JPH0843576A - Reactor core catcher - Google Patents

Abstract

PURPOSE:To prevent a large scale steam explosion by constituting a plurality of cooling units arranged in assembly in the space below a reactor vessel, filling the sealed shell with coolant and inert gas and forming thin wall part in the shell. CONSTITUTION:A space 4 is provided below a rector vessel 2 in a reactor building 1 and a concave part 6 is formed in its concrete floor 5. In the concave part 6, a multitude of coolant units 7 are arranged in assembly. In the units 7, steel ball shells with diameter of 1 to 10cm sealed inside with coolant 9 and inert gas 10, for example, are filled and on the shell 8 surface, many thin wall parts 11 are formed. When am accident occurs and molten core 12 from the core 3 penetrates the reactor vessel 2 to fall on the units 7, it comes into contact with the upper unit 7, heats them and boils the coolant 9 to make it discharge out of the thin parts 11. The melt 12, repeating this process, slowly flows down due to flow resistance and avoids large scale contact to be cooled. By this, a large scale explosion can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactor core catcher for cooling a core melt generated when a core installed in a fast breeder reactor or a light water reactor is melted.

[0002]

2. Description of the Related Art In a fast breeder reactor or a light water reactor, a core melt is efficiently cooled in preparation for core melting in the event of a severe accident, and its thermal energy is cooled so as not to be converted into mechanical energy. Reactor core catcher is installed.

Conventional reactor core catchers are basically classified into two types of cooling modes. That is, (1) the core melt that penetrates the reactor vessel is introduced into the coolant, and (2) the coolant is sprinkled on the dropped core melt.

[0004]

In (1) above, the possibility of steam explosion cannot be denied, and (2)
It is difficult to prove that the core melt deposited on the bottom of the reactor vessel can be sufficiently cooled.

Further, as a problem common to (1) and (2), in a light water reactor, the core melt may be ejected from a reactor vessel that has penetrated through the melt at a high pressure of about 70 atm, and this kinetic energy is absorbed. It was possible to mention that a shock absorber was needed to do this.

The present invention has been made to solve the above problems, and is effective for both fast breeder reactors and light water reactors, and excessive fuel-coolant interaction (FCI) in fast breeder reactors. Can cool the core melt without causing
It is an object of the present invention to provide a reactor core catcher that can absorb jet energy of core melt without causing steam explosion in a light water reactor.

[0007]

The present invention comprises a large number of cooling units collectively arranged in a space provided below a reactor vessel or a reactor pressure vessel of a nuclear reactor, the cooling units being cooled in a closed shell body. It is characterized in that a material and an inert gas are enclosed and a thin portion is formed in the shell body.

[0008]

When the core melt penetrates the reactor vessel and falls into the cooling unit, it first comes into contact with the upper cooling unit and heats through the shell (steel) to boil the coolant inside the shell. The pressure generated by this breaks either of the thin-walled parts, and the coolant is ejected.

Even if a large number of cooling units come into contact with the core melt at the same time, the region of the core melt cooled by the jet is local, and the core melt slowly intrudes downward due to the flow resistance of the cooling unit. Therefore, a large contact area is not created and therefore a large steam explosion does not occur.

Further, since the steel shell body has voids inside, it also serves as a shock absorber for the core melt ejected from the through hole of the reactor vessel. Further, the inert gas efficiently ejects the coolant inside the unit when the cooling unit bursts or the thin portion is damaged. In order to efficiently cool the core melt, the core melt is blown off every time it bursts to prevent the core melt from depositing before it is cooled.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a nuclear reactor core catcher according to the present invention will be described with reference to FIGS. 1 shows a state where the reactor core catcher of this embodiment is installed in the reactor building to receive the core melt, FIG. 2 shows the reactor core catcher in FIG. 1, and FIG. 2 shows the cooling unit in FIG.

In FIG. 1, reference numeral 1 partially shows a main part of a reactor building in which a reactor vessel 2 of a fast breeder reactor is installed. A reactor core 3 is installed in the reactor vessel 2. A space 4 is provided below the reactor vessel 2 in the reactor building 1,
In this space 4, a recess 6 is formed in the concrete floor 5 of the reactor building 1.

A large number of coolant units 7 are arranged in the recess 6 in a collective manner. FIG. 2 is an enlarged view of a state in which a large number of coolant units 7 are collectively arranged in the recess 6.
Shown in

As shown in FIG. 3, the coolant unit 7 has a closed diameter of 1 cm to 10 cm, and a coolant 9 and an inert gas 10 are enclosed in a spherical shell 8 made of steel, for example, to form a spherical shell 8.
A large number of semicircular thin-walled portions 11 are formed on the surface of the. The semicircular thin-walled portion 11 is, for example, a dimple formed on the surface of a golf ball, and has a thickness such that it is easily damaged by an internal / external pressure difference of several atmospheres.

The coolant 9 is, for example, liquid metal sodium used as a coolant in the case of a fast breeder reactor, and the inert gas 10 is, for example, argon gas.

In the first embodiment, however, in the unlikely event of a severe accident, the core 2 is generated as shown in FIG. 1, the core melt 12 penetrates the reactor vessel 2, and the cooling unit When it drops onto the cooling medium 7, it first comes into contact with the cooling unit 7 on the upper side, and the coolant 9 therein is boiled by heat conduction through the spherical shell 8. Due to the pressure generated as a result, one of the thin portions 11 is damaged and the coolant 9 is ejected.

A large number of cooling units 7 can simultaneously melt the core melt.
Even if it comes into contact with 12, the region of the core melt 12 that is cooled by the jet is local, and the core melt 12 slowly intrudes downward due to the flow resistance of the spherical shell 8. Therefore, no large contact area is created, avoiding large contact and cooling gradually.

Further, since the spherical shell 8 has a space for enclosing the inert gas 10, it serves as a shock absorber (buffer mechanism) for the core melt 12 ejected from the through hole of the reactor vessel 2. effective.

Although the first embodiment has been described as an example applied to a fast breeder reactor, it can be applied to the space below the reactor pressure vessel in a light water reactor as in the above embodiment, but in the case of a light water reactor. By using water other than liquid metal sodium as the coolant 9, a large-scale steam explosion can be prevented.

Besides the steel, the material of the spherical shell 8 is not particularly limited as long as it is a substance that does not cause water or metal reaction violently when it reaches a high temperature in contact with a cooling unit. is not.

Next, the second aspect of the present invention will be described with reference to FIGS.
An example will be described. The second embodiment is different from the first embodiment in that a cylindrical shell 13 is used in place of the spherical shell 8 and other parts are the same as those in the first embodiment, and therefore duplicated. The description of the part to be performed is omitted, and only the main part will be described.

That is, as shown in FIG. 4, a cylindrical shell body
Both ends of 13 are closed, the coolant 9 and the inert gas 10 are sealed inside, and a large number of semicircular thin-walled parts 11 are formed on the outer surface.

FIG. 5 (a) shows an example in which the above cylindrical shells 13 are uniformly arranged in one direction in the recess 6 as the coolant unit 7a and stacked in multiple stages to form a reactor core catcher. FIG. 5B shows another example in which the coolant units 7a are arranged vertically and horizontally in FIG.

However, in the second embodiment, as in the first embodiment, excessive fuel and
The core melt can be cooled without causing the coolant interaction (FCI), while the core melt can be cooled without causing steam explosion in the light water reactor, and the jet energy of the core melt can be absorbed.

[0025]

According to the present invention, even if the core melt penetrates the reactor vessel or the reactor pressure vessel during a severe accident in the reactor, it does not cause a large-scale steam explosion, and
Impact on the concrete below the reactor vessel or reactor pressure vessel can be mitigated and the core melt can be cooled.

[Brief description of drawings]

FIG. 1 is a vertical sectional view schematically showing a main part of a reactor building for explaining a first embodiment of a reactor core catcher according to the present invention.

FIG. 2 is a vertical sectional view showing the reactor core catcher in FIG.

FIG. 3 is an enlarged vertical sectional view showing the cooling unit in FIG.

FIG. 4 is a longitudinal sectional view showing a cooling unit in a second embodiment of the nuclear reactor core catcher according to the present invention.

5A is a vertical cross-sectional view showing an example of a nuclear reactor core catcher in which the cooling units in FIG. 4 are arranged, FIG.
FIG. 8A is a vertical cross-sectional view showing another example in (a).

[Explanation of symbols]

1 ... Reactor building, 2 ... Reactor vessel, 3 ... Reactor core, 4 ... Space, 5
... Concrete floor, 6 ... Recess, 7, 7a ... Coolant unit, 8 ... Spherical shell, 9 ... Coolant, 10 ... Inert gas, 11
… Thin-walled part, 12… Core melt, 13… Cylindrical shell.

Claims (3)

[Claims] 1. A plurality of cooling units collectively arranged in a space provided below a reactor vessel or a reactor pressure vessel of a nuclear reactor, the cooling unit enclosing a coolant and an inert gas in a closed shell. A core catcher for a nuclear reactor, characterized in that a thin portion is formed in the shell body. 2. The nuclear reactor core catcher according to claim 1, wherein the closed shell is formed of steel into a spherical or cylindrical container. 3. A large number of thin-walled portions formed on the shell have a thickness that is destroyed by the pressure of the coolant filled in the shell and the inert gas during heating, and are dimple-shaped on at least one surface of the shell. The reactor core catcher according to claim 1, wherein the core catcher is a reactor core catcher.