JP5443199B2 - Fast breeder reactor core structure - Google Patents

Description

  The present invention relates to a core structure of a fast breeder reactor.

  The fast breeder reactor of a large reactor has a characteristic that the reactivity system is not the maximum and a positive reactivity is introduced when liquid sodium as a coolant boils. For this reason, in the unlikely event of a failure of the reactor shutdown when the external power supply is lost, the coolant flow rate is suddenly lost at a high output, and therefore boiling occurs at the center of the core (the coolant flow rate is about 50%). %), A positive reactivity is introduced. As a result, molten fuel is released from the cladding tube in a part of the core region in the core, and a sudden boiling phenomenon (FCI) occurs due to contact with the coolant. Energy is released. At this time, the higher the simultaneity of the boiling regions, the greater the reactivity introduced into the core.

  Japanese Patent Laid-Open No. 4-81695 discloses that the power / flow ratio of a plurality of preceding fuel assemblies, which are some fuel assemblies arranged in the core of a fast reactor, is larger than that of other fuel assemblies, and these preceding fuels The assembly is arranged in an annular shape so as to surround the center of the core. With such a configuration, the core of the fast reactor is divided into a plurality of regions in the radial direction by the arrangement of the preceding fuel assemblies. If for some reason a primary shutdown pump that supplies coolant to the core trips but a reactor shutdown failure event that does not allow the reactor scram occurs, each of the preceding fuel assemblies will have other fuel assemblies due to a decrease in core flow rate. The temperature of the internal coolant is raised prior to the assembly. Since the temperature rise of the coolant in the preceding fuel assemblies is greater than that of the other fuel assemblies, a negative reactivity is introduced into each preceding fuel assembly. For this reason, the reactor power decreases, the reactor shifts to the reactor shutdown state, and fuel damage to the entire core can be prevented in advance. Furthermore, in the unlikely event that fuel damage occurs, this fuel damage is limited only to the preceding fuel assembly.

  In Japanese Patent Laid-Open No. 2-154194, in the core of a fast breeder reactor, a plurality of low enrichment fuel assemblies are annularly arranged in the core fuel region so as to surround the core center. These low enrichment fuel assemblies are less enriched in fissile plutonium than high enrichment fuel assemblies. Such a low enrichment fuel assembly is a fuel assembly having a low output and a low output / flow ratio. In the core of a fast breeder reactor described in Japanese Patent Application Laid-Open No. 2-154194, a plurality of core fuel regions loaded with highly enriched fuel assemblies are arranged in a ring shape and a plurality of low-rich materials having a small output / flow ratio. Divided into a plurality of regions including the highly enriched fuel assembly in the radial direction by the enriched fuel assembly.

Japanese Patent Laid-Open No. 4-81695 JP-A-2-154194

  In recent years, it has been clarified that even in a large fast breeder reactor due to the advancement of analysis and evaluation methods, the phenomenon of the cause process is relatively slow and there is no large energy release in the process. However, even if the fuel assembly is damaged during the process and the energy release accompanying the boiling of the coolant is small, the assembly duct (assembly wrapper tube) is melted and a large fuel melt pool is formed in the core. Is done. At this time, there is a risk that the reactivity is input to the core due to sloshing or the like of the fuel melt pool and energy is released.

  At present, there is knowledge that the molten fuel is dispersed vertically through the control rod duct and the like, so that a high reactivity is not introduced. However, in the unlikely event that the melting range in the core is wide and the fuel melt pool becomes large, the potential for increasing the input reactivity will remain.

  In the core of a fast breeder reactor described in Japanese Patent Laid-Open No. 2-154194, a high enrichment fuel assembly is formed in a radial direction by a plurality of low enrichment fuel assemblies having a small power / flow ratio arranged in an annular shape. Since the fuel is divided into a plurality of regions, the low enrichment fuel is arranged in a ring shape so that the dissolution of the fuel generated in the highly enriched fuel assembly loaded in one region spreads to other regions It can be prevented with a layer of aggregates. That is, in the core of the fast breeder reactor described in Japanese Patent Laid-Open No. 2-154194, it is possible to prevent the fuel melting from expanding in a wide range.

  As disclosed in Japanese Patent Laid-Open No. 2-154194, the formation of an annular low enrichment fuel assembly layer in the core fuel region in order to prevent the expansion of the fuel melting range is a fuel pin of the low enrichment fuel assembly. There is a need to produce fuel pellets with a low plutonium enrichment that are filled in. Japanese Patent Laid-Open No. 2-154194 discloses a fuel pellet having a large plutonium enrichment used for a high enrichment fuel assembly and a fuel pellet having a small plutonium enrichment used for a low enrichment fuel assembly (different compositions). Fuel pellets) must be manufactured, and a fuel pellet manufacturing line is provided for each enrichment, which complicates the fuel pellet manufacturing process. Also, management of each fuel pellet with different enrichment, each fuel pin filled with each fuel pellet, and a low enrichment fuel assembly and a highly enriched fuel assembly incorporating the corresponding fuel pin. Because the difference in plutonium enrichment does not appear in each structure, it is necessary to pay close attention.

  In order to construct the core of the fast breeder reactor described in Japanese Patent Laid-Open No. 2-154194, it is troublesome to manufacture the necessary fuel assemblies including fuel pellets.

  An object of the present invention is to provide a core structure of a fast breeder reactor that is easy to manufacture a fuel assembly and can suppress expansion of fuel melting.

A feature of the present invention that achieves the above-described object is that an upper core support member positioned below a core in which a plurality of fuel assemblies are disposed, a lower core support member disposed below the upper core support member, Tubular structure that is attached to the core support member and the lower core support member and that is provided at the lower end portion of each fuel assembly and has an entrance nozzle formed with a first coolant introduction port inserted therein to form a second coolant introduction port A plurality of connecting members,
The plurality of fuel assemblies includes a plurality of first fuel assemblies and a plurality of second fuel assemblies having nuclear fuel materials having substantially the same composition, and the core fuel region included in the core includes a plurality of first fuels. A plurality of first regions formed by loading the assembly, and a second region formed by loading the plurality of second fuel assemblies, each of the first regions being separated from each other by the second region; And
The flow passage area of the first coolant introduction port formed in the entrance nozzle of the second fuel assembly is larger than the flow passage area of the first coolant introduction port formed in the entrance nozzle of the first fuel assembly. There is in being.

  The flow passage area of the first coolant introduction port formed in the entrance nozzle of the second fuel assembly is larger than the flow passage area of the first coolant introduction port formed in the entrance nozzle of the first fuel assembly. Therefore, the coolant flow rate supplied to the second fuel assembly is greater than the coolant flow rate supplied to the first fuel assembly. Further, since the first fuel assembly and the second fuel assembly have nuclear fuel materials having substantially the same composition, the output generated in each fuel assembly is also substantially the same. Therefore, the ratio of the output of the second fuel assembly to the coolant flow rate supplied to the second fuel assembly is greater than the ratio of the output of the first fuel assembly to the coolant flow rate supplied to the first fuel assembly. Becomes smaller. Since the coolant flow rate supplied to the second fuel assembly is larger than the coolant flow rate supplied to the first fuel assembly, cooling is performed in a first fuel assembly loaded in one first region for some reason. Even when the material boils, the coolant does not boil in the second fuel assembly loaded in the second region. In this way, simultaneous boiling of the coolant in the first fuel assembly and the second fuel assembly is avoided. Therefore, even if fuel melting occurs in one first fuel assembly loaded in one first region for some reason, the second region prevents this fuel melting from expanding to another first region. Can do.

  Since the first fuel assembly and the second fuel assembly have nuclear fuel materials having substantially the same composition, the manufacture of the first fuel assembly and the second fuel assembly is facilitated.

The above object is to provide an upper core support member disposed below a core where a plurality of fuel assemblies are disposed, a lower core support member disposed below the upper core support member, an upper core support member, and a lower core. A plurality of tubular connecting members attached to the support member and provided at the lower end of each fuel assembly and having a second coolant inlet formed by inserting an entrance nozzle having a first coolant inlet formed therein; With
The plurality of fuel assemblies includes a plurality of first fuel assemblies and a plurality of second fuel assemblies having nuclear fuel materials having substantially the same composition, and the core fuel region included in the core includes a plurality of first fuels. A plurality of first regions formed by loading the assembly, and a second region formed by loading the plurality of second fuel assemblies, each of the first regions being separated from each other by the second region; And
The plurality of connection members include a plurality of first connection members into which the entrance nozzle of the first fuel assembly is inserted, and a plurality of second connection members into which the entrance nozzle of the second fuel assembly is inserted,
This is also achieved by the fact that the flow passage area of the second coolant introduction port formed in the second connection member is larger than the flow passage area of the second coolant introduction port formed in the first connection member. Can do.

  The flow passage area of the second coolant introduction port formed in the second connecting member into which the entrance nozzle of the second fuel assembly is inserted is the first connecting member into which the entrance nozzle of the first fuel assembly is inserted. Since the flow area of the formed second coolant introduction port is larger, the coolant flow rate supplied to the second fuel assembly is larger than the coolant flow rate supplied to the first fuel assembly. . The composition of each nuclear fuel material contained in the first fuel assembly and the second fuel assembly is substantially the same. Therefore, the ratio of the output of the second fuel assembly to the coolant flow rate supplied to the second fuel assembly is greater than the ratio of the output of the first fuel assembly to the coolant flow rate supplied to the first fuel assembly. Becomes smaller.

  Therefore, the flow area of the first coolant inlet formed in the entrance nozzle of the second fuel assembly is larger than the flow area of the first coolant inlet formed in the entrance nozzle of the first fuel assembly. As in the case of increasing the fuel flow, even if fuel melting occurs in a certain first fuel assembly loaded in one first region for some reason, this fuel melting will be expanded to the other first region. Two areas can prevent this. Furthermore, since the first fuel assembly and the second fuel assembly have nuclear fuel materials having substantially the same composition, the manufacture of the first fuel assembly and the second fuel assembly is facilitated.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacture of a fuel assembly is easy and the core structure of a fast breeder reactor which can suppress expansion of nuclear fuel melting can be obtained.

It is a cross-sectional view of the core in the core structure of the fast breeder reactor according to the first embodiment which is a preferred embodiment of the present invention, and is a cross-sectional view taken along the line II in FIG. It is a longitudinal cross-sectional view of the fast breeder reactor to which the core structure of the fast breeder reactor of the first embodiment is applied. FIG. 2 is a configuration diagram of a fuel assembly loaded in the core fuel region shown in FIG. 1, (A) is a side view of the fuel assembly loaded in a low flow rate region of the core fuel region, and (B) is a core fuel region. It is a side view of the fuel assembly loaded in the high flow rate region. FIG. 3 is an explanatory view showing support of a fuel assembly by a connecting pipe in the vicinity of the core support structure of the fast breeder reactor shown in FIG. 2, wherein (A) is a longitudinal sectional view of the support structure of the fuel assembly loaded in a low flow rate region; , And (B) are longitudinal sectional views of a support structure for a fuel assembly loaded in a high flow rate region. It is explanatory drawing which shows the support structure of the fuel assembly in the core structure of the fast breeder reactor of Example 2 which is another Example of this invention, and is a cross-sectional view in a core support structure, (A) is low FIG. 6 is a longitudinal sectional view of a support structure for a fuel assembly loaded in a flow rate region, and FIG. 5B is a longitudinal sectional view of a support structure for a fuel assembly loaded in a high flow rate region.

  Examples of the present invention will be described below.

  A core structure of a fast breeder reactor according to embodiment 1, which is a preferred embodiment of the present invention, will be described with reference to FIGS. 1, 2, 3 and 4. FIG.

  First, a fast breeder reactor to which the core structure reactor of the fast breeder reactor of this embodiment is applied will be described. As shown in FIG. 2, the fast breeder reactor includes a reactor vessel 15 and a core 1 disposed in the reactor vessel 15. The inner cylinder 16 is installed in the reactor vessel 15, and the upper core support plate 18 and the lower core support plate 19 are arranged in the inner cylinder 16 and installed in the inner cylinder 16. An upper core support plate (upper core support member) 18 is disposed below the core 1, and a lower core support plate (lower core support member) 19 is disposed below the upper core support plate 18. The connecting pipe support plate 20 is disposed below the lower core support plate 19 and attached to the inner cylinder 16. The upper ends of the plurality of connecting pipes (connecting members) 21 are attached to the upper core support plate 18, and the lower ends of the connecting pipes 21 are attached to the connecting pipe support plate 20. Each connecting pipe 21 passes through the lower core support plate 20 and is also attached to the lower core support plate 20. The upper core support plate 18, the lower core support plate 19, the connection pipe support plate 20, and the plurality of connection pipes 21 constitute the core support structure 17. An inlet nozzle 28 and an outlet nozzle 27 are provided in the reactor vessel 15.

  A shielding plug 23 is attached to the upper end portion of the reactor vessel 15 and seals the upper end portion of the reactor vessel 15. A part of the shielding plug 23 is a rotary plug (not shown), and the core upper mechanism 24 is attached to the rotary plug and passes through the rotary plug.

  The core 1 has a core fuel region 2 and a radial blanket region 3 as shown in FIG. Further, a shielding body region (not shown) in which a plurality of neutron shielding bodies 14 (see FIG. 2) are arranged is formed. A core fuel region 2 is disposed in the center of the core 1, and a radial blanket region 3 surrounds the core fuel region 2. A number of blanket fuel assemblies 12 are loaded into the radial blanket region 3. A shielding body region surrounds the radial blanket region 3. The lower end portion of each neutron shielding body 14 is inserted into each connecting tube 29 attached to the upper core support plate 18 and the lower core support plate 19. The connecting tube 29 supports the neutron shielding body 14.

  A plurality of fuel assemblies 4 (first fuel assemblies) and a plurality of fuel assemblies 11 (second fuel assemblies) are loaded in the core fuel region 2. In the fuel assembly 11, the ratio of the output generated in the fuel assembly to the coolant flow rate supplied to the fuel assembly (hereinafter referred to as the output / flow rate ratio) is smaller than that in the fuel assembly 4. A plurality of control rods 13 are arranged in the core fuel region 2. These control rods 13 are inserted into a control rod guide tube (not shown) disposed in the core fuel region 2 and supported by the core support structure 17 such as the upper core support plate 18. The control rod guide tube is disposed between the fuel assemblies loaded in the core fuel region 2.

  A plurality of fuel assemblies 11 having a small output / flow rate ratio are arranged in a row from one control rod guide tube arranged in the center of the core fuel region 2 toward the outer periphery of the core fuel region 2 in the radial direction. A high flow rate region 25 is formed. The core fuel region 4 is divided into two regions by a high flow rate region (second region) 25 formed from one control rod guide tube arranged at the center of the core fuel region 2 toward the outer periphery of the core fuel region 2. It is divided into 26A and 26B (hereinafter referred to as a low flow rate region). The fuel assemblies 4 are loaded in the low flow rate regions (first regions) 26A and 26B as fuel assemblies.

  The fuel assemblies 4 and 11 will be described with reference to FIG. As shown in FIG. 3A, the fuel assembly 4 includes a wrapper pipe 5 that is a cylinder having a regular hexagonal cross section, an entrance nozzle 9A that is sealed with a tubular body at its lower end, and a plurality of fuel pins (fuel Element) (not shown). Each fuel pin is filled with a plurality of fuel pellets made of nuclear fuel material containing fissile plutonium. These fuel pins are arranged in the wrapper pipe 5, and the entrance nozzle 9 </ b> A is attached to the lower end portion of the wrapper pipe 5. The entrance nozzle 9A has a plurality of orifices (first coolant introduction ports) 10A that are coolant inlets. A plurality of upper pads 7 and intermediate pads 8 are provided on the outer surface of the wrapper pipe 5 so as to maintain a distance between other adjacent fuel assemblies. A handling head 6 is provided at the upper end of the wrapper tube 5.

  The fuel assembly 11 is also configured similarly to the fuel assembly 4 as shown in FIG. The entrance nozzle 9B of the fuel assembly 11 is also formed with a plurality of orifices (first coolant inlets) 10B that are coolant inlets. In the fuel assemblies 4 and 11, the enrichment of the fissile plutonium (for example, plutonium 239) of the nuclear fuel material filled in each fuel pin is the same, and the composition of the nuclear fuel material used in these fuel assemblies is the same. It is substantially the same. The difference between the fuel assembly 4 and the fuel assembly 11 is that the flow area of one orifice 10B formed in the entrance nozzle 9B of one fuel assembly 11 is different from that of the entrance nozzle 9A of one fuel assembly 4. That is, it is larger than the flow path area of one formed orifice 10A. Other configurations of the fuel assembly 11 are the same as those of the fuel assembly 4. The total flow area of all the orifices 10B formed in the entrance nozzle 9B is larger than the total flow area of all the orifices 10A formed in the entrance nozzle 9A. In this embodiment, the number of orifices 10A formed in the entrance nozzle 9A is the same as the number of orifices 10B formed in the entrance nozzle 9B. In each fuel assembly, even if the flow area of one orifice 10B is smaller than the flow area of one orifice 10A, the number of orifices 10B is made larger than the number of orifices 10A, The total flow area of the orifice 10B may be larger than the total flow area of all the orifices 10A.

  The fuel assemblies 4 and 11 are supported by the core support structure 17 as shown in FIG. Specifically, the entrance nozzle 9A of the fuel assembly 4 is inserted into the connecting pipe 21 and supported as shown in FIG. A plurality of openings (second coolant introduction ports) 22 are formed in the connecting pipe 21. The entrance nozzle 9B of the fuel assembly 11 is inserted into the connecting pipe 21 and supported as shown in FIG. The connecting pipe 21 is also formed with a plurality of openings 22. The total flow path area of all the openings 22 formed in each connecting pipe 21 into which the fuel assemblies 4 and 11 are inserted is the same, and this total flow path area is formed in one fuel assembly 11. It is larger than the total flow area of all the orifices 10B.

  During operation of the fast breeder reactor, a liquid metal (eg, liquid sodium), which is discharged from an intermediate heat exchanger (not shown), enters the lower plenum 26 in the reactor vessel 15 from the inlet nozzle 28. Inflow. This liquid sodium is supplied to a plenum formed between the upper core support plate 18 and the lower core support plate 19 and passes through an opening 22 formed in the connecting pipe 22 and an orifice 10A formed in the entrance nozzle 9A. It is guided into the wrapper pipe 5 of the fuel assembly 4. The liquid sodium rising in the wrapper tube 5 is heated by the heat generated by the fission of the fissile plutonium contained in the fuel pin of the fuel assembly 4, and is discharged from the fuel assembly 4 to the upper plenum 25. .

  The liquid sodium introduced into the plenum formed between the upper core support plate 18 and the lower core support plate 19 passes through the opening 22 formed in the connecting pipe 22 and the orifice 10B formed in the entrance nozzle 9B. Guided into the wrapper tube 5 of the assembly 11. Also in the fuel assembly 11, the liquid sodium is heated to a high temperature like the fuel assembly 4, and is discharged from the fuel assembly 11 to the upper plenum 25. The high-temperature liquid sodium in the upper plenum 25 descends the annular region formed between the reactor vessel 15 and the inner cylinder 16, is discharged from the outlet nozzle 27, and is supplied to the intermediate heat exchanger.

  Since the total flow area of all the orifices 10B formed in the entrance nozzle 9B is larger than the total flow area of all the orifices 10A formed in the entrance nozzle 9A, it is supplied to each fuel assembly 11 forming the high flow rate region 25. The flow rate of the liquid sodium is higher than the flow rate of the liquid sodium supplied to the fuel assemblies 4 forming the low flow rate regions 26A and 26B. Therefore, the output / flow rate ratio of the fuel assembly 11 is smaller than the output / flow rate ratio of the fuel assembly 4. The outputs of the fuel assemblies 4 and 11 are substantially the same because the enrichment of the fissile plutonium is the same.

  In this embodiment, it is assumed that an abnormal state has occurred for some reason and liquid sodium has boiled in the fuel assembly 4. Since the flow rate of liquid sodium supplied to the fuel assembly 11 is larger than the flow rate of liquid sodium supplied to the fuel assembly 4, when liquid sodium boils in the fuel assembly 4, However, the boiling of liquid sodium has not yet occurred. In the present embodiment, the total flow area of all the orifices 10B at the entrance nozzle 9B is larger than the total flow area of all the orifices 10A at the entrance nozzle 9A. It is possible to avoid sodium boiling at the same time.

  When boiling of liquid sodium occurs in the fuel assembly 4 and the temperature of the fuel pin in the fuel assembly 4 rises excessively, there is a possibility that the fuel melts in which the nuclear fuel material in the fuel assembly 4 melts. For example, it is assumed that fuel melting occurs in a certain fuel assembly 4 in the low flow rate region 26A. The wrapper tube 5 of the fuel assembly 4 is also melted, and the fuel melt is propagated to other fuel assemblies 4 adjacent to the fuel assembly 4.

  As described above, the fuel melting propagates to each fuel assembly 4 in the low flow rate region 26 </ b> A, the fuel melting in the low flow rate region 26 </ b> A expands, and in the low flow rate region 26 </ b> A adjacent to the high flow rate region 25. A case is assumed in which fuel melting also occurs in the fuel assembly 4. Since a large amount of liquid sodium flows through the fuel assembly 11 having a small output / flow ratio in the high flow region 25, the fuel assembly in the low flow region 26A adjacent to the fuel assembly 11 is present. Even if 4 melts, melting of the fuel assembly 11 can be avoided. Therefore, it is possible to prevent the fuel melt of the fuel assembly 4 generated in the low flow region 26A from being blocked by the high flow region 25 and propagating to the low flow region 26B. When fuel melting occurs in the fuel assembly 4 in the low flow rate region 26A, liquid sodium flows through the fuel assembly 11 in the high flow rate region 25 without boiling.

  In the present embodiment, one control rod guide tube 13 is disposed at the center of the core fuel region 2, and a high flow region 25 extending in the radial direction is divided by the control rod guide tube 13. Assume a case where the fuel melting of the fuel assembly 4 generated in the low flow rate region 26A propagates and the control rod guide tube 13 disposed at the center of the core fuel region 2 is melted. When the control rod guide tube 13 is melted by the molten fuel, the molten nuclear fuel flows into the control rod guide tube 13 and falls in the control rod guide tube 13. Eventually, the dropped molten fuel reaches a region (for example, the lower plenum 26) where liquid sodium exists below the upper core support plate 18. Since a plurality of control rod guide tubes 13 are also arranged in the low flow rate region 26A, if several control rod guide tubes 13 are melted by the molten fuel, the molten fuel in the low flow rate region 26A is It falls to the lower plenum 26 and the like through the melted control rod guide tube 13. This molten fuel is cooled by liquid sodium in the lower plenum 26.

  In the present embodiment, the fuel melt pool generated in the low flow region 26A due to the melting of the fuel generated in the low flow region 26A is confined in the low flow region 26A by the formation of the high flow region 25, and is stored in the low flow region 26B. It can be prevented from expanding. When the fuel melting occurs in all the fuel assemblies 4 in the low flow rate region 26A, the release energy is generated when the fuel melting expands in the entire core fuel region when the high flow rate region 25 is not formed. It is assumed that the energy is reduced to 1/2 or less. Actually, it is assumed that the molten fuel in the fuel melt pool formed in the low flow rate region 26A falls below the upper core support plate 18 through the melted control rod guide tube 13, and in the low flow rate region 26A. The fuel melt pool in the reactor becomes smaller, and the released energy is further reduced.

  In the present embodiment, the composition of fuel pellets filled in each fuel pin provided in the fuel assembly 11 is the same as the composition of fuel pellets in the fuel assembly 4. For this reason, when manufacturing fuel pellets used for the fuel assemblies 4 and 11, it is not necessary to divide the production line of each fuel pellet used for these fuel assemblies. Therefore, it becomes easy to manufacture fuel pellets for the fuel assembly 4 having a large output / flow ratio and fuel pellets for the fuel assembly 11 having a small output / flow ratio. Further, since the enrichment and composition of the fissile plutonium in each fuel pellet of the fuel assemblies 4 and 11 are the same, it is not necessary to distinguish and manage the fuel pellets and fuel pins of both fuel assemblies. Management becomes easy. Since the fuel assembly 4 and the fuel assembly 11 have different flow path areas of the orifices formed in the entrance nozzle, the fuel assembly 4 and the fuel assembly 11 can be distinguished from each other by looking at the overview of the respective fuel assemblies. .

  According to this embodiment, the fuel assembly can be easily manufactured, and the expansion of fuel melting can be suppressed.

  The core structure of the fast breeder reactor according to embodiment 2, which is another embodiment of the present invention, will be described with reference to FIG.

  The core structure of the fast breeder reactor of the present embodiment is the same as that of the core structure of the fast breeder reactor of the first embodiment, and the adjustment of the coolant flow rate supplied to each fuel assembly loaded in the high flow rate region 25 and the low flow rate region 26A. 26B, the flow rate of the coolant supplied to each fuel assembly loaded in the fuel assembly is adjusted not by the flow area of the orifice formed in the entrance nozzle, but by the entrance nozzle of the fuel assembly loaded in each region. Further, the flow path area of the opening formed in each connecting pipe is changed. The other structure of the core structure of the fast breeder reactor of the present embodiment is the same as the core structure of the fast breeder reactor of the first embodiment.

  The core structure of the fast breeder reactor in the present embodiment will be described with a focus on the differences from the core structure of the fast breeder reactor in the first embodiment. In this embodiment, fuel assemblies 4A and 11A are loaded in the core fuel region 2 in place of the fuel assemblies 4 and 11 in the first embodiment. Also in the present embodiment, as in the first embodiment, the low flow regions 26A and 26B and the high flow region 25 are formed in the core fuel region 2. A plurality of fuel assemblies 4A (first fuel assemblies) are loaded in the low flow regions 26A and 26B, and a plurality of fuel assemblies 11A (second fuel assemblies) are loaded in the high flow regions 25. The fuel assemblies 4A and 11A used in this embodiment have the same configuration. Each fuel pin used in each of the fuel assemblies 4A and 11A has the same composition such as the enrichment degree of fissile plutonium. Further, the entrance nozzles 9 of the fuel assemblies 4A and 11A have the same shape (see FIGS. 5A and 5B), and the flow paths of the plurality of orifices 10C formed in these entrance nozzles 9 The area and number are the same. The fuel assemblies 4A and 11A have the same configuration, but for the sake of convenience, the fuel assemblies loaded in the low flow regions 26A and 26B and the fuel assemblies loaded in the high flow regions 25 are distinguished. The former is referred to as a fuel assembly 4A, and the latter is referred to as a fuel assembly 11A.

  In the first embodiment, one type of connecting pipe 21 is used, whereas in this embodiment, two types of connecting pipes 21A and 21B are used (see FIGS. 5A and 5B). There are a plurality of connecting pipes 21A and 21B, respectively. Like the connecting pipe 21 used in the first embodiment, each upper end is attached to the upper core support plate 18 and each lower end is connected to the connecting pipe support plate 20. It is attached. Each of the connecting pipes 21 </ b> A and 21 </ b> B is attached to the lower core support plate 20 and penetrates the lower core support plate 20. The core support structure 17A in this embodiment includes an upper core support plate 18, a lower core support plate 19, a connection tube support plate 20, and a plurality of connection tubes 21A and 21B.

  A plurality of openings (second coolant introduction ports) 22A are formed in the connection pipe 21A (first connection member), and a plurality of openings (second coolant introduction ports) are formed in the connection pipe 21B (second connection member). ) 22B is formed. The channel area of one opening 22B is smaller than the channel area of one opening 22A. The total flow area of all openings 22B formed in the connecting pipe 21B is larger than the total flow area of all openings 22A formed in the connecting pipe 21A. The total flow area of all orifices 10C formed in the entrance nozzles 9 of the fuel assemblies 4A and 11A is larger than the total flow area of all openings 22B formed in the connecting pipe 21B.

  Similar to the fuel assembly 11 in the first embodiment, the plurality of connecting pipes 21 </ b> B are arranged in a row from the single control rod guide tube 13 positioned at the center of the core fuel region 2 toward the outer periphery of the core fuel region 2. ing. The fuel assemblies 11A into which the entrance nozzles 9 are inserted into the connecting pipes 21B are also arranged in a row from the single control rod guide tube 13 located at the center of the core fuel region 2 toward the outer periphery of the core fuel region 2. ing. A high flow rate region 25 shown in FIG. 1 is formed in the core fuel region 2 by these fuel assemblies 11A. Low flow regions 26A and 26B shown in FIG. 1 are formed in the core fuel region 2 by the fuel assemblies 4A into which the entrance nozzles 9 are inserted into the respective connecting pipes 21A. Also in this embodiment, the core fuel region 2 is divided by the high flow region 25 into two regions, the low flow regions 26A and 26B.

  Liquid sodium existing between the upper core support plate 18 and the lower core support plate 19 is supplied to the fuel assembly 4A through the opening 22A of the connecting pipe 21A and the orifice 10C of the entrance nozzle 9, and the opening of the connecting pipe 21B. The fuel is supplied to the fuel assembly 11A through the section 22B and the orifice 10C of the entrance nozzle 9. The flow rate of liquid sodium supplied to the fuel assembly 4A is limited by a plurality of openings 22A formed in the connecting pipe 21A, and the flow rate of liquid sodium supplied to the fuel assembly 11A is pluralized in the connecting pipe 21B. This is limited by the opening 22B. Since the total flow area of all the openings 22B formed in the connecting pipe 21B is larger than the total flow area of all the openings 22A formed in the connecting pipe 21A, the flow rate of liquid sodium supplied to the fuel assembly 11A Is larger than the flow rate of liquid sodium supplied to the fuel assembly 4A. That is, the output / flow rate ratio of the fuel assembly 11A is smaller than the output / flow rate ratio of the fuel assembly 4A.

  For this reason, also in this embodiment, when fuel melting occurs in the fuel assembly 4A, which is the low flow rate region 26A, the fuel melting expands only in the low flow rate region 26A. As in the first embodiment, it is possible to prevent the fuel melt generated in the low flow region 26A from being blocked by the high flow region 25 and expanding to the low flow region 26B.

  Such a present Example can obtain each effect which arises in Example 1. FIG. In the present embodiment, the flow rates of the liquid sodium supplied to the fuel assemblies 4A and 11A are adjusted by the connecting pipes 21A and 21B, so the structures of the fuel assemblies 4A and 11A can be made the same. For this reason, the structure of the entrance nozzle 9 in each of the fuel assemblies 4A and 11A can be made the same. Moreover, the composition of the nuclear fuel material used for each of the fuel assemblies 4A and 11A is substantially the same. Therefore, the fuel assembly 4A can be loaded in the high flow area 25 and the fuel assembly 11A can be loaded in the low flow areas 26A and 26B. The fuel assembly loaded in the high flow area 25 and the low flow areas 26A and 26B. Therefore, it is easy to load the fuel assembly into the core fuel region 2. This is because the high flow area 25 is formed by the connecting pipe 21B provided in the core support structure 17A, and the low flow areas 26A and 26B are formed by the connecting pipe 21A provided in the core support structure 17A.

  In the first and second embodiments, the low flow regions 26A and 26B are divided by one row of high flow regions 25 passing through the center of the core fuel region 2, but a plurality of rows passing through the center of the core fuel region 2, for example, three rows By forming the high flow rate region 25, six low flow rate regions can be formed in the core fuel region 2. In addition, the high flow region 25 is not a straight line but is formed with one annular high flow region that surrounds the center of the core fuel region 2, thereby dividing the core fuel region 2 in the radial direction, thereby providing two annular low flow regions. Can be formed. A plurality of annular high flow areas may be formed concentrically.

  DESCRIPTION OF SYMBOLS 1 ... Core, 2 ... Core fuel area | region, 4, 4A, 11, 11A ... Fuel assembly, 5 ... Wrapper pipe | tube, 9, 9A, 9B ... Entrance nozzle, 10, 10A, 10B, 10C ... Orifice, 13 ... Control rod 15 ... Reactor vessel, 16 ... Inner cylinder, 17 ... Core support structure, 18 ... Upper core support plate, 19 ... Lower core support plate, 21, 21A, 21B ... Connection pipe, 22, 22A, 22B ... Opening 25 ... High flow rate region, 26A, 26B ... Low flow rate region.

Claims (4)

An upper core support member positioned below a core in which a plurality of fuel assemblies are disposed; a lower core support member disposed below the upper core support member; and the upper core support member and the lower core support member. And a plurality of tubular connecting members provided at the lower ends of the respective fuel assemblies and having an entrance nozzle formed with a first coolant introduction port and formed with a second coolant introduction port. ,
The plurality of fuel assemblies include a plurality of first fuel assemblies and a plurality of second fuel assemblies having nuclear fuel materials having substantially the same composition, and a core fuel region included in the core includes the plurality of core fuel regions. A plurality of first regions formed by loading the first fuel assemblies, and a second region formed by loading the plurality of second fuel assemblies, each of the first regions being the Separated from each other by a second region,
The flow area of the first coolant inlet formed in the entrance nozzle of the second fuel assembly is equal to the flow area of the first coolant inlet formed in the entrance nozzle of the first fuel assembly. A fast breeder reactor core structure characterized by being larger than the road area.   A plurality of the first coolant introduction ports are formed in the respective entrance nozzles of the first fuel assembly and the second fuel assembly, and all the first coolant passages formed in the entrance nozzles of the second fuel assembly. 2. The high speed operation according to claim 1, wherein a total flow passage area of the coolant introduction port is larger than a total flow passage area of all the first coolant introduction ports formed in the entrance nozzle of the first fuel assembly. Breeder reactor core structure. An upper core support member disposed below a core in which a plurality of fuel assemblies are disposed; a lower core support member disposed below the upper core support member; the upper core support member and the lower core support member; A plurality of tubular connecting members provided at the lower end of each of the fuel assemblies and having a second coolant inlet formed by inserting an entrance nozzle having a first coolant inlet formed therein. Prepared,
The plurality of fuel assemblies includes a plurality of first fuel assemblies and a plurality of second fuel assemblies having nuclear fuel materials having substantially the same composition, and a core fuel region included in the core includes the plurality of fuel assemblies. A plurality of first regions formed by loading the first fuel assemblies; and a second region formed by loading the plurality of second fuel assemblies, each of the first regions being the first region. Separated from each other by two regions,
The plurality of connecting members include a plurality of first connecting members into which the entrance nozzle of the first fuel assembly is inserted, and a plurality of second connecting members into which the entrance nozzle of the second fuel assembly is inserted. Including
The flow area of the second coolant introduction port formed in the second connection member is larger than the flow area of the second coolant introduction port formed in the first connection member. The fast breeder reactor core structure. A plurality of the second coolant introduction ports are formed in each of the first connection member and the second connection member, and the total flow passage area of all the second coolant introduction ports formed in the second connection member The core structure of a fast breeder reactor according to claim 3 , wherein is larger than a total flow passage area of all the second coolant introduction ports formed in the first connecting member.

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