Transfer from Light to Heavy Water

TABLE 5.2 Factors, AG Water Structural Entropy A j 5j/JK- moI and Structural Heat Capacity mol- Effects [51] and the Changes of the Hydrogen Bond Geometrical hb(i), of Representative Ions [53]  

This approach was apphed by Marcus and Ben-Naim [57] to ionic solutes X=I , but the experimentally measurable quantities, such as solubilities and EMF data, yielded rather unsatisfactory data for electrolytes [53]. Based on the assumption that the value is equal for K+ and Cl, the best available values at 25°C 

The effects of the ions on the structure of the water were then described by Marcus [51, 53] as the ratios AG bj, = A i °according to Equation 5.13. The water stracture effects of ions according to this approach are shown in Table 5.2 — structure makers having positive values and structure-breakers negative values. These results are unsatisfactory, due to the inaccuracy of the AjU,°° ° data, making the divalent cations Ba and Cd appear as strong water-structure breakers and LP as a mild structure breaker, contrary to aU other information concerning these ions. The available data for the nine alkah metal and hahde ions appear to be the most accurate, and their correlations with other quantities that describe the water structural effects of ions are  

Here A een is the difference in the strengths of the hydrogen bonds in D2O and H2O and AGhb is the change caused by the introduction of a particle of S in the average geometrical factors over all the configurations of the N water molecules of either kind  

Experimentally measurable quantities, such as solubilities, EMF data, etc., yield A/us° of Eq. (3.23) and the sublimation enthalpies of the D2O and H2O ices yield A °6hb values. Hence, AGhb, the effect of the solute S on the (hydrogen bonded) structure of water, can be determined. Non-ionic solutes, such as argon or methane, have positive values of AGhb (Ben-Naim 1975) and are known from several approaches to enhance the structure of water, diminishing with increasing temperatures. This is expected from the structure of water being diminished in this direction (Table 1.6). 

Marcus and Ben-Naim (1985) applied this approach to ionic solutes S. Unfortunately, the data for electrolytes are rather unsatisfactory and there are no 

Structure breaking ions E, I3-, 004-, Br04-, IO4-, Mn04-, TCO4-, Re04-, AuCL, , -1.1 

23) the geometrical hydrogen bonding parameters for the ions that describe their effects on the structure of the water. These may be taken for correlations with other quantities that describe the water structural effects of ions that are better established, such as Bi, and Astruc-5. The resulting expressions, calculated with = — 929 J mor are  

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Vesala, A. (1974) Thermodynamics of transfer of nonelectrolytes from light to heavy water. I. Linear free energy correlations of free energy of transfer with solubility and heat of melting of a nonelectrolyte. Acta Chemica Scand. A28, 839-845. 

Vesala, A. (1973) Thermodynamics of Transfer of Electrolytes from Light to Heavy Water. Ph.D. Thesis, University of Turku, Turku, Finland. 

Some work has been done on the rates of acid catalyzed reactions in various mixtures of light and heavy water, but it has not been possible to develop a useful criterion for choosing among different mechanisms. On the other hand, interesting results have been obtained on the dependence of the rate on the composition of the H2 O—D2 O mixture, the influence of the different isotope fractionation equilibria, and the role of activity coefficients of transfer of ions from light to heavy water [119—125]. 

The use of light water requires a compromise between neutron balance, general performances of the system and difficulties related to heat transfer and control problems. Characteristics are proposed and discussed, from the standpoint of continuity with respect to heavy water cooling. 

The aqueous raffinate from the first extraction cycle of light-water reactor (LWR) fuel reprocessing has an original volume of up to 5 m /MT of heavy metal. It is concentrated by evaporation, and the residues of the evaporated raffinates from further extraction cycles may be combined with the concentrate. The result of these operations is the HLW concentrate that wiU be transferred to the waste management section of the reprocessing plant. 

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