Radwaste Immobilization Using Microspheres
Immobilisation of Long-lived Radionuclides Using Ultraporous Blocks Based on Thermostable Microspheres
Tech Area / Field
- ENV-WDS/Waste Disposal/Environment
- ENV-WPC/Water Pollution and Control/Environment
8 Project completed
Senior Project Manager
Wol'f O V
Khlopin Radium Institute, Russia, St Petersburg
- Siberian Branch of RAS / Institute of Chemistry and Chemical Technology, Russia, Krasnoyarsk reg., Krasnoyarsk\nMining and Chemical Complex, Russia, Krasnoyarsk reg., Zheleznogorsk
- Forschungszentrum Jülich GmbH, Germany, Jülich\nSCK-CEN, Belgium, Mol
Project summaryLong–term activity of the several countries on nuclear weapons fabrication results in the great amounts of accumulated liquid Radioactive Waste (RW) with a wide spectrum of chemical composition and activity levels. Treatment of spent nuclear fuel also makes its contribution into important problem of ecologically safe RW management. New aspect of this problem is the disposition of excess nuclear plutonium in Russia and USA, when new types RW will be also formed.
In spite of that vitrification process of some High Level Waste (HLW) was realized in industrial scale in a number of countries, the development of alternative methods becomes actual to immobilize the various types of accumulated and recently formed RW with taking into account ecological and economical parameters.
One of that approaches is process of using of alumosilicate components of cinder forming, which are close to chemical composition of abyssal rocks. Glass crystalline hollow microspheres (cenospheres) present special interest. They are components of fly ash obtained from the high–temperature torch combustion of coal. Unique combination of such cenospheres properties as: microspherical design (20-500 micrometers), low bulk density (0.3-0.5 g/cm3), high hydrostatic compressive strength (about 20-30 MPa at 50% destruction), thermal stability (Tmelt= 1,300-1,400 °C), chemical stability and low price make cenospheres the perspective RW material for using in liquid RW immobilization technology.
Cenospheres are separated from intermediate products of fly ash into water and porous glass crystalline block is formed on their basis. This block is the primary matrices for RW immobilization (Rus. patent #2165110 “Ceramic Gubka for accumulation and solidification of liquid and extradangerous waste and the method of its production”, Anshits A.G. and others, published in B.I. #10, 2001). Porous matrices functions as a sponge, which is able to absorb a great amount of RW components. This amount depends on a value of open inside volume (or open porosity) and allows realizing RW immobilization process. Volume reduction factors are 5-20 depending on the salt content.
It is believed that the concentration, solidification and immobilization of radionuclides and the mineral components of radioactive and other hazardous waste in ultraporous ceramic blocks are made possible due to the following functional processes:
– absorption of solutions into the block volume by means of capillary forces and high wetting capability of the internal surface;
– water evaporation and its intensive release with the aid of a dry carrier gas at low temperatures (about 25 °C - 60 °C), by static heating into a resistance heat furnace, by hot air heating and also by MW heating;
– repeated absorption of the waste solution with a low salt content to achieve the required loading capacity;
– complete decomposition of salts and safe radionuclides fixation directly in the internal voids of the block at temperatures which are lower than the melting point of the block material;
– subsequent compacting of the block containing RW oxides components at high temperatures in form of glass–like or ceramic material.
Variation of porous matrices parameters (open porosity, apparent density, pores size, compressive strength, chemical and mineral–phase composition), which is demanded to solve appointed tasks and to obtain solidified RW final product, is necessary and can be realized if cenospheres of fixed composition are used. Preliminary experiments showed that stabilized composition and properties of cenospheres could be provided by microspheres separation into the fractions having close values of size, density, magnetic receptivity and definite morphological properties (for example, with perforated and non-perforated walls).
In contrast to existing ISTC project, which uses non-compacting microspheres with different morphology and dispersion, producing condition of matrices in the big block forms will be developed during this project. The special microspherical fractions with stabilized composition and properties, which are prepared as a result of some separation steps using “know–how” technology, will be used to produce these blocks.
The great work was performed in the creative close co-operation with the specialists of Federal State Unitary Enterprise ''Mining and Chemical Combine'' (FSUE MCC), Institute of Chemistry and Chemical Technology, Krasnoyarsk Scientific Centre of Siberian Branch of Russian Academy of Sciences (KSC ICCT SB RAS) and Research and Production Association ''V.G.Khlopin Radium Institute'' (RPA KRI) during Project #1370d performance. World scientific community was informed about prospects of the new material using. Creating of Web site (http://www.atom.nw.ru/rie/projects/gubka/), participation of Russian specialists with reports at International Conferences (“Topseal”, Brugges, Belgium; “Waste Management’00” Tucson, USA; “Prague 2000 Symposium”, Prague, Chech.rep.) built up a wide base of possible international cooperation on this material implementation for RW treatment.
Thus, in frame of direct cooperation with USA specialists the tests of porous matrices were conducted for RW immobilization at INEEL (Idaho, USA), which confirm absolutely their wide possibility to reduce collected liquid waste volumes.
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