JP2013044538A - Fuel takeout method, fuel loading method and fuel exchange method of nuclear reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the time required for exchange of fuel by exchanging the fuel of a nuclear reactor by one cell unit without using a blade guide.SOLUTION: In the present invention, in order to solve the problem, from the state that four fuel assemblies are loaded and a cross type control rod is entirely inserted, the diagonal two fuel assemblies of a cell are pulled out first, then the cross type control rod is partially pulled out, and the two remaining fuel assemblies are pulled out from the state. Thereafter, two new fuel assemblies are loaded so as to be diagonal to each other, then the cross type control rod is entirely inserted, and finally two remaining new fuel assemblies 9 are diagonally loaded.

Description

  The present invention relates to a nuclear fuel removal method, a fuel loading method, and a fuel exchange method, and in particular, a unit composed of a cross-shaped control rod and a set of two fuel arrays, two rows and two columns surrounding it. The present invention relates to a nuclear reactor fuel extraction method, a fuel loading method, and a fuel exchange method, which are constituted by a set of lattices (cells) and are suitable for a boiling water reactor.

  1 to 3 show a schematic configuration of a boiling water reactor to which the present invention is applied.

  As shown in the figure, a boiling water reactor includes a cylindrical reactor shroud 2 installed in a reactor pressure vessel 1, a reactor core 3 stored in the reactor shroud 2, and a reactor shroud. The steam-water separator 4 installed on the upper part of 2 and the steam dryer 5 installed further on the steam-water separator 4 are schematically configured.

  In the reactor core 3, a plurality of (872 in FIG. 2) fuel assemblies 9 having a rectangular pillar are arranged at a predetermined interval between an upper lattice plate 6 and a fuel support fitting (not shown) installed on the reactor core support plate 7. Is arranged. Between these fuel assemblies 9, a plurality of fuel rods 9 driven by a control rod drive mechanism 10 installed in the lower part of the reactor pressure vessel 1 (about one for four fuel assemblies 9) 205) is provided. 205 cross-shaped control rods 11 are arranged. The cross-shaped control rod 11 can be inserted / removed in the vertical direction (vertical direction in FIG. 1) using the control rod guide tube 12 as a guide, whereby the output of the core 3 can be controlled.

  Cooling water (light water) in the reactor pressure vessel 1 flows into the lower plenum 15 at the lower part of the reactor core 3 by the recirculation pump (internal pump) 14 provided at the lower part of the reactor pressure vessel 1 and rises from there. Then, it flows into the core 3. The cooling water in the reactor core 3 is heated by the fission reaction of the fissionable material contained in the fuel rod 16 provided in the fuel assembly 9 and rises as a gas-liquid mixed flow of steam and saturated water to the shroud head 17. Inflow.

  Thereafter, the steam separated from water by the steam separator 4 is dried by the steam dryer 5, flows out from the main steam pipe 18 of the reactor pressure vessel 1, and is supplied to a turbine (not shown). A generator (not shown) is driven by the rotational power to generate electricity. The steam that has passed through the turbine is condensed by a condenser (not shown), and becomes cooling water again, and is circulated from the water supply pipe 19 to the reactor pressure vessel 1.

  FIG. 4 shows the overall structure of the fuel assembly 9 described above, and FIG. 5 shows the arrangement of the fuel assembly 9 together with the upper lattice plate 6.

  4 and 5 and FIG. 3 described above, the fuel assembly 9 includes a plurality of fuel rods 16 enclosing cylindrical fuel pellets made of fissile material, and two water rods through which cooling water flows. 20. However, the fuel assembly shown in FIGS. 4 and 5 is an example, and the present invention is applicable even when the number of fuel rods, the water rod water, and their arrangement and shape are different.

  A plurality of fuel rods 16 and water rods 20 are arranged in a square grid of n rows and n columns (n = 9 in FIG. 3), and are arranged at predetermined intervals in the axial direction (vertical direction in FIG. 4). The distance between the fuel rod 16 and the water rod 20 is appropriately maintained by the spacer 21 to form a fuel bundle. The fuel assembly 9 includes an upper tie plate 22 and a lower tie plate 23 that respectively support the upper and lower ends of the fuel bundle, and a rectangular tube-shaped channel that surrounds the fuel bundle and forms the outer wall of the fuel assembly 9. And a box 24.

  Such a fuel assembly 9 is installed in a fuel support fitting as a set of four bodies. Further, the upper tie plate 22 of the fuel assembly 9 is passed through the upper lattice plate 6 and channel fasteners 25 provided on the upper side of the upper tie plate 22 (front side in FIG. 5) are mutually connected. It acts to be positioned. At this time, a gap (play) is provided between the upper tie plate 22 and the upper lattice plate 6 or between the channel fasteners 25 in consideration of workability when the fuel assembly 9 is loaded.

  The fully inserted cross-shaped control rod 11 is self-supporting by leaning on the enclosed fuel assembly 9. Even if the two diagonal fuel assemblies 9 are pulled out, the cross-shaped control rod 11 leans against the remaining two diagonal fuel assemblies 9 and does not fall down. However, when two adjacent fuel assemblies 9 are pulled out, there is a possibility that the cross-shaped control rod 11 loses its support to the pulled out fuel assembly 9 and falls down there.

  In other words, the cross-shaped control rod 11 used in the boiling water reactor cannot stand by itself when two adjacent fuel assemblies 9 are pulled out.

  For this reason, a jig for fixing the cross-shaped control rod called a blade guide so as not to fall down is used at the time of fuel replacement and fuel loading. This blade guide is installed so as to straddle the place where two diagonal fuel assemblies are loaded.

  A conventional fuel exchange in which the cross-shaped control rod is fixed so as not to fall using this blade guide will be described with reference to FIG.

  As shown in the figure, in the conventional fuel exchange, four fuel assemblies 9 are loaded and the cross-shaped control rod 11 is fully inserted (30). Pull out the assembly 9 (31), then install and fix the blade guide 28 so that the cross-shaped control rod 11 does not fall down (32), pull out the remaining two fuel assemblies 9 (33), and then The cross-shaped control rod 11 is fully pulled out (34), and finally the blade guide 28 is removed (35).

  For fuel replacement, for example, a checkered pattern fuel extraction method as described in Patent Document 1 is widely known. This checkered pattern fuel extraction method applies fuel exchange to all cells in the core, and about half of the fuel assemblies in the core are extracted in a checkered pattern at the beginning of the fuel replacement. . In this state, it has been confirmed that even if all the control rods are pulled out, it does not become critical.

Japanese Patent Laid-Open No. 9-304580

  The blade guide must be used to prevent the cruciform control rod from falling during fuel replacement work or fuel loading during periodic inspection in the conventional boiling water reactor described above. There was a problem that it took time. In addition, if all fuel assemblies in the core are arranged in a checkered pattern, there is a possibility that the fuel can be replaced without using a blade guide. However, even if only a small number of fuels are replaced, it is necessary to remove more than half of the fuel assemblies first. There is a problem that it takes time to work.

  The present invention has been made in view of the above points, and the object of the present invention is to change the fuel of a nuclear reactor in units of one cell without using a blade guide, and to shorten the time required for the replacement of fuel. It is an object of the present invention to provide a nuclear reactor fuel extraction method, a fuel loading method, and a fuel replacement method.

  In order to achieve the above object, a nuclear fuel cell according to the present invention is a unit cell comprising a cross-shaped control rod and a set of two rows, two columns and four fuel assemblies surrounding the rod. From the state in which the four fuel assemblies are loaded and the cruciform control rods are fully inserted, first, the diagonal fuel cell 2 is removed. The fuel assembly of the body is pulled out, then the cross-shaped control rod is partially pulled out, and finally the remaining two fuel assemblies are pulled out.

  Further, in order to achieve the above object, the nuclear reactor fuel exchange method according to the present invention comprises a unit cell composed of a cross-shaped control rod and a set of two rows and two columns and four fuel assemblies surrounding the rod. A fuel exchange method for a nuclear reactor in which the fuel assemblies of the cells are replaced, and from the state in which the four fuel assemblies are loaded and the cross-shaped control rods are fully inserted, Pull out the two corners of the fuel assembly, then pull out the cross-shaped control rod partially, pull out the remaining two fuel assemblies from this state, and then diagonally connect the two new fuel assemblies to each other. Next, the cross-shaped control rod is fully inserted, and finally, the remaining two new fuel assemblies 9 are loaded diagonally.

  Furthermore, in order to achieve the above object, the fuel loading method for a nuclear reactor according to the present invention is a unit cell composed of a cross-shaped control rod and a set of two rows and two columns and four fuel assemblies surrounding the rod. A fuel loading method for a nuclear reactor that loads the fuel assembly of the cell, wherein the fuel assembly is not loaded and all the cross-shaped control rods are pulled out, Insert the cruciform control rod partly to the extent that it can stand on its own, then load the two fuel assemblies diagonally to the cell, then insert the cruciform control rod fully, and finally the rest First, all the cells are loaded from the state in which the fuel assemblies of two diagonal bodies are loaded or all the fuel assemblies in the core are pulled out and all the cross-shaped control rods are all pulled out. Insert the cross-shaped control rod partly to the extent that it can stand on its own, and then In cells of Te, loaded with fuel assemblies of two diagonal body, then fully inserted cruciform control rods of all the cells, characterized in that the end loading all remaining fuel assembly.

  According to the present invention, it is possible to change the fuel of the nuclear reactor in units of one cell without changing the current nuclear reactor and without using a blade guide, thereby shortening the time required for the fuel exchange. be able to.

It is a figure which shows schematic structure of the boiling water reactor which is the application object of the fuel extraction method of the reactor of this invention, a fuel loading method, and a fuel exchange method. FIG. 2 is a horizontal sectional view of the entire core in FIG. 1. FIG. 2 is a horizontal sectional view of four fuel assemblies and a cross-shaped control rod in FIG. 1. FIG. 2 is a vertical sectional view showing the overall structure of the fuel assembly in FIG. 1. FIG. 2 is a horizontal sectional view showing the arrangement of four fuel assemblies in FIG. 1 together with an upper lattice plate. It is a flowchart which shows the fuel replacement | exchange method of the conventional nuclear reactor. In order to confirm the satisfaction of the reactor shutdown margin in the fuel replacement method of the nuclear reactor according to the present invention, the loading pattern of the fuel assembly as a result of the computer simulation in the core system using the fuel assembly having the fuel rod configuration of 10 rows and 10 columns ( It is a characteristic view which shows the relationship between a horizontal axis) and an effective neutron multiplication factor (vertical axis). It is a flowchart for demonstrating the fuel replacement method and fuel extraction method of the nuclear reactor which is Example 1 of this invention. It is a fragmentary sectional view which shows the partial drawing-out state of the cross-shaped control rod in Example 1 of this invention. It is a fragmentary sectional view which shows the full insertion state of the cross-shaped control rod in Example 1 of this invention. It is a flowchart for demonstrating the fuel loading method of the reactor which is Example 2 of this invention. It is a flowchart for demonstrating the fuel loading method of the nuclear reactor which is Example 3 of this invention.

  In the nuclear reactor fuel extraction method, fuel loading method, and fuel replacement method of the present invention, the cross-shaped control rod is partially removed when the fuel assembly is loaded (the cross-shaped control rod is partially The state of being pulled out or inserted is one of the means. Therefore, it must be ensured that the core does not become critical even in this state.

  The parameter indicating the criticality is called the effective neutron multiplication factor. The core becomes critical when the effective neutron multiplication factor reaches 1. The reactor core can maintain subcriticality with a margin even if all the cross-shaped control rods are fully inserted in a cold state, even if any one cross-shaped control rod is not inserted due to malfunction or the like. Designed. This is called furnace shutdown margin.

  The inventors of the present invention have a reactor core using a fuel assembly having a 10-row and 10-column fuel rod configuration and a core using a fuel assembly having a 9-row and 9-column fuel rod configuration. Computer simulations were performed using two types of systems. It was confirmed that both systems satisfy the furnace shutdown margin.

  In the following, the results of the study based on the former system will be described with reference to FIG. FIG. 7 shows the relationship between the loading pattern (horizontal axis) of the fuel assembly and the effective neutron multiplication factor (vertical axis) as a result of the computer simulation in the core system using the fuel assembly having the fuel rod configuration of 10 rows and 10 columns. Is.

  The items in FIG. 7 are the values of the effective neutron multiplication factor of the core at the time of cold as follows. That is, “CRfullin” in FIG. 7 is a state in which all fuel assemblies are loaded and the cross-shaped control rods are fully inserted, and “CRfullout” is a state in which all fuel assemblies are loaded and the cross-shaped control rods are all pulled out. “1 stack” indicates that the fuel assembly is loaded, and when all the cross-shaped control rods are inserted, only one cross-shaped control rod is fully pulled out in the core. “1 cell” indicates that the fuel assembly is loaded. When the cruciform control rods are fully inserted, only one diagonal fuel cell is loaded in a single cell in the core, and the cruciform control rods are fully pulled out, “1/4 Core” Is a state in which only two fuel assemblies are loaded for 1/4 of the cells in the core and the cross-shaped control rods are fully pulled out. “FullCore” is the diagonal for all cells in the core. Only two fuel assemblies are loaded and the cross-shaped control rod is fully pulled out Each state is shown.

  The white dots in FIG. 7 indicate the effective neutron multiplication factor in a state in which one cross-shaped control rod having the highest control rod value in the core has been removed.

  In FIG. 7, in a cold core using a fuel assembly having a 10 × 10 fuel rod configuration, all fuel assemblies are loaded and all cross-shaped control rods are fully inserted “CRfullin” The effective neutron multiplication factor is 0.947 in this calculation example. The maximum effective neutron multiplication factor when any one of the cross-shaped control rods is removed from this state is a value of 0.978 indicated by “1 stack” in the present calculation example. This value is the design target for the study. Generally, in the “1 stack” state, the furnace shutdown margin is satisfied.

  In the course of the fuel exchange method of the present inventors, the highest effective neutron multiplication factor is that the two diagonal fuel assemblies in the cell are extracted and the cross-shaped control rod in the cell is extracted. When Even at this time, it must be confirmed that the design target value of “1 stack” is not exceeded, that is, the furnace shutdown margin is satisfied.

  The black dot “1 cell” in FIG. 7 shows a state where two diagonal fuel assemblies are pulled out and only the cross-shaped control rods are pulled out in only one cell in the core. In this calculation example, it was 0.947. The white point is the case where the effective neutron multiplication factor is the highest among the cases where the cross-shaped control rod is pulled out at a place other than the target cell at that time, and the value is 0.978 in the present calculation example. Satisfied stop margin. The same calculation was performed for each of the other cells, and it was confirmed that the furnace shutdown margin was always satisfied.

  That is, the present inventors have found that the value of the water region after removing two fuel assemblies in the core at the cold temperature is equal to or greater than the value of the cross-shaped control rod.

  Even if the operation is performed on one cell, the effective neutron multiplication factor is not higher than “CRfullin” in FIG. 7, so even if it is performed on a plurality of cells, it is always lower than “CRfullin” in FIG. And the furnace shutdown margin is always satisfied. In addition, as shown in “fullCore” in FIG. 7, the effective neutron multiplication factor is particularly small when two diagonal fuel assemblies are extracted for all cells in the core and all cross-shaped control rods are extracted. Also confirmed.

  In this study, the cross-shaped control rod handled the state of full extraction. On the other hand, in the present invention, partial extraction and partial insertion of a cross-shaped control rod are used. Since the effective neutron multiplication factor in this case is smaller than that in the case of full extraction, the reactor shutdown margin is satisfied.

  The range (upper limit) of partial extraction and partial insertion is desirably a range in which the cross-shaped control rod can exhibit the effect of neutron absorption and can stand alone. That is, the area including the neutron absorber in the cross-shaped control rod overlaps the effective area of the fuel assembly, and when the cross-shaped control rod is inserted, the cross-shaped control rod does not fall down and the cross-shaped control rod tilts. Even so, it is desirable that the fuel assembly is not interfered with the removal and loading of the fuel assembly (an inclination of about 1 degree can be allowed and a length of up to 2.1 m can be inserted). For example, when the length of the cross-shaped control rod is divided into 24, a state where only the length of 1/24 or less is inserted is suitable.

  The lower limit of partial extraction and partial insertion in the present invention is a position where the upper end of the region including the neutron absorber in the cross-shaped control rod reaches the effective region of the fuel assembly.

  Embodiments of a fuel extraction method, a fuel loading method, and a fuel exchange method of the present invention reflecting the above examination results will be described below with reference to the drawings.

  FIG. 8 shows a flowchart of an embodiment of a process of replacing the fuel assembly 9 from a cell in which four fuel assemblies 9 are loaded and the cross-shaped control rod 11 is fully inserted.

  As shown in the figure, from the state where the four fuel assemblies 9 are loaded and the cross-shaped control rod 11 is fully inserted (40), first, the two fuel assemblies 9 on the diagonal of the cell are pulled out ( 41). Next, the cross-shaped control rod 11 is partially pulled out (42). That is, the region including the neutron absorber in the cross-shaped control rod 11 overlaps the effective region of the fuel assembly 9, and when the cross-shaped control rod 11 is inserted, the cross-shaped control rod 11 does not fall down. Even if the mold control rod 11 is tilted, the cross-shaped control rod 11 is partially pulled out so as not to interfere with the removal of the fuel assembly 9.

  FIG. 9 shows a state in which the cross-shaped control rod 11 is partially pulled out. As shown in the figure, the cross-shaped control rods 11 disposed between the fuel assemblies 9 supported by the fuel support bracket 13 and the control rod insertion holes 8 formed in the fuel support bracket 13 are cross-shaped as shown in FIG. The control rod 11 is pulled downward from the fully inserted state of the control rod 11 by the control rod drive mechanism 10 (see FIG. 1), and is driven to the partial extraction position shown in FIG.

  The partial extraction position shown in FIG. 9 is such that the above-described region including the neutron absorbing material in the cross-shaped control rod 11 overlaps the effective region of the fuel assembly 9 and the cross-shaped control rod 11 is inserted when the cross-shaped control rod 11 is inserted. Even if the mold control rod 11 does not fall down and the cross-shaped control rod 11 is tilted, it does not interfere with the removal of the fuel assembly 9 (an inclination of about 1 degree can be allowed, and a length up to 2.1 m can be inserted). Yes, for example, when the length of the cross-shaped control rod 11 is divided into 24, it is in a state of being pulled out by a length of 1/24 or less and 1/2 or less.

  Next, the remaining two fuel assemblies 9 are pulled out from the above state (43), and then the two new fuel assemblies 9 are loaded diagonally to each other (44). Next, as shown in FIG. 10, the cross-shaped control rod 11 is fully inserted (45) up to the position of the upper grid plate 6 by the control rod drive mechanism 10 (see FIG. 1). Finally, the remaining two new fuel assemblies 9 are loaded diagonally (46), and the fuel exchange operation for this cell is completed.

  Although the fuel exchange method has been described above, steps (40)-(41)-(42)-(43) in the flowchart of FIG. 8 show the fuel removal method.

  By such fuel take-out and fuel change work of this embodiment, the fuel can be extracted without using the blade guide, and the fuel change time can be shortened. In addition, by partially pulling out the control rod, the effect of the control rod appears and the neutron multiplication factor is lowered, so that the work can be performed more safely than when fully pulling out.

  FIG. 11 shows a flowchart of an embodiment of a process of loading the fuel assembly 9 into a cell in which the fuel assembly 9 is not loaded and the cross-shaped control rod 11 is fully pulled out (initial loading).

  As shown in the figure, from the state where the fuel assembly 9 is not loaded and all the cross-shaped control rods 11 are pulled out (50), first, the cross-shaped control rods 11 are moved as shown by arrows (a). Partial insertion (51) to the extent that it can stand by itself, that is, when the region containing the neutron absorber in the cross-shaped control rod 11 overlaps the effective region of the fuel assembly 9 and the cross-shaped control rod 11 is inserted Even if the cross-shaped control rod 11 does not fall down, and even if the cross-shaped control rod 11 is tilted, the cross-shaped control rod 11 is partially inserted so as not to interfere with the insertion of the fuel assembly 9 (the cross-shaped control rod in this embodiment) 11 is the same position as FIG. 9).

  The partial insertion position of the cross-shaped control rod 11 is such that the region including the neutron absorbing material in the cross-shaped control rod 11 described above overlaps the effective region of the fuel assembly 9 and the cross-shaped control rod 11 is inserted. Sometimes the cross-shaped control rod 11 does not fall down, and even if the cross-shaped control rod 11 is tilted, it does not interfere with the insertion of the fuel assembly 9 (an inclination of about 1 degree can be allowed and can be inserted up to 2.1 m in length. For example, when the length of the cross-shaped control rod 11 is divided into 24, it is in a state where it is inserted by a length not less than 1/24 and not more than 1/2.

  Next, from the above state, the two fuel assemblies 9 are loaded into the cell so as to be diagonal to each other (52), and then the cross-shaped control rod 11 is as shown in FIG. (53). Finally, the remaining two diagonal fuel assemblies 9 are loaded (54).

  By such a fuel loading operation of this embodiment, fuel can be inserted without using a blade guide, and the fuel replacement time can be shortened.

  FIG. 12 shows a flowchart of a nuclear reactor fuel loading method according to the third embodiment of the present invention.

  As shown in the figure, from the state where all the fuel assemblies 9 of the core are pulled out and all the cross-shaped control rods 11 are fully pulled out (60), first, the cross-shaped control rods 11 can be self-supported in all the cells. Partial insertion to the range (61). That is, the region including the neutron absorber in the cross-shaped control rod 11 overlaps the effective region of the fuel assembly 9, and when the cross-shaped control rod 11 is inserted, the cross-shaped control rod 11 does not fall down. Even if the mold control rod 11 is inclined, the cross-shaped control rod 11 is partially inserted so as not to interfere with the loading of the fuel assembly 9 (the partial insertion state of the cross-shaped control rod 11 in this embodiment is the same as in FIG. 9). Position).

  The partial insertion position of the cross-shaped control rod 11 is such that the region including the neutron absorbing material in the cross-shaped control rod 11 described above overlaps the effective region of the fuel assembly 9 and the cross-shaped control rod 11 is inserted. Sometimes the cross-shaped control rod 11 does not fall down, and even if the cross-shaped control rod 11 is tilted, it does not interfere with the insertion of the fuel assembly 9 (an inclination of about 1 degree can be allowed and can be inserted up to 2.1 m in length. For example, when the length of the cross-shaped control rod 11 is divided into 24, it is in a state where it is inserted by a length not less than 1/24 and not more than 1/2.

  Next, the two fuel assemblies 9 are loaded in all the cells from the above state (62), and then the cross-shaped control rods 11 of all the cells are fully inserted as in FIG. 10 (63). To do. Finally, all the remaining fuel assemblies 9 are loaded.

  All the fuel assemblies 9 in the core can be inserted by the fuel loading operation of the present embodiment. Further, the fuel exchange time can be shortened by inserting all the cross-shaped control rods 11 at the same time. In addition, the effective neutron multiplication factor at this time is particularly low, and it is possible to work efficiently with a large safety margin in terms of nuclear characteristics.

  DESCRIPTION OF SYMBOLS 1 ... Reactor pressure vessel, 2 ... Reactor shroud, 3 ... Core, 4 ... Steam separator, 5 ... Steam dryer, 6 ... Upper lattice plate, 7 ... Core support plate, 8 ... Control rod insertion hole, 9 DESCRIPTION OF SYMBOLS ... Fuel assembly, 10 ... Control rod drive mechanism, 11 ... Cross type control rod, 12 ... Control rod guide tube, 13 ... Fuel support bracket, 14 ... Internal pump, 15 ... Lower plenum, 16 ... Fuel rod, 17 ... Shroud head, 18 ... main steam pipe, 19 ... water supply pipe, 20 ... water rod, 21 ... spacer, 22 ... upper tie plate, 23 ... lower tie plate, 24 ... channel box, 25 ... channel fastener, 27a ... Peripheral surface, 28 ... blade guide.

Claims (10)

A nuclear reactor fuel extraction method for extracting a fuel assembly from a unit cell composed of a cross-shaped control rod and a set of two fuel cells and two rows and two columns surrounding the control rod,
From the state in which the four fuel assemblies are loaded and the cruciform control rods are fully inserted, first, the fuel assemblies of the two diagonal bodies of the cell are pulled out, and then the cruciform control rods are A method for removing fuel from a nuclear reactor, comprising partially extracting and finally extracting the remaining two fuel assemblies. The method for removing fuel from a nuclear reactor according to claim 1,
Partial extraction of the cruciform control rod means that the cruciform control rod when the region containing the neutron absorber in the cruciform control rod overlaps the effective region of the fuel assembly and the cruciform control rod is inserted A method for removing fuel from a nuclear reactor, wherein the rod does not fall down and does not interfere with removal of the fuel assembly even if the cross-shaped control rod is tilted. The method for removing fuel from a nuclear reactor according to claim 1,
The partial pulling out of the cruciform control rod means that the length of the cruciform control rod is pulled out by a length of 1/24 or less and 1/2 or less when the length of the cross control rod is divided into 24. Reactor fuel removal method characterized. A nuclear reactor fuel exchange method for exchanging the fuel assemblies in a unit cell composed of a cross-shaped control rod and a set of two rows and two columns and four fuel assemblies surrounding the rod.
From the state in which the four fuel assemblies are loaded and the cruciform control rods are fully inserted, first, the fuel assemblies of the two diagonal bodies of the cell are pulled out, and then the cruciform control rods are Partially withdrawn, withdrawing the remaining two fuel assemblies from this state, then loading the two new fuel assemblies diagonally with respect to each other, then inserting the full cross-shaped control rod, and finally And the remaining two new fuel assemblies 9 are loaded diagonally. The method for refueling a nuclear reactor according to claim 4,
Partial extraction of the cruciform control rod means that the cruciform control rod when the region containing the neutron absorber in the cruciform control rod overlaps the effective region of the fuel assembly and the cruciform control rod is inserted A method for refueling a nuclear reactor, characterized in that the rod does not fall down and does not interfere with the removal of the fuel assembly even if the cross-shaped control rod is tilted. The method for refueling a nuclear reactor according to claim 4,
The partial pulling out of the cruciform control rod means that the length of the cruciform control rod is pulled out by a length of 1/24 or less and 1/2 or less when the length of the cross control rod is divided into 24. Reactor fuel exchange method characterized. A nuclear fuel loading method for loading a fuel assembly of a unit cell composed of a cross-shaped control rod and a set of four fuel assemblies in two rows and two columns surrounding the rod,
From the state in which the fuel assembly is not loaded and all the cross-shaped control rods are pulled out, first, the cross-shaped control rods are partially inserted to the extent that they can stand on their own, and then 2 The fuel assembly is loaded diagonally with respect to each other, then the cross-shaped control rods are fully inserted, and finally the remaining two diagonal fuel assemblies are loaded. Fuel loading method. A nuclear fuel loading method for loading a fuel assembly of a unit cell composed of a cross-shaped control rod and a set of four fuel assemblies in two rows and two columns surrounding the rod,
From the state in which all the fuel assemblies of the core are pulled out and all the cross-shaped control rods are all pulled out, first, partially insert the cross-shaped control rods in a range where all the cells can stand on their own, and then In addition, all the cells are loaded with two diagonal fuel assemblies, then all the cross-shaped control rods of all cells are inserted, and finally all the remaining fuel assemblies are loaded. Reactor fuel loading method. The method of loading fuel in a nuclear reactor according to claim 7 or 8,
The partial insertion of the cruciform control rod means that the cruciform control rod is inserted when the region containing the neutron absorber in the cruciform control rod overlaps the effective region of the fuel assembly and the cruciform control rod is inserted. A fuel loading method for a nuclear reactor, characterized in that the rod does not fall down and does not interfere with the insertion of the fuel assembly even if the cross-shaped control rod is tilted. The method of loading fuel in a nuclear reactor according to claim 7 or 8,
The partial insertion of the cross-shaped control rod means that the length of the cross-shaped control rod is inserted by a length not less than 1/24 and not more than 1/2 when the length of the cross-shaped control rod is divided into 24. Reactor fuel loading method.

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