Method of decontamination of liquid radioactive waste

 

(57) Abstract:

The invention relates to the field of processing of intermediate level liquid waste from nuclear power plants, nuclear power plants, reprocessing plants, nuclear research centers. The inventive solution srednekraevyh liquid radioactive waste (LRW) adjust the pH to a value of 8-12, create salt content of the sum of inorganic and organic substances is not more than 25 g/l, is introduced into the prepared solution LRW selected fractions of natural sorbent and implement the sorption of radionuclides by mixing the solution of LRW with the sorbent. Then separate the produced radioactive sorbent from the solution by the method of filtration under pressure through ultra - or micro-porous membrane filter with a chemical coating, dropping the sorbent into the drive and cement in Geochemistry stone. Advantages of the method are that it allows you to simplify and reduce the cost of technological process of processing of LRW and facilitates handling of water-salt solutions. 9 C.p. f-crystals.

The invention relates to the field of nuclear energy and technology, in particular to the processing liquid intermediate level waste from nuclear power plants, nuclear energy ustanak radioactive waste (LRW) by LRW purification on selective sorbents after pre-treatment of various oxidants and subsequent cementation of radioactive sorbent (Lifanov F. A., Savkin, A. E., Slastnikov Y. T. Purification of high salt liquid radioactive waste by the method of selective sorption. In Proc. of "Radioactive waste. Storage, transportation, processing. The impact on humans and the environment. Abstracts". Proceedings of the international conference, October 14-18, 1996, S.-Petersburg: Administration of S.-Petersburg, CRISM "Prometey", report of the S-21, 1996.). The disadvantages of this method include the need to use special equipment, additional reagents and materials for the oxidation of liquid and recovery of radionuclides released from the oxidation products. Moreover, by implementing the use of expensive synthetic sorbents, the result is a cement compounds with relatively low resistance.

The closest technical solution is a method of treatment of liquid radioactive waste, including sorption of radionuclides on natural zeolites and cementing received radioactive zeolites using a knitting system containing granulated blast furnace slag and clay component in a mixture with a solution of sodium silicate (RF Patent 2154317, IPC G 21 F 9/12. Method for processing liquid radioactive waste. Published 10.08.2000 year, the zeolite, the resulting sorption from solution, not containing radionuclides.

The authors goal was to eliminate the mentioned disadvantages, to improve the quality of mineral-like matrices, simplify and reduce the cost of technological process of processing of LRW, to facilitate the handling of water-salt solutions.

To solve this problem, we propose a method of treatment of liquid radioactive waste, including the preparation of the starting solution LRW, including adjusting its pH to a value of from 8 to 12, the sorption of radionuclides on natural sorbent in static conditions by keeping natural sorbent in a prepared solution of LRW with the preliminary selection of the fraction of natural sorbent.

The proposed method differs from the previously known fact that in the prepared solution LRW create the salt content of the sum of inorganic and organic substances is not more than 25 g/l, selected fraction of natural sorbent with a particle size of not less than 0.1 μm, the separation of the resulting sorption of radioactive sorbent from the solution is performed by filtration under pressure through ultra - or micro-porous membrane filter with a chemical coating when the pressure drop across the filter is not less than 4 bar, radioactiv the ora through the membrane filter in the filtering process is supported by no more than 0.2 l/cm2C, the concentration of natural sorbent support of at least 5 g per 1 l of the prepared solution LRW, and sorption of radionuclides spend at least 1 h under stirring.

When conducting a multi-stage sorption by additional injection of sorbent into the solution at each stage of sorption of the most complete extraction of radionuclides from solution LRW reach, if the sorbent is injected at least two times. And either separated by filtration radioactive sorbent unite, dropping into the drive and cement in Geochemistry stone by applying the necessary binding system, or each additional maintenance sorbent in the solution obtained at the previous stages of radioactive sorbent is discharged into the drive and also cement. The choice of the binding system is determined by the properties of the used natural sorbent. The criterion for the choice of the sorbent, along with its sorption capacity and availability, is the similarity of the elemental composition and structure of groups of tumors formed in normal humidity conditions of mineral-like yocemento stone. The use of natural sorption materials allows for a small mechanical impact to translate aceski fragile.

The technical result of the invention is an integrated solution for the disposal of intermediate level srednekraevyh LRW, which can simplify the treatment of water-salt solutions after removing them Cs-137 and Sr-90, making the main contribution to the radioactivity LRW, to reduce the volume of the resulting solid radioactive waste in the form of mineral-like stone with high water resistance and mechanical strength, are subject to long-term storage and disposal.

The method is as follows.

In a solution of intermediate level srednekraevyh LRW adjust the pH to a value of 8-12, create salt content of the sum of inorganic and organic substances is not more than 25 g/l, selected fraction of natural sorbent is not less than 0.1 μm and injected into the prepared solution LRW not less than 5 g per 1 l of selected fractions of natural sorbent. Sorption of radionuclides is carried out with stirring solution of LRW with sorbent for at least 1 hour In necessary cases, carry out the above described operation, the introduction of sorbent and sorption under stirring at least twice. Radioactive sorbent is separated from the solution by filtration through ultra - or micro-porous membranes is bent discharge with plasma-chemical coating of the filter gidromolot filtrate and sent for cementing. For the implementation of the last operation prepare knitting mass mixing not more than 30 wt.% radioactive sorbent with the necessary dry ingredients. At lower filtration rate at 70-80% of the initial regenerate the filter, affecting the pulse shot of the filtrate from the hydraulic accumulator filter on the inner surface of the membrane within 3-5 C. the Discharge of the filtrate is due to the atmospheric air, pre-compressed purified water. The result is a sludge discharge from the external surface of the membrane filter. If necessary, the regeneration cycle is repeated.

The use of available and cheap natural sorption materials, in particular bleaching of the lands of the mold box and Tripoli Sitestogo field of Kaluga region (TU-2163-001-2612752-94, hereinafter called "Tripoli"), thus demonstrating the advantages of the proposed technical solutions. On the model solutions LRW examined the effectiveness of sorption extraction of the Tripoli radionuclides Cs-137 and Sr-90 at their separate and joint presence in static conditions, the separation efficiency fine Tripoli and sediment from tap water, researched techniques and recipes Immobiliser dispersnogo Tripoli from water by filtration through a microporous membrane filter on a plastic substrate with a chemical coating thickness of 7-12 microns and an average pore diameter of 0.1 to 0.3 μm on the test bench with a working capacity of 40 l have shown the possibility of reducing the concentration of Tripoli in the water with ~5 g/l to <0.001 g/L. Filtering rate for 90 min decreased from 2.2 to 1.7 l/min, with square filter surface ~0.8 m2.

Testing at SSC RF-IPPE them. academician A. I. Leypunsky the proposed method of disposal LRW showed that the use of Tripoli and clinoptilolite with a particle size of -80 microns for sorption-membrane extraction of radionuclides Cs-137 and Sr-90 from the water storage facility for spent fuel assemblies provided simultaneous purification of water from Cs-137 and Sr-90 from the level of specific activity of ~106Bq/l to <25 Bq/l, which is below the permissible specific activity of water in accordance with the norms of radiation safety NRB-96. The consumption of sorbent amounted to 15-20 kg/m, the total degree of sorption of radionuclides >99,9996%, the overall purification factor of ~105and the volume of radioactive waste after extraction of Cs-137 and Sr-90 and cementation of radioactive sorbent decreased 25-30 times. Identical results were obtained for LRW with a total salt content of up to 25 g/l, up to 4 g/g decontamination of organic substances, in particular anionic surfactants, Trilon B, oxalic acid and industrial oil at a flow rate of sorbent ~30 kg/m3. Sediment concentrations of sorbate in solution after filtration <<0.001 g/l

IP extraction of radionuclides using cheap and available natural materials, separation of radioactive sorbent filtering through legkonastraivaemy membrane filter, characterized by low adhesion of natural sorbents to the membrane material, and cementation of radioactive sorbents together with slimes with the necessary shlakovoza system in mineral-like stones, which has high water resistance and mechanical strength.

1. Method of decontamination of liquid radioactive waste, including the preparation of the starting solution of liquid radioactive waste, including adjusting its pH to a value of 8-12, the sorption of radionuclides on natural sorbent by extracts of natural sorbent prepared in liquid radioactive waste with a preliminary selection of the fraction of natural sorbent, characterized in that the prepared solution of liquid radioactive waste creates salinity amounts of inorganic and organic substances is not more than 25 g/l, selected fraction of natural sorbent with a particle size of not less than 0.1 μm, the Department resulting from sorption of radioactive sorbent from the solution is performed by filtration under pressure through ultra - or micro-porous membrane filter with chemical pokrycia cover and sent for recycling.

2. The method according to p. 1, characterized in that the radioactive sorbent discharge with plasma-chemical coating gidromolot filtrate.

3. The method according to p. 1 or 2, characterized in that the specific flow of the solution through a membrane filter in the filtering process is supported by no more than 0.2 l/SMS.

4. The method according to p. 1 or 3, characterized in that support concentrations of natural sorbent for at least 5 g per liter of prepared solution of liquid radioactive waste.

5. The method according to p. 1 or 4, characterized in that the sorption of radionuclides carried out under stirring.

6. The method according to p. 5, characterized in that the sorption of radionuclides spend at least 1 h

7. The method according to p. 6, characterized in that the sorption of radionuclides carried out by multistage additional injection of sorbent into the solution at each stage of sorption.

8. The method according to p. 7, characterized in that each additional introduction of sorbent in a solution of radioactive sorbent removed from the solution.

9. The method according to p. 7 or 8, characterized in that it further injected sorbent is at least two times.

10. The method according to p. 1 or 9, characterized in that the radioactive sorbent cement using it is

 

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