JP4129310B2 - Cutting method for residual ducts of radioactive contaminants - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for cutting ducts that leave radioactive contaminants penetrating a sealed chamber around a reactor pressure vessel of a nuclear power plant.
[0002]
[Prior art]
Nuclear power generation facilities have been steadily progressing for about 30 years since the start of commercial operation, but the operation period is generally assumed to be 30 to 40 years, and the operation will be terminated in the future. It is expected that something will come out.
In that case, it is necessary to decommission nuclear power facilities after the operation is completed. As for decommissioning of nuclear power generation facilities, consideration is being given to more economical measures on the premise of safety.
[0003]
Metal equipment, ducts, and piping (hereinafter referred to as ducts) that make up nuclear power generation facilities vary widely in material, plate thickness, shape, etc., and construction methods suitable for each equipment and duct are required. . Of these, the reactor internals, the reactor pressure vessel, and the primary ducts connected to the reactor are strongly radioactively contaminated and must be cut and removed more safely.
[0004]
FIG. 4 is a schematic diagram of a boiling water nuclear power generation facility. As shown in FIG. 4, the boiling water nuclear power generation facility is roughly divided into a building 1 containing a nuclear reactor and a building 2 containing a turbine 6 and a generator 7. In a building 1 containing a nuclear reactor, a reactor pressure vessel 3 is installed in a reactor containment vessel 4. A shielding wall 5 is provided around the reactor pressure vessel 3. A steam pipe 8 is installed between the reactor pressure vessel 3 and the turbine 6, and the turbine 6 is rotated by the steam generated in the reactor pressure vessel 3 and the generator 7 generates power. The steam enters the double water machine 9 after turning the turbine 6 and is circulated to the reactor pressure vessel 3 through the water supply pipe 10.
[0005]
A large number of sealed chambers are provided around the reactor pressure vessel 3 by the shielding walls 5 and the like. Each sealed chamber is provided with a ventilation system device (not shown) and prevents leakage of radioactivity to the outside. Each sealed chamber is installed with many tacts by steam pipes and ventilation system devices.
[0006]
As for the dismantling technology of the in-furnace structure, the in-furnace structure is mostly stainless steel, the radioactive concentration is high, and the structure is complicated. Therefore, the underwater plasma arc cutting technology by remote control is known.
As a cutting technique of the reactor pressure vessel 3, an arc saw cutting technique by remote control is known.
[0007]
As a technique for dismantling reactor pressure vessel connection ducts, a disk cutter cutting technique and a molded explosive cutting technique are known.
Regarding the disk cutter cutting technique, a cylindrical cutter is rotated from the inside of the pipe while being pressed against the pipe by the hydraulic pressure of the cylinder, and is cut by plastically deforming the metal, and no chips are generated during the cutting.
[0008]
On the other hand, as shown in FIG. 5, the molded explosive cutting technology includes a casing 12 in which an explosive 11 is molded in a concave shape made of copper or aluminum, and a molded explosive 15 equipped with an electric detonator 13 and a metal liner 14 is cut. It is installed inside the pipe 16 and exploded, and the metal liner 14 of the casing 12 hits the pipe 16 as a jet of high-speed metal particles by the explosion, and is cut by the impact force.
[0009]
[Problems to be solved by the invention]
The metal equipment and ducts that make up the nuclear power generation facility mentioned above, after decommissioning the equipment and ducts in the system before dismantling for the decommissioning of the nuclear power generation facility, By decontaminating radioactivity attached to the inner surface, the equipment and ducts can be reused to reduce the amount of radioactive waste. Generally, it is cut and removed prior to the reactor internal structure, reactor pressure vessel, etc., but the ducts penetrate the sealed chamber around the reactor pressure vessel, so it is limited to a limited space in the sealed chamber. Must be cut off with. For this reason, when a large cutting device is carried into the sealed chamber and the ducts are cut, the cutting work is complicated and accompanied by an explosion. Also, since radioactive contaminants remain on the inner walls of ducts, efforts must be made to prevent the spread of contamination. Moreover, time is required for the cutting work.
[0010]
Further, when the above-described disc cutter cutting technique and molded explosive cutting technique are used for cutting ducts in the sealed chamber, there are the following problems.
The disc cutter cutting technology is a method in which a cylindrical cutter is rotated from the inside of a pipe while being pressed against the pipe by hydraulic pressure to cut the metal, and one end of the pipe is cut in advance by another cutting device or the like. It must be possible to insert into ducts.
[0011]
The molded explosive cutting technique is to install the molded explosive 15 inside the pipe 16 to be cut, explode it, and cut it with its impact force. One end must be cut by another cutting device or the like so that the molded explosive 15 can be inserted into the ducts. Further, since the molded explosive 15 is inserted into the ducts and blasted, the radioactive contaminants remaining in the ducts are mixed with the blast and released into the sealed chamber. Therefore, it is necessary to decontaminate the ducts in the sealed chamber even after cutting.
[0012]
The present invention has been made to solve the above-described problems, and the ducts having radioactive contaminants that can cut the ducts penetrating the sealed chamber around the reactor pressure vessel by a safe and compact means in the sealed chamber. An object of the present invention is to provide a cutting method.
[0013]
[Problems to be solved by the invention]
According to a first aspect of the present invention, when cutting metal ducts penetrating a sealed chamber around a reactor pressure vessel of a nuclear power plant, a branch pipe in which a suction device is connected to the ducts outside the sealed chamber. The explosive is loaded inside the sealed chamber at the location to be cut in the outer circumferential direction, and after the explosive is loaded, the explosive is covered with a protective cover, and then the suction device is driven to evacuate the ducts. A method for cutting ducts that leave radioactive contaminants , characterized in that the explosive is detonated under pressure and the ducts are cut.
[0014]
According to a second aspect of the present invention , in the first aspect of the invention, a green house that includes the planned cutting site is temporarily installed before or after the explosive is loaded at the planned cutting site in the outer circumferential direction of the ducts. According to a third invention, in the first or second invention, an opening having an openable / closable door is provided on at least one wall of the sealed chamber, and an air bag having a suction device connected to the outside of the opening is attached. It is. According to the present invention, explosives are loaded at the locations where the ducts are to be cut in the outer circumferential direction and blasted. Therefore, the ducts are cut by receiving an impact force from the outside, and the generated blast is brought to a negative pressure in the ducts. Therefore, the radioactive contaminants mixed in the blast are sucked by the suction device through the branch pipes attached to the ducts as they are, and decontaminated by the filter or the like.
[0016]
Moreover, by using a protective cover containing explosives, the blast at the time of blasting can be reliably sucked into the ducts.
Even if the protective cover is damaged, it is protected by the greenhouse, and the blast leaked into the sealed chamber is sucked by a suction device through an air bag attached to the opening and decontaminated by a filter or the like. .
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described in detail below with reference to the drawings.
FIG. 1 is an overall layout showing an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the line AA before attaching a protective cover, and FIG. It is sectional drawing by -B line arrow.
[0018]
As shown in FIG. 1, a metal duct 22 is provided in a sealed chamber 21 installed around a reactor pressure vessel (not shown). The duct 22 is provided with a branch pipe 23 outside the sealed chamber 21, and a suction device 25 including a filter 24 is connected to the branch pipe 23. Here, a single duct 22 penetrating the sealed chamber 21 is shown, but the same applies to the case where a plurality of ducts 22 penetrate. Moreover, it is not limited to a duct, A metal pipe | tube etc. are also made into the object of cutting.
In the sealed chamber 21, a green house 39 is temporarily installed to include the planned cutting site before the explosive is loaded into the planned cutting site in the outer circumferential direction of the duct 22 to be cut. The green house 39 is a simple house made of a frame and a vinyl sheet. The green house 39 can be temporarily set after loading the explosive.
[0019]
In addition, an opening 27 having a door 26 that can be opened and closed is provided in at least one wall 21 a of the sealed chamber 21. An air bag 28 is attached to the outside of the opening 27, and a suction device 30 having a filter 29 is connected to the other end.
When the duct 22 is cut, an operator enters the sealed chamber from a door (not shown), and the molded explosive 31 is loaded at a planned cutting location in the outer circumferential direction of the duct 22 to be cut.
As shown in FIG. 2, the molded explosive 31 includes a ring-shaped strip 33 that forms a space portion 38 that is continuous in the circumferential direction at the inner center, and a ring-shaped explosive chamber 34 that is provided outside the strip 33. The explosive chamber 34 is provided with a loading port 35 and an electric detonator 36 is attached. Although the two-division method is adopted here, the present invention is not limited to this.
The molded explosive 31 is not limited to the above-described one, and a molded explosive or the like generally known in other fields can also be used.
[0020]
After the molded explosive 31 is loaded, a protective cover 32 is attached so as to cover the molded explosive 31. By the protective cover 32, the blast generated after the molded explosive 31 is detonated can be reliably sucked into the duct 22.
After the loading of the explosive and the attachment of the protective cover are completed, the suction device 25 is driven to make the inside of the duct 22 have a negative pressure, the molded explosive 31 is electrically ignited, and the duct 22 is cut.
[0021]
The blast generated by the blasting is sucked into the duct 22. Particulate radioactive contaminants separated from the inner wall of the duct 22 by the blast are removed by the high-performance filter 24 provided in the branch pipe 23 together with the metal powder generated by blasting, and the blast is purified and exhausted from the exhaust pipe. Released as. In addition, when exhaust gas is discharged, the radioactive gas exhaust is checked, and measures associated therewith are sufficiently performed.
A series of these operations are performed by a control device 37 provided outside the sealed chamber 21. Data necessary for cutting the ducts is input to the control device 37.
[0022]
The above-described cutting method for the duct 22 and the like is normally performed in a series of decommissioning of nuclear power generation facilities. Prior to cutting the ducts, primary cooling system equipment and ducts around the reactor pressure vessel The system is decontaminated in the system before dismantling, after which the equipment and ducts are dismantled and removed, and the reactor internals, reactor pressure vessel, etc. are remotely operated using a plasma arc cutting device, arc saw cutting device, etc. Is demolished by.
Therefore, the attachment of the branch pipe 23, the connection of the suction device 25 including the filter 24, and the like can be performed as a series of works for decommissioning the nuclear power generation facility. The suction device 25 provided with the filter 24 can be used not only for the single duct 22 of the sealed chamber 21 but also for cutting a plurality of ducts in time series.
Similarly, the air bag 28 attached to the opening 27 of the sealed chamber 21, the suction device 30 provided with the filter 29, etc. can be used in time series when cutting ducts in other sealed chambers.
[0023]
As described above, according to the method for cutting ducts of the present invention, ducts remaining with radioactive contaminants penetrating through a limited narrow sealed chamber can be cut in a short time using a compact device. Since it is possible to cut the ducts in the sealed room without carrying large equipment and devices in the sealed room, the cutting work is easy.
Further, in the present invention, since the inside of the ducts is set to a negative pressure, a molded explosive is loaded from the outside of the ducts and cut by blasting, no blast or the like is scattered in the sealed chamber.
In this case, the blast generated when the molded explosive is detonated can be reliably sucked into the ducts by the protective cover.
[0024]
In addition, by temporarily installing the green house 39 that includes the planned cutting site before or after loading the explosive at the planned cutting site in the outer circumferential direction of the duct 22 to be cut, the blast is not sufficiently sucked into the duct 22 or It can be used as a cushion space against the reverse pressure (wind) when a blast suddenly enters a vacuum.
[0025]
Further, the green house 39 can be used as a temporary work room for temporarily closing the cut after the duct 22 is cut, thereby preventing contamination in the sealed chamber 21.
In addition, an opening is provided in the sealed chamber, an air bag is attached, and a suction device equipped with a filter is connected. Even if the protective cover or the greenhouse 39 is damaged, the blast leaked into the sealed chamber is sealed. Appropriate treatment can be performed by sucking into the air bag from the room.
[0026]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a method capable of safely cutting the remaining ducts of radioactive contaminants penetrating the sealed chamber around the reactor pressure vessel by a compact means. Useful effects are brought about.
[Brief description of the drawings]
FIG. 1 is an overall layout showing an embodiment of the present invention.
2 is a cross-sectional view taken along line AA before attaching the protective cover of FIG. 1. FIG.
3 is a cross-sectional view taken along the line B-B before attaching the protective cover of FIG. 1;
FIG. 4 is a schematic view of a normal boiling water nuclear power generation facility.
FIG. 5 is a side view showing a state of a conventional explosive cutting device for ducts.
[Explanation of symbols]
21 Sealed chamber 22 Metal duct 23 Branch pipes 24, 29 Filters 25, 30 Suction device 26 Door 27 Opening portion 28 Air bag 31 Molded explosive 32 Protective cover 33 Band plate 34 Chamber 35 Loading port 36 Electric detonator 37 Control device 38 Space Part

Claims (3)

When cutting metal ducts penetrating the sealed chamber around the reactor pressure vessel of the nuclear power generation facility, a branch pipe connected to a suction device outside the sealed chamber is attached to the ducts, and the sealed The explosive is loaded inside the chamber at the location to be cut in the outer peripheral direction. After the explosive is loaded, the explosive is contained by the protective cover, and then the suction device is driven to depressurize the inside of the ducts to initiate the explosive. It is allowed, characterized by cutting the ducting, the cutting method of ducting the remaining radioactive contaminants. The ducts that remain radioactive contaminants according to claim 1 , characterized in that a green house is temporarily installed to include the planned cutting site before or after loading the explosive at the planned cutting site in the outer circumferential direction of the duct. Cutting method. An opening having a reclosable door in at least one wall of the sealed chamber is provided, characterized in that attaching the airbag which is connected to a suction device outside the opening, according to claim 1 or 2, radioactive A method for cutting ducts that remain contaminated.

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