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POSIVA Report 1998-13

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Name:

Solubilities of Uranium for TILA-99

Writer:

Kaija Ollila; Lasse Ahonen

Language:

English

Page count:

58

ISBN:

951-652-051-0; 1239-3096

Summary:

Working report: POSIVA 98-13, SOLUBILITIES OF URANIUM FOR TILA-99, engl.kielinen
Ollila Kaija*, Ahonen Lasse**
*VTT Chemical Technology
**Geological Survey of Finland

Abstract

This report presents the evaluation of the uranium solubilities in the reference waters of
TILA-99. The behaviour of uranium has been discussed separately in the near-field and
far-field conditions. The bentonite/groundwater interactions have been considered in the
compositions of the fresh and saline near-field reference waters. The far-field
groundwaters’ compositions include fresh, brackish, saline and very saline, almost
brine-type compositions. The pH and redox conditions, as the main parameters affecting
the solubilities, are considered.

A literature study was made in order to obtain information on the recent dissolution and
leaching experiments of UO2 and spent fuel. The latest literature includes studies on
UO2 solubility under anoxic conditions, in which the methods for simulating the
reducing conditions of deep groundwater have been improved. Studies on natural
uraninite and its alteration products give a valuable insight into the long-term behaviour
of spent fuel. Also the solubility equilibria for some relevant poorly known uranium
minerals have been determined.

The solubilities of the selected solubility-limiting phases were calculated using the
geochemical code, EQ3/6. The NEA database for uranium was the basis for the
modelling. The recently extended and updated SR ’97 database was used for
comparison. The solubility products for uranophane were taken from the latest literature.

The recommended values for solubilities were given after a comparison between the
calculated solubilities, experimental information and measured concentrations in natural
groundwaters. The experiments include several UO2 dissolution studies in synthetic
groundwaters with compositions close to the reference groundwaters.


Keywords:

uranium, UO2, solubility, simulated near-field and far-field groundwaters, oxidizing,
reducing conditions


POSIVA 98-13, SOLUBILITIES OF URANIUM FOR TILA-99, engl.kielinen
Ollila Kaija*, Ahonen Lasse**
*VTT Chemical Technology
**Geological Survey of Finland

Abstract

This report presents the evaluation of the uranium solubilities in the reference waters of
TILA-99. The behaviour of uranium has been discussed separately in the near-field and
far-field conditions. The bentonite/groundwater interactions have been considered in the
compositions of the fresh and saline near-field reference waters. The far-field
groundwaters’ compositions include fresh, brackish, saline and very saline, almost
brine-type compositions. The pH and redox conditions, as the main parameters affecting
the solubilities, are considered.

A literature study was made in order to obtain information on the recent dissolution and
leaching experiments of UO2 and spent fuel. The latest literature includes studies on
UO2 solubility under anoxic conditions, in which the methods for simulating the
reducing conditions of deep groundwater have been improved. Studies on natural
uraninite and its alteration products give a valuable insight into the long-term behaviour
of spent fuel. Also the solubility equilibria for some relevant poorly known uranium
minerals have been determined.

The solubilities of the selected solubility-limiting phases were calculated using the
geochemical code, EQ3/6. The NEA database for uranium was the basis for the
modelling. The recently extended and updated SR ’97 database was used for
comparison. The solubility products for uranophane were taken from the latest literature.

The recommended values for solubilities were given after a comparison between the
calculated solubilities, experimental information and measured concentrations in natural
groundwaters. The experiments include several UO2 dissolution studies in synthetic
groundwaters with compositions close to the reference groundwaters.


Keywords:

uranium, UO2, solubility, simulated near-field and far-field groundwaters, oxidizing,
reducing conditions


Keywords:

uranium; U02, solubility; simulated near-field and far-field groundwaters; oxidizing; reducing conditions

File(s):

Solubilities of Uranium for TILA-99 (pdf) (1.8 MB)


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