JP2911058B2 - Fast reactor core - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

 [Object of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fast reactor, and more particularly, to a fast reactor having an improved distribution structure of flow rate and calorific value of core components.

[0002]

2. Description of the Related Art Generally, the core of a fast reactor is composed of a large number of fuel assemblies loaded with fissile material, and sodium is mainly used as a coolant for removing heat from fuel. Normally, sodium does not evaporate and form voids, but assuming an accident, it has been confirmed that the core can be safely stopped even if sodium is voided.

As a response when sodium is voided, when the reactor core is small, neutrons leak from the reactor core greatly, so that a negative reactivity enters and the reactor core shuts down safely. However, the larger the core, the less neutron leakage,
The reactivity when sodium is voided is positive, and it is necessary to confirm the safety by performing a detailed analysis including other reactivity factors to determine whether or not the core shuts down safely. Therefore, if the void reactivity of sodium can be reduced, it is very valuable in terms of safety design.

[0004]

However, in terms of plant design, it is not preferable from the viewpoint of power generation cost to make the core power extremely small. On the other hand, in order to make the reactivity of the core when sodium is voided negative, in the conventional design, the core power had to be about 100 MWe or less. However, when the output is increased, a problem arises in that the void reactivity of sodium becomes positive.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a fast reactor core having a larger output with zero or negative void reactivity of sodium. [Configuration of the Invention]

[0006]

SUMMARY OF THE INVENTION A fast reactor core according to the present invention includes a fuel assembly loaded with fissile material, and a substantially cylindrical heating material having an independent coolant passage therein. The ratio of the heat inflow from the heat generating substance to the internal flow rate is equal to or higher than the ratio in the fuel assembly.

[0007]

The voiding of sodium may be caused by a decrease in the flow rate of the coolant, an increase in the temperature of the sodium and boiling, or a case in which a large amount of gas is mixed in the coolant outside the core and flows into the core.

In the above-described fast reactor core according to the present invention, when the flow rate of the coolant is reduced, the internal flow path of the void channel is first voided because the ratio of the heat inflow to the flow rate is equal to or more than that. Simultaneously or subsequently, the fuel assembly is also voided, but the neutrons generated in the fuel assembly leak in the vertical direction of the core from the void channel because the internal flow path of the void channel is voided, resulting in a negative reactivity. Become. When gas flows in from outside the core, the gas flows in from the coolant inflow hole of the void channel before the fuel assembly, and the same effect as in the case of a decrease in the coolant flow rate is obtained.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view showing one embodiment of the present invention.

The fast reactor core 10 includes a core portion 7 containing a fissile material, a shaft blanket portion 6 made of a parent material above and below the core portion 7, and a gas plenum portion 5 for storing fission gas.
, A plurality of fuel assemblies 2 disposed therein, and an internal flow passage 9 disposed in a gap between the fuel assemblies 2 and having a heating substance 8 disposed therein.
Are formed from a plurality of void channels 1 in which. Around the fast reactor core 10, a blanket assembly 3 containing a parent material and a neutron shield 4 are arranged.

The exothermic substance 8 is made of a material which reacts with neutrons or gamma rays leaking from the reactor core 7 to generate heat, and is suitably made of a metal such as stainless steel, hafnium, and tantalum. However, the ratio of the heat inflow from the heating material 8 to the flow rate of the coolant flowing from the lower part of the void channel internal flow path 9 is equal to or greater than the ratio of the heat inflow due to fission to the flow rate in the fuel assembly 2. The heat value of the heat generating substance 8 in the void channel 1 and the flow rate of the internal flow path are set.

With the above configuration, when the flow rate of the coolant is reduced, the internal flow path 9 of the void channel is first voided because the ratio of the heat inflow rate to the flow rate is equal to or more than that. at the same time,
Alternatively, the fuel assembly 2 is also voided, but the neutrons generated in the fuel assembly 4 leak from the void channel 1 in the vertical direction of the core due to the voiding in the internal flow path 9 of the void channel, resulting in a negative reaction. Give a degree effect.

FIG. 2 shows an embodiment corresponding to the case where gas flows from outside the core. The coolant inlet hole 14 of the void channel 11 is set above the coolant inlet hole 18 of the fuel assembly 17 in the vertical direction. The gas flowing between the upper support plate 16 supporting the core and the lower support plate 18 disposed below the upper support plate 16 is lighter than the coolant, and accumulates in the lower portion of the upper support plate 16. However, with the above configuration,
This gas flows into the void channel 11 before flowing into the fuel assembly 17, passes through the internal orifice 15 provided inside the void channel 11, and voids the inside of the internal flow channel 13. At the same time, the outside of the heat generating substance 12 disposed around the internal flow path 13 is also voided. Subsequently, the fuel flows into the fuel assembly 17 but has the same operation as that in the case of the above-described coolant flow rate reduction. As a result, the sodium void reactivity of the core of the present embodiment can be reduced to zero or negative as compared with the core having no void channel.

For example, the core height is 60 cm and the core diameter is about 34.
At 0 cm 2, the core height sodium void reactivity at 365 days burnup without bond channels is about 3 °. As shown in FIG. 3, a plurality of void channels 1 are arranged inside the fuel assembly 2 as shown in FIG. 3, and a blanket assembly 3 and a neutron shielding body 4 are arranged around the fuel assembly 2 group. The sodium void reactivity in a core of the same size is approximately -1 mm when the void channel is voided to the height of the upper shaft blanket (thickness: 35 cm) and the fuel assembly is voided to the height of the core. When the fuel assembly is voided up to 30 cm above the blanket height and the fuel assembly is voided up to the core height, it becomes about -3 mm.

The arrangement of the void channels according to the present invention is not limited to the above example, and the exothermic substance in the void channels is not limited to the material and shape of the above example.
In other words, the void channels may be arranged so that the reactivity of sodium voids becomes substantially zero or negative at the time of voids, and the heat generating substance may be set so that the calorific value satisfies the above-mentioned action. Therefore, as the void channel, a channel conventionally disposed in the core as a control rod channel may be changed to have the above-described operation.

Further, as a void generating means in the void channel, a substantially cylindrical container having a cavity in the void channel is arranged so as to float up and down. Alternatively, a void region is generated in the core height portion or the shaft blanket height portion so that the same operation as the above-described operation of the void channel occurs when the flow rate of the coolant is reduced by, for example, sealing high-pressure gas in the upper portion of the void channel. You may use the method of making it.

[0017]

According to the present invention, the sodium void reactivity of the fast reactor core can be reduced as compared with the core having no void channel, and the safety and the permitting properties can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a fast reactor core according to one embodiment of the present invention.

FIG. 2 is a perspective view showing a void channel and a fuel assembly shown in FIG. 1;

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

[Explanation of symbols]

 1, 11: void channel 2, 17: fuel assembly 3: blanket assembly 4: neutron shield 5: gas plenum 6: shaft blanket 7: core 8, 12, heating substance 9, 13: internal flow path

Claims (1)

(57) [Claims] 1. A fuel assembly loaded with fissile material,
A void channel having a substantially cylindrical heating substance having an independent coolant flow path therein and having a ratio of heat inflow from the heating substance to a flow rate in the internal flow path being equal to or higher than the ratio in the fuel assembly. A fast reactor core comprising: