JP2018040585A - Nuclear fuel material, fuel rod, fuel assembly, light water reactor core and nuclear fuel material manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To curtail a TRU generation amount in a light water reactor so that an environmental load can be reduced.SOLUTION: A nuclear fuel material is used for a light water reactor as a component mainly comprising plutonium and minor actinoid. The ratio of the mass of the minor actinoid against the mass of the plutonium is equal to or higher than the ratio of the mass of minor actinoid against the mass of plutonium when used fuel of the light water reactor where uranium fuel is used is reprocessed and separated. The ratio of the mass of the minor actinoid against the mass of the plutonium may be 0.75 or less.SELECTED DRAWING: Figure 6

Description

  Embodiments described herein relate generally to a nuclear fuel material, a fuel rod, a fuel assembly, a light water reactor core using these, and a method for producing the nuclear fuel material.

  In the case of a once-through cycle, the radiotoxicity of high-level radioactive waste generated at nuclear power plants, that is, the extent of the radiation emitted by radioactive materials in high-level radioactive waste, has exceeded 100,000 years. At a higher level than nature. After about 30 years of the radiotoxicity, the radiotoxicity caused by the trans-Uranium (TRU) nuclides becomes dominant. The long-term radiotoxicity of TRU nuclides is due to its long half-life.

  Therefore, if TRU can be extinguished, after about 500 years have passed, the radiotoxicity of high-level radioactive waste will be reduced to the same level as natural uranium, reducing the environmental impact of spent fuel. it can.

  High-level radioactive waste is currently planned to be stabilized and treated as a solidified glass, but it will be disposed of in geological formations. It is a load.

  For this reason, research on transmutation of TRU nuclides to short-lived nuclides has been in progress in order to shorten the management period of high-level radioactive waste and reduce the burden on the environment. As typical technologies for transmuting TRU nuclides to short-lived nuclides, annihilation treatment is performed using a transmutation method using fast neutrons generated in a fast reactor or a transmutation facility having an accelerator such as an accelerator-driven reactor (ADS). Technology is being considered.

  However, light water reactors are considered to be the main reactor types used in current and future nuclear power plants. For this reason, a considerable amount of TRU may accumulate until the operation of TRU transmutation using a fast reactor or an accelerator-driven reactor starts, and the number of facilities necessary for transmutation may increase. In addition, construction of facilities necessary for nuclear transmutation requires enormous capital investment.

  For this reason, a technique for suppressing TRU generated in a light water reactor has been studied. For example, a technique for increasing the burnup of nuclear fuel and reducing the amount of TRU generated by adjusting the ratio of plutonium and the core flow rate so that TRU can be recycled multiple times. Etc. are known.

Japanese Patent No. 5524582 JP 2013-33065 A JP 2003-107183 A

  In the current fuel design using uranium as a base material when burning TRU in a light water reactor, since the change in infinite multiplication factor accompanying combustion is large, in order to suppress the change in infinite multiplication factor, It is necessary to use a flammable poison. When using flammable poisons, the problem is that the removal burn-up degree decreases due to the residue of the flammable poison and the economic efficiency deteriorates, and the problem is that the design of a complex plutonium enrichment distribution is necessary due to the large change in output distribution was there. Furthermore, there has been a problem that new TRU is generated by uranium neutron capture reaction by using uranium as a base material.

  Thus, with the current technology, it was difficult to burn and reduce TRU in a light water reactor.

  The embodiment of the present invention has been made in view of such circumstances, and an object thereof is to suppress the TRU generation amount in a light water reactor in order to reduce the environmental load.

  In order to achieve the above-described object, the present embodiment is a nuclear fuel material used in a light water reactor with plutonium and minor actinoid as main components of nuclear fuel material, wherein the first ratio of the mass of the minor actinide to the mass of the plutonium Is characterized by being equal to or greater than a second ratio of minor actinide mass to plutonium mass when spent fuel in a light water reactor using uranium fuel is reprocessed and separated.

  Further, the fuel rod according to the present embodiment includes a plurality of fuel pellets arranged in a predetermined direction with plutonium and minor actinoids separated in reprocessing of spent fuel in a light water reactor as main components of nuclear fuel material, and the plurality of fuel pellets A cylindrical tube extending in the predetermined direction and closed at both ends, wherein the first ratio of the mass of the minor actinide to the mass of the plutonium is the reprocessing The mass of the minor actinoid when separated in is equal to or greater than the second ratio of the mass of the plutonium.

  Further, the fuel assembly according to the present embodiment includes a plurality of first fuel pellets arranged in a predetermined direction with plutonium and minor actinoids separated in the reprocessing of spent fuel in a light water reactor as main components of nuclear fuel material. And a cladding tube that houses the plurality of fuel pellets and extends in the same direction as the direction of the central axis of the fuel pellets and is closed at both ends, and is arranged in parallel with each other in a lattice shape A plurality of first fuel rods extending in a predetermined direction; and a first fuel rod bundling member that binds the plurality of first fuel rods to each other, wherein the mass of the minor actinide relative to the mass of the plutonium The ratio of 1 is equal to or greater than the second ratio of the minor actinide mass to the plutonium mass when separated in the reprocessing. To.

  Further, in the present embodiment, a plurality of first fuel assemblies arranged in a lattice form in parallel with each other and extending in the vertical direction, and between the plurality of first fuel assemblies or the plurality of first fuel assemblies. And a plurality of control members formed so as to be insertable / removable in the body, wherein the first fuel assembly includes plutonium and a minor actinide separated in the reprocessing of spent fuel of the light water reactor. And a plurality of first fuel pellets arranged in a predetermined direction as a main component of the nuclear fuel material, and a cylindrical shape that houses the plurality of fuel pellets and extends in the same direction as the central axis direction of the fuel pellets. A plurality of first fuel rods that are arranged in parallel with each other and extend vertically, and a first binding member that binds the plurality of first fuel rods to each other. And the minor First ratio to the mass of the plutonium mass Chinoido is characterized by the or larger equal to the second ratio to the mass of the plutonium mass of minor actinides when said separated in reprocessing.

  The nuclear fuel material manufacturing method according to the present embodiment includes a separation step of separating plutonium and minor actinides by reprocessing spent fuel in a light water reactor that uses uranium fuel, and the plutonium separated from the minor step and the minor A nuclear fuel material production step for producing a nuclear fuel material by adjusting a mass ratio of the actinide, wherein a ratio of a mass of the minor actinide in the nuclear fuel material to a mass of the plutonium is used in a light water reactor using the uranium fuel. It is characterized by being equal to or greater than the ratio of minor actinide mass to plutonium mass when spent fuel is reprocessed and separated.

  According to the embodiment of the present invention, the TRU generation amount can be suppressed in the light water reactor in order to reduce the environmental load.

It is a top view which shows the structure of the light water reactor core which concerns on 1st Embodiment. 1 is an elevational sectional view showing a configuration of a TRU fuel assembly according to a first embodiment. It is an elevation sectional view showing the composition of the TRU type fuel rod which constitutes the TRU type fuel assembly concerning a 1st embodiment. It is a graph which shows the example of a composition of TRU obtained by reprocessing of uranium type light water reactor fuel. It is a graph which shows the example of the composition of the minor actinide in TRU obtained by reprocessing of a uranium type light water reactor fuel. It is a graph explaining the composition of the TRU type nuclear fuel material which concerns on 1st Embodiment. It is explanatory drawing which shows the production | generation decay chain of an actinoid nuclide. It is a flowchart which shows the procedure of the manufacturing method of the TRU type | mold nuclear fuel material which concerns on 1st Embodiment. It is a graph which shows the example of the burnup dependence of an infinite multiplication factor when the ratio of minor actinide mass and plutonium mass is used as a parameter. It is a graph which shows the example of the dependence to the ratio of the minor actinide mass and plutonium mass of an initial infinite multiplication factor. It is a graph which shows the example of the dependence to the ratio of the minor actinoid mass of the change of an infinite multiplication factor, and plutonium mass. It is a graph which shows the example of the burnup dependence of the local output peaking coefficient when the ratio of the minor actinide mass and the plutonium mass is used as a parameter. It is a graph which shows the example of the dependence to the ratio of the minor actinoid mass and the plutonium mass of the change of a local output peaking coefficient. It is a graph which shows the comparison of the magnitude | size of the resonance absorption of a uranium fuel nuclide and a TRU nuclide. It is a graph which shows the example of the environmental load change of a spent fuel, and targets actinide nuclide and FP nuclide. It is a graph which shows the example of the environmental load change of spent fuel, and targets actinide nuclide. It is a top view which shows the structure of the light water reactor core which concerns on 2nd Embodiment. It is a sectional elevation showing the composition of the uranium type fuel assembly concerning a 2nd embodiment. FIG. 5 is an elevational sectional view showing a configuration of a uranium fuel rod constituting a uranium fuel assembly according to a second embodiment.

  Hereinafter, a nuclear fuel material, a fuel rod, a fuel assembly, a light water reactor core, and a method for manufacturing a nuclear fuel material according to an embodiment of the present invention will be described with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

  In the following embodiments of the present invention, for convenience of explanation, in order to distinguish from uranium fuel and the case where it is used, a nuclear fuel material, a fuel rod, a fuel assembly, and a light water reactor core are each a TRU nuclear fuel material. And TRU fuel rods, TRU fuel assemblies, and TRU light water reactor cores. Further, uranium fuel and nuclear fuel material, fuel rods, and fuel assemblies when using the uranium fuel are referred to as uranium-type nuclear fuel materials, uranium-type fuel rods, and uranium-type fuel assemblies.

[First Embodiment]
FIG. 1 is a plan view showing a configuration of a light water reactor core according to the first embodiment. In the following, an example of a boiling water reactor as a light water reactor will be described.

  The light water reactor core 10 according to the present embodiment includes a plurality of TRU fuel assemblies 100 and control rods 5 arranged in parallel with each other in a lattice shape and extending in the vertical direction. The control rod 5 is arranged at a central position of four TRU type fuel assemblies 100 that constitute one square block in plan view adjacent to each other, and is inserted and extracted.

  FIG. 2 is an elevational sectional view showing the configuration of the TRU fuel assembly according to the first embodiment. The TRU type fuel assembly 100 includes a plurality of TRU type fuel rods 200, a TRU type fuel rod binding member 150, and a channel box 104.

  Although the structure of the TRU type fuel rod 200 will be described with reference to FIG. 3, the plurality of TRU type fuel rods 200 are arranged in parallel with each other in a lattice shape and extend vertically.

  The TRU type fuel rod binding member 150 includes a lower lattice plate 102 and an upper lattice plate 103. The lower lattice plate 102 fixes the lower ends of the plurality of TRU fuel rods 200 and binds the plurality of TRU fuel rods 200 to each other. The upper lattice plate 103 fixes the upper ends of the plurality of TRU fuel rods 200 and binds the plurality of TRU fuel rods 200 to each other.

  Further, the TRU type fuel assembly 100 has a plurality of spacers 101 respectively arranged at a plurality of locations in the direction in which the plurality of TRU type fuel rods 200 extend. The spacer 101 positions the plurality of TRU fuel rods 200 and functions as a steady rest for the TRU fuel rods 200.

  FIG. 3 is an elevational sectional view showing the configuration of the TRU fuel rods that constitute the TRU fuel assembly according to the first embodiment.

  The TRU type fuel rod 200 includes a plurality of cylindrical TRU type fuel pellets 20 arranged in the axial direction with a predetermined direction and an axial direction aligned, a cladding tube 21 extending in a cylindrical shape for housing the pellets, and a cladding tube The upper end plug 22 that closes the upper end of 21 and the lower end plug 23 that closes the lower end of the cladding tube 21 are provided.

  The cladding tube 21, the upper end plug 22 and the lower end plug 23 form a sealed space, and a plurality of TRU fuel pellets 20 are stacked in the axial direction in the sealed space. A gas plenum 25 that is not occupied by the TRU fuel pellets 20 is formed in the upper part of the sealed space. The TRU type fuel pellet 20 is restrained by a spring 24 provided in the gas plenum 25 and fixed in position.

  The TRU type fuel pellet 20 uses plutonium (Pu) and minor actinoids (MA) separated in reprocessing of spent fuel in the light water reactor as the main components of the nuclear fuel material as the TRU type nuclear fuel material. Here, the minor actinoid refers to an actinoid other than uranium (U) and plutonium. In addition, the main component means that other than plutonium and minor actinoids are unavoidable impurities and there is nothing intentionally added. Therefore, it does not include combustible poisons used in the case of ordinary uranium fuel using enriched uranium.

  Here, as an example, the case where plutonium and minor actinoids separated in the reprocessing of spent fuel in a light water reactor is used as a TRU nuclear fuel material is shown, but the present invention is not limited to this. If it is plutonium and a minor actinide, the acquisition method is not ask | required.

  Here, a condition is added to the ratio of the mass of the minor actinide to the mass of plutonium of the TRU type nuclear fuel material used for the TRU type fuel pellet 20. Hereinafter, this condition will be described.

  Consider a case where spent fuel in a light water reactor that uses uranium fuel is reprocessed and separated. In this case, the ratio R0 of the mass MA0 of the minor actinoid and the mass PU0 of the plutonium is taken. That is, R0 = MA0 / PU0.

  FIG. 4 is a graph showing an example of TRU composition obtained by reprocessing light water reactor fuel using uranium fuel. The total mass of TRU is 100%.

  In this example, Pu239 is 43.1%, Pu240 is 26.2%, Pu241 is 12.3%, Pu242 is 7.7%, Np237 is 5.0%, Pu238 is 2.1%, and Am243 is 1. 6%, Np239 is 0.7%, Cm244 is 0.6%, Am241 is 0.5%, etc.

  FIG. 5 is a graph showing an example of the composition of minor actinoids in the TRU of FIG. The total mass of minor actinoids is 100%.

  In this example, Np237 is 58.6%, Am243 is 18.4%, Np239 is 7.8%, Cm244 is 6.6%, Am241 is 5.7%, Cm242 is 2.3%, etc. .

  In the examples of FIGS. 4 and 5, the total mass of minor actinides is about 9.4% of the total mass of plutonium in TRU, on the order of about 10%. That is, the aforementioned R0 is about 0.1.

  FIG. 6 is a graph for explaining the composition of the TRU nuclear fuel material according to the first embodiment.

  On the other hand, the ratio R of the mass MA of the minor actinide and the mass PU of plutonium in the nuclear fuel material used for the TRU fuel pellet 20 in the present embodiment is taken. That is, R = MA / PU. In the present embodiment, R ≧ R0.

  Further, as will be described later, the infinite multiplication factor decreases as the proportion of minor actinoids increases. The reactivity is required to maintain the critical system even at the end of the operation cycle. For this purpose, the reactivity in the initial core needs to be a predetermined value or more. That is, the minor actinide ratio R has an upper limit Rmax.

That is, the ratio R of the mass MA of the minor actinide and the mass PU of plutonium in the nuclear fuel material used for the TRU fuel pellet 20 in the present embodiment must satisfy the following condition.
Rmax ≧ R ≧ R0 (1)

  FIG. 7 is an explanatory diagram showing a production and decay chain of actinoid nuclides. In each circle, the atomic symbol and mass number of each nuclide are displayed. Each row in the horizontal direction in the figure is a nuclide belonging to the same atomic symbol. In addition, the vertical columns are nuclides having the same mass number.

  An upward arrow from each nuclide indicates beta decay and moves to the nuclide with one atomic number higher. The arrow pointing to the right indicates neutron capture and moves to a nuclide with the same atomic number and one larger mass number. The downward arrow indicates orbital electron capture and moves to the nuclide with the smallest atomic number. The arrow in the lower left direction indicates alpha decay, and it moves to a nuclide whose atomic number is 2 smaller and whose mass number is 4 smaller. The arrow to the left indicates neutron emission and moves to a nuclide with the same atomic number and a smaller mass number.

  In the case of uranium and plutonium, the odd nuclei U235, Pu239, Pu241 and the like are fissile nuclides. On the other hand, Am242 and Am244, which are even nuclei, are fissile nuclides for americium. Regarding curium, Cm243, which is an odd-numbered nucleus, is a fissile nuclide.

  The thick arrow pointing to the right is a reaction with a particularly large thermal neutron absorption cross section or a neutron absorption cross section in the resonance region. In this way, by the absorption of thermal neutrons or neutrons in the resonance region, mainly uranium and plutonium sequentially shift to americium and curium. In this process, nuclides with a large absorption cross section of thermal neutrons or neutrons in the resonance region function in the same manner as flammable poisons such as gadolinium (Gd155, Gd157) and erbium (Er167) and Will be transformed.

  FIG. 8 is a flowchart showing the procedure of the method for manufacturing the TRU-type nuclear fuel material according to the first embodiment.

  First, plutonium and minor actinoids are separated by reprocessing spent fuel in the light water reactor (step S01). Here, the spent fuel of the light water reactor may be a nuclear fuel of a light water reactor using uranium fuel, or a nuclear fuel of a light water reactor using a fuel according to the present embodiment. Here, as an example, the case where plutonium and minor actinoids separated in the reprocessing of spent fuel in a light water reactor is used as a TRU nuclear fuel material is shown, but the present invention is not limited to this. If it is plutonium and a minor actinide, the acquisition method is not ask | required.

  Next, the mass ratio R1 of the mass of minor actinoid to the mass of plutonium is adjusted from the separated plutonium and minor actinoid to produce a TRU nuclear fuel material (step S02). Here, plutonium and minor actinides do not correspond to one light water reactor on a one-to-one basis, but are necessary in a state where each of plutonium and minor actinides separated from spent fuel in a plurality of light water reactors is accumulated. There is a method of extracting and using a mass of plutonium and a necessary mass of minor actinides.

  However, it is not limited to this method. For example, the method may be performed by adding the necessary mass of minor actinoids to TRU. In this case, the amount to be separated between plutonium and minor actinides is reduced.

  Next, the TRU type fuel pellet 20 is manufactured using the TRU type nuclear fuel material (step S03). The TRU fuel rod 200 is manufactured using the TRU fuel pellet 20 (step S04). Further, the TRU type fuel assembly 100 is manufactured using the TRU type fuel rod 200 (step S05). Next, the manufactured TRU type fuel assembly 100 is loaded into the light water reactor core 10 (step S06). Thus, the light water reactor core 10 using the TRU type nuclear fuel material is formed.

  FIG. 9 is a graph showing an example of the burnup dependence of the infinite multiplication factor when the ratio of the minor actinide mass to the plutonium mass is used as a parameter. The horizontal axis represents the burnup (GWd / t). The vertical axis represents an infinite multiplication factor.

  When the TRU type nuclear fuel material according to the present embodiment is used, the value of the ratio R of the minor actinide mass to the plutonium mass is sequentially increased to 0.12, 0.34, 0.67, and 1.12. Shows the case. For comparison, the case where uranium fuel is used is shown.

  When uranium fuel is used, a flammable poison is used so that the initial reactivity is not excessively increased. In the early stages of combustion, the infinite multiplication factor increases as the combustible poison decreases. After that, after most of the combustible poison is burned, the infinite multiplication factor decreases almost in accordance with the deterioration characteristics due to the combustion of uranium fuel.

  On the other hand, in the case of the present embodiment, unlike uranium fuel, no flammable poison such as gadolinium is included, and therefore no peak is generated.

  Moreover, the slope of the decrease of the infinite multiplication factor is small regardless of the value of R. This is because minor actinide nuclides are generated as shown in FIG. 7 as plutonium fuel burns, and these minor actinoid nuclides contain fissionable nuclides as described above. This is because these nuclides contribute to the infinite multiplication factor.

  In the case of this embodiment, the infinite multiplication factor decreases as the value of R increases. This is because the ratio of nuclides having a large neutron absorption cross section increases as described above.

  FIG. 10 is a graph showing an example of the dependence of the initial infinite multiplication factor on the ratio of minor actinide mass to plutonium mass. The horizontal axis represents the ratio R between the minor actinide mass and the plutonium mass. The vertical axis represents the initial infinite multiplication factor of the characteristics shown in FIG. As described above, the initial infinite multiplication factor decreases as the ratio R of the minor actinide mass to the plutonium mass increases.

  Here, normally, the infinite multiplication factor required in the early stage of combustion is considered to be about 1.2. As shown by the solid line arrow in FIG. 10, in order to ensure the initial infinite multiplication factor 1.2, the ratio R of the minor actinide mass to the plutonium mass needs to be 0.75 or less. Therefore, Rmax in the above equation (1) is about 0.75.

  This is the minimum necessary condition, but the initial infinite multiplication factor normally used in the current design is about 1.3. As indicated by the broken line arrow in FIG. 10, in order to secure the initial infinite multiplication factor 1.3, the ratio R of the minor actinide mass to the plutonium mass needs to be 0.5 or less. Therefore, Rmax in the above formula (1) is about 0.5.

  FIG. 11 is a graph showing an example of the dependency on the ratio of the minor actinide mass to the plutonium mass for the change in the infinite multiplication factor. The horizontal axis represents the ratio R between the minor actinide mass and the plutonium mass. The vertical axis represents the difference between the infinite multiplication factor when the TRU fuel assembly is loaded and the infinite multiplication factor when the TRU fuel assembly is taken out, that is, the decrease of the infinite multiplication factor due to combustion. This decrease is smaller as the value of R increases, that is, the greater the ratio of minor actinoids, the less the infinite multiplication factor decreases.

  FIG. 12 is a graph showing an example of the burnup dependence of the local output peaking coefficient when the ratio of the minor actinide mass to the plutonium mass is used as a parameter. The horizontal axis represents the burnup (GWd / t). The vertical axis represents the local output peaking coefficient.

  As the value of the ratio R of the minor actinide mass to the plutonium mass sequentially increases to 0.12, 0.34, 0.67, and 1.12, the local output peaking coefficient at the beginning of combustion increases. However, when R is higher than 0.67, it is saturated.

  Also, as the combustion progresses, that is, as the burnup increases, the local output peaking coefficient monotonously decreases in any case, but the larger the ratio R of the minor actinoid mass to the plutonium mass, the smaller the slope of the decrease. Will grow.

  FIG. 13 is a graph showing an example of the dependency of the change in the local output peaking coefficient on the ratio between the minor actinide mass and the plutonium mass. As described with reference to FIG. 12, the local output peaking coefficient decreases monotonously, but the slope of decrease increases as the ratio R of the minor actinide mass to the plutonium mass increases. The degree of the reduction is shown in FIG. 13, and when R is 1.12, the degree of reduction is about twice that when R is 0.12.

  FIG. 14 is a graph showing a comparison of the magnitude of resonance absorption between uranium fuel nuclides and TRU nuclides. The horizontal axis indicates the nuclide, and the vertical axis indicates the magnitude of each resonance absorption (barn). In the case of uranium fuel, the presence of resonance absorption such as U238 can ensure a sufficiently negative, that is, negative, large Doppler coefficient. As shown in FIG. 14, the magnitude of resonance absorption of plutonium 240, plutonium 242, Am241, and Am243 is several times to several tens of times larger than U238. Therefore, the presence of these nuclides makes it possible to secure a sufficiently negative Doppler coefficient even without uranium.

  Next, the environmental impact reduction effect according to the present embodiment will be described with reference to a figure from JAEA-Data / Code 2010-012 “Database for Assessment of Potential Radiotoxicity of Spent Fuel” (Japan Atomic Energy Agency). To do.

  FIG. 15 is a graph showing an example of a change in environmental load of spent fuel, and targets actinide nuclides and FP nuclides. As shown in FIG. 15, when about 30 years or more have passed after the spent fuel is taken out, the contribution by the FP nuclide that has been dominant until then decreases, and the radiotoxicity caused by the actinoid nuclide becomes dominant.

  FIG. 16 is a graph showing an example of a change in the environmental load of spent fuel, and targets actinide nuclides, that is, uranium and trans-uranic (TRU) nuclides. Looking at the contents of the actinide nuclides that become dominant when more than 30 years have passed since the removal of spent fuel, the TRU nuclides, not uranium, are particularly dominant as shown in FIG. This is because the long-term radiotoxicity of TRU nuclides is due to their long half-life. Therefore, it is possible to reduce the environmental load due to spent fuel by reducing TRU.

  As mentioned above, although the characteristic at the time of using the TRU type | mold nuclear fuel material by this 1st Embodiment was demonstrated, it has shown that a core system can be comprised. As a result, it is possible to suppress the amount of TRU generated, thereby reducing the environmental load.

[Second Embodiment]
This embodiment is a modification of the first embodiment. FIG. 17 is a plan view showing a configuration of a light water reactor core according to the second embodiment. The light water reactor core 10 a according to the present embodiment further includes a uranium fuel assembly 300 as a constituent element in addition to the TRU fuel assembly 100.

  The number and arrangement of the TRU type fuel assemblies 100 and the uranium type fuel assemblies 300 can be set in accordance with the purpose and intended characteristics of the light water reactor core.

  FIG. 18 is an elevational sectional view showing the configuration of the uranium fuel assembly according to the second embodiment. The uranium fuel assembly 300 includes a plurality of uranium fuel rods 310, a spacer 301, a lower lattice plate 302 and an upper lattice plate 303 as uranium fuel rod binding members 350, and a channel box 304.

  The structure of the uranium fuel rod 310 will be described with reference to FIG.

  The uranium type fuel rod binding member 350 has a lower lattice plate 302 and an upper lattice plate 303. The lower lattice plate 302 fixes the lower ends of the plurality of uranium fuel rods 310 and binds the plurality of uranium fuel rods 310 to each other. The upper lattice plate 303 fixes the upper ends of the plurality of uranium fuel rods 310 and binds the plurality of uranium fuel rods 310 to each other.

  The uranium fuel assembly 300 includes a plurality of spacers 301 respectively disposed at a plurality of locations in the direction in which the plurality of uranium fuel rods 310 extend. The spacer 301 functions as a steady stop for the uranium fuel rods 310 while positioning the uranium fuel rods 310 among the plurality of uranium fuel rods 310.

  FIG. 19 is an elevational sectional view showing the configuration of the uranium fuel rods constituting the uranium fuel assembly according to the second embodiment.

  The uranium fuel rod 310 includes a plurality of cylindrical uranium fuel pellets 320 arranged in the axial direction with the predetermined direction and the axial direction aligned, a cladding tube 321 extending in a cylindrical shape for housing the pellets, and a cladding tube The upper end plug 322 that closes the upper end of 321 and the lower end plug 323 that closes the lower end of the cladding tube 21 are provided.

  The cladding tube 321, the upper end plug 322, and the lower end plug 323 form a sealed space, and a plurality of uranium fuel pellets 320 are stacked in the axial direction in the sealed space. A gas plenum 325 that is not occupied by the uranium fuel pellets 320 is formed in the upper part of the sealed space. The uranium type fuel pellet 320 is restrained by a spring 324 provided in the gas plenum 25 and fixed in position.

  The uranium fuel pellet 320 is a uranium fuel material that uses a nuclear fuel material containing uranium fuel. As the uranium fuel material, for example, a fuel material using a nuclear fuel material with a uranium enrichment of about 3% to 5%, or a nuclear fuel material based on a uranium enrichment of about 4% to 9% plutonium, for example, That is, there is a fuel material using MOX fuel.

  According to the present embodiment, for example, when introducing a TRU type nuclear fuel material, a core having a TRU type fuel assembly is partially constructed before a core using the TRU type nuclear fuel material is used. Applicable.

[Other Embodiments]
As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention.

  For example, in the embodiment, the case of a boiling water reactor is shown as an example of the light water reactor, but the present invention is not limited to this. For example, the present invention can be applied to a pressurized water reactor.

  Moreover, you may combine the characteristic of each embodiment. For example, the fuel assembly may be a combination of the TRU type fuel rod in the first embodiment and the uranium type fuel rod in the second embodiment.

  Furthermore, these embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  2 ... Uranium type fuel assembly, 5 ... Control rod (control member), 10, 10a ... Light water reactor core, 20 ... TRU type fuel pellet (first fuel pellet), 21 ... Cladding tube, 22 ... Upper end plug, 23 ... Lower end plug, 24 ... Spring, 25 ... Gas plenum, 100 ... TRU type fuel assembly (first fuel assembly), 101 ... Spacer, 102 ... Lower lattice plate, 103 ... Upper lattice plate, 104 ... Channel box, 150... TRU type fuel rod bundling member (first bundling member), 200... TRU type fuel rod (first fuel rod), 300... Uranium type fuel assembly (second fuel assembly), 301. 302 ... Lower lattice plate, 303 ... Upper lattice plate, 304 ... Channel box, 310 ... Uranium fuel rod (second fuel rod), 320 ... Uranium fuel pellet (second fuel pellet), 321 ... Cladding tube 322 ... upper end plug, 323 ... lower end plug, 324 ... spring 325 ... gas plenum, 350 ... uranium fuel rods binding member (the second binding member)

Claims (9)

Nuclear fuel material used in light water reactors with plutonium and minor actinides as the main components of nuclear fuel material,
The first ratio of the minor actinide mass to the plutonium mass is a second ratio of the minor actinide mass to the plutonium mass when the spent fuel of a light water reactor using uranium fuel is reprocessed and separated; Nuclear fuel material characterized by being equal or greater.   The nuclear fuel material of claim 1, wherein the first ratio is 0.75 or less.   The nuclear fuel material of claim 1, wherein the first ratio is 0.5 or less. A plurality of fuel pellets arranged in a predetermined direction with plutonium and minor actinides separated in the reprocessing of spent fuel in a light water reactor as main components of nuclear fuel material;
A cladding tube containing the plurality of fuel pellets and extending in the predetermined direction and closed at both ends;
Have
The first ratio of the minor actinide mass to the plutonium mass is equal to or greater than a second ratio of the minor actinide mass to the plutonium mass when separated in the reprocessing. Fuel rod to do. A plurality of first fuel pellets arranged in a predetermined direction with plutonium and minor actinides separated in the reprocessing of spent fuel in a light water reactor as main components of nuclear fuel material, the fuel pellets containing the plurality of fuel pellets A plurality of first fuel rods having a cylindrical tube extending in the same direction as the central axis of the pellet and closed at both ends, and arranged in parallel to each other in a lattice shape and extending in the predetermined direction When,
A first fuel rod binding member that binds the plurality of first fuel rods to each other;
With
The first ratio of the minor actinide mass to the plutonium mass is equal to or greater than a second ratio of the minor actinide mass to the plutonium mass when separated in the reprocessing. Fuel assembly.   A second fuel pellet having enriched uranium as a main component of nuclear fuel material and extending in a predetermined direction; and a cladding tube containing the fuel and extending in the same direction as the predetermined direction and closed at both ends. 6. The fuel assembly according to claim 5, further comprising a plurality of second fuel rods that are arranged in a lattice pattern and extend in parallel to each other in the predetermined direction. A plurality of first fuel assemblies arranged in a grid in parallel with each other and extending in the vertical direction;
A plurality of control members formed to be insertable / removable between the plurality of first fuel assemblies or in the plurality of first fuel assemblies;
A light water reactor core comprising:
The first fuel assembly is
A plurality of first fuel pellets arranged in a predetermined direction with plutonium and minor actinides separated in the reprocessing of spent fuel in a light water reactor as main components of nuclear fuel material, the fuel pellets containing the plurality of fuel pellets A plurality of first fuel rods extending in the vertical direction with a cylindrical tube extending in the same direction as the central axis of the pellet and closed at both ends, arranged in parallel with each other in a lattice shape;
A first binding member for binding the plurality of first fuel rods to each other;
With
The first ratio of the minor actinide mass to the plutonium mass is equal to or greater than a second ratio of the minor actinide mass to the plutonium mass when separated in the reprocessing. Light water reactor core. A second fuel pellet having enriched uranium as a main component of nuclear fuel material and extending in a predetermined direction; and a cladding tube containing the fuel and extending in the same direction as the predetermined direction and closed at both ends. A plurality of second fuel rods arranged in a lattice and extending vertically in parallel with each other;
A second fuel rod binding member for binding the plurality of second fuel rods to each other;
With
The light water reactor core according to claim 7, further comprising a second fuel assembly arranged in a grid in parallel with the first fuel assembly and extending in the vertical direction. A separation step of separating plutonium and minor actinides by reprocessing spent fuel in a light water reactor using uranium fuel;
A nuclear fuel material production step of producing a nuclear fuel material by adjusting a mass ratio of the plutonium and the minor actinide separated in the separation step;
Have
The ratio of the mass of the minor actinide in the nuclear fuel material to the mass of the plutonium is equal to the ratio of the mass of the minor actinide to the mass of the plutonium when the spent fuel of the light water reactor using the uranium fuel is reprocessed and separated. A method for producing nuclear fuel material characterized in that it is large or large.

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