JPS5940894B2 - Liquid metal purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid metal purification device for removing harmful impurities contained in liquid metals, such as sodium, potassium, and lithium, used as coolants in nuclear reactors and the like.

Generally, cold trapping method and hot trapping method are used as in-loop purification methods for liquid sodium.

The cold trapping method generally takes advantage of the fact that the solubility of impurity elements dissolved in liquid sodium decreases as the temperature decreases. This is a purification method in which sodium is precipitated and captured in a flow of sodium in the form of a compound with sodium and removed.The lower the operating temperature, the higher the purity of sodium.

For example, in the case of oxygen impurities, the concentration is about 30 ppm at 200°C.
However, at 150°C, it drops to about 10 ppm.

This cold trapping method typically uses 10 ppm
It is used as a refining device up to the front and back.

On the other hand, the hot trapping method is a method in which an impurity getter material is inserted into sodium and impurities in the sodium are removed and purified through a chemical reaction, and zirconium, titanium, etc. are used as the getter material. .

In the case of zirconium, oxygen in sodium is mainly removed by the chemical reaction shown by the following formula.

2Zr+O→Zr20 The oxygen concentration in equilibrium with zirconium in sodium at 650°C is theoretically 10'ppm or less from Al, and this hot trapping method is generally used as a purification device to achieve a concentration of 1 ppm or less.

In the case of such a hot trapping method, from the viewpoint of reaction rate, a high temperature of 650° C. or higher is usually used because the trapping rate is faster at higher temperatures.

As described above, the cold trapping method and the hot trapping method have completely different principles and are used at different temperatures, so they have been treated as separate devices in the past.

The cold trapping method is widely used for sodium loosing because it can be operated at low temperatures and is simple.The most typical structure thereof is as shown in Fig. 1, which consists of an outer cylinder 2 having cooling fins 1 and an outer cylinder 2 with cooling fins 1. It consists of an inner cylinder 4 which is placed inside and contains a filler 3. Sodium is introduced from an inlet 5 provided in the outer cylinder 2, and the sodium is passed through the space between the outer cylinder and the inner cylinder as shown in the arrow. It was introduced into the inner cylinder through a number of openings on the lower surface of the cylinder 4 and passed through the packing 3, so that impurities were deposited on the packing.

However, in such a device, impurities deposited in the cold trap are locally segregated, which blocks the flow path and narrows the effective utilization range, for example, 1/lO
It was often about 1/100.

Therefore, in order to promote precipitation and flooding effects, it is necessary to change the shape of the packing in the cold trap, change the flow conditions by installing baffles or bypass channels, and further improve the flow conditions in the cold trap. Methods such as controlling the temperature distribution have been considered, but they are complicated to operate, and no fundamental solution could be expected.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid metal refining apparatus that has both cold trapping and hot trapping functions, thereby improving the above-mentioned conventional drawbacks.

Embodiments of the present invention will be described in detail with reference to FIGS. 2 to 4. FIG. 2 shows an example of an apparatus embodying the invention, which includes a container or outer casing 10. and an inner casing 11 disposed within the outer casing.

Cooling fins 12 and a heater 13 are provided on the outer surface of the outer casing.
and an inlet pipe 14 connected to a liquid metal loop (not shown) for introducing liquid metal (for example, liquid sodium in this example) in the upper part of the outer casing.
is the provision.

The inner casing is provided with an outlet pipe 15 in its upper part for discharging purified sodium, and a number of openings 16 in its lower face.

The outlet pipe 15 is connected to the liquid metal loop.

Further, a getter material 17 and a filter 18 disposed on the upper surface of the getter material are housed inside the inner casing.

This filter has a mesh of approximately several tens of microns.

This getter material is made of metal zirconium, metal titanium, etc., and has multiple surfaces in the shape of a wire mesh or small pieces, and is configured to form a complicated sodium flow path.

The outer casing is surrounded by a heat insulating material 19, the lower part of which is connected via an inlet conduit 20 to a forced cooling device 21, such as a fan, and the upper part of this insulating material is connected to a forced cooling device 21 for cooling by this forced cooling device. Outlet conduit 22 for discharging wind
is the provision.

Note that the inlet pipe 14, the inlet conduit 20, and the outlet conduit 22 are provided with valves 23, 24, and 25, respectively.

Liquid sodium is introduced from the inlet pipe 14, passes through a passage 26 formed between the outer casing 10 and the inner casing 11 as shown by the arrow, and is cooled by the cooling fins 12.

This cooled sodium is introduced into the inner casing through the opening 16, and the introduced sodium is purified by depositing supersaturated impurities on the surface of the getter material 17.

The purified sodium rises up the inner casing and passes through passage 2.
It returns to the liquid metal loop from outlet pipe 15 through filter 18 while exchanging heat with the sodium flowing through 6.

The above process is a cold trapping method.

As the refining operation progresses, the amount of precipitated sodium oxide, etc. inside the inner casing increases, eventually clogging the flow path and causing an increase in flow resistance.

At this point, the system determines that cold trapping capacity has been reached and closes valve 23, stopping sodium from being introduced into the outer casing.

At the same time, the forced cooling device 21 that was cooling the container is stopped, and the valves 24 and 25 are closed.

Next, the heater 13 is operated to raise the temperature inside the container.

Heating is continued until the temperature of the container rises to 650 to 700°C, and after reaching this temperature, the heat insulating material 19 is used to heat the container.
Retained for 0 hours.

Sodium oxide trapped in the inner casing by being kept at high temperature is dissolved in sodium again, and the dissolved oxygen is mainly in the form of zirconium oxide or titanium oxide by the getter material zirconium or titanium. removed and fixed.

The purification process that includes this chemical reaction is the hot trapping method.

Through this process, the flow path blocked by the cold trapping method described above is restored.

The part that is occluded by the cold trapping method is a localized part within the inner casing, but in the hot trapping process, due to effects such as natural convection of sodium, the getter material inside the container uniformly contributes to the reaction.

After finishing the hot trapping process, stop the heating, operate the forced cooling device 21, cool the container to the cold trapping temperature, then open the valve 23, introduce the sodium in the loop, and cold trap again. Perform purification by method.

This alternating cold trapping and hot trapping continues until the getter material in the inner casing reaches capacity.

The capacity limit of the device is determined by the fact that the blockage of the flow path is not recovered even by the hot trapping method.

As hot trapping progresses, some of the oxides captured by the getter material flake off and, if mixed into the sodium flow, are removed by the filter 18.

The present invention can be used more effectively by installing two or more devices as described above in the same loop.

That is, in FIG. 3, two devices 34, 3 are connected to the loop 30 in parallel via a pump 31 and valves 32, 33, respectively.
5 is connected.

Sodium from loop 30 to pump 31 and valve 3
2 into a first device 33, where it is first purified by a cold trapping method.

After the first device reaches capacity, valve 32 is closed to shut off the first device 34, then valve 33 is opened to introduce sodium into the second device 35 and the cold
Continue purification by trapping method.

During this time, the first device 34 performs hot trapping and restores the blocked flow path.

After the second device 35 reaches its capacity, the first device 34 is operated again.

By continuing this process alternately, the purification process can be continued without interruption.

Further, in the present invention, the configuration of the purification apparatus is the same even if the getter material storage container 40 for hot trapping is separated from the container i41 for cold trapping as shown in FIG.

In this case, after the container 41 is closed by the cold trapping method, by heating the container 41 to 650 to 700°C, the sodium containing impurities passes through the connecting pipes 42 and 43 by natural circulation, as shown by the arrow. circulate,
The impurities are removed and fixed in the getter material 44 of the container 40.

The material of the getter material 45 in the container 41 may be other than the above-mentioned getter material, for example, a stainless steel wire mesh.

According to the present invention, there are the following effects compared to the conventional technology.

(1) The impurity trapping capacity is several times larger than that of a conventional cold trapping device for the same volume.

(2) Once a device based on the conventional cold trapping method starts to become clogged, there is almost no effective means to recover from it other than disassembly and cleaning. Road restoration can be performed.

(3) Compared to devices using the conventional hot trapping method, the heater capacity is small and a heat exchanger or cooler is not required, so it is inexpensive.

(4) Impurities are captured uniformly within the device, and local blockages can be prevented.

(5) Captured impurities can be prevented from scattering within the loop.

[Brief explanation of the drawing]

FIG. 1 G1 is a sectional view of a conventional cold trapping device, FIG. 2 is a sectional view showing an embodiment of a liquid metal refining device according to the present invention, and FIGS. FIG. 10...Outer casing, 11...Inner casing, 12...Cooling fins, 13...
... Heater, 17 ... Getter material, 18.
·····filter.

Claims (1)

[Claims] 1. Introducing a liquid metal to cool the flowing liquid metal,
The impurities in the liquid metal are precipitated and captured by the getter material by passing the cooled liquid metal through the getter material, and when the flow of the liquid metal stops due to the precipitation of the impurities, the impurities captured by the getter material are removed. A method for refining a liquid metal, characterized in that the liquid metal is caused to flow by heating and the impurities are removed as a chemical reaction product of the getter material.