JP2009250894A - Fuel assembly loaded in boiling water reactor, and reactor core using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve fuel economic performance of a fuel assembly, with a water channel to be loaded in a boiling water reactor, while ensuring the thermal tolerance thereof. <P>SOLUTION: The fuel assembly 81 comprises a plurality of fuel rods 51, 52 and 53, each having a nuclear fuel material stored in a cylindrical cladding tube, and aligned in a square-grid shape, with the lower end thereof being supported by a lower tie plate; and a water channel 38 extended in a square cylindrical shape in the same direction as the fuel rods 51, 52 and 53 to occupy a plurality of grid positions of the square grid, in which the fuel rods 51, 52 and 53 are aligned, and carrying a coolant in the inner part. The fuel rods 51, 52 and 53 include the standard fuel rod 51, the upper end of which is supported by an upper tie plate, and two or more kinds of partial length fuel rods 52, 53 which are smaller in length than the standard fuel rod 51 and differed in length to each other. At least one partial length fuel rod 52, 53 is disposed at a position adjacent to each side surface of the water channel 38. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel assembly loaded in a boiling water reactor and a core using the same.

  FIG. 18 is a partially enlarged cross-sectional view showing the arrangement of fuel assemblies in the core of a typical boiling water reactor (BWR). A BWR core is generally configured by arranging four fuel assemblies 15 as a set. The fuel assembly 15 is configured by arranging fuel rods 50 in a square lattice pattern. The fuel assembly 15 is loaded into the core in a state where a channel box 31 having a rectangular cross section surrounding the fuel assembly 15 is mounted. By providing the channel box 31, gap water regions 20 and 21 are formed on the outside of the channel box 31. The gap water regions 20 and 21 serve as flow paths through which light water of the coolant flows without boiling. The gap water region can be divided into two types: a gap water region 20 in which the control rod 19 is inserted and a gap water region 21 in which the control rod 19 is not taken in and out.

  The BWR core includes a C lattice core, an S lattice core and an N lattice core in which the areas of the gap water region 20 and the gap water region 21 are equal, and the area of the gap water region 20 which is larger than the area of the gap water region 21. There is a lattice core. In the C lattice core, the S lattice core, and the N lattice core, the fuel assembly 15 is disposed in the center of the unit cell 17. In the D lattice core, the fuel assembly 15 is arranged slightly eccentric from the center of the unit cell 17 to the opposite side of the control rod 19.

  A water rod 22 may be arranged near the center of the cross section of the fuel assembly 15. Further, an upper tie plate and a lower tie plate that support upper and lower ends of the fuel rod 50 and the water rod 22 are located at the upper and lower portions of the fuel assembly 15. Alternatively, a square water channel may be used instead of the water rod 22.

  During operation, slightly unsaturated cooling water flows into the fuel assembly 15 from the hole of the lower tie plate into the gap of the fuel rods 50 and is heated by the fuel rods 50 as it flows between the fuel rods 50 from the lower part to the upper part. It is boiled and flows out of the upper tie plate hole as a two-phase flow. As a result, the void ratio of the coolant is 0% at the lower part of the fuel assembly 15 but reaches about 70% at the upper part. For this reason, the moderator-to-fuel ratio, that is, the hydrogen-to-uranium ratio (H / U ratio), which is a factor that determines the nuclear characteristics of the fuel assembly 15, greatly varies depending on the axial position. This axial H / U ratio distribution has the effect of reducing the furnace shutdown margin.

  On the other hand, outside the channel box 31 of the fuel assembly 15 is provided a gap for arranging the control rod 19 and a neutron detector instrumentation tube (not shown). As described above, the gap is filled with saturated water, and gap water regions 20 and 21 are formed which serve as channels through which light water of the coolant flows without boiling.

  Due to the existence of such gap water regions 20 and 21, saturation is caused between the fuel rods 16 arranged in the peripheral portion of the fuel assembly 15 (region close to the gap) and the fuel rods 16 in the center of the fuel assembly 15. The effect of water is different. That is, the peripheral portion of the fuel assembly 15 near the gap water regions 20 and 21 is a region having a larger H / U ratio than the central portion. As described above, the H / U ratio, which is a factor that determines the nuclear characteristics, differs at the radial position (cross-sectional direction position) in the fuel assembly 15. This radial distribution of the H / U ratio has the effect of increasing local output peaking. In particular, in the D lattice core where the gap water region 20 into which the control rod 19 is inserted is wider than the area of the gap water region 21 where the control rod 19 is not taken in and out, the gap water region 20 into which the control rod 19 is inserted and the control. Unlike the C lattice core in which the area of the gap water region 21 where the rod 19 is not taken in and out is equal, the H / U ratio is greatly different between the side facing the control rod 19 and the opposite side.

  The H / U ratio is a parameter that determines the average energy of neutrons. FIG. 19 is a graph showing the behavior of the infinite multiplication factor when the horizontal axis represents H / U for a typical boiling water reactor fuel assembly. In FIG. 19, the case where the average enrichment of the fuel assembly is low is indicated by a solid line, and the case where the average enrichment of the fuel assembly is high is indicated by a broken line. As the H / U ratio increases, the neutron spectrum becomes soft, that is, the neutron average energy is lowered, the fission reaction with the nuclear fuel material is promoted, and the infinite multiplication factor is also increased. However, as the neutron spectrum becomes softer, the neutron absorption reaction by the moderator (light water) increases, so the infinite multiplication factor peaks at a certain H / U ratio, and when the H / U ratio is exceeded, the H / U ratio increases. As it increases, the infinite multiplication factor decreases.

  Therefore, high energy is obtained with as little fuel as possible, that is, from the viewpoint of fuel economy, this peak is the optimum value of the H / U ratio. In practice, an H / U ratio slightly smaller than the peak position is a practical optimum value from the viewpoint of setting the reactivity coefficient to a moderately negative value in order to ensure the safety of the nuclear reactor.

  As described above, improving and optimizing the axial / radial distribution of the H / U ratio is very important from the viewpoint of fuel economy, so that various improvements have been made in the past. Yes.

  In order to improve the H / U ratio in the axial direction of the fuel assembly, for example, Patent Document 1 discloses a method of providing partial length fuel rods whose effective fuel length is shorter than normal fuel rods. By providing the partial-length fuel rods, it is possible to increase the saturated water region where no phase change occurs and adjust the axial fuel loading, thereby improving the axial H / U ratio.

  There are also methods for increasing the number of water rods or increasing the size of the water rods in order to improve the H / U ratio in the radial direction of the fuel assembly. By such a method, the water rod region can be increased in the central region of the fuel assembly where the neutron moderating effect is not sufficient, and the radial H / U ratio can be improved. In particular, in the fuel assembly loaded in the D-grid core, the area of the gap water region on the side where the control rod is located and the gap water region on the opposite side are not equal, so the H / U ratio in the radial direction becomes non-uniform. Local power peaking tends to increase.

  For this, there is a method of adjusting the enrichment of uranium 235 of the fuel rod. In this method, the fuel rod on the side facing the narrow gap water region where the thermal neutron flux is small has a relatively high enrichment, and the fuel rod on the side facing the wide gap water region where the thermal neutron flux is large is relatively low in enrichment. And Thereby, both output differences are reduced and local output peaking in the radial direction is suppressed.

  In a boiling water reactor, as a method for improving the plant utilization rate and effectively utilizing uranium resources, there is a fuel burnup and a long-term operation cycle. Since it is necessary to increase the enrichment in order to increase the take-off combustion degree of the fuel assembly, the H / U ratio changes. Further, the extension of the residence time in the furnace due to the long-term operation cycle means that the fuel assembly is subjected to the influence of the H / U ratio being different in the axial direction and the radial direction in the core for a long time. The effect of the / U ratio is further expanded.

In order to improve the H / U ratio in the fuel assembly, a method of disposing a water rod or a water channel in the fuel assembly is disclosed (for example, see Patent Document 2). Further, in order to improve the H / U ratio, a method of disposing a fuel rod that does not have a fuel rod portion in a part of the effective length and allows a moderator to flow, such as a partial length fuel rod, is disclosed ( For example, see Patent Document 1). In some cases, the H / U ratio can be improved by specifying the arrangement of water rods, water channels, and partial-length fuel rods (see, for example, Patent Document 3). A method in which these methods are combined is disclosed in, for example, Patent Document 4 and Patent Document 5. Further, for example, Patent Document 6 and Patent Document 7 disclose a method in which the lengths of the partial-length fuel rods are two types.
Japanese Patent Laid-Open No. 52-50498 Japanese Patent Laid-Open No. 62-217186 JP-A-11-194190 Japanese Patent Laid-Open No. 11-109073 Japanese Patent Laid-Open No. 10-260281 JP 2005-274555 A JP 2006-184174 A

  When water rods or water channels that occupy a plurality of positions of the square lattice in which the fuel rods are arranged are provided in the fuel assembly, water as a moderator is arranged in a concentrated manner. For this reason, in the vicinity of the water rod or the water channel, the deceleration of neutrons is promoted, and as a result, the local linear power density of the fuel rod increases. When the local linear power density increases, a sufficient thermal margin cannot be secured. For this reason, it is necessary to reduce the enrichment of uranium loaded on the fuel rod at a position where the linear power density is locally increased.

  In order to increase the burnup of the fuel assembly, it is necessary to increase the average enrichment of the fuel assembly. However, in order to improve the H / U ratio, simply providing a water rod or a water channel results in lowering the enrichment of the surrounding fuel rods in order to secure a thermal margin. In particular, since the water channel has a rectangular tube shape, the number of fuel rods that are close to the water region inside the water channel is larger than that of the cylindrical water rod.

  Accordingly, an object of the present invention is to improve fuel economy while ensuring a thermal margin of a fuel assembly including a water channel loaded in a boiling water reactor.

  In order to achieve the above-mentioned object, the present invention provides a fuel assembly loaded in a boiling water reactor, wherein an upper tie plate, a lower tie plate spaced from the upper tie plate, and the lower tie plate are disposed. A plurality of fuel rods in which a nuclear fuel material is housed in a cylindrical cladding tube extending in a direction from the tie plate toward the upper tie plate, arranged in a square lattice and supported at the lower end by the lower tie plate, and the fuel rods A water channel extending in a rectangular tube shape in the same direction as the fuel rods so as to occupy a plurality of lattice positions of the square lattice arranged, and having a lower end supported by the lower tie plate through which the coolant flows. The fuel rod includes a standard fuel rod supported at the upper end of the upper tie plate and a partial length fuel rod shorter than the standard fuel rod; At least one partial-length fuel rod is disposed at a position adjacent to the surface, and the partial-length fuel rod disposed at a position adjacent to the side surface of the water channel is a long partial-length fuel rod and the long partial length And a short partial length fuel rod shorter than the fuel rod.

  Further, according to the present invention, in the core of a boiling water reactor loaded with a plurality of fuel assemblies, at least one of the fuel assemblies is disposed at an interval from the upper tie plate and the upper tie plate. A plurality of lower tie plates and a cylindrical cladding tube extending in a direction from the lower tie plate toward the upper tie plate, arranged in a square lattice and supported at the lower end by the lower tie plate The lower end of the fuel rod is supported by the lower tie plate that extends in a rectangular tube shape in the same direction as the fuel rod so as to occupy a plurality of lattice positions of a square lattice in which the fuel rod is arranged, and in which the coolant flows. The fuel rod includes a standard fuel rod having an upper end supported by the upper tie plate and a partial-length fuel rod shorter than the standard fuel rod. At least one partial-length fuel rod is disposed at a position adjacent to each side surface of the water channel, and the partial-length fuel rod disposed at a position adjacent to the side surface of the water channel is a long partial-length fuel rod; A short partial length fuel rod shorter than the long partial length fuel rod.

  According to the present invention, the fuel economy can be improved while ensuring the thermal margin of the fuel assembly including the water channel loaded in the boiling water reactor.

  An embodiment of a fuel assembly 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 perspective view of the first embodiment of the fuel assembly according to the present invention.

  The fuel assembly 81 according to the present embodiment has an upper tie plate 41 and a lower tie plate 42 that is disposed at a distance from the upper tie plate 41. Further, the fuel assembly 81 has a fuel rod 50 extending in a direction from the lower tie plate 42 toward the upper tie plate 41. The fuel rods 50 are arranged in a square lattice shape and are supported by the lower tie plate 42.

  The fuel assembly 81 has a water channel 38. The water channel 38 occupies a plurality of lattice positions of a square lattice in which the fuel rods 50 are arranged, and extends in a rectangular tube shape in the same direction as the fuel rods 50. Inside the water channel 38, a coolant is formed to flow. The lower end of the water channel 38 is supported by the lower tie plate 42. The water channel 38 does not have to be formed in a rectangular tube shape at all the portions from the lower end to the upper end, and a cylindrical tube may be connected to the upper portion and the lower portion.

  Further, the fuel assembly 81 may have a spacer 63 so that the fuel rod 50 and the water channel 38 are arranged at a predetermined lattice position even at a position away from the lower tie plate 42. The spacer 63 is supported by the water channel 38 at, for example, seven locations in the axial direction.

  This fuel assembly 81 is loaded on the core with a rectangular tubular channel box 31 having both ends open.

  FIG. 3 is a side view of the fuel rod in the present embodiment.

  The fuel rod 50 includes a standard fuel rod 51, a long partial length fuel rod 52, and a short partial length fuel rod 53. The long partial fuel rod 52 and the short partial fuel rod 53 are collectively referred to as a partial fuel rod. Each of the standard fuel rod 51, the long partial length fuel rod 52, and the short partial length fuel rod 53 has a nuclear cladding material 48 contained in a cylindrical cladding tube 48. Both ends of the cladding tube 48 are sealed with end plugs 43. The nuclear fuel material is contained in a cladding tube 48 as pellets 26 baked into a plurality of short cylindrical shapes, for example. The area where the nuclear fuel material is stored is called a fuel effective part.

  The long partial fuel rod 52 is shorter than the standard fuel rod 51. Accordingly, the fuel effective portion of the long partial fuel rod 52 is shorter than the standard fuel rod 51. The length of the fuel effective portion of the long partial fuel rod 52 is, for example, 16/24 of the length of the fuel effective portion of the standard fuel rod 51. The short partial length fuel rods 53 are shorter than the long partial length fuel rods 52. Accordingly, the effective fuel portion of the short partial fuel rod 53 is shorter than the standard fuel rod 51. The length of the fuel effective portion of the short partial length fuel rod 53 is, for example, 8/24 of the length of the fuel effective portion of the standard fuel rod 51. The standard fuel rod 51, the long partial length fuel rod 52, and the short partial length fuel rod 53 are all supported by the lower tie plate 42, and the lower ends of the fuel effective portions are at the same axial position.

  The upper end of the standard fuel rod 51 is supported by the upper tie plate 41. That is, the upper and lower ends of the standard fuel rod 51 are supported by the upper tie plate 41 and the lower tie plate 42. On the other hand, the upper ends of the long partial fuel rods 52 and the short partial fuel rods 53 are not supported by the upper tie plate 41.

  FIG. 4 is a cross-sectional view of a core using the fuel assembly of the present embodiment.

  Four fuel assemblies 81 are loaded in the boiling water reactor so as to surround one control rod 19 in four bodies, and form a substantially cylindrical core as a whole. Note that some fuel assemblies 81 in the peripheral portion of the core are arranged without facing the control rod 19. A plurality of neutron detectors 30 are provided between the fuel assemblies 81.

  FIG. 1 is a cross-sectional view showing the arrangement of fuel rods in the present embodiment.

  The fuel assembly 81 according to the present embodiment is loaded into the C lattice core in which the area of the gap water region 20 on the side where the control rod 19 is inserted is equal to the area of the gap water region 21 in the region where the control rod 19 is not inserted or removed. Is a fuel assembly. The gap water region 20 on the side where the control rod 19 is inserted may be loaded into the S lattice core or the N lattice core where the area of the gap water region 21 in the region where the control rod 19 is not taken in and out is equal. Alternatively, the gap water region 20 on the side where the control rod 19 is inserted may be loaded into a D-grid core that is larger than the area of the gap water region 21 in a region where the control rod 19 is not taken in and out.

  In this fuel assembly 81, the fuel rods 51, 52, 53 are arranged in a 9 × 9 square lattice. Further, the water channel 38 occupies a lattice position of 3 rows and 3 columns in the center of the cross section of the fuel assembly 81.

  At least one of a long partial length fuel rod 52 and a short partial length fuel rod 53 is disposed adjacent to each side surface of the water channel 38. In the present embodiment, one short part-length fuel rod 53 is disposed at the center in the cross-sectional direction of each side surface of the water channel 38. Further, long partial fuel rods 52 are arranged facing both end portions of each side surface of the water channel 38 in the cross-sectional direction. That is, all the fuel rods adjacent to the water channel 38 are either the long partial length fuel rods 52 or the short partial length fuel rods 53. Further, the fuel rod arranged at a position adjacent to the side surface of the water channel 38 is longer in the fuel rod closer to the end of the side surface in the cross-sectional direction.

  FIG. 5 is a graph showing an example of a change in the axial direction of the void ratio during normal operation of the boiling water reactor.

  In a boiling water reactor, the coolant flowing from the lower part of the core flows upward while being heated by the heat generated by the fission. The heated coolant boils while flowing upward, and voids are generated. The ratio of the cross-sectional area of the void to the cross-sectional area through which the coolant flows, that is, the void ratio increases as it goes above the core.

  In a fuel assembly loaded in a boiling water reactor, it is preferable to reduce pressure loss in a region where voids exist, that is, a two-phase flow part to some extent, in order to ensure stability. Therefore, in order to ensure stability, it is necessary to reduce the number of fuel rods in the two-phase flow part to some extent. In other words, a certain number of fuel rods with missing two-phase flow portions are required. When the defect length of the fuel rod in the two-phase flow part is determined, the total effective fuel length, that is, the loaded amount (inventory) of the nuclear fuel material is almost determined.

  Since the void ratio is low at the lower portion of the fuel assembly 81, the neutron moderation effect by the water channel 38 is relatively smaller than that at the upper portion where the void ratio is high. However, when the void ratio increases and the neutron moderation effect by the water channel 38 increases, the linear power density of the fuel rods 51, 52, 53 near the water channel 38 becomes relatively high. Further, the influence of the neutron moderating effect by the water channel 38 is greatest in the vicinity of the central portion of each of the four side surfaces of the water channel 38 in the cross-sectional direction. Therefore, in the fuel rods 51, 52, and 53 at positions adjacent to the water channel 38, the amount of fissile material must be suppressed in order to suppress the linear power density, particularly in the upper part in the axial direction where the void ratio is high. It may not be possible.

  FIG. 6 is a schematic diagram showing an example of enrichment of uranium contained in a fuel rod when the length of a partial length fuel rod is one type compared to the case where the length of a partial length fuel rod is two types. FIG. In FIG. 6, (a) and (c) are long partial length fuel rods when the lengths of partial length fuel rods are two types, and (b) is when the lengths of partial length fuel rods are two types. (D) thru | or (f) show the partial length fuel rod when the length of a partial length fuel rod is made into one kind. In FIG. 6, (a) to (c) and (d) to (f) are arranged in the order viewed from the water channel 38 side.

  In order to make the length of the missing portion of the fuel rod in the two-phase flow portion indicated by the dotted line in FIG. 6 the same as when the length of the partial length fuel rod is two types, the length of the partial length fuel rod is set to 1. The length of the partial length fuel rods ((d), (e), (f)) is longer than that of the short partial length fuel rods (b), and the long partial length fuel rods ((a), It is necessary to make it shorter than (c)). If the length of the partial-length fuel rods is one kind, the void ratio increases at the upper part of the partial-length fuel rod (e) facing the central portion of the side surface of the water channel 38 in the cross-sectional direction. When the neutron moderation effect is increased and uranium having a concentration of 4.9% by weight is loaded, the linear power density may become too high. For this reason, this portion may be loaded only with uranium having a concentration lower than 4.9% by weight.

  Moreover, in the nuclear fuel processing factory, the enrichment degree of uranium handled there is discontinuous from the viewpoint of ensuring the distinguishability of pellets. In addition, in order to simplify the design and facilitate the manufacture, it is preferable that the axial region in which pellets having the same concentration are loaded be long. Therefore, in the upper part of the partial-length fuel rod (e) facing the central portion in the cross-sectional direction of the side surface of the water channel 38, the region of a certain length differs to some extent from 4.9% by weight, for example, 3.9 It will be loaded with uranium enriched by weight. For this reason, if the length of the partial-length fuel rod is set to one type, the average of the uranium enrichment in the entire fuel assembly 81 is reduced, and the fuel economy is lowered.

  However, when the lengths of the partial length fuel rods are two types, the partial length fuel rods (b ) Can be a short part-length fuel rod. As a result, even if any of the partial-length fuel rods is loaded with uranium having a concentration of 4.9% by weight of uranium 235, a thermal margin can be ensured and the design has no safety problem. In particular, the effect is large in a fuel assembly having an average enrichment of uranium 235 of 3.9% by weight or more.

  In this embodiment, the effective fuel length of the long partial length fuel rod 52 is 16/24 of the standard fuel rod 51, and the effective fuel length of the short partial length fuel rod 53 is 8/24 of the standard fuel rod 51. However, the lengths of the partial-length fuel rods 52 and 53 are not limited to these. For example, a long or short one can be used as appropriate depending on the void ratio distribution in the axial direction.

  As described above, in the fuel assembly according to the present embodiment, two types of partial length fuel rods are used at positions adjacent to the water channel, and these are appropriately used depending on the location, so that uranium can be contained in the fuel rods. Maintains safety without lowering the concentration of. For this reason, it is possible to improve the fuel economy by increasing the average of the uranium enrichment in the entire fuel assembly while securing the thermal margin.

[Second Embodiment]
FIG. 7 is a cross-sectional view showing the arrangement of fuel rods in the second embodiment of the fuel assembly according to the present invention.

  The fuel assembly 82 of the present embodiment has a D-grid core in which the area of the gap water region 20 on the side where the control rod 19 is inserted is larger than the area of the gap water region 21 in the region where the control rod 19 is not inserted or removed. A fuel assembly to be loaded. This fuel assembly 82 also uses two types of partial length fuel rods, a long partial length fuel rod 52 and a short partial length fuel rod 53.

  In this fuel assembly 82, the fuel rods 51, 52, 53 are arranged in a 9 × 9 square lattice. Further, the water channel 38 occupies a lattice position of 3 rows and 3 columns in the center of the cross section of the fuel assembly 81.

  The long partial fuel rods 52 are arranged one by one adjacent to the side surface of the water channel 38 far from the control rod 19. These long part-length fuel rods 52 are arranged so as to face the central portion of the side surface of the water channel 38 in the cross-sectional direction. The short partial fuel rods 53 are arranged one by one adjacent to the side surface of the water channel 38 closer to the control rod 19. These short part-length fuel rods 53 are arranged so as to face the center portion of the side surface of the water channel 38 in the cross-sectional direction.

  Although the linear power density of the fuel rods tends to increase at positions adjacent to the side surface of the water channel 38, the enrichment of uranium may also occur at these positions depending on the design such as the enrichment of uranium contained in other fuel rods. In some cases, the standard fuel rods 51 can be arranged without lowering. Therefore, in the fuel assembly 82 according to the present embodiment, the standard fuel rods 51 are disposed at positions facing both ends of the side surface of the water channel 38 in the cross-sectional direction.

  Further, in the fuel assembly 82 loaded in the D lattice core, the closer to the control rod 19, the closer the area to the gap water region 20. For this reason, the fuel rod adjacent to the side surface of the water channel 38 closer to the control rod 19 has a higher linear power density than the fuel rod adjacent to the side surface of the water channel 38 farther from the control rod 19. Tend to be.

  Therefore, in the fuel assembly 82 of the present embodiment, the position of the side surface of the water channel 38 closer to the control rod 19 facing the central portion in the cross-sectional direction is long without reducing the enrichment of uranium. A partial-length fuel rod 52 is disposed. In this way, at the position facing the central portion in the cross-sectional direction of the side surface of the water channel 38, the length of the partial-length fuel rod is changed in accordance with the distance from the control rod 19, so that the fuel disposed there The line power density of the bar is suppressed, thermal margin is secured, and safety is maintained.

  As described above, in the fuel assembly according to the present embodiment, the standard fuel rods and the two partial length fuel rods are used at positions adjacent to the water channel, and these are appropriately used depending on the location. It maintains safety without reducing the enrichment of uranium in the rod. For this reason, it is possible to improve the fuel economy by increasing the average of the uranium enrichment in the entire fuel assembly while securing the thermal margin.

[Third Embodiment]
FIG. 8 is a cross-sectional view showing the arrangement of fuel rods in the third embodiment of the fuel assembly according to the present invention.

  The fuel assembly 83 of the present embodiment has a D-grid core in which the area of the gap water region 20 on the side where the control rod 19 is inserted is larger than the area of the gap water region 21 in the region where the control rod 19 is not taken in and out. A fuel assembly to be loaded. This fuel assembly 83 also uses two types of partial length fuel rods, a long partial length fuel rod 52 and a short partial length fuel rod 53.

  In this fuel assembly 83, the fuel rods 51, 52, 53 are arranged in a 9 × 9 square lattice. Further, the water channel 38 occupies a lattice position of 3 rows and 3 columns in the center of the cross section of the fuel assembly 81.

  Two long partial fuel rods 52 are arranged adjacent to the side surface of the water channel 38 closer to the control rod 19. These long partial fuel rods 52 are arranged so as to face both ends of the side surface of the water channel 38 in the cross-sectional direction. The short partial fuel rods 53 are arranged one by one adjacent to the side surface of the water channel 38 far from the control rod 19. These short part-length fuel rods 53 are arranged so as to face the center portion of the side surface of the water channel 38 in the cross-sectional direction.

  In the fuel assembly 82 loaded in the D lattice core, the closer to the control rod 19, the closer the area to the gap water region 20. For this reason, the fuel rod adjacent to the side surface of the water channel 38 closer to the control rod 19 has a higher linear power density than the fuel rod adjacent to the side surface of the water channel 38 farther from the control rod 19. Tend to be.

  For this reason, the standard fuel rod 51 may be used without lowering the enrichment of uranium at positions facing both ends in the cross-sectional direction of the side surface of the water channel 38 far from the control rod 19. Further, in the position facing the central portion in the cross-sectional direction of the side surface of the water channel 38 far from the control rod 19, the long partial length fuel rod 52 may be used without reducing the enrichment of uranium. is there.

  On the other hand, at the positions facing both ends in the cross-sectional direction of the side surface of the water channel 38 closer to the control rod 19, the long partial length fuel rod 52 or the standard fuel rod 51 is used without reducing the enrichment of uranium. In some cases, the linear power density becomes too high at the upper part in the axial direction. Therefore, in the fuel assembly 82, the short partial length fuel rods 53 are arranged at these positions. Therefore, these short partial length fuel rods 53 can be loaded with highly enriched uranium.

  Further, a standard fuel rod 54 loaded with uranium having a low enrichment is disposed at a position facing the central portion in the cross-sectional direction of the side surface of the water channel 38 far from the control rod 19. As a result, the linear power density of the fuel rods arranged at the position facing the central portion in the cross-sectional direction of the side surface of the water channel 38 far from the control rod 19 is suppressed, and safety is maintained.

  Thus, in the fuel assembly 82 of the present embodiment, the number of fuel rods loaded with uranium having a low enrichment is suppressed. For this reason, the average of the uranium enrichment in the whole fuel assembly 82 can be increased, and fuel economy can be improved.

  It should be noted that a partial length fuel rod shorter than the short partial length fuel rod 53 may be used at a position facing the central portion in the cross-sectional direction of the side surface of the water channel 38 far from the control rod 19. In this case, there is a possibility that a thermal margin can be ensured without reducing the enrichment of uranium in the partial length fuel rods that are shorter than the short length partial length fuel rods 53.

  As described above, in the fuel assembly according to the present embodiment, the standard fuel rods and the two partial length fuel rods are used at positions adjacent to the water channel, and these are appropriately used depending on the location. It maintains safety without reducing the enrichment of uranium in the rod. For this reason, it is possible to improve the fuel economy by increasing the average of the uranium enrichment in the entire fuel assembly while securing the thermal margin.

[Fourth Embodiment]
FIG. 9 is a cross-sectional view showing the arrangement of fuel rods in the fourth embodiment of the fuel assembly according to the present invention.

  In this fuel assembly 84, the fuel rods 51, 52, 53 are arranged in a 10 × 10 square lattice. Further, the water channel 38 is eccentrically arranged away from the control rod 19 from the center of the cross section of the fuel assembly 81 and occupies a lattice position of 3 rows and 3 columns.

  The fuel assembly 84 of the present embodiment is loaded on the C lattice core. The fuel assembly 84 may be loaded into an S lattice core, an N lattice core, or a D lattice core.

  Even in the fuel assembly 84 in which the fuel rods 51, 52, 53 are arranged in 10 rows and 10 columns, the linear output density of the fuel rods tends to increase at a position adjacent to the side surface of the water channel 38. In addition, this tendency is greatest when the side surface of the water channel 38 faces the central portion in the cross-sectional direction.

  Therefore, in the fuel assembly 84 of the present embodiment, one short part-length fuel rod 53 is arranged at the center in the cross-sectional direction of each side surface of the water channel 38. Further, long partial fuel rods 52 are arranged facing both end portions of each side surface of the water channel 38 in the cross-sectional direction. Therefore, as in the first embodiment, a thermal margin can be ensured without reducing the enrichment of uranium loaded on the fuel rods adjacent to the respective side surfaces of the water channel 38.

  As described above, in the fuel assembly according to the present embodiment, two types of partial length fuel rods are used at positions adjacent to the water channel, and these are appropriately used depending on the location, so that uranium can be contained in the fuel rods. Maintains safety without lowering the concentration of. For this reason, it is possible to improve the fuel economy by increasing the average of the uranium enrichment in the entire fuel assembly while securing the thermal margin.

[Fifth Embodiment]
FIG. 10 is a cross-sectional view showing the arrangement of the fuel rods in the fifth embodiment of the fuel assembly according to the present invention.

  The fuel assembly 85 of the present embodiment is arranged at the center of each of the four sides of the standard fuel rods 51 located on the four sides of the outer periphery of the fuel assembly 84 (see FIG. 9) of the fourth embodiment. Two pieces located at a time are used as short partial length fuel rods 53.

  Since the gap water regions 20 and 21 exist around the fuel assembly 85, the linear power density of the fuel rods 51, 52, and 53 tends to increase at the outermost peripheral position of the fuel assembly 85. For this reason, the uranium loaded on the fuel rods 51, 52, 53 arranged on the outermost periphery of the fuel assembly 85 may have a low enrichment in order to secure thermal margin and maintain safety. .

  On the other hand, in the fuel assembly 85 of the present embodiment, the short partial length fuel rods 53 are arranged at a part of the outermost peripheral position of the fuel assembly 85 where the relative linear power density increases at the upper part in the axial direction. Yes. For this reason, there is a case where a thermal margin can be ensured even if the enrichment of uranium in the short part length fuel rod 53 located on the outermost periphery is not lowered so much.

  Further, depending on the design such as enrichment of uranium contained in other fuel rods, the short partial length fuel rod 53 located on the outermost periphery may be used as the long partial length fuel rod 52 in some cases. Therefore, by setting the length of the partial-length fuel rods to two types, the degree of freedom in design is improved, and accordingly, fuel economy can be improved.

  As described above, by arranging the partial-length fuel rods in addition to the position adjacent to the water channel 38, the fuel economy can be further improved while ensuring the thermal margin.

[Sixth Embodiment]
FIG. 11 is a cross-sectional view showing the arrangement of the fuel rods in the sixth embodiment of the fuel assembly according to the present invention.

  In the fuel assembly 86 of the present embodiment, the standard fuel rods 51 located at the four corners of the outer periphery of the fuel assembly 84 (see FIG. 9) of the fourth embodiment are used as short partial length fuel rods 53. It is.

  Since the gap water regions 20 and 21 exist around the fuel assembly 86, the linear power density of the fuel rods 51, 52, and 53 tends to increase at the outermost peripheral position of the fuel assembly 86. For this reason, the uranium loaded on the fuel rods 51, 52, and 53 arranged on the outermost periphery of the fuel assembly 86 may have a low enrichment in order to maintain safety. This tendency is greatest at the four corners of the outermost periphery having the largest area facing the gap water regions 20 and 21.

  Therefore, in the fuel assembly 86 of the present embodiment, the short partial length fuel rods 53 are arranged at the four corners of the outermost periphery of the fuel assembly 86 where the relative linear power density is increased at the upper part in the axial direction. . For this reason, it is not necessary to suppress an increase in the linear power density at the upper part in the axial direction, and safety can be achieved even if the uranium enrichment of the short partial length fuel rods 53 located at the four corners of the outermost periphery is not significantly reduced. May be able to maintain.

  Further, depending on the design such as enrichment of uranium contained in other fuel rods, the short partial length fuel rod 53 located on the outermost periphery may be used as the long partial length fuel rod 52 in some cases. Therefore, by setting the length of the partial-length fuel rods to two types, the degree of freedom in design is improved, and accordingly, fuel economy can be improved.

  As described above, by arranging the partial-length fuel rods in addition to the position adjacent to the water channel 38, the fuel economy can be further improved while ensuring the thermal margin.

[Seventh Embodiment]
FIG. 12 is a cross-sectional view showing the arrangement of fuel rods in the seventh embodiment of the fuel assembly according to the present invention.

  The fuel assembly 87 of the present embodiment is different from the fuel assembly 86 (see FIG. 11) of the sixth embodiment in the arrangement of fuel rods adjacent to the water channel 38. In the fuel assembly 87 of the present embodiment, the long partial length fuel rod 52 or the short partial length fuel rod 53 is disposed at a position facing the central portion of the side surface of the water channel 38 in the cross sectional direction. In addition, standard fuel rods 51 are disposed at positions facing both end portions of the side surface of the water channel 38 in the cross-sectional direction.

  When the water channel 38 occupying the lattice position of 3 rows and 3 columns is provided in the fuel assembly 87 in which the fuel rods 51, 52 and 53 are arranged in 10 rows and 10 columns, the water channels 38 are necessarily arranged eccentrically. It becomes. The fuel assembly 87 generally maintains symmetry with respect to a diagonal line connecting the corner closest to the center of the control rod 19 and the corner farthest from the center, so that the center of the water channel 38 is on this diagonal line. To position.

  Therefore, the four side surfaces of the water channel 38 can be divided into two side surfaces close to the gap water regions 20 and 21 and two side surfaces far from the gap water regions 20 and 21. The coolant in the water gap regions 20 and 21 is closer to the two side surfaces near the gap water regions 20 and 21 of the water channel 38 than in the position adjacent to the two side surfaces far from the water gap regions 20 and 21. The effect of neutron moderation effect by is great. Therefore, the fuel rods arranged at the positions adjacent to the two side surfaces near the gap water regions 20 and 21 of the water channel 38 are the fuels arranged at the positions adjacent to the two side surfaces far from the gap water regions 20 and 21. The line power density tends to be higher than that of the bar.

  Therefore, in the fuel assembly 87 of the present embodiment, the short partial length fuel rods 53 are disposed at positions adjacent to the two side surfaces of the water channel 38 close to the gap water regions 20 and 21, so that the gap water in the water channel 38 is disposed. Long partial fuel rods 52 are disposed at positions adjacent to the two side surfaces far from the regions 20 and 21. In other words, two types of partial-length fuel rods are arranged corresponding to the asymmetry that inevitably arises in the arrangement of the fuel rods inside the fuel assembly 87. For this reason, safety can be maintained without significantly reducing the enrichment of uranium loaded in the fuel rod.

  As described above, in the fuel assembly 87 according to the present embodiment, two types of partial-length fuel rods are adjacent to the water channel 38 to cope with the asymmetry that inevitably occurs in the fuel assembly 87. Can be designed. For this reason, fuel economy can be improved, ensuring a thermal margin.

[Eighth Embodiment]
FIG. 13 is a cross-sectional view showing the arrangement of fuel rods in the eighth embodiment of the fuel assembly according to the present invention.

  The fuel assembly 88 of the present embodiment is different from the fuel assembly 86 (see FIG. 11) of the sixth embodiment in the arrangement of fuel rods adjacent to the water channel 38. In the fuel assembly 88 of the present embodiment, the short partial length fuel rod 53 is disposed at a position facing the central portion in the cross-sectional direction of the side surface of the water channel 38 closer to the control rod 19. Standard fuel rods 51 are arranged at positions facing both ends in the cross-sectional direction of the side surface of the water channel 38 closer to the control rod 19. Long partial fuel rods 52 are arranged at positions facing both ends in the cross-sectional direction of the side surface of the water channel 38 far from the control rod 19. Further, a standard fuel rod 54 loaded with uranium having a low enrichment is disposed at a position facing the central portion in the cross-sectional direction of the side surface of the water channel 38 far from the control rod 19.

  When the water channel 38 occupying the lattice position of 3 rows and 3 columns is provided in the fuel assembly 88 in which the fuel rods 51, 52 and 53 are arranged in 10 rows and 10 columns, the water channels 38 are necessarily arranged eccentrically. It becomes. The fuel rods disposed at the positions adjacent to the two side surfaces near the gap water regions 20 and 21 of the water channel 38 are compared with the fuel rods disposed at the positions adjacent to the two side surfaces far from the gap water regions 20 and 21. As a result, the line power density tends to increase.

  Therefore, in the fuel assembly 88 of the present embodiment, the short part-length fuel rod 53 is disposed at a position facing the central part in the cross-sectional direction of the two side surfaces far from the gap water regions 20 and 21 of the water channel 38. On the other hand, a standard fuel rod 54 with reduced uranium enrichment is arranged at a position facing the central portion in the cross-sectional direction of the two side surfaces of the water channel 38 close to the gap water regions 20 and 21. is doing. Thereby, the linear output density of the fuel rods arranged at the position facing the central portion of the side surface of the water channel 38 in the cross-sectional direction is suppressed.

  Further, the standard fuel rods 51 are disposed at positions facing both ends in the cross-sectional direction of the two side surfaces far from the gap water regions 20 and 21 of the water channel 38, whereas the gap water of the water channel 38 is disposed. Long partial length fuel rods 52 that are longer than the short partial length fuel rods 53 are disposed at positions facing both ends in the cross-sectional direction of the two side surfaces close to the regions 20 and 21. Accordingly, it is possible to increase the amount of the nuclear fuel material loaded on the fuel rods arranged at the positions facing both ends of the side surface of the water channel 38 in the cross sectional direction while maintaining safety.

  As described above, in the fuel assembly 88 according to the present embodiment, two types of partial-length fuel rods are adjacent to the water channel 38 to cope with the asymmetry that inevitably occurs in the fuel assembly 87. Can be designed. For this reason, fuel economy can be improved, ensuring a thermal margin.

[Ninth Embodiment]
FIG. 14 is a cross-sectional view showing the arrangement of the fuel rods in the ninth embodiment of the fuel assembly according to the present invention.

  The fuel assembly 89 according to the present embodiment has the arrangement of the fuel rods 51, 52, 53 around the water channel 38 of the fuel assembly 88 (see FIG. 13) according to the eighth embodiment. The control rod 19 is replaced symmetrically with respect to the diagonal line that does not pass through the center.

  When the fuel assembly 88 of the eighth embodiment is loaded on the D lattice core, the fuel rod facing the side closer to the control rod 19 of the water channel 38 is more suitable for the uranium loaded on the other fuel rods. Depending on the design such as the degree of enrichment, the linear power density may be higher than the fuel rod facing the side surface of the water channel 38 closer to the control rod 19. Therefore, in the fuel assembly 89 of the present embodiment, the short partial length fuel rod 53 is disposed at a position facing the central portion in the cross-sectional direction of the two side surfaces far from the control rod 19 of the water channel 38. On the other hand, a standard fuel rod 54 with a reduced uranium enrichment is disposed at a position facing the center in the cross-sectional direction of the two side surfaces close to the control rod 19 of the water channel 38. Thereby, the linear output density of the fuel rods arranged at the position facing the central portion of the side surface of the water channel 38 in the cross-sectional direction is suppressed.

  In addition, the standard fuel rods 51 are disposed at positions facing both ends in the cross-sectional direction of the two side surfaces far from the control rods 19 of the water channel 38, whereas they are close to the control rods 19 of the water channel 38. Long partial length fuel rods 52 that are longer than the short partial length fuel rods 53 are arranged at positions facing both end portions in the cross-sectional direction of the two side surfaces. As a result, the amount of nuclear fuel material loaded on the fuel rods arranged at the positions facing both ends in the cross-sectional direction of the side surface of the water channel 38 is increased while ensuring safety and maintaining safety. Can be made.

  As described above, in the fuel assembly 89 according to the present embodiment, two types of partial-length fuel rods are adjacent to the water channel 38 to cope with the asymmetry that inevitably occurs in the fuel assembly 89. Can be designed. Further, the design corresponding to the asymmetry in the fuel assembly 89 loaded in the D lattice core can be realized. For this reason, fuel economy can be improved, ensuring a thermal margin.

[Tenth embodiment]
FIG. 15 is a cross-sectional view showing the arrangement of fuel rods in the tenth embodiment of the fuel assembly according to the present invention.

  The fuel assembly 90 of the present embodiment is obtained by changing the fuel rod adjacent to the side surface closer to the control rod 19 of the water channel 38 of the fuel assembly 89 (see FIG. 14) of the ninth embodiment. is there. A standard fuel rod 54 having a low uranium enrichment is disposed at a position facing the central portion in the cross-sectional direction of the side surface of the fuel assembly 89 closer to the control rod 19 of the water channel 38. Further, short part-length fuel rods 53 are disposed at positions facing both ends in the cross-sectional direction of the side surface of the water channel 38 closer to the control rod 19.

  In the fuel assembly 89 of the ninth embodiment, the linear power density of the fuel rod adjacent to the side surface of the water channel 38 closer to the control rod 19 may be too high. In such a case, the linear power density can be suppressed by arranging the short partial length fuel rods 53 and the standard fuel rods 54 with low uranium enrichment as in the present embodiment.

  As described above, in the fuel assembly 90 according to the present embodiment, two types of partial-length fuel rods are adjacent to the water channel 38 to cope with the asymmetry that inevitably occurs in the fuel assembly 90. Can be designed. Moreover, the design corresponding to the asymmetry in the fuel assembly 90 loaded in the D lattice core is possible. For this reason, fuel economy can be improved, ensuring a thermal margin.

[Eleventh embodiment]
FIG. 16 is a cross-sectional view showing the arrangement of fuel rods in the eleventh embodiment of the fuel assembly according to the present invention.

  The fuel assembly 91 of the present embodiment faces both end portions in the cross-sectional direction of the side surface of the fuel assembly 85 (see FIG. 11) of the fifth embodiment that is far from the control rod 19 of the water channel 38. The fuel rod arranged at the position is changed. A standard fuel rod 51 is disposed at a position facing the central portion in the cross-sectional direction of the side surface of the fuel assembly 91 closer to the gap water regions 20 and 21 of the water channel 38. Further, short part-length fuel rods 53 are disposed at positions facing both ends in the cross-sectional direction of the side surface of the water channel 38 closer to the control rod 19.

  Even if the fuel rods adjacent to the water channel 38 are arranged in this manner, the linear power density of each fuel rod 51, 52, 53 can be reduced by appropriately designing the uranium enrichment of other fuel rods. May be able to average appropriately. That is, by making the partial length fuel rods of two types adjacent to the water channel 38, a design corresponding to the asymmetry that inevitably occurs inside the fuel assembly 90 becomes possible. For this reason, fuel economy can be improved, ensuring a thermal margin.

[Twelfth embodiment]
FIG. 17 is a cross-sectional view showing the arrangement of fuel rods in the twelfth embodiment of the fuel assembly according to the present invention.

  The fuel assembly 92 of the present embodiment has the arrangement of the fuel rods 51, 52, 53 around the water channel 38 of the fuel assembly 91 (see FIG. 16) of the eleventh embodiment. The control rod 19 is replaced symmetrically with respect to the diagonal line that does not pass through the center.

  Even if the fuel rods adjacent to the water channel 38 are arranged in this manner, the linear power density of each fuel rod 51, 52, 53 can be reduced by appropriately designing the uranium enrichment of other fuel rods. May be able to average appropriately. That is, by making the partial length fuel rods of two types adjacent to the water channel 38, a design corresponding to the asymmetry that inevitably occurs inside the fuel assembly 90 becomes possible. For this reason, fuel economy can be improved, ensuring a thermal margin.

[Other embodiments]
The above-described embodiments are merely examples, and the present invention is not limited to these. For example, in each of the above-described embodiments, two types of the partial length fuel rod are used, ie, the long partial length fuel rod and the short partial length fuel rod. However, three or more types of partial length fuel rods having different lengths are used. May be used. In this case, the partial length fuel rod having a different length from the long partial length fuel rod and the short partial length fuel rod may be longer than the long partial length fuel rod or shorter than the short partial length fuel rod. It may be shorter than the long partial length fuel rod and longer than the short partial length fuel rod. That is, at least one partial-length fuel rod is disposed at a position adjacent to each side surface of the water channel, and the lengths of the partial-length fuel rods disposed at positions adjacent to the side surface of the water channel are different from each other. It only needs to include a partial length fuel rod. Further, the present invention can be applied to a mixed oxide fuel (MOX fuel). It can also be implemented by combining the features of each embodiment.

It is a cross-sectional view showing the arrangement of fuel rods in the first embodiment of the fuel assembly according to the present invention. 1 is a perspective view of a first embodiment of a fuel assembly according to the present invention. 1 is a side view of a fuel rod in a first embodiment of a fuel assembly according to the present invention. 1 is a transverse cross-sectional view of a core using a first embodiment of a fuel assembly according to the present invention. It is a graph which shows the example of the axial direction change of the void ratio at the time of normal operation of a boiling water reactor. The figure which shows typically the example of the enrichment of the uranium stored in the fuel rod when the length of the partial length fuel rod is one type compared with the case where the length of the partial length fuel rod is two types It is. It is a cross-sectional view which shows arrangement | positioning of the fuel rod in 2nd Embodiment of the fuel assembly which concerns on this invention. It is a cross-sectional view which shows arrangement | positioning of the fuel rod in 3rd Embodiment of the fuel assembly which concerns on this invention. It is a cross-sectional view which shows arrangement | positioning of the fuel rod in 4th Embodiment of the fuel assembly which concerns on this invention. It is a cross-sectional view which shows arrangement | positioning of the fuel rod in 5th Embodiment of the fuel assembly which concerns on this invention. It is a cross-sectional view which shows arrangement | positioning of the fuel rod in 6th Embodiment of the fuel assembly which concerns on this invention. It is a cross-sectional view which shows arrangement | positioning of the fuel rod in 7th Embodiment of the fuel assembly which concerns on this invention. It is a cross-sectional view which shows arrangement | positioning of the fuel rod in 8th Embodiment of the fuel assembly which concerns on this invention. It is a cross-sectional view which shows arrangement | positioning of the fuel rod in 9th Embodiment of the fuel assembly which concerns on this invention. It is a cross-sectional view which shows arrangement | positioning of the fuel rod in 10th Embodiment of the fuel assembly which concerns on this invention. It is a cross-sectional view which shows arrangement | positioning of the fuel rod in 11th Embodiment of the fuel assembly which concerns on this invention. It is a cross-sectional view which shows arrangement | positioning of the fuel rod in 12th Embodiment of the fuel assembly which concerns on this invention. FIG. 2 is a partially enlarged cross-sectional view showing the arrangement of fuel assemblies in the core of a typical boiling water reactor. It is the graph which showed the behavior of the infinite multiplication factor when taking the H / U on the horizontal axis about the fuel assembly of a typical boiling water reactor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 15 ... Fuel assembly, 19 ... Control rod, 20 ... Gap water area, 21 ... Gap water area, 22 ... Water rod, 26 ... Pellet, 30 ... Neutron detector, 31 ... Channel box, 38 ... Water channel, 41 ... Upper tie plate, 42 ... Lower tie plate, 43 ... End plug, 48 ... Cladding tube, 50 ... Fuel rod, 51 ... Standard fuel rod, 52 ... Long part length fuel rod, 53 ... Short part length fuel rod, 54 ... Standard fuel rods, 63 ... spacers, 81 ... fuel assemblies, 82 ... fuel assemblies, 83 ... fuel assemblies, 84 ... fuel assemblies, 85 ... fuel assemblies, 86 ... fuel assemblies, 87 ... fuel assemblies, 88 ... Fuel assembly, 89 ... Fuel assembly, 90 ... Fuel assembly, 91 ... Fuel assembly, 92 ... Fuel assembly

Claims (8)

In a fuel assembly loaded into a boiling water reactor,
The upper tie plate,
A lower tie plate spaced from the upper tie plate;
A plurality of fuel rods containing nuclear fuel material in a cylindrical cladding tube extending in a direction from the lower tie plate toward the upper tie plate, arranged in a square lattice shape and supported at the lower end by the lower tie plate,
A water channel having a lower end supported by the lower tie plate that extends in a rectangular tube shape in the same direction as the fuel rods so as to occupy a plurality of lattice positions of the square lattice in which the fuel rods are arranged; ,
Have
The fuel rod includes a standard fuel rod having an upper end supported by the upper tie plate and a partial length fuel rod shorter than the standard fuel rod, and at least one of the fuel rods adjacent to each side surface of the water channel. A partial length fuel rod is disposed, and the partial length fuel rod disposed at a position adjacent to a side surface of the water channel includes a long partial length fuel rod and a short partial length fuel rod shorter than the long partial length fuel rod. A fuel assembly comprising:   The fuel assembly according to claim 1, wherein the number of rows and columns of the square lattice in which the fuel rods are arranged is 9 or more.   3. The fuel assembly according to claim 1, wherein the water channel occupies lattice positions of three or more rows and columns of a square lattice in which the fuel rods are arranged. 4.   4. The fuel according to claim 3, wherein the fuel rod arranged at a position adjacent to a side surface of the water channel has a longer length of the fuel rod closer to an end portion in a cross-sectional direction of the side surface. Aggregation.   The fuel assembly according to any one of claims 1 to 4, wherein all of the fuel rods adjacent to the water channel are the partial-length fuel rods.   The boiling water reactor has a D-grid core in which the area of the gap water region facing the control rod is larger than the area of the gap water region facing the control rod, Of the fuel rods arranged at positions adjacent to the side surfaces, the length of the fuel rod adjacent to the side surface close to the control rod of the water channel is a position corresponding to the side surface far from the control rod of the water channel. The fuel assembly according to any one of claims 1 to 5, wherein the fuel assembly is shorter than a length of the adjacent fuel rods. In the core of a boiling water reactor loaded with a plurality of fuel assemblies, at least one of the fuel assemblies is
The upper tie plate,
A lower tie plate spaced from the upper tie plate;
A plurality of fuel rods containing nuclear fuel material in a cylindrical cladding tube extending in a direction from the lower tie plate toward the upper tie plate, arranged in a square lattice shape and supported at the lower end by the lower tie plate,
A water channel having a lower end supported by the lower tie plate that extends in a rectangular tube shape in the same direction as the fuel rods so as to occupy a plurality of lattice positions of the square lattice in which the fuel rods are arranged; Have
The fuel rod includes a standard fuel rod having an upper end supported by the upper tie plate and a partial length fuel rod shorter than the standard fuel rod, and at least one of the fuel rods adjacent to each side surface of the water channel. A partial length fuel rod is disposed, and the partial length fuel rod disposed at a position adjacent to a side surface of the water channel includes a long partial length fuel rod and a short partial length fuel rod shorter than the long partial length fuel rod. A boiling water reactor core characterized by including:   The fuel assembly is arranged such that the area of the gap water region is different between the side facing the control rod and the opposite side, and the water rod among the fuel rods arranged at positions adjacent to the side surface of the water channel. The length of the fuel rod adjacent to the side of the channel close to the control rod is shorter than the length of the fuel rod adjacent to the side of the water channel corresponding to the side far from the control rod. Item 8. A boiling water reactor core according to Item 7.

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