PHYSICOCHEMICAL CHARACTERISTICS OF URANIUM MICROPARTICLES COLLECTED AT NUCLEAR FUEL CYCLE PLANTS. Abstract

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1 IAEA-SM-367/10/05/P PHYSICOCHEMICAL CHARACTERISTICS OF URANIUM MICROPARTICLES COLLECTED AT NUCLEAR FUEL CYCLE PLANTS G. Kaurov, V. Stebel kov, O. Kolesnikov, D. Frolov Laboratory for Microparticle Analysis Moscow, Russian Federation Abstract In the framework of the Russian Support Program [1] as well as under elaboration of Atlas of Uranium Microparticles from Industrial Dust at Nuclear Fuel Cycle Plants [2] there was carried out investigation of shape, size, surface structure, elemental and isotopic composition of uranium microparticles collected at nuclear fuel cycle plants. There is shown that isotopic composition of uranium in microparticles as well as morphology of particles characterizes the types of nuclear activity. 1. INTRODUCTION Any industrial process is accompanied by appearance of some quantity of microparticles of processed matter in the environment in immediate proximity to the manufacturing object. The quantity of these particles depends on many factors: type of process, type of matter, measures against migration of industrial dust. However there is not possible practically to eliminate the diffusion of these little particles at industrial sites as well as outside of these sites. The determination of characteristics of industrial dust microparticles at nuclear fuel cycle plants: form, size, structure of surface, elemental composition, isotopic composition, presence of fission products, presence of activation products, in conjunction with the ability to connect these characteristics with certain nuclear manufacturing processes can become the main technical method of detecting of undeclared nuclear activity. 2. POINTS OF SAMPLES COLLECTION The greatest dangers of proliferation of nuclear weapons are connected with production and using of highenriched uranium as well as of plutonium-239. Therefore among all types of nuclear plants the particular control must be propagated to the enrichment plants, fuel fabrication plants and reprocessing plants. The investigated uranium microparticles can be divided on following groups in correspondence with points of sample collection: 1) aerosol microparticles from region of a mining of uranium ore; 2) microparticles of industrial dust from enrichment plants; 3) microparticles of industrial dust from fuel fabrication plant; 4) microparticles from a hot cells of nuclear facilities. 3. PHYSICOCHEMICAL CHARACTERISTICS OF PARTICLES All investigated aerosol uranium microparticles in the regions of uranium ore mining are characterized by an extremely irregular form with surface type such as debris or scales. The sizes of an overwhelming majority of the particles collected in immediate proximity to a ventilating air-gusher of the mine are within tens of microns, mainly from 10 m to 50 m.

2 2 As a rule, these particles are composite and are represented by agglomerates of micron-sue objects of irregular form. The particles collected at 15 kms distance from the mine are within units of microns mainly from 2 m to 3 m, and have the form of scales. All aerosol uranium microparticles in the regions of uranium ore mining include oxygen and silicon besides uranium, and almost all include calcium, aluminum and iron. Isotopic composition of uranium in all these particles is natural, of course. On the photo 1 and 2 there are shown the particles concerned to two widely distributed types of particles in the regions of uranium ore mining. The surfaces of these particles are such as scale and such as debris accordingly. The photos are made with using scanning electron microscopy in regime of registration of secondary electrons. Photo 1. Aerosol uranium microparticle from the regions of uranium ore mining Photo 2. Aerosol uranium microparticle from the regions of uranium ore mining Presence of spherical uranium microparticles with fluorine and oxygen in samples, collected at the plant or near the plant, specifies the process of uranium isotopes separation in a uranium hexafluoride. Most of these spherical particles have sizes from 1 m to 2 m. Such typical particle is shown on photo 3.

3 3 Photo 3. Spherical uranium microparticle of industrial dust from uranium enrichment plant. Often in samples, collected at enrichment plants using gaseous technologies, conglomerates of spherical particles are found (photo 4). The particles in conglomerates also consist of uranium, fluoride and oxygen. Sizes of these particles are from 0.3 m to 0.6 m as a rule. Isotopic compositions of uranium in investigated particles are in interval from depleted uranium corresponding to the waste up to enriched uranium corresponding to the nomenclature of products of this plant. Photo 4. Conglomerate of spherical uranium microparticles of industrial dust from uranium enrichment plant. Production of uranium fuel is accompanied by formation of a great number of particles with irregular form such as debris with a smooth surface, sharp ribs and round holes of caverns (photo 5). These particles have sizes from 2 m to 20 m. Apparently, these particles are formed through splitting as a result of mechanical actions or thermotensions. Caverns on the particles surfaces are the consequences of air bubbles in the thickness of sintered matter. In addition, particles, having sizes from 2 m to 10 m and breccia-like surface with the size of agglomerated objects ranging from 0.1 m to 0.3 m (photo 6) characterize this manufacture.

4 4 Photo 5. Uranium microparticle of industrial dust from uranium fuel fabrication plant Photo 6. Uranium microparticle of industrial dust from uranium fuel fabrication plant The morphologies of uranium microparticles collected from hot cells, are, appearantely, related to the spent fuel procedures, which are typical for the given hot cell. The photos of microparticles collected at three different plants using hot cells (photos 7, 8, and 9) confirm this thesis. Photo 7. Uranium microparticle from the hot cell

5 5 Photo 8. Uranium microparticle from the hot cell Photo 9. Uranium microparticle from the hot cell Characteristic feature of microparticles from hot cells is registration of fission products, activation products, and plutonium in these particles. 4. CONCLUSIONS Thus, the information about morphological characteristics of uranium microparticles from industrial dust at nuclear fuel cycle plants, about isotopic composition of uranium in these particles as well as about presence of plutonium, fission products and activation products in these particles can be used nuclear activity types identification. The data about isotopic composition of uranium and plutonium, about elemental composition of microparticles including uranium and plutonium, about joint presence of uranium and plutonium, uranium and thorium as well as uranium and aluminum, zirconium, lithium, beryllium, oxygen and carbon indicate the purpose of nuclear matter production. Information about form, size, structure of the surface and elemental composition of microparticles can be used to determine technological features of product.

6 6 Furthermore, these data indicate the kind of equipment used for separation of uranium isotopes as well as the necessary types of chemical treatment of nuclear matter to transform this matter into weapon matter or the possibility to use the nuclear matter in weapon programs without additional chemical treatment. Morphological attributes: form, size and structure of the surface of individual microparticles can also be considered as characteristic attributes of formation conditions and, consequently, parameters of informative particles. REFERENCES [1] G. Kaurov, V. Stebel kov, O. Kolesnikov, etc. Analytical Procedures for Detecting the Undeclared Nuclear Activity. The Report of Laboratory for Microparticle Analysis, ID: RUS A 00999, 1998 [2] G. Kaurov, V. Stebel kov, O. Kolesnikov, D. Frolov, N. Valiullov. Atlas of Uranium Microparticles from Industrial Dust at Nuclear Fuel Cycle Plants. Laboratory for Microparticle Analysis, Report Moscow, 2000