Method for integrated processing of liquid radioactive waste

 

(57) Abstract:

The invention relates to chemical technology, specifically to the nuclear environment, and can be used in the processing of liquid radioactive waste (LRW) generated by the operation of the various nuclear power plants. For implementing the method carried out stepwise process processing of liquid radioactive waste containing radionuclides of cesium and strontium in the following sequence: first LRW serves on stage pretreatment, which may include blocks of mechanical treatment, ultrafiltration and microfiltration unit, then put them through selective inorganic sorbent on the basis of ferrocyanides transition metals copper, Nickel, cobalt and a porous inorganic carrier, then they are subjected to desalting and concentration one of the following methods: distillation, two-step, in which the first stage uses electro-membrane or reverse osmosis desalination, in the second stage of electroosmotic or distillation concentration. While desalination is carried out to obtain a concentrate of 20 to 70 g/DM3and concentration to obtain brine 180 - 250 g/DM3. The filtrates after the stage is a mini-type zeolite And, habasit hexagonal structure or natural zeolite monoclinic structure, which is used as the modified zeolite "Selex-KM". Brines and the spent sorbent is disposed by cementing in containers, or in the form of iron barrels with a capacity of 200 DM3or in the form of a concrete cube with dimensions: H B L = 1,52 1,52 1.4 m with a volume of 300 - 900 DM3. In another embodiment, the spent sorbent is disposed by including them in dry form in a reinforced concrete container with a volume of 300 DM3. 13 C.p. f-crystals, 1 table.

The invention relates to the field of chemical technology, specifically to the nuclear environment, and can be used in the processing of liquid radioactive waste (LRW) generated by the operation of the various nuclear power plants (NPP) NPP, vehicles (atomic icebreakers, submarines, floating NPP).

In the process of nuclear energy cycle form different types of LRW, which must then be processed with a view to their subsequent disposal in the compact solid form. As a rule, all types generated LRW have a well-defined chemical and radionuclide compositions defined OS used for decontamination of equipment.

In the operation of the NPP are three main types of LRW belonging to the class of medium - and low-level, the composition of which is given in the table.

Based on the ecological requirements existing in the Russian Federation and reflected in NRB 76/87 [1] and IAEA recommendations, the processing of LRW should include cleaning up the total content of active radionuclides is less than 10-10CI/L. As a rule, limiting this figure are the radionuclides cesium-137 and strontium-90 content in standard LRW is about 80%, and the chemical nature is that they are very difficult retrieved from salt solutions. In addition, due to sanitary requirements (SPORO-85) activity subject to final disposal in the form of cement blocks brine salinity 150 - 240 g/l should not exceed 1 to 10-4CI/L. This requirement for permissible levels of radiation exposure of maintenance personnel repositories.

Therefore, complex processing methods LRW include several chemical processes, including the removal of radionuclides, desalination of salt solutions to an acceptable discharge standards, the treatment of demineralized concrete is enantioface treated sorbents and formed at the stage of desalination brines [2, 3]. The only species formed during the processing of LRW waste must be cement blocks, corresponding to their specific requirements set forth in SPORO-85.

Closest to the described method, is a method for integrated processing of liquid radioactive waste containing radionuclides of cesium and strontium, which includes stages pretreatment, desalination and concentration, separation of the flow on the filtrate with a salt content of < 0.5 g/l and the brine with salinity 180 - 250 g/l, followed by purification of the filtrate on the sorbents to the radionuclide content < 10-10CI/l and disposal of brine and waste sorbents by their inclusion in the cement matrix [4].

In this way LRW sequentially subjected to the following stages of processing.

First, the solutions are sent to the stage pretreatment. Depending on the degree of contamination of suspended solids, petroleum products (TM) and surface-active substances (surfactants) this stage includes:

purification from suspended substances and petroleum products on special filters with filter material, retention of organic matter and petroleum products (foam, highly porous organic sorbents type TEW filter of 20 μm and ultrafiltration.

At low concentrations in the original LRW suspended solids and oil products from this stage eliminates the process of ultrafiltration.

On stage pretreatment can be used precipitation methods for removing various impurities, hardness salts, surfactants, iron, oxalates, which will interfere with the processes of concentration of salts in various ways. Then pre-treated solutions served on the main stage purification and desalination. This stage is a residue that can be implemented in both the high temperature and under vacuum. You can use other alternative methods: reverse osmosis, electrodialysis, or combinations thereof.

In all cases, almost all radionuclides (> 99%) are in concentrate 180 - 250 g/l, which is then subjected to the cementing of well-known methods.

The main disadvantage of this method is that it is impossible to clean LRW average activity level of 10-5CI/l and above without breaking the rules SPORO-85.

Indeed, when the concentration LRW 100 times, which is usually achieved all of the described methods, content - active radionuclides in con who Is on the order exceeds the allowable SPORO-85 standards.

Therefore, the degree of concentration of radionuclides in the solid phase, which is one of the main economic indicators of the whole process is quite low. Usually it does not exceed 50.

The present invention is to increase the degree of concentration of radionuclides in recyclable end product is a cement block, and thus reducing the amount of solid waste.

In addition, the invention aims to improve the environmental safety of the process LRW processing by reducing cycle disposal of radioactive cesium.

The task is achieved by the described method of processing of liquid radioactive waste containing radionuclides of cesium and strontium, which includes stages pretreatment, after which the liquid waste is passed through a selective inorganic sorbent, representing composite ferrocyanide sorbent on the basis of the ferrocyanides of transition metals (copper, Nickel, cobalt) and a porous inorganic carrier, desalting and concentration, which are by distillation or in two stages using the following processes: electro-membrane desalting and electroosmotic concentration; reverse osmosis from TDS < 0.5 g/l with its subsequent purification on sorbents selected from the range: zeolite sorbents type "A", chabazite hexagonal structure or a monoclinic structure type modified clinoptilolite brand "Selex-KM", and/or ion-exchange resin, and the concentrate TDS 180 - 250 g/l and its subsequent utilization with exhaust sorbents by their inclusion in the cement matrix.

A distinctive feature of the method is that before desalting LRW additionally passed through selective to the radionuclides of cesium and strontium inorganic sorbent-based transition metal ferrocyanides and a porous inorganic carrier.

Another difference method lies in the fact that, as a sorbent-based transition metal ferrocyanides and a porous inorganic carrier used sorbent on the basis of ferrocyanides copper, Nickel or cobalt.

Differences of this method are that the stage of purification of the filtrate using sorbents selected from the group of zeolites a, chabazite hexagonal structure or zeolites monoclinic structure type of the modified zeolite "Selex-KM and/or ion-exchange resin.

In addition, distinctive ol the t in two stages using a first electro-membrane desalination, and then electroosmotic concentration, or first reverse osmosis desalination, and then either electroosmotic concentration or distillation.

Another difference lies in the fact that reverse osmosis desalting is carried out to obtain a brine with a concentration of 60 to 100 g/DM3and distillation or electroosmotic concentration is carried out to obtain brine 180 - 250 g/DM3while the filtrate from stage distillation combined with the permeate from the stage reverse osmosis and sent for sorption purification.

Other differences of the method lies in the fact that the disposal of brine and waste sorbents are by making them homogeneous mixture of cement at a volume ratio of brine to the cement 0.3 to 0.8:1 and sorbents to cement 1 to 1.5: 9 and its inclusion in the container, which is used as the metal, made in the form of barrels of 200 DM3or concrete, is made in the form of a cube with dimensions H x B x L = 1.52 x 1.52 x 1.4 m and a volume of 300 - 900 DM3.

Another difference is that the disposal of spent sorbents are by their inclusion in a concrete block in the form of dry granules placed in CLASS="ptx2">

Example 1. Spend cleaning liquid radioactive waste type solutions II the following composition:

the salt content of 2 g/l; hardness of 35 mg/l; Cl-of-0.8 g/l; C2O4-3.6 mg/l; SAS - 6 mg/l; Trilon B - 14 mg/l; pH of 8.5; Sr - 2,1 10-5CI/l; Cs (134+137) 10-5CI/l, other radionuclides - 2,5 10-5CI/L.

Cleanup of lead in the following sequence.

The original solution is subjected to mechanical cleaning by passing it through the granular material (quartz sand, cultural).

After filtration the solution is supplied to the node softening, where it removes hardness salts to the level of 3 - 5 mg/l, and then the solution with a speed of 6 - 10 TO/h (volume of solution equal to the volume of the sorbent) is passed through the composite ferrocyanide sorbent-based transition metal ferrocyanide (FSC) grade NGA and sent for electrodialysis desalination in electrodialyzer with running diluate and brine cameras.

In the process, in electrodialyzer salt ions, including radioactive, are transferred from diluate cameras in brine, resulting in the desired degree of purification dilute salts. The brine solution from the cameras to the sky transfer salts with ions of hydrated water molecules is achieved the necessary degree of concentration of the brine to a value of 180 - 240 g/l

The electrodialyzers operate in the following modes:

- electrodialyzer desalination - 200 B; 3 A;

- electrodialyzer concentration - 150 B; 7 A.

Desalted prior to the salinity of 0.15 g/l solution of diluate camera electrodialyzer desalting served on the sorption column Packed with a synthetic zeolite of the type "A" brand CIP.

At the finish of the solutions are subjected to additional purification using filtration to prevent debris from entering the purified solution of fine particles (ash with sorbents).

In a purified solution content-active radionuclides is < 10-10CI/l, which corresponds to sbresny standards for NRB 76/87.

Highly concentrated brine (180 - 240 g/l of salt) electrodialyzer concentration (electroosmotic) direct on stage cementing, where by mixing with Portland cement 500 M with a volumetric ratio of water : cement 1 : 1 get a homogeneous mixture of brine with cement.

Homogeneous mixture stariway in primary packaging - metal barrel with a capacity of 200 l, where after curing receive the cement matrix, suitable for long-term storage or the th mechanical strength in compression with a force of 0.13 kgf/cm2.

Example 2. Spend the purification of solutions of type III having a salt content of 12 g/l; hardness 30 mEq/l; petroleum products (TM) - 200 mg/l; suspended solids 100 mg/l; content of other impurities at the level of example 1.

Cleanup of lead in the following sequence.

First LRW is passed through a filter with floating foam boot, then filtered through a cartridge filter element with filtration 20 micron.

When this is cleaned from NP 97% of suspended solids 95%. Filtering is carried out at an operating pressure of 0.2 - 0.3 MPa. Next LRW filtered under pressure of 0.04 MPa through the ultrafiltration module, where there is a complete purification from suspended solids, NP and surfactants. Throughout these stages is achieved by the removal of radionuclides with a factor 3 to 4.

After passing through the ultrafiltration module is passed through the FSC brand, MJA.

Then LRW at t - 15oC serves on the reverse osmosis unit, equipped with two roll-up of reverse osmosis elements SWHR 30-8040 and cartridge filters 20 and 5 μm. Filtering is carried out at an operating pressure of up to 5.9 MPa by serial transmission LRW through two elements.

Check sposoby at least 99.3%, and ions of calcium, magnesium, strontium, heavy metals, surfactants not less than 99.9%.

Desalted to salt content < 10 mg/l solutions are subjected to purification by passing through the zeolite monoclinic structure - modified clinoptilolite brand "Selex-KM". After purification solutions contain < 10-10CI/l - active radionuclides and can be discharged into open waters.

The concentrates from the stage reverse osmosis with a salt content of 80 - 100 g/l are collected in a special tank from where it is directed to the precipitation of hardness salts to their content of 0.3 - 0.5 mEq/L. of the Filtrate after precipitation direct to the final concentration using the methods of electro-osmosis or distillation. Electroosmotic concentration of lead as described in example 1. Distillation concentration of lead in the evaporation apparatus of the direct-flow type heat exchangers of the type of pipe-in-pipe, provided with a condenser for condensing the secondary pair.

Concentrates coming out of the evaporator, are the salt content of 250 g/l and specific activity 2 10-4CI/l, and the secondary steam condensate - salinity < 2 mg/l and the specific activity of < 10-9CI/L.

This condensate combine innately cation type KU-2-8 - es and strong-base anion-exchange type AB-17-8-Yak). Obtained after purification of the effluents have a specific activity of < 10-10CI/l and can be discharged into open waters. Concentrates 200 - 250 g/l is directed to the cementing conducted in example 1, except that use homogeneous mixture of brine with cement at a ratio of 0.8:1, and the container used reinforced concrete, made in the form of a cube with dimension H x B x L = 1.52 x 1.52 x 1.4 m and a capacity of 900 DM3.

Example 3. Are LRW purification in example 1, except that for processing a mixture of solutions I and II, containing 50 mg/l of ammonium ions and pH-10. Other components of the solution correspond to the shown in example 1. At the stage of purification of the filtrate with a salt concentration of 0.1 g/l consistently passed first through a modified clinoptilolite brand "Selex-KM, and then through synthetic zeolite Sabitova patterns brand JE-95. Cementation of waste carried out in two ways.

Brines with TDS 200 g/l are cementing in example 2. The spent sorbent is placed in a dry form in a reinforced concrete container with an internal volume of 300 DM3. Due to the fact that the thickness SUP>-2CI/kg

This is 500 times higher than the level of activity by the usual method of cementing with obtaining a homogeneous mixture of brine - waste sorbents cement.

In this case, the overall degree of concentration of radionuclides in the solid phase also increases considerably.

Example 4. Are LRW treatment, representing a mix of solutions I and II composition shown in example 3, the distillation method. Before parcoy solutions are subjected to a mechanical filter and passed through the FSC brand KIA representing cobalt ferrocyanide on a porous inorganic carrier.

The residue LRW conduct heat ferry with P = 0.4 MPa in the evaporation apparatus of the natural circulation privelage solution and remote heating chamber with the heat exchange surface 80 m2at atmospheric pressure.

Obtained after parki dice the remainder has a salt content of 200 g/DM3and the specific activity of 1.5 to 10-4CI/L. It is sent for cementing, which are similar to those described in example 3.

The secondary steam condensate has a specific activity of < 10-9CI/l and sent for treatment. The purification is carried out by passing/P> Thus, the described method allows the processes of complex processing of LRW more economical way. This is achieved by the fact that much of the activity ( 70 - 90%) is absorbed in CFS, which improves the overall degree of concentration of radionuclides in comparison with the known methods in 2 - 3 times, which means at the same time reduce the cost of long-term storage of solidified radioactive waste.

1. Method for integrated processing of liquid radioactive waste containing radionuclides of cesium and strontium, which includes stages pretreatment, desalination and concentration and separation of the flow on the filtrate with a salt content of < 0.5 g/DM3and the brine with salinity 180 - 250 g/DM3with subsequent purification of the filtrate on the sorbents to the radionuclide content < 10-10CI/l and disposal of brine and waste sorbents by their inclusion in the cement matrix, characterized in that before the desalting of liquid radioactive waste is additionally passed through selective to the radionuclides of cesium and strontium inorganic sorbent-based transition metal ferrocyanides and a porous inorganic carrier.

2. The method according to p. 1, otlichalis is rociando copper, Nickel or cobalt.

3. The method according to p. 1, characterized in that the treatment of the leachate lead by transmission through a sorbent selected from the group of zeolite sorbents type zeolites a, chabazite hexagonal structure or a monoclinic structure type clinoptilolite and/or ion-exchange resins.

4. The method according to p. 1, wherein the desalting and concentration lead by distillation.

5. The method according to p. 1, wherein the desalting and concentration of lead in two stages: first electro-membrane desalting, and then electroosmotic concentration.

6. The method according to PP.1 and 5, characterized in that the electro-membrane desalting is carried out to obtain a brine with a concentration of 20 to 60 g/DM3and electroosmotic concentration to obtain brine 180 - 200 g/DM3.

7. The method according to p. 1, wherein the desalting and concentration of lead in two stages: first, reverse osmosis desalination, and then electroosmotic or distillation concentration.

8. The method according to PP.1 and 7, characterized in that reverse osmosis desalting is carried out to obtain a brine with a concentration of 30 to 70 g/DM3and electr who eat what is reverse osmosis desalting is carried out to obtain brine salt concentration 60 - 100 g/DM3and distillation concentration to obtain brine 200 - 250 g/DM3while the filtrate from stage distillation combined with the permeate from the stage reverse osmosis and sent for sorption purification.

10. The method according to p. 1, characterized in that as the cement matrix for disposal of brine and/or waste sorbents use their homogeneous mixture of cement placed in the container.

11. The method according to PP.1 and 10, characterized in that the container used metal drums of 200 DM3.

12. The method according to PP.1 and 10, characterized in that the container used concrete block, made in the form of a cube with dimensions: H x B x L = 1,52 x 1,52 x 1.4 m and an internal volume of 300 - 900 DM3.

13. The method according to PP. 1 and 10, characterized in that as a homogeneous mixture of brine with cement, a mixture of the following ratio of components,% vol.: brine : cement= (0,3 - 0,8) : 1.

14. The method according to p. 1, characterized in that as the cement matrix for recycling of used sorbents used concrete block, made in the form of a cube, the clients in the form of dry granules inside the container.

 

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