Fast reactor core, and design method of fast reactor core

Abstract

To provide a fast reactor core capable of improving core performance by devising a loading method for TRUs with different impurity FP content, recovered through advanced reprocessing of spent fuel from light water reactors and fast reactors, and improving nuclear properties.SOLUTION: A fast reactor core 1 is a reactor core that is loaded with a radial fast reactor-origin metallic fuel 34, which includes Pu recovered from reprocessed fast reactor spent fuel, and a radial light water reactor-origin metallic fuel 33, which includes Pu recovered from reprocessed light water reactor spent fuel. The radial light water reactor-origin metallic fuel 33 is loaded adjacent to the radial blanket fuel assembly 5 around the fast reactor core 1, and the radial fast reactor-origin metallic fuel 34 is loaded at a position closer to the center of the fast reactor core 1 than the radial light water reactor-origin metallic fuel 33.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fast reactor core that can improve the nuclear characteristics of a fast reactor loaded with TRU (Pu+MA) containing impurity FP (Fission Product) recovered from the spent fuel of light water reactors and fast reactors by reprocessing in a period when these reactors coexist, and a method for designing a fast reactor core. [Background technology]

[0002] Patent Document 1 describes a method for storing intermediate products of a hybrid reprocessing process that includes a wet process for producing light water reactor fuel from spent light water reactor fuel, an aquapyro process for producing oxides containing plutonium and the like, and a dry process for electrolytically reducing the oxides to produce a metallic reduced product, which is then electrolytically refined to produce a metallic refined product, which is then distilled, and finally producing metallic fast reactor fuel.The document describes that the metallic intermediate product to be stored is a fast reactor ingot formed by distilling the metallic refined product, or a storage fuel slug that has the same composition as and is injection molded into a similar pin shape as metallic fuel slug, which is pin-shaped metallic fast reactor fuel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-94754 Summary of the Invention [Problem to be solved by the invention]

[0004] In a fast breeder reactor, the reactor core is generally placed inside a reactor vessel, which is filled with liquid sodium as a coolant.

[0005] The fuel assembly loaded into the reactor core includes multiple fuel rods containing plutonium-enriched depleted uranium (U-238), a trumpet tube surrounding the bundled fuel rods, an entrance nozzle supporting the lower ends of the fuel rods and neutron shielding located below the fuel rods, and a coolant outlet located above the fuel rods.

[0006] 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.

[0007] In a standard homogeneous core, the fuel assemblies loaded in the outer core region have a higher plutonium enrichment than the fuel assemblies loaded in the inner core region, resulting in a flatter radial power distribution in the core.

[0008] The nuclear fuel material stored in each fuel rod of a fuel assembly can be in 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 fuel pellets, are packed into the axial center of the fuel rod to a height of about 80 to 100 cm.

[0009] Furthermore, within the fuel rod, axial blanket regions filled with a plurality of uranium dioxide pellets made from depleted uranium are arranged above and below the MOX fuel filled region, respectively.

[0010] The inner core fuel assemblies loaded in the inner core region and the outer core fuel assemblies loaded in the outer core region each have a plurality of fuel rods filled with a plurality of MOX fuel pellets, and the outer core fuel assemblies have a higher Pu enrichment than the inner core fuel assemblies.

[0011] 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.

[0012] Neutrons generated by the fission reaction in the fuel assemblies loaded in the core fuel region leak from the core fuel region and 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 produced in each fuel rod of the blanket fuel assembly.

[0013] Control rods are also used when starting up and shutting down a fast breeder reactor and adjusting the reactor power output. Control rods consist of multiple neutron absorbing rods, each made of boron carbide (B4C) pellets sealed in a stainless steel cladding tube, and these neutron absorbing rods are housed in a hexagonal tube, just like the inner and outer core fuel assemblies. The control rods are configured in 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.

[0014] Methods for recovering nuclear fuel materials such as uranium and plutonium from spent fuel from nuclear reactors through reprocessing can be broadly divided into wet reprocessing, in which the spent fuel is dissolved in nitric acid to recover the nuclear fuel materials, and dry reprocessing, which does not use nitric acid.

[0015] Among the dry reprocessing methods, a dry reprocessing process using molten salt electrolysis is known for metallic fuel, in which spent fuel is dissolved in molten salt held in a dissolution tank and recovered using electrodes inserted into the dissolution tank.

[0016] By utilizing the electrochemical characteristics of actinides (U and transuranium elements TRU (Pu and minor actinides (MA))) and fission products in molten salt (a eutectic mixture of lithium chloride (LiCl) and potassium chloride (KCl) melted at approximately 500°C, hereafter referred to as molten LiCl-KCl) that are different in their ease of elution and deposition, actinides can be recovered from spent metallic fuel and separated from FP as follows.

[0017] Of the actinides dissolved from irradiated metallic fuel into molten LiCl-KCl, most of the U is collected using an iron cathode called a solid cathode, while the remaining U and TRU are collected in a liquid Cd cathode. At this time, some rare earth elements (RE) such as Ce, Pr, Nd, Pm, La, and Gd are also collected in the liquid Cd cathode and become impurities called FPs. These impurities absorb neutrons unnecessarily, so if they are loaded into the core of the fast reactor mentioned above together with the nuclear fuel (U and TRUs), it is known to cause a decrease in core performance, such as the breeding ratio.

[0018] In particular, when light water reactors and fast reactors coexist, if TRUs containing impurity FPs recovered from their respective spent fuels using advanced reprocessing methods with low decontamination requirements, such as molten salt electrolysis, are loaded into the core of a sodium-cooled metal-fuel fast reactor, the core performance will be reduced due to the wasteful neutron absorption of the impurity FPs, rare earth elements RE, and improvements are therefore required.

[0019] The purpose of this invention is to provide a fast reactor core and a design method for a fast reactor core that improves core performance by improving nuclear characteristics through a devised loading method for TRUs with different impurity FP content rates recovered through advanced reprocessing of spent fuel from light water reactors and fast reactors. [Means for solving the problem]

[0020] The present invention includes a plurality of means for solving the above-mentioned problems. One example is a method for designing a fast reactor core that loads fast reactor-origin fuel containing Pu recovered by reprocessing fast reactor spent fuel, and light water reactor-origin fuel containing Pu recovered by reprocessing light water reactor spent fuel, wherein the light water reactor-origin fuel is loaded at a position adjacent to a radial blanket on the periphery of the fast reactor core, and the fast reactor-origin fuel is loaded at a position closer to the center of the fast reactor core in the radial direction than the position at which the light water reactor-origin fuel is loaded, or the light water reactor-origin fuel is loaded at a position adjacent to an axial blanket on the periphery of the fast reactor core, and the fast reactor-origin fuel is loaded at a position closer to the center of the fast reactor core in the axial direction than the position at which the light water reactor-origin fuel is loaded. [Effects of the Invention]

[0021] According to the present invention, it is possible to realize an improvement in reactor core performance. Objects, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram showing the flow of nuclear material processes in a molten salt electrolysis method for recovering nuclear fuel to be loaded into the fast reactor core of Example 1. [Figure 2] 1 is a half horizontal cross-sectional view of the core of the fast reactor of the first embodiment. [Figure 3] 1 is a horizontal cross-sectional view of a core fuel assembly arranged on the central side of the core among the core fuel assemblies of a fast reactor of Example 1. FIG. [Figure 4] 1 is a horizontal cross-sectional view of a core fuel assembly arranged on the outer periphery of the core, among the core fuel assemblies of the fast reactor of Example 1. FIG. [Figure 5] 1 is a longitudinal sectional view of a core fuel assembly arranged on the central side of the core among the core fuel assemblies of a fast reactor of Example 1. FIG. [Figure 6] 1 is a longitudinal sectional view of a core fuel assembly arranged on the outer periphery of the core, among the core fuel assemblies of a fast reactor according to a first embodiment. FIG. [Figure 7] 1 is a vertical cross-sectional view of a fast reactor according to a first embodiment. [Figure 8] 1 is a half horizontal cross-sectional view of the core of a fast reactor according to a second embodiment. FIG. [Figure 9] FIG. 1 is a vertical cross-sectional view of a fast reactor according to a second embodiment. [Figure 10] FIG. 10 is a longitudinal sectional view of a core fuel assembly of a fast reactor according to a third embodiment. [Figure 11] FIG. 1 is a vertical cross-sectional view of a fast reactor according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the fast reactor core and the fast reactor core design method of the present invention will be described with reference to the drawings. In the drawings used in this specification, identical or similar reference numerals are used to designate identical or corresponding components, and repeated explanations of these components may be omitted.

[0024] Example 1 A first embodiment of a fast reactor core and a method for designing a fast reactor core according to the present invention will be described with reference to FIGS. 1 to 7. FIG.

[0025] In this embodiment, an example will be described in which the core of a sodium-cooled metallic fuel fast reactor is loaded with nuclear fuel such as U and TRU recovered by dry reprocessing using molten salt electrolysis for metallic fuel.

[0026] Nuclear fuel is recovered according to the nuclear material and process flow in the molten salt electrolysis method as shown in Figure 1. Figure 1 is a diagram showing the nuclear material and process flow in the molten salt electrolysis method for recovering nuclear fuel to be loaded into the fast reactor core of Example 1.

[0027] As shown in step 51 in Figure 1, after shearing, the spent fuel is placed in a stainless steel basket in an electrolytic cell, and the basket, containing U, TRU, and fission products FP, is immersed in molten salt LiCl-KCl (shown as molten salt (1) in the figure), which is a eutectic mixture of lithium chloride and potassium chloride melted at approximately 500°C, also in the electrolytic cell.

[0028] Thereafter, electrolysis is carried out using the basket as an anode, and U in the molten salt LiCl—KCl is selectively deposited on the surface of the solid cathode 52 .

[0029] Next, the cathode is replaced with a liquid Cd cathode 54, and electrolysis is performed. Most of the U is precipitated on the solid cathode 52, and the remaining U (denoted as U') and U' in the molten salt LiCl-KCl (denoted as molten salt (2)) after the TRU and FP are immersed, mainly rare earth elements RE (Ce, Pr, Nd, Pm, La, Gd) among the TRU and FP (step 53 in FIG. 1 ), are precipitated on the surface of the liquid Cd cathode 54.

[0030] The U', TRU, and RE / DF deposited on the surface of the liquid Cd cathode 54 are recovered and become the raw material 55 for the core fuel of a metallic fuel fast reactor. Here, DF is the decontamination factor of impurities FP, which is the ratio of the weight of each RE element immersed in the molten salt LiCl-KCl from spent fuel to the weight of each RE element, which is the impurity FP in the raw material for fast reactor fuel. In the case of the molten salt electrolysis method using the molten salt LiCl-KCl, the DF is approximately 10 based on the findings of previous research.

[0031] In this example, the period of operation is assumed to be a time when light water reactors and fast reactors coexist, and two types of spent fuel are assumed: fuel originating from a metallic fuel fast reactor and fuel originating from a full MOX pluthermal light water reactor.The ratio of the weight of Pu to the weight of all heavy metals (U and TRU) in each spent fuel (corresponding to the so-called Pu enrichment) is 16 wt% and 3 wt%, respectively.

[0032] In contrast, the Pu enrichment in the raw material of the core fuel of a metallic fuel fast reactor is 18 wt% for the inner core fuel and 22 wt% for the outer core fuel, as shown in the explanation of the metallic fuel core below.

[0033] Therefore, in the flow diagram of the nuclear material process for dry reprocessing using the molten salt electrolysis method shown in Figure 1, it is necessary to adjust the amount of uranium recovered at the solid cathode 52, ΔU = U - U', so that the Pu enrichment, Pu / (U' + TRU) × 100, becomes the values ​​for the inner core fuel and outer core fuel mentioned above (18 wt%, 22 wt%).

[0034] Figure 2 shows a horizontal cross section of half of the metallic fuel core in this embodiment, Figure 3 shows a horizontal cross section of the inner core fuel assembly, Figure 4 shows a horizontal cross section of the outer core fuel assembly, Figure 5 shows a vertical cross section of the inner core fuel assembly, Figure 6 shows a vertical cross section of the outer core fuel assembly, and Figure 7 shows a vertical cross section of the core.

[0035] As shown in the half-core horizontal cross-sectional view of FIG. 2, the fast reactor core 1 is composed of an inner core fuel region in which fast reactor-origin inner core fuel assemblies 2 are loaded, using radial fast reactor-origin metallic fuel 34 (see FIG. 5) containing Pu recovered by reprocessing fast reactor spent fuel; a first outer core fuel region surrounding the inner core fuel region and in which fast reactor-origin outer core fuel assemblies 3 are loaded, similarly using radial fast reactor-origin metallic fuel 34; a second outer core fuel region surrounding the first outer core fuel region and adjacent to the radial blanket fuel region in which blanket fuel is loaded, in which light-water reactor-origin fuel assemblies 4 are loaded, using radial light-water reactor-origin metallic fuel 33 (see FIG. 6) containing Pu recovered by reprocessing plutonium-thermal light-water reactor spent fuel; a radial blanket fuel region on the outer periphery of the inner core fuel region; a reflector region in which reflector assemblies 7 surrounding the radial blanket fuel region are arranged; and control rod assemblies 6 arranged in the core fuel region.

[0036] As shown in Figure 3, the fast reactor-origin inner core fuel assembly 2 and the fast reactor-origin outer core fuel assembly 3 have fast reactor-origin metallic fuel rods 23, each of which has a structure in which fuel is enclosed in a fuel rod cladding tube made of a U-Pu-MA-Zr alloy, arranged in a triangular pitch and densely packed inside a hexagonal stainless steel trumpet tube 25.

[0037] In the fast reactor origin inner core fuel assembly 2 and the fast reactor origin outer core fuel assembly 3, the area between the fast reactor origin metallic fuel rods 23 inside the trumpet tube 25 is filled with coolant sodium 24, which is the coolant that flows from below the fuel assembly to upstream.

[0038] The pitch of the fast reactor-origin inner core fuel assembly 2, fast reactor-origin outer core fuel assembly 3, and light water reactor-origin fuel assembly 4 (see Figure 4) is 161.4 mm, the diameter of the fuel rod cladding tube is 7.4 mm, and the diameter of the contained metal fuel rod is 5.5 mm. Although the diagram is simplified, there are 217 fuel rods in one fuel assembly.

[0039] Table 1 shows the specifications of a typical core fuel assembly.

[0040] [Table 1]

[0041] The Pu enrichment of the metallic fuel U-Pu-MA-Zr alloy of the core fuel assemblies is 18.0 wt% for the fast reactor origin metallic fuel rods 23 of the fast reactor origin inner core fuel assembly 2 and 22.0 wt% for the fast reactor origin metallic fuel rods 23 of the fast reactor origin outer core fuel assembly 3.

[0042] The U, Pu, and MA used in the fast reactor-originated metallic fuel rods 23 are metallic fuels recovered by dry reprocessing of the spent fuel of the fast reactor itself using the molten salt electrolysis method described above, or by dry reprocessing of the spent fuel of a pluthermal light water reactor using the molten salt electrolysis method described above. Details of these will be explained using Figures 5 to 7.

[0043] On the other hand, the light water reactor-origin fuel assembly 4 shown in Figure 4 has the same specifications as the fast reactor-origin inner core fuel assembly 2 and the fast reactor-origin outer core fuel assembly 3 shown in Figure 3 in terms of the fuel rod cladding tube and trumpet tube 25, but has light water reactor-origin metallic fuel rods 26, each of which has a structure in which fuel is enclosed in a fuel rod cladding tube made of a U-Pu-MA-Zr alloy, arranged in a triangular pitch and densely packed manner. The Pu enrichment of the light water reactor-origin metallic fuel rods 26 is 22.0 wt%.

[0044] In the light water reactor-origin fuel assembly 4, the area between the fast reactor-origin metallic fuel rods 23 inside the bell pipe 25 is also filled with coolant sodium 24, which is coolant flowing from below to upstream of the fuel assembly.

[0045] The U, Pu, and MA used in the metallic fuel rods 26 originating from a light water reactor are metallic fuels, and are recovered by dry reprocessing of spent fuel from a pluthermal light water reactor using the above-mentioned molten salt electrolysis method.

[0046] The structure of the fuel assembly in the height direction will be explained with reference to FIGS.

[0047] As shown in Figure 5, the fast reactor-origin metallic fuel rods 23 loaded in the fast reactor-origin inner core fuel assembly 2 and the fast reactor-origin outer core fuel assembly 3, which use both nuclear fuel originating from spent fuel of a fast reactor and nuclear fuel originating from a plutonium-thermal light-water reactor, are configured as follows: radial fast reactor-origin metallic fuel 34, upper axial light-water reactor-origin metallic fuel 35, lower axial light-water reactor-origin metallic fuel 36, upper axial blanket fuel 37, and lower axial blanket fuel 38 are stored inside a cylindrical stainless steel fuel cladding tube immersed in liquid bond sodium 27, and a gas plenum 28 for holding gaseous fission products FP is formed above them, and the fuel is sealed by welding an upper end plug 29 and a lower end plug 30.

[0048] Of these, the radial fast reactor-origin metallic fuel 34, the upper axial light water reactor-origin metallic fuel 35, and the lower axial light water reactor-origin metallic fuel 36 are loaded with cylindrical U-Pu-MA-Zr alloy. The upper axial blanket fuel 37 and the lower axial blanket fuel 38 are loaded with U-Zr alloy.

[0049] In this way, the upper axial metallic fuel 35 of light water reactor origin and the lower axial metallic fuel 36 of light water reactor origin are loaded at positions adjacent to the upper axial blanket fuel 37 and the lower axial blanket fuel 38 on the periphery of the fast reactor core 1, and the radial metallic fuel 34 of fast reactor origin is loaded at a position closer to the center of the fast reactor core 1 in the axial direction than the positions at which the upper axial metallic fuel 35 of light water reactor origin and the lower axial metallic fuel 36 of light water reactor origin are loaded.

[0050] The vertical length of the radial fast reactor-origin metallic fuel 34, which uses nuclear fuel originating from spent fuel of a fast reactor, is 800 mm, the upper axial light water reactor-origin metallic fuel 35 and the lower axial light water reactor-origin metallic fuel 36, which use nuclear fuel originating from spent fuel of a plutonium-thermal light water reactor, are both 100 mm, for a total of 1000 mm, and the vertical lengths of the upper axial blanket fuel 37 and the lower axial blanket fuel 38 are both 200 mm, for a total length of 1400 mm for these core fuels and the upper and lower axial blanket fuels.

[0051] Furthermore, since the neutron capture cross section of the long-lived FP Sm-151 is larger near the blanket fuel, which has a softer spectrum than the core fuel region, it is desirable to load nuclear fuel with a high proportion of impurity FP, i.e., a high amount of Sm-151 mixed in, into the upper axial light water reactor-origin metallic fuel 35 and the lower axial light water reactor-origin metallic fuel 36, which are close to the blanket fuel. This increases the amount of nuclear transmutation of Sm-151, a long-lived FP (LLFP), and further reduces its harmfulness.

[0052] The structure and dimensions of the light water reactor-origin fuel assembly 4 shown in Figure 6, which uses nuclear fuel originating from spent fuel of a plutonium-thermal light water reactor, are almost the same as those of the fast reactor-origin inner core fuel assembly 2 and the fast reactor-origin outer core fuel assembly 3, but differ in the following respects.

[0053] In the light water reactor-origin metallic fuel rod 26, the fuel portion is composed of one type of radial light water reactor-origin metallic fuel 33, the nuclear fuel used is of plutonium-thermal light water reactor origin, and the length is 1000 mm. The vertical lengths of the upper axial blanket fuel 37 and the lower axial blanket fuel 38 are both 200 mm, and the total length of these core fuels and the upper and lower axial blanket fuels is 1400 mm, the same as that of the fast reactor-origin metallic fuel rod 23.

[0054] In this way, the light water reactor-origin fuel assemblies 4 loaded with light water reactor-origin metallic fuel rods 26 using radial light water reactor-origin metallic fuel 33 are loaded at positions adjacent to the radial blanket fuel assemblies 5 on the periphery of the fast reactor core 1, and the fast reactor-origin inner core fuel assemblies 2 and fast reactor-origin outer core fuel assemblies 3 loaded with fast reactor-origin metallic fuel rods 23 using radial fast reactor-origin metallic fuel 34 are loaded at positions closer to the center of the fast reactor core 1 in the radial direction than the positions where the light water reactor-origin fuel assemblies 4 loaded with light water reactor-origin metallic fuel rods 26 using radial light water reactor-origin metallic fuel 33 are loaded.

[0055] Furthermore, it is desirable to load the radial light water reactor-origin metallic fuel 33 with nuclear fuel having a high ratio of impurity FP, i.e., a high amount of Sm-151 mixed in, as with the upper axial light water reactor-origin metallic fuel 35 and the lower axial light water reactor-origin metallic fuel 36. This increases the amount of nuclear transmutation of Sm-151, which is a long-lived FP (LLFP), and further enhances the effect of reducing the harmfulness.

[0056] A longitudinal cross section of the core is shown in Figure 7. As described above, the inner core fuel region is composed of radial fast reactor-origin metallic fuel 34, which uses nuclear fuel originating from spent fuel of a fast reactor, upper axial light water reactor-origin metallic fuel 35, and lower axial light water reactor-origin metallic fuel 36.

[0057] In addition, the outer core fuel region is composed of radial fast reactor-origin metallic fuel 34, which uses nuclear fuel originating from spent fuel of fast reactors, and radial light water reactor-origin metallic fuel 33, which uses only nuclear fuel originating from spent fuel of plutonium-thermal light water reactors.

[0058] The axial blanket fuel region is composed of upper axial light water reactor-origin metallic fuel 35 and lower axial light water reactor-origin metallic fuel 36, and is composed of an axial blanket fuel region surrounding the core fuel region and a reflector region surrounding that.

[0059] The metallic fuel fast reactor in this embodiment has an electric output of 311 MWe, a thermal output of 840 MW, and an average discharge burnup of the core fuel of about 100 GWd / t.

[0060] Based on previous research, the impurity FP contamination rate of the outer core fuel in this example, which uses nuclear fuel originating from a pluthermal light water reactor, is approximately 1.0 wt%. As mentioned above, the rate of Pu in the nuclear fuel (U, TRU) contained in the spent fuel (Pu / (U+TRU) x 100) is 16 wt% in the case of a metallic fuel fast reactor, and 3 wt% in the case of a pluthermal light water reactor.

[0061] When metallic fuel for fast reactors with the same Pu enrichment is produced by dry reprocessing using molten salt electrolysis, the proportion of impurity FP mixed into the fuel is 3 / 16 times higher if nuclear fuel originating from a fast reactor is used. Taking into account the difference in Pu enrichment, as shown in Table 2, which summarizes the impurity FP mixing rates for each core fuel region, the impurity FP mixed into the inner core fuel using nuclear fuel originating from a fast reactor is 0.15 wt%, and the impurity FP mixed into the outer core fuel with the same Pu enrichment is 0.19 wt%.

[0062] [Table 2]

[0063] As shown in Table 2 from Figure 2, the number of core fuel assemblies in each region is 58 for the inner core fuel, 50 for the outer core fuel using nuclear fuel originating from a fast reactor, and 42 for the outer core fuel using nuclear fuel originating from a pluthermal light water reactor, for a total of 150. Therefore, the weighted average contamination rate of the impurity FP in the core of the metallic fuel fast reactor of Example 1 is 0.40 wt%.

[0064] If all of the nuclear fuel in the core is recovered from dry reprocessing of spent fuel from plutonium-thermal light-water reactors, the average FP impurity contamination rate in the core is approximately 1.0 wt%, and in this case, the decrease in breeding ratio due to the contamination of FP impurities is -0.02. Therefore, when the average FP impurity contamination rate in the core is 0.40 wt%, the decrease in breeding ratio is -0.008, a smaller decrease. Furthermore, taking into account the differences in average neutron flux in each region, as shown in Table 2, the average FP impurity contamination rate in the core is 0.26 wt%, a 35% decrease, and the decrease in breeding ratio is accordingly further reduced.

[0065] From the above, in this embodiment, the core performance, represented by the breeding ratio, is improved compared to when all the nuclear fuel loaded into the core is spent fuel recovered by dry reprocessing from plutonium-thermal light water reactors.

[0066] As described above, the fast reactor core 1 of the first embodiment of the present invention is loaded with the radial fast reactor-origin metallic fuel 34 containing Pu recovered by reprocessing fast reactor spent fuel, and the radial light water reactor-origin metallic fuel 33 containing Pu recovered by reprocessing light water reactor spent fuel, and the radial light water reactor-origin metallic fuel 33 is loaded at a position adjacent to the radial blanket fuel assemblies 5 on the periphery of the fast reactor core 1, and the radial fast reactor-origin metallic fuel 34 is loaded at a position closer to the center of the fast reactor core 1 in the radial direction than the position where the radial light water reactor-origin metallic fuel 33 is loaded, thereby making it possible to further improve the core performance.

[0067] <Example 2> A fast reactor core and a design method for the fast reactor core according to a second embodiment of the present invention will be described with reference to Fig. 8 and Fig. 9. Fig. 8 is a half horizontal cross-sectional view of the fast reactor core according to the second embodiment, and Fig. 9 is a vertical cross-sectional view of the fast reactor according to the second embodiment.

[0068] The fast reactor core 1A of this embodiment is not loaded with the light water reactor-origin fuel assemblies 4 loaded with the light water reactor-origin metallic fuel rods 26 using the radial light water reactor-origin metallic fuel 33 in the fast reactor core 1 of Embodiment 1, and as shown in Figures 8 and 9, only upper axial light water reactor-origin metallic fuel 35 and lower axial light water reactor-origin metallic fuel 36 containing Pu recovered by reprocessing spent light water reactor fuel are loaded in positions adjacent to the upper axial blanket fuel 37 and lower axial blanket fuel 38 on the periphery of the fast reactor core 1A, and the radial fast reactor-origin metallic fuel 34 is loaded in a position closer to the center of the fast reactor core 1A in the axial direction than the positions where the upper axial light water reactor-origin metallic fuel 35 and the lower axial light water reactor-origin metallic fuel 36 are loaded.

[0069] The other configurations and operations are substantially the same as those of the fast reactor core and fast reactor core design method of the first embodiment described above, and the details are omitted here.

[0070] The fast reactor core and the design method of the fast reactor core according to the second embodiment of the present invention also provide substantially the same effects as those of the fast reactor core and the design method of the fast reactor core according to the first embodiment described above.

[0071] Example 3 A fast reactor core and a design method for a fast reactor core according to a third embodiment of the present invention will be described with reference to Fig. 10 and Fig. 11. Fig. 10 is a longitudinal sectional view of a core fuel assembly of the fast reactor according to the third embodiment, and Fig. 11 is a longitudinal sectional view of the fast reactor according to the third embodiment.

[0072] In the fast reactor core 1B of this embodiment, upper axial light water reactor-origin metallic fuel 35 and lower axial light water reactor-origin metallic fuel 36 are not used in the axial direction of the fast reactor-origin metallic fuel rods 23 loaded in the fast reactor-origin inner core fuel assembly 2 and the fast reactor-origin outer core fuel assembly 3 in the fast reactor core 1 of Example 1, and the fast reactor-origin metallic fuel rods 23B loaded in the fast reactor-origin inner core fuel assembly 2B and the fast reactor-origin outer core fuel assembly 3B have a fuel portion composed of one type of radial fast reactor-origin metallic fuel 34, and the only nuclear fuel used is that of fast reactor origin, and have upper axial blanket fuel 37 and lower axial blanket fuel 38.

[0073] That is, in the fast reactor core 1B, the radial metallic fuel 33 of light water reactor origin is loaded at a position adjacent to the radial blanket fuel assemblies 5 on the periphery of the fast reactor core 1B, and the radial metallic fuel 34 of fast reactor origin is loaded at a position closer to the center of the fast reactor core 1B in the radial direction than the position where the radial metallic fuel 33 of light water reactor origin is loaded.

[0074] The other configurations and operations are substantially the same as those of the fast reactor core and fast reactor core design method of the first embodiment described above, and the details are omitted here.

[0075] The fast reactor core and the design method of the fast reactor core according to the third embodiment of the present invention also provide substantially the same effects as those of the fast reactor core and the design method of the fast reactor core according to the first embodiment described above.

[0076] Example 4 A fast reactor core and a method for designing a fast reactor core according to a fourth embodiment of the present invention will be described.

[0077] The fast reactor core of this embodiment has the same configuration of the core fuel assemblies and the core as the fast reactor core 1 of the first embodiment, the fast reactor core 1A of the second embodiment, or the fast reactor core 1B of the third embodiment.

[0078] The difference from Examples 1 to 3 is that the reprocessing method for recovering nuclear fuel (U, TRU) from spent fuel of light water reactors and fast reactors is an advanced aqueous reprocessing method using nitric acid.

[0079] In the wet reprocessing method with low decontamination, the decontamination factor DF of the impurity FP is about one order of magnitude larger than that of the dry reprocessing method described in Example 1. In other words, DF = 100. In this case, the proportion of the impurity FP mixed into the fast reactor fuel is about one order of magnitude smaller, at 0.1 wt%. Therefore, compared to the case where the impurity FP is not mixed, the decrease in breeding ratio is -0.002, and the core performance is further improved.

[0080] The decrease in breeding ratio due to the mixing of impurities FP is reduced by about one order of magnitude, but in this embodiment as well, the nuclear fuel used in the inner core fuel assemblies and the fuel assemblies near the center of the outer core is spent fuel from fast reactors recovered through advanced aqueous reprocessing, and the nuclear fuel used in the fuel assemblies adjacent to the radial blanket of the outer core is spent fuel from plutonium-thermal light water reactors recovered through advanced aqueous reprocessing. As a result, the effect of being able to reduce the decrease in breeding ratio compared to when the nuclear fuel used in all core fuel assemblies is spent fuel from plutonium-thermal light water reactors recovered through advanced aqueous reprocessing is the same as in any of Embodiments 1 to 3.

[0081] The other configurations and operations are substantially the same as those of the fast reactor core and fast reactor core design method of any one of the first to third embodiments described above, and details thereof will be omitted.

[0082] The fast reactor core and the design method of the fast reactor core according to the fourth embodiment of the present invention also provide substantially the same effects as those of the fast reactor core and the design method of the fast reactor core according to any one of the first to third embodiments described above.

[0083] <Other> It should be noted that the present invention is not limited to the above-described embodiment, and includes various modifications. The above-described embodiment has been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to an embodiment having all of the described configurations.

[0084] It is also possible to replace 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, or to add, delete, or replace part of the configuration of each embodiment with the configuration of another embodiment.

[0085] For example, in the above examples, the reprocessing method was described as using a dry reprocessing method using molten salt electrolysis or an advanced wet reprocessing method, but similar effects can be obtained when using a reprocessing method with low decontamination other than the above.

[0086] Although the example has been given in which sodium is used as the coolant, the same effect can be achieved by using lead or lead-bismuth.

[0087] Furthermore, although metal fuel is used as the fuel, the same effect can be obtained with MOX fuel or nitride fuel.

[0088] Moreover, similar effects can be obtained for any combination of each of the above coolants and each of the above fuels. [Explanation of symbols]

[0089] 1, 1A, 1B...Fast reactor core 2, 2B... Inner core fuel assembly originating from a fast reactor 3,3B…Outer core fuel assembly originating from fast reactor 4... Fuel assemblies originating from light water reactors 5...Radial blanket fuel assembly (radial blanket) 6...Control rod assembly 7…Reflector aggregate 23,23B…Metal fuel rods derived from fast reactors 24...Sodium coolant 25...Bumblebee 26...Metal fuel rods originating from light water reactors 27...Bond sodium 28...Gas plenum 29...Upper end plug 30...Lower end plug 33...Radial light water reactor-origin metallic fuel (light water reactor-origin fuel) 34...Radial fast reactor origin metal fuel (fast reactor origin fuel) 35...Upper axial metal fuel of light water reactor origin (fuel of light water reactor origin) 36...Lower axial metal fuel of light water reactor origin (fuel of light water reactor origin) 37...Upper axial blanket fuel (axial blanket) 38...Lower axial blanket fuel (axial blanket) 51...Step 52...Solid cathode 53...Step 54...Liquid Cd cathode 55...Raw materials

Claims

1. A fast reactor core loaded with fast reactor-origin fuel containing Pu recovered by reprocessing fast reactor spent fuel, and light water reactor-origin fuel containing Pu recovered by reprocessing light water reactor spent fuel, the light water reactor-origin fuel is loaded adjacent to a radial blanket at the periphery of the fast reactor core; The fast reactor-origin fuel is loaded at a position closer to the center of the fast reactor core in the radial direction than the position at which the light water reactor-origin fuel is loaded. Fast reactor core.

2. A fast reactor core loaded with fast reactor-origin fuel containing Pu recovered by reprocessing fast reactor spent fuel, and light water reactor-origin fuel containing Pu recovered by reprocessing light water reactor spent fuel, the light water reactor-origin fuel is loaded adjacent to an axial blanket at the periphery of the fast reactor core; The fast reactor-origin fuel is loaded at a position closer to the center of the fast reactor core in the axial direction than the position at which the light water reactor-origin fuel is loaded. Fast reactor core.

3. 2. The fast reactor core according to claim 1, the light water reactor-origin fuel is loaded adjacent to an axial blanket at the periphery of the fast reactor core; The fast reactor-origin fuel is loaded at a position closer to the center of the fast reactor core in the axial direction than the position at which the light water reactor-origin fuel is loaded. Fast reactor core.

4. The fast reactor core according to claim 1 or 2, The reprocessing is a dry reprocessing method using molten salt electrolysis. Fast reactor core.

5. The fast reactor core according to claim 1 or 2, The reprocessing is an advanced aqueous reprocessing method. Fast reactor core.

6. A method for designing a fast reactor core loaded with fast reactor-origin fuel containing Pu recovered by reprocessing fast reactor spent fuel, and light water reactor-origin fuel containing Pu recovered by reprocessing light water reactor spent fuel, comprising: loading the light water reactor-origin fuel adjacent to a radial blanket at the periphery of the fast reactor core; The fast reactor-origin fuel is loaded at a position radially closer to the center of the fast reactor core than the position at which the light water reactor-origin fuel is loaded, or loading the light water reactor-origin fuel adjacent to an axial blanket at the periphery of the fast reactor core; The fast reactor-origin fuel is loaded at a position in the axial direction closer to the center of the fast reactor core than the position at which the light water reactor-origin fuel is loaded. Fast reactor core design methods.

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