JPH0545485A - Fast reactor core - Google Patents

Abstract

PURPOSE:To obtain a core of a fast reactor which can attain a larger power while the void reactivity of the core by a coolant is kept zero or negative. CONSTITUTION:A core of a fast reactor is constructed of a disk-shaped upper nuclear fuel substance 26 provided on the upper side from the center in the axial direction of the core, a disk-shaped nuclear fuel substance 28 provided on the lower side from the center in the axial direction of the core and a disk- shaped lower gas plenum space 29 located between the upper nuclear fuel substance and the lower nuclear fuel substance and accommodating a fissile gas produced from the nuclear fuel substances.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fast reactor core using liquid metal as a coolant, and more particularly to a fast reactor core having an improved fuel assembly.

[0002]

2. Description of the Related Art A fast reactor using a liquid metal as a coolant constitutes a core by loading a large number of fuel assemblies filled with a nuclear fuel material, and a sodium coolant mainly removes heat from the fuel. Used as. In this liquid metal cooled fast reactor, when the flow rate of the coolant decreases for some reason, the temperature of the coolant increases, the density of the coolant decreases, and the reactivity increases.

The reactivity of a fast reactor depends on the power output of a nuclear reactor, and is negative in a small reactor, but becomes positive in a medium-sized reactor or a large reactor, and the reactor power is increased due to a decrease in coolant density. There is a fear.

In a fast reactor, sodium, which is a coolant, usually does not evaporate to form voids. However, in the unlikely event of an accident, even if sodium forms voids, the reactor can be safely shut down and the core It is designed to maintain safety.

As a response of the reactor when sodium, which is a coolant, is voided, when the core is small, neutron leakage from the core is large, so that the reactivity becomes negative as described above. The core can be safely stopped.

On the other hand, when the core of a fast reactor becomes large, the leakage of neutrons from the core becomes small and the reactivity when sodium, which is a coolant, becomes void becomes positive.
In this positive reactivity state, it is necessary to confirm the safety of the core by performing a detailed analysis including other reactivity factors to determine whether or not the core can be safely stopped.

The positive reactivity of sodium as a coolant can be reduced by increasing the neutron leakage from the core and softening the neutron spectrum. In order to suppress and reduce the reactivity, measures have been taken to soften the neutron spectrum by loading a neutron absorbing substance in the core or by loading a neutron moderator such as beryllium or hydrogen zirconium.
In any case, if the void reactivity of sodium, which is a coolant, becomes small, the safety and reliability of the core will be further improved, and it will be of great value in the safety design of the reactor.

[0008]

In a nuclear power plant such as a fast reactor, it is not desirable from the viewpoint of core safety in designing the plant that the core power is extremely small in terms of power generation cost.

Further, even if sodium, which is the coolant, should be voided, in order to make the reactivity of the core negative, the reactor output must be a small reactor of, for example, about 100 MWe. There is a problem that the voiding reactivity of sodium becomes positive when the core power is exceeded.

The present invention has been made in consideration of the above points, and provides a fast reactor core capable of obtaining a core having a larger output while maintaining the void reactivity of the core by the coolant to be zero or negative. The purpose is to do.

[0011]

In order to achieve the above object, in the present invention, a disk-shaped upper nuclear fuel material provided above the axial center of the core and below the axial center of the core are provided. A cylindrical core central axis region having a disk-shaped lower nuclear fuel material and a disk-shaped gas plenum space for accommodating fissionable gas generated from the nuclear fuel material between the upper nuclear fuel material and the lower nuclear fuel material And an annular diameter blanket region in which a radial blanket fuel assembly is annularly loaded on the outer peripheral side of the core center axis region, and an annular neutron shielding region in which a neutron shield is loaded outside the diameter blanket region. A fast reactor core consisting of

Further, in the present invention, a disc-shaped upper nuclear fuel material provided above the axial center of the core, a disc-shaped lower nuclear fuel material provided below the axial direction of the core, and the upper nuclear fuel. Material and the lower core nuclear fuel material, and a cylindrical core central axis region having a disc-shaped coolant flow channel region, and a radial blanket fuel assembly is annularly formed on the outer peripheral side of the core central axis region. A fast reactor core comprising a loaded annular blanket region and an annular neutron shield region loaded with a neutron shield outside the radial blanket region.

[0013]

According to the present invention, the disk-shaped upper nuclear fuel material is provided above the axial center of the core, and the disk-shaped lower nuclear fuel material is provided below the axial center of the core. A disc-shaped gas plenum space containing a fissionable gas generated from the nuclear fuel material is set between the upper nuclear fuel material and the lower nuclear fuel material.

Therefore, when sodium, which is the coolant, is voided for some reason, the neutrons generated from the fissile material of both fuel elements are
Mainly leaks in the radial direction. This leakage reduces or renders the reactivity negative.

Void reactivity can be reduced and safety and reliability can be further improved, as compared with a core loaded with a fuel assembly in which fuel elements are arranged in one stage in the axial direction.

A disc-shaped coolant passage region may be provided between the upper nuclear fuel material and the lower nuclear fuel material. Due to this coolant channel region, the core particles generated from the fissile material mainly leak in the radial direction. This leakage can reduce or make the reactivity negative.

[0017]

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

FIG. 1 is a core configuration diagram showing an example of a liquid metal cooling type fast reactor core provided with a core according to the present invention, which is cut into a fan shape. At the center of the core, a column-shaped core central axis region 22 is formed in which a large number of fuel assemblies filled with nuclear fuel material are loaded. On the outer peripheral side of the core central axis region 22, an annular diameter blanket region 24 in which the radial blanket fuel assemblies are annularly loaded is formed. An annular neutron shield region 25 loaded with a neutron shield is formed outside the radial blanket region. The core central axis region 22 is divided into upper and lower sides with the axial center of the core as a boundary.

A disc-shaped upper nuclear fuel material 26 is provided above the axial center of the core, and a disc-shaped upper gas plenum space 27 containing fissionable gas generated from the nuclear fuel material above the disc-shaped upper nuclear fuel material 26.
Have. A disk-shaped lower nuclear fuel material 28 is formed below the axial center of the core, and a disk-shaped lower gas plenum space 29 containing fissionable gas generated from the nuclear fuel material is formed above the disk-shaped lower nuclear fuel material 28.

FIG. 2 is a vertical cross-sectional view showing a fuel assembly forming the core central axis region 22 of the fast reactor core according to the present invention. FIG. 3 is an enlarged cross-sectional view showing the XX arrow direction of FIG. The fuel assembly is formed of a fuel element bundle 3 in which fuel elements 2 are arranged in a hexagonal regular shape in a regular hexagonal tubular trumpet tube 1. A coolant passage 8 is formed by the space formed by the inner wall of the trumpet tube 1 and the outer wall of the fuel element 2.

The coolant flows out through the coolant inlet 5 in the lower part of the fuel assembly, through the entrance nozzle 6, the coolant passage 8 and the inside of the handling head 4. FIG. 4 is a vertical cross-sectional view showing the fuel element 2 that constitutes the fuel element bundle 3. The fuel element 2 is an upper fuel element 30 and a lower fuel element 40 that are vertically connected.

The upper fuel element 30 is constructed by sealing both ends of a cladding tube 33 containing a nuclear fuel material 31 and a gas plenum region 32 containing a fission product gas above it with end plugs 34 and 35. The lower fuel element 40 has a structure similar to that of the upper fuel element 30, and is constructed by sealing both ends of a cladding tube 43 containing a nuclear fuel material 41 and a gas plenum region 42 above it with end plugs 44 and 45. There is. Both fuel elements 30, 40 are the upper fuel element 30
The lower end plug 35 and the upper end plug 44 of the lower fuel element 40 are joined and integrated. Next, the operation of this embodiment having such a configuration will be described. The upper fuel element 30 and the lower fuel element 40 are vertically connected. The gas plenum space 42 in the lower fuel element 40 is arranged on the connection side of both fuel elements 30, 40.

When sodium, which is the coolant, is voided for some reason, the nuclear fuel material of both fuel elements 30, 40
Neutrons are generated from 31, 41, but the gas plenum space
Break into 42. The neutrons that have entered the space 42 mainly leak in the radial direction, and the reactivity decreases or becomes negative.

The selection of the length of the gas plenum space 42 located between the fuel elements 30 and 40 is a major factor in determining the void reactivity. That is, as the gas plenum space is lengthened, the rate of neutron leakage increases and the void reactivity decreases, but when the length exceeds a certain level, the effect saturates. On the other hand, if the gas plenum space is lengthened, the size of the core becomes larger because the fuel assembly becomes longer. Therefore, the length of the gas plenum space is selected based on the balance between the void reactivity reduction target and the fuel assembly increase suppression.

According to such an embodiment, the neutrons generated from the nuclear fuel material are leaked in the radial direction from the gas plenum region by connecting the fuel elements and providing the gas plenum space in the intermediate portion in the axial direction. As a result, the reactivity can be reduced or a negative reactivity can be provided. As a result, the void reactivity can be remarkably reduced as compared with the core loaded with the fuel assembly in which the fuel elements are arranged in only one stage in the axial direction, and the safety and reliability of the fast reactor core are further improved. be able to. Next, another embodiment of the present invention will be described with reference to FIGS.

FIG. 5 shows the fuel element of the second embodiment. The fuel element 2 is composed of an upper fuel element 30 in which a gas plenum space 32 is arranged below a nuclear fuel material 31 in the upper part. In the lower part, the gas plenum space above the nuclear fuel material 41.
It consists of a lower fuel element 40 having 42. Both fuel elements 30 and 40 are connected and integrated. In this embodiment, two gas plenum spaces 32, 42 are provided between the nuclear fuel substances 31, 41 of both fuel elements 30, 40. This will increase the axial extent of neutron leakage in the radial direction. When the coolant is boiling or when the coolant is lost such as when the flow rate of the coolant is reduced, it is possible to increase the leakage of neutrons from the core in the radial direction and further increase the reactivity reduction amount.

FIG. 6 shows a fuel assembly of the third embodiment. This fuel assembly consists of an upper fuel element 30 and a lower fuel element.
Assembled from 40. A coolant flow passage region 10 is formed between the fuels 30 and 40. As shown in FIG. 7, the upper fuel element 30
Are formed from a nuclear fuel material 31 and a gas plenum space 32 above it. As shown in FIG. 8, a lower fuel element 40 is assembled from a nuclear fuel material 41 and a gas plenum space 42 below the nuclear fuel material 41. In this embodiment, the nuclear fuel material of both fuel elements 30, 40 is
The coolant flow path region 10 is arranged between 31 and 41. Although neutrons are generated from the nuclear fuel materials 31 and 41, the coolant flow passage region
Penetrates 10 and leaks mainly in the radial direction. Due to this leak,
The degree of repulsion decreases or becomes negative. FIG. 9 is a vertical sectional view of a fuel element 2 showing a fourth embodiment according to the present invention.

The upper nuclear fuel material 31 is arranged in the upper part and the lower nuclear fuel material 41 is arranged in the lower part, and a gas plenum space 42 is formed between the both nuclear fuel materials 31, 41. The upper part, the middle part of the cladding tube 43,
The lower part is configured by sealing with end plugs 34, 46, 45, respectively.
In this embodiment, a gas plenum space 42 is provided at a height of the single fuel element 2 in the middle and high areas. Neutrons leak in the radial direction via the plenum space 42.

Therefore, when the coolant is lost, such as when the coolant is boiling or when the flow rate of the coolant is reduced, neutrons from the nuclear fuel materials 31 and 41 can be leaked in the radial direction, which can greatly contribute to the reduction of the reactivity.

[0030]

As described above, according to the present invention,
The sodium void reactivity due to the coolant can be reduced, a larger power reactor core can be obtained, and even a large reactor can sufficiently contribute to the safety and soundness of the reactor.

[Brief description of drawings]

FIG. 1 is a core configuration diagram showing a first embodiment of a fast reactor core according to the present invention by cutting it into a fan shape.

FIG. 2 is a vertical sectional view showing a first embodiment of a fuel assembly for a fast reactor according to the present invention.

FIG. 3 is an enlarged cross-sectional view showing the direction of arrow XX in FIG.

FIG. 4 is a vertical sectional view showing a first embodiment of a fuel element of a fast reactor according to the present invention.

FIG. 5 is a vertical sectional view showing a second embodiment of the fuel element according to the present invention.

FIG. 6 is a vertical sectional view showing a third embodiment of the fuel assembly of the fast reactor according to the present invention.

7 is a vertical cross-sectional view showing the upper fuel element of FIG.

FIG. 8 is a vertical cross-sectional view showing the lower fuel element of FIG.

FIG. 9 is a vertical sectional view showing a fourth embodiment of the fuel element of the fast reactor according to the present invention.

[Explanation of symbols]

10 ... Coolant flow passage area 22 ... Core center axis area 24 ... Diameter blanket area 25 ... Neutron shield area 26 ... Upper nuclear fuel material 28 ... Lower nuclear fuel material 29 ... Lower gas plenum space

Claims (2)

[Claims] 1. A disc-shaped upper nuclear fuel material provided above the axial center of the core, a disc-shaped lower nuclear fuel material provided below the axial center of the core, the upper nuclear fuel material, and a lower portion. A cylindrical core central axis region having a disc-shaped gas plenum space for accommodating a fissile gas generated from the nuclear fuel material, and a radial blanket fuel assembly on the outer peripheral side of the core central axis region. A fast reactor core consisting of an annular blanket region loaded with an annular shape and an annular neutron shield region loaded with a neutron shield outside the diameter blanket region. 2. A disc-shaped upper nuclear fuel material provided above the axial center of the core, a disc-shaped lower nuclear fuel material provided below the axial direction of the core, the upper nuclear fuel material and the lower nuclear fuel. A cylindrical core central axis region having a disc-shaped coolant flow passage region set between substances, and an annular shape in which a radial blanket fuel assembly is annularly loaded on the outer peripheral side of the core central axis region. Fast reactor core consisting of a diameter blanket region and a ring-shaped neutron shielding region loaded with a neutron shield outside the diameter blanket region.