RU2419901C1 - Method of long-term storage of solid radioactive wastes - Google Patents

Abstract

FIELD: ecology. ^ SUBSTANCE: method of long-term storage of solid radioactive wastes (SRW) includes their storage in depots and isolation by filling of gaps between SRW, and also between walls and a bottom of the depot with a buffer fill in the form of natural materials mixture, formed when the quartz sand is mixed with additives. The buffer fill is used in the form of a loose mix of natural materials with the particle size ëñ5 mm, and the additives are natural zeolites from a group of carcass aluminosilicates (for instance, clinoptilolite), iron-containing minerals (for instance, ferric oxide, ferric hydroxide, acicular iron ore) and magnesium oxide, at the following ratio of components, wt %: quartz sand 50-80, natural zeolites of a group of carcass aluminosilicates 15-45, iron-containing minerals 1-15, magnesium oxide 1-15. ^ EFFECT: improved environmental safety in storage of radioactive wastes, reduced labour intensiveness and technical simplification of depot filling processes and solid radioactive wastes withdrawal from a depot when it is liquidated.

Description

The invention relates to the field of environmental protection, and more specifically to the field of long-term storage of both solid and solidified radioactive waste (RAW). Most effectively, the claimed invention can be used when storing packages of low- and medium-level waste in near-surface storage.

A great deal of experience has been gained in the world practice of near-surface disposal of radioactive waste, on the basis of which modern concepts of construction and operation of storage facilities have been developed. In the creation and operation of radioactive waste storage facilities, they adhere to the principle of multi-barrier protection, which includes natural and engineering barriers. An indispensable component of the engineering barrier is buffer filling - the material surrounding RW packages and used to limit the rate of migration of radionuclides from RW packages to the near zone, to minimize the contact time of RW packages with atmospheric precipitation and (or) groundwater (Near-surface disposal of radioactive waste. Safety requirements NP-069-06. Ecological Bulletin of Russia. 2007. Issue 01. - P.26) [1], sorption of radionuclides, deposition of radionuclides, gas evolution control. In addition, the long-term functional characteristics of the buffer backfill should allow in the future the possibility of extracting waste packages with their subsequent processing and (or) disposal.

A known method for the burial in the ground of containers with radioactive waste (Japan Patent No. 6031882 - B4, IPC G21F 9/36, publ. 04/27/1994) [2], including filling the space around the containers with radiation shielding material, which is a mixture of cement-cement mortar and zeolite adsorbent.

The disadvantages of this method are: its increased environmental hazard due to the fact that the aggregate containing cement mortar hardens over time, turning into a cement stone, characterized by the presence of voids and cracks, low sorption properties with respect to radionuclides of radioactive waste, which results in the possibility of moisture penetrating into the storage, leaching of radionuclides from radioactive waste and their removal into the environment, as well as the complexity and technical complexity of the extraction process i waste in case of liquidation of storage

A known method of the disposal of radioactive waste (Japan Patent No. 6031883 - B4, IPC G21F 9/36, publ. 04/27/1994) [3], according to which the gaps between the containers and the walls of the storage are filled with filler material, consisting of 1-30% of the powder Portland cement clinker or a mixture of this powder with blast furnace slag granulated in water and 70-99% of dried sand and / or dried soil.

The disadvantages of this method are: its increased environmental hazard to the environment, due to the possibility of moisture penetrating into the storage, leaching of radionuclides from radioactive waste and their removal into the environment due to the fact that the aggregate containing Portland cement clinker or a mixture of it with blast furnace slag in contact with moisture hardens, turning into a cement stone, characterized by the presence of voids and cracks, low sorption properties in relation to radionuclides of radioactive waste, as well as the complexity and technical complication of the waste recovery process in the event of storage liquidation.

A known method for the disposal of solid or solidified radioactive waste (Patent of Russia, No. 2069906 - C1, IPC 6 G21F 9/24, publ. 11/27/96, bull. No. 33) [4], in which the space between containers with waste is filled with material representing a mixture of bentonite and red mud (waste from alumina production according to the Bayer method) in a volume ratio of 1: 1.

The disadvantages of this method are: its increased environmental hazard to the environment, due to the possibility of violation of the tightness of the storage and even its destruction due to an increase in the volume of the buffer filler containing bentonite when it interacts with moisture, an increase in the contact time of RW with water and an increase in the leachability of radionuclides from - due to a decrease in the filtration properties of the material of the buffer filler containing bentonite, which is capable of swelling and forming when interacting with water linisty monolith and complexity of technical complexity and waste recovery process for the disposal repository.

Closest to the proposed method is a method for long-term storage of solid radioactive waste (Russian Patent, No. 2 357 308 - C2, IPC 6 G21F 9/00, publ. 05/27/2009, bull. No. 15) [5], including their storage in storage and isolation by filling the voids between the waste, as well as between the walls and the bottom of the storage, with a fluid buffer aggregate formed by mixing sand and clay rocks with water, thereby creating an additional barrier to the spread of radionuclides; as a barrier material, a mixture of sand-clay natural rock containing 15-30% clay minerals and 40-60% quartz (main constituents) with water is used with a ratio of 1 kg of rock to 2-8 liters of water; filling the voids in the waste storage with a sandy-clay fluid solution starts from the bottom (from the bottom) and is carried out in stages, in separate portions, with exposure after injection of each portion from 5 to 30 days to achieve maximum compaction of the layer.

The disadvantages of this method are: its increased environmental hazard to the environment due to leachability of radionuclides from radioactive waste and their release into the environment. This is due to the fact that during the hardening of the fluid composition formed by mixing sand-clay natural materials with water, a clay monolith is formed, which is characterized by the presence of voids and cracks, as a result of which there is a chance of water entering the storage and its contact with radioactive waste. The presence of a barrier in the form of a clay monolith increases the contact time of RAW with water, while radionuclides are washed out of them, and their release into the environment is possible. The increased environmental hazard of this method is also due to the weak sorption properties of sand-clay rocks in relation to radionuclides in the presence of competitive ions and in the form of various complexes.

Due to the fact that the storage is filled with a fluid composition, special preparation of the storage is required, which consists in the construction of injection wells using drilling tools and the installation of casing pipes. The process of injection of a fluid composition is carried out in stages with intervals from 5 to 30 days using special equipment for its injection. All these circumstances lead to an increase in the complexity and technical complication of this method. Due to the fact that over time hardening and compaction of the fluid composition with the formation of a clay monolith occurs, the complexity increases and the process of extracting waste from the hardened monolith is complicated, because sophisticated equipment and the adoption of additional measures to prevent environmental pollution and re-irradiation of the personnel conducting the work will be required.

The technical result of the proposed method for the long-term storage of solid radioactive waste is to increase environmental safety when storing radioactive waste, reducing the complexity and technical simplification of the processes of filling the storage and removing solid radioactive waste from the storage during its liquidation.

The specified technical result is achieved due to the fact that a method of long-term storage of solid radioactive waste (SRW) is proposed, including their storage in storages and isolation by filling the voids between the SRW, as well as between the walls and the bottom of the storage buffer filling in the form of a mixture of natural materials formed when mixing quartz sand with additives, moreover, buffer filling is used in the form of a loose mixture of natural materials with a particle size of ≤5 mm, and natural zeolites from coarse materials are used as additives PP of frame aluminosilicates (e.g. clinoptilolite), iron-containing minerals (e.g. hematite, iron hydroxide, goethite) and magnesium oxide, in the following ratio, wt.%:

quartz sand 50-80 natural zeolites from the group frame aluminosilicates 15-45 iron minerals 1-15 magnesium oxide 1-15.

Distinctive features of the proposed method for the long-term storage of solid radioactive waste is that buffer filling is used in the form of a loose mixture of natural materials with a particle size of ≤5 mm, and natural zeolites from the group of frame aluminosilicates (for example, clinoptilolite) and iron-containing minerals (for example, are used as additives) , hematite, iron hydroxide, goethite) and magnesium oxide, in the following ratio of components, wt.%:

quartz sand 50-80 natural zeolites from the group frame aluminosilicates 15-45 iron minerals 1-15 magnesium oxide 1-15

In the proposed method, to fill the voids between the SRW, a mixture of natural materials with particle sizes ≤5 mm is used. The use of a mixture of natural materials with a particle size> 5 mm is impractical due to the fact that the quality of filling the voids between the SRW decreases, the bulk properties of the buffer backfill deteriorate, and the specific surface of the buffer backfill material decreases, as a result of which its sorption properties with respect to radionuclides are reduced.

In this range are the particle sizes of natural materials obtained directly from deposits. Therefore, for the preparation of the mixture does not require their preliminary preparation and grinding, which reduces the complexity and simplifies the process when implementing the proposed method. The storage is filled with a loose mixture, which is fed into the storage under the influence of gravity without the use of additional equipment.

When the quartz sand is contained in the buffer filling within the specified limits, the buffer filling material has a high filtration coefficient, due to which, in case of water penetration into the storage, the duration of its contact with waste packages is reduced, therefore, the amount of washed radionuclides is reduced, which ensures environmental safety when implementing the proposed method. In addition, the material of the buffer backfill maintains flowability and does not form a monolith during long-term storage, as a result of which when removing SRW in the event of the liquidation of the storage facility after the adoption of the appropriate decision, special equipment is not required, which reduces the complexity and simplifies the process when implementing the proposed method. When the sand content is less than 50 wt.%, The filtration coefficient of the buffer backfill material decreases, which leads to a deterioration of environmental safety during waste storage, as well as the loss of flowability of the buffer backfill material during long-term storage, which will complicate the technological process of SRW removal in the event of liquidation of the storage after acceptance of the corresponding solutions. When the sand content is more than 80 wt.%, The sorption capabilities of the buffer backfill material are reduced, which affects environmental safety when implementing the proposed method.

When the content of natural zeolites in the buffer bed is within the indicated limits due to their high absorption ability with respect to radionuclides and their resistance to high temperatures, ionizing radiation, due to their unique porous structure, the sorption capacity of the buffer bed is significantly increased, which ensures environmental safety when implementing the proposed way. Introduction to the composition of the buffer backfill of natural zeolites in an amount of more than 45 wt.% Is impractical, because however, material costs increase significantly without a significant increase in the sorption capacity of the buffer backfill. The increase in material costs is due to the fact that this natural material has a higher cost compared to quartz sand; in addition, the shipping cost of natural zeolites is quite high due to the fragmentation and relatively rare distribution of their deposits. Introduction to the composition of the buffer backfill of natural zeolites in an amount of less than 15 wt.% Significantly reduces its sorption properties, which impairs environmental safety when implementing the proposed method.

When the content of iron-containing minerals in the buffer filling is within the specified limits, iron-containing films are formed on the surface of the quartz mineral grains, which form new sorption centers and increase the sorption capabilities of the material with respect to radionuclides, especially actinides (Sorption ²³⁷ Np (V), ²³⁸ U (VI ) and ¹³⁷ Cs on clayey rocks: the role of surface films of Fe (III) compounds. M. N. Sabodina, E. V. Zakharova, S. N. Kalmykov, K. V. Pokholok, A. A. Menyaylo. Radiochemistry. - 2008. - T.50. - No. 1. - P.81-86) [6], which ensures environmental I have security by the proposed method. Introduction to the composition of the buffer backfill of iron-containing minerals in an amount of more than 15 wt.% Is impractical, because however, material costs increase significantly without a significant increase in the sorption capabilities of the buffer backfill. The increase in material costs is due to the fact that this natural material has a higher cost compared to quartz sand; in addition, the cost of delivery of iron-containing minerals is quite high due to the fragmentation and relatively rare distribution of their deposits. Introduction to the composition of the buffer backfill of iron-containing minerals in an amount of less than 1 wt.% Significantly reduces its sorption properties, which reduces environmental safety when implementing the proposed method.

When the content of magnesium oxide in the buffer bed is within the specified limits, it acquires the ability to absorb undesirable CO ₂ generated during storage of waste containing a large amount of organic materials, and as a result, buffer properties to maintain an alkaline pH. (Behavior of MgO as a CO _2. Scavenger at the Waste Isolation Pilot Plant (WIPP), Carlsbad New Mexico. JLKrumhansl, HWPapenguth, PC Zhang, Mater. Res. Soc. Symp. Proc. - 2000. - Vol.608. - P.155-160) [7]. Due to this, the ability of the buffer backfill to retain Pu and other actinides increases, which ensures environmental safety when implementing the proposed method. Introduction to the composition of the buffer backfill of magnesium oxide in an amount of more than 15 wt.% Is impractical, because however, material costs increase significantly without a significant increase in the sorption capabilities of the buffer backfill. The increase in material costs is due to the fact that this natural material has a higher cost compared to quartz sand; in addition, the cost of delivery of magnesium oxide is quite high due to the fragmentation and relatively rare distribution of their deposits. The introduction of magnesium oxide into the buffer backfill in an amount of less than 1 wt.% Significantly reduces its sorption properties.

Example 1

SRW was placed in storage. The voids between the SRW, as well as between the walls and the bottom of the storage, were filled with buffer backfill in the form of a loose mixture of natural materials with a particle size of 5 mm, including quartz sand (50 wt.%), Clinoptilolite (30 wt.%), Hematite (10 wt.% ) and magnesium oxide (10 wt.%). The storage was filled with buffer backfill using construction equipment, and the voids between the SRW, as well as between the walls and the bottom of the storage, were filled by gravity. Due to the fact that the buffer backfill is in a loose state, there was a qualitative filling of all voids in the storage volume. Preliminary preparation of the storage before filling is not required. The filling process is one-step. This significantly reduces the complexity and simplifies the process when implementing the proposed method in comparison with the prototype.

To compose the mixture used natural materials obtained directly from deposits and industrial enterprises, without prior preparation. Used quartz sand of local origin.

Observations of the state of the repository for 1.5 years did not reveal the release of radionuclides into the environment from SRW located in the repository; it was noted that the insulating material of the backfill retains its bulk properties over a long period of time.

Example 2

The sorption capabilities of the buffer backfill material proposed in the present method and the buffer backfill material from the prototype were investigated. For this, the materials were kept in radionuclide solutions for 20 days under static conditions at room temperature. The specific activity of the radionuclide in the liquid phase was determined at the beginning and end of the experiment. According to the results of the activity change, the indices of sorption of radionuclides were calculated: distribution coefficient (K _p , ml / g) and degree of sorption (C,%).

Comparative data on the sorption capabilities of these materials are presented in the table.

Table Indicators of sorption of radionuclides by materials of buffer backfill Type of radionuclide Prototype buffer backfill Buffer filling proposed in the present method Distribution coefficient (K _p , ml / g) Sorption (C,%) Distribution coefficient (K _p , ml / g) Sorption (C,%) Cs ¹³⁷ - - 6545 ≈100 Cs ¹³⁷ (in the presence of competitive Cs ions) 45-51 ≈96 6693 ≈100 Sr ⁹⁰ - - 1985.7 99.79 Sr ⁹⁰ (in the presence of competitive Na ions) - - 4434 ≈100 Sr ⁹⁰ (in the presence of competitive Ca ions) - - 3140 99.9 Sr ⁹⁰ (in the presence of competitive Sr ions) 17-27 89 2150 99.8 U ²³⁵ (in the form of a cation) 24.6 89.9 81.56 96.9 U ²³⁵ (in the form of anionic complexes) 9.2 81.2 53.58 96.2 Pu ²³⁸ - - 7.25 75.76 Pu ²³⁸ ( _solution pH ≈10) 50-52 ≈80 128.6 92.1

From the above data it is seen that the buffer material obtained as a result of the implementation of the proposed method has good sorption characteristics with respect to a wide range of radionuclides in various forms, which significantly exceed the sorption characteristics of the buffer material from the prototype [5].

The results obtained indicate that, due to the optimal physicochemical and sorption properties of the buffer backfill material, the proposed method provides reliable isolation of SRW in the storage, and therefore, environmental safety when storing SRW for a long time with minimal material and labor costs; the technological process for extracting SRW from the storage after making the appropriate decision will also be simple and not requiring large labor costs.

The proposed method for the long-term storage of solid radioactive waste was implemented in the Gul MosNPO "Radon" when creating an experimental stand simulating the storage conditions of radioactive waste in a near-surface storage.

Claims (1)

A method for long-term storage of solid radioactive waste, including their storage in storage facilities and isolation by filling the voids between solid radioactive waste, as well as between the walls and the bottom of the storage, with a buffer backfill in the form of a mixture of natural materials formed by mixing silica sand with additives, characterized in that it is used buffer filling in the form of a loose mixture of natural materials with a particle size of ≤5 mm, and natural zeolites from the group of frame aluminosilicates are used as additives (for example Mer, clinoptilolite), iron-containing minerals (for example, hematite, iron hydroxide, goethite) and magnesium oxide in the following ratio of components, wt.%:
quartz sand 50-80 natural zeolites from the group of frame aluminosilicates 15-45 iron minerals 1-15 magnesium oxide 1-15