RU2114061C1 - Method of high-concentrated uranium processing - Google Patents

Abstract

FIELD: chemical technology, nuclear materials. SUBSTANCE: high-concentrated uranium is placed to nitric acid solution. Extractive purification of uranium from plutonium, alloying metals and products of radioactive element degradation is carried out using tributyl phosphate solution in hydrocarbon solvent. Denitration of uranium solution to oxides is carried out in low-temperature air plasma. Obtained uranium oxides are fluorinated in homogeneous mixture with calcium and/or magnesium oxides at their content 0.5-2 wt. -% of uranium content in mixture. Calcium and/or magnesium can be added to uranium solution before denitration. Invention ensures to process high-concentrated uranium to low-concentrated product. EFFECT: increased purity degree of uranium from plutonium and output of process. 3 cl, 1 tbl

Description

 The invention relates to a technology for the processing of highly enriched uranium, in particular weapons grade, into low enriched energy.

 A known method of diluting highly enriched uranium by mixing oxide powders of highly enriched uranium and low enriched obtained in one way or another (A. Makkhidzhani et al. "Nuclear materials through dull glass?", IEEP PRESS, 1995).

 The disadvantage of this method of diluting highly enriched uranium with low enriched is the lack of homogeneity of the mixed powder mixture.

Known fluoride-gas technology for the processing of highly enriched uranium, followed by dilution of the enriched uranium hexafluoride with low enriched uranium hexafluoride. The method includes the following operations:
- oxidation of highly enriched metallic uranium into uranium dioxide;
- the interaction of highly enriched uranium dioxide with hydrofluoric acid to produce uranium tetrafluoride;
- burning of uranium tetrafluoride in a fluorine stream with the formation of highly enriched uranium hexafluoride;
- dilution of enriched uranium hexafluoride with low enriched uranium hexafluoride (A. Makkhidjani et al. "Nuclear materials through dull glass?").

The disadvantages of this method are:
- insufficient purification of uranium from the decay products of uranium-232, especially thorium-228, thallium-208 and bismuth-212, which have hard gamma radiation;
- insufficient purification from plutonium in operations to obtain uranium tetrafluoride and its subsequent fluorination, which requires additional operations to purify uranium hexafluoride from residual plutonium content in it.

Closest to the technical nature of the proposed method is a method of processing highly enriched uranium, including the following operations (Bashlachev V.N. et al. Report at the 4th scientific and technical conference of the Siberian Chemical Plant, Serersk, May 28-31, 1996):
- oxidation of metallic uranium to nitrous oxide-uranium;
- dissolution of uranium oxide-uranium in a solution of nitric acid;
- two extraction cycles for the purification of uranium from plutonium, alloying metals, and radioactive decay products;
- denitration of a uranium reextract of the second extraction cycle by precipitation of ammonium polyuranate salts with a 25 wt.% ammonia solution, followed by processing of the mother liquors together with water-tail solutions to discharge standards for uranium content;
- calcination of moles of ammonium polyuranate to uranium oxide;
- fluorination of nitrous oxide of highly enriched uranium to uranium hexafluoride, followed by its dilution with low enriched uranium hexafluoride.

The disadvantages of this method, taken by us as a prototype, are:
- multi-cycle process (two extraction cycles for purification of uranium from plutonium, alloying metals, products of radioactive decay; ammonia precipitation of salts of ammonium polyuranate; calcination of salts of ammonium polyuranate; fluorination of uranium oxide-oxide), as a result, the volume of aqueous solutions increases by 3-5 times compared with the volume of the original solution;
- relatively low productivity due to the multi-cycle process as a whole and the duration of individual operations in particular;
- the complexity of the hardware-technological scheme as a whole.

 The aim of the invention is to increase the degree of purification of uranium from plutonium in fluorination operations, which will increase the productivity of the technological process of processing highly enriched uranium as a whole by eliminating the second extraction cycle, reduce the volume of aqueous solutions, and simplify the hardware-technological scheme.

 This goal is achieved by the fact that in the proposed method, including the conversion of highly enriched uranium to a solution, extraction purification of uranium from plutonium, alloying metals and radioactive decay products with a solution of tributyl phosphate in a carbon diluent, denitration of nitric acid solutions of uranium to oxides, fluorination of uranium oxides to uranium fluoride, uranium oxides are carried out in a homogeneous mixture with oxides of calcium and / or magnesium, with a content of 0.5 to 2 wt.% of the content of uranium in the initial mixture; denitrate nitric acid solutions of uranium containing calcium and / or magnesium; denitration is carried out in low-temperature air plasma.

 Fluorination of uranium oxides in a homogeneous mixture with calcium and / or magnesium oxides with a content of the last 0.5-2 wt. % of the uranium content in the mixture increases the coefficients of purification of uranium from plutonium due to the formation of non-volatile complex compounds of fluorides of alkaline earth elements with plutonium hexafluoride, the elimination of local overheating in the fluorination apparatus, protection of the internal surfaces of the fluorination apparatus from burns due to the formation of a skull layer of refractory fluorides on them calcium and / or magnesium, simplification of the hardware-technological scheme of processing highly enriched uranium by eliminating the second ext ktsionnogo cycle.

 The introduction of calcium and / or magnesium into a nitric acid solution of uranium, followed by its denitration in low-temperature air plasma, makes it possible to obtain a perfectly homogeneous mixture of oxide powders with a higher dispersion, specific surface area, and activity, which will have a positive effect on the process of their fluorination.

 The proposed method was tested in pilot plants of RF-plasma-chemical denitration and fluorination of uranium oxide powders.

Example. Uranium reextract of the first extraction cycle of the composition: uranium 50-300 g / l, plutonium 100 Bq / g U, nitric acid 0.5 mol / l, calcium and / or magnesium 0-2 wt.% Of the uranium content was denitrated at HF plasma-chemical installation in the following modes of its operation:
oscillatory power of the plasma torch ... 60 kW;
plasma gas ... air;
air consumption for plasma formation ... 12 nm ³ / h;
air consumption for spraying ... 10 nm ³ / h;
solution flow rate ... 15-20 l / h;
the temperature of the plasma gas at the exit of the plasma torch ... 3000-5000 ^o C;
the temperature of the dust and gas stream leaving the plasma-chemical reactor ... 400-500 ^o C.

The resulting mixture of powders of uranium oxides with oxides of alkaline earth elements was fluorinated with fluorine in the continuous operation of the installation. The mass flow rate of the powder of metal oxides is 2 kg / h, fluorine is 1 kg / h, the temperature of the reaction mixture is 400-500 ^o C.

 The data obtained during the experiments are shown in the table.

 From the data presented in the table, it follows that the presence in the powders of uranium oxide of particles of powder of calcium and / or magnesium oxides homogeneously distributed in it substantially affects the coefficients of purification of uranium from plutonium, and a sharp increase in the cleaning coefficients is observed when they contain calcium oxides and / or magnesium 0.5 wt.% of the uranium content. A further increase in the content of oxides of alkaline earth metals does not lead to a significant increase in the coefficients of purification of uranium from plutonium.

 The plutonium content in uranium hexafluoride in the presence of 0.5-2 wt.% Of the mass of uranium oxides of alkaline earth metals in the initial uranium oxide was 0.04-0.06 Bq / g U, which meets the technical requirements for purified HEU.

 The process of fluorination of uranium oxides in the presence of homogeneously distributed alkaline earth metal oxides in it proceeded without local overheating of the loaded mixture and the presence of significant temperature drops along the entire length of the reactor.

 Thus, the implementation of the proposed method will allow to obtain highly enriched uranium hexafluoride with a plutonium content that meets the requirements of the specifications, suitable for obtaining uranium hexafluoride from it for energy purposes, while the existing technological scheme excludes the second extraction cycle for purifying uranium from plutonium, the operation of ammonia deposition of ammonium polyuranate salts and operations related to the processing of mother liquors.

 In addition, the second extraction cycle can be used as the first, which will increase the productivity of extraction plants for processing enriched uranium by about 2 times.

Claims (3)

 1. A method of processing highly enriched uranium, including the production of uranium oxides and fluorination of the obtained uranium oxides to uranium hexafluoride, characterized in that the uranium oxides are obtained by the conversion of highly enriched uranium to a nitric acid solution, by the extraction purification of uranium from plutonium, alloying metals and radioactive decay products with a solution of tributyl phosphate in hydrocarbon diluent and denitration of uranium solutions to oxides, and uranium oxides in a homogeneous mixture with oxides of calcium and / or magnesium with the content of the latter 0.5 - 2 wt.% of the uranium content in the mixture.  2. The method according to p. 1, characterized in that the denitration is subjected to nitric acid solutions of uranium containing calcium and / or magnesium.  3. The method according to PP. 1 and 2, characterized in that the denitration is carried out in a low-temperature air plasma.

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