JPS6193994A - Device for removing impurity in liquid metal - 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] [Field of Application of the Invention] The present invention relates to an apparatus for removing impurities in liquid metal,
In particular, the present invention relates to an apparatus for removing impurities in liquid metal suitable for removing radioactive impurities from sodium metal, which is a cooling fluid in a fast breeder reactor (FBR).

[Background of the invention]

Items used to evaluate the performance of equipment for removing impurities in liquid metals include impurity capture efficiency, pressure drop, possibility of recovering the capture material, wear of the capture material itself, and replaceability of the capture material.

There is the efficiency of flow of impurities, etc.

Conventionally, the method of removing radioactive corrosion products contained in the coolant of the primary cooling system of a fast reactor is to use a trapping material (usually a thin plate, mesh, etc.) in a container installed in the flow path for the coolant. A method has been proposed in which the trapping material is filled and adsorbed to the trapping material to remove it. (JP-A-58-201095, JP-A-58-219495, JP-A-58-21flj4
(No. 96 Publication) When evaluating the above-mentioned items regarding these conventional techniques, first of all, regarding the method of JP-A-58-201095, the specific surface area is relatively large and the capture efficiency is good. % volume of granular nickel, the pressure drop is large, and there is no way to recover the granular nickel that has flowed into the coolant flow path, so it must be circulated within the cooling system. Furthermore, as the granular trapping materials move randomly within the container, they come into contact with each other, causing the nickel in the trapping material itself to wear away, or impurities attached to the surface to peel off, resulting in corrosion-generated impurities. may not be captured efficiently. In addition, since the removal device is fixed to the flow path and the capture material is filled therein, it is not easy to replace it. Also.

Regarding the flow of impurities, diffusion within the laminar bottom layer becomes rate-determining, and the adsorption probability of impurities is limited.

Next, JP-A-58-219495 and JP-A-58
The method of Publication No. 219496 has the disadvantage that the specific surface area cannot be increased because it uses a plate-shaped capture material (in order to increase the specific surface area, the removal device must be made quite large). The pressure drop is large, and there is no way to recover the captured material that has flowed into the coolant, so it must be circulated within the cooling system. Especially JP-A-58-2194
In No. 95, there are moving parts in the high-temperature sodium, and their abrasion resistance and durability are problematic (capture efficiency will be significantly reduced if they break down).Furthermore, the removal device is fixed in the flow path, and the plate Since the shaped trapping material is also fixedly installed therein, it is not easy to replace it. Furthermore, regarding the flow of impurities, diffusion within the laminar bottom layer becomes rate-determining, and the adsorption probability of impurities is limited.

[Objective of the Invention] The object of the present invention is to efficiently remove impurities in the coolant such as radioactive corrosion products and fission products in the primary coolant of a fast reactor, and to prevent radioactive impurities from entering the equipment and piping of the primary cooling system. An object of the present invention is to provide an apparatus for removing impurities in liquid metal that reduces deposition of substances and makes maintenance of a fast reactor safe and easy.

[Summary of the invention]

The present invention utilizes the property that radioactive corrosion products in the coolant are easily adsorbed by certain materials, for example, manganese is easily captured by nickel. is injected into the coolant to reduce the thickness of the laminar bottom layer that determines the adsorption rate, increasing the adsorption rate, capturing corrosion products, etc., and applying a magnetic field to the magnetic filter inserted in the coolant to magnetize or It is characterized by removing impurities by demagnetizing and collecting or discharging corrosion products and the like together with magnetic particles, thereby superimposing an adsorption effect and a filter effect.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

First, FIG. 3 shows the overall configuration of the present invention. The primary cooling system of a fast reactor is reactor 1. It consists of an intermediate heat exchanger (not shown) and a pipe 2 connecting these. Branched from reactor 1, pump 3. Valve 4. Magnetic trap 5. Valve 6
The circuit consisting of is an impurity purification circuit. magnetic trap 5
A metal particle (hereinafter referred to as particle) injection device 7. and a backwash liquid storage container 11 via a valve 10;
In addition, a backwash container 8 is connected to the rear stage through a valve 9.The zero particle injection device 7 and the backwash container 8 each have a valve 12 connected thereto through a valve 9.
．． An inert gas (hereinafter referred to as gas) supply source 14 is connected via 13 .

In a fast reactor, a nuclear reactor 1 is loaded with uranium or plutonium as fuel, and the fuel is fissioned to generate heat, which is transferred to an intermediate heat exchanger by liquid metal sodium flowing through a pipe 2.

As the operating time of a fast reactor passes, the constituent elements of the primary cooling system structural materials are eluted into the liquid metal sodium, which is the coolant. When the eluted elements flow through the reactor 1 together with the coolant, they are activated and become radioactive corrosion products. A portion of the coolant containing radioactive corrosion products is led by pump 3 to the purification circuit. Particles are injected into the coolant through a pipe from the particle injection device 7, the particles are dispersed in the coolant, and the radioactive corrosion products are adsorbed and captured by the particles in the coolant. This coolant flows into the magnetic trap 5, and particles and non-radioactive stable nuclides also adhere to the filter section.

The coolant, which has reduced the concentration of corrosion products in this way, returns to the reactor 1 via the valve 6.

Next, details of the magnetic trap 5 and the injection section of the particle injection device 7 will be explained with reference to FIG. The magnetic trap is placed in a trap container 19. Upper and lower magnetic poles 16. High gradient magnetic filter between magnetic poles18. It consists of a magnetic pole 16 and a coil 17 outside the container. Upstream of the magnetic trap, an orifice-shaped pipe is provided as an injection part of the particle injection device 7 at the center of the pipe through which the coolant flows. Note that the filter may be a general magnetic filter, but a high gradient magnetic filter is preferable.

The coolant containing radioactive corrosion products introduced by the pump from the nuclear reactor passes through the valve 4 and then flows upward into the trap vessel 19 . In the previous stage, due to the flow of coolant, 1
A pressure difference is created between the inside and outside of the injection tube of the particle injection device, and particles are injected into the coolant. Particles injected into the coolant come into contact with atomic or molecular corrosion products, and the corrosion products are adsorbed onto each particle. A permanent magnet or a coil is attached to the outside of the trap container 19 and a direct current is passed therethrough, thereby generating a magnetic field within the trap container 19. The generated magnetic field is made uniform by the magnetic poles.

Magnetize the fine wire filter of the filling. In the filter section magnetized in this way, the magnetic flux becomes denser and denser, resulting in high gradient magnetism.

When a coolant containing particles that have adsorbed corrosion products is flowed from below to above, the particles are captured and attached to the filter by a large magnetic force. The operation continues in this state, and when the pressure at the entrance and exit of the trap container 19 is detected and the pressure becomes higher than a predetermined pressure, or the radioactivity intensity at the filter part of the trap container 19 exceeds a predetermined value, Automatically perform backwashing to restore trap function. This backwashing method will be described later.

Next, injection particles and magnetic traps will be explained.

If the particles injected into the coolant are considered spherical, the specific surface area of particles with radius r is proportional to 1/r. When ultrafine particles with extremely small r are used, the specific surface area becomes a very large value. Even when adsorbing the same corrosion products, the adsorption efficiency is better if particles with a larger specific surface area are used.However, the filter density of the magnetic trap also needs to be larger, and the pressure loss of the coolant also increases.

As an example, consider a magnetic trap in which particles having a particle diameter of 0.1 to several hundred μm are injected into a coolant. The amount of injection should be several hundred ppm based on the coolant. At most 10 koe is sufficient for the external magnetic pole. The diameter of the filter is 0.1 to innφ, the length is several hundred centimeters, and the filling rate is 5.
~20%. Coolant filtration rate is 5 to 150 nn/
s, the pressure loss is 0.05 to 0.2 kg/cJ, which poses no practical problem. A capture rate of 80 to 90% or more can be stably achieved not only for injected particles but also for stable nuclides.

It is known that nickel, for example, is good for adsorbing radioactive manganese as the injection particle.

Nickel is a ferromagnetic material at room temperature, but one curio (35
When the temperature exceeds 0 to 360°C, it becomes a paramagnetic material.

When a coolant containing radioactive manganese adsorbed nickel particles and other impurities is passed through a high-gradient magnetic filter, the particles become magnetized in the magnetic field and are attracted to the filter's fine wires, allowing only the coolant to flow away.

The capture performance of a high-gradient magnetic filter is greatly influenced by the magnetism and particle size of impurities in the coolant, as well as the magnetic field, the wire diameter and filling rate of the filter with a filtration rate of 1, and so on. For this reason,
After manufacturing a magnetic trap, it is necessary to select the particle size of the injected particles. One method for selecting a zero particle size is to mix particles with an appropriate particle size distribution into water or gas, and then insert them into the magnetic trap. The smallest particle size that achieves 100% capture efficiency is selected. Selecting the smallest particle size provides the largest specific surface area. If particles with such a large specific surface area are injected into the coolant, the frequency of collisions with atomic or molecular radioactive corrosion products increases, the particles grow, and are easily captured by a filter.

Next, the state of particles attached to the magnetic trap will be explained with reference to FIG. Particles of 2° are attached to the filter thin wire 18. The attached particles 20 have radioactive corrosion products adsorbed on them;
There are a variety of magnetized types, including those that are in an injected state and those that have adsorbed corrosion products of stable nuclides. Even if a large amount of the injected particles adhere to the filter thin wire 18, the flow of the inflowing coolant will be disturbed by the filter thin wire 18. In addition, unlike a normal filter with only thin wires, the specific surface area of the thin wires is extremely large due to the attached particles as mentioned above, which increases the frequency of collisions with JM particles or molecular impurities. , the capture efficiency is improved.

As described above, when particles are injected into the coolant, impurities in the coolant can be efficiently captured by a magnetic trap. However, with magnetic traps that have a fixed capture capacity, their capture performance deteriorates after long hours of operation. Therefore, it is necessary to regenerate the filter section of the magnetic trap by backwashing.

The reproduction method will be explained with reference to FIG.

During the operation for capturing impurities in the coolant, the valves 4 and 6 are always open, and the valves 12 and 15 are opened and closed as necessary. On the other hand, during backwashing for magnetic trap regeneration, after confirming that the valves 12 and 15 are closed in the impurity capture operation state, the valve 9 is opened, a predetermined amount of coolant is allowed to flow into the backwash container 8, and then closed. Next, the valve 13 is opened, and gas is supplied from the gas supply source 14 to the backwash container 8 to pressurize it. After pressurizing to a predetermined pressure, close the valves 4 and 6 and open the valve 10. Either remove the permanent magnet attached to the outside of the magnetic trap 5, or cut off the power to the coil and open the valve 9 to cool it. The material is abruptly passed from the backwash container 8 to the magnetic trap 6 and ends with the material flowing into the backwash liquid storage container 11. By backwashing, particles and impurities attached to the filter thin wires of the magnetic trap 5 are transferred to all backwash liquid storage containers 11.

Backwash coolant is normally required to be several tens of times larger than the filter volume. This results in a large amount of waste liquid.

Therefore, as shown in FIG.
A supernatant liquid transfer pipe 23 is provided for transferring the supernatant liquid to. A valve 22 is attached to the transfer pipe. The backwash liquid storage container 11 is covered with a radiation shield 21 and is provided with a gas system piping 24. When the particles settle, gas is supplied from the gas system piping 24 to pressurize the liquid in the backwash liquid storage container 6. On the other hand, the backwash container 8
This gas pressure difference causes the supernatant liquid in the backwash liquid storage container 11 to be transferred to the backwash container 8 via the valve 22 in preparation for the primary backwash. in this way.

Recycling backwash fluid can minimize waste fluid containing radioactive materials.

Next, the operation pattern of the magnetic trap will be explained with reference to FIG. As the operating time of the fast reactor progresses.

First, a defined amount of particles is injected into the coolant. The injected particles adhere to the filter wire of the magnetic trap, creating a pressure difference between the entrance and exit of the magnetic trap. As the operation continues, various impurities in the coolant are adsorbed and captured by the filter section, and the differential pressure increases until it reaches a preset value. Therefore, backwash processing for regenerating the magnetic trap is automatically performed. After the regeneration process is completed, particles are injected again and operation is continued, and the radioactive corrosion products are adsorbed and captured by the particles, and the radioactivity intensity reaches a preset value. Therefore, the magnetic trap regeneration process is performed again. Various impurities in the coolant are captured and removed using this operating pattern until the reactor's lifespan.

In addition, in the example of the operation pattern shown in Fig. 5, the second
The reason why the second peak of radioactivity intensity is higher than the first peak even though the peak of This is thought to be due to In that case, the radioactivity intensity will increase even though the volume will not increase much.

In another embodiment according to the invention, particles are injected into the coolant as a trap for corrosion products in the primary cooling system.

It is also conceivable to use it in colloidal form. Radioactivity detection monitors are installed at important points in the primary cooling system, and when the radiation exceeds a set value, magnetic filters are inserted into the coolant to remove particles, or particles are continuously introduced into the coolant. Another possible method is to provide a bypass circuit in the primary cooling system piping, provide a magnetic trap in this bypass circuit, and continuously remove particles.

In any case, when particles are dispersed in sodium and the particles, for example nickel, are corroded by the sodium, there is a possibility that the corrosion products adsorbed on the nickel surface will be dissolved again. However, nickel is known to have good coexistence with sodium. C
, F. Cheng (Corrosion-NACE v
According to OQ, 28 Ha I Jan, 1972), the amount of corrosion is about 0.8 μm per year at 500°C.

In the coolant, nickel has already been eluted from the core components, and a nearly constant concentration of nickel is dissolved in the sodium, which reduces dissolution from particulate nickel. Particles are not used continuously for a year, but as mentioned above, when a certain amount of corrosion products are adsorbed by the granules, they are collected and replaced with new ones. It can be considered that there is almost no possibility that the capture material will be corroded by sodium, thereby reducing its thickness and reducing the capture efficiency of corrosion products.

Let us consider the capture efficiency of corrosion products according to the present invention. What is the process by which corrosion products are adsorbed onto the wall surface?

In a turbulent flow field, the rate at which corrosion products diffuse in the laminar flow bottom layer formed at the interface between the wall surface and the coolant is rate-determining. Therefore, the thinner the laminar flow bottom layer, the greater the rate of adsorption of corrosion products. When particles are trapped in the mesh packed bed, the flow of the coolant becomes more complex than in simple shapes such as circular pipes and flat plates.

Here, to simplify the problem, we will compare the heat transfer coefficients around a flat plate and a circular tube, assuming that an analogy between heat transfer and mass transfer holds. This is shown in FIG. The vertical axis in Figure 6 shows the ratio of the mass transfer rate between a circular tube and a flat plate. Taking an example where the Reynolds number is 104, the mass transfer rate of one cylinder is 76. circle,. Wow, it's crazy. Yu. 1. Yo, yotsu. , (Although the comparison was made using a cylindrical shape, it is thought that the mass transfer rate will improve even more if it is a spherical shape. Therefore, compared to one in which 1 ordinary flat plate is arranged,
The spherical shape facilitates the heat transfer rate, that is, mass transfer for adsorption, and increases the capture rate of corrosion products from about 1 to 2 digits.
It can be seen that there is an order of magnitude improvement.

As mentioned above, the present invention is applicable to fast reactor
Although it is effective as a removal device for radioactive corrosion products in the secondary cooling system, it is not necessarily limited to this. It is also effective in removing corrosion products from the secondary cooling system, and by applying the present invention, it is also effective in preventing corrosion products from adhering to the heat transfer tube surface and reducing heat transfer efficiency. . Furthermore, the present invention can also be applied as a device for removing impurities from the coolant in nuclear reactors that use water or heavy water as the coolant.

〔Effect of the invention〕

According to the present invention, in a fast reactor cooling system, a device for injecting particles into the coolant and a magnetic trap are provided, and impurities in the coolant can be captured by adsorption by the particles and adsorption by particles attached to the magnetic trap. Impurities such as radioactive corrosion products contained in the primary system can be reduced. As a result, the amount of radioactive impurities deposited on the surface of the secondary cooling system equipment piping can be reduced, and maintenance and repair of the secondary cooling system equipment and piping becomes easier.

Furthermore, it is possible to reduce the need for shielding equipment for reducing the exposure dose rate, which has the effect of improving safety and economic efficiency in fast reactors.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the magnetic trap and particle injection device of the impurity removal device of the present invention, Figure 2 is a diagram showing the state of particles attached to the magnetic trap, and Figure 3 is a diagram showing the present invention in the primary cooling system of a fast reactor. Block diagram showing the overall configuration of the incorporated embodiment, No. 4
The figure shows in more detail the backwash-related parts of the embodiment in Figure 3;
FIG. 5 is a diagram showing the operating pattern of the apparatus of the present invention, and FIG. 6 is a diagram showing the ratio of heat transfer in a flat plate and a cylinder. 1... Nuclear reactor, 2... Pipe, 3... Pump, 4
... Valve, 5... Magnetic trap, 6... Valve, 7...
・Metal particle injection device, 8... Backwash container, 9... Valve,
10... Valve, 11... Backwash liquid storage container, 12...
・Valve, 13... Valve, 14... Inert gas supply source, 1
5... Valve, 16... Magnetic pole, 17... Coil, 18
...filter, 19...trap container, 20...
Particle, 21...Radiation-resistant body, 22...Valve, 2
3...Supernatant liquid transfer pipe, 24...Gas system piping.

Claims (1)

[Claims] 1. A device for removing impurities from liquid metal used as a nuclear reactor coolant, comprising a device for injecting particles that adsorb impurities into the liquid metal, and a means for capturing the particles. A device for removing impurities in liquid metal, characterized by: 2. The liquid metal according to claim 1, wherein the particles are magnetic particles, and the capturing means includes a magnetic filter disposed in the liquid metal flow path and a means for magnetizing the filter by applying a magnetic field thereto. Medium impurity removal equipment. 3. In a device for removing impurities from liquid metal used as a nuclear reactor coolant, a device for injecting particles that adsorb impurities into the liquid metal, and means for capturing the particles;
1. An apparatus for removing impurities in liquid metal, comprising means for collecting and discharging captured impurity-adsorbing particles from a capturing means. 4. In claim 3, the particles are magnetic particles, the capturing means includes a magnetic filter disposed in the liquid metal flow path and means for applying a magnetic field to the magnetic filter and magnetizing it, and the collecting and discharging means is the capturing means. 1. An apparatus for removing impurities in liquid metal, which is a means for backwashing and collecting and discharging impurity-adsorbed particles.