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Liquid Radioactive Wastes Processing

#T-1141


Methods of Decontamination, Utilization, and Deactivation of Liquid Radioactive Wastes

Tech Area / Field

  • ENV-RED/Remediation and Decontamination/Environment
  • ENV-RWT/Radioactive Waste Treatment/Environment
  • ENV-WDS/Waste Disposal/Environment

Status
3 Approved without Funding

Registration date
17.03.2004

Leading Institute
Tajik State National University, Tajikistan, Dushanbe

Collaborators

  • Institut für Radiochemie, Germany, Dresden

Project summary

Liquid radioactive wastes are produced in the result of:
- operation of nuclear power plants (NPP) and atomic submarines;
- conducting nuclear investigations and research works in radiochemical laboratories;
- activity of some medical and biological establishments.

In composition of Liquid Radioactive Wastes, along with radionuclides, are included radioactive colloid particles in ionic state (mainly those of oxides and hydroxides of metals, structural materials), various complex-forming reagents of organic and inorganic nature, surface-active substances, toxic anions, turbine oils, and etc on the background of high concentrations of salts, mainly sodium nitrate.

The most important fission products are the radionuclides: Cs-137; (Sr-90+V-90); V-91; (Sr-95+Nb-95); (Ce-90+Ce-144); (Ru-106+103); Ba-133; (Nb-124+125); Sn-133 and some others. As a result of corrosion of structural materials and in the process of interaction with neutrons may be formed the following radioactive products of corrosion (RPC): Fe-55, Fe-56, Cr-51, Mn-52, Mn-54, Co-60, Co-58, Ni-63, V-48 and others.

Liquid Radioactive Wastes also differ according to their activity levels:


- medium-level – Leaking of a contour, regenerative solutions, solution from equipment deactivation and washings of a contour;
- and low-level – solutions from deactivation of buildings and cloths.

Today one of the most important tasks of physics, chemistry, and ecology is purifying of Liquid Radioactive Wastes from radionuclides and decontamination, utilization, and deactivation of these radionuclides.

It is well known that the Republic of Tajikistan has its own Waste Repository Site (including for Liquid Radioactive Wastes), which has a great need in purifying from radionuclides.

The aims of the Project are:


- determination of nuclide composition of Liquid Radioactive Wastes;
- search of effective methods of Liquid Radioactive Wastes purifying;
- investigation (using coprecipitation-sorption methods and different sorbents) and finding of optimal conditions for concentration and extraction of radionuclides;
- determination of utilization methods for some radionuclides using extraction and chromatographic methods;
- purifying of Liquid Radioactive Wastes from radionuclides, toxic anions and Surface Active Substances, disposal of purified water into drainage system and storage of received sludge-concentrates with other solid radioactive wastes.

These aims may be achieved by the Project participants by the way of investigation of the methods of concentration, extraction and determination of radioactive isotopes of chemical elements using coprecipitation-sorption, extraction, and chromatographic methods of analysis.

Extraction of radioactive isotopes from Liquid Radioactive Wastes may be carried out using the methods of distillation, precipitation, filtering, coagulation, adsorption by different sorbents, ion exchange, extraction, and various combinations of the mentioned methods.

Catching of radioactive mixtures by filtering materials (in %) is: for quartz sand – 72-89; activated charcoal – 92; glauconite – 83; activated alumina – 94. As we can see the usual natural sorbents do not allow to extract properly the radionuclides from radioactive solutions.

During complete purifying of Liquid Radioactive Wastes from radionuclides it is necessary to take into account all the factors, which influence their extraction on storage media, and to find optimal conditions for concentration and extraction of radionuclides. These factors include: colloid-formation state and presence of complex-forming reagents (particularly organic ones like Trilon B, which masks the radionuclides and prevents their sorption by carriers). For proper coagulation of radionuclides are needed: first, collapse of colloid state of radionuclides by reagents-coagulants, and, second, oxidation of organic complexing agents. Organic complexing agents and Surface Active Substances may be collapsed by powerful oxidants (like ozone and mixture of ozone with oxygen, potassium permanganate and other oxidants). In order to have a complete coagulation of catalyst carriers and extraction of radionuclides from the solution it is necessary to precipitate them in the presence of 2-5% ethyl alcohol, which improves coagulation and decreases solubility of inorganic precipitations in water.

Implementation of the project will allow to:


1. determine the nuclide composition and presence of other components in Liquid Radioactive Wastes;
2. propose new inorganic sorbents for effective purification of Liquid Radioactive Wastes from radionuclides;
3. show the optimal conditions for concentrating of radionuclides on catalyst carriers depending from pH medium and presence of saline backgrounds in the solution;
4. determine the conditions of utilization of the most important isotopes by sorption, extraction, and ion exchange methods;
5. show application of natural sorbents of Tajikistan (like aluminosilicate) for group concentrating and extraction of radionuclides;
6. formulate the recommendations for future investigations of Liquid Radioactive Wastes with the purpose of their decontamination, utilization and deactivation.

The results, received under this project, are very important for purification of Liquid Radioactive Wastes from radionuclides and other toxic substances, which in its turn improves the environment. Competence of the project participants is on the high level. The developed methods and preliminary results of investigation on the project theme were published scientific journals and registered as patents (e.g. Rustamov S. Patent N251 TJ, Method of utilization of liquid radioactive waste).

The proposed project will substantially support the fundamental and applied researches in Tajikistan aimed on investigation of sorption processes with organic and inorganic sorbents, which are used for purification of Liquid Radioactive Wastes, extraction of metals from the structure of secondary raw material and natural objects, and for extraction and purification of other chemical compounds.

The role of foreign collaborators in the project will include the following:


- Exchange of information in the process of project implementation;
- Providing comments to the technical reports (semi-annual, annual, and final) to be sent to the ISTC;
- Meetings during different conferences and seminars;
- Possible joint articles for publication in scientific journals.


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