JPH06102390A - Shock absorber for control rod - Google Patents

Abstract

PURPOSE:To prevent the damage of a hearth section in a reactor in case a control rod is dropped. CONSTITUTION:A shock absorber 17 is provided in a control rod guide hole on the bottom section 13a of a core support structure on a hearth section. The shock absorber 17 is stacked with multiple round dish-like cushioning bodies 18 so that dish-like recesses are reversed in sequence in the stacking direction, a top plate 19 is stacked on the uppermost cushioning body 18 in face contact, and a bottom plate 20 is inserted between the lowermost cushioning body 18 and the bottom section 13a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shock absorber for a control rod suitable for a nuclear reactor such as a high temperature gas reactor,
In particular, the present invention relates to a shock absorber for a control rod that can prevent damage to the hearth due to the impact when the control rod should fall in a high temperature gas furnace.

[0002]

2. Description of the Related Art Generally, in a high temperature gas reactor such as a high temperature engineering test research reactor, a plurality of vertical holes having an axial cross section of, for example, a hexagon are drilled on a hearth part in a reactor containing the high temperature gas. A plurality of control rod guide holes that communicate in the vertical direction are formed by stacking a plurality of graphite blocks that are aligned so that the axial centers of these vertical holes coincide with each other and arranging a large number of these blocks in the horizontal direction. Together with this, a core support structure for supporting the core is formed.

A control rod is inserted into each control rod guide hole,
Or by controlling the nuclear reaction of the core by being pulled out,
As a result, it controls the reactor power. Each control rod is housed in each control rod guide tube which is concentrically arranged above and communicates with each control rod guide hole, and is hung from the upper part of the nuclear reactor by a wire.

In a high temperature gas reactor, a core supporting structure for supporting a core (not shown) and a hearth portion are made of graphite, but the hearth portion is designed as an irreplaceable structure.
A shock absorber for a control rod is required that will not damage the hearth even if the wire that suspends the control rod is cut and the control rod falls onto the hearth.

Therefore, as a conventional control rod shock absorber, as shown in FIG. 5, a shock absorbing metal bellows 2 is attached to the lower end of the control rod 1, and when the control rod 1 falls, this bellows 2 is attached. Collides with the bottom of the core support structure on the hearth, and compressively deforms in the axial direction to absorb and absorb the impact energy, thereby preventing damage to the hearth.

[0006]

However, in such a conventional control rod shock absorber, since the weight of the metal bellows 2 itself is applied to the wire for suspending the control rod 1, creep damage of the wire is prevented. There is a possibility of promotion. Furthermore, since the metal bellows 2 that drops when the wire is cut directly collides with the bottom of the core support structure on the hearth, the hearth may be damaged to some extent.

Therefore, the present invention has been made in consideration of such circumstances, and its purpose is to reduce the load burden on the wire for suspending the control rod to reduce the probability of the control rod falling accident, and to prevent it from happening. It is an object of the present invention to provide a shock absorber for a control rod that can prevent damage to the hearth when the control rod falls. Another object of the present invention is to easily collect the fragments of the buffer body which are destroyed when the control rod is dropped.

[0008]

The present invention is configured as follows to solve the above problems.

The invention according to claim 1 of the present application (hereinafter, referred to as the first
Of the invention) is a control rod that is housed in a control rod guide hole of a core support structure in which a plurality of graphite blocks are laminated on the hearth of a nuclear reactor, and is movably suspended in the axial direction. In the control rod shock absorber that receives a drop of, a plurality of buffer bodies made of a brittle material having a curved surface are formed on the bottom of the core support structure, and adjacent buffer bodies are separated from each other in the control rod guide hole. It is characterized in that it is laminated so as to form.

Further, in the invention according to claim 2 of the present application (hereinafter referred to as the second invention), the buffer body is one of a dish shape and an annular shape having an open bottom portion, and the dish-shaped concave portion thereof is It is characterized in that they are laminated so that they are alternately turned in the laminating direction.

Further, in the invention according to claim 3 of the present application (hereinafter referred to as the third invention), the lowermost buffer body is placed on the bottom portion of the core support structure via the solid bottom plate, This bottom plate has a recess for receiving and storing the broken pieces of the buffer,
It is characterized by forming a flow path for passing a fluid.

[0012]

In the unlikely event that the control rod falls, a plurality of buffer bodies that receive the control rod will be destroyed, so that the impact energy of the control rod drop is converted into the fracture energy of the buffer body, and the impact energy is absorbed. The impact force transmitted to the hearth can be reduced and damage to the hearth can be prevented.

Also, since the control rod shock absorber is placed on the bottom of the core support structure on the hearth and not attached to the control rod, the load burden on the wire for suspending the control rod is reduced. can do. Therefore, it is possible to reduce the probability that the control rod will fall due to the cutting of the wire. Furthermore, since the gap can be formed by overlapping the curved surfaces of the buffer body,
The cushioning body is easily broken, and the impact force is absorbed accordingly.

Further, according to the third aspect of the present invention, since the debris when the buffer body is broken can be accommodated in the recess of the bottom plate, the debris can be easily collected.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a cross-sectional view of an essential part of an embodiment including the first to third inventions of the present application.
Contains high temperature gas and has a hearth 1
2 is provided, and a core support structure 13 that supports a core (not shown) is provided on the hearth 12.

In the core support structure 13, a plurality of bottom blocks made of graphite having vent holes for passing hot gas are first laid on the hearth section 12 to form a bottom section 13a, and then the bottom section 13a is formed. For example, a plurality of graphite blocks each having a hexagonal axial cross section and having a plurality of vertical holes formed in the axial direction are laminated in multiple layers so that the vertical holes are concentric in the vertical direction. The vertical holes form a plurality of control rod guide holes 13b, 13b ... Which communicate with each other in the vertical direction, and are arranged in the horizontal direction to form a support structure for supporting the core.

The control rod guide holes 13b are concentrically communicated with the control rod guide pipes 14, 14 at the upper side in the figure, and each control rod guide pipe 14 has a control rod 15 housed therein in a wire. It hangs up and down freely by 16,
The control rod 15 is inserted into or extracted from a core (not shown) by appropriately raising and lowering the control rod guide tube 14 and a control rod guide hole 13b communicating with the control rod guide hole 14b to control the neutron absorption amount of the core. It controls the reactivity and thus the reactor power.

The shock absorbers 17 for control rods shown in FIG. 1 are installed on the bottom portion 13a, which is the first stage of the core support structure 13 in each control rod guide hole 13b. Each shock absorber 17 is formed by stacking a plurality of round plate-shaped shock absorbers 18, 18, ... A graphite disk-shaped bottom plate 20 is concentrically interposed between the lower surface of the body 18 and the upper surface of the bottom portion 13a.

When the control rod 15 is dropped, the upper plate 19 is
This is the first part to receive this, and as shown in FIG. 3 (a), a hollow cylindrical body is formed, and high temperature gas is passed through the hollow part.

Each buffer body 18 has a main body 18a made of graphite,
It is made of ceramics, concrete, cement, brick, or the like, and is formed in the shape of a circular dish with a concave curved surface that is concave downward on the upper surface in the figure as shown in FIG. 3 (b). Through hole 18b penetrating in the thickness direction at the center of the
As shown in FIG. 1, a pair of upper and lower shock absorbers 1
The dish-shaped recesses 8 and 18 are concentrically opposed to each other and overlap each other, and a plurality of pairs are stacked in the vertical direction in the drawing to form a gap between the buffers 18 and 18. Is easily destroyed by the impact force from above.

The bottom plate 20 receives the debris when the buffer body 18 for receiving the control rod 15 is damaged by the fall of the control rod 15 by any chance. As shown in FIG. A central recessed portion 20b ₁ opening upward in the drawing is formed in the center of the upper portion of 20, and a lateral hole 20b ₂ laterally communicating with the concaved portion 20b ₁ is radially penetrated to communicate with the middle of the lateral hole 20b _2. The vertical hole 20b ₃ is made to penetrate to the lower bottom surface. For this reason, for example, gas or the like can be passed through the horizontal holes 18b ₂ and the vertical holes 18b ₃ in a state where the fragments of the buffer 18 are contained in the central recess 20b ₁ .

If the control rod 15 falls in the control rod guide tube 14 and the control rod guide hole 13b due to breakage of the wire 16, for example, it first collides with the upper plate 19 of the shock absorber 17. At this time, as shown in FIG. 1, since the upper plate 19 is substantially in surface contact with the buffer 18 immediately below it, the impact force received by the upper plate 19 is evenly transmitted to the buffer 18 immediately below it. It Therefore, the buffer 18 is finely broken.

Therefore, the impact energy is formed as the breaking energy of the plurality of buffer bodies 18, that is, the fracture surface forming energy, and since the buffer bodies 18 are finely broken, the impact energy absorption rate is high. As a result, the impact force transmitted to the bottom 13a of the core support structure 13 and the hearth 12 can be attenuated, and damage to the hearth 12 can be prevented.

FIG. 4 shows an example of the structure when a shock test is performed on the shock absorber 17 constructed as described above.
Steel control rod guide tube 14a used in the high temperature gas furnace 11
The control rod 15a suspended from the wire 16 is housed in the upper portion of the control rod guide tube 14a. The control rod 15a has the same weight as that used in the high temperature gas furnace 11 (for example, 96.6 kg).

Further, the floor 21 inside the control rod guide tube 14a.
A load meter 23, which is electrically connected to the oscilloscope 22 and measures an impact load, is placed on the top of the load meter 23. Further, a graphite lower support plate 24 is provided on the load meter 23 according to the present invention. The shock absorber 17 was placed. As the shock absorber 17, fifteen graphite buffer bodies 18 were laminated, and a graphite top plate 19 and a bottom plate 20 were used.

Then, the wire 16a is cut by a wire cutter, and the height when the control rod 15 is fully withdrawn is about 5 m.
Then, the control rod 15a was dropped. Then, the lower end of the control rod 15 first collides with the upper plate 19 of the shock absorber 17, and the shock force destroys some of the shock absorbers 18. For this reason, the impact load is increased by the shock absorber 17.
While being transmitted to the lower portion of the shock absorber 18, it is absorbed as breaking energy of the shock absorber 18 and is sufficiently damped when the impact load reaches the bottom plate 20. At this time, the maximum impact load measured by the load meter 23 through the oscilloscope 22 is 1982 kg.
It was f (19.4N), and it was confirmed that it was about 1/2 or less of the allowable value.

Further, since the lower support plate 24 was hardly damaged, the actual equipment of the high temperature gas furnace 11 has sufficient performance to protect the hearth 12 when the control rod 15 falls. It has been found.

Further, in this impact test, some of the fragments of the buffer 18 dropped on the bottom plate 20. The fragment is in the central recess 2
Because it was housed in 0b ₁ it was confirmed that it can be easily accommodated the debris.

[0030]

As described above, according to the present invention, since a plurality of buffer bodies made of brittle material are laminated on the hearth side of the control rod guide hole, the control rod should be placed in the control rod guide hole. If it falls, the buffer body receives it and the buffer body itself is destroyed, so that the impact force can be absorbed by the destruction and the impact force can be attenuated.

Therefore, since it is possible to reduce the transmission of the impact force when the control rod is dropped to the hearth portion, it is possible to prevent the hearth portion from being damaged.

Further, since the shock absorber is mounted on the bottom of the hearth side without being attached to the control rod, the load applied to the wire for suspending the control rod can be reduced. Therefore, it is possible to reduce the stress of the wire, reduce the probability of a control rod drop accident due to the cutting of the wire, and enhance safety.

Further, according to the third aspect of the present invention, since the broken pieces of the buffer body can be received and accommodated by the recesses, the broken pieces can be easily collected.

[Brief description of drawings]

FIG. 1 is a front view of an embodiment of a shock absorber for a control rod including the first to third inventions of the present application.

FIG. 2 is a partial vertical cross-sectional view of a high temperature gas reactor incorporating the embodiment of the present invention shown in FIG.

3 (a) is a vertical cross-sectional view of the upper plate shown in FIG. 1, (b).
Is a vertical cross-sectional view of the cushioning body shown in FIG. 1, and (c) is a half-mounting vertical cross-sectional view of the bottom plate shown in FIG.

FIG. 4 is a diagram showing an example of a configuration of an impact test for one embodiment of the present invention shown in FIG. 1 and the like.

FIG. 5 is a longitudinal sectional view showing a part of a conventional control rod shock absorber.

[Explanation of symbols]

 11 High Temperature Gas Reactor 12 Hearth 13 Core Support 13a Bottom of Core Support 13b Control Rod Guide Holes 14 and 14a Control Rod Guide Tubes 15 and 15a Control Rods 16 and 16a Wires 17 Shock Absorber 18 Buffer 19 Upper Plate 20 Bottom Plate 21 floor 22 oscilloscope 23 load cell 24 lower support plate

Claims (3)

[Claims] 1. A control rod which is housed in a control rod guide hole of a core support structure in which a plurality of graphite blocks are laminated on a hearth of a nuclear reactor and which is movably suspended in an axial direction thereof. In a shock absorber for a control rod that receives a drop, a plurality of buffer bodies made of a brittle material having a curved surface are formed on the bottom of the core support structure in the control rod guide hole.
A shock absorber for a control rod, characterized in that the buffer bodies adjacent to each other are laminated so as to form a gap therebetween. 2. The buffer body is one of a dish shape and an annular shape having an open bottom portion, and the dish-shaped recesses are laminated so as to alternately face each other in the laminating direction. Item 1. A shock absorber for a control rod according to item 1. 3. The bottom buffer body is mounted on the bottom of the core support structure via a solid bottom plate, and the bottom plate receives a broken piece of the buffer body and accommodates the fluid therein. The control rod shock absorber according to claim 1 or 2, wherein a flow passage is formed.