the total ISA concentration ([ISA]tot) can be described as[Zr]  [Zr 4 ]   [Zr(OH) 4m m ]   [Zr(OH) x (ISA) 4y x  y ]mx, y[ISA]tot  [ISL]  [HISA]  [ISA ]   y[Zr(OH) x (ISA)4y x  y ]

x, yThe solubility data in the neutral to alkaline pH range wereanalyzed to determine the complex formation constants
β142 and β152. The parameter values are determined in theleast squares fitting analysis. The fixed parameters werecorrected by SIT. In the alkaline pH region, one of the hydroxyl groups on the alkyl chain of ISA may be deprotonated to form the Zr(OH)4(ISA)(ISA-H)3－complexes.
REFERENCES:[1] Hummel W et al. Chemical Thermodynamics of Compounds and Complexes of U, Np, Pu, Am, Tc, Se, Ni andZr with Selected Organic Ligands. Elsevier, North-Holland, Amsterdam (2005).
[2] Sasaki T et al., Radiochim. Acta, 94, (2006) 489-494.
[3] Rai D et al., J. Solution Chem., 38, (2009) 1573-1587.
[4] Sasaki T et al., J. Nucl. Sci. Technol., 45, (2008) 735739.

PR3-2

Solubility of Zr(OH)4(am) in the Presence of Carbonate
Ion in Dilute to Concentrated NaNO3

T. Kobayashi, S. Nakajima, T. Sasaki, A. Uehara1
Graduate School of Engineering, Kyoto University
Research Reactor Institute, Kyoto University

1

INTRODUCTION: For the safety assessment of radioactive waste disposal, it is necessary to predict radionuclide solubility limits under relevant disposal conditions.
Actinide elements such as uranium, neptunium and plutonium in the radioactive waste have long half-life andthe solubilities are primarily controlled by sparingly soluble hydroxides of tetravalent actinides (An(OH)4(am)).
In spite of the strong hydrolysis reaction, the complex
formation of An(IV) with carbonate is one of the mostimportant reactions for the reliable prediction of theAn(IV) solubility. Since part of low-level wastes (TRU
waste) generated from Japanese nuclear reprocessing
process contain considerable amount of nitrate salt, an
impact of dilute to concentrated NaNO3 on the complex
formation of An(IV) carbonate need to be clarified within
the context of co-disposal of TRU waste and high level
waste. Although a comprehensive literature review has
been performed on the thermodynamic constant of actinide including the An(IV) carbonate [1], the literature
data on An(IV) carbonate at high ionic strength is stilllacking. In the present study, we focus on the complex
formation of Zr(IV) carbonate, which is known as ananalogue of An(IV). Zirconium is also a relevant elementin the safety assessment of radioactive waste disposal,
since it has a high yield among the uranium fission products and zirconium metal is used as a fuel-cladding inlight water reactors. However, limited thermodynamic
data on Zr carbonate at low to high ionic strength isavailable [2]. Zr solubility in carbonate solution containing 0.1 to 5.0 mol/dm3 (M) NaNO3 was measured anddiscussed based on the thermodynamic constant and existing activity correction model.
EXPERIMENTS: Amorphous zirconium hydroxidesolid phase (Zr(OH)4(am)) was pre-precipitated andwashed with purified water. The Zr(OH)4(am) was thenadded into the solutions at certain pH, total carbonate
concentration ([C]tot), and ionic strength (I). The pH wasadjusted in the range of pHc 7 - 12 by HNO3/NaOH andthe ionic strength was controlled to be 0.1, 0.5, 2.0 and
5.0 mol·dm–3 (M) by NaNO3. The [C]tot was adjusted tobe 0.015 - 0.1 M by NaHCO3. After given aging time, thesupernatant of the sample solution was filtrated thoughultrafiltration membranes (10 kDa NMWL) and Zr concentration was determined by ICP-MS.
RESULTS: In the presence of carbonate, the solubility

28P3-2of Zr(OH)4(am) increased, indicating the formation of Zr
pHc at 8 < pHc < 9, and, after this point, decreased withcarbonate complexes. The solubility was independent of
increasing pHc. The solubility at around pHc 12 wasaround 10−8 M. At pHc 8.2, the slope of Zr solubility (log[Zr]) against [C]tot was determined to be about 4, suggesting that four carbonates were mainly involved in thedominant Zr carbonate complexes. The relationship between Zr solubility and [C]tot was similar between pHc
8.2 to 10.9, while no significant relationship was observed at pHc 11.7. In the pHc range of 8–9, the solubility
at I = 5.0 was about 1.5 orders of magnitude higher thanthat at I = 0.1, while in contrast, little difference wasfound between different ionic strengths at pHc > 9. The
slope of Zr solubility against [C]tot at I = 0.1-5.0 was also
about 4, suggesting that four carbonate ions were involved. In the case that conditions of high ionic strengthand [C]tot less than 0.01 M were employed, the slope
showed slightly lower values than those at low ionicstrength, which suggested the formation of an alternativeor additional Zr carbonate complex.
The equilibrium reactions for the formation of the Zr
carbonate complexes Zr(OH)x(CO3)y(4−x−2y)+ can be described as:
Zr 4  xOH   yCO32  Zr(OH) x (CO3 ) 4y x  2 ylog 1xy  [Zr(OH) x (CO3 ) 4y x 2 y ] [Zr 4 ][OH  ]x [CO32 ] y

Under the conditions of the present study, the solubilityof Zr(OH)4(am) was described as a sum of the concentrations of hydrolysis species and carbonate complexes. The
solubility data were analyzed by assuming Zr(CO3)44−,
Zr(CO3)56−, and Zr(OH)2(CO3)22− from literatures [2].
The º1xy and ion interaction coefficient values forZr(OH)x(CO3)y(4−x−2y)+ were determined.
The large ion interaction coefficient values forZr(CO3)44− and Zr(CO3)56− were a consequence of theminor effects of ionic strength on solubility under highcarbonate concentration. The results observed in thisstudy indicated that a highly negatively charged Zr carbonate complex was less stable at high ionic strength,compared to the analogous Th complex [3].
REFERENCES:[1] Guillaumont R. et al., Update on the Chemical Thermodynamics of Uranium, Neptunium, Plutonium, Americium and Technetium. Elsevier, Amsterdam (2003).
[2] Brown P. et al., Chemical Thermodynamics of Zirconium. Elsevier, Amsterdam (2005).
[3] Altmaier M. et al., Radiochim. Acta 94, 495-500(2006).

PR3-3

Electrochemical Analysis for the Redox Reaction of UO22+ inCalcium Chloride Hydrate Melts

A. Uehara1, T. Nagai2, and T. Fujii3
1

Research Reactor Institute, Kyoto University
Nuclear Fuel Cycle Engineering Lab., Japan Atomic
Energy Agency
3
Graduate School of Engineering, Osaka University
2

INTRODUCTION:

The calcium chloride hexahydrate, CaCl2·6H2O,
and similar hydrate melts are of considerable interest
as solvents with properties intermediate between thoseof aqueous solution and molten salts. Activity coefficients, viscosity and structural analyses indicate thatthe water molecule in CaCl2·6H2O melts strongly coordinates to the calcium ion showing that this melt is aliquid with the properties of an ionic melt composed ofbulky hydrated calcium cations and chloride anions.
Namely, this material has advantages such as inorganic-based melt and low melting point. There are a few
studies on the electrochemistry of uranium ions in hydrate melts. Cohen [1] has investigated the formationof UO2+ in concentrated CaCl2 and LiCl using bulk
electrolysis followed by absorption spectrophotometry.
Bansal et al. [2] reported that UO22+ was reversibly
reduced to UO2+, which can be further reduced to UO2
in Ca(NO3)2·4H2O melt.
In the present study, redox reactions of uranium ionssuch as U4+ and UO22+ in CaCl2·nH2O hydrate melt (n= 6 – 10) were investigated by electrochemical methods. The chemical behavior of uranium ions in the hydrate melt was compared with that in the other solvents such as high temperature [3] or room temperature [4] molten salts, organic solvents [5] and relatively low concentration solution of hydrochloric acid [6].
EXPERIMENTAL:

For the electrochemical measurements, athree-electrode system 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 was used as a reference electrode.
This reference electrode, in which was put an aqueous
solution containing 1 M LiCl along with a Ag wire of
1 mm diameter coated by AgCl. For voltammetric operation, the platinum mesh electrode was employed asa counter electrode. Electrochemical measurement
systems, Hz-5000 (Hokuto Denko Co.) were used forthe cyclic voltammetry and the linear sweep voltammetry. Controlled-potential electrolysis was carriedout in order to identify the electrode reaction. In thisexperiment, a rotating carbon electrode was employed
as a working electrode to enhance the efficiency of theelectrolysis. The counter electrode was also a platinum

28P3-5mesh electrode, and the counter phase was separated
by glass membrane filter 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 the measurements over the wavelength from 400 to
900 nm. These measurements were carried out at 300± 2 K.
RESULTS:

Voltammograms for the redox reaction of 0.05 M
UO2Cl2 in 6.9 M CaCl2 were measured by using aplatinum working electrode. When the potential scanning rate, v, was from 0.01 to 0.5 V s−1, a cathodic
peak current (Ic,1) was observed at −0.090 V (vs.
Ag|AgCl) corresponding to the reduction of UO22+ toUO2+ as Eq. (1);
UO22+ +e−

⇄ UO2+(1)

The Ic,1 was proportional to the square of v between
0.01 and 0.5 V s−1 and the concentration of UO22+ between 5 × 10−3 and 0.06 M. These results indicatedthat the Ic,1 were controlled by the diffusion of UO22+.
An anodic peak current (Ia,1) was observed at 0.025 V
under the potential sweep rate, v, from 0.1 to 0.5 V s−1.
Mid-point potential between cathodic and anodic
peaks was found to be −0.058 V. Assuming that theelectrode reaction of the UO22+|UO2+ couple is reversible, the diffusion coefficient of UO22+ at 298 K
can be calculated to be 1.7 × 10−7 cm2 s−1, which wasmore 10 times smaller than that in diluted electrolyte
solutions such as 0.1 M HClO4 (7.3 × 10−6 cm2 s−1).
On the other hand, at v < 0.1 V s−1, anodic peak potential shifted positive from 0.025 to 0.165 V. This shiftsuggests that disproportionation of UO2+ occurs after
the reduction of UO22+ as following reaction [2] which
is not observed in acidic HCl but room and high temperature ionic liquids [3,4];
2 UO2+ ⇄ UO22+ + UO2(2)REFERENCES:[1] D. Cohen, J. Inorg. Nucl. Chem. 32 (1970) 3525.
[2] N.P. Bansal and J.A. Plambeck, Electrochim. Acta, 23(1978) 1053.
[3] T. Nagai, A. Uehara, T. Fujii, O. Shirai, N. Sato and H.
Yamana, J. Nucl. Sci. Technol. 42 (2005) 1025.
[4] P. Giridhar, K.A. Venkatesan, T.G. Srinivasan and P.R.
Vasudeva Rao, Electrochim. Acta, 52 (2007) 3006.
[5] L. Martinot, D. Laeckmann, L. Lopes, T. Materne andV. Muller, J. Alloys Comp. 185 (1992) 151.
[6] W.E. Harris and I.M. Kolthoff, J. Am. Chem. Soc. 69(1947) 446.

PR3-4

Electronic Absorption Spectra of Selenium in LiCl-KCl Eutectic Melt

Y. Sakamura1, T. Murakami1, K. Uozumi1, A. Uehara2
and T. Fujii3than 406 nm seemed to overlap, which might be due tothe formation of Se22- ions.
Se + Se2-  Se22-

1

INTRODUCTION: The electrolytic reduction technique in LiCl-Li2O melts has been developed for
pyrochemical reprocessing of spent oxide fuels [1]. At thecathode, actinide oxides are reduced to their metals:
MO2 + 4 e  M + 2 O
-

2-

(1)

where M denotes actinides such as U and Pu. Similar tooxygen, chalcogen fission products such as Se and Te are
dissolved into the melt in the form of divalent anion.
Recently, the authors have been studied electrochemical behavior of Na2Se in LiCl-KCl eutectic melt to extract Se from molten salts [2]. The cyclic voltammogramsof glassy carbon electrode indicated that the deposition of
Se proceeded in two steps at the anode: the oxidation of
Se2- to Se22- occurred followed by the oxidation of Se22to Se, which was similar to the electrochemical behaviorof sulfur [3]. When Cu was used as the anode, Cu2Se wasdeposited at the potentials more negative than the potential of Se deposition. To verify the redox mechanism of
Se, a spectroscopic study was conducted.
EXPERIMENTS: LiCl-KCl-Na2Se mixture was prepared by heating a quartz tube containing LiCl-KCl eutectic (59:41 mole ratio, Aldrich-APL) and Na2Se (99.8%
purity, Alfa Aesar) at 723 K. The Se concentration wasdetermined to be 0.123 wt% by ICP-AES analysis.
LiCl-KCl eutectic (3.075 g) was loaded in a rectangular cylinder quartz cell (10 x 10 mm) used for absorption spectrometry and heated to 723 K in an electric furnace. The experimental apparatus was previously described in detail by Nagai et al. [4] The following steps
were carried out and then the absorption spectrum of themelt was measured by using an UV/Vis/NIR spectrophotometer (V-570, JASCO).
(1) 0.278 g of the LiCl-KCl-Na2Se mixture was added.
(2) 0.235 g of the LiCl-KCl-Na2Se mixture was added.
(3) 0.252 g of the LiCl-KCl-Na2Se mixture was added.
(4) 0.015 g of Se on a mullite tube was immersed in themelt.
(5) The Se was removed from the melt.
(6) A Cu rod (2 mm) was immersed in the melt.
RESULTS: Fig. 1 shows absorption spectra of the
LiCl-KCl-Na2Se melt measured during the steps (1)-(6).
The absorption peak at 406 nm corresponding to Se2- ions
was increased by adding the LiCl-KCl-Na2Se mixture(steps (1)-(3)). The Se concentration in the melt was
0.022 wt% after step (3). After Se was added into themelt by step (4), an absorption band in the range lower

28P3-6(2)

In fact, the Se concentration in the melt was increased to
0.027 wt% after 1.5 h and the melt became darker brownas visually observed in Fig. 2.
After the Cu rod immersion (step (6)), the absorption
peak gradually decreased and went back to 406 nm,
which might be due to the decomposition of Se22- to giveSe2- and Cu2Se.
Se22- + 2 Cu  Se22- + Cu2Se(3)

In summary, the results of this spectroscopic study are
consistent with the results of electrochemical measurement [2]. However, the Se concentration was finally decreased to 0.013 wt% and the absorption peak at 406 nm
became low. The reasons for mass loss should be clarified.
2.0(1) 0.278 g of salt added(2) 0.513 g of salt added(3) 0.765 g of salt added(4) 0.5 h after Se immersion(4) 1.0 h after Se immersion(4) 1.5 h after Se immersion(6) 0.33 h after Cu immersion(6) 0.83 h after Cu immersion

1.5

AbsorbanceCentral Research Institute of Electric Power Industry
2
Research Reactor Institute, Kyoto University
3
Graduate School of Engineering, Osaka University

1.0

0.5

0.0
250

406 nm

500

750

1000

Wavelength (nm)Fig. 1
Absorption spectra of LiCl-KCl-Na2Se melt
measured during steps (1)-(6).
Step (3)

Step (4)Fig. 2
The quartz cell containing LiCl-KCl-Na2Se
melt after steps (3) and (4).
REFERENCES:[1] Y. Sakamura and M. Akagi, Nucl. Technol. 179(2012) 220-233.
[2] Y. Sakamura and M. Iizuka, Proc. The 48th Symposium on Molten Salt Chemistry, p. 1-2, Niigata Univ.,
Japan, Nov. 24-25, 2016, in Japanese.
[3] D. Warin, Z. Tomczuk and D.R. Vissers, J.
Electrochem. Soc., 130 (1983) 64-70.
[4] T. Nagai, T. Fujii, O. Shirai and H. Yamana, J. Nucl.
Sci. Technol., 41 (2004) 690-695.

PR3-5 Coordination Structure around La3+ Ion in Concentrated Aqueous Solutions of LiCl
N. Ohtori, Y. Ishii1, A. Uehara2, T. Fujii3composition ratio, the present MD results show someunderestimates in La-Cl and overestimates in La-O.

Department of Chemistry, Niigata University
1
Graduate School of Science and Technology, Niigata
University
2
Research Reactor Institute, Kyoto University
3
Department of Sustainable Energy and Environmental
Engineering, Graduate School of Engineering, Osaka
University

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, 4]. The water molecules wereconstrained by SHAKE algorithm. The number of particles included in the simulation cell is shown in Table 1.
Time step was 1.0 fs.
RESULTS: Figures 1 and 2 show the radial distribution function and coordination number of O atom or Cl−
ion around La3+ ion in 14 M aqueous solution of LiCl.
Although, regarding distances between La3+ and O or Cl−,
the present MD results are in good agreement with thoseof first-principles MD[5], regarding the peak heights, itshows poor agreements. Although the experimental results of coordination number follow rather simple
Table 1 Number of particles included the simulation cellfor aqueous solutions of LiCl containing La3+ ion.
[Cl–] /
mol dm–3

H2O

Li

0
1
3
8
14

1108
1086
1040
924
782

0
20
60
160
280

28P3-7+

Number of unit
Cl–
La3+
3
23
63
163
283

1
1
1
1
1

first-principles MD: La-O: La-Cl
this work: La-O: La-Cl

25
20

g(r)

10

5

0

2

3

4

5

6

r/Å
Fig.1 Radial distribution function of O atom or Cl−
ion around La3+ ion in 14 M aqueous solution of
LiCl.
10
8
6

NligandINTRODUCTION: 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].
Then, we analyzed coordination structure around uranyl
ions in 14 M LiCl aqueous solution in more detail andcompared the results with experimental results[3]. In thisstudy, we report the results of MD simulation for concentrated aqueous solutions of LiCl containing La3+ ion anddiscuss coordination structure around La3+ ion.

30

: Total: H 2O4: expt.
: composition ratio: this work

: Cl-

2
0
0

2

4

6

8

10

12

14

cLiCl / M
Fig.2 Concentration dependence of coordination
number of O atom or Cl− ion around La3+ ion inaqueous solution of LiCl.
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).
[4] S. Díaz-Moreno, S. Ramos, and D.T. Bowron, J. Phys.
Chem. A, 115, 6575 (2011).
[5] L. Petit, R. Vuilleumier, P. Maldivi, and C. Adamo, J.
Phys. Chem. B, 112, 10603 (2008).

PR3-6 Study of Isotope Separation of Strontium and Calcium via Chemical Exchange Reaction
R. Hazama, Y. Sakuma1, T. Yoshimoto, T. Fujii2, T. Fukutani3, Y. Shibahara3
Graduate School of Human Environment, Osaka Sangyo
University
1
Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology,
2
Graduate School of Engineering, Osaka University
3
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 (LLE), an appropriate
crown-ether can be used not only for separation of metal
ions, but also for separation of isotope[1].
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).
A 20 ml aqueous solution (3M CaCl2) and 200 ml organic solution (0.07M DC18C6 in chloroform) were stirred
by a magnetic stirrer for 30 m/60 m at room temperatureand separated. This LLE was iterated six times (1－6)[2].
Natural samples of Ca must be purified to remove potassium because 40K interferes on 40Ca, thus purification
by cation exchange resin (DOWEX 50WX8) was conducted prior to isotope analysis. Samples with ultrapure
0.1M HNO3 were loaded onto this ion exchange column
in order to extract the Ca-fraction. After rinsing the column with ultrapure 8M HNO3 the Ca-fraction was collected, evaporated to dryness and then dissolved in ultrapure HNO3 to form Ca(NO3)2. About 30μg of Ca in
the nitrate form (1μL) are loaded onto the single Re
filament in combination with the so called “sandwich-technique” of Ta2O5-activator, which stabilizes thesignal intensity [3].
All Ca isotope measurements were carried out by the
TIMS, KURRI. The TRITON multicollector is operated
in positive mode with a 10 kV acceleration voltage andequipped with nine Faraday cups as detection system, butcannot account for the dispersion of the whole Ca isotope
mass range from 40 to 48 amu. During the first sequence,
the masses of 40, 42, 43 and 44 are measured simultaneously and during the second sequence, the masses 43, 44
and 48 are measured. Table 1 shows a summary of theexperimental conditions for Ca isotope analysis using

TIMS.
Property
Accelerating voltage
Source vacuum
Analyzer vacuum
Faraday cup
Baseline(each block)

Setting
10 kV
1 × 10-7 mbar
6 × 10-9 mbar
9
Delay time: 10 s
Integration time: 16 s
Data collection
Blocks/run: 6
Scans/block: 10
Integration time: 4 s
Idle time: 3 s
Analyzing temperature1500 – 1580 ℃: 3A
Boiling point@1 atm:
1487℃
Table 1. Experimental condition used for Ca isotope
analysis by TIMS.
RESULTS: The linearity of the plots in Fig. 1 indicatesthat the isotope effects show the normal mass dependence.

Fig 1. Mass dependence of observed Ca isotope separation: Preliminary. Circle/Square:30m , Triangle/Cross:60m for stirring and standing for separation, respectively.
REFERENCES:[1]B.E. Jepson et al., J. Inorg. Nucl. Chem.38(1976)1175.
[2]R. Hazama et al., Proc. 6th Recontres du Vietnam, The
Gioi Publishers (2007) 383: arXiv: 0710.3840.
[3]A. Heuser et al., Int.J.Mass Spec. 220(2002)385.

採択課題番号 28P3-9 ストロンチウム及びカルシウムの化学交換法における同位体分別研究
プロジェクト （大産大院・人間環境）硲 隆太、義本孝明 （東工大・原子炉研）佐久間洋一（阪大・工）藤井俊行（京大・原子炉）福谷哲、芝原雄司

Mutual Separation of Nd and Pr by Molten Salt Electrolysis

H. Sekimoto1, A. Uehara2, T. Fujii3
1

Department of Physical Science and Materials Engineering, Iwate University
2
Research Reactor Institute, Kyoto University
3
Department of Sustainable Energy and Environmental
Engineering, Osaka University

INTRODUCTION:
Mutual separation of Nd, Dy and Pr is essentially important for the recycling of the neodymium
magnet. Uehara et al. reported on the mutual separationof La and Nd utilizing the disproportionation reaction ofNd(II) to metallic Nd and Nd(III) in LiCl-KCl molten salt[1]. This technique seems quite attractive comparing withthe conventional processes such as the ion exchange process and the solvent extraction process in terms of theenvironmental load. We have investigated the absorption
spectra of ions of Nd, Dy and Pr in CaCl2-LiCl eutectic
molten salt and the electrochemical behaviors them [2,3].
In this study, the mutual separation of Nd and Pr in
CaCl2-LiCl eutectic molten salt using molten metallic tin
cathode and graphite anode was examined.
EXPERIMENTS:
Electrochemical experiments and the absorption spectrometry were conducted in the argon atmosphere, where the concentration of oxygen and water
was controlled below 1 ppm. 4 g of metallic tin, 6.20 g of
CaCl2, and 3.80 gram of LiCl were weighed and inserted
in a quartz optical cell attached with cylindrical quartz
tube. The sample heated at 750 C in an electric furnace
to be melt. 0.0370 g of NdCl3 and 0.0384 g of PrCl3 weredissolved in the molten salt, and thus, the initial concentration of Nd(III) and Pr(III) in the molten salt was 0.211
mass% and 0.217 mass%, respectively. The temperature
was then controlled to be kept at 700 C. After that, atungsten rod was immersed in the molten metallic tinphase to make working electrode. A graphite rode and theAg-AgCl reference electrode also immersed in the molten
salt phase as counter electrode and reference electroderespectively. Potentiostatic electrolysis was conducted at-1300 mV vs the Ag-AgCl electrode for 2700 s.
Absorbances of Nd(III) and Pr(III) dissolved in the CaCl2-LiCl eutectic molten salt were measured before and after electrolysis. The concentrations ofneodymium and praseodymium in the molten salt phaseand metallic tin phase were determined by ICP-OES.
RESULTS:

Figure 1 shows absorption spectra of themolten salt containing Nd(III) and Pr(III). Solid line anddotted line corresponds the spectrum before and after
electrolysis, respectively. The peak intensity at 589 nm
which is due to the absorption by Nd(III) decreased from
0.62 to 0.34. The peak intensity at 1546 nm which is due

28P3-10to the absorption by Pr(III) decreased from 0.082 to 0.060.
This means that Nd(III) and Pr(III) were electrochemically reduced. The concentration of Nd and Pr in themolten salt after the electrolysis determined by ICP-AES
were 0.145 mass% and 0.148 mass% and, respectively.
The concentration ratio of Nd and Pr in the molten salt
after the electrolysis was 0.98, which was almost samevalue as that before the electrolysis; 0.97. On the other
hand, the concentration of Nd and Pr was 0.0566 mass%and 0.0702 mass%, respectively. The concentration ratioof Nd and Pr in the molten salt after the electrolysis was
0.81. In CaCl2-LiCl eutectic molten salt, Nd(III) is reduced to Nd(II) which is then decomposed to metallic
neodymium and Nd(III) with disproportionation reaction,
while Pr(III) is reduced to Pr [3]. It is considered that
Pr(III) was reduced on molten metallic tin cathode toform Sn-Pr alloy. But, Nd(III) is reduced to on the tin
cathode Nd(II), which decomposed to metallic neodymium and Nd(II) in molten salt phase. A part of the metallic neodymium react with Sn to form Sn-Nd alloy. Consequently, the concentration ratio of Nd and Pr in metallic
tin decreased comparing that in molten salt.

0.8
Before electrolysis
After electrolysis

0.6
AbsorbancePR3-7

Nd(III)

0.4
0.2

Pr(III)

0.0
300

600

900

1200 1500 1800

Wavelength,  / nm
Fig. 1. Absorption spectra of the molten salt containing Nd(III) and Pr(III). Solid line and dotted line
corresponds the spectrum before and after electrolysis, respectively.
REFERENCES:[1] A. Uehara, K. Fukasawa, T. Nagai, T. Fujii, and H. Yamana,
J. Nuclear Mater., 414, 336 (2011).

[2] H. Sekimoto, A. Uehara, T. Fujii, H. Yamana, KURRI Progress report, (2014).
[3] H. Sekimoto, A. Uehara, T. Fujii, H. Yamana, KURRI Progress report, (2016).

PR3-8Correction of Coincidence Sum Effect by Using
Cs and 137Cs Produced through a Photo Nuclear Reaction

134

Research Reactor Institute, Kyoto University
1
Central Research Institute of Electric Power Industry
INTRODUCTION: The migration of radioactive cesium in plants is often investigated with respect to thecompetition of potassium. Among potassium isotopes,
43
K is useful for tracer experiments. This nuclide can beproduced from calcium and is referred to carrier free; its
radioactivity can be regulated to enough for experiments.
The immediate purification of 43K is required because of
its short half life, T1/2 = 22.3 h. In this study the purification methods are investigated by using 134Cs and 137Cs,
instead of 43K, for the convenience of experiment and on
considering that both elements are alkaline metals andhence exhibit a similar chemical behavior. In addition,these cesium nuclides were used to correct coincidence
sum effect on γ-spectrometry. Without attention to thiseffect, the evaluation of 134Cs radioactivity would be incorrect. In order to correct the coincidence sum effect,134
Cs and 137Cs were produced through a photo nuclear
reaction and the isotopic ratios of 134Cs to 137Cs measuredby Thermal Ionization Mass Spectrometry (TIMS) and
γ-spectrometry were compared.
EXPERIMENTS: Radioactive cesium nuclides, 134Cs
and 137Cs, were produced through irradiation of barium
chloride with photons generated by the bombardment of
platinum with high-energy electrons. The barium target
material was encapsulated in a quartz tube under vacuum.
The irradiated material dissolved with H2O was addedwith ammonium carbonate [1] or ammonium oxalate [2]to precipitate barium and thus to purify cesium in thesolution. The cesium solution, containing ammonium
chloride and/or oxalate, was evaporated to remove thesesalts. An aliquot of the purified solution was used to determine an isotopic ratio by TIMS [3] and the obtained
value was converted to activity ratio of 134Cs/137Cs. A 5
mL of the solution was used to determine radioactivity
with a high-purity Ge semiconductor detector where thesample was located 0 cm and 10 cm away from the detector. The radioactivity of 134Cs and 137Cs was evaluatedfrom 605-keV and 661-keV gamma ray, respectively.
RESULTS: The irradiated barium chloride sample wasstored for four months prior to cesium separation. The
cesium separation was conducted by precipitating barium
carbonate or barium oxalate. Both precipitation methods
showed high decontamination factor and high cesium
recovery. However, ammonium carbonate was adopted to

28P3-11

remove barium because the deposition of oxalate occurred and this remaining cannot be removed by evaporation. The activity ratio of 134Cs/137Cs in purified cesium
solution was determined by TIMS and g-spectrometry.
The isotopic ratio of 134Cs/137Cs measured by TIMS was
0.126, which was equivalent to 1.824 in activity ratio.
The radioactivity ratio of 134Cs/137Cs measured by
γ-spectrometry was 1.63 and 1.82 at 0 cm and 10 cm
from the detector surface, respectively (Fig. 1) and thisdifference was ascribed to the coincidence sum effect.
The value obtained at 10 cm was agreement with thevalue by TIMS, which means the sum effect can be ignored by keeping a distance of 10 cm from the detector
surface.

1.85
Activity ratio of 134Cs/137Cs

T. Kubota, S. Fukutani, Y. Shibahara, T. Ohta1

1.80

1.75

1.70

1.65
TIMS
gamma-spectrometry

1.60
0

5
10
Distance / cm

Fig. 1. Activity ratio of 134Cs and 137Cs as a function of
distance between the sample and the detector surface.
REFERENCES:[1] Handley et al., Anal. Chem., 31 (1959) 332.
[2] Sugihara et al., Anal. Chem., 31 (1959) 44.
[3] Y. Shibahara et al., J. Nucl. Sci. and Tech., 54, (2016)
158-166.