JP2017062140A - Manufacturing method of reactor control rod and reactor control rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide manufacturing method of reactor control rod capable of increasing the amount of δ ferrite in welded metal part and reducing the porosity, and a reactor control rod manufactured by using the manufacturing method.SOLUTION: Disclosed manufacturing method reactor control rod includes the steps of: preparing at least two members of stainless steel to be welded constituting a support structure of a reactor control rod; and laser-welding the members to be welded via a welding metal part by irradiating with a laser beam while supplying a welding metal rod of stainless steel to a part of the respective members to be welded and while supplying a shield gas. The shape at a focus point of the laser beam is rectangular, and the shield gas is an inert gas which does not include components of the member to be welded.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for manufacturing a reactor control rod and a reactor control rod.

  For the welding of nuclear facilities in a nuclear facility, high-quality welding without weld defects such as porosity and weld cracking is required. Generally, TIG (Tungsten Inert Gas) welding or laser welding is applied to these weldings.

  When a tie rod made of stainless steel and a sheath constituting a control rod, which is a furnace internal structure, are welded by TIG welding, the weld metal part is completely welded, so that crevice corrosion does not occur. However, due to the thermal effect of TIG welding, tie rod contraction and sheath deformation are seen, which affects the quality of the control rod, such as straightness, and is a cause of spending time on correction work.

  On the other hand, in the case of laser welding the tie rod and the sheath, crevice corrosion does not occur because they are completely welded similarly to TIG welding. In addition, since there is less thermal influence than TIG welding, there is less tie rod shrinkage and sheath deformation, and quality such as straightness of the control rod is improved. However, since the cooling rate is faster than TIG welding, the amount of δ ferrite (δ ferrite generation amount) is reduced in the laser weld metal part, and high temperature cracking is likely to occur.

As a known technique related to the manufacture of a reactor control rod using TIG welding or laser welding, there is, for example, Patent Document 1. Patent Document 1 discloses a method and apparatus for manufacturing a nuclear reactor control rod in which components are joined to each other by laser welding or TIG welding. The YAG laser beam or CO ₂ laser beam is irradiated through the optical system at a position shifted within 2 mm in parallel from the previous position, and the target position after the second pass is shifted within the range of 0.1 to 0.2 mm and several Either pass the laser beam or irradiate the laser beam while moving in a circular motion within 2mm, or place a prism in front of the condenser lens, and use this prism to rotate the focal position of the laser beam. And the like. According to Patent Document 2, by performing welding with laser light, the amount of heat input can be reduced, deformation after processing can be suppressed, and the welding speed can be increased to improve productivity. The control rod, its manufacturing method and manufacturing apparatus can be provided.

  As a technique for controlling (improving) the amount of δ ferrite in a laser welded part, for example, there is Patent Document 2. Patent Document 2 relates to a method for manufacturing a boiling water reactor control rod, in which the laser irradiation angle is set to 60 to 80 ° obliquely from the sheath side, and the Cr (chromium) / Ni (nickel) equivalent ratio of the welding wire is 1. .6 to 1.9. In Patent Document 2, the amount of δ ferrite in the laser weld is controlled by the laser welding conditions and the composition of the laser welding wire. According to Patent Document 1, high-precision, high-quality, high-reliability control for boiling water reactors is achieved by a laser welding method that has excellent weldability, suppresses high-temperature cracking, and minimizes deformation and residual stress during welding. It is said that the bar can be easily manufactured.

JP 2000-329885 A Japanese Patent No. 496154

However, as described above, in laser welding with a high cooling rate, the amount of δ ferrite decreases, and when nitrogen (N ₂ ) is used as a shielding gas at the time of welding as in Patent Document 2, Cr of the weld metal part is used. The equivalent / Ni equivalent ratio is reduced and the amount of δ ferrite is further reduced. On the other hand, it is known that the amount of δ ferrite is improved by changing the shielding gas from N ₂ gas to argon (Ar) gas. However, when argon gas is used as the shielding gas, porosity is generated in the weld metal part. It becomes difficult to obtain a weld metal part having no weld defect.

  Furthermore, stainless steel, which is the material of the members that make up the reactor control rod (eg, tie rods and sheaths), has a carbon content as a countermeasure against stress corrosion cracking that occurs in the sensitized region of the weld heat affected zone in high-temperature water. Reduced to 0.02% by mass. In order to compensate for the strength reduction due to this carbon content reduction, stainless steel is employed in which nitrogen (N) is added and the N content is about 0.04 mass% or more. The nitrogen content in the case without normal N addition is 0.02% by mass or less. By adding N, the Cr / Ni equivalent ratio of the weld metal part is lower than when N is not added (Cr / Ni equivalent ratio ≦ 1.4). For this reason, the Cr / Ni equivalent ratio of the tie rod and the sheath is lower than that of ordinary austenitic stainless steel, the amount of δ ferrite is reduced, and the hot cracking susceptibility of the welded portion is increased.

  In Patent Documents 1 and 2 described above, no study has been made to achieve both an increase in the amount of δ ferrite in the weld metal part and a suppression of porosity, and the high quality required in recent years for reactor control rods is sufficiently satisfied. It may not be possible.

  Therefore, in view of the above circumstances, the present invention provides a method for manufacturing a reactor control rod capable of increasing the amount of δ ferrite in the weld metal part and reducing the porosity, and a reactor manufactured using the manufacturing method. It is to provide a control rod.

  In order to achieve the above object, the present invention provides a step of preparing at least two stainless steel welded members constituting a support structure for a nuclear reactor control rod, and stainless steel is provided on a part of each of the welded members. A welding step of supplying a weld metal wire made of metal and irradiating a laser beam while supplying a shielding gas to laser weld the member to be welded through a weld metal portion, and condensing the laser beam Provided is a method for manufacturing a nuclear reactor control rod, wherein the shape of a point is a rectangle, and the shield gas is an inert gas that does not contain a component of the member to be welded.

  The present invention also includes a support structure for a nuclear reactor control rod, which is a welded structure in which at least two welded members made of stainless steel are welded via a weld metal part, and the amount of δ ferrite in the weld metal part Is 2% by mass or more, and the number of porosity is 0.2 or less per mm.

  According to the present invention, a method for manufacturing a reactor control rod capable of increasing the amount of δ ferrite in a laser weld metal part and reducing the porosity, and a reactor control rod manufactured using the method are provided. can do.

It is a schematic diagram which shows an example of the manufacturing method (welding process) of the reactor control rod which concerns on this invention. It is a schematic diagram which shows the shape (rectangle) of the condensing point of a laser beam, and the shape of the energy density distribution of a laser beam. It is a schematic diagram which shows the shape (circle) of the condensing point of a laser beam, and the shape of the energy density distribution of a laser beam. It is a graph which shows the relationship of (delta) ferrite amount of a weld metal part, and Cr / Ni equivalent ratio of a weld metal part. It is a graph which shows the relationship between the number of the porosity of a weld metal part, and a laser energy density. It is a schematic diagram which shows the relationship of the ratio of the width / depth of a laser weld metal part. It is a top view which shows an example of the nuclear reactor control rod which concerns on this invention. It is a disassembled perspective view which shows an example of the nuclear reactor control rod which concerns on this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments, and various improvements and modifications can be made without departing from the scope of the present invention.

[Reactor control rod manufacturing method]
Hereinafter, a method for manufacturing a reactor control rod according to the present invention will be described. FIG. 1 is a schematic view showing an example of a method (welding step) for manufacturing a reactor control rod according to the present invention. The method for manufacturing a reactor control rod according to the present invention includes a step of preparing at least two stainless steel members (members to be welded) 1 and 2 constituting the reactor control rod, A welding process (laser welding process) in which each part is laser-welded is provided, and a welding structure (control rod support structure) that accommodates the reactor control rod is manufactured in this process.

  In the step of preparing the member to be welded, a member constituting the nuclear reactor control rod is prepared. In this embodiment, a tie rod having a cross-shaped cross section and a sheath having a U-shaped cross section are used as a member to be welded. These configurations will be described in detail later. The configuration of the nuclear reactor control rod to which the present invention is applied is not limited to this, and any configuration may be used as long as it can be manufactured by laser welding. In the following description of the manufacturing method, the case where the fin step portion of the tie rod 1 and the convex tip portion of the sheath 2 are welded will be described as an example.

  In the laser welding process, laser light 4 oscillated from a laser oscillator (not shown) is transmitted by a fiber, and the transmitted laser light 4 is collected and is welded through the laser processing head 5. Irradiated to the welding point. The shield nozzle 7 sprays a shield gas 6 on the upper part of the keyhole formed in the laser beam irradiation part of the member to be welded so that welding fume does not adhere to the laser beam irradiation part. A welding metal wire (welding wire) 8 is supplied to a molten pool generated at a laser beam irradiation site via a wire feeding nozzle 9 by a wire feeding device (not shown).

  In this invention, the inert gas which does not contain the component of a to-be-welded member is used as the shielding gas 6 in a welding process, and the shape of the condensing point of the laser beam 4 is made into a rectangular shape. By doing in this way, it becomes possible to increase the quantity of (delta) ferrite in the weld metal part 3, and to reduce the porosity (weld defect) in the weld metal part 3. FIG.

  Hereinafter, the effects of the present invention will be demonstrated based on Example 1, Comparative Example 1, and Comparative Example 2. The welding process was performed under different conditions in Example 1, Comparative Example 1 and Comparative Example 2, and the amount of δ ferrite and the number of porosity in the weld metal part were evaluated. Table 1 shows the welding conditions.

  The welding process was performed according to the following procedure. First, the laser processing head 5 is conveyed to the laser welding start position, and the shield gas 6 is caused to flow from the shield nozzle 7. When the laser welding wire 8 is fed from the wire feeding device and the fin step portion of the tie rod 1 comes into contact with the laser welding wire 8, the laser beam 4 is irradiated from the laser beam machining head 5, and the laser beam machining head 5 moves simultaneously. It travels, laser welding is started, and welding is performed by laser to a predetermined portion of the member 1 to be welded.

  FIG. 2A is a schematic diagram showing the shape (rectangle) of the condensing point of the laser beam and the shape of the energy density distribution of the laser beam, and FIG. 2B is the shape (circular shape) of the condensing point of the laser beam and the energy density of the laser beam. It is a schematic diagram which shows the shape of distribution. The shape of the laser condensing point of Example 1 was a rectangle (top hat type energy density distribution 21a ′) shown in FIG. 2A, and the shape of the laser condensing point of Comparative Examples 1 and 2 was a circle shown in FIG. 2B. A direct focusing semiconductor laser was used as the laser oscillator.

  First, the relationship between the type of the shielding gas 7 and the amount of δ ferrite in the weld metal part 3 will be described. FIG. 3 is a graph showing the relationship between the amount of δ ferrite in the weld metal part 3 and the Cr / Ni equivalent ratio of the weld metal part. The amount of δ ferrite in the weld metal part 3 was measured using a ferrite scope. The Cr / Ni equivalent ratio was calculated from the composition of the welded members 1 and 2 and the welding wire 8 and the penetration ratio. In addition, the relationship between Cr / Ni equivalence ratio and each component composition of a to-be-welded member is as the following formula | equation (1). The Cr equivalent represents an index of Cr, molybdenum (Mo), silicon (Si), and niobium (Nb), which are ferrite forming elements that exhibit the same effect as Cr. Ni equivalent represents an index of Ni, manganese (Mn), carbon (C), and N, which are austenite-forming elements that exhibit the same effect as Ni.

Cr / Ni equivalent ratio = (Cr equivalent: [Cr] + [Mo] +1.5 [Si] +0.5 [Nb]) / (Ni equivalent: [Ni] +0.5 [Mn] +30 [C] +30 [C] N]) ... Formula (1)
(In formula (1), [] indicates the content (% by mass) of each component.)
The Cr / Ni equivalent ratio shown in FIG. 3 is a value before welding, and is not a value considering the amount of N ₂ absorbed from the shield gas to the weld metal part 3 during welding.

As a result of investigating the laser welding metal portion 3 between the fin step portion of the tie rod 1 and the sheath 2 convex tip portion of Example 1 (shield gas: Ar gas), the fin step portion of the tie rod 1 and the sheath 2 convex tip portion The Cr / Ni equivalent ratio (calculated value) of the laser weld metal part 3 was 1.44 to 1.47. Further, as a result of investigating the ferrite amount of the laser weld metal part 3, the amount of δ ferrite (actual value) of the laser weld metal part 3 between the fin step part of the tie rod 1 and the sheath 2 convex tip part is 3.3-5. It was 0.0 mass%. On the other hand, in the case of Comparative Example 1 (shield gas: N ₂ ), the relationship between the Cr / Ni equivalent ratio of the laser weld metal part 3 and the amount of δ ferrite is as follows: The amount of δ ferrite was 1.4% to 4.4%.

From the above results, it can be seen that the use of Ar as the shielding gas 6 increases the amount of δ ferrite as compared with the case where N ₂ gas is used as the shielding gas 6. EXAMPLE 1 A tie rod having a Cr / Ni equivalent ratio of 1.4% or less is obtained by extrapolating the relationship between the Cr / Ni equivalent and the ferrite content of the weld metal part 3 between the fin step part of the tie rod 1 and the convex tip part of the sheath 2. Also in the sheath, it can be seen that the amount of δ ferrite of the laser weld metal part 3 can be secured at 2% or more if the Cr / Ni equivalent ratio is 1.37 or more. In the case of the same Cr / Ni equivalent ratio, the amount of δ ferrite is increased when argon gas is used as the shielding gas 6 than when N ₂ gas is used as the shielding gas 6. This is considered to be because by using Ar gas as the shielding gas 6, it is possible to prevent a decrease in the Cr / Ni equivalent ratio of the weld metal part during welding, compared to the case of using N ₂ gas.

  If the shielding gas 6 is an Ar gas other than an inert gas that does not include a component of the member to be welded, that is, an inert gas that does not affect the Cr / Ni equivalent ratio represented by the above formula (1), It is considered that the same effect as that obtained when Ar gas is used can be obtained. For example, it is considered that the same effect can be obtained even if helium (He) gas is used instead of Ar gas.

  Next, the relationship between the shape of the laser beam condensing point and the amount of δ ferrite will be described. FIG. 4 is a graph showing the relationship between the number of porosity of the weld metal part and the laser energy density. The number of porosity was evaluated by radiographic testing (RT) of the weld bead. In both Example 1 and Comparative Example 2, a plurality of welded structures (welded bodies of members to be welded) are produced, and the evaluation results of each welded structure are plotted.

As shown in FIG. 4, in the case of Example 1 having a rectangular beam shape, the laser energy density is 3 to 5 kW / mm ² , and the porosity of the weld metal part 3 is 0.2 or less per 1 mm. On the other hand, in the case of Comparative Example 2 in which the beam shape is circular, the laser energy density is about 22 kW / mm ² and the porosity of the weld metal part 3 is 1 to 2.6 per 1 mm. From this result, it can be seen that in Example 1, the laser energy density is low and the porosity number can be suppressed, but in Comparative Example 2, the energy density is high and porosity generation cannot be suppressed.

  The above results are discussed below. When the beam shape is rectangular, the energy per unit area is small compared to the circular shape, and it is considered that the generation of porosity can be suppressed by lowering the energy density. In addition, it is considered that the number of porosity generations is largely caused by the beam shape. Porosity is thought to be caused by bubbles that accompany evaporation at the tip of the keyhole and trapped in the solidification wall during transport by hot water flow. If argon gas is used as the shielding gas 6 regardless of whether the condensing point of the laser beam 4 is circular or rectangular, bubbles are likely generated at the tip of the keyhole. However, the number of generated porosity is smaller when the beam shape is circular but the beam diameter is large. For this reason, it is considered that the number of bubbles generated is smaller in the rectangular shape with a lower energy density than in the circular shape of the condensing point of the laser beam 4. Further, when the condensing point is rectangular, the keyhole width is long, so that the bubbles generated at the tip of the keyhole are likely to dissipate, and it is assumed that the bubbles are not easily trapped in the keyhole.

  The shape of the condensing point may be a square or a rectangle as long as it is a rectangle. Moreover, if the shape of the condensing point is rectangular, the shape of the energy density distribution is not limited, but the top hat type is more preferable in the Gaussian type and the top hat type shown in FIG. 2A. This is because the top hat type has a lower energy density at the center (peak) than the Gaussian type, so evaporation of molten metal and bubbles are less generated at the tip of the keyhole, resulting in suppression of porosity in the weld metal. This is because it is considered effective.

  As described above, in the method for manufacturing a reactor control rod according to the present invention, the inert gas that does not include the component of the member to be welded is used as the shielding gas 6 in the laser welding process, and the shape of the condensing point of the laser light 4 is rectangular. By using a mold, it is possible to increase the amount of δ ferrite in the weld metal part 3 and to reduce the porosity (weld defect) in the weld metal part 3.

[Reactor control rod]
Next, a reactor control rod produced by using the above-described method for producing a reactor control rod according to the present invention will be described. 6A is a top view showing an example of a reactor control rod according to the present invention, and FIG. 6B is an exploded perspective view showing an example of a reactor control rod according to the present invention. The reactor control rod shown in FIGS. 6A and 6B is a structure in which a laser welded structure of an austenitic stainless steel tie rod 1 having a cross-shaped cross section and an austenitic stainless steel sheath 2 having a U-shaped cross section is supported by the reactor control rod. Include as body. In the present invention, the “reactor control rod” includes this support structure. There are 21 welding points 67 on one surface of the tie rod 61 and the sheath 64, which is 168 in total. According to the method for manufacturing a reactor control rod according to the present invention described above, the reactor control rod according to the present invention exhibits sufficient high-temperature strength because the amount of δ ferrite in the weld metal part is a sufficient amount. Can do. Furthermore, since the number of porosity in the weld metal part is small, the reliability is excellent. Therefore, according to the present invention, a high-quality reactor control rod can be provided.

The composition of the members to be welded (tie rod 61 and sheath 64) is not particularly limited, but is preferably austenitic steel shown below. About carbon (C), it is an austenite stabilization element, and 0.03 mass% or less is preferable from a viewpoint of an intensity | strength improvement. In order to maintain the stress corrosion resistance, 0.02% by mass or less is more desirable. The N composition is an austenite stabilizing element, and is preferably 0.03% by mass or more from the viewpoint of improving the strength. The content of N in a general tie rod and sheath is 0.04% by mass or more. When N ₂ gas is used as the shielding gas 6, the N composition of the laser welded portion 3 between the fin step portion of the tie rod 1 and the convex tip portion of the sheath 2 increases from the N composition of the tie rod 1 and the sheath 2. N is an austenite strengthening component and promotes austenitization by being contained in the weld metal part, resulting in a decrease in the amount of δ ferrite. In the present invention, by using Ar gas as the shielding gas, the value of the Cr / Ni equivalent ratio of the weld metal part is reduced even when the N content (0.04% by mass or more) of a general tie rod and sheath is used. And a decrease in the amount of δ ferrite can be prevented.

  Next, the relationship between the width and depth ratio of the weld metal part, the penetration ratio, and the amount of δ ferrite will be described. FIG. 5 is a schematic diagram showing the relationship of the width / depth ratio of the laser weld metal part. As Example 2, a welded structure having a / b = 1.7 to 2.3 was prepared. a / b can be changed according to welding conditions. The welding conditions in the case of a / b = 1.7 are a laser output of 2.8 kW, a welding speed of 0.5 m / min, and a wire feed speed of 3.0 m / min. The other conditions are the same as in Example 1. It is. The welding conditions in the case of a / b = 2.3 are a laser output of 2.5 kW, a welding speed of 1.0 m / min, and a wire feed speed of 1.1 m / min. It is the same.

  For the welded structure of a / b = 1.7 to 2.3, the penetration ratio (calculated value) and the amount of δ ferrite (measured value) of the member to be welded (tie rod) were evaluated. The evaluation results are shown in Table 2.

  As a result of investigating the amount of δ ferrite in the laser weld metal part 3, the amount of δ ferrite in the laser weld metal part 3 between the fin step portion of the tie rod 1 and the sheath 2 convex tip portion was 3.3 to 5% by mass. It can be seen that the welded structure of Example 2 has an amount of δ ferrite that can sufficiently prevent high temperature cracks that are likely to occur in the laser weld metal part 3.

In addition to the above evaluation, the N atom content of the weld metal portion 3 between the fin step portion of the tie rod 1 of Example 2 and the sheath 2 convex tip portion was measured. After laser welding of the tie rod 1 and the sheath 2, a sample of the weld metal part 3 was taken, and the N gas content inside the weld metal was measured by an inert gas dissolution heat conduction method. As a result, when using the _{N 2} gas to the shielding gas 6, N atom content of the weld metal portion 3 is 600-800 ppm. There are cases where the tie rod 1 and sheath 2 components and welding conditions vary. On the other hand, when Ar is used for the shielding gas 6, since N does not enter the weld metal part 3 from the outside, the N atom content of the weld metal part is the same as that of the tie rod 1, laser welding wire 8 and sheath 2 used. Of these, the N content is the highest but the N content or less. The N content of the weld metal portion varies depending on the penetration ratio of the molten tie rod 1, the sheath 2, and the laser welding wire 8.

  As described above, according to the present invention, a method of manufacturing a reactor control rod capable of increasing the amount of δ ferrite in a laser weld metal part and reducing the porosity, and an atom produced using the method It has been shown that furnace control rods can be provided.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. The above-described embodiments are illustrative of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of a certain embodiment. Moreover, it is also possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  DESCRIPTION OF SYMBOLS 1 ... Tie rod, 2 ... Sheath, 3 ... Weld metal part, 4 ... Laser beam, 5 ... Laser processing head, 6 ... Shield gas, 7 ... Shield nozzle, 8 ... Welding wire, 9 ... Wire feed nozzle, 20a ... Laser Shape of light condensing point (rectangle), 20b ... Shape of laser light condensing point (circular), 21a ... Energy density distribution of laser light (Gaussian type), 21a '... Energy density distribution of laser light (top hat) Mold), 21b ... energy density distribution of laser light, 61 ... tie rod, 62 ... fin, 64 ... sheath, 65 ... convex tip of sheath, 66 ... control rod, 67 ... welding point, 68 ... cooling hole, 69 ... Control rod support structure, 70 ... handle, 71 ... drop speed limiter.

Claims (18)

Preparing at least two stainless steel welded members that constitute the support structure of the reactor control rod;
A welding process in which a weld metal wire made of stainless steel is supplied to a part of each of the members to be welded, and laser welding is performed while supplying a shielding gas to laser weld the members to be welded through a weld metal portion. And having
A method for manufacturing a nuclear reactor control rod, wherein the condensing point of the laser beam is rectangular, and the shield gas is an inert gas that does not contain a component of the member to be welded.   The method for manufacturing a reactor control rod according to claim 1, wherein the inert gas is Ar or He. The N content of the welded member is 0.04% by mass or more, and the equivalent ratio of Cr and Ni represented by the following formula (1) is 1.4 or less. A method for producing the reactor control rod according to claim 1.
Cr / Ni equivalent ratio = (Cr equivalent: [Cr] + [Mo] +1.5 [Si] +0.5 [Nb]) / (Ni equivalent: [Ni] +0.5 [Mn] +30 [C] +30 [C] N]) ... Formula (1)
(In formula (1), [] indicates the content (% by mass) of each component.)   The method for manufacturing a nuclear reactor control rod according to claim 1, wherein the C content of the welded member is 0.02 mass% or less.   2. The method of manufacturing a nuclear reactor control rod according to claim 1, wherein the shape of the energy density distribution of the laser beam is a Gaussian type or a top hat type.   The method for manufacturing a nuclear reactor control rod according to claim 1, wherein a ratio a / b between the width a and the depth b of the weld metal part is 1.7 or more.   The method for manufacturing a nuclear reactor control rod according to claim 1, wherein a penetration ratio of the welded member is 30 to 50%.   8. The N content in the weld metal part is equal to or lower than the N content of the welded member and the weld metal wire, but having the highest N content. 2. A method for manufacturing a reactor control rod according to item 1.   The method for manufacturing a nuclear reactor control rod according to any one of claims 1 to 7, wherein an amount of δ ferrite in the weld metal part is 2 mass% or more.   The method for manufacturing a nuclear reactor control rod according to any one of claims 1 to 7, wherein the number of porosity of the weld metal part is 0.2 or less per mm.   The method for manufacturing a nuclear reactor control rod according to any one of claims 1 to 7, wherein the members to be welded are a tie rod having a cross-shaped cross section and a sheath having a U-shaped cross section. A reactor control rod support structure which is a welded structure in which at least two welded members made of stainless steel are welded via a weld metal part;
A nuclear reactor control rod characterized in that the amount of δ ferrite in the weld metal part is 2% by mass or more and the number of porosity is 0.2 or less per mm. The N content of the welded member is 0.04% by mass or more, and the equivalent ratio of Cr and Ni represented by the following formula (1) is 1.4 or less. Reactor control rod as described.
Cr / Ni equivalent ratio = (Cr equivalent: [Cr] + [Mo] +1.5 [Si] +0.5 [Nb]) / (Ni equivalent: [Ni] +0.5 [Mn] +30 [C] +30 [C] N]) ... Formula (1)
(In formula (1), [] indicates the content (% by mass) of each component.)   The nuclear reactor control rod according to claim 12, wherein the C content of the welded member is 0.02 mass% or less.   The reactor control rod according to claim 12, wherein a ratio a / b between the width a and the depth b of the weld metal portion is 1.7 or more.   The nuclear reactor control rod according to claim 12, wherein a penetration ratio of the welded member is 30 to 50%.   13. The nuclear reactor control according to claim 12, wherein the N content of the weld metal portion is equal to or less than the N content of the welded member and the weld metal wire having the highest N content. rod.   13. The nuclear reactor control rod according to claim 12, wherein the member to be welded is a tie rod having a cross-shaped cross section and a sheath having a U-shaped cross section.

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