U.S. patent application number 09/836478 was filed with the patent office on 2002-05-02 for fabrication process of uranium foil having fine grains solidified rapidly from melt using cooling roll, and the fabrication apparatus.
This patent application is currently assigned to KOREA ATOMIC ENERGY RESEARCH. Invention is credited to Jang, Se-Jung, Kim, Chang-Kyu, Kim, Eung-Soo, Kim, Ki-Hwan, Oh, Seok-Jin.
Application Number | 20020050335 09/836478 |
Document ID | / |
Family ID | 19696341 |
Filed Date | 2002-05-02 |
United States Patent
Application |
20020050335 |
Kind Code |
A1 |
Kim, Chang-Kyu ; et
al. |
May 2, 2002 |
Fabrication process of uranium foil having fine grains solidified
rapidly from melt using cooling roll, and the fabrication
apparatus
Abstract
The present invention is concerned with the fabrication process
of low or high enrichment uranium and uranium alloy foil, and the
fabrication apparatus therefor. Uranium (U) and uranium alloy
[U--(A)Q--(B)X--(C)Y (Q: Al, Fe, Ni, Si, Cr, Zr element, X: Al, Fe,
Ni, Si, Cr, Zr element, Y: Al, Fe, Ni, Si, Cr, Zr element,
Q.noteq.X.noteq.Y, (A).ltoreq.1 wt %, (B).ltoreq.1 wt %,
(C).ltoreq.1 wt %)] foil are directly obtained from a melt, not
through a vacuum induction melting & casting, ingot cutting,
hot-rolling and heat-treatment process, but through melt spinning
or a twin-roll casting process. Major advantages have been obtained
as follows: 1) a simplified process without the hot-rolling process
and heat-treatment process, 2) an improvement in productivity and
process economics in foil fabrication, and 3) a high purity and a
high quality of the foil.
Inventors: |
Kim, Chang-Kyu; (Yoosung-Ku,
KR) ; Kim, Ki-Hwan; (Yoosung-Ku, KR) ; Oh,
Seok-Jin; (Seo-Ku, KR) ; Jang, Se-Jung;
(Yoosung-Ku, KR) ; Kim, Eung-Soo; (Yoosung-Ku,
KR) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN, PLLC
Suite 600
1050 Connecticut Avenue, N.W.
Washington
DC
20036-5339
US
|
Assignee: |
KOREA ATOMIC ENERGY
RESEARCH
|
Family ID: |
19696341 |
Appl. No.: |
09/836478 |
Filed: |
April 18, 2001 |
Current U.S.
Class: |
164/463 ;
164/480 |
Current CPC
Class: |
B22D 11/0622 20130101;
C22C 43/00 20130101; B22D 11/0697 20130101 |
Class at
Publication: |
164/463 ;
164/480 |
International
Class: |
B22D 011/06 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2000 |
KR |
00-64237 |
Claims
What is claimed is:
1. A method for fabricating a uranium foil having fine randomly
oriented grains by rapidly solidifying a melt of uranium or uranium
alloy directly using a cooling roller, wherein the uranium alloy is
U--(A)Q--(B) X--(C)Y, in which Q is selected from the group
consisting of Al, Fe, Ni, Si, Cr, and Zr elements, X is selected
from the group consisting of Al, Fe, Ni, Si, Cr, and Zr elements,
and Y is selected from the group consisting of Al, Fe, Ni, Si, Cr,
and Zr elements, and Q.noteq.X.noteq.Y, (A).ltoreq.1 wt %,
(B).ltoreq.1wt %, (C).ltoreq.1 wt %.
2. An apparatus for fabricating a uranium foil having fine randomly
oriented grains by solidifying rapidly a melt of uranium or uranium
alloy directly using a cooling roller, comprising a heat-resistant
crucible (2) equipped with a tundish having a slot (1), an
induction coil (3) connected to a high frequency generating
apparatus (not shown) to heat the crucible (2), a vacuum pump
system (5) for obtaining an appropriate vacuum within the chamber
(4), a roller (6) and side dams (not shown) installed in the
chamber (4), a gas-feeding valve (7) for feeding gas into the
chamber (4) and a recovery container (8) for collecting the
fabricated foil.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to a fabrication
process for uranium foil having fine crystalline grains solidified
rapidly from a melt using cooling rolls, and foil fabrication
apparatus. In particular, the present invention relates to low or
high enrichment uranium and uranium alloy foil, the fabrication
apparatus, and the fabrication process therefore wherein uranium
(U) and uranium alloy [U--(A)Q--(B)X--(C)Y (Q: Al, Fe, Ni, Si, Cr,
Zr element, X: Al, Fe, Ni, Si, Cr, Zr element, Y: Al, Fe, Ni, Si,
Cr, Zr element, Q.noteq.X.noteq.Y, (A).ltoreq.1 wt %, (B).ltoreq.1
wt %, (C).ltoreq.1 wt %)] foils are directly cast from a melt, not
through a vacuum induction melting & casting, ingot-cutting,
hot-rolling and heat-treatment process, but through a
twin-roll-casting process.
[0003] 2. Description of the Prior Art
[0004] Generally, the conventional fabrication method for uranium
foil has the disadvantages of complicated processes as follows:
casting the uranium or the uranium alloy after holding at about
1300.degree. C. in a vacuum induction furnace; cutting the
resulting rod-type ingot to suitable size for hot rolling at
600.degree. C. or higher; rolling through many passes a thick piece
of the ingot to gradually thin it to fabricate a uranium foil of
100-200 .mu.m thickness; and finally heat-treatment at 800.degree.
C. and quenching the fabricated uranium foil to produce the
required gain size and orientation.
[0005] In the conventional method, the uranium must be heated and
rolled under vacuum or in an inert atmosphere because it is a
reactive material. The hot rolling is repeated several times to
obtain a suitable thickness of the uranium foil. As the hot-rolling
process takes long time, productivity is relatively low. A
washing/drying process must be done to remove surface impurities
after hot rolling. In order to obtain the fine grain structure
which has a more stable behavior during irradiation, heat-treatment
and quenching must be performed. The high hardness and low
ductility of uranium or uranium alloy make it difficult to roll the
foil. The foil is liable to crack owing to residual stress during
the process, resulting in a low yield. The present invention is
expected to improve the economy of producing uranium foil, due to a
higher productivity and yield than the conventional method.
[0006] Meanwhile, a uranium foil having excessive residual stress
from hot rolling may be deformed or damaged during thermal cycling
during irradiation. Furthermore, deformed areas or cracks generated
during thermal cycling may act as penetration paths through which
there can be an interdiffusion reaction of the uranium with a
coating layer, such as Al or Ni, which serves as a protector
against the reaction of the uranium with a fixed tube in an
irradiation target.
SUMMARY OF THE INVENTION
[0007] The present invention aims to alleviate the problems as
described above. Low or high enrichment uranium and uranium alloy
foil are fabricated through twin-roll casting of a uranium melt
without a hot-rolling process and heat-treatment process. An
improvement in productivity and process economics due to process
simplification and better quality from the absence of any residual
stress on the foil are expected.
[0008] Accordingly, the said objects of the present invention can
be achieved by providing a uranium foil solidified rapidly by
twin-roll casting, and an apparatus and a method for fabricating
the same.
[0009] More specifically, the present invention is achieved by
providing an apparatus and a method for fabricating the uranium
foil wherein low or high enrichment uranium and alloy element
material are weighed and then charged into a heat-resistant
crucible equipped with a tundish having a slot. The crucible is
mounted at the inner part of a vacuum chamber in which a vacuum of
10.sup.-3 torr or higher can be maintained by a vacuum pump system.
Then, the uranium and the alloying elements are melted by high
frequency electric power. The alloy melt is fed through the slot to
the space between side dams and two rotating rolls driven by an
electric motor, and thin foil is formed by pressing the partly
solidified melt with the cold rolls. The foil produced is further
cooled by supplying inert cooling gas.
BRIEF DESCRIPTION OF THE DRAWING
[0010] The above objects, features and advantages of the present
invention will be more clearly understood from the following
detailed description taken in conjunction with the accompanying
drawing, in which:
[0011] FIG. 1 shows a schematic view of a configuration of an
apparatus for fabricating the uranium foil according to the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0012] With reference to FIG. 1, there is an apparatus for
fabricating the uranium foil by twin rolls according to the present
invention.
[0013] The apparatus of the present invention comprises: a
heat-resistant crucible (2), a tundish having a slot (1), an
induction coil (3) connected to a high-frequency generation
apparatus (not shown) to increase the temperature of the crucible
(2), a vacuum pump system (5) for evacuating the chamber (4) to an
appropriate degree of vacuum, a roller (6) installed in the chamber
(4), side dams with a resistance heater (not shown) for preventing
a rapid decrease of the uranium melt temperature after pouring from
the crucible and for guiding the uranium melt into the roller (6),
a gas-feeding valve (7) for supplying a cooling gas into the
chamber (4), and a recovery container (8) for collecting the
fabricated foil.
[0014] Uranium and alloy elements are charged at the lower part of
the heat-resistant crucible (2) mounted at the upper part of the
chamber (4). Also a stopper (9) is installed in the crucible. The
induction coil (3) mounted around the heat-resistant crucible (2)
superheats the charged material to about 200.degree. C. higher than
the melting temperature by the high frequency generation
apparatus.
[0015] The vacuum pump system (5) allows an inner part of the
chamber (4) to be evacuated to a suitable vacuum of 10.sup.-3 torr
or higher and is connected to one side of the chamber (4).
[0016] The roller (6) is positioned in the same central plane as
the slot (1) in the chamber (4). Also, the roller is operated by an
electric motor (not shown) to manufacture the uranium foil from an
alloy melt poured through the slot (1). The preheated side dams
(not shown) prevent the rapid decrease of the uranium melt
temperature after pouring from the crucible and guide the uranium
melt into the roller (6).
[0017] The alloy melt fed through the slot (1) is fabricated into
uranium foil by the rotating rolls driven by the electric motor,
and the resulting foil is rapidly cooled under argon or helium
cooling gas.
[0018] The gas-feeding valve (7), connected to the chamber (4),
feeds inert argon or helium cooling gas into the chamber (4) to
rapidly cool the uranium foil fabricated by the cooling roller
(6).
[0019] The inert argon or helium cooling gas, flowing into the
chamber (4) through the gas-feeding valve (7), is injected into the
chamber (4) through gas nozzles mounted at the upper part of the
chamber (4).
[0020] The recovery container (8) at the bottom part of the chamber
(4) collects the thin foil (10) manufactured in the chamber
(4).
[0021] A better understanding of the present invention may be
obtained in light of the following examples which are set forth to
illustrate, but are not to be construed to limit, the present
invention.
EXAMPLE 1
[0022] To fabricate low or high enrichment uranium foil, uranium
material is charged into a heat-resistant crucible (2) having a
slot (1). The crucible (2) and an insulation material (not shown)
are assembled in proper order in a fabrication apparatus.
[0023] Then, the steel chamber in the apparatus equipped with the
crucible (2) is evacuated to a vacuum of 10.sup.-3 torr or higher
by a vacuum pump system (5).
[0024] A high frequency generator (3) is operated to superheat the
charge material of the crucible to a temperature of about
200.degree. C. higher than the melting temperature of the
uranium.
[0025] When the rotation speed of the roller (6) driven by the
electric motor is stabilized at about 300 rpm, a stopper (9) placed
in the crucible (2) is lifted upward to discharge an alloy
melt.
[0026] The poured alloy melt passes through the slot (1) of 1-mm
width and then is fed to the space between the preheated side dams
(not shown) and the roller (6) rotating at about 300 rpm to form
the thin foil (10).
[0027] Then, a gas-feeding valve (7) is operated to supply the
chamber (4) with the inert cooling gas, whereby the foil (10)
fabricated by the roller (6) is rapidly solidified (at a rate
greater than 10.sup.3.degree. C./sec).
[0028] Because a uranium foil having fine and randomly orientated
grains is directly obtained by such a rapid solidification effect,
it is not necessary to heat-treat the foil and quench from about
800.degree. C. to form fine grains. The uranium foil is collected
within a recovery container (8) installed at the bottom of the
chamber (4).
[0029] The foil in the recovery container (8) is about 125 .mu.m
thick and the foil with an acceptable thickness is recovered at
about 90% yield.
[0030] A piece of uranium foil prepared as previously described is
assembled with other components to fabricate an irradiation target,
in order to charge into a reactor for producing fission isotope
.sup.99Mo, the only parent nuclide of .sup.99mTc, which is an
extremely useful tool for medical diagnosis.
EXAMPLE 2
[0031] This invention is applied to a uranium alloy of low or high
enrichment uranium [U--(A)Q--(B)X--(C)Y (Q: Al, Fe, Ni, Si, Cr, Zr
elements, X: Al, Fe, Ni, Si, Cr, Zr elements, Y: Al, Fe, Ni, Si,
Cr, Zr elements, Q.noteq.X.noteq.Y, (A).ltoreq.1 wt %, (B).ltoreq.1
wt %, (C).ltoreq.1 wt %)] foil for the irradiation target.
[0032] For the fabrication of U-500 ppm Fe-1200 ppm Al-500 ppm Ni
alloy foil, uranium and alloy elements including Fe, Al and Ni are
appropriately weighed according to the desired alloy composition
and charged to the crucible. The steel chamber (4) is evacuated to
10.sup.-3 torr or higher using the vacuum pump system (5) as
described in a fabrication procedure for uranium foil.
[0033] As such, when the crucible (2) and the insulation material
(not shown) are assembled in the proper order in the apparatus, the
high frequency generator (3) is operated to superheat the charge
material of the crucible to a temperature about 200.degree. C.
higher than the melting temperature of the uranium alloy.
[0034] When the rotation speed of the roller (6) operated by the
electric motor is stabilized at about 300 rpm, the stopper (9)
placed in the crucible (2) is lifted upward to feed the alloy
melt.
[0035] The discharged alloy melt passes through the slot (1) of 1.2
mm width and then is fed to the space between the preheated side
dams (not shown) and the roller (6) rotating at the high speed of
300 rpm to form the thin foil (10).
[0036] Then, the gas-feeding valve (7) is operated to inject the
inert cooling gas into the chamber (4), whereby the foil (10)
fabricated by the roller (6) is quickly solidified
(10.sup.3.degree. C./sec or faster).
[0037] Because the uranium alloy foil having fine and randomly
orientated grains is directly obtained by such a rapid
solidification effect, it is not necessary to heat-treat the hot
rolled foil and quench from about 800.degree. C. to form fine
grains. The uranium alloy foil is collected within a container (8)
installed at the bottom of the chamber (4).
[0038] The foil in the recovery container (8) is about 150 .mu.m
thick, and foil with a suitable thickness is recovered at a 90% or
higher yield.
[0039] A piece of uranium foil prepared as previously described is
assembled with other components to fabricate an irradiation target,
in order to charge into a reactor for producing fission isotope
.sup.99Mo, the only parent nuclide of .sup.99mTc, which is an
extremely useful tool for medical diagnosis.
[0040] The fabrication process of uranium alloy foil by the present
invention is greatly simplified compared to the conventional
fabrication method, which includes a vacuum induction melting
process, a repetitive hot-rolling process, a washing/drying process
for removing impurities, such as surface oxides, and a
heat-treatment process for obtaining fine isotropic grains.
[0041] Since the melt of uranium or uranium alloy is rapidly cooled
to directly fabricate the uranium foil, the uranium or uranium
foil, being difficult to roll due to its high toughness, can be
easily fabricated.
[0042] A long time period is required to conduct the repetitive
troublesome conventional hot-rolling process to adjust the
thickness of a uranium ingot. In contrast, the alloy melt may be
cast at once to fabricate large amounts of the foil in a few
minutes by the present invention, thereby having a high
productivity.
[0043] In addition, because the uranium is lacking in ductility,
the uranium foil may be damaged and cracked owing to an induced
stress during the hot-rolling process, which leads to a low yield
and a reduced economic efficiency.
[0044] However, the foil fabrication process by rapid
solidification of the present invention has a 90% or higher yield
through which several kilograms of the foil can be directly
fabricated in a few minutes. The foil fabrication process, using
preheated side dams and a cooling roller, facilitates control of
the width of the foil. Accordingly, the yield of uranium is very
high and the economics are highly favorable because enriched
uranium is very expensive.
[0045] Furthermore, foil fabricated by twin rolling has smaller
stress than foil obtained through repetitive hot rolling of a
uranium plate. Accordingly, deformation or cracking of the foil
generated by thermal cycling during the irradiation process can be
prevented. Defects in deformation areas or cracks can act as
penetration paths for elements in the coating layer of the target.
The interaction between coating layer and target will be enhanced
by the defects or cracks. However, the foil fabricated by the
present invention does not have such paths.
[0046] Commonly, uranium foil undergoes large anisotropic growth
during irradiation in a reactor. However, the uranium foil of the
present invention has homogeneous and fine grains with random
orientation so as to prevent the uranium foil from excessively
growing during irradiation.
[0047] The present invention has been described in an illustrative
matter, and it is to be understood that the terminology used is
intended to be of the nature of description rather than of
limitation. Many modifications and variations of the present
invention are possible in light of the above teachings. Therefore,
it is to be understood that, within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described.
* * * * *