Sorption of Actinides in Well-Defined Oxidation States on Geologic Media
- PDF / 317,521 Bytes
- 8 Pages / 420.48 x 639 pts Page_size
- 86 Downloads / 156 Views
B. ALLARD, U. OLOFSSON, B. TORSTENFELT, H. KIPATSI AND K. ANDERSSON Department of Nuclear Chemistry, Chalmers University of Technology, S-412 96 Gdteborg, Sweden
INTRODUCTION The long-lived actinides and their daughter products largely dominate the biological hazards from spent nuclear fuel already from some 300 years after
1
the discharge from the reactor and onwards make reliable assessments
of
. Therefore
the geochemistry
it
is
essential to
of these elements
concept for long-term storage of spent fuel or reprocessing waste, It
is
well known that the interaction between e.g.
water and exposed geologic media, system due to this interaction, of the element etc.).
question
redox properties;
Pu(VI),
ground-
a geologic
oxidation state,
existence of complexes
of particular importance for
considering various oxidation states are possible in
mental potential-pH-range
-
any
are largely dependent on the chemical state
(e.g.
The effects of the chemical conditions is
the actinides, -
in
actinides in
and the retention of them in
in
etc.
(U(IV)-U(VI),
the environ-
Np(IV)-Np(V),
Pu(III)-Pu(IV)-Pu(V)-
especially with hydroxide (hydrolysis)
and carbonate (always
Am(III)).
complexation,
present at a total concentration usually in
the mM-range).
Much of the confusion concerning the interpretation of experimental
actinide
distribution data can most likely be related to a poor characterization and control of important chemical parameters such as -
pH
-
redox potential
-
concentrations
of complexing anions
(including carbonate from the water-
air equilibrium). This is
particularly the case for plutonium.
The purpose of the present study is
to get information on the mechanisms
of actinide sorption on geologic material under well-defined conditions and using actinides
in
oxidation
that would
state,
discrete
oxidation
states
For
americium,
the
only
be obtained under oxic conditions and in the 5 absence of strong complexing agents, would be the trivalent state . For thorium,
only the tetravalent
oxic conditions and in
state would exist in
aqueous
solution. Under
the pHl-range of environmental interest neptunium and
776 uranium would exist entirely as penta- and hexavalent species, respectively, 5 in solution . By performing experiments under oxic conditions Am(III), Th(IV),
Np(V)
and U(VI)
would be obtained purely in
one single oxidation
state without any rigorous control of the redox potential. serve as importance
reference of
systems.
Hereby,
characterizing
the
it
redox
is
possible
properties
to
Thus,
they may
illustrate
of e.g.
the
a potential
geologic repository site and the effect of a sudden change of the pH or redox potential on the retention of a specific actinide.
EXPERIMENTAL Radionuclides Radionuclides according to Table I are being used in
this study. For those
of the elements where long-lived as well as short-lived isotopes were available, the sorption studies were performed at two different nuclide concentrations.
All nuc
Data Loading...
