JP2013050395A - Processing method and processing structure of nuclear reactor having control rod generating heat - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a processing method of a nuclear reactor A having a control rod already generating heat.SOLUTION: A processing method of a nuclear reactor includes: stacking planar blocks 1 made of precast concrete into two stacks that are opposite with each other, and installing concrete between the opposite block stacks 1 to form a retaining wall 3; surrounding circumference of a nuclear reactor A with the retaining wall 3; injecting water into a water injection area surrounded by the retaining wall 3 to cool a control rod in the nuclear reactor A; continuing the cooling operation until fuel reaches a state not to be damaged; and then installing concrete into the water injection area surrounded by the retaining wall 3.

Description

  The present invention relates to a processing method and a processing structure of a nuclear reactor in which a control rod generates heat for some reason.

Reactor fuel rods are made of radioactive isotopes, such as 235 uranium.
When such uranium reacts, it emits radiation, and when it reacts, it turns into a stable substance that does not cause fission.
Therefore, it can be said that completely stopping the reaction in the nuclear reactor is equivalent to making all the radioisotopes stable.
However, since it takes hundreds of years to become a stable isotope, it is impossible to wait for it to completely stop, and the reaction is aborted and discarded as radioactive waste.
A control rod is inserted to abort the reaction, but the fission reaction does not stop as soon as it is inserted, and the reaction converges slowly over a certain period of time.
At that time, it is necessary to cool the nuclear fuel.
This is because when the control rod is injected, no fission reaction occurs, but decay heat continues to be generated in this state.
Therefore, if the cooling is not continued, the fuel itself melts, causing the worst situation of melting the core.
When the bottom of the pressure vessel falls out, the melt falls on the containment floor and becomes high temperature and high pressure, and there is a possibility that the reactor containment vessel will be damaged on a large scale and may be destroyed with explosion.

Such generation of heat leads to a great danger, and thus cooling is necessary. However, in reality, even if water is poured, it cannot be easily cooled.
The reason is that water cannot be cooled due to overheating and cannot be cooled, water cannot be injected with the internal pressure of the steam, or water pressure higher than the internal pressure is required for water injection.
For this reason, water can be discharged from the outside, but in a nuclear reactor where the control rod generates heat for some reason, the operator is exposed to the explosion and cannot approach it, and water is sprayed from a distance.
This is just like putting a bucket in a distant place and sprinkling with a hose towards the bucket.

On the other hand, a method of solidifying the reactor with concrete can be assumed.
However, if the reactor where the control rods are generating heat is solidified with concrete, the heat cannot be released with the concrete, so there is a risk that the fuel rods will melt.
If the fuel rod melts, there is a danger of melting down, so it is important to cool it first and bring it to a point where it does not melt.

How long will it have to continue cooling?
It is said that it takes one year to cool the fuel to a state where it is not damaged after full operation.
For example, Three Mile Island has been cooling for two years after the accident.

JP2010-8091A. JP 2008-309703 A. Japanese Patent Application Laid-Open No. 2008-304353.

  Conventional technologies related to nuclear reactor processing are limited to a technology for dismantling a reactor in a healthy state (Patent Document 1), a technology for removing (Patent Document 2), a decontamination method before dismantling (Patent Document 3), and the like. The treatment method of the reactor that generates heat from the control rod has not been considered so far, and there is no existing technology.

The processing method of the nuclear reactor in which the control rod of the present invention that has solved the problems of the conventional apparatus as described above generates heat is formed by stacking the precast concrete planar blocks facing each other and putting the concrete between the opposing blocks. Casting to form a retaining wall, surrounding the reactor with this retaining wall, injecting water into the water injection area surrounded by the retaining wall to cool the control rod in the reactor, and this cooling does not damage the fuel This is characterized by placing concrete in the water injection area surrounded by the retaining wall.
The processing structure of the nuclear reactor in which the control rod of the present invention generates heat is a retaining wall that surrounds the periphery of the nuclear reactor. Retaining wall formed by casting and water injection device that cools the control rod in the reactor by pouring water into the water injection area surrounded by the retaining wall, and then placing concrete into the water injection area surrounded by the retaining wall It is characterized by comprising a concrete placing device.

Since the method for treating a nuclear reactor in which the control rod of the present invention generates heat is as described above, the following effects can be obtained.
<I> Retaining walls that surround the reactor form a water injection zone and a concrete placement zone.
<B> Therefore, a separate structure is unnecessary, and both steps can be performed continuously, which is extremely economical.
<C> Since only the concrete block is installed, it can be constructed, cooled and fixed by remote operation even when the worker cannot access, and is highly practical.

  Embodiments of a reactor processing method according to the present invention will be described below in detail with reference to the drawings.

<1> Preconditions As described above, the present invention relates to a nuclear reactor treatment method in which a control rod is already generating heat, not a sound reactor disassembly or repair.

<2> Concrete block Since the present invention is the subject method based on the above, work and members that can be performed by a machine from a distance without employing as close as possible are adopted.
For this purpose, for example, a block 1 made of precast concrete having an L-shaped and T-shaped cross section is produced in a factory and carried to the vicinity of the nuclear reactor.
This block 1 has a wall surface portion 12 and a bottom surface portion 11 formed in a cross-sectional L shape and a T shape, and the wall surface portion 12 can be made independent by taking a large area of the bottom surface portion 11. .
A substance that blocks radioactivity, such as a lead plate, may be attached to the surface of the wall surface portion 12 and the bottom surface portion 11 of the block 1, or particles having such a function may be mixed in the concrete.
A material having pores such as zeolite or diatomaceous earth can be mixed in the concrete of the block 1.
Further, the inner side surface of the wall surface portion 12 of the block 1 may be inclined to the outside, that is, the protruding bottom surface portion 11 side.
Furthermore, if the shape and type of the block 1 are simplified, not only mass production can be performed under high quality control in the factory, but also local assembly time can be minimized.

<3> Coupling between blocks A coupling portion 13 having a known combination shape such as irregularities is formed on the end face of the block 1 so that the blocks 1 adjacent in the horizontal direction can be coupled firmly.
Further, a connecting portion made of a known combination shape such as irregularities is formed on the upper and lower surfaces of the block 1 so that the blocks 1 in the vertical direction can be firmly connected.
The connecting portion 13 is not only composed of concrete itself, but is formed by embedding or retrofitting the steel connecting portion 13.
Further, a rubber packing or the like is attached to the end face of the block 1 so as to maintain a high water-stopping property.
It is also possible to apply an adhesive during the on-site connection.
Since the coupling portion 13 is configured by concave-convex fitting, the degree of freedom of bending of the coupling portion 13 is increased, and the coupling portion 13 can be applied to straight and curved arrangements.

<4> Installation of block The above-described block 1 is installed facing each other.
That is, the wall portions 12 of the two blocks 1 are placed facing each other with the bottom surface portion 11 facing outward.
And the space where a plane and a cross section are a rectangle can be formed by partitioning the both end surfaces of the wall surface part 12 which opposes with a slat.
Reinforcing bar 14 is installed inside this space, and concrete is cast to form one concrete block 2.
By carrying out this concrete lump 2 adjacently and continuously, the long retaining wall 3 can be formed.
The retaining wall 3 surrounds one or more reactors A to form a wide water injection area.
The retaining wall 3 is preliminarily calculated and given a predetermined weight so as to withstand the water pressure caused by water injection described later.
Further, an adhesive can be applied between the lower surface of the bottom surface portion 11 of the block 1 and the ground surface to be installed, or between the upper surface of the lower concrete block 2 and its adhesive force can be utilized.
The installation of the block 1 can be performed in a state where a person does not approach the contaminated area by using, for example, a device known as an air cushion that injects compressed air and moves it up from the floor.
As described above, when the block 1 formed by inclining the inner side surface of the wall surface portion 12 toward the protruding bottom surface portion 11 side is opposed to each other, a reverse C-shaped space is formed between them. When placed, a more stable shape can be obtained.

<5> Stacking of retaining walls After the first-stage retaining wall 3 is formed in the above process, the wall surfaces 12 of the two blocks 1 are placed facing each other in the same process as described above.
Then, similarly to the step of the first-stage retaining wall 3, the reinforcing bar 14 is disposed, and concrete is placed to form the second-stage retaining wall 3.
In that case, since the internal water pressure decreases as the upper level is reached, the interval between the two wall surfaces 12 is narrow, that is, the thin retaining wall 3 is constructed.
In this way, the thin retaining walls 3 having a short cross section in the horizontal direction are piled up as they go up.
When a block having an L-shaped cross section is used, a stable shape can be obtained if the distance between the upper end outside the wall surface portion 12 of the lower block and the outer end of the bottom surface portion 11 of the upper block are the same. Can be stacked.
These operations are performed by remotely operating an unmanned crane.
By repeating the above steps, one or a plurality of reactors A can be surrounded by the retaining wall 3 having a height of 40 to 50 m, for example.

<6> Water injection The area surrounded by the retaining wall 3 is filled with injection water 4 from an external water injection device.
Since this water injection process is not water discharge from a distant place but water injection into the retaining wall 3 using a pipe or the like, it is possible to fill the injected water 4 without waste.
Since one or more reactors A are located in the center of the water injection area, if the doors and windows are opened, the injected water 4 fills the reactor A as cooling water. Become.
In this way, the control rod in the reactor A can be cooled over a long period of time.
However, the injected water 4 injected in this step becomes high-concentration radioactively contaminated water.

<7> Placing concrete Cooling by water injection in the above steps is continued until the fuel is not damaged.
If the state can be confirmed, the filling concrete 5 is poured from the concrete placing device into the water injection area surrounded by the retaining wall 3.
As this filling concrete 5, a highly fluid ready-mixed concrete is placed using a treme tube.
If it is high fluidity concrete, it can flow into the details of the reactor A and solidify to form a complete filling state.
Alternatively, underwater concrete called hydrocleat is placed.
Alternatively, the aggregate is put in advance, and then pre-packed concrete for injecting the mortar content of the concrete is placed.
Before and after the filling concrete 5 is placed, it is also possible to cover the whole by forming a ceiling in the upper part of the water injection area surrounded by the retaining wall 3.
If there is a filling material instead of concrete, it can be used.

<8> Treatment of contaminated water The contaminated water pushed up by the filling concrete 5 is made to flow into the treatment device 6 through a passage established in a part of the retaining wall 3.
The contaminated water that has flowed in removes oil in the treatment device 6 and removes radioactive cesium using zeolite that absorbs radioactive substances.
Furthermore, radioactive substances are precipitated and separated on the bottom of the water with special chemicals to reduce the contamination concentration to about 1/10000.
If seawater is mixed in the cooling water, the salt content is removed and the water is desalinated, then returned to the reactor A and reused as cooling water.
Even if such a treatment is performed, radioactive materials are not lost, but the volume of contaminated water is reduced to facilitate management and safety.

Explanatory drawing of the state which surrounded the nuclear reactor which the control rod of this invention is producing | generating with the retaining wall. Explanatory drawing of the installation state of a concrete block. Explanatory drawing of the state which laid concrete between concrete blocks. Explanatory drawing of the state which poured water into the water injection area surrounded by the lower retaining wall. Explanatory drawing of the state which poured water into the water injection area which built the retaining wall to the upper stage. Explanatory drawing of the state which is placing concrete in the inside surrounded by the retaining wall. Explanatory drawing of the state in which the nuclear reactor is surrounded and fixed with concrete.

1: Block
2: Concrete block
3: Retaining wall
4: Injection water
5: Filled concrete
6: Processing device
A: Reactor

Claims (4)

Install a block made of precast concrete, consisting of a bottom and a wall, facing each other,
Concrete is placed between the blocks facing the wall to form a retaining wall,
This retaining wall surrounds the reactor,
Water is injected into the water injection area surrounded by the retaining wall to cool the control rod in the reactor,
Continue this cooling process until the fuel is not damaged,
After that, cast concrete into the water injection area surrounded by the retaining wall.
A method of treating a nuclear reactor where control rods are generating heat. A block made of precast concrete, consisting of a bottom and a wall,
The cross section is L-shaped or T-shaped.
A method for treating a nuclear reactor in which the control rod according to claim 1 generates heat. A retaining wall that surrounds the reactor,
Stacked precast concrete surface blocks facing each other,
A retaining wall formed by placing concrete between opposing blocks;
Cooling water to be poured into the retaining wall;
Consists of concrete filled inside the retaining wall,
Reactor processing structure where control rods generate heat. A block made of precast concrete, consisting of a bottom and a wall,
The cross section is L-shaped or T-shaped.
A reactor processing structure in which the control rod according to claim 3 generates heat.

Images