JPS61184489A - Shielding plug - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a shielding plug for a liquid metal cold section type fast breeder reactor, and in particular to a heat shielding plate of the shielding plug and a shielding shell surrounding the heat shielding plate. The present invention relates to a shielding plug that can suppress thermal stress and thermal deformation caused by natural convection occurring in an annular gap.

[Technical background of the invention and its problems] In general, the reactor vessel of a liquid metal cooled nuclear reactor has a reactor core and a primary coolant for cooling the core inside, so its integrity is high. Reliability is required. However, in liquid metal cooled reactors, the cold W at the core exit
The material temperature is high, and the temperature of the reactor vessel shell in contact with the core outlet coolant is therefore high, making the design of the reactor vessel extremely difficult as it requires strict high-temperature structural design conditions.

On the other hand, as shown in FIG. 8, the heat shielding layer 21 of the shielding plug 4.5 is mounted to close the upper open end of the above-mentioned furnace vessel 1.
An annular gap is formed between the shield body 25 and the shield body 25 .

It is very difficult to form this gap into a gap that can prevent the generation of natural convection due to manufacturing restrictions such as manufacturing tolerances of the shielding body 25 and from the viewpoint of preventing mutual interference due to thermal deformation.

Therefore, natural convection as shown schematically by arrows in FIG. This causes thermal stress and thermal deformation. Furthermore, natural convection reduces the heat insulating performance of the heat shielding layer 21, resulting in an increase in the temperature of the upper surface of the shielding plug 4.5 and an increase in the cooling capacity of the shielding plug 4.5. Further, the heat shielding layer 21 has a large movement opening within the shielding shell 25 during an earthquake, which causes earthquake resistance problems such as collisions with the shielding shell 25.

[Object of the Invention] The present invention has been made in view of the above circumstances, and its purpose is to suppress natural convection in the annular gap between the heat shield layer and the shield body of the shield plug, thereby reducing heat. It is an object of the present invention to provide a shielding plug that can prevent a decrease in the heat insulation performance of the shielding layer, relieve the thermal stress of the furnace vessel and the shielding shell due to circumferential natural convection, and further improve the seismic resistance of the heat shielding layer.

[Summary of the Invention] That is, the present invention provides a shielding plug that houses a heat shielding layer in a shielding zone and closes an upper opening of a reactor vessel. This is a shielding plug characterized by a mouth in which an annular leaf spring is arranged in the annular gap to divide the annular gap in the height direction.

[Embodiments of the Invention] Hereinafter, the present invention will be described in detail with reference to the drawings of one embodiment.

In FIG. 1, a reactor core 3 is installed within a reactor vessel 1 and filled with a coolant 2 (generally sodium). A fixed plug 4 is mounted on the upper end of the opening of the furnace vessel 1. A rotary plug 5 is eccentrically provided on the fixed plug 4. The fixed plug 4 and the rotating plug 5 are collectively referred to as a shielding plug. This shielding plug can be of single, double or triple rotation type depending on the fuel exchange method, but since the present invention can be applied to any type of rotation type, the - type rotation type will be explained here. This rotary plug 5 is rotatably installed, and includes a fuel exchanger (not shown), a core upper mechanism 6,
Others are installed.

During normal operation of the nuclear reactor, the coolant 2 reaches a considerably high temperature (generally around 500° C.) and heats the lower surface of the shielding plug through the core cover gas 7.

A gas layer using cover gas 7 and a heat shielding layer 21 having a laminated plate structure made of plate materials are disposed below the shielding plug. As shown in FIG. 3, the heat shield layer 21 includes a plurality of thin (for example, 5n) heat shield plates 22 and a relatively thick (for example, 5 nm) heat shield layer sandwiched between the heat shield plates 22. 30) The heat shield plate 23 is located at the upper and lower ends of the heat shield layer 21, and the relatively thick (for example, 30 nm) heat shield plate 24 is connected between the heat shield plates 22, 23, and 24. It is composed of a spacer 28 and a rod 29 that are held and fixed in the gap.

FIG. 4 is a detailed view of the vicinity of the outer periphery of the heat shield plate 23. An annular spring 27 is attached to the outer periphery of the heat shield plate 23 by bolts or the like so as to close the gap with the shield body 25 over the entire circumference. On the other hand, seismic supports 26 divided in the circumferential direction are attached to the inner peripheral surface of the shielding body 25 facing the outer periphery of the heat shielding plate 23 by bolts or the like.

The thickness H of the seismic support 26 is set as follows. That is, the heat shield plates 22, 23, and 24 are stacked one by one from the bottom, and once the heat shield plate 23 is installed, the heat shield plate 23 and the shield r! Measure the distance to the inner circumference of A25. After actually measuring a plurality of points along the circumferential direction, the heat shielding plate 23 is positioned so that the distance between the edges is uniform. Thereafter, the distance is actually measured again, and the thickness 1 of the seismic support 26 is set so that the distance between the heat shield plate 23 and the seismic support 26 is small enough to prevent mutual interference even due to thermal deformation.

In this embodiment, an example is shown in which the annular spring 27 is attached to the heat shielding plate 23 side and the seismic support 26 is attached to the shielding body 25 side, but they may be attached on the same side or vice versa.

Further, the cross-sectional shape of the annular spring 27 may be as shown in FIGS. 5 to 7 in addition to that shown in FIG. 4.

Furthermore, the heat shield plate 23, the annular spring 27, and the seismic support 26 may be installed in several stages in the axial direction.

Next, the operation and effects of the shielding plug according to the present invention configured as described above will be explained. In the shielding plug configured as described above, the annular spring 27 is attached to the gap 31 between the heat shield layer 21 and the shield body 25, so that the gap 31 is partitioned in the height direction. At this time, it has been found that if the axial temperature conditions and gap width are the same, the shorter the gap height is, the less likely natural convection will occur. Therefore, it is easy to attach a plurality of annular springs 27 so that the gap height is such that natural convection can be ignored from an engineering point of view.

On the other hand, since the seismic support 26 is attached to the shield 1N25, the heat shield layer 21 during an earthquake is supported by the seismic support 26 by just moving the heat shield plate 23 through a small gap.
Further, the heat shield plate 22 and the heat shield plate 24 are supported by rods 29. Note that since the movement opening of the heat shield plate 23 during an earthquake is limited, the stroke of the annular spring 27 does not need to be extremely large, and the soundness of the annular spring 27 is maintained in this state.

[Effect of the Invention 1] As described above, according to the present invention, natural convection occurring in the gap between the heat shielding layer of the shielding plug and the shielding shell can be effectively suppressed, and the natural convection caused by the natural convection can be suppressed. The large circumferential temperature distribution, thermal stress and thermal deformation can be alleviated, and a highly reliable shielding plug can be obtained.

Furthermore, by suppressing natural convection within the heat shielding layer, it is possible to prevent a decrease in insulation performance that would lead to an increase in the temperature of the upper surface of the shielding plug, an increase in the cooling capacity of the shielding plug, etc., and a highly reliable shielding plug can be obtained. Furthermore, when the seismic support is arranged as in the embodiment, the amount of movement of the heat shielding layer within the shielding shell during an earthquake can be kept small, so a shielding plug with excellent earthquake resistance can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view schematically showing a nuclear reactor to which an embodiment of the present invention is applied, and FIG. 2 is a schematic diagram showing natural convection occurring in the gap between the heat shielding layer of the shielding plug and the shielding shell. 3 and 4 are longitudinal sectional views showing essential parts of the present invention,
5 to 7 show modified examples of the cross-sectional shape of the annular spring, and FIG. 8 is a longitudinal sectional view showing a conventional nuclear reactor. 1...Reactor vessel 2...Coolant 3...Core 4...Fixing plug 5... ...... Rotating plug 21 ... Heat shielding layer 22.23.24 ... Heat shielding plate 25 ...... Shielding body 26 ... ...Earthquake support 27 ...... Ring-shaped spring representative patent attorney Noriyuki Chika (one idiot) Figure 1 Figure 2 Figure 3r! 7I Figure 5 Figure 6 Figure 7 Figure 8

Claims (2)

[Claims] (1) In a shielding plug that houses a heat shielding layer in the shielding shell and closes the upper opening of the reactor vessel, the annular gap formed between the heat shielding layer and the shielding shell has an annular shape. A shielding plug characterized by having an annular leaf spring arranged to divide the gap in the height direction. (2) The shielding plug according to claim 1, wherein a plurality of annular leaf springs are installed at intervals in the height direction of the annular gap.