DE1771966A1 - Process for the production of multi-component nuclear fuels - Google Patents

Description

W.R. Grace & Co. (US 67O 452 - prio 25-9-67

New York, NYASt.A. A 12214 - 5636)

Hamburg, August 6, 1968

Process for the production of multi-component nuclear fuel

The invention relates to a process for the production of small nuclear fuel particles from oxides of at least two metals the Aktlnidengruppe.

In the manufacture of fuel elements from brines in the form of microspheres, products with extremely advantageous physical properties obtained. The microspheres can be sintered to high density at much lower temperatures than is possible when manufacturing the fuel elements using conventional ceramic processes. The microspheres can Manufactured in sizes from a few microns to 1000 microns and above and allow very easy handling of the nuclear fuel.

Today fuel elements are required which contain not just one component but two or more components. So there is for example, a need for fuels made from uranium and plutonium oxide or thorium and uranium oxide, which fissures

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contain material such as U 235 or U 2j5jj.

In the known process, these multicomponent fuels are precipitated together from solutions of salts corresponding metals or by physically mixing the dried oxide particles and then crushing them, Presses etc. manufactured using conventional ceramic techniques. They are also made from mixed oxide sols according to one Process in which a solution or a sol of the second component is added to an SOl of the first component.

The differences in the level of radiotoxicity of each Components in a two-component fuel increases the Difficulties in making mixed oxide sol products by these conventional processes. Uranium oxide (U 2 ^ 8) can be used without danger with normal laboratory equipment be handled. Plutonium, on the other hand, can only be handled in radiation protection boxes and other complicated facilities. These difficulties are increased significantly if the production of mixed oxide fuels is reduced to operational Production is transferred.

A process for the production of these mixed fuel systems has now been developed in which the two components are

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can be handled separately in facilities suitable for the individual components. This system offers a Significant improvement over the conventional way of working «in which both components are combined in each stage were treated, so that extremely complicated facilities were required for each stage and for all of the material to be processed.

The present invention accordingly provides a method for producing nuclear fuel from oxides of at least two actinide metals proposed, in which one brings together microspheres from a nuclear breeding material with a fissile material in the liquid or gaseous phase and impregnating the microspheres with the fissile material and then converting the fissile material into an insoluble form. For this purpose, the microspheres can be mixed with a sol or a solution, preferably an aqueous solution, of a salt Impregnate the fissile component and then transfer it into the oxide in the pores of the matrix. You can do the microspheres too impregnate with the additional material in gaseous form, e.g. PuFg, UFg etc., and then precipitate this in the pores and in the oxides convict.

According to one embodiment of the method according to the invention

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the microbeads are shaped with the fissile material an aqueous solution of one of its salts is impregnated and, after impregnation, the excess water is removed and that fissile material precipitated out of solution.

The particles can be dried to different extents. the Microspheres, which form a matrix for the other component, can be referred to as microsphere-shaped gels. The term "gel" can therefore be used to describe the matrix material to be used.

The invention provides a process for the production of mixed oxide fuels in only a few process stages, so that the Main work can be done with usual facilities. This procedure eliminates the possibility of contamination of the plants with fissile material up to the last process, } level excluded.

Before the invention is explained in more detail in individual examples, some preferred features of the process according to the invention are to be described in general below.

In a preferred embodiment of the method, the breeding material or the matrix is first produced in microsphere form (thorioic oxide or uranium oxide) and then with the desired

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The amount of the fissile component as a solution of a salt or added as a sol of the component. The impregnated microspheres are then washed, dried and calcined into the finished product.

Generally speaking, the preferred embodiment includes the The following stages:

1. Choice and solution of the starting materials for the fuel.

2. Manufacture of aquasoles or suitable modified ones Solutions of the raw materials *

3 · Manufacture of microspheres from the brines or modified Solutions.

4. Addition of a sparse material to the NLkrokugeln »

5. Washing, drying and sintering of those containing the additive Microspheres.

In the first stage of the process according to the invention, the selected materials to be used as breeding material and fissile material. The substances mainly used as a matrix are processed or exhausted uranium oxide (U 238) alone or in a mixture with other substances such as thorium oxide. Thorium oxide (Th 232) can also be used as breeding material will. The fissile second component of the microspheres can for example consist of uranium oxide or plutonium oxide. So For example, uranium oxide (U 238) can be impregnated as a matrix with plutonium oxide or the fissile isotopes U 233 or U 235

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will. Thus, in one embodiment of the invention Processed thorium oxide or uranium oxide as breeding material and plutonium or another isotope of uranium than that as breeding material. used as a fissile material. Sin more genius Thoriiimoxyd-uranium oxide fuel can be produced by impregnating Thorium oxide microspheres can be produced with U 233 or U 235.

The breeding material or the matrix, i.e. uranium oxide or thorium oxide, is first produced as a solution of the nitrate, chloride or the like, which is then converted into the sol form. the Brines can be made by several methods, of which the following are preferred:

1. Electrodialysis using anion-permeable membranes.

2. Controlled hydrolysis with urea.

3. Ion exchange using resins in the hydroxide form. -

♦ · Peptieatlon of washed hydroxides with elner acid, 5. Electrolysis of solutions with oxidation of the anions to a volatile compound.

In the next stage of the process according to the invention, the sols are converted into microspheres. The method of manufacture of KLkrokugeln is not part of the present invention and

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let Described in detail in U.S. Patent 3,331,785. Briefly summarized, this procedure consists in "that one the Brine transferred in droplet form and the brine droplets in an im Qegenetrom solutions led to them! Ttelsäule dries. the The resulting microspheres are drawn off and washed at the PuQ of the column.

The process can be used as a preliminary stage in the manufacture of a colloid the nuclear fuel and the drying of the colloid a QeI in microsphere form.

The matrix can be in powder oil, microspheres or in the form of from larger spheroids also produced by a process be, in which one salt of the breeding material with a water-soluble resin mixed, which increases the viscosity in an alkaline medium. This solution then becomes education introduced by microspheres or spheroids in the form of drops into an aqueous alkaline solution. The resulting particles or spherules are then separated; soaked and dried.

However, the microspheres or particles can be prepared by any other method described in the technical and patent literature, provided that the finished product is porous enough to contain the desired amount of cleavable

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- 8 material to hold on to.

It is assumed that the thorium oxide and uranium oxide microspheres in the process according to the invention, the solutions or sols containing the cleavable component in their cavities where they are then converted into an insoluble form * dried and can be sintered.

The fissile used to impregnate the microspheres Material can be used as a solution or as a sol in an inorganic or organic solvent. Preferably an aqueous solution of a salt is used, as this results in a higher concentration of the fissile material solution can. The nitrates (Pu-VI, U-VI) are preferred, but the chlorides, sulfates, etc. can also be used to produce the Impregnation solution can be used. The one for impregnation

The fissile material solutions used can be in concentration / of approx 0.1 to 700 g per liter can be produced. Acetone is preferred as the organic solvent. Other suitable solvents are diethyl ether, dibutyl ether, methyl isobutyl ketone, tributyl phosphate, trlootylamine, trilaurylamine, cyclohexyldilaurylamine, determined mte alcohols and the like.

If uranium dioxide microspheres are used as breeding material,

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they can at this stage due to the presence of hexavalent Uranium contain an excess of stoichiometric amount of oxygen. Hexavalent uranium is more soluble in aqueous media than tetravalent uranium. In this case, the microspheres must to be reduced to the dioxide if the product is to be free of sludge and the like between the particles. The reduction can be carried out in any way, for example by treatment with hydrogen or the like. These However, the stage can also be omitted if a non-aqueous solvent is used for the preparation of the impregnation agent will. The hydrogen treatment is carried out at a temperature of 300 to 900 ° C for about 1 to about hours. In the case of the method according to the invention, this stage can without affecting the microsphere structure or porosity be terminated at low temperatures.

A suitable method of impregnating the spheres is to slowly mix the agitated microspheres with the solution of the fissile salt or the sol. If uranium oxide is used as breeding material, it is preferable to move the balls Rait a stream of inert gas, which prevents the oxidation of the uranium oxide to the hexavalent state. Any suitable Inert gases such as helium, argon, neon, nitrogen and the like can be used, with argon being preferred. In the laboratory

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The microspheres are conveniently made by regulating the gas flow moves in the area surrounding the microspheres. the However, balls can also be moved in other mechanical ways, for example by stirring, shaking and the like. In any case, the balls must be agitated during impregnation in order to ensure that the balls are evenly impregnated to achieve with the solution or the sol of the fissile component. With what amount of impregnation agent the microspheres ™ to be impregnated depends on the desired in the finished product Concentration of cleavable material and is expediently regulated by adjusting the solution concentration. If necessary, a second impregnation can also be applied to be carried out by more impregnating agents.

When using solutions, the microspheres are usually impregnated to the point where they just begin to get wet. After impregnation, the microspheres are useful for removing water with an organic solvent such as Treated hexanol. Solvents other than hexanol can also be used, the choice of which depends on the Preparation of the solution of the fissile material depends on the solvents used.

After the microspheres are freed of excess water

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are, the gap material is expediently precipitated as hydroxide in the cavities of the microspheres. The cleavable component can of course also be precipitated as a carbonate, oxalate and the like. Compounds which do not leave any contaminating residue on the impregnated product, such as, for example, gaseous or liquid ammonia, are preferred as the base. In general, the microspheres are suspended in an aqueous ammonia solution for precipitation. Preferably, concentrated aqueous ammonia is used for this purpose, but ammonia concentrations between 5 and 30 % by weight can generally be used. However, the precipitation can also take place with gaseous HH-z. In general, the precipitation is complete in about 10 minutes. However, shorter or longer times may also be required depending on the method of operation and the system.

Thus, when the microspheres are impregnated with an aqueous solution of a salt of the fissile element, they are removed excess water with a dehydrating solvent and then uses ammonia as a precipitant.

To remove excess ammonia, anions, hexanol or Other solvents, the microspheres are then washed with deionized water. Generally about 250 ml of deionized water per g of microsphere to remove all To remove impurities. Then the micro

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- 12 balls dried under vacuum.

The last stage of the process according to the invention is sintering. For this purpose, the microspheres are preferably about 0.5 to 7 hours in a hydrogen-nitrogen atmosphere and heated at 300 to 700 ⁰ C then sintered to 6 hours at 1000 ⁰ C to l800 ° C for a further 0.5.

The matrix particles can of course also by sieving or other processes are separated according to size and only the particles of a certain size range are impregnated with the fissile materials will. According to one embodiment of the method according to the invention, one starts from a very wide variety of microspheres Size, separates the particles of a certain size range from these differently sized particles off and subjects only the particles of this size range to the impregnation step of the process.

The invention is illustrated in more detail by the following examples, but is not restricted to the same. As fissile materials uranium oxide microspheres became very cumbersome to handle and are not available for general laboratory experiments impregnated with cerium dioxide and thorium oxide. Thorium oxide was chosen as an analogous compound for plutonium oxide,

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as it has a similar crystal structure. Cerium dioxide was used as a analogous compound chosen for the chemical behavior of plutonium oxide in the wet state.

At s P ₁ IeI _{1 m} 1

In this example, the uranium oxide microspheres were made with a Impregnated thorium nitrate solution. The uranium oxide JÜkrokugeln were as described in U.S. Patent 3,331,785 Process manufactured and then subjected to a pretreatment, in which she was in a hydrogen atmosphere for 3 hours were heated to 500 ° C. By this treatment, the hexavalent uranium oxide converted into tetravalent uranium oxide.

To prepare the impregnation solution, 20 g of thorium nitrate were dissolved in 15 ml of water. This solution was added dropwise to the UOp-ML microspheres. The impregnation was carried out in a glove box in an argon atmosphere. % While adding the impregnant, the microspheres were stirred. A total of about 12.9 ml of solution was required to impregnate the 20.2 g of uranium oxide microspheres to the point where they were just wet. The sample was then treated with 2.5 ml of 1: 5 ammonium hydroxide. The ammonia was removed by careful decantation. No precipitate was found in the ammonia filtrate. The balls were then unaffected

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damaged and showed no precipitation on their external surfaces. Outwardly, the balls looked exactly the same as before the impregnation.

The impregnated balls were then under a for 4 hours Dried infrared lamp. Subsequent to this drying, the sample was dried under vacuum according to the following schedule:

30 minutes at 40 ° C
60 minutes at 60 ° C
90 minutes at 80 ° C
90 minutes at 100 ^° C
90 minutes at 120 ⁰ C.

The microspheres were then kept under vacuum for 8 hours at room temperature and then the vacuum was released with nitrogen. After that, the bullets were undamaged. The dried microspheres were sintered by the following treatment: First, the temperature was raised within one hour to 350 ° C, then brought within 2 hours from 350 to 500 ⁰ C and held for 1 hour at 500 ° C. The temperature was then increased to 1400 ° C. over the course of 90 minutes and held at this level for 90 minutes and then cooled rapidly. The entire sintering process was carried out in a hydrogen atmosphere. No sludge was formed between the particles, and the surfaces of the microspheres did not have small crystal particles. The sample was checked for thorlum content below "

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seeks; it contained 10.51% by weight of thorium. In addition, the sample was subjected to X-ray analysis, in which it showed a single-phase diagram. The X-ray diffraction lines were sharp, indicating the complete formation of a solid solution. The unit cell _{constant a Q} was calculated to be 5.4851 8. The weight percentage value for a solid solution, which results from an approximate calculation from this unit cell, corresponds to 15 wt. £ ThO ₂ . I.

Upon metallographic examination, the microspheres showed a uniform fine-grained cross-section.

Another sample of the microspheres was placed in a special resin embedded, ground to reveal the spherical cross-section, polished and examined with an electron microprobe. The control elements of the microprobe device were at their highest Thorium sensitivity set. There were the transverse ^ scanned sections of various microspheres; it was found that the redistribution of the thorax in the individual spheres and was even from one ball to another.

The density of the microspheres was determined by the mercury displacement method determined and was 10.64 g / cnr.

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Bel8Eiel_2

In this example, uranium oxide microspheres were made with ceria impregnated.

The uranium oxide microspheres used for impregnation were produced in the same manner as in Example 1 and pretreated in a hydrogen atmosphere _{to reduce the uranium oxide to the stoichiometric UO 2.} In addition, a solution of 20 g of cereal nitrate in 15 ml of water was prepared. The microbeads were then impregnated with this solution to such an extent that they were just wet. The impregnation was carried out with the same equipment and procedure as in Example 1. The sample was then treated with 3.5 ml of concentrated ammonium hydroxide diluted with water in a ratio of 1: 5. The ammonia was removed by decantation. No precipitate was found in the ammonia filtrate. The impregnated microspheres were dried under an infrared lamp for 5 hours and then washed for δ hours. After washing, the sample was dried under vacuum as in Example 1.

The dried MikVokugeln were then sintered according to the following schedule: First, the temperature was published in a hydrogen atmosphere within 4 1/4 hours slowly to 1000 ⁰ C

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- it -

increased, then brought to 14OO ° C in the course of 1 hour and Maintained between 1400 and 1485 ° C for 1 1/2 hours. Thereafter the product was cooled under hydrogen. It / had no sludge was accumulated between the particles and no crystal particles had settled on the surfaces of the microspheres educated. The product had a density of 10. T g / cnr, one Cer analysis showed a Ce Og content of 1.9 wt. It I

A metallographic examination was carried out as in Example 1, which showed that the microspheres had a uniform fine-grained cross section. The microspheres were also subjected to X-ray analysis. From the calculation of the unit cell, it was found that a complete solid solution was obtained. The width of the X-ray lines indicated a single phase product. A sample of the microspheres was made as in Example 1 for examination with an electron microprobe, which showed a homogeneous and uniform distribution: _{ti of} the cerium content in the individual spheres and from one sphere to the other.

Example 3

This example shows the manufacture of Thorium Oxide impregnated UOg balls using an improved Waschteohnik described.

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The same procedure as in Example 1 was followed. An aqueous solution of 20 g of thorium nitrate in 15 ml of water was used as the impregnating agent for the uranium oxide. The microspheres were so far impregnated _P that they were just wet. They were then immersed in dry hexanol to remove the water. The hexanol was carefully filtered off under vacuum so that the impregnated microspheres were not damaged. The microspheres were then treated with honey-centered ammonium hydroxide, then drained and then washed with water for 8 hours. The washed sample was dried under vacuum as in Examples 1 and 2. Subsequently, it was sintered in hydrogen according to the following scheme: The temperature was raised slowly within J50 minutes at 1000 ⁰ C and then maintained for 2 hours at 1400-1485 ° C. The product was cooled under hydrogen.

Thorium analysis showed that the product was 4.52% by weight of thorium contained. The density of the product was 10.73.

Example 4

After the process of impregnating microspheres with a fissile material using the Thoriuraoxyd- and ceria analogs had been worked out, uranium oxide

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toiicrokugeln rait plutonium oxide impregnated.

A suitable group of pure porous UOg microspheres (Ig) was placed in a glove box in a filter funnel with a glass frit insert. These UOg microspheres consisted of unsintered microspheres which had been produced according to the process described in US Pat. No. 3,331,785. For pretreatment, the microspheres were heated ^{to 50O 0} C for about 5 hours in a hydrogen atmosphere. In addition, an approximately 6 molar plutonium base solution was prepared in nitric acid, which contained approximately 60 g plutonium per liter. To prepare the impregnation solution, 2.2 ml of this basic solution were diluted with 4.4 ml of deionized water. This impregnation solution was added dropwise to the UOp microspheres. The addition was carried out in a glove box in an air atmosphere. During the addition, the microspheres were continuously agitated with a stream of argon passed through the funnel. In order to impregnate the balls until they began to wet, a total of about 0.40 ml of impregnation solution was required.

The balls were then mixed with about JO ml of dry hexanol washed »to remove the water. The hexanol was removed by filtration under vacuum. The whole treatment was carried out very carefully so as not to damage the impregnated microspheres.

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The sample was then treated with about 90 ml of concentrated aqueous ammonia. The treatment time was 15 minutes. then the ammonia was very carefully filtered off under vacuum. No precipitate was found in the ammonium filtrate. the The balls were then undamaged and showed no precipitation ge on their surface. The impregnated microspheres were then washed with 500 ml of deionized water for 4 hours, no physical change in the microspheres was observed.

After washing, the sample was vacuum dried according to the following schedule:

30 minutes at 40 ° C

60 minutes at 60 ° C

90 minutes at 80 ° C

90 minutes at 120 ⁰ C.

The microspheres were then cooled to room temperature under vacuum for 8 hours, followed by the vacuum with nitrogen was repealed. The spheres were outwardly unchanged.

The microspheres were then placed in a molybdenum shell for sintering given. The sintering was carried out in an atmosphere of 50 parts by volume of hydrogen and 50 parts by volume of nitrogen in one Horizontal furnace carried out with the following zones: one

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600 ° C zone about 60 cm long, an intermediate zone about 75 cm long and a 1677 ° O zone about 120 cm long. The bowl was passed through the furnace at a speed of 22 cm per hour. In total, the molybdenum bowl with the microspheres took 24 hours to pass through the furnace. The balls stayed in the 1677 ⁰ G zone for a total of about 5 to 6 hours. Microspheres of good spherical shape with no sludge between the particles and no crystal particles on the surfaces of the microspheres were obtained.

The density of the product was determined with a xyloi pycnometer and was 10.43 g / enr. To investigate on theirs Plutonium content, the microspheres were dissolved in a mixture of nitric acid and hydrochloric acid and the solution in a Column ion exchange resin adsorbed. The plutonium was out eluted from the column and determined by titration. Thereafter included the microspheres 1.2% by weight of plutonium calculated as metal or 1.36 wt. $ 6 plutonium calculated as

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Claims (1)

WR Grace St Co. ** (US 67O 452 - prio 25.9.1967 New York, NY / V.St.A. A 12214 - 5636) Hamburg, August 6, 1968 Patent claims 1. A method for manufacturing a nuclear fuel of oxides $ of at least two metals of the actinide, characterized in that microspheres bringing together of a nuclear breeder material with a fissile material in liquid or gaseous phase and impregnating the microspheres with the fissionable material, and then the fissile material converted into an insoluble form. 2. The method according to claim 1, characterized in that one the fissile material as an aqueous solution of one of its * Salts used to remove the excess water after impregnation removed and the fissile material then precipitates out of solution. 2 · The method according to claim 2, characterized in that the excess water with a dehydrating solvent removed and then ammonia used as a precipitant. 109887/1520 BATH ORIGINAL - tr - ■ '■ -' ■ · χι K. Process according to Claim I ₁ , characterized in that the cleavable material is used as the solvent for its hydroxide and then converted into the insoluble oxide form. 5. Process according to claims 1 to 4, characterized in that » that the Mlkrokugeln after transferring the fissile Material in the insoluble form dries and calcines. I. 6. Process according to claims 1 to 5 * characterized in that » that in a preliminary stage a colloid of a nuclear breeding material is produced and the colloid becomes a QeI in the form of a microsphere dries. 7. The method according to claim 6 »characterized» that one the colloidal breeding material to dry in the form of drops a dehydrating organic solvent leads and they r essentially in the gel state as spheroid particles withdraw from this. 8. The method according to claims 6 and 7, characterized in that » that the gel can be seen as microspheres of various particle sizes withdraws »from these microspheres of a certain particle size range and only the separated particles are subjected to the impregnation step. ' 109887/1520 9. The method according to claims 2 and 6, characterized in that that an aqueous solution of a fissile material is used and the colloid is produced as an aqueous colloid. 10. The method according to claim 9, characterized in that the colloidal brood material in drop form by a drying Solvent leads and is removed from the solvent as spheroid particles essentially in gel form. 11. The method according to claims 9 and 10, characterized in that that thorium oxide is used as breeding material and uranium in the liquid phase is used as fissile material. 12. The method according to claim 11, characterized in that the uranium is brought together in hexavalent form with the QeI. . 12 · The method according to claim 11, characterized in that the fissile material
Uranyl nitrate used. as a fissile material in the liquid phase, a solution of 109887/1520 BATH ORIGINAL