RU2491666C2 - Method to manufacture fuel element of nuclear reactor - Google Patents

Abstract

FIELD: power engineering.

SUBSTANCE: method to introduce a uranium compound into a matrix consists in impregnation of a porous graphite block with a solution of a metal-organic uranium compound. The metal organic uranium compound is β - uranyl diketonate. The β - uranyl diketonate is uranyl acetylacetonate. A dissolvent is a mixture of acetone with isopropyl alcohol and water at the ratio of (65-70):(4-5):(25-31). Drying is carried out on air for at least 48 hours. Blocks are burnt at 360-380°C for at least 1.5 hours.

EFFECT: even distribution of fissionable materials in a porous matrix, reduced time and simplified performance of a process cycle, improved efficiency.

6 cl, 1 dwg, 3 tbl

Description

The invention relates to the field of nuclear engineering and can be used for the manufacture of fuel elements (fuel elements) of research nuclear reactors.

A known method of introducing a uranium compound into a matrix in the manufacture of a dispersion type fuel element. The dispersion composition containing the grains of matrix material and particles of fissile material taken in appropriate fractions is placed in the shell. Such an assembly is passed through a heater, where as the assembly passes, local zone melting of the matrix material and distribution of fissile material in the melt zone (in the matrix) takes place. As the assembly leaves the heater zone, directional crystallization of the matrix material occurs, providing a non-porous matrix and reliable adhesion of the dispersion composition to the inner surface of the fuel cladding. To reliably ensure the replenishment of the melt zone with components and uniformly dense distribution of the grains in the matrix, the assembly is vibrated. The process is conducted in a vacuum. The sealing of the second end of the fuel rod is carried out by welding methods after appropriate mechanical and chemical preparation (RF patent No. 2086015, G21C 21/02, publ. 07.27.1997).

The disadvantage of this method is that the resulting matrix is practically free of pores, which causes difficulty in compensating for swelling of the fuel. In addition, the disadvantage is the complexity of the manufacture of the fuel rod.

A known method of introducing a uranium compound into a matrix in the manufacture of a fuel element of a nuclear reactor, in which a material made of particles of aluminum oxide or particles of zirconium or particles of an aluminum-zirconium alloy forming a lower end plug is filled into a metal shell, then a mixture of particles of uranium an aluminum intermetallic compound and particles of an inert diluent, and then material from particles of aluminum oxide, or particles of zirconium, or particles of an aluminum-zirconium alloy, is poured into the shell, o razuyuschy upper end plug. The pores between the particles are filled with an aluminum alloy, for example, an alloy of the composition Al + 12% Si, or Al + 12% Si + 2% Ni. The shell on both sides is sealed with end caps (RF patent No. 2389089, publ. 05/10/2010., Bull. No. 13, IPC ⁹ G21C 3/20).

The disadvantage of this method is the difficulty of achieving volumetric uniformity of the distribution of uranium in the matrix, as well as the fact that the matrix practically does not contain pores, which causes difficulty in compensating for the swelling of the fuel. In addition, the disadvantages of the method include multistage and complexity in the manufacture of the matrix and the fuel rod.

There is also known a method of introducing a uranium compound into a matrix in the manufacture of a fuel element of a nuclear reactor, in which a mixture of particles containing a fissile isotope in the required amount and particles of a heat-conducting matrix are pressed into porous blocks with a pore volume of 5-30 vol.%, Which are placed in a sealed metal shell. For the manufacture of the core, particles of uranium alloy with 9 wt.% Molybdenum taken in an amount of 20-55 vol.% Can be used, and the matrix can be made of aluminum or zirconium powder taken in an amount of 35-60 vol.% (RF patent No. 2125305, publ. 20.01.1999., IPC ⁹ G21C 3/20). This technical solution is selected as a prototype of the proposed method.

The disadvantage of this method is the difficulty of manufacturing a matrix with a given value and uniform distribution of free volume over the matrix to compensate for the swelling of the fuel.

The objective of the present invention is to simplify the process cycle and increase the uniformity of the distribution of fissile materials in the porous matrix, increase productivity.

The technical result achieved using the present invention is as follows:

- uniform distribution of fissile materials in the porous matrix (± 6 ÷ 10%);

- reducing the time of the technological cycle, which significantly increases productivity (6 blocks weighing 3000 g each are prepared within 1 hour);

- simplification of the manufacturing method of fuel rods.

To solve this problem and achieve a technical result, a method for introducing a uranium compound into a matrix is proposed, in which according to the invention a uranium compound is introduced into a graphite matrix by impregnation of a porous graphite block with a solution of an organometallic uranium compound in an organic solvent or a mixture of organic solvents, followed by drying and annealing, Uranyl β-diketonate is used as the organometallic compound of uranium.

Uranyl acetylacetonate is used as uranyl β-diketonate.

The solvent used is acetone or a mixture of acetone with isopropyl alcohol and water in the ratio (65-70) :( 4-5) :( 25-31) Drying is carried out in air for 90 minutes to 48 hours, and the blocks are annealed at temperature of 360-380 ° C for at least 1.5 hours.

The uniform distribution of the organometallic compound of uranium is achieved by reducing the effect of trapped air in the porous matrix at a low boiling point of the solvents, reducing the viscosity and carrying out the impregnation process under vacuum. The use of simple equipment, carrying out the impregnation process with a residual vacuum (200-250 mm Hg) leads to short times of the technological cycle, which increases the productivity of the method (within 1 hour of impregnation of 6 blocks of 3000 g each, which with a 6-hour working day gives 30-36 blocks).

Figure 1 presents a block sawing scheme for determining the uniform distribution of uranium.

The block is cut into 24 parts.

Figure 1 shows the locations of cuts 1-1, 2-1, 3-1, 4-1, 5-1.

The inventive method of introducing a uranium compound into a graphite matrix is implemented as follows.

The graphite block is wiped with an organic solvent to remove grease stains, kept for 2-3 minutes and weighed to an accuracy of 0.01 g. This is the initial weight of P ₀ g. Then the block is saturated with water under vacuum, the excess moisture is removed from the surface with filter paper and again weighed. This is the weight of P _H2O g.

Porosity is calculated by the formula P = (P _H2O- P ₀ ) / P ₀ * 100%.

Then the block is dried at a temperature of 250-300 ° C, cooled and weighed. This block weight is used in further calculations.

To impregnate the blocks with uranium, a solution of an organometallic compound of uranium in an organic solvent or a mixture of several solvents is prepared. This solution is poured into a steel bath in which a graphite block is placed. The bath is sealed with a lid. The bath is pumped out for 10-15 seconds to a residual pressure of 170-200 mm Hg. Under these conditions, the block is aged for 7-10 minutes. Then the bath communicates with the atmosphere, the tap closes and pumping is repeated again. Usually, three operations (cycles) are enough to fill the entire pore space with a uranium-containing solution. The impregnated block is removed and weighed to estimate the amount of uranium absorbed.

If there is one bath, 6 blocks are made within one hour. After extraction, all the blocks are dried, then placed in a furnace with a controlled temperature of 360-380 ° C and kept for at least 1.5 hours. After annealing, the blocks are removed from the furnace, cooled and weighed. By weight gain determine the amount of uranium oxide. It has been experimentally proved that when using the organometallic compound of uranium in an organic solvent (acetone) or its mixture with alcohol (isopropyl) and water, the chemical form of stabilization of uranium is uranium trioxide.

Example 1. The method of introducing a compound of uranium into a graphite matrix by impregnation with a solution of uranyl acetylacetonate in acetone.

~ 210 grams of uranyl acetylacetonate are dissolved in 800 ml of acetone. The concentration of the prepared solution is determined by a gamma-spectrometric or gravimetric method. Based on the required characteristics for the final uranium-graphite block, the concentration of the working solution is calculated by the formula:

, где $${\displaystyle \sum V_{R\mathrm{but}\mathrm{from}t\mathrm{at}\mathrm{about}R\mathrm{but}}=V_0+\frac{T_0*V_0}{T_{\mathrm{one}}}}\left(\mathrm{one}\right)$$

where

∑V of _solution — total volume of solution, ml;

V ₀ - the initial volume of the solution, ml;

T ₀ , T ₁ - titer of the initial and desired solutions.

The resulting solution with a concentration of 55.6 mg / ml in a volume of 600 ml was carefully transferred to the impregnation bath. A graphite block weighing 3,008.72 grams and a porosity of 11.69% (volume) is placed in the prepared solution and the bath is closed with a lid. The system is pumped out to a residual pressure of 170-200 mm Hg. Under these conditions, the block is held for ~ 60 seconds. After that, air is let into the bath to atmospheric pressure and the evacuation procedure is repeated to a residual pressure of 170-200 mm Hg, kept under vacuum for 3-4 minutes and combined with the atmosphere. This procedure is repeated one more time with intermediate holding under discharge for 3-4 minutes.

The impregnated block is removed from the bath and held in air for 2 minutes, and then weighed to determine the mass of the absorbed solution.

The block is dried in air for 90 minutes, after which it is placed in an oven and annealed at a temperature of 360-380 ° C for 1.5 hours. The finished uranium-graphite block has the following characteristics:

m (block) = 3031.48 g;

m (UO ₃ in the block) = 22.75 g.

Example 2. A method of manufacturing a fuel element by impregnation with a solution of uranyl acetylacetonate in a mixture of 70% vol. acetone: 30% vol. water.

~ 183 grams of uranyl acetylacetonate are dissolved in 800 ml of acetone. The concentration of the prepared solution is determined by a gamma-spectrometric or gravimetric method. Based on the required characteristics to the final uranium-graphite block, the concentration of the working solution is calculated by the formula (1); it is 46.1 mg of uranium / ml; the total volume of the solution was 1932 ml. Volume ratios are calculated according to the formula (2) and (3):

$$V_{\mathrm{but}cet\mathrm{about}n\mathrm{but}}=0,7*\Sigma V_{R\mathrm{but}\mathrm{from}t\mathrm{at}\mathrm{about}R\mathrm{but}}\begin{array}{ccc}& & \end{array}\left(2\right)$$

, где $$V_{\mathrm{at}\mathrm{about}d\mathrm{but}}=0,3*\Sigma V_{R\mathrm{but}\mathrm{from}t\mathrm{at}\mathrm{about}R\mathrm{but}}\begin{array}{ccc}& & \end{array}\left(3\right)$$

where

V _acetone , V _water - estimated amount of acetone and water, ml.

As a result of the calculations, we obtain the following volumes:

the volume of acetone is 1352 ml, and the volume of water is 580 ml. The resulting solution with a concentration of 46.1 mg / ml in a volume of 600 ml and carefully transferred to the bath for impregnation. A graphite block weighing 3024.39 grams and a porosity of 11.5% (volume) is placed in the prepared solution, and the bath is closed with a lid. The system is pumped out to a residual pressure of 170-200 mm Hg. Under these conditions, the block is held for ~ 60 seconds. After that, air is let into the bath to atmospheric pressure and the evacuation procedure is repeated to a residual pressure of 170-200 mm Hg, kept under vacuum for 3 minutes and combined with the atmosphere. This procedure is repeated one more time with an intermediate exposure under vacuum for 4 minutes.

The impregnated block is removed from the bath and held in air for 2 minutes and then weighed. The block is dried in air for at least 20 hours, after which it is placed in an oven and annealed at a temperature of 360-380 ° C for 1.5 hours. The finished uranium-graphite block has the following characteristics:

m (block) = 3037.82 g;

m (UO ₃ block) = 13.43 g.

Example 3. The method of introducing a compound of uranium into a graphite matrix by impregnation with a solution of uranyl acetylacetonate in a mixture of 70% vol. acetone: 4% vol. isopropyl alcohol: 26% v / v. 241.86 grams of uranyl acetylacetonate are dissolved in 1500 ml of acetone. The concentration of the prepared solution is determined by a gamma-spectrometric or gravimetric method. Based on the required characteristics for the final uranium-graphite block, the concentration of the working solution is calculated by the formula (1), it is 47.1 mg of uranium / ml, the total solution volume is 2510 ml. The ratios of volumes are calculated according to the formulas: (2), (4) and (5):

, $$V_{\mathrm{and}s\mathrm{about}PR\mathrm{about}P\mathrm{and}l\mathrm{about}\mathrm{at}s\mathrm{th}\mathrm{from}P\mathrm{and}Rt}=0,0\mathrm{four}*\Sigma V_{R\mathrm{but}\mathrm{from}t\mathrm{at}\mathrm{about}R\mathrm{but}}\begin{array}{ccc}& & \end{array}\left(\mathrm{four}\right)$$

,

, где $$V_{\mathrm{at}\mathrm{about}d\mathrm{but}}=0,26*\Sigma V_{R\mathrm{but}\mathrm{from}t\mathrm{at}\mathrm{about}R\mathrm{but}}\begin{array}{ccc}& & \end{array}\left(5\right)$$

where

V _{isopropyl alcohol} - the estimated amount of isopropyl alcohol, ml

As a result of the calculations, the following volumes are obtained: the volume of acetone is 1753 ml, the volume of isopropyl alcohol is 100 ml, and the volume of water is 657 ml.

The resulting solution with a concentration of 47.1 mg / ml in a volume of 600 ml and carefully poured into the bath for impregnation. A graphite block weighing 3103.72 grams and a porosity of 10.4% (volume) is placed in the prepared solution and the bath is covered with a lid. The system is pumped out to a residual pressure of 170-200 mm Hg. Under these conditions, the block is kept for ~ 60 seconds. After that, air is let into the bath to atmospheric pressure and the evacuation procedure is repeated to a residual pressure of 170-200 mm Hg, kept under vacuum for 2 minutes and air is let in. This procedure is repeated one more time with an intermediate exposure under vacuum for 3 minutes. The impregnated block is removed from the bath and held in air for 2 minutes and then weighed.

The block is dried in air for at least 48 hours, after which it is placed in an oven and annealed at a temperature of 360-380 ° C for 1.5 hours. The finished uranium-graphite block has the following characteristics:

m (block) = 3123.05 g;

m (UO ₃ in the block) = 23.28 g.

To determine the uniform distribution of uranium, the manufactured block was sawn into pieces, as shown in figure 1. 24 parts weighing approximately 30-35 g were obtained from a block weighing 805 grams. In addition, graphite chips were collected, which were marked and weighed. To obtain objective data on the uranium content, parts of the block and chips were treated 3-4 times with concentrated nitric acid, and the solutions were measured on a γ-spectrometer in standard geometry. The results are shown in tables 1 and 2.

Table number 1 Uranium content in graphite chips No. p / p Fragment number Weight of graphite chips, g Found uranium, mg Mass fraction of uranium,%

$$b_{0,95}=\frac{t_b\cdot S}{\sqrt{n}}$$

one. 1-1 6.8 36.7 0.54 0.500 ± 0.052 2. 1-2 4.2 22.7 0.54 3. 2-1 6.3 26.6 0.42 four. 2-2 4.6 24.4 0.53 5. 4-1 6.6 29.9 0.45 6. 5-1 5.8 28.9 0.52

Table number 2 Uranium content in graphite blocks No. p / p Block number Unit weight, g Found uranium, mg Mass fraction of uranium, mg

$$b_{0,95}=\frac{t_b\cdot S}{\sqrt{n}}$$

one. one 34.8 162.1 0.46 0.46 ± 0.03 2. four 30.9 154.4 0.5 3. 5 34.0 151.3 0.45 four. 7 31.6 155.6 0.49 5. 8 31.8 143.3 0.45 6. 10 30.8 118.1 0.4 7. 12 30,0 138.9 0.46 8. fourteen 29.2 121,2 0.41 9. 17 31,2 123.7 0.40 10. eighteen 33.0 133.0 0.40 eleven. 21 34.7 173.5 0.51 12. 22 32,3 154.6 0.48

To assess the uniform distribution of uranium over the depth of a graphite block, cores were taken from a sample weighing 750 g. The drilling diameter was 8.0 mm, and the drilling depth was 52 and 72 mm. The core locations were randomly selected. The resulting chips were analyzed for uranium content by direct γ-spectrometric measurements. The data obtained are shown in table 3.

Based on the experimental data given in tables No. 1-3, we can conclude: as a result of the experiments, the uniformity of the distribution of uranium in the graphite block is ± 6.5-10%.

Claims (6)

1. A method of introducing a uranium compound into a matrix, characterized in that the uranium compound is introduced into the graphite matrix by impregnation of the porous graphite block with a solution of an organometallic compound of uranium in an organic solvent or a mixture of organic solvents, followed by drying and annealing, with β- being used as an organometallic compound uranyl diketonate. 2. The method according to claim 1, characterized in that uranyl acetylacetonate is used as uranyl β-diketonate. 3. The method according to claim 1, characterized in that the solvent used is a mixture of acetone with isopropyl alcohol and water in a ratio of 65-70: 4-5: 25-31. 4. The method according to claim 1, characterized in that the drying is carried out in air for at least 48 hours 5. The method according to claim 1, characterized in that the blocks are annealed at a temperature of 360-380 ° C for at least 1.5 hours 6. The method according to claim 1, characterized in that the chemical form of stabilization of uranium is uranium trioxide.