AU2003259592B2

AU2003259592B2 - Method and apparatus for producing uranium foil and uranium foil produced thereby

Info

Publication number: AU2003259592B2
Application number: AU2003259592A
Authority: AU
Inventors: Se-Jung Jang; Chang-Kyu Kim; Eung-Soo Kim; Ki-Hwan Kim; Seok-Jin Oh
Original assignee: Korea Atomic Energy Research Institute KAERI; Korea Hydro and Nuclear Power Co Ltd
Current assignee: Korea Atomic Energy Research Institute KAERI; Korea Hydro and Nuclear Power Co Ltd
Priority date: 2003-03-31
Filing date: 2003-10-30
Publication date: 2010-02-04
Anticipated expiration: 2023-10-30
Also published as: KR20040085555A; FR2852970B1; FR2852970A1; AU2003259592A1; ZA200309615B; KR100557823B1; AR042805A1

Description

P/00/0II Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION Invention Title: METHOD AND APPARATUS FOR PRODUCING URANIUM FOIL AND URANIUM FOIL PRODUCED THEREBY The following statement is a full description of this invention, including the best method of performing it known to me: METHOD AND APPARATUS FOR PRODUCING URANIUM FOIL AND URANIUM FOIL PRODUCED THEREBY BACKGROUND OF THE INVENTION 5 Field of the Invention The present invention relates to a method and an apparatus for continuously producing a uranium foil with enhanced characteristics, a uniform thickness and a broad .0 width, in which molten metal is retained in a furnace by reducing the pressure within the furnace and increasing the pressure within a chamber, the molten metal is discharged to the outer circumference of a cooling roll and formed into the foil via a slot of the furnace under the condition that the 5 slot is located close to the cooling roll, and the foil is rapidly cooled by the contact with the cooling roll so that fine crystalline granules of the uranium foil with irregular orientation are formed. 0 Description of the Related Art In a method for producing a uranium foil known to the skilled in the art, an ingot is made of uranium or uranium alloy, cut, and then fed through the hot rolling process, thereby being formed into the foil. 5 More specifically, the ingot is maintained at a constant 1 temperature of 1, 300'C and then cast into a sheet in a vacuum inductive melting furnace. Otherwise, the ingot is cut into sheets with a proper size, and then the cut sheets repeatedly go through hot rolling and heat treatment processes at a 5 temperature of 600'C under the inert gas atmosphere so that the thickness of the sheet is gradually reduced. Finally, a uranium foil with a thickness of 100pm to 500gm is produced. In order to prevent the swelling of the uranium foil during the irritation test, an isotropic structure of the foil 10 having fine crystalline granules of the foil is required. Such isotropic structure of the foil is obtained by the heating process at 800'-C and subsequently the quenching process. Therefore, the conventional method for producing the 15 uranium foil is very complicated and troublesome. Moreover, since the uranium or uranium alloy retains rigidity while lacking ductility, the hot rolling of the uranium or uranium alloy is very difficult. During the rolling process, the residual stress existing 20 in the uranium causes cracks in the foil, thereby producing defective foils and reducing the recovery rate of the uranium. Therefore, the conventional method for producing the uranium foil with the reduced recovery rate is noneconomical. Since uranium is an easily oxidizable material, the 25 uranium must go through the hot rolling process under a vacuum 2 condition or an inert gas atmosphere. Accordingly, the repetition of the hot rolling processes of the uranium is very troublesome, requires a long period of time, and remarkably reduces the productivity of the uranium foil. 5 The produced uranium foil having residual stress due to the repetition of the hot rolling process may be deformed or damaged due to such thermal cycling during the production or the irradiation. The method for producing uranium foil by the hot rolling LO process further requires an additional process for removing impurities such as a surface-oxidized product mixed at the rolling process, thereby being complicated. SUMMARY OF THE INVENTION L5 Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method and an apparatus for continuously producing a uranium foil with enhanced ?0 characteristics, a uniform thickness and a broad width, in which molten metal is retained in a furnace by reducing the pressure within the furnace and increasing the pressure within a chamber, the molten metal is discharged to the outer circumference of a cooling roll and formed into the foil via a 5 slot of the furnace under the condition that the slot is 3 located close to the cooling roll, and the foil is rapidly cooled by the contact with the cooling roll so that fine crystalline granules of the uranium foil with irregular orientation are formed. 5 It is another object of the present invention to provide a method and an apparatus for producing a uranium foil with rigidity without requiring the rolling process. It is still another object of the present invention to provide a method and an apparatus for mass-producing a uranium LO foil with excellent characteristic in a short period of time, in which the recovery rate of the uranium is increased. It is yet another object of the present invention to provide a method and an apparatus for producing a uranium foil without imparting residual stress to the foil. L5 It is still yet another object of the present invention to provide a uranium foil with an isotropic structure, in which fine crystalline granules having different orientation are irregularly disposed. In accordance with one aspect of the present invention, 20 the above and other objects can be accomplished by the provision of a method for producing a uranium foil, comprising the steps of: (a) charging a furnace provided with a nozzle in its bottom with uranium alloy, and heating the furnace under the 25 vacuum condition; 4 (b) breaking the vacuum in a chamber before the uranium alloy is melted, and filling the chamber and the furnace with an inert gas until the chamber and the furnace reach designated pressures; 5 (c) sealing the furnace after the chamber and the furnace is completely filled with the inert gas, and additionally injecting inert gas into the chamber so that the chamber has a higher pressure than the furnace to generate a counterpressure in the furnace; LO (d) continuously heating the uranium alloy during the maintaining of the counterpressure so as to form completely molten uranium alloy with a designated temperature, and moving the furnace downward so that a slot approaches the outer circumference of a cooling roll rotated at a designated speed; L5 (e) injecting inert gas into the furnace so that the counterpressure in the furnace is broken after the slot approaches the cooling roll, and discharging the molten uranium alloy to the outer circumference of the cooling roll at a uniform pressure via the slot so as to cast the molten .0 uranium alloy into a foil via the slot; (f) rotating the cooling roll and the foil thereon so that the foil is rapidly cooled after one side of the foil formed from the molten uranium alloy discharged via the slot contacts the outer circumference of the cooling roll; and 25 (g) feeding the cooled and solidified foil into a 5 collection tray located close to the cooling roll. In accordance with another aspect of the present invention, there is provided an apparatus for producing a uranium foil, comprising: 5 a vacuum unit including: a hermetically sealed chamber; an exhaust pump installed at the outside of the chamber; and an exhaust pipe for connecting the chamber and the L0 exhaust pump, the vacuum unit serving to form a vacuum state in the chamber; a melting and discharging unit including: a furnace installed within the chamber; a nozzle integrally formed at a bottom of the .5 furnace; a slot formed at an end of the nozzle; and a high frequency induction coil wound around an outer surface of the furnace; a contact cooling unit including a cooling roll 0 positioned below the slot within the chamber and rotated at a designated speed so that one side of the foil formed from the molten uranium alloy discharged via the slot contacts the outer circumference of the cooling roll; a moving unit for moving the furnace upward and downward 5 so that the slot is close to the cooling roll; 6 a sealing unit located between the moving unit and the furnace for hermetically sealing and fixing the furnace; a counterpressure generating unit including: a gas feed pipe connected to the chamber and 5 provided with a gas supply valve; and a furnace flow pipe connected to the chamber and the furnace via the sealing unit and provided with a switching valve; and a jetting unit including a gas injection pipe branched LO from the furnace flow pipe and provided with a gas injection valve. BRIEF DESCRIPTION OF THE DRAWINGS LS The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a block diagram illustrating a method for .0 producing a uranium foil in accordance with an embodiment of the present invention; Fig. 2 is a schematic longitudinal-sectional view of an apparatus for producing a uranium foil in accordance with the first embodiment of the present invention; 5 Fig. 3 is a schematic side view of the apparatus of Fig. 7 2; Figs. 4a to 4f are partially broken-away longitudinal sectional views of the apparatus, illustrating its operation, in accordance with the first embodiment of the present 5 invention, and more specifically: Fig. 4a is an enlarged longitudinal-sectional view of the apparatus, illustrating the melting of uranium alloy under the vacuum condition; Fig. 4b is an enlarged longitudinal-sectional view LO of the apparatus, illustrating the filling of a chamber with inert gas; Fig. 4c is an enlarged longitudinal-sectional view of the apparatus, illustrating the forming of counterpressure; Fig. 4d is an enlarged longitudinal-sectional view L5 of the apparatus, illustrating the discharging of molten uranium alloy when a slot approaches a cooling roll; Fig. 4e is an enlarged view of a part "A" of Fig. 4d; and Fig. 4f is an enlarged longitudinal-sectional view 0 of the apparatus, illustrating the adjusting of the jetting angle of the molten uranium alloy; Fig. 5 is a photograph of a uranium foil produced by a first example of the method in accordance with the embodiment of the present invention, taken by a scanning electron 5 microscope; 8 Fig. 6 is a graph illustrating a pattern of the uranium foil produced by the first example of the method in accordance with the embodiment of the present invention, obtained by X ray diffraction; 5 Fig. 7 is a photograph of a uranium foil produced by a second example of the method in accordance with the embodiment of the present invention, taken by a scanning electron microscope; and Fig. 8 is a graph illustrating a pattern of the uranium LO foil produced by the second example of the method in accordance with the embodiment of the present invention, obtained by X-ray diffraction. DESCRIPTION OF THE PREFERRED EMBODIMENTS L5 Now, preferred embodiments of the present invention will be described in detail with reference to the annexed drawings. Fig. 1 is a block diagram illustrating a method for producing a uranium foil in accordance with an embodiment of .0 the present invention. With reference to Fig. 1, the method for producing the uranium is described, as follows. The above method for producing the uranium foil comprises, in sequence, accessible distance setting step (SO), vacuum heating step (S10), inert gas filling step (S20), .5 counterpressure generating step (S30), slot approaching step 9 (S40), molten uranium alloy-jetting and foil-forming step (S50), contact cooling step (S60), and foil collecting step (S70). The above method for producing the uranium foil may be 5 applied to uranium alloy as well as uranium. Particularly, the uranium alloy contains uranium and three elements (hereinafter, referred to as U-Q-X-Y). The Q, X, and Y elements are different ones selected from the group consisting of Al, Fe, Ni, Si, Cr, Zr, Mo, and Nb. The Q element is LO present in an amount of 0 to 10 wt.%, the X element is present in an amount of 0 to 1 wt.%, and the Y element is present in an amount of 0 to 1 wt.%. More specifically, at accessible distance setting step (SO), a furnace moves downward so that a slot of the furnace [5 contacts the outer circumference of a cooling roll. Such a position of the slot is designated as the zero point. Then, the furnace moves upward so that the slot of the furnace is located close to the outer circumference of the cooling roll. Such a position of the slot is designated as a proximal .0 position. The designated proximal position of the slot is precisely determined relative to the cooling roll. At vacuum heating step (S10), the furnace provided with a nozzle in its bottom is charged with uranium alloy, and a chamber for accommodating the furnace is hermetically sealed so 15 that a vacuum is formed in the chamber. When the chamber 10 reaches a proper degree of vacuum, the furnace is heated by a high frequency induction coil wound around the outer surface of the furnace. Here, the furnace is heated by a high frequency induction 5 coil wound so that the uranium alloy is degassed and melted under the vacuum condition. Preferably, at vacuum heating step (S10), the degree of vacuum within the chamber is in the range of 10~3 ~ 10~5 torr. In case that the degree of vacuum within the chamber is not .0 less than 10~3 torr, it is difficult to degas the uranium alloy. On the other hand, in case that the degree of vacuum within the chamber is not more than 10~5 torr, the excessive degree of vacuum is formed within the chamber and it is difficult to fill the chamber with an inert gas and to 5 generate a counterpressure in the chamber. At inert gas filling step (S20), before the uranium alloy is melted under the vacuum condition by heating the furnace at vacuum heating step (S10), the vacuum in the chamber is broken, and the chamber and the furnace are filled 0 with an inert gas until the chamber and the furnace reach designated pressures. Here, the vacuum in the chamber must be broken before the uranium alloy is melted, in order to generate the counterpressure before molten uranium alloy is discharged from 5 the furnace via the nozzle into the chamber. 11 At counterpressure generating step (S30), after the chamber and the furnace is completely filled with the inert gas at inert gas filling step (S20), the furnace is sealed. Then, the inert gas is further injected into the chamber so 5 that the chamber has a higher pressure than the furnace, thereby generating a counterpressure in the furnace. Here, counterpressure generating step (S30) serves to prevent the uranium alloy from being leaked via the nozzle in the bottom of the furnace during the melting by means of the .0 difference of pressure between the furnace and the chamber. Preferably, the difference of pressure between the furnace and the chamber is in the range of 30 torr to 300 torr. In case that the difference of pressure is not more than 30 torr, the molten uranium alloy is leaked via the 5 nozzle due to the weight of the alloy. 'In case that the difference of pressure is not less than 300 torr, the furnace is damaged or the molten uranium alloy overflows the furnace. At slot approaching step (S40), the uranium alloy is continuously heated during the maintaining of the 0 counterpressure at counterpressure generating step (S30) so as to form the molten uranium alloy with - a designated temperature. Then, the furnace moves downward so that the slot approaches the outer circumference of the cooling roll uniformly rotated at a high speed. 5 Here, preferably, the temperature of the molten uranium 12 alloy at slot approaching step (S40) is in the range of 1,150 to 1, 400'C. In case that the temperature of the molten uranium alloy is not more than 1,150'C, the uranium alloy cannot be completely melted. In case that the temperature of the molten 5 uranium alloy is not less than 1, 400"C, the molten uranium alloy is excessively overheated. Further, preferably, the distance between the slot and the cooling roll at slot approaching step (S40) is in the range of 0.3mm to 1.0mm. In case that the distance between .0 the slot and the cooling roll is not more than 0.3mm, the molten uranium alloy discharged from the furnace is solidified around the slot, thereby preventing the efficient production of the foil. On the other hand, in case that the distance between the slot and the cooling roll is not less than 1.0mm, 5 the molten uranium alloy is irregularly discharged from the furnace via the slot to the cooling roll, thereby causing the foil solidified on the outer circumference of the cooling roll to have irregularities to be not smooth. At molten uranium alloy-jetting and foil-forming step 0 (S50), after the slot approaches the cooling roll, the inert gas is further injected into the furnace, thereby breaking the counterpressure in the furnace. Then, the molten uranium alloy is discharged as a foil form to the outer circumference of the cooling roll at a uniform pressure via the slot. 5 Here, preferably, the width of the slot is in the range 13 of 0.3mm to 1.0mm. In case that the width of the slot is not more than 0.3mm, the foil is cut, and thus the foil cannot be produced continuously. On the other hand, in case that the width of the slot is not less than 1.0mm, the foil has 5 irregularities on its upper surface to be not smooth. Further, preferably, the blast pressure of the molten uranium alloy via the slot of the nozzle at molten uranium alloy-jetting and foil-forming step (S50) is in the range of 0.2kg/cd to 2.5kg/cd. In case that the blast pressure of the L0 molten uranium alloy is not more than 0.2kg/cd, it is difficult to properly discharge the molten uranium alloy via the slot. On the other hand, in case that the blast pressure of the molten uranium alloy is not less than 2.5kg/cd, since the molten uranium alloy is excessively discharged via the 5 slot, it is difficult to produce the foil with a uniform thickness. At contact cooling step (S60), after the foil formed from the molten uranium alloy discharged via the slot contacts the outer circumference of the cooling roll, the cooling roll 0 is rotated along with the foil thereon, thereby rapidly cooling the foil. Here, preferably, the rotational speed of the cooling roll is in the range of 200rpm to 1,200rpm. In case that the rotational speed of the cooling roll is not more than 200rpm, 5 since the foil-shaped molten uranium alloy is stacked on the 14 outer circumference of the cooling roll, the foil cannot have the uniform thickness. On the other hand, in case that the rotational speed of the cooling roll is not less than 1,200rpm, the foil cannot have the uniform thickness and be 5 continuously formed. At foil collecting step (S70), the cooled and solidified foil is contained and collected by a collection tray located close to the cooling roll. In accordance with the above-described method for LO producing the uranium foil, the uranium alloy is degassed and melted under the vacuum condition, completely melted under the condition that the leakage of the alloy is prevented by the counterpressure generated in the furnace and the chamber by means of the inert gas, formed into the foil by being [5 discharged via the slot, and contacting the cooling roll so as to be rapidly cooled when the slot approaches the cooling roll. Accordingly, it is possible to easily produce the uranium foil having fine crystalline granules. Fig. 2 is a schematic longitudinal-sectional view of an 0 apparatus for producing a uranium foil in accordance with the first embodiment of the present invention. With reference to Fig. 2, the apparatus for producing the uranium foil is described, as follows. The apparatus for producing the uranium foil comprises a 5 vacuum unit 10a, a melting and discharging unit 20a, a contact 15 cooling unit 30a, a moving unit 40a, a sealing unit 50a, a counterpressure generating unit 60a, a jetting unit 70a, a collecting unit 80a, and jetting angle control unit 90a. The vacuum unit 10a forms a vacuum in a chamber lla. The melting 5 and discharging unit 20a is located within the chamber lla, and serves to melt uranium or uranium alloy and cast the molten uranium or alloy into a foil. The contact cooling unit 30a contacts the foil cast by the melting and discharging unit 20a, thereby rapidly cooling the foil. The moving unit 40a L0 moves a furnace 21a downward so that a slot 23a of the furnace 21a closely approaches the outer circumferences of cooling roll 31a. The counterpressure generating unit 60a serves to generate a counterpressure in the chamber lla and the furnace 21a. The jetting unit 70a jets the molten uranium alloy from 5 the furnace 21a through the slot 23a. The collecting unit 80a serves to collect the produced foil. The jetting angle control unit 90a horizontally moves the furnace 21a, thereby controlling a jetting angle of the molten uranium alloy toward the cooling roll 31a. 0 More specifically, the vacuum unit 10a includes the hermetically sealed chamber lla, and an exhaust pump 12a located at the outside of the chamber lla and connected to the chamber lla via an exhaust pipe 13a. Air within the chamber lla is exhausted to the outside via the exhaust pipe 13a by 5 the operation of the exhaust pump 12a. Thus, the inside of 16 the chamber lla has a proper degree of vacuum. The melting and discharging unit 20a includes the furnace 21a made of transparent quartz, a nozzle 22a installed through the bottom of the furnace 21a and provided with a slot 5 23a, and a high frequency induction coil 24a wound around the outer circumference of the furnace 21a. The furnace 21a is charged with uranium or uranium alloy, and then heated by the high frequency induction coil 24a so that the uranium alloy is melted to form molten uranium alloy. The molten uranium alloy 10 is jetted via the slot 23a, thereby being cast into a foil. The contact cooling unit 30a includes a cooling roll 31a positioned below the slot 23a within the chamber lla and rotated at a designated speed. The foil discharged from the furnace 21a through the slot 23a contacts the cooling roll L5 31a, thereby being rapidly cooled. The moving unit 40a includes a sliding rod 41a connected to the top of the furnace 21a, a hydraulic cylinder 42a fixed to the top of the sliding rod 41a by a fixing plate 43a so that the sliding rod 41a is moved downward by the hydraulic 20 cylinder 42a, a spiral rotary shaft 44a rotatably connected to the fixing plate 43a, a worm gear 45a engaged with the spiral rotary shaft 44a, and a knob 46a for rotating the worm gear 45a. Here, The sliding rod 41a of the moving unit 40a is 25 moved downward by the operation of the hydraulic cylinder 42a 17 so that the slot 23a of the furnace 21a closely approaches the outer circumference of the cooling roll 31a. First, the sliding rod 41a is lowered by the operation of the worm gear 45a due to the turning of the knob 46a so 5 that the distance between the slot 23a and the cooling roll 31a can be predetermined by a user. Then, when the slot 23a becomes close to the outer circumference of the cooling roll 31a, the position of the slot 23a is adjusted by the operation of the hydraulic cylinder 42a so that the distance between the 0 slot 23a and the cooling roll 31a reaches the predetermined value. The sealing unit 50a is located at the top of the furnace 21a, and serves to hermetically seal and fix the furnace 21a. 5 The counterpressure generating unit 60a includes a gas feed pipe 61a provided with a gas supply valve 62a, and a furnace flow pipe 63a provided with a switching valve 64a for connecting the furnace 21a and the chamber lla. An inert gas is injected into the chamber 11a and the 0 furnace 21a via the gas feed pipe 61a so that the chamber 1la and the furnace 21a have the same pressure. Subsequently, the switching valve 64a of the furnace flow pipe 63a is locked, and the inert gas is further injected only into the chamber 11a via the gas feed pipe 61a so that there occurs the 5 difference of pressure between the chamber 11a and the furnace 18 21a. Thereby, the molten uranium alloy obtained by the heating of the furnace 21a by the high frequency induction coil 24a is not discharged from the furnace 21a to the chamber lla via the slot 23a. 5 The jetting unit 70a includes a gas injection pipe 71a branched from the furnace flow pipe 63a, and a gas injection valve 72a installed in the gas injection pipe 71a. When the molten uranium alloy is obtained within the furnace 21a, the gas injection valve 72a is unlocked so that the inert gas is .0 injected into the furnace 21a via the gas injection pipe 71a and the furnace flow pipe 63a. Thus, the molten uranium alloy is jetted from the furnace 21a into the chamber lla through the slot 23a. The collecting unit 80a includes a blade 81a positioned 5 to be in contact with the cooling roll 31a so as to remove the rapidly cooled foil from the outer circumference of the cooling roll 31a, a guide plate 82a for supporting the blade 81a and guiding the foil, and a collection tray 83a located close to the guide plate 82a for containing the collected 0 foil. Here, the blade 81a is made of Teflon, thus easily removing the cooled foil from the outer circumference of the cooling roll 31a without causing damage to the surface of the cooling roll 31a. 5 The jetting angle control unit 90a is located between 19 the sealing unit 50a and the sliding rod 41a. The jetting angle control unit 90a horizontally moves the furnace 21a, thereby adjusting the angle of jetting the molten uranium alloy from the furnace 21a toward the outer circumference of 5 the cooling roll 31a via the slot 23a. Preferably, the furnace flow pipe 63a connected to the furnace 21a is made of flexible material, thereby allowing the furnace 21a to be freely moved by the jetting angle control unit 90a. LO Hereinafter, with reference to Fig. 3, the apparatus for producing the uranium foil in accordance with the first embodiment of the present invention as shown in Fig. 2 is described in detail. As shown in Fig. 3, the sliding rod 41a being movable L5 upward and downward by the hydraulic cylinder 42a is inserted into the chamber 1la. The jetting angle control unit 90a is located below the sliding rod 41a. The sealing unit 50a is located below the jetting angle control unit 90a. The furnace 21a, which is opened at its top, is positioned under the 20 sealing unit 50a. The nozzle 22a and the slot 23a are installed in the bottom of the furnace 21a. The cooling roll 31a operated by a motor is located below the slot 23a. Windows 14a are formed through the front surface of the chamber 11a, and the exhaust pump 12a connected to the exhaust 25 pipe 13a is provided at the rear surface of the chamber 11a. 20 The jetting angle control unit 90a includes a guide rail 91a and a guide block 93a. The guide rail 91a provided with a feed screw 92a is positioned between the sealing unit 50a and the sliding rod 41a so as to horizontally move the sealing 5 unit 50a. The guide block 93a is located below the guide rail 91a and moved by the rotation of the feed screw 92a. When the user rotates the feed screw 92a, the guide block 93a moves back and forth along the guide rail 91a, thus allowing the slot 23a to horizontally move along the outer 0 circumference of the cooling roll 31a. Thereby, the molten uranium alloy is jetted from the furnace 21a via the slot 23a toward the cooling roll 31a at a proper angle. The furnace 21, the nozzle 22a, and the slot 23a are integrally formed, and made of transparent quartz so that the 5 user observes the melting of the uranium alloy in the furnace 21a through the windows 14a. Accordingly, just before the molten uranium alloy is discharged from the furnace 21a via the slot 23a, the counterpressure can be properly generated in the furnace 21a and the chamber 11a. o Figs. 4a to 4f are partially broken-away longitudinal sectional views of the apparatus, illustrating its operation, in accordance with the first embodiment of the present invention. More specifically, Fig. 4a is an enlarged longitudinal 5 sectional view of the apparatus, illustrating the melting of 21 the uranium alloy under the vacuum condition; Fig. 4b is an enlarged longitudinal-sectional view of the apparatus, illustrating the filling of the chamber with inert gas; 5 Fig. 4c is an enlarged longitudinal-sectional view of the apparatus, illustrating the forming of counterpressure; Fig. 4d is an enlarged longitudinal-sectional view of the apparatus, illustrating the discharging of the molten uranium alloy when the slot approaches the cooling roll; 10 Fig. 4e is an enlarged view of a part "A" of Fig. 4d; and Fig. 4f is an enlarged longitudinal-sectional view of the apparatus, illustrating the adjusting of the jetting angle of the molten uranium alloy. 15 With reference to Figs. 4a to 4f, the operation of the apparatus for producing the uranium foil is described, as follows. As shown in Fig. 4a, the furnace 21a located within the chamber 1la is charged with the uranium alloy, and the chamber 20 lla is hermetically sealed. Then, air within the chamber lla is discharged to the outside via the exhaust pipe 13a by the operation of the exhaust pump 12a so that a vacuum is formed in the chamber lla. The furnace 21a is heated by the high frequency induction coil 24a so that the uranium alloy within 25 the furnace 21a is melted to form molten uranium alloy. 22 Here, the switching valve 64a of the furnace flow pipe 63a connected to the sealing unit 50a for connecting the furnace 21a and the chamber 11a is unlocked so that the furnace 21a and the chamber 11a have a designated degree of 5 vacuum, thereby degassing the uranium alloy to be melted. As shown in Fig. 4b, before the furnace 21a is heated by the high frequency induction coil 24a so that the uranium alloy is completely melted, the exhaust pump 12a is stopped, thereby breaking the vacuum in the chamber 11a. Then, the gas LO supply valve 62a is unlocked so that the inert gas is introduced into the chamber 11a via the gas feed pipe 61a and simultaneously into the furnace 21a via the furnace flow pipe 63a. Thereby, the chamber 11a and the furnace 21a have the same pressure. L5 As shown in Fig. 4c, the switching valve 64a of the furnace flow pipe 63a is locked so that the chamber lla and the furnace 21a are sealed. Then, the inert gas is further introduced into the chamber 11a via the gas feed pipe 61a so that the chamber 11a has a higher pressure than the furnace ?0 21a, thereby generating a counterpressure in the furnace 21a due to the difference of pressure between the chamber 11a and the furnace 21a. Under the condition that the counterpressure generated in the furnace 21a is maintained, as shown in Fig. 4d, the ?5 furnace 21a is continuously heated by the high frequency 23 induction coil 24a so as to form the molten uranium alloy at a designated temperature. Then, the sliding rod 41a is moved downward so that the slot 23a of the furnace 21a closely approaches the outer circumference of the cooling roll 31a 5 uniformly rotated at a high speed. After the slot 23a closely approaches the outer circumference of the cooling roll 31a, the gas injection valve 72a is unlocked so that the inert gas is injected into the furnace 21a via the gas injection pipe 71a and the furnace LO flow pipe 63a. Thereby, the molten uranium alloy is jetted from the furnace 21a to the outer circumference of the cooling roll 31a at a uniform pressure. When the molten uranium alloy is jetted to the outer circumference of the cooling roll 31a from the furnace 21a L5 located close to the cooling roll 31a, the molten uranium alloy is jetted and simultaneously cast into a foil via the slot 23a. The foil is positioned on the outer circumference of the cooling roll 31a, and rotated along with the rotation of the cooling roll 31a, thereby being rapidly cooled to form 0 fine crystalline granules. The obtained uranium foil with fine crystalline granules is separated from the cooling roll 31a by the blade 81a, and guided and transferred along the guide block 82a. As shown in Fig. 4e, the molten uranium alloy, jetted ?5 and cast into the foil via the slot 23a of the nozzle 22a, and 24 then positioned on the outer circumference of the cooling roll 31a, is rotated by the rotation of the cooling roll 31a, thereby being rapidly cooled. Since the molten uranium alloy is jetted to the cooling 5 roll 31a via the slot 23a at the uniform pressure, the uranium foil with a uniform thickness is continuously produced. Further, since the foil contacts the cooling roll 31a and is rapidly cooled, the high-purity and high-quality uranium foil having fine crystalline granules, irregular crystal LO orientation, and excellent mechanical characteristics is produced. As shown in Fig. 4f, when a user rotates the feed screw 92a, the guide block 93a is transferred along the guide rail 91a, thereby horizontally moving the furnace 21a above the L5 cooling roll 23a. Thus, the angle of jetting the molten uranium alloy from the furnace 21a to the outer circumference of the cooling roll 31a via the slot 23a is properly adjusted. Hereinafter, two examples of the method for producing the uranium foil in accordance with the second embodiment of 20 the present invention are described in detail. <Example 1> Uranium 500g is introduced into the furnace with a diameter of 50mm, made of quartz, and a vacuum is formed within the chamber by the operation of the exhaust pump. 25 When the degree of vacuum in the chamber reaches 10-5 25 torr, the furnace is heated by the high frequency induction coil. Before the uranium is melted, the vacuum in the chamber is broken and the high-purity inert gas is injected into the chamber until the pressure of the chamber and the furnace 5 reaches 600 torr. Here, in order to prevent the molten uranium from being leaked via the slot with a length of 45mm and a width of 0.6mm, the furnace is sealed and the inert gas is further injected into the chamber so that the pressure of the chamber L0 reaches 650 torr. Thus, a counterpressure is generated in the furnace due to the difference of pressure between the furnace and the chamber, i.e., 50 torr. When the temperature of the molten uranium in the furnace, measured by a thermocouple, reaches 1,300'C, the .5 furnace is moved downward by the operation of the hydraulic cylinder located above the chamber so that the distance between the nozzle and the cooling roll is 0.5mm. Simultaneously, the molten uranium is discharged at a pressure of 0.5kg/cul from the furnace to the outer circumference of the 0 cooling roll rotated at a high speed of 800rpm, thereby being formed into a uniform and continuous uranium foil with a length of 45mm. The uranium foil formed by the jetting via the slot contacts the outer circumference of the cooling roll, thus 5 being rapidly cooled so that fine uranium crystalline granules 26 with irregular orientation are formed at the room temperature. Accordingly, the method of the present invention does not require a heat treatment process, in which uranium is maintained at a temperature of 800'C and then quenched so that 5 the crystalline granules of the uranium are fine, conventionally employed to produce a uranium foil by means of hot rolling. The above foil is collected by the collection tray located close to the chamber. The proper thickness of the LO produced foil is in the range of 100gm to 150gm. The recovery rate of the foil with the proper thickness is more than 99%. With reference to Figs. 5 and 6 respectively showing a photograph taken by a scanning electron microscope and a graph obtained by X-ray diffraction, the produced uranium foil is L5 described, as follows. As shown in Figs. 5 and 6, the produced uranium foil has an ot-U phase. The uranium foil has fine and uniform crystalline granules with a size of less than approximately 10gm, and its crystalline orientation is irregular. ?0 The produced uranium foil does not have impurities such as oxidized substance, or air voids at its surface. <Example 2> Hereinafter, the production of a foil made of uranium alloy containing U-Mo(7wt.%) is described. The uranium alloy ?5 lkg is introduced into the furnace with a diameter of 75mm, 27 made of quartz, and a vacuum is formed within the chamber by the operation of the exhaust pump. When the degree of vacuum in the chamber reaches 10-5 torr, the furnace is heated by the high frequency induction 5 coil. Before the uranium alloy is melted, the vacuum in the chamber is broken and the high-purity inert gas is injected into the chamber until the pressure of the chamber and the furnace reaches 600 torr. Here, in order to prevent the molten uranium alloy from 0 being leaked via the slot with a length of 70mm and a width of 0.3mm, the furnace is sealed and the inert gas is further injected into the chamber so that the pressure of the chamber reaches 700 torr. Thus, a counterpressure is generated in the furnace due to the difference of pressure between the furnace 5 and the chamber, i.e., 100 torr. When the temperature of the molten uranium alloy in the furnace, measured by the thermocouple, reaches 1,350'C, the furnace is moved downward by the operation of the hydraulic cylinder located above the chamber so that the distance 0 between the slot and the cooling roll is 0.8mm. Simultaneously, the inert gas is injected into the furnace so that the molten uranium alloy is discharged at a pressure of 1.Okg/cud from the furnace to the outer circumference of the cooling roll rotated at a high speed of 500rpm, thereby being 5 formed into a uniform and continuous uranium foil with a width 28 of 70mm. The uranium foil formed by the jetting via the slot contacts the outer circumference of the cooling roll, thus being rapidly cooled so that fine uranium crystalline granules 5 with an isotropic ' y-U phase are formed at the room temperature. Accordingly, the method of the present invention does not require a heat treatment process, in which uranium is maintained at a temperature of 800'C and then quenched, conventionally employed to produce a uranium foil by means of 10 hot rolling. The above foil is collected by the collection tray located close to the chamber. The proper thickness of the produced foil is in the range of 200pm to 300pm. The recovery rate of the foil with the proper thickness is more than 99%. 15 With reference to Figs. 7 and 8 respectively showing a photograph taken by a scanning electron microscope and a graph obtained by X-ray diffraction, the produced uranium alloy foil is described, as follows. As shown in Figs. 7 and 8, the produced uranium alloy 20 foil containing U-Mo(7wt.%) has the y-U phase. The uranium alloy foil has fine and uniform crystalline granules with a size of less than approximately lpm. The produced uranium alloy foil containing U-Mo(7wt.%) does not have impurities such as oxidized substance, or air 25 voids at its surface. 29 As apparent from the above description, the present invention provides a method and an apparatus for producing a uranium foil with fine particles, and a uranium foil produced thereby. 5 The method for producing the uranium foil of the present invention does not require a vacuum induced melting process for obtaining an ingot of metal including low or high-grade uranium, a hot rolling process repeated several time for obtaining a thin foil, a washing and drying step for removing LO impurities such as surface oxidized substances, a heat treatment process for obtaining fine and isotropic crystalline granules, thus being simplified compared to the conventional method for producing a foil. The foil of the present invention is produced by melting L5 uranium or uranium alloy and rapidly cooling the molten uranium or uranium alloy. Accordingly, it is possible to easily produce the foil from uranium, which is rarely rolled. Compared to the conventional hot rolling process requiring a long time for repeating the process several times 20 so as to adjust the produced uranium ingot, the method of the present invention produces a great quantity of the foil in several minutes by rapidly cooling the molten uranium or uranium alloy, thereby improving the productivity. The method of the present invention increases the 25 recovery rate of the uranium or uranium alloy to more than 99% 30 and produces several kg of the foil in several minutes, thereby maximizing the recovery rate of the uranium or uranium alloy and the economic efficiency. Compared to the foil produced by the conventional hot 5 rolling process, the foil of the present invention, produced only by cooling the molten uranium or uranium alloy, does not impart residual stress, thereby being protected from deformation and/or damage due to the thermal cycling during the production or irradiation process. .0 The foil of the present invention has fine and uniform crystalline granules with irregular orientation, thus generally having an isotropic structure and being less swollen during the irradiation process. The foil of the present invention has an isotropic y-U .5 phase being metastable at room temperature, thereby being used as a nuclear fuel for research reactors, which has fine air voids produced by nuclear fission, and stably moving in the reactors. Although the preferred embodiments of the present 0 invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 5 31

Claims

1. A method for producing a uranium foil, comprising the steps of: 5 (a) charging a furnace provided with a nozzle in its bottom with uranium alloy, and heating the furnace under the vacuum condition; (b) breaking the vacuum in a chamber before the uranium alloy is melted, and filling the chamber and the furnace with LO an inert gas until the chamber and the furnace reach designated pressures; (c) sealing the furnace after the chamber and the furnace is completely filled with the inert gas, and additionally injecting inert gas into the chamber so that the L5 chamber has a higher pressure than the furnace to generate a counterpressure in the furnace; (d) continuously heating the uranium alloy during the maintaining of the counterpressure so as to form completely molten uranium alloy up to a designated temperature, and ?0 moving the furnace downward so that a slot approaches the outer circumference of a cooling roll rotated at a designated speed; (e) injecting inert gas into the furnace so that the counterpressure in the furnace is broken after the slot ?5 approaches the cooling roll, and discharging the molten 32 uranium alloy to the outer circumference of the cooling roll at a uniform pressure via the slot so as to cast the molten uranium alloy into a foil via the slot; (f) rotating the cooling roll and the foil thereon so 5 that the foil is rapidly cooled after one side of the foil formed from the molten uranium alloy discharged via the slot contacts the outer circumference of the cooling roll; and (g) feeding the cooled and solidified foil into a collection tray located close to the cooling roll. LO

2. The method as set forth in claim 1, wherein the uranium alloy contains uranium and three elements [U-Q-X-Y], said Q, X, and Y elements being different ones selected from the group consisting of Al, Fe, Ni, Si, Cr, L5 Zr, Mo, and Nb, wherein the Q element is present in an amount of 0 to 10 wt.%, the X element is present in an amount of 0 to 1 wt.%, and the Y element is present in an amount of 0 to 1 wt.%. 20

3. The method as set forth in claim 1, wherein a degree of vacuum in the chamber at the step (a) is in the range of 10~3 ~ 10-5 torr, a pressure in the chamber at the step (b) is 600 torr, and a pressure in the chamber at the step of (c) is 700 torr, and 25 wherein at the steps (d) and (e), a temperature of the 33 molten uranium alloy is in the range of 1, 150 to 1, 400*C, a width of the nozzle is in the range of 0.3 to 1.0mm, a blast pressure of the molten uranium alloy via the slot of the nozzle is in the range of 0.2 to 2.5kg/ci, a distance between 5 the nozzle and the cooling roll is in the range of 0.4 to 1.0mm, and a rotational speed of the cooling roll is in the range of 200 to 1,200rpm.

4. The method as set forth in claim 1, .0 wherein a degree of vacuum in the chamber at the step (a) is in the range of 10-3 ~ 10-5 torr, a pressure in the chamber at the step (b) is in the range of 400 to 730 torr, and a pressure in the chamber at the step of (c) is 430 to 760 torr, and .5 wherein at the steps (d) and (e), a temperature of the molten uranium alloy is in the range of 1,150 to 1,400*C, a width of the nozzle is in the range of 0.3 to 1.0mm, a blast pressure of the molten uranium alloy via the slot of the nozzle is in the range of 0.2 to 2.5kg/cd, a distance between .0 the nozzle and the cooling roll is in the range of 0.4 to 1.0mm, and a rotational speed of the cooling roll is in the range of 200 to 1,200rpm.

5. The method as set forth in claim 1, .5 prior to the step (a), further comprising the step of 34 (a') moving the furnace downward so that the slot contacts the outer circumference of the cooling roll, said position of the slot being designated as the zero point, and moving the furnace upward from the zero point so that the slot is located 5 close to the cooling roll, said position of the slot being used as a predetermined proximal position.

6. The method as set forth in claim 1, wherein a difference of pressure between the furnace and .0 the chamber at the step (c) is in the range of 30 to 300 torr.

7. The method as set forth in claim 1, wherein a degree of vacuum in the chamber at the step (a) is in the range of 10- to 10~5 torr. 5

8. The method as set forth in claim 1, wherein a temperature of the molten uranium alloy is in the range of 1,150 to 1,400'C. 0

9. The method as set forth in claim 1, wherein a width of the slot is in the range of 0.3 to 1.0mm.

10. The method as set forth in claim 1, 5 wherein a blast pressure of the molten uranium alloy via 35 the slot is in the range of 0.2 to 2.5kg/cduf.

11. The method as set forth in claim 1, wherein a distance between the slot and the cooling roll 5 is in the range of 0.3 to 1.0mm.

12. The method as set forth in claim 1, wherein a rotational speed of the cooling roll is in the range of 200 to 1,200rpm. .0

13. A uranium foil produced by the method as set forth in claim 1, wherein the foil has fine crystalline granules with a size of less than 10pm, and has irregular crystalline .5 orientation.

14. An apparatus for producing a uranium foil, comprising: a vacuum unit including: .0 a hermetically sealed chamber; an exhaust pump installed at the outside of the chamber; and an exhaust pipe for connecting the chamber and the exhaust pump, said vacuum unit serving to form a vacuum state ?5 in the chamber; 36 a melting and discharging unit including: a furnace installed within the chamber; a nozzle integrally formed at a bottom of the furnace; 5 a slot formed at an end of the nozzle; and a high frequency induction coil wound around an outer surface of the furnace; a contact cooling unit including a cooling roll positioned below the slot within the chamber and rotated at a o designated speed so that one side of the foil formed from the molten uranium alloy discharged via the slot contacts the outer circumference of the cooling roll; a moving unit for moving the furnace upward and downward so that the slot is close to the cooling roll; 5 a sealing unit located between the moving unit and the furnace for hermetically sealing and fixing the furnace; a counterpressure generating unit including: a gas feed pipe connected to the chamber and provided with a gas supply valve; and ?0 a furnace flow pipe connected to the chamber and the furnace via the sealing unit and provided with a switching valve; and a jetting unit including a gas injection pipe branched from the furnace flow pipe and provided with a gas injection 25 valve. 37

15. The apparatus as set forth in claim 14, wherein the moving unit includes: a sliding rod connected to the sealing unit and 5 vertically inserted into the chamber; a hydraulic cylinder fixed to an end of the sliding rod; and a fixing plate installed at the outside of the chamber so as to fix the hydraulic cylinder. [0

16. The apparatus as set forth in claim 14, wherein the furnace and the nozzle are made of transparent quartz, and a window is formed through the surface of the chamber so as to correspond to the furnace. L5

17. The apparatus as set forth in claim 14, further comprising a collecting unit including: a blade made of Teflon contacting the outer circumference of the cooling roll; ?0 a guide plate for supporting the blade; and a collection tray located close to the guide plate so as to be connected to the chamber and sealed.

18. The apparatus as set forth in claim 14, 25 further comprising a jetting angle control unit 38 including: a guide rail positioned between the sealing unit and the moving unit so as to horizontally move the sealing unit, and provided with a feed screw; and a guide block located below the guide rail and moved by the rotation of the 5 feed screw.

19. The apparatus as set forth in claim 15, wherein the moving unit further includes: a spiral rotary shaft rotatably connected to the fixing plate so that the 10 sliding rod accurately moves;. a worm gear engaged with the spiral rotary shaft; and a knob installed at one side of the worm gear for rotating the worm gear. 15

20. A method for producing a uranium foil substantially as hereinbefore described with reference to the drawings.

21. An apparatus for producing a uranium foil substantially as hereinbefore described with reference to the drawings. 20 KOREA ATOMIC ENERGY RESEARCH INSTITUTE and KOREA HYDRO & NUCLEAR POWER CO., LTD. By their patent attorneys PIPERS 25 30 October 2003 39