Metal material for fuel rod gap filling and preparation method thereof

Abstract

The invention belongs to the field of nuclear fuel, and particularly discloses a metal material for fuel rod gap filling and a preparation method of the metal material. The metal material comprises the following components in parts by mass: 0.01 to 44.5 parts of lead, 0.01 to 56.5 parts of bismuth, 0.01 to 61.9 parts of tin, 0.01 to 5 parts of magnesium and 0.01 to 5 parts of zirconium; and the melting point of the metal material is less than 300 DEG C. The metal material disclosed by the invention has a lower melting point and a higher heat conductivity coefficient, is applied to the in-pile service process of the fuel rod of the advanced reactor, is molten at a loop temperature to be in a liquid state, fills a gap, immerses and seals a fuel core block section, and serves as an excellent heat-conducting medium, so that heat transfer between the fuel rod core block and a cladding is realized, and the heat transfer efficiency is improved. The core block and the cladding are combined to reduce the temperature of the nuclear fuel, meanwhile, the gasification phenomenon does not exist, the phenomenon of irradiation swelling-fission gas release does not occur, the contact force between the core block and the cladding is reduced, and the service life of the fuel rod is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of nuclear fuel, specifically relating to a metallic material for filling gaps in fuel rods and its preparation method. Background Technology

[0002] Traditional rod-shaped nuclear fuel consists of a metallic cladding and pellets containing fissile material, with inert gases such as helium filling the gap between the cladding and pellets. The poor heat transfer performance of the gas gaps in advanced reactors with high operating power leads to temperature rises of hundreds of degrees Celsius between the cladding and pellets, significantly increasing the fuel's operating temperature and negatively impacting long-term operational stability and transient safety margins. To optimize heat transfer between the fuel rod pellets and cladding to reduce fuel temperature, the industry has explored various low-melting-point metals (such as alkali metals and welding alloys) as gap-filling materials to replace gas filling. These metals have relatively low melting points, below the primary circuit operating temperature, ensuring they remain liquid within the reactor core, and also exhibit good thermal conductivity. During operation within the fuel rod reactor, the low-melting-point metal filler remains liquid, fully encapsulating the pellets and acting as an excellent heat transfer medium, thus improving the thermal performance of the fuel rods.

[0003] In the US sodium-cooled fast reactors EBR-II and FFTF, some batches of fuel rods utilize interstitial liquid sodium filling, combined with stainless steel cladding and metallic fuel. While this improves the thermal performance of the fuel rods to some extent, sodium reacts chemically with oxide fuels. Furthermore, sodium's low boiling point poses a vaporization risk upon contact with high-temperature fuel pellets, thus affecting the normal operation of the fuel rods. Existing technologies have also explored using gallium as the liquid metal material; however, gallium is highly corrosive to metallic cladding, reducing cladding thickness and significantly decreasing fuel rod lifespan. Summary of the Invention

[0004] In order to overcome at least one of the technical problems existing in the prior art, one of the objectives of the present invention is to provide a metal material for filling fuel rod gaps.

[0005] The second objective of this invention is to provide a method for preparing a metallic material for filling gaps in fuel rods.

[0006] The third objective of this invention is to provide a nuclear fuel rod.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a metallic material for filling gaps in fuel rods, comprising the following components in parts by weight: 0.01 to 44.5 parts lead, 0.01 to 56.5 parts bismuth, 0.01 to 61.9 parts tin, 0.01 to 5 parts magnesium, and 0.01 to 5 parts zirconium; wherein the melting point of the metallic material is <300°C.

[0008] In some embodiments of the present invention, the thermal conductivity of the metallic material used to fill the fuel rod gaps is 15~20 W / m / K.

[0009] In some embodiments of the present invention, 96℃ ≤ melting point of the metallic material < 300℃; in some embodiments of the present invention, the melting point of the metallic material is any value or a range formed by any two of the following: 96℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 299℃.

[0010] In some embodiments of the present invention, the mass fraction of lead is any value or a range formed by any two of the following: 0.01 parts, 1 part, 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 40 parts, and 44.5 parts.

[0011] In some embodiments of the present invention, the mass fraction of bismuth is any one of 0.01 parts, 1 part, 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 42 parts, 44 parts, 45 parts, 46 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 55 parts, 56.5 parts, or a range formed by any two of these values.

[0012] In some embodiments of the present invention, the mass fraction of tin is any one of 0.01 parts, 1 part, 5 parts, 10 parts, 12 parts, 14 parts, 15 parts, 15.5 parts, 16 parts, 18 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 42 parts, 44 parts, 45 parts, 46 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 55 parts, 60 parts, 61.9 parts, or a range of any two of these values.

[0013] In some embodiments of the present invention, the mass fraction of magnesium is any one of 0.01 parts, 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, or a range formed by any two of these values.

[0014] In some embodiments of the present invention, the mass fraction of zirconium is any one of 0.01 parts, 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, or a range formed by any two of these values.

[0015] In some embodiments of the present invention, the mass ratio of magnesium to zirconium is ≤11.2; in some embodiments of the present invention, the mass ratio of magnesium to zirconium is any value of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 11.2 or a range formed by any two of them.

[0016] In some embodiments of the present invention, the mass ratio of bismuth to lead is 1:(0.6~0.7); in some embodiments of the present invention, the mass ratio of bismuth to lead is any value of 1:0.6, 1:0.61, 1:0.62, 1:0.63, 1:0.64, 1:0.65, 1:0.66, 1:0.67, 1:0.68, 1:0.69, 1:0.7 or a range formed by any two of them.

[0017] In some embodiments of the present invention, the mass ratio of bismuth to tin is 1:(0.3~0.35); in some embodiments of the present invention, the mass ratio of bismuth to tin is any value of 1:0.3, 1:0.31, 1:0.32, 1:0.33, 1:0.34, 1:0.35 or a range formed by any two of them.

[0018] In some embodiments of the present invention, the mass ratio of bismuth to magnesium is 1:(0.04~0.05); in some embodiments of the present invention, the mass ratio of bismuth to magnesium is any value of 1:0.04, 1:0.041, 1:0.042, 1:0.043, 1:0.044, 1:0.045, 1:0.046, 1:0.047, 1:0.048, 1:0.049, 1:0.05 or a range formed by any two of them.

[0019] In some embodiments of the present invention, the material of the core is selected from at least one of actinide nitrides, actinide oxides, and actinide silicides. In some embodiments of the present invention, the material of the core is at least one of uranium nitride, plutonium nitride, uranium oxide, plutonium oxide, uranium silicide, and plutonium silicide.

[0020] In some embodiments of the present invention, the radius of the core block is 2.5~6mm.

[0021] The second aspect of the present invention provides a method for preparing the metallic material for filling the fuel rod gaps as described in the first aspect of the present invention, comprising the following steps: Tin and zirconium are melted and mixed, and then mixed with magnesium to obtain a tin-magnesium-zirconium alloy; Lead and bismuth are melted and mixed, then melted and mixed with a tin-magnesium-zirconium alloy, and finally cast to obtain the metal material.

[0022] In some embodiments of the present invention, the melting temperature of tin and zirconium in the step of melting and mixing is 1800~1900°C; in some embodiments of the present invention, the melting temperature of tin and zirconium in the step of melting and mixing is any value of 1800°C, 1810°C, 1820°C, 1830°C, 1840°C, 1850°C, 1860°C, 1870°C, 1880°C, 1890°C, 1900°C, or a range formed by any two of these values.

[0023] In some embodiments of the present invention, the melting and mixing time of tin and zirconium is 3 to 30 minutes; in some embodiments of the present invention, the melting and mixing time of tin and zirconium is any value of 3 minutes, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, or a range formed by any two of these values.

[0024] In some embodiments of the present invention, the step of melting and mixing tin and zirconium is carried out under inert gas protection at a pressure of 0.5 to 1.5 bar; in some embodiments of the present invention, the melting and mixing pressure is any value or a range formed by any two of 0.5 bar, 0.6 bar, 0.7 bar, 0.8 bar, 0.9 bar, 1 bar, 1.1 bar, 1.2 bar, 1.3 bar, 1.4 bar, and 1.5 bar.

[0025] In some embodiments of the present invention, the step of melting and mixing tin and zirconium is performed by electromagnetic stirring.

[0026] In some embodiments of the present invention, the melting and mixing temperature in the step of melting and mixing with magnesium is 1000~1100℃; in some embodiments of the present invention, the melting and mixing temperature in the step of melting and mixing with magnesium is any value or a range formed by any two of 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃, 1060℃, 1070℃, 1080℃, 1090℃, and 1100℃.

[0027] In some embodiments of the present invention, the melting and mixing time in the step of melting and mixing with magnesium is 3 to 30 min; in some embodiments of the present invention, the melting and mixing time in the step of melting and mixing with magnesium is any value of 3 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min or a range formed by any two of these values.

[0028] In some embodiments of the present invention, the step of melting and mixing with magnesium is carried out under the protection of an inert gas at a pressure of 2.5 to 3.5 bar; in some embodiments of the present invention, the melting and mixing pressure is any value of 2.5 bar, 2.6 bar, 2.7 bar, 2.8 bar, 2.9 bar, 3.0 bar, 3.1 bar, 3.2 bar, 3.3 bar, 3.4 bar, 3.5 bar, or a range formed by any two of these values.

[0029] In some embodiments of the present invention, the melting and mixing method in the step of melting and mixing with magnesium is electromagnetic stirring.

[0030] In some embodiments of the present invention, the melting and mixing temperature of lead and bismuth in the step of melting and mixing is 1100~1200°C; in some embodiments of the present invention, the melting and mixing temperature of lead and bismuth in the step of melting and mixing is any value of 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, 1150°C, 1160°C, 1170°C, 1180°C, 1190°C, 1200°C, or a range formed by any two of these values.

[0031] In some embodiments of the present invention, the melting and mixing time of lead and bismuth in the step of melting and mixing is 20 to 60 minutes; in some embodiments of the present invention, the melting and mixing time of lead and bismuth in the step of melting and mixing is any value of 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes or a range formed by any two of them.

[0032] In some embodiments of the present invention, the step of melting and mixing lead and bismuth is carried out under the protection of an inert gas at a pressure of 0.5 to 1.5 bar; in some embodiments of the present invention, the melting and mixing pressure is any value or a range formed by any two of 0.5 bar, 0.6 bar, 0.7 bar, 0.8 bar, 0.9 bar, 1 bar, 1.1 bar, 1.2 bar, 1.3 bar, 1.4 bar, and 1.5 bar.

[0033] In some embodiments of the present invention, the melting and mixing method in the step of melting and mixing lead and bismuth is electromagnetic stirring.

[0034] In some embodiments of the present invention, the melting and mixing temperature in the step of melting and mixing with the tin-magnesium-zirconium alloy is 1100~1200℃; in some embodiments of the present invention, the melting and mixing temperature in the step of melting and mixing with the tin-magnesium-zirconium alloy is any value or a range formed by any two of 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, and 1200℃.

[0035] In some embodiments of the present invention, the melting and mixing time in the step of melting and mixing with tin-magnesium-zirconium alloy is not less than 5 minutes; in some embodiments of the present invention, the melting and mixing time in the step of melting and mixing with tin-magnesium-zirconium alloy is 5 to 30 minutes; in some embodiments of the present invention, the melting and mixing time in the step of melting and mixing with tin-magnesium-zirconium alloy is any value of 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, or a range formed by any two of these values.

[0036] In some embodiments of the present invention, the step of melting and mixing with the tin-magnesium-zirconium alloy is carried out under inert gas protection at a pressure of 2.5 to 3.5 bar; in some embodiments of the present invention, the melting and mixing pressure is any value or a range formed by any two of 2.5 bar, 2.6 bar, 2.7 bar, 2.8 bar, 2.9 bar, 3.0 bar, 3.1 bar, 3.2 bar, 3.3 bar, 3.4 bar, and 3.5 bar.

[0037] In some embodiments of the present invention, the melting and mixing method in the step of melting and mixing with tin-magnesium-zirconium alloy is electromagnetic stirring.

[0038] In some embodiments of the present invention, the inert gas includes at least one of argon and xenon.

[0039] In some embodiments of the present invention, the preparation of the tin-magnesium-zirconium alloy further includes a step of grinding after cooling, which is performed after the step of molten mixing with magnesium. Grinding can turn the tin-magnesium-zirconium alloy into alloy powder, which is beneficial to the uniform dispersion of alloy components in subsequent steps.

[0040] In some embodiments of the present invention, grinding is performed by grinding into powder under vacuum or argon gas.

[0041] In some embodiments of the present invention, the zirconium is nuclear-grade sponge zirconium.

[0042] The preparation method in this invention minimizes burn-off and oxidation, ensuring accurate formulation of the finished product.

[0043] A third aspect of the present invention provides a nuclear fuel rod comprising a casing and a core segment; the core segment is disposed within the casing; the core segment is formed by arranging at least two of the cores; a gap is formed between the casing and the core segment; the gap is filled with the metallic material described in the first aspect of this invention.

[0044] In some embodiments of the present invention, the housing includes a shell, a first end plug, and a second end plug; one end of the shell is welded to the first end plug, and the other end of the shell is welded to the second end plug.

[0045] In some embodiments of the present invention, a spring is provided between the first end plug and / or the second end plug and the core segment.

[0046] In some embodiments of the present invention, the nuclear fuel rod further includes a reflector core or a breeding core; the reflector core or breeding core is located between the spring and the core segment.

[0047] In some embodiments of the invention, the nuclear fuel rod further includes a pad; the pad is located between the spring and the breeding core.

[0048] The beneficial effects of this invention are: the metallic material in this invention has a low melting point and a high thermal conductivity. When applied in the service life of advanced reactor fuel rods, the metallic material melts at the primary circuit temperature and becomes liquid, filling the gaps and immersing the sealed fuel pellet section, acting as an excellent heat transfer medium. This enables heat transfer between the fuel rod pellets and the cladding, thereby reducing the temperature of the nuclear fuel. At the same time, there is no gasification phenomenon, and no irradiation swelling-fission gas release phenomenon occurs. This reduces the contact force between the pellets and the cladding, and extends the service life of the fuel rods.

[0049] Furthermore, the metallic material in this invention can form a protective layer on the inner surface of the cladding, preventing continuous corrosion. The material itself is not corrosive to the cladding or fuel pellets, and exhibits high compatibility with oxide fuels and nitride fuels, thus improving nuclear fuel safety. It also demonstrates good chemical compatibility with oxide and nitride fuels. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the fuel rod structure in Example 2. Detailed Implementation

[0051] The specific implementation of the present invention will be further described in detail below with reference to the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described in detail below are those that can be implemented or understood by those skilled in the art by referring to the prior art. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0052] In some embodiments of the present invention, the present invention provides a metallic material for filling gaps in fuel rods, comprising the following components in parts by weight: 0.01-44.5 parts lead, 0.01-56.5 parts bismuth, 0.01-61.9 parts tin, 0.01-5 parts magnesium, and 0.01-5 parts zirconium; the melting point of the metallic material is <300°C.

[0053] In some embodiments of the present invention, 96℃ ≤ melting point of the metallic material < 300℃; in some embodiments of the present invention, the melting point of the metallic material is any value or a range formed by any two of the following: 96℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 299℃.

[0054] In some embodiments of the present invention, the mass fraction of lead is any value or a range formed by any two of the following: 0.01 parts, 1 part, 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 40 parts, and 44.5 parts.

[0055] In some embodiments of the present invention, the mass fraction of bismuth is any one of 0.01 parts, 1 part, 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 42 parts, 44 parts, 45 parts, 46 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 55 parts, 56.5 parts, or a range formed by any two of these values.

[0056] In some embodiments of the present invention, the mass fraction of tin is any one of 0.01 parts, 1 part, 5 parts, 10 parts, 12 parts, 14 parts, 15 parts, 15.5 parts, 16 parts, 18 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 42 parts, 44 parts, 45 parts, 46 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 55 parts, 60 parts, 61.9 parts, or a range of any two of these values.

[0057] In some embodiments of the present invention, the mass fraction of magnesium is any one of 0.01 parts, 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, or a range formed by any two of these values.

[0058] In some embodiments of the present invention, the mass fraction of zirconium is any one of 0.01 parts, 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, or a range formed by any two of these values.

[0059] In some embodiments of the present invention, the ratio of the mass of magnesium to the mass of zirconium is ≤11.2; in some embodiments of the present invention, the ratio of the mass of magnesium to the mass of zirconium is any value of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 11.2 or a range formed by any two of them.

[0060] In some embodiments of the present invention, the mass ratio of bismuth to lead is 1:(0.6~0.7); in some embodiments of the present invention, the mass ratio of bismuth to lead is any value of 1:0.6, 1:0.61, 1:0.62, 1:0.63, 1:0.64, 1:0.65, 1:0.66, 1:0.67, 1:0.68, 1:0.69, 1:0.7 or a range formed by any two of them.

[0061] In some embodiments of the present invention, the mass ratio of bismuth to tin is 1:(0.3~0.35); in some embodiments of the present invention, the mass ratio of bismuth to tin is any value of 1:0.3, 1:0.31, 1:0.32, 1:0.33, 1:0.34, 1:0.35 or a range formed by any two of them.

[0062] In some embodiments of the present invention, the mass ratio of bismuth to magnesium is 1:(0.04~0.05); in some embodiments of the present invention, the mass ratio of bismuth to magnesium is any value of 1:0.04, 1:0.041, 1:0.042, 1:0.043, 1:0.044, 1:0.045, 1:0.046, 1:0.047, 1:0.048, 1:0.049, 1:0.05 or a range formed by any two of them.

[0063] In some embodiments of the present invention, the material of the core is selected from at least one of actinide nitrides, actinide oxides, and actinide silicides. In some embodiments of the present invention, the material of the core is at least one of uranium nitride, plutonium nitride, uranium oxide, plutonium oxide, uranium silicide, and plutonium silicide.

[0064] In some embodiments of the present invention, the radius of the core block is 2.5~6mm.

[0065] In some embodiments of the present invention, a method for preparing a metallic material for filling fuel rod gaps is provided, comprising the following steps: Tin and zirconium are melted and mixed, and then mixed with magnesium to obtain a tin-magnesium-zirconium alloy; Lead and bismuth are melted and mixed, then melted and mixed with a tin-magnesium-zirconium alloy, and finally cast to obtain the metal material.

[0066] In some embodiments of the present invention, the melting temperature of tin and zirconium in the step of melting and mixing is 1800~1900°C; in some embodiments of the present invention, the melting temperature of tin and zirconium in the step of melting and mixing is any value of 1800°C, 1810°C, 1820°C, 1830°C, 1840°C, 1850°C, 1860°C, 1870°C, 1880°C, 1890°C, 1900°C, or a range formed by any two of these values.

[0067] In some embodiments of the present invention, the melting and mixing time of tin and zirconium is 3 to 30 minutes; in some embodiments of the present invention, the melting and mixing time of tin and zirconium is any value of 3 minutes, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, or a range formed by any two of these values.

[0068] In some embodiments of the present invention, the step of melting and mixing tin and zirconium is carried out under inert gas protection at a pressure of 0.5 to 1.5 bar; in some embodiments of the present invention, the melting and mixing pressure is any value or a range formed by any two of 0.5 bar, 0.6 bar, 0.7 bar, 0.8 bar, 0.9 bar, 1 bar, 1.1 bar, 1.2 bar, 1.3 bar, 1.4 bar, and 1.5 bar.

[0069] In some embodiments of the present invention, the step of melting and mixing tin and zirconium is performed by electromagnetic stirring.

[0070] In some embodiments of the present invention, the melting and mixing temperature in the step of melting and mixing with magnesium is 1000~1100℃; in some embodiments of the present invention, the melting and mixing temperature in the step of melting and mixing with magnesium is any value or a range formed by any two of 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃, 1060℃, 1070℃, 1080℃, 1090℃, and 1100℃.

[0071] In some embodiments of the present invention, the melting and mixing time in the step of melting and mixing with magnesium is 3 to 30 min; in some embodiments of the present invention, the melting and mixing time in the step of melting and mixing with magnesium is any value of 3 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min or a range formed by any two of these values.

[0072] In some embodiments of the present invention, the step of melting and mixing with magnesium is carried out under the protection of an inert gas at a pressure of 2.5 to 3.5 bar; in some embodiments of the present invention, the melting and mixing pressure is any value of 2.5 bar, 2.6 bar, 2.7 bar, 2.8 bar, 2.9 bar, 3.0 bar, 3.1 bar, 3.2 bar, 3.3 bar, 3.4 bar, 3.5 bar, or a range formed by any two of these values.

[0073] In some embodiments of the present invention, the melting and mixing method in the step of melting and mixing with magnesium is electromagnetic stirring.

[0074] In some embodiments of the present invention, the melting and mixing temperature of lead and bismuth in the step of melting and mixing is 1100~1200°C; in some embodiments of the present invention, the melting and mixing temperature of lead and bismuth in the step of melting and mixing is any value of 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, 1150°C, 1160°C, 1170°C, 1180°C, 1190°C, 1200°C or a range formed by any two of them.

[0075] In some embodiments of the present invention, the melting and mixing time of lead and bismuth in the step of melting and mixing is 20 to 60 minutes; in some embodiments of the present invention, the melting and mixing time of lead and bismuth in the step of melting and mixing is any value of 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes or a range formed by any two of them.

[0076] In some embodiments of the present invention, the step of melting and mixing lead and bismuth is carried out under the protection of an inert gas at a pressure of 0.5 to 1.5 bar; in some embodiments of the present invention, the melting and mixing pressure is any value or a range formed by any two of 0.5 bar, 0.6 bar, 0.7 bar, 0.8 bar, 0.9 bar, 1 bar, 1.1 bar, 1.2 bar, 1.3 bar, 1.4 bar, and 1.5 bar.

[0077] In some embodiments of the present invention, the melting and mixing method in the step of melting and mixing lead and bismuth is electromagnetic stirring.

[0078] In some embodiments of the present invention, the melting temperature in the step of melting and mixing with the tin-magnesium-zirconium alloy is 1100~1200℃; in some embodiments of the present invention, the melting temperature in the step of melting and mixing with the tin-magnesium-zirconium alloy is any value or a range formed by any two of 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, and 1200℃.

[0079] In some embodiments of the present invention, the melting and mixing time in the step of melting and mixing with tin-magnesium-zirconium alloy is not less than 5 minutes; in some embodiments of the present invention, the melting and mixing time in the step of melting and mixing with tin-magnesium-zirconium alloy is 5 to 30 minutes; in some embodiments of the present invention, the melting and mixing time in the step of melting and mixing with tin-magnesium-zirconium alloy is any value of 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, or a range formed by any two of these values.

[0080] In some embodiments of the present invention, the step of melting and mixing with the tin-magnesium-zirconium alloy is carried out under inert gas protection at a pressure of 2.5 to 3.5 bar; in some embodiments of the present invention, the melting and mixing pressure is any value or a range formed by any two of 2.5 bar, 2.6 bar, 2.7 bar, 2.8 bar, 2.9 bar, 3.0 bar, 3.1 bar, 3.2 bar, 3.3 bar, 3.4 bar, and 3.5 bar.

[0081] In some embodiments of the present invention, the melting and mixing method in the step of melting and mixing with tin-magnesium-zirconium alloy is electromagnetic stirring.

[0082] In some embodiments of the present invention, the inert gas includes at least one of argon and xenon.

[0083] In some embodiments of the present invention, the preparation of the tin-magnesium-zirconium alloy further includes a step of grinding after cooling, which is performed after the step of molten mixing with magnesium. Grinding can turn the tin-magnesium-zirconium alloy into an alloy powder, which is beneficial for the uniform dispersion of the alloy components in subsequent steps.

[0084] In some embodiments of the present invention, grinding is performed by grinding into powder under vacuum or argon gas.

[0085] In some embodiments of the present invention, the zirconium is nuclear-grade sponge zirconium.

[0086] The preparation method in this invention minimizes burn-off and oxidation, ensuring accurate formulation of the finished product.

[0087] In some embodiments of the present invention, the present invention provides a nuclear fuel rod comprising a shell and a core segment; the core segment is disposed within the shell; the core segment is formed by arranging at least two of the cores; a gap is formed between the shell and the core segment; the gap is filled with the aforementioned metallic material.

[0088] In some embodiments of the present invention, the housing includes a shell, a first end plug, and a second end plug; one end of the shell is welded to the first end plug, and the other end of the shell is welded to the second end plug.

[0089] In some embodiments of the present invention, a spring is provided between the first end plug and / or the second end plug and the core segment.

[0090] In some embodiments of the present invention, the nuclear fuel rod further includes a reflector core or a breeding core; the reflector core or breeding core is located between the spring and the core segment.

[0091] In some embodiments of the invention, the nuclear fuel rods further include a pad; the pad is located between the spring and the breeding core.

[0092] The specific implementation of the present invention will be further described in detail below with reference to specific embodiments and comparative examples: Early life: refers to the initial stage of a reactor's operating cycle.

[0093] Example 1 This example provides a metallic material for filling gaps in fuel rods, which is composed of lead:bismuth:tin:magnesium:zirconium in a mass ratio of 32.0:50.0:15.5:2.25:0.25. Under standard atmospheric pressure, lead (Pb) has a melting point of 327.46℃. Bismuth (Bi) has a melting point of 271.5℃; Tin (Sn) has a melting point of 231.93℃; Magnesium (Mg) has a melting point of 650℃; Zirconium (Zr) has a melting point of 1855℃.

[0094] This invention prepares an alloy material by mixing five elements—lead, bismuth, tin, magnesium, and zirconium—in the above-mentioned proportions. The melting point of this alloy material is 140°C. This is because the alloy system formed by mixing these elements in this proportion is closer to the eutectic point. The system has a complex composition, severe lattice distortion, and lower interatomic chemical bond binding than a purer system, resulting in a lower melting point.

[0095] The present invention also provides a method for preparing the above-mentioned metallic material for filling the gaps in fuel rods, specifically including the following steps: (1) Weigh each metal according to the mass ratio of lead:bismuth:tin:magnesium:zirconium 32.0:50.0:15.5:2.25:0.25. Add tin powder and sponge zirconium to a melting furnace with 1 bar argon atmosphere and heat to 1900℃ to melt, and continuously stir electromagnetically to promote melting.

[0096] (2) Pressurize to 3 bar and cool to 1100℃, add the corresponding proportion of high-purity magnesium powder, and continuously stir electromagnetically to promote melting. Cool to room temperature to obtain the precursor alloy tin-zirconium-magnesium, and grind it into powder in argon or vacuum.

[0097] (3) In a melting furnace with an argon atmosphere of 1 bar, lead metal powder and bismuth metal powder are added in proportion, the temperature is raised to 1100℃, and after electromagnetic stirring for 30 min, the pressure is raised to 3 bar and the precursor tin zirconium magnesium powder is added. Electromagnetic stirring is carried out continuously for a stirring time of not less than 30 min to promote melting.

[0098] (4) The lead-bismuth-tin-magnesium-zirconium alloy melt is cast into a cylindrical metal material for filling the gap between fuel rods. Its volume is slightly smaller than the inner diameter of the cladding tube and slightly larger than the volume of the fuel pellet-cladding gap.

[0099] Example 2 like Figure 1 As shown, this example provides a fuel rod, including a stainless steel casing 1, a pellet 3, a second end plug 5, a first end plug 6, and a spring 7. One end of the stainless steel shell 1 is connected to the first end plug 6 by welding, and the other end of the stainless steel shell 1 is connected to the second end plug 5 by welding. Inside the stainless steel shell 1, 50 core blocks 3 are stacked sequentially along the direction from the first end plug 6 to the second end plug 5; A spring 7 is provided between the core block 3 closest to the second end plug 5 and the second end plug 5; There is a gap 2 between the core block 3 and the stainless steel shell 1, and the width of the gap 2 is 0.1mm; Gap 2 is filled with the metallic material from Example 1; The material of core block 3 is UO2, and the radius of core block 3 is 400mm.

[0100] The fuel rods in this example are prepared using a method that includes the following steps: (1) When manufacturing fuel rods, the metal material in Example 1 is placed in an empty stainless steel cladding 1 in which the first end plug 6 has been welded; (2) Insert the core block 3 above the metal material and heat the stainless steel shell 1 to melt the cylindrical metal material. Apply pressure to the core block 3 so that the liquid surface of the molten metal material gradually submerges the core block 3, so that the core block 3 is completely submerged by the molten metal material. At the same time, continuously vibrate the stainless steel shell 1 to promote the expulsion of air bubbles from the liquid surface.

[0101] (3) Insert spring 7 to press in the second end plug 5 and weld it. Slowly cool the fuel rod from bottom to top. At this time, the metal material is re-solidified, and finally the fuel rod in this example is obtained.

[0102] When the fuel rods are running in the primary circuit, the melting point of the metal material in the fuel rods is lower than the operating temperature of the primary circuit, thus melting into liquid metal. The liquid metal conducts heat to the fuel pellets 3 during the operation of the fuel rods.

[0103] Comparative Example 1 This example provides a fuel rod, including a stainless steel cladding, a pellet, a second end plug, a first end plug, and a spring; One end of the stainless steel cladding is connected to the second end plug by welding, and the other end of the stainless steel cladding is connected to the first end plug by welding. The stainless steel cladding shell contains 50 core blocks stacked sequentially from the first end plug to the second end plug inside. A spring is installed between the core block closest to the second end plug and the second end plug; There is a gap between the core block and the stainless steel cladding, with a gap width of 0.1 mm; The gap is filled with 1 bar of helium gas; The core material is UO2, and the core radius is 400mm.

[0104] Performance testing: The fuel rods from Example 2 and Comparative Example 1 were applied to a reactor with a core inlet temperature of 300°C and a linear power of 35 kW / m.

[0105] In Comparative Example 1, the initial gas thermal conductivity was approximately 0.6 W / m / K, the temperature rise caused by air gap heat transfer (referring to the temperature difference from the inner wall of the cladding to the outer surface of the core) was around 1200℃, and the core center temperature was around 2700℃.

[0106] In Example 2, the fuel rods are filled with a metallic material with a lead:bismuth:tin:magnesium:zirconium mass ratio of 32.0:50.0:15.5:2.25:0.25. During normal operation of the primary circuit, the metallic material is in a liquid state, and its thermal conductivity varies from 15 to 20 W / m / K depending on the temperature. The temperature rise caused by heat transfer (referring to the temperature difference from the inner wall of the cladding to the outer surface of the pellet) is 10°C, and the temperature at the center of the pellet is 1300°C.

[0107] In summary, Comparative Example 1, due to the use of traditional inert gas filling, has low thermal conductivity and is easily contaminated by the release of fission gases, resulting in a temperature rise much greater than that of the metal material used in Example 1 for filling the gaps. This causes the fuel rods to operate under unfavorable high-temperature conditions, reducing their service life. Therefore, the metal material used for filling the fuel rod gaps protected by this invention can significantly optimize the heat transfer performance of advanced reactor fuel rods.

[0108] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A metallic material for filling gaps in fuel rods, characterized in that: The composition comprises the following components in parts by weight: lead 0.01~44.5 parts, bismuth 0.01~56.5 parts, tin 0.01~61.9 parts, magnesium 0.01~5 parts, zirconium 0.01~5 parts; the melting point of the metal material is <300℃.

2. The metallic material for filling fuel rod gaps according to claim 1, characterized in that: The ratio of the mass of magnesium to the mass of zirconium is ≤11.

2.

3. The metallic material for filling fuel rod gaps according to claim 1, characterized in that: The mass ratio of bismuth to lead is 1:(0.6~0.7). And / or, the mass ratio of bismuth to tin is 1:(0.3~0.35); And / or, the mass ratio of bismuth to magnesium is 1:(0.04~0.05).

4. The method for preparing the metallic material for filling the fuel rod gaps according to any one of claims 1 to 3, characterized in that: Includes the following steps: Tin and zirconium are melted and mixed, and then mixed with magnesium to obtain a tin-magnesium-zirconium alloy; Lead and bismuth are melted and mixed, then melted and mixed with a tin-magnesium-zirconium alloy, and then cast to obtain the metal material.

5. The method for preparing the metallic material for filling fuel rod gaps according to claim 4, characterized in that: The step of moltenly mixing tin and zirconium has at least one of the following characteristics: (a1) The melting and mixing temperature is 1800~1900℃; (a2) The melting and mixing time is 3~30 min; (a3) The melt mixing is carried out under the protection of an inert gas at a pressure of 0.5~1.5 bar; (a4) The melting and mixing method is electromagnetic stirring.

6. The method for preparing the metallic material for filling fuel rod gaps according to claim 4, characterized in that: The step of melt mixing with magnesium has at least one of the following characteristics: (b1) The melting and mixing temperature is 1000~1100℃; (b2) The mixing time for the melt mixing is 3~30 min; (b3) The melt mixing is carried out under inert gas protection at a pressure of 2.5 to 3.5 bar; (b4) The melting and mixing method is electromagnetic stirring.

7. The method for preparing the metallic material for filling fuel rod gaps according to claim 4, characterized in that: The step of melting and mixing lead and bismuth has at least one of the following characteristics: (c1) The melting and mixing temperature is 1100~1200℃; (c2) The melting and mixing time is 20~60 min; (c3) The melt mixing is carried out under the protection of an inert gas at a pressure of 0.5~1.5 bar; (c4) The melting and mixing method is electromagnetic stirring.

8. A nuclear fuel rod, characterized in that: It includes a housing and a core segment; the core segment is disposed within the housing; the core segment is formed by arranging at least two of the core blocks; a gap exists between the housing and the core segment; the gap is filled with the metallic material according to any one of claims 1 to 3.

9. The nuclear fuel rod according to claim 8, characterized in that: The housing includes a shell, a first end plug, and a second end plug; one end of the shell is welded to the first end plug, and the other end of the shell is welded to the second end plug.

10. The nuclear fuel rod according to claim 8, characterized in that: A spring is provided between the first end plug and / or the second end plug and the core segment.

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