Method for processing weapons-grade highly enriched uranium and its alloys in the fuel material for use in nuclear reactors

 

(57) Abstract:

Essence: highly enriched uranium is oxidized by oxygen in the air, and then produce the fluorination with elementary fluorine at its excess above the stoichiometric 5 - 50%. Received hexafluoride purified by the method of centrifugal separation with subsequent offset with 235 uranium hexafluoride, the content of which is lower than in the fuel material, by shifting the gas streams of high - and low-enriched uranium hexafluoride. At the final stage of the product before packaging Desublimers. 4 C. p. F.-ly, 1 Il.

The invention relates to a method of eliminating nuclear weapons by processing weapons-grade highly enriched uranium metal and its alloys for further use as fuel in nuclear reactors.

Highly enriched uranium is a uranium with an enrichment of u-235 above 20 wt. low enriched uranium from 1.5 to 5 wt. raw uranium 0,711 wt.

Known methods of processing uranium metal are generally to the processing of natural uranium or reprocessing of spent nuclear fuel.

Thus, known methods of processing after the s impurities and separation of elements, included in spent nuclear fuel. The end product of these processes is uranium oxide [1]

There are ways to recycle fuel from uranium or oxide fluoride methods, as liquid solutions or melts of salts, and in the gas phase. The end product of these processes is uranium hexafluoride [1]

Known methods of processing natural or depleted uranium, which include both obtaining uranium oxides and getting hexafluoride [1]

There are also known methods of processing enriched uranium (uranium-235 up to 4 wt.), in which the main problems are the issues of nuclear safety and loss prevention uranium-235 [1]

All known methods do not solve the basic problem of the invention, which consists in the elimination of weapons-grade (containing uranium-235 80-94 wt.) highly enriched uranium metal and its alloys and bring it to fuel nuclear reactors that meet international standards [2, 3]

In known publications [4, 5] discusses aspects of the removal or destruction of "specific attributes" (original form) of weapons-grade highly enriched uranium metal after the dismantling of nuclear weapons, different adreaction.

The closest in technical essence and the achieved effect is a method for processing weapons-grade highly enriched uranium metal and its alloys in the fuel material for use in nuclear reactors. The method involves the oxidation of a metal highly enriched uranium mixed oxide of highly enriched uranium from natural uranium oxide fluorination of a mixture of oxides, purification of enriched uranium hexafluoride two-stage distillation, obtaining low-enriched uranium hexafluoride by mixing purified hexafluoride uranium hexafluoride uranium up to 5% enrichment by weight of the final mixture of 5% hexafluoride with natural uranium hexafluoride and packing finished product in cylinders "30" [5]

The disadvantage of this method is the multistage process of mixing, first at the stage of the oxides, and then at the stage hexafluoride.

Preliminary mixture of oxides of highly enriched uranium with natural can be explained by the inability to clean in the distillation apparatus of the highly enriched uranium due to the fact that these devices according to their design features do not have adenomatosnuu configuration, which leads to low t is sociologistswho uranium water (liquid) technology, that is undesirable because of the emergence of liquid radioactive waste and the introduction of a neutron moderator (hydrogen and carbon), and increase the probability of spontaneous nuclear chain reaction.

The aim of the invention is the elimination of nuclear weapons by processing highly enriched weapons-grade uranium and its alloys for use of products of processing as a fuel source for nuclear reactors.

A high degree of enrichment of weapons-grade uranium (85-97 wt. uranium-235) made additional adjustments to the task, namely, the need for safeguards for the prevention of spontaneous nuclear chain reaction at all stages of processing, which resulted in severe restrictions on the geometric dimensions of the equipment used.

In addition, the aim was to improve technological process and eliminate the appearance of liquid radioactive waste in the processing of highly enriched weapons-grade uranium.

This is solved by the creation of a method of processing weapons-grade highly enriched uranium metal and its alloys in the fuel material for use in nuclear reactors, including the oxidation of highly enriched metal the material for use in nuclear reactors by mixing hexafloride different degrees of enrichment with subsequent filling of the fuel material in the container, in which, according to the invention, the oxidation of uranium metal carry oxygen at a temperature of 700-1100aboutWith, followed by fluorination of the resulting oxides of uranium elemental fluorine in excess of fluoride greater than stoichiometric at 5-50 wt. then the enriched uranium hexafluoride purified by the method of centrifugal separation, followed by mixing it with uranium hexafluoride containing uranium-235 below content in the fuel material, by continuously combining the two gas streams, and the resulting fuel material before filling Desublimers (Fig. 1).

Optimal methods of fluoridation are: fluoridation of highly enriched uranium oxides at a temperature of 300-400aboutWith under stirring and the excess of fluoride above the stoichiometric 5-10% and fluorination at a temperature of 1400-1500aboutWith in excess of fluoride greater than stoichiometric by 10-50% with the introduction of the oxides in the reaction zone at a gas-carrier.

Purification of highly enriched uranium hexafluoride carried out by the method of centrifugal separation cascade of gas centrifuges to impurity content of 10-4-10-5wt.

The offset of the two gas streams is carried out by reeved metal weapons-grade uranium hexafluoride conduct dry methods i.e. without the use of a liquid technologies in devices adrenoreceptor execution.

The temperature oxidation 700-1100aboutWith the organization of the cyclical process of heating-cooling allows to speed up the process of obtaining uranium oxides and thereby improve the efficiency of the process due to self-cleaning of the surface of uranium metal at the moment of transition from the modification and reduction of the metal by 0.7% Temperature - transition varies depending on the presence of alloying elements from 720 to 810aboutC. When conducting the oxidation below 700aboutWith the process slows down and becomes unproductive, because on the surface of uranium metal forms a dense oxide film, impeding the flow of oxygen to the reaction surface. When the temperature oxidation from 700aboutWith up to 1100aboutWith monotonically increases the rate of oxidation.

Increasing the process temperature above 1100aboutWith can lead to uncontrolled burning of uranium (due to ekzotermicheskie oxidation process), its melt, failure of equipment and violation of nuclear safety.

From this point of view for oxidation of uranium metal and its alloys riodic to similar consequences, as the temperature increases above 1100aboutC.

After a transaction, oxidation of the resulting oxides (nitrous oxide) uranium pulverized and subjected to fluorination.

Choice as a fluorinating agent of elemental fluorine is caused by the necessity of obtaining uranium hexafluoride, which is impossible to obtain when interacting with other fluorinating agents, for example, with hydrogen fluoride.

The temperature of the fluorination is not the determining factor for the decision of a task of the elimination of nuclear weapons by processing highly enriched weapons-grade uranium and its alloys and the use of products of processing as a fuel source for nuclear reactors. Although fluoridation of highly enriched uranium oxides will occur at any temperature in the range from 200 to 1600aboutWith the correct choice of temperature fluorination allows to optimize both the process of fluoridation, and the process of purification of uranium hexafluoride.

Therefore, an additional difference of the proposed method against known is the choice of modes of fluoridation, which depends on many factors, such as the composition of highly enriched uranium, i.e., the presence or the and etc.

Thus, low-temperature fluorination at 300-400aboutWith is selected in the presence of uranium oxide appreciable quantities of alloying components, which at these temperatures do not form volatile fluorides and can be separated at this stage of uranium.

Choice of excess elemental fluorine from 5 to 10% above the stoichiometric at a low temperature mode fluoridation due to larger area of contact time fluorination. The process will go and when large quantities of fluoride, up to 50% above stoichiometric, but with a greater amount of fluoride that is returned in the beginning of the process, will be contaminated with harmful impurities, which is undesirable.

If necessary, increase the speed and performance of the fluorination process, as well as the processing of highly enriched uranium oxide not containing significant quantities of alloying components, uses a high temperature method of fluorination at a temperature of 1400-1500aboutWith and excess fluorine 10-50% above stoichiometric. In this case, powdered uranium oxide is fed into the flame reactor for gas-carrier, for example, nitrogen.

Choice of excess elemental fluorine from 10 to 50% above the stoichiometric is italinate to 3 kg/ h process established, thus it is necessary to maintain an excess of fluoride in proportion to productivity growth.

When excess fluoride less than 10% is not ignition of the reaction mixture. The excess over 50% impractical because of the difficulties arising from the utilization and conversion of fluorine. This method also lends itself well to automation and spacing.

Gaseous enriched uranium hexafluoride may be contaminated with fluoride, molybdenum, tungsten, rhenium and other gaseous impurities.

The choice of method of centrifugal separation cascade of gas centrifuges for cleaning highly enriched uranium hexafluoride due to the possibility of the release of highly enriched uranium hexafluoride from all without exception gaseous impurities with molecular weight less than the molecular weight of the uranium hexafluoride, the construction of the treatment cascade is adenomatosnuu that allows you to clear the uranium hexafluoride the highest enrichment (up to 97 wt. uranium-235) and to use only single-stage mixing.

Highly enriched uranium hexafluoride, cleaned up their content 10-4-10-5wt. centrifugal cleaning stage.

Then the purified gaseous enriched uranium hexafluoride is mixed with uranium hexafluoride containing uranium-235 below content in the fuel material. This is another distinctive feature of the invention in comparison with the prototype, which is that not only change methods of operations and their modes, but the sequence of these operations. So, instead of the three operations of mixing in the method-prototype stage after oxidation, during and after fluorination, in the method according to the invention uses only one operation of mixing after purification of highly enriched uranium hexafluoride. The choice of a particular composition hexafluoride to mix it with the highly enriched uranium hexafluoride is associated with the content of uranium-235, the amount of undesirable impurities uranium-234 and uranium is 236 and the composition and amount of the fuel material.

When mixing highly enriched hexafluoride, for example, 97 wt. uranium-235, if necessary, obtain the composition of the fuel material, for example, 80 wt. uranium-235, can be rented for mixing hexafluoride containing uranium-235 from 79% to hexafluoride urial, i.e. the more ready of the fuel material to be obtained, the greater the degree of enrichment should be the second mixed stream.

On pipelines installed regulating the flow devices that allow greater precision in adjusting the composition of the finished product, avoiding getting married.

Mixed uranium hexafluoride Desublimers, stariway vessel, heated to 90-110aboutC, incubated for 4 h (homogenized) and pour in the tank "30".

P R I m e R 1. In the apparatus for oxidation downloaded item products from weapons-grade highly enriched uranium metal that has been contaminated by plutonium (U mass not more than 6000 g) were heated to 900aboutWith the flow of air and stood up to full oxidation.

The resulting uranium oxides were crushed and fed into a horizontal reactor for low-temperature fluorination with periodic stirring.

In the process of heating up to 300aboutWith consumption and fluoride 5-10% of the stoichiometric formed oxychoride uranium that with increasing temperature up to 400aboutTo turn into uranium hexafluoride. Access to the hexafluoride reaches 97,9% utilization of fluorine 85-90%

raised in a centrifugal cascade (cascade of gas centrifuges), where is cleaned from the fluorides of the elements with molecular weight below the molecular mass of uranium hexafluoride.

Cleared up to 10-4-10-5wt. the uranium hexafluoride is served in the collection of the purification cascade and forth on desublimation. From the installation of desublimate highly enriched uranium hexafluoride enriched to 90% u-235 in the gas phase through the flow metering device is fed into a manifold mixing. There through the flow metering device is uranium hexafluoride enriched to 1.5% uranium-235.

Consumption of highly enriched uranium hexafluoride is 0,3388 g/s, and low-enriched 9,6612 g/S. the merger of the two streams and their mixing received the product yield is equal to 10 g/c with a concentration of 4.4% uranium-235. Gaseous product Desublimers, sativa his vessel, heated to 90-110aboutC, incubated for 3-6 h at this temperature and poured into cylinders "30" as the fuel material.

P R I m m e R 2. Oxidation of weapons-grade highly enriched uranium metal, not containing impurity elements was carried out in accordance with example 1. The resulting milled uranium oxides was applied in the horizontal reactor is and 15-17% Yield of uranium hexafluoride reaches approximately 98% utilization of fluorine 40-44%

The resulting uranium hexafluoride is cleaned of the residual unreacted fluoride by desublimate and then is further processed without purification cascade of gas centrifuges.

Unreacted fluorine after cleaning is sent to the reactor for fluorination for reuse.

P R I m e R 3. In the apparatus for oxidation download detail products Armory alloy on the basis of highly enriched uranium by weight of less than 6000 g, the installation was sealed, was provided by the air and heated to 700aboutC. In the process of heating and air supply uranium due to ekzotermicheskie oxidation process is heated to the phase transition temperature of uranium-modification (772aboutC). This was accompanied by a decrease in volume of the metal and salootdelenie oxide film from the metal surface. When the temperature reached 800aboutWith the heating turned off.

On the oxidation of metallic uranium by weight of 6000 g spent 5 hours Extracted from the apparatus of oxidation of the oxide of highly enriched uranium were crushed in a mill, then on the gas-carrier (nitrogen) was applied to the feeder-dispenser for aeration followed by continuous transportation of the mixture in the reaction zone flame reactor flare Toya on stoichiometry, lit the torch and set the temperature of 1400-1500aboutC. the Rate of fluorination was 5 kg of oxide in 1 ch. Output of uranium hexafluoride per cycle achieved 99.9% of

To reduce the speed of fluoridation to 3 kg/h it is necessary to reduce the flow of elemental fluorine to more than 10% required by stoichiometry, and to increase the rate of fluorination above 5 kg/h it is necessary to increase the supply of elemental fluorine in excess of 30% up to 50% of the required stoichiometry. The release of uranium hexafluoride per cycle in all modes reaches 99.9% of

Further processing of the received hexafluoride were performed as in example 1.

P R I m e R 4. Processing details of the items are weapons based alloy of highly enriched uranium in oxidation, fluorination and purification were conducted as in example 3.

The operation of mixing and the concentration of flows was calculated by the following dependency:

G1C1+ G2C2G3C3< / BR>
G1+ G2G3where G1the flow of uranium hexafluoride with a high degree of concentration, g/s;

C1the concentration of uranium-235 in the uranium hexafluoride with a high degree of enrichment,

G2races uranium low enriched,

G3the flow of uranium hexafluoride, obtained after mixing, g/s;

WITH3the concentration of uranium hexafluoride, obtained after mixing,

Setting the necessary concentration in the finished uranium hexafluoride and quantity of the finished product, selected concentration and flow of the original flows hexafloride uranium.

All technological scheme of processing of weapons-grade uranium supplied by instruments of analysis of gas streams before filing them in the cleaning stage, after cleaning in the cleaning stage prior to submission to the device of mixing and after mixing. In the cleaning stage and the mixing apparatus is a pressure control gas flows. To avoid increasing the concentration of uranium-235 for the limits on the gas flow provided by the emergency protection and lock that automatically prevent admission of gaseous products.

The invention can be applied to manufacturing of hexafloride uranium with varying degrees of enrichment of uranium-235 in relation to fuel nuclear reactors as energy and transport for submarines and space.

1. METHOD for PROCESSING WEAPONS-grade highly ENRICHED URANIUM AND who uranium, the fluorination of uranium oxides, purification of uranium hexafluoride from impurities and obtaining fuel for nuclear reactors with a mixture of hexafloride different degrees of enrichment with subsequent filling of the fuel material in the container, characterized in that the oxidation of uranium metal carry oxygen at a temperature of 700 - 1100oWith, followed by fluorination of the resulting oxides of uranium elemental fluorine in excess of fluoride greater than stoichiometric to 5 - 50%, then the enriched uranium hexafluoride purified by the method of centrifugal separation, followed by mixing it with uranium hexafluoride containing uranium-235 below content in the fuel material, by continuously combining the two gas streams, and the resulting fuel material before filling Desublimers.

2. The method according to p. 1, characterized in that the oxides of uranium foryouth at a temperature of 300 - 400oWith under stirring and the excess of fluoride greater than stoichiometric by 5 - 10%.

3. The method according to p. 1, characterized in that the oxides of uranium foryouth at a temperature of 1400 - 1500oWith in excess of fluoride greater than stoichiometric by 10 - 50% with the introduction of the oxides in the reaction zone at gaseousness method of centrifugal separation cascade of gas centrifuges to impurity content of 10-4- 10-5wt.%.

5. The method according to p. 1, characterized in that the mixing of the two gas streams is carried out by regulating the expenditure of each stream in accordance with the content of uranium-235.

 

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