RU2065214C1 - Method for vitrifying radioactive and toxic waste in induction-arc furnaces - Google Patents

Abstract

FIELD: vitrifying radioactive and toxic waste. SUBSTANCE: induction-arc furnace crucible is charged with vitrifying material and electricity conducting material (aqueous suspension of ferricferrous oxide with concentration of the latter 40-85 mass percent) is introduced in charge. Suspension is introduced in center of charge surface until spot appears, spot size meeting the following requirements: 0.5 Dn is smaller than or equal to 0.7 Dm, where Dn is inner diameter of crucible; Dm is average diameter of spot. Initial melt is formed and waste is introduced in it together with vitrifying charge; melt is homogenized and cooled down until vitrified block is obtained. EFFECT: improved speed of waste vitrifying; reduced degree of radionuclide wear.

Description

 The claimed method relates to the field of environmental protection. It can be most effectively used in the technology for the disposal of radioactive and toxic waste (RATO) by vitrification.

 To date, the most common heating methods for vitrification of radioactive and toxic waste are heating in resistance furnaces, induction heating, and heating by passing alternating current through the melt (electrode heating).

 Known, for example, is the method of vitrification of RATO in a single-use crucible placed in a seven-zone resistance furnace with silicon carbide heaters / 1 /.

 However, the use of resistance furnaces as a heating source is hindered by the relatively low thermal conductivity of molten glass melt / of the order of 3 W / (m deg) /, which makes it impossible to evenly distribute the temperature in a large volume of the melt, and therefore degrades the quality of the resulting product.

 Another known method of vitrification of radioactive and toxic waste is the vitrification method in ceramic melters, in which the energy for melting the glass is supplied by passing alternating current between the electrodes through the molten glass / 2 /.

 The disadvantage of this method is the possible foaming of the melt, leading to poor penetration of the glass melt, deterioration in the quality of the resulting glass and the consequent increased volatility of radionuclides.

 The closest in technical essence to the claimed object is a method of vitrification of RATO, including loading a glass-forming charge into the crucible of an induction furnace, introducing into the charge an electrically conductive material (pieces of graphite), which creates a starting melt, introducing into the starting melt the RATO along with the glass-forming charge homogenizing the resulting melt and its cooling / 3 /.

 The disadvantages of this method are: low speed vitrification process; emergency process; increased ablation of radionuclides.

 The advantages of the proposed method are an increase in the vitrification rate of RATO, ensuring emergency safety of the process and reducing the degree of entrainment of radionuclides.

These advantages are achieved due to the fact that in the inventive method, which includes all the operations of the prototype, a suspension of ferrous oxide (Fe ₃ O ₄ - magnetite) in water with a magnetite content of 40-85% by weight is used as an electrically conductive material. in an amount that provides coating a part of the surface of the original glass-forming mixture with a concentric spot, provided:
0.5 D _p ≅ D _m ≅ 0.7 D _p ,
where D _{p is the} inner diameter of the crucible, and D _{m is the} average diameter of the spot.

 In the inventive method, the magnetite sludge is quickly dehydrated and compacted, which leads to an increase in the rate of heat transfer and, therefore, to accelerate the formation of the starting melt (on average, 1.5-2 times in comparison with the prototype). With further melting of the charge, iron oxide-oxide dissolves in the starting melt, increasing its electrical conductivity and accelerating the further process of RATO vitrification. In this case, the presence of a layer of magnetite sludge on the surface of the melt, eliminating the possibility of local overheating, reducing the lifetime of the open surface of the starting melt by reducing the duration of the starting process and the absence of the need for an oxidizing agent lead to a decrease in the entrainment of radionuclides.

 Reducing the accident hazard of the process is achieved due to the fact that due to its ferromagnetic properties, magnetite sludge is localized at the site of the highest concentration of electromagnetic field energy (in the center of the melter) and its contact with the melter walls, the possibility of breakdown and destruction of the crucible are excluded.

When D _m , less than 0.5 D _p , the amount of sludge is not enough for efficient heating; when D _m greater than 0.7 D _p , there is a danger of accidental contact of the sludge with the walls of the melter.

 The inventive method is implemented as follows.

In the crucible load the initial portion of the glass-forming mixture composition: 10 wt. In ₂ O ₃ , 70 wt. SiO ₂ , 20 wt. Al ₂ O ₃ in such an amount that, when melting, its melt occupies a volume equal to 10% of the crucible volume, after which an aqueous suspension of magnetite is poured onto the surface of the initial portion of the glass-forming charge in an amount of 10% of the melt volume of the initial portion of the glass-forming charge (volume of an aqueous suspension of magnetite It may range from 8 to 15% of the melt volume. this D _m will satisfy the requirement of _n 0,5D ≅D ≅0,7D _{m n).} The concentration of iron oxide-iron oxide in an aqueous suspension of magnetite is 65 wt. Then, the mixture is heated from the electric power source until it is melted. After that, a mixture of RATO together with a glass-forming charge in a ratio of 30 wt. RATO and 70 wt. glass-forming charge (the above ratio can vary between 20-40 wt. RATO and 60-80 wt. glass-forming charge). After melting the mixture, it is kept in the molten state until complete homogenization due to self-mixing of the melt with bubbles of exhaust gases. The homogenized melt is drained, cooled and sent for burial.

 Compared with the selected prototype, the inventive method allows to reduce the duration of the starting melt creation by 1.5-2 times, to reduce the entrainment of volatile forms of radionuclides by 3-10 times and to prevent the accident risk of the RAB vitrification process.

Claims (1)

The method of vitrification of radioactive and toxic waste in an induction furnace, which consists in loading a glass-forming charge into the crucible of the furnace, introducing electrically conductive material into the mixture, creating a starting melt, introducing radioactive and toxic waste into the melt together with the glass-forming charge, homogenizing the melt and cooling it, characterized in that as an electrically conductive material use an aqueous suspension of ferrous oxide-oxide with a concentration of ferrous oxide of iron oxide of 40 to 85 wt. in this case, the suspension is introduced into the center of the charge surface until a spot is formed, the size of which satisfies the requirement
0.5D _p ≅ D _m ≅ 0.7D _p ,
where D _{p the} inner diameter of the crucible;
D _{m is the} average diameter of the spot.