JP5171151B2 - Control rod for boiling water reactor - Google Patents

Description

  The present invention relates to a boiling water reactor control rod, and more particularly to a boiling water reactor control rod suitable for reducing irradiation-induced stress corrosion cracking.

  In general, in order to control the amount of fission chain reaction in a boiling water reactor, a control rod that houses a neutron absorber is used. This control rod has a cross-shaped cross section, and is inserted into a cross-shaped gap formed between four cylindrical fuel channel boxes erected in the vertical direction while moving in the vertical direction.

  The control rod for boiling water reactor is a tie rod with a cross-shaped cross section and a U-shaped cross-section that contains a neutron absorber inside and welds a U-shaped opening across each tip of the cross-section of the tie rod. A handle that is provided at the upper end of the tie rod in the axial direction and is welded to the tie rod and the sheath, and a lower support member that is provided at the lower end of the tie rod in the axial direction and is welded to the tie rod and the sheath. (For example, Patent Document 1).

  In such a boiling water reactor control rod, the welding connection between the handle and the sheath is performed by inserting the lower end of the handle formed in a cross shape like the tie rod inside the U-shape of the sheath, and at the lower end of the handle. The upper end of the sheath is fitted to a step provided according to the thickness of the sheath, and the fitting is welded over the entire length.

JP 2003-185777 A

  However, in the technique described in Patent Document 1, since the fitting portion between the handle and the sheath is welded over the entire length, there is a tensile residual stress in the vicinity of the welded portion, and irradiation-induced stress corrosion is caused. There is a risk of cracking.

  Irradiation-induced stress corrosion cracking is caused by the overlap of stress, irradiation environment, and corrosive environment. Therefore, in order to maintain the safe operation of the reactor, it is necessary to improve the durability against irradiation-induced stress corrosion cracking.

  An object of the present invention is to provide a control rod for a boiling water reactor having excellent durability against irradiation-induced stress corrosion cracking in the vicinity of a welded portion between a sheath and a handle.

  In order to solve the above problems, a boiling water nuclear reactor control rod according to the present invention includes a tie rod having a cross-sectional shape and a U-shaped cross-section and containing a neutron absorbing material therein and each tip of the tie rod having a cross-section. A sheath in which the U-shaped opening is welded across the portion, a handle provided at the upper end portion in the axial direction of the tie rod and welded to the tie rod and the sheath, and a tie rod and sheath provided at the lower end portion in the axial direction of the tie rod. In the control rod for boiling water reactors with a lower support member welded to the handle, the handle is inserted inside the U-shape of the sheath, and the weld-affected zone between the handle and the sheath can reduce the welding residual stress of the sheath It is characterized by having a residual stress reducing structure.

  That is, since the residual stress reduction structure is provided in the weld affected portion between the handle and the sheath, the tensile residual stress in the vicinity of the welded portion of the sheath can be reduced, and therefore, among the three factors that cause irradiation-induced stress corrosion cracking. Stress can be reduced, and durability against irradiation-induced stress corrosion cracking can be improved.

  In this case, the residual stress reducing structure may be a structure in which the weld between the handle and the sheath is partially welded along the direction of the weld line. According to this, since the welding length is short compared with the case where it welds over the full length of the U-shape of a sheath, the tensile residual stress which generate | occur | produces in the welding part vicinity of a sheath can be reduced.

  In this case, it can be set as the structure which provided the notch part in the edge part except partial welding. According to this, since the weld length is short compared with the case of welding over the entire length of the U-shape, the tensile residual stress generated in the vicinity of the welded portion of the sheath can be reduced, and the non-direction in the direction along the weld line can be reduced. Since the gap in the welded portion is eliminated, crevice corrosion in the welded portion can be reduced.

  Further, the residual stress reducing structure can be a structure in which a long hole is provided in the sheath along the direction of the weld line between the handle and the sheath. According to this, since the end part near the center part of the long hole is close to the free end, the tensile residual stress during welding can be relaxed. Here, the total length of the long holes in the weld line direction is 11% or more of the total weld length of the handle and the sheath, and the cross-sectional area of the sheath at the position where the long holes are provided is the control rod scram. It is desirable to have a cross-sectional area that can withstand the tensile load of time.

  ADVANTAGE OF THE INVENTION According to this invention, the tensile residual stress of the welding part vicinity with a sheath can be reduced, and the control rod for boiling water reactors excellent in the durability with respect to irradiation-induced stress corrosion cracking can be provided.

  Hereinafter, the present invention will be described based on embodiments.

(Embodiment 1)
FIG. 1 is a perspective view showing the configuration of a boiling water reactor control rod according to an embodiment of the present invention, FIG. 2 is a front view of the boiling water reactor control rod, and FIGS. It is the elements on larger scale which show the welding part of a sheath and a handle.

  As shown in FIG. 1, the boiling water nuclear reactor control rod of the present embodiment has a U-shaped cross-shaped tie rod 1 and a U-shaped cross-section of the tie rod 1 sandwiched between the tip portions of the tie rod 1. The sheath 2 to which the opening is welded, the handle 3 provided at the upper end in the axial direction of the tie rod 1 and welded to the tie rod 1 and the sheath 2, and the tie rod 1 and the sheath provided at the lower end in the axial direction of the tie rod 1 2, a lower support member 4 welded to 2, a neutron absorber 5 (for example, a hafnium flat tube) housed in a U-shape of the sheath 2, and a control rod welded to the lower support member 4 and not shown. It is comprised from the connector 6 for connecting with a drive mechanism apparatus.

  The handle 3 and the lower support member 4 are composed of four arm-shaped portions that project radially at an angular interval of 90 degrees to form a cross shape. The tie rod 1 connecting the handle 3 and the lower support member 4 has a relatively short length of four radially projecting arm-shaped portions with respect to the arm 3 projecting from the handle 3 and the lower support member 4. Is formed. In the present embodiment, the lower support member 4 is provided at the lower portion of the tie rod 1, but a drop speed limiter may be provided instead.

  As shown in FIG. 2, a plurality of cooling holes 7 are provided in the vicinity of the upper end portion of the sheath 2 along the direction of the weld line so that the attachment position of the neutron absorber 5 can be confirmed. A plurality of cooling holes 8 are provided coaxially with the cooling holes 9 of the neutron absorber 5. The handle 3 is provided with a tongue 10 for suspending the neutron absorber 5, and the lower support member 4 is provided with a tongue 11 for coupling with the neutron absorber 5. Further, a roller 12 is rotatably supported on the handle 3, and a control rod is smoothly inserted into a cross-shaped gap formed between four cylindrical fuel channel boxes (not shown). Yes.

  As shown in FIG. 3 (a), a handle 3 is inserted inside the U-shape of the sheath 2, and convex portions are provided at upper ends of both surfaces sandwiching the handle 3 of the sheath 2. A welded portion 13 that is partially welded (for example, TIG welded or the like) is provided so as to overlap the stepped portion provided at the lower portion of the handle 3. Moreover, as shown in FIG.3 (b), you may provide the weld parts 14 and 15 which carried out partial welding of two different places. At this time, the length (L1) of the welded portion 13 and the sum of the lengths of the welded portions 14 and 15 (L2 + L3) are equal to the total length (L0) of the convex portion of the sheath 2 in order to withstand the tensile load during the control rod scram. 20 to 65%.

  According to this configuration, since the welding length is shorter than the case where the convex portion of the sheath 2 is welded over the entire length, the tensile residual stress generated in the vicinity of the welded portion of the sheath 2 can be reduced. The durability against corrosion cracking can be improved.

In this embodiment, the sheath 2 and the handle 3 are TIG welded, but a welding method using YAG laser light or CO ₂ laser light may be used. 3 (a) and 3 (b) show the welded portion of the U-shaped one surface of the sheath 2, but the opposite side of the handle 3 is also shown in FIGS. 3 (a) and 3 (b). A weld is provided at the target position. Moreover, although the welding part was provided in one place or two places, you may provide in several places as needed.

(Embodiment 2)
4 (a) and 4 (b) are partial enlarged views showing a welded portion of a sheath and a handle of a boiling water reactor control rod according to another embodiment of the present invention, and FIG. It is -A arrow sectional drawing. As shown in the figure, the boiling water reactor control rod of the present embodiment is different from the first embodiment in that a cut portion 16 is provided at the upper end of the sheath 2 instead of the cooling hole 7. Other configurations are the same as those shown in FIGS.

  As shown in FIG. 4A, the cut portion 16 is a rectangular concave portion having a corner formed in an arc shape, and a stepped portion provided at the lower portion of the handle 3 with a convex portion of the upper end portion excluding the cut portion 16. Are provided with welded portions 19 and 20 which are overlapped and welded. Further, as shown in FIG. 4 (b), notches 17 and 18 are provided at two different locations on the upper end of the sheath 2, and the convex portion of the upper end of the sheath 2 excluding the notches 17 and 18 is defined as the lower part of the handle 3. You may provide the welding parts 21,22,23 which were piled up and welded to the level | step-difference part provided in this. At this time, the sum of the lengths of the welded portions 19 and 20 (L4 + L5) and the sum of the lengths of the welded portions 21, 22, and 23 (L6 + L7 + L8) are convex so that the length can withstand the tensile load during the control rod scram. 20 to 65% of the total length (L0) of the part. Further, in order to effectively reduce the tensile residual stress generated in the sheath 2 and ensure a predetermined strength, the length (L9) in the axial direction of the tie rod 1 of the cut portions 16, 17 and 18 is set to 20 mm or less.

  According to this structure, since the welding length is short compared with the case where the convex part of the sheath 2 is welded over the full length, the tensile residual stress which generate | occur | produces in the welding part vicinity of the sheath 2 can be reduced. Moreover, since the gap of the non-welded portion in the direction along the weld line is deleted as compared with the first embodiment, the crevice corrosion of the welded portion can be reduced.

  In the present embodiment, the shape of the cut portions 16, 17, and 18 is a rectangle having a curvature at the corner, but the shape is not limited to this as long as the tensile residual stress can be reduced.

(Embodiment 3)
5 (a) and 5 (b) are partially enlarged views showing a welded portion of a sheath and a handle of a boiling water reactor control rod according to another embodiment of the present invention, and FIG. It is -B arrow sectional drawing. As shown in the figure, the boiling water nuclear reactor control rod of the present embodiment is different from that of the first embodiment in that a rectangular hole 24 formed in the direction of the weld line is provided instead of the cooling hole 7 and the sheath 2 This is to have a welded portion 25 that is welded over the entire length (L0) with the convex portion of this portion overlapped with a stepped portion provided at the lower portion of the handle 3.

  As shown in FIG. 5A, the hole 24 has a rectangular corner formed in an arc shape and is disposed between the welded portion 25 and the lower end of the tongue-shaped portion 10. Moreover, as shown in FIG.5 (b), you may provide the holes 26 and 27 in two places from which the direction of a welding line differs. At this time, the length (L10) of the hole 24 or the sum of the lengths of the holes 26 and 27 (L11 + L12) is set to 11% or more of the total length (L0) of the welded portion 25. Further, the length (L13 + L14) or (L15 + L16 + L17) of the shortest portion where the sheath 2 remains from the position where the hole 24 or the holes 26, 27 is provided is 20 to 65% of the total length (L0) of the convex portion. For example, it can have a cross-sectional area that can withstand the tensile load during the control rod scram.

  Conventionally, the total length in the direction of the weld line of the cooling holes provided in the vicinity of the welded portion is about 10% of the length of the welded portion. On the other hand, in this embodiment, for example, in FIG. 5A, the length of the hole 24 in the direction of the weld line is 11% or more of the total length of the welded portion, and the vicinity of the center portion of the hole 24. Therefore, the tensile residual stress generated on the sheath surface between the welded portion 25 and the hole 24 and the tensile residual stress generated on the surface of the sheath opposite to the welded portion 25 with respect to the hole 24 are reduced. Can be relaxed.

  Further, in order to effectively reduce the tensile residual stress generated in the sheath 2, the axial length (L18) of the tie rod 1 from the lower end portion of the hole 24 or the holes 26 and 27 to the welded portion is arranged in a range of 30 mm or less. Is done. In addition, the hole 24 or the holes 26 and 27 of the present embodiment are formed in a rectangular shape, but may be any oblong hole. It is not limited to this if possible.

  Although the welded portion 25 of this embodiment is welded over the entire length (L0), it may be partially welded at one place or a plurality of places as in the first embodiment. Moreover, although the number of holes was provided in one place or two places, you may provide in multiple places as needed.

It is a perspective view which shows the structure of the control rod for boiling water reactors of one Embodiment of this invention. It is a front view of the control rod for boiling water reactors. It is the elements on larger scale which show the welding part of a sheath and a handle. (A), (b) is the elements on larger scale which show the welding part of the sheath and handle | steering_wheel of the boiling water reactor control rod of other embodiment of this invention, and (c) is the AA arrow of (a). FIG. (A), (b) is the elements on larger scale which show the welding part of the sheath of the control rod for boiling water reactors of another embodiment of this invention, and a handle, (c) is BB arrow of (a). FIG.

Explanation of symbols

1 Tie rod 2 Sheath 3 Handle 4 Lower support member 5 Neutron absorber 6 Connector

Claims (3)

A tie rod having a cross-shaped cross section, a sheath formed in a U-shaped cross-section and containing a neutron absorber inside, and having a U-shaped opening welded across each tip of the cross-section of the tie rod, and the axial direction of the tie rod A boiling water atom provided with a handle that is provided at the upper end of the tie rod and is welded to the tie rod and the sheath; and a lower support member that is provided at the lower end in the axial direction of the tie rod and is welded to the tie rod and the sheath. In furnace control rods,
Said handle has a lower end portion is inserted inside the U-shaped upper end portion of the sheath, the sheath is cut portion of one or more rectangular upper portion is formed, the upper end of the sheath, excluding the cut portion A control rod for a boiling water reactor, wherein a portion is welded to the handle . The boiling water reactor control rod according to claim 1 ,
A control rod for a boiling water reactor , wherein the cut portion has a rectangular corner formed in an arc shape . In the control rod for boiling water reactor according to claim 1 or 2 ,
A boiling water reactor control rod, wherein the total weld length of the portion where the upper end of the sheath is welded to the handle is 20 to 65% of the total length of the upper end edge of the sheath.

Images