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Workreport 1997-25

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Name:

Olkiluodon pohjavesikemia - suolainen ja murtovesi - suolaisen referenssiveden resepti

Writer:

Ulla Vuorinen; Kaija Ollila; Margit Snellman

Language:

Finnish

Page count:

66

Summary:

Working report: Vuorinen, U., Snellman, M. & Ollila, K.
GROUNDWATER CHEMISTRY AT OLKILUOTO - SALINE AND
BRACKISH GROUNDWATER - RECIPE FOR SALINE REFERENCE
WATER

ABSTRACT

A reference water with a well known composition can be used in research related to
safety analyses such as experimental solubility studies, diffusion and sorption studies
and solubility calculations. Experimental solubility studies in Finland have so far been
performed with the simulated fresh granitic groundwater (Allard). However, solubility
calculations have in addition been performed using fresh groundwater from the
Kivetty area and brackisha and saline groundwater from Olkiluoto area. In this study
the groundwaters collected from Olkiluoto area in 1989-1995 have been evaluated.
The brackish and saline groundwaters representing at best these groundwater types in
the area have been chosen for further processing. In this context one groundwater
sample (OL-KR1/T3, sampling depth 613-618 m), representing the saline
groundwater type at Olkiluoto, was chosen. The chemistry of this sample was the
basis for the oxic and anoxic saline reference groundwaters developed. In order to
produce the recipes for both the oxic and anoxic saline reference waters
hydrogeochemical modelling (EQ3/6 code) was used to determine the equilibrium
state with the atmospheres (oxic=equilibrium with air, anoxic=equilibrium with
nitrogen gas atmosphere) as well as certain solid phases. No precipitation of phases
(e.g. calcite), which could disturb experimental studies and their interpretation, should
occur in the reference waters. Based on the modelled equilibrium contents recipes
were developed for both the oxic and anoxic reference water by choosing suitable
chemicals and the amounts. The pH-value of the oxic reference water was adjusted to
correspond to calcite equilibrium (pH=7,4) and the pH-value of the anoxic water was
adjusted to 8,3 according to the field value obtained for the corresponding
groundwater sample. The chemistry of the prepared basic version of the oxic as well
as the anoxic reference water was followed for sometime in order to establish the
stability. Both reference waters are weakly buffered and thus small changes downward
in the measured pH-values were observed.

Besides the basic version of the anoxic reference water modelling was also used to
examine redox species and Eh values of the saline groundwater sample. For uranium
dissolution tests in anoxic conditions different waters were prepared by adding redox
species (e.g., Fe (II), S(-II)) to the basic composition of the anoxic saline reference
water. Thus the prepared waters contained either one or both of the redox species. By
adding a larger amount of sulphide (5ppm) caused the redox state to change to a lower
level than adding merely iron or a smaller amount of sulphide. Depending on the
added sulphide amount the pH rises, up to about 9,5. The chemistry of these redox
species containing waters will be followed more closely within the uranium solubility
tests.

Keywords: Olkiluoto groundwater chemistry, saline reference water
Vuorinen, U., Snellman, M. & Ollila, K.
GROUNDWATER CHEMISTRY AT OLKILUOTO - SALINE AND
BRACKISH GROUNDWATER - RECIPE FOR SALINE REFERENCE
WATER

ABSTRACT

A reference water with a well known composition can be used in research related to
safety analyses such as experimental solubility studies, diffusion and sorption studies
and solubility calculations. Experimental solubility studies in Finland have so far been
performed with the simulated fresh granitic groundwater (Allard). However, solubility
calculations have in addition been performed using fresh groundwater from the
Kivetty area and brackisha and saline groundwater from Olkiluoto area. In this study
the groundwaters collected from Olkiluoto area in 1989-1995 have been evaluated.
The brackish and saline groundwaters representing at best these groundwater types in
the area have been chosen for further processing. In this context one groundwater
sample (OL-KR1/T3, sampling depth 613-618 m), representing the saline
groundwater type at Olkiluoto, was chosen. The chemistry of this sample was the
basis for the oxic and anoxic saline reference groundwaters developed. In order to
produce the recipes for both the oxic and anoxic saline reference waters
hydrogeochemical modelling (EQ3/6 code) was used to determine the equilibrium
state with the atmospheres (oxic=equilibrium with air, anoxic=equilibrium with
nitrogen gas atmosphere) as well as certain solid phases. No precipitation of phases
(e.g. calcite), which could disturb experimental studies and their interpretation, should
occur in the reference waters. Based on the modelled equilibrium contents recipes
were developed for both the oxic and anoxic reference water by choosing suitable
chemicals and the amounts. The pH-value of the oxic reference water was adjusted to
correspond to calcite equilibrium (pH=7,4) and the pH-value of the anoxic water was
adjusted to 8,3 according to the field value obtained for the corresponding
groundwater sample. The chemistry of the prepared basic version of the oxic as well
as the anoxic reference water was followed for sometime in order to establish the
stability. Both reference waters are weakly buffered and thus small changes downward
in the measured pH-values were observed.

Besides the basic version of the anoxic reference water modelling was also used to
examine redox species and Eh values of the saline groundwater sample. For uranium
dissolution tests in anoxic conditions different waters were prepared by adding redox
species (e.g., Fe (II), S(-II)) to the basic composition of the anoxic saline reference
water. Thus the prepared waters contained either one or both of the redox species. By
adding a larger amount of sulphide (5ppm) caused the redox state to change to a lower
level than adding merely iron or a smaller amount of sulphide. Depending on the
added sulphide amount the pH rises, up to about 9,5. The chemistry of these redox
species containing waters will be followed more closely within the uranium solubility
tests.

Keywords: Olkiluoto groundwater chemistry, saline reference water

Keywords:

Olkiluodon pohjavesikemia; suolainen referenssivesi

File(s):

Olkiluodon pohjavesikemia - suolainen ja murtovesi - suolaisen referenssiveden resepti (pdf) (1.5 MB)


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