RU2597242C1 - Method of cleaning liquid radioactive wastes from organic impurities - Google Patents

Abstract

FIELD: processing and recycling of waste.

SUBSTANCE: invention relates to means of handling liquid radioactive wastes. Method of processing liquid radioactive wastes (LRW) contains comprises following main steps: feeding initial solution of liquid radioactive wastes, evaporation of liquid radioactive wastes, adjusting pH of initial solution, adding activated pyrolusite to initial solution, stirring obtained suspension, heating suspension, withdrawal of steam released with its subsequent condensation, sampling released gases and their chromatographic analysis, formation of dry residue, as well as cementing of dry residue.

EFFECT: expansion of application and simplification of cleaning process.

6 cl, 3 dwg, 2 ex

Description

The invention relates to the field of liquid radioactive waste management and can be used at nuclear power plants for the purification of liquid radioactive waste (LRW) from organic impurities, including surfactants.

A known method of electrochemical decomposition of the organic content of conductive aqueous waste solutions [RF Patent No. 2286949 "Method and device for underwater decomposition of the organic content of conductive aqueous waste solution". Published July 16, 2002]. The method is based on the destruction of organic materials in conductive waste solutions by means of an electric arc discharge created between immersed electrodes and a solution. The method is applicable for LRW with a concentration of organic impurities of 17 g / l and a pH of 8-13.

The disadvantages of the method include the need to enter into the system of chemical agents and a complex procedure for implementing the method.

Closest to the claimed technical solution is a method for processing liquid radioactive waste by oxidizing organic impurities with ozone to form oxides of constituent elements (СО ₂ and Н ₂ О) [RF Patent No. 2268513, IPC G21F 9/06, G21F 9/20 “Method for processing liquid radioactive waste. " Published January 20, 2006]. The method consists in the fact that the organic components of liquid radioactive waste are oxidized to a gaseous state, and mineral ionic components, including radionuclides, are suspended in the form of metal hydroxides by supplying ozone to the stream, the stream of oxidized waste is separated into condensed sludge and liquid phase, selective sorbents carry out post-treatment of the liquid phase from the remaining radionuclides in the ionic form, and the resulting sludge and spent sorbents are converted into solid form and sent for a long period manning, while before treatment with ozone, the waste stream by filtration on a mesh filter material is cleaned of suspended particles.

This method has the following disadvantages:

- ozone is a chemically unstable substance that requires generation and continuous supply into the solution throughout the process;

- the need for filtration.

To eliminate these disadvantages in the method of purification of liquid radioactive waste from organic impurities, including the preparation of the initial solution, the decomposition of organic impurities and obtaining a dry residue, it is proposed:

- the initial solution of liquid radioactive waste is evaporated to a concentration of organic impurities of at least 150 g / l and adjust its pH to a value of 5-12;

- serve and maintain the sorbent in a solution of liquid radioactive waste;

- heat the resulting suspension to complete decomposition of organic impurities and cement the resulting dry residue of the suspension.

In particular cases of the implementation of the method it is proposed:

- when cleaning liquid radioactive waste, use chemically activated pyrolusite as a sorbent;

- the concentration of activated pyrolusite to maintain at least 5 g per 1 liter of the prepared solution of liquid radioactive waste:

- sorption of organic impurities is carried out by mixing the resulting suspension;

- after heating the suspension, the resulting condensate should be sent for processing;

- the degree of decomposition of organic impurities is determined by chromatographic analysis of the evolved gases.

The technical result consists in expanding the applicability of the method and simplifying the cleaning process.

The essence of the method is as follows.

To achieve the highest efficiency of sorption purification, the initial solution of liquid radioactive waste is evaporated to a concentration of organic impurities of at least 150 g / l.

It was experimentally shown that the most effective sorption of organic impurities on pyrolusite occurs in the pH range of 5-12, therefore, the pH of the evaporated solution of liquid radioactive waste is adjusted.

When cleaning liquid radioactive waste, chemically activated pyrolusite is used as a sorbent. Pyrolusite is chemically activated to enhance its sorption properties. Pyrolusite activation involves the conversion of surface Mn ⁴⁺ to Mn ⁶⁺ and is carried out by treating the pyrolusite with inorganic acids.

The sorbent is fed into the prepared solution of liquid radioactive waste and maintained at a concentration of at least 5 g of activated pyrolusite per 1 liter of prepared solution for the greatest sorption extraction of organic impurities from liquid radioactive waste.

The sorbent is kept in a solution of liquid radioactive waste for at least 1 hour in order for the sorption process to go fully.

To increase the efficiency of purification of liquid radioactive waste from organic impurities, sorption is carried out by mixing the resulting suspension.

When heated, activated pyrolusite acts as a catalyst for the decomposition of organic impurities to form oxides of constituent elements. Therefore, the resulting suspension is heated at a temperature of 100-150 ° C until complete decomposition of organic impurities.

The degree of decomposition of organic impurities is judged by the results of a chemical analysis of the gases emitted.

After heating the suspension, the resulting condensate is sent for processing.

After calcination, the resulting dry residue of the suspension is cemented using glass, ceramics, bitumen, cement, polymers and other materials as a matrix.

Testing of the proposed method for purification of liquid radioactive waste from organic impurities is presented in examples 1 and 2. Figure 1 shows a flow diagram of a method for processing liquid radioactive waste, which takes the following notation: 1 - stock solution of LRW, 2 - concentration of LRW, 3 - adjustment pH of the initial solution, 4 - addition of activated pyrolusite to the initial solution, 5 - mixing of the resulting suspension, 6 - heating of the suspension, 7 - discharge of the released steam with its subsequent condensation, 8 - selection of samples gases and their analysis, 9 - dry solids formation, 10 - dry solids cementing.

In figures 2 and 3, examples of specific solutions of the present method are presented in the form of dependences of the coefficient of purification from the purified water and the efficiency of sorption on the concentration of APAW.

Example 1

Research work was carried out to clean the source water of the VPU of the Beloyarsk NPP with activated pyrolusite. In this work, during the purification process, the VPU source water was evaporated to a concentration of organic impurities of 150 g / l, the pH of the resulting solution was adjusted to a value of 8.6. Pyrolusite was activated by soaking it in a solution of nitric acid. Through filling the sorbent, at a concentration of 7 g per 1 liter of solution, 20 column volumes of the prepared solution were passed through a pump. A column volume is understood to mean purification of 200 liters of water with one liter of sorbent before its regeneration.

The cleaning efficiency of the prepared solution was determined by the residual content of organic impurities in the purified solution. The efficiency of water treatment at the Beloyarsk NPP VPU from natural organics (humic acids, fulvic acids) was 70% (Fig. 2).

Example 2

A series of works was conducted on the purification of liquid radioactive waste from the radioactive waste workshop at FSUE SSC RF-IPPE. In this work, during the cleaning process, the solution of liquid radioactive waste was evaporated to a concentration of organic impurities of 150 g / l, the pH of the resulting solution was adjusted to a value of 7.0.

Pyrolusite was activated by soaking it in a solution of nitric acid. To 1 liter of the prepared solution of liquid radioactive waste, 5 g of activated pyrolusite was added and stirred using a magnetic stirrer for 1 hour. Next, the resulting suspension was heated at a temperature of 150 ° C until complete decomposition of organic impurities. The degree of decomposition of organic impurities was determined by chromatographic analysis of the evolved gases. Condensate formed by heating the suspension was sent for processing. The obtained dry residue of the suspension was a free-flowing black powder, the value of the accumulated activity of the powder does not exceed the value of the minimum significant activity for NRB.

As a result of the studies, it was found that the sorption efficiency of sodium oleates, stearates and palmitates (OP-7.10) with activated pyrolusite is 80% (Fig. 3).

The use of the invention will provide a comprehensive solution to the problem of purification of liquid radioactive waste, including the sorption extraction of organic substances, such as ACAS, using pyrolusite. The release of radioactive pyrolusite is not required, so there is no need to use filters that require processing after the end of their life. The cementing of the radioactive solids is carried out in a known manner, for example using clinker cement.

Claims (6)

1. The method of purification of liquid radioactive waste from organic impurities, including the preparation of the initial solution, the decomposition of organic impurities and obtaining a dry residue, characterized in that the initial solution of liquid radioactive waste is evaporated to a concentration of organic impurities of at least 150 g / l, adjust its pH to a value 5-12, the sorbent is fed and kept in a solution of liquid radioactive waste, the resulting suspension is heated until the organic impurities are completely decomposed, and the resulting dry residue of the suspension is cemented t 2. The method according to p. 1, characterized in that when cleaning liquid radioactive waste, chemically activated pyrolusite is used as a sorbent. 3. The method according to p. 2, characterized in that the concentration of activated pyrolusite is supported by at least 5 g per 1 liter of prepared solution of liquid radioactive waste. 4. The method according to p. 3, characterized in that the sorption of organic impurities is carried out by mixing the resulting suspension. 5. The method according to p. 1, characterized in that after heating the suspension, the resulting condensate is sent for processing. 6. The method according to p. 1, characterized in that the degree of decomposition of organic impurities is determined by chromatographic analysis of the gases released.

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