JP2009052967A - Control rod and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control rod which can prevent cracking in a sheath from appearing, and to provide a method for manufacturing the control rod. <P>SOLUTION: A frame is composed by mounting a handle 3 and a lower part support member 5 on a tie rod 2 by welding. An upper part hafnium tubular body 9A and a lower part hafnium tubular body 9B are mounted on a handle 3 and the lower part support member 5, respectively. The tie rod 2 is heated. Tabs 10 formed on the lateral end of the sheath 8 are mounted on the heated tie rod 2 by welding. The upper end of the sheath 8 and its lower end are welded onto the handle 3 and the lower part support member 5, respectively. In this state, the upper part hafnium tubular body 9A and the lower part hafnium tubular body 9B are laid out in the sheath 8. The drop in the temperature of the sheath 8 and the frame to normal temperature imparts axial compressive residual stress extends over the entire axial length of the sheath 8. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a control rod and a manufacturing method thereof, and more particularly to a control rod having a tie rod, a handle, a lower support member, and a sheath suitable for use in a boiling water reactor and a manufacturing method thereof.

  A control rod used in a boiling water reactor is inserted into a core loaded with a fuel assembly during operation of the reactor to control the reactor power. All control rods are withdrawn from the core at the end of the operating cycle. An example of the control rod is described in JP-A-9-61576. In this control rod, a flat hafnium cylindrical body, which is a neutron absorbing member, is disposed in a sheath constituting the blade. Two hafnium cylinders are present in the axial direction of the control rod. Japanese Patent Application Laid-Open No. 9-61576 describes the manufacture of the control rod as follows.

  A handle is attached to the upper end of the tie rod. The handle has a handle body and an upper tongue extending downward from the handle body. A lower support member having a lower support member main body and a lower tongue-shaped portion extending upward from the lower support member main body is attached to a lower end portion of the tie rod. An assembly of the handle, the tie rod and the lower support member is referred to as a frame.

  The upper tongue of the handle is inserted into the upper end of the upper hafnium cylinder, and the upper hafnium cylinder is fixed to the upper tongue with a pin. The lower tongue-like portion of the lower support member is inserted into the projecting end portion of the lower hafnium cylindrical body, and the lower hafnium cylindrical body is fixed to the lower lower portion by a pin. A plurality of upper hafnium cylinders attached to the upper tongue and a plurality of lower hafnium cylinders attached to the lower tongue are inserted into a stainless steel sheath having a U-shaped cross section. Is done. Thereafter, the upper end, the lower end and the side end of the sheath are welded to the handle, the lower indicating member and the tie rod, respectively. A plurality of tabs (projections) are formed in the axial direction of the control rod at the side end of the sheath, and these tabs are welded to the tie rod.

  One blade is formed by the sheath and the plurality of hafnium cylinders. The control rod has four blades extending in all directions from the tie rod. The control rod used in the boiling water reactor has a cross-shaped cross section.

JP-A-9-61576

  Generally, when welding is performed, compressive plastic strain is generated in the welded portion. Compressive plastic strain causes shrinkage deformation at a site where deformation is not constrained. On the other hand, tensile residual stress is generated at a portion where deformation is constrained.

  In the control rod, first, the tie rod and the sheath tab are welded. Tensile residual stress is generated in the welded portion, and compressive residual stress is generated around the welded portion. Next, welding of the handle and the sheath, and the lower support member and the sheath is performed. Since the displacement of the sheath in the control rod axis direction caused by these weldings is restrained by the welded portion of the tab and the tie rod, a tensile residual stress is generated over a wide area of the sheath.

  In boiling water reactors, the control rods receive neutron irradiation during the operation period. Stress corrosion cracking (SCC) may occur when the environment, material, and tensile stress, which are generation factors, overlap. In addition, the cracks that have occurred may develop. It is known that SCC can be suppressed by removing one of the three generation factors. It is important to suppress the tensile residual stress to a low level and to make it compressive stress in order to suppress the occurrence of SCC and to stop the progress even if it occurs.

  The objective of this invention provides the control rod which can prevent generation | occurrence | production of the crack in a sheath, and its manufacturing method.

  A feature of the present invention that achieves the above-described object resides in that axial compressive residual stress is applied to the handle-side end of the sheath member. Since compressive residual stress in the axial direction is applied to the end portion, it is possible to prevent the occurrence of cracks in the sheath member.

  The above-described object can also be achieved by applying an axial compressive residual stress over the entire axial length of the sheath member. Since the compressive residual stress in the axial direction is applied over the entire axial length of the sheath member, the occurrence of cracks in the sheath member can be prevented.

  The above-described purpose is that after the welding of the sheath member and the tie rod is finished, or after the welding of the sheath member and the tie rod, the handle, and the lower support member is finished, heat is incident on the tie rod to remove a part of the tie rod. It can also be achieved by melting the tie rod in the axial direction, solidifying the melted portion of the tie rod, and forming a molten portion extending in the axial direction in the tie rod. The formation of the melted portion increases the contraction deformation in the axial direction of the tie rod, and causes the sheath member to contract in the axial direction. As a result, compressive residual stress is applied to the sheath member, and cracks can be prevented from occurring in the sheath member.

  According to the present invention, it is possible to prevent a crack from occurring in the sheath member.

  Examples of the present invention will be described below.

  A preferred embodiment of the present invention will be described with reference to FIGS. The control rod 1 of this embodiment is used in a boiling water reactor. Note that control rods of Examples 2 to 5 described later are also applied to the boiling water reactor. The control rod 1 has a tie rod 2, a handle 3, a lower support member 5, and four blades 7. The handle 3 includes a plurality of upper tongues 4 extending downward. The lower support member 5 includes a plurality of lower tongue portions 6 extending upward. The handle 3 and the lower support member 5 are cross-shaped in cross section. As shown in FIG. 2, the control rod 1 has a cross-shaped cross section, and four blades 7 extend from the tie rod 2 in all directions. Each blade 7 includes a plurality of flat upper hafnium cylinders 9A and a plurality of flat lower hafnium cylinders 9B, which are neutron absorbing members, in a stainless steel sheath 8 having a U-shaped cross section. It is arranged. Each sheath 8 has a plurality of tabs 10 arranged in the axial direction of the control rod 1 at the side end. Each tab 10 is welded to the tie rod 2. The upper end of the sheath 8 is attached to the handle 3 and the lower end of the sheath 8 is attached to the lower support member 5 by welding. Each upper tongue 4 is inserted into the upper end of a separate upper hafnium cylinder 9 A, and each upper hafnium cylinder 9 A is attached to the upper tongue 4 by a pin 11. Each lower tongue 6 is inserted into the upper end of a separate lower hafnium cylinder 9B, and each lower hafnium cylinder 9B is attached to the lower tongue 6 by a pin 11.

  The control rod 1 is manufactured by a manufacturing method described below. A cruciform handle 3 is attached to the upper end of the tie rod 2 and a cruciform lower support member 5 is attached to the lower end of the tie rod 2 by welding. Thereafter, the upper hafnium cylindrical body 9 </ b> A is attached to the upper tongue 4 and the lower hafnium cylindrical body 9 </ b> B is attached to the lower tongue 6. In a state where the upper hafnium cylindrical body 9A and the lower hafnium cylindrical body 9B are disposed between the inner surfaces of the U-shaped sheath 8, the side end of the sheath 8, that is, the tab 10 is moved toward the tie rod 2. . Each tab 10 is overlaid on the surface of the tie rod 2.

  Before welding the sheath 8 to the tie rod 2, the handle 3 and the lower support member 5, the frame constituted by the tie rod 2, the handle 3 and the lower support member 5 is heated in the heating region 12 (see FIG. 1). The heating region 12 exists in the tie rod 2 at least between the upper end of the sheath 8 and the lower end of the sheath 8. The frame is heated so that the temperature of the frame is higher than the temperature of the sheath 8. This heating is performed by applying a burner flame to the entire frame. After heating the frame, the sheath 8 is welded to the tie rod 2, handle 3 and lower support member 5. First, the sheath 8 and the tie rod 2 are welded. Two tabs 10 located on both side ends of the sheath 8 and facing each other with the tie rod 2 interposed therebetween are located in the center in the axial direction of the tie rod 2 are welded to the tie rod 2 using a welding torch. On both sides of the tie rod 2, the other tabs 10 are sequentially welded to the tie rod 2 using a welding torch from the welded tabs 10 toward the handle 3 and the lower support member 5.

  The welding of the sheath 8 and the tie rod 2 will be specifically described with reference to FIG. The control rod 1 has four sheaths 8, and when these sheaths 8 are welded to the tie rods 2, it is necessary to perform welding at eight points in the axial direction of the tie rods 2. As shown in FIG. 2, the torch 13 is arranged at each of eight welding positions in a certain cross section, and the tab 10 and the tie rod 2 are welded using these welding torches 13, respectively. Since eight welding torches 13 are used for welding, the time required for welding the tie rod 2 and the sheath 8 can be shortened. If the welding torch 13 cannot be disposed at eight locations around the tie rod 2, the sheath 8 may be welded to the tie rod 2 one by one in order. When welding the sheath 8 to the tie rod 2 one by one, the frame is heated to finish welding the first sheath 8 and the tie rod 2, the sheath 8 and the handle 3, and the sheath 8 and the lower support member 5, Thereafter, the other sheaths 8 are sequentially welded.

  After the welding of the sheath 8 and the tie rod 2 is finished, the upper end of the sheath 8 and the handle 3 and the lower end of the sheath 8 and the lower support member 5 are welded. After the welding of the sheath 8 to the handle 3 and the lower support member 5 is completed, the intermediate product of the control rod 1 joined by welding is kept for a long time (for example, until the whole temperature becomes a uniform temperature). 12 hours). After this time has elapsed, the manufacturing process of the control rod 1 is completed. The manufactured control rod 1 is applied with compressive residual stress over the entire length of the sheath 8 in the axial direction of the control rod 1. In the sheath 8 of the control rod 1, a residual stress distribution indicated by a solid line 14 is formed in the axial direction of the control rod 1 as shown in FIG. 3. The residual stress distribution in the axial direction of the control rod 1 indicated by the solid line 14 is a compressive residual stress. Since such compressive residual stress is formed over the entire length of the sheath 8 in the axial direction, the risk of cracking in the sheath 8 can be eliminated. In FIG. 3, the residual stress distribution indicated by the broken line 15 is for a conventional control rod (the control rod described in JP-A-9-61576). In the conventional control rod, as shown by the broken line 15, tensile residual stress is formed at the upper end portion and the lower end portion of the sheath 8. The length from the upper end and the lower end of the sheath 8 of the region where the tensile residual stress occurs when the axial length of the sheath 8 is L0 and the length of the region where the tensile residual stress occurs in the axial direction of the tie rod 2 is L1. L1 is 0.2L0. In particular, in the conventional control rod, a crack is generated at the upper end portion of the sheath 8 that has been inserted into the core for a long time. Since the control rod 1 is provided with compressive residual stress at the upper end portion and the lower end portion of the sheath 8, it is possible to prevent a crack from occurring at the upper end portion of the sheath 8.

  A mechanism in which compressive residual stress is applied to the upper end portion and the lower end portion of the sheath 8 in the control rod 1 will be described with reference to FIG. Assume a stress evaluation line 16 inside the tie rod 2 in the direction in which the blade 7 extends perpendicular to the axial direction of the tie rod 2 and a stress evaluation line 17 in the sheath 8 in that direction in which the blade 7 extends. If a frame placed in a freely stretchable state without restraining deformation is heated to a uniform temperature throughout the frame, and the temperature of the entire frame is raised, the frame does not generate any stress. It expands uniformly in the direction. In this state, the stress distribution 18 in the axial direction of the control rod along the stress evaluation line 16 before welding of the tie rod 2 and the sheath 8 is zero. Further, the stress distribution 19 in the axial direction of the control rod along the stress evaluation line 17 before welding of the tie rod 2 and the sheath 8 is also zero.

  After the frame is heated, the tab 10 and the tie rod 2 are joined by welding, and the upper end portion and the lower end portion of the sheath 4 are aligned with the handle 3 and the lower support member 5 to perform welding. If these are left after the end of welding, the sheath 8 and the frame are connected by a welded portion, so heat is transferred from the frame to the sheath 8 by heat conduction. Further, the temperature of the sheath 8 and the frame becomes equal to the ambient temperature after a sufficient time has elapsed due to heat transfer with the ambient air. When the temperature of the sheath 8 and the entire frame is lowered to room temperature, the stress distribution 18 of the tie rod 2 after the tie rod 2 and the sheath 8 are welded becomes a tensile stress having a value T as shown in FIG. The stress distribution 19 of the sheath 8 after the welding becomes a compressive stress having a value S as shown in FIG. That is, a tensile residual stress in the axial direction of the control rod is applied to the tie rod 2, and a compressive residual stress in the axial direction is applied to the entire length of the sheath 8 in the axial direction. In particular, in this embodiment, when the welding of the sheath 8 and the frame is started, the temperature of the sheath 8 is lower than the temperature of the tie rod 2, so when the temperature of the frame and the sheath 8 is lowered to room temperature, A compressive residual stress in the axial direction can be applied over the entire length of the sheath 8 in the axial direction.

  A mechanism in which compressive residual stress is applied to the upper end portion and the lower end portion of the sheath 8 after the frame is heated will be described. In FIG. 3, the tensile residual stress generated at the end of the sheath was 180 MPa at the maximum when the mock-up specimen was manufactured and measured. Therefore, it is only necessary to give the sheath a strain that generates a compressive stress whose absolute value is greater than 180 MPa.

The distance between the handle 3 of the frame before heating and the lower support member 5 is Lt (mm). Let the length of the sheath before being welded to the frame be (Lt + d) (mm). Further, the cross-sectional area of the tie rod 2 shown in FIG. 2 is A (mm ² ), and the cross-sectional area of four sheaths is B (mm ² ). The tie rod 2 and the sheath 8 are made of SUS316L stainless steel, which is the same material. The Young's modulus of SUS316L stainless steel is E (MPa), and the linear expansion coefficient is α (1 / ° C.).

  5A to 5C schematically show the tie rod 2 and the sheath 8 as rods. 5A, 5B, and 5C, the tie rod 2 is represented by a tie rod 2A for convenience, and the sheath 8 is also represented by a sheath 8A for convenience.

  FIG. 5A schematically illustrates a state in which the frame is not heated before welding of the tie rod 2, the handle 3, the lower support member 5, and the sheath 8. The length of the tie rod 2A is Lt (mm), and the length of the sheath 8A is (Lt + d) (mm). No stress is generated in each cross section. The tie rod 2 is simulated by a rod-shaped tie rod 2A having a cross-sectional area A, and the four sheaths 8 provided on the blade 7 are simulated by four rod-shaped sheaths 8A each having a cross-sectional area B / 4. .

  FIG. 5B schematically shows a state in which the frame is heated before welding the tie rod 2, the handle 3, the lower support member 5, and the sheath 8. The heating temperature is adjusted so that the axial elongation of the frame is d (mm). Even when the heating of the frame is completed, the frame is stretched and deformed, but no stress is generated. At this stage, the tie rod 2 and the sheath 8 are welded, the handle 3 and the sheath 8 are welded, and the lower support member 5 and the sheath 8 are welded.

  FIG. 5C schematically shows a state at the time when the welding of the tie rod 2, the handle 3, the lower support member 5 and the sheath 8 is completed and the temperature of the entire frame is lowered to the initial temperature. Since the frame and the sheath 8 are connected by a welded portion, the lengths in the axial direction are equal. The amount of contraction of the sheath 8A from the initial state is δL. The amount of elongation of the tie rod 2A from the initial state is (d−δL).

  In this state, a tensile stress of E × (d−δL) / Lt (MPa) is generated in the cross section of the tie rod 2A. A compressive stress of E × δL / (Lt + d) (MPa) is generated in the cross section of the sheath 8A. The internal force in each cross section is a value obtained by multiplying the respective cross-sectional areas. The tie rod 2A has a tensile force of (E × (d−δL) / Lt) × A, and the sheath 8A has (E × δL / ( Lt + d)) × B compression force. Considering the balance of internal forces, the absolute value of the tensile force of the tie rod 2A and the compressive force of the sheath 8A must be equal, and the equation (1) is established.

(E × (d−δL) / Lt) × A = (E × δL / (Lt + d)) × B (1)
By arranging the expression (1), the expression (2) is obtained.

δL / (Lt + d) = d / (((A + B) / A) × Lt + d) (2)
The left side of the equation (2) is the compressive strain generated in the sheath 8A in the state of FIG. The right side of equation (2) does not include the contraction amount δL. The stress can be obtained by multiplying the strain generated in the sheath 8A by the Young's modulus. When the frame and the sheath 8A are welded after the frame is heated, and the stress generated in the sheath 8A due to the entire temperature is σth, the stress σth is a compressive stress whose absolute value is given by the equation (3). .

σth = E × d / (((A + B) / A) × Lt + d) (3)
When the absolute value of the compressive stress given by the equation (3) is larger than 180 MPa, which is the maximum value of the tensile residual stress of the sheath portion measured by the mock-up specimen, the residual stress of the sheath 8A is reduced to the compressive stress. Become. That is, when the inequality (4) including the extension amount d of the sheath 8A is established, the residual stress of the sheath 8A can be made a compressive stress.

σth <E × d / (((A + B) / A) × Lt + d) (4)
Here, the amount of elongation d of the frame due to heating can be obtained by equation (5), where ΔT (° C.) is the temperature difference between the initial temperature and the completion of heating.

d = α × ΔT × Lt (5)
By substituting the equation (5) into the equation (4) and arranging the temperature difference ΔT, the equation (6) is obtained.

ΔT> (1 / α) × ((A + B) / A) / (E / σth−1) (6)
Here, in the SUS316L austenitic stainless steel, the Young's modulus E is 195000 (MPa), and the linear expansion coefficient α is 1.52 × 10 ⁻⁵ (1 / ° C.). A cross-sectional area of the tie rod 2 is 420 (mm ² ), and a cross-sectional area of four sheaths 8 is B is 632 (mm ² ). Further, σth = 180 (MPa). By substituting these values into equation (6), equation (7) is obtained.

ΔT> 152 (° C.) (7)
Therefore, when the initial temperature of the sheath 8 is 20 ° C., the frame temperature is heated so that the temperature difference ΔT is larger than 152 ° C., that is, the frame is heated higher than 172 ° C. By welding the sheath 8 and the frame, the tensile residual stress at each end of the sheath 8 can be compressed.

  As an example, for a structure in which a tensile stress of 180 MPa is generated at the end of the sheath 8 when welding without heating the frame, the initial temperature of the sheath 8 is 20 ° C. and the frame is heated to 200 ° C. Assume that the frame and the sheath 8 are subsequently welded. The temperature difference ΔT between the sheath 8 and the frame at the time of starting the welding becomes 180 ° C. Here, the distance Lt between the handle 3 of the frame before heating and the lower support member 5 is 3600 (mm). At this time, from equation (5), the amount of extension d of the frame is 9.85 mm. The length of the sheath 8 in the axial direction is set to 3609.85 (mm) at the stage of processing the sheath member in consideration of the temperature difference to be generated. At this time, there is no gap between the handle 3 and the sheath 8 or between the lower support member 5 and the sheath 8. Next, the tie rod 2 and the sheath 8, the handle 3 and the sheath 8, and the lower support member 5 and the sheath 8 are welded. The residual stress at the time when the overall temperature drops after these weldings are completed becomes a compressive stress of 32 MPa in the state where the initial temperature is reached. On the sheath 8, in the vicinity of the center portion of the sheath 8 that is away from the end portion of the sheath 8, the compressive residual stress is larger in absolute value than the end portion, that is, the absolute value is larger than 32 MPa. In each welding of the sheath 8, the handle 3, and the lower support member 5, the end of the sheath 8 is melted by welding heat input. For this reason, the length of the sheath 8 is set to be longer than 3609.95 mm. As shown in the example, a dimensional accuracy of the order of 0.01 mm is not necessary. For example, it may be 3615 mm. At this time, both ends of the sheath 8 overlap each of the handle 3 and the lower support member 5 with a width of 2.575 mm (= (3615-3609.85) / 2). For example, in the case of TIG welding, the melt width Is about 6 mm, the extra sheath member can be melted during welding to form a welded portion.

  If the number of tabs 10 formed on the sheath 8 is large, the temperature of the heated frame may decrease as the tabs 10 are sequentially welded to the tie rod 2. At this time, the region on the frame where the tab 10 is not welded may be heated again to weld the tab 10, the handle 3, and the lower support member 5.

  In addition, when the tab 10 of the sheath 8 and the tie rod 2 are welded instead of heating the entire frame first, the tie rod 2 is adjacent to the tab 10 that has undergone certain welding in the welding progress direction. The latter tab is welded while heating the one span area between the tabs. In this way, heating and tab welding may be performed sequentially for each span. Accordingly, when the entire frame is heated, it is possible to avoid a decrease in the temperature of the frame when the tab 10 close to the handle 3 or the lower support member 5 is reached.

  For the heating of the frame, for example, high frequency induction heating can be used instead of the flame of the burner. By using high frequency induction heating, it is possible to preheat the frame to a high temperature in a short time. In this high frequency induction heating, for example, a high frequency induction heating coil capable of heating the entire frame at a time is used. Alternatively, a high frequency induction heating coil having a length between tabs adjacent to each other in the axial direction of the tie rod 2 may be used.

  The welding of the tab 10 to the tie rod 2 is also possible, for example, by sequentially performing from the tab 10 closest to the handle 3 toward the lower support member 5 side. Conversely, the tab 10 may be welded from the lower support member 5 side toward the handle 3.

  The welding of the plurality of tabs 10 to the tie rod 3 is performed sequentially from the tab located in the central portion in the axial direction of the tie rod 4 toward the tab located in the vicinity of the handle 2 and the lower support member 3. On the other hand, welding can be performed while maintaining symmetry. For this reason, welding deformation such as bending of the tie rod 2 can be reduced.

  Heating of the welded portion is generally performed as preheating in, for example, carbon steel welding. For this reason, the present embodiment in which the frame is heated can improve the residual stress without newly preparing equipment. Therefore, it is possible to manufacture a control rod having a preferable residual stress distribution that does not cause cracking while suppressing an increase in cost.

  In the control rod 1, the welding of the handle 3, the lower support member 5, the tie rod 2 and the sheath 8 has a small amount of heat input, so that almost no welding deformation occurs. Therefore, even if the sheath 8 and the tie rod 2 are welded after the welding of the sheath 8 and the handle 3 and the sheath 8 and the lower support member 5 is finished, the compressive residual stress equivalent to that of this embodiment is applied to the sheath. can do.

  A control rod according to another embodiment of the present invention will be described with reference to FIG. The control rod 1A of this embodiment is manufactured by omitting heating in the lower region of the tie rod 2.

  As described above, in the conventional control rod, the widest region where the tensile residual stress is generated becomes the tensile residual stress at the upper end portion and the lower end portion of the sheath 8 (see FIG. 3). The location where the sheath is cracked is the upper end portion of the sheath 8 as described above. For this reason, in the present embodiment, the upper end portion of the tie rod 2 of the frame (for example, a range of 0.2 L0 from the upper end of the sheath 8) is heated, and then the tab 10 is welded to the tie rod 2 as in the first embodiment. The upper end and the lower end of the sheath 8 are welded to the handle 3 and the lower support member 5, respectively. Although a tensile residual stress is formed at the lower end of the sheath 8, the period during which the lower end of the sheath 8 is inserted into the reactor core in a single operation cycle is short. Cracks do not occur.

  The control rod 1A can apply compressive residual stress in the axial direction to the sheath 8 in a region having a length L1 from the upper end of the sheath 8 where the sheath 8 is cracked. For this reason, since the heating area | region of the tie rod 3 decreases compared with the control rod 1 of Example 1, the time which manufactures 1A of control rods can be shortened. The present embodiment can also obtain the effects produced in the first embodiment.

  A method for manufacturing a control rod according to another embodiment of the present invention will be described with reference to FIG. In the same manner as in the first embodiment, the handle 3 and the lower support member 5 are welded to the tie rod 2 to constitute a control rod frame. In the manufacturing method of the control rod 1B of the present embodiment, the tension device 21 is used.

  The configuration of the tensioning device 21 will be briefly described. The tension device 21 includes a highly rigid frame member 22, a load addition shaft 25, and a shaft rotation device 26. The frame member 22 has beam members 23 and 24 arranged in parallel. The tension mechanism 30 provided in each of the beam members 23 and 24 includes a load application shaft 25, a shaft rotating device 26, a holding member 27, and a U-shaped load application jig 28. The load application shaft 25 passes through the beam members 23 and 24 and meshes with a shaft rotation device 26 provided on the beam members 23 and 24. Four U-shaped load application jigs 28 are attached to a holding member 27 provided at one end of the load application shaft 25. A pin 29 is attached to each load application jig 28. The load application shaft 25 is formed with a screw on its outer surface, and this screw meshes with a worm gear provided on the shaft rotation device 26.

  The frame of the control rod 1 </ b> B is disposed between the beam member 23 and the beam member 24. The four load applying jigs 28 of the tension mechanism 30 provided on the beam member 23 are attached to the handle 3 using pins 29, respectively. Four load application jigs 28 of the tension mechanism 30 provided on the beam member 24 are attached to the lower support member 5 using pins 29, respectively. At least one of the shaft rotation devices 26 is rotated to move the corresponding load application shaft 25 in the axial direction of the tie rod 2, and the handle 3 and the lower support member 5 are pulled in the axial direction. Thereby, an axial tensile stress is applied to the frame. The frame, in particular, a state in which a tensile stress is applied to the tie rod 2 is maintained, and the plurality of tabs 10 of the sheath 8 are sequentially welded to the tie rod 2 as in the first embodiment. Thereafter, the upper end of the sheath 8 and the handle 3 are welded, and the lower end of the sheath 8 and the lower holding member 5 are welded. After all the welding of the sheath 8 to the frame is completed, the shaft rotating device 26 is rotated in the reverse direction to release the tensile force applied to the frame. Each load application jig 28 is removed from the handle 3 and the lower support member 5.

  A mechanism in which axial compressive residual stress is applied to the sheath 8 in the control rod 1B manufactured by the manufacturing method of the present embodiment will be described with reference to FIG. In the state where the groove of the sheath 8 is aligned with the tie rod 2 constituting the frame to which the axial tensile stress is applied by the tension device 21, no axial stress is generated in the sheath 8. That is, the stress distribution 19 in the axial direction of the control rod along the stress evaluation line 17 is zero. On the other hand, the tie rod 2 is subjected to a tensile stress in the axial direction of the value T <b> 1 by the tensile force of the tension device 21. That is, the stress distribution 18 in the axial direction of the control rod along the stress evaluation line 16 is a tensile stress having a value T1. After the above-described welding between the sheath 8 and the frame is completed, the tensile force applied to the tie rod 2 is removed by the tension device 21, whereby a compressive displacement in the axial direction is applied to the sheath 8. As a result, an axial tensile residual stress having a value T2 that is smaller than the value T1 is generated in the tie rod 2, and the stress distribution 19 generated in the sheath 8 is an axial compressive residual stress having a value S.

  The control rod 1 </ b> B manufactured in this embodiment is also given compressive residual stress over the entire axial length of the sheath 8. For this reason, generation | occurrence | production of the crack in the sheath 8 can be prevented. Furthermore, since the present embodiment uses the tensioning device 21, the tie rod 2 is uniformly stretched along the central axis of the tie rod 2. It is possible to easily apply a tensile force to the frame without causing deformation that adversely affects the dimensional accuracy of the product, such as bending deformation, in the frame. As a result, the dimensional accuracy of the completed control rod can be ensured.

  The tensile load applied to the frame by the tensioning device 21 may be released before the welding of the sheath 8 and the frame is completed, for example, when the welding of some of the tabs 10 of the sheath 8 is completed. good. In this case, in the axial range where the tab 10 is welded in a state where a tensile load is applied, the axial tensile stress generated in the sheath 8 by the welding can be reduced. Further, only when the tab 10 is welded in a region where it is necessary to reduce the tensile residual stress, an axial compressive residual stress is applied to the upper end portion of the sheath 8 even if a tensile load is applied to the tie rod 2. .

  A load applying jig 28 may be attached in the middle of the tie rod 2 in the axial direction to apply a tensile load locally to the tie rod 2. For example, a load applying jig 28 is attached in advance to a position where a tensile load is applied to the tie rod 2. When welding for joining the tie rod 2 is started from the tab 10 located in the center portion in the axial direction of the tie rod 1 and the tab 10 near the handle 2 is welded, the load applying jig 28 The tensile load is applied to the tie rod 2 by applying a tensile load. Next, tab welding at the remaining position and welding of the sheath 8 to the handle 3 and the lower support member 5 are performed. By removing the applied tensile load, it is possible to reduce the tensile residual stress in the region of the tie rod 2 to which the tensile load was applied during the welding of the tab.

  In addition, after the welding of the sheath 8 and the frame is completed, the handle 3 and the lower support member 5 may be removed after applying a tensile load so that an axial tensile stress is generated on the tie rod 1. . In this case, plastic deformation occurs in all the welds of the sheath 8 and the frame, thereby reducing the tensile residual stress. When a tensile load is applied to a region where tensile stress is generated in the welded portion, in the region where tensile residual stress is generated, yielding on the tensile side occurs at a lower tensile load than other regions. For this reason, the tensile plastic strain remains in the weld after the tensile load is removed. When deformation due to tensile plastic strain is constrained in the surrounding region, the plastic strain becomes residual compressive stress. That is, compressive residual stress can be applied to the upper end portion of the sheath 8.

  A method for manufacturing a control rod according to another embodiment of the present invention will be described with reference to FIG. In the same manner as in the first embodiment, the handle 3 and the lower support member 5 are welded to the tie rod 2 to constitute a control rod frame. Similar to the first embodiment, the upper hafnium cylindrical body 9A and the lower hafnium cylindrical body 9B are attached to the frame. In the manufacturing method of the control rod 1C of the present embodiment, the compression device 31 is used.

  The configuration of the compression device 31 will be briefly described with reference to FIGS. 9 and 10. The compression device 31 includes a load addition shaft 32, a shaft rotation device 33, a beam member 34, and a claw member 35. Two shaft rotation devices 33 and two beam members 34 are provided. The load application shaft 32 is threaded on the outer surface. Each shaft rotation device 33 is provided with a worm gear that meshes with the load application shaft 32 and is movably attached to the load application shaft 32. The beam member 34 is attached to the shaft rotation device 33. A pair of claw members 35 is provided on the beam member 34.

  A compression device 31 is attached to the sheath 8 welded to the frame, and the compression device 31 applies a compressive deformation to the sheath 8 in the axial direction. By this compressive deformation, axial compressive stress is applied to the sheath 8. The attachment of the compression device 31 to the sheath 8 will be described. A pair of claw members 35 provided on the beam member 34 existing at one end of the load application shaft 32 are inserted into two cooling holes 36 formed at one end of the sheath 8 and are hooked on the sheath 8. A pair of claw members 35 provided on the other beam member 34 existing at the other end of the load application shaft 32 are inserted into two cooling holes 36 formed at the other end of the sheath 8, Be hooked. The shaft rotating device 33 is driven to rotate the load adding shaft 32, and the distance between the pair of beam members 34 is narrowed. Thereby, axial compressive stress is applied to the sheath 8.

  The sheath 8 to which the compressive stress is applied is welded to the tie rod 2, the handle 3, and the lower support member 5 in the same manner as in the first embodiment. When all the welding between the sheath 8 and the frame is completed, the shaft rotating device 33 is rotated in the reverse direction to remove the compressive force applied to the sheath 8.

  In the control rod 1C manufactured by the manufacturing method of the present embodiment, a mechanism in which an axial compressive residual stress is applied over the entire axial length of the sheath 8 will be described with reference to FIG. In a state where the groove of the sheath 8 to which compressive stress is applied in the axial direction is combined with the tie rod 2 constituting the frame, the stress distribution 18 in the axial direction of the control rod along the stress evaluation line 16 is zero. In the sheath 8, the stress distribution 19 in the axial direction of the control rod along the stress evaluation line 17 becomes a compressive stress having a value S. In this state, the sheath 8, the tie rod 2, the handle 3 and the lower support member 3 are welded. After the welding of the sheath 8 and the frame is completed, the compressive device 31 removes the axial compressive load applied to the sheath 8. As a result, the axial displacement added to the sheath 8 is eliminated. An axial tensile displacement is added to the tie rod 2. As a result, the stress distribution 18 of the tie rod 2 becomes a tensile residual stress having a value T. The stress distribution 19 generated in the sheath 8 is given a compressive residual stress of value S. According to this embodiment, an axial compressive residual stress is applied over the entire axial length of the sheath 8. It is possible to prevent the sheath 8 from being cracked.

  The sheath 8 is a thin plate compared to the tie rod 2. Therefore, the compressive load can be applied to the sheath 8 with a device smaller than the device that applies the tensile load to the tie rod 2 in the third embodiment.

  A method for manufacturing a control rod according to another embodiment of the present invention will be described with reference to FIG. The control rod 1 </ b> D manufactured by the manufacturing method of the present embodiment forms a melting part 37 on the surface of the tie rod 2. The melting part 37 is a non-filler melting part, for example, and is solidified.

  A method for manufacturing the control rod 1D will be described. As in the first embodiment, a frame in which the tie rod 2, the handle 3, and the lower support member 5 are integrated is formed. Thereafter, the plurality of tabs 10 of the sheath 8 are sequentially welded to the tie rod 2. The upper end of the sheath 8 is welded to the handle 3 and the lower end of the sheath 8 is welded to the lower support member 5. An upper hafnium cylindrical body 9A and a lower hafnium cylindrical body 9B are disposed in the sheath 8. The steps so far in the method of manufacturing the control rod 1D are the same as the conventional control rod manufacturing steps.

  In the present embodiment, after all the welding of the sheath 8 to the frame is completed, the melting portion 37 is formed on the surface of the tie rod 2. The melting portion 37 extends from the handle 3 toward the lower support member 5 in the axial direction of the tie rod 2. The formation of the melting part 37 is performed as follows. The welding torch is moved along the axial direction of the tie rod 2 while the flame of the welding torch is applied to the surface of the tie rod 2. Due to the irradiation of the flame, heat is applied to the surface of the tie rod 2 (heat incidence), and a one-pass melting portion 37 is formed from the upper end of the tie rod 2 toward the lower end thereof. Four welding torches are arranged around the tie rod 2 at the same position in the axial direction of the tie rod 2, and these welding torches are moved together in the axial direction of the tie rod 2, so that the four melting portions 37 are simultaneously connected to the tie rod 2. Can be formed on the surface. When the melting part 37 is solidified, shrinkage deformation occurs on the surface of the tie rod 2 along the melting part 37. The contraction deformation of the tie rod 2 along the melting part 37 causes the sheath 8 to deform in the axial direction. Due to the contraction deformation in the axial direction of the sheath 8, an axial compressive residual stress is applied to the sheath 8 over the entire length of the sheath 8. For this reason, it can prevent that a crack generate | occur | produces in the sheath 8. FIG.

  The melting of the tie rod 2 to form the melting portion 37 is performed after the welding of the sheath 8 and the tie rod 2 is finished and before the sheath 8 and the handle 3 and the lower support member 5 are welded, and the sheath 8 and the tie rod 2, the handle 3 and It is performed either after each welding of the lower support member 5 is completed.

  The melted portion 37 formed on the surface of the tie rod 2 is formed along the welded portion of the tab 10 and the tie rod 2 as a melted portion 37A discontinuous in the axial direction of the tie rod 2, as in the control rod 1E shown in FIG. You may form in the vicinity of a welding part. The formation of the melted portion 37 </ b> A can also apply an axial compressive residual stress over the entire axial length of the sheath 8. For this reason, it is possible to prevent the sheath 8 from being cracked.

  A mechanism by which the tensile residual stress can be reduced and the compressive residual stress can be applied in the sheath 8 of the control rod 1E will be described with reference to FIG. In the welded portion 38 between the tab 10 of the sheath 8 and the tie rod 2, a residual stress distribution 39 is formed which becomes a tensile stress in the welded portion 38 and a compressive stress around the welded portion 38 in the weld line direction. By forming the melted portion 37 on the surface of the tie rod 2 so that the compressive stress region in the stress distribution 40 generated by the melted portion 37 overlaps the region of the tensile stress generated by the welded portion 38, the tensile stress of the stress distribution 39 is obtained. And the compressive stress of the stress distribution 40 can be superimposed. For this reason, the tensile stress of the stress distribution 39 is reduced by the compressive stress of the stress distribution 40. The control rod 1E applies compressive residual stress to the upper end portion and the lower end portion of the sheath 8 as shown by the solid line 14 in FIG. 3 by a melting portion 37A shorter than the case where the melting portion 37 is formed over the entire axial length of the tie rod. Can do. The control rod 1E can shorten the time required to form the melted portion on the surface of the tie rod 2 as compared with the control rod 1D.

  In the control rod 1E, the contraction deformation in the axial direction of the tie rod 2 due to the formation of the melting portion 37A increases as the temperature of the region of the tie rod 2 existing between the melting portions 37A decreases. For this reason, in the manufacture of the control rod 1E, a sufficient time is taken from the time when all the welding of the sheath 8 and the frame is finished, and the plurality of melting portions 37A are formed after the temperature of the sheath 8 and the frame is lowered to room temperature. It is desirable to start work to do. In the control rod 1D, when four melting portions 37 are formed one by one on the surface of the tie rod 2, after the formation of one melting portion 37, the temperature of the sheath 8 and the frame is lowered to room temperature, It is desirable to form the next melting part 37 on the surface of the tie rod 2. By forming such a melting part 37, the contraction deformation in the axial direction of the tie rod 2 of the control rod 1D increases. Accordingly, the compressive residual stress applied to the sheath 8 increases.

  By forming a melted portion on the surface of the tie rod 2 between the welded portion 38 closest to the handle 3 and the welded portion 38 next to the handle 3, the tensile residual stress at the upper end of the sheath 8 is changed to a compressive residual stress. be able to.

  Formation of the molten part on the surface of the tie rod 2 can be formed by heat input using a TIG torch that does not supply weld metal (melting metal). When the molten portion is formed while supplying the weld metal on the surface of the tie rod 2, the contraction deformation of the tie rod 2 is increased because the contraction force of the weld metal can be used. For this reason, the compressive residual stress given to the sheath 8 can also be increased.

  It is also possible to form the melting portion 37 and the plurality of melting portions 37 </ b> A on the surface of the tie rod 2. Thereby, the sheath 8 tensile residual stress can be reduced more effectively, and the axial compressive residual stress can be effectively applied over the entire axial length of the sheath 8. When forming the melting part 37 and the melting part 37A on the tie rod 2, it is preferable to form the melting part 37A after forming the melting part 37.

  When the melted portion 37 or the melted portion 37A is formed on the tie rod 2, the interval between the dendritic structures increases in the tie rod 2. Therefore, compressive residual stress can be applied to the sheath 8 by forming the melted portion 37 or the melted portion 37A in the tie rod 2 so that the dendritic structure is wider than the base material portion not receiving heat input.

It is explanatory drawing which shows the process of heating a tie rod in the process of manufacturing the control rod of Example 1 which is one suitable Example of this invention. FIG. 2 is an explanatory view showing the arrangement of a welding torch during welding of a sheath and a tie rod in the cross section of the control rod shown in FIG. 1. It is explanatory drawing which shows distribution of the residual stress which generate | occur | produces in the sheath of the control rod shown in FIG. 1, and the control rod of a prior art example. It is explanatory drawing which shows the stress distribution before and behind welding of the control rod shown in FIG. FIG. 1 schematically shows a tie rod and a sheath of the control rod shown in FIG. 1, and (A) is an explanatory view schematically showing a state in which the frame is not heated before welding of the tie rod, the handle and the lower support member to the sheath. , (B) is an explanatory view schematically showing a state in which the frame is heated before welding of the tie rod, handle, lower support member and sheath, and (C), each welding of the tie rod, handle, lower support member and sheath is completed. Furthermore, it is explanatory drawing which shows typically the state at the time of the temperature of the whole flame | frame falling to initial temperature. It is explanatory drawing which shows the process of heating a tie rod in the process of manufacturing the control rod of Example 2 which is another Example of this invention. It is explanatory drawing which shows the manufacturing method of the control rod which is the other Example of this invention. It is explanatory drawing which shows the stress distribution before and behind the welding of the control rod manufactured by the method of FIG. It is explanatory drawing which shows the manufacturing method of the control rod which is the other Example of this invention. 9 shows a state where the compression device shown in FIG. 9 is attached to the sheath, where (A) is an enlarged view of a portion IX in FIG. It is explanatory drawing which shows the stress distribution before and behind the welding of the control rod manufactured by the method of FIG. It is explanatory drawing which shows the manufacturing method of the control rod which is the other Example of this invention. It is explanatory drawing which shows the manufacturing method of the control rod which is the other Example of this invention. It is explanatory drawing which shows the residual stress distribution in the welding part vicinity of the tab of the control rod manufactured by the method of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,1A-1E ... Control rod, 2 ... Tie rod, 3 ... Handle, 5 ... Lower support member, 7 ... Blade, 8 ... Sheath, 9A ... Upper hafnium cylindrical body, 9B ... Lower hafnium cylindrical body, 10 ... Tab , 12, 20 ... heating region, 21 ... tensioning device, 31 ... compression device, 37, 37A ... melting part.

Claims (24)

A tie rod, a handle attached to one end of the tie rod, a lower support member attached to the other end of the tie rod, and attached to the tie rod, the handle and the lower support member, and extends from the tie rod in all directions. And four sheath members having a U-shaped cross section, and a neutron absorbing member disposed in each sheath member,
A control rod, wherein a compressive residual stress is applied to an end of the sheath on the handle side. A tie rod, a handle attached to one end of the tie rod, a lower support member attached to the other end of the tie rod, and attached to the tie rod, the handle and the lower support member, and extends from the tie rod in all directions. And four sheath members having a U-shaped cross section, and a neutron absorbing member disposed in each sheath member,
A control rod, wherein a compressive residual stress is applied over the entire axial length of the sheath.   The control rod according to claim 1, wherein an axial tensile residual stress is applied to the tie rod. A tie rod, a handle attached to one end of the tie rod, a lower support member attached to the other end of the tie rod, and attached to the tie rod, the handle and the lower support member, and extends from the tie rod in all directions. And four sheath members having a U-shaped cross section, and a neutron absorbing member disposed in each sheath member,
A control rod characterized in that a melted portion that extends in the axial direction of the tie rod and melts and hardens is formed on the surface of the tie rod.   The control rod according to claim 4, wherein the melting portion is continuously formed between an upper end of the sheath member and a lower end of the sheath member.   The control rod according to claim 4, wherein the melted portion is formed intermittently in the axial direction of the tie rod, and the melted portion is arranged alongside the welded portion of the tie rod and the sheath member.   The dendritic structure interval in the heat input region where heat is applied to the tie rod to form the melted portion is wider than that of the dendritic structure in the region other than the heat input region in the tie rod. The control rod according to any one of claims 4 to 6.   A frame member is manufactured by attaching a handle to one end of the tie rod and attaching a lower support member to the other end of the tie rod, attaching a neutron absorbing member to the frame member, heating the tie rod of the frame member, and crossing Welding a sheath member having a U-shaped surface to the heated tie rod, the handle, and the lower support member in a state where the neutron absorbing member exists in the sheath member. A control rod manufacturing method characterized by the above.   The method of manufacturing a control rod according to claim 8, wherein the temperature of the tie rod is higher than the temperature of the sheath member by the heating.   The method for manufacturing a control rod according to claim 8 or 9, wherein the tie rod is heated by a flame burner.   The method of manufacturing a control rod according to claim 8 or 9, wherein the tie rod is heated by high frequency induction heating.   The method of manufacturing a control rod according to claim 8, wherein the tie rod is heated in a region corresponding to an end portion of the sheath on the handle side.   The welding of the sheath member to the tie rod is arranged in the axial direction of the tie rod and welding a plurality of protrusions that are a part of the sheath member to the tie rod. The manufacturing method of the control rod for nuclear reactors of any one of Claims 1.   The method of manufacturing a control rod according to claim 13, wherein a range of heating of the tie rod is in the vicinity of the protrusion welded to the tie rod.   A frame member is manufactured by attaching a handle to one end of the tie rod and attaching a lower support member to the other end of the tie rod, attaching a neutron absorbing member to the frame member, and applying an axial tensile force of the tie rod to the tie rod. In addition to the above, the sheath member having a U-shaped cross section is formed in the state that the neutron absorbing member exists in the sheath member and the tensile force is applied to the tie rod. And a control rod manufacturing method comprising welding to the lower support member.   16. The method of manufacturing a control rod according to claim 15, wherein the tensile force is applied to the tie rod by pulling the handle and the lower support member in opposite directions using a tension device.   A frame member is manufactured by attaching a handle to one end of the tie rod and attaching a lower support member to the other end of the tie rod, attaching a neutron absorbing member to the frame member, and cross-sectionally comparing the axial compression force of the tie rod. In addition to the U-shaped sheath member, the sheath member to which the compressive force is applied, the tie rod, the handle, and the lower support in a state where the neutron absorbing member exists in the sheath member. A control rod manufacturing method comprising welding to a member.   The control rod manufacturing method according to claim 17, wherein the compressive force is applied to the sheath member by compressing the sheath member in the axial direction using a compression device.   A sheath in which a handle is attached to one end of a tie rod and a lower support member is attached to the other end of the tie rod, a neutron absorbing member is attached to the frame member, and a cross section is U-shaped A member is welded to the tie rod, the handle and the lower support member in a state where the neutron absorbing member is present in the sheath member, and after the welding of the sheath member and the tie rod is completed, and the sheath member; After the welding of the tie rod, the handle and the lower support member is finished, heat is applied to the tie rod to melt a part of the tie rod in the axial direction of the tie rod, and the melted portion of the tie rod And forming a melted portion extending in the axial direction in the tie rod. Method of manufacturing that the control rod.   The method of manufacturing a control rod according to claim 19, wherein the heat incidence is continuously performed on the tie rod between one end of the sheath member and the other end of the sheath member. The welding of the sheath member to the tie rod is to arrange a plurality of protrusions that are arranged in the axial direction of the tie rod and are a part of the sheath member to the tie rod,
The method of manufacturing a control rod according to claim 19, wherein the heat incidence is discontinuous in the axial direction and is performed along a welded portion of the protrusion and the tie rod.   The method of manufacturing a control rod according to any one of claims 19 to 21, wherein the heat incidence is performed using a TIG torch.   The method of manufacturing a control rod according to any one of claims 19 to 21, wherein the heat incidence is performed while supplying molten metal.   The method for manufacturing a control rod according to any one of claims 8 to 23, wherein welding of the four sheath members extending in four directions from the tie rod and the tie rod is performed together.

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