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Treatment of Liquid Radioactive Waste with Organic Components

#B-567


Development and Test of Technology for Treatment of Liquid Radioactive Waste Containing Organic Substances

Tech Area / Field

  • ENV-RWT/Radioactive Waste Treatment/Environment

Status
3 Approved without Funding

Registration date
02.08.2000

Leading Institute
Institute of Radioecological Problems, Belarus, Minsk

Supporting institutes

  • Khlopin Radium Institute, Russia, St Petersburg

Collaborators

  • University of Thessaloniki / Department of Chemistry, Greece, Thessaloniki\nSCK-CEN, Belgium, Mol\nNational Academy of Sciences / National Research Council, USA, DC, Washington\nAEA Technology, UK, Didcot\nUniversity of Reading / Chemistry Department, UK, Reading\nIdaho National Engineering and Environmental Laboratory, USA, ID, Idaho Falls

Project summary

The aim of the Project is to develop an advanced technological solution for the problem of mixed radioactive waste treatment. Development of the technology will involve:

– Development of combined method (оzonization and biochemical destruction) and search for optimal conditions for destruction of organic compounds in solution;

– Development of effective methods for removal of radionuclides from solution, containing residual quantities of organic substances, on the basis of scientific data on specification of radionuclides in aqueous solution.

At present, there are two principal ways for treatment of Liquid Radioactive Wastes (LRW). In Russia and countries of the CIS the most widely used at method NPPs is evaporation. However, this method involves a high consumption of energy and, hence, is expensive. Also, the degree of evaporation is limited - concentration of salts in solution has to be not higher than 400-450g/l. So, this method has limitations in terms of future development. Alternative methods for removal of radionuclides involve such principal operations as chemical sedimentation, coagulation and sorption on ion-exchange resins. Behavior of radionuclides in these processes is largely determined by their distribution between various complex forms in solution, since every such form has inpidual physic-chemical properties. Consequently, the more profound our knowledge becomes on the composition, structure, thermodynamic stability of radionuclide complexes, and the behavior of each complex form in the extraction processes, the more efficient one may expect technological schemes to be.

Maintenance of installations for LRW treatment shows that the presence of organic compounds in LRW sharply decrease the efficiency of sorption and coagulation processes and, also, worsen the quality of solution after evaporation, because of foam formation and changes in solution surface properties. Despite the fact that there are a number of processes, currently used for destruction of organic complexes (ozonization, chemical destruction, photocatalytic destruction, biochemical destruction, UV-destruction), there are no sufficiently developed technological solutions and installations for treatment of LRW containing substantial amounts of organic substances.

A novel method – combination оf ozonization and biochemical destruction - is proposed for solution of the first task - destruction of organic compounds in aqueous solution. A preliminary study (Radievy Institute) has shown that this method has great potential.

In the framework of this task a laboratory study will be carried out on destruction of a series of organic compounds. This study will include the search for an optimal combination of ozone and biochemical destruction methods and optimal conditions for destruction of each organic compound separately or several compounds together. We understand ‘optimal’ conditions to be when organic matter undergoes not complete destruction but only a level of concentration, whereby it does not hinder removal of radionuclides from solution. Also, new variants of ozone and biochemical destruction of organic compounds, combining the processes of homogeneous/heterogeneous catalysis and film regime of ozonization, will be studied.

The idea of our approach to solve the second task – removal of radionuclides from solution – is to maximally use the physic-chemical properties of various species, in the form of which radionuclides can be present in solution. Work on this task will be based on previously obtained data on the state of radionuclides in aqueous solution (by one of the groups (IREP). In addition, further studies will be performed on the specification of radionuclides (Fe, Cr, Co, Mn, and some others) in aqueous solution and regularities of their sorption behavior on different absorbers. Special attention will be paid to the change of mononuclear and polynuclear hydroxocomplex sorption activity with destruction of organic substances.

It is foreseen that as a result of this study such conditions will be found for all investigated radionuclides, with the highest sorption ability or in a colloidal (pseudocolloidal) form, which can be easily extracted from solution by centrifugation or filtration through a semipermiable membrane.


At the final stage of this project technological schemes, developed by the groups, will be united. Two versions will be considered for removal of radionuclides from solution– sorption-filtration and sorption-centrifugation (in-flow centrifugation). The developed technology will be tested at a pilot installation (Radievy Institute), using real LRW from Leningrad NPP.


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