Method and apparatus for volume crystallization of plutonium dioxide

FIELD: nuclear engineering.

SUBSTANCE: proposed method for volume crystallization of plutonium dioxide includes treatment of molten alkali-metal chlorides with plutonium compound dissolved therein, as well as treatment of melt obtained in the process by oxygen-containing gas mixture and precipitation of large-crystal plutonium dioxide on bath bottom. In the process closed-porosity graphite granules are disposed on melt surface, their contact with melt being afforded as they are consumed. Apparatus for volume crystallization of plutonium dioxide from molten alkali-metal chlorides with plutonium compound dissolved therein has bath, cover, melt mixing system, and device for feeding soluble plutonium compounds and gas mixture to melt. Bath, parts and assemblies contacting the melt are made of ceramic material shielded at melt boundary level with pyrographite parts. Gas mixture feeding devices have ceramic and pyrographite tubes.

EFFECT: enhanced durability of equipment.

3 cl, 4 dwg

 

Known and can be adopted as the prototype of "the Way of the conversion of the plutonium-gallium alloy in plutonium dioxide" (patent No. 2179530, BIPM No. 5-2002), according to which the plutonium dioxide is obtained from a melt prepared dissolved in the metal alloy of plutonium (SMEs). That is, before the actual process of bulk crystallization in the melt is placed SMEs, which then dissolve in for some time (several hours), passing through the melt chlorine gas.

Chlorine, interacting with SMEs, translates it into soluble in the melt state in connection ul3and GaCl3reactions

2Pu(meth)+3l22ul3(I)

Ga(meth)+CL2GaCl2(II)

GaCl2+1/2Cl2GaCl3(III)

After complete dissolution of the SMR feed chlorine into the melt cease and serves oxygen-containing gas mixture specified in the patent, the ratio of the volume of gases).

Thus, the conversion used in this method consists of two stages: preparation (dissolution SMEs) and the primary and preparatory stage for a significant proportion of time the entire process. This means that there is a possibility to increase the productivity of the process for obtaining plutonium dioxide by eliminating (a significant decrease in the Oia time) preparatory stage of the process.

Another important factor is the high reactivity of SMEs in relation to the structural material, including pyrographite (graphite) and ceramics of various types. Contact SME (metallic plutonium) in the molten state carbon-based materials leads to the formation of plutonium carbides, and therefore, the expenditure part of the structural material, that is, to the damage of the bath (dissolution).

The preparation of the melt can be carried out in a ceramic tub, but not all ceramic materials are compatible with molten plutonium metal. Among them, oxides of alkaline earth metals (BeO, MgO, Cao), but EEO unsuitable because of the danger of high neutron background, the MgO and Cao are easily dissolved under the action of chlorine when dissolved SMEs.

Preparation melt by dissolving fine dioxide plutonium ponograficos crucible using chlorine gas requires such a long time, so Kok plutonium dioxide refers to the number of sparingly soluble substances. In addition, when the dissolution reactions occur

Rio2+Cl2PuO2Cl2(4)

PuO2Cl2+Cl2uCl4+O2(5)

Rio2Cl2+O+CL2PuCl4+CO2(6)

PuO2+C+2Cl2PuCl4+CO2(7).

That is, during the dissolution also occurs expenditure of the material of the bath, which leads to a reduction of the resource.

The technical result of the invention is to increase the service life of the bath for the process of bulk crystallization of plutonium dioxide and other parts in contact with the melt.

That is, when the load in the melt is ready mortar forms of plutonium (for example, trichloride PU) eliminates the undesirable effects associated with the consumption of the material of the bath and other parts, increases the service life of the apparatus, and hence (by reducing the number of stops to replace bath) the volumetric efficiency of the process of crystallization. In addition, the performance of the process as a whole also increases due to the almost complete elimination stage of preparation of the melt, because it boils down to loading soluble compounds prepared in a separate process, not associated with the considered. It should be borne in mind that under-soluble chemical compound of plutonium can be understood, first, the connection to the analogue, in common with the anions of the salt-solvent, i.e. a compound with chlorine (chloride). This can be trichloride plutonium in individual form, composition (mixture on the reverse or "fresh" salt (NaCl-KCl)PuCl3or others with whom otnoshenijah. In the circulating salt may be present and oxygen-containing compounds Rio2Cl2and Rio2CL3and PuCl4in complex form, for example Cs2PuCl6salt , which can be made according to the technology with the use of aqueous solutions. For convenience of loading and storing, repackaging and dispensing downloadable salts can be manufactured in a granular state using known methods, for example by melting substances (mixtures) in an inert atmosphere and pouring the melt in the form of droplets through a capillary into the liquid, not interacting with chlorides.

In the process of bulk crystallization, as described in the prototype, the inevitable stage of transfer of dissolved compounds of plutonium dioxide is their transfer to the oxygen-containing soluble form of plutonium Rio2Cl or Rio2CL2:

uCl3+O2PuO2Cl+Cl2↑ (8),

PuCl4+O2PuO2Cl2(9),

and only then

Rio2CL→ PuO2(TV)+1/2Cl↑ (10)

PuO2Cl2PIO2(TV)+Cl2↑ (11).

(writing reactions in this form and in the description of the method according to the application for the patent and prototype are equal).

Thus, in the melt in the process volume Krista is the implementation of the ions are always present PuO 22+(PuO2+or (as amended prototype)2-that interact with carbon according to reaction (6) or

With+2-CO2↑ (12).

To resolve the damaging effects of oxygen ions on the material of the bath and other details, you can make it ceramic, for example of the most technologically advanced material - fused or fused quartz.

However, according to NIIAR research (in press references there) showed that plutonium dioxide in this process has the ability to settle not only in the volume of the melt, but also in the form of a layer on the surface of the quartz at the phase boundary, i.e. at the level of the border of the melt and the quartz tube is hammered from the inside out completely in a short time. The layer of plutonium dioxide bonded to quartz so tightly that can destroy a tub or other items which are submerged in the melt. The end of the quartz tube, also representing the three-phase boundary, hammered, and the process is terminated, requiring replacement of the tube. Thus, the ceramic materials are of limited use because of the reduction of the term of service, and due to possible losses of plutonium (translation into working product for cleaning impurities from quartz), which generally reduces productivity of the process volume is me crystallization.

The service life of ceramic products, including baths, increase using to protect their surfaces in three-phase region of carbon-containing materials which are in the process of "burn", but can be replaced without replacing the tub. These materials can be applied, for example, in the form of rings from pyrographite in two variants: with shoulder of the enlarged diameter or without shoulder with the placement on the shoulder of quartz products, for example, as shown in figures 1 and 2. To replace them (residues removal and installation "fresh"), you must either remove the protected item from the melt, or to stop the process and remove the device cover to replace the ring that protects the tub. Option, not requiring the operation of Assembly and disassembly", consisting in the use of granules of carbon-containing material capable of resist on the surface of the melt. In the initial state, these granules must have an effective density lower than the density of the melt. In particular, for a melt such as NaCl-KCl they must have a large closed porosity. As they will shrink in size and to sink, and then "burn" until the end of the reaction (6). Therefore, it is necessary to carry out their uploading to maintain a permanent layer on the surface of the melt, as shown in figure 3.

Since the gas supply tube phase C is on is not only at the level of the melt, but at the level of the outlet, it protects using the composition from quartz 6 and ponograficos 7 tubes, and metal nepela connected with grundbuch 9. These three elements of the seal between the gasket 8, additional biasing device (for example, pressure hollow screw 12, as shown in figure 4.

For fastening articles 6, 7, 9 and transmitted provided details: coupler 10 and bracket 11, and the corresponding slots in the sleeve 10 and ponograficos tube 7.

Description of the method

In a bath 1 of quartz with melt 2, closed the lid, install the necessary device: circulation pipe, a stirrer, a tube for supplying gas. Tub 1, a circulation tube and stirrer protected by rings 3 of pyrographite with the shoulder (figure 1) or rings 4 without fillets (figure 2). Instead of rings can be used granules 5 from pyrographite with high porosity (figure 3).

In the melt 2 serves soluble therein the connection of plutonium, such as trichloride plutonium in the individual condition, mixed with the circulating salt, mixed with oxygen-containing chloride salts of plutonium, in the form of double salts Cs2PuCl6including and mixed with the circulating salt. All layers can be prepared in a granular condition. After loading soluble compounds of plutonium through gaspode the next tube (figure 4) serves oxygen-containing gas mixture, carry out the process of bulk crystallization of plutonium dioxide. While plutonium dioxide falls to the bottom of the tank, whence it is extracted in a known manner. Then plutonium dioxide free from salts and other impurities and used for a purpose.

Some of the granules from pyrographite "burned" during the precipitation of plutonium dioxide, the quantity compensate for the additional load.

If used rings from pyrographite, as they "wear and tear" process stop ring replace.

Combined gas-feeding pipe (4) is also replaced as "burning" the end of ponograficos tube 7, up to this point "healed" hole on the end of the quartz tube 6 does not occur.

1. Method of bulk crystallization of plutonium dioxide, comprising preparing a melt of alkali metal chlorides with soluble therein connection plutonium processing of the obtained melt oxygen-containing gas mixture and precipitation of crystalline plutonium dioxide at the bottom of the tank, characterized in that the surface of the melt is placed granules of graphite with closed porosity, ensuring their constant contact with the melt as they are spending.

2. The method according to claim 1, characterized in that as soluble in the melt connection plutonium use trichloride plutonium.

3. Apparatus for volumetric Crist is lisali dioxide plutonium in molten chlorides of alkali metals are soluble in it connection plutonium includes tub, cover, stirring of the melt feeder soluble compounds of plutonium and gas mixture in the melt, characterized in that tub, parts and components in contact with the melt, made of ceramic, secured borders melt products from pyrographite and device for feeding a gas mixture containing ceramic and pyrographite tube.

4. The apparatus according to claim 3, characterized in that the product of pyrographite made in the form of rings such width that their upper edge is located in the gas phase, and the bottom is below the level of the melt.



 

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EFFECT: enhanced durability of equipment.

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