The particulars of radioactive contamination of concrete wastes by 137 Cs were studied. x-Ray phase analysis and chemical analysis show that clayey materials, including Al 2 O 3 , Fe 2 O 3 , K 2 O, and MgO, on which 137 Cs sorption is possible, were present in the concrete wastes. The content and form in which 137 Cs was found in radioactive concrete wastes from nuclear power facilities as well as in model samples were determined. When the wastes were treated with nitric acid the binder dissolved and a polydisperse suspension formed. The suspension consisted of three phases: solution, fine suspension, and rapidly settling precipitate of heavy filler particles. x-Ray phase analysis was performed and the 137 Cs mass ratio and distribution in the phases were determined. The possibility of decontaminating the concrete by a reagent method was evaluated.Large amounts of radwastes, a considerable fraction of which consist of concrete structures, are inevitably produced when nuclear power facilities are decommissioned. There are many known methods for decontaminating concrete. Usually, concrete structures are decontaminated by mechanical removal of the surface layer using different equipment, as a result of which secondary wastes in the form of fragmented concrete are formed [1]. Ordinarily, such wastes are conditioned by incorporation into cement prepared using liquid radwastes [2] or by saturation with a highly penetrating cement solution [3]. As a result, the volume of the cemented radwastes and correspondingly the storage costs increase.As a rule, concrete wastes are classified as medium-and low-level. 137 Cs is one of the main contaminating γ-and β-emitting radionuclides. Its half-life is about 30 years, so that cool-down of the wastes to lower the activity to a safe level is of little use and in many cases removing this isotope from concrete will make it possible to remove such wastes from the radwaste category.The objective of the present work is to assess the possibility of volume 137 Cs decontamination of fragmented concrete wastes. Concrete is a nonuniform composite material, so that to develop a method of decontamination it is necessary to study the form in which the radionuclides, specifically, 137 Cs, are found in the wastes.The objects of study were concrete wastes from the rehabilitation of radiologically hazardous facilities: sample 1 -a 25-kg concrete block with γ-ray dose rate 0.1 m away from the surface to 500 μSv/h and sample 2 -fragmented wastes with γ-ray dose rate 0.1 m from the surface not exceeding the background level. In addition, model samples obtained by contaminating clean concrete with a radioactive solution as well as by cementing a radioactive solution were studied.For γ-spectrometric analysis, the waste fragments were comminuted and average samples were taken. The samples were subjected to radiometric analysis performed using an ORTEC-GEM 35P (Finland) automated four-channel gamma spectrometer with a semiconductor detector in the central laboratory of the Moscow Scientific and Industria...
The possibility of concentrating liquid radwastes by evaporation from the surface of porous plates is examined. It is shown by means of tests of a laboratory setup and an experimental stand that liquid radwastes can be concentrated to salt content 319 g/liter at a temperature far below the evaporation temperature of water and with specific energy consumption 20 times lower that the specific heat of vaporization of water. The results of the tests of the experimental setup with capacity up to 43 kg/h with respect to the evaporated water are described; this setup has been incorporated in the EKO mobile modular water purification complex used at the MosNPO Radon for reprocessing radioactive water from various organizations.When liquid radwastes are purified by, for example, evaporation, membrane separation followed by regeneration, and other methods, secondary wastes which are often represented by liquid concentrates are always formed. It is obvious that their volume must be decreased to a minimum, since the costs of concentrating the wastes and then storing them for a long time are very high. Evaporation of water (thermal or natural) [1,2] or membrane concentration of water impurities [2, 3] are ordinarily used for this purpose.The main drawbacks of thermal evaporation are high complexity and high metal content of the equipment, high specific energy consumption, temperature close to the boiling point of water, and often elevated pressure in the channels of the evaporation apparatus. Natural evaporation requires dry air and large-size equipment (water-cooling towers, ponds, or evaporation vessel). Membrane methods likewise are not devoid of substantial drawbacks. The pressure in reverseosmosis apparatus reaches 8 MPa, and the salt content of the concentrates is rarely greater than 50 g/liter. In concentration by electro-osmosis, the salt content of the brine can reach 250 g/liter but in such apparatus hydrogen or corrosive gases are often the products of electrode reactions. Membrane distillation [4] makes it possible to attain a concentrate with salt content 500 g/liter, but if surfactants are present in the solution than this method rapidly becomes ineffective. The process is characterized by low specific capacity and overgrowth in the capillaries during the concentration process.The objective of the present work was to develop a technology for concentrating liquid radioactive wastes at a temperature much lower than the boiling point of water and a mobile facility for implementing this process. Building and testing the facility were also part of the problem considered in this work.The crux of the technology is that the liquid wastes are fed from above into a press-filter type evaporation chamber assembled from porous, channeled, hydrophyllic plates and air with relative moisture content 100% is passed through the channels formed in the plates (Fig. 1). The radioactive solution flows down along the plates under gravity. In the process, water is continually removed from the solution by evaporation and therefore the r...
A substantial quantity of solid radwastes consists of contaminated building materials, primarily, different grades of concrete. The largest amount of concrete arises during decommissioning of objects of nuclear power and radiochemical enterprises which have outlived their service life, are unprofitable, or do not meet modern safety requirements [1]. To make these objects radiation-safe, building structures must be completely or partially disassembled, primarily by mechanical methods (explosions, breaking or sawing into pieces, and so forth) [2]. This debris ranges in size from dust particles to pieces with mass up to hundreds of kilograms and is placed in special long-term storage (burial) sites. Since it is expensive to build and service such sites, it is economically desirable to develop technologies that decrease the volume of the wastes which are to be stored for a long time (buried). According to OSPORB-99 [1], building materials from which radionuclides have been removed are largely low-level wastes and accordingly need not be classified as radioactive wastes.Radioactive building materials which are contaminated with long-lived α emitters present the greatest danger. The most stringent norms have been established for them -these materials are considered to be radioactive when their content of uranium or transuranium elements ranges from 1 kBq/kg and higher for 226 Ra (in equilibrium with the decay products) to 10 kBq/kg and higher [1]. For materials contaminated with radionuclides with a long half-life, the method of delayed disassembly or cool-down to allow the activity to drop to acceptable levels is unacceptable, which makes the problem of handling such materials of great current interest.Our objectives in the present work were to study the particularities of the contamination of real concrete wastes by uranium isotopes and to develop a method for decontaminating such wastes.Real radioactive concrete wastes from the research center and an industrial enterprise of the nuclear fuel cycle were the object of the present investigations (Fig. 1). The wastes were represented by debris containing residues of the binder (Fig. 1a) and fragments of a thin-wall (35 mm thick) reinforced concrete structure with two plane-parallel boundaries (Fig. 1b). For radiometry and radiochemical analyses, the waste fragments were ground and medium samples were taken. The analysis was performed in the central laboratory of the MosNPO Radon, which is accredited in the system of radiation-monitoring laboratories. x-Ray phase analysis of the waste samples was performed with a DRON-4 diffractometer which automatically recorded the diffraction pattern in steps using filtered FeK α radiation. A binder fraction with particle size less than 2.5 mm was sieved to investigate the concrete sample (see Fig. 1a). The x-ray phase analysis data show that CaCO 3 (calcite), SiO 2 (α quartz), 3CaO·Al 2 O 3 ·CaCO 3 ·12H 2 O, 4CaO·Al 2 O 3 ·13H 2 O are present in the binder fraction. The radionuclide composition of the binder is represented by 234,235...
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