An unconventional approach to solving the problem of complex processing of thorium-containing nuclear raw materials and spent nuclear fuel
High temperature helium fluid reactors (HTHFR) are capable of generating heat with a temperature of about 1000°C, which can be used to produce electricity with high efficiency in a direct gas turbine cycle and for supplying high-temperature heat and electricity to hydrogen production processes, technological processes in chemical, oil refining processes, metallurgical and other industries, as well as for desalination of water.
The HTHFR reactors can use both closed and open fuel cycles using uranium, plutonium and thorium. The concept of an open nuclear fuel cycle (ONFC) based on thorium involving uranium and weapon grade plutonium has been tested most extensively on such reactors. The advantages of ONFC based on thorium will increase even more if the cost of producing thorium nuclear material is significantly reduced compared to uranium. This can be achieved either by direct improvement of mining technology and processing of thorium-containing raw materials, or using any features of the genesis and composition of such materials.
If the cost of nuclear fuel can be considered a quantity determined only by the level of technology of its manufacture, then its cost is determined by a number of factors independent of the excellence technological factors. For example, uranium-containing ore mined in the Republic of South Africa is offered on the world market at the lowest price. This fact is not due to the perfection of ore mining technology, but to the fact that it is mined along with gold ore at the same workings. In this regard, some useful thorium-containing mineral fossils secreted monazite. The power and number of deposits of monazite sands can regarded as one of the potential sources of raw materials for large-scale thorium nuclear energy. Monazite (Ce, La, Y, Th)P04 contains about 12% of thorium dioxide ThO,. Under the action of concentrated acid solutions, for example, nitric or hydrochloric, on the monazite, a mixture of salts of cerium, lanthanum, yttrium and thorium is formed. Modern technological methods allow to separate the thorium concentrate from this mixture in the form of this or other chemical compound. The remaining pulp represents a very valuable raw material to obtain either in the form of compounds, or in the pure form of rare earth metals. Thus, it is possible to implement a technological option in which the thorium concentrate is an associated material in the preparation of cerium, lanthanum and yttrium concentrates.
Technology will be based on the phenomenon of induced selective drift of cationic aquacomplexes in salt solutions under the action of asymmetric electric fields whose frequency does not exceed tens of kilohertz.
The separation element diagram of the technological cell is shown in Fig. 4.8.
The input of the element (pipe for supplying solution 1, Fig. 4.7), receives the initial mixture of 2 components (an aqueous solution of a mixture salts Ce(NO,), and Y(NO.), with concentrations of 3.5 and
Fig. 4.7. Technological cell: 1 - pipe for supplying the solution; 2 - nozzles for sampling the solution; 3 - pipe for the selection and organization of forced circulation of the solution; 4 - potential, isolated from solution of the grid; 5 - solution.
Fig. 4.8. Scheme of the separation element.
3 g//, respectively - the feed stream L with concentrations C and C , respectively. Two streams emerge from the element: 2 - selection of L' (aqueous solution, enriched with Ce3+, branch side 2, Fig. 4.7) and 3 - dump L' (water solution enriched from Ce3+, branch side side 3, Fig. 4.7).
The concentrations of the components in the selection are equal: Ce3+ - C". ; Y3+ - C and in the dump C"and C", respectively. In this case, the selection is enriched with Ce3+ cations and depleted in Y3+ cations, and the dump, on the contrary, is depleted in Ce3+ cations and enriched in Y3+ cations.
Table 4.1 shows the experimentally determined values of quantities in the accepted notation.
Thus, after 4 hours of exposure to the field with intensity E+ = 14.3 V/cm, the asymmetry coefficient A~/A+ = 0.66, with a frequency of 1.6 kHz per aqueous solution of a mixture of salts of Ce(N03)3 and Y(N03)3 the values of the concentrations in the absence of circulation of the solution through the separation element make up: C' = 1.00249; C = 0.99751; C"= 1.00000; C"= 1.00179. The relative
I J I j
concentrations of the cations of cerium and yttrium at this comprises: Rt = 1.00000 (stock solution); R' = C'JC' = 1.00499 (selection) and R" ij = C7C''= 0.99821 (dumping'}.
The separation factors in an element without solution circulation make up:
- - a = R^/R = 1.00499;
- - in the clumping 6 = R /R" = 1.00179;
- - full q = a • p =У1.00679У
- 1 ц у r v
Thus, it is possible to implement a technological option in which the thorium concentrate is a by-product with obtaining concentrates of cerium, lanthanum and yttrium.
Table 4.1. Concentrations of components in accepted designations
Concentration, arb. units
Fig. 4.9. Modified system of extraction purification of solutions of Th nitrites.
Figure 4.9 shows a modified scheme of extraction purification of a solution of thorium nitrate, allowing to extract from the aqueous raffinate of the target REE. A well-proven process flow diagram adds a new link to extract industrially significant amounts of the target REE (e.g., yttrium or cerium).
In the case of complex hydrochloric acid technologies for the rare metals, the schematic diagram of the extraction of REE from aqueous raffinate containing hydrochloric acid and REE chlorides will not change. Of course, the optimal combination of electric field parameters of the mixture of chlorides present in an aqueous solution will be different.
In this case, the orders of magnitude of the electric field strength and its frequencies will not change. Separation cell design, the circuitry and power of the high-frequency asymmetric electric field generation system will remain unchanged. Thus, the developed technology is universal in relation to the scheme of extraction purification of thorium and to the technology of rare-metal raw materials.
Technology is not literally electrochemical in direct meaning of its term, since mass transfer occurs in solutions electrically insulated from electrodes onto which the voltage source is ‘loaded’.
.These features and the fact that the amplitude values of the electric field at which the phenomenon occurs are units of volts per centimeter, allow one to attribute the technology to energy-saving.
Spent nuclear fuel (SNF) contains a significant amount of platinoids whose atomic nuclei are fission fragments of fuel cores. Their content in SNF depends on the type of reactor, type and depth of burnout, SNF holding time and a number of other parameters. For thermal neutron reactors with UO, fuel and the depth of burnout of 33 GW • day/t after 10 years of ageing on average per ton the fuel accumulates 2.1 kg of ruthenium, 0.4 kg of rhodium and 1.2 kg of palladium. In the fuel of fast neutron reactors, the accumulation of these metals increases by an order of magnitude. Thus, SNF for the content of platinum metals should be considered, and is currently considered by experts as an alternative source of these metals.
Without changing the time-tested technologies for SNF processing, one can supplement them with one or more links in which dividing cascades will operate, allowing extraction of valuable metals from aqueous solutions of salts. The results of studies show the possibility and feasibility of using the effect of electroinduced selective drift
Fig.. 4.10. Improved scheme of the first extraction cycle of the Purex process.
in the traditional Purex process. Separation cascades based on the effect of electroinduced selective drift, are supposed to be introduced into the general technological scheme of the Purex process in two stages (Fig. 4.10).
The first separation cascade is supposed to be introduced before the first extraction cycle to extract nitrate from the composition of the nitric acid solution of the most active radionuclides. These include fission products like Zr, Nb, Sr, Ce and other REEs. Removing the listed fission products, which are hard у-emitters, not only reduces the radiation load on the extractant, increasing thereby its capacity, but also reduces its destruction due to the action of у radiation. This measure will significantly reduce radiation effects on chemicals and solvents in the process of reprocessing the irradiated nuclear fuel therefore reducing the amount of medium-level waste and reducing the set of elements from which basic products should be cleaned. The use of the second separation cascade in the technological scheme of Purex-process is supposed to be extracted from nitric acid solutions
(water-tail solutions) after the first extraction cycle of the platinum metals.
Effects in biotechnology and medicine
Water makes up the base of the blood stream, cytoplasm and intercellular fluid. In all of these fluids, in varying concentrations, inorganic substances, proteins, sugars, and cell formations are present that are hydrated and have the appropriate hydration shell. Blood can be considered as a heterogeneous multicomponent system containing red blood cells, white blood cells, platelets, which are suspended in a colloidal solution of the electrolytes, proteins and lipids. Almost all blood components are hydrated, and their rotational mobility plays an important role in the bioenergy of the body. Rotational mobility as was shown above, is controlled by an external asymmetric electric field of low tension, which allows the latter to be used for selective exposure to certain blood components, cytoplasm or intercellular fluid, enhancing or inhibiting the mobility of certain components. Selective drift effect of the solvated ions can also be used in the technology of purification of blood from harmful compounds, each of which is characterized by a specific value of the rotational transition frequency into the translational component of motion.
The defining feature of all biologically active molecules is their chirality. Molecules can be considered as geometric bodies. If there are no symmetry of the elements of the Sn groups in the molecule, then such a molecule is chiral. Similar molecule and its mirror images are pairs of isomers that are not compatible with each other. Such isomers are called mirror antipodes, or enantiomers, (enantiomers are synonymous with chiral molecules). For example, a methane molecule is achiral (see Fig. 4.11), so as its minor reflection is fully compatible with the original image during movement, and the bromofluorochloromethane molecule is chiral, so both she and
Fig. 4.11. Molecule of methane is achiral (6 planes of symmetry a, 3 axes symmetry S4).
Fig. 4.12. .Chromium bromofluorochloromethane molecules - pair of enantiomers.
her mirror image are pairs of isomers (see Fig. 4.12) that do not fit together. In doing so, the physical properties of the enantiomers are identical. A mixture of enantiomers is called a racemate. So, during the synthesis of bromofluorochlomethane, molecules of two geometric shapes can form. As a result the synthesized bromofluorochloromethane will be a mixture of two enantiomers, i.e. a racemate.
Chirality is crucial in the synthesis of complex compounds with pharmacological properties. Since natural sources can no longer satisfy the existing need for biologically active compounds, the method of cleavage of racemates, i.e. separation, is used to obtain enantiomers included in the racemic mixture. There are 3 ways of cleavage of racemates: mechanical, biochemical and chemical. The chemical method is currently the main method of separation of racemates. Its essence is the translation of both enantiomers into diastereomers, the physical properties of which already differ, with their subsequent separation.
If we consider the solution of the racemate in the approximation of the existence in its volume of a self-consistent electric field, then in it there are 3 carriers of a polarization charge induced by an external nelectric field - solvent molecules and solvated enantiomer molecules. The action of an external asymmetric electric field on the solution of the racemate will lead to the excitation of a rotational- translational motion of the solvated enantiomer molecules, and differences in the drift parameters of each of the enantiomers will result to their separation in space and will provide the possibility of their selective extraction from solution. Thus, the effect of selective drift can be used in the synthesis of biologically active substances or for a controlled change in the properties of their solutions.