RU2754771C1 - Method for disposal of radioactive waste and container for storage thereof - Google Patents

Abstract

FIELD: radioactive waste disposal.SUBSTANCE: invention relates to methods for the preparation and disposal of radioactive waste (RW). The method includes the formation of sealed unified metal unit packages (UP) with solidified radioactive waste and increased protection against the migration of radionuclides. UPs with more hazardous RW are placed closer to the center of the masonry array than with less hazardous ones. The metal body of the unit package is lined from the inside with a layer of clay mixture and sheet glass adjacent to the clay mixture.EFFECT: invention allows combining burial (final isolation) in one engineering structure of all classes of solidified radioactive waste - from very low-level radioactive waste (LLRW) to intermediate-level radioactive waste (ILRW) and, after long exposure, high-level radioactive waste (HLRW).4 cl, 3 dwg

Description

State of the art

From the prior art, methods of final isolation are widely known - burial of radioactive waste (RW) in geological formations of the earth's crust, in which a natural or artificial cavity is filled with RW in various packages or containers, which implies isolation of RW from the environment for a period of potential hazard of RW ~ 1000 years caused by the natural decay of most radionuclides in the composition of radioactive waste, with the main emphasis being placed on long-term reliable isolation of radioactive waste from groundwater, with which radioactive waste radionuclides can move in underground horizons, polluting the environment.

A description and analysis of applied concepts for the disposal of low and intermediate level waste (LILW) or transuranic (TRU) waste, adopted in different countries, are given in (TW Hicks. TD Baldwin, PJ Hooker. PJ Richardson, NA Chapman, IG McKinley and FB Neall / Concepts for the Geological Disposal of Intermediate-Level Radioactive Waste, Galson Sciences Limited report lo NDA-RWMD. 2008).

Belgium has adopted a concept for the disposal of LILW in tunnels in plastic clay bedrock using waste containers protected in concrete disposal facilities, which are axially disposed in concrete lined tunnels. In France, the concept is to dispose of LILW in hardened clayey host rock in tunnels with waste containers packed in concrete overpacks that are stacked in concrete-lined tunnels; a separate disposal area is allocated for waste containing organic matter. According to the Swiss concept, the disposal of LILW should be carried out in tunnels in the enclosing marl rocks, with waste containers packed in concrete blocks for disposal, which are laid in concrete-lined tunnels covered with a gas-permeable solution. According to the accepted concept of Japan, TRU wastes should be transported to the tunnel in hard or soft rock, with waste containers poured into steel containers that are placed in the tunnels (lined with concrete in soft rock) and with cement slurry included as backfill; some waste has a bentonite barrier, and waste containing nitrates is separated into a separate disposal area. Sweden has adopted the concept of burying LILW inside caves in crystalline host rock with waste packed in concrete and steel containers that are piled into caves (low level waste) or poured into concrete vaults inside caves (high level waste); the caves are filled with rubble, which acts as a hydraulic separator. According to the concept adopted by Canada, the disposal of LILW should be carried out in a limestone enclosing rock with the placement of LILW and shielded containers with LILW in separate rooms (without subsequent filling). The German concept provides for the disposal of LILW in caverns of clay formations, with the waste packages being placed in steel containers and cemented, and then stacked in piles in the caverns; caverns are filled with solution.

However, due to the complexity and high costs of implementation, most of these concepts related to the use of geological structures are still under development or are no longer developed in accordance with the original designs. In accordance with the ALARA principle (abbreviated as As Low As Reasonably Achievable) adopted in the nuclear industry, formulated as a principle of dose optimization back in 1954 by the International Commission on Radiological Protection in order to minimize the harmful effects of ionizing radiation, in the current economic conditions in the practice of neutralization To reduce the costs of radioactive waste, more attention should be paid to engineering structures, primarily near-surface ones, as the least costly.

Known storage for radioactive waste of a near-surface type, used for the containment of containers with solid radioactive waste (application JP 2013210359 A, Japan // MKI G21F 9/24, 10.10.2013), including a semi-buried near-surface repository for placing containers with solid radioactive waste and a support system radiation safety, including the lower protective engineering barrier of the storage facility and the upper protective engineering barrier of the storage facility.

The disadvantages of this method of final isolation are low environmental safety due to possible flooding of containers with radioactive waste located below ground level, violation of their tightness and the possibility of migration of radionuclides from them into the environment.

There is a known method of burial of supertoxic industrial waste (RF patent No. 2317160, publ. 02/20/2008), which includes sequential laying of a waterproof screen, compacting it, laying and compaction of waste, covering the waste with a second waterproof screen, compaction and filling it with a layer of soil-vegetable soil with subsequent planting of plants. Insulating material IM-1, containing oil sludge, limestone in small lump form, drilling waste, clayey rocks, biological products impregnated with liquid bitumen or tar, is used as a waterproof screen. Before stacking, cemented blocks are formed from supertoxic waste in a humid environment at 40-60 ° C for 1-3 days, including: supertoxic waste, Portland cement, river sand, insulating material IM-1 with the following ratio of components, wt. h .: supertoxic waste - 1 wt. hours, Portland cement - 0.1-0.3 wt. hours, river sand - 0.1-0.3 wt. hours, insulating material IM-1 - 0.05-0.1 wt. hours, which are covered with liquid bitumen or tar for 3-5 minutes, then cooled and sent for laying.

The disadvantage of this method is the increased fire hazard and biological degradation of bitumen.

A known method of burying solid radioactive waste in near-surface repositories (RF patent No. 2366011, publ. 27.08.2009). When the waste is buried, the burial site is doned from the bottom and from the sides with a layer of 0.5 to 1.5 m of a compacted mixture of clay with bauxite slurry. After filling the burial ground with waste, the top is embanked so that the vertical layout of this waterproofing layer ensures the drainage of atmospheric precipitation. Bauxite sludge is obtained by roasting bauxite ore together with lime and soda and subsequent washing with water to remove soluble sodium compounds.

The disadvantages of this method are the presence of specific ingredients and the high complexity of processes for using the method.

The concept of a storage facility for near-surface radioactive waste used for the localization of VLLW is known (Alternative concepts of the final stages of VLLW management / AA Abramov [et al.] // Safety of nuclear technologies and the environment. - M., 2012. - No. 3 - P.29-36.), Including a lower protective engineering barrier formed by the base, a bed with a drainage system in the form of a reinforced concrete slab, containers and packaging with VLLW, as well as an upper protective engineering barrier formed by an upper cushion of sand, a layer of bentonite, a covering high-density polyethylene films, topcoat containing a drainage layer of stone chips or gravel, a waterproofing layer of clay and a cover layer of turf.

The disadvantages of the well-known repository are:

- low environmental safety due to the absence of elements in the structures forming the lower protective engineering barrier that exclude the contact of containers and packages with VLLW with water, in emergency situations associated with flooding of the storage, and the migration of radionuclides into the environment, as well as the lack of systems that ensure the implementation monitoring and operational management of the environmental safety of the storage facility during its service life without violating the integrity of protective engineering barriers;

- limited area of application, extending only to the localization of VLLW, due to the low reliability of protective engineering barriers.

The prototype in terms of the technical nature of the claimed method of disposal of radioactive waste is a near-surface radioactive waste storage facility used for localization of solidified LRW (Atomic Strategy XXI, No. 153, Vitaly Uzikov // Optimization of LRW disposal technology / ProAtom Information Agency, St. Petersburg, 2019 , pp. 14-19.)

At the same time, it is proposed to transfer LRW of medium and low activity (including VLLW) first into a high-salt solution with a salt content of 700-900 g / l, and then use it to obtain unified cement blocks suitable for dense packing at final isolation points. With this approach, the main structural material of such engineering structures is the UCB themselves, based on high-salt LRW concentrates, and the formation of the array from blocks should be carried out so that on its periphery there are low-level (LLW) or very low-level blocks (VLLW), and to the central part of the array, activity blocks gradually increased to the level of average active (MAO).

The disadvantages of this method are:

- insufficient environmental safety due to the high leachability of the cement compound in situations associated with flooding of the storage, causing the possible migration of radionuclides into the environment;

- the possible risk of radionuclide release into the environment during transport and technological operations with open blocks of the cement compound;

- the possibility of destruction of cement compound blocks during transport and technological operations.

The closest analogue to the claimed method is a method for the preparation and disposal of radioactive waste (RF patent No. 2537815, publ. 01/10/2015), including the delivery of radioactive waste from their manufacturers to the disposal site, preparation of delivered radioactive waste, including the processing of surface radioactive waste contaminated with radionuclides, placement of prepared radioactive waste in the volume of disposal, final isolation from the environment, characterized in that for effective, reliable and final disposal of radioactive waste, open mine workings with a completed mining cycle are used - mining or mining quarries with a rock base, in which equipment is produced for the unloading site and preparation of radioactive waste for burial, a MRAW processing point, a transport network for the transfer of radioactive waste to a quarry for disposal, upon readiness for operation of which, the delivery of radioactive waste from their producers to the disposal site is carried out without restrictions on origin - technogenic, natural radionuclides PRN, according to activity - low-level LLW, medium-level IWW, high-level HLW, in terms of design, materials, shapes, dimensions, time and conditions of the previous storage of containers and packages of RW, mostly in standardized metal unit packages of EU cubic form, prepare the delivered RW for disposal - repair of packages and containers, restoration of their anticorrosive coatings, overloading of worn-out packages into new ones, MRAO is recycled, removing radioactive contamination by complex deep decontamination, as a result of which the deactivated and admissible for unlimited use metal is excluded from burial and returned to economic circulation, and the secondary radioactive waste from processing is compacted, solidified, enclosed in EU and together with the prepared packages are transferred to a quarry, in which the bottom-base is covered with imported clay, covering all bottom irregularities, leveling and compacting the layer to a flat horizontal platform, on which the delivered RW using constructive feature of the EU, they are built in volumetric blocks or block-containers with the provision of gaps between the blocks and the walls of the quarry to a height not exceeding the design strength of the unified EU, after which the gaps are filled with clay, allow it to settle for sedimentation, fill the gaps and block the upper cut of the RAW blocks with clay and all the gaps, closing the individual clay insulation of each of the assembled blocks of the first tier and forming the platform-base of the second tier, on which the block-tiered filling of the open pit is continued up to the upper design mark, after which the unfilled part of the open pit is covered with clay, closing the contour of the clay insulation of the volume filled with radioactive waste and backfilled with soil from overburden dumps, completing the last stage in the final disposal of radioactive waste and reclamation of the open pit with the restoration of the pristine natural landscape.

The disadvantages of this method are the complexity of carrying out transport and technological operations in an open pit, high dose loads on personnel during operations to decontaminate MRAO, the lack of technology for conditioning secondary radioactive waste directly at disposal sites, and the accumulation of atmospheric precipitation in the open pit when it is filled.

The essence of the invention

The claimed invention is aimed at creating a universal effective technology for reliable and long-term final isolation of solidified radioactive waste of varying degrees of hazard at minimal cost.

The technical result is achieved due to the fact that the method of disposal of radioactive waste and the design of a single package provide protection against the release of hazardous radionuclides into the environment due to the use of sorbent and insulating materials that are not subject to degradation over time (glass, bentonite clay or its analogs) and have a relatively low price.

Improving the reliability of long-term isolation - disposal of radioactive waste is achieved due to:

application of the nesting principle, in which unit packages (PU) in a metal case with a higher level of radiation hazard for the environment are placed closer to the center of the masonry than PU with a lower level of radiation hazard. Thus, the structure of the EU placement in the masonry array prevents the migration of radionuclides into the environment;

use for engineering barriers preventing the release of hazardous radionuclides into the environment, sorbing and insulating materials that are not subject to degradation over time (glass, bentonite clay or its analogs).

Increasing the efficiency of the method is achieved by:

use in the final isolation of solidified radioactive waste of universal unit packages with a metal body, in which the cement compound occupies 90-95%, in contrast to non-returnable protective containers NZK-150-1.5P, where the useful capacity for the compound is 40% of the total volume of the container;

the cost of acceptance for disposal by the national operator NZK-150-1.5P is 200 thousand rubles / m ³ , i.e. 750 thousand rubles for receiving the container. Together with the cost of NZK-150-1.5P, the cost of transferring 1.5 m ^{3 of} solidified radioactive waste will amount to 870 thousand rubles. at rates of 2017. The costs of transferring a similar volume of solidified radioactive waste in metal unit packages lined with glass and bentonite clay from the inside will amount to 50 thousand rubles. for the cost of unified EU and 330 thousand rubles. for storage volume - in the amount of 380 thousand rubles, i.e. 2.3 times lower than with existing technology.

A radical reduction in the costs of the final isolation of class 2 RW when using the claimed method is achieved by the fact that it allows you to abandon the construction of expensive deep burial sites, the cost of isolation of which is 700 thousand rubles / m ³ . The claimed method makes it possible to ensure reliable isolation at one disposal site for radioactive waste of solidified RW of the 2nd, 3rd, 4th and 6th class using the technology of remote storage of EU in accordance with the nesting principle. The use of industrial robots with a vacuum gripper in transport and technological operations makes it possible to make metal unit packaging of a simple form, technological and low cost. The simple form of EU and the use of an industrial robot with a vacuum gripper on the platform of an overhead crane makes it possible to automate and optimize the process of forming masonry from EU with radioactive waste of different hazard classes in accordance with the nesting principle, which reduces the dose load on personnel and the risk of accidents as a result of personnel errors.

The analysis of the prior art showed that the claimed set of essential features set forth in the claims is unknown. It has been found that the claimed technical solution does not follow explicitly from the prior art. The invention is new, has an inventive step and is industrially applicable.

Description of drawings

The inventive method is illustrated by figures presented on:

FIG. 1 - General diagram of the structure of a complex facility for near-surface disposal of radioactive waste using industrial manipulators with a vacuum grip;

FIG. 2 - Construction of a single package with a cement compound, the shell of which is lined from the inside with sheet glass;

FIG. 3 - Diagram of the structure of the stacking of single packages of different classes of radiation hazard in a complex near-surface disposal site.

An example of a specific execution

As a non-limiting example, Fig. 1 shows the application of the claimed method in a near-surface disposal facility for radioactive waste (1), equipped with an overhead crane (2) with a cargo trolley (3), on which an industrial manipulator (4) is installed, equipped with a gripper (5), allowing to carry out transport and technological operations with single packages of a cement compound of radioactive waste of a rectangular shape, lined with metal (6). Unit packages (6) are stacked at the disposal site (1) in accordance with the nesting principles, when EUs with a higher level of radiation hazard to the environment are placed closer to the center of the masonry than EUs with a low level of radiation hazard, placed closer to the periphery of the masonry. On the periphery of the masonry, EU with a very low level of radioactivity (VLLW) are laid in a thick layer, the main role of which is to create a reliable zone of long-term protection against the migration of hazardous radionuclides into the environment from the center of the masonry (7). EUs with a higher level are placed closer to the center (8), and those with the highest radioactivity are placed in the center of the masonry (9).

The structure of a unit package (6) is shown in Fig. 2. The metal case of the EU has the shape of a rectangular parallelepiped (10). From the inside, the metal walls of the EU are lined with sheet glass (11), which makes it possible to provide reliable and long-term protection against the migration of radionuclides from the cement compound of the package (12) beyond its boundaries.

Single packs (6) are stacked with an industrial manipulator (4) in layers, observing the required gap between the side edges, which, after complete laying of the layer (tier), is filled with bentonite (montmorillonite) clay or its mixture (Fig. 3, 13). Then the entire layer of EU is covered with an even layer of bentonite clay (14), after which the next layer of EU is laid.

To ensure the possibility of using a vacuum gripper by an industrial manipulator, the EU height must be limited so that atmospheric pressure ensures reliable pressing of the package to the gripper. To do this, it is necessary to fulfill the condition for the permissible EU height based on the ratio:

,

,

where h _EU is the maximum height of a single package, cm;

F _ЕУ - area of the base of the prism ЕУ, cm ² ;

F _vac - vacuum gripping area, cm ² ;

P _vac - vacuum pressure, kg / cm ² ;

P _at - atmospheric pressure, kg / cm ² ;

ρ _EU is the average density of a unit package, kg / cm ² .

To increase the level of long-term protection against the migration of hazardous radionuclides, in addition to filling the gaps between the EU with bentonite clay, layers of sheet glass are installed. After corrosive destruction of metal shells of EU, glass, which can retain its properties for thousands of years, will take over the role of reliable barriers preventing the migration of hazardous radionuclides. The formation of cracks in the glass will have little effect on its insulating properties, since the cracks will be filled with particles of bentonite clay.

The claimed method for the final isolation of solidified radioactive waste of different classes corresponds to the actual distribution of the volumes of accumulated radioactive waste, for example, liquid radioactive waste. Most of them belong to RW with low and very low levels of radioactivity (LLW and VLLW). Therefore, after conditioning LRW in a cement compound and filling with EU with this compound, the number of unit packages with LLW and, especially, VLLW will many times exceed the amount of EU with medium and high activity levels (CW and HLW). EU with VLLW do not pose a great threat to the environment, but, based on their quantity, they can serve as a good and long-term engineering barrier with guaranteed parameters of radiation protection against the release of hazardous radionuclides from the disposal site for millennia. Therefore, the entire peripheral area of the masonry is formed from EU with a low and very low level of radioactivity (LLW and VLLW), which, in terms of the volume of the masonry, should occupy at least 60% of the total volume. Thus, while solving the problem of accumulating large volumes of LLW and VLLW, the engineering problem of reliable long-term isolation of hazardous radionuclides in a relatively simple and reliable engineering structure with well-calculated parameters of long-term protection is being solved.

The simplicity of the technology for the production of packages, their filling with a cement compound and sealing, as well as the low cost of sheet steel, sheet glass and clay ensure the efficiency of the proposed method. This makes it possible to create standardized equipment for the production of EU, which will eliminate the costs of enterprises for the design and production of their own systems for the formation of unit packages with a cement compound of various classes of radiation hazard. The transportation of EU to the final isolation point should be carried out using specially designed transport and packaging sets (TUK), which will ensure that all the requirements of regulatory documents for the safe transportation of radioactive waste are met.

The use of the claimed invention will improve the reliability of long-term isolation of radioactive waste disposal and its efficiency, as well as reduce the cost of final isolation and dose loads on personnel during operations on radioactive waste disposal.

Claims (11)

1. A method of disposal of radioactive waste, including the delivery of solidified radioactive waste of various levels of radioactivity in unified metal unit packages (UU) from their manufacturers to the point of final isolation, made in the form of regular prisms, UU, using a transport and handling mechanism, are placed in the masonry of the point at the same level ensuring the design gaps between them, thereby forming a tier of masonry, after which the upper part of the EU and all the gaps between them are covered with a clay mixture based on montmorillonite clay, closing the individual isolation of each EU of the formed tier with a clay mixture and forming a base platform for the next layer, on where the block-tiered filling of the masonry is continued up to the upper design level, the massif of EU masonry with solidified radioactive waste of different levels of radioactivity at the final isolation point is formed in such a way that the EU with a higher level of radiation hazard to the environment are located closer to the center in masonry than EU with a lower level of radiation hazard, characterized in that the metal body of the unit package is lined from the inside with a layer of clay mixture and sheet glass adjacent to the clay mixture. 2. The method of disposal of radioactive waste according to claim 1, characterized in that a layer of sheet glass is additionally placed between the tiers. 3. A method for burying radioactive waste according to claim 1 and 2, characterized in that a layer of sheet glass is additionally placed between the side faces of the EU. 4. The method of disposal of radioactive waste according to claim 1, characterized in that during transport and handling operations with EU, a vacuum gripper is used, and the height of EU does not exceed the value determined by the formula

, where h _EU is the maximum height of a single package, cm; F _ЕУ - area of the base of the prism ЕУ, cm ² ; F _vac - vacuum gripping area, cm ² ; P _vac - vacuum pressure, kg / cm ² ; P _at - atmospheric pressure, kg / cm ² ; ρ _EU is the average density of a unit package, kg / cm ² .

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