Manufacturing method of ceramic fuel pellets for fuel elements of nuclear reactor

IPC classes for russian patent Manufacturing method of ceramic fuel pellets for fuel elements of nuclear reactor (RU 2421834):

G21C3/02 - Fuel elements

Another patents in same IPC classes:

Method for coprecipitation of actinides with different oxidation states and method of obtaining mixed actinide compounds / 2408537
Invention can be used to produce heat resistant compounds based on mixed oxides, nitrides or carbides of actinides. A stabilising monovalent cation consisting of oxygen, carbon, nitrogen and hydrogen atoms only or a compound such as a salt which forms the said cation, is added to one or more solutions of actinide(s) containing at least one actinide An¹ and at least one actinide An'¹. A solution or mixture consisting of at least an actinide An¹ with oxidation state (IV), at least one actinide An'¹ with oxidation state (III) and the said stabilising monovalent cation is obtained. A solution of oxalic acid or one of its salts or derivative of that salt is added to the obtained mixture, resulting in simultaneous precipitation of said actinides An¹ (IV) and An'¹ (III), as well as a portion of the stabilising monovalent cation from the said mixture. The obtained precipitate is calcined.

Fuel element, working holder and water-cooled power reactor with heat power ranging from 1150 mw to 1700 mw / 2381576
Invention relates to nuclear engineering, particularly to design of fuel elements and working holders assembled from the said fuel elements, used in water-cooled nuclear power reactors with heat power ranging from 1150 MW to 1700 MW. The fuel element of a water-cooled power reactor has cylindrical shell with end caps and a fuel column made from nuclear fuel tablets inside the shell. The length L_FC of the fuel column ranges from 2.480 m to 2.700 m. Total length L_cap of parts of the end caps protruding from the cylindrical shell is not less than 5·10^-3 m. The working holder of such a reactor has a head, a tail and a bundle of fuel elements with a fuel column. The ratio of the length L_FC of the fuel column to the dimension L_T between the upper end of the head and the lower end of the spherical surface of the tail ranges from 0.8276 to 0.9000. The length L_H of the head ranges from 120 10^-3 m to 163 10^-3 m. The distance L_T from the lower end of the spherical surface to the upper end of the tail ranges from 90 10^-3 m to 238 10^-3 m. The water-cooled power reactor with heating power ranging from 1150 MW to 1700 MW has a core made from the working holders, a moving plate and a bottom plate of the core barrel with mounting sockets for tails of the working holders. At least one working holder with the design given above is fitted in the core.

Reactor fuel element / 2360305
Invention refers to nuclear engineering and namely to fuel elements design, which are used for forming active zones of nuclear reactors, in particular, for high energy intensive active zones of research reactors. Fuel element has cruciform cross section. Fuel element blades are narrowed at the bottom and widened in central portion. On the blade end a spacer protrusion can be made.

Investigation method of radiation behaviour of nuclear reactor minute particles / 2357302
Invention refers to nuclear power engineering, and namely to investigation methods of minute particles of high-temperature gas cooled reactors. Investigation method of radiation behaviour of nuclear reactor minute particles consists in radiation of samples with high energy ions with subsequent isothermal annealing at temperature of 1500°C and more and analysis of samples prior to and after radiation. Samples made in the form of minute particle simulators with protective coverings and hemispheres prepared therefrom are pressed into matrix coal graphite composition thus forming a disc. Samples are located in the disc as a monolayer in a near-surface layer. Simulators of minute particles contact one of two flat disc surfaces. Hemispheres are led as equatorial sections to the same surface. Carbon microspheres containing stable isotopes of fission products and calcium phosphates are used as simulators of minute particles. Analysis of radiation damages is carried out by comparing structures of protective coverings on simulators of minute particles and protective coverings on hemispheres of simulators of minute particles.

Nuclear reactor fuel element / 2347289
Fuel element is used in power reactors of low capacity on thermal neutrons to increase reliability and energy production. Nuclear reactor fuel element comprises shell with end plugs, core in the form of nuclear fuel particles distributed in matrix, compensator installed inside shell in the area of fuel element active part with the help of spacer component, compensator is arranged with the area of cross section in the range from 0.1 to 0.3 of fuel element cross section area, nuclear fuel particles are made in the form of granules from uranium dioxide with size from 0.2 to 1.0 mm and porosity from 3 to 6%, uranium density in core is specified from 5.5 to 6.5 g/cm³, total mass of uranium in fuel element is specified from 100 to 210 g, compensator is made from thin-walled tight gas-filled tube, compensator cross section is made in the form of cross with two axes of symmetry and rounded ribs and cavities.

Platy nuclear fuel containing regularly disposed large spherical particles of u-mo or u-mo-x alloy and method for its production / 2317599
Proposed nuclear fuel has regularly disposed large spherical particles of U-Mo or U-Mo-X stable gamma-phase alloy. Diameter of particles uniformly disposed in at least one additional layer on aluminum shell ranges between 300 and 700 μm. Proposed method for producing platy nuclear fuel includes production of stable gamma-phase spherical particles of alloy U-Mo or U-Mo-X, disposition of particles on aluminum shell, application of aluminum powder onto product obtained, and rolling.

Method for recovering serviceability of nuclear reactor fuel assembly subchannel / 2302671
Proposed method for recovering serviceability of nuclear reactor fuel assembly subchannel includes reactor shutting down, dismounting of standard floor blocks from subchannel, and removal of fuel assembly. Process channel is checked for serviceability. Channel is visually inspected within reactor for integrity and channel inner diameter profile is measured. Then process channel pre-removal operations are made. Process channel is removed from subchannel and placed in storage. Construction clearance between process channel and graphite stacking is recovered by calibrating graphite column including finishing of central bore internal diameter to desired size and expansion device segment is installed between guard plate and top graphite block. Graphite column is checked for condition by inspecting inner surface of column. Telescopic joint height and inner diameter of graphite column central bore are measured. Then process channel removed earlier and found serviceable by its check results is reinstalled in fuel assembly subchannel. After that final mounting operations are conducted including welding of process channel to adjacent structures and formation of nuclear reactor subchannel.

Method for producing fuel composition for nuclear reactor / 2295165
Can of desired size is filled with finely dispersed fuel and in addition with material forming solid matrix at temperature equal to or higher than fuel melting point. This can filled with finely dispersed fuel and material forming solid matrix is heated to temperature equal to or higher than fuel melting point is heated and cooled down.

Heat-generating element for research reactors and a based on it heat-generating assembly (versions) / 2267175
The invention is pertaining to the field of nuclear power engineering, in particular, to production of heat-generating elements (further - fuel elements) and the heat-generating assemblies (further - fuel elements assemblies) for research reactors using a low (less than 20 %) enriched nuclear material. The technical result of the invention is enhancement of production capabilities for upgrading the existing research reactors, the fissile regions of which differ in dimensions and forms, using the universal rod-shaped fuel element and the based on it fuel elements assembly. The fuel element is made in the form of a tubular sealed on its end faces by plugs shell made out of an aluminum alloy of 0.30 up to 0.45 mm thick with four distancing screw-type ribs on the outer surface. The diameter of a circumscribed circle of a fuel element cross section makes from 4.0 - 8.0 mm. Each rib protrudes above the shell from 0.4 up to 1,0 mm in height and is placed in the cross section plane at an angle of 90° to the neighboring rib and twisted in spiral with a step from 100 up to 400 mm, predominantly from 300 up to 340 m. Inside the shell there is a fuel core made out of a dispersive composition of uranium-containing particles and an aluminum alloy, in which a volumetric content of uranium-containing particles makes up to 45 %, the uranium-containing particles dimension makes from 63 up to 315 microns, and the shell and the core have a diffusion cohesion among themselves, formed at the fuel elements manufacture by the method of a joint extrusion through a forming array of a composite cylindrical blank consisting of the fuel element core, the plugs and the shell. On the basis of the aforesaid fuel element the versions of the heat-generating assemblies are developed for research reactors of different types with various geometrical forms of the fissile regions.

Fuel cell and gas-cooled nuclear reactor using such fuel cells / 2265899
Fuel cell 10 designed for use in gas-cooled nuclear reactor has assembly of two adjacent fuel plates 12a, 12b disposed relative to one another and shaped so that they form channels 14 for gaseous coolant flow. Fuel plates 12a, 12b incorporate elementary fissionable particles, better non-coated ones, implanted in metal matrix. Metal coating may be deposited on both ends of each plate 12a and 12b.

Fuel rod for water-moderated water-cooled power reactor / 2244347
Proposed fuel rod designed for use in water-cooled water-moderated power reactors such as type VVER-1000 reactor has fuel core disposed in cylindrical can. Outer diameter of fuel rod is chosen between 7.00 ^. 10^-3 and 8.79 ^. 10^-3m and fuel core diameter is between 5.82 ^. 10^-3 and 7.32 ^. 10^-3m and mass, between 0.93 and 1.52 kg, fuel core to fuel rod length ratio being between 0.9145 and 0.9483.

Method for producing tubular three-layer fuel elements / 2248049
Proposed method includes production of powder mixture, powder mixing in plasticizer environment, cold molding in core billet with plasticizer, thermal sintering, hot molding-calibration of fuel core, core placing in can made in the form of sleeve with annular slot, calibration, hot molding through die, and drawing; inner surface of external can of sleeve is provided with longitudinal bulges and outer surface bears bulge location marks; fuel core is provided with longitudinal flats and placed in sleeve taking care to align bulges of the latter with core flats; in the course of drawing marks are aligned on arbor ribs.

Process line for fuel element manufacture / 2256250
Process line primarily used for manufacturing fuel elements for VVER-1000 and VVER-440 reactors has charged can weighing device built integral with can-and-plug assembly weighing device that determines net weight of charged can by internal components, box holding devices for discharging fuel pellets from rejected fuel element, destructive testing of helium pressure within can, and preparing specimens for metallographic inspection.

Method for manufacturing fuel elements / 2264668
Core for three-layer assembly that has sleeve, circular core, and plugs is provided with longitudinal bonds made of sleeve material and three-layer tube obtained upon joint hot extrusion and drawing is cut along bonds; segments obtained in the process are drawn through slit die.

FIELD: power industry.

SUBSTANCE: pellets are pressed in two stages; at that, first, pressing of workpiece of internal core of pellet with axial hole is performed from moulding powder of highly-enriched uranium dioxide UO₂, which contains alloying additives, by using press mould of smaller diameter. Then, obtained workpiece is put into press mould of larger diameter; after that, the gap formed between workpiece and internal wall of press mould is filled with moulding powder from low-enriched uranium dioxide UO₂ for creation of outer layer of pellet and the second pressing stage is performed. It is proposed to obtain moulding powder of low-enriched uranium dioxide UO₂ by using water technology including preparation of uranyl nitrate solution, two-stage deposition of ammonium polyuranate with hydrogen nitride, calcination of deposit, and reduction of monoxide-oxide to uranium dioxide UO₂. Size of granules of low-enriched powder of UO₂ uranium dioxide shall be less than 100 mcm.

EFFECT: higher burnout degree of nuclear fuel.

4 cl, 3 dwg, 2 tbl, 2 ex

The present invention relates to the nuclear industry and may find use in the manufacturing of ceramic fuel pellets of uranium dioxide for fuel elements of nuclear reactors.

A known method of making pelletized fuel for fuel cells, including the preparation of press powder of uranium dioxide (UO₂), enriched in uranium 235, the phasic mixture with a dry binder and powder nitrous-oxide of uranium (U₃O₈the pressing of tablets in the matrix, sintering the pellets in a gaseous reducing environment, the dry binder is used which does not contain metal plasticizer in an amount of 0.1%and 0.5% by weight of oxides of uranium (see RF patent №2360308, IPC G21C 3/62 BI No. 18, 2009).

There is also known a method of manufacturing a preformed nuclear fuel (see RF patent №2255386, IPC G21C 3/62), adopted as a prototype, which consists in preparing a press powder, extrusion of pellets, sintering the pellets in a reducing environment by their movement in counter-current movement of the restorative environment. According to the invention in a press powder enter the oxides of aluminum and silicon, which upon sintering the pellets to form the aluminosilicate contributing to the coarsening of grains of uranium dioxide and increases the hardness compensated plasticine is updated.

However, as we know, the quality of fuel pellets of uranium dioxide characterized by their microstructure, including the size and shape of the grain. These parameters significantly affect the performance of the tablets of the oxides of uranium and, therefore, fuel elements (cartridges). In particular, the microstructure depends what quantity of gas products is retained in the fuel, the nature of the interaction of the fuel with the shell. Therefore, to reduce outgassing seek to obtain tablets with a large grain. On the other hand, to reduce the interaction of the fuel with the shell you want finer grain.

The above methods do not allow to obtain tablets with controlled grain size on its periphery and a Central region, and there is no possibility of the radial regulating the content of the fissile isotope that is not possible to increase the degree of burn-up to 80-100 GW·d/t U.

The technical result of the invention aims to obtain a combined ceramic fuel pellets for fuel elements of a nuclear reactor having a controlled grain size and radial distribution of the fissile isotope that will allow for a greater degree of burnout.

The technical result is achieved in that in the method of manufacturing a ceramic fuel pellets for fuel elements is s nuclear reactor, including the preparation of press powder of uranium dioxide UO₂in a mixture with a binder, compressing the tablets and their sintering in a reducing environment, the pressing of tablets according to the invention, is carried out in two stages, in this case, initially spend extrusion billet inner core tablets with the axial hole of the press powder of highly enriched uranium dioxide UO₂containing alloying elements, using the mold of smaller diameter, then the resulting billet is placed in a mold of larger diameter, after which the gap formed between the workpiece and the inner wall of the mold, fill the press powder from discouraging uranium dioxide UO₂to create the outer layer of the tablet and carry out the second stage of pressing, the pressure P₁in the first stage does not exceed half of the P₂- pressure in the second stage, followed by their sintering in a reducing environment.

According to claim 2, the inner core as alloying additives may contain oxides of Al, Si, Cr, Nb or Ti.

In addition, according to p.3 of the claims of the press-powder low-enriched uranium dioxide UO₂offered by water technologies, including the preparation of a solution of uranyl nitrate, the two-stage deposition osakapolice ammonium ammonia, the course of annealing, recovery of nitrous oxide to uranium dioxide UO₂while the deposition of paloranta ammonium in the first stage is carried out at pH₁6,5-6,6, and the second stage at pH₂9,0-9,5.

According to claim 4 of the formula of the invention the size of the granules of low-enriched powder of uranium dioxide UO₂should be less than 100 microns.

This technology of ceramic fuel pellets allows you to get a secure grip of the outer layer of the tablet with its inner core. For any given density of sintered pellets within 95-96% of theoretical density, it is necessary to provide a density of compaction from 48 to 52% of theoretical density. This is achieved by two-stage pressing, the pressure of the inner core of the first stage P₁does not exceed 1/2 of the molding core in General, R₂.

Below are examples of implementation of the proposed method of manufacture of ceramic fuel pellets.

Example 1. For receiving the inner core of ceramic fuel pellets prepared two uranyl nitrate solution: 1st solution using commercial powder of uranium dioxide UO₂10%enrichment in²³⁵U, the 2nd solution using commercial powder of uranium dioxide UO₂depleted by²³⁵U. Wasp is doing paloranta ammonium (PUA) was performed in two stages by the method of simultaneous draining to the buffer of two solutions: solution of uranyl nitrate and 22-25%-aqueous solution of NH ₄OH. Deposition POIX from the 1st solution in the first stage was carried out at pH₁of 6.8-7.0 and the second stage at pH₂8,0-8,2. Deposition POIX from the 2nd solution in the first stage was carried out at pH₁6,5-6,6 and the second phase pH₂9,0-9,5. PH₁and pH₂are optimal. The obtained precipitation was progulivali to nitrous oxide at a temperature of 650°C. Then pursued recovery of nitrous oxide to UO₂hydrogen at 700°C. the uranium dioxide Powder UO₂mixed with plasticizer (solution of polyvinyl alcohol (glycerol). To obtain press powder extruded briquettes (checkers) at a pressure of 1.3-1.5 t/cm². The briquettes were crushed and rubbed through a sieve: press powder of uranium dioxide UO₂10%enrichment through a sieve with mesh size 400 µm, and press the powder of low-enriched uranium dioxide UO₂through a sieve with a mesh size of 100 microns. Using the mold outer diameter of 8.5 mm and an inner diameter of 2.4 mm of powder 10%enrichment pre-compressed billet inner core ceramic fuel pellets at a pressure P₁in the range of 1.2-1.3 t/cm². Then pressed billet inner core ceramic fuel pellets transferred to a second mold having an external diameter of 10 mm Free space between the workpiece and the inner walls of the Oh of the mold was filled with granules of depleted uranium dioxide UO ₂and made the second stage of pressing at a pressure P₂equal to 2.5 t/cm². Sintering of pellets was carried out at a temperature of 1750°C in an atmosphere of hydrogen for 3 hours. Characteristics of sintered ceramic fuel pellets are shown in table 1, which shows that the average density of the sintered pellets was of 10.73±0.02 g/cm³that meets the specifications for ceramic fuel pellets.

Figure 1 shows the microstructure (before etching) tablets UO₂10%enrichment with an outer layer of UO₂depleted. The transition boundary from the inner core of ceramic fuel pellets to the external layer is absent, which indicates good adhesion of the outer layer with the inner core. The boundary is shown on a cut this tablet after etching, the microstructure of which is presented in figure 2.

Example 2. For receiving the inner core of ceramic fuel pellets used industrial powder of uranium dioxide UO₂2%enrichment for the²³⁵U made way dry conversion powder No. 1. In powder No. 1 were added oxides of Al, Si and Cr in the amount of less than 0.4 wt.%. For making the outer layer of ceramic fuel pellets used depleted uranium, which was prepared with water rest the R uranyl nitrate. Deposition of paloranta ammonium (PUA) was performed in two stages by the method of simultaneous draining to the buffer of two solutions: solution of uranyl nitrate and 22-25%-aqueous solution of NH₄OH, when values of the first stage pH₁6,5-6,6, and the second stage pH₂9,0-9,5. The precipitate was probalily to nitrous oxide U₃O₈at a temperature of 650°C, and then restored to UO₂hydrogen at 700°C, the obtained powder No. 2. Each powder of uranium dioxide UO₂(No. 1 and No. 2) was mixed with the plasticizer (solution of polyvinyl alcohol (glycerol). To obtain press powder initially extruded briquettes (checkers) at a pressure of 1.3-1.5 t/cm². The briquettes were crushed and rubbed through a sieve: uranium dioxide UO₂No. 1 is through a sieve with mesh size 400 µm, and then uranium dioxide UO₂No. 2 through a sieve with a mesh size of 100 microns. Using the mold with an outer diameter of 8.5 mm and an inner diameter of 2.4 mm pre-compressed from powder No. 1 billet inner core ceramic fuel pellets at a pressure P₁in the range of 1.2-1.3 t/see Then the preparation was transferred to a second mold having an external diameter of 10 mm Free space between the workpiece and the inner wall of the mold filled with the granulate of depleted uranium dioxide UO₂(powder No. 2) and made a second pressing at a pressure P₁that is equally the m 2.5 t/cm ². Sintering of pellets was carried out at a temperature of 1750°C in a reducing atmosphere of hydrogen for 3 hours. Characteristics of sintered pellets are shown in table 2, from which it follows that the average value of the density is 10.63±0.02 g/cm³that meets the specifications for ceramic fuel pellets.

Figure 3 presents the microstructure of the ceramic fuel pellets UO₂, 2%enrichment for the²³⁵U with an outer layer of UO_2,depleted by²³⁵U. the transition Boundary from the inner core of ceramic fuel pellets to the outer layer shows better adhesion of the outer layer with the inner core.

Thus, the proposed method is compared with previously known allows to obtain a composite ceramic fuel pellets for fuel elements of a nuclear reactor having a controlled grain size and radial distribution of the fissile isotope that will allow for a greater degree of burnout.

td align="center" namest="c4" nameend="c5" rowspan="1" colspan="1"> Density, g/cm³

Table 1.
No. of tablets.	The external diameter, mm	Internal diameter, mm	Height, mm	Shrinkage, %
geometric	hydrostatic
1	to $ 7.91	1,9	6,89	10,28	10,71	20,90
2	to 7.93	1,9	6,89	10,36	10,75	20,70
3	7,99	1,9	6,98	10,35	a 10.74	20,10
4	to 7.93	1,9	6,99	10,31	of 10.73	20,70

Table 2.
No. tablet	The external diameter, mm	Internal diameter, mm	Height, m the	Hydrostatic density, g/cm³
1	8,0	1,9	6,92	10,65
2	of 8.06	1,9	6,95	or 10.60
3	8,04	1,9	6,93	10,63

1. A method of manufacturing a ceramic fuel pellets for fuel elements of a nuclear reactor, including the preparation of press powder of uranium dioxide UO₂in a mixture with a binder, compressing the tablets and their sintering in a reducing environment, wherein the pressing of tablets is carried out in two stages, in this case, initially spend extrusion billet inner core tablets with the axial hole of the press powder of highly enriched uranium dioxide UO₂containing alloying elements, using the mold of smaller diameter, then the resulting billet is placed in a mold of larger diameter, and the gap formed between the workpiece and the inner wall of the mold, fill the press powder of low-enriched dioxide from the Ana UO ₂for the formation of the outer layer of the tablet and carry out the second stage of pressing, the pressure P₁in the first stage does not exceed half of the P₂- pressure in the second stage, followed by their sintering in a reducing environment.

2. The method according to claim 1, characterized in that the inner core as alloying additives contains oxides of Al, Si, Cr, Nb or Ti.

3. The method according to claim 1, characterized in that the press-powder low-enriched uranium dioxide UO₂receive by water technologies, including the preparation of a solution of uranyl nitrate, the two-stage deposition of sediment paloranta ammonium ammonia, the course of annealing, recovery of nitrous oxide to uranium dioxide, with the deposition of paloranta ammonium in the first stage is carried out at pH₁6,5-6,6, and the second stage at pH₂9,0-9,5.

4. The method according to claim 1 or 3, characterized in that the granule size of low-enriched powder of uranium dioxide UO₂is less than 100 μm.