JP2017058330A - Core shroud and nuclear reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a core shroud capable of improving the form accuracy of a shroud body.SOLUTION: A core shroud 20 includes: an upper plate; a lower plate; and a shroud body 23 that is disposed between the upper plate and the lower plate and covers the periphery of fuel assemblies 10. The shroud body 23 includes a plurality of main body blocks 31 that extend vertically and are arranged along the outermost fuel assemblies 10. Each of the main body blocks 31 is attached to the upper plate and the lower plate. Adjacent main body blocks 31 are not welded to each other.SELECTED DRAWING: Figure 5

Description

  Embodiments of the present invention relate to a core shroud and a nuclear reactor.

  Generally, a core holding structure called a core barrel (also called a core tank) that holds a core including a plurality of fuel assemblies is installed in a pressure vessel of a pressurized water reactor. A core shroud for accommodating the fuel assembly is provided inside the core barrel. The fuel assemblies are each formed in a rectangular shape in plan view, arranged in a lattice shape, and arranged in the core shroud so that the outermost periphery is along the circumference.

  A core shroud of a conventional pressurized water reactor has a plurality of thin plates formed into a stepped shape by being bent along the outermost fuel assembly. These thin plates are arranged in the circumferential direction, and adjacent thin plates are welded together to constitute a shroud cylinder of the core shroud. The upper and lower ends of each thin plate are welded to the upper plate and the lower plate, and the middle portion of each thin plate is welded to a plurality of rings arranged on the outer peripheral side of the thin plate. The inner surface of the shroud cylinder is formed along the outermost fuel assembly, and a predetermined interval is provided between the inner surface of the shroud cylinder and the outermost fuel assembly. With such a configuration, a gap serving as a coolant flow path for cooling the fuel assembly is formed between the shroud cylinder and the fuel assembly.

U.S. Pat. No. 4,409,179

  However, as described above, when the core shroud is manufactured, a plurality of thin plates constituting the shroud cylinder are welded to each other, so that welding deformation may occur in the shroud cylinder. In particular, when the number of welded portions between such thin plates increases, the shape accuracy of the shroud cylinder may decrease. This may make it difficult to ensure the accuracy of the gap between the shroud cylinder and the outermost fuel assembly.

  Each embodiment according to the present invention has been made in consideration of such points, and an object thereof is to provide a core shroud and a nuclear reactor capable of improving the shape accuracy of the shroud cylinder.

  The core shroud according to the embodiment accommodates a plurality of fuel assemblies that are each formed in a rectangular shape in plan view and arranged in a lattice shape so that the outermost periphery is along the circumference. A gap serving as a coolant channel is formed between the body and the body. The core shroud includes an upper plate, a lower plate, and a shroud body that is provided between the upper plate and the lower plate and covers the periphery of the fuel assembly. The shroud cylinder has a plurality of main body blocks arranged along the outermost fuel assembly, each extending in the vertical direction. Each of the main body blocks is attached to the upper plate and the lower plate, respectively. Adjacent main body blocks are not welded to each other.

  The nuclear reactor according to the embodiment includes a reactor pressure vessel, a core barrel installed in the reactor pressure vessel, and the above-described core shroud provided inside the core barrel.

  According to the embodiments of the present invention, the shape accuracy of the shroud cylinder can be improved.

FIG. 1 is a longitudinal sectional view showing an example of a schematic configuration of a pressurized water reactor according to a first embodiment of the present invention. FIG. 2 is a diagram showing a schematic configuration of the core shroud of FIG. FIG. 3 is a plan view of the upper plate shown in FIG. FIG. 4 is a plan view of the lower plate shown in FIG. 5A is a cross-sectional view of the shroud cylinder of FIG. 2, and FIG. 5B is an enlarged view of a portion A of FIG. 5A. FIG. 6 is a cross-sectional view showing a modification of FIG. FIG. 7 is a cross-sectional view of a shroud cylinder according to the second embodiment of the present invention. FIG. 8 is a partial cross-sectional view of a shroud cylinder according to the third embodiment of the present invention. FIG. 9 is a partial cross-sectional view of a shroud cylinder according to the fourth embodiment of the present invention. FIG. 10 is a cross-sectional view showing a modification of FIG. Fig.11 (a) is a top view of the main body block in the 5th Embodiment of this invention, FIG.11 (b) is a side view of Fig.11 (a). FIG. 12 is a diagram showing a schematic configuration of the core shroud according to the sixth embodiment of the present invention. 13 is a cross-sectional view of the shroud cylinder of FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
The core shroud and the nuclear reactor in the first embodiment will be described with reference to FIGS. Here, first, a schematic configuration of a pressurized water reactor will be described as an example of a nuclear reactor with reference to FIG.

  As shown in FIG. 1, a pressurized water reactor 1 includes a cylindrical reactor pressure vessel 2 having a central axis extending in the vertical direction (vertical direction in FIG. 1), and a coolant provided in the reactor pressure vessel 2. An inlet nozzle 3 and a coolant outlet nozzle 4, and a core barrel 5 installed in the reactor pressure vessel 2 are provided. Among these, a core barrel nozzle portion 6 is provided at an upper portion of the core barrel 5, and the core barrel nozzle portion 6 communicates with the coolant outlet nozzle 4. Thereby, the coolant flowing out from the coolant outlet nozzle 4 is prevented from being mixed with the coolant flowing in from the coolant inlet nozzle 3. A downcomer portion 7 in which the coolant flowing in from the coolant inlet nozzle 3 flows downward is provided between the side wall of the reactor pressure vessel 2 and the core barrel 5. In addition, a flow skirt 8 that rectifies the flow of the coolant is provided at the lower portion of the reactor pressure vessel 2. With such a configuration, the coolant flowing in from the coolant inlet nozzle 3 flows into the core barrel 5 through the downcomer portion 7 and the flow skirt 8 to cool the fuel assembly 10 described later, and then in the core barrel 5. From the coolant outlet nozzle 4 through the core barrel nozzle portion 6.

  A control rod drive mechanism 9 is installed in the upper part of the reactor pressure vessel 2, and a fuel assembly 10 described later is used to control the reactor output and stop the reaction in the pressurized water reactor 1 in an emergency. A control rod can be inserted into the inside.

  As shown in FIG. 2, a core shroud 20 that houses a plurality of fuel assemblies 10 (see FIGS. 3 to 5) is provided inside the core barrel 5. The core shroud 20 is placed on the lower core support plate 11 of the core barrel 5. The lower core support plate 11 is provided with dowel pins 12 for fixing the core shroud 20 to the core barrel 5. The upper part of the core shroud 20 is supported by the upper core support plate 13. An alignment plate 14 is fixed to the core barrel 5, and the core shroud 20 is positioned in the circumferential direction with respect to the core barrel 5.

  Next, the core shroud 20 in the present embodiment will be described with reference to FIGS.

  As shown in FIG. 2, the core shroud 20 includes an upper plate 21, a lower plate 22, and a shroud body 23 that is provided between the upper plate 21 and the lower plate 22 and covers the periphery of the fuel assembly 10. I have. Among these, a gap 24 (described later) is formed between the shroud cylinder 23 and the outermost fuel assembly 10. The upper plate 21 and the lower plate 22 are preferably formed of austenitic stainless steel.

  As shown in FIG. 3, the upper plate 21 is provided with an upper opening 25 having a shape along the outermost fuel assembly 10. From the upper opening 25, coolant that flows through a gap 24 (described later) between the shroud cylinder 23 and the outermost fuel assembly 10 flows out.

  An upper flow hole 26 is provided in the upper plate 21. This upper flow hole 26 is for letting out the coolant flowing into the outer peripheral side of the shroud cylinder 23 (more specifically, the area between the shroud cylinder 23 and the core barrel 5) as a bypass flow. In the present embodiment, eight upper flow holes 26 are provided in the upper plate 21, and two sets of these upper flow holes 26 form a set at equal intervals in the circumferential direction (at intervals of 90 °). ) Is formed. The upper flow hole 26 is formed radially outside the shroud cylinder 23 and communicates with a region on the outer peripheral side of the shroud cylinder 23.

  Further, the upper plate 21 is provided with a plate key groove 27 that fits with the above-described alignment plate 14 (see FIG. 2) provided in the core barrel 5. The plate key groove 27 is formed on the outer peripheral portion of the upper plate 21. In the present embodiment, the upper plate 21 is provided with four plate key grooves 27. These plate key grooves 27 are formed at equal intervals in the circumferential direction (at intervals of 90 °). Each plate keyway 27 engages with the corresponding alignment plate 14, whereby the upper plate 21 is positioned in the circumferential direction with respect to the core barrel 5.

  As shown in FIG. 4, the lower plate 22 is provided with a lower opening 28 having a shape along the outermost fuel assembly 10. The coolant flows from the lower opening 28 into the gap 24 between the shroud cylinder 23 and the outermost fuel assembly 10.

  A lower flow hole 29 is provided in the lower plate 22. The lower flow hole 29 is for allowing the coolant to flow into the outer peripheral side of the shroud cylinder 23 as a bypass flow. In the present embodiment, eight lower flow holes 29 are provided in the lower plate 22, and these two lower flow holes 29 form a pair and are equally spaced in the circumferential direction (at 90 ° intervals). ) Is formed. The lower flow hole 29 is formed radially outside the shroud cylinder 23 and communicates with a region on the outer peripheral side of the shroud cylinder 23.

  The lower plate 22 is provided with a plate pin hole 30 into which the above-described dowel pin 12 (see FIG. 2) provided in the lower core support plate 11 of the core barrel 5 is fitted. In the present embodiment, four plate pin holes 30 are provided in the lower plate 22. These plate pin holes 30 are formed at equal intervals in the circumferential direction (at intervals of 90 °). The plate pin hole 30 is formed on the radially outer side than the shroud body 23. The core shroud 20 is fixed to the core barrel 5 by fitting the corresponding dowel pins 12 into the respective plate pin holes 30.

  Next, the shroud cylinder 23 will be described with reference to FIG.

  As shown in FIG. 5A, the shroud cylinder 23 is a plurality of main body blocks 31 each extending in the vertical direction (direction perpendicular to the paper surface in FIG. 5A), and the outermost fuel assembly 10. Has a plurality of main body blocks 31 arranged along the line. Each main body block 31 is formed seamlessly.

  In the present embodiment, the upper end of each main body block 31 is attached to the upper plate 21 by welding, and the lower end is attached to the lower plate 22 by welding. The adjacent main body blocks 31 are in contact with each other but are not welded to each other. In addition, the description that the adjacent main body blocks 31 are not welded to each other means that the boundary between the main body blocks 31 is not welded for the purpose of welding the adjacent main body blocks 31 to each other. Yes. Therefore, the description allows welding at the boundary between the upper end portions of adjacent main body blocks 31 (the vicinity of the upper plate 21) for the purpose of welding the main body block 31 to the upper plate 21, For the purpose of welding the main body block 31 to the lower plate 22, it is used to allow welding at the boundary of the lower end portion of the adjacent main body block 31 (the vicinity of the lower plate 22).

  Each main body block 31 is formed in a rectangular parallelepiped shape (rectangular shape in plan view). Here, the fuel assembly 10 is formed in a rectangular shape in plan view, and the plurality of fuel assemblies 10 are arranged in a lattice shape and the outermost periphery is along the circumference. Main body blocks 31 are arranged along the outermost fuel assembly 10 among the plurality of fuel assemblies 10 arranged in this manner. The main body block 31 is preferably formed of austenitic stainless steel as a material, like the upper plate 21 and the lower plate 22.

  The main body block 31 has an inner corner portion 32 that faces the fuel assembly 10 and is defined by the two side surfaces 31 a and 31 b of the main body block 31. The inner corner portion 32 is a corner portion of the four corner portions of the main body block 31 that is disposed in the inner surface region 33 that defines the inner surface 23 a of the shroud cylinder 23, and protrudes toward the inside of the shroud cylinder 23. Means part. At least a part of the two side surfaces 31a and 31b defining the inner corner portion 32 constitutes an inner surface 23a of the shroud body 23, and faces the corresponding side surfaces 10a and 10b of the outermost fuel assembly 10. Yes. A predetermined interval is provided between the two side surfaces 31a and 31b of the main body block 31 and the corresponding side surfaces 10a and 10b of the fuel assembly 10, and this interval is determined by the shroud body 23 and the outermost fuel assembly. A gap 24 serving as a coolant flow path provided between the body 10 and the body 10 is formed. In the form shown in FIG. 5A, the rectangular parallelepiped main body block 31 is arranged along the outermost fuel assembly 10, so that the outer surface 23b of the shroud cylinder 23 is stepped in plan view. It is formed in the shape of.

  As shown in FIG. 5 (b), the widths Xa and Xb of the inner surface region 33 that defines the inner surface 23 a of the shroud body 23 on the side surfaces 31 a and 31 b of the main body block 31 are the corresponding side surfaces 10 a and 10 b of the fuel assembly 10. The width Ya is greater than or equal to 10b. In the form shown in FIG. 5B, the width Xa of the main body block 31P is substantially the same as the width Ya of the fuel assembly 10, and the width Xb is substantially the same as twice the width Yb. The width Xa of the main body block 31Q is substantially the same as the width Ya of the fuel assembly 10, and the width Xb is substantially the same as the width Yb. Further, the width Xa of the main body block 31R is substantially the same as twice the width Ya of the fuel assembly 10, and the width Xb is substantially the same as the width Yb. For the sake of clarity, reference numerals 31a and 31b indicating side surfaces other than the main body block 31P, reference numeral 33 indicating an inner surface region, and side surfaces of the fuel assembly 10 other than the fuel assembly 10 corresponding to the main body block 31P are shown. Reference numerals 10a and 10b are omitted.

  On the other hand, adjacent main body blocks 31 are in contact with each other. More specifically, the main body blocks 31 are in contact with each other in the contact region other than the above-described inner surface region 33 among the side surfaces 31 a and 31 b of the main body block 31. For this reason, the total width (the total width of the inner surface region 33 and the contact region) Xta, Xtb of the side surfaces 31a, 31b of the main body block 31 is equal to or greater than the widths Xa, Xb described above. In the main body block 31P shown in FIG. 5B, the width Xta is larger than the width Xa, and the width Xtb is substantially the same as the width Xb. For the sake of clarity, illustrations of Xta and Xtb other than the main body block 31P are omitted.

  The main body block 31 is preferably formed in a solid shape. In this case, the strength of the main body block 31 can be improved, and the neutron reflection function of the shroud body 23 can be enhanced. However, the present invention is not limited to this, and the main body block 31 may be formed in a hollow shape (for example, a square pipe shape) as shown in part B of FIG. In this case, the shroud body 23 can be reduced in weight while ensuring the strength of the main body block 31 to some extent.

  In the form shown in FIG. 5A, the shroud cylinder 23 further includes four auxiliary blocks 34. As with the main body block 31, the auxiliary block 34 has an upper end attached to the upper plate 21 by welding and a lower end attached to the lower plate 22 by welding. Further, the auxiliary block 34 constitutes the inner surface 23a of the shroud cylinder 23 and has one side surface facing the corresponding side surface of the fuel assembly 10, but the inner corner portion 32 such as the main body block 31 is provided. Not done. Further, the auxiliary block 34 is in contact with the adjacent main body blocks 31, but is not welded to these main body blocks 31. The auxiliary block 34 may be formed thinner than the main body block 31 as long as the strength as the shroud cylinder 23 can be secured.

  Next, the operation of the present embodiment having such a configuration will be described. Here, the manufacturing method of the core shroud 20 is demonstrated first.

  First, the main body block 31 and the auxiliary block 34 are placed on the lower plate 22. At this time, the main body block 31 and the auxiliary block 34 are arranged along the outermost fuel assembly 10 to be accommodated. Subsequently, the lower end of the main body block 31 and the lower end of the auxiliary block 34 are welded to the lower plate 22, respectively. Next, the upper plate 21 is placed on the main body block 31 and the auxiliary block 34, and then the upper end of the main body block 31 and the upper end of the auxiliary block 34 are welded to the upper plate 21. In this way, the core shroud 20 having the shroud body 23 constituted by the main body block 31 and the auxiliary block 34 is obtained. However, the adjacent main body blocks 31 are not welded to each other, and the adjacent main body block 31 and the auxiliary block 34 are not welded to each other. For this reason, the shroud cylinder 23 is prevented from being deformed during manufacturing, and the shroud cylinder 23 can be manufactured with high accuracy. Note that the welding between the blocks 31 and 34 and the lower plate 22 can also be performed after the upper plate 21 is placed on the blocks 31 and 34.

  Next, the flow of the coolant during operation of the pressurized water reactor 1 will be described.

  During the operation of the pressurized water reactor 1, coolant is supplied from the piping (not shown) outside the reactor pressure vessel 2 to the inside of the reactor pressure vessel 2 through the coolant inlet nozzle 3 shown in FIG. 1. The The supplied coolant flows downward in a downcomer portion 7 formed between the side wall of the reactor pressure vessel 2 and the core barrel 5, and is rectified by a flow skirt 8 provided at the lower portion of the reactor pressure vessel 2. After that, the direction of the flow can be changed upward. Then, the coolant flows into the inside of the core barrel 5 through a communication hole (not shown) of the lower core support plate 11. The coolant flowing into the inside of the core barrel 5 rises while cooling the fuel assembly 10 and the core shroud 20, passes through the core barrel nozzle portion 6 and the coolant outlet nozzle 4, and is connected to the piping outside the reactor pressure vessel 2 ( (Not shown).

  During this time, a part of the coolant flowing into the inside of the core barrel 5 passes through a lower opening 28 provided in the lower plate 22 of the core shroud 20 and enters a gap 24 between the shroud body 23 and the fuel assembly 10. Inflow. The coolant that has flowed up rises in the gap 24 while cooling the fuel assembly 10. As described above, since the shroud cylinder 23 is accurately formed, the gap 24 is uniform in the circumferential direction. Thereby, the coolant flowing around the outermost fuel assembly 10 can be equalized. The coolant that has cooled the fuel assembly 10 flows out of the core barrel 5 through the upper opening 25 provided in the upper plate 21.

  On the other hand, another part of the coolant flowing into the inside of the core barrel 5 flows into the outer peripheral side of the shroud cylinder 23 through the lower flow hole 29 provided in the lower plate 22 of the core shroud 20. The inflowing coolant ascends the outer periphery of the shroud cylinder 23 as a bypass flow, and cools the shroud cylinder 23. Then, the coolant flows out of the core barrel 5 through the upper flow hole 26 provided in the upper plate 21.

  Thus, according to this Embodiment, since the adjacent main body blocks 31 are not mutually welded, the shape accuracy of the shroud cylinder 23 can be improved. As a result, the accuracy of the gap 24 between the shroud cylinder 23 and the outermost fuel assembly 10 can be improved, and the gap 24 can be made uniform in the circumferential direction. For this reason, an appropriate gap 24 can be ensured between the shroud cylinder 23 and the outermost fuel assembly 10, the cooling of the fuel assembly 10 is equalized, and the fuel assembly 10 is efficiently cooled. The burnup can be made uniform.

  Further, according to the present embodiment, in each of the side surfaces 31 a and 31 b of the main body block 31, the widths Xa and Xb of the inner surface region 33 that defines the inner surface 23 a of the shroud cylinder 23 correspond to the corresponding side surfaces 10 a of the fuel assembly 10. The widths Ya and Yb are 10b or more. Thereby, the thickness of each main body block 31 can be increased to improve the strength, and the rigidity of the shroud cylinder 23 can be improved. Further, since the thickness of the main body block 31 is increased, the neutron reflection function of the shroud body 23 can be improved.

  In the above-described embodiment, the example in which the main body block 31 is formed in a rectangular parallelepiped shape has been described. However, the present invention is not limited to this, and as shown in FIG. 6, the main body block 31 may be formed such that the outer surface 23 b of the shroud cylinder 23 is circular in plan view. Accordingly, the flow rate of the coolant can be made uniform in the circumferential direction on the outer peripheral side of the shroud cylinder 23, the coolant can be prevented from flowing unevenly, and the cooling efficiency of the shroud cylinder 23 can be improved. .

(Second Embodiment)
Next, a core shroud and a nuclear reactor according to the second embodiment of the present invention will be described with reference to FIG.

  The second embodiment shown in FIG. 7 is mainly different in that the main body block has a plurality of inner corner portions, and the other configuration is the first embodiment shown in FIGS. 1 to 5. Is almost the same. In FIG. 7, the same parts as those of the first embodiment shown in FIGS. 1 to 5 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 7, in the present embodiment, the shroud body 23 of the core shroud 20 is a plurality of (for example, four) main body blocks 35 each extending in the vertical direction, and the outermost fuel assembly. 10 have a plurality of main body blocks 35 arranged along 10. The main body block 35 has a plurality of (for example, four) inner corner portions 32. The main body block 35 is formed in a size corresponding to the four main body blocks 31 and the auxiliary blocks 34 shown in FIG. The adjacent main body blocks 35 are in contact with each other but are not welded to each other. Therefore, the coolant leakage path that can be formed between the adjacent main body blocks 35 can be reduced. Since the main body block 35 is configured in the same manner as the main body block 31 shown in FIGS. 5A and 5B except for the points described above, detailed description thereof is omitted here.

  In the present embodiment shown in FIG. 7, as in FIG. 6, the main body block 35 is formed such that the outer surface 23b of the shroud cylinder 23 is circular in plan view. However, the present invention is not limited to this, and as shown in FIG. 5A, the outer surface 23b of the shroud cylinder 23 may be formed in a stepped shape in plan view.

  Thus, according to the present embodiment, the main body block 35 of the shroud body 23 has the plurality of inner corner portions 32. As a result, the number of main body blocks 35 constituting the shroud cylinder 23 can be reduced, and the leakage path of the coolant that can be formed between the adjacent main body blocks 35 can be reduced. For this reason, it can suppress that the coolant which flows through the gap 24 between the shroud cylinder 23 and the fuel assembly 10 flows to the outer peripheral side of the shroud cylinder 23, and the cooling efficiency of the fuel assembly 10 can be improved. Further, the strength of the main body block 35 can be improved, and the rigidity of the shroud cylinder 23 can be further improved.

(Third embodiment)
Next, a core shroud and a nuclear reactor according to a third embodiment of the present invention will be described with reference to FIG.

  In the third embodiment shown in FIG. 8, the main body block includes a convex portion and a concave portion, and the convex portion of one main body block of a pair of adjacent main body blocks fits into the concave portion of the other main body block. However, the other configuration is substantially the same as that of the first embodiment shown in FIGS. In FIG. 8, the same parts as those of the first embodiment shown in FIGS. 1 to 5 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 8, in the present embodiment, the main body block 31 includes a convex portion 36 and a concave portion 37, and the convex portion 36 of one main body block 31 of the pair of adjacent main body blocks 31 is the other. The main body block 31 is fitted in the recess 37. That is, one main body block 31 is in contact with both adjacent main body blocks 31, but a convex portion 36 is provided on a side surface in contact with one main body block 31, and a side surface in contact with the other main body block 31. A recess 37 is provided. The convex portion 36 and the concave portion 37 extend in the vertical direction (a direction perpendicular to the paper surface of FIG. 8), and are formed in the entire area of the main body block 31. In addition, the convex part 36 (or concave part 37) is provided in one of the adjacent main body block 31 and the auxiliary block 34, and the concave part 37 (or convex part 36) is provided in the other, and these convex part 36 and concave part are provided. 37 may be fitted.

  Thus, according to the present embodiment, the convex portion 36 of one main body block 31 of the pair of adjacent main body blocks 31 is fitted into the concave portion 37 of the other main body block 31. This can complicate the shape of the coolant leakage path that can be formed between the adjacent main body blocks 31. For this reason, it can suppress that the coolant which flows through the gap 24 between the shroud cylinder 23 and the fuel assembly 10 flows to the outer peripheral side of the shroud cylinder 23 through the leak path. Moreover, the adjacent main body blocks 31 can be firmly coupled to each other, and the rigidity of the shroud cylinder 23 can be further improved.

(Fourth embodiment)
Next, a core shroud and a nuclear reactor according to a fourth embodiment of the present invention will be described with reference to FIG.

  In the fourth embodiment shown in FIG. 9, the body block includes a first recess and a second recess, and the first recess of one body block of the pair of adjacent body blocks is the other body block. The key block is mainly fitted to the first recess and the second recess facing each other, and the other configuration is the first embodiment shown in FIGS. It is almost the same as the form. In FIG. 9, the same parts as those of the first embodiment shown in FIGS. 1 to 5 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 9, in the present embodiment, the main body block 31 includes a first concave portion 38 and a second concave portion 39, and the first main body block 31 of the pair of adjacent main body blocks 31. The recess 38 faces the second recess 39 of the other body block 31. That is, one main body block 31 is in contact with both adjacent main body blocks 31, but the first concave portion 38 is provided on the side surface in contact with one main body block 31, and the side surface in contact with the other main body block 31. A second recess 39 is provided in the first. The first recess 38 and the second recess 39 extend in the vertical direction (direction perpendicular to the paper surface of FIG. 9), and are formed in the entire area of the main body block 31.

  The key block 40 is fitted in the first recess 38 and the second recess 39 facing each other. The key block 40 extends in the vertical direction and has the same vertical length as the main body block 31. The key block 40 has a thermal expansion coefficient larger than that of the main body block 31. For example, for the key block 40, a material having a high coefficient of thermal expansion among austenitic stainless steel or a steel material having a small carbon component can be suitably used. One of the adjacent main body block 31 and auxiliary block 34 is provided with a first recess 38 (or second recess 39), and the other is provided with a second recess 39 (or first recess 38). The key block 40 may be fitted into the first recess 38 and the second recess 39.

  Thus, according to the present embodiment, the first recess 38 of one body block 31 of the pair of adjacent body blocks 31 faces the second recess 39 of the other body block 31 and faces each other. The key block 40 is fitted in the first recess 38 and the second recess 39. This can complicate the shape of the coolant leakage path that can be formed between the adjacent main body blocks 31. For this reason, it can suppress that the coolant which flows through the gap 24 between the shroud cylinder 23 and the fuel assembly 10 flows to the outer peripheral side of the shroud cylinder 23 through the leak path. Moreover, the adjacent main body blocks 31 can be firmly coupled to each other, and the rigidity of the shroud cylinder 23 can be further improved.

  Further, according to the present embodiment, the key block 40 has a thermal expansion coefficient larger than that of the main body block 31. As a result, when the temperature rises during operation, the key block 40 expands more than the main body block 31, thereby improving the adhesion between the key block 40 and the first recess 38 and the key block 40 and the second recess 39. Adhesion can be improved and it can function as a heat seal (a seal whose sealing function is improved by a temperature rise). For this reason, it can further suppress that the coolant which flows through the gap 24 between the shroud cylinder 23 and the fuel assembly 10 flows to the outer peripheral side of the shroud cylinder 23 through the leak path. Further, since the adhesion between the key block 40 and the recesses 38 and 39 is improved, the key block 40 can be prevented from moving in the first recess 38 and the second recess 39. As a result, the adjacent main body blocks 31 can be more firmly coupled, and the rigidity of the shroud cylinder 23 can be further improved. In particular, the key block 40 acts as a cold fit, and the adjacent main body blocks 31 can be more firmly coupled.

  In the present embodiment described above, for example, as shown in FIG. 10, a main body pin hole 41 is provided in the main body block 31, a key pin hole 42 is provided in the key block 40, and the main body pin hole 41 and the key pin are provided. A configuration in which the block pin 43 is fitted in the hole 42 can also be adopted. In this case, the key block 40 can be coupled to the main body block 31 by the block pins 43, and the adjacent main body blocks 31 can be coupled more firmly. In the form shown in FIG. 10, the key block 40 does not have to have a larger thermal expansion coefficient than the thermal expansion coefficient of the main body block 31, but the thermal expansion coefficient of the key block 40 is higher than that of the main body block 31. When it is larger than the expansion coefficient, the key block 40 can be more firmly coupled to the main body block 31 by the heat sealing function described above.

  As shown in FIG. 10, the key pin hole 42 and the block pin 43 preferably pass through the key block 40. In this case, the key block 40 can be more strongly coupled to the main body block 31 by the block pin 43, and the adjacent main body blocks 31 can be further more firmly coupled to each other.

(Fifth embodiment)
Next, a core shroud and a nuclear reactor according to a fifth embodiment of the present invention will be described with reference to FIG.

  The fifth embodiment shown in FIG. 11 is mainly different in that a plurality of coolant grooves into which coolant flows are provided in a region defining the outer surface of the shroud body in the main body block. The configuration is substantially the same as that of the first embodiment shown in FIGS. In FIG. 11, the same parts as those in the first embodiment shown in FIGS. 1 to 5 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIGS. 11A and 11B, in the present embodiment, the coolant flows into the outer surface region 44 that defines the outer surface 23b of the shroud cylinder 23 in the main body block 31 (preferably a plurality of coolants). A) coolant groove 45 is provided. That is, the coolant groove 45 is formed on the surface of the main body block 31 on the core barrel 5 (see FIG. 2) side. As shown in FIG. 11B, each coolant groove 45 extends in the vertical direction and is formed in the entire area of the main body block 31. Such a coolant groove 45 may be formed in the auxiliary block 34 shown in FIG.

  Thus, according to the present embodiment, the coolant groove 45 is provided in the outer surface region 44 that defines the outer surface 23 b of the shroud body 23 in the main body block 31. As a result, the coolant that has flowed into the outer peripheral side of the shroud cylinder 23 as a bypass flow can flow into the coolant groove 45. For this reason, the contact area between the shroud cylinder 23 and the coolant can be increased, and the cooling efficiency of the shroud cylinder 23 can be improved. Further, thermal deformation of the shroud cylinder 23 can be suppressed. Furthermore, the main body block 31 can be reduced in weight by providing the main body block 31 with the coolant groove 45.

(Sixth embodiment)
Next, a core shroud and a nuclear reactor according to the sixth embodiment of the present invention will be described with reference to FIGS.

  The sixth embodiment shown in FIGS. 12 and 13 is mainly different in that it further includes a restraining ring provided on the outer peripheral side of the shroud cylinder and restraining the shroud cylinder from the outside in the radial direction. These are substantially the same as those of the first embodiment shown in FIGS. In FIG. 12 and FIG. 13, the same parts as those of the first embodiment shown in FIG. 1 to FIG.

  As shown in FIGS. 12 and 13, the core shroud 20 in the present embodiment further includes a restraining ring 46 that is provided on the outer peripheral side of the shroud body 23 and restrains the shroud body 23 from the outside in the radial direction. The inner surface of the restraining ring 46 is formed along the outer surface 23 b of the shroud cylinder 23. In the form shown in FIG. 12, two restraining rings 46 are provided on the outer peripheral side of the shroud body 23, and the two restraining rings 46 are arranged at different positions in the vertical direction. Then, the distance between the upper restraint ring 46 and the upper restraint ring 46, the distance between the upper restraint ring 46 and the lower restraint ring 46, and the distance between the lower restraint ring 46 and the lower plate 22 become equal. Yes. The restraining ring 46 is preferably not welded to the shroud body 23. In this case, it can suppress that the shape precision of the shroud trunk | drum 23 falls.

  As shown in FIG. 13, the constraining ring 46 is provided with a ring flow hole 47. The ring flow hole 47 is for allowing the coolant rising on the outer peripheral side of the shroud body 23 to pass as a bypass flow. In the present embodiment, the restraining ring 46 is provided with eight ring flow holes 47, and two of these ring flow holes 47 form a pair and are equally spaced in the circumferential direction (at 90 ° intervals). ) Is formed.

  As described above, according to the present embodiment, the constraining ring 46 that restrains the shroud cylinder 23 from the radially outer side is provided on the outer peripheral side of the shroud cylinder 23. As a result, it is possible to prevent the shroud body 23 from expanding radially outward due to a rise in temperature during operation. Further, it is possible to suppress deformation of the shroud body 23 due to earthquake acceleration during an earthquake. For this reason, the accuracy of the gap 24 between the shroud cylinder 23 and the outermost fuel assembly 10 can be further improved.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof. Moreover, as a matter of course, these embodiments can be partially combined as appropriate within the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Pressurized water reactor 2 Reactor pressure vessel 5 Core barrel 10 Fuel assembly 10a, 10b Side surface 20 Core shroud 21 Upper plate 22 Lower plate 23 Shroud body 23a Inner surface 23b Outer surface 24 Gap 31 Main body block 31a, 31b Side surface 32 Inner corner 33 Inner surface area 35 Main body block 36 Convex part 37 Concave part 38 First concave part 39 Second concave part 40 Key block 44 Outer surface area 45 Coolant groove 46 Restraint ring Xa, Xb width Ya, Yb width

Claims (9)

A plurality of fuel assemblies, each of which is formed in a rectangular shape in a plan view and arranged in a lattice shape so that the outermost periphery is along the circumference, are accommodated between the outermost fuel assemblies. A core shroud that forms a gap that becomes a flow path,
An upper plate,
A lower plate,
A shroud cylinder provided between the upper plate and the lower plate and covering the periphery of the fuel assembly,
The shroud cylinder has a plurality of body blocks arranged along the outermost fuel assembly, each extending in the vertical direction.
Each of the body blocks is attached to the upper plate and the lower plate,
The core shroud, wherein the adjacent main body blocks are not welded to each other. The body block has an inner corner facing the fuel assembly and defined by two side surfaces;
2. The core shroud according to claim 1, wherein a width of a region defining an inner surface of the shroud body in each of the side surfaces of the main body block is equal to or larger than a width of a corresponding side surface of the fuel assembly.   3. The core shroud according to claim 1, wherein the main body block is formed such that an outer surface of the shroud body is circular in a plan view.   The core shroud according to any one of claims 1 to 3, wherein the main body block is formed in a hollow shape. The main body block includes a convex portion and a concave portion,
5. The convex portion of one of the main body blocks of a pair of adjacent main body blocks is fitted into a concave portion of the other main body block. 6. Core shroud. The main body block includes a first recess and a second recess,
The first concave portion of one of the main body blocks of the pair of adjacent main body blocks faces the second concave portion of the other main body block,
The core shroud according to any one of claims 1 to 4, wherein a key block is fitted in the first recess and the second recess facing each other.   The core according to any one of claims 1 to 6, wherein a plurality of coolant grooves into which coolant flows are provided in a region of the main body block that defines an outer surface of the shroud cylinder. Shroud.   The core shroud according to any one of claims 1 to 7, further comprising a constraining ring that is provided on an outer peripheral side of the shroud cylinder and that constrains the shroud cylinder from outside in the radial direction. A reactor pressure vessel;
A core barrel installed in the reactor pressure vessel;
A nuclear reactor comprising the core shroud according to any one of claims 1 to 8, which is provided inside the core barrel.

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