JPH06222176A - Core of fast reactor - Google Patents

Abstract

PURPOSE:To provide greater outputs with a negative temperature coefficient of coolant. CONSTITUTION:A number of reactor core fuel assemblies 1, each loaded with a fissionable material, are arranged in a honeycomb and a plurality of gas-sealed assemblies 2 are disposed among the core fuel assemblies 1. Blanket fuel assemblies 3 and neutron shields 4 are arranged outside the honeycomb-shaped core fuel assemblies 1. Each of the gas-sealed assemblies 2 is blocked at its upper end with gas sealed therein and has a coolant inlet through its lower portion to allow coolant therein. As the temperature of the coolant varies, the level of the coolant varies in the vertical direction. As a result, neutron leakage increases in the direction of the axis of the core and negative reactivity is increased so that the characteristic safety of the core in the case of accidents is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of core components in a liquid metal cooled fast breeder reactor (hereinafter referred to as "fast reactor"),
The present invention relates to a fast reactor core with an improved arrangement.

[0002]

2. Description of the Related Art Generally, in a core of a fast reactor, a large number of fuel assemblies loaded with fissile materials are arranged in a honeycomb shape, and a blanket fuel assembly and a neutron shield are arranged outside the honeycomb-shaped fuel assemblies. The body is arranged and configured. Further, in a fast reactor, generally sodium is mainly used as a coolant for removing heat from the core.

Normally, sodium does not cause an abnormal temperature rise, but in the unlikely event of an accident, it has been confirmed that the core will safely shut down even if sodium rises above a prescribed temperature. There is.

As for the response when the temperature of sodium becomes high and the density becomes low, when the core is small, a large amount of neutron leaks from the core, so that a negative reactivity is introduced and the core is safely stopped.

However, when the core becomes large, the leakage of neutrons decreases, and the reactivity becomes positive when the temperature of sodium becomes high. As to whether or not the core will be safely shut down, it is necessary to perform a detailed analysis including other reactivity factors to confirm the safety.

Therefore, if the reactivity effect due to the temperature rise of sodium, that is, the temperature coefficient of the coolant can be made negative, it is very valuable in safety design.

[0007]

By the way, in view of plant design, it is not preferable from the viewpoint of power generation cost to make the core output extremely small. On the other hand, when the temperature of sodium rises, in order to make the reactivity of the core negative
It should be less than 100MWe. However,
There is a problem that the coolant temperature coefficient becomes positive when the output is increased.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a core of a fast reactor having a negative coolant temperature coefficient and a larger output.

[0009]

The present invention comprises a number of fuel assemblies loaded with fissile material and a gas encapsulation assembly disposed between these fuel assemblies, the gas encapsulation assembly comprising: It is configured to include a substantially cylindrical cavity having an enclosed gas and a coolant inflow hole therein, and the liquid level of the coolant in the cavity is changed from the upper part including the core top level to the lower part by the change of the coolant temperature. It is characterized by being

[0010]

[Function] As a cause of abnormal temperature rise of sodium,
There are cases where the coolant flow rate decreases and the sodium temperature rises, and where the reactor output rises due to the insertion of external reactivity such as withdrawal of control rods.

When the flow rate of the coolant is reduced, the temperature of the coolant around the gas-filled assembly rises, so that the enclosed gas thermally expands, and the internal liquid surface is lowered from the upper portion to the lower portion by the core top level to form a cavity.

At the same time, both the fuel assembly and the coolant temperature rise, but since the inside of the gas-filled assembly is hollow below the core height level, the neutrons generated in the fuel assembly are gas-filled assemblies. Mainly leaks in the upper direction of the core, resulting in a negative reactivity. Even when the furnace output is increased, the coolant temperature rises, so that the same effect is obtained as when the coolant flow rate is reduced.

[0013]

EXAMPLE A first example of the core of a fast reactor according to the present invention will be described with reference to FIGS. 1 and 2. 1 is a plan view of the core, and FIG. 2 is a schematic vertical sectional view of FIG.

In FIG. 1, reference numeral 1 is a core fuel assembly without marking, 2 is a gas-filled assembly with c, 3 is a blanket fuel assembly with B, and 4 is neutron shielding. The body is indicated by dots, and 5 is indicated by a control rod with P.

As shown in FIG. 2, the core fuel assembly 1 has a core portion 6 containing a fissionable material in the central portion, and this core portion 6
And an axial blanket portion 7 made of a parent substance, and a gas plenum portion 8 for accumulating fission gas above and below the axial blanket portion 7.

As shown in FIG. 2, the gas-filled assembly 2 has an upper end sealed with a sealed gas 9 inside, and a coolant inlet hole 10 provided at a lower portion thereof, and an internal coolant 11 through which the coolant flows. It consists of what you have. Note that reference numeral 12 indicates a liquid level at normal times.

A gas 9 enclosed inside the core fuel assembly 1
A plurality of gas-filled assemblies 2 each containing Al, and a blanket assembly 3 containing a parent substance outside the core fuel assembly 1.
And the neutron shield 4 is surrounded.

The enclosed gas 9 is preferably an inert gas such as argon gas, but is not particularly limited. However, the coolant inlet hole 10
Due to the pressure of the coolant flowing in from the liquid level, it is higher in the normal state than the core apex level, and in the case of an accident such as a decrease in the flow rate or an increase in the reactor output, the amount is reduced by the volume increase due to the temperature rise of the enclosed gas And the internal shape of the gas-filled assembly 2 is set.

With the above construction, in the event of a coolant flow rate reduction accident, the hollow portion expands downward in the gas-filled assembly. At the same time, the coolant temperature also rises in the core fuel assembly 1, but since the upper part of the internal coolant 11 of the gas-filled assembly is hollow, neutrons generated in the core fuel assembly 1 are emitted from the gas-filled assembly 2. Leaks toward the upper part of the core, giving a negative reactivity effect.

The height of the liquid surface of the internal coolant 11 is usually higher than the axial blanket portion 7, and the amount of filled gas and the internal shape of the gas filled assembly 2 are set so as to be in the vicinity of the center of the core in the event of an accident. Set it arbitrarily. This can increase the negative reactivity effect, but there is no particular limitation on the amount and shape of the enclosed gas.

For example, in the case of a flat core having a core height of 100 cm and a core diameter of about 300 cm, the coolant temperature coefficient after 365 days of combustion when the gas-filled assembly 2 is not arranged is about 5.1.
× 10 ⁻⁶ ΔK / K / ° C. On the other hand, when the gas-filled assemblies are arranged as shown in FIG. 1, the coolant temperature coefficient in the cores of the same size is such that the liquid level in the gas-filled assemblies 2 is 90 ° C. from the core top height level. A negative reactivity coefficient of about 6.9 × 10 ^-6 ΔK / K / ° C is obtained when the enclosed gas expands due to the temperature rise and becomes hollow up to a level 10 cm below the core top.

Next, a second embodiment of the core of the fast reactor according to the present invention will be described with reference to FIGS. 3 and 4. In this embodiment, the same parts as those in FIGS. 1 and 2 are designated by the same reference numerals, and the description of the overlapping parts will be omitted.

The second embodiment differs from the first embodiment in that the gas-filled assemblies 2 are arranged in the central portion of the core as shown in FIG. 3, and the control rods 5 are arranged adjacent to each other. The gas-filled assembly 2 is then arranged, and the gas-filled assembly is arranged in an annular shape.

According to the second embodiment, it is possible to promote the effect of neutron leakage toward the center of the core at the time of an accident and utilize the neutron leakage toward the control rod 5.

In this case, as shown in FIG. 4, a gas plenum portion 8 may be arranged between the axial blanket portion 7 and the core portion 6 of the core fuel assembly 1, or the axial blanket portion 7 may be deleted. This makes it easier for the leaked neutrons in the upper direction to leak through the gas plenum portion 8. In the figure, reference numeral 13 indicates the liquid level at the time of the accident.

In the present invention, the arrangement of the gas-filled aggregate is not limited to the above embodiment, and the structure of the gas-filled aggregate is not limited to the above example. That is, the gas-filled assembly may be arranged so that the temperature coefficient of the coolant becomes negative in the event of an accident, and its shape and configuration may be set so as to satisfy the above-mentioned action.

For example, in the upper cavity of the gas filled assembly, a gas temperature raising fin connected from the inside to the outer cylindrical metal portion is arranged so as to promote the rise of the temperature of the filled gas. Alternatively, an aggregate lifting preventing weight is arranged in the gas filled assembly for preventing the gas filled assembly from rising due to the pressure of the coolant. Hafnium is used as the weight.

Further, in order to detect the leakage of the enclosed gas due to the damage of the aggregate, a structure such as enclosing the tag gas conventionally used for detecting the damage of the fuel pin can be considered.

[0029]

According to the present invention, as the temperature of the core rises, the temperature of the enclosed gas rises, and the liquid level of the coolant in the gas-enclosed assembly is lowered to below the core height top level. Neutron leakage increases and negative reactivity is inserted.
Therefore, the intrinsic safety in case of a core accident is improved.

[Brief description of drawings]

FIG. 1 is a plan view schematically showing a first embodiment of a fast reactor core according to the present invention.

FIG. 2 is a vertical sectional view schematically showing the core of the fast reactor in FIG.

FIG. 3 is a plan view schematically showing a second embodiment of the core of the fast reactor according to the present invention.

FIG. 4 is a longitudinal sectional view schematically showing the core of the fast reactor in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Core fuel assembly, 2 ... Gas encapsulation assembly, 3 ... Blanket fuel assembly, 4 ... Neutron shield body, 5 ... Control rod, 6 ... Core part, 7 ... Axial blanket part, 8 ... Gas plenum part, 9 … Enclosed gas, 10… Coolant inflow hole, 11… Internal coolant, 12… Liquid level at normal time, 13… Liquid level at accident.

Claims (1)

[Claims] 1. A multiplicity of fuel assemblies loaded with fissile material, and a gas-filled assembly disposed between these fuel assemblies, wherein the gas-filled assembly has a sealed gas and a coolant therein. A high speed characterized by including a substantially cylindrical cavity having an inflow hole, in which the liquid level of the coolant changes from the upper part including the core top level to the lower part due to the change of the coolant temperature The core of the furnace.