RU2199164C2 - Device for case-hardening finely dispersed radioactive and toxic wastes by impregnation - Google Patents

Abstract

FIELD: recovery of radioactive wastes including finely dispersed bulk of radioactive and toxic wastes having voids. SUBSTANCE: Cement mortar is supplied under pressure through probe to container pre- filled with radioactive wastes and the latter are impregnated throughout entire bulk due to filling all its voids and pores with cement mortar. Volume of end cement compound obtained in the process equals that of bulk radioactive wastes. Device has hermetically sealed working box with window provided with rubber gloves and door set in motion by means of operating mechanism; vibrating-plate truck that mounts radioactive waste container; probe; probe displacement mechanism; cement mortar preparation unit; ventilation system and decontamination system. EFFECT: simplified design of case-hardening hardware, enhanced radiation safety and capacity of device, improved quality of end product. 1 dwg

Description

 The invention relates to the field of processing of radioactive (RW) and toxic waste, in particular, by cementing, and is intended for the monolithization of finely dispersed radioactive and toxic waste (non-combustible and non-compressible fragments of building structures and dismantled plants, ash residues from RW incineration, spent granular sorbents, ion-exchange resins, etc.), followed by the burial of the final cement compound in near-surface storage tanks. The most effectively claimed device can be implemented when cementing the ash residue formed during the burning of radioactive waste and which is a polydisperse powdery dusting material with large inorganic (glass, ceramic, metal) inclusions. The device can also be used for joint cementing of liquid and solid radioactive waste. The device is intended for operation at nuclear power plants and radioactive waste disposal sites.

 A device for cementing radioactive waste [1], including a container for dry cement, a container for radioactive waste and reagents, a barrel with a load for mixing and a rotating device. The barrel with the load for mixing placed in it is filled with dry cement, solid radioactive waste and the shutting liquid phase, closed with a lid and rotated simultaneously in several planes. After reaching the required degree of homogenization of the mixture, the barrel together with the load for mixing and the resulting cement compound is sent for disposal.

The disadvantages of the known device are:
- a significant increase in the volume of the final cement compound compared to the initial volume of radioactive waste (1.5-2 times), which leads to an increase in the cost of construction and maintenance of storage facilities for radioactive waste. The increase in volume is associated both with the presence of a mixing load buried together with the final compound, and with the need to increase the fluidity of the cement mortar (increase the volume of the liquid phase of the mortar, or decrease the degree of inclusion of radioactive waste) for the normal operation of the mixer when mixing radioactive waste with cement mortar;
- the formation of a large number of secondary liquid radioactive waste, for which further processing is necessary, due to the presence of metering and mixing equipment in contact with the radioactive waste and requiring decontamination;
- low degree of inclusion of radioactive waste in the final cement compound (for example, when cementing ash, the degree of filling is 20-30% by weight, while cementing spent ion-exchange resins and granular sorbents, 10-20% by weight);
- increased danger and unreliability of the device due to the possibility of mechanical damage to the equipment with a mixing load or large inclusions present, for example, in the ash residues of RW incinerators due to insufficient preliminary sorting of waste;
- the formation of an insufficiently homogeneous final cement compound, characterized by the presence of voids, which during long-term storage leads to a decrease in its necessary technical characteristics (compressive strength, leaching rate), and, ultimately, to a relatively quick destruction of the main barrier to the exit of radionuclides into the environment Wednesday

 Closest to the proposed is a device for curing the ash residue of organic radioactive waste [2], containing a sealed chamber communicating with it through the dispensers of the container for the ash residue, cement and grout, a container for curing and a control unit for operating the device located outside the chamber, characterized in that in the sealed chamber under the outlet of the ash residue and cement dispensers there is a vibratory conveyor, under the edge of which a container, vibrating table, gripping mechanism for moving container and a pneumatic cover for sealing the container, in the case of which there are mounted fittings for connecting pipelines from the containers of the casserole, compressed air supply systems and creating a vacuum, and coarse and fine filters are installed outside the chamber in the pipeline of the vacuum creating system, and on the compressed feed system air pressure regulator. The solidification of RAW in the container consists in mixing the ash residue with cement in dry form, transporting them to the container on a vibratory conveyor and feeding the cushion with an aerodynamic shock to the evacuated container by changing the pressure in the container from vacuum to excess.

The disadvantages of the device are:
- complex hardware design of the cementing process, associated, in particular, with the evacuation of the container and alternating multiple pressure changes in the container from vacuum to excess;
- reduced productivity associated with the inability to 100% use the useful volume of the barrel due to repeated repetitions of cementing in one container by aerodynamic impact;
- the presence of radiation-hazardous stages of the technological process (dosing of radioactive waste, mixing dusty dry radioactive waste with cement in dry form on a vibratory conveyor) and equipment in contact with the radioactive waste (dosers, vibratory conveyor);
- the formation of liquid (decontamination water) and solid (coarse and fine filters) secondary radioactive waste requiring further processing.

The technical task is to improve the cementing process of finely dispersed radioactive and toxic waste, namely in:
- simplification of the hardware design of the device;
- increase radiation safety during operation of the device;
- increase device performance;
- receipt during operation of the device of the final cement compound with a volume equal to the initial bulk volume of radioactive waste;
- improving the quality of the final cement compound.

 To solve the technical problem, a device is proposed for impregnation of radwaste cementing, containing a sealed working box, a container for radwaste, a vibrating pad, a dispensing container and a device operation control unit located outside the box, characterized in that the sealed working box contains a window equipped with rubber gloves, and a door driven by a drive, moreover, the sealed working box is equipped with a ventilation system, which includes a weight gauge for determining the level of vacuum and it is in the form of a pipe connected to the process ventilation and a decontamination system consisting of a decontamination nozzle, a pipe with an electromagnetic valve installed on it and a drain pipe located in the bottom of the sealed working box and designed to drain decontamination water, also the sealed working box contains a probe with holes made in the lower part of the probe, and a probe moving mechanism located in the upper part of the sealed working box and equipped with a cement level gauge solution; in addition, the vibration platform for placing the container with radioactive waste is mounted on a cart with a drive, and the container with radioactive waste further comprises a lid; The cement preparation unit includes the above-mentioned metering tank for water, equipped with a water level meter and solenoid valves at the inlet and outlet of the metering tank for water, as well as a water meter and mixer, including a pipe for water, a pipe for loading cement and a drain pipe with electromagnetic a valve, the mixer being connected via a pipeline to a drain pipe for draining decontamination water in an airtight working box; in addition, the device comprises a system for supplying cement mortar to a container with radioactive waste, including a metering pump and an electrocontact pressure gauge installed on it.

 The device is simplified by the use of a probe (disposable or permanent) and a metering pump for supplying cement mortar to a container with radioactive waste, which allows a fundamentally new way to cement the radioactive waste by impregnation directly in the container (for example, in standard 100-200 liter barrels) without preliminary sorting of radioactive waste and without mixing of radioactive waste with cement mortar, which leads to the exclusion of sorting, mixing and dosing equipment from the device and significantly increase degree of incorporation of radioactive waste in the final cementitious compound without increasing its volume compared with the initial volume of bulk waste.

 Reducing the amount of equipment in contact with radioactive waste in the device will not only simplify the device and reduce capital costs for equipment, but also increase process productivity by reducing the stages of the process and the device’s operating time, as well as by reducing the amount of secondary liquid radioactive waste, generated in large quantities during the decontamination of equipment and requiring further processing.

 Impregnation of radioactive waste with a high-permeability cement mortar, carried out in the proposed device by means of a metering pump and a probe, allows using the space between the radioactive waste particles in the bulk volume to homogenize the radioactive waste without mixing them with the cement in special mixers, which leads to the final cement compound during operation the volume equal to the initial bulk volume of waste, and accordingly to reduce the cost of construction and maintenance of radioactive waste storage.

 The metering pump allows you to transport cement mortar through a pipeline under a pressure of not more than 1 MPa, controlled by an electric contact pressure gauge, and to supply cement mortar to the bottom of the container with radioactive waste.

 A disposable probe is a pipe with a length equal to the height of the container with radioactive waste, with expansion in the lower part and openings for free passage of cement mortar. The disposable probe is used for cementing relatively large radioactive waste (fragments of dismantled plants, construction waste, ceramics, metal, etc.), is installed in the container until the radioactive waste is filled, and disposed of together with the resulting cement compound.

 A constant probe is introduced into a container already filled with finely divided radioactive waste, and is a tube with a pointed tip and holes in the lower part. After cementing the radioactive waste, the probe is removed and used repeatedly.

 The holes in the lower part of the probe serve to supply cement to the bottom of the container with radioactive waste, which allows the cement solution to fill all the smallest voids and pores of the radioactive waste with high efficiency, impregnating the waste evenly and in all directions from the bottom to the top of the container and guaranteeing the quality of the resulting cement compound throughout the entire volume of radioactive waste.

 Radiation safety during operation of the device is increased mainly due to the elimination of radiation-hazardous stages of dosing and mixing dry dusting radioactive and toxic wastes, as well as the corresponding equipment from the device (dispensers, mixers, vibratory conveyors).

 In addition, radiation safety is enhanced by isolating the container with radioactive waste from the working area, which helps to prevent contamination of the working surfaces of the equipment and the air of the working area with radionuclides, since most of the finely dispersed radioactive waste coming to cement is a loose, dusty, radiation hazardous material.

 In the proposed device, cementing is carried out in an airtight box with a vacuum of at least 20 mm water column. The cementing process is controlled from the control unit of the device located outside the working box. Contamination of the working surfaces of equipment in the box is controlled by radiation safety devices. At the end of cementing, the box is decontaminated by water and collected in the bottom of the working box. To drain decontamination water, the device has a drain pipe with an electromagnetic valve, which allows you to return decontamination water through a pipeline to the mixer for use in subsequent cementing. The return of decontamination water to the mixer allows the device to be operated without the formation of secondary radioactive waste, requiring further processing, which also increases the productivity of the process.

 The quality of the final cement compound is improved not only by thoroughly impregnating the radioactive waste with the cement mortar supplied through the probe, but also by including a cement mortar preparation unit, which includes a metering tank for water, a water level meter, solenoid valves at the tank inlet and outlet, dispenser, water meter and mixer. The unit allows you to accurately meter water and cement, to regulate the composition of the mortar during the process, which improves the quality of highly penetrating cement mortar. A cement mortar prepared in this way is able to more fully and evenly fill the voids and pores of finely dispersed radioactive waste, which leads to a durable, resistant to aggressive environmental factors (seasonal temperature changes, washing out of radionuclides with groundwater) final cement compound with a high degree of filling according to the radioactive waste.

 In addition, the vibration of the container with the obtained impregnation compound on the vibration pad provided by the device allows to obtain a homogeneous final cement compound, which improves its quality (increases compressive strength, reduces the leaching parameters of radionuclides).

 Thus, the proposed combination of distinctive features allows you to fully solve the technical problem.

 The drawing shows a diagram of the inventive device for cementing by impregnation of fine and toxic radioactive waste. The device consists of a sealed working box 1 with a window with rubber gloves 2 and a door equipped with a drive 3, and the box is equipped with a ventilation pipe 4 and a drag gauge 5, and a decontamination system, including a pipeline for decontamination water 6 with an electromagnetic valve 7 installed on it, a nozzle for decontamination 8 and a drain pipe 9 for draining decontamination water, equipped with an electromagnetic valve 10, a trolley with a drive and a vibration plate 11 mounted on it with a container for RA placed on it About 12, probe 13, the mechanism for moving the probe 14 with the level gauge for filling the container with cement mortar 15, the cement preparation unit, consisting of a metering tank for water 16, a water level meter 17, a water meter 18, electromagnetic valves at the inlet and outlet of the metering tank 19 and 20, a mixer 21 with a pipe for supplying water 22, a pipe for supplying cement 23 and a drain pipe 24, equipped with a solenoid valve 25, a metering pump 26, a pipe 27 with an electric contact pressure gauge 28 mounted on it.

 The device operates as follows.

 The container 12 is filled with radioactive waste, mounted on a trolley with a vibrating platform 11, fed into the working box 1 and is fixed there. The door 3 is closed, a vacuum of at least 20 mm of the water column is created in the working box 1, controlled by the testimony of the weight gauge 5, then the lid is removed from the container 12. The required amount of tap water (or liquid radioactive waste, or decontamination water) is supplied to the mixer of cement mortar 21 through the nozzle 22, the water volume is controlled by the water meter 18, the mixer 21 is turned on. Cement (or cement with additives improving the additives) is loaded through the nozzle 23 quality of mortar and final cement compound), cement mortar is being prepared. The probe 13 is introduced into the container with RAO 12 using the mechanism for moving the probe 14. The metering pump 26 is turned on, the prepared cement mortar through the drain pipe 25 is supplied under a pressure of not more than 1 MPa from the mixer 21 through the pipe 27 through the holes of the probe 13 into the bottom of the container with RAO 12. During the impregnation, the following parameters are monitored: pressure in the discharge pipe 27 via an electric contact pressure gauge 28; cement consumption by the capacity of the metering pump 26; filling the container according to the level gauge of cement mortar 15 mounted on the mechanism for moving the probe 14. After filling the container with RAO 12 with cement mortar, the metering pump 26 is turned off, the probe 13 is removed from the container 12 with the resulting cement compound. The container 12 is closed by a lid and vibrates on the vibration platform 11. The door 3 of the working box 1 is opened, the container 12 with the cement compound is transported to the RW storage facility. The ventilation of the working box is turned off. At the end of the work, the preparation unit and the cement mortar supply system, including a mixer 21, a metering pump 26 and a pipe 27, are washed. The wash solution is poured into the mixer 21 and used in the next cementing cycle. Work box 1 at the end of the work is deactivated as follows. Solenoid valve 7 opens on decontamination pipeline 6. Through decontamination nozzle 8, water is supplied to working box 1 to flush all surfaces of the box. After washing, decontamination water is collected in the bottom of the working box 1. Through the drain pipe 9, equipped with an electromagnetic valve 10, decontamination water is piped into the mixer 21 for use in the following cementing cycles. Thus, during the operation of the device does not generate secondary radioactive waste.

 In MosNPO "Radon" conducted research and experimental testing of the proposed device using various radioactive waste. Tests have shown that all the assigned technical tasks are fully implemented in the proposed device. The results are shown in the table.

 Cementing of radioactive waste by impregnation at the proposed installation allows to exclude from the technological process equipment used in known devices for sorting, grinding and dosing of radioactive waste, which greatly simplifies the process. Equipment for mixing radioactive waste with cement mortar is also excluded from the technological process, which eliminates damage to the mixers by large fragments of radioactive waste and avoids the formation of secondary waste generated during the deactivation of mixers and batchers. The reduction in the number of equipment and, accordingly, the duration of the device, as well as the absence of the formation of secondary radioactive waste, requiring additional processing, can increase the productivity of the claimed device by 20-30% compared with known devices.

 By reducing the number of operations and equipment in contact with radioactive waste, as well as by performing cementing in a sealed working box isolated from the working area, radiation safety is increased during the cementing process.

 The proposed device allows a highly penetrating cement mortar to fill all the voids and pores of the RAW during the impregnation process, which leads to the final cement compound with a volume equal to the initial bulk volume of the RAW, as well as to improving the technical characteristics of the resulting cement compound, namely, the degree of inclusion of RAW into the cement compound is increased. (for example, for the ash residue from RW incineration up to 50-65% by mass, while when using known devices up to 30-40% by mass), the strength of the final cement increases ntnogo compound and the reduced radionuclide leach rate, by obtaining a homogeneous dense compound without voids (see. Table).

 The proposed device allows to increase the productivity of the cementing process, to increase radiation safety during the process, to simplify the process and to obtain the final cement compound with improved properties and volume not exceeding the initial bulk volume of monolithic radwaste. This device can be manufactured using standard equipment in the conditions of RW conditioning at nuclear power plants and radioactive waste disposal sites.

LITERATURE
1. Nikiforov A. S., Kulichenko V.V., Zhikharev M.I. Neutralization of liquid radioactive waste. - M .: Energoatomizdat, 1985, p.132-133.

2. Syromyatnikov VN, Guseltsov Yu.N., Flit V.Yu., Myslinsky A.E. The method of curing in the container the ash residue from the burning of organic radioactive waste and the device for its implementation. Patent SU 1435057 A1, MKI ⁵ G 21 F 9/16, claimed 4167053/25 from 12.22.86, publ. 10/30/93, bull. 39-40.

Claims (1)

 A device for cementing by impregnation of fine radioactive and toxic wastes containing a sealed working box, a container for radioactive waste, a vibrating pad, a dispensing container and a device control unit located outside the box, characterized in that the sealed working box contains a window equipped with rubber gloves, and the door is driven by a drive, and the sealed working box is equipped with a ventilation system, which includes a weight gauge for determining the level of vacuum and made in the form of a pipe connected to the process ventilation, and a decontamination system, consisting of a decontamination nozzle, a pipeline with an electromagnetic valve mounted on it and a drain pipe located in the bottom of the sealed working box, designed to drain decontamination water, also a sealed working box contains a probe with holes made in the lower part of the probe and a mechanism for moving the probe located in the upper part of the sealed working box and equipped with a cement level meter tnoy solution; in addition, a vibratory platform for accommodating a container with radioactive waste is mounted on a trolley with a drive, and the container with radioactive waste further comprises a lid; The cement preparation unit includes the above-mentioned metering tank for water, equipped with a water level meter and solenoid valves at the inlet and outlet of the metering tank for water, as well as a water meter and mixer, including a pipe for water, a pipe for loading cement and a drain pipe with electromagnetic a valve, the mixer being connected via a pipeline to a drain pipe for draining decontamination water in an airtight working box; in addition, the device comprises a system for supplying cement mortar to a container with radioactive waste, including a metering pump and a pipeline with an electric contact pressure gauge installed on it.

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