RU2756525C1 - Method for discharging a melt with separation of phases using a melting plug - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to methods for improving discharge apparatuses with a melting plug. The invention can be used both in metallurgy and pyrochemical technologies of processing nitride spent nuclear fuel (SNF), e.g., during transportation of molten media from apparatus to apparatus, separation of phases in such processes as "soft chlorination" and electrolysis. The method for discharging the melt includes heating the charge, melting the stopping plug, and discharging the melt. The stopping plug is melted by a heater moved along a vertical axis, the molten metal is discharged after crystallisation of the salt phase, and the plug is made of a low-melting metal.

EFFECT: invention provides a possibility to separate the phases of a low-melting metal and a salt system.

3 cl, 2 ex

Description

The invention relates to methods for improving fusible plug drainage devices.

The invention can be used both in metallurgy and in pyrochemical technologies for reprocessing nitride spent nuclear fuel (SNF), for example, when transporting molten media from apparatus to apparatus, phase separation in processes such as "soft chlorination" and electrolysis. When reprocessing "low-temperature" high-background spent nuclear fuel with the above technologies, phase separation of low-melting metal and electrolyte is required, reducing the contact time of personnel involved in SNF reprocessing with equipment to reduce dose loads, and the use of separated media in the further process chain.

In practice, methods are known for draining molten metals and other melts (slags, matte) using vacuum ladles, boreholes and through tap holes (V.I.Beregovsky, BB Kistyakovsky. Metallurgy of copper and nickel. M .: Metallurgy, 1972. P. 62, 82-83, 109, 288. A.I.Belyaev. Metallurgy of light metals. Moscow: Metallurgy, 1970. P. 228. V. V. Stender. Applied electrochemistry. Kharkov: Kharkov State University, 1961.S. 432, 439). The borehole slot is sealed with refractory clay, sometimes with inserts (breaks, bushings, plugs). To release the melt, the holes are burned with oxygen or the liners are pierced. The holes are also covered with a refractory mass, sometimes with liners. After tapping the metal, the bore holes and tap holes are sealed manually or with a pneumatic gun. The disadvantages of this method are the complexity in organizational and technical terms, and as a consequence, their use in extremely rare cases or in emergency situations.

A known method of transferring electrolyte in pyrochemical methods (Patent US 6800262, publ. 05.10.2004). For transfer to the refining electrolyzer, the molten mixture LiCl-KCl-UCl ₃ (electrolyte), prepared in a separate apparatus, was cooled and granulated under an inert gas atmosphere or in vacuum (without air access) to prevent its contamination with oxygen-containing compounds, then in solid form was transported to working apparatus for electrochemical processing of contaminated uranium (analogue of metal SNF). As you can see, such a method for preparing an electrolyte is multistage, complex in terms of equipment, expensive, and poorly fits into a closed fuel cycle. In addition, during storage and transportation of electrolyte, even in a sealed container, it is practically impossible to completely avoid its contact with air.

As a prototype, a method for draining the melt with a plug melted with special heating from an auxiliary material with a higher melting point, described in the "Device for draining the melt" (AS USSR No. 469872, publ. 05.05.1975), was selected. The method is carried out as follows. After turning on the heating, the part of the heater that is thinned at the groove heats up faster than its other parts. Before melting, the casting mold, which is in the apparatus, is located in it so that the bottom of the mold is under the groove in the colder part of the heater. After melting the charge, the elevator lifts the mold and the crucible until the groove on the heater aligns with the bottom of the mold. In this case, the plug enters the zone of a higher temperature, melts, and the melt from the crucible is poured into the mold. The disadvantage is that this method can be implemented with complete drainage of the entire volume of the melt and cannot be used to drain a part of the melt, and as a result cannot be used as a phase separator in SNF reprocessing operations. Also, the disadvantage is the use of equipment with certain geometric dimensions suitable for a particular apparatus, since the groove is located at a given distance.

The objective of the invention is to develop a method that makes it possible to transfer the molten charge from the original crucible (apparatus) to the receiving crucible (apparatus), as well as to separate the phases of the low-melting metal metal and the salt phase (electrolyte), thereby eliminating the need for mechanical separation of cooled phases, applicable, for example , at pyrochemical operations of SNF reprocessing.

The problem is solved by the fact that in the method for draining the melt, including heating the charge, melting the stopper plug and draining the melt, the stopper plug is melted by a heater movable along the vertical axis, the molten metal is drained after crystallization of the salt phase, and the plug is made of low-melting metal.

The plug is made from cadmium.

The plug is made from lead.

The method is carried out as follows.

At the end of the process of melting the charge in the main part of the reactor, the heating is turned off and cooled to the crystallization temperature of the molten electrolyte, then the heater is moved with a lifter to the area of the drain pipe and this zone is heated to the melting temperature of the metal cadmium or lead plug. Upon reaching a predetermined temperature, the plug melts and flows together with the molten metal from the reactor into a receiving vessel, which is transferred for further processing. The salt phase remains in the reactor for further operations, or is heated and drained.

Example 1

The reactor is loaded with a previously prepared tooling with a bottom drain pipe, with a fused metal cadmium plug. Next, the prepared salt phase, consisting of lithium chloride with previously known data on the amount of metallic cadmium, is placed in a reactor and heating is turned on. At a temperature of 650 ° C, an exposure is carried out for 6 hours, after which the reactor is cooled, the tooling is removed and the melting of lithium chloride and the unchanged position of the cadmium plug are noted. Next, the tooling is reloaded into the reactor, the heater is moved with the aid of a lifter to the area of the stopper plug and heated to a temperature of 350 ° C. Exposure is carried out at this temperature for 2 hours, as a result of which the cadmium plug melts and flows down with the bulk of the molten cadmium into the receiving container. The heating is turned off and the reactor is cooled to room temperature, the assembly is removed, the amount of separated cadmium from the mass of lithium chloride is estimated. The percentage of separation of cadmium from the electrolyte is 98%.

Example 2

The reactor is loaded with a previously prepared tooling with a bottom drain pipe, with a fused metal lead plug. Next, the prepared salt phase, consisting of lithium chloride with previously known data on the amount of metallic lead, is placed in a reactor and heating is turned on. At a temperature of 650 ° C, an exposure is carried out for 6 hours, after which the reactor is cooled, the tooling is removed and the melting of lithium chloride and the unchanged position of the lead plug are noted. Next, the tooling is reloaded into the reactor, the heater is moved with the help of a lift to the area of the stopper plug and heated to a temperature of 360 ° C. Exposure is carried out at this temperature for 2 hours, as a result, the metal lead plug melts and flows down with the bulk of the molten lead into the receiving container. The heating is turned off and the reactor is cooled to room temperature, the assembly is removed, the amount of lead separated from the mass of lithium chloride is estimated. The percentage of lead separation from the electrolyte is 96.3%.

The claimed method has advantages over the prototype: simpler apparatus designs and less complex hardware and technical design make the process of pouring the melt more accessible; a cork made of low-melting material is used, which in turn reduces the overall cost of the process; Also, the method makes it possible to separate the phases of the low-melting metal and the salt system, reducing the contact time of the personnel involved in SNF reprocessing.

Claims (3)

1. The method for draining the melt, including heating the charge, melting the stopper plug and draining the melt, characterized in that the stopper plug is melted by a heater movable along the vertical axis, the molten metal is drained after crystallization of the salt phase, and the plug is made of low-melting metal. 2. The method according to claim 1 is characterized in that the plug is made of cadmium. 3. The method according to claim 1 is characterized in that the plug is made of lead.