JPS6331753B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid metal cooled nuclear reactor, and in particular to suppressing thermal stress caused by natural convection occurring in an annular gap between a reactor vessel and a shielding plug and preventing radiation streaming in the gap. Relating to a nuclear reactor equipped with a mechanism.

The reactor vessel of a liquid metal cooled nuclear reactor has a reactor core and a primary coolant for cooling the reactor core inside thereof, and therefore, high reliability is required regarding its soundness. However, in liquid metal cooled nuclear reactors, the temperature of the coolant at the core exit is high, and therefore the temperature of the reactor vessel shell in contact with the core outlet coolant is high, requiring severe high-temperature structural design conditions for the design of the reactor vessel. It is becoming more difficult. On the other hand, the first
As shown in the figure, an annular gap 8 is formed between the shielding plug 5 mounted on the tower and closing the upper opening end of the above-mentioned furnace vessel 1 and the above-mentioned furnace vessel body. Natural convection as schematically shown in FIG. 2 occurs in this gap, resulting in non-uniform temperature distribution in the circumferential direction of the furnace vessel, which causes thermal stress and deformation of the furnace vessel. Furthermore, since the radiation inside the reactor is not shielded through the annular gap and leaks to the upper part of the reactor, there are problems such as the formation of areas with locally high radiation dose rates.

The present invention was made in view of the above circumstances, and
The objective is to provide a nuclear reactor in which natural convection in the annular gap between the reactor vessel and the shielding plug is suppressed and radiation streaming in the gap is reduced.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal cross-sectional view showing the concept of a nuclear reactor to which the present invention is applied, and FIG. 3 is an enlarged cross-sectional view of essential parts of the present invention.

The reactor vessel 1 has a reactor core 7 housed therein, and is supported by a support structure 18 . The upper opening of the furnace vessel 1 is closed by a shielding plug 5, which is supported by a support spacer 19 installed on the upper part of a support structure 18. An inlet nozzle 3 is provided at the bottom of the reactor vessel 1 containing the reactor core 7 supported by a core support structure 16 extending inward from the body of the reactor vessel 1 in a brim shape, and an outlet nozzle is provided at the side of the body. 2 is provided. Coolant liquid level 17 and the shielding plug 5
A cover gas space 6 is formed between the two.
An annular gap 8 is provided between the furnace vessel 1 and the shielding plug 5.
is formed. In the annular gap 8, there is a stepped cylindrical shield body 10 with a thicker wall on the lower side.
The shielding plug 5 is suspended from a flange at the upper end of the furnace vessel 1, and the shielding plug 5 is formed in a stepped shape to match the shield shell 10. Further, a ring-shaped convection prevention plate 11 is installed at the lower end of the shield shell 10 to limit the gap between the shield shell and the lower ends of the furnace vessel 1 and the shielding plug 5.

Next, the operation and effects of the nuclear reactor according to the present invention configured as described above will be explained. In the nuclear reactor configured as described above, the shield shell 10
is attached directly to the furnace vessel 1, so that the width of the annular gap 12 formed therebetween can be made very small. By reducing the gap width, for the same axial temperature distribution, the flow resistance in the annular gap increases, thereby suppressing the generation of natural convection. Moreover, by reducing the gap width, the radiation transmitted through the same portion is also reduced. Generally, the shielding plug 5 is not directly mounted on the reactor vessel 1, so the width of the gaps 14 and 15 formed between the shielding shell 10 and the shielding plug 5 is approximately several tens of millimeters. The flow is separated by a stepped section,
Since the natural convection that begins to occur in the lower gap 14 is attenuated in the stepped portion, the upper gap 15 is hardly affected by the natural convection in the lower part. As mentioned above, the natural convection in the gap is restricted by the stepped part, and when the axial temperature conditions and gap width are the same, the shorter the gap height, the more natural convection occurs in the lower gap. Although it becomes difficult to do so, by separating at the stepped portion, the gap height of the lower gap portion is also reduced, so generation of natural convection in the lower gap portion is also suppressed. In addition, radiation streaming leaking from the gap is also significantly reduced because the stepped upper part is closed and a shielding plug is installed. moreover,
By installing a convection prevention ring 11 at the lower end of the shield shell 10 to limit the gap between the furnace vessel and the shielding plug, the cover gas in the gaps 12 and 14 is separated from the high-temperature in-furnace cover gas 6. Furthermore, convection in the gap is restricted. Since the convection prevention ring 11 has a divided structure, if it is installed after the shielding shell 10 and shielding plug 5 are attached to the furnace vessel, the gap width between the furnace vessel, the shielding plug, and the convection prevention ring can be reduced. can be set extremely small, further increasing the convection prevention effect.

As explained above, according to the present invention, natural convection occurring in the gap between the furnace vessel and the shielding plug can be suppressed,
A highly reliable nuclear reactor can be obtained by alleviating the large circumferential temperature distribution, thermal stress, and thermal deformation of the reactor vessel and shielding plug caused by natural convection.
Furthermore, since natural convection is suppressed, it also has the effect of restricting the adhesion of coolant vapor that migrates to the gap due to cover gas convection. Further, by reducing the gap width and providing a stepped structure, radiation streaming is reduced, so a nuclear reactor with excellent radiation shielding effects can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view schematically showing a nuclear reactor to which the present invention is applied, FIG. 2 is a perspective view schematically showing natural convection occurring in the gap between the reactor vessel wall and the shielding plug, and FIG. FIG. 3 is a longitudinal sectional view showing the main part of the present invention. DESCRIPTION OF SYMBOLS 1... Furnace vessel, 5... Shielding plug, 10... Shade shell, 11... Convection prevention plate.

Claims (1)

[Scope of Claims] 1. In a fast breeder nuclear reactor that includes a reactor vessel that houses a reactor core and is open at the top, and a shielding plug that closes the opening of the reactor vessel, the reactor vessel and the shield A cylinder having a thin upper wall and a thicker lower wall is provided in the gap formed between the plug and the plug, and an annular ring is attached to the bottom of the cylinder so as to cover the gap. Reactor. 2. The nuclear reactor according to claim 1, wherein the annular ring is divided into a plurality of parts.