Metal founding – Means providing inert or reducing atmosphere – In continuous casting apparatus
Reexamination Certificate
2002-11-18
2004-09-21
Lin, Kuang Y. (Department: 1725)
Metal founding
Means providing inert or reducing atmosphere
In continuous casting apparatus
C164S256000, C164S263000, C164S474000
Reexamination Certificate
active
06793005
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for continuously casting a uranium rod by melting a metallic substance reduced from nuclear spent fuels, and more particularly to a method and an apparatus for continuously casting a uranium rod so that impurities generated in melting the metallic substance reduced from nuclear spent fuels are easily removed, the molten metal is easily degassed, the oxidation of uranium is prevented, and residue of the molten metal does not remain in a crucible.
2. Description of the Related Art
Generally, nuclear spent fuels generated during nuclear power generation still comprise a great quantity of uranium. In order to effectively store and manage the nuclear spent fuels, the nuclear spent fuels are reduced to a metallic substance without any separation and purification, and then cast into a uranium rod for storage.
By casting the metallic substance reduced from nuclear spent fuel into a uranium rod, the nuclear spent fuel can be easily stored and treated, and recycled as a nuclear fuel, thereby creating an economic benefit.
In order to achieve such economic benefit, a method for continuously casting the metallic substance reduced from nuclear spent fuels into the uranium rods is used. For conventional continuous casting, a method and an apparatus for melting a uranium ingot and degassing the molten uranium in an air-sealed chamber with a designated degree of vacuum and then extracting a uranium rod from the air-sealed chamber by a start rod and a driving roller are proposed.
However, in the conventional continuous casting method and apparatus, since the cast uranium rod is pulled down from the bottom of the air-sealed chamber, it is very difficult to maintain the designated degree of vacuum of the air-sealed chamber. As a result, the uranium rod around the bottom surface of the air-sealed chamber, in which the vacuum is reversed, is easily oxidized.
In order to solve the aforementioned problem, another continuous casting method and its apparatus are proposed. Herein, the air-sealed chamber is filled with an inert gas, and then the continuous casting of a uranium rod is carried out.
In the inert gas atmosphere, the molten metal cannot be sufficiently degassed, thereby manufacturing a poor quality uranium rod.
Further, in order to prevent the oxidation of uranium, a great quantity of inert gas must be continuously supplied to the air-sealed chamber, thereby wasting the inert gas.
In order to solve the aforementioned problems according to the use of the inert gas, another continuous casting method and its apparatus are proposed. Herein, the nuclear spent fuel is melted in the air-sealed chamber under the vacuum condition, and the uranium rod is pushed out from the top of the air-sealed chamber by the high-pressure inert gas.
In this continuously casting method and apparatus, since the uranium rod is pushed upward by the high pressure, the degassing and the prevention of oxidation are possible. However, the molten metal is not completely exhausted. That is, the residue of the molten metal remains in the air-sealed chamber.
The residue of the molten metal in the air-sealed chamber is easily hardened. As a result, in order to reuse the air-sealed chamber, a step for removing the hardened residue of the molten metal is necessary. Further, since workers cannot be easily close to the air-sealed chamber containing the radioactive residue of the molten metal, in order to reuse the continuous casting apparatus, additional steps and much time are required, thereby drastically shorting a recycle rate of the continuous casting apparatus.
Moreover, the workers removing the radioactive substance, i.e., the residue of the molten metal, are exposed to the environmental contaminants such as the radioactivity, thereby being unsafe to perform.
This continuous casting apparatus does not comprise a shielding chamber. Therefore, when the cast uranium rod is pushed out from the top surface of the air-sealed chamber, noxious gas exhausted along with the uranium rod cannot be properly sucked and the radioactivity cannot be shielded.
Further, the above-described continuous casting apparatus comprises a mold serving as a straw for sucking the molten metal within the crucible. The mold in the crucible must have a sufficient length. The outer surface of the uranium rod molded via the long mold is easily damaged, thereby increasing a defective ratio of uranium rods.
In order to suck and pull up the uranium rod from the molten metal within the crucible, the lower part of the mold must be put into the molten metal. Therefore, the repeated insertion of the mold into the molten metal accumulates the damage of the mold, and the mold is contaminated with radioactivity.
In order to minimize the residue of the molten metal in the crucible, the crucible must be moved upward within the air-sealed chamber under high temperature and high pressure conditions, thereby causing breakdowns or failures of the apparatus and break-out of the cast uranium rod due to the non-uniform suction.
SUMMARY OF THE INVENTION
Therefore, the present invention provides a method for continuously casting a uranium rod, in which the impurities generated in melting a metallic substance reduced from a nuclear spent fuel (that is a highly radioactive substance) is easily removed, the molten metal is easily degassed, the oxidation of uranium is prevented, and residue of the molten metal does not remain in the crucible.
The present invention provides a method for continuously casting a uranium rod, in which the inert gas filled in the air-sealed chamber has a constant pressure similar to atmospheric pressure.
The present invention provides a method for continuously casting a uranium rod, in which the cast uranium rod is continuously pulled down without being breakout.
The present invention provides a method for continuously casting a uranium rod, in which the cast uranium rod molded via a mold is cooled at a constant temperature.
The present invention provides a method for continuously casting a uranium rod, in which the first cooled uranium rod is secondarily and completely cooled by the inert gas prior to being exhausted into the shielding chamber.
The present invention provides a method for continuously casting a uranium rod, in which a noxious gas exhausted along with the uranium rod is completely sucked.
The present invention provides a method for continuously casting a uranium rod, in which the exhausted uranium rod is cut without interfering with the continuous casting process.
The present invention provides a method for continuously casting a uranium rod, in which the cut uranium rod is transferred and stored.
The present invention provides an apparatus for continuously casting a uranium rod, in which the impurities generated in melting a metallic substance reduced from a nuclear spent fuel (that is a highly radioactive substance) are easily removed, the molten metal is easily degassed, the oxidation of uranium is prevented, and residue of the molten metal does not remain in the crucible.
The present invention provides an apparatus for continuously casting a uranium rod, in which a region including a driving roller under the air-sealed chamber is shielded from the radioactivity generated from the cast uranium rod.
The present invention provides an apparatus for continuously casting a uranium rod, in which the uranium rod within the mold is not breakout due to the sudden temperature difference but is continuously pulled down.
The present invention provides an apparatus for continuously casting a uranium rod, in which the thermal losses in the crucible and the mold are prevented by an adiabatic material.
The present invention provides an apparatus for continuously casting a uranium rod, in which the uranium rod, molded via the mold and pulled down from the mold, is firstly cooled.
The present invention provides an apparatus for continuously casting a uranium rod, in which a start rod inserted into the crucible is stably supported and fixed.
The
Jang Se-Jung
Kim Chang-Kyu
Kim Ki-Hwan
Lee Yoon-Sang
Park Seong-Won
Cantor & Colburn LLP
Korea Atomic Energy Research Institute
Lin Kuang Y.
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