Immobilization of radioactive elements

Solid State Reaction - Hexaaluminates have been long known as interesting materials for many applications (electrical ceramics, matrices for permanent immobilization of radioactive elements from nuclear wastes and refractory cement and concrete). For many years ceramists prepared hexaaluminates via solid state reaction for both crystallographic and application purposes.6... 

It is necessary to install air filters in the rimning nuclear power plants with the special aim to adsorb effectively radioactive iodine vapors emitted upon malfunctions of the nuclear power plants. The normal or minor malfunction of nuclear power plants may result in the generation of considerable amounts of radioactive elemental and small amoimts of organic iodine vapor or dust. The iodine waste, due to being fission intermediates, is the primary target for effective entrapment and immobilization to prevent the spreading of nuclear contaminants. If iodine can be effectively immobilized, then the majority of radioactivity remains localized. 

The stabilization of the nuclear waste products is usually performed by immobilizing the oxides of the radioactive material in glass. This process is known as vitrification. The environmental aspects of storing large quantities of radioactive glass logs are related to the leachability of the elements from the glass structure. 

For instance, the structural chemical approach was used to elaborate such crystalline materials as ceramics for immobilization of actinides and other dangerous elements and isotopes present in radioactive waste. The approach was efficient in modelling new lanthanide phosphates of framework NZP-type structure [94, 95] and of the langbeinite structure type [97-101]. 

The studies on the immobilization of heavy metals in concrete have been developed for the last 20 years [316-320]. It has been found that the concrete is a very effective heavy metals immobilizing matrix. The combinations with AFm phases are formed these phases have a layer stracture and the exchange of OH ions with monovalent and bivalent anions is possible [317]. The strong adsorption on C-S-H gel is an important factor, and morphology of this phase is markedly modified [318]. Cement with zeolites addition can be applied to immobihze the radioactive elements [319]. Special cement with high aluminates content has shown high effectiveness for heavy metals immobilization [320]. 

Further evidence for the ability of chemical processes within the shale to retard important radionuclides, is provided by the distribution of Ce and Ba. These elements are chemical analogues for the radiologically important elements Th and Ra respectively, which are important constituents of many radioactive wastes. The elevated levels of Ce and Ba in the shale matrix, compared to the levels in the calcite veins (Table 2) may be evidence that these elements were relatively immobile during the formation of the calcite veins. An implication is that Th and Ra would also have been relatively immobile under these conditions (undisturbed far-field conditions). Such investigations require, however, better characterization of the mineral sinks for Ba, Ce and other trace elements, and determination of the calcite crystallization mechanisms. 

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