Method of processing oxalate mother waters and pulp wastes containing transuranium elements

FIELD: process engineering.

SUBSTANCE: invention relates to treatment of radioactive fluid and pulpy wastes formed in recovery of radiated nuclear fuel. Proposed method comprises destructing oxalate ions in mother waters by nitric acid in the presence of variable-valency metal ions. Processing of oxalate mother solution and pulpy wastes comprises mixing mother solution with solid phase of hydroxide pulp.

EFFECT: power savings, decreased amount of radioactive wastes.

3 cl, 3 tbl

 

The invention relates to the field of processing liquid and will be dissolved radioactive waste (radwaste)generated during the reprocessing of irradiated nuclear fuel (SNF), and can be used in radiochemical industry.

In many enterprises for the processing of irradiated nuclear fuel (SNF) accumulated hydroxide will be dissolved RAO, containing actinoid elements and ions of metals of variable valence. The tightening of the requirements for the storage of radioactive waste, necessitates the processing of such raw. To dissolve the hydroxide will be dissolved RAO typically use solutions of nitric acid, containing oxidants or reductants [Zakharova E.V., Ermolayev, V. M., Bondin, V.V. and others Studying the possibility of using solutions of different composition for decontamination production insoluble precipitation of radionuclides, primarily from plutonium. The report IPC RAS and MCC, 2003, inv. No. 13-16/1250 from 23.09.03]. After dilution of the pulp to extract from them actinoid elements are used, as a rule, the extraction method of processing.

At the same time on reprocessing of spent fuel one of the final stages of SNF processing is oxalate deposition of transuranium elements (TUE). Use this operation in the flow charts associated with certain difficulties, uslovlennyj inevitable obtaining relatively large amounts of oxalate mother solutions. These solutions are not drainage, so as to contain 100 mg/l TUE. The concentration of nitric acid oxalate in the mother solution is 160-200 g/l to Return uterine solutions in the extraction cycle does not allow the concentration to 10 g/l of oxalic acid, which significantly affects the extraction behavior of uranium, plutonium, and neptunium. In order oxalate uterine solutions containing TUE, process, you must destroy them in the oxalate ions.

There is a method of destruction of the oxalate ions when Parke mother solutions of nitric acid with a concentration of 12 mol/l [Jenkins J.L., Keen N.I., Wain A.G. Extractive and physical metallurgy of plutonium and it's alloys. New York: Intersci. Publ. 1960. R].

The disadvantages of this method are: low rate of oxidation of oxalic acid nitrate-ions and high energy costs.

There is a method of destruction of the oxalate ions by oxidation of their strong oxidizers [Plutonium. The Handbook, edited by Vic. - M.: Atomizdat, 1971, so S-409].

The disadvantages of this method are: high consumption of oxidants and weight increase of radioactively contaminated salts, resulting from the use of the method, requiring subsequent processing and immobilization.

A known method of disposal mother solutions by oxidation of oxalate ions and nitric acid in the presence of the cat is Isadora - ions of metals of variable valency, which is used as the ions of manganese. This mother liquor is introduced into contact with the silica gel containing manganese ions. The process is conducted by heating until complete evaporation of aqueous solutions of [the Patent of Russian Federation №2111562, CL G21F 9/04, G21F 9/16 from 20.05.1998]. This method is chosen as a prototype.

The disadvantages of this method are the high energy costs and the increase in the mass of radioactive waste through the use of additional reagent silica gel with salts of manganese, requiring subsequent processing and immobilization.

The aim of the proposed method is to reduce energy costs and reducing the mass of generated radioactive waste through the use of joint processing of Queen cells containing transuranium elements, and solid phase hydroxide slurry waste of radiochemical production.

This goal is achieved by the fact that instead used in the known method the radiation of pure silica gel, containing manganese, use the waste of radiochemical production - hydroxide radioactive slurry containing actinoid elements and ions of metals of variable valence, in the presence of which is the destruction of the oxalate ions. The concentration of nitric acid oxalate in the mother solution directed to account the aims with the solid phase of slurries, is 60-200 g/l

The use of this slurry allows you to destroy the oxalate ions in solution at room temperature and does not create an increase in the mass of generated radioactive waste by eliminating the use of additional radiation pure reagents.

The inventive method is tested in laboratory conditions. In the experiment used the production mother liquor generated during the reprocessing of irradiated nuclear fuel (see table 1, solution 1). In addition, treatments were carried out with solutions 2 and 3 (table 1), obtained by dilution of the original stock solution with distilled water in 2 and 3 times, respectively.

Table 1
The compositions of the solutions taken to process
The number of treatment and mortarHNO3, g/lH2C2O4, g/lRi, mg/lU, g/lNH4NO3, g/l
Solution 119084113,230
Solution 2 95420,56,615
Solution 3632,713,74,410

The processing solutions of the proposed method was performed by solid phase hydroxide radioactive slurry, the composition of which is given in table 2.

Table 2
The composition of the hydroxide pulp
Component or indicatorDimensionThe magnitude component or indicator
PUmg/l37,0
Uraniumg/l14,8
EDRR/l·11,1
The activity of β-emitting nuclidesCI/l2,9
Aluminum is g/l1,8
Manganeseg/l3,1
Irong/l11,4
Chromeg/l3,2
Silicon dioxideg/l5,2
Nickelg/l3,1
Sodium nitrateg/l334
Sodium carbonateg/l<2,0
Sodium hydroxideg/l7,3
Water-insoluble solid phaseg/l57,7

In the experiment the proposed method used a portion hydroxide slurry with a volume of 4 ml Volume of solution before treatment was 50 ml. Pace is the atur solutions when processing samples of the solid phase was 20-22°C. The duration of contact of the solutions with samples of the solid phase under stirring was 4 o'clock the Remainder of nerastvorimaya solid phase of the pulp is connected to another portion of the slurry is directed to communicating with the new portion of oxalate stock solution. The examples were carried out in a measuring glass cylinders.

The results presented in table 3 show that during the processing of the original mother liquor or its diluted solution is the destruction of the oxalate ions. In the resulting decantate is a decrease in the total acidity of the solution due to the destruction of the oxalate ions and nitric acid in the course of redox reactions and partial neutralization of the acid metal hydroxides. The chemical composition of the obtained solutions are suitable for processing extraction methods.

1. A method of processing oxalate mother solutions radiochemical production containing transuranium elements, including the breakdown in the mother solution of the oxalate ions nitric acid in the presence of metal ions of variable valence, characterized in that the processing oxalate stock solution will be dissolved and waste carried out jointly by mixing the mother liquor from the solid phase hydroxide slurry.

. The method according to claim 1, characterized in that the concentration of nitric acid oxalate in the mother solution directed to the contact with the solid phase of slurries is 60-200 g/l

3. The method according to claim 1, characterized in that the balance nerastvorimaya solid phase of the pulp is connected to another portion of the slurry is directed to communicating with the new portion of oxalate stock solution.



 

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