Krasin V.P., Soyustova S.I.
Federal State Educational Institution of Higher Professional Education "Moscow State Industrial University", Moscow, Russia
The use of liquid low melting point metals as coolants for nuclear reactors, particularly sodium, has led to a growing interest in the solution chemistry of these liquids to further the understanding of many of corrosion problems encountered in their use. A detailed knowledge of the thermochemical data on Na-O-H system is needed for utilization of steam/water leak detecting systems since they function by measuring the hydrogen activity in sodium and this is influenced by the oxygen which is also introduced during these leaks. A procedure for calculating the thermodynamic activity coefficients of oxygen and hydrogen in dilute Na–O–H system melts in the temperature range 300–600°C was suggested. The thermodynamic activity coefficients of hydrogen in liquid sodium calculated by the coordination-cluster model equations were used to determine the equilibrium hydrogen pressure over melts. The equations of the coordination cluster model are useful to provide understanding of a relationship between thermodynamic properties and local ordering in the melt. The model allows to estimate the fraction of oxygen atoms in the configuration of definite type and, thus enables to make the conclusion about cluster composition of the melt. The calculation results were compared with theexperimental partial hydrogen pressures over the Na(excess) - Na2O-NaH system at XO=XH. The calculated valueswere in qualitative agreement with the experimental data.
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