Method for decontaminating radioactive metal wastes by electroslag remelting

FIELD: decontaminating metal wastes by way of their remelting.]

SUBSTANCE: proposed method includes delivery of metal to be decontaminated to water-cooled ingot-forming equipment and decontamination of melt using refining slag. Refining slag in the form of melt is first to be fed to ingot-forming equipment. Then pre-melted radioactive metal wastes are fed at speed affording maintenance of permanent level of molten refining slag within current-conducting section of ingot-forming equipment at which metal ingot decontaminated from radionuclides in the course of remelting can be drawn out.

EFFECT: enhanced economic efficiency of method.

3 cl, 1 dwg

 

The invention relates to the nuclear industry and can be used for deep decontamination of radioactive metallic waste generated during the decommissioning of nuclear installations and dismantling contaminated with radioactivity equipment in order to reuse the metal.

In the nuclear industry is the problem of reuse of decontaminated metal, which consists in the fact that for the production of any products you are already at the stage of melting to ensure decontamination of the obtained ingot with minimum residual radioactive contamination less than 3.7·103Bq/kg, and the distribution of impurities in the ingot must be uniform to facilitate radiometric control (especially α-active nuclides), and not to cause secondary pollution during the production process outside the controlled zone. The distribution of stable components and their concentrations in multicomponent alloys (e.g. stainless steel) must be uniform and conform to the specified values in order not deteriorated specifications decontaminated steel (mechanical strength, resistance to intergranular corrosion and so on).

There is a method of decontamination of radioactive metallic waste indukti is authorized furnace using specially selected refining slag, when decontaminated metal is melted in an induction furnace and processed refining slag, followed by casting of molten metal in the mold to obtain an ingot of the desired size (see Application Germany No. 3331383, CL G 21 F 9/30 and G 21 F 7/06, 1986).

Significant disadvantages of the known method is that the homogeneous metal ingot is difficult because of differences in the physical and physico-chemical properties of already solidified and crystallized metal, and also because of the uneven distribution of temperature and shrinkage of the metal. As a result of chemical heterogeneity in ingots both stable and radioactive components. In addition, end and parietal parts of the ingots is captured particles contaminated slag, which requires additional machining of bars (roughing, cutting, forging and so on).

When the execution of another known from the prior art method, including the supply of decontaminated metal in the water-cooled mold and cleaning of the melt using a refining slag, eliminates some of the shortcomings described in the analog, and residual radioactive contamination sufficiently evenly distributed in the volume of the ingot, is a high chemical homogeneity Deaktivierung the ingot, slag inclusions are not present in it. This method is a method of decontamination of radioactive metallic waste electroslag remelting process in which the decontaminated metal is supplied for melting in the form of a consumable electrode remelting is carried out in the presence of refining slag (see Treatment of plutonium-contaminated metallic Waste by the electroslag Melting method/ Ochiiai A., Kitagawa K., Samada Y., Tzuhama S., Ohsaka//Conditioning Radioactive Wastes Storage and disposal. Proc. Int., Symp. Utrecht. 21-25 July, 1982. Vienna. - Vienna, 1983. - R-190). This method is the closest way to the same destination to the claimed invention by a combination of traits and adopted for the prototype.

For reasons that impede the achievement of specified following technical result when using the known method, taken as a prototype, is that in the known method of decontamination of radioactive metallic waste electroslag remelting process requires a special manufacturing consumable electrode and its preparation for loading, including operations such as pre-casting with subsequent rental or forging of the obtained ingot for maximum density and a given geometry, which leads to additional costs. In addition, a disadvantage of this known method is that the melting refining slag is carried out directly in the mould and ZAT is ATA power are 1200-1600 kW· h/ tonne decontaminated metal.

The task of the invention is the reduction in the number of pre-technological operations when receiving a re-usable metal remaining in the decommissioning of nuclear installations and dismantling of equipment that has been contaminated by radioactivity.

The technical result - increase in the efficiency of the method of decontamination of radioactive metallic waste electroslag remelting process while maintaining the quality and all the technical characteristics of the ingot decontaminated metal due to the reduction of energy consumption, simplify radiometric monitoring of residual contamination and obtain an ingot, which does not require subsequent additional processing (circumcision defective parts ingots, normalizing annealing and colagiovanni alloys).

This technical result in the implementation of the invention is achieved in that in the known method of decontamination of radioactive metallic waste electroslag remelting process in which metal waste is fed into the water-cooled mold and cleaning of the melt is performed using the refining slag, the peculiarity lies in the fact that the mould is connected to a network of electric current, first download a refining slag in view of the melt, and then served previously molten radioactive metal waste at a speed that facilitates maintaining a constant level of refining molten slag within the boundaries of the conductive sections of the mold and allowing you to pull the ingot purified from radionuclides metal during melting.

Given the special conditions, the method, firstly, characterized in that the mould is connected to the alternating-current circuit, and secondly, the preliminary melt radioactive metal waste is conducted in the presence of refining slag and after pre-melt refining slag in the same auxiliary furnace. In addition, the feature of the method lies in the fact that the ingot out of the mold through the land down platform from conductive mold.

The use of conductive mold can be decontaminated material in the form of a melt, which eliminates additional operations for the production and finishing of a consumable electrode. Loading the conductive mould pre-refined molten slag helps to ensure that the quality of the ingot, which does not require additional processing (crop defective parts of the ingot, normalizing annealing and colagiovanni alloy), and the content of the mod who offered radioactivity meets the requirements for reuse of the metal. Speed optimization, which is the pre-molten protective metal, and the rate of withdrawal of the ingot during melting ensure stabilization of the directional solidification process, which eliminates the capture strand particles contaminated slag.

Conducted by the applicant, the analysis of the prior art available to patent and scientific and technical information sources has allowed to establish that similar, characterized by signs, identical to all the essential features of the invention, the applicant is not found,

The definition of the identified unique prototype, as the most similar in essential features analogue, has identified a set of essential towards perceived by the applicant to the technical result of the distinctive features in the proposed method, set forth in the claims that, according to the applicant, allows to conclude that according to this invention, the condition of “novelty”.

The results of the additional search known solutions to identify signs consistent with the distinctive features of the claimed device, showed that the claimed invention not apparent to the expert in the obvious way from the prior art, as defined by the applicant of the prior art revealed no effect of the transformation is, provided the essential features of the claimed invention, to achieve a technical result. Therefore, the applicant proposes accordance with this invention, the criterion of “inventive step”.

The drawing shows the setup diagram for decontamination of radioactive metallic waste electroslag remelting process, consisting of columns 1, in which the fixed mold 2 and moving the column 1, the carriage 3 with the platform 4. Platform 4 is installed and secured seed 5 connected to the conductors 6 and the mold 2 in the upper conductive part connected to the other conductors 7. The molten conductive refining slag 8 and decontaminated metal 9 get in one and the same auxiliary furnace 10. Liquid conductive refining slag and the melt decontaminated metal are fed into the mold 2 through the spout 11.

The method is as follows.

Refinement conductive slag melt in the auxiliary furnace 10 and is drained through the dispenser 11 in the conductive mold 2 so that the melt refining slag 8 was located in the upper conductive and the average of the intermediate section of the mold 2, and make the connection of the mold 2 to the alternating-current circuit 12, which ensures the maintenance ø the aka in the molten state. Subject decontamination of radioactive metallic waste load in the form of pieces in the auxiliary furnace and in the presence of refining slag melt, after which the melt is fed into the dispenser 3, from which the molten metal 5 preset speed is served in the mold 2 to the conductive mirror refining slag. During melting can produce additive alloying components in the ingot by filing ligatures (in the form of powder, shot, sponge) into the mould with molten protective metal. The rate of dispensing molten metal must be such that the level of electrically conductive slag in the upper section of the mold was the same. For this purpose select the appropriate speed lowering down of the carriage 3 with the platform 4. When the ingot is deactivated metal is extruded from the mold and is deposited weld metal crystallization. At the end of the process, the carriage 3 reaches its extreme lower position, and the power of the mould is turned off. After cooling of the ingot and slag are unloading position: ingot sent for further use, and the slag in the form of the cured radioactive waste - to long-term storage.

After decontamination proposed method stainless steel 18CR10NITI mechanical, corros the district and chemical properties fully consistent with bars, industrial steel 18CR10NITI. The total residual radioactivity steel α-emitters was less than 2.6·10-9CI/kg and γ-emitters is less than 1·10-7mg EQ. radium/kg decontaminated steel. Electricity costs amounted to: electroslag decontamination - 700 kW·h/t and 300 kW·h/t in advance remelting refining slag and radioactive metal waste.

Thus, when using the claimed method of the foregoing data suggest the following cumulative conditions:

the tool embodying the claimed invention in its implementation, is intended for use in industry, namely in the nuclear industry for deep decontamination of radioactive metallic waste generated during the decommissioning of nuclear installations and dismantling contaminated with radioactivity equipment in order to reuse metal;

for the inventive method, it is described in the independent clause sets out the claims, confirmed the possibility of its implementation using the steps described in the application of tools and methods.

This allows the applicant to claim that the claimed invention meets the criterion of "industrial applicability".

1. The method of decontamination of radioactive metallic environment, the Dov electro-slag remelting, including supply of decontaminated metal in the water-cooled mold and cleaning of the melt using a refining slag, characterized in that the mould is connected to a network of electric current, first download a refining slag in the form of a melt, then serve pre-molten radioactive metal waste at a speed that facilitates maintaining a constant level of refining molten slag within the boundaries of the conductive sections of the mold and allowing you to pull the ingot purified from radionuclides metal during melting.

2. The method according to claim 1, characterized in that the mould is connected to the alternating-current circuit.

3. The method according to claim 1, characterized in that the ingot out of the mold through the land down platform from conductive mold.



 

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