JP6426070B2 - Reactor - Google Patents

Description

  The present invention relates to a nuclear reactor.

  Generally, a large number of fuel assemblies disposed in the core of a nuclear reactor such as a boiling water reactor are supported at the upper end by an upper grid plate and supported at the lower end by fuel supports of a core support plate. ing.

  In the above-described nuclear reactor, when an external force acts due to the occurrence of an earthquake or the like, the fuel assembly vibrates with the upper grid plate and the fuel support fitting as the support points. At this time, when the fuel assembly and the building or internal structure of the reactor resonate, the fuel assembly is largely deformed, which makes it difficult to insert the control rod between the fuel assemblies. Therefore, when an external force is applied to the reactor, it is necessary to separate resonances between the fuel assembly and the building of the reactor and the internal structures of the reactor by separating natural cycles. On the other hand, a method has been proposed in which an opening is provided in the upper grid plate, reactor water is leaked to shorten the natural cycle of the fuel assembly, and resonance between the fuel assembly and the building is avoided (Patent Document 1 etc.) See).

JP-A-8-278384

  In Patent Document 1, the amount of change in the natural period of the fuel assembly depends on the amount of leakage of the reactor water from the opening provided in the upper grid plate. Therefore, depending on the amount of leakage, the natural cycle of the fuel assembly may not change much, which is insufficient as a method for avoiding the resonance between the fuel assembly and the building and internal structures of the reactor.

  The present invention has been made in view of the above, and it is an object of the present invention to provide a nuclear reactor capable of avoiding the resonance between the fuel assembly and the reactor building and internal structures even when an external force acts on the reactor. Do.

In order to achieve the above object, a nuclear reactor according to the present invention includes a pressure vessel, a core shroud housed in the pressure vessel, a core housed in the core shroud and loaded with a fuel assembly, and the fuel assembly A first grid plate for holding the upper end of the core, a core support plate for supporting the lower end of the fuel assembly, and a second grid plate provided between the first grid plate and the core support plate; wherein the second grating plate, characterized in that it is configured to move up and down.

  According to the present invention, it is possible to provide a nuclear reactor capable of avoiding resonance between the fuel assembly and the building and internal structures of the nuclear reactor even when an external force acts on the reactor.

BRIEF DESCRIPTION OF THE DRAWINGS It is a longitudinal cross-sectional view showing schematic structure of one structural example of the nuclear reactor which concerns on 1st Embodiment of this invention. FIG. 1 is a partial structural view of the vicinity of a pressure vessel of a nuclear reactor according to a first embodiment of the present invention. FIG. 1 is a partial structural view of a core shroud and the vicinity thereof of a nuclear reactor according to a first embodiment of the present invention. It is the flowchart which showed the procedure of movement of the movable grating board concerning a 1st embodiment of the present invention. FIG. 5 is a partial structural view of the vicinity of a core shroud of a nuclear reactor according to a second embodiment of the present invention. It is a fragmentary structural view of a core shroud neighborhood of a nuclear reactor concerning a 3rd embodiment of the present invention. It is a fragmentary structural view of the core shroud neighborhood of a nuclear reactor concerning a 4th embodiment of the present invention. It is a fragmentary structural view of a core shroud neighborhood of a nuclear reactor concerning a 5th embodiment of the present invention. It is a fragmentary structural view of a core shroud neighborhood of a nuclear reactor concerning a 5th embodiment of the present invention. It is the flowchart which showed the fall procedure of the movable grating board concerning a 5th embodiment of the present invention.

First Embodiment
(Constitution)
1. Reactor FIG. 1 is a longitudinal sectional view showing a schematic configuration of a configuration example of a reactor according to the present embodiment. In the present embodiment, an improved boiling water reactor (ABWR) is illustrated as a nuclear reactor. As shown in FIG. 1, the reactor 100 includes a reactor pressure vessel (pressure vessel) 2, a reactor containment vessel (containment vessel) 101, and a reactor building (building) 102.

  The containment vessel 101 is formed in a cylindrical shape so as to be airtight. The pressure vessel 2 is stored in the storage vessel 101. The building 102 is provided on the outer peripheral side of the storage container 101 so as to surround the storage container 101.

  FIG. 2 is a partial structural view of the vicinity of the pressure vessel of the nuclear reactor according to the present embodiment. As shown in FIG. 2, the pressure vessel 2 includes an upper grid plate (first grid plate) 3, a movable grid plate (second grid plate) 4, a core shroud 5, a core support plate 6, and a control rod drive mechanism housing 7. , A control rod guide tube 10, a steam separator 11, and a steam dryer 12.

  The core shroud 5 is formed in a cylindrical shape, and stores a core 9 in which a plurality of fuel assemblies 8 each including a plurality of fuel rods are loaded. A plurality of control rod guide pipes 10 are provided below the core 9 in the pressure vessel 2. Control rod guide tube 10 houses control rod 18 (see FIG. 3). A plurality of control rod drive mechanism housings 7 are provided on the bottom 2 </ b> A of the pressure vessel 2. The upper portion of the control rod drive mechanism housing 7 penetrates the bottom 2 </ b> A of the pressure vessel 2 and is connected to the lower portion of the control rod guide pipe 10. The upper portion of the control rod guide tube 10 is fitted into the core support plate 6. A control rod drive mechanism (not shown) is provided inside the control rod drive mechanism housing 7 so that the control rod 18 stored in the control rod guide tube 10 can be inserted into the core 9 ing. The steam-water separator 11 is provided above the core shroud 5 and has a function of separating steam from a gas-liquid two-phase flow including steam and water. The steam dryer 12 is provided above the steam-water separator 11 and has a function of removing moisture from the steam supplied from the steam-water separator 11. The pressure vessel 2 is provided with a main steam nozzle 13. The main steam nozzle 13 is connected to a main steam pipe (not shown) connected to a steam turbine (not shown), and has a function of delivering the steam supplied from the steam dryer 12 to the steam turbine. An annular downcomer 14 is formed between the wall surface of the pressure vessel 2 and the core shroud 5. The down pump 14 is attached with an internal pump 15 for circulating a coolant (cooling water).

  FIG. 3 is a partial structural view of the vicinity of the core shroud of the nuclear reactor according to the present embodiment.

  As shown in FIG. 3, the upper grid plate 3 is provided on the top of the core shroud 5. The upper lattice plate 3 is formed in a lattice shape as viewed from above, and holds the upper end portion of the fuel assembly 8 to restrain the displacement of the fuel assembly 8 in the horizontal direction. A plurality of outer peripheral holes (not shown) are formed in the circumferential direction at the outer peripheral portion of the upper grid plate 3. The core support plate 6 is provided below the core shroud 5. The core support plate 6 is provided with a plurality of fuel support fittings 17. The core support plate 6 supports the lower end portion of the fuel assembly 8 via the fuel support fitting 17. In the present embodiment, as viewed from above, except for the fuel assembly 8 disposed on the outermost peripheral side of the core 9, the core support plate 6 with the four fuel assemblies 8 as one set via the fuel support fitting 17 Support. The fuel assemblies 8 disposed on the outermost peripheral side of the core 9 are supported by the core support plate 6 via the fuel support fitting 17 one by one. A plurality of outer peripheral holes (not shown) are formed in the circumferential direction corresponding to the outer peripheral holes of the upper lattice plate 3 also in the outer peripheral portion of the core support plate 6.

  A plurality of guide rods 16 are provided in the core shroud 5. The guide rods 16 are arranged circumferentially along the inner wall surface of the core shroud 5 corresponding to the outer lattice holes of the upper grid plate 3 and the core support plate 6. Guide rods 16 are arranged to extend downward from upper grid plate 3 toward core support plate 6. The upper end portion of the guide rod 16 penetrates the upper lattice plate 3 through the outer peripheral hole of the upper lattice plate 3 and is supported by the bearing 19, and the lower end portion of the core support plate 6 via the outer peripheral hole of the core support plate 6. And is supported by a bearing 20 and configured to be rotatable relative to the upper grid plate 3 and the core support plate 6. In the present embodiment, the guide rod 16 is formed with the groove 16A.

  The movable grid plate 4 is provided between the upper grid plate 3 and the core support plate 6 in parallel with the upper grid plate 3 and the core support plate 6. The movable grid plate 4 is formed in a grid shape as viewed from above. The grid position of the movable grid plate 4 corresponds to the grid position of the upper grid plate 3. A plurality of outer peripheral holes (not shown) are formed in the outer peripheral portion of the movable grid plate 4 in the circumferential direction corresponding to the outer peripheral holes of the upper grid plate 3 and the core support plate 6. A guide rod 16 is inserted through the outer peripheral hole of the movable grid plate 4. In the present embodiment, a large number of balls (not shown) are provided so as to roll freely between the wall surface of the outer peripheral hole of the movable grid plate 4 and the groove 16A of the guide rod 16. The rod 16 is configured to be screwed. Therefore, when the guide rod 16 is rotationally driven, the movable grid plate 4 moves up and down along the guide rod 16 between the upper grid plate 3 and the core support plate 6 (the feed mechanism of the movable grid plate 4 is a ball screw Using the

  As shown in FIG. 3, the nuclear reactor 100 according to the present embodiment further includes a sensor device 21, a control device 23 and a drive device 28.

  The sensor device 21 is attached to the nuclear reactor 100, and measures the vibration of the nuclear reactor 100. In the present embodiment, the case where the sensor device 21 is an accelerometer and the vibration acceleration of the reactor 100 is measured will be described. The sensor device 21 outputs the measured vibrational acceleration of the nuclear reactor 100 to the control device 23 as a signal 22.

  The control device 23 includes a storage unit 25 and a position acquisition unit 26. The storage unit 25 stores a table (hereinafter, referred to as a first acceleration table) indicating the relationship between the vibration acceleration of the reactor 100 and the optimum position of the movable grid plate 4. In this specification, the optimum position of the movable grid plate 4 means that the natural period of the fuel assembly 8 is separated from the natural period of the building 102 and the internals of the reactor with respect to the vibration acceleration of the reactor 100. The position of the movable grid plate 4 which can be made is referred to, and is set for each vibration acceleration of the reactor 100. The position acquisition unit 26 is electrically connected to the sensor device 21, the storage unit 25, and the drive device 28. The position acquisition unit 26 receives the signal 22 from the sensor device 21, and from the first acceleration table stored in the storage unit 25, a movable grid plate corresponding to the vibration acceleration of the nuclear reactor 100 measured by the sensor device 21. The optimum position of 4 is acquired, and the drive signal 27 is output to the drive unit 28 to move the movable grid plate 4 to the optimum position.

  The driving device 28 is connected to the guide rod 16. The drive device 28 receives the drive signal 27 from the control device 23 and rotates the guide rod 16 to move the movable grid plate 4 up and down, and arranges the movable grid plate 4 at an appropriate position. The drive device 28 can adopt, for example, a motor.

(Operation)
FIG. 4 is a flowchart showing the procedure of movement of the movable grid plate according to the present embodiment. Hereinafter, the moving procedure of the movable grid plate 4 according to the present embodiment will be described on the assumption that the reactor 100 is vibrating.

  The sensor device 21 measures the vibration acceleration of the nuclear reactor 100, and outputs it to the position acquisition unit 26 of the control device 23 (step S1). The position acquisition unit 26 receives the vibration acceleration measured by the sensor device 21 and acquires the optimum position of the movable grid plate 4 corresponding to the vibration acceleration from the first acceleration table stored in the storage unit 25 (step S2). Then, the position acquisition unit 26 outputs the drive signal 27 to the drive device 28 so that the movable grid plate 4 moves to the optimum position (step S3). The drive device 28 receives the drive signal 27 from the position acquisition unit 26, and rotationally drives the guide rod 16 to move the movable grid plate 4 to the optimum position (step S4). The above-described operation (steps S1 to S4) is repeated at regular time intervals.

(effect)
(1) In the present embodiment, the movable grid plate 4 is provided between the upper grid plate 3 and the core support plate 6. Therefore, the natural period of the fuel assembly 8 can be separated from the natural period of the building 102 and the reactor internals. Therefore, even when an external force acts on the reactor 100, resonance between the fuel assembly 8 and the building 102 and internal structures can be avoided, and the vibration of the fuel assembly 8 can be suppressed.

  In particular, in the present embodiment, the movable grid plate 4 is configured to be movable up and down. Therefore, by moving the upper grid plate 3 to change the distance to the movable grid plate 4, the natural cycle of the fuel assembly 8 is adjusted, and the fuel assembly 8 and the building 102 and the reactor internal structure are adjusted. The resonance can be avoided and the vibration of the fuel assembly 8 can be suppressed.

  Furthermore, in the present embodiment, the vibration acceleration of the nuclear reactor 100 is measured, and the movable grid plate 4 is moved to the optimum position according to the measured value. As described above, the optimum position means the position of the movable grid plate 4 which can move the natural cycle of the fuel assembly 8 from the natural cycle of the building 102 and the internal structure with respect to the vibration acceleration of the reactor 100. Therefore, even when an external force having various natural cycles such as an earthquake acts on the reactor 100, resonance between the fuel assembly 8 and the building 102 and internal structures is avoided, and the vibration of the fuel assembly 8 can be reduced. It can be suppressed.

  (2) The above-mentioned optimum position has a higher radiation intensity than the vicinity of the upper grid plate 3. As described above, in the present embodiment, since the movable grid plate 4 is configured to be movable up and down, the movable grid plate 4 can be held in the vicinity of the upper grid plate 3. Therefore, the embrittlement of the movable grid plate 4 can be suppressed, and the maintainability of the reactor 100 can be improved. Further, since the movable grid plate 4 can be raised to the vicinity of the upper grid plate 3, when the upper grid plate 3 is configured to be removable from the core shroud 5, the movable grid plate 4 may become brittle. This is advantageous for the work of replacing the movable grid plate 4.

Second Embodiment
(Constitution)
FIG. 5 is a partial structural view of the vicinity of the core shroud of the nuclear reactor according to the present embodiment. In FIG. 5, the same parts as those in the first embodiment described above are denoted by the same reference numerals, and the description will be appropriately omitted. The present embodiment differs from the first embodiment in the length of the guide rod 16. The other configuration is the same as that of the first embodiment.

  As shown in FIG. 5, in the present embodiment, a bearing 20 for supporting the lower end portion of the guide rod 16 is provided between the upper grid plate 3 and the core support plate 6. That is, in the present embodiment, the lower end portion of the guide rod 16 is supported between the upper grid plate 3 and the core support plate 6 without the guide rod 16 penetrating the core support plate 6. The position at which the bearing 20 is provided is not particularly limited as long as it is between the upper grid plate 3 and the core support plate 6.

(effect)
In the present embodiment, in addition to the same effects as in the first embodiment, the following effects can be obtained.

  In the present embodiment, the bearing 20 is provided between the upper grid plate 3 and the core support plate 6, and the lower end portion of the guide rod 16 is supported between the upper grid plate 3 and the core support plate 6. Therefore, the length of the guide rod 16 can be shortened as compared with the first embodiment, and the manufacturing cost can be reduced accordingly.

Third Embodiment
(Constitution)
FIG. 6 is a partial structural view in the vicinity of the core shroud of the nuclear reactor according to the present embodiment. In FIG. 6, the same parts as those in the first embodiment described above are denoted by the same reference numerals, and the description will be appropriately omitted. The present embodiment differs from the first embodiment in that the guide rod 29 and the movable grid plate 31 are further provided. The other configuration is the same as that of the first embodiment.

  As shown in FIG. 6, the guide rod 29 is provided on the inner peripheral side (the central axis side of the core shroud 5) of the guide rod 16 in the core shroud 5. In the present embodiment, a plurality of inner circumferential hole portions (not shown) are formed in the circumferential direction on the inner circumferential side of the outer circumferential hole portion of the upper grid plate 3, On the side, a plurality of inner circumferential holes (not shown) are formed in the circumferential direction corresponding to the inner circumferential holes of the upper grid plate 3. The guide rods 29 are arranged in the circumferential direction, corresponding to the upper lattice plate 3 and the inner peripheral holes of the core support plate 6. In the present embodiment, the groove 29A is formed in the guide rod 29.

  The movable grid plate 31 is provided between the movable grid plate 4 and the core support plate 6. The movable grid plate 31 is formed in a grid shape so that grid positions correspond to grid positions of the upper grid plate 3 when viewed from above. The movable grid plate 31 is formed with a plurality of inner circumferential hole portions (not shown) in the circumferential direction corresponding to the inner circumferential hole portions of the upper grid plate 3 and the core support plate 6. A guide rod 29 is inserted through the inner circumferential hole of the movable grid plate 31. In this embodiment, a large number of balls (not shown) are provided rotatably between the wall surface of the inner circumferential hole of the movable grid plate 31 and the groove 29A of the guide rod 29, and the movable grid plate 31 and the guide rod 29 are configured to screw together. Therefore, when the guide rod 29 is driven to rotate, the movable grid plate 31 moves up and down along the guide rod 29 between the movable grid plate 4 and the core support plate 6. In addition, although the case where the two movable grating plates 4 and 31 are provided is illustrated in this embodiment, three or more movable grating plates may be provided.

  The storage unit 25 of the control device 23 is a table (hereinafter, referred to as a second acceleration table) indicating the relationship between the vibration acceleration of the reactor 100 and the optimum position of the movable grid plate 4 or 31 instead of the first acceleration table. Is stored. In the present specification, the combination of the optimum positions of the movable grid plates 4 and 31 means the natural period of the fuel assembly 8 with respect to the vibration acceleration of the reactor 100 as the natural period of the building 102 and the internal structure of the reactor. The combination of the positions of the movable grid plates 4 and 31 which can be separated from each other is set for each vibration acceleration of the reactor 100. The position acquisition unit 26 acquires the optimum position of the movable grid plate 4 or 31 corresponding to the vibration acceleration of the reactor 100 from the second acceleration table stored in the storage unit 25, and sends the drive signal 27 to the drive device 27. To move the movable grid plates 4 and 31 to their optimum positions through the drive unit 28 respectively.

(effect)
In the present embodiment, in addition to the same effects as in the first embodiment, the following effects can be obtained.

  In the present embodiment, the movable grid plate 31 is further provided between the movable grid plate 4 and the core support plate 6, and the movable grid plates 4 and 31 are respectively moved to optimum positions. Therefore, the natural period of the fuel assembly 8 can be changed more flexibly than in the first embodiment. Therefore, it can be further separated from the natural cycle of the building 102 and the reactor internals, and the vibration of the fuel assembly 8 can be further suppressed.

Fourth Embodiment
(Constitution)
FIG. 7 is a partial structural view of the vicinity of the core shroud of the nuclear reactor according to the present embodiment. In FIG. 7, the same parts as those in the third embodiment described above are given the same reference numerals, and the description will be appropriately omitted. The present embodiment is different from the third embodiment in that the guide grid 29 is not provided and the movable grid plate 31 is provided with the connecting portion 32. The other configuration is the same as that of the third embodiment.

  As shown in FIG. 7, the connecting portion 32 is erected on the outer peripheral side of the movable grid plate 31 from the upper surface of the movable grid plate 31, and the movable grid plate 31 is used as the movable grid plate 4. It is connected. That is, in the present embodiment, the movable grid plate 4 and the movable grid plate 31 are integrally formed via the connecting portion 32. In the present embodiment, the inner circumferential hole may not be formed in the movable grid plates 4 and 31.

(effect)
In the present embodiment, in addition to the same effects as the third embodiment, the following effects can be obtained.

  In the present embodiment, since the movable grid plate 4 and the movable grid plate 31 are integrally formed, the movable grid plate 4 and the movable grid plate 31 can be moved integrally. Therefore, the movable grid plates 4 and 31 can be moved by an operation simpler than that of the third embodiment. In addition, since it is not necessary to provide the guide rod 29 for guiding the movement of the movable grid plate 31 in the vertical direction, it can be manufactured more easily than in the third embodiment.

Fifth Embodiment
(Constitution)
8 and 9 are partial structural views in the vicinity of the core shroud of the nuclear reactor according to the present embodiment. In FIGS. 8 and 9, the same parts as those in the first embodiment described above are denoted by the same reference numerals, and the description will be appropriately omitted. In the present embodiment, a vertical member 33 is provided instead of the guide rod 16, and the grid plate support 34 and the grid plate receiver 35 are provided on the inner wall surface of the core shroud 5. It differs from the first embodiment in that it comprises a portion 36. The other configuration is the same as that of the first embodiment.

  As shown in FIG. 8, the vertical member 33 is provided in the core shroud 5. The vertical members 33 are columnar members disposed to extend downward from the upper grid plate 3 toward the core support plate 6. The vertical members 33 are arranged in the circumferential direction along the inner wall surface of the core shroud 5 corresponding to the outer lattice holes of the upper grid plate 3 and the core support plate 6. The vertical member 33 has the upper end inserted into the outer peripheral hole of the upper grid plate 3 and the lower end inserted into the outer peripheral hole of the core support plate 6 and is fixed to the upper grid plate 3 and the core support plate 6 There is. In the present embodiment, no groove is formed in the vertical member 33, and the vertical member 33 is inserted into the outer peripheral hole of the movable grid plate 4.

  The grid plate support (first support) 34 has an outer end (an end remote from the central axis of the core shroud 5) connected to the wall surface of the core shroud 5, and an inner end (central axis of the core shroud 5). The end on the near side is formed at the free end and disposed in the core shroud 5. The first support portion 34 is provided downward from the upper grid plate 3 by a size slightly larger than or equal to the thickness in the vertical direction of the movable grid plate 4, and the upper surface of the movable grid plate 4 is the upper grid plate 3. The movable grid plate 4 is supported so as to abut (or approach) the lower surface of The first support portion 34 is connected to the drive device 28, and is configured such that the inner end is retracted to the wall surface side (outer end side) of the core shroud 5 via the drive device 28. Therefore, in the present embodiment, in a state where the movable grid plate 4 is supported by the first support portion 34, the first support portion 34 is driven by the drive device 28 so that the inner end portion faces the wall surface side of the core shroud 5. When retracted, the support of the movable grid plate 4 is released, and the movable grid plate 4 falls downward along the guide rods 16 (see FIG. 9).

  The grid plate receiving portion (second support portion) 35 has an outer end connected to the wall surface of the core shroud 5, an inner end formed at a free end, and disposed in the core shroud 5. The second support portion 35 is provided below the first support portion 34 and supports the movable grid plate 4 falling from the first support portion 34 (see FIG. 9). The position where the second support portion 35 is provided is below the first support portion 34, and the natural cycle of the fuel assembly 8 corresponds to the building 102 and the reactor internal structure against an external force having various natural cycles. It is not particularly limited as long as it is a position where it is possible to suppress the vibration of the fuel assembly 8 by avoiding the resonance of the fuel assembly 8 with the building 102 and the reactor internal structure, apart from the natural period of.

  In the present embodiment, the storage unit 25 of the control device 23 stores the threshold value (setting value) of the vibration acceleration of the nuclear reactor 100 instead of storing the first acceleration table. The comparison unit 36 is electrically connected to the sensor device 21, the storage unit 25, and the drive device 28. The comparison unit 36 inputs the measured value of the sensor device 21 (vibration acceleration of the nuclear reactor 100) from the storage unit 25 to each other, compares the measured value of the sensor device 21 with the threshold value, and measures the measured value of the sensor device 21. When the threshold value is exceeded, the drive signal 27 is output to the drive device 28 to remove the first support portion 34 from the movable grid plate 4 and drop the movable grid plate 4 onto the second support portion 35.

(Operation)
FIG. 10 is a flow chart showing the falling procedure of the movable grid plate according to the present embodiment. Hereinafter, the falling procedure of the movable grid plate 4 according to the present embodiment will be described.

  The sensor device 21 measures the vibration acceleration A of the nuclear reactor 100, and outputs it to the comparison unit 36 of the control device 23 (step S11).

  The comparison unit 36 inputs the measured value (vibration acceleration A) of the sensor device 21 and the threshold value As from the storage unit 25, and compares the vibration acceleration A with the threshold value As (step S12). If the vibration acceleration A is equal to or higher than the threshold value As (A 振動 As) (Yes), the comparison unit 36 determines that the movable grid plate 4 needs to be dropped, and moves the procedure to step S13. On the contrary, when the vibration acceleration A is less than the threshold value As (A <As) (No), the comparison unit 36 determines that the movable grid plate 4 does not need to be dropped, and ends the procedure.

  If it is determined in step S12 that the movable grid plate 4 needs to be dropped along the vertical member 33, the comparison unit 36 outputs the drive signal 27 to the drive device 28 (step S13). The driving device 28 receives the driving signal 27 from the comparing portion 36, drives the first support portion 34 to remove the first support portion 34 from the movable grid plate 4, and the movable grid plate 4 is used as the second support portion. It is dropped onto 35 (step S14). The above-described operation (steps S11 to S14) is repeated every fixed time.

(effect)
In the present embodiment, in addition to the same effects as in the first embodiment, the following effects can be obtained.

  In the present embodiment, the movable grating plate 4 is supported by the first support portion 34, and the first support portion 34 is removed from the movable grating plate 4 if necessary, and the movable grating plate 4 is mounted on the second support portion 35. Let fall. Therefore, the movable grid plate 4 can be moved more quickly than in a configuration using a ball screw. Therefore, as compared with the first embodiment, the natural period of the fuel assembly 8 can be quickly separated from the natural period of the building 102 and the reactor internal structure, and the fuel assembly 8 and the building 102 and the reactor internal structure The resonance can be avoided to suppress the vibration of the fuel assembly 8.

<Others>
The present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiment is described in detail to explain the present invention in an easy-to-understand manner, and is not necessarily limited to one having all the described configurations. For example, it is also possible to delete part of the configuration of each embodiment.

  In each embodiment mentioned above, the case where the 2nd lattice board 4 was constituted so that movement in the up-and-down direction was possible was illustrated. However, the essential effect of the present invention is to provide a nuclear reactor capable of avoiding the resonance between the fuel assembly and the building and internal structures of the reactor even when an external force is applied to the reactor. The second grid plate 4 is not necessarily limited to the above-described configuration as long as the target effect is obtained. For example, the second grid plate 4 may be fixedly provided between the upper grid plate 3 and the core support plate 6.

  Further, in the fifth embodiment, the case where the first support portion 34 is configured such that the inner end portion is retracted to the wall surface side of the core shroud 5 is illustrated. However, as long as the above-described essential effect is obtained, the present invention is not necessarily limited to the above-described configuration. For example, the first support portion 34 may be inclined with an arbitrary axis as a fulcrum so that the inner end portion contacts the wall surface of the core shroud 5. In short, the configuration of the first support portion 34 is not limited as long as the support of the movable grid plate 4 can be removed and the movable grid plate 4 can be dropped onto the second support portion 35.

  Moreover, in each embodiment mentioned above, although the improved boiling water reactor (ABWR) was illustrated as a nuclear reactor, the same may be said of a boiling water reactor (BWR).

2 Reactor pressure vessel (pressure vessel)
3 Upper grid plate (first grid plate)
4 Movable grid plate (second grid plate)
Reference Signs List 5 core shroud 6 core support plate 8 fuel assembly 9 core 16 guide rod 21 sensor device 23 control device 28 drive device 33 vertical member 34 grid plate support portion (first support portion)
35 Grid plate support (second support)
100 reactors

Claims (4)

A pressure vessel,
A core shroud housed in the pressure vessel;
A core stored in the core shroud and loaded with a fuel assembly;
A first grid plate holding an upper end of the fuel assembly;
A core support plate supporting a lower end portion of the fuel assembly;
A second grid plate provided between the first grid plate and the core support plate;
The nuclear reactor, wherein the second grid plate is configured to move up and down. In the reactor according to claim 1 ,
A guide rod screwing with the second grid plate and extending downward from the first grid plate;
A nuclear reactor, comprising: a driving device connected to the guide rod and rotationally driving the guide rod to move the second lattice plate up and down. In the reactor according to claim 2 ,
A sensor device for measuring the vibration of the reactor;
A nuclear reactor which is connected to the sensor device and the drive device, and outputs a drive signal to the drive device based on the measurement value of the sensor device to move the second grid plate. In the reactor according to claim 1 ,
A vertical member extending downwardly from the first grid plate;
A first support that supports the second grid plate;
A second support portion provided below the first support portion and supporting the second grid plate falling from the first support portion;
A driving device connected to the first support and driving the first support;
A sensor device for measuring the vibration of the reactor;
The driving device is connected to the sensor device and the driving device, and when the measured value of the sensor device exceeds a threshold, a driving signal is output to the driving device to disconnect the first support from the second grid plate, and And a control device for dropping the two grid plates onto the second support.

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