JP6239279B2 - Molten fuel cutting device and cutting method thereof - Google Patents

Description

  Embodiments of the present invention relate to a molten fuel cutting apparatus and a cutting method thereof for cutting in order to take out nuclear fuel that has been melted and solidified (hereinafter referred to as molten fuel) in a nuclear power plant, for example.

  In the operation of taking out molten fuel in a nuclear power plant, it is generally important to ensure critical safety in order to handle nuclear fuel that has solidified after being melted. Based on the knowledge of the accident at the Three Mile Island nuclear power plant in the United States, molten fuel takes various forms such as crust (outer skin) and particle size debris, and mechanical crushing and cutting are required when removing molten fuel It is thought that it becomes. Generally, in order to take out the molten fuel, a drill or other cutting device is used to cut the molten fuel (for example, see Patent Document 1).

  When cutting the molten fuel, the ratio of the molten fuel and the water around it changes, so the molten fuel may reach a critical level. Therefore, when taking out the molten fuel, it is necessary to take some measures to ensure the subcriticality of the molten fuel.

  Examples of methods that have been studied so far include a method of injecting a gel-like substance containing a neutron absorber from a cutting device, a method of introducing particles composed of a neutron absorber, and the like. However, grasping the amount and position of these neutron absorbers remaining in the molten fuel region is a problem in critical management (for example, see Non-Patent Document 1).

JP 2013-19875 A

Proceedings of the Atomic Energy Society of Japan "Spring Annual Meeting 2013" (March 26-28, 2013, Kinki University Higashi Osaka Campus) H34

  By the way, in the molten fuel cutting method and the method for ensuring subcriticality, it is difficult to predict the policy itself for ensuring subcriticality and the actual behavior of the neutron absorber used to ensure subcriticality. It is cited as a general problem.

  In particular, the neutron absorber has a great influence on the criticality, and the effective multiplication factor of neutrons varies greatly depending on the behavior of the position where the neutron absorber exists. Therefore, when a neutron absorbing material whose behavior is difficult to predict, such as liquid, granular, and gel, is used, there arises a critical safety problem that the effective multiplication factor cannot be predicted.

  In addition, when liquid, granular and gel neutron absorbers are used, although it is considered to be somewhat effective to ensure subcriticality during the cutting operation, cooling water is introduced from the region where the molten fuel exists after the cutting operation. At the same time, there is a risk that the neutron absorber flows out. Therefore, there is a demand for a molten fuel cutting method that ensures that the neutron absorber remains in the region where the molten fuel is present and that subcriticality is ensured during and after the cutting operation.

  The problem to be solved by the embodiments of the present invention is to provide a molten fuel cutting device and a cutting method thereof capable of sufficiently ensuring critical safety during the operation while cutting the molten fuel.

In order to achieve the above object, a molten fuel cutting apparatus according to an embodiment of the present invention is a molten fuel cutting apparatus that uses a cutting tool to cut solid fuel that has been solidified after being melted. look containing neutron absorbing material, wherein the cutting tool is removably attached to the drive unit for driving the cutting tool through the detachable unit, development unit area spreads when the cutting tool is disconnected from the detachable portion Is provided in the cutting tool .
A molten fuel cutting device according to another embodiment of the present invention is a molten fuel cutting device that uses a cutting tool to cut nuclear fuel that has solidified after being melted, and the cutting tool uses the first neutron absorbing material. The cutting tool is divided into a front end side and a rear end side in an axial direction, a cutting portion provided on the front end side for cutting the solidified nuclear fuel, and provided on the rear end side and provided on the first end side. A neutron absorbing portion including a neutron absorbing material is joined.
Furthermore, the molten fuel cutting device according to another embodiment of the present invention is a molten fuel cutting device that uses a cutting tool to cut the nuclear fuel that has solidified after being melted, and the cutting tool uses the first neutron absorbing material. And at least a part of the cutting tool is covered with a container containing a second neutron absorbing material, and the container is torn during the cutting of the cutting tool and the second neutron absorbing material leaks out. To do.

A molten fuel cutting method according to an embodiment of the present invention includes a cutting step of cutting a nuclear fuel that has solidified after being melted using a cutting tool including a first neutron absorber , and the cutting tool is disposed before the cutting step. A tool attaching step for attaching to the drive unit for driving the cutting tool, and a tool leaving step for separating the cutting tool from the attaching / detaching portion after the cutting step and leaving the solidified nuclear fuel in a cut place. It is characterized by.

  According to the embodiment of the present invention, it is possible to sufficiently ensure the critical safety during the operation while performing the cutting operation of the molten fuel.

1 is a schematic elevation view showing a first embodiment of a molten fuel cutting device according to the present invention. It is a schematic elevation view which shows the state which cut | disconnected the cutting tool of FIG. It is the schematic which shows the state which cuts molten fuel using the cutting tool of FIG. It is the schematic which shows the state which leaves the cutting tool after cutting molten fuel using the cutting tool of FIG. It is the schematic which shows the state by which the cutting tool of FIG. FIG. 2 is a schematic view showing a state where a plurality of the cutting tools of FIG. 1 are left in granular molten fuel. It is an enlarged elevation view which shows the cutting tool of 2nd Embodiment of the molten fuel cutting device which concerns on this invention. It is an enlarged elevation view which shows the cutting tool of 3rd Embodiment of the molten fuel cutting device which concerns on this invention. It is sectional drawing by the IX-IX line of FIG. It is an expanded elevation view which shows 4th Embodiment of the molten fuel cutting device which concerns on this invention. It is a schematic block diagram which shows 5th Embodiment of the molten fuel cutting device which concerns on this invention. It is a schematic block diagram which shows the state which the cutting tool of FIG. 11 exposed from the lower end of a hollow tube. It is a schematic block diagram which shows the state which performs a cutting operation | work, ejecting a fluid with the cutting device of FIG. It is a schematic elevation view which shows 6th Embodiment of the molten fuel cutting device which concerns on this invention. It is a schematic elevation view which shows the state which the expansion | deployment part of the cutting tool shown in FIG. 14 expanded.

  Embodiments of a molten fuel cutting device according to the present invention will be described below with reference to the drawings.

(First embodiment)
(Constitution)
FIG. 1 is a schematic elevational view showing a first embodiment of a molten fuel cutting device according to the present invention. FIG. 2 is a schematic elevation view showing a state where the cutting tool of FIG. 1 is cut off.

  As shown in FIG. 1, the molten fuel cutting apparatus according to the present embodiment includes a cutting tool 1 made of a material including a neutron absorber (first neutron absorber), and a drive unit that rotationally drives the cutting tool 1. 2 and an attachment / detachment part 3 that enables the cutting tool 1 to be attached / detached from the drive part 2.

  The drive unit 2 is attached to one end of a suspending unit 12 formed in an elongated bar shape. The other end of the hanging portion 12 extends to an operation floor (not shown) and is operated by an operator. One end of a cable (not shown) is connected to the drive unit 2, and the other end of the cable is connected to a power supply device installed on the operation floor. When the power switch of this power supply device is turned on, the drive unit 2 is driven.

  The material of the cutting tool 1 has a high neutron absorption effect such as tungsten, tungsten carbide, hafnium, hafnium alloy, dysprosium alloy, rhenium, rhenium alloy and the like, boron added to these, or diamond coated, etc. In addition, a solid material having characteristics of high strength and high hardness is used as a cutting tool.

  The cutting tool 1 is capable of cutting molten fuel, which is a molten nuclear fuel, such as a drill bit, a bite, an end mill, a reamer, and a hob. A drill bit is applied to the cutting tool 1 of the present embodiment. Therefore, the drive unit 2 of the present embodiment uses a rotational drive mechanism such as a motor.

  Note that the cutting tool 1 may be a scissor that does not rotate. Therefore, the cutting tool 1 may be rotated or hit when the molten fuel described later is cut. When the molten fuel is hit, the cutting tool 1 crushes the molten fuel. In the present embodiment, this case is also included in the cutting operation.

  In the present embodiment, the drive unit 2 is provided integrally with the attachment / detachment unit 3. Not limited to this, the cutting tool 1 can be driven by some means such as providing a flexible shaft between the drive unit 2 and the attachment / detachment unit 3 and transmitting the driving force of the drive unit 2 to the attachment / detachment unit 3 through the flexible shaft. For example, the drive unit 2 may be installed at a remote location.

  The attachment / detachment unit 3 only needs to be capable of mechanically attaching / detaching the cutting tool 1 by remote operation. For example, the attachment / detachment unit 3 can be detached from the cutting tool 1 by operating from the operation floor, such as a hexagonal chuck. I just need it.

(Function and effect)
Next, the effect | action of this embodiment is demonstrated using FIGS.

  FIG. 3 is a schematic view showing a state in which molten fuel is cut using the cutting tool of FIG. FIG. 4 is a schematic view showing a state in which the cutting tool is left after cutting the molten fuel using the cutting tool of FIG. FIG. 5 is a schematic view showing a state in which a plurality of the cutting tools of FIG. 1 are left in the molten fuel. FIG. 6 is a schematic view showing a state where a plurality of the cutting tools of FIG. 1 are left in the granular molten fuel.

  First, after attaching the cutting tool 1 to the detachable part 3, the operator suspends the hanging part 12 from the operation floor to the position of the molten fuel 4.

  Next, as shown in FIG. 3, the molten fuel 4 is cut using a cutting tool 1 made of a material containing a neutron absorber. The cutting tool 1 is pierced into the molten fuel 4 by cutting the molten fuel 4. Thereby, since the neutron absorbing material is inserted into the molten fuel 4 and the control rod is functionally inserted, the criticality of the molten fuel 4 can be reduced.

  Here, as a condition that may reach the criticality during the cutting operation of the molten fuel 4, the ratio of the water to the cut molten fuel 5 changes due to the movement of the cut molten fuel 5, and the neutron It is conceivable that the decelerating condition is suitable for fission. Also in that case, the criticality can be suppressed because the cutting tool 1 which is a neutron absorber is located in the vicinity of the cut molten fuel 5.

  Further, after the cutting operation of the molten fuel 4 is completed, the cutting tool 1 is pulled out so that the cut molten fuel 5 moves. Water enters the hole formed by cutting in this way, and the molten fuel 4 The criticality may be reached due to factors such as changes in the neutron moderation state.

  Therefore, in this embodiment, as shown in FIG. 4, the cutting tool 1 is not pulled out after cutting, but the operator operates the detachable portion 3 from the operation floor to separate the cutting tool 1 and leave it in the molten fuel 4. To do. This prevents the molten fuel 5 that has been cut by moving the cutting tool 1 from moving, prevents water from entering the holes formed by the cutting, and keeps the cutting tool 1 as a neutron absorber in the molten fuel 4. be able to.

  After the end of one cutting operation, a new cutting tool 1 is mounted on the detachable portion 3 and the operation is performed again. By repeating this operation, it is possible to obtain a state in which many neutron absorbers exist in the molten fuel 4 as shown in FIG.

  Moreover, as shown in FIG. 6, the cutting tool 1 can be left as a neutron absorber also for the granular molten fuel 6. The remaining interval is preferably about 10 cm to 50 cm from the viewpoint of reactivity value. This interval is a value that becomes subcritical when the cutting tool 1 is placed in a 10-50 cm square two-dimensional infinite system with the most reactive fuel composition that can be considered on the spot. It is desirable to set to.

  Therefore, in the present embodiment, since the solid cutting tool 1 including the neutron absorbing material that is less likely to flow out of the cooling water can be disposed on the molten fuel 4 or the granular molten fuel 6, the cutting operation and the cutting operation can be performed. Later criticality safety can be greatly increased.

  Moreover, in this embodiment, the cutting tool 1 is not disposable by one time cutting | disconnection by collect | recovering the molten fuel 5 cut while cutting with the cutting tool 1, and can be used in multiple times.

  As described above, according to the present embodiment, the cutting tool 1 includes the neutron absorbing material, so that the critical safety during the operation can be sufficiently ensured while the molten fuel 4 is crushed and cut.

  Further, according to the present embodiment, after the cutting tool 1 is cut, the cutting tool 1 is not pulled out from the molten fuel 4 and the cutting tool 1 is separated by operating the attaching / detaching portion 3 and is left in the molten fuel 4 to complete the operation. Subsequent criticality safety can be sufficiently secured.

(Second Embodiment)
(Constitution)
FIG. 7 is an enlarged elevation view showing the cutting tool of the second embodiment of the molten fuel cutting apparatus according to the present invention. The following embodiment is a modification of the first embodiment. The same components as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted, and different configurations and operations are described. To do.

  The cutting tool 1 of the present embodiment is divided into two parts in the axial direction on the front end side and the rear end side. In the cutting tool 1, a neutron absorbing portion 7 provided on the rear end side in the axial direction and a cutting portion 8 provided on the front end side in the axial direction are joined. In order to join the neutron absorbing portion 7 and the cutting portion 8, for example, the joining portions of the two are welded or a male screw is formed on the joining surface side of the cutting portion 8, while a female screw is formed on the joining surface side of the neutron absorbing portion 7. Can be joined by screwing them together.

  The neutron absorber 7 includes a neutron absorber, and has a function of contacting the molten fuel 4 or the granular molten fuel 6 on the outer peripheral surface thereof to ensure critical safety. The cutting part 8 is a high-hardness / high-strength member, and contacts the molten fuel 4 or the granular molten fuel 6 at the lower part to cut the molten fuel 4 or the granular molten fuel 6. Here, the neutron absorber 7 using the neutron absorbing material may be made of boron-added stainless steel or the like in addition to any of the materials described in the first embodiment.

  The cutting portion 8 may be made of, for example, a metal such as tungsten, hafnium, zirconium, gadolinium, molybdenum, cobalt, iron, or an alloy thereof, or a ceramic such as diamond, zirconia, or alumina.

(Function and effect)
In the present embodiment configured as described above, the cutting portion 8 is divided into two in the axial direction on the front end side and the rear end side and provided on the front end side in the axial direction, and the neutron absorption portion provided on the rear end side in the axial direction. 7 is joined.

  The cutting part 8 that requires high hardness and high strength uses a material with high cost and high strength, but the neutron absorption part 7 using a neutron absorbing material requires high strength and high hardness. A material with a high neutron absorption cross section is used, although not. Therefore, the manufacturing cost of the cutting tool 1 can be suppressed by increasing the degree of freedom of material selection of the cutting tool 1 and suppressing the specification of expensive materials.

(Third embodiment)
(Constitution)
FIG. 8 is an enlarged elevation view showing the cutting tool of the third embodiment of the molten fuel cutting device according to the present invention. 9 is a cross-sectional view taken along line IX-IX in FIG.

  As shown in FIGS. 8 and 9, a cutting tool 9 made of a material including the neutron absorbing material of the present embodiment includes a tool body 9b in which a hollow portion 9a is formed along the axial direction, and the hollow portion 9a. It is comprised from the neutron absorber 9c accommodated in the inside as the 1st neutron absorber which comprises the cutting tool 1 of the said 1st Embodiment. The tool body 9b in which the hollow portion 9a is formed can be made of a material that does not include a cemented carbide or a neutron absorber used for general tools, and the tool body 9b is made of a material having a property different from that of the first neutron absorber. Two neutron absorbers can be used.

  As the neutron absorber 9c, materials having a large neutron absorption cross section such as boron, hafnium, gadolinium, cadmium, rhenium, erbium, samarium, or a compound thereof can be used, and various materials can be considered. .

  However, if the neutron absorber 9c leaks through the hole of the hollow portion 9a, it needs to be closed by welding, a lid, a screw, or the like.

(Function and effect)
In the present embodiment configured as described above, the hollow portion 9a is formed in the tool body 9b of the cutting tool 9, and the neutron absorber 9c is accommodated in the hollow portion 9a. Can be selected regardless of. Moreover, since the material of the tool body 9b can be selected regardless of the neutron absorption effect, sufficient workability can be ensured by using a cemented carbide or the like used for a normal tool. Furthermore, for the neutron absorber 9c, for example, when using gadolinia, it is possible to obtain a large neutron absorption effect compared to when using metal hafnium that can also be used as the material of the cutting tool 1 of the first embodiment. . For this reason, both the workability and the neutron absorption effect during the cutting operation of the molten fuel can be sufficiently secured with a simple configuration. When gadolinia or boron is used as the neutron absorbing material, a powdery material such as gadolinium oxide or boron carbide is often used. In this embodiment, the hollow portion 9a provided in the tool body 9b of the cutting tool 9 is used. Therefore, even if the neutron absorber 9c is a powdered material such as gadolinium oxide or boron carbide, there is no need to perform additional processing, etc. A certain cutting tool 9 can be realized.

  Further, according to the present embodiment, it is possible to reduce the usage amount of a material having high cost, strength and hardness by the volume of the hollow portion 9a and to use a material having a large neutron absorption cross section regardless of the strength and hardness. This can increase cost effectiveness.

(Fourth embodiment)
(Constitution)
FIG. 10 is an enlarged elevation view showing a fourth embodiment of the molten fuel cutting device according to the present invention.

  As shown in FIG. 10, the present embodiment includes a cutting tool 1 made of a material containing a neutron absorber as in the first embodiment, and a container 11 that wraps at least a part of the cutting tool 1. ing. In this container 11, the 2nd neutron absorber 10 similar to the said 3rd Embodiment is accommodated. The container 11 is made of plastic, vinyl, thin metal, or other material that is damaged when the molten fuel 4 and the granular molten fuel 6 are cut and the contents of the neutron absorbing material 10 leak to the surroundings.

  As the neutron absorber 10, among the materials mentioned in the third embodiment, a material mixed with a powder or gel-like base material, or a material that stays around after leaking from the container 11, such as a granule, may be used. it can.

(Function and effect)
In this embodiment configured as above, the container 11 is torn at the start of the cutting of the molten fuel 4 or the granular molten fuel 6 so that the neutron absorbing material 10 leaks from the container 11 and the neutron absorbing material 10 is cut. The molten fuel 5 is supplied to the part and mixed with the cut molten fuel 5.

  Thereby, even when the cut molten fuel 5 is deposited around the cutting tool 1 and when it is moved from the periphery of the cutting tool 1, the critical safety of the cut molten fuel 5 can be improved. .

(Fifth embodiment)
(Constitution)
FIG. 11 is a schematic configuration diagram showing a fifth embodiment of the molten fuel cutting device according to the present invention. FIG. 12 is a schematic configuration diagram showing a state in which the cutting tool of FIG. 11 is exposed from the lower end of the hollow tube. FIG. 13 is a schematic configuration diagram showing a state in which a cutting operation is performed while ejecting a fluid with the cutting apparatus of FIG.

  As shown in FIGS. 11 to 13, the present embodiment includes a cutting tool 1, a drive unit 2, an attachment / detachment unit 3, a suspension unit 12, a hollow tube 13, and a fluid 15 containing a neutron absorber. It has. In the present embodiment, the cutting tool 1, the drive unit 2, and the detachable unit 3 are collectively referred to as a cutting device.

  The suspending portion 12 moves the cutting device, transmits a driving force, and the like, and can pass through the hollow tube 13 while the cutting device is suspended. The hollow tube 13 is provided with the above-described cutting device having a gap 13a, and a fluid 15 containing a neutron absorbing material flows through the gap 13a. The length of the hollow tube 13 is set to a point where the fluid 15 containing the neutron absorbing material is injected into the hollow tube 13 or longer. The cutting tool 1 is exposed to the outside from the hollow tube 13 when the molten fuel 4 is cut.

  Here, as the fluid 15 containing the neutron absorbing material, for example, boric acid water, water containing boron fine particles, or a gel-like substance can be considered. However, the neutron absorber is not limited to these materials.

(Function and effect)
In the present embodiment, as shown in FIG. 13, when the cutting tool 1 reaches the cavity 14 existing inside the molten fuel 4, the cutting tool 1 that is a neutron absorber is sufficiently inserted into the cavity 14. There is a possibility that water existing in the surrounding area may invade before. When water enters the cavity 14, the amount of the moderator in the molten fuel 4 may be greatly changed, reaching the criticality.

  Therefore, in this embodiment, the cutting operation is performed while ejecting the fluid 15 containing the neutron absorbing material in the cutting direction from the hollow tube 13 including the cutting device. Thereby, even before the cutting tool 1 including the neutron absorber is sufficiently inserted into the cavity 14 in the molten fuel 4, the subcriticality can be maintained by the neutron absorption effect of the fluid 15 including the neutron absorber. it can. Further, after the cutting operation is completed, the cutting tool 1 is separated from the attaching / detaching portion 3 and left in the cavity portion 14 in the molten fuel 4 as in the first embodiment.

  Thus, according to this embodiment, even if the inside of the molten fuel 4 has an unexpected shape, it is possible to proceed with the cutting operation while ensuring critical safety. In addition, the amount of the coolant can be reduced as compared with the fluid 15 containing the neutron absorber.

(Sixth embodiment)
(Constitution)
FIG. 14 is a schematic elevation view showing a sixth embodiment of the molten fuel cutting apparatus according to the present invention. FIG. 15 is a schematic elevational view showing a state in which the developed portion of the cutting tool shown in FIG. 14 is expanded.

  As shown in FIG. 14, the developing tool 16 whose area increases when the cutting tool 1 of the present embodiment is separated from the detachable part 3 is attached. The developing portion 16 is given an elastic force by a spring (not shown) in a direction in which the developing portion 16 is always deployed.

  Therefore, as shown in FIG. 15, the developing unit 16 develops when the cutting tool 1 is separated from the attachment / detachment unit 3 and separates the position of the cutting tool 1 left in the molten fuel 4 or the granular molten fuel 6. Hold at the designated location.

(Function and effect)
As described above, according to the present embodiment, the position of the cutting tool 1 left in the molten fuel 4 or the granular molten fuel 6 is separated from the cutting tool 1 made of the neutron absorbing material separated by the attaching / detaching portion 3. , And can be held at a location separated by the expanding portion 16. Thereby, the unexpected movement of the cutting tool 1 comprised with the neutron absorber can be avoided, a planned critical safety measure can be formulated, and the cutting operation of the molten fuel can be performed.

(Other embodiments)
Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  For example, the second embodiment can be combined with at least one of the fourth embodiment, the fifth embodiment, and the sixth embodiment. The sixth embodiment can be combined with at least one of the second to fifth embodiments.

  DESCRIPTION OF SYMBOLS 1 ... Cutting tool, 2 ... Drive part, 3 ... Detachable part, 4 ... Molten fuel, 5 ... Cut molten fuel, 6 ... Granular molten fuel, 7 ... Neutron absorption part, 8 ... Cutting part, 9 ... Cutting tool , 9a ... hollow part, 9b ... tool body, 9c ... neutron absorber (first neutron absorber), 10 ... neutron absorber (second neutron absorber), 11 ... container, 12 ... hanging part, 13 ... hollow tube, 13a ... void, 14 ... cavity, 15 ... fluid containing neutron absorber, 16 ... deployment part

Claims (11)

A molten fuel cutting device for cutting nuclear fuel that has solidified after being melted with a cutting tool,
The cutting tool only contains the first neutron absorbing material,
The cutting tool is detachably attached to a drive unit that drives the cutting tool via an attachment / detachment unit,
Providing the cutting tool with a development part that expands in area when the cutting tool is separated from the detachable part;
A molten fuel cutting device. A molten fuel cutting device for cutting nuclear fuel that has solidified after being melted with a cutting tool,
The cutting tool includes a first neutron absorber;
The cutting tool is divided into a front end side and a rear end side in an axial direction, a cutting portion provided on the front end side for cutting the solidified nuclear fuel, and a first neutron absorption provided on the rear end side. Joining the neutron absorption part including the material,
A molten fuel cutting device. The at least part of the cutting tool is covered with a container containing a second neutron absorbing material, and the container is torn when the cutting tool is cut, and the second neutron absorbing material leaks out. The molten fuel cutting device according to 1 or 2 . A molten fuel cutting device for cutting nuclear fuel that has solidified after being melted with a cutting tool,
The cutting tool includes a first neutron absorber;
At least a part of the cutting tool is covered with a container containing a second neutron absorber, and the container is torn during the cutting of the cutting tool, and the second neutron absorber leaks;
A molten fuel cutting device. 5. The molten fuel cutting device according to claim 2, wherein the cutting tool is detachably attached to a drive unit that drives the cutting tool via an attachment / detachment unit . The molten fuel cutting device according to claim 5 , wherein the cutting tool is provided with a development portion that increases in area when the cutting tool is separated from the attachment / detachment portion . The molten fuel cutting device according to claim 1, wherein the cutting tool has a hollow portion formed along an axial direction, and the first neutron absorbing material is accommodated in the hollow portion . The said cutting tool is arrange | positioned in a hollow tube, The said cutting tool is exposed from the said hollow tube at the time of the cutting | disconnection of the said solidified nuclear fuel, It is any one of Claim 4 thru | or 7 characterized by the above-mentioned. molten fuel cutting device according.   The molten fuel cutting device according to claim 8, wherein the cutting tool is disposed with a gap in the hollow tube and allows a fluid containing a second neutron absorber to flow from the gap. A cutting step of cutting the nuclear fuel solidified after being melted by using a cutting tool containing the first neutron absorber;
Before the cutting step, a tool attachment step of attaching the cutting tool to a drive unit that drives the cutting tool;
After the cutting step, the cutting tool is separated from the attaching / detaching portion, and a tool leaving step for leaving the solidified nuclear fuel in a place where it is cut, and
A molten fuel cutting method characterized by comprising : The molten fuel cutting method according to claim 10 , wherein in the cutting step, the second neutron absorbing material is supplied to the cutting portion.

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