JPH04106496A - Nuclear reactor control rod - Google Patents

Abstract

PURPOSE:To prevent corrosion products and the like by constituting neutron absorber with a multitude of divided neutron absorber elements and two plates of hafnium metal having water path holes etc. so as to move in the wing. CONSTITUTION:Inside of each of neutron absorber elements 28a-28d, a moderator flow path 32 is formed between hafnium metal plates 30, as shown for example by the element 28a, and also a moderator flow path 33 is formed between the outer surface of each metal plate 30 and the inner surface of sheath 17. Therefore, the moderator stagnates to be dead water only in a small part, and generation of corrosion products is prevented. Although the metal plates 30 can generate heat during absorbing neutron and void can be generated due to temperature rise in reactor water, the support fixer pins 36 penetrated and arranged between the metal plates 30 becomes resistances, water path holes 34 are provided in each metal plate 30, and void is rapidly exhausted outside through the water path holes 34 and sheath water holes 19. Thus the reactivity worth of the control rods is never lowered.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a control rod for a nuclear reactor that adjusts and controls the reactor power of a nuclear reactor, and particularly to a control rod for a long-life nuclear reactor. Concerning sticks.

(Prior Art) FIG. 10 and FIG. 11 show a conventional nuclear reactor control rod, and this nuclear reactor control rod 1o.

The tip structure member 12 has a handle 11, the end structure member 14 has a speed limiter 13, and the tip structure member 1.
2 and the terminal structural member 14, and a deep U-shaped sheath 17 with an open end attached to each protruding leg of this central tie rod 15 to form a wing 16. A long-life neutron absorber 18 is loaded into each wing 16 of the sheath 17, and a large number of sheath water passage holes 19 are provided in the plate surface of each sheath 17.

As shown in FIG. 11(A), the neutron absorber 18 is composed of a plurality of neutron absorbing elements 18a, 18b, . . . divided in the axial direction of the reactor control rod 100. all have the same structure.

That is, for example, as shown for the neutron absorption element 18a in FIG.
Hf) In a flux strap type hafnium control rod, in order to increase the reaction value of the control rod, a channel 21 for passing water, which is a moderator, is provided between the two hafnium metal plates 20. It is formed. In order to maintain a gap between the hafnium metal plates 20 that are the flow paths 21, a top-shaped spacer 22 is interposed between the two hafnium metal plates 20, and each hafnium Each hafnium metal plate 20 is fixed to the sheath 17 through the cooling hole 23 of the metal plate 20.
It is fixed in contact with the inner surface.

(Problems to be Solved by the Invention) In the conventional nuclear reactor control rod 100, the spacer 22, the hafnium metal plate 20, and the inner surface of the sheath 17 are in close contact with each other. between the hafnium metal plate 20 and the sheath 17
The water acting as a moderator trapped between the two becomes dead water (still water), which reduces corrosion resistance due to electrochemical causes and makes corrosion products more likely to occur.

When corrosion products occur in the gap, a wedge action acts to force the sheath 17 to expand, resulting in a large bending stress. The sheath 17 placed in a corrosive environment has a problem in that stress corrosion cracking is likely to occur due to a decrease in corrosion resistance and a large tensile stress load.

In addition, each neutron absorption element 1 constituting the neutron absorber 18
8a, 18b,... have exactly the same structure,
Since the amount of neutron irradiation is not considered at all, the neutron absorbing element in the upper part reaches its nuclear lifetime even though the neutron absorbing element in the lower part, which has a lower neutron irradiation amount, has not reached its nuclear lifetime. There is also the problem that control rods that have reached the end of their useful life must be disposed of as waste.

The present invention has been made in consideration of the above-mentioned circumstances, and there is no risk of corrosion etc., and there is no need to waste control rods that have a remaining nuclear lifespan of being disposed of as waste. The purpose is to provide inexpensive and lightweight control rods for nuclear reactors.

[Structure of the invention]

(Means for Solving the Problems) As a means for achieving the above object, the present invention provides a central tie rod having a cross-shaped cross section that connects the tip structural member and the terminal structural member, and an open end on each protruding leg of the central tie rod. In a control rod for a nuclear reactor, which is equipped with a deep U-shaped sheath that is attached to form a wing, and a long-life neutron absorber loaded in each wing, the neutron absorber is attached to the shaft of the control rod. It is composed of a plurality of neutron absorption elements divided in the direction, and the neutron absorption characteristics of each neutron absorption element are determined according to the neutron irradiation amount in that division, and each neutron absorption element is The neutron absorbing element is composed of two hafnium metal plates that are connected and fixed with a narrow outer dimension interval and have water holes, and this neutron absorption element is loosely fitted into the wing, and a support that passes through the two hafnium metal plates and the sheath. It is characterized by being fixed within the wing using a fixing pin.

(Function) In the nuclear reactor control rod according to the present invention, a predetermined gap is formed between the outer surface of the two hafnium metal plates and the inner surface of the sheath, which improves the flow of the moderator and eliminates the generation of dead water. . Therefore, there is no reduction in corrosion resistance, the generation of corrosion products is suppressed, and it is possible to prevent the occurrence of stress corrosion cracking.

In addition, hafnium metal plates generate heat when absorbing neutrons, raising the temperature of the reactor water and creating voids. If this is significant, the moderator will not flow between the hafnium metal plates, and control However, in the case of the present invention, a support fixing pin is placed between two hafnium metal plates, and this acts as a resistance, so voids generated between the hafnium metal plates are normally eliminated. It is discharged to the outside of the sheath through the water hole, making it possible to suppress a decrease in the reactivity value of the control rod. In addition, a moderator between hafnium metal plates,
Replacement with reactor water outside the sheath is promoted, making it possible to improve the cooling effect.

In addition, the neutron absorption characteristics of each neutron absorption element are determined according to the neutron irradiation amount in that category, so there is no need to waste control rods that still have a nuclear life remaining, such as having to dispose of them as waste. .

(Example) Hereinafter, a first example of the present invention will be described with reference to FIGS. 1 to 5.

FIG. 1 shows an example of a nuclear reactor control rod according to the present invention, and this nuclear reactor control rod 10 includes a tip structure member 12 having a handle 11 and an end structure member 14 having a speed limiter 13. , a central tie rod 15 with a cross-shaped cross section that connects these two tank building materials 12 and 14, and an open end attached to each protruding leg of this central tie rod 15 to form a wing 1.
6 and a long-life neutron absorber 28 loaded into each of the four wings 16. , a large number of sheath water passage holes 19 are provided.

The neutron absorber 28, as shown in the left half of FIG. (The right half of the figure shows the state in which no neutron absorption elements are loaded.) As shown in FIG. It is determined that the neutron absorption characteristics gradually decrease toward the bottom.

Specifically, each of the neutron absorption elements 28a to 28d is composed of two hafnium metal plates 3o, as described later, and the thickness of the hafnium metal plates 3o is gradually decreased from the upper layer to the lower layer. , whereby the reactivity effect decreases sequentially from the upper stage to the lower stage. By adopting such a structure, the nuclear lifetimes of the neutron absorbing elements 28a to 28d are made approximately equal, thereby eliminating wasteful disposal of control rods with remaining nuclear lifetimes as waste.

Each of these neutron absorption elements 28a to 28d is shown in FIG.
), (B) and as shown in FIG. 5, taking the neutron absorption element 28a as an example, it is constructed by connecting two hafnium metal plates 30 in a rectangular tube shape with side plates 31a and 31b on both sides. A moderator flow path 32 is formed inside the chamber.

The two hafnium metal plates 3 of this neutron absorption element 28a
The dimension between the outer surfaces of 0 is set to a smaller value than the inner dimension of the wing 16, and when the neutron absorption element 28 is inserted into the wing 16, as shown in FIG. 4(B), each hafnium metal plate A moderator flow path 33 is also formed between the outer surface of the sheath 3o and the inner surface of the sheath 17.

Further, as shown in FIG. 4(A) and FIG. 5, a water passage hole 34 is provided in the widthwise central portion of both hafnium metal plates 3o, and the water passage hole 34 is located at both sides. A support fixing pin through hole 35 is provided in each of the support fixing pin through holes 35 . Each of these support fixing pin through holes 35 has a fourth
Figure (A).

As shown in (B), the support fixing pin 36 that is fixed through the sheath 17 is inserted, so that the neutron absorbing element 28a is fixed in position within the wing 16 without contacting the inner surface of the sheath 17. It has become.

Next, the function of this nuclear reactor control rod will be explained.

Inside each of the neutron absorbing elements 28a to 28d, as shown in FIGS. 4 and 5, taking the neutron absorbing element 28a as an example, a moderator flow path 3 is provided between two hafnium metal plates 30.
2 are formed, and moderator flow paths 33 are also formed between the outer surface of each hafnium metal plate 3o and the inner surface of the sheath 17. Therefore, there is no part where the moderator remains and becomes dead water, and the generation of corrosion products can be prevented.

Furthermore, when the hafnium metal plates 30 absorb neutrons, they generate heat, which may raise the temperature of the reactor water and cause voids. A pin 36 is disposed through the pin 36 and serves as a resistance, and each hafnium metal plate 30 is provided with a water passage hole 34, so that voids can be quickly drained through the water passage hole 34 and the sheath water passage hole 19. is discharged to the outside. Therefore, there is no risk of reducing the reactivity value of the control rod. Furthermore, replacement of the moderator between the hafnium metal plates 30 with the reactor water outside the wing 16 is promoted, and the cooling effect can be improved.

FIG. 6 shows a second embodiment of a control rod for a nuclear reactor according to the present invention, in which side plates 31a and 31b connecting both sides of two hafnium metal plates 30 are divided into a plurality of pieces in the vertical direction. In other respects, it has the same configuration and function as the nuclear reactor control rod shown in the first embodiment.

With this configuration, each of the neutron absorbing elements 28a to 28d is lightweight, and as a result, the control rod can be made lightweight.

FIGS. 7(A) and 7(B) show a third embodiment of the nuclear reactor control rod of the present invention, in which two hafnium metal plates 3
0 are interconnected at the center in the width direction by spacing pins 40, and in other respects, it has the same configuration as the reactor control rod shown in the first embodiment and has the same function. It is.

With this configuration, it is possible to prevent the central portions of the hafnium metal plates 30 from coming into contact with each other due to bending, and also to prevent the neutron absorbing elements 2 from coming into contact with each other.
The mechanical strength of 8a to 28d can also be improved.

FIGS. 8(A) and 8(B) show a fourth embodiment of the nuclear reactor control rod of the present invention, in which each neutron absorbing element 28a to 28
d is constructed in a cylindrical shape using only two hafnium metal plates 30 without using side plates 31a and 31b (see FIG. 5), and in other respects, the nuclear reactor shown in the first embodiment is It has the same structure and function as the control rod.

Even with this configuration, the same effects as the nuclear reactor control rod shown in the first embodiment can be expected.

FIGS. 9(A) and 9(B) show a fifth embodiment of the nuclear reactor control rod of the present invention, and this nuclear reactor control rod has a fourth embodiment.
Similar to the nuclear reactor control rod shown in the embodiment, each of the neutron absorption elements 28a to 28d is formed into a cylindrical shape using only two hafnium metal plates 30, and is arranged, for example, two each in the direction in which the wings 16 protrude. This is how it was done. In other respects, it has the same configuration as the nuclear reactor control rod shown in the first embodiment, and has the same function.

With this configuration, the same effect as the spacing pin 40 of the nuclear reactor control rod shown in the third embodiment can be obtained.

〔Effect of the invention〕

As explained above, according to the control rod for a nuclear reactor according to the present invention, the hafnium metal plate is not fixed in contact with the inner surface of the sheath, so the moderator does not accumulate and become dead water, and corrosion products It is possible to prevent the occurrence of Therefore, corrosion does not occur in the hafnium metal plate, sheath, support fixing pin, etc.

In addition, even if voids occur between the hafnium metal plates, the support fixing pin acts as a resistance, and the voids are discharged to the outside through the water holes, which prevents a decrease in the reactivity value of the control rod and reduces speed. Since the replacement of materials is promoted, the cooling effect can also be improved.

Furthermore, since the neutron absorption characteristics of each neutron absorption element are determined according to the neutron irradiation amount in that category, there is no waste in disposing of control rods with remaining nuclear lifetimes as waste.

[Brief explanation of drawings]

Fig. 1 is a partially cut perspective view showing an embodiment of a control rod for a nuclear reactor according to the present invention, Fig. 2 is an explanatory view schematically showing the inside of a wing, and Fig. 3 corresponds to Fig. 2. A diagram showing the axial reactivity distribution, Figure 4 (A) is an enlarged view of the main part of Figure 1, Figure 4
Figure (B) is a sectional view taken along line rV-IV in Figure 4 (A), Figure 5 is an enlarged perspective view showing the structure of the neutron absorption element, and Figure 6 is Figure 5 showing the second embodiment of the present invention. 7(A) is a corresponding view to FIG. 4(A) showing the third embodiment of the present invention, and FIG. 7(B) is a sectional view taken along the line ■-■ of FIG. 7(A). , FIG. 8(A) is a view corresponding to FIG. 4(A) showing the fourth embodiment of the present invention, FIG. 8(B) is a sectional view taken along the line ■-■ of FIG. 8(A), and FIG. 9(A) is the same as FIG. 4(A) showing the fifth embodiment of the present invention.
9(B) is a sectional view taken along line IX-IX in FIG. 9(A), FIG. 10 is a partial perspective view showing a conventional control rod for a nuclear reactor, and FIG. 11(A) is an enlarged view of the main part of Figure 10,
FIG. 11(B) is a sectional view taken along the line XI-XI of FIG. 11(A). 10... Nuclear reactor control rod, 12... Tip structure material, 1
4... End structural material, 15... Center tie rod, 16
...Wing, 17... Sheath, 28... Neutron absorber, 28a, 28b, 28c, 28d-... Neutron absorption element, 30... Hafnium metal plate, 32.33.
...Flow path, 34...Water hole, 36...Support fixing pin.

Claims (1)

[Claims] A central tie rod with a cross-shaped cross section that connects the tip structural member and the terminal structural member, a deep U-shaped sheath with an open end attached to each protruding leg of this central tie rod to form a wing, and a deep U-shaped sheath that is loaded into each wing. In a nuclear reactor control rod equipped with a long-life neutron absorber, the neutron absorber is composed of a plurality of neutron absorbing elements divided in the axial direction of the control rod, and each neutron absorbing element absorbs neutrons. The absorption characteristics are determined according to the amount of neutron irradiation in that category,
Each neutron absorbing element is composed of two hafnium metal plates connected and fixed at an outer dimension interval narrower than the inner dimension of the wing and having a water passage hole, and the neutron absorbing element is loosely fitted inside the wing. A control rod for a nuclear reactor, characterized in that it is fixed in a wing by two hafnium metal plates and a support fixing pin penetrating the sheath.