Support structure for control rod drive mechanism housing

Abstract

This invention provides a support structure for a control rod drive mechanism housing that can withstand seismic loads. [Solution] The support structure 1 of the control rod drive mechanism housing of the present invention comprises a first support structure 5 provided on the lower flange 2 of the CRDH and a second support structure 8 provided on the lower flange 2 of another CRDH adjacent to the lower flange 2 of the CRDH. The load is transmitted to the third support structure 3 via the first support structure 5, the second support structure 8, and the lower flange 2, thereby increasing the load-bearing area between the first support structure 5 and the second support structure 8 and transmitting the load to satisfy a predetermined load value.

Description

Technical Field

[0001] The present invention relates to a support structure for a control rod drive mechanism housing.

Background Art

[0002] In a nuclear power plant, control rods are arranged at the center of a plurality of fuel assemblies. Then, the control rods are inserted into and withdrawn from the fuel assemblies by a control rod drive mechanism. Thereby, the nuclear fission of uranium 235 forming the fuel rods is controlled, and steam is generated by the heat of nuclear fission energy released by the nuclear fission. Then, the steam power of the steam is supplied to a turbine to rotate a generator to generate electricity. By the way, a control rod drive mechanism housing (hereinafter referred to as CRDH) lateral restraint, which is a device for restraining the lateral displacement of the housing of the control rod drive mechanism during an earthquake, is described in Non-Patent Document 1.

[0003] Non-Patent Document 1 describes that "the control rod drive mechanism housing lateral restraint supports the control rod drive mechanism housing in the horizontal direction during an earthquake and transmits the load to the control rod drive mechanism housing restraint beam. Adjacent control rod drive mechanism housings are in contact with each other via the control rod drive mechanism housing lateral restraint, so that the load in the compression direction is transmitted, but the load in the tensile direction is not transmitted."

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Non-Patent Document 1 describes a support structure for CRDH. The support structure described in Non-Patent Document 1 requires further seismic reinforcement (a challenge) to cope with the increased seismic load, that is, the load-bearing capacity of the components must be several times greater. This invention was made to solve the above problems and aims to provide a support structure for a control rod drive mechanism housing that can withstand seismic loads. [Means for solving the problem]

[0006] To solve the aforementioned problems, the support structure for the control rod drive mechanism housing of the present invention comprises a first support structure provided on the lower flange of a CRDH and a second support structure provided on the lower flange of another CRDH adjacent to the lower flange of the CRDH, wherein the load is transmitted to a third support structure via the first support structure, the second support structure, and the lower flange, and the load is transmitted by widening the load-bearing area between the first support structure and the second support structure to satisfy a predetermined load value. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a support structure for a control rod drive mechanism housing that can withstand seismic loads. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic bottom view of the lower flange group of the control rod drive mechanism housing (CRDH) to which the lateral restraint of the CRDH is attached, as viewed from below according to the first embodiment of the present invention. [Figure 2A] This is an enlarged view of section I in Figure 1. [Figure 2B] This is a cross-sectional view taken along line II-II in Figure 2A. [Figure 2C] This is an enlarged view of section XV in Figure 1. [Figure 3A] This is a plan view of the base with bolts. [Figure 3B]It is a cross-sectional view taken along line III-III of FIG. 3A. [Figure 3C] FIG. 3C is a perspective cross-sectional view taken along line IV-IV of FIG. 3A. [Figure 4A] It is a plan view of the second-stage base. [Figure 4B] It is a view taken in the direction of arrow V of FIG. 4A. [Figure 4C] It is a view taken in the direction of arrow VI of FIG. 4B. [Figure 5A] It is a front view of the set bolt. [Figure 5B] It is a view taken in the direction of arrow VII of FIG. 5A. [Figure 6A] FIG. 6A is a plan view of the base without bolts. [Figure 6B] It is a cross-sectional view taken along line VIII-VIII of FIG. 6A. [Figure 6C] It is a cross-sectional view taken along line IX-IX of FIG. 6B. [Figure 7] It is a partially enlarged view of a group of CRDH lateral restraints with an expanded load-bearing area in the second embodiment. [Figure 8A] It is a side view of the CRDH lateral restraint in the second embodiment. [Figure 8B] It is a cross-sectional view taken along line XIII-XIIII of FIG. 8A. [Figure 8C] It is a view taken in the direction of arrow XIV of FIG. 8B. [Figure 9A] It is an equivalent view of the main part of the CRDH lateral restraint shown in FIG. 1 in the third embodiment. [Figure 9B] It is a front view showing the spherical top bolt constituting the CRDH lateral restraint. [Figure 10] It is a bottom view showing the effect of the CRDH lateral restraint in the comparative example (conventional). [Figure 11] It is a bottom view showing the effect of the CRDH lateral restraint in the third embodiment (the present invention).

Mode for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described in detail with appropriate reference to the drawings. (First Embodiment) In nuclear power plants, control rods are moved in and out between multiple fuel rods using a control rod drive mechanism within the reactor core, where numerous fuel rods are arranged. This absorbs neutrons generated by the nuclear fission of uranium-235 in the fuel rods, thereby controlling the uranium-235 fission reaction. Fuel rods are made from materials such as cadmium (Cd) and hafnium (Hf).

[0010] In detail, the reactor core is surrounded by light water, which acts as both a moderator and a coolant. The light water slows down the neutrons generated by the nuclear fission of uranium-235 in the fuel rods, while the control rods absorb these neutrons, thereby controlling the nuclear fission reaction of uranium-235 in the fuel rods. The control rod drive mechanism (CRD) normally moves the control rods vertically via a motor and ball screws, and in the event of a power outage, it uses hydraulic pressure to insert the control rods between the fuel rods, thereby stopping the uranium-235 nuclear fission reaction.

[0011] Figure 1 is a schematic bottom view of the lower flange group of the control rod drive mechanism housing (CRDH) to which the lateral restraint 1 of the control rod drive mechanism housing (CRDH) is attached, as viewed from below. The control rod drive mechanism housing (CRDH) lateral restraint 1 of the first embodiment is a device that restrains the lateral displacement of the lower flange 2 fixed to the control rod drive mechanism housing during an earthquake.

[0012] In a boiling water reactor (BWR), below the pressure vessel (not shown), multiple control rod drive mechanism housings (CRDHs), which are long cylindrical structures, are installed vertically (perpendicular to the plane of the paper in Figure 1), with the lower flanges of the CRDHs, which are the flanges that connect to the control rod drive mechanisms, arranged at narrow intervals. Figure 1 is a cross-sectional view of the vicinity of the lower end of a control rod drive mechanism housing (CRDH), and in addition to the lower flange 2 of the CRDH, it also shows the control rod drive mechanism housing (CRDH) lateral restraint 1 and the control rod drive mechanism housing restraint beam 3 (hereinafter referred to as CRDH restraint beam 3), etc.

[0013] Below the pressure vessel (not shown) that houses numerous fuel rods (not shown), as shown in Figure 1, numerous cylindrical lower flanges 2 extend downward, spreading out horizontally (on the plane of the paper in Figure 1). Furthermore, in the horizontal plane shown in Figure 1, a CRDH lateral restraint 1 is provided between the lower flange 2 and the adjacent lower flange 2, where the bolt head 5 and the boltless base 8 are in surface contact, as shown in Figure 2A.

[0014] Figure 2A is an enlarged view of section I in Figure 1. Figure 2B is a cross-sectional view taken along line II-II in Figure 2A. Figure 2C is an enlarged view of section XV in Figure 1. As shown in Figure 1, CRDH restraint beams 3, such as H-shaped steel with high bending rigidity (EI), are provided at the ends of numerous lower flanges 2 and groups of CRDH lateral restraints 1. In this configuration, during an earthquake, the CRDH lateral restraint 1 supports the lower flange 2 of the CRDH horizontally through surface contact between the bolt head 5 and the boltless base 8, and transmits the load generated during the earthquake to the CRDH restraint beam 3.

[0015] In detail, during an earthquake, the elastic energy (=kx) due to the vibration of numerous lower flanges 2 and CRDH lateral restraint groups 1 is lost. 2 The energy ( / 2) is transmitted to the CRDH restraint beam 3. The CRDH restraint beam 3 absorbs the transmitted elastic energy by elastically deforming. This provides vibration isolation for the control rod drive mechanism housing (CRDH).

[0016] <CRDHラテラルレストレント1> As shown in Figure 2A, the CRDH lateral restraint 1 of the first embodiment is configured to include a bolted base 4, a second-stage base 7, a set bolt 5B, and a boltless base 8. The bolt head 5 of the set bolt 5B has a large bolt diameter. To elaborate, for example, it has a larger bolt diameter than the one described on page 14 of Non-Patent Document 1, "Supplement to Building-Equipment Coupled Seismic Response Analysis" (comparative example). A bolted base 4, a second-stage base 7, and a set bolt 5B with a bolt head 5 are fixed to the lower flange 2. A boltless base 8 is fixed to the lower flange 2 adjacent to the lower flange 2.

[0017] In this way, the bolt head 5 fixed to the lower flange 2 and the boltless base 8 fixed to the adjacent lower flange 2 are in surface contact. During an earthquake, the load generated by the surface contact between the bolt head 5 and the boltless base 8 is transmitted from the lower flange 2 to the adjacent lower flange 2, and then through the CRDH lateral restraint 1 to the CRDH restraint beam 3.

[0018] As shown in Figure 2C, the CRDH restraint beam 3 is in surface contact with a bolted base 4 fixed to the adjacent lower flange 2 and a set bolt 5C with a short bolt head 5c1 fixed to the second-stage base 7. Furthermore, set bolt 5C is a set bolt having a bolt head 5c1 with a shorter head length than the bolt head 5 of the aforementioned set bolt 5B.

[0019] As shown in Figure 2A, the bolted base 4 is fixed to the lower flange 2 of the CRDH by fastening a pair of countersunk screws b1 to it. The bolted base 4 has a conical cylindrical surface 4a formed therein that provides clearance for the countersunk screws b1 (see Figures 3A and 3B).

[0020] Figure 3A is a plan view of the bolted base 4. Figure 3B is a section view of Figure 3A taken along line III-III, and Figure 3C is a perspective view of Figure 3A taken along line IV-IV. The bolted base 4 has an elongated, roughly rectangular parallelepiped shape, and its lower surface 4s (see Figure 3B) is formed in a roughly cylindrical shape along the outer circumferential surface 2g of the lower flange 2 (see Figure 2A). As shown in Figure 2A, the second-stage base 7 is fixed to the bolted base 4 by screwing a pair of bolts b2 into the female threads 4b of the bolted base 4. The second-stage base 7 has through holes (clear holes) 7a (see Figure 4A) through which the bolts b2 are inserted.

[0021] Figure 4A is a plan view of the second-tier base 7. Figure 4B is a view of Figure 4A in the direction of arrow V, and Figure 4C is a view of Figure 4B in the direction of arrow VI. The second-stage base 7 is secured by screwing the set bolt 5B into the central female thread 7b. The second-stage base 7 has a stepped, elongated rectangular parallelepiped shape, with thin-walled fixing portions 7k formed at both ends.

[0022] Figure 5A is a front view of the set bolt 5B, and Figure 5B is a view taken in the direction of arrow VII in Figure 5A. The set bolt 5B has a bolt head 5 and a male threaded portion 5o.

[0023] As shown in Figure 2A, a boltless base 8 is secured to the lower flange 2 of another adjacent CRDH by fastening a pair of countersunk screws b1. Figure 6A is a plan view of the boltless base 8. Figure 6B is a section view taken along line VIII-VIII of Figure 6A, and Figure 6C is a section view taken along line IX-IX of Figure 6B. The boltless base 8 has an elongated, roughly rectangular parallelepiped shape, and its lower surface 8s (see Figure 6B) is formed in a roughly cylindrical shape along the outer circumferential surface 2g of the lower flange 2 (see Figure 2A). The boltless base 8 has a conical cylindrical surface 8a that provides clearance for the countersunk screw b1 (see Figures 3A and 3C).

[0024] The bolted base 4, set bolt 5B, second-stage base 7, and boltless base 8 that constitute the CRDH Lateral Restraint 1 described above are formed from forged high-load-bearing manganese (Mn) austenitic stainless steel GXM1 to meet high-spec load-bearing requirements. Furthermore, CRDH Lateral Restraint 1 may use materials other than high-manganese (Mn) austenitic stainless steel GXM1, as long as the required strength is satisfied.

[0025] <Effects and Effects> According to the CRDH lateral restraint 1 (support structure for control rod drive mechanism housing) of the first embodiment, by increasing the bolt diameter of the bolt head 5 compared to the conventional product (comparative example), the load-bearing area of ​​the area subjected to seismic load can be increased. In other words, it is possible to reduce the load applied to the unit area of ​​the bolt head 5 (set bolt 5B). Therefore, it is possible to reduce the stress (internal force) generated in the bolt head 5 (set bolt 5B). The comparative example is described on page 14 of Non-Patent Literature 1, "Supplement to Building-Equipment Coupled Seismic Response Analysis" (https: / / www.nra.go.jp / data / 000313362.pdf).

[0026] In other words, the contact area (load-bearing area) of the bolt head 5 of the set bolt 5B is increased so that the load (stress) meets the predetermined load value. The predetermined load value is, for example, the load regulatory value set by the Nuclear Regulation Authority.

[0027] Furthermore, due to the increase in the bolt diameter of the bolt head 5, the base section is divided into a two-tiered structure consisting of a bolted base section 4 and a second-tier base 7. This allows the CRDH lateral restraint 1 to be fixed using the existing female thread 2m (see Figure 2A) of the lower flange 2. Therefore, it is possible to create a structure that allows the CRDH lateral restraint 1 to be installed in narrow existing CRDH structures.

[0028] In this case, adding screw holes to the lower flange 2 in a confined space is difficult, but this structure allows the use of the existing female thread 2m, eliminating the need to add screw holes. Furthermore, the lower flange 2 and the bolted base 4 and boltless base 8 of the first stage of the base are fastened together by countersunk screws b1. Therefore, there is a possibility that the countersunk screws b1 may loosen over time and fall off. However, as shown in Figure 2A, the second stage base 7 and the bolt head 5 that transmits the load are structured to block the countersunk screws b1 of the bolted base 4 and boltless base 8, respectively, thus preventing the countersunk screws b1 from falling off.

[0029] Based on the above, it is possible to provide a support structure for the CRDH lateral restraint 1 that improves seismic resistance and can withstand excessive seismic loads, within the range of dimensions that can be installed between the control rod drive mechanism housings (CRDH).

[0030] (Second Embodiment) Figure 7 is a partially enlarged bottom view of the CRDH lateral restraint 21 group with an expanded load-bearing area according to the second embodiment. The CRDH lateral restraint 21 of the second embodiment is provided with a reinforcing base 9 covering the bolted base 24 described in the first embodiment, and the number of load-transmitting bolts is increased to two bolts 25B. This doubles the load-transmitting area and reduces the load applied to each bolt by half. By using two load-transmitting bolts 25B, the structure increases (doubles) the area that receives the applied load.

[0031] <Overall Structure> The lower flange 2 of the CRDH is fixed to the existing base 28 and the reinforcing base 9, and bolts 25B (see Figure 7) having bolt heads 25 are screwed into the reinforcing base 9. Meanwhile, the lower flange 2 of the adjacent CRDH is fixed to the existing base 28 and the boltless reinforcing base 19 (see Figure 7). The bolt head 25 of the bolt 25B, which is fixed to the lower flange 2 of the CRDH, and the boltless reinforcing base 19, which is fixed to the adjacent lower flange 2 of the CRDH, are in surface contact, and the load is transmitted.

[0032] As shown in Figure 7, the bolt heads 25 of bolts 25B, which are fixed to the lower flange 2 of the CRDH at the end of the CRDH restorative beam 3 via the existing base 28 and the reinforcing base 9, are in surface contact with the lower flange 2 of the CRDH. In the second embodiment, the seismic load applied to the lower flange 2 of the CRDH is transmitted to the CRDH restrain beam 3 through surface contact with the bolt head 25 in the CRDH lateral restrain 21.

[0033] <CRDHラテラルレストレント21> Figures 8A to 8C show the CRDH lateral restraint 21 of the second embodiment with an expanded load-bearing area.

[0034] Figure 8A is a side view of the CRDH lateral restraint 21 of the second embodiment. Figure 8B is a cross-sectional view taken along line XIII-XIII in Figure 8A. Figure 8C is a view taken along arrow XIV in Figure 8B.

[0035] The reinforcing base 9, which covers the existing base 28 as shown in Figures 8A and 8B, has a structure in which the basic existing base 28 and the reinforcing base 9 are fastened together with bolts b5. The reinforcing base 9 has an elongated, roughly rectangular parallelepiped shape that covers the existing base 28. One side 9a of the reinforcing base 9 (see Figure 8B) is formed in a roughly cylindrical shape that follows the outer circumferential surface 2g of the lower flange 2 of the CRDH (see Figure 2A). The reinforcing base 9 has a recessed space inside for accommodating the existing base 28. In the center of the reinforcing base 9, there is an insertion hole 9b through which the bolt fastening support 28b of the existing base 28 is inserted.

[0036] On one side and the other side of the center of the reinforcing base 9, along with the existing base 28, a pair of through holes 9d are provided through which bolts b5, which are fixed to the lower flange 2, are inserted. One side of the reinforcing base 9 is provided with a pair of female threads 9c into which load-transferring bolts 25B are screwed. The CRDH lateral restraint 21 is assembled to the lower flange 2 as follows:

[0037] As shown in Figure 7, the existing base 28 is placed along the outer circumferential surface 2g of the lower flange 2, and the existing base 28 is covered with a reinforcing base 9, to which two bolts 25B (see Figure 7) are screwed into the female thread 9c. Then, bolt b5 (see Figure 7) is inserted through the insertion hole 9d of the reinforcing base 9 and the insertion hole of the existing base 28, and screwed into the female thread 2m (see Figure 2A) of the lower flange 2. In this way, the reinforcing base 9 and the existing base 28 of the CRDH lateral restraint 21 are fixed to the lower flange 2.

[0038] This configuration allows the CRDH lateral restraint 21 to fasten two load-transfer bolts 25B to a pair of female threads 9c of the reinforcing base 9. As shown in Figure 7, a boltless reinforcing base 19, which does not have female threads 9c, is fixed to the adjacent lower flange 2 with bolts b5, covering the existing base 28. In other words, the boltless reinforcing base 19 has a structure in which the reinforcing base 9 does not have a female thread 9c into which the load-transferring bolt 25B is screwed.

[0039] In this way, the reinforcing base 9 fixed to the lower flange 2, the bolt head 25 of the bolt 25B, and the boltless reinforcing base 19 fixed to the adjacent lower flange 2 make surface contact, and the load during an earthquake is transmitted.

[0040] <Effects and Effects> According to the second embodiment, the bolt heads 25 of the load-transmitting bolts 25B are made into two, increasing the area that receives the applied load. As a result, the area that receives the load transmitted to the lower flange 2 of the CRDH is increased and can be transmitted to the CRDH restraint beam 3. This reduces the load applied to each load-transmitting bolt 25B, and thus reduces the generated stress. For example, the contact area of ​​the bolt head 25 of bolt 25B is increased by increasing the number of bolts 25B so that the load (stress) meets the predetermined load value. The predetermined load value is, for example, the load regulatory value set by the Nuclear Regulation Authority.

[0041] Furthermore, the reinforcing base 9 and the boltless reinforcing base 19 that cover the existing base 28 are fastened to the existing base 28 with bolts b5. Therefore, since there is no need to replace the existing base 28, a CRDH lateral restraint 21 with good workability can be provided. In the second embodiment, the case with two bolts 25B was illustrated, but the configuration may be made with three or more bolts to reduce the load applied to each bolt.

[0042] (Third embodiment) Figure 9A is a bottom view of the main part of the CRDH lateral restraint 31 shown in Figure 1 of the third embodiment. Figure 9B is a front view showing the spherical top bolt 35B that constitutes the CRDH lateral restraint 31. A bolted base 24 is fixed to one side of the lower flange 2 of the CRDH by fastening it with bolt b6.

[0043] The bolted base 24 shown in Figure 9A is fastened with the spherical top bolt 35B shown in Figure 9B. One side of the spherical top bolt 35B has a spherical top portion 6 on the bolt head 35. The other side of the spherical top bolt 35B has a male thread 35m (see Figure 9B) threaded onto it. Meanwhile, a boltless base 38 is fixed to the outer circumferential surface 2g of the lower flange 2 of the adjacent CRDH by fastening it with bolts b6. The bolted base 24 has a roughly rectangular parallelepiped base support 24a and a roughly rectangular parallelepiped bolt fastening support 24b that is smaller than the base support 24a.

[0044] One side 24a1 of the base support 24a is formed in a substantially cylindrical shape along the outer peripheral surface 2g of the lower flange 2. A pair of through holes 24a3 are provided at both ends of the base support 24a through which fixing bolts b6 are inserted. A bolt-fastened support 24b is formed on the other side 24a2 of the base support 24a.

[0045] At the center of the bolt fastening support 24b, an internal thread 24b1 into which the spherical top bolt 35B is screwed is engraved. The boltless base 38 shown in Fig. 9A has a substantially rectangular parallelepiped base support 38a and a substantially rectangular parallelepiped spherical top receiving support 38b smaller than the base support 38a. One surface 38a1 of the base support 38a is formed in a substantially cylindrical surface shape along the outer peripheral surface 2g of the lower flange 2.

[0046] At both ends of the base support 38a, a pair of insertion holes 38a3 through which the fixing bolts b6 are inserted are provided. On the other surface of the base support 38a, a spherical top receiving support 38b is formed. At the top of the spherical top receiving support 38b, a spherical concave portion 38b1, which is a spherical concave portion where the spherical top 6 of the spherical top bolt 35B slides, is recessed. The bolted base 24, the spherical top bolt 35B, and the boltless base 38 that make up the CRDH lateral restraint 31 are formed of forged products of high manganese (Mn) austenitic stainless steel GXM1 having high load-bearing capacity. Note that the CRDH lateral restraint 31 may be made of a material other than high manganese (Mn) austenitic stainless steel GXM1 as long as it is a material that satisfies the required strength.

[0047] <Assembly and Installation of CRDH Lateral Restraint 31> On the bolted base 24, the spherical top bolt 35B is screwed into the internal thread 24b1, and the spherical top bolt 35B is fixed to the bolted base 24. On the lower flange 2 of the CRDH, the bolted base 24 is fixed by inserting the bolt b6 into the insertion hole 24a3 (see Fig. 9A) and screwing it into the internal thread 2m. On the other hand, on the lower flange 2 of the adjacent CRDH, the boltless base 38 is fixed by inserting the bolt b6 into the insertion hole 38a3 (see Fig. 9A) and screwing it into the internal thread 2m.

[0048] Thus, a bolted base 24 and a boltless base 38 are fixed to the lower flange 2 of the CRDH, respectively, to which the spherical top bolt 35B is fixed (see Figure 9A). As shown in Figure 1, the CRDH restrain beam 3 is in contact with the CRDH lateral restrain 31, which is fixed to the lower flange 2 of the CRDH. During an earthquake, the CRDH lateral restraint 31 between the lower flanges 2 of the CRDH horizontally supports the lower flanges 2 of the CRDH, and the load is transmitted to the CRDH restraint beam 3.

[0049] <Effects and Effects> Figure 10 is a bottom view showing the effect of the comparative example (conventional) CRDH lateral restraint 101. In the comparative example (conventional), a pair of bolted base portions 104 and a pair of boltless base portions 108 are fixed to the lower flange 102 of the control rod drive mechanism housing (CRDH).

[0050] A flat top bolt 105B is fixed to the bolted base portion 104. The top 105B1 of the flat top bolt 105B is flat. The top 108a of the boltless base portion 108 is flat.

[0051] As shown in Figure 10, when a load F1 is applied in the X direction of the horizontal XY plane, the top 105B1 of the planar top bolt 105B of the bolted base portion 104 and the top 108a of the base portion 108 without bolts are in contact in a planar manner. Therefore, the load is transmitted only through the contact between the top 105B1 of the planar top bolt 105B of the bolted base portion 104 and the top 108a of the base portion 108 without bolts, which are perpendicular to the X direction. Consequently, the load F1 applied to a single planar top bolt 105B is large. Therefore, the comparative example (conventional) CRDH lateral restraint 101 has a problem with its load-bearing capacity against large loads.

[0052] Figure 11 is a bottom view showing the effect of the CRDH lateral restraint 31 of the third embodiment (the present invention). In Figure 11, when a load f1 is applied in one direction (arrow α11 in Figure 11), the load f1 is transmitted by sliding between the spherical top 6 of the spherical top bolt 35B of the bolted base 24 fixed to the lower flange 2 of the CRDH and the spherical recess 38b1 of the boltless base 38 fixed to the lower flange 2 of the adjacent RDH. Therefore, the load f1 is distributed and transmitted not only in the X direction of the horizontal plane but also in the Y direction. Consequently, the load applied to a single spherical top bolt 35B is reduced.

[0053] From the above, by providing a spherical portion 6 on the bolt head 35 of the spherical top bolt 35B, the load-transmitting area of ​​the bolt head 35 increases compared to the case where the top portion 105B1 of the bolt head of the comparative example (conventional) is flat (see Figure 10). As shown in Figure 11, by forming a spherical portion 6 on the bolt head 35, it becomes possible to transmit the load not only in the X-axis direction (horizontal direction) of the bolt head 35, but also in the Y-axis direction (horizontal direction), which is horizontal and perpendicular to the X-axis direction. In other words, it becomes possible to distribute the load applied to each bolt. For example, by providing a spherical portion 6 on the bolt head 35 of the spherical top bolt 35B, the contact area of ​​the bolt head 35 is increased, so that the load (stress) satisfies the predetermined load value. The predetermined load value is, for example, the load regulatory value set by the Nuclear Regulation Authority.

[0054] Based on the above, it is possible to provide a support structure for the control rod drive mechanism housing lateral restraint 31 that improves seismic resistance and can withstand excessive seismic loads, within the range of dimensions that can be installed between CRDH.

[0055] <<Other Embodiments>> 1. In the third embodiment described above, a spherical top bolt 35B with a spherical top was used as an example, but the top can be a convex curved surface other than a sphere, or a concave curved surface, as long as it can distribute and transmit the load in the horizontal direction.

[0056] 2. Although the first to third embodiments described above were explained using boiling water reactors as examples, they are applicable not only to boiling water reactors but also to pressurized water reactors.

[0057] 3. The present invention is not limited to the embodiments and modified configurations described above, and various modified and specific forms are possible within the scope of the appended claims. [Explanation of Symbols]

[0058] 1, 21, 31 CRDH Lateral Restraint (Support structure for control rod drive mechanism housing) 2 Lower flange 3. CRDH beam (third support structure) 5, 5c1, 15, 25 Bolt heads (first support structure) 5B Set bolts (first support structure, bolts) 8. Boltless base (second support structure) 15B, 25B bolts 35 Bolt head (curved bolt head, first support structure)

Claims

1. A first support structure provided on the lower flange of the CRDH, The system comprises a second support structure provided on the lower flange of another CRDH adjacent to the lower flange of the aforementioned CRDH, The load is transmitted to the third support structure via the first support structure, the second support structure, and the lower flange. The load-bearing area between the first support structure and the second support structure is expanded to satisfy a predetermined load value and transmit the load. A support structure for a control rod drive mechanism housing, characterized by the above.

2. A first support structure provided on the lower flange of the CRDH, The system comprises a second support structure provided on the lower flange of another CRDH adjacent to the lower flange of the aforementioned CRDH, The load is transmitted to the third support structure via the first support structure, the second support structure, and the lower flange. The first support structure has bolts that contact the second support structure and transmit the load, By increasing the bolt diameter of the bolt head of the aforementioned bolt, the area over which the load is transmitted is increased. A support structure for a control rod drive mechanism housing, characterized by the above.

3. In the support structure for the control rod drive mechanism housing according to claim 2, It is equipped with a reinforcing base that covers the base portion, The aforementioned bolts consist of multiple bolts, and the load applied to each bolt is reduced. A support structure for a control rod drive mechanism housing, characterized by the above.

4. A first support structure provided on the lower flange of the CRDH, The CRDH comprises a second support structure provided on the lower flange adjacent to the lower flange, The load is transmitted to the third support structure via the first support structure, the second support structure, and the lower flange. The first support structure and the second support structure transmit the load by spreading it horizontally. A support structure for a control rod drive mechanism housing, characterized by the above.

5. A first support structure provided on the lower flange of the CRDH, The CRDH comprises a second support structure provided on the lower flange adjacent to the lower flange, The load is transmitted to the third support structure via the first support structure, the second support structure, and the lower flange. The first support structure has bolts with bolt heads that contact the second support structure and transmit the load, The bolt has a curved bolt head that contacts the second support structure, and the direction of the applied load is distributed by the curved bolt head. A support structure for a control rod drive mechanism housing, characterized by the above.

6. In the support structure for the control rod drive mechanism housing according to claim 5, The bolt head is spherical. A support structure for a control rod drive mechanism housing, characterized by the above.

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