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  • Author or Editor: V. Jedináková-Křížová x
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Abstract  

This report identifies a number of mechanisms that retard radionuclide migration, describes methods that are used to study such retardation phenomena and evaluates the extent to which this methods may be used to diagnose radionuclide migration through various types of geologic media. A qualitative, quantitative and applicable basis for ion exchange modelling in clay have provided. Caesium and strontium are taken as a reference elements, and itsK d values obtained from both batch and diffusion experiments are explained and independently predicted by the model.

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Abstract  

Quality of several vitrified radwastes specimens was demonstrated on their hydrolytic resistance. The type of water corrosion mechanism and structural features were also elucidated. The time dependence of the corrosion process proved two subsequent mechanisms of water attack. The first stage is controlled by diffusion. Later the silicate matrix is damaged and its surface layer dissolved. Ultimately, the quality of glass is evaluated from the point of view of possible radioactivity releases.

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Abstract  

The mechanisms of transport and retaidation processes, chemistry and migration behaviour of radionuclides of fission products and actinides in engineered barriers, especially bentonites, have been summarised. A “critical group of radionuclides” is proposed for thorough investigation of their retardation properties in natural sorbents. The evaluation of accessible data of retardation and transport parameters relevant for the conditions of underground deep repository to be projected is carried out from point of view their possible inclusion into a data-bank. The effect of solubilities and dissolution reactions, diffusion and sorption/desorption, complexation and variations in the aqueous phase composition, pH-value and oxidation-reduction properties and other phenomena on Kd values is discussed. Attention is devoted to thermodynamic modelling and its validation for evaluation of various phenomena in the buffer/backfill-ground water systems.

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Abstract  

Selectivity of the isotope dilution analysis with substoichiometric separation for silver determination in platinum has been investigated. From dilute sulfuric acid in the presence of hydroxylamine sulfate silver can be extracted with substoichiometric amount of dithizone in chloroform.

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Abstract  

Selectivity of isotope dilution analysis with substoichiometric separation for caesium determination has been investigated. Caesium can be extracted with a substoichiometric amounts of bis 1,2-dicarbollylcobaltate in nitrobenzene in the presence of dibenzo-18-crown-6. The method is selective. Other metal ions (K+, Na+, Mg2+, Ca2+, Fe3+, Al3+) do not interfere.

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Abstract  

The conditions for the synthesis of rhenium compounds (pH, reaction time, concentration of reducing agent) have been determined previously by thin-layer chromatography. A Britton-Robinson buffer solution has been selected as a carrier electrolyte due to its possible use in a wide interval of pH, mainly at optimal pH for the formation of the complexes studied. The same electrolyte has been previously applied also in case of the study of rhenium and technetium complexes by polarography. The electrophoretic experiments have been carried out under both standard and reverse polarities with direct UV detection at the wavelength 214 nm and 20 °C. The signal of perrhenate has been observed at the reverse polarity (outlet+, inlet–), of reduced rhenium [probably Re(IV)] under normal polarity. The formation of rhenium complexes with EDTA has been shown by lowering of the cationic rhenium signal due to the addition of the ligand. The rhenium complexes with EDTA are observable at reverse mode of CE. The formation of rhenium complexes with HEDP (hydroxyethylidenediphosphonic acid) has been studied in two different carrier electrolytes — 40 mM Britton-Robinson buffer solution and 50 mM phosphate buffer with 20 mM HEDP. The mechanism of perrhenate reduction by stannous chloride and of the formation of rhenium complexes with EDTA has been determined. The necessity of the presence of ascorbic acid as an antioxidant in the reaction mixture at different pH values has been described as well.

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Abstract  

The effect of the pH of the aqueous phase on the sorption of134Cs,85Sr,125I and99Tc radionuclides has been investigated. Different types of bentonites from north-western Bohemia 85 in mixture with quartz sand have been used for the experiments with134Cs and85Sr. ThK d values have been determined using a batch method. The effect of the redox potential Eh on the sorption of radionuclides and the speciation of radionuclides125I and99Tc has also been investigated. Polarography has been used for speciation of the radionuclides.

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Abstract  

Sorption and diffusion processes with134Cs and85Sr in natural bentonites have been investigated. The distribution coefficients (K d) have been determined by a batch method. Various factors affecting theK d value as water-to-bentonite ratio, concentration of the competitive cations in the aqueous phase or bentonite-to-sand ratio in the mixed sorbents have been evaluated. A comparison of the sorption and diffusion data has been made.

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Abstract  

The isotope dilution with substoichiometric separation for the determination of strontium has been investigated. Strontium can be extracted with a substoichiometric amount of bis-1,2-dicarbollylcobaltate in nitrobenzene in the presence of 15-crown-5. It has been found, that Li+, Mg2+, Ca2+ and Fe3+ do not interfere in the strontium determination but the high extraction of K+, Na+ and NH4 + ions results in marked influence.

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