JP5784515B2 - Reactor fuel removal method and apparatus - Google Patents

Description

  Embodiments described herein relate generally to an in-reactor fuel extraction method and apparatus for extracting fuel from a nuclear reactor when damage has occurred in the core of a boiling water reactor.

  If the reactor core is damaged due to an accident such as loss of cooling water, the fuel in the reactor must be removed using a different method than usual. Moreover, when the reactor building and the reactor are damaged, it is assumed that the existing reactor equipment cannot be used.

  Non-Patent Document 1 reports a method for removing fuel in a nuclear reactor after an accident at a three-mile island (TMI) nuclear power plant in the United States where melting of the core has occurred. This technique is a method of removing fuel from a damaged core.

TMI-2 DEFUELING TOOLS ENGINEERING REPORT, Bechtel North American Power Corporation, GEND-INF-073, published in February 1986

  However, the method described in Non-Patent Document 1 is performed in a pressurized water reactor (PWR) and cannot be directly used for a boiling water reactor (BWR). Moreover, it is impossible to divert the existing reactor building and the reactor as they are depending on the damage situation of the reactor building and the reactor.

  An object of an embodiment of the present invention is to provide an in-reactor fuel extraction method and apparatus that can easily extract core fuel even after a severe accident occurs in a boiling water reactor.

In order to achieve the above-mentioned object, a method for extracting fuel in a nuclear reactor according to an embodiment of the present invention includes a temporary building that surrounds an existing nuclear reactor building provided with a boiling water reactor having a vertical axis. A temporary building installation step to be installed; a lifting device mounting step for attaching a lifting device to the temporary building; and when a severe accident occurs in the boiling water reactor, the reactor is located above the core fuel in the boiling water reactor. A reactor internal structure removing step for sequentially removing a plurality of reactor internal structures installed in the reactor using the lifting device, and a fuel extracting step for removing the core fuel using the lifting device after the reactor structure removing step If, have a, a temporarily storing temporary pool the furnace structure removed and installed in the existing reactor building outside the and said temporary building, before being removed in this temporary pool Characterized Rukoto move with the lifting device in the furnace structure.

An in-reactor fuel extraction device according to an embodiment of the present invention includes a temporary building installed so as to surround an existing nuclear reactor building provided with a boiling water reactor having a vertical axis, and the temporary building When a severe accident occurs in the boiling water reactor, the plurality of in-core structures installed above the core fuel in the boiling water reactor are removed, and the core fuel is taken out. A temporary pool for temporarily storing the reactor internal structure removed outside the existing reactor building and inside the temporary building .

According to an embodiment of the present invention, the core fuel even after a severe accident in a boiling water reactor has occurred can be easily taken out, it becomes possible to improve the workability.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional configuration diagram showing an entire boiling water reactor applied to an embodiment of an in-reactor fuel removal method according to the present invention. FIG. 2 is an elevational sectional view showing a reactor pressure vessel in the embodiment of FIG. 1. It is the schematic which shows the standing section of the temporary building and nuclear reactor building used for embodiment of FIG. FIG. 2 is a schematic plan view showing a DS pool and a spent fuel pool used in the embodiment of FIG. 1. It is a flowchart which shows one Embodiment of the fuel extraction method in a nuclear reactor which concerns on this invention. It is a block diagram which shows the state of step S3 in the flowchart of FIG. It is a block diagram which shows the state of step S10 in the flowchart of FIG.

  Hereinafter, an embodiment of a fuel extraction method in a nuclear reactor according to the present invention will be described with reference to the drawings.

  FIG. 1 is a vertical cross-sectional configuration diagram showing an entire boiling water reactor applied to an embodiment of an in-reactor fuel removal method according to the present invention. FIG. 2 is an elevational sectional view showing a reactor pressure vessel in the embodiment of FIG.

  In addition, the following embodiment demonstrates the method of taking out fuel, when the existing nuclear reactor building and nuclear reactor are damaged by disasters, such as an earthquake.

  As shown in FIG. 1, the existing reactor building 1 is composed of an operating floor 2, a reactor well 3, a reactor containment vessel 4, and a number of rooms in which various devices are arranged. The reactor well 3 is closed with a shield plug 6. A reactor pressure vessel 5 is installed in the reactor containment vessel 4. The reactor containment vessel 4 and the reactor pressure vessel 5 are installed with their axes in the vertical direction.

  Below the shield plug 6, an upper cover 7 of the reactor containment vessel, a thermal insulator 9 and an upper cover 8 of the reactor pressure vessel are installed in this order from the upper side to the lower side.

  As shown in FIG. 2, the reactor pressure vessel 5 contains cooling water and a shroud 17 that also serve as a moderator. A core fuel 18 and a control rod 21 are accommodated in the shroud 17. Above the shroud 17, various in-furnace structures such as an upper lattice plate 15, a shroud head 12, a shroud head bolt 13, a guide pin 14, and a steam dryer 11 are installed.

  A reactor core support plate 16 and a fuel support bracket 19 are installed in the reactor pressure vessel 5. The fuel support bracket 19 holds the core fuel 18, has a hole for supplying cooling water, and has a hole through which the control rod 21 is inserted. The control rod 21 is guided by the control rod guide tube 20 and is raised or lowered into the core fuel 18.

  The control rod guide tube 20 passes through a hole in the upper plate of the core support plate 16 and is installed on a CRD (control rod drive mechanism) housing 29 at the bottom of the furnace. A fuel support bracket 19 that supports four fuel assemblies as the core fuel 18 is inserted and installed on the upper portion of the control rod guide tube 20. Accordingly, these fuel assemblies are supported by the upper lattice plate 15 and the core support plate 16, and the fuel support fitting 19, the control rod guide tube 20 and the CRD housing 29 support the weight of the core fuel 18.

  Next, the temporary building and various pools in this embodiment will be described.

  FIG. 3 is a schematic view showing a vertical section of a temporary building and a reactor building used in the embodiment of FIG. FIG. 4 is a schematic plan view showing a DS pool and a spent fuel pool used in the embodiment of FIG.

  As shown in FIG. 3, the temporary building 25 is installed so as to surround the entire existing reactor building 1. In this temporary building 25, an overhead crane 23 which is an example of a lifting device and a temporary pool 24 are installed. In the present embodiment, a crawler crane or a tower crane may be installed instead of the overhead crane 23 as a lifting device. The temporary building 25 is installed when the existing reactor building 1 is damaged and an existing facility such as an overhead crane cannot be used. The temporary building 25 is installed with a space in which the overhead crane 23 can move with respect to the existing reactor building 1.

  As shown in FIG. 4, a DS pool 26 is installed on one side of the reactor well 3. A spent fuel pool 27 is installed on the other side of the reactor well 3. In this embodiment, the temporary pool 24 installed in the temporary building 25, the DS pool 26 and the spent fuel pool 27 installed in the existing reactor building 1 are used.

  Next, the fuel removal method of the present embodiment using the temporary building 25 and the overhead crane 23 will be described with reference to FIGS.

  FIG. 5 is a flowchart showing an embodiment of the in-reactor fuel removal method according to the present invention. FIG. 6 is a block diagram showing the state of step S3 in the flowchart of FIG. FIG. 7 is a block diagram showing the state of step S10 in the flowchart of FIG.

  Here, step S1 shown in FIG. 5 is the temporary building installation step of the present embodiment, step S2 is the lifting device installation step, steps S3 to S8, and step S10 are the reactor internal structure removal steps, step S9, and step S11. Corresponds to the fuel removal step.

  As shown in FIG. 5, in step S <b> 1, the temporary building 25 is installed so as to surround the existing nuclear reactor building 1 provided with the boiling water reactor whose axis is the vertical direction.

  In step S <b> 2, the overhead crane 23 is attached to the ceiling in the temporary building 25.

  In step S3, after installing the temporary building 25 provided with the overhead crane 23, the shield plug 6 is removed as shown in FIG. 6, and the work platform 31 having a radiation shielding function is installed on the operating floor 2. The work platform 31 is used for a worker to perform work. When the shield plug 6 cannot be removed due to deformation or the like, the shield plug 6 is removed by cutting and dividing.

  In step S4, after the work platform 31 is installed, the reactor well 3 is filled with water and the upper cover 7 of the reactor containment vessel is removed. Before filling the reactor well 3, it is confirmed in advance that the bellows 28 shown in FIG. 1 is not damaged.

  Step S <b> 5 is a step of removing the heat retaining stand 9. Specifically, in step S5, after removing the upper cover 7 of the reactor containment vessel, it is confirmed whether or not hydrogen remains in the inside of the heat insulation base pipe 10 connected to the heat insulation base 9, and the heat insulation base pipe Make 10 cuts.

  Next, after cutting the heat retaining stand piping 10, the bolts and nuts fixing the heat retaining stand 9 are removed. If the nut cannot be removed by turning, the bolt and the flange of the heat retaining stand 9 are cut and the bolt and nut are removed. After removing the bolts and nuts, the heat-insulating rack 9 is lifted by the overhead crane 23, transferred to a transport container and carried out.

  Step S6 is a process of removing the upper lid 8 of the reactor pressure vessel. Specifically, step S6 removes the nut for the RPV (reactor pressure vessel) stud 22 after removing the heat retaining stand 9. If the nut cannot be removed due to deformation of the RPV stud 22 or the like, the nut or the RPV stud 22 is cut.

  After removing the RPV stud 22, the upper cover 8 of the reactor pressure vessel is lifted and carried out by the overhead crane 23. If it cannot be lifted because the upper cover 8 of the reactor pressure vessel is fixed or the like, the flange and canopy of the upper cover 8 of the reactor pressure vessel are cut and carried out.

  In step S7, after the upper cover 8 of the reactor pressure vessel is unloaded, the steam dryer 11 is lifted by the overhead crane 23, and the DS pool (pool for storing the steam dryer and the steam separator) 26 or the temporary pool 24 is used. Move to. When the steam dryer 11 cannot be lifted due to sticking or deformation, the sticking part or the deforming part is cut and lifted, or is shredded in a furnace using a shredding device (not shown) and carried out. .

  Step S8 removes the shroud head bolt 13 using the shroud head bolt wrench after carrying out the steam dryer 11. When the shroud head bolt 13 cannot be removed, the shroud head bolt 13 is removed by cutting the shroud head bolt nut between the shroud 17 and the shroud head 12 or the shroud head bolt nut.

  When the guide pin 14 of the shroud head 12 cannot be removed, the lower part of the guide pin 14, the nut or the guide pin bracket for fixing the guide pin 14 is cut, and the guide pin 14 is taken out.

  After removing the shroud head bolt 13, the shroud head 12 is lifted and moved to the DS pool 26 or the temporary pool 24. If the shroud head 12 cannot be lifted for reasons such as sticking or deformation, it is lifted by cutting the sticking portion and the deforming portion, or is shredded in a furnace using a shredding device (not shown) and carried out.

  Step S9 is a step of taking out the core fuel 18. Specifically, in step S9, after the shroud head 12 is carried out, the state of the core fuel 18 is confirmed, the melting range is investigated, and the healthy fuel is packed into the canister 30 shown in FIG. 7 and carried out.

  In step S10, after carrying out the healthy fuel, it is confirmed whether or not the fuel can stand by itself, and the upper lattice plate 15 is removed. The removed upper lattice plate 15 is moved to the spent fuel pool 27, the DS pool 26 or the temporary pool 24, cut, packed into the canister 30 and carried out. If the fuel is not self-supporting, the upper grid plate 15 is cut in the furnace, packed into the canister 30 and carried out. Further, when the upper lattice plate 15 is deformed and fixed, the deformed and fixed portions are cut and the upper lattice plate 15 is removed, or the entire upper lattice plate 15 is cut and carried out.

  After the upper grid plate 15 is unloaded, the removable fuel is taken out. In addition, the melted fuel in the core is set in a state where it can be recovered by a method such as cutting, pulverization, or cutting. The molten fuel in such a state is recovered in the canister 30 which is a recovery container by being gripped, peeled off and sucked using a gripper, a peeling device, and a suction device.

  After the core fuel 18 is taken out, if the core support plate 16 is not deformed or the deformation is small, the fuel support bracket 19, the control rod 21, and the control rod guide tube 20 are removed. If the fuel support bracket 19, the control rod 21, and the control rod guide tube 20 are deformed and have a melt attached thereto, the deformed portion and the melt are cut and removed.

  Further, before and after the removal of the core fuel 18, the fuel deposited and fixed on the upper surface of the core support plate 16 is collected. When the deformation of the core support plate 16 is excessive, the entire core support plate 16 is cut and carried out.

  In step S11, after the core support plate 16 is unloaded, the fuel at the bottom of the furnace is taken out. Specifically, when the molten fuel is not fixed, the bottom head is taken out in a lump, moved into the DS pool 26 and the temporary pool 24, chopped, stuffed, and carried out. When the molten fuel is fixed, the molten fuel is cut, pulverized, and cut using a cutting device, a pulverizing device, and a cutting device so that the molten fuel can be recovered. The molten fuel thus made is collected in the canister 30 by being gripped, peeled off, and sucked using a gripper, a peeling device, and a suction device.

  After the fuel at the bottom of the furnace is taken out, the molten fuel in the CRD housing 29 and the neutron flux measuring tube housing is taken out. When the molten fuel is fixed, the molten fuel is cut, pulverized, and cut using a cutting device, a pulverizing device, and a cutting device in the same manner as described above so that the molten fuel can be recovered. The molten fuel thus made is collected in the canister 30 by being gripped, peeled off, and sucked using a gripper, a peeling device, and a suction device.

  After the molten fuel in the CRD housing 29 and the neutron flux measuring tube housing is taken out, the molten fuel deposited outside the furnace is accessed and taken out from the CRD housing 29 or the molten penetrating portion. The extraction of the core fuel 18 and the fuel at the bottom of the reactor is completed through the above steps.

  As described above, according to the present embodiment, the temporary building 25 is installed so as to surround the existing reactor building 1 in step S1, the overhead crane 23 is attached in the temporary building 25 in step S2, and the boiling is performed in steps S3 to S8. When a severe accident occurs in the water reactor, a plurality of in-reactor structures are sequentially removed using the overhead crane 23, and the core fuel 18 is taken out using the overhead crane 23 in step S9. Even after a severe accident occurs in the furnace, the core fuel 18 can be easily taken out, and the workability can be improved.

  Further, according to the present embodiment, the temporary pool 24 for temporarily storing the removed in-furnace structure in the temporary building 25 is installed, and the removed in-furnace structure in the temporary pool 24 is used with the overhead crane 23. The volume for temporarily storing the in-furnace structure can be increased.

  Although the embodiment of the present invention has been described as described above, this embodiment is presented as an example and is not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  For example, in the above embodiment, each cut-in-furnace internal structure or fuel is packed in the canister 30 and recovered, but the present invention is not limited to this and may be recovered with a cask.

  DESCRIPTION OF SYMBOLS 1 ... Existing reactor building, 2 ... Operating floor, 3 ... Reactor well, 4 ... Reactor containment vessel, 5 ... Reactor pressure vessel, 6 ... Shield plug, 7 ... Top cover of reactor containment vessel, 8 ... Atom Top cover of furnace pressure vessel, 9 ... Insulation rack, 10 ... Insulation rack piping, 11 ... Steam dryer, 12 ... Shroud head, 13 ... Shroud head bolt, 14 ... Guide pins, 15 ... Upper lattice plate, 16 ... Core support plate , 17 ... shroud, 18 ... core fuel, 19 ... fuel support fitting, 20 ... control rod guide tube, 21 ... control rod, 22 ... RPV stud, 23 ... overhead crane (lifting device), 24 ... temporary pool, 25 ... temporary Building, 26 ... DS pool, 27 ... used fuel pool, 28 ... bellows, 29 ... CRD housing, 30 ... canister, 31 ... work platform

Claims (7)

A temporary building installation step of installing a temporary building so as to surround an existing nuclear reactor building provided with a boiling water reactor having a vertical axis;
A lifting device attaching step for attaching a lifting device to the temporary building;
When a severe accident occurs in the boiling water reactor, a reactor internal structure that sequentially removes a plurality of reactor internal structures installed above the core fuel in the boiling water reactor using the lifting device A material removal step,
After the reactor internal structure removal step, a fuel removal step of taking out core fuel using the lifting device;
I have a,
A temporary pool for temporarily storing the removed in-core structure is installed outside the existing reactor building and in the temporary building, and the removed in-core structure is removed from the temporary pool using the lifting device. reactor fuel extraction wherein the Rukoto the moved.   The plurality of in-core structures are installed in the order of a shield plug, a reactor containment vessel top cover, a thermal insulator, a reactor pressure vessel top cover, a steam dryer, a shroud head bolt, a shroud head, and an upper grid plate from the top to the bottom. The method for removing fuel in a nuclear reactor according to claim 1, wherein the removal is performed using the lifting device in the order of installation from above.   3. The reactor according to claim 1, wherein after the fuel support fitting, the control rod, the control rod guide tube, and the core support plate are further removed using the lifting device, the molten fuel at the bottom of the reactor is taken out. Fuel removal method. 4. The atom according to claim 1 , wherein a work platform having a radiation shielding function is installed on an operating floor of the existing reactor building, and the work is performed on the work platform. 5. In-furnace fuel removal method. A temporary building installed so as to surround an existing reactor building provided with a boiling water reactor having a vertical axis;
  When a severe accident occurs in the boiling water reactor attached to the temporary building, removing a plurality of in-core structures installed above the core fuel in the boiling water reactor, and A lifting device for taking out the core fuel;
  With
  An in-reactor fuel take-out apparatus comprising a temporary pool for temporarily storing the reactor internal structure removed outside the existing reactor building and in the temporary building. The plurality of in-reactor structures include a shield plug, a reactor containment vessel top cover, a thermal insulation rack, a reactor pressure vessel top cover, a steam dryer, a shroud head bolt, a shroud head, an upper grid plate, and a core support plate from above to below. The in- reactor fuel take-out device according to claim 5, which is installed in order . The in-reactor fuel extraction device according to claim 5 or 6, wherein a work platform having a shielding function against radiation is installed on an operating floor of the existing reactor building .

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