JPH04258790A - Fast reactor core - Google Patents

Abstract

PURPOSE:To provide a fast reactor core having zero or negative void reactivity of sodium and a large output. CONSTITUTION:A fast reactor core is constituted of a fuel aggregate 2 loaded with a fissionable material and a void channel 1 containing a nearly cylindrical heating material 8 provided with an independent cooling material passage 9 inside and having the ratio of the heat inflow quantity from the heating material 8 against the quantity in the inner passage equal to or higher than the ratio in the fuel aggregate 2.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to fast reactors, and more particularly to a fast reactor core with improved flow rate and calorific value distribution structure 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 the fuel. Normally, sodium does not evaporate and form voids, but in the unlikely event of an accident, we have confirmed that the reactor core will be able to shut down safely even if sodium becomes voids.

[0003] In response to voiding of sodium, when the reactor core is small, the leakage of neutrons from the reactor core is large, so a negative reactivity occurs, and the reactor core is safely stopped. However, as the reactor core becomes larger, the leakage of neutrons decreases, and the reactivity when sodium voids becomes positive.Therefore, whether the core can be safely shut down depends on details including other reactivity factors. It becomes necessary to conduct a detailed analysis and confirm its safety. Therefore, if the void reactivity of sodium can be reduced, it is of great value in terms of safety design.

0004

[Problems to be Solved by the Invention] However, in terms of plant design, it is undesirable to reduce the core output to an extremely low level from the viewpoint of power generation costs. On the other hand, in order to make the reactivity of the reactor core negative when sodium voids, in the conventional design, the core power had to be reduced to 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 the above circumstances, and an object thereof is to provide a fast reactor core with zero or negative void reactivity of sodium and higher output. [Structure of the invention]

[0006]

[Means for Solving the Problems] A fast reactor core according to the present invention includes a fuel assembly loaded with fissile material and a substantially cylindrical exothermic material having an independent coolant flow path therein. The fuel assembly is characterized in that it is comprised of a void channel in which the ratio of the amount of heat inflow from the exothermic substance to the internal amount is greater than or equal to the ratio in the fuel assembly.

[0007]

[Operation] Possible causes of voiding of sodium are that the flow rate of the coolant decreases and the sodium temperature rises and boils, or that a large amount of gas mixes with the coolant outside the core and flows into the core.

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

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples 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 reactor core 7 containing fissile material, and a large number of fuel assemblies arranged above and below the core 7, including an axial blanket section 6 made of parent material and a gas plenum section 5 for accumulating fission gas. body 2 and this fuel assembly 2
It is composed of a plurality of void channels 1 which are arranged in gaps and form an internal flow path 9 in which a heating substance 8 is disposed. A blanket assembly 3 containing a parent material and a neutron shield 4 are arranged around the fast reactor core 10.

The exothermic substance 8 is made of a material that generates heat by reacting with neutrons or gamma rays leaking from the reactor core 7, and metals such as stainless steel, hafnium, and tantalum are suitable. However, the ratio of the amount of heat inflow from the heat generating substance 8 to the flow rate of coolant flowing from the lower part of the void channel internal flow path 9 is equal to or higher than the ratio of the amount of heat inflow due to nuclear fission to the flow rate in the fuel assembly 2. The calorific value of the exothermic substance 8 in the void channel 1 and the flow rate of the internal flow path are set as follows.

With the above configuration, when the coolant flow rate decreases, the internal flow path 9 of the void channel is voided first because the ratio of the heat inflow amount to the flow rate is equal to or higher than that. Simultaneously or subsequently, the fuel assembly 2 also becomes voided, but since the internal flow path 9 of the void channel is voided, the neutrons generated in the fuel assembly 4 leak from the void channel 1 in the vertical direction of the core, resulting in negative gives a reactivity effect.

Next, FIG. 2 shows an embodiment corresponding to the case where gas flows in from outside the core. The coolant inflow hole 14 of the void channel 11 is the coolant inflow hole 18 of the fuel assembly 17.
It is set higher than the vertical direction. The gas that has flowed between the upper support plate 16 that supports the core and the lower support plate 18 disposed below the upper support plate 16 is lighter than the coolant, so it accumulates under the upper support plate 16 . However, with the above configuration, this gas flows into the void channel 11 before entering the fuel assembly 17, passes through the internal orifice 15 disposed inside the void channel 11, and flows into the internal flow path 13. Turn into a void. At the same time, the outside of the exothermic substance 12 disposed around the internal flow path 13 is also voided. Subsequently, the coolant also flows into the fuel assembly 17, but the effect is similar to that in the case of the decrease in the coolant flow rate described above. As a result,
The sodium void reactivity of the core of this embodiment can be reduced to zero or negative compared to a core without void channels.

For example, when the core height is 60 cm and the core diameter is about 340 cm, the sodium void reactivity at the core height at a 365-day burnup without bond channels is about 3 $. Then, as shown in Fig. 3, a plurality of void channels 1 are arranged inside a fuel assembly 2, and a blanket assembly 3 and a neutron shielding body 4 are arranged around this 2 group of fuel assemblies. The sodium void reactivity in a core of the same size is approximately -1$ if the void channels are voided to the height of the upper shaft blanket (35 cm thick) and the fuel assemblies are voided to the height of the core; If voids are formed to 30 cm above the blanket height and the fuel assembly is voided to the core height, the cost will be approximately -3 dollars.

The arrangement of the void channels of the present invention is not limited to the above example, and the material and shape of the exothermic substance in the void channels are not limited to the above examples. That is, the void channels may be arranged so that the sodium void reactivity becomes approximately zero or negative during voiding, and the exothermic substance may be set such that the calorific value satisfies the above effects. Therefore, a channel conventionally arranged in the reactor core as a control rod channel may be changed to have the above function as a void channel.

Further, as a void generating means in the void channel, a generally cylindrical container having a cavity is arranged in the void channel so as to float vertically. Alternatively, by sealing high-pressure gas in the upper part of the void channel, etc., a void area is created at the core height or shaft blanket height so that the same effect as that of the void channel described above occurs when the coolant flow rate decreases. You may also use the method of

[0017]

According to the present invention, the sodium void reactivity of a fast reactor core can be reduced compared to a core without void channels, and safety and approval properties can be greatly improved.

[Brief explanation of the drawing]

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

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

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

[Explanation of symbols] 1, 11... Void channel 2, 17... Fuel assembly 3... Blanket assembly 4...
Neutron shielding body 5...gas plenum
6...Shaft blanket 7...Reactor core
8,12...pyrogen 9,
13...Internal flow path

Claims (1)

[Claims] Claim 1: A fuel assembly loaded with fissile material and a substantially cylindrical exothermic substance having an independent coolant passage therein, the ratio of the amount of heat inflow from the exothermic substance to the flow rate in the internal passage. A fast reactor core characterized in that it is comprised of void channels whose ratio is greater than or equal to the ratio in the fuel assembly.