JPH09211167A - Gas charged assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress streaming of neutron upward and prevent temperature rising by using boron carbide pellets for upper shield and providing cooling function of the boron carbide pellets. SOLUTION: The liquid level 11 of coolant sodium 2 during rated operation is determined so that the sodium 2 pressure and charged gas 3 pressure balance. If a pump terminates and pressure at cooling lowers, the charged gas 3 pushes down the liquid level of sodium 2 so as to balance with this pressure. If the gas temperature does not rise following the sodium 2 temperature, the gas 3 does not swell enough and the sodium 2 liquid level is lowered to the coolant liquid level 10 at pump termination. By providing a shielding element 21 in the upper part of a duct 6, neutron streaming upward the gas charged assembly can be suppressed low and the heat in the boron carbide due to neutron radiation can be sufficiently cooled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas-filled assembly arranged in the core of a liquid metal-cooled fast breeder reactor, and more particularly to a gas-filled assembly with improved upper shielding performance.

[0002]

2. Description of the Related Art Generally, the core of a fast breeder reactor is composed of a large number of fuel assemblies loaded with fissile material and is used as a liquid metal coolant for removing heat from the fuel of the fuel assemblies. Mainly sodium is used.

Normally, the temperature of each part of the core is stably maintained by keeping the flow rate constant, but the core can be safely stopped even if the cooling capacity is lowered such as by stopping the coolant pump. It is like this.

When an abnormal event such as a decrease in flow rate occurs in the nuclear reactor, a scrum signal is transmitted and scram is promptly carried out to reach a sufficiently safe reactor shutdown state. On the other hand, even if it is assumed that scram cannot be performed, the negative reactivity is passively injected and the reactor power is reduced, thereby ensuring the integrity of the core.

[0005] As a passive furnace shutdown mechanism for this purpose, for example, a gas-filled assembly 1 as shown in FIG. 8 has been proposed.
This gas-filled assembly 1 is shown in FIG.
Measures are taken to arrange the fuel cells between 16 or in the fuel assembly 16 from the center to the periphery.

As shown in FIG. 8, this gas-filled assembly 1 encloses the coolant sodium 2 and the filled gas 3 flowing in through the entrance nozzle 4 in the lower shield 9, the upper shield 7, and the duct 6, and the upper portion. A handling head 8 for handling is arranged on the shield 7. An entrance nozzle 4 having a coolant inflow hole 5 is attached to the lower shield 9. The reference numeral 10 indicates the coolant liquid level 10 when the pump is stopped.

Thus, the gas-filled assembly 1 shown in FIG.
In the rated operation, the charged gas 3 is compressed by the discharge pressure of the pump, and the coolant level 11 in the rated operation rises to near the upper shaft blanket upper end level 12 above the core upper end level 13. If the sodium coolant pressure drops due to a pump stop accident, etc., the coolant liquid level when the pump stops
10 drops below the core lower end level 14 to near the lower shaft blanket lower end level 15.

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 shut down the reactor.

FIG. 9 shows a fast reactor core. This fast reactor core 20 includes a core fuel assembly 16 and a blanket fuel assembly.
17, the neutron shield 18, and the control rod 19, and the gas-filled assembly 1 is arranged in the fast reactor core 20.

[0010]

Incidentally, the upper shield 7 of the gas-filled assembly 1 has a function of suppressing neutrons from streaming upward from the gas-filled assembly 1. Conventionally, neutrons are shielded by stainless steel, but due to higher combustion of the core etc., neutron flux increases and it is not possible to satisfy the shielding performance, so it is preferable to use boron carbide pellets with excellent shielding performance instead of stainless steel. Conceivable. However, when boron carbide pellets react with neutrons, they generate more heat than stainless steel, and there is a problem that they must be cooled sufficiently.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a gas-filled assembly having boron carbide pellets as the upper shield and having a cooling function for the boron carbide pellets.

[0012]

SUMMARY OF THE INVENTION The present invention includes cavities located between or at the outer periphery of a number of fissile material loaded fuel assemblies and having enclosed gas and coolant inlet holes within the duct. In a gas-filled assembly in which the liquid level of the sodium coolant in the internal cavity changes from the upper part to the lower part including the core upper level due to the change of the coolant pressure, (1) The upper shield part of the duct contains boron carbide pellets. A shielding element having a cooling function is installed. (2) A straight tubular flow pipe is installed in the center of the duct by suspending it from the lower end of the upper shield, and the tip of the straight tubular flow pipe is cooled inside the duct. By positioning the coolant below the liquid level, the coolant is allowed to flow into the upper shield to cool the boron carbide pellets. (3) The number of straight tubular flow pipes installed at the lower end of the upper shield is set to multiple. , For some reason In the case where a part of the straight pipe-shaped flow path pipe is blocked is also coolant flows into the upper shield, the boron carbide pellets enhanced reliability to be cooled,
(4) Instead of the straight tubular flow path pipe installed at the lower end of the upper shield, a spiral flow path tube is provided along the inner wall of the duct to serve as a steady rest and improve vibration resistance, (5) Install an inner duct with the upper end closed inside the duct, cool the boron carbide pellets by flowing coolant from the entrance nozzle into the upper shield through these ducts, (6) at the lower end of the upper shield. A flow hole is provided to allow a coolant to flow into the shielding element from the side of the duct to cool the boron carbide pellets. (7) An electromagnetic pump is provided above the upper shield to allow the coolant to flow in and to remove the boron carbide pellets. It is characterized by cooling.

According to (1), as a cooling function of the shielding element, a large number of flow passage holes for flowing a coolant are provided in the pellets of boron carbide to prevent heat generation, thereby shielding neutrons above the gas-filled assembly. And the life of the boron carbide pellets can be extended.

According to (2), when a straight tubular flow pipe is provided in the center of the duct from the lower end of the upper shield and the tip of the flow pipe is located below the liquid surface of the coolant inside the duct, the entrance nozzle On the other hand, the coolant flowing from the inside compresses the enclosed gas inside the duct and rises to the rated liquid level. On the other hand,
It flows into the flow path pipe, flows into the inside of the upper shield, and flows out from the handling head. Since the coolant flows around the shielding element containing the boron carbide pellets, the boron carbide pellets are cooled.

According to (3), when a plurality of straight tubular flow pipes are provided, even if some of the flow pipes are closed for some reason and the coolant does not flow, cooling is performed from other flow pipes. The material flows into the top shield, allowing the boron carbide pellets to cool.

According to (4), a spiral flow passage pipe is used instead of the straight pipe passage pipe installed at the lower end of the upper shield, and the outer surface of the flow passage pipe is aligned with the inner wall of the duct during an earthquake. Since the spiral flow passage tube is supported by the duct, the coolant flows into the upper shield without damaging the runout and damaging the boron carbide pellets.

According to (5), the duct of the gas filled assembly is doubled, and the upper end of the inner duct is closed with an end plug to form a filled gas space. Coolant is introduced from the entrance nozzle into the gap between the outer and inner ducts, flows inside the upper shield, and flows out from the handling head. Since the coolant flows around the shielding element containing the boron carbide pellets, the boron carbide pellets are cooled.

According to (6), a flow hole is provided at the lower end of the upper shield so that the coolant flows in from the side, flows inside the upper shield, and flows out from the handling head. Since the coolant flows around the shielding element containing the boron carbide pellets, the boron carbide pellets are cooled.

According to (7), the flow hole for outflow is provided at the lower end of the upper shield, the coolant is made to flow in from the handling head, the inside of the upper shield is made to flow, and the coolant is made to flow out from the side. Since the coolant flows around the shielding element containing the boron carbide pellets, the boron carbide pellets are cooled.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of a gas-filled assembly corresponding to claim 1 of the present invention will be described with reference to FIG. The gas-filled assembly 1a according to the present embodiment has a cylindrical duct 6
And an entrance nozzle 4 having a coolant inflow hole 5 connected to the lower portion of the duct 6 for positioning with a core support structure (not shown), and shielding neutrons from the core connected to the entrance nozzle 4. The lower shield 9, the upper shield 7 connected to the upper portion of the duct 6, the handling head 8 connected to the upper end of the upper shield 7, and the duct 6
It has a coolant sodium 2 sealed inside and a fill gas 3 made of an inert gas such as inert argon.

In the upper shield 7, boron carbide (B
₄ and the shielding element 21 containing therein the pellet C) are provided, a plurality of coolant channels 22 are formed in the covering element 21. The coolant passage 22 is not communicated with the inside of the duct 6 by an end plug 23 that also serves as a shield that closes the upper end of the duct 6, but is forcibly cooled by a cooling device (not shown) from the outside.

Next, the operation of this embodiment will be described. The liquid level 11 of the coolant such as sodium 2 during the rated operation is determined so that the pressure of sodium 2 and the pressure of the enclosed gas 3 are in equilibrium. When the pump stops and the pressure at the time of cooling decreases, the enclosed gas 3 pushes down the liquid level of sodium 2 so as to balance this pressure.

However, unless the gas temperature rises following the temperature of the sodium 2, the enclosed gas 3 does not expand sufficiently, so the liquid level of the sodium 2 cannot be pushed down to the coolant liquid level 10 when the pump is stopped. Therefore, the streaming of neutrons is not sufficient and the predetermined function is not sufficiently fulfilled.

Therefore, in the present embodiment, by providing the shielding element 21 on the upper part of the duct 6, it is possible to suppress the streaming of neutrons above the gas-filled assembly to a low level as compared with the conventional example. The heat generated from the boron carbide pellets due to the neutron irradiation can be sufficiently cooled.

Next, second to fourth embodiments corresponding to claims 2 to 4 of the present invention will be described with reference to FIGS. 2 to 4. In the figure, the same parts as those in FIG. 1 are denoted by the same reference numerals.
In FIG. 2, the gas-filled assembly 1b according to the second embodiment.
Are an entrance nozzle 4 having a coolant inflow hole 5 for positioning with a core support structure, an upper shield 7 and a lower shield 9 for shielding neutrons from the core connected to the upper and lower ends of a duct 6. , A shielding element 21 containing boron carbide pellets installed in the upper shield 7, a sealing gas 3 and sodium 2 for promoting neutron streaming sealed in the duct 6, and a treatment provided at the upper end of the upper shield 7. And a straight tubular flow pipe 24 that is suspended from an end plate 23 provided at the upper end of the duct 6 and extends downward in the duct 6.

The sodium 2 flowing in from the coolant inflow hole 5 of the entrance nozzle 4 rises to the coolant level 11 during the rated operation while compressing the enclosed gas 3. The liquid level 11 of the coolant during the rated operation is substantially determined by the volume and pressure of the enclosed gas 3 and the pressure of sodium 2, and becomes constant when the pressure of the enclosed gas 3 and the pressure of sodium 2 reach equilibrium.

On the other hand, sodium 2 also flows into the flow path pipe 24, flows from the flow path pipe 24 through the coolant flow path 22 of the shielding element 21 inside the upper shield 7, and flows out of the handling head 8.
At this time, since the flowing sodium 2 has a lower temperature than the shielding element 21, the shielding element 21 can be cooled.

Further, since the lower end of the passage pipe 24 is located below the coolant liquid level 10 when the pump is stopped and is not exposed in the enclosed gas 3, the enclosed gas 3 leaks from the passage pipe 24. There is nothing to do.

FIG. 3 shows a gas-filled assembly 1c in which a plurality of flow path pipes 24 are installed in FIG. 2, and when sodium 2 no longer flows into one of the plurality of flow path tubes 24 for some reason. However, it is possible to cool the shielding element 21 by flowing sodium 2 from the other flow path pipe 24.

FIG. 4 shows the gas-filled assembly 1d in which the spiral flow pipe 25 is installed in the duct 6, and the spiral flow pipe 25 is shown.
Is installed so as to come into contact with the inner wall of the duct 6 and has a role of a steady rest, so that it is less likely to be damaged even by strong shaking or vibration.

Next, a fifth embodiment of the gas-filled assembly according to claim 5 of the present invention will be described with reference to FIG. The gas-filled assembly 1e of the present embodiment is provided with the coolant inflow hole 5
Entrance nozzle 4 for positioning with the core support structure and a lower shield 9 for shielding neutrons from the core
And an upper shield 7 provided with a shielding element 21 containing boron carbide pellets, an enclosed gas 3 that promotes neutron streaming, an inner duct 26 and an end plug 23 that serve as a boundary of the enclosed gas 3, and an upper shield 7. It comprises a handling head 8 for handling provided at the upper end of the duct and a duct 6 for forming a coolant channel 27 for cooling the shielding element 21. A coolant passage hole 30 is formed in the upper portion of the lower shield 9.

The sodium 2 flowing in from the coolant inflow hole 5 of the entrance nozzle 4 rises to the coolant level 11 during the rated operation while compressing the enclosed gas 3. On the other hand, sodium 2 also flows into the duct 6 from the coolant passage hole 30 of the lower shield 9 through the passage hole 27 between the inner duct 26 and the duct 6 to cool the shield element 21 inside the upper shield 7. While rising, it flows out from the handling head 8.

Next, referring to FIG. 6, a sixth embodiment of the gas-filled assembly according to claim 6 of the present invention will be described. The gas-filled assembly 1f of the present embodiment is provided with the coolant inflow hole 5
Entrance nozzle 4 for positioning with the core support structure and a lower shield 9 for shielding neutrons from the core
And an upper shield 7 provided with a shielding element 21 containing boron carbide pellets, a sealed gas 3 for promoting neutron streaming, a duct 6 serving as a boundary of the sealed gas 3, and a handling head 8 for handling. It

A flow hole 28 is provided below the upper shield 7, and the external sodium 2b flows into the upper shield 7 through the flow hole 23 and rises while cooling the shield element 21 from the coolant passage 22 to be handled. It flows out from the head 8.

Next, referring to FIG. 7, a seventh embodiment of the gas-filled assembly according to claim 7 of the present invention will be described. The gas-filled assembly 1g of the present embodiment has a coolant inflow hole 5
Entrance nozzle 4 for positioning with the core support structure and a lower shield 9 for shielding neutrons from the core
And an upper shield 7 provided with a shield element 21 containing boron carbide pellets, an enclosed gas 3 for promoting neutron streaming, a duct 6 serving as a boundary of the enclosed gas 3, and an upper shield 7 provided on the upper shield 7. A handling head 8 for handling, an electromagnetic pump 29 provided in the handling head 8, an end plate 23 that closes the upper end of the duct 6, and a flow hole provided on the side surface between the end plate 23 and the upper shield 7.
It consists of 28 and.

According to this embodiment, an electromagnetic pump 29 is provided inside the handling head 8, and this electromagnetic pump 29 forces the external sodium 2b to flow into the inside of the upper shield 7. The inflowing external sodium 2b descends while cooling the shielding element 20, and flows out from the flow hole 28 provided in the lower portion of the upper shield 7.

[0037]

According to the present invention, by using boron carbide pellets having excellent shielding performance instead of stainless steel for the upper shield, neutrons can be streamed above the gas-filled aggregate as compared with the conventional example. It can be suppressed to a low level, and the heat generated by the irradiation of the boron carbide pellets can be sufficiently cooled.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a first embodiment of a gas filled assembly according to the present invention.

FIG. 2 is a longitudinal sectional view showing a second embodiment of the gas filled assembly according to the present invention.

FIG. 3 is a longitudinal sectional view showing a third embodiment of the gas filled assembly according to the present invention.

FIG. 4 is a longitudinal sectional view showing a fourth embodiment of the gas filled assembly according to the present invention.

FIG. 5 is a longitudinal sectional view showing a fifth embodiment of the gas-filled assembly according to the present invention.

FIG. 6 is a longitudinal sectional view showing a sixth embodiment of the gas-filled assembly according to the present invention.

FIG. 7 is a vertical sectional view showing a gas-filled assembly according to a seventh embodiment of the present invention.

FIG. 8 is a longitudinal sectional view showing a conventional gas filled assembly.

9 is a schematic top view of a fast breeder reactor core in which the gas-filled assembly in FIG. 8 is arranged.

[Explanation of symbols]

1 (conventional), 1a to 1g (present invention) ... a gas-filled assembly,
2 ... Sodium, 3 ... Filled gas, 4 ... Entrance nozzle, 5 ... Coolant inflow hole, 6 ... Duct, 7 ... Top shield,
8 ... Handling head, 9 ... Lower shield, 10 ... Coolant liquid level when pump is stopped, 11 ... Coolant liquid level during rated operation, 12 ... Upper shaft blanket upper level, 13 ... Core upper level, 14 ... Core Lower end level, 15 ... Lower shaft blanket Lower end level, 16 ... Core fuel assembly, 17 ... Blanket fuel assembly, 18 ... Neutron shield, 19 ... Control rod, 20 ... Fast reactor core, 21 ... Shielding element, 22 ... Cooling Material flow path, 23 ... End plate, 24
… Straight tubular flow pipe, 25… Spiral flow pipe, 26… Inner duct,
27 ... Coolant channel, 28 ... Flow hole, 29 ... Electromagnetic pump,
30 ... Coolant channel hole.

Claims (7)

[Claims] 1. A duct having a liquid metal coolant and an enclosed gas, an upper shield and a handling head at an upper portion of the duct, and a lower shield and a coolant inlet hole formed at a lower portion of the duct. A gas-filled assembly having an entrance nozzle, characterized in that a boron carbide pellet is included in the upper shield body to provide a shielding element having a cooling function. 2. A straight tubular flow pipe is provided by suspending it from substantially the center of the lower end of the upper shield, and providing the straight pipe flow pipe with its tip positioned below the liquid surface of the coolant in the duct. The gas-filled assembly according to claim 1, wherein a coolant passage hole communicating with the upper end of the gas-filled element is formed in the shielding element. 3. The gas-filled assembly according to claim 1, wherein a plurality of the straight tubular flow pipes are provided. 4. The straight tubular flow pipe is a spiral flow pipe,
The gas-filled assembly according to claim 1, wherein an outer peripheral surface of the spiral flow path pipe is provided along an inner wall surface of the duct. 5. An inner duct having concentrically closed upper ends is provided in the duct, and a coolant flowing from the entrance nozzle between the inner duct and the duct flows into the shielding element. The gas-filled assembly according to claim 1, wherein a passage is provided. 6. The gas filled assembly according to claim 1, wherein a flow hole for allowing a coolant to flow into the shielding element from a side portion of the duct is provided at a lower end of the upper shielding body. 7. An electromagnetic pump is provided above the shielding element, and a flow hole for letting out a coolant that has cooled the shielding element is provided below the upper shielding body. Gas filled assembly.