RU2137230C1 - Method for decontaminating liquid radioactive and toxic materials - Google Patents

Abstract

FIELD: nuclear power engineering. SUBSTANCE: method involves filling capsule containing porous ceramic and provided with sublimate trap with liquid radioactive or toxic materials, their evaporation, thermolysis of dry residue, and entrapping of high-vapor- pressure sublimates; evaporation and thermolysis of dry residue are effected in capsule directly in ceramic pores and upon termination of thermolysis capsule is sealed. Evaporation is conducted at 70-90 C and thermolysis, at 700-900 C. All operations are made in hermetically sealed chamber at pressure of 0.01-0.05 MPa. Products of thermolysis enter in reaction with ceramic material and form stable chemical compositions. Radioactive wastes and toxic materials treated in this way can be buried not only in deep beds but also in near-surface pits under natural cooling conditions. EFFECT: improved reliability and environmental friendliness of process. 4 cl, 1 dwg

Description

 The invention relates to nuclear energy, namely to the management of radioactive waste (RW), but can be effectively used in other industries, for example, in the chemical industry for the removal of especially dangerous toxicants from the biosphere.

 A known method of disposal of radioactive waste in the deep layers of the lithosphere, including the placement of solid, heat-generating materials in sealed, thick-walled vessels (Sobolev I.A., Khomchik L.M. Disposal of radioactive waste at centralized sites. - M .: Energoizdat, 1983, 128 S. )

 The disadvantage of this method is the complexity of manufacturing vessels and the danger of their equipment, as well as technological difficulties in implementation.

There is also a method for the disposal of radioactive waste, including heat-generating, water-tail nitrate solutions formed in the process of regeneration of spent nuclear fuel, which consists in evaporation and thermolysis of the liquid phase on the surface of the glass melt, obtaining vitrified mass and pouring the latter into metal capsule containers equipped with a brewed a sealing cover (Nikifirov A.S., Kulichenko V.V., Zhikharev M.I. Neutralization of liquid radioactive waste. - M .: Energoizdat, 1985, p. 92-94.)
This method has significant disadvantages: the concentration of radioactive waste is limited for reasons of long-term durability of the glass (matrix), in connection with which the storage volume increases, the equipment necessary to implement the known method is characterized by high cost, high energy intensity, low productivity, the complexity of repairs and the generation of own waste in the form of lining of furnaces and other parts, aggressive water-tail solutions intended for curing by vitrification must be able to withstand for a long time (3-10 years) stored in continuously cooled containers in order to reduce their radiation hazard, which dramatically increases both the cost of redistribution and the risk of accidents with catastrophic environmental consequences, long-term (for hundreds of years) storage of vitrified radioactive waste even in underground voids at a depth of 100-1000 m the likelihood of environmental disasters as a result of geological disasters and the destruction of both structural materials and glass under the influence of radiation.

 The purpose of the invention is to increase reliability, environmental safety and reduce the cost of complex procedures for the disposal of radioactive waste and other highly hazardous substances (toxicants).

 This goal is achieved by the fact that liquid radioactive and toxic waste is poured sequentially into capsules pre-filled with porous ceramics and equipped with a trap of sublimates, evaporated and thermolysis of the dry residue of evaporation directly in the pores of the ceramics, while capturing sublimates of the vapor phase, and after completion of thermolysis dry residue capsules clog.

Evaporation is carried out at a temperature of 70-90 ^o C, and thermolysis at 700-900 ^o C in a sealed chamber at a pressure in the latter of 0.01 - 0.05 MPa.

 The stabilization of thermolysis products in the form of a mixture of oxides is carried out by their interaction with the material of the ceramic matrix, which leads to the formation of a thermally stable conglomerate directly in the pores and microchannels of the filler.

 An important link in the implementation of the method of neutralization is the capsule, and the outer diameter of the capsule can vary widely depending on the composition of the storage materials, but the advantages of the method are most fully realized when using ball capsules with a diameter of 50 to 250 mm, which is 50-80% of diameter of casing pipes, i.e. the least capital-intensive wells, because only in this case, the free movement of the capsules along the trunk to the underground tank (cavity) is ensured.

 The main feature of the method of RW neutralization is that the capsule is filled with porous ceramics, for example, of porous corundum doped with zirconium oxide, and artificial materials (“synrocs”) with porosity of 50-80% have optimal properties.

 The high porosity of the filler provides intensive absorption (absorption) of the solution.

The RAW solution is poured into the capsule through a special hole equipped with a funnel and begins to evaporate at a temperature of 70-90 ^o C. At a temperature of less than 70 ^o C, the evaporation process is slow, and at a temperature of more than 90 ^o C there are emissions of the solution.

The solution is poured and the evaporation operation is carried out repeatedly until the required level of pore filling with a dry residue is achieved (from 1.0 to 1.5 kg / kg), after which the temperature in the furnace placed in a sealed chamber is raised to 700-900 ^o C for decomposition (thermolysis ) of the dry residue in the form of nitrate salts with the formation of a mixture of nuclide oxides directly in the pores of the ceramic (at a temperature of less than 700 ^o C the thermolysis process is slow and incomplete, and at a temperature above 900 ^o C there are technological complications).

In the process of heating the RAW solutions, evaporation of volatile components such as cesium, americium, technitium, etc. takes place, in connection with which, to trap the specified sublimates, a trap is installed inside the porous ceramic block (a drawing shows a photograph of a capsule with filler and a sectional capsule ) The trap of environmentally hazardous sublimates is filled with adsorbent-getter powder, and above the adsorbent layer there is a solder layer with a melting point of 900-950 ^o C.

 The immobilization of fuel nuclides in a porous ceramic matrix is carried out by sequential operations in a sealed chamber, the walls of which serve as radiation protection, and a pressure of 0.01-0.05 MPa is constantly maintained in the chamber, which eliminates the release of volatile harmful substances into the atmosphere.

 Maintaining a pressure of less than 0.01 MPa is associated with an increase in the cost of equipment, and more than 0.05 MPa increases the risk of breakthrough toxicants.

After the completion of thermolysis, which is accompanied by gas evolution, and the restoration of the vacuum in the chamber, the temperature in the capsule heating furnace is raised to 900-950 ^o C, which leads to the melting of the solder on the surface of the sublimation traps and its blockage.

 The sealed capsule is transferred from the furnace heaters to the welding unit, also located in the volume of the sealed chamber, where two prefabricated steel hemispheres are connected, as a result of which a second layer of the container is formed, which additionally protects the ceramic filler, moreover, the connection of the hemispheres is carried out mainly by contact welding, as the most reliable and technologically advanced.

 The subsequent steps of the method consist in moving the two-layer capsules through the chamber lock to the second welding block, with which the hemispheres of the third (outer) layer are connected, i.e. The final product is a three-layer sealed ball container.

 In order to increase the reliability of the method, the outer layer of capsules is made of heat-resistant and heat-resistant alloy, and its surface is covered with a thin (0.1-0.3 mm) layer of refractory materials using known methods of plasma spraying.

 Single capsules made according to the proposed method with heat release of the order of 50 Wt (45 kcal / h) are stored in a cooled tank and transported to a landfill.

 A specific example of the method.

 Operation 1. In a spherical capsule with a diameter of 130 mm and a volume of 1.15 L, made in the form of a case made of mild steel surrounding a ceramic filler, a RAO nitrate solution with a heat release of 30-70 W / l was poured, and the capsule was previously introduced through the lock into an airtight the camera.

The capsule was placed in a resistance furnace and heated to 80 ^° C. The solution was poured and evaporated in batches, sequentially and repeatedly until the weight of the capsule was increased to 4.0 kg, and upon reaching the required ceramic pore filling with a dry residue, the temperature in the furnace was raised to 800 ^° C for the purpose of decomposition (thermolysis) of the dry nitrate residue with the formation of a mixture of nuclide oxides directly in the pores and microchannels of the filler.

The harmful sublimates of Cs, Am, and other components with high vapor pressure were adsorbed in the getter layer in a condenser trap, after which the temperature in the furnace was raised to 950 ^° C and held for 0.5 h. This operation led to the melting of the solder in the trap and clogged capsules.

 The capsule removed from the furnace was moved within the sealed chamber to the welding unit, with the help of which the primary capsule was placed between two steel hemispheres and connected by contact welding, pressing the hemispheres and passing electric wires through them. current.

 Two-layer, sealed capsules were in-line removed through the lock from the protective, sealed chamber and additionally protected by another layer, placing the capsule inside hemispheres made of chromium alloy doped with tungsten, interconnected by argon-arc welding, and at the final stage the surface of the external, welded-stamped body capsules were coated with hafnium oxide, 0.1 mm thick.

 Hermetically sealed, spherical capsules manufactured by the described methods were accumulated in a refrigerated storage.

Further neutralization of the radioactive waste placed (immobilized) in ceramic matrices, hermetically surrounded by multilayer, heat-resistant, provides for their descent and placement in artificial underground caverns through the trunks of typical wells, up to 4-5 km deep and holding the ensemble (set) of capsules for the time required for heating the underlying rocks to a solid-liquid state (1200-1250 ^o C), which provides spontaneous, environmentally friendly lowering of the ensemble into the deep layers of the lithosphere.

 The proposed solution is suitable not only for the irretrievable burial of radioactive waste and other toxicants in deep seams, which excludes their entry into the biosphere, but also for safe storage in near-surface mines, with a depth of up to 100-300 m in conditions of natural air cooling. This reduces the cost of servicing the storage facilities and it is advantageous to utilize cheap heat of radioactive decay for a long time (30-50 years).

Claims (4)

 1. The method of neutralizing liquid radioactive and toxic materials, including their evaporation, thermolysis and portioned filling of the liquid phase into capsule containers, characterized in that the liquid phase is filled into capsules pre-filled with porous ceramics and equipped with a sublimation trap, and evaporation and thermolysis of the dry residue they are carried out directly in the pores of ceramics, while capturing sublimates with high vapor pressure, and after the end of thermolysis of the dry residue, the capsule is sealed.  2. The method according to p. 1, characterized in that the evaporation process is carried out at a temperature of 70-90 ° C, and the thermolysis process at a temperature of 700-900 ° C.  3. The method according to PP. 1 and 2, characterized in that all operations are carried out in a sealed chamber at a pressure of 0.01-0.05 MPa.  4. The method according to PP. 1-3, characterized in that the thermolysis products interact with porous ceramics and form stable chemical compounds.