Method for hardening liquid highly active wastes

FIELD: chemistry.

SUBSTANCE: method involves converting wastes to a gel-like state and is characterised by that solutions of highly active wastes are mixed with zirconium and iron salts and glycerine to concentration of said salts of not less than 0.12, 0.6 and 0.25 M/l respectively, holding the obtained mixture for not less than 2.5 hours, followed by adding to the mixture a solution of mono-substituted potassium phosphate in phosphoric acid to molar ratio of components Zr:Fe:K:PO4=1:3:2:5-8, drying, calcining the obtained polymer gel of zirconyl phosphate at 70-90°C and 300-400°C, respectively, and melting the obtained granules at 980-1000°C.

EFFECT: converting wastes into compact material which is suitable for long-term and safe storage.

3 cl, 2 tbl, 1 ex

 

The invention relates to a method of curing a liquid high-level waste resulting from reprocessing of nuclear fuel, with the aim of converting them into a compact material, suitable for long-term and safe storage.

Wastes in addition to fission products contain inactive elements included in the structural materials of fuel assemblies, the main of which are zirconium and iron.

A method of refining high-level waste nuclear reactors, including calcification HLW mixing calcinate HLW with TiO2, CaO, ZrO2, Al2About3heat the mixture in a reducing atmosphere to the working temperature from 1000°C to 1500°C under a pressure below atmospheric, the shutter speed at the operating temperature until crystals form a ceramic material, and cooled to obtain a solid material suitable for long term storage.

As a result of implementation of the known method is the formation of zirconolite ceramics with the calcinate HLW. [US patent N 4274976, G21F 9/34, publ. 23.06.81.]

Similar to the above is the method of processing high-level waste nuclear reactors containing radioactive elements actinides group (uranium, plutonium, neptunium, and so on), as well as zirconium and rare earth E. the elements, under which these wastes calicivirus, calcinate mixed with oxides of titanium, calcium and manganese in the following ratio, wt.%: TiO2- 50-60, Cao - 10-20, IGOs - 5-15, calcinate high-level waste - 15-25, the resulting mixture is heated in an oxidizing atmosphere up to operating temperature 1100-2000°C at a pressure below atmospheric, maintained at a working temperature until crystals form a ceramic material, after which the final product is cooled to obtain a solid material suitable for long term storage. The result is the formation of ceramic, which contains a crystalline material whose composition is characterized by the generic formula of (CA, Mn, REE)4(An, Zr, Ti)2Ti7O22, which by its physico-chemical nature, but also against the elements actinides groups, zirconium and rare earth elements similar to zirconolite, and the higher the pressure, the faster the process of crystal formation derived ceramic product. [Pat. Of the Russian Federation No. 2140106, G21F 9/16, publ. 10.10.1999.]

The disadvantage of this method is the low quality of the finished product due to its low resistance (applicable to HLW), the value of which is defined by total speed vymyvaemosti actinides from the of zirconolite at 90°C, is 10-4-10-5g/m2day.

Taken as a prototype method for processing waste generated during processing teplosistema assemblies of a nuclear reactor, characterized by moving them in a ceramic matrix. For this solution waste pre denitrify formaldehyde, which is then mixed mainly with titanium oxide, barium, calcium, and optionally aluminum, niobium. The resulting suspension is dried, annealed, at a temperature of 650-800°C, crushed to form powder. Next, the powder is pressed at 1000-1400°C and is sintered in a reducing atmosphere in the temperature range of 1000-1400°C.

When this is achieved the formation of the ceramic medium containing phase hollandite, perovskite and zirconolite containing 30-60 wt.% TiO2, 1-10 wt.% BaO, 1-10 wt.% CaO, in which it is assumed dissolution and fixation of fission products. (Journal of the Russian Federation No. 2002115623, G21F 9/00, publ. 20.12.2003,)

Despite the seeming simplicity of performance and chemical resistance of the obtained ceramics, this method is not without disadvantages. The method does not provide uniform distribution of fission products in the volume of the matrix, which negatively affects their long-term storage, a multi-stage process for the synthesis of a matrix, use of restorative environments and temperatures over 1000°C, significant costs oxides for turning rest the RA in the suspended state.

The objective of the invention is to simplify the recycling process - curing liquid waste while maintaining thermal and hydrolytic stability of the resulting monolithic material.

The problem is solved by a method of curing a liquid high-level waste and convert them into a gel-like state characterized by the introduction into the waste solutions of salts of zirconium, iron, and glycerol to a concentration of them in solutions, respectively, not less than 0.12, 0.6 and 0,23 M/l, maintaining the mixture for at least 2.5 hours, adding to the mixture of the solution of one-deputizing potassium phosphate in phosphoric acid to the molar ratio Zr:Fe:K:PO4=1:3:2:5-8, and subsequent drying, calcination of the obtained polymer gel zirconolite respectively, at 70-90°C and 300-400°C and melting the obtained granules at 980-1000°C.

Preferably, as salts of zirconium and iron to use respectively circinelloides and nitrate iron.

Usually use 2-2,1 M/l solution of potassium phosphate in 4 M phosphoric acid.

Thus, to simplify the process of solidification of liquid wastes is proposed instead of the oxide matrix using zirconium-iron-phosphate matrix, not inferior in its thermal and hydrolytic stability of the ceramic matrix specified in the prototype. When the eat the synthesis of the matrix occurs in the liquid phase upon mixing of the waste solution with the addition of metal salts with a solution of potassium phosphate in phosphoric acid. The method is based on the tendency of aqueous solutions of zirconium to the formation of polymeric compounds, educational opportunities, a significant number of simple and complex phosphates.

Previously in the liquid waste will be required in the amount of salts of zirconium and iron, as well as glycerin. The role of the latter is reduced to the formation of complex compounds with zirconium, and later to the denitration of the mixed solution. As the mixture is injected solution KH2PO4in phosphoric acid. After some time there is gelation of zirconolite, which is governed by the process of chelation circoncision with glycerin and process temperature. The resulting homogeneous gel zirconolite transparent and glassy, yellowish color. The gel is dried, calcined at t=300-400°C until the end of the selection oxides of nitrogen, if necessary, crushed and melted at a temperature of about 1000°C. the resulting melt the vitreous, has a color ranging from light brown to dark brown depending on the composition and quantity of waste and represents a solid solution of simple and complex phosphates of fission products in zelenotsvitna glass and partly in the form of independent phases, cemented with glass.

Drying of the gel may be done in two ways. First option: mixed solution before heliopaths what I poured into plastic trays and dried in a stream of hot air (70-90°C). Second option: mixed solution was dispersed into droplets in the heated mineral oil obtaining in the end a spherical particle gel matrix, which speeds up the drying process and eliminates the need for grinding of the product.

Example

Prepare a solution of the waste to obtain a zirconium-iron-phosphate matrix. For this purpose, we first define the content of zirconium and iron in the waste and adjust them in accordance with a molar ratio by adding salts circinelloides - ZrOCl28H2O and nitrate iron - Fe(NO3)39H2O to their concentration in the solution, respectively, not less than 0.12 and 0.6 M/l and glycerol - 0,23 M/l (molar ratio of zirconium:glycerol=1:1,1). These concentrations provide a sufficiently strong and durable gel zirconolite. The prepared solution is incubated to equilibrium for 2.5 hours

Next, prepare a solution of one-deputizing phosphate potassium - KN2RHO4by dissolving 4-molar phosphoric acid to the concentration in the solution of 2 M/L.

The behavior of zirconium in solution is difficultly predicted for many reasons, including the history of its origin and the storage time of its salts. So the pre-test process of gelation at low volumes. Record the time the I beginning of gel formation in the mixed solution to determine the time of his life. Time correction "life" performed by adding glycerol or cooling solutions. Mix the bulk of the waste with a 2 M/l solution of potassium phosphate 4 M/l phosphoric acid, poured into plastic trays or dispersed into droplets in mineral oil. The drying is conducted by a stream of heated air (70-90°C), then calcined at 300-400°C before the termination of the allocation of nitrogen oxides and melt obtained granules at a temperature of about 1000°C.

The resulting polymer gel zirconolite characterized by a molar ratio Zr:Fe:K:PO4=1:3:2:6. The gel effectively absorbs microwave radiation, which allows for the annealing and melting in a microwave oven.

Test hydrolytic stability of the matrix on the leaching of transuranic elements was carried out as follows.

Prepared 120 ml of nitric acid solution of simulators fission products, the corresponding salt and radionuclide composition of waste reprocessing plants. The solution was divided in two, each part of which is introduced aliquots of nitric acid solutions of Np-239 and Pu-239 Am-241 in another part.

Dissolved in each part of the solution sample ZrOCl28H2Oh and Fe(MO3)3N2On to a final concentration of 0.2 M/l and 0.6 M/l, respectively. Introduced and mixed in a solution of glycerin to its content of about 23 M/l and has withstood 2.5 h to establish equilibrium. At the same time prepared under moderate heat 2 M/l solution KN2RHO44 M phosphoric acid.

Mixed the resulting solution with a solution of potassium phosphate (2 M/l KN2RHO44 M/l MN3RHO4). After the formation of the gel zirconolite, which occurred on 36 minutes from start of mixing at a temperature of 22°C (molar ratio Zr:Fe:K:PO4=1:3:2:5-8), the gels were dried, calcined and melted in landowych crucible at a temperature of 980-1000°C.

Data on the samples are presented in table 1.

Table 1
Nucle-dyThe mass of the nuclide in the volume of the prepared matrix mgThe amount of BC in the volume of the prepared matrixThe weight of the sampleThe surface of the sample, cm2Mass fraction of actinide in the original sample, %
Np-237of 5.41.4×10510,418,20,052
Am-2410,1of 1.27×1079,9 of 17.50,001
Pu-2394,51,0×1070,045

Hydrolytic leaching was carried out at a temperature of 90°With a radiometric determination of the content of radionuclides in pixelated.

The obtained results data hydrolytic stability at a temperature of 90°C and the ratio of STB./VH2O≤10, R is the rate of leaching are presented in table 2.

Table 2
Time, dayR, g/(cm2·day)
Np-237PU-239Am-241
11,7·10-57,0·10-57,2·10-5
31,8·10-56,2·10-66,1·10-6
71,3·10-53,6·10-73,0·10-7
14 5,4·10-65,7·10-74,9·10-7
213,9·10-77,4·10-76,4·10-7
288,1·10-84,5·10-75,1·10-7

Thus, the proposed method allows to process acidic solutions (up to 2.5 M/l in nitric acid) and get compact product with an apparent density of from 2.2 to 2.6 g/cm3that order, and reduces the volume of waste. Hydrolytic stability matrix limits the rate of leaching of incorporated radionuclides in the range from 10-6up to 10-8g/cm2day (90°C), which are accepted as predicted during long-term storage.

1. The method of curing the liquid high-level waste by converting waste into a gel-like state, characterized by the fact that in solutions of high-level waste is injected salt of zirconium, iron, and glycerol to a concentration of them in solutions, respectively, not less than 0.12, 0.6 and 0,23 M/l, incubated the mixture for at least 2.5 h and then adding to the mixture of the solution of one-deputizing phosphate potassium phosphate, cyclotide molar ratio Zr:Fe:K:PO 4=1:3:2:5-8, drying, calcining, the resulting polymer gel zirconolite respectively, at 70-90°C and 300-400°C and melting the obtained granules at 980-1000°C.

2. The method according to claim 1, characterized in that salts of zirconium and iron using, respectively, circinelloides and nitrate iron.

3. The method according to claim 1, characterized in that use 2-2,1 M/l solution of potassium phosphate in 4 M phosphoric acid.



 

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