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  • Author or Editor: I. Plećaš x
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Abstract  

Transport phenomena involved in the leaching of a radioactive material from a concrete composite matrix into surrounding water are investigated using three methods based on theoretical equations. These are: a diffusion equation derived for a plane source model, a rate equation for diffusion coupled with a first-order reaction and an empirical method employing a polynomial equation. The results are compared with respect to their applicability to the 137Cs leaching data. The results presented in this paper are part of those obtained in a 25-year mortar and concrete testing project which will influence the design of radioactive waste management for a future Serbian radioactive waste disposal center.

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Summary  

Leach characteristics of 137Cs and 60Co radionuclides from spent mix bead ion exchange resins and both ordinary Portland cement and cement mixed with two kind of natural sorbents (bentonite and clinoptilolite) have been studied using the International Atomic Energy's (IAEA) standard leach method. The waste immobilization performance of low-level wastes in natural sorbent mixtures was determined. The solidification matrix was a standard Portland cement mixed with 290-350 (kg/m3) spent mix bead exchange resins, with or without 1-10% of bentonite or/and clinoptilolite. The leaching rates from the cement-bentonite matrix were measured after 300 days as 60Co: (1.20-9.72) . 10-5 cm/d and 137Cs: (1.00-9.22) . 10-4 cm/d. From the leaching data, the apparent diffusivity of cobalt and cesium in cement-bentonite or/and clinoptilolite matrix with a waste load of 350 kg/m3 of spent mix bead exchange resin was calculated as 60Co: (1.0-5.9) . 10-6 cm2/d and 137Cs: (0.48-2.4) . 10-4 cm2/d. The compressive strength of these samples is determined according to the ASTM standards.

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Summary  

Leach characteristics of 54Mn and 85Sr radionuclides from ordinary Portland cement have been studied using International Atomic Energy’s (IAEA) standard leach method. The retardation factors, K F, and coefficients of distribution, k d, have been determined using a simplified mathematical model for analyzing the migration of radionuclides. The lowest leaching values after 60 days were achieved in samples with 5% of vermiculite. Results presented in this paper are the examples of results obtained in a 10 year mortar and concrete testing project, which will influence the design of the engineered trench system for a future central Serbian radioactive waste storage center.

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Abstract  

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.

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Abstract  

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.

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Abstract  

Results are presented of a series of experimental tests performed to determine the influence of matrix characteristics on the leaching mechanism of copper aluminium oxychloride immobilized into cement matrices. The objective of this research was to investigate the leaching mechanism of copper as a constituent of copper aluminium oxychloride (CAOX).

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Abstract  

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 equation2,3. 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.

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Abstract  

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.

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Abstract  

To assess the safety of disposal of a radioactive waste-cement composite, the leaching of137Cs from a waste composite into a surrounding fluid has been studied. Leaching tests were carried out in accordance with a method recommended by IAEA.1 The leachability was measured as a function of bentonite clay to cement ratio. The fraction of137-Cs leached from a specimen of Portland cement is 0.03–0.13 at a leaching time of 400 d. Results presented in this paper are examples of data obtained in a 10 y mortar and concrete testing project, which will influence the design of the engineered trench system for a future Yugoslav radioactive waste storage center.2,3

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Abstract  

Determination of retardation factors and coefficients of distribution using a simplified mathematical model for analyzing the migration of leachate and radioactive material contained in radioactive waste burial concrete trench systems has been developed. Results show that concrete for engineered trench systems secures radionuclide preservation in solidified medium for longer than 300 years. These results will be used for constructing future radioactive waste storing centers in Yugoslavia.

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