JP6699882B2 - Nuclear fuel compact, method of manufacturing nuclear fuel compact, and nuclear fuel rod - Google Patents

Description

  Embodiments of the present invention relate to a nuclear fuel compact containing a burnable poison for controlling a nuclear reaction, a method for manufacturing the nuclear fuel compact, and a nuclear fuel rod in which the nuclear fuel compact is stacked and loaded in a cladding tube.

  When a nuclear power plant leads to a serious accident such as power loss due to damage from a large-scale natural disaster, and if the cooling equipment that cools the core cannot be driven, the reactor can be stopped by inserting control rods. Even so, the inside of the reactor becomes hot due to decay heat from fission products in the fuel.

  Although metal materials have been mainly used in the reactor internal structure of a light water reactor that uses water as a coolant, these metal materials are oxidized by high temperature steam and metal-water reaction to generate hydrogen.

  If a serious accident occurs and the temperature inside the reactor becomes high, and hydrogen is generated due to the reaction between the steam in the reactor containment vessel and the metal material, the hydrogen concentration in the reactor containment vessel increases, and depending on the conditions, hydrogen combustion may occur. This may impair the integrity of the containment vessel.

Critical to enhance the safety of even the reactor at the accident, non-metallic material the cladding tube of a nuclear fuel rod occupying most in the structure of the furnace, for example, SiC long fiber-reinforced SiC composite material (hereinafter, "SiC _f / A configuration using a “SiC composite material” is considered.

This SiC _f /SiC composite material is a material that avoids the weakness of monolithic ceramics, which is the weak point of monolithic ceramics, by imparting pseudoductility by peeling or sliding at the interface between the fibers and the ceramics that solidify the fibers. On the other hand, when the SiC _f /SiC composite material is applied to the cladding tube, it is difficult to avoid damage such as separation inside the material, and when damage occurs inside the material, the fission product gas generated by fission is generated. There was a risk of leakage to the outside of the cladding.

  Therefore, in order to give the fission product gas confinement performance to the fuel element itself containing the nuclear fuel material in the cladding tube, the cladding particle fuel that covers the central core (kernel) containing the nuclear fuel material with the cladding layer for confining the fission product gas. Research and development of a technique using a nuclear fuel compact, which is obtained by dispersing and processing the above in a base material, is being carried out. The technique using the coated particle fuel is a technique that has been conventionally applied to a high temperature gas reactor.

JP 2007-127484 A

  By the way, in the conventional light water reactor fuel, in order to suppress the excessive reactivity of the fuel body in the early stage of combustion, a combustible poison such as gadolinium or boron having a large neutron absorption cross-section is directly mixed with the nuclear fuel material, and the work molding is performed. It is used as a fuel pellet containing burnable poison.

  In this case, since most of the nuclear fuel rods in which the fuel pellets are stacked and enclosed are loaded with the nuclear fuel material, the rate of closing the nuclear fuel material in the fuel pellet due to the mixture of combustible poisons is reduced, and the loading of the nuclear fuel material is reduced. The amount did not drop extremely.

  On the other hand, when a nuclear fuel compact composed of coated particle fuel is used as the LWR fuel, if a combustible poison is mixed in the core containing the nuclear fuel material, the amount of nuclear fuel material that can be loaded in the core is limited. However, the reduction of the loading amount of nuclear fuel material due to the mixture of combustible poisons becomes a big problem.

  The present invention has been made in consideration of such circumstances, and when a coated particle fuel is used as the LWR fuel, the burnable poison is arranged in the vicinity of the nuclear fuel material without lowering the loading amount of the nuclear fuel material. A nuclear fuel compact capable of achieving the above, a method for producing the nuclear fuel compact, and a nuclear fuel rod in which the nuclear fuel compact is stacked in a cladding tube and loaded.

In a nuclear fuel compact according to an embodiment of the present invention, a central nucleus containing a nuclear fuel material, a spherical coated particle fuel coated with a coating layer holding a fission product gas produced by fission, and absorbing the neutrons, A burnable poison for adjusting the fission reactivity, and a matrix containing the coated particle fuel in a dispersed state, and a part of the burnable poison mixed in is a portion of the coated particle fuel. A burnable poison particle having a spherical shape smaller than a diameter, the diameter of the burnable poison particle being 0.22 times the diameter of the coated particle fuel, and the burnable poison particle dispersed in the matrix; It is characterized by being contained as.

In the method for producing a nuclear fuel compact according to an embodiment of the present invention, a step of forming a spherical coated particle fuel by coating a central nucleus containing a nuclear fuel material with a coating layer holding a fission product gas produced by fission, A step of mixing a powdery base material and a powdery combustible poison, a mixed powder of the base material and the combustible poison, and the coated particle fuel are mixed, and a sintering aid is added. And sintering to form a matrix, wherein a portion of the burnable poison mixed with the substrate is a burnable poison particle having a spherical shape smaller than a diameter of the coated particle fuel. The diameter of the burnable poison particles is 0.22 times the diameter of the coated particulate fuel, and the burnable poison particles are dispersed and contained in the matrix.

  According to an embodiment of the present invention, when a coated particle fuel is used as a light water reactor fuel, a burnable poison can be arranged in the vicinity of the nuclear fuel material without reducing the loading amount of the nuclear fuel material, and the production of the nuclear fuel compact and the nuclear fuel compact. Methods and nuclear fuel rods for loading nuclear fuel compacts in a cladding stack.

The schematic block diagram of the nuclear fuel rod by which the nuclear fuel compact which concerns on this embodiment is loaded. (A) is a figure explaining the structure of the nuclear fuel compact which concerns on 1st Embodiment, (B) is sectional drawing of the coated particle fuel which concerns on this embodiment. The phase diagram in aluminum oxide-yttrium oxide. The phase diagram in aluminum oxide-gadolinium oxide. The flowchart which shows the manufacturing method of the nuclear fuel compact which concerns on this embodiment. (A) is a figure explaining the structure of the nuclear fuel compact which concerns on 2nd Embodiment, (B) is the elements on larger scale in a matrix. (A) is a figure explaining the structure of the nuclear fuel compact which concerns on 3rd Embodiment, (B) is a figure which shows an example of arrangement|positioning of the coating particle fuel and burnable poison particle contained in a matrix.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 shows a longitudinal sectional view of a nuclear fuel rod 11 according to this embodiment.

  The nuclear fuel rods 11 are loaded by stacking a plurality of nuclear fuel compacts 10 inside a hollow cylindrical cladding tube 12. An upper end plug 13 and a lower end plug 14 are provided at the upper end and the lower end of the cladding tube 12, and the nuclear fuel compact 10 is sealed in the cladding tube 12 by the both end plugs.

For the cladding tube 12, a material having sufficient stability under high temperature conditions such as a zircaloy alloy, a stainless alloy, or a SiC _f /SiC composite material is used. In particular, by using the SiC _f /SiC composite material, generation of hydrogen and oxidation heat due to an oxidation reaction with high-temperature water can be suppressed, and the progress thereof can be delayed in the case of a serious accident that causes core melting or the like.

  A plenum 15 is provided in the upper portion of the cladding tube 12 as a constant space in which the nuclear fuel compacts 10 are not stacked. The plenum 15 serves as a gas reservoir containing the fission product gas emitted from the nuclear fuel compact 10.

  A plenum spring 16 having a spring shape is provided in the plenum 15. One end of the plenum spring 16 is connected to the upper end plug 13 and the other end is locked to the nuclear fuel compact 10, so that the nuclear fuel compact 10 is covered. It is fixed in the tube 12.

  FIG. 2(A) is a diagram illustrating the configuration of the nuclear fuel compact 10 according to the first embodiment, and (B) is a cross-sectional view of the coated particle fuel 17.

  The nuclear fuel compact 10 according to the present embodiment includes a particulate coated particle fuel 17 in which a central nucleus 20 containing a nuclear fuel material is coated with a coating layer that holds a fission product gas produced by fission, and a nuclear fission by absorbing neutrons. A matrix 18 in which a burnable poison for adjusting the reactivity is mixed and the coated particle fuel 17 is dispersedly contained.

  The coated particle fuel 17 is a particulate nuclear fuel element composed of a plurality of concentric spherical regions, a central core 20 (kernel) containing a nuclear fuel material is formed in the central portion, and a plurality of coatings are provided so as to cover the central core 20. Layers have been formed.

As the nuclear fuel material, uranium oxide (UO ₂ ) enriched from uranium 235, plutonium, or the like is used. The core 20 containing the nuclear fuel material can be molded by using an existing method such as a dry method or a wet method used for a fuel for a high temperature gas reactor. The chemical form of the nuclear fuel material is not limited to oxides, and nitrides, carbides, and the like that can stably form the central core 20 are used.

  The plurality of coating layers covering the central nucleus 20 are for holding (confining) the fission product gas generated by the fission in the central nucleus 20, and a buffer made of low-density carbon in order from the central nucleus 20 to the outside. It is composed of a layer 21, a pyrolytic carbon layer 22, a SiC layer 23, and a pyrolytic carbon layer 24. These coating layers are formed, for example, by vapor deposition and coating around the central core 20 by thermal decomposition of vapor deposition gas in a fluidized bed.

  Note that FIG. 2B shows an example of a coating layer and is not limited to a coating layer including four layers, and a coating layer such as a pyrolytic carbon layer may be added. It is good, and it may be composed of three or less coating layers.

  The matrix 18 is a metal-ceramic containing a coated particle fuel 17 dispersed therein, in which a burnable poison for absorbing neutrons and adjusting the reactivity of fission is mixed. Examples of the base material of the matrix 18 include silicon carbide, titanium alloy, aluminum oxide and the like.

  In the matrix 18, a powdery base material and a powdery combustible poison are uniformly mixed to form a mixed powder, and the coated particle fuel 17 is added to the mixed powder. Then, a sintering aid is added to this mixture and the mixture is sintered to form a columnar shape. The coated particle fuel 17 is sintered so as to be dispersed in the matrix 18. As a sintering method for forming the matrix 18, an existing method for forming ceramics such as a liquid phase sintering method is used.

As the burnable poison, an element having a large neutron absorption cross section is used, and for example, gadolinium or boron having a large thermal neutron absorption cross section, or a compound of gadolinium or boron is used. Examples of the gadolinium compound include gadolinium oxide (Gd ₂ O ₃ ), and examples of the boron compound include zirconium diboride (ZrB ₂ ).

  In particular, the neutron absorption reaction of gadolinium is mainly due to the (n,γ) reaction of gadolinium 155 and gadolinium 157. After the reaction, gadolinium 156 and gadolinium 158 are stable nuclides and are the same type of element as gadolinium before the reaction.

  Therefore, although the damage such as the formation of lattice defects may occur due to the strong radiation field during the combustion, the change in the chemical property of the matrix 18 during the combustion of the burnable poison is suppressed to the minimum, and the nuclear fuel compact 10 is protected. Can be stably maintained.

A material having a lower melting point than the base material of the matrix 18 is selected as the sintering aid, and for example, a mixed material of aluminum oxide (Al ₂ O ₃ ) and yttrium oxide (Y ₂ O ₃ ) can be used. .

FIG. 3 shows a phase diagram of a binary system in Al ₂ O ₃ and Y ₂ O ₃ . In the figure, α-Al ₂ O ₃ means a trigonal Al ₂ O ₃ polymorph, and each of C and H means a cubic crystal and a hexagonal Y ₂ O ₃ polymorph. In addition, E _{1 to} E ₃ in the figure represent eutectic points (eutectic), and P represents peritectic points (pereticic).

Since the melting point can be lowered by adjusting the mixing ratio of Al ₂ O ₃ and Y ₂ O ₃ , the temperature of the sintering process can be lowered. For example, when Al ₂ O ₃ :Y ₂ O ₃ =4:1 is selected as the substance ratio, the melting point can be lowered to 1829° C. (eutectic point E ₁ ).

According to the state diagram of FIG. 3, _Al 2 _O 3 with a substance amount _ratio: Y ₂ O 3 = _4: If 1 is selected, the matrix 18 which is formed after the sintering process and _Al 2 _{O 3} Y ₃ Al ₅ O ₁₂ (YAG) is present as a mixture.

Specifically, the mole fractions of Y ₂ O ₃ and YAG at the eutectic point E ₁ are 19.5 mol% and 37.5 mol %, respectively. Converting this into a weight fraction, Y ₂ O ₃ and YAG are 35.6 wt% and 57.0 wt %, respectively. Further, when the weight ratio of the Al ₂ O ₃ phase is calculated using the lever principle, Al ₂ O ₃ is present in the sintering additive in a weight ratio of 38%.

Since Al ₂ O ₃ has poor coexistence with high temperature water, the sintering temperature can be lowered by using Al ₂ O ₃ and Y ₂ O ₃ as sintering aids, while the matrix 18 of the matrix 18 can be used in a high temperature water environment. Corrosion resistance may be reduced.

Since the nuclear fuel compact 10 is laminated inside the cladding tube 12, it does not directly contact with high-temperature reactor water during normal times, but it may be in contact with high-temperature water during abnormal times such as breakage. For this reason, it is desirable that the matrix 18 has corrosion resistance to high-temperature water, and it is desirable to reduce the amount of Al ₂ O ₃ present in the matrix 18.

Therefore, by using _Gd 2 _{O 3} as a burnable poison, by using the state transition of the _Al 2 _{O 3} to consider how to reduce the abundance of _Al 2 _{O 3} in the matrix 18.

FIG. 4 shows a phase diagram of a binary system in Al ₂ O ₃ and Gd ₂ O ₃ . Note that each of H, A, and B means high-temperature hexagonal crystal, A-type hexagonal crystal, and B-type monoclinic crystal Gd ₂ O ₃ .

According to the state diagram of FIG. 4, when the molar fraction of Al ₂ O ₃ is decreased from 100%, when the molar fraction of Al ₂ O ₃ is 62.5%, the Gd ₃ Al ₅ O ₁₂ It can be seen that the solid phase is changed and the solid phase of Al ₂ O ₃ disappears.

Based on the composition of Gd ₃ Al ₅ O _12, consider the amount of Gd required to change to a solid phase Gd ₃ Al _{5 O 12.} The ratio of Gd and Al is Gd/(Gd+Al)=3/8=0.6/1.6, and the material amount ratio is Gd:Al=0.6:1.0. That is, the ratio of the amounts of substances _Al 2 _{O 3} and _{Gd 2 O 3, Gd 2 O} 3 is not less than 0.6 times the _Al 2 _{O 3,} the solid phase of _Al 2 _{O 3} is no longer present.

Al ₂ O ₃ at the eutectic point E ₁ (FIG. 3) is calculated to be 0.003682 mol/g sintering aid. Is _Gd 2 _{O 3} of 0.6 times this substance amount (= 0.002209mol), the amount of substance required for changing the _Al 2 _{O 3} in the solid phase of _Gd 3 _Al 5 _{O 12.} When this is converted to 1 g of the sintering aid, 0.8 g of Gd ₂ O ₃ can be calculated as the necessary weight.

That is, based on the weight of the sintering aid, if the weight of Gd ₂ O ₃ is 0.8 times or more that of the sintering aid, the generation of the solid phase of Al ₂ O ₃ that reduces the corrosion resistance is suppressed. be able to.

  FIG. 5 is a flowchart showing the manufacturing procedure of the nuclear fuel compact 10 according to the present embodiment (see FIG. 2 as appropriate). Here, a case where SiC is used as the base material of the matrix 18 will be described as an example.

  In the particle formation step S10, the central core 20 containing the nuclear fuel material is coated with a plurality of coating layers to form the particulate coated particulate fuel 17.

  In the mixing step S11, the powdery combustible poison and the silicon carbide base material are mixed so as to be uniform.

  In the sintering step S12, the mixed powder of burnable poison and silicon carbide and the coated particle fuel 17 are mixed. Then, a sintering aid is added and a sintering process is performed to form a columnar matrix 18. At this time, the coated particle fuel 17 is sintered so as to be dispersed in the matrix 18.

  As described above, by mixing the powdery combustible poison and forming the matrix 18, when a nuclear fuel substance is added to the central core 20 or when the coated particle fuel 17 is surrounded by a coating layer (overcoat) containing the combustible poison. The burnable poison can be arranged in the vicinity of the nuclear fuel material without reducing the loading amount of the nuclear fuel material in the nuclear fuel compact 10 as compared with the case of providing the layer.

  Further, since the burnable poison is uniformly distributed in the matrix 18, the unevenness of combustion can be reduced.

(Second embodiment)
FIG. 6A is a diagram illustrating the configuration of the nuclear fuel compact 10 according to the second embodiment, and FIG. 6B is a partially enlarged view of the surface of the matrix 18. It should be noted that duplicate description will be omitted for configurations or functions common to the first embodiment.

  The second embodiment is characterized in that the porosity of the matrix 18 is adjusted so that the gas generated by nuclear fission is discharged to the outside of the matrix 18 and escaped into the free space of the cladding tube 12 (FIG. 1). Here, the case where SiC is used as the base material of the matrix 18 and boron is used as the burnable poison is considered.

  Boron has a role as a burnable poison and is widely used as a sintering aid for SiC, and assists in the sintering of the matrix 18.

  On the other hand, the neutron absorption by boron is mainly due to the (n,α) reaction of boron 10. Since α is a helium nucleus, helium gas (He gas) is generated with neutron absorption. Since boron mainly exists at grain boundaries of SiC, He gas generated by the (n, α) reaction exists as grain boundary gas bubbles.

  When He gas generated by neutron absorption by boron accumulates in the nuclear fuel compact 10, gas swelling (gas expansion) may occur.

  When the nuclear fuel compact 10 expands, a certain clearance is secured between the cladding tube 12 (FIG. 1) and the nuclear fuel compact 10, but the cladding tube 12 and the nuclear fuel compact 10 come into contact with each other, and the cladding tube 12 is covered. There is a risk of increasing the load.

  Therefore, as shown in FIG. 6B, pores for discharging He gas generated by neutron absorption by boron to the outside of the matrix 18 are provided in the crystal grain boundaries that are boundaries of the SiC crystal grains.

  When considering pores in the shape of an oblate ellipsoid having a major axis/minor axis ratio of about 3 to 4, the threshold value of percolation (permeation) by pores is about 20% by volume. Therefore, if the porosity is 20% or more in terms of the volume ratio of the matrix 18, connected clusters can exist, and at this time, pores are generated throughout the matrix 18.

  Therefore, by adjusting the porosity of the matrix 18 to 20% or more, even when the He gas is generated inside the matrix 18, the He gas is allowed to pass through the pores in the free space of the cladding tube 12. Can be escaped through. As the method for adjusting the porosity, an existing method for adjusting the porosity of the porous SiC ceramics is used.

  As described above, by arranging the generated He gas to escape from the nuclear fuel compact 10 into the free space in the cladding tube, the gas swelling of the matrix 18 in the nuclear fuel compact 10 can be reduced and the stability of the nuclear fuel compact 10 is improved. be able to.

  Further, since the α particles themselves are non-radioactive, even if helium gas leaks out from a microcrack in the cladding tube 12 or the like, it does not lead to leakage of radioactivity.

(Third Embodiment)
FIG. 7A is a diagram illustrating the configuration of the nuclear fuel compact 10 according to the third embodiment, and FIG. 7B is a diagram illustrating an example of the arrangement of the coated particle fuel 17 and the burnable poison particles 25. It should be noted that duplicated description of configurations or functions common to those of the first embodiment will be omitted.

  In the third embodiment, some of the burnable poisons mixed in the matrix 18 are burnable poison particles 25 smaller than the diameter of the coated particle fuel 17, and the burnable poison particles are dispersed in the matrix 18. It is characterized in that it is contained.

  The powdery combustible poison alone mixed with the sintering aid may be insufficient as the amount of the combustible poison depending on the condition of the nuclear design. In this case, it is possible to increase the neutron absorption cross section without changing the chemical composition by concentrating the combustible poison into isotopes having a large neutron absorption cross section such as boron 10, gadolinium 155, and gadolinium 157. This is not easy from a technical point of view and manufacturing cost.

  Therefore, when sintering the matrix 18, the combustible poison particles 25 are dispersed in the matrix 18 by mixing the particulate combustible poison particles 25 together with the powder combustible poison particles into the base material. Include.

  By making the diameter of the combustible poison particles 25 smaller than the diameter of the coated particle fuel 17, the combustible poison particles 25 are dispersed and contained in the matrix 18 without significantly reducing the filling rate of the coated particle fuel 17. be able to.

  As described above, the spherical combustible poison particles 25 are dispersed and contained in the matrix 18, so that the amount of the combustible poison can be easily adjusted without performing isotope concentration.

  Further, when the two spheres of the coated particle fuel 17 and the burnable poison particles 25 are filled, the radius r of the small sphere (the burnable poison particles 25) inscribed in the gap between the closely packed spheres has a geometrical arrangement. In consideration of the above, the radius is 0.22 times the radius R of the large sphere (coated particle fuel 17).

  By setting the radius r of the burnable poison particles 25 to 0.22 times the radius R of the coated particle fuel 17, the burnable poison particles 25 can be present in the gaps between the closely packed coated particle fuel 17 and It is possible to minimize the influence on the filling rate of the particulate fuel 17, that is, the loading amount of the nuclear fuel material.

When there is a possibility that the burnable poison particles 25 to be mixed resulting in breaking the chemical balance reacts with sintering aid, on the surface of the burnable poison particles 25, for suppressing the film reaction You may form. This film is formed on the surface of the burnable poison particles 25 by chemical vapor deposition of SiC, for example.

  According to the nuclear fuel compact of each of the embodiments described above, by mixing powdery combustible poisons to form a matrix, when a coated particle fuel is used as the light water reactor fuel, the loading amount of the nuclear fuel substance in the fuel compact. It is possible to place the burnable poison in the vicinity of the nuclear fuel material without reducing the temperature.

  Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and the gist of the invention, and are also included in the invention described in the claims and the scope equivalent thereto.

10 Nuclear Fuel Compact 11 Nuclear Fuel Rod 12 Cladding Tube 13 Upper End Plug 14 Lower End Plug 15 Plenum 16 Plenum Spring 17 Coated Particle Fuel 18 Matrix 20 Kernel 21 Buffer Layer 22 Pyrolytic Carbon Layer 23 SiC Layer 24 Pyrolytic Carbon Layer 25 Combustible Poison particle

Claims (10)

A spherical coated particle fuel in which a central nucleus containing a nuclear fuel material is coated with a coating layer holding a fission product gas produced by fission,
A matrix containing a burnable poison for absorbing neutrons and adjusting the reactivity of the nuclear fission, and containing the coated particle fuel in a dispersed state,
A part of the burnable poison to be mixed is a burnable poison particle having a spherical shape smaller than the diameter of the coated particle fuel, and the diameter of the burnable poison particle is 0.22 of the diameter of the coated particle fuel. a fold, nuclear fuel compact, characterized in that the burnable poison particles are contained and dispersed in said matrix.   The nuclear fuel compact according to claim 1, wherein a surface of the burnable poison is provided with a coating of SiC.   The nuclear fuel compact according to claim 1 or 2, wherein the combustible poison contains at least one of gadolinium and boron.   The nuclear fuel compact according to any one of claims 1 to 3, wherein the matrix is formed of ceramics of silicon carbide.   The nuclear fuel compact according to any one of claims 1 to 4, wherein the porosity of the matrix is 20% or more. A nuclear fuel rod, wherein the nuclear fuel compact according to any one of claims 1 to 5 is stacked and filled inside a cladding tube. A spherical coated particle fuel in which a central nucleus containing a nuclear fuel material is coated with a coating layer holding a fission product gas produced by fission,
A matrix containing a burnable poison for absorbing neutrons and adjusting the reactivity of the nuclear fission, and containing the coated particle fuel in a dispersed state,
A part of the burnable poison mixed in is burnable poison particles, the diameter of the burnable poison particles is 0.22 times the diameter of the coated particle fuel, and the porosity of the matrix is 20%. A nuclear fuel compact characterized by the above. A spherical coated particle fuel in which a central nucleus containing a nuclear fuel material is coated with a coating layer holding a fission product gas produced by fission,
A matrix containing a burnable poison for absorbing neutrons and adjusting the reactivity of the nuclear fission, and containing the coated particle fuel in a dispersed state,
A part of the burnable poison mixed in is burnable poison particles, and the diameter of the burnable poison particles is 0.22 times as large as the diameter of the coated particle fuel. Forming a spherical coated particle fuel by coating the central nucleus containing the nuclear fuel material with a coating layer holding a fission product gas produced by fission,
Mixing the powdered base material with the powdered burnable poison,
A step of mixing the mixed powder of the base material and the burnable poison and the coated particle fuel, adding a sintering aid and performing a sintering process to form a matrix,
A part of the burnable poison mixed in the base material is a burnable poison particle having a spherical shape smaller than the diameter of the coated particle fuel, and the diameter of the burnable poison particle is the diameter of the coated particle fuel. 0.22 times, and the burnable poison particles are contained in the matrix in a dispersed manner. Using a mixture of aluminum oxide and yttrium oxide as the sintering aid,
The burnable poison includes gadolinium oxide,
The method for producing a nuclear fuel compact according to claim 9 , wherein the weight of the gadolinium oxide is 0.8 times or more the weight of the sintering aid.

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