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Combustion Mode for Radioactive Waste Immobilization

#3053


The Development of a Method for Fixation and Compaction of Radioactive High-Level Waste in Combustion Mode

Tech Area / Field

  • ENV-RWT/Radioactive Waste Treatment/Environment

Status
3 Approved without Funding

Registration date
22.04.2004

Leading Institute
Tomsk Scientific Center, Russia, Tomsk reg., Tomsk

Supporting institutes

  • Tomsk State University, Russia, Tomsk reg., Tomsk\nInstitute of Problems of Chemical Physics, Russia, Moscow reg., Chernogolovka\nSiberian Chemical Combine, Russia, Tomsk reg., Seversk\nInstitute of Structural Macrokinetics and Material Science, Russia, Moscow reg., Chernogolovka

Collaborators

  • University of Notre Dame / Department of Chemical and Biomolecular Engineering, USA, IN, Notre Dame\nColorado School of Mines, USA, CO, Golden\nFlorida State University / Department of Chemistry and Biochemistry, USA, FL, Tallahassee\nUniversity of Toronto / Institute for Aerospace Studies, Canada, ON, Toronto\nHansung University, Korea, Seoul\nUniversity of Calgary, Canada, AB, Calgary\nUniversity College London / Chemistry Department, UK, London

Project summary

The goal of the project is the development of an efficient method for immobilization and compaction of radioactive high-level waste (HLW) of radiochemical plants.

The method is based on a chemical encapsulation of HLW, namely, the bonding of radionuclides with matrix components into chemical compounds. The main approach to the enhancement of chemical encapsulation efficiency is the organization of two-barrier protection preventing the emission of the radionuclides from the matrix. It is supposed that the transuranic elements demanding for a superprolonged storage will be immobilized in a strong crystalline lattice of the microcrystals. The microcrystals themselves will be contained in a shell of alumosilicate phases, which will create a second additional barrier for radionuclides migration.

In the course of the project realization the matrix materials intended for a solid retention of radionuclides will be created. The retention will be performed via a chemical interaction of the matrix materials with the nanosized oxide compositions of radionuclides, which will be produced using plasmachemical method.

The application of the plasmachemical method for oxide production from the solutions in one stage will allow excluding the operations of the deposition, drying, calcination, grinding, and sizing of the oxides produced.

The process of HLW immobilization will be carried out in combustion mode. In this mode the heating of the reaction mixture and formation of the oxide-silicate melt occur only due to exothermal interaction of the initial components (without external heat source). A high chemical activity of the nanopowders will provide for reaching the thermodynamical equilibrium at their interaction with the melt in combustion mode.

At present the problem of HLW immobilization is solved via vitrification in the furnaces. On the one hand, the aluminophosphate (Russia) and borosilicate (France, Great Britain) glasses do not provide for a prolonged HLW storage due to a high speed of leaching. The method suggested will allow one to exclude this disadvantage. On the other hand, power and materials consumption at the application of furnace technologies, the problem of maintaining a stable mode of melting and safe handling of the melt require for high material expenses to organize the process. The application of the exothermal combustion process to produce the melt will allow one to exclude the power consumption, to reduce the materials consumption and simplify the process equipment as compared to the furnace process of the waste treatment.

The suggested method for immobilization and compaction includes the plasmachemical production of oxides from aqueous solutions; the preparation of the initial powdered mixtures capable of exothermal interaction; the initiation of the chemical reaction in a sealed volume leading to the formation of the oxide-silicate melt; formation of the compact product at melt cooling.

Expected results and their application. The project implementation will result in the development of the method for HLW immobilization and compaction via introduction of disperse materials into exothermal mixtures and for obtaining of a compact product with chemically encapsulated radionuclides. The method will be based on the knowledge on the formation of highly active oxide nanocompositions, on exothermal interactions of the components in powdered mixtures resulting in the formation of the oxide-silicate melt, on the formation of the phase composition, micro- and macrostructure of the solid product during melt cooling, on radionuclides leaching from immobilizing matrices obtained in the course of the project implementation:

In the course of the project implementation:


- a plasmachemical installation for production of radionuclides oxides and their compositions will be modified;
- an installation for the production of the matrices for radioactive materials in combustion mode will be manufactured;
- kinetic regularities and the mechanism of the formation of the oxides and their composition will be studied, their physico-chemical properties will be investigated;
- a mathematical stimulation of the evolution of the structural transformations of the aluminosilicate matrix materials containing the radionuclides will be carried out;
- matrix aluminosilicate materials of the new generation intended for a strong immobilization and prolonged retention of the radionuclides will be developed;
- the compositions of exothermal mixtures for synthesis of the aluminosilicate matrix materials in combustion mode will be developed, the characteristics of the ignition and combustion of such mixtures will be studied theoretically and experimentally;
- the additives for exothermal mixtures for the production of matrix materials containing the radionuclides in the most strongly chemically bound form will be found;
- chemical and phase compositions, the microstructure and mechanical strength of the samples obtained will be determined;
- kinetic regularities governing the radionuclides leaching from immobilizing matrix materials will be studied.

The project anticipates the realization of the following main tasks:

1. Study of the process of oxide powders production from water solutions under the conditions of a low-temperature plasma.


2. Experimental investigation of the process for matrix materials production in combustion mode.
3. Study of the structure and physicochemical properties of the synthetic matrices obtained.
4. Mathematical simulation of the processes of chemical and structural transformations of matrix materials containing radionuclides, and of the processes of ignition and combustion of the powdered mixtures used to synthesize matrices.
5. Preparation and justification of the recommendations for further technological development of the process of solidification of radioactive waste using plasmachemical technology and synthesis in combustion mode.

The scientific value of the project is in the investigation of kinetic regularities governing the formation of the nanopowders and their physicochemical properties; on the basis of the mathematical models developed the dynamics of chemical, phase and structural transformations in aluminosilicate matrix materials containing radionuclides will be quantitatively evaluated, the mechanism of ignition and combustion of the heterogeneous “metal-oxidizer-additives” systems will be studied theoretically and experimentally, the influence of structural peculiarities of oxide films covering the surface of metal powders on this mechanism will be revealed.

The practical value of the project is determined by its final target, i.e., the development of the method for immobilization and compaction of radioactive high-level waste in combustion mode using the plasmachemical method to produce the initial components of the charge as well as by the formulation of physicochemical concepts on the principles of the selection of aluminosilicate materials providing for the lowest rates of radionuclides leaching.

It is expected that a team consisting of various specialists will participate in the project. Previously this team has successfully collaborated in the activities connected to the development of the technologies for nuclear materials processing, to the development and production of solid propellants. The personnel of the Tomsk Scientific Centre of the Siberian Branch of the Russian Academy of Sciences (RAS), Siberian Group of Chemical Enterprises, Tomsk State University, Institute of Structural Macrokinetics and Material Science Problem of RAS, Institute of Physical Chemistry Problems of RAS are high-skilled researchers in the field of development of plasmachemical technology and technology of radioactive materials handling, ignition and combustion of condensed systems, physical chemistry of high-temperature processes, kinetics of heterogeneous processes.


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