Fuel assembly for sodium-cooled metal-fueled fast reactor, reactor core, and manufacturing method of fuel assembly

Abstract

To provide a fuel assembly for a sodium-cooled metal-fueled fast reactor capable of carrying out nuclear transformation more MA by increasing the mass of MA loaded into a reactor core before, a reactor core, and a manufacturing method of fuel assembly.SOLUTION: Any one or more of an inner reactor core fuel assembly 2, a blanket fuel 204 in an upper-axis direction in the outer reactor core fuel assembly 3, a lower axial blanket fuel 205, and the radial blanket fuel 212 in the radial blanket fuel assembly 4 is a U-Pu-MA-Zr alloy with a lower Pu enrichment than the reactor core fuel 203, in which the MA enrichment and Pu enrichment satisfies the relationship 0wt%<MA enrichment≤Pu enrichment.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a fuel assembly, a reactor core, and a method for manufacturing the fuel assembly for a sodium-cooled metal-fueled fast reactor, which increases the amount of nuclear transmutation of minor actinides (MA) and contributes to reducing the harmfulness of radioactive waste and streamlining geological disposal sites. [Background technology]

[0002] Patent Document 1 describes that a fuel element in which metallic fuel containing minor actinides (MA) is enclosed within a fuel cladding tube has a two-layer fuel material region consisting of a central metallic fuel in cross section and an outer peripheral metallic fuel surrounding the outer periphery of the central metallic fuel in cross section, the central metallic fuel in cross section is rod-shaped fuel with a high minor actinide content, and the outer peripheral metallic fuel is granular or cylindrical metallic fuel with a low minor actinide content or containing no minor actinides, and the fuel element has a gas plenum region defined by the inner surface of the fuel cladding tube between a porous intermediate end plug and a lower end plug. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-26372 A Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, in a fast breeder reactor, the core is placed in a reactor vessel, which is filled with liquid sodium as a coolant. The fuel assemblies loaded into the core include multiple fuel rods containing plutonium-enriched depleted uranium (U-238), a trumpet tube surrounding the bundled multiple fuel rods, an entrance nozzle supporting the lower ends of the fuel rods and neutron shields located below the fuel rods, and a coolant outlet located above the fuel rods.

[0005] The core of a fast breeder reactor has a core fuel region having an inner core region and an outer core region surrounding the inner core region, a blanket fuel region surrounding the core fuel region, and a shield region surrounding the blanket region.

[0006] In a standard homogeneous core, the fuel assemblies in the outer core region have a higher plutonium enrichment than the fuel assemblies in the inner core region, resulting in a flatter radial power distribution in the core.

[0007] The nuclear fuel material stored in each fuel rod of a fuel assembly can take the form of metal fuel, nitride fuel, or oxide fuel. Of these, oxide fuel has the most proven track record. Mixed oxide fuel, which is a mixture of Pu and depleted uranium oxides, i.e., MOX (Mixed Oxide Fuel) fuel pellets, are packed in the axial center of the fuel rod to a height of about 80 to 100 cm. Furthermore, within the fuel rod, axial blanket regions filled with multiple uranium dioxide pellets made of depleted uranium are arranged vertically above and below the MOX fuel packing region.

[0008] The inner core fuel assembly loaded in the inner core region and the outer core fuel assembly loaded in the outer core region each have a plurality of fuel rods filled with a plurality of pellets of MOX fuel, the outer core fuel assembly having a higher Pu enrichment than the inner core fuel assembly.

[0009] A blanket fuel region surrounding the core fuel region is loaded with blanket fuel assemblies having a plurality of fuel rods filled with a plurality of uranium dioxide pellets made of depleted uranium.

[0010] Among the neutrons generated by the nuclear fission reaction occurring in the fuel assemblies loaded in the core fuel region, neutrons that leak from the core fuel region are absorbed by U-238 in each fuel rod of the blanket fuel assemblies loaded in the blanket fuel region. As a result, Pu-239, a fissile nuclide, is newly generated in each fuel rod of the blanket fuel assembly.

[0011] Control rods are used when starting up and shutting down a fast breeder reactor and when adjusting the reactor power output. The control rods have multiple neutron absorbing rods made of boron carbide (B4C) pellets sealed in stainless steel cladding tubes, and these neutron absorbing rods are housed in a trumpet tube with a regular hexagonal cross section, just like the inner and outer core fuel assemblies. The control rods are composed of two independent systems, the main reactor shutdown system and the backup reactor shutdown system, and an emergency shutdown of the fast breeder reactor is possible using only one of the main reactor shutdown system or the backup reactor shutdown system.

[0012] Among the high-level radioactive waste (HLW) generated during the reprocessing of spent fuel from nuclear reactors, minor actinides (MA) such as americium (Am) and curium (Cm) retain radioactivity for a long period of time.

[0013] Research is being conducted to separate and recover this MA from HLW and transmute it in a fast reactor to reduce the harmfulness of the HLW, and to allow the decay heat to decay over several hundred years, thereby streamlining geological disposal sites and reducing the environmental burden. One example of such a technology is described in Patent Document 1.

[0014] In order to further rationalize geological repositories by using a sodium-cooled metal-fueled fast reactor to transmute the MA contained in the HLW generated during the reprocessing of spent fuel from light water reactors, it will be necessary to increase the amount of MA loaded into the reactor core within the limits of void reactivity in order to increase the amount of transmutation.

[0015] An object of the present invention is to provide a fuel assembly, a core, and a method for manufacturing the fuel assembly for a sodium-cooled metal-fueled fast reactor, which is capable of transmuting a larger amount of MA by increasing the weight of MA loaded into the core as compared to conventional methods. [Means for solving the problem]

[0016] The present invention includes a plurality of means for solving the above problems. For example, among the fuel assemblies for a sodium-cooled metal fuel fast reactor using a metal fuel, a core fuel assembly or a radial blanket fuel assembly, one or more of the axial blanket fuel in the core fuel assembly and the blanket fuel in the radial blanket fuel assembly is a U-Pu-MA-Zr alloy with a lower Pu enrichment than the core fuel, which is a low Pu enrichment alloy, and satisfies the relationship of 0 wt% < MA enrichment ≦ Pu enrichment.

Advantages of the Invention

[0017] According to the present invention, the weight of MA loaded in the core can be increased compared with the conventional case, and more MA can be transmutated. Problems, configurations, and effects other than those described above will be clarified by the description of the following embodiments.

Brief Description of the Drawings

[0018] [Figure 1] It is a horizontal cross-sectional view of the core of the fast reactor of Example 1. [Diagram 2] It is a horizontal cross-sectional view of the core fuel assembly of the fast reactor of Example 1. [Diagram 3] It is a horizontal cross-sectional view of the radial blanket fuel assembly of the fast reactor of Example 1. [Figure 4] It is a longitudinal cross-sectional view of the core fuel assembly of the fast reactor of Example 1. [Diagram 5] It is a longitudinal cross-sectional view of the radial blanket fuel assembly of the fast reactor of Example 1. [Figure 6] It is a longitudinal cross-sectional view of the core in the fast reactor of Example 1. [Figure 7] It is a diagram showing the relationship between the Pu enrichment and the MA enrichment in the fast reactor of Example 2. [Figure 8] It is a longitudinal cross-sectional view of the core in the fast reactor of Example 3. [Figure 9] It is a longitudinal cross-sectional view of the inner core fuel assembly of the fast reactor of Example 3.

Modes for Carrying Out the Invention

[0019] Hereinafter, the fuel assembly, core, and method for manufacturing the fuel assembly for a sodium-cooled metal fuel fast reactor according to the present invention will be described with reference to the drawings. In the drawings used in this specification, the same or corresponding components are designated by the same or similar reference numerals, and repeated description of these components may be omitted.

[0020] <Example 1> A fuel assembly for a sodium-cooled metal fuel fast reactor, a reactor core, and a method for manufacturing the fuel assembly according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 6. FIG.

[0021] First, an overview of the sodium-cooled metal-fueled fast reactor core will be explained using Figure 1. Figure 1 shows a horizontal cross section of half the core.

[0022] The core 1 of the sodium-cooled metal-fueled fast reactor shown in FIG. 1 is composed of an inner core fuel region in which inner core fuel assemblies 2 are loaded, an outer core fuel region which is a region surrounding the inner core fuel region and in which outer core fuel assemblies 3 are loaded, a radial blanket fuel region which is a region surrounding the outer core fuel region and in which radial blanket fuel assemblies 4 are loaded, a reflector assembly 5 which further surrounds the radial blanket fuel region, and a control rod assembly 6 arranged in the core fuel region.

[0023] FIG. 2 shows horizontal cross-sectional views of the inner core fuel assembly 2 and the outer core fuel assembly 3 in this embodiment, and FIG. 3 shows horizontal cross-sectional views of the radial blanket fuel assembly 4.

[0024] The inner core fuel assembly 2 and the outer core fuel assembly 3 shown in FIG. 2 are configured by closely arranging the core fuel assembly fuel rods 7 containing a U-Pu-MA-Zr alloy in a triangular pitch inside a hexagonal stainless steel trumpet tube 9.

[0025] The area between the core fuel assembly fuel rods 7 inside the trumpet tube 9 is filled with coolant sodium 10 that flows upstream from below the inner core fuel assemblies 2 and the outer core fuel assemblies 3. The pitch between the inner core fuel assemblies 2 and the outer core fuel assemblies 3 is, for example, 161.4 mm, the cladding tube of the core fuel assembly fuel rods 7 has a diameter of 7.4 mm, and the contained core fuel assembly fuel rods 7 have a diameter of 5.5 mm.

[0026] Although the figure is simplified, the number of core fuel assembly fuel rods 7 provided in one inner core fuel assembly 2 or one outer core fuel assembly 3 is 217.

[0027] The Pu enrichment of the metallic fuel U-Pu-MA-Zr alloy of the core fuel assemblies is 20.8 wt% in the inner core fuel assembly 2 and 25.0 wt% in the outer core fuel assembly 3. The MA enrichment is 5 wt% in both the inner core fuel assembly 2 and the outer core fuel assembly 3.

[0028] On the other hand, the horizontal cross-sectional specifications of the radial blanket fuel assembly 4 shown in FIG. 3 are substantially the same as those of the inner core fuel assembly 2 and the outer core fuel assembly 3 described above, but the fuel enrichment and the fuel composition in the vertical direction are different, as described later.

[0029] The structure of the fuel assembly in the height direction will be described with reference to Figures 4 and 5. Figure 4 is a vertical cross-sectional view of a core fuel assembly, and Figure 5 is a vertical cross-sectional view of a radial blanket fuel assembly.

[0030] As shown in FIG. 4, the fuel rods 201 loaded in the inner core fuel assembly 2 and the outer core fuel assembly 3 are stored in a cylindrical fuel cladding tube 202 immersed in liquid bond sodium 207, and the core fuel 203 loaded with a cylindrical U-Pu-MA-Zr alloy, the upper axial blanket fuel 204 loaded with a low Pu-enriched U-Pu-MA-Zr alloy, and the lower axial blanket fuel 205 loaded with a low Pu-enriched U-Pu-MA-Zr alloy. A gas plenum 206 for holding gaseous fission products FP is formed above them, and the upper end plug 208 and the lower end plug 209 are welded together to seal the fuel rods.

[0031] Generally, when loading MA into the blanket fuel region in a MOX fuel core to increase the MA transmutation amount, (U,MA)O2, which is an oxide mixture of U and MA, is used as the blanket fuel. However, in the case of metal fuel, it is impossible to produce a stable reactor fuel by simply mixing U and MA.

[0032] Therefore, in this embodiment, for the upper axial blanket fuel 204 and the lower axial blanket fuel 205 in the inner core fuel assembly 2 and the outer core fuel assembly 3 described above, a U-Pu-MA-Zr alloy with a low Pu enrichment degree lower than that of the core fuel 203 is used. Further, from the perspective of fuel manufacturing, it is necessary to satisfy the relationship of 0 wt% < MA enrichment degree ≤ Pu enrichment degree for the MA enrichment degree and the Pu enrichment degree.

[0033] For example, the longitudinal length of the core fuel 203 is 1000 mm, and the longitudinal lengths of both the upper axial blanket fuel 204 and the lower axial blanket fuel 205 are 200 mm, with a total of 1400 mm.

[0034] In contrast, the structure and dimensions of the radial blanket fuel assembly 4 and the main structure and dimensions of the fuel rods 8 of the radial blanket fuel assembly shown in FIGS. 3 and 5 are basically the same as those of the inner core fuel assembly 2 and the outer core fuel assembly 3, but the differences are as follows.

[0035] Among the fuel rods 211 shown in FIG. 5, for the radial blanket fuel 212, similar to the above-mentioned upper axial blanket fuel 204 and lower axial blanket fuel 205, a U-Pu-MA-Zr alloy with a low Pu enrichment degree lower than that of the core fuel 203 is used. Further, from the perspective of fuel manufacturing, it is necessary to satisfy the relationship of 0 wt% < MA enrichment degree ≤ Pu enrichment degree for the MA enrichment degree and the Pu enrichment degree.

[0036] The longitudinal length of the radial blanket fuel 212 is 1400 mm, which is the total length of the core fuel 203 of the inner core fuel assembly 2 and the outer core fuel assembly 3, the upper axial blanket fuel 204, and the lower axial blanket fuel 205.

[0037] For example, the MA enrichment of the U-Pu-MA-Zr alloy used in the upper and lower axial blanket fuels in the inner core fuel assembly 2 and the outer core fuel assembly 3 in FIG. 2 and the radial blanket fuel in the radial blanket fuel assembly 4 in FIG. 3 is all 10 wt%, and the Pu enrichment is all 13 wt%.

[0038] FIG. 6 shows a longitudinal section of the core 1. As shown in FIG. 6, the inner and outer core fuel regions are composed of an inner core fuel region 32, an outer core fuel region 33, an upper axial blanket fuel region 34, and a lower axial blanket fuel region 35. Further, a radial blanket fuel region 36 surrounding the core fuel region and a reflector region 37 surrounding it further constitute the outer core fuel region on the peripheral side.

[0039] Among these, the upper axial blanket fuel region 34, the lower axial blanket fuel region 35, and the radial blanket fuel region 36 use a U-Pu-MA-Zr alloy with a low Pu enrichment that is lower than that of the core fuel. Further, from the perspective of fuel manufacturing, it is necessary to satisfy the relationship of 0 wt% < MA enrichment ≤ Pu enrichment.

[0040] In the metal fuel fast reactor of this embodiment, for example, its electrical output is 311 MWe, the thermal output is 840 MW, and the average burnup of the core fuel taken out is about 100 GWd / t.

[0041] Generally, in a fast reactor, when MA is loaded in the core fuel region, the void reactivity increases due to the hardening of the neutron spectrum and the fast fission effect of MA nuclides, etc. However, in the axial blanket fuel region and the radial blanket fuel region around the core, since the neutron leakage is large, the void reactivity is a negative region.

[0042] Therefore, in addition to the core fuel region, the void reactivity of this embodiment in which MA is loaded also in each region of the upper axial blanket fuel 204, the lower axial blanket fuel 205, and the radial blanket fuel 212 is the same as that of a metal fuel core loaded with a U-Pu-MA-Zr alloy with 5 wt% enriched MA added only to the core fuel region, which is 7 dollars and lower than the limit value.

[0043] The amount of nuclear transmutation of MA can be increased to about 140 kg / GWe-Y, which is 1.8 times that in the case of adding 5 wt% enriched MA only to the core fuel region, to about 80 kg / GWe-Y for the metal fuel core of this embodiment.

[0044] Table 1 shows the specifications of the core fuel assembly.

[0045]

Table 1

[0046] Next, a manufacturing method of the inner core fuel assembly 2, the outer core fuel assembly 3, and the radial blanket fuel assembly 4 for a sodium-cooled metal fuel fast reactor using the metal fuel according to this embodiment will be briefly described.

[0047] In the manufacturing method of the fuel assembly of this embodiment, one or more of the upper axial blanket fuel 204, the lower axial blanket fuel 205 in the inner core fuel assembly 2 and the outer core fuel assembly 3, and the radial blanket fuel 212 in the radial blanket fuel assembly 4 are made of a low Pu-enriched U-Pu-MA-Zr alloy with a lower Pu enrichment than the core fuel, and are manufactured so as to satisfy the relationship of 0 wt% < MA enrichment ≤ Pu enrichment. For other structures, materials, and their manufacturing methods, known techniques are adopted.

[0048] Next, the effects of this embodiment will be described.

[0049] Among the inner core fuel assembly 2, outer core fuel assembly 3, and radial blanket fuel assembly 4 for the sodium-cooled metal fuel fast reactor using the metal fuel of Example 1 of the present invention described above, one or more of the upper axial blanket fuel 204 and lower axial blanket fuel 205 in the inner core fuel assembly 2 and outer core fuel assembly 3 and the radial blanket fuel 212 in the radial blanket fuel assembly 4 are U-Pu-MA-Zr alloys with a lower Pu enrichment than the core fuel, and satisfy the relationship of 0 wt% < MA enrichment ≦ Pu enrichment.

[0050] As a result, compared with the case where MA is added only to the core fuel, more MA can be loaded without increasing the void reactivity, so that the nuclear conversion amount of MA can be increased compared with the conventional case.

[0051] <Example 2> The fuel assembly, core, and method for manufacturing the fuel assembly for the sodium-cooled metal fuel fast reactor of Example 2 of the present invention will be described with reference to FIG. 7.

[0052] In this example, except for the values of the Pu enrichment and MA enrichment of the U-Pu-MA-Zr alloy used for the upper axial blanket fuel 204, lower axial blanket fuel 205, and radial blanket fuel 212, the configurations, dimensions, specifications such as the reactor output, etc. of the core and fuel assembly are the same as those of the fast reactor of Example 1.

[0053] FIG. 7 is a diagram showing the relationship between the Pu enrichment 62 and MA enrichment 63 in the U-Pu-MA-Zr alloy used for the axial and radial blanket fuels in the core of the metal fuel fast reactor shown in Example 1.

[0054] In FIG. 7, the straight line 64 indicates a straight line with a gradient of 45° where the Pu enrichment and MA enrichment are the same. The region where the U-Pu-MA-Zr alloy can be manufactured is the region below the straight line 64 where MA enrichment ≦ Pu enrichment.

[0055] As the fuel composition of transuranic elements TRU, assuming the fuel composition represented by the following formula (1) when multi-recycled in a metal fuel core, using the standard nuclear calculation method for fast reactors in Japan, and using the nuclear data set for fast reactors based on the nuclear data library JENDL-4.0 with rich experience, as shown in Example 1, in the axial and radial blanket regions, the production amount exceeds the consumption amount of Pu, that is, the condition of Pu enrichment for the so-called internal conversion ratio exceeding 1 was evaluated by core analysis.

[0056] Pu238 / Pu239 / Pu240 / Pu241 / Pu242 / Np237 / Am241 / Am243 / Cm244 / Cm245 = 1.1 / 66.0 / 25.2 / 2.4 / 2.4 / 0.4 / 1.6 / 0.5 / 0.4 / 0.1 wt% …(1) As a result, it was found that the internal conversion ratio exceeds 1 when the Pu enrichment is 12 wt% or less.

[0057] Therefore, in order for the breeding ratio of the core of the metal fuel fast reactor shown in Example 1 to exceed 1 and for fuel breeding to be possible, combined with the manufacturable region of the above U-Pu-MA-Zr alloy, the triangular range shown in range 65 of FIG. 7, that is, the Pu enrichment and the MA enrichment need to have the relationship represented by the following formula (2).

[0058] 0 wt% < MA enrichment ≤ Pu enrichment ≤ 12 wt% … (2) Similar to Example 1, when the Pu enrichment of the inner core fuel is 20.8 wt% and the Pu enrichment of the outer core fuel is 25.0 wt%, and the MA enrichment is 5 wt% in both cases, in the U-Pu-MA-Zr alloy of the axial blanket fuel at the upper and lower parts of the core fuel assembly and the radial blanket fuel of the radial blanket fuel assembly, when the MA enrichment satisfies the condition of formula (2) and is the same as that of the core fuel at 5 wt% and the Pu enrichment is also 5 wt%, the MA transmutation amount is 96 kg / GWe-Y, which is reduced to about 1.2 times that when only 5 wt% of MA is added to the core fuel region, but the breeding ratio of the core exceeds 1 and fuel breeding becomes possible.

[0059] The other configurations and operations are substantially the same as those of the fuel assembly, the core, and the method for manufacturing the fuel assembly for a sodium-cooled metal-fueled fast reactor according to the first embodiment described above, and therefore details are omitted here.

[0060] The fuel assembly, core, and fuel assembly manufacturing method for a sodium-cooled metal-fueled fast reactor according to the second embodiment of the present invention also have substantially the same effects as those of the fuel assembly, core, and fuel assembly manufacturing method for a sodium-cooled metal-fueled fast reactor according to the first embodiment described above.

[0061] <Example 3> A fuel assembly, a core, and a method for manufacturing the fuel assembly for a sodium-cooled metal fuel fast reactor according to a third embodiment of the present invention will be described with reference to Fig. 8 and Fig. 9. Fig. 8 is a view showing a longitudinal section of the core of this embodiment, and Fig. 9 is a view showing a longitudinal section of an inner core fuel assembly.

[0062] The difference between the core of this embodiment shown in Fig. 8 and the core of the metallic fuel fast reactor of embodiment 1 shown in Fig. 6 is that the core is non-homogeneous in the axial direction, with an inner blanket fuel region 44 disposed in the central region in the height direction of the inner core fuel assembly 2A. The other upper inner core fuel region 42 and lower inner core fuel region 43 are substantially the same as the inner core fuel region 32.

[0063] As shown in FIG. 9, the fuel rods 52 of the inner core fuel assembly 2A are stored in a cylindrical fuel cladding tube 202 immersed in liquid bond sodium 207, and include an upper core fuel 53 and a lower core fuel 54 loaded with cylindrical U-Pu-MA-Zr alloy, an inner blanket fuel 55 loaded with low Pu-enriched U-Pu-MA-Zr alloy between them, an upper axial blanket fuel 204, and a lower axial blanket fuel 205. A gas plenum 206 for holding gaseous fission products FP is formed above them, and an upper end plug 208 and a lower end plug 209 are welded to seal the fuel rods.

[0064] The MA enrichment of the U-Pu-MA-Zr alloy used for the upper axial blanket fuel 204 and the lower axial blanket fuel 205 is 10 wt% in both cases, similar to Example 1, and the Pu enrichment is 13 wt% in both cases.

[0065] Also, the internal blanket fuel 55 is a U-Pu-MA-Zr alloy that satisfies the relationship of 0 wt% < MA enrichment ≤ Pu enrichment. For example, a U-Pu-MA-Zr alloy with a low Pu enrichment is used, where the Pu enrichment and the MA enrichment are both 5 wt%, and the longitudinal length is 200 mm. The upper core fuel 53 and the lower core fuel 54 are U-Pu-MA-Zr alloys with a Pu enrichment of 25.0 wt% and an MA enrichment of 5 wt%, and the longitudinal height of both is 400 mm.

[0066] Other configurations and operations are substantially the same as those of the fuel assembly, core, and fuel assembly manufacturing method for the sodium-cooled metallic fuel fast reactor of Example 1 described above, and details are omitted.

[0067] In the fuel assembly, core, and fuel assembly manufacturing method for the sodium-cooled metallic fuel fast reactor of Example 3 of the present invention, substantially the same effects as those of the fuel assembly, core, and fuel assembly manufacturing method for the sodium-cooled metallic fuel fast reactor of Example 1 described above can be obtained.

[0068] Also, by using an internal blanket fuel 55 that is a U-Pu-MA-Zr alloy and satisfies the relationship of 0 wt% < MA enrichment ≤ Pu enrichment in the axial center region of the inner core fuel assembly 2A, since the loading amount of MA loaded in the core does not change, the MA conversion amount is the same as that in Example 1. However, because an internal blanket fuel with a low Pu enrichment of 5 wt% is arranged at the axial center of the inner core fuel, compared with the core of the metallic fuel fast reactor of Example 1, the axial power peaking and the maximum burnup are suppressed, the margin for fuel integrity increases, and since the burnup reactivity is reduced by about 20%, the safety margin during a scram failure control rod miswithdrawal event (UTOP: Unprotected Transient Over Power) increases.

[0069] <Other> The present invention is not limited to the above-mentioned embodiment, but includes various modified examples. The above-mentioned embodiment has been described in detail to explain the present invention in an easily understandable manner, and the present invention is not necessarily limited to the embodiment having all of the described configurations.

[0070] It is also possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace part of the configuration of each embodiment with the configuration of another embodiment.

[0071] For example, in the above embodiment, the coolant is sodium, but the same effect can be achieved with lead or lead-bismuth.

[0072] Although metal fuel is used as the fuel, the same effect can be obtained with MOX fuel or nitride fuel.

[0073] Furthermore, the same effect can be obtained for any combination of each of the above coolants and each of the above fuels. [Explanation of symbols]

[0074] 1...Core 2,2A…Inner core fuel assembly 3…Outer core fuel assembly 4...Radial blanket fuel assembly 5…Reflector aggregate 6…Control rod assembly 7...Core fuel assembly fuel rod 8...Radial blanket fuel assembly fuel rod 9…Bumblebee 10…Sodium coolant 32…Inner core fuel area 33…Outer core fuel area 34...Upper axial blanket fuel region 35…Lower axial blanket fuel region 36...Radial blanket fuel region 37…Reflector area 42…Upper inner core fuel region 43…Lower inner core fuel region 44…Inner blanket fuel area 52...Fuel rod 53…Upper core fuel 54…Lower core fuel 55…Internal blanket fuel 62…Pu enrichment 63…MA enrichment 64...Line where Pu enrichment is the same as MA enrichment 65... Region showing the range in which MA-containing metallic fuel can be produced and fuel breeding is possible 201…Fuel rod 202…Fuel cladding tube 203…Core fuel 204…Upper axial blanket fuel 205…Lower axial blanket fuel 206…Gas plenum 207…Bond sodium 208…Upper end plug 209…Lower end plug 211…Fuel rod 212...Radial blanket fuel

Claims

1. Among fuel assemblies for a sodium-cooled metal-fueled fast reactor using metal fuel, a core fuel assembly or a radial blanket fuel assembly, At least one of the axial blanket fuel in the core fuel assembly and the blanket fuel in the radial blanket fuel assembly is a U-Pu-MA-Zr alloy having a low Pu enrichment degree, the Pu enrichment degree being lower than that of the core fuel, and the MA enrichment degree and the Pu enrichment degree satisfy the relationship of 0 wt% < MA enrichment ≦ Pu enrichment. fuel assembly.

2. 2. The fuel assembly of claim 1, The MA enrichment and the Pu enrichment of at least one of the axial blanket fuel and the blanket fuel satisfy the relationship of 0 wt%<MA enrichment≦Pu enrichment≦12 wt%. fuel assembly.

3. 2. The fuel assembly of claim 1, Among the core fuel assemblies, an inner blanket fuel is used in an axial center region of an inner core fuel assembly, the inner blanket fuel being made of the U-Pu-MA-Zr alloy, and the MA enrichment and the Pu enrichment satisfy the relationship of 0 wt%<MA enrichment≦Pu enrichment. fuel assembly.

4. A core of a sodium-cooled metal-fueled fast reactor loaded with the fuel assembly according to claim 1.

5. A method for manufacturing a fuel assembly for a sodium-cooled metal-fueled fast reactor using metal fuel, comprising the steps of: At least one of the axial blanket fuel in the core fuel assembly and the blanket fuel in the radial blanket fuel assembly, The alloy is a U-Pu-MA-Zr alloy having a lower Pu enrichment than the core fuel, and is manufactured so that the MA enrichment and Pu enrichment satisfy the relationship 0 wt% < MA enrichment ≦ Pu enrichment. A method for manufacturing a fuel assembly.

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