JPS5933865B2 - Nuclear reactor core support device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a core support device for a sodium-cooled fast breeder reactor.

Generally, a sodium-cooled fast breeder reactor is provided with a so-called hydraulic hold-down type core support device that prevents the fuel assembly from floating due to the fluid pressure of the coolant.

Conventionally, such a core support device is provided with a plurality of core support plates to form a high-pressure section through which high-pressure coolant flows and a low-pressure section through which low-pressure coolant flows, and the entrance nozzle of the fuel assembly is connected to the high-pressure section. The coolant in the high-pressure part is passed through the entrance nozzle so that its lower end reaches the low-pressure part, and the coolant in the high-pressure part flows into the entrance nozzle through an orifice hole formed on the circumferential surface of the entrance nozzle, acting on the inside of the bottom surface of the entrance nozzle. The structure is designed to prevent the fuel assembly from floating due to the differential pressure between the fluid pressure in the high-pressure part that acts on the outside of the bottom of the entrance nozzle and the fluid pressure in the low-pressure part that acts on the outside of the bottom surface of the entrance nozzle, and to facilitate the loading and unloading of the fuel assembly during fuel exchange. has been done.

However, such conventional devices have a complicated structure due to the formation of a high-pressure part and a low-pressure part, and also have the problem that a sufficient force for pressing down the fuel assembly cannot be obtained.

In addition, in conventional models, the entrance nozzle of the fuel assembly is inserted so as to penetrate through the high-pressure part and reach the low-pressure part, so it is necessary to seal at multiple locations. There was also the problem that the seating condition of the seal surface at the seal location was uncertain, leading to increased leakage of coolant and inaccurate flow rate distribution of coolant to each fuel assembly.

The present invention has been made based on the above circumstances, and its purpose is to have a simple structure, obtain sufficient force to press down the fuel assembly, and improve the distribution of the coolant flow rate to each fuel assembly. The objective is to obtain a core support device for a nuclear reactor that can be made accurately.

The present invention will be described below with reference to embodiments shown in the drawings.

1 and 2 show a first embodiment of the present invention, in which 1 is a reactor vessel and 2 is a coolant inlet pipe.

A core support plate 3 is provided horizontally within the reactor vessel 1, and the reactor vessel 1 is divided into an upper part and a lower part by this core support plate 3.

A large number of support sleeves 4 are vertically attached to the center of the core support plate 3, and the entrance nozzles 6 of the fuel assemblies 5 are attached to these support sleeves 4. inserted and supported.

Further, blanket fuel assemblies 7 are loaded around the core support plate 3.

As shown in FIG. 2, the support sleeve 4 has a hollow cylindrical shape with both ends open, and its upper end is attached to the core support plate 3.

A sealing member 8 with a tapered diameter is provided at the upper end of this support sleeve 4, and a sealing surface 9 formed at the upper part of the entrance nozzle 6 of the fuel assembly 5 is seated on this sealing member 8. and is configured to maintain a seal.

Further, the inner diameter of the lower part of this support sleeve 4 is expanded to form a flow section 10, and the upper part is an entrance nozzle 6.
The closed portion 11 is formed by reducing the inner diameter to an extent slightly larger than the outer diameter of the closed portion 11 .

A coolant such as liquid sodium supplied to the lower part of the reactor vessel 1 is passed through the lower end opening of the support sleeve 4 into the flow section 10.
, flows into the entrance nozzle 6 through orifice holes 12 .

Note that the length of this flow section 10 is set in accordance with the flow rate distribution of the coolant, and is configured so that a flow rate corresponding to the number of orifice holes 12 opened in this flow section 10 is given. ing.

Further, a labyrinth portion 13 is provided on the inner circumferential surface of the lower end portion of the closing portion 11.
is formed, and is configured to prevent the coolant from flowing into the closing portion 11.

A negative pressure generator 14 is provided within the opening at the lower end of the support sleeve 4 .

This negative pressure generating body 14 has a circular cross section, and its outer diameter is largest at the center and continuously decreases toward the lower and upper ends.

The negative pressure generator 14 is supported concentrically with the inner surface of the communication portion 10 of the support sleeve 4 with a predetermined gap between them by a plurality of radially provided ribs 15 .

Therefore, between the outer circumferential surface of the negative pressure generator 14 and the inner circumferential surface of the flow section 10 of the support sleeve 4, the cross-sectional area of the flow path decreases continuously from the bottom, that is, from the inflow direction of the coolant, and then continuously increases again. A venturi portion 16 is formed.

Further, a circular concave negative pressure chamber 17 is formed on the upper surface of this negative pressure generator 14 .

The inner diameter of this negative pressure chamber 17 is formed to be slightly larger than the outer diameter of the lower end of the entrance nozzle 6, and the lower end of the entrance nozzle 6 is accommodated within this negative pressure chamber 17.

In addition, a labyrinth portion 1 is provided on the upper inner circumferential surface of this negative pressure chamber 17.
8 is formed and configured to prevent coolant from flowing into this negative pressure chamber 17 from the flow portion 10 of the support sleeve 4 .

The negative pressure generating body 14 includes the venturi portion 16.
Negative pressure passages 19 are formed in the outer circumferential surface of the negative pressure generating body 14 corresponding to the narrowest portions thereof, and communicate with the inside of the negative pressure chamber 17.

The negative pressure generator 17, the support sleeve 4, etc. are made of a corrosion-resistant material such as stainless steel, or their surfaces are coated with a highly corrosion-resistant material.

In the first embodiment of the present invention configured as described above, the coolant flows from the lower part of the reactor vessel 1 through the venturi section 16 into the flow section 10 of the support sleeve 4, and further through the orifice hole 12 of the entrance nozzle 6. entrance nozzle 6
and is introduced into the fuel assembly 5.

When the coolant passes through the venturi section 16, its flow rate increases, and the static pressure of the venturi section 16 becomes lower than the static pressure within the flow section 10 of the support sleeve 4, generating negative pressure.

Therefore, the cooling member in the negative pressure chamber 17 is sucked into the venturi portion 16 via the negative pressure passage 19, and the inside of this negative pressure chamber 17 becomes negative pressure.

Therefore, the pressure difference between the static pressure in the circulation chamber 10 and the negative pressure in the negative pressure chamber 17 acting on the inner surface of the bottom of the entrance nozzle 6 urges the fuel assembly 5 downward and prevents it from floating up.

In this first embodiment, a large number of support sleeves 4 are provided on the core support plate 3, and these support sleeves 4...
Since the negative pressure generating body 14 is simply provided within the lower end of the valve, the structure is simple and manufacturing is easy.

Further, the negative pressure in the negative pressure chamber 17 can be made sufficiently low by reducing the cross-sectional area of the narrowest part of the venturi part 16. For example, by setting the flow velocity at the narrowest part to about 20 m/s, the surrounding A negative pressure that is approximately 2.0 kg/crj lower than the static pressure of is obtained, and lifting of the fuel assembly 5 can be reliably suppressed.

Furthermore, even if some coolant flows into the negative pressure chamber 17 from the gap between the inner surface of the negative pressure chamber 17 and the outer surface of the entrance nozzle 6, a large amount of this coolant flows into the venturi portion 16 via the negative pressure passage 19. Since suction is possible, the negative pressure within the negative pressure chamber 17 can be maintained sufficiently.

Therefore, since some leakage is allowed between the inner surface of the negative pressure chamber 17 and the outer surface of the entrance nozzle 6, there is no need to seal the lower end of the entrance nozzle 6 by seating it on the negative pressure generator 14.

Therefore, the entrance nozzle 6 only needs to be seated and sealed at one location on the sealing member 8 at the upper end of the support sleeve 4, and since the entire load is applied to this one seating location, the seating state is stable and sufficient sealing is achieved. As a result, the coolant does not leak above the core support plate 3, the flow rate can be accurately regulated, and the flow rate distribution to each fuel assembly 5 is also accurate.

Note that the first invention is not limited to the first embodiment described above.

For example, FIG. 3 shows a second embodiment of the invention.

In this second embodiment, another core support plate 20 is provided below the core support plate 3, and the lower end of the support sleeve 4 is fixed by this lower core support plate 20.

A through hole 21 is formed in the lower core support plate 20 in correspondence with the lower end opening of the support sleeve 4 .

Inside this through hole 21 is a fitting member 2 having a convex upper surface.
2 is attached by a plurality of ribs 23...
The fitting member 22 is configured to fit into a recess 24 formed on the lower surface of the negative pressure generator 14 to increase the mounting strength of the negative pressure generator 14.

The second embodiment has the same structure as the first embodiment except for the above-mentioned points, and the parts in FIG. 3 corresponding to the first embodiment are given the same reference numerals and the explanation thereof will be omitted.

In this second embodiment, both upper and lower ends of the support sleeve 4 are fixed to the core support plate 3.degree. 20, and the negative pressure generator 14 is supported via the fitting member 22, so it is structurally strong. , highly reliable.

Furthermore, FIG. 4 shows a third embodiment of the present invention.

This third embodiment has two core support plates 25.
26, and the upper end of the support sleeve 4 is attached to these core support plates 25, 26.

Further, a labyrinth portion is not provided on the inner surface of the negative pressure chamber 17, but instead a labyrinth portion 27 is provided on the outer peripheral surface of the lower end portion of the entrance nozzle 6.

The third embodiment has the same structure as the first embodiment except for the above points, and the same reference numerals are given to the parts corresponding to the first embodiment in FIG. 4, and the explanation thereof will be omitted.

In this third embodiment, since the support sleeve 4 is fixed by the two core support plates 25 and 26, it is structurally strong and has high reliability.

Furthermore, the present invention is not limited to the above-described embodiments; for example, the diameter of the inner surface of the lower end opening of the support sleeve may be continuously reduced to form a venturi portion.

As mentioned above, the present invention provides a support sleeve on the core support plate,
A negative pressure generator is provided in the lower end opening of the support sleeve to form a venturi part, and a negative pressure chamber in which the lower end of the entrance nozzle is housed is formed on the upper surface of the negative pressure generator. A negative pressure passage that opens and communicates with a negative pressure chamber is provided.

Therefore, the negative pressure generated in this venturi portion is introduced into the negative pressure chamber, urges the fuel assembly downward, and prevents the fuel assembly from floating up.

This kind of device is simply a support sleeve equipped with a negative pressure generator attached to the core support plate, and its structure is simple, and only the support sleeve and the negative pressure generator are precisely machined. It is easy to manufacture because other parts do not require very precise machining.

Further, sufficient negative pressure can be obtained by simply reducing the cross-sectional area of the long and narrow portions of the venturi portion, and lifting of the fuel assembly can be reliably prevented.

In addition, since some leakage is allowed between the negative pressure chamber and the lower end of the entrance nozzle, the seating seal of the entrance nozzle only needs to be placed in one place at the upper end of the support sleeve, which stabilizes the seating state and ensures a reliable seal. The results are outstanding, with little coolant leakage and accurate flow rate control such as flow rate distribution.

[Brief explanation of the drawing]

1 and 2 show a first embodiment of the present invention;
The figure is a longitudinal sectional view of the whole, and Figure 2 is a longitudinal sectional view of the main parts.
Further, FIG. 3 is a longitudinal sectional view of the main part of the second embodiment, and FIG. 4 is a longitudinal sectional view of the main part of the third embodiment. DESCRIPTION OF SYMBOLS 1... Reactor vessel, 3... Core support plate, 4... Support sleeve, 5... Fuel assembly, 6... Entrance nozzle, 12...
... Orifice hole, 14 ... Negative pressure generator, 1
6... Venturi section, 17... Negative pressure chamber, 19... Negative pressure passage, 20... Core support plate, 25.26... ...Core support plate, 28...
...Support sleeve 0

Claims (1)

[Scope of Claims] 1. A core support plate provided in a reactor vessel, a hollow cylindrical support sleeve with open upper and lower ends, which is attached to the core support plate and into which an entrance nozzle of a fuel assembly is inserted; a negative pressure generating body that is provided in the lower end opening of the support sleeve and forms a venturi portion in which the cross-sectional area of the flow path is continuously contracted and expanded between the outer peripheral surface of the support sleeve and the inner peripheral surface of the support tube; a negative pressure chamber formed on the upper surface of the negative pressure generator and accommodating the lower end of the entrance nozzle; and a negative pressure passage that opens on the outer peripheral surface of the negative pressure generator corresponding to the venturi portion and communicates with the negative pressure chamber. A nuclear reactor core support device characterized by comprising: 2. A patented device characterized in that a labyrinth portion is formed on the inner peripheral surface of the upper end of the negative chamber or the outer peripheral surface of the lower end of the entrance nozzle of the fuel assembly.