A method of processing highly enriched uranium

 

(57) Abstract:

The invention relates to the processing of highly enriched weapons-grade uranium (HEU) to low enriched uranium for energy purposes. The method includes the electrochemical dissolution of highly enriched uranium in solution 2-5 mol/l nitric acid at a temperature not exceeding 50oAnd the initial anode current density of 0.2-1.5 a/cm2that after the dissolution of 85-90 wt. % of uranium is carried out in the presence of hydrazine when its concentration in the solution of 4-8 g/l, the resulting solution is directed to the extraction refining and subsequent processing of reextract to uranium oxides. The invention reduces processing cycle of the APU, to improve the quality and stability of extraction refining of obtaining uranium required purity plutonium.

The invention relates to the processing of highly enriched weapons-grade uranium (HEU) to low enriched uranium for energy purposes.

There is a method of processing HEU, including the oxidation of uranium, followed by mixing the obtained oxide with oxide of low-enriched uranium [1]. Obtained in this way, the uranium oxide contains plutonium and decay products is islow, purification of the obtained uranium hexafluoride by the method of centrifugal separation cascade of gas centrifuges with subsequent mixing with the gas stream hexafluoride low-grade enrichment [2]. The disadvantage of this method is to obtain a product containing plutonium above the level set by the international standard.

The closest technological essence is a way of processing of HEU, including the following transactions: transfer of metal shavings; oxidation chip to nitrous oxide; the dissolution of nitrous oxide in nitric acid; the restoration and stabilization of plutonium to the trivalent state by using hydrazine; extraction refining using tributyl phosphate (TBP) in paraffin diluent; the precipitation of ammonium diuranate from reextract, drying and calcining it to oxides [3].

The resulting oxides HEU can be directed to the fluorination up hexafluoride, followed by mixing with uranium hexafluoride low-grade enrichment. This method allows to obtain a conforming product, but includes a lot of operations on transfer of metal in the form convenient for dissolution: the transfer of metal shavings, burning shavings, grinding and sieving nitrous oxide. To forgive is received nitrous oxide and contamination of its products corrosion of equipment. In addition, at the stage of dissolving operation undissolved residue reaches 2% of the initial mass, which calls for a two-stage filtration solutions. In addition, one estrazioni cycle is not ensured stable cleaning HEU from plutonium.

The objective of the invention is to develop ways to reduce the number of expensive operations, compounded by the requirements of the nuclear safety and industrial hygiene.

The problem is solved in that in the method for processing of HEU, including the production of nitric acid solution of uranium containing plutonium to the trivalent state, the extraction refining and processing reextract to uranium oxides, obtaining nitric acid solution of uranium perform electrochemical solvent of highly enriched uranium in solution 2-5 mol/l nitric acid at a temperature not exceeding 50oC and the initial anode current density of 0.2 - 1.5 a/cm2and after dissolution 85-90 wt.% uranium electrochemical dissolution of lead in the presence of hydrazine when its concentration in the solution of 4-8 g/l

The inventive method is as follows.

Highly enriched uranium pre-p is topasna geometry. The body of the cell, made of conductive material, resistant to nitric acid, (stainless steel, titanium and so on) performs the function of the cathode. A solution of 2-5 mol/l nitric acid circulates on a cell - capacity - cell". The temperature of the electrolyte is maintained within the range of 25-50oC by cooling of the cell or the tank or running water. The initial anode current density is maintained within the range of 0.2 - 1.5 a/cm2to ensure current 97-99%. The dissolution rate of uranium is proportional to the flow of electric current and 1,4 - 1,6 g/ACAS.

Studies have shown that increasing the temperature of the electrolyte over 50oC is accompanied by release of oxides of nitrogen caused by chemical interaction of nitric acid with metallic uranium.

After the dissolution of 85 to 90 wt.% uranium electrolytic dissolution of lead in the presence of hydrazine when its concentration in the solution of 4-8 g/l, the achieved rate developments tetravalent uranium 0.3 - 0.4 grams/ACAS and provides the necessary degree of recovery of the plutonium to the trivalent state.

By increasing the concentration of hydrazine in the electrolyte over P CLASS="ptx2">

Depending on the content of plutonium HEU varying in the present limits of the concentration of hydrazine and the amount of residual uranium subjected to electrochemical dissolution in the presence of hydrazine, can be obtained in solution the concentration of tetravalent uranium, necessary to achieve the required degree of purification of uranium from plutonium extraction.

Example. Metallic HEU in the form of a rod of mass 200 g containing plutonium 460 Bq/g electrochemically dissolved in a water-cooled cell, the building which served as the cathode, HEU - anode. The current strength was maintained at the level z0 And anodic current density as the dissolution of the rod HEU was increased from 0.25 to 1.5 a/cm2. As a source of electrolyte used nitric acid to 3.9 mol/l For 0.5 hours until the end of the dissolution, when the solution turned 90 wt. % HEU in the electrolyte was added hydrazine in the amount of 8 g/L. the dissolution Process lasted 4 hours, the temperature of the electrolyte was maintained 45oC. after dissolution was obtained solution composition

The total uranium - 182,4 g/l

The total uranium (IV) - 6.6 g/l

Hydrazine - 5.5 g/l

Nitric acid and 2.1 mol/L.

The solution was contacted in a separating funnel with 25% TBP (solvent RED 1) at ACL/g of uranium, that meets the requirements for quality of commercial nitrous oxide.

The invention eliminates time-consuming transfer of metal shavings, its oxidation to oxides, grinding, sieving and packaging and, accordingly, the equipment for these operations. In the process of getting solution of uranium costs are reduced filtering solution, reduces the amount of nitrous gases. Reduce the amount of waste HEU and costs of recycling, improving the quality and stability of extraction refining, which allows it in one stage production of standard uranium for plutonium content.

Sources of information

1. A. Makhijani, E., Makhijani. Nuclear materials through a glass darkly? IEEP PRESS, 1995.

2. RF patent N 2057377, G 21 C 19/42, 48, publ. 27.03.96.

3. C. N. Bashlachev, B. A. Belov, A. A. Gushchin and other Development technologies for cleaning returnable uranium from micro-quantities of plutonium, output circuit and reducing the amount of water and tailings solutions. Report at the fourth scientific conference of the Siberian chemical combine, Seversk, may 28-31, 1996 (prototype).

A method of processing highly enriched uranium, including the production of sotokoto of reextract to uranium oxides, characterized in that the receiving nitrate solution to uranium carried out by electrochemical dissolution of highly enriched uranium in solution 2 to 5 mol/l of nitric acid at a temperature not exceeding 50oC and the initial anode current density of 0.2 - 1.5 a/cm2and after the dissolution of 85 to 90 wt.% uranium electrochemical dissolution of lead in the presence of hydrazine when its concentration in solution of 4 - 8 g/L.

 

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