JP5049693B2 - Boiling water reactor control rod - Google Patents

Description

  The present invention relates to a control rod for a boiling water reactor, and more particularly to a control rod structure using hafnium metal.

  A boiling water atom with a structure in which a hafnium elliptic tube as a neutron absorber is encapsulated in a sheath having a substantially U-shaped cross section to form one blade, and four blades are fixed to a tie rod having a cross-shaped cross section. A furnace control rod is used (see, for example, Patent Document 1).

  In recent years, it has been reported that cracks occur on the sheath surface of boiling water reactor control rods. This crack is considered to be irradiation-induced stress corrosion cracking (IASCC) that occurs when three environmental factors of stress, corrosion, and irradiation overlap.

  The sheath surface of the control rod installed in the nuclear reactor has a tensile residual stress environment generated by welding of the sheath and tie rod and sheath and handle during the manufacturing process, a corrosive environment of the gap between the sheath and the hafnium elliptic tube, and nuclear fuel. It has been reported that cracks are likely to occur on the sheath surface due to IASCC because three factors such as the high irradiation environment of neutrons and γ rays generated by the fission reaction of IASCC overlap.

Japanese Patent Application Laid-Open No. 09-061576 (Page 3, FIGS. 3 and 4)

  IASCC can be prevented by removing any one of the environmental factors of stress, corrosion, and irradiation. Since the control rod is used in the nuclear reactor, it is difficult to remove the irradiation environment among the three environmental factors.

  In a control rod using a hafnium elliptic tube according to the prior art, a tensile residual stress is generated on the sheath surface as the sheath and the handle and the sheath and the tie rod are welded. As a method for reducing the residual stress environment, post-weld heat treatment is known. However, in the case of control rods, it is difficult to apply post-weld heat treatment due to structural and dimensional accuracy constraints.

  Regarding the corrosive environment, crevice corrosion occurs when impurities, corrosion products, etc. contained in the core coolant accumulate in the gap between the sheath in the tensile residual stress range existing on the sheath surface and the hafnium elliptic tube.

  An object of the present invention is to provide a control rod for a boiling water reactor having a structure in which the crevice corrosion environment between a sheath and a hafnium elliptic tube is improved and the IASCC resistance is improved.

  In order to solve the above-described problems, the present invention provides a tie rod having a substantially cross-shaped cross section, a sheath having a substantially U-shaped cross section and enclosing a hafnium elliptic tube as a neutron absorber and partially welded to the tie rod; In the control rod of a boiling water reactor consisting of a handle attached by welding to the lower end of the sheath and a lower support plate or drop speed limiter attached to the lower end of the sheath, the gap between the sheath and the flat portion of the hafnium elliptic tube is widened. We propose a control rod for boiling water reactors.

  In order to widen the gap between the sheath and the flat portion of the hafnium elliptic tube, a recess is formed in the flat portion of the hafnium elliptic tube, or the flat portion of the hafnium elliptic tube is thinned, or the surface of the flat portion of the hafnium elliptic tube Is corrugated.

  The present invention also includes a tie rod having a substantially cross-shaped cross section, a sheath having a substantially U-shaped cross section and containing a hafnium elliptic tube as a neutron absorber and partially welded to the tie rod, and attached to the upper end of the sheath by welding. A hafnium elliptic tube corresponding to the tensile residual stress range of the sheath partially welded to the tie rod in a control rod of a boiling water reactor consisting of a handle and a lower support plate or drop speed limiter attached to the lower end of the sheath by welding We propose a boiling water reactor control rod with an arc-shaped or U-shaped notch at the end.

  The present invention further includes a tie rod having a substantially cross-shaped cross section, a sheath having a substantially U-shaped cross section and containing a hafnium elliptic tube as a neutron absorber and partially welded to the tie rod, and attached to the upper end of the sheath by welding. In a control rod of a boiling water reactor consisting of a handle and a lower support plate or a drop speed limiter attached to the lower end of the sheath by welding, a hafnium elliptic tube corresponding to the tensile residual stress range of the handle and the sheath to be welded We propose a boiling water reactor control rod with a thin upper plate.

  To widen the gap between the sheath and the flat portion of the hafnium elliptic tube, and form an arc-shaped or U-shaped notch at the end of the hafnium elliptic tube corresponding to the tensile residual stress influence range of the sheath partially welded to the tie rod You can also.

  The gap between the sheath and the flat portion of the hafnium elliptic tube may be widened, and the upper plate thickness of the hafnium elliptic tube corresponding to the range of influence of the tensile residual stress of the sheath to be welded to the handle may be reduced.

  An arc or U-shaped notch is formed at the end of the hafnium elliptic tube corresponding to the tensile residual stress influence range of the sheath partially welded to the tie rod, and the tensile residual stress influence range of the sheath welded to the handle is supported. It is also possible to process the thin plate thickness of the hafnium elliptic tube.

  Combining all three types of means above, widening the gap between the sheath and the flat part of the hafnium elliptic tube, and arcing or concentrating at the end of the hafnium elliptic tube corresponding to the range of the tensile residual stress effect of the sheath partially welded to the tie rod Further, the upper plate thickness of the hafnium elliptic tube corresponding to the range of influence of the tensile residual stress of the handle and the sheath to be welded can be reduced.

  According to the present invention, in the control rod of the boiling water reactor, basically, the gap between the sheath and the flat portion of the hafnium elliptic tube is widened, so that accumulation of corrosion products is prevented and generated on the sheath surface. Suppresses radiation-induced stress corrosion cracking, improves control rod reliability, and contributes to continuous and stable operation of the reactor.

  When widening the gap between the sheath and the hafnium elliptic tube, the blade width and sheath thickness are the same as the control rod applied to each nuclear power plant due to constraints such as the current space with nuclear fuel and other equipment. Therefore, only the shape of the hafnium elliptic tube contained in the sheath is changed to improve the gap.

  An arc-shaped or U-shaped notch was formed at the end of the hafnium elliptic tube in the tensile residual stress influence range of the sheath surface near the weld between the tie rod and the sheath. Crevice corrosion can be reduced by improving the gap and preventing the accumulation of corrosion products due to coolant flow.

  Since the upper plate thickness of the hafnium elliptic tube corresponding to the tensile residual stress influence range of the sheath to be welded to the handle is thinned in the tensile residual stress influence range of the sheath surface near the welded portion between the handle and the sheath, the sheath and hafnium The gap with the elliptic tube is increased, and crevice corrosion can be reduced. The plate thickness of the hafnium elliptic tube is designed to maintain sufficient neutron absorption capability in the reactor core, so the plate thickness considering the increase in gap should be such that it does not affect the neutron absorption capability of the control rod. is there.

  Next, an embodiment of a control rod for a boiling water reactor according to the present invention will be described with reference to FIGS.

  FIG. 1 is a diagram showing the overall structure of a control rod of a boiling water reactor to which the present invention is applied.

  A control rod of a boiling water reactor has a skeleton structure called a frame, with a handle 2 attached to the upper end of a tie rod 1 having a cross-shaped cross section and a lower support member or drop speed limiter 3 attached to the lower end of the tie rod 1. Is formed.

  A hafnium elliptic tube 5 having an approximately half length of the tie rod 1 and having an elliptical cross-sectional shape is attached to the frame as a top hafnium on the tongue-like portion 2a of the handle and fixed by a pin 6.

  Similarly, a hafnium elliptic tube 5 having an approximately half length of the tie rod 1 and an elliptical cross section is attached to the lower support member or the tongue-like portion 3a of the drop speed limiter 3 as a lower hafnium and fixed by a pin 6.

  The upper hafnium and the lower hafnium are enclosed in a stainless steel sheath 4 having a substantially U-shaped cross section. The end of the sheath is fixed to the handle 2, the tie rod 1, the lower support member, or the drop speed limiter 3 to form one blade.

  When the other three blades are fixed so that the cross-sectional shape is substantially a cross, a control rod is formed.

  FIG. 2 shows a tie rod and one blade of an AA cross section perpendicular to the longitudinal axis of the hafnium elliptic tube in a control rod of a boiling water reactor according to the prior art, for comparison with the following embodiment of the present invention. It is a figure which shows the sheath of a minute, and a hafnium elliptic tube.

  There is only a slight gap G0 between the conventional hafnium elliptic tube 5 and the sheath 4 whose most surface is flat.

  FIG. 3 is a cross-sectional view taken along line AA perpendicular to the longitudinal axis of the hafnium elliptic tube in Embodiment 1 of the control rod of the boiling water reactor according to the present invention. FIG.

  The hafnium elliptic tube 7 of the first embodiment employs a hafnium elliptic tube 8a that has a flat portion of the hafnium elliptic tube bent inward and has a depression in the center.

  The gap G1 between the sheath 4 and the hafnium elliptic tube 8a is G1> G0 as compared with the gap G0 of the conventional control rod. When this hafnium elliptic tube 8a is included, the gap G1 between the sheath 4 and the hafnium elliptic tube 8a is larger than the conventional gap G0, so that the coolant present in the gap G1 can flow, and the corrosion products Accumulation can be prevented and the crevice environment can be mitigated.

  The shape of the hafnium elliptic tube 7 includes a hafnium elliptic tube 8b in which the flat portion of the hafnium elliptic tube is bent inward and has a hollow in the center, and the hafnium elliptic tube 8b is thinned by cutting or rolling. , A hafnium elliptic tube 8c having a hafnium flat portion in the shape of a corrugated plate, and in any case, the gap between the sheath 4 and the hafnium elliptic tube 7 satisfies G1> G0.

  FIG. 4 is a partial cross-sectional view showing a relationship among a handle, a tie rod, and one upper blade among side surfaces parallel to the longitudinal axis of the tie rod in Embodiment 2 of the control rod of the boiling water reactor according to the present invention. is there.

  In the second embodiment, an arc-shaped or U-shaped notch 13 is formed at the end of the hafnium elliptic tube 12 corresponding to the tensile residual stress influence range of the sheath 4 partially welded to the tie rod 1. That is, the hafnium elliptic tube 12 has an arc-shaped or U-shaped notch 13 in the vicinity of the welded portion 10 between the tie rod 1 and the sheath tab 9 and in the vicinity of the welded portion 11 between the handle 2 and the sheath 4.

  The arc-shaped or U-shaped notch 13 increases the clearance between the sheath 4 and the hafnium elliptic tube 12 in the range of influence of the tensile residual stress on the sheath surface in the vicinity of the welded portion 10 and the welded portion 11, and accumulates corrosion products. Prevent and mitigate crevice corrosion environment in the range of tensile residual stress.

  FIG. 5 is a partial cross-sectional view showing a relationship among a handle, a tie rod, and one of the upper blades of the side surfaces parallel to the longitudinal axis of the tie rod in the third embodiment of the control rod of the boiling water reactor according to the present invention. is there.

  In the third embodiment, the plate thickness T of the upper processed surface 15 of the hafnium elliptic tube 14 corresponding to the range of influence of the tensile residual stress of the sheath 2 welded to the handle 2 is processed to be thinner than the original plate thickness t of the hafnium elliptic tube 14. (T <t).

  Since the welded portion 11 between the handle 2 and the sheath 4 has a longer weld length than the welded portion 10 between the tie rod 1 and the sheath tab 9, the range of influence of tensile residual stress generated on the surface of the sheath 4 is also increased. If the thickness T of the upper processing surface 15 of the hafnium elliptic tube 14 in the range of influence of the tensile residual stress is made thinner than the original thickness t of the hafnium elliptic tube 14, the gap between the sheath 4 and the upper processing surface 15 increases, so that corrosion occurs. It can prevent stagnation of products and mitigates crevice corrosion environment.

  FIG. 6 is a partial cross-sectional view showing a relationship among a handle, a tie rod, and one of the upper blades of the side surfaces parallel to the longitudinal axis of the tie rod in the fourth embodiment of the control rod of the boiling water reactor according to the present invention. is there.

  The fourth embodiment employs a hafnium elliptic tube 16 in which the arc-shaped or U-shaped notch 13 of the second embodiment of FIG. 4 and the upper processed surface 15 of the third embodiment of FIG. 5 are combined.

  When this hafnium elliptic tube 16 is adopted, the gap between the sheath 4 near the welded portion and the hafnium elliptic tube 16 increases both the improvement range of the gap and the gap size as compared with the case where each is constructed alone. The effect of preventing corrosion is further enhanced.

  In addition, although Example 4 was the combination of Example 2 and Example 3, the combination of Example 1 and Example 2, the combination of Example 1 and Example 3, Example 1 and Example 2 Even in combination with Example 3, a synergistic effect exceeding the effect of each Example alone can be obtained.

It is a figure which shows the whole structure of the control rod of the boiling water reactor used as the application object of this invention. For comparison with the embodiment according to the present invention, the sheath and hafnium of a tie rod and one blade in the AA cross section perpendicular to the longitudinal axis of the hafnium elliptic tube in the control rod of the boiling water reactor according to the prior art It is a figure which shows an elliptical tube. FIG. 5 is a diagram showing a tie rod, a sheath for one blade, and a hafnium elliptic tube in the AA cross section perpendicular to the longitudinal axis of the hafnium elliptic tube in the first embodiment of the control rod of the boiling water reactor according to the present invention. is there. It is a fragmentary sectional view which shows the relationship between a handle | steering-wheel, a tie rod, and one piece of an upper blade among the side surfaces parallel to the longitudinal direction axis | shaft of the tie rod in Example 2 of the control rod of the boiling water reactor by this invention. It is a fragmentary sectional view which shows the relationship between a handle | steering-wheel, a tie rod, and one piece of an upper blade among the side surfaces parallel to the longitudinal direction axis | shaft of the tie rod in Example 3 of the control rod of the boiling water reactor by this invention. It is a fragmentary sectional view which shows the relationship between a handle | steering-wheel, a tie rod, and one piece of an upper blade among the side surfaces parallel to the longitudinal direction axis | shaft of the tie rod in Example 4 of the control rod of the boiling water reactor by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tie rod 2 Handle 3 Falling speed limiter or lower support member 4 Sheath 5 Conventional hafnium elliptic tube 6 Pin 7 Hafnium elliptic tube 8a Hafnium elliptic tube 8b having a hollow Hafnium elliptic tube 8c having a thin wall Hafnium elliptic tube 9 Sheath tab 10 Tab welded portion 11 Handle welded portion 12 Notched hafnium elliptic tube 13 Arc-shaped or U-shaped notched 14 Hafnium elliptic tube 15 with thinned upper plate thickness Work surface 16 Notch and upper plate thickness Thinned hafnium elliptic tube

Claims (9)

A tie rod having a substantially cross-shaped cross section, a sheath having a substantially U-shaped cross section and containing a hafnium elliptic tube as a neutron absorber and partially welded to the tie rod, a handle attached to the upper end of the sheath by welding, In a control rod of a boiling water reactor consisting of a lower support plate or a drop speed limiter attached to the lower end of the sheath by welding,
A control rod for a boiling water nuclear reactor, wherein an arc-shaped or U-shaped notch is formed at an end of the hafnium elliptic tube corresponding to a tensile residual stress influence range of the sheath partially welded to the tie rod. In the control rod of the boiling water reactor according to claim 1,
A recess is formed in the flat portion of the hafnium elliptic tube, and the gap between the sheath and the flat portion of the hafnium elliptic tube is wider than the distance between the longitudinal end of the hafnium elliptic tube and the sheath. Control rod for boiling water reactor. A tie rod having a substantially cross-shaped cross section, a sheath having a substantially U-shaped cross section and containing a hafnium elliptic tube as a neutron absorber and partially welded to the tie rod, a handle attached to the upper end of the sheath by welding, In a control rod of a boiling water reactor consisting of a lower support plate or a drop speed limiter attached to the lower end of the sheath by welding,
A control rod for a boiling water reactor, wherein the upper plate thickness of the hafnium elliptic tube corresponding to the tensile residual stress influence range of the sheath to be welded to the handle is thinned. In the boiling water reactor control rod according to claim 3,
A recess is formed in the flat portion of the hafnium elliptic tube, and the gap between the sheath and the flat portion of the hafnium elliptic tube is wider than the distance between the longitudinal end of the hafnium elliptic tube and the sheath. Control rod for boiling water reactor. In the control rod of the boiling water reactor according to claim 4,
A control rod for a boiling water nuclear reactor, wherein an arc-shaped or U-shaped notch is formed at an end of the hafnium elliptic tube corresponding to a tensile residual stress influence range of the sheath partially welded to the tie rod. A tie rod having a substantially cross-shaped cross section, a sheath having a substantially U-shaped cross section and containing a hafnium elliptic tube as a neutron absorber and partially welded to the tie rod, a handle attached to the upper end of the sheath by welding, In a control rod of a boiling water reactor consisting of a lower support plate or a drop speed limiter attached to the lower end of the sheath by welding,
The gap between the sheath and the flat portion of the hafnium elliptic tube is larger than the distance between the end portion in the major axis direction of the hafnium elliptic tube and the sheath , and the tensile residual stress influence range of the sheath is partially welded to the tie rod. A control rod for a boiling water reactor, in which an arc-shaped or U-shaped notch is formed at the end of the hafnium elliptic tube corresponding to. A tie rod having a substantially cross-shaped cross section, a sheath having a substantially U-shaped cross section and containing a hafnium elliptic tube as a neutron absorber and partially welded to the tie rod, a handle attached to the upper end of the sheath by welding, In a control rod of a boiling water reactor consisting of a lower support plate or a drop speed limiter attached to the lower end of the sheath by welding,
The gap between the sheath and the flat portion of the hafnium elliptic tube is wider than the distance between the end portion in the major axis direction of the hafnium elliptic tube and the sheath , and the tensile residual stress is affected by the sheath to be welded to the handle. A control rod for a boiling water reactor, wherein the corresponding upper thickness of the hafnium elliptic tube is thinned. A tie rod having a substantially cross-shaped cross section, a sheath having a substantially U-shaped cross section and containing a hafnium elliptic tube as a neutron absorber and partially welded to the tie rod, a handle attached to the upper end of the sheath by welding, In a control rod of a boiling water reactor consisting of a lower support plate or a drop speed limiter attached to the lower end of the sheath by welding,
An arc-shaped or U-shaped notch is formed at the end of the hafnium elliptic tube corresponding to the tensile residual stress influence range of the sheath partially welded to the tie rod, and the tensile residual of the sheath welded to the handle A control rod for a boiling water reactor, wherein the upper plate thickness of the hafnium elliptic tube corresponding to the stress-affected range is thinned. A tie rod having a substantially cross-shaped cross section, a sheath having a substantially U-shaped cross section and containing a hafnium elliptic tube as a neutron absorber and partially welded to the tie rod, a handle attached to the upper end of the sheath by welding, In a control rod of a boiling water reactor consisting of a lower support plate or a drop speed limiter attached to the lower end of the sheath by welding,
The gap between the sheath and the flat portion of the hafnium elliptic tube is larger than the distance between the end portion in the major axis direction of the hafnium elliptic tube and the sheath , and the tensile residual stress influence range of the sheath is partially welded to the tie rod. An arc-shaped or U-shaped notch is formed at the end of the hafnium elliptic tube corresponding to the above, and the upper plate thickness of the hafnium elliptic tube corresponding to the tensile residual stress influence range of the sheath to be welded to the handle is set. A control rod for a boiling water reactor characterized by thin processing.

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