JPH08297186A - Core for fast reactor - Google Patents

Abstract

PURPOSE: To suppress the fluctuation of the liquid level, suppress the fluctuation of the reactor output, and maintain the integrity of a structural material. CONSTITUTION: A gas-sealed assembly 1a has sodium 2 and filler gas 3 in a wrapper tube 6, has an upper shielding body 7 and a handling head 8 at the upper section, and has an entrance nozzle formed with a weight lower shielding body 9 and an orifice 5 at the lower section. Multiple gas-sealed assemblies la containing an entrance nozzle 20 having a small-diameter inflow port of sodium 2 and an entrance nozzle 21 having a large-diameter inflow port are formed. The gas-sealed assemblies 1a are arranged between a fuel assembly in a core to constitute the core for a fast reactor. Since the gas-filled assemblies 1a have different pressure losses on the inflow ports of sodium 2, the liquid level of sodium 2 is fluctuated for each gas-filled assembly having the same natural frequency, the liquid levels in all gas-sealed assemblies 1a are suppressed from being fluctuated at the same amplitude and the same frequency, and the fluctuation of the reactor output can be suppressed.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Generally, a core for 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, the temperature of each part of the core is stably maintained by keeping the flow rate constant, but it is now possible to safely stop the core even if the cooling capacity drops, such as by stopping the coolant pump. ing.

When an abnormal phenomenon such as a decrease in flow rate occurs in the nuclear reactor, a scrum signal promptly scrams to shut down the nuclear reactor, resulting in a sufficiently safe reactor shutdown state. On the other hand, even if you can not scrum,
If the negative reactivity is passively input and the reactor power decreases,
The integrity of the core is secured.

A gas-filled assembly has been proposed as a passive reactor shutdown mechanism for that purpose, and a reactor core in which the gas-filled assembly 1 as shown in FIG. 9 is arranged between fuel assemblies or in the peripheral portion is considered.

This gas-filled assembly 1 has a trumpet tube 6 and an entrance nozzle 4 connected to the lower part of the trumpet tube 6.
Of the sodium 2 flowing in through the orifice 5 and the enclosed gas 3 covering the liquid surface of the sodium 2 are enclosed by the upper shielding plate 7 and the trumpet tube 6, and the handling head 8 is connected to the upper part of the trumpet tube 6 for easy handling. A weight (lower shield) 9 for preventing floating is arranged below the trumpet tube 6.

However, during the rated operation of the gas-filled assembly 1, the filled gas is compressed by the discharge pressure of the pump, and the sodium coolant liquid level 11 moves from the core upper end level 13 to the upper upper blanket upper end level 12. It is rising.
On the other hand, if the sodium coolant pressure drops due to a pump stop accident, etc., the liquid level will drop and
To lower liquid level 10 near the lower end of the lower blanket of the lower shaft when the pump is stopped.

As a result, neutrons from the core can be vertically streamed through the gas space of the gas-filled assembly to give a negative reactivity to the core and safely stop the reactor.

FIG. 10 is a schematic top view of the gas-filled assembly 1 loaded into a fast reactor core, in which reference numeral 16 is a core fuel assembly, 17 is a blanket fuel assembly, and 18 is a neutron shield. , 19 are control rods, respectively.

[0009]

By the way, if the gas-filled assemblies arranged between or in the vicinity of the fuel assemblies during normal operation are all formed in the same shape and have the same natural frequency, The liquid surface of the sodium coolant inside the gas-filled assembly vibrates all at once due to fluctuations in the pump discharge pressure.

In this case, the gas region in the gas-filled assembly also fluctuates simultaneously according to the liquid surface of the sodium coolant, and the neutron streaming from the core fluctuates. Therefore, there is a problem in that the reactor output of the entire core fluctuates, and a stable plant operation state cannot be obtained.

Further, the temperature of the structural material rises due to the γ heat generation of the upper shield 7 installed above the gas-filled assembly, which is an unfavorable problem in structural design. Furthermore, in a low flow rate type event, the gas region in the gas-filled assembly initially undergoes adiabatic expansion, which slows down the liquid level compared to isothermal expansion, so it is important to promote heat input to the gas. . There is a problem that neutron streaming effect cannot be expected at the time of power increase event.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to prevent fluctuations in the liquid surface of the sodium coolant inside the gas-filled assembly at the same amplitude and at the same frequency, or in the gas-filled assembly. An object of the present invention is to provide a fast reactor core that suppresses fluctuations in reactor output and enables stable plant operation by making the body have a structure that suppresses fluctuations in the internal liquid level of sodium coolant.

According to the present invention, in the above-mentioned gas-filled assembly, the upper shield disposed above the assembly is γ from the core.
Since the structural material rises in temperature due to γ heat generation due to line radiation and is not preferable in structural design, a coolant passage path from inside or outside the aggregate is provided inside the upper shield of the gas-filled aggregate, By cooling the upper shield, the soundness of the gas-filled assembly structural material is ensured, and a highly safe core for a fast reactor is provided.

In the gas-filled assembly according to the present invention, at the time of a flow rate decrease type event, the gas region in the assembly initially undergoes adiabatic expansion, and the sodium coolant liquid level lowering speed is slower than the isothermal expansion. Since it is important to promote heat input to the gas, it promotes heat transfer between the internal gas of the gas-filled assembly and the coolant inside or outside the assembly, promotes isothermal expansion, and promptly accelerates the core. It is intended to provide a highly safe core for a fast reactor by allowing negative reactivity insertion into the core.

According to the present invention, in the gas-filled assembly,
At the time of power increase type event, the structure is such that the neutron streaming effect due to the increase of the gas region cannot be expected,
Even during a power-up type event, the internal gas of the gas-filled assembly is positively heated to expand its temperature and lower the sodium coolant liquid level, thereby promoting neutron streaming and negative reaction to the core. It is to provide a core for a fast reactor with high safety that enables repeated insertion.

[0016]

SUMMARY OF THE INVENTION The present invention is directed to a plurality of core fuel assemblies loaded with fissile material, and a sealed gas and coolant inlet in a trumpet tube between or at the outer periphery of the plurality of core fuel assemblies. Having a shield and a handling head on the upper part of the trumpet tube, having a shield and an entrance nozzle on the lower part of the trumpet tube, due to the pressure change of the coolant,
A fast reactor core comprising a gas-filled assembly configured to change from an upper part to a lower part including the core upper level, (1) two or more types of gas-filled assemblies having different natural frequencies It is characterized by being placed inside.
(2) It is characterized in that a structure having a structure that suppresses the liquid level vibration in the gas-filled assembly is arranged in the core. (3) The upper shield structure member of the gas-filled assembly is provided with a coolant introducing passage from inside and outside the gas-filled assembly, and one having a structure for cooling the shield is arranged in the core. To do.
(4) It is characterized in that a structure having a structure that promotes heat transfer between the enclosed gas in the gas-enclosed assembly and the coolant inside or outside the gas-enclosed assembly is arranged in the core. (5) A core having a structure in which a substance that generates heat by neutron irradiation is installed in the gas-filled assembly, and the filled gas is positively heated by the heat radiation from the heating element even in the event of a power increase type to expand the temperature. It is characterized by being placed inside.

[0017]

[Action]

(1) The liquid level of the sodium coolant in the gas-filled assembly is almost determined by the coolant inlet pressure and the filled gas pressure of the gas-filled assembly, but the gas filling when the coolant inlet pressure changes Regarding the fluctuation of the liquid level in the assembly, the pressure loss characteristic of the gas-filled assembly is an important factor. The gas-filled assemblies have different pressure losses in the gas-filled assemblies due to the presence or absence of structures such as baffle plates provided for each gas-filled assembly or the difference in shape.

Therefore, the coolant flowing out of or inflowing from the gas-filled assembly has a different natural frequency of the liquid surface for each gas-filled assembly having a different pressure loss, and has the same specific characteristic when the pressure at the coolant inlet changes. Different liquid level fluctuations occur for each gas-filled assembly having a frequency, so that fluctuations of the sodium coolant liquid level in the gas-filled assembly with the same amplitude and the same frequency do not occur in the entire core. Therefore, the volume fluctuation of the gas region also differs for each gas-filled assembly, and the fluctuation of the furnace output can be suppressed.

(2) The coolant flowing out of the gas-filled assembly or flowing into the gas-filled assembly due to pressure fluctuations at the gas-filled assembly inlet may be a baffle plate installed in the gas-filled assembly. Due to the structure with increased pressure loss, the liquid level of sodium coolant is lowered or the rising speed is reduced to suppress the fluctuation of the liquid level, and the volume of the gas region is maintained,
The fluctuation of the furnace output can be suppressed.

(3) The upper shield heated by γ heat is cooled by circulating a coolant taken in from the inside or outside of the gas-filled assembly to the inside of the structure to cool the shield. Controls temperature rise. Therefore, the soundness of the structural material of the gas filled assembly can be ensured.

(4) The enclosed gas in the gas-enclosed assembly, which maintains good heat transfer with the tube wall of the trumpet tube, promotes sufficient heat input in the decrease of the sodium coolant liquid level in the event of a low flow rate type event. Therefore, the rate of decrease of the liquid level of the sodium coolant is not slowed down, and prompt insertion of the negative reactivity is promoted.

(5) The gas in the gas-filled assembly in which the gas flow path and the heating element are installed is warmed by the heating element heated by the neutron irradiation at the time of the power rising type event, and circulates in the gas flow path. While expanding the temperature. This temperature expansion pushes up the liquid surface of the sodium coolant in the gas-filled assembly, promotes neutron streaming, and enables negative reactivity insertion.

[0023]

EXAMPLE A first example of a fast reactor core according to the present invention will be described with reference to FIGS. FIG. 1 is a longitudinal sectional view showing two kinds of gas-filled assemblies according to the present invention loaded in a core for a fast reactor in the same figure, and FIG. 2 is a fast reactor loaded with the gas-filled assemblies according to the present invention. It is a top view which shows the core for construction roughly.

The gas-filled assembly shown in FIG. 1 has a large number of core fuel assemblies 16 in which fissionable materials are loaded in the core and axial blanket parts made of parent material are arranged above and below as described in FIG. Placed in or around. Further, as shown in FIG. 10, these core fuel assemblies 16 are taken in by a blanket assembly 17 containing a parent substance and a neutron shield 18 to form a fast reactor core according to the present invention.

The difference of this embodiment from the conventional example is that the structure of the gas-filled assembly and the arrangement in the core are improved, and the same parts as those in FIGS. 9 and 10 are designated by the same reference numerals. That is, as shown in FIG. 1, the gas-filled aggregate 1a
In (2), two types are prepared: a gas-filled assembly having an entrance nozzle 20 having a smaller coolant inlet diameter and a gas-filled assembly having an entrance nozzle 21 having a larger inlet diameter. FIG. 2 shows a core for a fast reactor in which the gas-filled assembly 22 having a smaller inlet diameter and the gas-filled assembly 23 having a larger inlet diameter shown in FIG. 1 are arranged in the core. In FIG. 2, reference numeral 16 is a core fuel assembly, 17 is a blanket fuel assembly, 18 is a neutron shield, and 19 is a control rod.

According to the present embodiment, the gas-filled assembly 22 having the entrance nozzle 20 having a small coolant inlet diameter.
The internal pressure loss becomes large, and the natural frequency of the liquid level vibration is different from that of the gas-filled assembly 23 having the entrance nozzle 21 having a large inlet diameter.

Therefore, in this embodiment, as compared with the case where the conventional gas-filled assemblies having the same inflow port diameter are arranged in the core, in this embodiment, the volume variation of the gas region in the gas-filled assemblies in the entire core is Since it is suppressed and neutral streaming is also stabilized, it is possible to suppress fluctuations in reactor output of the entire core.

FIG. 3 shows a second embodiment of the present invention. That is, in the gas-filled assembly 1b of this embodiment, the baffle plate 24 is provided in the trumpet tube 6 below the sodium coolant liquid level 11 in the trumpet tube 6. That is, sodium 2 and enclosed gas 3 are contained in the trumpet tube 6, and a baffle plate 24 is provided in two stages below the sodium coolant liquid level 11. Then, two types of the gas-filled assembly provided with the baffle plate 24 and the gas-filled assembly not provided with the baffle plate 24 are arranged in the core to form a fast reactor core.

According to the present embodiment, since the vibration itself of the liquid surface is also suppressed, it is also effective to dispose only the gas-filled assembly provided with the baffle plate 24 in the core. A perforated plate may be provided instead of the baffle plate 24. Further, a baffle plate can be similarly arranged at the orifice 5 of the entrance nozzle 4 or in the vicinity thereof.

FIG. 4 shows a gas-filled assembly 1c according to the third embodiment of the present invention. The gas-filled assembly 1c of this embodiment is different from the conventional example of FIG. 9 in that a partition plate 37 is provided at a height between the core upper end level 13 and the core lower end level 14 so that the inside can be filled with sodium 2. 38 is provided in a part of the trumpet tube 6, and the sodium 2 in the upper part of the trumpet tube 6 communicates with the lower part of the assembly through a communication hole 39.

This communication hole 39 has the effect of suppressing the vibration of the liquid surface itself, and the natural frequency of the liquid surface is different from that of the gas-filled assembly without the partition plate 37. Therefore, by arranging the gas-filled aggregate 1c of the present embodiment together with the gas-filled aggregate of each of the above-mentioned embodiments in the core, it is possible to suppress the output fluctuation as described above. Further, in the gas-filled assembly 1c, the negative reactivity effect can be increased because the gas volume at the core center height portion that gives a positive reactivity due to the formation of voids in sodium is small.

Next, a fourth embodiment of the present invention will be described with reference to FIG. As shown in FIG. 5, the gas-filled assembly 1d of the fourth embodiment of the present invention is an assembly coolant introduction path for introducing sodium 2 having an inlet hole arranged below the core region in the structural material cross section of the trumpet tube 6. 29 is provided, and the introduction path 29 penetrates the structural material cross section of the trumpet pipe 6 and communicates with the upper shield cooling path 30 provided in the structural material cross section of the upper shield 7. The cooling passages 30 are provided at several locations inside the upper shield 7, and are open above the upper shield 7.

According to this embodiment, the pressure of the gas-filled assembly entrance nozzle portion (equal to the coolant introduction plenum pressure)
And the upper shield cooling channel due to the difference in pressure outside the gas-filled assembly
Coolant is introduced at 30. The flow rate of the coolant can be controlled by appropriately setting the flow path resistance.

Next, a fifth embodiment of the present invention will be described with reference to FIG. In the fifth embodiment of the present invention shown in FIG. 6, in order to allow sodium 2 to flow from the outside of the gas-filled assembly 1e, an outside-assembly coolant introduction path 31 is provided below the upper shield 7 above the trumpet tube 6. The introduction passage 31 communicates with the upper shield cooling passage 30 provided in the cross section of the structural material of the upper shield 7. The cooling passages 30 are provided in several places inside the upper shield 7, and open at the upper end surface of the upper shield 7.

According to the present embodiment, the buoyancy of the coolant in the upper shield cooling passage 30 heated by the upper shield 7 causes the upper shield cooling passage 30 around the gas-filled aggregate (between adjacent aggregates).
A coolant having a temperature relatively lower than that of the coolant inside is introduced into the upper shield cooling passage 30.

As a result, sodium from the inside or the outside of the gas-filled assembly flows inside the structural material of the upper shield 7 and removes heat energy from the heat generated by the γ heat of the upper shield 7, thereby cooling it. It is possible to secure the soundness of the structural material of the aggregate.

Next, a sixth embodiment of the present invention will be described with reference to FIG. As shown in FIG. 7, in the gas filled assembly 1f of the present embodiment, the fins 32 are arranged at the axial position of the filled gas 3 in the trumpet tube 6 toward the inside of the trumpet tube 6.

According to this embodiment, the temperature of the fins 32 rises due to heat conduction with the wall of the trumpet tube 6, and the fins 32 are heated.
The temperature of the sealed gas in the gas sealed assembly is raised by heat transfer from the. Therefore, in the low flow rate type event, sufficient heat input is received at the decrease of the sodium coolant level 11 so that the rate of decrease of the sodium coolant level 11 does not decrease and promotes rapid negative reactivity insertion. It becomes possible.

When the fins 32 are not provided, the enclosed gas is He gas having a good heat transfer coefficient to promote the temperature rise due to the heat transfer with the sodium inside and outside the trumpet tube 6, and the same effect can be obtained. It is also possible to give.

Next, a seventh embodiment of the present invention will be described with reference to FIG. FIG. 8 is a vertical sectional view showing a gas-filled assembly 1g loaded in the core of a fast reactor according to the present invention.

As shown in FIG. 8, the gas-filled assembly 1g according to the seventh embodiment has an inner cylinder 33 and a partition 34 inside the trumpet tube 6.
Are provided concentrically to divide the inside of the trumpet tube 6 into a plurality of sections, and a partition 34 for a passage path of the enclosed gas is provided between the inner wall of the trumpet tube 6 and the inner cylinder 33 having the coolant liquid level 11. A heating element (hafnium etc.) 35 is installed under the flow path. This heating element
As the material of 35, a material that generates heat by neutron absorption such as hafnium is effective, but a γ heating element such as tantalum or stainless steel may be used.

According to this embodiment, the heating element 35 is heated by the neutron irradiation from the core during the power increase type event,
The temperature of the enclosed gas 3 is raised to generate a circulating flow 36 of gas. The temperature of the enclosed gas 3 rises while circulating in the flow path path between the inner wall of the trumpet tube 6 and the inner tube 33, and the expanded gas expands to push down the liquid surface of the sodium coolant in the assembly, thereby reducing neutron streaming. Enable promotion.

As another example of this embodiment, the heating element 35 is made of a porous material to increase the contact area with the enclosed gas 3 and accelerate the radiant heat transfer of the gas. As a result, the effect of the above embodiment can be further improved. Also, the inner cylinder
Fins are provided on the 33 to promote radiative heat transfer from the heating element 35 to the inner cylinder 33. As a result, the temperature of the inner cylinder rises and an upward flow is generated above the heat generating element, and the gas is heated by radiation from the wall and natural convection, and the above effect can be further improved.

[0044]

According to the present invention, during normal operation of the fast reactor, fluctuations in the reactor output due to fluctuations in the liquid level are suppressed and stable operation is achieved, as compared with the conventional core for a fast reactor loaded with gas-filled assemblies. You can get the status. Moreover, the soundness of the structural material of the gas-filled assembly can be ensured, and the negative reactivity insertion effect at the time of the flow rate reduction type event can be promoted. Furthermore, even in the case of an output increase type event, a negative reactivity insertion effect can be expected, and safety and approval are greatly improved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a gas-filled assembly loaded in a core of a fast reactor core according to a first embodiment of the present invention.

FIG. 2 is a schematic top view showing a fast reactor core loaded with the gas-filled assembly in FIG.

FIG. 3 is a vertical sectional view showing a second embodiment of the gas-filled assembly in FIG.

FIG. 4 is a longitudinal sectional view showing a third embodiment of the gas-filled assembly in FIG.

FIG. 5 is a longitudinal sectional view showing a gas-filled assembly loaded in the core of a fast reactor according to a fourth embodiment of the present invention.

FIG. 6 is a vertical sectional view showing a fifth embodiment of the gas-filled assembly in FIG.

FIG. 7 is a vertical cross-sectional view showing a gas-filled assembly loaded in the core of a fast reactor according to a sixth embodiment of the present invention.

FIG. 8 is a vertical cross-sectional view of a gas-filled assembly loaded in the core of a fast reactor core according to a seventh embodiment of the present invention.

FIG. 9 is a vertical sectional view schematically showing a gas-filled assembly loaded in the core of a conventional fast reactor.

FIG. 10 is a schematic top view showing a conventional fast reactor core loaded with a gas-filled assembly.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Gas-encapsulated aggregate, 1a-1g ... Gas-encapsulated aggregate according to the present invention, 2 ... Sodium, 3 ... Encapsulated gas, 4 ... Entrance nozzle, 5 ... Orifice, 6 ... Trumpet tube, 7 ... Upper shield, 8 … Handling head, 9… Weight, 10… Liquid level when pump is stopped, 11… Sodium coolant liquid level, 12… Upper axis blanket upper level, 13… Core upper level, 14… Core lower level, 15… Lower axis Bottom level of blanket, 16 ... Core fuel assembly, 17 ... Blanket fuel assembly, 18 ... Neutron shield, 19 ... Control rod, 20 ... Entrance nozzle with small inlet diameter, 21 ... Entrance nozzle with large inlet diameter, 22 … Gas inlet assembly with smaller inlet diameter, 23… Gas inlet assembly with larger inlet diameter, 24… Baffle plate, 25… Sodium, 29… Coolant introduction passage in assembly, 30… Top shield cooling Passage, 31 ... Coolant introduction passage outside the assembly, 32 ... Fins, 33 ... Inner cylinder, 34 ... Partition, 35 ... Heating element, 36 ... Gas circulation flow, 37 ... Partition plate, 38 ... Inflow / outflow hole, 39 ... Communication Hole.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuguo Yokoyama 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock company, Toshiba Yokohama Works (72) Hiroshi Matsumoto 8 Shinsugita-cho, Isogo-ku, Yokohama, Kanagawa Company Toshiba Yokohama Office

Claims (13)

[Claims] 1. A core for a fast reactor comprising a number of fuel assemblies loaded with fissile material and a gas encapsulation assembly arranged between these fuel assemblies or on the outer periphery of the fuel assembly. Is a trumpet tube, gas is sealed in the trumpet tube, the trumpet tube has a liquid metal coolant inflow hole, a shield and a handling head in the upper part, a shield and an entrance nozzle in the lower part, A core for a fast reactor, comprising a gas-filled assembly having a small coolant inlet diameter of an entrance nozzle and a gas-filled assembly having a large coolant inlet diameter arranged in a core. 2. The gas-filled assembly comprises a baffle plate provided with and without a baffle below the liquid surface of the coolant, and these gas-filled assemblies are arranged in the core or the baffle plate is provided. The core for a fast reactor according to claim 1, wherein only the gas-filled assembly provided with the plate is arranged in the core. 3. The gas-filled assembly is made up of one having a communication hole below the liquid surface of the coolant in the trumpet pipe and one having no communication hole. The gas-filled assembly is disposed in the core or the communication hole is provided. The core for a fast reactor according to claim 1, wherein only the gas-filled assembly having the holes is arranged in the core. 4. The gas-filled assembly comprises a perforated plate and a perforated plate below the liquid surface of the coolant in the trumpet tube, and these gas-filled assemblies are arranged in the core or the perforated plate. 2. The fast reactor core according to claim 1, wherein only the gas-filled assembly provided with is arranged in the core. 5. The gas-filled assembly comprises a baffle plate provided with a baffle plate and a baffle plate not provided at the coolant inlet port, and the gas-filled assembly is arranged in the core, or the coolant is provided. The gas-filled assembly having a baffle plate provided in the inflow port alone is arranged in the core.
The described fast reactor core. 6. The gas-filled assembly has two or more kinds of gas-filled assemblies in a core, a gas-filled assembly in which a portion for narrowing a flow passage is provided in a trumpet tube and a gas-filled assembly in which a flow passage is not narrowed. The core for a fast reactor according to claim 1, wherein the core is arranged. 7. An upper cooling member which is provided with an assembly cooling introduction passage in the trumpet tube so that the cooling material in the gas filling assembly can be taken into the trumpet tube of the gas filling assembly, and which communicates with the assembly cooling introduction passage. The core for a fast reactor according to claim 1, wherein a cooling passage is provided in the upper shield. 8. An outside-aggregate coolant introduction path communicating with the upper shield cooling passage is provided in the upper shield so that a coolant can be taken into the trumpet tube of the gas enclosed aggregate from the outside of the gas enclosed aggregate. 1. The method according to claim 1, wherein
The described fast reactor core. 9. The core for a fast reactor according to claim 1, wherein fins are provided in a trumpet tube of the gas-filled assembly. 10. The fast reactor core according to claim 1, wherein the gas sealed in the trumpet tube of the gas sealed assembly is He gas. 11. An inner cylinder is provided in the trumpet tube of the gas-filled assembly, and a partition for a passage path of the filled gas is provided between the inner wall of the trumpet tube and the inner tube having the coolant liquid level. The core for a fast reactor according to claim 1, wherein a heating element that generates heat by neutron irradiation is installed below the flow path. 12. The fast reactor core according to claim 11, wherein in the gas-filled assembly in which the gas flow path and the heating element are installed, the heating element is a porous body. 13. The core for a fast reactor according to claim 11, wherein, in the gas-filled assembly in which the gas flow path and the heating element are installed, fins are provided in an inner cylinder around the heating element.