JPH022602B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a cold trap having a structure in which an insulating gas layer is provided between a cooling section for incoming liquid metal and an impurity trapping section.

[Prior Art] A cold trap is a purification device that captures impurities in a liquid metal using a mesh or the like filled in a low-temperature part by utilizing the difference in their saturation solubility. For example, when dirty liquid sodium is cooled, dissolved impurities become supersaturated and precipitate out.

As shown in FIG. 3 or 4, for example, in a conventional cold trap, an insulating gas layer 14 is provided between a cooling section 10 for inflowing liquid sodium and an impurity trapping section 12, and the cooling section 10 and the impurity trapping section are separated. 12 is prevented, and the temperature of the impurity trapping section 12 filled with mesh or the like is made uniform to prevent the impurity trapping ability from decreasing. The cooling unit 10 has a configuration in which, for example, a large number of cooling pipes 16 are arranged in a circumferential manner, cooling gas flows through the inside, and liquid sodium flows down the outside.

The heat insulating gas layer 14 has a structure in which an inert gas such as argon gas or titanium gas is introduced into the inside of a double-layered partition plate arranged coaxially on the outside and inside, and the lower part as shown in FIG. There are open types and closed types as shown in Figure 4.

[Problems to be Solved by the Invention] However, in the bottom open type, when the pressure drop in the impurity trapping section 12 increases as impurities are captured, the inert gas in the insulating gas layer 14 is compressed by the internal pressure of the cold trap. However, the sodium liquid level 13 in the insulating gas layer 14 rises and allows heat exchange in that area, which has the disadvantage that the function of the insulating gas layer 14 is significantly reduced. In particular, in mesh external precipitation type cold traps, if the temperature of the impurity trapping section is not uniform, local trapping of impurities will occur and the pressure drop in the impurity trapping section will increase. Compression of layers→
Heat exchange between the cooling section and the impurity trapping section → non-uniform temperature in the impurity trapping section → local capture of impurities → increase in pressure drop in the impurity trapping section → This leads to a vicious cycle. In other words, there is a drawback that when the pressure drop in the impurity trapping section starts to rise, it accelerates.

In order to eliminate these drawbacks, the lower end of the double wall structure is expanded to form a large part for storing insulating gas, so that even if the pressure drop in the impurity trap increases, the liquid level of the liquid metal in the insulating gas layer remains constant. There are also structures that have been devised to prevent it from rising too much.

However, in any case, as long as the bottom part is open, it is not possible to completely suppress the rise in the liquid metal level in the insulating gas layer, and some degree of heat exchange between the cooling section and the impurity trapping section is unavoidable. . This means that an area with a lower temperature than the impurity capture area is created in the cold trap, and in order to suppress the generation of radioactive corrosion products, the temperature of the impurity capture area is set to 110°C.
If an attempt is made to lower the temperature to around 30°F, there will be areas within the cold trap that are lower than that temperature, and there is a possibility that sodium will solidify in those areas.

In other words, in the case of an open-bottom cold trap, it is not possible to lower the temperature of the impurity trapping part to about 110℃, and it is difficult to reduce the oxygen concentration in sodium to about 1 ppm, resulting in the generation of radioactive corrosion products. It is not suitable for low-temperature operation where the temperature can be suppressed.

On the other hand, in the case of a closed type as shown in FIG. 4, there is little heat exchange between the cooling section and the impurity trap, and the temperature of the impurity trap almost matches the lowest temperature in the cold trap. Therefore, even if the temperature of the impurity trapping section is lowered to about 110°C, there is no risk of sodium solidifying in other parts. In addition, a constant insulating gas layer is secured regardless of the internal pressure of the cold trap, so as mentioned earlier, when the pressure drop in the impurity trap begins to rise, it accelerates, which is seen in the open-bottom type. Such a vicious cycle will never occur.

However, in this closed type, the temperature of the partition plate that forms the insulating gas layer differs between the cooling section and the impurity trapping section, so a large thermal stress is applied to the lower part of the insulating gas layer due to the difference in the amount of thermal expansion. Therefore, in order to deal with this, detailed stress analysis is required for structural design, which has the disadvantage of increasing manufacturing costs.

In addition, in order to prevent excessive thermal stress from being applied to the lower part of the insulating gas layer, the set temperature drop rate of the cold trap is restricted, making operation difficult. the result,
In normal operation, in the case of the purification system of the cold trap comprehensive test equipment, even if there is an economizer on the cold trap inlet side, the sodium temperature in the system cannot be raised above 350°C. In addition, even if the sodium circulation is restarted after a temporary stop due to a power outage, etc., the sodium temperature in the system should be lowered to near the cold trap temperature, and the temperature difference in the insulating gas layer should not exceed a predetermined value. You may have to start cycling sodium.

The purpose of the present invention is to eliminate the drawbacks of the prior art as described above, and to avoid various restrictions regarding thermal stress.
Moreover, even if the pressure drop in the impurity capture section starts to rise, a sufficient insulating gas layer can always be ensured, so the temperature of the impurity capture section and the lowest temperature inside the cold trap can be made almost the same, making it fully compatible with low-temperature operation. The object of the present invention is to provide a cold trap that can also have a long service life.

[Means for Solving the Problems] The present invention, which can achieve the above objects, includes a cooling section that lowers the temperature of the inflowing liquid metal, and an impurity trapping section that captures impurities in the liquid metal. In this cold trap, the structure of the insulating gas layer located between the two has been devised.

In the present invention, this insulating gas layer is composed of partition plates arranged in three layers. The first partition plate located on the cooling section side and the second partition plate located on the impurity capture section side have a structure in which the upper part is sealed but the lower part is open. The third partition plate divides the insulating gas layer into two, and the upper part of the third partition plate is open and the lower part is connected to either the first or second partition plate and is sealed. .

[Function] When triple partition plates are provided as described above, the insulating gas layer is divided into two, and there is a gap between the first partition plate and the third partition plate and between the third partition plate and the second partition plate. An insulating gas layer is formed between the two. As the impurities are trapped, the pressure drop in the impurity trap increases, and the liquid metal enters the gap between the two insulating gas layers, the lower end of which is open, and the liquid level rises.

However, since a constant amount of insulating gas is always secured on the other gap side, it prevents heat exchange between the cooling section and the impurity trapping section, prevents the temperature of the impurity trapping section from rising, and lowers the minimum temperature of the cold trap. The temperature of the impurity trapping section can be made almost the same.

Therefore, with the above-described configuration, the cold trap can be operated at low temperatures.

[Embodiment] FIG. 1 is an explanatory diagram showing an embodiment of a cold trap according to the present invention. The inside of the cylindrical body 20 is partitioned by an insulating gas layer provided coaxially, with the outside serving as a cooling section 22 for lowering the temperature of the incoming liquid sodium, and the inside serving as an impurity trapping section 24 for capturing impurities in the sodium. ing. A cooling gas inlet pipe 26 is connected to the lower part of the body 20, and a cooling gas outlet pipe 28 is connected to the upper part. Also, fuselage 2
Tube sheets 30 and 32 are attached to the upper and lower parts of the body 20, respectively, and a large number of cooling pipes 34 are arranged circumferentially along the inner wall of the body 20 so as to pass between the tube sheets.

A sodium inlet pipe 36 is installed so as to penetrate the upper part of the body 20 and the upper tube plate 30, and a sodium outlet pipe 38 is connected to the impurity trapping part 24 filled with stainless steel mesh or the like. Connected to the top.

The liquid sodium to be purified is sodium inlet pipe 3.
6 into the fuselage 20 and flows down through the peripheral cooling section 22. On the other hand, the cooling gas enters the body 20 from the cooling gas inlet pipe 26 and rises through a large number of cooling pipes 34 arranged in parallel around the periphery. In this process, heat exchange is performed with the liquid sodium flowing down, and the warmed cooling gas further rises and flows out from the cooling gas outlet pipe 28. The liquid sodium cooled in the cooling section 22 has its flow direction reversed at the lower tube plate 32 and passes through the impurity trapping section 24.
There, impurities are precipitated and removed, and the purified sodium flows out through the sodium outlet pipe 38. Such a sodium purification operation is basically the same as that of a conventional cold trap.

The adiabatic gas layer prevents heat exchange between the cooling section 22 and the impurity trapping section 24. This insulating gas layer has double-structured partition plates 42 and 44 that are vertically disposed around the demister container upper lid 40 located at the upper end of the impurity trapping section 24. Outside (cooling section side)
The first partition plate 42 located on the inside and the second partition plate 44 located on the inside (on the impurity trapping part side) are both connected to the upper lid 40 to form a sealed structure, and have an open structure at the bottom. An inert gas such as argon gas is put between the double partition plates 42 and 44, and the upper part has a sealed structure, so even if sodium flows into the cold trap, it will remain inactive. The structure is such that the gas has no place to escape and remains as it is as an insulating gas layer.

Now, the points in which the present invention is significantly different from the prior art are as follows.
Such a first partition plate 42 and a second partition plate 44
A third partition plate 46 is provided coaxially between the two to divide the insulating gas layer into two, and the upper part of the third partition plate 46 is open, but the lower part is connected to the lower end of the second partition plate 44. The point is that it has a connected and sealed structure. This connection is configured to be airtight and prevent sodium from entering from below. In this embodiment, both the second partition plate 44 and the third partition plate 46 are narrowed so that their lower ends have a small diameter, and a large gas reservoir 48 is created near the bottom of the open first partition plate.
The shape is such that it is formed.

FIG. 2 is an explanatory diagram showing the relationship between the position in the cold trap of such a structure, the temperature of the cooling section, and the temperature of the impurity trapping section. When the cold trap is new, the pressure drop in the impurity capture section is small, and the sodium liquid level in the insulating gas layer is at a low position (sign
(denoted as L ₁ ). As the trap is used for a long period of time and the amount of impurities captured increases, the pressure drop in the impurity capture section increases, and the internal pressure of the cold trap compresses the insulating gas layer, thereby increasing the sodium liquid level (indicated by the symbol L ₂ ). . A large gas reservoir 48 is provided in the lower part between the first partition plate 42 and the third partition plate 46, and although this can considerably suppress the rise in the sodium liquid level, it has its own limits. , it is inevitable that it will rise as shown in Figure 2. However, in the present invention, the insulating gas layer is double, so even if sodium enters the outer (cooling section side) insulating gas layer, sodium will not flow into the inner (impurity trapping section side) insulating gas layer. Therefore, a sufficient insulating gas layer can always be ensured. Therefore, heat exchange between the cooling section 22 and the impurity trap 24 becomes extremely small, and the impurity trap temperature and the lowest temperature in the cold trap almost match, and regardless of the level of pressure drop, the temperature inside the impurity trap becomes extremely low. temperature can be kept almost constant.

[Effects of the Invention] As described above, the present invention has a structure in which the insulating gas layer is divided by the third partition plate whose lower part is sealed, so that there is always a sufficient insulating gas layer regardless of the pressure drop in the impurity trapping section. Therefore, the heat exchange between the cooling part and the impurity trapping part is extremely small, and the temperature of the impurity trapping part and the lowest temperature in the cold trap are almost the same, which has the effect of being able to cope with low-temperature operation. For example, in the case of liquid sodium purification, the temperature of the impurity capture section is
Even if the temperature is lowered to about 110°C, there is no risk of sodium solidifying in other parts, making it possible to operate at low temperatures with the aim of suppressing the generation of radioactive corrosion products.

In addition, as mentioned above, even if the pressure drop in the impurity trapping section increases, the function of the insulating gas layer does not deteriorate, which eliminates the drawbacks of the mesh external precipitation type cold trap with the bottom open type insulating gas layer, namely the impurity trapping section. This eliminates the drawback that the pressure drop is accelerated when it starts to rise, and has the effect of extending the life of the cold trap.

Furthermore, since all the partition plates forming the insulating gas layer in the present invention have free ends, they are not subject to thermal stress constraints, and therefore thermal stress analysis is not required, reducing manufacturing costs. Operation becomes easier because there are no restrictions on the trap's set temperature drop rate, etc.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the cold trap according to the present invention, FIG. 2 is an explanatory diagram showing the temperature distribution of the cooling section and impurity trapping section during operation, and FIGS. 3 and 4 are FIG. 3 is an explanatory diagram showing each conventional technique. 20... Body, 22... Cooling section, 24... Impurity capturing section, 26... Cooling gas inlet piping, 28...
Cooling gas outlet piping, 34...Cooling pipe, 36...Sodium inlet pipe, 38...Sodium outlet pipe, 42...First partition plate, 44...Second partition plate, 46...Third partition Board.

Claims (1)

[Claims] 1. A cooling section that lowers the temperature of the inflowing liquid metal, an impurity trapping section that captures impurities in the liquid metal, and an insulating gas layer located between the two, the insulating gas layer being arranged in a double layer. In a cold trap having a structure in which the first and second partition plates are sealed at the top and opened at the bottom to fill the inside with gas, there is a space between the first partition plate and the second partition plate. A third partition plate is provided to divide the insulating gas layer into two, and a third
A cold trap characterized in that the upper part of the partition plate is open, and the lower part is connected to either the first or second partition plate and sealed.