Core of fast reactor capable of transmuting minor actinoid and method for nuclear transmutation of minor actinoid

Abstract

To provide a fast reactor core capable of improving nuclear transmutation amount of minor actinide (MA) while suppressing generation of Na void.SOLUTION: A core of a fast reactor capable of transmuting MA includes: a core fuel placed in a central area of the core; an upper axial blanket fuel placed in an upper axial blanket area on an upper side of the central area; a lower axial blanket fuel placed in a lower axial blanket area on a lower side of the central area; and a radial blanket fuel placed in a radial blanket area on an outer radial side of the central area. The MA content of the lower axial blanket fuel and the radial blanket fuel, which have no possibility of Na void formation, is greater than the MA content of the upper axial blanket fuel.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a core of a fast reactor capable of transmuting minor actinides and a method for transmuting minor actinides.

Background Art

[0002] In the reprocessing of spent nuclear fuel generated from a light water reactor or the like, U (uranium) and Pu (plutonium) are recovered from a solution of the spent nuclear fuel. In the highly active liquid waste (hereinafter also referred to as HALW) remaining after recovering U and Pu, in addition to fission products (hereinafter also referred to as FP), minor actinides (hereinafter also referred to as MA) such as Np (neptunium), Am (americium), and Cm (curium) are included. HALW is planned to be vitrified through a concentration process and disposed of in a geological formation.

[0003] Some of the MA have nuclides with a long half-life on the order of 10,000 years, which is a factor increasing the burden in the disposal of HALW. Therefore, nuclear transmutation technologies for separating MA from HALW and transmuting the separated MA into different elements using a fast reactor or an accelerator (ADS) have been studied. Patent Document 1 discloses a core in which a fuel containing transuranic elements (TRU) such as MA is heterogeneously arranged in a central region.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The MA content of the core fuel is generally up to about 5% by mass, and the MA content of the blanket fuel is generally up to about 30% by mass. This is because as the MA content rate increases, the neutron emission rate or heat generation density increases, so the need for measures such as neutron shielding or cooling increases, making manufacturing difficult. Furthermore, when the MA content increases, there is also a problem that voids in the liquid metal Na (sodium) coolant are likely to occur. Therefore, in conventional nuclear transmutation technologies, the amount of MA loaded into the core of a fast reactor cannot be increased much, and the annual MA transmutation amount is at most 0.006 - 0.02 t-MA / (GW·year). Assuming the reprocessing amount of the Rokkasho Reprocessing Plant (800 tHM / year), since the annual MA generation amount is about 1.0 t-MA / year, the MA transmutation by the fast reactor cannot catch up with the MA generation amount. This disclosure has been made to solve the above problems, and an object thereof is to provide a core of a fast reactor capable of transmuting MA and a method for transmuting MA that can improve the MA transmutation amount while suppressing the generation of Na voids.

Means for Solving the Problems

[0006] In order to solve the above problems, the core of a fast reactor capable of transmuting MA according to this disclosure includes core fuel arranged in the central region of the core, upper axial blanket fuel arranged in the upper axial blanket region above the central region, lower axial blanket fuel arranged in the lower axial blanket region below the central region, and radial blanket fuel arranged in the radial blanket region outside the radial direction of the central region. The core of the fast reactor is such that the MA content of each of the lower axial blanket fuel and the radial blanket fuel where there is no possibility of Na void generation is more than the MA content of the upper axial blanket fuel. In addition, the method for nuclear conversion of MA according to the present disclosure is a method for nuclear conversion of MA in the core of a fast reactor including core fuel disposed in the central region of the core, upper axial blanket fuel disposed in the upper axial blanket region above the central region, lower axial blanket fuel disposed in the lower axial blanket region below the central region, and radial blanket fuel disposed in the radial blanket region outside the radial direction of the central region. The method includes making the MA content of each of the lower axial blanket fuel and the radial blanket fuel, in which there is no possibility of Na void generation, greater than the MA content of the upper axial blanket fuel.

Advantages of the Invention

[0007] According to the core of the fast reactor capable of nuclear conversion of MA according to the present disclosure, it is possible to improve the MA nuclear conversion amount while suppressing the generation of Na voids. According to the method for nuclear conversion of MA according to the present disclosure, it is possible to improve the MA nuclear conversion amount while suppressing the generation of Na voids.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

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Figure 11

Embodiments for Carrying Out the Invention

[0009] In this specification, MA (minor actinide) is an element excluding Pu among the transuranic elements belonging to the actinide, and mainly indicates Np, Am, and Cm. In this specification, blanket fuel is a general term for radial blanket fuel, upper axial blanket fuel, lower axial blanket fuel, and internal blanket fuel. "~" indicating a numerical range means including the numerical values described before and after it as the lower limit value and the upper limit value. The scales of each part in the drawings may be different from the actual ones for convenience of explanation.

[0010] <First Embodiment> With reference to FIG. 1, an example of the configuration of a fast reactor equipped with the reactor core 1 in the first embodiment of the present disclosure will be described. As shown in the figure, the fast reactor 100 of this example includes a reactor core 1, a reactor vessel 2, a guard vessel 3, a coolant inlet pipe 4, a coolant outlet pipe 5, an upper reactor core mechanism 7, and a fixed plug 8.

[0011] The reactor core 1 is a heat source containing fissile material. The detailed configuration of the reactor core 1 will be described later. The reactor vessel 2 is a vessel that houses the reactor core 1. The reactor vessel 2 has a cylindrical shape with a bottom surface. The reactor core 1 is fixed at the lower part inside the reactor vessel 2 via the in-vessel structure 9. The upper opening of the reactor vessel 2 is covered by the fixed plug 8. The fixed plug 8 is supported by the structure of the reactor building (reactor vessel pedestal 6).

[0012] The guard vessel 3 covers the reactor vessel 2 from the outside. That is, the reactor vessel 2 and the guard vessel 3 form a double-wall structure. Thereby, even when the coolant leaks from the reactor vessel 2, the coolant is retained by the guard vessel 3, and leakage to the outside is suppressed.

[0013] The coolant inlet pipe 4 guides the coolant (primary coolant) led from the outside into the reactor vessel 2. In the present embodiment, the coolant is liquid metal Na. The end of the coolant inlet pipe 4 is located below the core 1 in the reactor vessel 2. Thereby, the inside of the reactor vessel 2 is filled with the coolant. The coolant outlet pipe 5 discharges the coolant in the reactor vessel 2 to the outside. The end of the coolant outlet pipe 5 is located above the core 1 in the reactor vessel 2.

[0014] The upper core structure 7 includes a control rod drive mechanism 71, a rotary plug 72, and a rotary plug drive device 73. The control rod drive mechanism 71 is a device for inserting and withdrawing control rods for controlling the progress of the nuclear fission reaction into and from the core 1 described later. The control rod drive mechanism 71 moves the control rod forward and backward in the vertical direction. The rotary plug 72 is a device for positioning equipment for replacing nuclear fuel (for example, a core fuel assembly 30 described later) in the core 1. The rotary plug 72 is driven by the rotary plug drive device 73.

[0015] Next, the configuration of the core 1 will be described with reference to FIGS. 2 to 3. As shown in FIGS. 2 to 3, the core 1 includes a core fuel 11, an upper axial blanket fuel 13, a lower axial blanket fuel 14, a radial blanket fuel 12, and a neutron shield 15.

[0016] The core fuel 11, the upper axial blanket fuel 13, the lower axial blanket fuel 14, the radial blanket fuel 12, and the neutron shield 15 are each housed in a hexagonal trumpet tube, treated as an assembly, and arranged in the accommodation parts provided in each region. The hexagons corresponding to the core fuel 11, the radial blanket fuel 12, and the neutron shield 15 shown in FIG. 2 each represent one assembly. In the following description, arranging in the accommodation parts provided in the regions is abbreviated as "arranging in the regions".

[0017] The core fuel 11 is arranged in the central region of the core 1. The core fuel 11 will be described in detail later. The central region is located at the center of the core 1. The central region has a hexagonal column shape. In plan view, the central region is composed of an inner region and an outer region located radially outside the inner region. The inner region has a hexagonal column shape coaxial with the central region. A plurality of control rods 16 can be inserted into a part of the inner region. By controlling the insertion amount of the control rods 16 between the core fuels 11, the nuclear fission of the core fuel 11 is controlled. The outer region surrounds the inner region without a gap. The outer region has an annular hexagonal shape in plan view. The core 1 according to this embodiment is a homogeneous core in which only the core fuel 11 and the control rods 16 are arranged in the central region.

[0018] The upper axial blanket fuel 13 is arranged in the upper axial blanket region above the central region (the upper side in FIG. 3). The upper axial blanket fuel 13 will be described in detail later. The upper axial blanket region covers the upper side of the central region. The thickness of the upper axial blanket region is, for example, 20 to 30 cm. Note that the thickness of the upper axial blanket region means the width in the vertical direction. The vertical direction is the axial direction of the core.

[0019] The lower axial blanket fuel 14 is disposed in the lower axial blanket region on the lower side of the central region (the lower side in FIG. 3). The lower axial blanket fuel 14 will be described in detail later. The lower axial blanket region covers the lower side of the central region. The thickness of the lower axial blanket region is, for example, 20 to 30 cm. Note that the thickness of the lower axial blanket region means the width in the vertical direction.

[0020] The thickness of the lower axial blanket region may be the same as or different from the thickness of the upper axial blanket region, but it is preferably thicker than the thickness of the upper axial blanket region. Although details will be described later, the MA content of the lower axial blanket fuel 14 is higher than the MA content of the upper axial blanket fuel 13. Therefore, by making the thickness of the lower axial blanket region thicker than the thickness of the upper axial blanket region, the amount of MA loaded into the core 1 can be increased, and the MA nuclear conversion amount is further improved.

[0021] The radial blanket fuel 12 is disposed in the radial blanket region on the outer side in the radial direction of the central region. The radial blanket fuel 12 will be described in detail later. The radial blanket region surrounds the outer side in the radial direction of the central region, the outer side in the radial direction of the upper axial blanket region, and the outer side in the radial direction of the lower axial blanket region over the entire circumference. The radial blanket region forms a hexagonal annular shape in plan view. The thickness of the radial blanket region is, for example, 20 to 30 cm. Note that the thickness of the radial blanket region means the width in the radial direction. A neutron source may be disposed at a position adjacent to the central region of the radial blanket region.

[0022] The neutron shield 15 is disposed in the shield regions on the outer side in the radial direction of the radial blanket region, on the upper side of the upper axial blanket region, and on the lower side of the lower axial blanket region, respectively. The shielding body region on the radially outer side of the radial blanket region (hereinafter also referred to as the radial shielding body region) surrounds the radially outer side of the radial blanket region over the entire circumference. The radial shielding body region forms an annular shape with a hexagonal shape in plan view. The shielding body region above the upper shaft blanket region (hereinafter also referred to as the upper shaft shielding body region) covers the upper side of the upper shaft blanket region and the upper side of the radial blanket region. The shielding body region below the lower shaft blanket region (hereinafter also referred to as the lower shaft shielding body region) covers the lower side of the lower shaft blanket region and the lower side of the radial blanket region. The neutron shielding body 15 may be a known neutron shielding body. The neutron shielding body 15 contains, for example, iron or a hydrogen material.

[0023] During the operation of the core 1, the core fuel 11 generates heat by causing a nuclear fission material to undergo nuclear fission using neutrons generated from itself or neutrons generated from an arbitrarily arranged neutron source as a trigger. The insertion amount of the control rod 16 is adjusted to control the progress of this nuclear fission reaction. In blanket fuels such as the upper shaft blanket fuel 13, the lower shaft blanket fuel 14, and the radial blanket fuel 12, the reaction proceeds in a state where the fast nuclear fission reaction is reduced compared to the core fuel 11. Also, in the blanket fuel, the amount of nuclear fission material generated by the nuclear fission reaction is larger than that of the core fuel 11. The neutron shielding body 15 shields neutrons and suppresses the leakage of neutrons outside the core 1.

[0024] Subsequently, with reference to FIG. 4, the configuration of the assembly will be described in detail. FIG. 4 is an example of an assembly (hereinafter also referred to as a core fuel assembly) arranged in the central region in plan view. As shown in the figure, the core fuel assembly 30 has a trumpet tube 31, an entrance nozzle 32, a handling head 33, and a plurality of core fuel elements 40.

[0025] The trumpet tube 31 has a cylindrical shape centered on an axis Ac extending in the vertical direction. Further, the trumpet tube 31 has a hexagonal cross-sectional shape when viewed from the direction of the axis Ac. The lower opening of the trumpet tube 31 is closed by an entrance nozzle 32. Inside the entrance nozzle 32, a flow path (not shown) for guiding the coolant into the trumpet tube 31 is formed. The entrance nozzle 32 is formed with an opening for communicating this flow path with the outside. A handling head 33 is attached to the upper opening of the trumpet tube 31. The handling head 33 is a portion that is gripped by a device when transporting the core fuel assembly 30. Inside the trumpet tube 31, directly above the entrance nozzle 32, a plurality of core fuel elements 40 are arranged at intervals in a direction perpendicular to the axis Ac. The coolant guided from the opening of the entrance nozzle 32 circulates in the space around and above the core fuel element 40.

[0026] Referring to FIG. 5, the configuration of the core fuel element 40 will be described. As shown in the figure, the core fuel element 40 includes a cylindrical cladding tube 41 extending in the vertical direction, a plenum spring 43, core fuel 11, upper axial blanket fuel 13, and lower axial blanket fuel 14 accommodated inside the cladding tube 41, and upper end plugs 48 and lower end plugs 49 provided at both ends of the cladding tube 41.

[0027] The core fuel 11, upper axial blanket fuel 13, and lower axial blanket fuel 14 are each formed into cylindrical pellet shapes. A plurality of lower axial blanket fuels 14, a plurality of core fuels 11, and a plurality of upper axial blanket fuels 13 are filled in this order so as to be stacked from below the cladding tube 41. The uppermost upper axial blanket fuel 13 is pressed downward by the plenum spring 43. The plurality of core fuels 11 are located in the central region when the core fuel assembly 30 is arranged in the central region. The plurality of upper axial blanket fuels 13 are located in the upper axial blanket region when the core fuel assembly 30 is arranged in the central region. The plurality of lower axial blanket fuels 14 are located in the lower axial blanket region when the core fuel assembly 30 is arranged in the central region.

[0028] An assembly arranged in the radial blanket region in plan view (hereinafter, also referred to as a radial blanket fuel assembly) is the same as the core fuel assembly 30 except that the radial blanket fuel 12 is accommodated instead of the core fuel 11, the upper axial blanket fuel 13, and the lower axial blanket fuel 14.

[0029] <Blanket Fuel> The blanket fuel is a fuel with a lower content of fissile material (e.g., Pu) compared to the core fuel. The blanket fuel typically contains U. When the U in the blanket fuel absorbs neutrons generated from the core fuel, U-238 in the U is converted to Pu-239, becoming new fuel.

[0030] In the present embodiment, the blanket fuel includes the upper axial blanket fuel 13, the lower axial blanket fuel 14, and the radial blanket fuel 12. At least the lower axial blanket fuel 14 and the radial blanket fuel 12 contain MA, and the MA content of each of the lower axial blanket fuel 14 and the radial blanket fuel 12 is higher than the MA content of the upper axial blanket fuel 13. Since the upper axial blanket region located above the core fuel 11 is a place where void generation is likely, when the MA content of the upper axial blanket fuel 13 increases, Na voids are likely to occur. On the other hand, since the lower axial blanket region and the radial blanket region not located above the core fuel 11 are places where void generation is impossible, even if the MA content of the lower axial blanket fuel 14 or the radial blanket fuel 12 is increased, Na voids do not occur. The upper axial blanket fuel 13 may or may not contain MA. However, from the perspective of increasing the MA loading amount into the core and further improving the MA nuclear conversion amount, it is preferable to contain MA.

[0031] The blanket fuel can further contain other elements other than those described above. Examples of other elements include lanthanoids (hereinafter also referred to as Ln). Ln is a general term for elements with atomic numbers from 57 to 71. Ln is likely to be accompanied by MA when separating MA from high-level radioactive liquid waste (hereinafter also referred to as HALW), which is a waste liquid obtained by separating U and P from a solution of spent nuclear fuel, and it is assumed that the accompanying amount is up to about 0.1 times that of MA.

[0032] The blanket fuel preferably does not contain moderators such as H, Be, and C. Conventionally, adding a moderator to the target has been considered. However, around a MA content of 30 mass%, even if a moderator is added, the nuclear conversion efficiency (disappearance rate) of MA does not change significantly. Also, when the blanket fuel contains a moderator, during the reprocessing of the spent blanket fuel after MA nuclear conversion, there are effects such as an increase in the amount of hydrogen gas generated. By the blanket fuel not containing a moderator, the impact on the reprocessing side after MA nuclear conversion can be mitigated.

[0033] Examples of the composition of the upper axial blanket fuel 13 include the following composition. However, the MA content of the upper axial blanket fuel 13 is less than the MA content of each of the lower axial blanket fuel 14 and the radial blanket fuel 12. U content: 70 - 90 mass%, MA content: 10 - 30 mass%, Ln content: 0 - 3 mass%. Here, the total of U and MA does not exceed 100 mass%. The content of each component is the ratio to the total mass of the upper axial blanket fuel 13 arranged in the upper axial blanket region. The upper axial blanket fuel 13 may further contain other components as needed.

[0034] The compositions of the plurality of upper axial blanket fuels 13 in the upper axial blanket region may be the same or different from each other. For example, some of the plurality of upper axial blanket fuels 13 arranged in the upper axial blanket region may contain MA, and some may not contain MA. From the viewpoint of increasing the MA loading amount into the core and further improving the MA conversion amount, it is preferable that each of the plurality of upper axial blanket fuels 13 in the upper axial blanket region contains MA, and it is also preferable that each MA content is not less than the lower limit value of the above range. From the viewpoint of suppressing the generation of Na voids, it is preferable that the MA content of each of the plurality of lower axial blanket fuels 14 in the lower axial blanket region is not more than the upper limit value of the above range.

[0035] Examples of the composition of the lower axial blanket fuel 14 include the following compositions. U content: 70 - 90 mass%, MA content: 10 - 30 mass%, Ln content: 0 - 3 mass%. Here, the total of U and MA does not exceed 100 mass%. The content of each component is the ratio with respect to the total mass of the lower axial blanket fuel 14 arranged in the lower axial blanket region. The lower axial blanket fuel 14 may further contain other components as necessary.

[0036] The compositions of the plurality of lower axial blanket fuels 14 in the lower axial blanket region may be the same or different from each other. For example, some of the plurality of lower axial blanket fuels 14 arranged in the lower axial blanket region may contain MA, and some may not contain MA. From the viewpoint of increasing the MA loading amount into the core and further improving the MA conversion amount, it is preferable that each of the plurality of lower axial blanket fuels 14 in the lower axial blanket region contains MA, and it is also preferable that each MA content is not less than the lower limit value of the above range. From the viewpoint of ease of manufacturing blanket fuel, it is preferable that the MA content of each of the plurality of lower axial blanket fuels 14 in the lower axial blanket region is not more than the upper limit value of the above range.

[0037] Examples of the composition of the radial blanket fuel 12 include the following compositions. U content: 70 to 90 mass%, MA content: 10 to 30 mass%, Ln content: 0 to 3 mass%. Here, the total of U, MA, and Ln does not exceed 100 mass%. The content of each component is the ratio with respect to the total mass of the radial blanket fuel 12 arranged in the radial blanket region. The radial blanket fuel 12 may further contain other components as necessary.

[0038] The compositions of the plurality of radial blanket fuels 12 in the radial blanket region may be the same or different. For example, the MA contents of the plurality of radial blanket fuels 12 may be the same or different. Some of the plurality of radial blanket fuels 12 arranged in the radial blanket region may contain MA, and some may not contain MA. From the viewpoint of increasing the MA loading amount into the core and further improving the MA conversion amount, it is preferable that each of the plurality of radial blanket fuels 12 in the radial blanket region contains MA, and it is also preferable that the MA content of each is not less than the lower limit value of the above range. From the viewpoint of ease of manufacturing blanket fuel, it is preferable that the MA content of each of the plurality of radial blanket fuels 12 in the radial blanket region is not more than the upper limit value of the above range.

[0039] As a method for manufacturing blanket fuel (such as radial blanket fuel 12, upper axial blanket fuel 13, lower axial blanket fuel 14, etc.), known methods can be used. For example, a method of producing a fuel for a fast reactor by denitration, conversion, and sintering treatment from a solution containing MA and U, and shaping it into an arbitrary shape such as a pellet as necessary can be mentioned. A solution containing MA and U can be obtained, for example, by adding U to a radioactive composition containing MA. The radioactive composition containing MA may contain Ln or the like.

[0040] The radioactive composition containing MA can be obtained, for example, by separating MA from HALW (MA separation) and purifying the separated MA (MA purification). In general, since Ln is entrained with MA in MA separation, MA and Ln are separated in MA purification. MA separation can be carried out by known methods. For example, a method including a process of extracting MA from HALW together with Ln by a solvent extraction method (hereinafter also referred to as an extraction process), or a method including a process of adsorbing MA and Ln in HALW to an adsorbent and eluting the MA and Ln adsorbed to the adsorbent can be mentioned. The method including the extraction process may further include a process of back-extracting MA and Ln from the extract obtained by the extraction process after the extraction process. MA purification can be carried out by known methods. For example, a solvent extraction method and an extraction chromatography method using an extractant such as COMPO or TODGA can be mentioned.

[0041] Before manufacturing the blanket fuel, a solution containing MA and U or a radioactive composition containing MA may be stored in advance to attenuate the highly exothermic MA contained in the solution or radioactive composition. Examples of the highly exothermic MA include Cm-242 (half-life of about 163 days) and Cm-244 (half-life of about 18 years). The solution or radioactive composition may be stored in a liquid state, or may be solidified and stored in the form of a solid. In terms of a small storage load, it is preferable to store it in the form of a solid. Examples of the solidification treatment include a decomposition treatment, a hydrothermal treatment, and a glass solidification treatment. The solid is dissolved in a nitric acid aqueous solution or the like after storage and used for manufacturing the blanket fuel. As the storage method, a known method as a storage method for radioactive waste can be used. For example, a method of storing a plurality of canisters containing the solidified body in a cask and storing them in a storage facility can be mentioned. The storage period can be appropriately set according to the nuclide to be decayed.

[0042] <Core fuel> The core fuel 11 is typically MOX fuel and contains a mixed oxide of U and Pu. The core fuel 11 can further contain MA. From the viewpoint of increasing the MA loading amount into the core and further improving the MA conversion amount, it is preferable that the core fuel 11 contains MA. The core fuel 11 can further contain other components other than those described above. Examples of other components include Ln.

[0043] Examples of the composition of the core fuel 11 include the following compositions. U content: 65 - 75 mass%, Pu content: 20 - 30 mass%, MA content: 1 - 3 mass% Ln content: 0 - 0.3 mass%. Here, the total of U, Pu, MA, and Ln does not exceed 100 mass%. The content of each element is the ratio to the total mass of the core fuel arranged in the central region of the core. The core fuel 11 may further contain other components as necessary.

[0044] The compositions of the plurality of core fuels 11 in the central region may be the same or different. Typically, the core fuel 11 includes the core fuel arranged in the inner region of the central region (hereinafter also referred to as the inner core fuel) and the core fuel arranged in the outer region of the central region (hereinafter also referred to as the outer core fuel). Usually, the outer core fuel has a higher content rate of fissile materials (e.g., Pu) than the inner core fuel. Some of the plurality of core fuels 11 arranged in the central region may not contain MA.

[0045] As shown in FIG. 6, the central region may be divided into an upper part and a lower part, and the MA content of the core fuel 11b in the lower part may be made higher than the MA content of the core fuel 11a in the upper part. The core fuel 11a in the upper part may or may not contain MA. As shown in FIG. 7, the central region may be divided into an upper part, a lower part, and an intermediate part therebetween, the MA content of the core fuel 11b in the lower part may be made higher than the MA content of the core fuel 11c in the intermediate part, and the MA content of the core fuel 11c in the intermediate part may be made higher than the MA content of the core fuel 11a in the upper part. The core fuel 11a in the upper part may or may not contain MA. The closer to the lower end of the central region, the lower the tendency of void generation. As described above, by providing a gradient in the MA content in the central region, it is possible to suppress the generation of Na voids in the central region, increase the MA loading amount, and further improve the MA transmutation amount.

[0046] As a method for manufacturing the core fuel 11, a known method can be used in the same manner as the method for manufacturing the blanket fuel.

[0047] (MA transmutation) The core fuel 11, the radial blanket fuel 12, the upper axial blanket fuel 13, the lower axial blanket fuel 14, and the neutron shield 15 are arranged in a predetermined region of the core of the fast reactor to form the core 1 (homogeneous core), and by operating the fast reactor for an arbitrary period, the transmutation of MA contained in each fuel is performed.

[0048] After the MA transmutation, the operation of the fast reactor may be stopped, and the fuel after the MA transmutation (core fuel 11, radial blanket fuel 12, upper axial blanket fuel 13, lower axial blanket fuel 14, etc. Hereinafter, also referred to as "spent fuel") may be taken out from the core 1. At this time, the neutron shield 15 may be taken out together with the spent fuel.

[0049] After taking out the spent fuel from the core 1, the spent fuel may be reprocessed. In the reprocessing of blanket fuel, the mutual separation of MA and Pu can be carried out. The mutual separation of MA and Pu can be implemented by a known method such as a solvent extraction method.

[0050] (Function and effect) In the core with the above configuration, since the MA content of each of the lower axial blanket fuel 14 and the radial blanket fuel 12 is made higher than the MA content of the upper axial blanket fuel 13, while suppressing the generation of Na voids, the MA loading amount into the core of the fast reactor can be increased, and the MA nuclear conversion amount can be improved more than before.

[0051] <Second Embodiment> Referring to FIGS. 8 to 9, the core 1A in the second embodiment will be described. As shown in FIGS. 8 to 9, the core 1A is the same as the core 1 in the first embodiment except that it further includes an internal blanket fuel 17.

[0052] The internal blanket fuel 17 is arranged in the central region of the core 1A. In the present embodiment, the internal blanket fuel 17 is arranged between a plurality of core fuels 11 in the vertical direction in the inner region of the central region. The inner region has a structure in which a layer of the core fuel 11, a layer of the internal blanket fuel 17, and a layer of the core fuel 11 are stacked in this order from the bottom. The core 1A of the present embodiment is an axially heterogeneous core in which the core fuel 11 and the internal blanket fuel 17 are arranged in layers in the axial direction of the central region. In the present embodiment, a part of the core fuel 11 accommodated in the core fuel assembly 30 is replaced with the internal blanket fuel 17.

[0053] The internal blanket fuel 17 may or may not contain MA, but from the viewpoint of increasing the MA loading amount into the core and further improving the MA nuclear conversion amount, it is preferable to contain MA.

[0054] Examples of the composition of the internal blanket fuel include the following compositions. U content: 70 - 90 mass%, MA content: 10 - 30 mass%, Ln content: 0 - 3 mass%. Here, the total of U, MA, and Ln does not exceed 100 mass%. The ratio of each component is the ratio with respect to the total mass of the internal blanket fuel 17 disposed in the central region. The internal blanket fuel 17 may further contain other components as required.

[0055] The compositions of the plurality of internal blanket fuels 17 in the central region may be the same or different. For example, the MA contents of the plurality of internal blanket fuels 17 may be the same or different. Some of the plurality of internal blanket fuels 17 disposed in the central region may contain MA and some may not contain MA.

[0056] (MA conversion) The MA conversion in the second embodiment can be carried out in the same manner as the MA conversion in the first embodiment, except that, as fuel, in addition to the core fuel 11, the upper axial blanket fuel 13, the lower axial blanket fuel 14, and the radial blanket fuel 12, the internal blanket fuel 17 is loaded into the core of the fast reactor.

[0057] After the MA conversion, the operation of the fast reactor may be stopped, and the spent fuel may be removed from the core 1A. At this time, the neutron shield 15 may be removed together with the spent fuel. After removing the spent fuel, reprocessing of the spent fuel may be performed.

[0058] (Function and effect) In the core configured as described above, since the MA content of each of the lower axial blanket fuel 14 and the radial blanket fuel 12 is made higher than the MA content of the upper axial blanket fuel 13, while suppressing the generation of Na voids, the MA loading amount into the core of the fast reactor can be increased, and the MA conversion amount can be improved compared to the conventional case. Also, in this embodiment, by also including MA in the internal blanket fuel 17, the MA loading amount can be further increased compared to the first embodiment.

[0059] <Third Embodiment> Referring to FIGS. 10 to 11, the core 1B in the third embodiment will be described. As shown in FIGS. 10 to 11, the core 1B is the same as the core 1A in the second embodiment, except that the arrangement of the internal blanket fuel 17 is different and the inner core fuel 11A is arranged as the core fuel 11 in the outer region of the central region. Note that the outer core fuel 11B may be arranged in the outer region.

[0060] The internal blanket fuel 17 is arranged in the central region of the core 1B. In the present embodiment, the internal blanket fuel 17 is arranged between a plurality of core fuels 11 in the radial direction of the central region. More specifically, the internal blanket fuel 17 is arranged at the center of the inner region in a plan view, and is arranged in an annular shape by connecting a plurality of control rods 16 surrounding it, and is also dispersedly arranged at a plurality of locations in the outer region. The internal blanket fuel 17 is arranged over the entire axial direction of the central region. The core 1B of the present embodiment is a radially heterogeneous core in which the core fuel 11 and the internal blanket fuel 17 are mixed in the radial direction of the central region. In the present embodiment, a part of the core fuel assembly 30 is replaced with an assembly (internal blanket fuel assembly) that houses the internal blanket fuel 17 instead of the core fuel 11.

[0061] The compositions of the plurality of internal blanket fuels 17 within the central region may be the same or different. For example, the MA content of each of the plurality of internal blanket fuels 17 may be the same or different. Some of the plurality of internal blanket fuels 17 arranged in the central region may contain MA and some may not contain MA. As shown in FIGS. 6 and 7, the central region may be divided into two or three parts in the vertical direction, and a gradient may be provided in the MA content of the internal blanket fuel 17. When the central region is divided into two or three parts in the vertical direction, the preferable range of the MA content in the upper part of the central region is the same as the preferable range of the MA content in the upper axial blanket fuel, and the preferable range of the MA content in the lower part of the central region is the same as the preferable range of the MA content in the lower axial blanket fuel.

[0062] (MA nuclear conversion) In the third embodiment, the MA nuclear conversion can be carried out in the same manner as in the first embodiment, except that, as fuel, in addition to the core fuel 11, the upper axial blanket fuel 13, the lower axial blanket fuel 14, and the radial blanket fuel 12, the internal blanket fuel 17 is loaded into the core of the fast reactor.

[0063] After the MA nuclear conversion, the operation of the fast reactor may be stopped, and the spent fuel may be taken out from the core 1A. At this time, the neutron shield 15 may be taken out together with the spent fuel. After taking out the spent fuel, reprocessing of the spent fuel may be performed.

[0064] (Function and effect) In the core with the above configuration, since the MA content of each of the lower axial blanket fuel 14 and the radial blanket fuel 12 is made higher than the MA content of the upper axial blanket fuel 13, while suppressing the generation of Na voids, the MA loading amount into the core of the fast reactor can be increased, and the MA conversion amount can be improved compared to the conventional case. Further, in the present embodiment, by also including MA in the internal blanket fuel 17, the MA loading amount can be further increased compared to the first embodiment. Furthermore, in the present embodiment, since the core fuel 11 and the internal blanket fuel 17 are mixed in the radial direction of the central region, the inner core fuel 11A with a relatively low content rate of fissile material can also be arranged in the outer region of the central region. Thereby, the MA conversion amount can be improved by utilizing high-energy neutrons from the core fuel.

[0065] <Other Embodiments> As described above, the embodiments of the present disclosure have been explained. However, each configuration and their combinations in the above embodiments are examples, and additions, omissions, substitutions, and other changes of the configuration are possible without departing from the gist of the present disclosure.

[0066] When performing MA conversion, the configuration of the core may be changed according to the supply-demand balance of fissile materials such as Pu. For example, when the demand for Pu increases, the supply amount of Pu can be increased by loading a blanket fuel composed of U that does not contain MA.

[0067] Examples of changing the core configuration to perform MA conversion are shown below. For example, first, a step S1-1 of arranging the core fuel 11, the upper axial blanket fuel 13, the lower axial blanket fuel 14, the radial blanket fuel 12, and the neutron shield 15 in a predetermined region of the core of the fast reactor to form a core 1 (homogeneous core) and operating the fast reactor for an arbitrary period to perform MA conversion is performed. After step S1-1, a step S1-2 of stopping the operation of the fast reactor and removing the core fuel 11, the upper axial blanket fuel 13, the lower axial blanket fuel 14, the radial blanket fuel 12, and the neutron shield 15 from the core 1 is performed. After step S1-2, core fuel 11, internal blanket fuel 17, upper axial blanket fuel 13, lower axial blanket fuel 14, radial blanket fuel 12, and neutron shield 15 are arranged in a predetermined region of the core of the fast reactor to form core 1A (an axially heterogeneous core), and step S1-3 of operating the fast reactor for an arbitrary period is performed. After step S1-3, the operation of the fast reactor may be stopped, and step S1-4 of removing core fuel 11, internal blanket fuel 17, upper axial blanket fuel 13, lower axial blanket fuel 14, radial blanket fuel 12, and neutron shield 15 from core 1A may be performed. After step S1-4, step S1-1 or step S1-3 may be performed again, or core fuel 11, internal blanket fuel 17, upper axial blanket fuel 13, lower axial blanket fuel 14, radial blanket fuel 12, and neutron shield 15 may be arranged in a predetermined region of the core of the fast reactor to form core 1B (a radially heterogeneous core), and step S1-5 of operating the fast reactor for an arbitrary period may be performed. Further, step S1-6 of reprocessing the fuel (spent fuel) removed in step S1-2 or the like may be performed.

[0068] <Supplementary Note> The core of the MA-convertible fast reactor and the MA conversion method described in each embodiment are understood as follows, for example. (1) The core of the MA-convertible fast reactor according to the first aspect includes core fuel arranged in the central region of the core, upper axial blanket fuel arranged in the upper axial blanket region above the central region, lower axial blanket fuel arranged in the lower axial blanket region below the central region, and radial blanket fuel arranged in the radial blanket region outside the radial direction of the central region. In the core of the fast reactor, the MA content of each of the lower axial blanket fuel and the radial blanket fuel with no possibility of Na void generation is greater than the MA content of the upper axial blanket fuel. According to the above configuration, while suppressing the generation of Na voids, the loading amount of MA into the core of the fast reactor can be increased, and the MA conversion amount can be improved more than before. For example, the annual MA conversion amount can be set to about 0.1 to 0.15 t-MA / (GW·year).

[0069] (2) The core of the fast reactor capable of converting MA according to the second aspect is the core of the fast reactor in (1), wherein the central region is divided into two parts, upper and lower, and the MA content of the core fuel in the lower part is higher than the MA content of the core fuel in the upper part. According to the above configuration, while suppressing the generation of Na voids in the central region, the loading amount of MA into the core of the fast reactor can be further increased, and the MA conversion amount can be further improved.

[0070] (3) The core of the fast reactor capable of converting MA according to the third aspect is the core of the fast reactor in (1), wherein the central region is divided into three parts, upper, lower, and an intermediate part therebetween, and the MA content of the core fuel in the lower part is higher than the MA content of the core fuel in the intermediate part, and the MA content of the core fuel in the intermediate part is higher than the MA content of the core fuel in the upper part. According to the above configuration, while suppressing the generation of Na voids in the central region, the loading amount of MA into the core of the fast reactor can be further increased, and the MA conversion amount can be further improved.

[0071] (4) The core of the fast reactor capable of converting MA according to the fourth aspect is the core of any one of the fast reactors in (1) to (3), and further includes internal blanket fuel disposed in the central region, and the internal blanket fuel contains MA. According to the above configuration, the loading amount of MA into the core of the fast reactor can be further increased, and the MA conversion amount can be further improved. Also, by disposing the internal blanket fuel in the central region, the contact area between the core fuel and the blanket fuel can be increased, and the MA conversion efficiency can be further improved.

[0072] (5) The core of the fast reactor capable of transmuting MA according to the fifth aspect is the core of any one of the fast reactors of (1) to (4), and the thickness of the lower axial blanket region is thicker than the thickness of the upper axial blanket region. According to the above configuration, it is possible to increase the loading amount of the lower axial blanket fuel having a higher MA content than the upper axial blanket fuel, and it is possible to further improve the amount of MA transmutation.

[0073] (6) The method for transmuting MA according to the sixth aspect is a method for transmuting MA in the core of a fast reactor including core fuel disposed in the central region of the core, upper axial blanket fuel disposed in the upper axial blanket region above the central region, lower axial blanket fuel disposed in the lower axial blanket region below the central region, and radial blanket fuel disposed in the radial blanket region outside the radial direction of the central region, wherein the MA content of each of the lower axial blanket fuel and the radial blanket fuel is made higher than the minor actinide content of the upper axial blanket fuel. According to the above configuration, while suppressing the generation of Na voids, it is possible to increase the MA loading amount into the core of the fast reactor and improve the MA transmutation amount more than before. For example, the annual MA transmutation amount can be set to about 0.1 to 0.15 t-MA / (GW·year).

[0074] (7) The method for transmuting MA according to the seventh aspect is the method for transmuting MA of (6), wherein the central region is divided into upper and lower parts, and the MA content of the core fuel in the lower part is made higher than the MA content of the core fuel in the upper part. According to the above configuration, while suppressing the generation of Na voids in the central region, it is possible to further increase the MA loading amount into the core of the fast reactor and improve the MA transmutation amount more.

[0075] (8) The method for nuclear conversion of MA according to the eighth aspect is the method for nuclear conversion of MA in (6), wherein the central region is divided into an upper part, a lower part, and an intermediate part therebetween, the MA content of the core fuel in the lower part is made higher than the MA content of the core fuel in the intermediate part, and the MA content of the core fuel in the intermediate part is made higher than the MA content of the core fuel in the upper part. According to the above configuration, while suppressing the generation of Na voids in the central region, the MA loading amount into the core of the fast reactor can be further increased, and the MA nuclear conversion amount can be further improved.

[0076] (9) The method for nuclear conversion of MA according to the ninth aspect is the method for nuclear conversion of MA in any one of (6) to (8), wherein the core further includes an internal blanket fuel disposed in the central region, and the internal blanket fuel contains MA. According to the above configuration, the MA loading amount into the core of the fast reactor can be further increased, and the MA nuclear conversion amount can be further improved. Also, by disposing the internal blanket fuel in the central region, the contact area between the core fuel and the blanket fuel can be increased, and the MA nuclear conversion efficiency can be further improved.

[0077] (10) The method for nuclear conversion of MA according to the tenth aspect is the method for nuclear conversion of MA in any one of (6) to (9), wherein the thickness of the lower axial blanket region is made thicker than the thickness of the upper axial blanket region. According to the above configuration, the loading amount of the lower axial blanket fuel having a higher MA content than the upper axial blanket fuel can be increased, and the MA nuclear conversion amount can be further improved.

Explanation of symbols

[0078] 100 Fast reactor 1 Core 2 Reactor vessel 3 Guard vessel 4 Coolant inlet pipe 5 Coolant outlet pipe 6 Reactor vessel pedestal 7 Upper core mechanism 8 Fixed plug 9 In-vessel structures 11 Core fuel 11A Inner core fuel 11B Outer core fuel 12 Radial blanket fuel 13 Upper axial blanket fuel 14 Lower axial blanket fuel 15 Neutron shield 16 Control rod 17 Inner blanket fuel 30 Core fuel assembly 31 Trumpet tube 32 Entrance nozzle 33 Handling head 40 Core fuel element 41 Cladding tube 43 Plenum spring 48 Upper end plug 49 Lower end plug 71 Control rod drive mechanism 72 Rotating plug 73 Rotating plug drive device Ac axis

Claims

1. Core fuel disposed in the central region of the core, Upper axial blanket fuel disposed in the upper axial blanket region above the central region, Lower axial blanket fuel disposed in the lower axial blanket region below the central region, Radial blanket fuel disposed in the radial blanket region outside the radial direction of the central region, A core of a fast reactor comprising: The minor actinide content of each of the lower axial blanket fuel and the radial blanket fuel with no possibility of Na void generation is greater than the minor actinide content of the upper axial blanket fuel, A core of a fast reactor capable of nuclear conversion of minor actinides.

2. The central region is divided into upper and lower parts, and the minor actinide content of the core fuel in the lower part is greater than the minor actinide content of the core fuel in the upper part. The core of the fast reactor according to claim 1.

3. The central region is divided into upper, lower, and middle parts therebetween, and the minor actinide content of the core fuel in the lower part is greater than the minor actinide content of the core fuel in the middle part, and the minor actinide content of the core fuel in the middle part is greater than the minor actinide content of the core fuel in the upper part. The core of the fast reactor according to claim 1.

4. Further comprising internal blanket fuel disposed in the central region, The internal blanket fuel contains minor actinides. The core of the fast reactor according to claim 1.

5. The thickness of the lower axial blanket region is greater than the thickness of the upper axial blanket region. The core of the fast reactor according to claim 1.

6. Core fuel disposed in the central region of the core, Upper axial blanket fuel disposed in the upper axial blanket region above the central region, Lower axial blanket fuel disposed in the lower axial blanket region below the central region, Radial blanket fuel disposed in the radial blanket region outside the radial direction of the central region, A method for nuclear conversion of minor actinides in a core of a fast reactor comprising: Increasing the minor actinide content of each of the lower axial blanket fuel and the radial blanket fuel with no possibility of Na void generation to be greater than the minor actinide content of the upper axial blanket fuel, A method for nuclear conversion of minor actinides.

7. The method for nuclear conversion of minor actinides according to claim 6, wherein the central region is divided into an upper part and a lower part, and the minor actinide content of the core fuel in the lower part is made higher than the minor actinide content of the core fuel in the upper part.

8. The method for nuclear conversion of minor actinides according to claim 6, wherein the central region is divided into an upper part, a lower part, and an intermediate part therebetween, the minor actinide content of the core fuel in the lower part is made higher than the minor actinide content of the core fuel in the intermediate part, and the minor actinide content of the core fuel in the intermediate part is made higher than the minor actinide content of the core fuel in the upper part.

9. The core further includes an internal blanket fuel disposed in the central region. The method for nuclear conversion of minor actinides according to claim 6, wherein the internal blanket fuel contains minor actinides.

10. The method for nuclear conversion of minor actinides according to claim 6, wherein the thickness of the lower axial blanket region is made thicker than the thickness of the upper axial blanket region.

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