JPH0754285B2 - Sampling method and apparatus for precipitated impurities in liquid sodium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a technique for capturing and collecting a precipitation-type impurity contained in a small amount in liquid sodium by a jig using a mesh. The main impurities in liquid sodium are oxygen impurities and hydrogen impurities, but the present invention is a technique capable of trapping other unknown impurities of extremely low concentration.
Therefore, the present invention can be used for sodium sampling in fast breeder reactors using liquid sodium and various plants.

[Prior Art] Liquid sodium is used as a coolant in a fast breeder reactor, and great attention is paid to the impurity concentration in the main system sodium flowing at high temperature. The main target impurities in the purity control of liquid sodium were oxygen impurities and hydrogen impurities. The concentration of these impurities can be easily measured by a plugging meter. The principle of this measurement is that when the sodium temperature is gradually lowered, impurities in the orifice part become supersaturated at a certain temperature and precipitation begins and the sodium flow rate decreases, so the impurity concentration can be determined by detecting the temperature at that time. It is possible to do. Although the plugging meter cannot determine the impurity component, the lower the plugging temperature, the higher the sodium purity may be, which is an effective and simple means for sodium purity control.

In order to analyze the components of impurities in liquid sodium, it is necessary to sample the flowing liquid sodium. A flow-through method is a typical example of the sampling device. This is composed of a sampling pipe that diverts sodium from a part of the sodium circulation system pipe, a device that forcibly cools it, and the like. Sampling is performed by introducing sodium into a sampling pipe and sufficiently flushing the inside of the pipe, forcibly cooling the sampling pipe to cool and solidify the sodium in the pipe, and remove the entire pipe from the pipe joint portion.

[Problems to be Solved by the Invention] In recent years, there have been cases where unknown impurities other than oxygen and hydrogen impurities are deposited on a plugging meter, which hinders stable plugging temperature measurement. It is extremely important to sample and analyze this unknown impurity in order to investigate the cause of its occurrence and to evaluate the soundness of system equipment and the operation method.

However, since the concentration of this unknown impurity in sodium is extremely low, it is extremely difficult to capture an amount sufficient to analyze and confirm the component of the unknown impurity by the conventional sampling technique. In addition, there is a problem such as segregation because a temperature difference occurs in the sampling tube during cooling, which makes it more difficult to capture unknown impurities.

It is an object of the present invention to solve the above technical problems and to provide a sampling technique for precipitating impurities in liquid sodium that can easily capture unknown impurities other than oxygen and hydrogen impurities that adversely affect the plugging meter. .

[Means for Solving the Problems] In the present invention capable of achieving the above object, the temperature of liquid sodium flowing in a sampling tube is controlled to deposit only an intended impurity, and the deposited impurity is used by a mesh. It is configured to capture. The temperature range controlled here is higher than the precipitation temperature of oxygen impurities and hydrogen impurities and below the precipitation temperature of unknown impurities other than those. Sampling will be performed after a certain period of time has passed after stopping the purification operation of the sodium circulation system.

A principle diagram of the sampling device is shown in FIG. This device has a sampling tube 10 in which liquid sodium flows.
Further, a forced cooling device 17 for controlling the temperature of the liquid sodium, a temperature sensor 12 for detecting the sodium temperature, and an impurity trap 16 using a mesh 14 provided in the sampling tube 10 are provided. Here forced cooling device 17
Is composed of a large number of cooling fins 18 formed on the outer periphery of the sampling tube 10 and a cooling fan 20. The temperature sensor 12 may be a thermocouple or the like. The impurity capturing unit 16 has a structure that makes it easy to take out the internal mesh 14.

[Operation] Oxygen impurities, hydrogen impurities, and unknown impurities dissolved in liquid sodium have a temperature dependency, and have a characteristic of precipitating when liquid sodium is cooled below the saturation temperature of each impurity. Of these impurities, oxygen and hydrogen impurities are mixed with air from outside the system or adhered to the fuel assembly or the like. As shown in Fig. 3, when the sodium purification operation by the cold trap is stopped in the sodium circulation system, the plugging temperature (saturation temperature) of oxygen and hydrogen impurities is the same as before the cold trap was stopped, unless oxygen and hydrogen impurities are mixed. The plugging temperature of unknown impurities increases with time. Therefore, it is considered that unknown impurities are eluted from the system structural material.

From these facts, the solubilities of oxygen impurities, hydrogen impurities, and unknown impurities in sodium are shown in FIG.
Assuming that they are on the line, (1) in the temperature range (a), oxygen impurities, hydrogen impurities,
Also, no precipitation occurs because it is above the saturation temperature of unknown impurities.

(2) In the temperature range (b), the temperature is higher than the saturation temperature of oxygen impurities and hydrogen impurities, and is equal to or lower than the saturation temperature of unknown impurities, so only unknown impurities are deposited.

(3) In the temperature range (c), the temperature is higher than the saturation temperature of oxygen impurities and is equal to or lower than the saturation temperature of hydrogen impurities and unknown impurities, so that hydrogen impurities and unknown impurities are precipitated.

(4) In the temperature range (d), oxygen impurities, hydrogen impurities,
And the saturation temperature of unknown impurities is lower than the saturation temperature, all of these impurities precipitate.

The sampling method of the present invention utilizes the temperature dependence of unknown impurities, and the fact that the oxygen impurities and hydrogen impurities have different saturation temperatures. By controlling the temperature within the range shown in FIG. It is not affected by oxygen impurities and hydrogen impurities, and only unknown impurities other than those are deposited. In order to control the temperature of the liquid sodium flowing in the sampling tube 10 within this temperature range (b), the air volume by the cooling fan 20 may be controlled based on the signal from the temperature sensor 12.

Impurities precipitated in sodium are captured by the mesh 14 installed in the sampling tube 10. By using the mesh 14 to capture unknown impurities, it is possible to simulate the orifice hole diameter of the plugging meter in which unknown impurities actually precipitate in the sodium circulation system, and the precipitated impurities can be easily collected for analysis. .

[Embodiment] FIG. 4 is an explanatory view showing an embodiment of the sampling apparatus according to the present invention. The sampling device 30 has a three-dimensionally meandering sampling tube 32 for downsizing. One end of the sampling tube 32 is used as a sodium inlet 34, and the other end is used as a sodium outlet 36. The straight portion on the sodium inlet side of the sampling tube 32 is the impurity quantitative analysis sodium sampling portion 38, and the sodium outlet side is the unknown impurity trap portion 40. The middle part to which the cooling fins 42 are attached becomes the cooling part 44. A thermocouple 46 is inserted as a temperature sensor on the sodium outlet side to measure the temperature of sodium flowing in the sampling tube 30. This temperature information is used to control the cooling device.

The sodium sampling unit 38 for quantitative analysis of impurities on the inlet side is a unit for sampling sodium for quantitatively analyzing the concentration of unknown impurities in sodium. The cooling unit 44 is a unit that cools sodium flowing in at a high temperature to a temperature equal to or lower than the saturation temperature of an unknown impurity, and the cooling fin improves the cooling effect of sodium. Actually, a cooling fan (not shown) is provided for forced cooling.

The impurity trap portion 40 provided on the sodium outlet side is a portion into which a trapping element is inserted. The details are shown in FIG. Three types of trapping elements 50a, 50b, 50c are incorporated in the impurity trapping section 40. Here, it is inserted into the Swagelok joint 52 and the capturing elements 50a, ..., 50c
It can be easily fixed and removed. The structure of the capture element is shown in FIG. This is a capturing element 50a, and has a structure in which three plain weave meshes 54 are sandwiched by a pair of mesh holders 56 each having an opening formed in the center. This fixes the mesh 54 and prevents it from falling and scattering.

In order to investigate unknown impurities, it is necessary to deposit them and collect them as granules, and the grain size of the precipitates should be large to some extent. However, unknown precipitation characteristics of impurities (relation with sodium flow rate: if the flow rate (flow rate) is slow, it takes time to increase the precipitate particle size, and if the flow rate is too fast, the precipitates peel off). Three capture elements having different shapes (aperture diameter and number of openings) are inserted. It should be noted that the three meshes 54 are combined so that a coarse one (for example, 4 mesh) in the middle is sandwiched by a fine one (for example, 20 mesh), and the same one is used for the three-stage capturing elements.

Since unknown impurities are precipitated and captured in the impurity capturing section 40, the temperature of the impurity capturing section 40 must be equal to or lower than the saturation temperature of unknown impurities. However, when the temperature is lower than the saturation temperature of oxygen and hydrogen impurities, they are also precipitated and may be blocked before the grain size of unknown impurities becomes sufficiently large. Therefore, as described above, the temperature is controlled to a temperature slightly higher than the saturation temperature of oxygen and hydrogen impurities (the temperature range shown in FIG. 2B). This temperature control is performed by adjusting the air volume of the cooling fan based on the temperature signal from the thermocouple 46. For example, in the case of the fast experimental reactor “JOYO”, the saturation temperature (plugging temperature) of unknown impurities is about 200 ° C. and the saturation temperature of oxygen and hydrogen impurities is about 130 ° C., so that it is within the range of 130 to 200 ° C. Actually, in order to obtain a large particle size in a short time, it is preferable that the temperature is equal to or higher than the saturation temperature of oxygen and hydrogen impurities and is as low as possible, and the target is 150 ° C.

After the impurities are captured by the capturing element, the sampling tube 30 is further cooled to solidify the sodium, and the sodium is separated from the sodium inlet 34 and the sodium outlet 36. Then, sodium is collected from the sodium sampling unit 38 for quantitative analysis of impurities,
Also, the swagelok joint is removed, each trapping element is removed, and the mesh is removed to collect precipitated impurities.

Next, application examples of the present invention will be described. When the saturation temperature of the unknown impurities cannot be higher than the saturation temperatures of the oxygen and hydrogen impurities, the unknown impurities can be investigated by utilizing the fact that the saturation temperatures of the respective impurities are different. For example, assume that the unknown impurity saturation temperature is between the hydrogen impurity saturation temperature and the oxygen impurity saturation temperature. As shown in FIG. 7, a plurality of meshes are installed in the sampling tube 60. Here, three stages are provided. Sampling tube 60
Cool while flowing sodium in. As a result, a temperature gradient is formed in the length direction of the sampling tube, and the impurities are deposited on the mesh at the portion where the saturation temperature of each impurity is lower than the temperature.

The first mesh 61 is at position A where the oxygen impurity reaches the saturation temperature.
And a position B where the unknown impurity reaches the saturation temperature.
The second mesh 62 is provided between a position B where the unknown impurities reach the saturation temperature and a position C where the hydrogen impurities reach the saturation temperature.
The third mesh 63 is provided at a position where the saturation temperature of hydrogen impurities is lower than the saturation temperature. If such a relationship is maintained, the oxygen impurities start to precipitate at the position A, so that only the oxygen impurities precipitate on the first mesh 61. Since unknown impurities also start to be precipitated from the position B, both oxygen impurities and unknown impurities are precipitated on the second mesh 62. Further, at the position C, hydrogen impurities are deposited, so that all the impurities are deposited on the third mesh 63. Therefore, unknown impurities can be investigated by comparing the elements of the precipitates of at least the first mesh 61 and the second mesh 62.

Such a method can be dealt with by slightly changing the sampling device. That is, the insertion portion of the trapping element may be dispersed in the sampling tube, and the cooling portion may be installed in front of each trapping element.

[Advantages of the Invention] As described above, according to the present invention, the temperature of the liquid sodium flowing in the sampling tube is controlled to precipitate the target impurities, and the deposited impurities are captured using a mesh. It has become possible to easily and efficiently collect unknown impurities (very small concentrations of unknown impurities other than oxygen and hydrogen impurities) that could not be analyzed by the sodium sampling technology of. By investigating this unknown impurity that is considered to be eluted from the system structural material, it is possible to evaluate the soundness of system equipment and the like using liquid sodium and to examine the operation method.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the principle of the present invention, FIG. 2 is an explanatory diagram of its temperature control, and FIG. 3 is a graph showing a change in saturation temperature of unknown impurities. FIG. 4 is an overall explanatory view showing an embodiment of the sampling device according to the present invention, FIG. 5 is a detailed explanatory view of the impurity trapping portion thereof, and FIG. 6 is an exploded view of the trapping element. FIG. 7 is an explanatory diagram showing an application example of the present invention. 10 ... Sampling tube, 12 ... Temperature sensor, 14 ... Mesh, 16 ... Impurity trap, 18 ... Cooling fin, 20 ...
… A cooling fan.

Claims (2)

[Claims] 1. A sodium sampling portion for quantitative analysis of impurities in the straight portion on the inlet side, a meandering cooling portion in the middle portion, and an impurity trap portion in the straight portion on the outlet side are continuous, and in the impurity trap portion, Using a sampling tube having a structure in which a plurality of trap elements having different aperture diameters or numbers and having a built-in mesh are inserted at intervals, the temperature of liquid sodium flowing in the impurity trap portion of the sampling tube is controlled. , A temperature range higher than the precipitation temperature of oxygen impurities and hydrogen impurities and equal to or lower than the precipitation temperature of unknown impurities other than those, and only the target unknown impurities are precipitated and captured on the mesh of the capture element, and then ,
The sampling tube is further cooled to solidify sodium, and separated from the sodium flow path on the inlet side and the outlet side,
A method for sampling precipitated impurities in liquid sodium, which comprises collecting sodium from a sodium sampling unit for quantitative analysis of impurities, removing each capturing element from the impurity capturing unit, removing a mesh, and collecting unknown precipitated impurities from the mesh in a crystalline state. 2. A sampling tube provided with a sampling tube through which liquid sodium flows, a forced cooling device for controlling the temperature of liquid sodium, and a temperature sensor for detecting the temperature of flowing liquid sodium. Includes a sodium sampling portion for quantitative analysis of impurities in the straight portion on the inlet side, a cooling portion having a three-dimensionally meandering tubular shape and cooling fins on the outer peripheral surface, and an impurity trap portion for the straight portion on the outlet side. In the continuous structure, a plurality of trapping elements sandwiching a plurality of plain weave meshes with mesh holders having different opening diameters or numbers are detachably inserted at intervals in the impurity trapping part, and Sampling device for precipitated impurities in liquid sodium, whose inlet and outlet can be combined and separated from the sodium flow path.