RU2518501C2 - Conditioning of liquid radioactive wastes - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to environmental protection, particularly, to processing liquid radioactive or chemical wastes and can be used at nucleate power plants outballing. Solidification of liquid radioactive wastes is performed by mixing them with polymer material and drying the mix thereafter. Note here that radioactive solutions are added many times to solidified solution.

EFFECT: immobilisation of various solutions, reduced quantity of processing steps, fast localisation of wastes in emergency.

2 cl

Description

The invention relates to the field of environmental protection, and in particular to the field of liquid radioactive waste processing, their isolation, and can also be used in non-radioactive industrial waste processing technology.

The most effectively claimed invention can be used in the processing of liquid radioactive waste (LRW) of nuclear power plants (NPPs) and toxic industrial waste in order to minimize waste volumes and concentrate them in the solid phase, which ensures reliable localization of radioactive and harmful chemicals from the environment . The proposed method for immobilizing liquid radioactive waste can be useful both at the stage of decommissioning of nuclear power plants, and in case of emergencies at the facilities of the nuclear and chemical industries.

Currently, there are many known methods for processing liquid radioactive waste and non-radioactive industrial waste.

Waste treatment methods (including their preliminary treatment) are based on the use of a wide variety of physicochemical processes.

The choice of a particular waste processing process (or combinations thereof) is due to the need to achieve the maximum reduction in the volume of waste and at the same time ensure their reliable isolation from the environment.

To solve the problem of processing LRW waste at nuclear power plants, a combination of traditional systems and methods of evaporation, deposition, and ion exchange are used. (Kopylov A.S., Verkhovsky E.I. Special water treatment at nuclear power plants. - M.: Higher School, 1988. - 208 p.)

Deep evaporation is used to further concentrate bottoms. Along with a number of advantages, it should be noted that the use of the evaporation process of accumulated LRW will reduce their volume by no more than 2–3 times.

Sedimentary methods are quite traditional for organizing the processes of processing radioactive waste of various origins. At the same time, these methods are practically not applicable to Russian nuclear power plants due to the presence of a number of ligands in solutions, primarily oxalate and EDTA ions, as well as surfactants.

The process of ion-exchange purification of radioactive concentrates of nuclear power plants is mainly used for deep purification of radionuclides ^134,137 Cs. (In the literature, this process is called “cesium selective sorption”.)

In addition to solving the problem of reducing the volume of any category of waste, the ultimate goal of the processing technology is to ensure a minimum release of radioactive and toxic substances into the environment.

When choosing materials suitable for the safe removal of radioactive nuclides from the biosphere, the main focus is on their chemical stability.

Numerous studies of various matrices (cements, bitumen, ceramics, polymers, glass-like materials, etc.) have shown that cement is the most versatile material for curing radioactive solutions of the NAO and CAO categories. (Sobolev I.A. et al. The practice of cementing liquid radioactive waste in an experimental setup. - Collection of reports of a scientific and technical conference of experts from the CMEA countries. Studies in the field of processing and disposal of radioactive waste, GDR, 1967, M., 1968, .306-315. Stabilization of High Salt Waste Using a Cementations Process Salt Containing Mixed Waste Treatment. OST / TMS ID 1683 Mixed Waste Focus Area Demonstrated at Oak Ridge National Laboratory (ORNL) Oak Ridge, Tennessee.)

A known method of processing radioactive sludge and sediment. (Patent of the Russian Federation No. 22989867. Published: 04/10/2005.) The method includes the production of a radioactive deposit and a filtrate. Then the dehydrated radioactive sediment is heated and milled. Next, the crushed pieces are cemented with a highly penetrating cement mortar with a weight ratio of the liquid phase - cement of 0.6-1.4. An advantage of the invention is to reduce the amount of waste, increase radiation safety and reduce the energy intensity of the process.

According to the method of cementing radioactive waste (Patent of the Russian Federation No. 2315380. Published on January 20, 2008) after the radioactive cement compound has hardened, the free volume of the container is filled with a non-radioactive protective coating based on a mineral binder.

The main disadvantage of the operation of cementing liquid radioactive waste is the need to carry out the operation of neutralizing acidic solutions that cannot be included in the cement.

The introduction of special additives, as well as the combination of cementing and adsorption, inevitably leads to a significant increase in the volume of cured products that are sent for disposal.

A known method of immobilizing LRW using a variety of polymeric materials with the formation of chemically stable products. (Technical report series No 289. MANAGEMENT OF LOW AND INTERMEDIATE LEVEL RADIOACTIVE WASTES WITH POLYMERS. International Atomic Energy Agency, Vienna (1988).)

A method of curing LRW into an organosilicon elastomer matrix (ECOR) is known in the literature. (S.T. Belyaev, I.K.Shvetsov, B.S. Kalinichenko and others. New material for radioactive waste management. Abstracts. Fifth Russian Conference on Radiochemistry RADIOCHEMISTRY - 2006.)

The disadvantage of this method is the incompatibility of the material with acid solutions. The neutralization of acid LRW not only leads to an increase in the volume of waste, but also causes the appearance of sediments and suspensions, the removal of which requires additional equipment (filters) and additional operations for the management of sediments.

There is a method of disposing of radioactive waste by curing it and obtaining material suitable for disposal (US Patent 4056362, publ. 01.11.1977). Liquid radioactive waste (LRW) is mixed with reagents capable of forming solid products with the formation of chemically stable products.

A partially polymerized aqueous emulsion of urea and formaldehyde (urea-formaldehyde resin, MF) is used as a curing agent. An aqueous solution of sodium bisulfate is used as a catalyst for stimulating polymerization.

The disadvantage of this method is the limitations of the nomenclature of waste that can be recycled, since this method is not applicable to solutions with high acidity and some types of waste, such as soap solutions and concentrated Na ₂ S0 ₄ solution _{, are} difficult to mix with MF resins.

Closest to the claimed invention is a method for the disposal of radioactive waste by curing using polymers manufactured by Nochar (Nochar® Corp., USA), and obtaining products suitable for disposal. Immobilization of LRW is carried out by mixing liquid radioactive waste with a polymer with stirring. The resulting product, which does not contain a liquid phase, is dried and sent for long-term storage. ("Nochar Petrobond Absorbent Polymer, Tritiated Oil So-Udification", Innovative Technology Summary Report, DOE / EM-0598, U.S. Department of Energy.) This method, by its technical nature and the achieved effect, is closest to the claimed one and is selected as a prototype.

The disadvantage of this method is the increase in the volume of generated solid waste significantly compared with the initial volume of LRW, which in turn leads to an increase in the required storage volumes and, consequently, to an unjustified increase in capital costs.

The problem solved by the invention is to reduce the volume of formed solid and the required amount of polymeric materials.

To achieve such a technical result, in the proposed method, LRW is mixed with a polymer material and waste solidification. After that, the resulting composition is dried and a new portion of LRW is added to the already cured material. (The number of cycles carried out (repetition of operations "curing LRW - drying") is limited only by the specific activity and salinity of LRW.)

The method is as follows.

1 parts by weight the radioactive solution is mixed with 0.05-0.5 parts by weight polymer material and in this case, the initial mixture is cured. After 10-30 days of storage after removal of the bulk of the water, a new portion of LRW is added to the cured products and the product is dried again.

The exposure time (drying) is selected depending on the selected polymer material and storage conditions. If drying is carried out at room temperature, then the minimum exposure time of the cured composition before adding the next portion is at least 5-10 days.

If it is possible to dry the cured material at an elevated temperature (and under discharge), the exposure time before adding the next portion of the solution is reduced to 2-5 days.

After several curing - drying operations, the final isolation of the waste in the container and its transportation to the storage in the form of solid waste are carried out.

Compared with the prototype, immobilization of the most diverse solutions is achieved without any preparation and reduction of the volume of waste sent to storage.

Among the other advantages of the proposed method, it is necessary to indicate a reduction in the number of technological stages compared to traditional technologies and the possibility of urgent localization of waste in case of emergencies at the facilities of the nuclear and chemical industries.

The foregoing is illustrated, but not limited to the following examples.

Example 1

To 50 ml of the model radioactive solution was added 17.8 g of the Stockocorb solid polymer-hydrogel (Manufacturer - Germany, http://my.mail.ni/community/gidrogel). The ratio of the mass of the polymer (T) to the mass of the solution (G) was approximately T: G-1: 3.9. The curing of the solution took place within 2-3 minutes, and the resulting composition was kept in air at room temperature for 42 days. The loss of water mass was 92% of the original.

After that, a new portion of a model solution (45 ml) of the same composition is added to the cured and dried product, and drying of the cured composition is repeated for 40 days. The weight loss of water was 67% of the weight of the re-added solution.

Thus, after 2 cycles of LRW curing - drying, the volume of the obtained product was approximately 42 cm ³ , which is approximately 2 times less than the volume of the initial solution (45 ml + 40 ml).

Example 2

To 15 ml of the model radioactive solution was added 4 g of KNOX Material solid polymer (Manufacturer - United States, Knox Fertilizer Company, Inc., http://www.ci.knoxville.tn.us/solidwaste/hazwaste.asp). The ratio of the mass of the polymer (T) to the mass of the solution (G) was approximately T: G-1: 3.9. The cured composition was aged in air at room temperature for 42 days. The loss of water mass was 87% of the original.

After that, a new portion of a model solution (12 ml) of the same composition is added to the cured and dried product, and drying of the cured composition is repeated for 40 days. The weight loss of water was 59% of the weight of the re-added solution.

In this experiment, after 2 cycles of LRW curing - drying, the volume of the obtained product was approximately 11.5 cm ³ , which is approximately 2.2 times less than the volume of the initial solution (15 ml + 12 ml).

Example 3

This example shows the results of a series of experiments conducted with real radioactive solutions. Petrobond polymers manufactured by Nochar (Nochar® Corp., USA) were used as a polymeric material capable of curing LRW.

The experiments were carried out in polyethylene glasses with a volume of 100 ml. The beaker was placed in a weighed polymer amount of 10 g, then poured 50 ml of a solution of radioactive waste of the following composition: A _Σβ -1,1-10 ^-6 Ci / l, A _Σα -2,7-10 ^-7 Ci / l, the concentration of Uranium 7 mg / L; HNO ₃ - 0.07 mol / L.

Taking into account the presence of organic impurities in real solutions, the following were used in the work: Nochar polymer No. 960 and mixtures of Nochar No. 960 and Nochar No. 910 polymers.

After mixing the solution and the polymer, the resulting cured compositions were held in air at room temperature.

As moisture was removed, fresh portions of the SAO solution were added to the polyethylene glasses with cured samples in order to involve the maximum amount of the solution into the polymer matrix.

The conditions for this series of experiments on solidification of waste and the achieved concentration factor (in relation to the initial volume of the solution) are presented in the table.

Table Cycle No. (curing and air drying) The volume of the solution and the ratio of T: W during curing. Loss of mass of the solution from the sample after curing and drying in air. The achieved concentration factor in relation to the initial volume of the solution After 10 days,% After 24 days,% After 56 days,% Series of experiments No. 1. Polymer Nochar No. 960 1st cycle The volume of the solution is 50 ml, the polymer mass is 10 g (T: W = 1: 5) 43.7 84.7 93.2 ≈ 5.0 2nd cycle 35.0 47.8 64.0 ≈ 10.0 Series of experiments No. 2. A mixture of polymers Nochar No. 960 (95%) and Nochar No. 910 (5%) 1st cycle The volume of the solution is 50 ml, the polymer mass is 10 g 43.6 82,4 93.0 ≈ 5.0 2nd cycle 33,4 42,2 61.9 ≈ 10.0 Series of experiments No. 3. A mixture of polymers Nochar No. 960 (90%) and Nochar No. 910 (10%) 1st cycle The volume of the solution is 50 ml, the polymer mass is 10 g. 40.8 81.4 92.8 ≈ 5.0 2nd cycle 34.1 47.9 65.0 ≈ 10.0

As noted above, the number of LRW curing - drying operations is limited only by the specific activity and salinity of the LRW of a particular batch of waste.

But after only the first 2 cycles, a concentration factor of 10 is achieved.

Claims (2)

1. A method of immobilizing liquid radioactive waste, comprising mixing the waste with a polymer material and drying the resulting mixture, characterized in that the immobilization process is carried out by repeatedly adding new portions of the radioactive solution to the cured and dried product - a polymer saturated with a radioactive solution. 2. The method according to claim 1, characterized in that the drying of the solidified waste is carried out for 5-30 or more days.