JPS6313518Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structure for suppressing thermal stress in an inner member or an outer member forming an annulus gap in a cover gas space of a device using liquid metal.

In this invention, the annulus gap is defined as the space between the reactor vessel and the shielding plug in a liquid metal-cooled fast breeder reactor, between various rotating plugs, and in the equipment in the cooling system where a free surface of liquid metal exists inside. ,
For example, it refers to the narrow cylindrical gap formed in the upper part of a mechanical sodium pump. Therefore,
The inner or outer members that form the annulus gap include the upper wall member of the reactor vessel, various upper reactor shielding plugs, the upper wall member of the vessel in cooling system equipment, and the inner casing facing the upper wall member of the vessel. means the members, etc. The present invention suppresses thermal stress applied to these components in nuclear reactors, etc.
The present invention relates to a structure that can prevent these members from thermally bending or from generating excessive thermal stress.

Taking a sodium-cooled reactor vessel as an example, as shown in Fig. 1, a large rotary plug 4, a small Equipment such as a rotating plug 5 and a furnace upper mechanism 6 are installed, and an annulus gap 7 is formed around each of them. In addition to what is shown in the diagram, such an annulus gap may be used for mechanical pumps,
It is also formed in through holes for intermediate heat exchangers in pool-type sodium-cooled fast reactors, but in either case, the lower end of the gap is at a high temperature, while the upper end of the gap is at a low temperature.

In recent years, various tests and studies have revealed that natural convection of cover gas as shown in FIG. 2 occurs in such a gap where there is a relatively large temperature difference between the upper and lower sides. This convection becomes an upward flow at one location in the circumferential direction of the gap, and a downward flow at another location. Therefore, in the vicinity of the upward flow, the surrounding wall is heated by the high temperature gas, while in the vicinity of the downward flow, the surrounding wall is cooled by the flow of the cooled gas.
The simultaneous heating and cooling of the gap surrounding wall causes a large temperature difference in the circumferential direction of the annulus gap forming member. In experiments conducted by the present inventors, the change in the height direction of this temperature difference (the difference between the temperature at the point where the upward flow occurs and the temperature difference at the point where the downward flow occurs) is as shown in Figure 3. Become. That is, a peak of temperature difference ΔT〓 _,nax appears near the center of the gap in the height direction. If such a large temperature difference occurs during reactor operation, the equipment inside the through-hole may become thermally bent and deformed with respect to the vertically drawn center axis, or be damaged by excessive thermal stress. Sometimes even.

Conventionally, in order to eliminate such temperature differences,
A mechanism has been proposed in which a convection prevention baffle plate in the form of a full plate or a fin is installed inside the gap, thereby preventing natural convection of gas. However, such a mechanism is extremely difficult to use in gaps between equipment already installed in the primary system of the reactor, and when equipment moves up and down or rotates inside the through hole. However, installing such a plate does not necessarily mean that new mechanical failures will not occur.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a structure that can suppress thermal stress caused by natural convection of the cover gas in the annulus gap without using a baffle plate or the like. be.

In order to achieve this objective, the inventors of the present invention have conducted various investigations and tests, and have repeatedly studied various factors related to the magnitude of the circumferential temperature difference in the annulus gap. According to the results, it was found that this temperature difference ΔT depends on the thickness of the inner and outer walls of the cylinder. That is, the thicker the wall, the smaller the temperature difference ΔT〓 becomes, and the thinner the wall, the larger the temperature difference ΔT〓 becomes. This can be explained using Figure 2.
This is because the thicker the wall, the greater the heat conduction through the wall between the high temperature side 10 and the low temperature side 11, which are formed at two locations apart in the circumferential direction. From this, it can be seen in Fig. 2 that if the inside of the inner cylinder 9 is filled with a substance with high thermal conductivity, the heat conduction between the high temperature side and the low temperature side will be better, and the temperature difference ΔT will be smaller. is expected. To confirm this, Figure 4 shows a height of approximately
When a double gap 12 of 2.8 m, diameter 1.6 m, and width 15 mm is formed, and the filling 14 inside the stainless steel inner wall 13 is used as a heat insulating material (experimental line of λ = 1.0, λ...thermal conductivity)
When a metallic substance (steel ball) has a thermal conductivity 400 to 500 times that of a heat insulating material (λ = 400
~500 experimental line) circumferential temperature difference ΔT〓 is ΔT〓/
ΔT _l (where ΔT _l is the average temperature difference between the upper and lower ends of the gap)
It is expressed in the form of From the same figure, it can be seen that when the thermal conductivity of the filling is high, the maximum value of the temperature difference (ΔT〓 _{, nax} shown in FIG. 3) becomes smaller for the same ΔT _l .

In an actual nuclear reactor, the diameter D of the gap formed in the through hole increases as the reactor becomes larger. In particular, in the case of a large rotating plug at the top of the reactor vessel shown in FIG. 1 and a corresponding fixed plug, the diameter is proportional to the diameter of the reactor vessel. Generally, as the diameter D increases in this way, ΔT〓 _,nax around the gap also tends to increase approximately in proportion to it. Therefore,
The larger the furnace, the more measures need to be taken to reduce ΔT〓 _,nax . FIG. 5 summarizes the data obtained with various test devices so far and shows how an increase in the gap diameter D affects ΔT〓 _,nax / _ΔTl . All of these data are plots of data obtained using test equipment having approximately the same gap cross-sectional dimensions of 1.5 to 20 m in height and 15 to 25 mm in gap width, but differing only in diameter D. In the figure, the range indicated by a is the range when the filling in the inner cylinder is entirely made of heat insulating material or a low thermal conductivity material with approximately the same thermal conductivity, but the general tendency is as described above. As described above, ΔT〓 _,nax / _ΔTl , that is, the maximum temperature difference _{ΔT〓 ,nax} for the same gap upper and lower temperature difference ΔTl increases as the diameter D increases. However, if the filling is made of a highly thermally conductive material whose thermal conductivity λ is 400 to 500 times or 2300 times that of the insulation material, as shown by b (steel balls) and c (graphite) in the figure, It can be seen that ΔT〓 _{, nax} /ΔT _l can be significantly reduced, and an increase in the diameter D can be effectively dealt with.

This invention was developed based on the results of such surveys and tests.
This design is designed to improve the thermal conductivity of the annulus gap forming member, thereby reducing the temperature difference in the circumferential direction. That is, the present invention is characterized in that at least one of the inner member and outer member forming the annulus gap is provided with a heat conduction path made of a highly thermally conductive material and extending continuously in the circumferential or radial direction of the member. This is a thermal stress suppression mechanism for the annulus gap forming member. In view of its principle, the present invention is particularly suitable for alleviating thermal stress in the annulus gap of large-diameter large furnaces. To be more specific, first of all, regarding the inner cylinder that forms the gap, in order to make the heat conduction as good as possible, in addition to fixing the internal structure and the inner cylinder wall by welding, screwing, etc. We use materials with high thermal conductivity such as aluminum, copper, and graphite as much as possible for internal structures, and we also use high thermal conductive materials (e.g. aluminum powder,
(copper powder, graphite pieces, etc.). Similar measures will be taken for the outer cylinder. In this way, by providing a heat conduction path other than the walls, the heat conduction, which conventionally was mainly based on circumferential heat conduction between the inner and outer cylinder walls that form the annulus gap, can be improved. , thereby significantly reducing ΔT〓 _,nax .

Examples of the present invention will be described below. Large rotating plugs and fixed plugs sometimes use stainless steel or carbon steel blocks as internal radiation shields. Conventionally, as shown in FIG. 6, these radiation shields 14 were thermally separated from the surrounding wall 15, so the heat conduction between the surrounding wall and the radiation shield was not good. In order to improve this problem, measures as shown in FIG. 7A are taken. In this Figure 7A, the 6th
In the figure, the small rotation plug 5 and the furnace upper mechanism 6 installed on the center side of the large rotation plug 4 are omitted from illustration, and only the parts related to the present invention are shown. As can be seen from FIG. 7A, the radiation shield 14
A high heat conductive material 16 is filled in the gap between the radiation shield 14 and the outer wall 15, and a plate made of a high heat conductive material is also placed above or below the radiation shield 14. In this way, as shown in FIG. 7B, the conventional flow of heat only q along the surrounding wall 15 is now changed to the flow q of heat passing through the highly thermally conductive material 16 and the radiation shield 14. ′ increases the overall heat flow, and as a result, ΔT〓 _,nax becomes smaller. In addition,
In FIG. 7B, the symbol H represents a high temperature region, and the symbol C represents a low temperature region.

FIG. 8 is an example of measures taken for the heat shield plate attached to the large rotation plug 4. Heat shield plate 2
1 and the heat shield cylinder 22, and if necessary, to improve the radial heat conduction of the heat shield plate 21 itself, a high thermal conductive material such as aluminum is placed inside the stainless steel heat shield plate 23. Insert 24. Further, in order to smooth the flow of heat in the radial direction, it is preferable that the heat shield plates 21 are brought into contact with each other at a position close to the center thereof, as shown in FIG. 9. By doing so, the large temperature difference that has been occurring around the heat shield plate can be significantly reduced. In the figure, numeral 25 is a heat shield plate for the small rotation plug, numeral 26 is a through hole for the furnace upper mechanism, and arrows indicate heat flow.

In nuclear reactor-related facilities, the 10th
As shown in the figure, a ring 31 made of a highly thermally conductive material is crimped with a fixing band 32 or the like as a heat conduction path to the outer wall of the outer member 30 forming the gap, thereby reducing ΔT〓 _,nax . be able to. The ring 31 may have a multi-stage configuration if necessary. Such a configuration can be easily applied to a pump that is already used in a nuclear reactor and is difficult to modify, and has high reliability.

In addition, regarding the inside of the pump, as shown in FIG.
1 is made of a highly thermally conductive material such as graphite, or when the radiation shield 41 can only be made of a material with low thermal conductivity, a plate 42 of a highly thermally conductive material is partially incorporated to form a heat conduction path. Let it form.

Since the present invention has the above-mentioned configuration, it is possible to suppress the thermal stress caused by the natural convection of the cover gas in the annulus gap without using a baffle plate, etc., and when the equipment moves vertically or rotates in the annulus gap. There is no problem even if it is. In addition, it is compatible with large furnaces with large gap diameters, and can be applied to existing pumps, as well as preventing thermal curvature of the annulus gap forming member and excessive thermal stress.
This is extremely serious.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the reactor vessel and shielding plug, Figure 2 is an explanatory diagram showing the natural convection of the cover gas in the annulus gap, and Figure 3 is the height direction of the temperature difference between two points in the circumferential direction of the gap wall. Figure 4 is a diagram showing the relationship between various filling materials and wall temperature difference. Figure 5 is a diagram showing the relationship between various filling materials and the diameter of the annulus gap and ΔT〓 _,nax /ΔT _l FIG. 6 is a diagram showing the structure around the radiation shield in the conventional large-rotation plug, FIG. 7A is an explanatory diagram showing an embodiment of the present invention, and B is an explanatory diagram showing the heat flow. Figure, Figure 8,
FIG. 9, FIG. 10, and FIG. 11 are explanatory views showing other embodiments of the present invention, respectively. 3... Reactor vessel, 4... Large rotating plug, 5...
...Small rotating plug, 6... Furnace upper mechanism, 7... Annulus gap.

Claims (1)

[Claims for Utility Model Registration] 1. At least one of the inner and outer members forming the annulus gap is made of a highly thermally conductive material selected from stainless steel, carbon steel, graphite, aluminum, and copper. A thermal stress suppression mechanism for an annulus gap forming member, characterized in that a heat conduction path is provided that extends continuously in the circumferential direction or radial direction of the member. 2. The mechanism according to claim 1 of the utility model registration claim, in which the heat conduction path is plate-shaped. 3. The mechanism according to claim 1 of the utility model registration claim, in which the heat conduction path is ring-shaped. 4. The mechanism according to claim 3, wherein a ring-shaped heat conduction path is provided in one or more stages on the outer peripheral surface of the outer member forming the annulus gap.