CN117253631A - Manufacturing method of uranium nitride fuel pellets - Google Patents
Manufacturing method of uranium nitride fuel pellets Download PDFInfo
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- CN117253631A CN117253631A CN202311229548.9A CN202311229548A CN117253631A CN 117253631 A CN117253631 A CN 117253631A CN 202311229548 A CN202311229548 A CN 202311229548A CN 117253631 A CN117253631 A CN 117253631A
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- 239000008188 pellet Substances 0.000 title claims abstract description 87
- MVXWAZXVYXTENN-UHFFFAOYSA-N azanylidyneuranium Chemical compound [U]#N MVXWAZXVYXTENN-UHFFFAOYSA-N 0.000 title claims abstract description 71
- 239000000446 fuel Substances 0.000 title claims abstract description 48
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 32
- 238000005245 sintering Methods 0.000 claims abstract description 56
- 239000000843 powder Substances 0.000 claims abstract description 42
- 238000000034 method Methods 0.000 claims abstract description 18
- 230000005496 eutectics Effects 0.000 claims abstract description 6
- 239000007791 liquid phase Substances 0.000 claims abstract description 6
- 239000011230 binding agent Substances 0.000 claims description 17
- 239000011812 mixed powder Substances 0.000 claims description 16
- 238000010438 heat treatment Methods 0.000 claims description 12
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 8
- 239000002202 Polyethylene glycol Substances 0.000 claims description 8
- 229920001223 polyethylene glycol Polymers 0.000 claims description 8
- 238000003825 pressing Methods 0.000 claims description 7
- 239000004372 Polyvinyl alcohol Substances 0.000 claims description 6
- 229910052786 argon Inorganic materials 0.000 claims description 6
- 229920002451 polyvinyl alcohol Polymers 0.000 claims description 6
- 238000002156 mixing Methods 0.000 claims description 5
- 229910018072 Al 2 O 3 Inorganic materials 0.000 claims description 4
- 239000012300 argon atmosphere Substances 0.000 claims description 4
- 239000012299 nitrogen atmosphere Substances 0.000 claims description 4
- 229910021193 La 2 O 3 Inorganic materials 0.000 claims description 3
- 229910004298 SiO 2 Inorganic materials 0.000 claims description 3
- 238000011534 incubation Methods 0.000 claims 1
- 229910052770 Uranium Inorganic materials 0.000 description 12
- JFALSRSLKYAFGM-UHFFFAOYSA-N uranium(0) Chemical compound [U] JFALSRSLKYAFGM-UHFFFAOYSA-N 0.000 description 12
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical class CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 9
- 230000008569 process Effects 0.000 description 8
- 239000000463 material Substances 0.000 description 6
- 238000002844 melting Methods 0.000 description 6
- 239000002245 particle Substances 0.000 description 6
- 238000000498 ball milling Methods 0.000 description 5
- 238000001816 cooling Methods 0.000 description 5
- 239000007789 gas Substances 0.000 description 5
- 230000008018 melting Effects 0.000 description 5
- 239000003758 nuclear fuel Substances 0.000 description 5
- OOAWCECZEHPMBX-UHFFFAOYSA-N oxygen(2-);uranium(4+) Chemical compound [O-2].[O-2].[U+4] OOAWCECZEHPMBX-UHFFFAOYSA-N 0.000 description 5
- FCTBKIHDJGHPPO-UHFFFAOYSA-N uranium dioxide Inorganic materials O=[U]=O FCTBKIHDJGHPPO-UHFFFAOYSA-N 0.000 description 5
- 238000005984 hydrogenation reaction Methods 0.000 description 4
- 238000007873 sieving Methods 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- 229910001868 water Inorganic materials 0.000 description 4
- 239000012298 atmosphere Substances 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 238000005121 nitriding Methods 0.000 description 3
- -1 nitrogen-containing compound Chemical class 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 2
- 239000000853 adhesive Substances 0.000 description 2
- 230000001070 adhesive effect Effects 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 229910010293 ceramic material Inorganic materials 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 238000006356 dehydrogenation reaction Methods 0.000 description 2
- 238000007599 discharging Methods 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 230000004992 fission Effects 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 229910017604 nitric acid Inorganic materials 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000005253 cladding Methods 0.000 description 1
- 239000000306 component Substances 0.000 description 1
- 238000000748 compression moulding Methods 0.000 description 1
- 239000008358 core component Substances 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000004134 energy conservation Methods 0.000 description 1
- 238000011049 filling Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000011068 loading method Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
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- 230000009467 reduction Effects 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
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Classifications
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
- G21C3/42—Selection of substances for use as reactor fuel
- G21C3/58—Solid reactor fuel Pellets made of fissile material
- G21C3/62—Ceramic fuel
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
- C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/64—Burning or sintering processes
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
- C04B2235/65—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes
- C04B2235/656—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes characterised by specific heating conditions during heat treatment
- C04B2235/6562—Heating rate
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
- C04B2235/65—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes
- C04B2235/656—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes characterised by specific heating conditions during heat treatment
- C04B2235/6567—Treatment time
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
- C04B2235/65—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes
- C04B2235/658—Atmosphere during thermal treatment
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
- C04B2235/65—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes
- C04B2235/658—Atmosphere during thermal treatment
- C04B2235/6581—Total pressure below 1 atmosphere, e.g. vacuum
Abstract
A method for manufacturing uranium nitride fuel pellets, comprising the steps of: providing UN powder, adding and UO into the UN powder 2 An oxide capable of forming a eutectic liquid phase at a temperature not exceeding 1800 ℃ as a sintering aid and pressed to obtain a green pellet; and (3) carrying out vacuum sintering at 1800-1950 ℃ to obtain the uranium nitride fuel pellets. The method can realize the sintering manufacture of the uranium nitride core blocks under the normal pressure condition, simplify the processing flow and reduce the manufacturing cost.
Description
Technical Field
The invention belongs to the field of nuclear power, and particularly relates to a manufacturing method of uranium nitride fuel pellets.
Background
Along with the continuous improvement of energy conservation and emission reduction requirements, nuclear power is used as clean, efficient and stable energy, and becomes an important link in a new energy system. For nuclear power plants, the fuel pellets are the core components of the reactor, and the performance and quality of the pellets directly affect the performance and safety of the plant. UO (UO) 2 As nuclear fuel pellet materials, the nuclear fuel pellet materials have the advantages of good chemical/irradiation stability, good water corrosion resistance, high melting point and the like, so the nuclear fuel pellet materials are widely used in commercial light water piles at present. However, UO 2 The uranium density is low, and the fuel filling quantity capable of effectively carrying out the reaction in the fuel rod is small; meanwhile, the heat conduction performance is poor, even if the shutdown is still carried out, the complete cooling can still be carried out for a long time, and potential safety hazards exist when accidents occur in the nuclear power station. Therefore, uranium Nitride (UN) having a high melting point, high thermal conductivity, and high uranium density is one of the hot potential candidates for fuel pellets of new generation nuclear power plants. However, the UN manufacturing process is complex, and the existing scheme generally adopts high-pressure sintering or field-assisted sintering and other processes, so that the manufacturing process is difficult and the cost is high. Therefore, the uranium nitride manufacturing process with simple method and good economy has a strong application prospect for reducing the cost of the fuel pellet of the nuclear power station.
Disclosure of Invention
The invention aims to provide a manufacturing method of uranium nitride fuel pellets, which simplifies the manufacturing process of uranium nitride pellets.
According to an embodiment of the present invention, there is provided a uranium nitride fuel pellet sintering method including the steps of: providing a UN powder, mixing the UN powder with a sintering aid to obtain a mixed powder, wherein the sintering aid is configured as an oxide powder, and the oxide powder can be mixed with UO 2 Forming a eutectic liquid phase at a temperature of no more than 1800 ℃; pressing the mixed powder to obtain a green compact of the core block; for the green core blockSintering is carried out at 1800-1950 ℃ to obtain uranium nitride fuel pellets.
By adopting the method, the sintering condition of UN powder is effectively reduced by adding the sintering aid, and the uranium nitride fuel pellets can be sintered by using common heating equipment under normal pressure, so that the sintering process of the uranium nitride pellets is simplified, and the manufacturing cost is reduced.
Further, in some embodiments, the sintering aid comprises Fe 3 O 4 、Fe 2 O 3 、ZrO 2 、Al 2 O 3 、La 2 O 3 、SiO 2 、Y 2 O 3 、MgO、CaO、CeO 2 Or a combination of one or more of BaO. The sintering aid of the components can form a low-melting eutectic liquid phase with an oxide film layer on the surface of the UN powder, so that the sintering temperature is effectively reduced.
Further, in some embodiments, the sintering aid is added in an amount of 1% -5% by weight. The addition amount of the sintering aid is too low, and the UN powder is insufficiently sintered; excessive addition can lead to increased impurities in the fuel pellets, reducing fission efficiency.
Further, in some embodiments, a binder is also added to the mixed powder. The binder can reduce friction between powders and promote the flow of the powders during the compression molding process.
Further, in some embodiments, the binder is configured as polyethylene glycol or polyvinyl alcohol. The adhesive can reduce friction force among powder bodies in the green compact pressing process, promote powder body flow, improve green compact density, provide bonding effect and increase green compact strength.
Further, in some embodiments, the binder is added in an amount of 0.05% to 0.5% by weight. The addition amount of the binder is too low, the friction force among powder particles is large, and the green compact pressing density is low; excessive addition of the binder may cause generation of more gas during sintering, easily form defects such as pores, and may leave excessive carbon impurities.
Further, in some embodiments, the green pellet has a pressed density of 60% to 75% t.d., where t.d. is the theoretical density. By adjusting the forming pressure, the density of the green pellet can be adjusted.
Further, in some embodiments, the sintering soak time is 30-90 minutes.
Further, in some embodiments, prior to sintering the green pellet, a degluing step is included that heats the green pellet to 400-800 ℃ in a furnace, holding for 0.5-2 hours, to fully gasify the binder and expel it from the green pellet. And before the sintering temperature is reached, the heat preservation is carried out at a lower temperature, so that the binder is fully gasified and escapes from the green compact of the core block, and the defects of air holes or cracks and the like left by expanding gas in the green compact during high-temperature sintering are avoided.
Further, in some embodiments, the pellet sintering is performed under vacuum or an argon or nitrogen atmosphere. If sintering is performed in a vacuum atmosphere, the vacuum degree is required to be <0.1Pa. If argon or nitrogen atmosphere is used, the gas pressure is 0.1-0.2MPa.
Further, in some embodiments, after the degumming step, the temperature is raised to the temperature required for the vacuum sintering at a rate of 5 ℃/min to 10 ℃/min.
Further, in some embodiments, the uranium nitride fuel pellets produced have a density of not less than 80% t.d., where t.d. is the theoretical density. The method can be used for preparing the fuel pellets with higher density under the condition of normal pressure heating.
Detailed Description
The present invention will be described in further detail with reference to the following examples.
Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment herein. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments limited to the same embodiment. Those skilled in the art will appreciate that embodiments herein may be combined with other embodiments without structural conflict.
In the description herein, the meaning of "plurality" is at least two.
In order to cope with the challenges of climate change, the worldwide demand for green energy is increasing, and fossil energy is being increasingly challenged and challenged. Efficient and stable nuclear power independent of fossil raw materials is becoming an important link in new energy systems. Light water reactors are the most commercially mature and widespread type of reactor today, and the nuclear fuel pellets in the fuel rods directly determine the performance and safety of the reactor. The metallic uranium fuel is basically eliminated because the metallic uranium fuel is easily deformed and even reacts with the fuel rod cladding material during the fission reaction. While uranium dioxide (UO) 2 ) The ceramic material has a melting point reaching 2800 ℃, stable chemical property, basically does not react with materials such as water, sodium, stainless steel and the like, and has good irradiation resistance, so the fuel pellet which is currently used as the main stream is widely applied. However, the uranium dioxide density is only 10.96g/cm 3 The density of uranium element in the manufactured fuel pellets is also low, and the effective proliferation coefficient and the burnup depth are not ideal in the use process of the fuel pellets as fuel. Furthermore, uranium dioxide is used as a ceramic material, so that the heat conducting performance is poor, the size of a fuel pellet is limited on one hand, and on the other hand, when a reactor accident occurs, the reactor needs to be shut down, even if forced cooling measures are adopted, the central area of the fuel pellet can be cooled to a safe temperature range only by taking a long time, and the safety of the existing uranium dioxide fuel pellet which is increasingly concerned in nuclear power safety can not fully meet the requirement.
Compared with uranium dioxide, uranium Nitride (UN) has better chemical inertness, irradiation resistance and melting point of 2650 ℃ and density of 14.32g/cm 3 Has good heat conducting property. Therefore, uranium nitride fuel pellets are becoming a popular candidate for fuel pellets for new generation nuclear reactors. However, the current uranium nitride manufacturing process generally depends on high-pressure sintering or field-assisted sintering, and has high requirements on manufacturing equipment, so that the manufacturing cost is high, and mass production is difficult to realize.
In order to solve the above problems, an embodiment of the present invention provides a uranium nitride fuel pellet manufacturing method including:
firstly, providing UN powder, in a preferred embodiment with a particle size of not more than 50 μm for sintering, mixing the UN powder with a sintering aid, which is used with UO 2 Oxide powders capable of forming a eutectic liquid phase at temperatures not exceeding 1800 ℃, in a preferred embodiment the sintering aid comprises in particular Fe 3 O 4 、Fe 2 O 3 、ZrO 2 、Al 2 O 3 、La 2 O 3 、SiO 2 、Y 2 O 3 、MgO、CaO、CeO 2 Or a combination of one or more of BaO. In a preferred embodiment, the sintering aid is added in an amount of 1% -5% by weight.
Next, a binder, which in a preferred embodiment may be polyethylene glycol or polyvinyl alcohol, is added to the mixed powder in the form of an absolute alcohol solution. In a preferred embodiment, the binder is added in an amount of 0.05% -0.5% by weight.
Next, the mixed powder of the polyethylene glycol or polyvinyl alcohol added absolute alcohol solution is dried and then put into a mold for pressing to obtain a green pellet, and in a preferred embodiment, the green pellet obtained by pressing has a green pellet density of 60% -75% t.d., wherein t.d. is a theoretical density.
Finally, the green pellets are sintered in a furnace, which may be a vacuum furnace or an atmosphere furnace with argon or nitrogen as a shielding gas in various embodiments. In the preferred embodiment, the sintering control pressure of the vacuum furnace is less than 0.1Pa, and the gas pressure of the furnace in the argon or nitrogen atmosphere is controlled to be 0.1-0.2MPa. Preserving heat for 30-90min at 1800-1950 ℃ to obtain the finished product of uranium nitride fuel pellets. In a preferred embodiment, the sintered pellets have a density of not less than 80% t.d.
In a preferred embodiment, the green pellets are further degummed prior to sintering, the degumming process comprising the steps of: heating the green pellet to 400-800 deg.c in a heating furnace for 0.5-2 hr to gasify the adhesive in the green pellet and to escape from the inside of the green pellet to avoid forming pores and other defects in the pellet during sintering. After degumming is completed, the temperature is raised to the temperature required by sintering at a rate of 5-10 ℃/min.
In a preferred embodiment, the uranium nitride fuel pellets are sintered as follows:
first, prepare UN: cleaning the uranium ingot by using nitric acid to remove an oxide layer on the surface of the uranium ingot; feeding uranium ingots into a hydrogenation furnace for hydrogenation and dehydrogenation; ball-milling into powder, and nitriding in nitriding furnace to obtain nitrogen-containing compound (including U) 2 N 3 UN, etc.); ball milling and sieving again, and heating and denitrifying in a denitrification furnace to obtain pure UN powder; sieving to obtain pure UN powder with particle size of about 1 μm.
Next, 1wt% of Fe was added to the UN powder 3 O 4 The powder was thoroughly mixed by a ball mill to obtain a mixed powder.
Adding polyethylene glycol absolute alcohol solution with concentration of 2wt% into the mixed powder, and uniformly mixing according to the proportion that the polyethylene glycol content is 0.1wt% of the total amount of the mixed powder. And heating the mixed and wetted powder to 50 ℃ and drying to obtain the mixed powder containing the binder.
The mixed powder containing the binder is filled into a mould and pressed into a green pellet, and the addition of the polyethylene glycol alcohol solution can reduce the friction force among the powder, promote the flow of the powder and control the pressure to ensure that the density of the green pellet reaches 65 percent T.D.
And (3) feeding the green pellet into a vacuum furnace, vacuumizing to below 0.1Pa, heating to 600+/-30 ℃, and preserving heat for 1 h+/-5 min to degum, so that polyethylene glycol is gasified and decomposed, and escapes from the green pellet.
And then heating to 1900 ℃ at a speed of 5 ℃/min, preserving heat for 1h to finish sintering, and discharging from the furnace after natural cooling to obtain the uranium nitride core block.
In another embodiment, the uranium nitride fuel pellets are sintered as follows:
first, prepare UN: cleaning the uranium ingot by using nitric acid to remove an oxide layer on the surface of the uranium ingot; feeding uranium ingots into a hydrogenation furnace for hydrogenation and dehydrogenation; ball-milling into powder, and feeding into nitriding furnaceNitriding to obtain nitrogen-containing compounds of uranium (including U 2 N 3 UN, etc.); ball milling and sieving again, and heating and denitrifying in a denitrification furnace to obtain pure UN powder; sieving to obtain pure UN powder with particle size of about 40 μm.
Next, 1.5wt% of a sintering aid was added to the UN powder, wherein 10wt% of the sintering aid was ZrO 2 90wt% of Al 2 O 3 The powder was thoroughly mixed by a ball mill to obtain a mixed powder.
Adding 0.4wt% of polyvinyl alcohol into the mixed powder, adding absolute alcohol, ball milling, mixing uniformly, and drying at 50 ℃.
And (3) loading the dried mixed powder into a mould, pressing into a green pellet, and controlling the pressure to enable the green pellet density to reach 60% T.D.
And (3) sending the green pellet into an atmosphere sintering furnace, vacuumizing, introducing high-purity argon, heating to 750+/-30 ℃, preserving heat for 1.5 h+/-5 min, and degumming to enable the polyvinyl alcohol to be gasified and decomposed, and escape from the green pellet.
And then heating to 1950 ℃ at a speed of 10 ℃/min, preserving heat for 2 hours to finish sintering, and discharging from the furnace after natural cooling to obtain uranium nitride pellets.
In one comparative example, the UN powder was prepared in the same manner as in the above examples, and the UN powder was directly pressed into green bodies, followed by sintering at 1900 c and holding for 1 hour to obtain uranium nitride pellets.
In the preparation of UN powder, the unavoidable presence of UO on the surface of powder particles 2 A layer. Since the comparative example does not add sintering aid during sintering, UO with melting point as high as 2800 ℃ is obtained 2 The oxide layer prevents diffusion and recrystallization between the UN powders, the UN is difficult to sinter into a whole, and void residues exist among UN powder particles, so that the highest density of the sintered uranium nitride pellets does not exceed 76% t.d. In the embodiment, the binder and the absolute ethyl alcohol are added, so that powder flows fully during prepressing forming of the green pellet, and higher density can be achieved; by adding a sintering aid, the sintering aid is mixed with UO at a temperature higher than 1800 DEG C 2 The mixture of (2) enters the liquid phase zone, eliminating the obstruction to the process of re-crystallization of UN,sintering aid with UO during cooling 2 At least part of the uranium nitride pellets undergo eutectic reaction and remain in the grain boundary position formed by UN sintering in the form of finer precipitates, and the density of the obtained uranium nitride pellets is above 80 percent T.D.
According to the uranium nitride pellet manufacturing method provided by the embodiment of the invention, the sintering of UN powder can be realized under normal pressure, the manufacturing of the uranium nitride pellet can be realized by a simpler process and a lower manufacturing cost, and the mass production and the application of the reactor fuel pellet are facilitated.
The above-described embodiments are intended to explain the present invention in detail so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the claims, the method steps or material compositions involved are optimized or replaced equivalently, and the implementation of the embodiments in the different embodiments is combined without any principle conflict, which falls within the scope of the present invention.
Claims (12)
1. A method for manufacturing uranium nitride fuel pellets, comprising the steps of:
providing a UN powder, mixing the UN powder with a sintering aid to obtain a mixed powder, wherein the sintering aid is configured as an oxide powder, and the oxide powder can be mixed with UO 2 Forming a eutectic liquid phase at a temperature of no more than 1800 ℃;
pressing the mixed powder to obtain a green compact of the core block;
and sintering the green pellet at 1800-1950 ℃ to obtain the uranium nitride fuel pellet.
2. A method of manufacturing uranium nitride fuel pellets according to claim 1, wherein the sintering aid includes Fe 3 O 4 、Fe 2 O 3 、ZrO 2 、Al 2 O 3 、La 2 O 3 、SiO 2 、Y 2 O 3 、MgO、CaO、CeO 2 Or a combination of one or more of BaO.
3. The method of manufacturing uranium nitride fuel pellets according to claim 1 or 2, wherein the sintering aid is added in an amount of 1% to 5% by weight.
4. The method of manufacturing uranium nitride fuel pellets according to claim 1 or 2, wherein a binder is further added to the mixed powder.
5. The method of producing uranium nitride fuel pellets according to claim 4, wherein the binder is added in an amount of 0.05 to 0.5% by weight.
6. A method of manufacturing a uranium nitride fuel pellet according to claim 1 or claim 2, wherein the green pellet has a pressed density of 60% to 75% t.d., where t.d. is the theoretical density.
7. A method of manufacturing uranium nitride fuel pellets according to claim 1 or claim 2, wherein the sintering incubation time is 30 to 90 minutes.
8. The method of manufacturing uranium nitride fuel pellets according to claim 4, further comprising a degumming step of heating the pellet green body to 400-800 ℃ in a vacuum furnace, and holding the temperature for 0.5-2 hours to fully gasify the binder and discharge from the pellet green body, before sintering the pellet green body.
9. The method of manufacturing uranium nitride fuel pellets according to claim 8, wherein after the degumming step, the temperature is raised to a temperature required for the sintering at a rate of 5 ℃/min to 10 ℃/min.
10. The method for manufacturing uranium nitride fuel pellets according to claim 1 or 2, wherein the sintering is performed under vacuum or under an argon or nitrogen atmosphere.
11. The method of manufacturing uranium nitride fuel pellets according to claim 4, wherein the binder is polyethylene glycol or polyvinyl alcohol.
12. A method of manufacturing a uranium nitride fuel pellet according to claim 1 or claim 2, wherein the density of the manufactured uranium nitride fuel pellet is not less than 80% t.d., where t.d. is the theoretical density.
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