Patent Publication Number: US-2015069680-A1

Title: Electromagnetic pump, quench tank, and liquid metal loop

Description:
FIELD 
     The present invention relates to an electromagnetic pump, a quench tank, and a liquid metal loop used for circulations of liquid metals such as liquid lithium. 
     BACKGROUND 
     Conventionally, an electromagnetic pump as described in Patent Literature 1 is known. The electromagnetic pump is configured that a plurality of stator iron-cores is radially arranged in the radially outer side of a concentric double cylinder and the stator iron-core is provided with a plurality of comb-teeth-shaped slots in each of which a plurality of annular coils is arranged. The concentric double cylinder is configured with an outer tube and an inner tube between which a duct is formed. The inner tube includes an inner iron-core for allowing lines of magnetic force to pass through. Further, both end portions of the inner tube are conically formed. The outer tube is connected to a circulation loop path of liquid sodium of a fast breeder reactor. 
     Each coil is arranged in order along the flow direction so as to form a three-phase alternating current winding so that a progressive magnetic field is generated along the flow direction in the duct when a three-phase alternating current is supplied to the coil of the electromagnetic pump. Further, a voltage is induced in the fluid by so-called the Fleming&#39;s right-hand rule to generate an induced current which produces the Lorentz force acting on the fluid itself. The liquid metal is transferred by the progressive magnetic field and the electromagnetic force generated by the induced current. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Patent Application Laid-open No. 62-178153 
       
    
     SUMMARY 
     Technical Problem 
     In a conventional loop, the height of the loop pipe is kept to be about 10 m in the inlet side of an electromagnetic pump so that the back pressure of the electromagnetic pump can be kept, thereby preventing cavitation. However, there is a problem that the large height of the loop pipe makes the apparatus large. The present invention is made to solve such problem. 
     Solution to Problem 
     According to an aspect of the present invention, an electromagnetic pump includes: an outer cylinder; an inner cylinder; a duct that is formed between the outer cylinder and the inner cylinder to allow a conductive liquid to flow therethrough; and an electromagnetic coil provided in an outer side of the outer cylinder. A radial cross sectional area of the duct at an inlet side is larger than a radial cross sectional area at an outlet side. 
     When a large radial cross sectional area is provided in the inlet side of the duct, the flow velocity in the inlet side is reduced, which further prevents cavitation. Therefore, the height of the circulation loop of the conductive liquid to which the electromagnetic pump is applied can be reduced. 
     According to another aspect of the present invention, an electromagnetic pump includes: an outer cylinder; an inner cylinder; a duct that is formed between the outer cylinder and the inner cylinder to allow a conductive liquid to flow therethrough; and an electromagnetic coil provided in an outer side of the outer cylinder. An inner surface of the outer cylinder and an outer surface of the inner cylinder have inclination angles against an axial direction such that a radial cross sectional area of the duct at an inlet side is larger than a radial cross sectional area at an outlet side. 
     By providing inclination angle to the inner surface of an outer cylinder and the outer surface of an inner cylinder, the radial cross sectional area of the duct formed between the outer cylinder and the inner cylinder changes. As in such manner, when a larger radial cross sectional area is provided in the inlet side of the duct, the flow velocity in the inlet side can be reduced, which provides the effect of preventing cavitation as well as the effect of reducing the height of the loop. 
     Advantageously, in the electromagnetic pump, a radial gap between the outer cylinder and the inner cylinder is approximately same along an axial direction. 
     Since the electromagnetic coil uniformly generates the magnetic field in the duct, the magnetic flux density does not change drastically along the axial direction of the duct. 
     According to still another aspect of the present invention, an electromagnetic pump includes: an outer cylinder; an inner cylinder; a duct that is formed between the outer cylinder and the inner cylinder to allow a conductive liquid to flow therethrough; and an electromagnetic coil provided in an outer side of the outer cylinder. Either of an inner surface of the outer cylinder or an outer surface of the inner cylinder has an inclination angle against an axial direction such that a radial cross sectional area of the duct at an inlet side is larger than a radial cross sectional area at an outlet side, and the other is formed parallel to the axial direction. 
     Even for such configuration in which the radial cross sectional area of the duct formed between the outer cylinder and the inner cylinder changes, when a larger radial cross sectional area is provided in the inlet side of the duct, the flow velocity in the inlet side is reduced, which prevents cavitation and provides effect of reducing the height of the loop. 
     Advantageously, in the electromagnetic pump, control is carried out such that a high current is flowed in an inlet side of the electromagnetic coil. 
     That is, in the present invention, providing a larger gap between the outer cylinder and the inner cylinder in the inlet side may cause difference in the magnetic field in the duct between the inlet side and the outlet side, so that a larger current is provided to the inlet side of the electromagnetic coil to provide a uniform magnetic field along the axial direction of the duct. In this manner, the flow velocity in the inlet side can be reduced along the axial direction of the duct, thereby preventing cavitation. 
     According to still another aspect of the present invention, a quench tank, arranged in a circulation path of a liquid metal loop, for separating and cooling liquid metal steam or mixed gas in a liquid metal introduced in a tank main body, includes any of the electromagnetic pumps described above, an inlet side of which is connected to the tank main body. 
     According to still another aspect of the present invention, a liquid metal loop includes the quench tank described above. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a front view illustrating an electromagnetic pump according to a first embodiment of the present invention. 
         FIG. 2  is a radial cross sectional view taken along the line A-A of the electromagnetic pump illustrated in  FIG. 1 . 
         FIG. 3  is a cross sectional view taken along the line B-B of the electromagnetic pump illustrated in  FIG. 1 . 
         FIG. 4  is a front view illustrating an electromagnetic pump according to a second embodiment of the present invention. 
         FIG. 5  is a radial cross sectional view taken along the line A-A of the electromagnetic pump illustrated in  FIG. 4 . 
         FIG. 6  is a cross sectional view taken along the line B-B of the electromagnetic pump illustrated in  FIG. 4 . 
         FIG. 7  is a front view illustrating an electromagnetic pump according to a third embodiment of the present invention. 
         FIG. 8  is a radial cross sectional view taken along the line A-A of the electromagnetic pump illustrated in  FIG. 7 . 
         FIG. 9  is a cross sectional view taken along the line B-B of the electromagnetic pump illustrated in  FIG. 7 . 
         FIG. 10  is a front view illustrating a quench tank according to a fourth embodiment of the present invention. 
         FIG. 11  is a side view of the quench tank illustrated in  FIG. 10 . 
         FIG. 12  is a top view of the quench tank illustrated in  FIG. 10 . 
         FIG. 13  is a cross sectional view of the quench tank illustrated in  FIG. 10 . 
         FIG. 14  is a cross sectional view of a cylindrical body. 
         FIG. 15  is a cross sectional view illustrating a cylindrical body of a quench tank according to a fifth embodiment of the present invention. 
         FIG. 16  is a cross sectional view illustrating a quench tank according to a sixth embodiment of the present invention. 
         FIG. 17  is a cross sectional view taken along the line A-A in  FIG. 16 . 
         FIG. 18  is a cross sectional view illustrating a quench tank according to a seventh embodiment of the present invention. 
         FIG. 19  is a cross sectional view taken along the line A-A in  FIG. 18 . 
         FIG. 20  is a cross sectional view taken along the line B-B in  FIG. 18 . 
         FIG. 21  is a cross sectional view taken along the line C-C in  FIG. 18 . 
         FIG. 22  is a block diagram illustrating a liquid metal loop of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       FIG. 1  is a cross sectional view along the flow direction of an electromagnetic pump according to a first embodiment of the present invention.  FIG. 2  is a radial cross sectional view taken along the line A-A of the electromagnetic pump illustrated in  FIG. 1 .  FIG. 3  is a cross sectional view taken along the line B-B of the electromagnetic pump illustrated in  FIG. 1 . An electromagnetic pump  100  is configured that a housing  1  includes therein an outer cylinder  2  made of stainless steel, an inner cylinder  3  made of stainless steel and arranged inside the outer cylinder  2 , and an electromagnetic coil  4  arranged around the outer cylinder  2 . 
     The outer cylinder  2  is configured as a conical frustum having a large diameter in the inlet side and a small diameter in the outlet side. Note that, the interface connected to the loop pipe (edge  2   a  of the outer cylinder) is provided as a straight pipe. Similarly, the inner cylinder  3  has a large diameter in the inlet side and a small diameter in the outlet side. A duct  5  is formed between the outer cylinder  2  and the inner cylinder  3 . The duct  5 , formed as a space between the outer cylinder  2  and the inner cylinder  3 , has an annular shape. Further, the radial cross sectional area of the duct  5  is large in the inlet side and small in the outlet side. 
     An inner iron-core  6 , which allows lines of magnetic force to pass through, is provided in the inner cylinder  3 . A support plate  7  for supporting the inner cylinder  3  is radially provided between the outer circumferential surface of the inner cylinder  3  and the inner circumferential surface of the outer cylinder  2 . The four support plates  7  are evenly provided along the circumferential direction at each of the portions near the front end and the rear end of the inner cylinder  3 . A conical cap  8  is provided in each of the front portion and rear portion of the inner cylinder  3 . 
     The electromagnetic coil  4  is configured with a stator iron-core  10  having a plurality of slots  9  formed in a comb-teeth shape and coils  11  arranged in the slots  9 . A thin steel plate having slots  9  formed in a comb-teeth shape is laminated to form a laminated iron-core having a predetermined thickness. The stator iron-core  10  is configured with laminated iron-cores evenly arranged around the outer cylinder  2 . The surface of the stator iron-core  10  opposing the outer cylinder is inclined along the inclination angle of the outer cylinder  2 , so that the stator iron-core  10  makes contact with the outer circumferential surface of the outer cylinder  2  without a space in between when the stator iron-core  10  is arranged around the outer cylinder  2 . The inclination angle is the angle of the inner surface of the outer cylinder  2  or the outer surface of the inner cylinder  3  against the axial direction of the electromagnetic pump  4 . 
     The external of the stator iron-core  10  is supported by the inner circumferential surface of the housing  1 . Further, the coil  11  wound in an annular shape is arranged in each slot  9 . Each coil  11  is arranged in order along the flow direction of the liquid metal to form a three-phase alternating current winding. Since the difference in diameter between the inner cylinder  2  and the outer cylinder  3  is constant along the flow direction in the duct  5 , uniform electromagnetic force can be applied to the liquid metal along the flow direction by supplying a constant current to the electromagnetic coil  4 . 
     Now, the operation of the electromagnetic pump  100  will be described. When a three-phase alternating current is supplied to the coil  11  of the electromagnetic pump  100 , a progressive magnetic field is generated in the flow direction in the duct  5 . Further, a voltage is induced in the fluid by so-called the Fleming&#39;s rule to generate an induced current which produces the Lorentz force acting on the fluid itself. The liquid metal is transferred by the progressive magnetic field and the electromagnetic force generated by the induced current. 
     Further, as for the electromagnetic pump  100 , since the cross sectional area of the duct  5  is large in the inlet side, the flow velocity of the liquid metal in the inlet side is reduced, thereby preventing cavitation in the electromagnetic pump  100 . Therefore, the effect of reducing the height of the loop can be expected. In some cases, there will be no requirement for the loop height so that the apparatus can be made compact in size. 
     Further, the inclination angle of the outer cylinder  2  may be provided slightly larger than the inclination angle of the inner cylinder  3 . In this manner, the cross sectional area of the duct  5  in the inlet side can be made larger than the cross sectional area of the duct  5  in the outlet side (not illustrated in the drawing). 
     Second Embodiment 
       FIG. 4  is a cross sectional view along the flow direction of an electromagnetic pump according to a second embodiment of the present invention.  FIG. 5  is a radial cross sectional view taken along the line A-A of the electromagnetic pump illustrated in  FIG. 4 .  FIG. 6  is a cross sectional view taken along the line B-B of the electromagnetic pump illustrated in  FIG. 4 . An electromagnetic pump  200  is configured that a housing  1  includes therein an outer cylinder  202  made of stainless steel, an inner cylinder  203  made of stainless steel and arranged inside the outer cylinder  202 , and an electromagnetic coil  204  arranged around the outer cylinder  202 . 
     The outer cylinder  202  is configured of three blocks. A first block  50  is configured as a straight pipe having a large diameter extending along the axial direction, a second block  51  is configured as a conical frustum shape continuously extending from the first block  50 , and a third block  52  is configured as a straight pipe having a smaller diameter than the first block  50  extending along the axial direction. 
     Similarly, the inner cylinder  3  is composed of a first block  50  configured as a straight circular pipe having a large diameter extending along the axial direction, a second block  51  configured as a conical frustum shape, and a third block  52  configured as a straight circular pipe having a small diameter extending along the axial direction. In the second block  51 , the outer cylinder  202  and the inner cylinder  203  have the same inclination angle. The inclination angle is the angle of the inner surface of the outer cylinder  202  or the outer surface of the inner cylinder  203  against the axial direction of the electromagnetic pump  200 . 
     A duct  205  is formed between the outer cylinder  202  and the inner cylinder  203 . The duct  205 , formed as a space between the outer cylinder  202  and the inner cylinder  203 , has an annular shape. In the first block  50 , the cross sectional area of the duct  205  is constant since both the outer cylinder  202  and the inner cylinder  203  are straight. In the second block  51 , the cross sectional area of the duct  205  gradually decreases along the flow direction since the second block  51  is configured as a conical frustum. In the third block  52 , the cross sectional area of the duct  205  is constant since both the outer cylinder  202  and the inner cylinder  203  are straight. 
     An inner iron-core  206 , which allows lines of magnetic force to pass through, is provided in the inner cylinder  203 . A support plate  7  for supporting the inner cylinder  203  is radially provided between the outer circumferential surface of the inner cylinder  203  and the inner circumferential surface of the outer cylinder  202 . The four support plates  7  are evenly provided along the circumferential direction at each of the portions near the front end and the rear end of the inner cylinder  203 . A conical cap  8  is provided in each of the front portion and rear portion of the inner cylinder  203 . The tip of the cap  8  may have a spherical shape. 
     The electromagnetic coil  204  is configured with a stator iron-core  210  having a plurality of slots  9  formed in a comb-teeth shape and coils  11  arranged in the slots  9 . A thin steel plate having slots  9  formed in a comb-teeth shape is laminated to form a laminated iron-core having a predetermined thickness. The stator iron-core  210  is configured with the laminated iron-cores evenly arranged around the outer cylinder  202 . In the second block  51 , the surface of the stator iron-core  210  opposing the outer cylinder is inclined along the inclination angle of the outer cylinder  202 , so that the stator iron-core  210  makes contact with the outer circumferential surface of the outer cylinder  202  without a space in between when the stator iron-core  210  is arranged around the outer cylinder  202 . The inclination angle is the angle of the inner surface of the outer cylinder  202  or the outer surface of the inner cylinder  203  against the axial direction of the electromagnetic pump  200 . 
     The external of the stator iron-core  210  is supported by the inner surface of the housing  1 . Further, the coil  11  wound in an annular shape is arranged in each slot  9 . Each coil  11  is arranged in order along the flow direction of the liquid metal to form a three-phase alternating current winding. Since the difference in diameter between the inner cylinder  203  and the outer cylinder  202  is constant along the flow direction in the duct  205 , uniform electromagnetic force can be applied to the liquid metal along the flow direction by supplying a constant current to the electromagnetic coil  204 . 
     Even in the electromagnetic pump  200  configured as described above, since the cross sectional area of the duct  205  is large in the inlet side of the electromagnetic pump  200 , the flow velocity in the inlet side is reduced, thereby preventing cavitation in the electromagnetic pump  200 . 
     Third Embodiment 
       FIG. 7  is a cross sectional view along the flow direction of an electromagnetic pump according to the first embodiment of the present invention.  FIG. 8  is a radial cross sectional view taken along the line A-A of the electromagnetic pump illustrated in  FIG. 7 .  FIG. 9  is a radial cross sectional view taken along the line B-B of the electromagnetic pump illustrated in  FIG. 7 . The electromagnetic pump is configured that a housing  1  includes therein an outer cylinder  302  made of stainless steel, an inner cylinder  303  made of stainless steel and arranged inside the outer cylinder  302 , and an electromagnetic coil  304  arranged around the outer cylinder  302 . 
     The outer cylinder  302  is a straight pipe having an inner surface parallel to the axial direction. The inner cylinder  303  is configured as a conical frustum having a small diameter in the inlet side and a large diameter in the outlet side. A duct  305  is formed between the outer cylinder  302  and the inner cylinder  303 . The duct  305 , formed as a space between the outer cylinder  302  and the inner cylinder  303 , has an annular shape. The inclination angle is the angle of the inner surface of the outer cylinder  302  or the outer surface of the inner cylinder  303  against the axial direction of the electromagnetic pump  300 . Since the electromagnetic pump  300  according to the third embodiment has the inner cylinder  303  formed in a conical frustum, the cross sectional area of the duct  305  is large in the inlet side and small in the outlet side. 
     An inner iron-core  306 , which allows lines of magnetic force to pass through, is provided in the inner cylinder  303 . A support plate  7  for supporting the inner cylinder  303  is radially provided between the outer circumferential surface of the inner cylinder  303  and the inner circumferential surface of the outer cylinder  302 . Four support plates  7  are evenly provided along the circumferential direction at each of the portions near the front end and the rear end of the inner cylinder  303 . A conical cap  8  is provided in each of the front portion and rear portion of the inner cylinder  303 . The tip of the cap  8  may have a spherical shape. 
     The electromagnetic coil  304  is configured with a stator iron-core  310  having a plurality of slots  9  formed in a comb-teeth shape and coils  11  arranged in the slots  9 . A thin steel plate having slots  9  formed in a comb-teeth shape is laminated to form a laminated iron-core having a predetermined thickness. The stator iron-core  310  is configured with the laminated iron-cores evenly arranged around the outer cylinder  302 . The surface of the stator iron-core  310  opposing the outer cylinder makes contact with the outer circumferential surface of the outer cylinder  302  without a space in between. 
     The external of the stator iron-core  310  is fixed to the inner surface of the housing  1 . Further, the coil  11  wound in an annular shape is arranged in each slot  9 . Each coil  11  is arranged in order along the flow direction of the liquid metal to form a three-phase alternating current winding. Since the difference in diameter between the inner cylinder  303  and the outer cylinder  302  gradually decreases along the flow direction in the duct  305 , the current supplied to the electromagnetic coil  304  is raised in the inlet side to apply uniform electromagnetic force to the liquid metal along the flow direction. 
     Even in the electromagnetic pump  300  configured as described above, since the cross sectional area of the duct  305  is large in the inlet side, the flow velocity in the inlet side is reduced, thereby providing the effect of preventing cavitation in the electromagnetic pump  300 . 
     Though not illustrated in the drawings, the outer cylinder may be configured as a conical frustum having a large diameter in the inlet side and a small diameter in the outlet side, and the inner cylinder may have a small diameter in the inlet side and the large diameter in the outlet side. Further, the outer cylinder may be configured as a conical frustum having a large diameter in the inlet side and a small diameter in the outlet side, and the inner cylinder may be configured as a circular pipe having the outer surface extending straight along the axial direction. Also in such configuration, since the area of the duct in the inlet side is larger than the outlet side, the similar effect can be obtained. 
     The electromagnetic pumps  100  to  300  according to the first to third embodiments can be applied to various plants and products such as a Boron Neutron Capture Therapy (BNCT) ( ) nuclear reactors, nuclear fusion reactors, fast breeder reactors, etc. 
     Fourth Embodiment 
     An example of the application of the electromagnetic pumps  100  to  300  of the present invention to a quench tank will be described below.  FIG. 10  is a front view illustrating a quench tank according to a fourth embodiment of the present invention.  FIG. 11  is a side view of the quench tank illustrated in  FIG. 10 .  FIG. 12  is a top view of the quench tank illustrated in  FIG. 10 .  FIG. 13  is a cross sectional view of the quench tank illustrated in  FIG. 10 . A quench tank  400  is configured with a tank main body  401  connected by a pipe to a receiver of a target forming unit which forms a liquid metal target and a cylindrical body  402  approximately horizontally provided in the bottom portion of the tank main body  401 . The tank main body  401  has a cylindrical structure made by sheet metal processing. A pipe  403  from the target forming unit is provided on the upper side surface of the tank main body  401  so as to be tangential to the cylindrical shape of the tank main body  401 . So that the liquid metal introduced from the pipe  403  circulates along an inner surface  401   a  of the tank main body  401  and enters a free liquid level (the flow of the liquid metal is illustrated in a dot-line arrow in the drawing). The target forming unit is configured with a nozzle for planarly jetting the liquid metal so as to cross the region irradiated with a proton beam and the receiver configured with a diffuser for receiving the jetted liquid metal. 
     In the lower part of the tank main body  401 , four current plates  404  are radially provided from the axis of the cylinder so as to surround the central portion of the cylinder. The current plate  404  may be a flat plate, a mesh plate, or a punching metal. The number of current plates  404  is not limited to four. 
     The cylindrical body  402  is slightly inclined so as to lower a distal end  402   a  against the tank main body  401 . Inside the cylindrical body  402 , as illustrated in  FIG. 14 , a plurality of separation plates  405  is arranged so as to have inclination against the vertical direction. The gap between adjacent separation plates  405  is determined by an ascending rate of the bubble and a residence time in the cylindrical body, and preferably in a range of 3 cm to 5 cm specifically. The angle of the separation plate  405  is not limited. However, as illustrated in  FIG. 14(   a ), the angle against the axial direction of the tank main body  401  is preferably in a range of 45 degrees to 60 degrees from the vertical direction. Further, as illustrated in  FIG. 14(   b ), the separation plate  405  is provided throughout approximately the entire length of the cylindrical body  402 . The length of the cylindrical body  402  is determined based on the capacity of separating bubbles. 
     An outlet for the liquid metal is provided in the downstream of the separation plate  405 . The pipe connected to the outlet is connected to a pump constituting a liquid metal loop. The pipe extending from the pump is connected to the target forming unit via a heat exchanger. In this manner, the liquid metal loop is configured. 
     On the bottom, in the downstream side, of the cylindrical body  402 , any of the electromagnetic pumps  100  to  300  described in the first to third embodiments is provided. Any of the electromagnetic pumps  100  to  300  is provided such that the side having the large cross sectional area of the duct is attached to the cylindrical body  402 . The outlet of any of the electromagnetic pumps  100  to  300  is connected to the pipe of the circulation loop. 
     Now, the behavior of the liquid metal in the quench tank will be described. The liquid metal of which temperature is raised by irradiation with a proton beam is introduced from the target forming unit to the tank main body  401  through a pipe  3 . Since the pipe  403  is connected to the tank main body  401 , tangential to the cylindrical shape, the introduced liquid metal circulates along the inner surface  401   a  of the tank main body  401  and enters the free liquid level. In this step, the bubble is introduced from the free liquid level. 
     After circulatingly entering the free liquid level, the liquid metal swirlingly moves in the tank main body  401 . The current plate  404  provided inside the lower part of the main body stops the circulation of the liquid metal, and the liquid metal rests in the lower part of the tank main body  401 . On the side surface of the lower part of the tank main body  401 , a hole  407  corresponding to the cylindrical body  402  is provided. The tank main body  401  and the cylindrical body  402  communicates through the hole  407 . A second current plate  408  formed of a mesh plate or a punching metal is provided on the hole  407 . As illustrated in  FIG. 14(   a ), as the liquid metal flows along the longitudinal direction of the cylindrical body  402 , the bubble included in the liquid metal ascends. Since the separation plates  405  are arranged in the cylindrical body with a predetermined small gap therebetween, the bubble ascends for a short distance to hit against the surface of the separation plate  405  and grows by uniting with other bubbles. 
     As the bubble grows, the buoyancy of the bubble increases, raising the ascending rate of the bubble. Thus, the bubble ascends by rollingly moving along the inclined surface of the separation plate  405 . The bubble unites with nearby bubbles to grow during the ascending and further increases its volume until the bubble reaches the free liquid level. Such process happens in each space between separation plates  405 . The grown bubble in the liquid metal flowing along the longitudinal direction of the cylindrical body  402  disappears when the bubble reaches the free interface. When the bubble grows and the ascending rate increases, the bubble ascends within a shorter time, which can efficiently remove the bubble and reduce the length of the cylindrical body  402 . 
     Then, the liquid metal from which sufficient amount of bubble is removed is suctioned by any of the electromagnetic pumps  100  to  300  to be transferred to the circulation loop. Since the electromagnetic pumps  100  to  300  have a large duct cross sectional area in the inlet side, sufficient back pressure can be kept without providing a large loop height, so that the cavitation in the electromagnetic pumps  100  to  300  can efficiently be prevented. The electromagnetic pumps  100  to  300  transfer the liquid metal again to the target forming unit. 
     When the liquid metal is jetted to form a target, bubbles are likely to be mixed into the liquid metal in the receiver. Therefore, it is extremely useful to remove the bubble in the cylindrical body  402  for the case in which the target is formed by the liquid metal jet. 
     As described above, according to the quench tank  400  of the present invention, by providing a plurality of separation plates  405  in the cylindrical body  402 , the separation plate  405  can grow and remove the bubble rapidly in the flowing liquid metal. Therefore, the length of the cylindrical body  402  can be reduced, enabling downsizing of the quench tank  400 . Further, since the cavitation in the electromagnetic pumps  100  to  300  can be prevented, mixing of bubbles in the circulation loop can be minimized. 
     The target forming unit may be a conventional type in which a liquid metal is supplied with high speed to a curved back plate to form a liquid film. 
     Fifth Embodiment 
       FIG. 15  is a cross sectional view illustrating a cylindrical body of the quench tank according to a fifth embodiment of the present invention. The quench tank has an approximately the same configuration as the fourth embodiment but differs in the shape and arrangement of the separation plate  5 . The rest of the configuration is same as the quench tank  400  of the fourth embodiment, and therefore will not be described. In the quench tank, a punching metal having a plurality of holes  502  is provided as a separation plate  501 . A plurality of separation plates  501  is approximately horizontally arranged. The liquid metal flowing down from the tank main body  401  passes through a plurality of layered separation plates  501 . The bubble included in the liquid metal hits against the back surface of each separation plate  501  to grow by uniting with other bubbles. The buoyancy of the bubble increases as the bubble grows, and the bubble ascends through the hole  502  of the separation plate  501 . The bubble grows at the separation plate  501  in the upper layer by further absorbing other bubbles and ascends through the hole  502 . Finally, the grown bubble having a large volume reaches the free interface of the liquid metal in the cylindrical body  2  and disappears. 
     The separation plate  502  formed of a punching metal also grows the bubble and increases its ascending speed, so that the horizontal distance required for separating the bubble can be reduced. Therefore, the cylindrical body can be shortened, enabling downsizing of the quench tank. 
     Although not illustrated in the drawing, the similar effect can be obtained by configuring the separation plate  501  with a mesh plate. That is, when a bubble grows by hitting against the surface of the mesh, the ascending speed of the bubble increases. The growing bubble gains larger buoyancy and moves to the upper layer through the mesh. After further continuing growing, the bubble disappears upon reaching the free liquid level of the liquid metal. As described above, when the bubble grows and increases its ascending speed, the bubble can be removed within a shorter time. Thereby, the bubble can efficiently be removed so that the length of the cylindrical body can be shortened. The optimum mesh size is determined by the tank capacity, the flow velocity of the liquid metal, etc. 
     Sixth Embodiment 
       FIG. 16  is a cross sectional view illustrating a quench tank according to a sixth embodiment of the present invention.  FIG. 17  is a cross sectional view taken along the line A-A in  FIG. 16 . A quench tank  600  has a cylindrical tank main body  601 , and a pipe  603  from the target forming unit described above is connected to the upper part of the tank main body  601 . Further, the pipe  603  is tangentially provided to the cylindrical body. SO that the liquid metal introduced from the pipe  603  circulates along the inner surface  601   a  of the tank main body  601  and enters the free liquid level. 
     In the lower part of the tank main body  601 , four current plates  604  are radially provided from the axis of the cylinder so as to surround the central portion of the cylinder. The current plate  604  is preferably a mesh plate to promote adhesion of the bubble. Otherwise, the current plate  604  may be a punching metal in which a large number of small holes are formed. The number of the current plates  604  is not limited to four. The upper part of the current plate  604  is supported by a support plate  602 , and the lower part of the current plate  604  is supported by a bottom plate  605  of the tank main body  601 . The length of the current plate  604  is determined based on the required performance of removing bubbles. 
     On the bottom portion  605  of the tank main body  601 , any of the electromagnetic pumps  100  to  300  according to the first to third embodiment is provided. Any of the electromagnetic pumps  100  to  300  is provided such that the side having the large cross sectional area of the duct is attached to the tank main body  601 . The outlet of any of the electromagnetic pumps  100  to  300  is connected to the pipe  603  of the circulation loop. The pipe  603  extending from any of the electromagnetic pumps  100  to  300  is connected to the target forming unit via a heat exchanger. In this manner, the liquid metal loop is configured. 
     Now, the behavior of the liquid metal in the quench tank will be described. The liquid metal of which temperature is raised by irradiation with a proton beam is introduced from the target forming unit to the tank main body  601  through the pipe  603 . Since the pipe  603  is connected to the tank main body  601 , tangential to the cylindrical shape, the introduced liquid metal circulates along the inner surface of the tank main body  601  and enters the free liquid level. In this step, the bubble is introduced from the free liquid level. 
     After circulatingly entering the free liquid level, the liquid metal swirlingly moves in the tank main body  601 . The current plate  604  provided inside the lower side of the main body stops the circulation of the liquid metal, and the liquid metal rests in the lower part of the tank main body  601 . The bubble included in the liquid metal touches the current plate  604  and adheres thereto, and then grows by uniting with adjacent bubbles. The buoyancy of the bubble increases as the bubble grows, and the bubble ascends along the current plate  604 . During the process, the bubble continues growing by absorbing small bubbles existing nearby. The grown bubble obtains higher ascending rate in the liquid metal and finally disappears upon reaching the free liquid level in the tank main body  601 . 
     The liquid metal from which sufficient amount of bubble is removed is suctioned by any of the electromagnetic pumps  100  to  300  to be transferred to the circulation loop. Since the electromagnetic pumps  100  to  300  have a large duct cross sectional area in the inlet side, sufficient back pressure can be kept without providing a large loop height, so that the cavitation in the electromagnetic pumps  100  to  300  can efficiently be prevented. The electromagnetic pumps  100  to  300  transfer the liquid metal again to the target forming unit. 
     As described above, according to the quench tank  600  of the present invention, by providing a plurality of separation plates  604  in the lower part of the tank main body  601 , the separation plate  604  can grow and rapidly remove the bubble in the flowing liquid metal. Therefore, the separation region of the bubble can be reduced compared to the case in which the bubble ascends without using any additional means. As a result, the quench tank  600  can be downsized. Further, since cavitation in the electromagnetic pump is prevented, mixing of bubbles into the circulation loop can be minimized. 
     Seventh Embodiment 
       FIG. 18  is a cross sectional view illustrating a quench tank according to a seventh embodiment of the present invention.  FIG. 19  is a cross sectional view taken along the line A-A in  FIG. 18 .  FIG. 20  is a cross sectional view taken along the line B-B in  FIG. 18 .  FIG. 21  is a cross sectional view taken along the line C-C in  FIG. 18 . A quench tank  700 , having an approximately the same configuration as the quench tank  600  of the sixth embodiment, is characterized in that the dimensions of a current plate  704  is reduced and a wing-shaped current plate is provided above the current plate  704 . The rest of the configuration is same as the quench tank  600  of the sixth embodiment, so that the descriptions on those parts are omitted, and the same component is appended with the same reference sign. The quench tank  700  includes an upper wing  701  and a lower wing  702 . Each of the upper wing  701  and the lower wing  702  is configured with three wings. 
     The upper wing  701  and the lower wing  702  have predetermined inclined shapes. The surface of the wing is configured with a mesh member  706  provided in a metal plate frame  705 . Inclination angles of the upper wing  701  and the lower wing  702  are determined based on the flow angle of the liquid metal along the inner wall of the tank main body  601 . The inclination angle of the upper wing  701  is more gradual than the lower wing  702 . 
     The angle between the flow direction of the liquid metal flowing along the inner wall  601   a  of the tank main body  601  and the vertical direction gradually decreases as the liquid metal flows from the upper part to the middle portion of the tank main body  601 . In the upper part of the tank main body  601 , the introduced liquid metal circulates with high velocity so that the angle between the flow direction of the liquid metal and the vertical direction is large. Therefore, the inclination angle of the upper wing  701  is set to a large angle corresponding to the flow direction of the liquid metal. 
     Similarly, the inclination angle of the lower wing  702  is set corresponding to the angle of flow direction of the liquid metal in the middle portion of the tank main body  601 . The four current plates  704  provided in the lower part of the tank main body  601  are slightly smaller than those of the sixth embodiment. The function of the current plate  704  is same as the sixth embodiment described above. 
     The behavior of the liquid metal in the quench tank will be described. The liquid metal of which temperature is raised by irradiation with a proton beam is introduced from the target forming unit to the tank main body  601  through the pipe  603 . Since the pipe  603  is connected to the tank main body  601 , tangential to the cylindrical shape, the introduced liquid metal circulates along the inner surface of the tank main body  601 . 
     The upper wing  701  guides the liquid metal to maintain its circulating direction. That is, the upper wing  701  maintains the flow direction of the liquid metal along the inner surface of the tank main body  601  so as to prevent the liquid metal from abruptly changing the descending angle. Subsequently, the lower wing  702  further maintains the flow direction of the liquid metal, and consequently, the liquid metal is smoothly introduced to the free liquid level. The current plate  704  provided inside the lower side of the tank main body  601  stops the circulation of the liquid metal, and the liquid metal rests in the lower part of the tank main body  601 . The bubble included in the liquid metal touches the current plate  704  and adheres thereto, and then grows by uniting with adjacent bubbles. 
     The buoyancy of the bubble increases as the bubble grows, and the bubble ascends along the current plate  704 . During the process, the bubble continues growing by absorbing small bubbles existing nearby. The grown bubble obtains higher ascending rate in the liquid metal and finally disappears upon reaching the free liquid level in the tank main body  601 . 
     The liquid metal from which sufficient amount of bubble is removed is suctioned by any of the electromagnetic pumps  100  to  300  to be transferred to the circulation loop. Since the electromagnetic pumps  100  to  300  have a large duct cross sectional area in the inlet side, sufficient back pressure can be kept without providing a large loop height, so that the cavitation in the electromagnetic pumps  100  to  300  can efficiently be prevented. The electromagnetic pumps  100  to  300  transfer the liquid metal again to the target forming unit. 
     As described above, according to the quench tank  700  of the present invention, the upper wing  701  and the lower wing  702  guide the liquid metal to enter the free liquid level with moderate speed, so that the bubble is not likely to be produced. Further, since the separation plate  704  grows and rapidly removes the bubble, the separation region of the bubble can be reduced compared to the case in which the bubble ascends without using any additional means. As a result, the quench tank  700  can be downsized. Further, since the cavitation in the electromagnetic pumps  100  to  300  can be prevented, mixing of bubbles in the circulation loop can be minimized. 
     Eighth Embodiment 
       FIG. 22  is a block diagram illustrating a liquid metal loop of the present invention. A liquid metal loop  800  includes any of the quench tanks  400  to  700  according to the fourth to seventh embodiments in the circulation path. A target forming unit  801  of the liquid metal loop  800  is configured with a nozzle  802  for planarly jetting the liquid metal so as to cross the region irradiated with a proton beam and a receiver  803  configured with a diffuser for receiving the jetted liquid metal. Thus, bubbles are easily mixed in the liquid metal in the receiver  803 . The bubble included in the liquid metal is removed in any of the quench tanks  400  to  700 . The liquid metal, from which the bubble is removed, is transferred to any of the electromagnetic pumps  100  to  300 . Since the electromagnetic pumps  100  to  300  can sufficiently reduce pressure loss, cavitation can efficiently be prevented in the electromagnetic pumps  100  to  300 . The electromagnetic pumps  100  to  300  transfer the liquid metal again to the target forming unit  801  through a heat exchanger  805 . 
     According to the liquid metal loop  800 , since the target is formed by the jet of the liquid metal, a back plate behind the liquid metal is not necessary as in the conventional art. Therefore, the damage of a structure by a neutron can be suppressed. The quench tanks  400  to  700  are preferable for such target forming unit  801 . 
     Further, according to the embodiment described above, the aspect of the present invention can be specified as described below. 
     A quench tank, arranged in a circulation path of the liquid metal loop, for separating and cooling liquid metal steam or mixed gas included in the liquid metal introduced in the tank main body is provided. The quench tank is characterized in that the tank main body has a separation region for forming an approximately horizontal flow of the liquid metal, a separation plate configured of a plate having a plurality of holes or a mesh plate is arranged in the separation region so as to be approximately horizontal to the flow direction of the liquid metal, and an inlet side of any of the electromagnetic pumps according to the first to third embodiments is connected to the separation region. 
     A quench tank, arranged in a circulation path of the liquid metal loop, for separating and cooling liquid metal steam or mixed gas included in the liquid metal introduced in the tank main body is provided. The quench tank is characterized in that the tank main body has a separation region for forming an approximately horizontal flow of the liquid metal, a separation plate, tilted toward the vertical direction, configured of a plate having a plurality of holes or a mesh plate is arranged in the separation region, and an inlet side of any of the electromagnetic pumps according to the first to third embodiments is connected to the separation region. 
     A quench tank, arranged in a circulation path of the liquid metal loop, for separating and cooling liquid metal steam or mixed gas included in the liquid metal introduced in the tank main body is provided. The quench tank is characterized in that the tank main body has a separation region for forming an approximately horizontal flow of the liquid metal, a separation plate which is curved about the longitudinal axis such that the cross section has at least one inverted concave shape, and is provided with a hole in the middle portion which is an apex of the inverted concave shape and/or in the mid slope, is arranged in the separation region, and an inlet side of any of the electromagnetic pumps according to the first to third embodiments is connected to the separation region. 
     A quench tank, arranged in a circulation path of the liquid metal loop, for separating and cooling liquid metal steam or mixed gas included in the liquid metal introduced in the tank main body is provided. The quench tank is characterized as follows. The tank main body has a separation region, connected to the tank main body, for forming an approximately vertical flow of the liquid metal. A separation plate having a concave shape provided with a hole in the middle portion which is the bottom of the concave shape and a small hole in the mid slope between the edge and the bottom of the concave shape is arranged in the separation region such that the distance between the bottom of the separation plate and the bottom plane of the separation region is kept in a predetermined gap. An introducing port for introducing the liquid metal from the tank main body is provided between the separation plate in the separation region and the bottom plane of the separation region. An outlet for the liquid metal is provided above the separation plate in the separation region. Further, an inlet side of any of the electromagnetic pumps according to the first to third embodiments is connected to the separation region. 
     Note that, the separation region may be separated from the tank main body. 
     A quench tank, arranged in a circulation path of the liquid metal loop, for separating and cooling liquid metal steam or mixed gas included in the liquid metal introduced in the tank main body is provided. The quench tank is characterized in that a separation plate configured of a mesh plate or a punching plate is vertically arranged in the lower part of the tank main body, and an inlet side of any of the electromagnetic pumps according to the first to third embodiments is connected to the bottom part of the tank main body. Further, a wing having an inclination angle corresponding to the flow angle, along the inner surface of the tank main body, of the liquid metal may be provided above the separation plate in the tank main body. 
     REFERENCE SIGNS LIST 
     
         
         
           
               100  electromagnetic pump 
               1  housing 
               2  outer cylinder 
               3  inner cylinder 
               4  electromagnetic coil 
               5  duct 
               6  inner iron-core 
               9  slot 
               10  stator iron-core 
               11  coil