Investigations of the Solution Behaviour of NaCl in the Quinary System NaCl-KCl-MgCl 2 -MgSO 4 -H 2 O at Different Tempe
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SCIIEIFIC BASISFOR RADIOACTIVE WASTE 1MN15C2EV Werner. Dutze, editor INVESTIGATIONS OF THE SOLUTION BEHAVIOUR OF NaCl IN THE QUINARY SYSTEM NaCl-KCl-MgCl
R.CON•RADT,
2 -MgSO4-H
2O
AT DIFFERENT TEMPERATURES
H.EENGELKE and A.KAISER
Fraunhofer-Institut
:fr Silicatforschung, Wtirzburg,
Germany
INTRODUCTION The German concept of high level waste final storage by the aid of waste glasses is
based on rock salt formations as deposits.
Investigations consider
the accidental case of water entrance into the deposit where the waste forms then are exposed to highly concentrated salt brines at elevated temperatures and pressures. In
order to achieve standard corrosion conditions for the investigations of
waste forms,
a set of salt brines of definite composition has been generally
accepted as oossible corroding agents. The agreement is
based on a model for
the process of a hypothetical water entrance saying that in the initial
period
the entering water apnroaches a solution equilibrium at lower temperatures with the solid phases containing sodium, potassium and magnesium sulfates and chlorides.
In the rock salt environment of the deposit higher temperatures will
occur due to the radioactivity of the waste forms.
That is
why an additional
uptake of NaCl by the "standard brines" has to be taken into account.
However,
data concerning this fact are not available. Therefore the intent of the investigations was to determine the additional amount of NaCI which can be dissolved at high temperatures in the so-called Q-solution mentioned below.
EXPERIIMENTAL SET UP The investigations of the quinary system up to 200°C require a transparent apparatus able to stand nressures of t16 bar. The apparatus used is a simplified version of an exnerimental equipment described for other investigations Through an inlet N2 is
led into the Duran-50 glass container to build up a
pressure high enough to prevent its liquid content from boiling. A teflon tube is
inserted into the mixture to provide samnling through a teflon valve.
488 heated in a bath of silicon oil fitted with a thermocouple
The container is for temperature
control and a calibrated thermometer.
Both the oil bath and the
mixtures in the reaction volume can be stirred by a magnetic
stirrer. Heating
devices around the inlet and outlet regions avoid condensation.
EXPERIMENTAL RESULTS The starting point of the investigations was the invariant point Q of the quinary system NaCl-KCl-MgCl
2 -MgSO4-H20
position of this solution (Q-solution)
at 55°C according to D'Ans 2. The comis
given in table 1.
TABLE 1 COMPOSITION OF THE Q-SOLUTION AT 55°C IN g/100 g 1,45
NaCl KCl
4,75
MgCl
26,80
2
1,40
MgSO 4
65,6o
H120
100,00
The other mixtures investigated contain the same amounts of KCl, MgSO 4
and H2 0 but increasing amounts of NaCl.
> 100 g for these mixtures.)
(Thus,
MgCl 2 ,
the total weight becomes
Every mixture was directly weighed into the glass
container and heated within zO,5 h close below the temperature at which complete dissolution was
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