DK146497B - PROCEDURE FOR THE MANUFACTURING OF THE SIGNIFICANT CIRCUIT, ACTINID CONTAINING PARTICLES - Google Patents

Description

146497 i

The invention relates to a process for the preparation of substantially round actinide-containing particles.

In the preparation of round, actinide-containing, as well as uranium-containing particles, the usual technique is to disperse an aqueous actinide-containing sol, which may also, if desired, also contain a surfactant, in an organic liquid, e.g. petroleum or carbon tetrachloride, so that the aqueous phase drops solidify under the dispersion conditions in the organic liquid, the aqueous liquid being wholly or substantially immiscible with the organic liquid. The dispersed droplets of the sun assume spherical shape due to their surface tension in the dispersed state of the organic liquid. The round particles thus formed usually have a web of organic liquid adhering to the surface of the particles.

When the particles of gel or hydroxide material formed after separation from the organic liquid 20 are subjected to a wash to remove soluble salts such as nitrates and / or chlorides, the said organic liquid film often causes difficulties.

In the past, the precautions described below have been used to improve the washing process:

After forming in a relatively viscous organic phase, the round particles were separated and washed with petroleum ether and then eluted with an aqueous phase. Residues of petroleum ether in some cases caused problems.

For this reason, the washing with petroleum ether was followed by a new washing process with methanol. After washing with methanol, the final washing process was performed in this case with an aqueous rinse phase. It can be seen from this that the process used makes the preparation of round particles difficult.

Another proposed measure includes regeneration of the organic phase. Forming oils can in some cases be regenerated by contacting the oil with a layer of adsorbent material. The adsorbent material collects the decomposition products of the oil. In the past, the decomposition products of the forming oil have sometimes continued to adhere to the spheres, thus interfering with washing.

In the known manner, when preparing a granular material in an organic liquid, this material is obtained in the form of mechanically weak particles to which the said thin layer of organic material adheres.

10 To remove this thin layer by washing with an aqueous liquid, a strong mechanical re-rinse is required. · Such a powerful mechanical washing treatment can easily damage the mechanically weak particles and thus readily reduce their yield.

15 From, for example, German submission no.

In a similar preparation of oxide gel particles by dispersing an aqueous oxide sol in an organic liquid, it is known to add the surfactant to the organic liquid. The purpose of this is to prevent the newly formed drops in the organic liquid from sticking together or adhering to the wall of the column used for the preparation. The gel particles formed, which, even after separation, adhere to an organic liquid film, are not subjected to any washing process as in the previously known process, but are subjected to a special drying process, possibly using a steam distillation, to remove most of the the water with adherent organic liquid.

The process of the present invention is of the prior art in which an aqueous liquid containing one or more actinide compounds and, if desired, carbon and / or a surfactant is dispersed in an organic liquid immiscible with 35 water under such conditions. the dispersed droplets of the aqueous phase form substantially round solid inorganic gel or hydroxide particles, after which these solid particles are separated from the organic phase and washed with an aqueous liquid and then dried and sintered, and the process is characterized in that the liquid organic phase contains a surface-active agent with an HLB value of from 7 to less than 10.0 and that an aqueous liquid is used for washing the solid particles separated from the organic phase. contains a surfactant with an HLB value of from 10.0 to 14.

In this process, a drastic mechanical washing process is not required, and pendant residues of the organic phase can be easily washed away by a mild washing treatment with an aqueous liquid. The round particles produced by the process of the invention are usually used. as fuel or fuel elements in nuclear reactors and is composed of actinide metals and oxides thereof, including uranium dioxide, uranium trioxide, thorium dioxide, plutonium dioxide, plutonium trioxide, zirconium dioxide, beryleium oxide and yttrium oxide and mixtures thereof, from which dense metal microbes can be prepared. As mentioned, the balls may optionally contain carbon, usually colloidal carbon, which, under the conditions of heating and processing known in the art, converts the particles 25 into dense metal carbide beads.

Said HLB number is a measure of the hydrophilic-lipophilic balance of the surfactant. For a surfactant which is "100% hydrophilic", the HLB number is set to 20. For a nonionic, surfactant based on esters of fatty acids, the HLB number can be calculated from the formula: HLB = 20 ( 1- |), where S = the saponification number of the ester, and A = the acid number of the formed acid.

For forionogenic surfactants, the HLB number can be determined experimentally.

Thus, a surfactant with an HLB number = 10 will be 50% hydrophilic and 50% lipophilic.

4 148497

Thus, the surfactant in the organic phase has a certain overweight of lipophilic character, the HLB number being less than 10, namely in the range 7-10, while the surfactant in the aqueous wash phase has a certain overweight of hydrophilic character, The HLB number is at least 10, namely in the range of 10 - 14.

As an example of a useful combination of organic phase, surfactant in the organic phase and surfactant in the aqueous wash phase, the following can be mentioned:

Organic phase - one or more alkyl-substituted benzenes, wherein the alkyl chain has an average carbon atom number of approx. 12 (a suitable alkylbenzene mixture is "Dobane PT-12").

15 "Organic phase surfactant - an agent based on a mixture of polyoxyethylene sorbitol fatty acid and alkylarylsulfonate (a suitable surfactant is" Atlox 3386 "with an HLB number of 9.6).

Aqueous phase surfactant - an agent 20 based on a mixture of polyoxyethylene sorbitan esters of fatty acids and of resin acids and alkylarylsulfonates (a suitable surfactant is "Atlox 3335" with an HLB number of 13.0).

"Dobane PT-12" is a mixture of alkyl benzenes sold by Shell Nederland N.V.

"Atlox 3386" and "Atlox 3335" are commercially available products from Atlas Chemical Industries.

The liquid inorganic phase to be dispersed in the organic phase consists of actinide metal hydroxide sols or metal salt solutions or anion-poor actinide metal salt solutions or mixtures of these liquids. As mentioned above, carbon powder may be dispersed, by the surfactant, in the liquid urogenic phase.

According to a preferred embodiment of the method, free ammonia and / or one or more ammonia-releasing agents may be incorporated into the organic phase. The latter may conveniently be mixed with the metal hydroxide sol, or the solution of metal salt or anion-poor metal salt before distribution thereof in the organic phase.

Ammonia releasing agents are e.g. urea, hexamethylenetetramine, ammonium carbonate, potassium cyanate, ammonium cyanate, acetamide, formamide, etc. After mixing the ammonia-releasing agent with the inorganic phase, it is advantageous for the mixed liquids to cool before dispersing.

It is possible to maintain a concentration of ammonia or ammonia releasing agent in the organic phase.

It may further be convenient in a manner known per se to add an ammonia solution to the aqueous washing phase.

To improve the properties of the final products, the aqueous inorganic phase containing actinide constituents may also contain constituents of the elements ZrIV, HfIV, Y111, Se111 and trivalent rare earths.

A liquid inorganic phase which is particularly suitable for dispersion consists essentially of an aqueous solution of uranyl nitrate or anion-low uranyl nitrate. In this case, the aqueous wash phase may conveniently consist of aqueous ammonia to which a surfactant is added.

The method according to the invention is explained in more detail below by means of an example.

Example

An aqueous anion-poor uranyl nitrate solution was mixed with urea and hexamethylenetetramine solution and the solution was sprayed over a hot organic liquid containing a surfactant.

The aqueous solution consisted of a volume portion of an aqueous nitrate-deficient uranyl nitrate solution having a molar concentration of UO-1NO3 (g) (OH) - ^ of 2.85 and the solution was mixed with cooling to 10 ° C with 146497 6 1.2 parts by volume cooled aqueous solution of hexamethyl-entetramine and urea, and the concentration of both the ammonia-releasing compounds was 3 molar.

The organic liquid heated to 95 ° C consisted of a mixture of alkyl-substituted benzenes whose side chains contained, on average, 12 carbon atoms ("Dobane PT-12").

The lipophilic surfactant ("Atlox 3386") constituted 0.2% by volume of the organic phase and 10 was based on a mixture of polyoxyethylene sorbitol fatty acid and alkylarylsulfonate. The drops of the uranyl nitrate solution which dropped into the organic liquid solidified as a result of the elevated temperature which also caused the ammonia-releasing compounds to decompose to form ammonia. After separation from the organic phase, the obtained granular material was washed with an aqueous ammonia solution containing 0.2% by volume of a hydrophilic surfactant ("Atlox 3335", HLB = 13.0).

The pH of the aqueous ammonia solution was 9 or greater and maintained at this level by the addition of more concentrated ammonia solution.

In the said washing process, the organic phase was substantially completely removed from the granular material which could then be dried and sintered.