JPH06258481A - Fast breeder reactor - Google Patents

Abstract

PURPOSE:To prevent the activation of a secondary sodium coolant without making a reactor vessel large in size and thereby to reduce exposure of an operator by providing a neutron shield inside a connecting pipe provided by boring in a core support plate. CONSTITUTION:An entrance nozzle 4 is provided in the lower end part of a fuel assembly and fitted in a connecting pipe 6 provided by boring in a core support plate 5 and it supports the fuel assembly. A radial shield 3 holds a shield 20 inside and shields 21 and 22 are provided integrally in upper and lower inside parts thereof. A neutron shield 10 is constructed by providing a shielding material 10a inside the nozzle 4 and a shielding material 10b inside the connecting pipe 6. The shield 10 absorbs and reduces neutrons permeating through an axial shield provided in the lower part of a core so that they may not reach an intermediate heat exchanger. By a simplified structure, in this way, activation of a secondary sodium coolant can be prevented and thereby an improvement can be attained in reduction of exposure of an operator at the time of periodic inspection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fast breeder reactor having an intermediate heat exchanger, and more particularly to a neutron shield disposed inside the fast breeder reactor.

[0002]

2. Description of the Related Art Generally, in a fast breeder reactor, various neutron shields are provided from the viewpoint of preventing activation of structures and sodium coolant and exposure of workers involved in the fast breeder reactor due to the nature of handling fast neutrons. Is installed. However, although this neutron shield is a necessary structure in the fast breeder reactor, it also affects the design size and quantity of the entire fast breeder reactor depending on the location where it is placed, so that the conventional efficient layout is a design requirement. It was one.

FIG. 3 shows a conventional example of a fast breeder reactor.
The core 1 supported by the core support plate 5 is housed in the center of the reactor vessel 9. In order to remove the heat generated in the core 1, the primary sodium coolant 12 is used as the main circulation pump 1
3 through the high pressure plenum 14 to the core 1. The primary sodium coolant 12 that has cooled the core 1 is guided to the intermediate heat exchanger 7. This intermediate heat exchanger 7 is connected to an external pipe (not shown) and a steam generator (not shown),
A secondary cooling system is formed in combination with a secondary sodium coolant that flows inside and serves as a heat transport medium. In this intermediate heat exchanger 7, the primary sodium coolant 12 that has cooled the core 1 and has reached a high temperature exchanges heat with the secondary sodium coolant in the secondary cooling system, is removed of heat, and then is recirculated to the main circulation. It is guided to the core 1 by the pump 13.

On the other hand, in the core 1, fast neutrons are generated by a nuclear reaction, and in order to prevent activation of the structure by the fast neutrons, an axial shield 2 and a radial shield are provided around the core 1. A body 3 is arranged. Also,
In the intermediate heat exchanger 7, the secondary sodium coolant is circulated in order to remove the heat of the primary sodium coolant 12 that has cooled the core 1 as described above, and captures and absorbs neutrons leaking from the core 1. There is a risk that it will be activated. When this secondary sodium coolant is activated,
It is not desirable from the viewpoint of protection of workers from exposure during maintenance and inspection of the external piping (not shown) of the secondary cooling system and the steam generator (not shown). Therefore, it is necessary to prevent activation of the secondary sodium coolant, and the local shield 8 is arranged around the lower portion of the intermediate heat exchanger 7.

In the neutron shield of the fast breeder reactor configured as described above, the fast neutrons generated from the core 1 are provided around the core 1 around the axial shield 2, the radial shield 3 and the intermediate heat exchanger 7. It was shielded by the local shield 8.

With reference to FIG. 4, the detailed structure of the axial shield 2 will be described while showing the fuel assembly 16 constituting the core 1. The fuel assembly 16 is formed by assembling a plurality of fuel rods 15, and the entrance nozzle 4 is installed at the lower end portion thereof. The entrance nozzle 4 is fitted into a connecting pipe 6 formed in the core support plate 5 to support the fuel assembly 16. The axial shield 2 is formed as an upper shield 2a and a lower shield 2b at the upper and lower inner portions of the fuel assembly 16, respectively. In the figure, arrows A and B
Indicates the flowing direction of the coolant.

[0007]

In the above configuration,
Since the axial shield is integrally formed on the upper and lower parts of the fuel assembly, the installation length thereof directly affects the overall length of the fuel assembly. At the time of periodic inspection, it is necessary to remove the fuel assembly from the upper part of the core, move it inside the reactor vessel while submerged in the primary sodium coolant, and replace it. For this reason, the overall length affected the internal height of the reactor vessel.

On the other hand, in the radial direction around the core, the dimensions of the main circulation pump and the intermediate heat exchanger dominate the inner diameter of the reactor vessel, so the radial shield has a sufficient thickness for shielding. It was possible to have

From the above, the axial shield is restricted in the design dimensions of the reactor vessel in its design size as compared with the radial shield. Therefore, there is a high possibility that neutrons that reach the intermediate heat exchanger will reach through the axial shield, and in order to further shield the neutrons, there is a local shield at the bottom of the intermediate heat exchanger as described above. It was provided.

However, since this local shield is disposed at a position corresponding to the outlet of the primary sodium coolant in the intermediate heat exchanger, the local shield secures the flow path of the primary sodium coolant. However, it was necessary to construct a shield, and its structure was complicated.

On the other hand, in order to strengthen the axial shield installed in the lower part of the core to suppress neutrons reaching the lower part of the intermediate heat exchanger, it is necessary to increase the installation size of the axial shield. is there. As a result, as described above, it was necessary to extend the inner height of the reactor vessel, resulting in an increase in the quantity of the reactor vessel. Furthermore, since the axial shield is provided inside the fuel assembly, it is necessary to extend the axial length of the fuel assembly itself. Therefore, it is necessary to increase the size of the fuel assembly handling device.

The present invention has been made in consideration of the above conventional circumstances, and an object thereof is to provide an efficient shielding structure and to activate the secondary sodium coolant without increasing the size of the reactor vessel. (EN) Provided is a neutron shield which can be prevented and thus can reduce the exposure of workers.

[0013]

In order to achieve the above object, in the present invention, a connecting pipe which is bored in a core support plate which supports a core and through which a radial shield surrounding the core is inserted. A neutron shield for a fast breeder reactor, characterized in that a neutron shield is provided inside.

[0014]

In the fast breeder reactor having the above structure, neutrons that have passed through the axial shield at the lower part of the core are shielded by the neutron shield arranged inside the connecting pipe.

As a result, the neutrons reaching the intermediate heat exchanger are suppressed and reduced, and the local shield around the intermediate heat exchanger can be made simpler than before, and at the same time, the activation of the secondary sodium coolant can be reduced. it can. Therefore, it is possible to reduce the exposure dose of the worker during the periodic inspection.

[0016]

EXAMPLE A first example of a neutron shield for a fast breeder reactor according to the present invention will be described below with reference to FIGS. 1 and 2.

In FIG. 1, the same parts as those in FIG. 3 showing the conventional example are designated by the same reference numerals, and the description of the configuration thereof will be omitted. As shown in FIG. 1, the neutron shield 10 of the fast breeder reactor of the present invention is disposed below the radial shield 3 and below the core support plate 5.

The detailed structure of the neutron shield 10 will be described with reference to FIG. In FIG. 2, the radial shield 3 accommodates the shield 20 inside, and the shield 2 is provided on the upper and lower inner portions.
1, 22 are arranged integrally. The neutron shield 10 is constructed by disposing a shield 10a inside the entrance nozzle 4 provided below the radial shield 3 and a shield 10b inside the connecting pipe 6 adjacent thereto. Has been done. The radial shield 3 generates heat by absorbing neutrons, but its calorific value is so small that it can be ignored as compared with the fuel assembly. Therefore, the decrease in the cooling capacity due to the increase in the pressure loss of the primary sodium coolant 12 due to the installation of the neutron shield 10 in the entrance nozzle 4 and the connecting pipe 6 has no effect.

In the neutron shield 10 thus constructed, the neutrons that have passed through the axial shield 2 installed below the core 1 can be absorbed so as not to reach the intermediate heat exchanger 7.

At this time, since the neutron shield is not installed in the region below the neutron shield 10, the neutrons that have passed through the axial shield 2 pass through the region below the neutron shield 10 to generate intermediate heat. It is possible to reach the exchanger 7. However, when it exists in such a region and penetrates the neutron transmission path shown by the arrow 11 in FIG. 1, the neutron transmission distance from the axial shield 2 to the intermediate heat exchanger 7 becomes long.

For example, in the case of a fast breeder reactor with an electric output of 300,000 Kw, if the conventional neutron transmission distance is 3 m, the neutron transmission distance in the case of the present invention is about 5 m. In the neutron transmission path 11 that passes through the axial shield 2 and further below the neutron shield 10, the primary sodium coolant 12
Is filled. Therefore, the effect of the neutron shielding by the primary sodium coolant 12 is promoted with the increase of the neutron transmission distance, and in the case of the present invention, the neutrons reaching the intermediate heat exchanger 7 are about 1% of the conventional values. . From the above, the neutron shield of the fast breeder reactor of the present invention can absorb and reduce the neutrons that reach the intermediate heat exchanger 7.

[0022]

As described above, in the fast breeder reactor according to the present invention, the neutron shield is provided inside the connecting pipe which is bored in the core support plate and through which the radial shield is inserted. The activated structure can prevent activation of the secondary sodium coolant. Therefore, it is possible to improve the reduction of the exposure of the worker during the periodic inspection.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of a fast breeder reactor according to the present invention.

FIG. 2 is an enlarged vertical sectional view showing the structure of the neutron shield shown in FIG.

FIG. 3 is a vertical cross-sectional view showing a conventional example of a fast breeder reactor.

FIG. 4 is an enlarged vertical sectional view of the neutron shield shown in FIG.

[Explanation of symbols]

1 ... Core 2 ... Axial shield 3 ... Radial shield 4 ... Entrance nozzle 5 ... Core support plate 6 ... Communication pipe 7 ... Intermediate heat exchanger 8 ... Local shield 9 ... Reactor vessel 10 ... Neutron shield 10a , 10b ... Shielding material 11 ... Neutron transmission path 12 ... Primary sodium coolant 13 ... Main circulation pump 14 ... High pressure plenum 15 ... Fuel rod 16 ... Fuel assembly 20, 21, 22 ...
Shielding material

Claims (1)

[Claims] 1. A core which is cooled by a liquid metal coolant and is provided with a radial shield around the core, a core support plate which supports the core, and a primary sodium coolant which exchanges heat with the core through the core. In a fast breeder reactor having an intermediate heat exchanger that transfers heat to a sub-sodium coolant, a neutron shield is provided inside a connecting pipe that is bored in the core support plate and through which the radial shield is inserted. Fast breeder reactor.