JP7082805B2 - Liquid metal loop corrosion suppression mechanism - Google Patents

Description

The present invention relates to a mechanism for suppressing cavitation erosion of a tank that receives a jet of liquid metal in a liquid metal loop for generating neutrons.

As a method of generating neutrons, there is a method of colliding charged particles such as protons, deuterons, and electrons accelerated by an accelerator with a target in a vacuum. In order to accelerate the charged particles, it must be in a vacuum, and beryllium and lithium as targets must be placed in a vacuum. When the target is irradiated with charged particles, the target generates heat, so cooling is required. In the case of solid beryllium, since it does not react with water, the back side of the solid beryllium can be cooled directly with water, but since the energy of the charged particles to be irradiated is large, the solid to which the charged particles accelerated in the vacuum in the accelerator hit. The cooling water on the back side of beryllium may boil.

In the case of solid lithium, since it reacts with water, it cannot be cooled directly with water, and it is coated on a copper plate with good thermal conductivity, but when the copper plate is cooled with water, the cooling water boils. There is a risk. As described in Patent Document 1, an invention is also disclosed in which a proton beam is irradiated to a jet of liquid lithium ejected from a nozzle as a target to generate neutrons.

Lithium includes the stable isotopes lithium 6 and lithium 7, and lithium 7 accounts for 92.5%. When a proton and lithium-7 undergo a nuclear reaction, beryllium-7 and neutrons are generated, but beryllium-7 returns to lithium-7 by electron capture with a half-life of about 53 days. Since beryllium-7 is insoluble in liquid lithium and has a higher specific gravity than liquid lithium, it accumulates at the bottom of a container or the like and does not affect the flow of liquid lithium. Therefore, it can be continuously used as a liquid metal loop.

For example, a charged particle for generating neutrons requires energy on the order of MeV in the case of a proton and several tens of MeV orders in the case of an electron, and the current value of the charged particle when a large amount of neutrons are required is about 10 mA. Since it is necessary, the calorific value when irradiating the liquid metal with charged particles is several tens of kW or more. Therefore, the temperature rise is suppressed by, for example, flowing the liquid metal at a high speed of 10 to 20 m / sec in the flow velocity of the flow that receives the charged particles and generates heat. Then, after flowing the jet of the liquid metal into the tank, the liquid metal is cooled while the liquid metal circulates in the piping system from the tank to the nozzle.

Japanese Patent No. 5808215

However, when the liquid metal is circulated, if the high-speed liquid flow ejected from the nozzle hits a bent pipe or the like as it is, cavitation (generation and disappearance of bubbles) occurs at that part, and this cavity (bubble) is crushed. Occasionally, small, high-speed droplets hit the tube wall, causing erosion. Further, when the jet of liquid metal collides with the inner wall of the tank, cavitation occurs in the collided portion as well. Furthermore, vacuum cavitation occurs from the beginning even when the jet flow hits the liquid surface in a vacuum atmosphere, and since the cavity in the liquid is crushed in the liquid, it does not come into contact with the housing, so there is no erosion, but inside the tank. Bubbles (cavities) generated in the liquid (torn off) from the liquid surface are vacuum voids, and when these voids move with the flow and collapse on the wall surface, erosion occurs on the wall surface, and dents gradually increase on the wall surface. , There is a risk of holes and liquid metal leaking. Even if the jet does not directly collide with the tank in this way, cavitation erosion can occur if air bubbles (cavities) drift in the tank together with the turbulent flow below the liquid surface and collide with the inner wall.

It should be noted that the accelerator that can be used in a vacuum atmosphere cannot be connected, and this is just a hypothetical explanation. A cavity is created. In this case, since the cavity contains gas, the cavity is lifted by buoyancy without being crushed, and the gas bubbles are only crushed by popping at the liquid surface, so that the above-mentioned cavitation erosion does not occur. It can be said that this patent is a problem unique to vacuum.

Therefore, an object of the present invention is to suppress cavitation erosion of a tank that receives a jet of liquid metal in a liquid metal loop for generating neutrons.

In order to solve the above problems, the liquid metal loop corrosion suppression mechanism of the present invention irradiates the liquid metal ejected from the nozzle with charged particles to generate neutrons, and then cools the liquid metal. In a liquid metal loop having a pipe for circulating to the nozzle, a tank for storing the liquid metal after being irradiated with the charged particles before sending it to the pipe, and a magnetic field inside the housing of the tank. The liquid metal jet is generated by increasing the viscosity of the liquid metal inside the housing of the tank by the magnetic field generating means provided with the magnetic field generating means arranged outside the wall so as to generate the liquid metal. It is characterized in that the cavity generated when the cavity is received on the center side of the tank is suppressed so as not to reach the inside of the housing of the tank.

Further, in the corrosion suppressing mechanism, the magnetic field generating means is characterized in that a plurality of magnets are arranged outside the tank to form a multi-pole type.

Further, the erosion suppression mechanism is characterized in that the cavity is prevented from circulating in the pipe by making the flow velocity of the liquid metal sent from the tank to the pipe slower than the ascending speed of the cavity. do.

Further, the anti-corrosion mechanism prevents the cavity from circulating in the pipe by slowing the liquid metal sent from the tank to the pipe in a further rectifying tank at a speed slower than the ascending speed of the cavity. It is characterized by that.

Further, in the corrosion suppressing mechanism, the tank is characterized in that a wire mesh for preventing splashes is arranged above the liquid surface of the liquid metal.

Further, the liquid metal loop of the present invention is characterized by having the above-mentioned anticorrosion mechanism.

According to the present invention, in the liquid metal loop for generating neutrons, the life of the tank can be extended by suppressing the cavitation erosion of the tank that receives the jet of the liquid metal. Further, by limiting the region where cavitation occurs by receiving the jet flow by a magnetic field, the tank can be miniaturized, and the cost and the capacity of the fluid used can be minimized. Further, by eliminating bubbles in the pipe under the tank by circulating the flow of the liquid metal that catches the jet flow at a speed slower than the floating speed of the cavity, it is possible to suppress the bubbles from circulating in the pipe.

It is a figure which shows the outline of the liquid metal loop which uses the erosion suppression mechanism of the liquid metal loop of this invention. It is a figure which shows the outline of the liquid metal loop for supplementally explaining FIG. It is a figure which shows the tank which used the erosion suppression mechanism of the liquid metal loop of this invention. It is sectional drawing when the tank which used the erosion suppression mechanism of the liquid metal loop of this invention was cut by AA. It is a figure explaining the miniaturization of the tank using the erosion suppression mechanism of the liquid metal loop of this invention. It is a figure which shows the application example of the tank which used the erosion suppression mechanism of the liquid metal loop of this invention. It is a figure which shows the application example of the tank which used the erosion suppression mechanism of the liquid metal loop of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Those having the same function are designated by the same reference numerals, and the repeated description thereof may be omitted.

The mechanism for suppressing corrosion of the liquid metal loop according to the present invention will be described. FIG. 1 is a diagram showing an outline of a liquid metal loop. FIG. 2 is a diagram showing an outline of a liquid metal loop for supplementally explaining FIG. 1. FIG. 3 is a diagram showing a tank using the anti-corrosion mechanism. FIG. 4 is a cross-sectional view when the tank is cut at AA. FIG. 5 is a diagram illustrating the miniaturization of the tank. 6 and 7 are views showing an application example of the tank.

As shown in FIG. 1, first, the liquid metal loop 100 drives the liquid metal 200 by the electromagnetic pump 150, and the jet flow 200a of the liquid metal 200 ejected from the nozzle 110 at high speed exceeds the threshold value obtained from the accelerator 120. The neutron 220 is generated by irradiating the jet 200a of the target liquid metal 200 with the charged particles 210 having energy. Then, the jet 200a of the liquid metal 200 after being irradiated with the charged particles 210 is received by the tank 300, and the liquid metal 200 is stored for being sent out to the pipe 130 (although it is a slow flow, it circulates in the pipe system). Yes). After that, the liquid metal 200 whose temperature has risen due to the irradiation of the charged particles 210 is cooled and circulated by the cooler 140 installed in the middle of the pipe 130.

Although the system is the same, the optimum liquid metal 200 differs depending on the type of charged particles 210, and the neutron generation mechanism also differs. Therefore, for the sake of simplicity, only the case of protons is used. Incidentally, when the charged particle 210 is a proton (MeV order), liquid lithium (Li) is used as the target, and the neutron generation mechanism is a proton nuclear reaction. When deuterons are used for charged particles 210, the threshold of acceleration energy required for neutron generation becomes lower, the amount of neutrons generated increases compared to proton irradiation of the same energy, and high-energy neutrons 220 are also generated, but thermal neutrons and heat For applications that use external neutrons, protons are used. When the charged particles 210 are electrons (several tens of MeV orders), a liquid heavy metal mercury or lead-bismuth eutectic alloy is used as the target, and the neutron generation mechanism is also a photonuclear reaction by electron braking gamma rays. Although the neutron generation efficiency by this photonuclear reaction is not good, it can be used for applications such as imaging where the cost of the electron beam accelerator is low and the amount of neutrons is small.

The nozzle 110 is a discharge port for flowing down the liquid metal 200 in a strip shape having a predetermined width and thickness. The liquid metal 200 has an absorption length that receives heat per unit time, for example, as a jet stream 200a at a speed of 10 to 20 meters per second so that the temperature does not rise too much due to the heat energy when the charged particles 210 are irradiated. By lengthening the temperature, the amount of heat absorbed in a unit area is reduced.

The charged particle 210 is accelerated by an accelerator 120 such as a linear accelerator, a cyclotron, or a synchrotron. The energy (several tens of kW or more) when the charged particles 210 are irradiated is set within the thickness of the jet 200a of the liquid metal 200. As for the calorific value, for example, since the melting point of lithium is about 180 ° C., the temperature becomes about 250 ° C. by irradiating the liquid metal 200 at about 220 ° C. with the charged particles 210.

The tank 300 is a container in which the liquid metal 200 discharged from the nozzle 110 and flowing down is contained. Since the jet 200a of the liquid metal 200 flows in at a high speed, cavitation occurs due to collision with the wall surface of the tank 300 or the liquid surface of the liquid metal 200 accumulated in the tank 300 depending on the direction of the nozzle.

Cavitation is a state in which bubbles are generated locally at the liquid metal 200 when the pressure is lower than the vapor pressure, and the bubbles are dented from a part around the bubbles in a short time, and the dented part has a corner. It is a crushing phenomenon. Cavitation on the wall surface of the tank 300 causes the wall surface to be gradually scraped to increase dents, which causes holes in the wall surface due to erosion. Therefore, the jet 200a of the liquid metal 200 is not on the wall surface side but on the center side of the tank 300. Let it flow down.

If the liquid metal 200 is flown along a slope 111 such as a slide as shown in FIG. 2, if the slope 111 has irregularities such as seams, the liquid metal 200 may collide with the slope 111 and cause cavitation. The jet that emerges from the nozzle without connecting the slope 111 connected from the nozzle outlet to the liquid level in the tank 300 flows straight down into the vacuum to the liquid level without using the slope 111 like a slide. It is preferable to let it. Further, when the liquid metal 200 flows diagonally, it easily hits the wall surface of the tank 300, so that it is preferable to allow the liquid metal 200 to flow down perpendicularly to the bottom surface of the tank 300.

The pipe 130 connects the tank 300 to the nozzle 110, and transfers the liquid metal 200 in the tank 300 to the nozzle 110 by using an electromagnetic pump 150 or the like. The flow rate of the liquid metal 200 is controlled by using an electromagnetic flow meter 160 or the like. Further, the liquid metal 200 is cooled by the cooler 140. For example, since lithium reacts with water, it is cooled by oil or the like.

As shown in FIG. 3, the tank 300 is, for example, a container having an empty upper surface, a pipe 130 connected to the lower surface, and a cylindrical housing 300a on the side surface. A plurality of (for example, four) magnets 400 are arranged on the outside of the housing 300a as magnetic field generating means. A magnetic field is generated by the plurality of magnets 400, and a yoke 410 is also arranged as a joint iron on the outside of the magnets 400 in order to control the path of the magnetic field lines.

The jet flow 200a varies in size depending on the application, flows down into the tank 300 in the form of a liquid curtain having a width w (for example, 5 to 25 cm) and a thickness t (for example, 1 to 25 mm), and is stored in the tank 300. It plunges into the liquid surface of the liquid metal 200. Cavitation occurs in the vicinity of the jet 200a, and a large number of bubbles (voids), the cavity 310, are generated below the liquid surface, or droplets rise on the liquid surface. The cavity 310 drifts on a flow that spreads toward the housing 300a of the tank 300, or collapses on the way.

The magnet 400 may be a permanent magnet or an electromagnet, but a magnetic field may be generated on the housing 300a side of the tank 300. The magnetic field may be, for example, a magnetic flux density of 0.3 T (tesla) or more on the liquid side of the housing 300a. The liquid metal 200 is a conductive fluid, and its viscosity changes depending on the strength of the magnetic field. When the magnetic field is generated by the magnet 400, the viscosity of the liquid metal 200 on the housing 300a side of the tank 300 increases, and the viscosity increase region 320 is generated.

As shown in FIG. 4, along the outer circumference of the cylindrical housing 300a, for example, four magnets 400 are arranged at equal intervals so that the magnetic poles change alternately to form a multipolar type. A magnetic field is generated by the magnetic field lines as shown in the figure, the viscosity increasing region 320 is formed on the housing 300a side, and the viscosity of the liquid metal 200 is improved from the center side. Although the case of four magnets is shown in FIG. 4, the number of magnets that can obtain the required magnetic flux density must be arranged in order to obtain the required viscosity on the liquid side of the housing 300a.

Even if the jet flow 200a falls to the center side of the tank 300, it becomes difficult for the flow to proceed from the boundary with the viscosity increasing region 320 toward the housing 300a. That is, the cavity 310 is also suppressed so as not to go beyond the boundary with the viscosity increasing region 320. Erosion is suppressed because the cavity 310 does not reach the housing 300a side. On the central side, the cavity 310 rides on the flow of circulation toward the pipe 130 or collapses in the middle.

As shown in FIG. 5, since the region d in which the cavity 310 exists is narrowed by the viscosity increasing region 320, the inner diameter D of the housing 300b of the tank 300 can also be reduced. For example, in an ordinary tank 300, when the width w of the jet 200a is 200 mm and the thickness t is 25 mm, in order to prevent erosion due to cavitation, the diameter φ of the housing 300b is 4 to 5 times the jet width. It is necessary to make it 800 to 1000 mm or more, which is the above, but it may be about 3 times by applying a magnetic field. Further, in a small tank 300 to which a magnetic field is applied, when the width w of the jet 200a is 70 mm and the thickness t is 2 mm, the diameter φ of the housing 300b may be 100 to 150 mm, which is about twice that.

Further, since the droplet 200b may rise when the jet 200a collides with the liquid surface, the wire mesh 330 may be arranged above the liquid metal 200 in the tank 300. The wire mesh 330 may be left open in the central portion through which the jet 200a passes. By catching the droplets 200b with the wire mesh 330, the droplets 200b are prevented from reaching the housing 300b.

Further, according to the experiment, the depth at which the cavity 310 is formed by the jet 200a plunging into the liquid surface is about 400 mm at a width of 50 mm × thickness of 0.6 mm × a flow velocity of 30 m / s of the jet 200a, so that the cavity 310 is on the pipe 130 side. In order not to go to the tank 300, the depth of the molten metal in the tank 300 should be 400 mm or more, and the ascending speed of the cavity 310 varies depending on the diameter of the cavity 310, but it is about 20 cm / s, so the downward flow velocity in the tank 300. Must determine the inner diameter D of the tank 300 from the flow rate of the jet flow 200a so that the flow velocity is slower than the ascending speed of the cavity 310 so that the cavity 310 does not go to the pipe 130 side.

As shown in FIG. 6, even if the cavity 310 does not reach the housing 300a, it is not preferable that air bubbles in the cavity 310 remain in the liquid metal 200 circulating in the pipe 130. A rectifying tank 340 may be provided. It is possible to increase the height of the tank 300 to eliminate air bubbles by the time it reaches the pipe 130, but since the cavity 310 is generated on the liquid surface, it may be difficult for the air bubbles to rise, so that the air bubbles are eliminated. It is better to provide a rectifying tank 340 to eliminate it.

Therefore, even if the liquid metal 200 containing bubbles is sent from the tank 300 to the rectifying tank 340, the flow velocity in the rectifying tank 340 may be slowed down to remove the bubbles. For example, when the bubbles rise at a rate of 2 cm / sec, if the flow velocity of the liquid metal 200 circulating in the pipe 130 is reduced to 1 cm / sec, the bubbles are likely to escape upward.

Further, as shown in FIG. 7, by increasing the diameter of the lower portion of the housing 300b, the speed at which the liquid metal 200 flows into the pipe 130 may be slowed down, so that air bubbles may easily rise. By preventing air bubbles from entering the pipe 130, cavitation erosion is eliminated, the efficiency of circulation and cooling of the liquid metal 200 is improved, and the flow is stabilized.

According to the present invention, in the liquid metal loop for generating neutrons, the life of the tank can be extended by suppressing the cavitation erosion of the tank that receives the jet of the liquid metal. Further, by limiting the region where cavitation occurs by receiving the jet flow by a magnetic field, the tank can be miniaturized, and the cost and the capacity of the fluid used can be minimized. Further, by eliminating bubbles in the pipe under the tank by circulating the flow of the liquid metal that catches the jet flow at a speed slower than the floating speed of the cavity, it is possible to suppress the bubbles from circulating in the pipe.

Although examples of the present invention have been described above, the present invention is not limited thereto. The generated neutrons can be used in other fields of neutron science such as medical facilities dealing with BNCT (Boron Neutron Capture Therapy) and IFMIF (International Fusion Materials Irradiation Facility). For example, in BNCT, cancer cells that have taken up boron 10 are irradiated with neutrons, and the cancer cells are killed by α particles and lithium 7 that have a range similar to the size of the cells generated by the nuclear reaction between boron 10 and neutrons. However, only cancer cells can be selectively destroyed without causing much damage to normal cells.

100: Liquid metal loop 110: Nozzle 111: Slope 120: Accelerator 130: Piping 140: Cooler 150: Electromagnetic pump 160: Electromagnetic flow meter 200: Liquid metal 200a: Jet 200b: Splash 210: Charged particles 220: Neutron 300: Tank 300a: Housing 300b: Housing 310: Cavity 320: Viscous increase region 330: Wire mesh 340: Rectification tank 400: Magnet 410: York

Claims (6)

In a liquid metal loop having a pipe for irradiating a liquid metal ejected from a nozzle with charged particles to generate neutrons and then cooling the liquid metal and circulating it to the nozzle.
A tank for storing the liquid metal after being irradiated with the charged particles before sending it to the pipe, and a tank for storing the liquid metal.
A magnetic field generating means arranged so as to generate a magnetic field inside the housing of the tank is provided.
By forming a region in the liquid metal in the tank that makes it difficult for the flow to proceed toward the housing by the magnetic field generating means, the cavity generated when the jet of the liquid metal is received on the center side of the tank is the tank. Suppress so that it does not reach the inside of the housing,
A mechanism for suppressing corrosion of liquid metal loops. The magnetic field generating means is a multi-pole type by arranging a plurality of magnets on the outside of the tank.
The mechanism for suppressing corrosion of a liquid metal loop according to claim 1. By making the flow velocity of the liquid metal sent from the tank to the pipe slower than the ascending speed of the cavity, the cavity is prevented from circulating in the pipe.
The mechanism for suppressing corrosion of a liquid metal loop according to claim 1 or 2. The liquid metal sent from the tank to the pipe was made slower than the ascending speed of the cavity in a further rectifying tank so that the cavity did not circulate in the pipe.
The mechanism for suppressing corrosion of a liquid metal loop according to any one of claims 1 to 3. In the tank, a wire mesh for preventing splashes is arranged above the liquid surface of the liquid metal.
The mechanism for suppressing corrosion of a liquid metal loop according to any one of claims 1 to 4. The anti-corrosion mechanism according to any one of claims 1 to 5.
It features a liquid metal loop.

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