9. TRU and Nuclear Chemistry

概要

TITLE:

9. TRU and Nuclear Chemistry

AUTHOR(S):

CITATION:

9. TRU and Nuclear Chemistry. KURNS Progress Report 2022, 2021: 225233

ISSUE DATE:
2022-07

URL:
http://hdl.handle.net/2433/275852
RIGHT:

CO9-1

Nuclides sorption onto rock samples in the presence of humic acid

T. Sasaki, Q. Zhao, T. Saito1, R. Tonna, N. Sato2, A.
Kirishima2, D. Akiyama2, K. Takamiya1, T. Kobayashi, S.
Sekimoto1
Graduate School of Engineering, Kyoto University
1
Institute for Integrated Radiation and Nuclear Science,
Kyoto University
2
Institute of Multidisciplinary Research for Advanced
Materials, Tohoku University
INTRODUCTION: Safer handling of high-level radioactive wastes (HLW) produced from nuclear recycling is
a major scientific and engineering challenge. Although
the possibility of early failure of HLW packages after
repository closure is low, the radionuclides (RNs) could
leach to the biosphere. The sorption reaction of RNs onto
host rock would be exploited as an effective barrier to
inhibit the migration. Simulation-, field-, and laboratory-based studies have demonstrated that the sorption of
RNs would be significantly affected by natural organic
matters, such as humic acid (HA) molecules in groundwater, by complexation or colloidal formations [1,2]. In
addition, the gamma rays stemming from the decay of
RNs penetrate through the steel canisters of HLW with a
long-term gamma irradiation field will be generated near
the packages. The gamma irradiation would affect the
chemical properties of HA, subsequently leading to interactions between HA and RN. Nevertheless, the effect
of gamma-irradiated HA on the sorption of RN has not
been clarified yet.
This study was aimed at elucidating the dependence of
gamma-irradiated HA solutions on the sorption of RNs. It
can enable the prediction of radionuclide migration and
help establish a sorption coefficient database. For this
purpose, this research was conducted on investigating the
impact of gamma irradiation on the complexation of HA
with non-radioactive Cs and Eu, including the apparent
formation constant and the complexation affinity in terms
of molecular-weight fractions.

Migration

Humic acid

Mn+(aq)

MM-HA

Gamma field

MSorbed

MM-HA,sorb

Fig. 1 Typical sorption and complexation of RNs (M) in
the presence of humic acid and a groundwater systems.
EXPERIMENTS: The pH of the irradiated HA solution was adjusted to around 8. Stock metal solution was
added to the HA solution to obtain an initial metal con-

centration of ca. 10−8 mol/dm3. The rock powder was put
into a polycarbonate tube. The metal–HA solutions were
either not aged or aged for a few months prior to the following process, named as the co-sorption and pre-contact
systems. Samples were placed horizontally and shaken
gently at room temperature. After a contact time of 1
month, the supernatant was filtered through a membrane
filter with a pore size of 0.20 μm. The filtrates were analyzed using a total organic carbon analyzer and ICP-MS
for TOC and metal concentrations, respectively. For
comparison, the metal concentration was also measured
by using a 10 kDa pore size filter. Recovery experiments
were also carried out for the loss of HA and metal ions in
the metal–HA system using a 0.20 μm pore size filter
under the same experimental conditions [3].
RESULTS: Batch sorption experiments were performed to evaluate the effect of gamma-irradiated HA on
the sorption reactions of Cs and Eu at neutral pH. The
purified Aldrich HA in solution was irradiated by a 60Co
source at KURNS of gamma rays up to 100 kGy. The
irradiation reduced the sorption coefficients of the HA
molecules.
In the absence of HA, the sorption coefficient of trivalent
Eu ions was as high as the reported values. In the presence of non-irradiated HA, the sorption of Eu complexed
with HA was suppressed owing to the formation of neutral or negatively charged complexes in aqueous phase.
Although the ratio of HA- and non-complexed species
was more than 10, the ratio in the solid phase was less
than 1. The ratio was evaluated based on the difference in
metal and TOC concentration solutions filtered by a different pore size filter. The result indicated the ratios decreased with dose, suggesting that the metal complexation affinity of the decomposed fragments of HA was
lower than that of the non-irradiated one.
On the other hand, the Cs sorption was not affected by
HA and the gamma irradiation dose, probably due to a
weak complexation ability of monovalent cation with HA.
And, it indicates an insignificant contribution of HA to
Cs sorption onto the rock surface. This new method to
evaluate the molecular-weight distribution of species in
liquid and solid would provide more quantitative findings
of the impact of HA on the sorption of metal ions onto
rock sample. Further experimental investigation of the
sorption mechanism will provide more detailed insight
into the different impacts of HA on RNs.
REFERENCES:
[1] J.F. McCarthy et al., T.C.J. Yeh, Water Resour. Res.
32 (1996), 1223–1238.
[2] J.F. McCarthy et al., Hydrol. 30 (1998), 49–77.
[3] Qi Zhao et al., J. Hazard. Mater., Vol. 428, 128211,
2022.

R3013
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Solid phase transformation of lanthanide oxide to hydroixde in aqueous solutions

T. Kobayashi, R. Nanjo, Y. Sato, T. Sasaki, R. Motokawa1,
S. Sekimoto2, K. Mori2, K. Takamiya2
Graduate School of Engineering, Kyoto University
1
Japan Atomic Energy Agency
2
Institute for Integrated Radiation and Nuclear Science,
Kyoto University
INTRODUCTION:
For the safety assessment of
high-level radioactive waste disposal, it is important to
establish a robust prediction of the migration behavior of
radionuclides under relevant disposal conditions. Actinides with long-half-lives behave as polyvalent metal
ions and easily hydrolyzed to form amorphous hydroxide
precipitates at neutral pH of groundwater. The sparingly
soluble amorphous hydroxides are considered to play as
solubility-limiting solid phases to dominate the migration
behavior of actinides [1]. However, due to decay heat
from the high-level waste, the amorphous hydroxides are
possibly transformed into more thermodynamically stable
solid phases during the long-time migration scenario. On
the other hand, some of crystalline oxides known as stable solid phases are reported to be partly converted to
hydroxides in aqueous solutions under certain conditions
[2]. Although it is necessary to elucidate the stable state
of solid phase in long-term disposal system, there are still
some open questions on the stability of hydroxide-oxide
solid phases in aqueous solutions. In the present study,
we focus on the trivalent lanthanum oxide-hydroxide
solid phases as chemical analogous of trivalent americium and curium. Lanthanum crystalline oxide was prepared and aged in aqueous solutions at 90 ℃. After given
aging periods, the solid phases were investigated by
X-ray and neutron diffraction techniques.
EXPERIMENTS: Lanthanum oxide (La2O3) were
purchased from the manufacturer and heat at 1000 ℃ for
2 hours to remove possible residual hydroxides. Then
given amount of La2O3 was added in a sample solution.
The sample solution was prepared by D2O and the initial
pH was adjusted to pH 8 by DCl/NaOD with small portion of pH buffer (TAPS). The ionic strength (I) was set
to I = 0.1 by adding appropriate amount of NaClO4. After
the sample solution with the solid phase was heated at
90 ℃ for 1, 3, 7 hours, the solid phase was separated and
dried. In order to prevent the possible contamination of
proton (H) and possible transformation by atmospheric
H2O, preparation of sample solution, aging, and drying
were performed in an Ar glove box. The X-ray diffraction
patterns were collected by Smartlab (Rigaku), The neutron diffraction pattern was collected by the versatile
compact neutron diffractometer (VCND) located at the
B-3 beam port of the Kyoto University research reactor
(KUR) [3]. A Cu monochromator with 40 mm diameter
was used to monochromatize the neutron wavelength of
1.0Å. The beam size was approximately 10 mm in width
and 30 mm in height. The beam flux was 1.3×105 n/s･

cm2 during the operation at the power of 5 MW on KUR.
RESULTS: Figure 1 shows the X-ray and neutron diffraction patterns of initial La2O3 and the solid phase after
aging at 90 ℃ for 1 hour. The X-axis represent the lattice
plane spacing d (d = /2 sin , =1.54 Å for X-ray diffraction and =1.0 Å for neutron diffraction). By comparing the XRD patterns before and after the aging, peaks
corresponding to La2O3 disappeared and those corresponding to La(OH)3 appeared. This indicated that the
initial La2O3 almost completely converted to crystalline
La(OH)3 even after 1 hour. The XRD patterns of the solid
phases after 3 and 7 hours aging were found to show no
significant difference to that after 1 hour. Figure 1 also
shows the neutron diffraction patterns of before and after
the aging. The pattern seems to include both peaks corresponding to La2O3 and La(OH)3. Further confirmation
is needed by the measurement of longer aging periods.

1h aging at 90℃

XRD

Relative intensity

CO9-2

initial La2O3(cr)

ND
1h aging at 90℃

initial La2O3(cr)

1

2

3

4

5

6

d (Å)

Fig. 1. X-ray and neutron diffraction patterns of initial La2O3 and the solid phase after aging at 90 ℃ for
1 hour.
REFERENCES:
[1] 包括的技術報告：わが国における安全な地層処分
の実現－適切なサイトの選定に向けたセーフティケ
ースの構築－, NUMO-TR-20-03 (2021).
[2] Md.Moniruzzaman et al., J. Nucl. Radiochem. Sci.,
20,32-42 (2020).
[3] K. Mori et al., JPS Cnf.Proc., 33, 011093 (2021).

R3015
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CO9-3

Electrochemical U dissolution from U-Ru alloy in LiCl-KCl-UCl3 melt

T. Murakami1, Y. Sakamura1, K. Uozumi1 and K. Takamiya2

ratio of U from spent metallic fuels.

Central Research Institute of Electric Power Industry
Institute for Integrated Radiation and Nuclear Science,
Kyoto University

1

2

INTRODUCTION: Electrochemical dissolution of actinides in molten chloride salt is performed in electrorefining process of spent metallic fuels. ...

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