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POSIVA Report 1997-9

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Name:

Dissolution of Unirradiated U02 Fuel in Synthetic Saline Groundwater Experimental Methods and Preliminary Results

Writer:

Kaija Ollila

Language:

English

Page count:

28

ISBN:

951-652-034-0; 1239-3096

Summary:

Working report: POSIVA-raportti POSIVA-97-09, 28 sivua
ISBN 951-652-034-0


DISSOLUTION OF UNIRRADIATED UO2 FUEL IN SYNTHETIC SALINE
GROUNDWATER - EXPERIMENTAL METHODS AND PRELIMINARY
RESULTS


ABSTRACT

This report presents the experimental methods and preliminary results obtained from
dissolution experiments of unirradiated UO2 pellets in synthetic saline reference
groundwater (I = 0.5 M). The composition of the synthetic groundwater is based on
groundwater studies within the site investigations of spent fuel disposal in the Olkiluoto
area. Redox conditions include oxic (air-saturated) and anoxic (anaerobic glove box,
N2). An attempt is made to adjust the Eh of the aqueous phase under N2 atmosphere by
the addition of natural redox species of groundwater, e.g. S2-, Fe2+, in order to keep
uranium predominantly in the tetravalent state. The earlier stability tests have shown
that low Eh values, -300...-200 mV, can be maintained for a time period of several
months in Allard groundwater with these redox species. Under these conditions it is
expected that dissolved uranium is partially at the tetravalent state. The release of
uranium is measured during static batch dissolution experiments at 25 C. The ratio of
pellet surface area to water volume is varied.

Under oxic (air-saturated) conditions, uranium would seem to attain a steady state in
saline groundwater at a lower level (4 10-6 mol/l) than in Allard groundwater
(2 10-5 mol/l). The modelling calculations (EQ3/6) predict that uranyl silicates and
CaUO4 are potential U-bearing secondary phases in saline groundwater.

Under anoxic conditions, the addition of redox species lowers the uranium
concentrations in the aqueous phase. The effect is greatest in the amounts of uranium
measured in the filtered samples. The uranium concentrations at low Eh in the filtered
samples are close to the theoretical solubility of UO2.

Keywords: UO2, solubilities, batch experiments, air-saturated, reducing conditions



POSIVA-raportti POSIVA-97-09, 28 sivua
ISBN 951-652-034-0


DISSOLUTION OF UNIRRADIATED UO2 FUEL IN SYNTHETIC SALINE
GROUNDWATER - EXPERIMENTAL METHODS AND PRELIMINARY
RESULTS


ABSTRACT

This report presents the experimental methods and preliminary results obtained from
dissolution experiments of unirradiated UO2 pellets in synthetic saline reference
groundwater (I = 0.5 M). The composition of the synthetic groundwater is based on
groundwater studies within the site investigations of spent fuel disposal in the Olkiluoto
area. Redox conditions include oxic (air-saturated) and anoxic (anaerobic glove box,
N2). An attempt is made to adjust the Eh of the aqueous phase under N2 atmosphere by
the addition of natural redox species of groundwater, e.g. S2-, Fe2+, in order to keep
uranium predominantly in the tetravalent state. The earlier stability tests have shown
that low Eh values, -300...-200 mV, can be maintained for a time period of several
months in Allard groundwater with these redox species. Under these conditions it is
expected that dissolved uranium is partially at the tetravalent state. The release of
uranium is measured during static batch dissolution experiments at 25 C. The ratio of
pellet surface area to water volume is varied.

Under oxic (air-saturated) conditions, uranium would seem to attain a steady state in
saline groundwater at a lower level (4 10-6 mol/l) than in Allard groundwater
(2 10-5 mol/l). The modelling calculations (EQ3/6) predict that uranyl silicates and
CaUO4 are potential U-bearing secondary phases in saline groundwater.

Under anoxic conditions, the addition of redox species lowers the uranium
concentrations in the aqueous phase. The effect is greatest in the amounts of uranium
measured in the filtered samples. The uranium concentrations at low Eh in the filtered
samples are close to the theoretical solubility of UO2.

Keywords: UO2, solubilities, batch experiments, air-saturated, reducing conditions



Keywords:

U02; solubilities; batch experiments; air-saturated; reducing conditions

File(s):

Dissolution of Unirradiated U02 Fuel in Synthetic Saline Groundwater Experimental Methods and Preliminary Results (pdf) (414.6 KB)


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