Leaching studies of137Cs from ion-exchange resin incorporated in cement or bitumen

Leaching of¹³⁷Cs from ion-exchange resin incorporated in cement and bitumen composite using two methods based on theoretical equations has been developed. These were: Method I, diffusion equation derived for a plane source model¹ and Method II, empirical model employing a polynominal equation^2,3. Results presented in this paper are examples of data obtained in a cement and bitumen testing project which will influence the design of a future radioactive waste storage center.     

Study of the 137Cs adsorption performance of ion-eroded cement

For this study, ion-eroded cement was prepared from the cement required for construction of middle- and low-level radioactive waste repositories in caves. The properties for adsorption of ¹³⁷Cs on cement before and after ion erosion were investigated. XRF, XRD, SEM–EDS and BET were used to analyse various cement materials. The effects of reaction time, solid–liquid ratio, initial radioactivity and different ions on adsorption were studied by static batch experiments. When the initial radioactivity was 1114.5 Bq L^?1 and the solid–liquid ratio was 5 g L^?1, the adsorption equilibrium time was 12 h. Adsorption of ¹³⁷Cs on ion-eroded cement was more effective than that on untreated cement. The adsorption process was consistent with the pseudosecond-order kinetic model and the Freundlich isotherm model, and the process involved multilayer chemisorption. This study provides basic research data for construction of a disposal repository.

     

Comparative interpretation of leaching137Cs from radwaste sludge immobilized in cement

This paper presents results from studies made to determine the leachability of¹³⁷Cs from immobilized evaporator sludge from a Pressurized Water Reactor with cement. Leaching of¹³⁷Cs from cement matrix using three methods based on theoretical equations has been developed. These were: Method I, diffusion equation derived for a plane source model, Method II, rate equation for diffusion coupled with a first-order reaction. The leaching data were also analyzed by an empirical method employing a polynomial equation —Method III. Results presented in this paper are examples of data obtained in a cement testing project which will influence the design of a future radioactive waste storage center.     

Modeling of the sorption behavior of 137Cs in soils

A model has been used, based on the simultaneous occurrence of the sorption and desorption processes, to describe the sorption behavior of ¹³⁷Cs in soils in Hong Kong reservoir. By fitting the experimental data with a single parameter, relatively constant sorption and desorption rate constants were obtained. The theory also provided an estimate on the number of sorption sites for different masses of soils. Attempts have been made to explain the findings for different types of soils. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of curing time on the fraction of137Cs leached from cement matrix

To assess the safety of disposal of radioactive waste material in concrete, curing conditions and time of leaching radionuclide¹³⁷Cs have been studied. Leaching tests in concrete were carried out in accordance with a method recommended by IAEA¹.     

Comparative interpretation of leach rate of137Cs and60Co from cement matrix

A technique for leaching¹³⁷Cs and⁶⁰Co from a cement matrix, using three methods based on theoretical equations, has been developed. These were: Method I, diffusion equation derived for a plane source model, Method II, rate equation for diffusion coupled with a first-order reaction. The leaching data were also analyzed by an empirical method employing a polynomial equation, Method III. Results presented in this paper are examples of data obtained in a cement testing project which will influence the design of the future radioactive waste storage center.     

Extraction-chromatographic separation of137mBa from137Cs

The possibilities of extraction-chromatographic separation of^137mBa from¹³⁷Cs in genetic succession were studied, using columns filled with support beads loaded with the extractant H⁺[)–(3)–1,2–B₉C₂H₁₁]₂Co^–, further referred to as dicarbolide-H⁺, in nitrobenzene. The dependence of the amount of separable activities on experimental conditions was established. Optimal conditions were selected for the separation process. The effects of isotopic and nonisotopic carriers of^137mBa on the separation and the degree on saturation of extraction-chromatographic column with Ba²⁺ ions were evaluated. The effects of acidity of the elution solutions, of flow-through velocity, the amount of elution solution and the quality of carrier beads on the separation process were assessed. The extraction-chromatographic yield was calculated and the number of possible repeated elution cycles for^137mBa with saline and some other eluents was determined.     

Rapid determination of 137Cs in environmental samples--purification of 137Cs by ammonium molybdophosphate column separation]

A rapid method for the determination of 137Cs in environmental samples was proposed. The principal technic employed in this study is based on column separation of 137Cs using ammonium molybdophosphate mixed with glass fiber to eliminate contribution of natural radionuclides such as 40K and 87Rb. The separation of cesium from potassium and rubidium was performed by the elution with 0.5m ammonium nitrate solution. The time required for separation of cesium was five hours as compared with the conventional cation exchange separation which required thirteen hours. The chemical yield of cesium carrier was normally more than 90 percent. The results obtained were compared with that by the conventional methods using Bio-Rex cation exchange separation and the good agreement between the two methods was obtained.     

The biological half-life of137Cs in snails

The biological half-life of¹³⁷Cs in snails Helix pomatia after a single administration of contaminated diet has been investigated. The calculation was based on the retention of¹³⁷Cs in snails in vivo. It was found that loss of cesium from snails can be explained by a two-exponential retention curve leading to biological loss constants _{B 1}=0.27 d^–1 and _{B 2}=0.024 d^–1, which correspond to biological half-lives of T_{B 1}=2.5 d and T_{B 2}=28.5 d respectively. The equation describing the retention of¹³⁷Cs in snails is also presented.     

Leaching behavior of some radionuclides from cement matrix incorporating exhausted polymeric resins

Exhausted poly(acrylamide-acrylic acid) impregnated with zirconium phosphate {P(AM-AA)-ZrP} produced from the treatment process of radioactive liquid waste was incorporated in different types of cement to prevent widespreading of radionuclides into the human environment. The rates at which ⁶⁰Co, ⁶⁵Zn and ^152,154Eu are leached from Ordinary Portland Cement (OPC) and Blast Furnace Slag Cement (BFSC) were measured. From the leaching data the leach coefficients of ⁶⁰Co, ⁶⁵Zn and ^152,154Eu were determined and were found to vary between 1.62^.10^-8 to 7.06^.10^-10 cm²/day and 1.01^.10^-8 to 8.93^.10^-9 cm²/day in OPC and BFSC, respectively. In general, the radionuclide leaching rates followed the order: ^152,154Eu>⁶⁵Zn>⁶⁰C o. The leach coefficient was found to be dependent on the composition of the leachants and varied in the order: distilled water > ground water > synthetic sea water. The effect of NaNO₃ concentration in the wastes on the leach coefficient of ⁶⁰Co from OPC was also studied     

Separation of 137Cs from nuclear waste

Sodium zirconate is one member of a family of new inorganic ion exchange materials which have high affinity for all actinides and fission product cations except for Cs⁺. A combination of cold, tracer and high level liquid waste experiments with sodium zirconate has shown that 70–80 and 80–100% of the Cs⁺ in high level liquid waste remains in solution following batch or column equilibration, respectively. The fact that ¹³⁷Cs can be obtained in relatively pure form permits subsequent conversion directly to an insoluble radiation source. This is of prime importance in areas such as sewage sludge sterilization via γ-ray irradiation.     

Extraction of137Cs by cobalt dicarbolide

The possibility of the use of chlorinated cobalt dicarbolide, H⁺C₄B₁₈H₁₅Cl₇Co⁻, it nitrobenzene for the selective extraction of¹³⁷Cs from mixtures of⁹⁵Zr−⁹⁵Nb,¹⁰⁶Ru-¹⁰⁶Rh and¹⁴⁴Ce was studied. The effect of aqueous phase acidity on the distribution ratio of Cs, Ru and Zr as well as the effect of the amount of isotopic and non-isotopic carriers of alkali metals on the distribution ratio were determined. Separation factors for cesium from ruthenium, zirconium and cerium were calculated, all being extracted from nitric acid solutions. The efficiency of cesium separation was verified by gamma-spectrometry.     

Retention of137Cs by algal polysaccharides

The retention of¹³⁷Cs in algal polysaccharides has been studied. Alginic acid showed higher retention value than the tested alginate samples. The retention of¹³⁷Cs in carrageen types and agar was first investigated. The binding capacities were found to be equal for carrageenan types and agar.     

Adsorption of 137Cs on titanate nanostructures

Various types of sodium and potassium titanate nanostructures (nanotubes, nanofibers, nanoribbons, nanwires) were synthesized and characterized by X-ray diffraction, SEM and TEM, as well BET and BJH methods. Adsorption of radiotracer ¹³⁷Cs⁺ ions from aqueous solutions on synthesized titanate nanostructures was investigated in batch technique as a function of contact time, concentration of sodium ions and pH of the solutions. It was found that among the studied nanostructures nanotubes shows the highest selectivity for ¹³⁷Cs, which is related to a zeolitic character of Cs⁺ adsorption. The efficient adsorption of ¹³⁷Cs was obtained in Na⁺ solutions with concentration below 10^?2 M, at pH 7–9 and in contact time above 2 h. Moreover, nanotubes have the higher specific surface area than other nanostructures, which results in better availability of ion exchange groups and high ion exchange capacity. These properties of nanotubes indicate that they may be used for adsorption of ¹³⁷Cs from various types of nuclear wastes.     

Transfer of 137Cs and stable Cs in soil-grass-milk pathway in Aomori, Japan

The soil-to-grass transfer factors and grass-to-milk transfer coefficients were determined for ¹³⁷Cs and stable Cs in soil, grass and milk samples collected in Aomori Prefecture, Japan. The concentrations of ¹³⁷Cs in the soil and grass samples collected from 25 sampling sites were 13±12 Bq.kg^-1 and 2.0±2.1 Bq.kg^-1 dry wt., respectively. The geometric mean of soil-to-grass transfer factor of ¹³⁷Cs was 0.13 and its 95% confidence interval was 0.017-0.98. The transfer factor of ¹³⁷Cs was higher than that of stable Cs, and they had a positive correlation. The concentration of K in the soil affected both transfer factors. The concentration of ¹³⁷Cs in milk samples collected from 16 sites was 76±43 mBq.kg^-1 fresh wt. and had a good correlation with that of stable Cs. The geometric mean of grass-to-milk transfer coefficient of ¹³⁷Cs was 0.0027, assuming that a cow's total daily intake was 20 kg of dry grass. The transfer coefficient of ¹³⁷Cs was positively correlated with that of stable Cs.     

Mobilization and fractionation of137Cs in calcareous soils

Mobility of¹³⁷Cs was investigated in columns of calcareous loam and clay soils leached under river water, NH₄OAc, KCl, CaCl₂, and EDTA. Fractionation of Cs into ten sequential fractions was accomplished in the leached soils as well as in soil samples received carrier-free¹³⁷Cs and incubated for 60 d. At the end of 90 d of leaching with river water and CaCl₂, the bulk of Cs applied (>97%) was found to remain in the upper 1 cm of soil columns. On the other hand, the reduction in Cs concentration was approximately 30% with NH₄OAc, 18% with KCl, and 10 to 25% with EDTA. The major soil constituents appeared to be responsible for retaining Cs were clay, silt, and Fe oxides. The leaching consistently increased the magnitude of fractions bound to clay minerals and in most cases decreased the fractions of water soluble, exchangeable, carbonate, and organic matter.     

Translocation and depuration of137Cs in tea plants

Translocation and percent distribution of¹³⁷Cs in different parts of the tea plant have been investigated from the foliar aborption and root uptake in Chemobyl contaiminated soil during 1987–1994. The results showed that the transfer of the radionuclide from soil to the plant occurred only in the roots during this long period. On the other hand, the present data confirmed that the new leaves of the plant directly accumulated¹³⁷Cs from the stem in growing seasons after translocation into the stem from leaves during the Chemobyl accident. The natural depuration rate of¹³⁷Cs in the stem part of tea plant is estimated as on effective half-life 1750 days.