JP2008145360A - Initial core of boiling water reactor, and operation method for boiling water reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce radial power peaking factor in an initial core having an area arrayed with unit loading units, and to enhance thermal characteristics. <P>SOLUTION: The initial core 11 for a boiling water reactor includes a unit loading unit arranging area to arrange the unit loading units 75 arrayed with one low enrichment fuel assemblies 3 and three high enrichment fuel assemblies 1, 2 having a higher content of fissile material than that of the low enrichment fuel assembly, to be surrounded by four control rods 21, so as to make adjacent each other the low enrichment fuel assemblies 3 included in the respective unit loading units 75, and an inside of the unit loading unit arranging area has the central area 71, and an intermediate area formed in a radial outside of the central area 71, and having higher content of an average fissile material per unit loading unit than that of the central area 71. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an initially loaded core and operating method of a boiling water reactor.

  In nuclear reactors, neutrons are absorbed by fissionable materials, causing fission, and neutrons released along with the energy continue to produce energy by a chain reaction. The state in which this chain reaction is in equilibrium is called criticality, and the reactor operated at a constant power continues to maintain this state. In addition, the state in which the chain reaction increases is called supercritical, and the state in which the chain reaction decreases is called subcritical.

  Since a nuclear reactor must be operated without refueling for a predetermined period of time, for example, about one year, more nuclear fissionable material is loaded in the core than is necessary for maintaining criticality. Therefore, in the period up to the middle of the predetermined operation period, the nuclear reactor becomes supercritical without the control material.

  This excess reactivity is referred to as excess reactivity, and it is important to appropriately control the excess reactivity throughout the operation period. As a technique for controlling the excess reactivity throughout the operation period, a technique in which a flammable poison is mixed into the fuel is well known. A flammable poison is a neutron absorber that gradually burns and decreases in the amount of material throughout the operation period. Gadolinia, which is used in combination with nuclear fuel materials, is known.

  The infinite multiplication factor of the fuel assembly containing the combustible poison increases once with combustion and then decreases. Generally, if the number of fuel rods containing a flammable poison increases, the infinite multiplication factor at the initial stage of combustion decreases. Further, if the concentration of the flammable poison is increased, the time when the flammable poison is burned out can be delayed, so that the maximum value of the infinite multiplication factor can be suppressed. For this reason, the excess reactivity can be appropriately controlled by the combination of the mixing concentration of the flammable poison and the number of fuel rods mixed with it.

  In the initial loading core, a part of the loaded fuel assembly is taken out after the operation of the first cycle is completed and replaced with a new replacement fuel assembly. The fuel assembly taken out in the first cycle has a lower burnup and generates less energy than other fuel assemblies. For this reason, the fuel economy increases as the number of fuel assemblies taken out in the first cycle decreases.

  However, if the core average enrichment is simply increased in order to improve fuel economy, thermal characteristics such as the minimum critical power ratio and the maximum linear power density deteriorate, and the safety of the reactor may be impaired. Therefore, in order to make effective use of fissile material, an initially loaded core using a plurality of fuel assemblies having different uranium enrichments in accordance with the period of stay in the reactor is known.

For example, Patent Document 1 discloses an initial loading core in which unit loading units composed of four fuel assemblies in two rows and two columns are regularly arranged. This unit loading unit is composed of one low-enriched fuel and three highly-enriched fuels, and is arranged so that the low-enriched fuel 4 included in the four unit loaded units forms a control cell adjacent to each other. Further, the gadolinia-containing fuel rods are unevenly distributed so that many gadolinia-containing fuel rods are located on the side of the high-concentration fuel included in the unit loading unit facing the low-concentration fuel. By arranging such fuel rods, deterioration of thermal characteristics due to the spectrum mismatch effect is suppressed.
Japanese Patent No. 3186546

  However, in the case of a core in which unit loading units are regularly arranged, the closer to the center of the core, the smaller the leakage of neutrons, and thus the radial output peaking tends to be higher. For this reason, thermal characteristics deteriorate near the center of the core, and the thermal limit value may not be satisfied.

  Therefore, an object of the present invention is to reduce the radial output peaking of the initial loading core having the region where the unit loading units are arranged, and to improve the thermal characteristics.

  In order to achieve the above-mentioned object, the present invention squares a cell composed of four rectangular fuel cells that extend in the vertical direction and surround a control rod insertion portion in which one control rod can be inserted in the vertical direction. A core in which the fuel assemblies are arranged in a square lattice shape including a region arranged in a grid and extending in a vertical direction, and one low enriched fuel assembly in the fuel assembly and its low Each unit loading unit includes unit loading units in which three highly concentrated fuel assemblies having a greater content of fissile material than the concentrated fuel assemblies are arranged in two rows and two columns surrounded by four control rod insertion portions. In the initial loading core of a boiling water reactor having unit loading unit arrangement areas arranged so that the low enriched fuel assemblies are adjacent to each other, a central area formed inside the unit loading unit arrangement area, Unit packaging An intermediate region formed inside the unit arrangement region in a radially outer direction than the central region, and having a larger average fissile material content per unit loading unit than the central region; To do.

  Further, the present invention provides a region in which cells made up of four tetragonal cylindrical fuel assemblies that surround a control rod insertion portion in which one control rod can be inserted in the vertical direction and extend in the vertical direction are arranged in a square lattice shape. Including a fuel cell assembly arranged in a substantially cylindrical region extending in the vertical direction and having a square lattice shape, wherein the fuel assembly includes one low enriched fuel assembly and the low enriched fuel assembly. The low enriched fuel assembly included in each unit loading unit is a unit loading unit in which three highly enriched fuel assemblies having a large content of fissile material are arranged in two rows and two columns surrounded by four control rod insertion portions. In a first loading core of a boiling water reactor having unit loading unit arrangement areas arranged so that their bodies are adjacent to each other, a central area formed inside the unit loading unit arrangement area, and the unit loading unit arrangement area of Said formed outward in the radial direction from the central region to the section, the content of the average burnable poison amount per the unit loading unit is characterized by having the intermediate region is smaller than that of the central region.

  Further, the present invention provides a region in which cells made up of four tetragonal cylindrical fuel assemblies that surround a control rod insertion portion in which one control rod can be inserted in the vertical direction and extend in the vertical direction are arranged in a square lattice shape. Including a fuel cell assembly arranged in a substantially cylindrical region extending in the vertical direction and having a square lattice shape, wherein the fuel assembly includes one low enriched fuel assembly and the low enriched fuel assembly. The low enriched fuel assembly included in each unit loading unit is a unit loading unit in which three highly enriched fuel assemblies having a large content of fissile material are arranged in two rows and two columns surrounded by four control rod insertion portions. In the initial loading core of a boiling water reactor having unit loading unit arrangement regions arranged so that the bodies are adjacent to each other, the first low-concentration fuel assembly composed of four low-enriched fuel assemblies arranged in two rows and two columns Control cell and 2 rows and 2 columns The total of the contents of the fissile material in the fuel assembly that constitutes the unit loading unit that includes the four low enriched fuel assemblies arranged and includes the low enriched fuel assemblies is the first enriched fuel assembly. And a second control cell that is smaller than the total content of fissile substances in the fuel assembly constituting the unit loading unit including the low-enriched fuel assembly of the control cell.

  Further, the present invention provides a region in which cells made up of four tetragonal cylindrical fuel assemblies that surround a control rod insertion portion in which one control rod can be inserted in the vertical direction and extend in the vertical direction are arranged in a square lattice shape. Including a fuel cell assembly arranged in a substantially cylindrical region extending in the vertical direction and having a square lattice shape, wherein the fuel assembly includes one low enriched fuel assembly and the low enriched fuel assembly. The low enriched fuel assembly included in each unit loading unit is a unit loading unit in which three highly enriched fuel assemblies having a large content of fissile material are arranged in two rows and two columns surrounded by four control rod insertion portions. In the initial loading core of a boiling water reactor having unit loading unit arrangement regions arranged so that the bodies are adjacent to each other, the first low-concentration fuel assembly composed of four low-enriched fuel assemblies arranged in two rows and two columns Control cell and 2 rows and 2 columns The sum of the contents of the combustible poisons in the fuel assembly, which is composed of the four low enriched fuel assemblies arranged in the unit loading unit and includes the low enriched fuel assemblies, And a second control cell that is larger than the total content of combustible poisons in the fuel assembly constituting the unit loading unit including the low enriched fuel assembly of the control cell.

  Further, the present invention provides a region in which cells made up of four tetragonal cylindrical fuel assemblies that surround a control rod insertion portion in which one control rod can be inserted in the vertical direction and extend in the vertical direction are arranged in a square lattice shape. Including a fuel cell assembly arranged in a substantially cylindrical region extending in the vertical direction and having a square lattice shape, wherein the fuel assembly includes one low enriched fuel assembly and the low enriched fuel assembly. The low enriched fuel assembly included in each unit loading unit is a unit loading unit in which three highly enriched fuel assemblies having a large content of fissile material are arranged in two rows and two columns surrounded by four control rod insertion portions. A unit loading unit arrangement area arranged so that the bodies are adjacent to each other, a central area formed inside the unit loading unit arrangement area, and a radial direction from the central area inside the unit loading unit arrangement area Outside In a method for operating a boiling water reactor having an initial loading core formed and having an intermediate region in which an average fissile material content per unit loading unit is larger than the central region, The control rod inserted into the control rod insertion portion surrounded by a control cell composed of four low enriched fuel assemblies arranged in two rows is used for nuclear reactor control.

  Further, the present invention provides a region in which cells made up of four tetragonal cylindrical fuel assemblies that surround a control rod insertion portion in which one control rod can be inserted in the vertical direction and extend in the vertical direction are arranged in a square lattice shape. Including a fuel cell assembly arranged in a substantially cylindrical region extending in the vertical direction and having a square lattice shape, wherein the fuel assembly includes one low enriched fuel assembly and the low enriched fuel assembly. The low enriched fuel assembly included in each unit loading unit is a unit loading unit in which three highly enriched fuel assemblies having a large content of fissile material are arranged in two rows and two columns surrounded by four control rod insertion portions. A unit loading unit arrangement area arranged so that the bodies are adjacent to each other, a central area formed inside the unit loading unit arrangement area, and a radial direction from the central area inside the unit loading unit arrangement area Outside In a method for operating a boiling water reactor having an initially loaded core formed with an intermediate region formed and having an average flammable poison content per unit loading unit smaller than the central region, 2 The control rods inserted into the control rod insertion portions surrounded by control cells composed of four low enriched fuel assemblies arranged in two rows and two columns are used for nuclear reactor control.

  Further, the present invention provides a region in which cells made up of four tetragonal cylindrical fuel assemblies that surround a control rod insertion portion in which one control rod can be inserted in the vertical direction and extend in the vertical direction are arranged in a square lattice shape. Including a fuel cell assembly arranged in a substantially cylindrical region extending in the vertical direction and having a square lattice shape, wherein the fuel assembly includes one low enriched fuel assembly and the low enriched fuel assembly. The low enriched fuel assembly included in each unit loading unit is a unit loading unit in which three highly enriched fuel assemblies having a large content of fissile material are arranged in two rows and two columns surrounded by four control rod insertion portions. A first control cell comprising four low-enriched fuel assemblies arranged in two rows and two columns, with unit loading unit arrangement regions arranged so that the bodies are adjacent to each other, and arranged in two rows and two columns The four low enriched fuel assemblies The unit containing the low enriched fuel assemblies, and the unit of the unit loading unit that includes the low enriched fuel assemblies, the sum of the contents of the fissile material in the fuel assemblies is the unit including the low enriched fuel assemblies of the first control cell. In a method for operating a boiling water reactor comprising an initial loading core formed with a second control cell that is smaller than the total content of fissionable substances in the fuel assembly constituting the loading unit, A first step of using the control rod inserted into the control rod insertion portion surrounded by the first control cell for controlling the nuclear reactor, and the second control cell being enclosed after the first step. And a second step of using the control rod inserted into the control rod insertion portion for controlling a nuclear reactor.

  Further, the present invention provides a region in which cells made up of four tetragonal cylindrical fuel assemblies that surround a control rod insertion portion in which one control rod can be inserted in the vertical direction and extend in the vertical direction are arranged in a square lattice shape. Including a fuel cell assembly arranged in a substantially cylindrical region extending in the vertical direction and having a square lattice shape, wherein the fuel assembly includes one low enriched fuel assembly and the low enriched fuel assembly. The low enriched fuel assembly included in each unit loading unit is a unit loading unit in which three highly enriched fuel assemblies having a large content of fissile material are arranged in two rows and two columns surrounded by four control rod insertion portions. A first control cell comprising four low-enriched fuel assemblies arranged in two rows and two columns, with unit loading unit arrangement regions arranged so that the bodies are adjacent to each other, and arranged in two rows and two columns The four low enriched fuel assemblies The unit containing the low enriched fuel assembly of the first control cell, wherein the total content of combustible poisons in the fuel assembly constituting the unit loading unit including the low enriched fuel assembly is In a method for operating a boiling water reactor comprising a first loading core formed with a second control cell that is larger than the total content of combustible poisons in the fuel assembly constituting the loading unit, A first step of using the control rod inserted into the control rod insertion portion surrounded by the first control cell for controlling the nuclear reactor, and the second control cell being enclosed after the first step. And a second step of using the control rod inserted into the control rod insertion portion for controlling a nuclear reactor.

  ADVANTAGE OF THE INVENTION According to this invention, the radial output peaking of the initial loading core which has the area | region which arranged the unit loading unit can be reduced, and a thermal characteristic can be improved.

  Embodiments of the core of a boiling water reactor according to the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or similar structure, and the overlapping description is abbreviate | omitted.

[First Embodiment]
FIG. 2 is a transverse cross-sectional view (horizontal cross-sectional view) in the first embodiment of the core of the boiling water nuclear reactor according to the present invention. FIG. 3 is a cross-sectional view of the fuel assembly in the present embodiment. FIG. 2 is a diagram showing the upper left quarter of the cross section of the core, and the remaining portion is rotationally symmetric with respect to the illustrated portion with the central axis in the vertical direction of the core as the symmetry axis. Note that the entire core does not need to be rotationally symmetric, and may be mirror-symmetrical or a core without symmetry.

  The boiling water reactor has a region 10 in which spaces 22 in which square-tubular fuel assemblies 26 are arranged are arranged in a square lattice pattern. The region 10 is formed in a substantially cylindrical shape as a whole, and the axis of the fuel assembly 26 is directed in the same direction as the axis of the cylinder. Fuel assemblies 26 are arranged in these spaces 22 to form a core.

  The space 22 in which the fuel assembly 26 is arranged is slightly larger than the fuel assembly 26, and the control rod 21 can be inserted between the four adjacent fuel assemblies 26. A space 22 in which a fuel assembly 26 that is not adjacent to the control rod 21 is also present in a part of the region 10 on the outer side in the radial direction.

  In the core of the present embodiment, 872 fuel assemblies 26 are loaded, and 205 control rods 21 are arranged.

  The fuel assembly 26 includes cylindrical fuel rods 24 arranged in a square lattice in 9 rows and 9 columns, and a rectangular tube-shaped water channel 25 arranged in the center of the array of fuel rods 24. Yes. The water channel 25 occupies an area of nine fuel rods 24 in 3 rows and 3 columns. The fuel rod 24 and the water channel 25 are held by tie plates (not shown) provided at both ends in the axial direction and spacers (not shown) provided at several locations in the axial direction. The outer periphery of the fuel assembly 26 is surrounded by a rectangular tubular channel box 23.

  Inside the fuel rod 24, a fissile material such as uranium 235 is stored as a pellet baked into a cylindrical shape together with uranium 238, for example. The enrichment of uranium 235 in each fuel rod 24 is different for each fuel rod 24, and the amount of fissile material contained in each fuel rod 24 is also different for each fuel rod 24. In addition, you may provide the area | region where enrichment differs in the axial direction of the fuel rod 24. FIG.

  FIG. 1 is a quarter cross-sectional view showing the arrangement of fuel assemblies in the first cycle of the core in the present embodiment. Reference numerals 1, 2, and 3 indicate the types of the fuel assemblies 26, and the same reference numerals indicate the fuel assemblies in which the fuel rods 24 are arranged in the same manner.

  The core 11 of the first cycle, that is, the initial loading core 11 is composed of three types of fuel assemblies 1, 2, and 3. These are the high enriched high gadolinia fuel assembly 1, the highly enriched low gadolinia fuel assembly 2, and the low enriched fuel assembly 3. The highly enriched high gadolinia fuel assembly 1 and the highly enriched low gadolinia fuel assembly 2 are collectively referred to as highly enriched fuel assemblies 1 and 2.

  The core 11 includes a central region 71, an intermediate region 72, and an outer peripheral region 73.

  The highly enriched low gadolinia fuel assemblies 2 are arranged in the outer peripheral region 73.

  Control cells 74 are formed in the central region 71 and the intermediate region 72. The control cell 74 is a set (cell) of fuel assemblies in which all four fuel assemblies surrounding a certain control rod 21 are the low enriched fuel assemblies 3. The control rod 21 located mainly in the control cell 74 is used for the control by the control rod 21 of the operating core.

  Moreover, the center area | region 71 and the intermediate | middle area | region 72 are comprised by the unit loading unit 75 arranged in the square lattice shape. The unit loading unit 75 is composed of four fuel assemblies 1, 2, 3 surrounded by four control rods 21. These four fuel assemblies 1, 2, 3 are one low enriched fuel assembly 3 and three highly enriched fuel assemblies 1, 2. Accordingly, there are four types of unit loading units 75: those that do not include the highly enriched and high gadolinia fuel assemblies 1, those that include one, those that include two, and those that include three.

  FIG. 4 is a cross-sectional view showing an example of the arrangement of fuel rods of a unit loading unit 75 including three highly enriched high gadolinia fuel assemblies 1. FIG. 5 is a cross-sectional view showing an example of the arrangement of the fuel rods of the unit loading unit 75 including one highly enriched high gadolinia fuel assembly 1.

  4 and 5, the positions indicated by U1, U2, and U3 indicate that uranium fuel rods are disposed, and the positions indicated by G indicate that gadolinia-containing fuel rods are disposed. W indicates the position of the water channel.

  A uranium fuel rod is a fuel rod 24 that does not contain a flammable poison such as gadolinia inside, and a fuel rod containing gadolinia is a fuel rod 24 that contains a flammable poison such as gadolinia together with a fissile material. It is. The uranium fuel rods indicated by U1, U2, and U3 each have a different enrichment of uranium 235, the enrichment of the uranium fuel rod indicated by U1 is the highest, and the enrichment of the uranium fuel rod at the location indicated by U3 is the lowest. . The enrichment of the uranium fuel rod indicated by U1 is, for example, 4.9 wt%.

  In the central region 71 and the intermediate region 72, the ratio of the highly enriched high gadolinia fuel 1 per unit loading unit 75 when averaged over all the unit loading units 75 formed in the central region 71 is formed in the intermediate region 72. It is formed so as to be larger than the average of all unit loading units 75 to be used. That is, the unit loading unit 75 formed in the central region 71 contains a relatively large amount of the highly enriched and high gadolinia fuel 1. On the other hand, the unit loading unit 75 formed in the intermediate region contains a relatively large amount of the highly enriched low gadolinia fuel 2.

  Since the neutron leakage is smaller as it is closer to the central axis of the core, if all the unit loading units 75 in the central region 71 and the intermediate region 72 have the same ratio of the highly enriched high gadolinia fuel assembly 1, the central axis of the core The radial output peaking tends to increase in the near region. In such a case, in the region close to the central axis of the core, thermal characteristics such as maximum line power density and minimum limit power ratio may deteriorate.

  In the core 11 of the present embodiment, since the ratio of the highly enriched high gadolinia fuel 1 is increased in the central region 71 of the core 11, radial output peaking can be suppressed, and the thermal characteristics are improved. can do.

  In the highly enriched high gadolinia fuel assembly 1 and the highly enriched low gadolinia fuel assembly 2, more gadolinia-containing fuel rods are arranged on the side opposite to the side facing the control rod 21. Therefore, in all the unit loading units 75, gadolinia-containing fuel rods are unevenly distributed on the side facing the low enriched fuel assembly 3. For this reason, it is possible to suppress deterioration of thermal characteristics due to spectrum mismatch.

[Second Embodiment]
FIG. 6 is a cross-sectional view showing the fuel rod arrangement of the unit loading unit in the central region in the second embodiment of the core of the boiling water reactor according to the present invention.

  The initial loading core of the present embodiment is obtained by replacing part of the highly concentrated fuel assemblies 1 and 2 in the central region 71 of the initial loading core 11 of the first embodiment with the intermediate concentrated fuel assembly 4. is there.

  The intermediate enriched fuel assembly 4 is obtained by, for example, making the enrichment of the fuel rod 24 located on the surface facing the low enriched fuel assembly 3 lower than that of the highly enriched fuel assemblies 1 and 2. The average enrichment of the medium enriched fuel assembly 4 is lower than that of the highly enriched fuel assemblies 1 and 2 and larger than that of the low enriched fuel assembly 3.

  By disposing the intermediate concentrated fuel assembly 4 in the central region 71 of the initially loaded core 11 as described above, radial output peaking in the central region 71 can be suppressed, and thermal characteristics can be improved. .

  Further, since fuel rods with relatively low enrichment are unevenly distributed on the side facing the low enriched fuel assembly 3, deterioration of thermal characteristics due to spectrum mismatch can be suppressed.

[Third Embodiment]
FIG. 7 is a ¼ cross-sectional view showing the arrangement of the fuel assemblies in the first cycle of the core in the third embodiment of the core of the boiling water reactor according to the present invention.

  In the core 12 of the present embodiment, as in the first embodiment, the central region 71 and the intermediate region 72 are formed by unit loading units 75 (see FIG. 1) arranged in a square lattice pattern. The unit loading unit 75 includes one low enriched fuel assembly 3 and three highly enriched fuel assemblies 1 and 2.

  In the central region 71 and the intermediate region 72, control cells 76 and 77 are formed as in the first embodiment. The control cells 76 and 77 are composed of four low-enriched fuel assemblies 3 that surround the control rod 21.

  There are two types of control cells 76 and 77 in the core 12 of the present embodiment. The first control cell 76 is a cell in which the highly enriched low gadolinia fuel 2 is disposed at a position facing the low enriched fuel assembly 3 constituting the cell. The second control cell 77 is a cell in which the highly enriched high gadolinia fuel 1 is disposed at a position facing the low enriched fuel assembly 3 constituting the cell.

  In the first cycle of the boiling water reactor in which the core 12 is formed, when starting up and reaching a steady operation, first, a control rod is inserted into the first control cell 76, and the control rod is operated. Control the reactor. The process of inserting the control rod only into the first control cell 76 and controlling the nuclear reactor will be referred to as the first process. Thereafter, a control rod is inserted into the second control cell 77, and the reactor is controlled by operating the control rod. The step of inserting the control rod into the second control cell 77 and controlling the nuclear reactor will be referred to as the second step. In the second step, the control rod of the first control cell 76 may be operated, or all the control rods of the first control cell 76 may be pulled out.

  If all the unit loading units 75 in the central region 71 and the intermediate region 72 are the same unit loading unit, the low enriched fuel constituting the control cells 76 and 77 regardless of whether or not the control rods are inserted for a long time during operation. The fuel assembly facing the assembly 3 becomes a specific fuel assembly 26 such as the highly enriched high gadolinia fuel 1. However, in the vicinity of the control cells 76 and 77 in which the control rod 21 is inserted, the output suppression effect by the control rod 21 is large, and the thermal characteristics have a large margin.

  In the present embodiment, the highly enriched high gadolinia fuel 1 is disposed at a position facing the low enriched fuel assembly 3 constituting the second control cell 77. Therefore, in the initial stage of the first cycle, the heat output is suppressed by gadolinia in the state where the control rod 21 is not inserted in the second control cell 77, that is, in the vicinity of the second control cell 77 even in the first step. The thermal characteristics have a large margin.

  Further, the highly enriched low gadolinia fuel 2 is disposed at a position facing the low enriched fuel assembly 3 constituting the first control cell 76. In the initial stage of the first cycle, the control rod 21 is inserted in the first control cell 76, that is, in the first step, the output suppression effect by the control rod 21 is large, so the gadolinia amount in the vicinity thereof is large. There is no room for thermal characteristics.

  As described above, the highly enriched fuel assembly around the first control cell 76 into which the control rod 21 is inserted in the initial stage of the first cycle of the initially loaded core 12 is the highly enriched low gadolinia fuel assembly 2. It avoids unnecessary use of gadolinia and improves neutron economy.

  Further, instead of the highly enriched high gadolinia fuel assembly 1 facing the low enriched fuel assembly 3 of the second control cell 77, the intermediate enriched fuel assembly 4 in the third embodiment may be used. In this way, the thermal limit value is satisfied by reducing the enrichment of the fuel assembly around the second control cell 77 in which the control rod 21 is not loaded in the initial stage of the first cycle of the initial loading core 12. You can also In such a case, by reducing the number of medium enriched fuel assemblies 4 as much as possible, it is possible to avoid a decrease in the core average enrichment for suppressing deterioration of thermal characteristics due to the spectrum mismatch effect.

  In addition, this invention is not limited to each above-mentioned embodiment, It can implement with various forms. For example, each of the above-described embodiments has been described with respect to the 872 core. However, the present invention can be applied to a smaller or larger core. Also, the fuel assembly has been described using 9 × 9 type fuel, but other types of fuel, for example, fuel in which fuel rods are arranged in 10 rows and 10 columns may be used. It can also be applied to uranium / plutonium mixed oxide fuel. These fuel assemblies may be mixed. As an example of the flammable poison, gadolinia is used as an example, but other flammable poisons such as elbia may be used.

  Furthermore, it can be implemented by combining the features of the embodiments.

FIG. 2 is a ¼ cross-sectional view showing the arrangement of the fuel assemblies in the first cycle of the core in the first embodiment of the core of the boiling water reactor according to the present invention. 1 is a ¼ transverse cross-sectional view in a first embodiment of a core of a boiling water reactor according to the present invention. 1 is a cross-sectional view of a fuel assembly in a first embodiment of a core of a boiling water reactor according to the present invention. 1 is a cross-sectional view showing an example of arrangement of fuel rods of a unit loading unit including three highly enriched high gadolinia fuel assemblies 1 in a first embodiment of a core of a boiling water reactor according to the present invention. 1 is a cross-sectional view showing an example of arrangement of fuel rods of a unit loading unit including one highly concentrated high gadolinia fuel assembly 1 in a first embodiment of a core of a boiling water reactor according to the present invention. It is a cross-sectional view which shows the fuel rod arrangement | positioning of the unit loading unit of the center area | region in 2nd Embodiment of the core of the boiling water reactor which concerns on this invention. FIG. 6 is a ¼ cross-sectional view showing the arrangement of fuel assemblies in the first cycle of the core in the third embodiment of the core of the boiling water reactor according to the present invention.

Explanation of symbols

1, 2, 3, 4 ... Fuel assembly, 11, 12 ... Core of the first cycle (initial loading core), 21 ... Control rod, 23 ... Channel box, 24 ... Fuel rod, 25 ... Water channel, 26 ... Fuel Aggregate, 71 ... central area, 72 ... intermediate area, 73 ... outer peripheral area, 74, 76, 77 ... control cell, 75 ... unit loading unit,

Claims (8)

One control rod extends in the vertical direction, including a region in which cells composed of four quadrangular cylindrical fuel assemblies extending in the vertical direction are surrounded by a control rod insertion portion in which the control rod can be inserted in the vertical direction. A core in which the fuel assemblies are arranged in a square lattice pattern in a substantially cylindrical region, and one low enriched fuel assembly of the fuel assemblies and a content of fissile material than the low enriched fuel assembly. Unit loading units in which three high enrichment fuel assemblies with large size are arranged in two rows and two columns surrounded by the four control rod insertion portions are arranged so that the low enrichment fuel assemblies included in each unit loading unit are adjacent to each other. In the initial loading core of the boiling water reactor with the unit loading unit arrangement area arranged in
A central region formed inside the unit loading unit arrangement region;
An intermediate region that is formed inside the unit loading unit arrangement region on the outer side in the radial direction than the central region, and has a larger average fissile material content per unit loading unit than the central region,
A first loaded core of a boiling water reactor characterized by having: One control rod extends in the vertical direction, including a region in which cells composed of four quadrangular cylindrical fuel assemblies extending in the vertical direction are surrounded by a control rod insertion portion in which the control rod can be inserted in the vertical direction. A core in which the fuel assemblies are arranged in a square lattice pattern in a substantially cylindrical region, and one low enriched fuel assembly of the fuel assemblies and a content of fissile material than the low enriched fuel assembly. Unit loading units in which three high enrichment fuel assemblies with large size are arranged in two rows and two columns surrounded by the four control rod insertion portions are arranged so that the low enrichment fuel assemblies included in each unit loading unit are adjacent to each other. In the initial loading core of the boiling water reactor with the unit loading unit arrangement area arranged in
A central region formed inside the unit loading unit arrangement region;
An intermediate region that is formed inside the unit loading unit arrangement region on the outer side in the radial direction than the central region, and the content of the average flammable poison amount per unit loading unit is smaller than the central region,
A first loaded core of a boiling water reactor characterized by having: One control rod extends in the vertical direction, including a region in which cells composed of four quadrangular cylindrical fuel assemblies extending in the vertical direction are surrounded by a control rod insertion portion in which the control rod can be inserted in the vertical direction. A core in which the fuel assemblies are arranged in a square lattice pattern in a substantially cylindrical region, and one low enriched fuel assembly of the fuel assemblies and a content of fissile material than the low enriched fuel assembly. Unit loading units in which three high enrichment fuel assemblies with large size are arranged in two rows and two columns surrounded by the four control rod insertion portions are arranged so that the low enrichment fuel assemblies included in each unit loading unit are adjacent to each other. In the initial loading core of the boiling water reactor with the unit loading unit arrangement area arranged in
A first control cell comprising four low enriched fuel assemblies arranged in two rows and two columns;
The total of the contents of the fissile material in the fuel assembly, which is composed of the four low enriched fuel assemblies arranged in 2 rows and 2 columns and constitutes the unit loading unit including the low enriched fuel assemblies, A second control cell that is smaller than the total content of fissile material in the fuel assembly constituting the unit loading unit including the low-enriched fuel assembly of the first control cell;
A first loaded core of a boiling water reactor characterized by having: One control rod extends in the vertical direction, including a region in which cells composed of four quadrangular cylindrical fuel assemblies extending in the vertical direction are surrounded by a control rod insertion portion in which the control rod can be inserted in the vertical direction. A core in which the fuel assemblies are arranged in a square lattice pattern in a substantially cylindrical region, and one low enriched fuel assembly of the fuel assemblies and a content of fissile material than the low enriched fuel assembly. Unit loading units in which three high enrichment fuel assemblies with large size are arranged in two rows and two columns surrounded by the four control rod insertion portions are arranged so that the low enrichment fuel assemblies included in each unit loading unit are adjacent to each other. In the initial loading core of the boiling water reactor with the unit loading unit arrangement area arranged in
A first control cell comprising four low enriched fuel assemblies arranged in two rows and two columns;
Composed of four low enriched fuel assemblies arranged in two rows and two columns, and the total content of combustible poisons in the fuel assemblies constituting the unit loading unit including the low enriched fuel assemblies is A second control cell that is larger than the total content of combustible poisons in the fuel assembly constituting the unit loading unit including the low-enriched fuel assembly of the first control cell;
A first loaded core of a boiling water reactor characterized by having: One control rod extends in the vertical direction, including a region in which cells composed of four quadrangular cylindrical fuel assemblies extending in the vertical direction are surrounded by a control rod insertion portion in which the control rod can be inserted in the vertical direction. A core in which the fuel assemblies are arranged in a square lattice pattern in a substantially cylindrical region, and one low enriched fuel assembly of the fuel assemblies and a content of fissile material than the low enriched fuel assembly. Unit loading units in which three high enrichment fuel assemblies with large size are arranged in two rows and two columns surrounded by the four control rod insertion portions are arranged so that the low enrichment fuel assemblies included in each unit loading unit are adjacent to each other. Comprising a unit loading unit arrangement region arranged in a central region formed inside the unit loading unit arrangement region, and formed inside the unit loading unit arrangement region outside in the radial direction from the central region, An intermediate region larger content of the average fissile material per position loading unit as compared to the central region, the boiling water reactor operating method having the initial core which is formed,
Boiling water characterized in that the control rod inserted into the control rod insertion portion surrounded by a control cell comprising four low enriched fuel assemblies arranged in two rows and two columns is used for reactor control. Type reactor operation method. One control rod extends in the vertical direction, including a region in which cells composed of four quadrangular cylindrical fuel assemblies extending in the vertical direction are surrounded by a control rod insertion portion in which the control rod can be inserted in the vertical direction. A core in which the fuel assemblies are arranged in a square lattice pattern in a substantially cylindrical region, and one low enriched fuel assembly of the fuel assemblies and a content of fissile material than the low enriched fuel assembly. The unit enriched fuel assemblies included in each unit loading unit are arranged in two rows and two columns surrounded by four control rod insertion portions, so that the low enriched fuel assemblies are adjacent to each other. Comprising a unit loading unit arrangement region arranged in a central region formed inside the unit loading unit arrangement region, and formed inside the unit loading unit arrangement region outside in the radial direction from the central region, A smaller middle area content of position average burnable poison amount per loading unit as compared to the central region, the boiling water reactor operating method having the initial core which is formed,
Boiling water characterized in that the control rod inserted into the control rod insertion portion surrounded by a control cell comprising four low enriched fuel assemblies arranged in two rows and two columns is used for reactor control. Type reactor operation method. One control rod extends in the vertical direction, including a region in which cells composed of four quadrangular cylindrical fuel assemblies extending in the vertical direction are surrounded by a control rod insertion portion in which the control rod can be inserted in the vertical direction. A core in which the fuel assemblies are arranged in a square lattice pattern in a substantially cylindrical region, and one low enriched fuel assembly of the fuel assemblies and a content of fissile material than the low enriched fuel assembly. Unit loading units in which three high enrichment fuel assemblies with large size are arranged in two rows and two columns surrounded by the four control rod insertion portions are arranged so that the low enrichment fuel assemblies included in each unit loading unit are adjacent to each other. The first control cell comprising the four low-enriched fuel assemblies arranged in 2 rows and 2 columns, and the four low energy arrays arranged in 2 rows and 2 columns Consisting of a concentrated fuel assembly, it The sum of the contents of the fissile material in the fuel assembly constituting the unit loading unit including the low enriched fuel assembly constitutes the unit loading unit including the low enriched fuel assembly of the first control cell. In a method for operating a boiling water reactor comprising a first loaded core formed with a second control cell smaller than the total content of fissile materials in the fuel assembly,
A first step of using the control rod inserted into the control rod insertion portion surrounded by the first control cell for controlling a nuclear reactor;
A second step of using the control rod inserted in the control rod insertion portion surrounded by the second control cell after the first step for control of a nuclear reactor;
A method for operating a boiling water reactor characterized by comprising: One control rod extends in the vertical direction, including a region in which cells composed of four quadrangular cylindrical fuel assemblies extending in the vertical direction are surrounded by a control rod insertion portion in which the control rod can be inserted in the vertical direction. A core in which the fuel assemblies are arranged in a square lattice pattern in a substantially cylindrical region, and one low enriched fuel assembly of the fuel assemblies and a content of fissile material than the low enriched fuel assembly. Unit loading units in which three high enrichment fuel assemblies with large size are arranged in two rows and two columns surrounded by the four control rod insertion portions are arranged so that the low enrichment fuel assemblies included in each unit loading unit are adjacent to each other. The first control cell comprising the four low-enriched fuel assemblies arranged in 2 rows and 2 columns, and the four low energy arrays arranged in 2 rows and 2 columns Consisting of a concentrated fuel assembly, it The sum of the contents of combustible poisons in the fuel assembly constituting the unit loading unit including the low enriched fuel assembly constitutes the unit loading unit including the low enriched fuel assembly in the first control cell. In a method for operating a boiling water reactor comprising a first control core formed with a second control cell that is larger than the total content of combustible poisons in the fuel assembly,
A first step of using the control rod inserted into the control rod insertion portion surrounded by the first control cell for controlling a nuclear reactor;
A second step of using the control rod inserted in the control rod insertion portion surrounded by the second control cell after the first step for control of a nuclear reactor;
A method for operating a boiling water reactor characterized by comprising:

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