Induced nuclear reactions: processes – systems – and elements – Fission reactor material treatment – Impurity removal
Reexamination Certificate
2000-07-21
2002-10-29
Carone, Michael J. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Fission reactor material treatment
Impurity removal
C376S353000, C015S001700, C015S104050
Reexamination Certificate
active
06473481
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for cleaning the inside of control rod guide tubes guiding control rods of a nuclear reactor.
Guide tubes each guiding a control rod of a nuclear reactor in a vertical direction are installed on the bottom of a nuclear reactor pressure vessel. Dust in the pressure container of a nuclear reactor penetrate into the control guide tubes, deposit on the bottom of the control rod guide tubes and are piled up.
As a cleaning operation of removing the dust that has accumulated on the bottom of the control rod guide tubes, there is a known cleaning method of penetrating a cleaning apparatus into the each of the control rod guide tubes from the upper portion of the pressure container of nuclear reactor and cleaning the bottom portions thereof inside the control rod guide tubes.
The cleaning method is disclosed in U.S. Pat. No. 5,030,410. In this method, an operation of opening a lid on an upper portion of the pressure container of nuclear reactor and an operation of taking out various apparatus and control rods inside the control rod guide tubes from the nuclear reactor pressure container are described. It is a matter of course that after the inside of the control rod guide tubes are cleaned, the prior condition of the nuclear reactor pressure container must be restored, so that reverse operations to the above operations become necessary.
Those operations are not simple or economical. Additionally, upon operation of cleaning the insides of control rod guide tubes, a sucking operation of sucking up dust in the control rod guide tubes upward against their weight is performed. The height from the upper portion of the nuclear reactor pressure container to the bottom of each of the control rod guide tubes is great, so that facilities provided for the sucking operation are large in scale and not economical.
An operation method of cleaning the insides of control rod guide tubes without each of the above-mentioned operations is disclosed in U.S. Pat. No. 4,534,932 and the corresponding JP A 59-224599 and explained as follows.
That is, a cleaning apparatus is inserted inside a housing of a control rod drive mechanism connected to each of the control rod guide tubes, and the upper portion of the cleaning apparatus is caused to reach the bottom in the control rod guide tube. An upper portion of the cleaning apparatus is provided with a brush or ultrasonic vibrator and a delivery port of washing water.
Debris that has accumulated on the bottom inside the control rod guide tubes is floated upward by rotating the brush or by ultrasonic waves emitted from the ultrasonic vibrator, and washed out by washing water delivered in the form of a jet from the delivery port. The washing water including the debris flows down inside the cleaning apparatus and is discharged out of the nuclear reactor pressure vessel. A method of separating debris from an inner surface of the control rod guide tube by a flush in this manner and washing out the debris out of the nuclear reactor pressure vessel also is disclosed in JP A 61-99899.
In those methods, since it is unnecessary to take out structures above the control rod guide tubes out of the nuclear reactor pressure vessel, the amount of work is reduced. However, in those methods, since debris is suspended inside the control rod guide tubes, it is possible that the suspended debris adheres once again to the control rods in the control rod guide tubes and the inner surfaces of control rod guide tubes.
A method of separating debris from the inner surfaces of control rod guide tubes by applying a high pressure water jet onto the inside of control rod guide tube instead of brushing by brush, and washing the debris out of the nuclear reactor pressure vessel is disclosed in JP B 58-15758, JP B 58-15759 and JP B60-35640.
In the method of such high pressure water jet onto the inside of control rod guide tube, it is possible to prevent the control rod guide tube inner surface from being damaged by friction between the brush and the control rod guide tube inner surface. However, even in such a method, debris may be suspended inside the control rod guide tube, so that it is possible that the suspended debris adheres once again to the control rods in the control rod guide tubes and the inner surfaces of control rod guide tubes.
Therefore, an object of the present invention is to make it possible to clean inner bottom portions of control rod guide tubes of a nuclear reactor without having to remove apparatuses inside the nuclear reactor pressure vessel as well as the control rods, and remove debris on the inner bottoms of the reactor control rod guide tubes without agitating the debris.
SUMMARY OF THE INVENTION
A first invention is a control rod guide tube cleaning apparatus in a nuclear reactor, which comprises a rod member, one end side portion of which has the thickness such that the end side portion can pass through an inside of a connecting portion between a housing of a control rod drive mechanism and a control rod guide tube, a nozzle for sucking water, mounted on the rod member on the one end side so that the nozzle can go in and out of the rod member, a means for rotating the rod member in a horizontal direction, and a water passage for leading water sucked in the nozzle to an outside of the housing along the rod member.
In the invention, the following operation is attained. That is, the rod member is inserted into the control rod guide tube through the inside of the housing, then the nozzle is caused to be out of the rod member to face the bottom inside the control rod guide tube. Next, dust piled up on the bottom inside the control rod guide tube is sucked together with water inside the control rod guide tube and discharged out of the housing through the water passage. Such a cleaning operation is performed so hat the dust piled up on the bottom inside the control rod guide tube is discharged out of the housing while changing a horizontal rotation position of the nozzle by rotating the rod member in the horizontal direction. According to such a cleaning operation, it is possible to suppress to agitate dust inside the control rod guide tube to suspend it, so that dispersion of the dust can be suppressed.
A second invention is the control rod guide tube cleaning apparatus, in which the water passage is formed by making the rod member hollow, in the above-mentioned first invention.
According to the second invention, the following operation is attained in addition to the first invention. That is, the water and dust sucked in the nozzle can be discharged out of the housing through the water passage formed inside the rod member, so that it is unnecessary to add a new construction for forming the water passage.
According to the third invention, the following operation can be obtained in addition to the second invention. That is, since the nozzle opening which is a suction port for sucking dust during the cleaning operation can be faced to the bottom inside the control rod guide tube, dust piled up on the bottom inside the control rod guide tube can be sucked efficiently in the nozzle opening.
A fourth invention is the control rod guide tube cleaning apparatus, in which the nozzle has a passage opening facing an inlet of the water passage under the condition that the nozzle is disposed outside the rod member, and the passage opening communicates with the nozzle opening, in the third invention.
According to the fourth invention, the following operation can be obtained in addition to the third invention. That is, when the nozzle is put out of the rod member, the water passage faces the passage opening of the nozzle whereby a portion from the nozzle opening to the water passage is automatically disposed under a condition of communication, and a course can be attained for leading the dust and water sucked in the nozzle out of the housing.
A fifth invention is the control rod guide tube cleaning apparatus, in which the rod member has a thickness such that the rod member can be inserted in the housing of a control
Ishii Tsutomu
Izumi Kiyoshi
Miyahara Tsumoru
Yonemura Hideo
Carone Michael J.
Semunegus Lulit
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