JP6921767B2 - Melt core holding device and nuclear facility - Google Patents

Description

An embodiment of the present invention relates to a molten core holding device and a nuclear facility for holding a melt generated when the core melts at the time of a nuclear accident.

In a water-cooled reactor, the core may melt if the core continues to be inadequately cooled due to an accident such as loss of primary coolant. In such a case, an emergency core cooling system (ECCS) is usually operated to remove the residual heat of the core. As a result, an accident in which the core melts (hereinafter referred to as a core meltdown accident) is prevented.

However, it is assumed that the emergency core cooling system does not operate for some reason and other devices capable of injecting cooling water into the core cannot be used. When a core meltdown accident actually occurs, the high-temperature core melt (molten core, debris) may melt down to the bottom (lower mirror) of the reactor pressure vessel and penetrate the bottom. The core melt penetrating the bottom of the reactor pressure vessel may fall into the portion of the reactor containment vessel facing the bottom of the reactor pressure vessel (hereinafter referred to as the containment vessel floor).

The floor of such a containment vessel is usually composed mainly of concrete. When a high-temperature core melt comes into contact with the containment floor and reacts with concrete, non-condensable gas such as carbon dioxide and hydrogen is generated, and the concrete on the containment floor is melted and eroded. When the reaction between the concrete on the floor of the containment vessel and the core melt continues, the reactor is stowed due to the erosion of the concrete and the increase in pressure inside the containment vessel due to the non-condensable gas generated by the reaction with the concrete. The vessel may be damaged.

Therefore, when the core melt comes into contact with the floor of the containment vessel, the core melt is cooled so that the temperature of the contact surface is equal to or lower than the erosion temperature of concrete (for example, 1500 K or lower), or the core melt is cooled. It is required that the concrete of the containment vessel floor does not come into direct contact with the concrete.

Therefore, conventionally, in case the core melt falls from the reactor pressure vessel, the core melt that falls through the reactor pressure vessel is received vertically below the reactor pressure vessel in the dry well. A technique for providing a core melt holding device (so-called core catcher) has been proposed. In this technique, the cooling water stored in the pressure suppression pool at the time of a core meltdown accident is guided to the core melt holding device to cool the core melt holding device and the core melt.

Japanese Patent No. 3150451

An object to be solved by the present embodiment is to provide a molten core holding device and a nuclear facility having improved cooling performance of the core melt.

In order to solve the above problems, the core melt holding device according to the present embodiment is installed below the nuclear pressure vessel in the reactor containment vessel that houses the nuclear pressure vessel that houses the core, and is described in the event of an accident. A core melt holding device that holds the core melt generated when the core melts, and includes a closed container installed on a predetermined installation surface and a porous body contained in the closed container and containing water. , And the porous body is installed in multiple layers in the vertical direction .

The nuclear facility according to the present embodiment is installed in the core, the reactor pressure vessel accommodating the core, and below the reactor pressure vessel in the reactor pressure vessel, and when the core melts at the time of an accident. A nuclear facility having a core melt holding device for holding the generated core melt, the core melt holding device is housed in a closed container installed on a predetermined installation surface and the closed container. A porous body containing water is provided , and the porous body is installed in multiple layers in the vertical direction .

According to this embodiment, it is possible to further improve the cooling performance of the core melt.

It is a schematic vertical sectional view which shows the structure of the nuclear power facility to which the core meltdown apparatus of 1st Embodiment is applied. FIG. 3 is a schematic vertical cross-sectional view showing an enlarged view of the core melt holding device and its surroundings in FIG. FIG. 5 is a schematic vertical cross-sectional view showing an enlarged state of the core melt holding device of FIG. 1 when the core melt is dropped. FIG. 5 is a schematic vertical cross-sectional view showing an enlarged state of holding a core melt of the core melt holding device of FIG. 1. It is a schematic vertical sectional view which shows the structure of the nuclear power facility to which the core melt holding device of the modification of 1st Embodiment is applied. It is a schematic vertical sectional view which shows the core meltdown apparatus of 2nd Embodiment in an enlarged manner. It is a schematic vertical cross-sectional view which shows the core meltdown apparatus of the modification of 2nd Embodiment in an enlarged manner. It is a schematic vertical cross-sectional view which shows the core meltdown apparatus of 3rd Embodiment in an enlarged manner. It is a schematic enlarged vertical cross-sectional view which shows the main part of the core meltdown apparatus of 4th Embodiment in an enlarged manner. It is a schematic vertical cross-sectional view which shows the core meltdown apparatus of 5th Embodiment in an enlarged manner. It is a schematic vertical sectional view which shows the core meltdown apparatus of 6th Embodiment in an enlarged manner. 6 is a schematic vertical cross-sectional view showing an enlarged view of a core meltdown device of a modified example of the sixth embodiment. It is a schematic vertical sectional view which shows the core meltdown apparatus of 7th Embodiment in an enlarged manner. It is a schematic vertical sectional view which expands and shows the structure of the nuclear power facility to which the core meltdown apparatus of 8th Embodiment is applied.

Hereinafter, the core meltdown device and the nuclear facility according to the present embodiment will be described with reference to the drawings.

(First Embodiment)
FIG. 1 is a schematic vertical cross-sectional view showing the configuration of a nuclear facility to which the core meltdown device of the first embodiment is applied. FIG. 2 is a schematic vertical cross-sectional view showing the core meltdown device of FIG. 1 and its surroundings in an enlarged manner. FIG. 3 is a schematic vertical cross-sectional view showing an enlarged state of the core melt holding device of FIG. 1 when the core melt is dropped. FIG. 4 is a schematic vertical cross-sectional view showing an enlarged state in which the core melt of the core melt holding device of FIG. 1 is held.

As shown in FIG. 1, the nuclear facility 1 is a plant facility for a boiling water reactor, and the reactor pressure vessel 10 is installed in the reactor containment vessel 12. The core 11 is housed in the reactor pressure vessel 10. The space in the reactor containment vessel 12 includes a dry well 13 for accommodating the reactor pressure vessel 10 and a wet well 15 in which the pressure suppression pool 14 is formed. The dry well 13 and the pressure suppression pool 14 communicate with each other through a vent pipe 16.

The reactor pressure vessel 10 is supported by a cylindrical pedestal 17 made of concrete with an open top. A concrete pedestal bottom 18 is formed on the bottom of the pedestal 17. Of the dry well 13, the space below the reactor pressure vessel 10 and above the pedestal bottom 18 surrounded by the pedestal side wall 19 is called the pedestal space 20. A wet well 15 is formed around the pedestal side wall 19.

Although the present embodiment describes an example in which a drain sample is not formed on the pedestal bottom 18, it can also be applied to an example in which a part of the pedestal bottom 18 is dug to form a drain sample.

A core meltdown device 21 is arranged in the pedestal side wall 19 on the upper surface of the pedestal bottom 18. The core melt holding device 21 has a structure capable of holding and cooling the core melt that breaks through the bottom of the reactor pressure vessel 10 and falls in the event of a core meltdown accident.

In this embodiment, a water injection pipe 23 for supplying cooling water from the outside of the reactor containment vessel 12 above the core melt holding device 21 in the event of a core meltdown accident is provided. A water injection valve 24 is provided in the pedestal space 20 in the middle of the water injection pipe 23. In FIG. 1, water is guided from the outside of the reactor containment vessel 12, but the present invention is not limited to this, and a water source may be provided inside the reactor containment vessel 12.

The core melt holding device 21 has a water resistant airtight container 30 as shown in FIG. The closed container 30 is installed along the upper surface of the pedestal bottom 18 and the inner surface (predetermined installation surface) of the pedestal side wall 19. The closed container 30 includes a substantially circular bottom surface portion 31 extending horizontally on the upper surface of the pedestal bottom portion 18, and a side surface portion 32 extending upward along the periphery of the bottom surface portion 31. The closed container 30 is sealed by the upper lid 33. The upper lid 33 has a recess 33a formed on the upper surface thereof.

For example, synthetic resin or metal is used as the constituent material of the closed container 30, and it is desirable that the material is inert to the components of the core melt (debris). Therefore, synthetic resin or metal is also used as the material of the upper lid 33.

The porous body 35 is housed in the closed container 30. Materials such as alumina and calcium silicate are used as the constituent materials of the porous body 35. The constituent material of the porous body 35 is not limited to these materials, and may be cloth, paper, or the like. The porous body 35 is a material having a large number of small pores, which has good air permeability and a large surface area. The porous body 35 is formed of a substantially circular horizontal portion 36 extending horizontally on the upper surface of the closed container 30 and a side wall portion 37 extending upward along the circumference of the horizontal portion 36. The porous body 35 is impregnated with water before the start of operation of the reactor (when the core meltdown device 21 is installed, when the reactor is periodically inspected, etc.).

The closed container 30 is sealed by the upper lid 33 to prevent water from evaporating from the porous body 35 during the operation of the reactor. The upper lid 33 also has a function of cushioning the impact when the core melt falls. Further, since the porous body 35 retains water for a long period of time, it is desirable to mix the porous body 35 and the closed container 30 with a preservative made of a material that does not chemically affect the water.

Next, the operation of this embodiment will be described.

As shown in FIG. 3, when a core meltdown accident occurs, the core melt 5 falls through the bottom of the reactor pressure vessel 10. The core melt 5 melts the upper lid 33 of the closed container 30 of the core melt holding device 21, and the core melt 5 comes into contact with the porous body 35 containing water. The heat of the core melt 5 is removed by evaporation of water contained in the porous body 35. Therefore, while water is present in the porous body 35, the temperature of the porous body 35 is maintained at about the boiling temperature of water. As a result, the core melt 5 can be held by the porous body 35 without melting the porous body 35 as shown in FIG.

After a certain period of time in which water is present in the porous body 35, the temperature of the dried portion of the porous body 35 rises and melts, so that the porous body 35 is eroded. However, if water is injected from the water injection pipe 23 before the porous body 35 runs out of water, the water permeates into the porous body 35, and erosion of the porous body 35 by the core melt 5 can be prevented. More specifically, the injected water permeates the porous body 35 from the portion where the upper lid 33 is damaged by the impact or heat of the fall of the core melt 5.

Specifically, for example, it is assumed that it takes 10 minutes from the fall of the core melt 5 to the injection of water. If the decay heat of the core melt 5 is 10 MW, the amount of evaporated water required to hold the core melt 5 is 2.66 × 10 ³ kg from the latent heat of water. Since the density of water at 100 ° C. is about 960 kg / m ³ , 2.77 ^{m 3} of water needs to be evaporated.

Assuming that the inner diameter of the pedestal 17 is 6 m and the porosity of the porous body 35 is 0.7, the porous body 35 having a thickness (height in the vertical direction) of about 14 cm may be used. In reality, not all water is effectively used, so it is necessary to set the thickness of the porous body 35 with a margin. However, it can be seen that holding the core melt 5 without injecting water for about 10 minutes can be sufficiently coped with by the realistic thickness of the porous body 35.

As described above, according to the present embodiment, the closed container 30 is installed on the predetermined installation surface, the porous body 35 is housed in the closed container 30, and the porous body 35 contains water. The core melt 5 can be cooled by the water contained in the porous body 35 even before the cooling water for cooling the melt 5 is injected. As a result, it is possible to improve the cooling performance of the core melt 5 before injecting the cooling water, and by extension, the holding function of the core melt 5 can be improved.

Further, the core melt holding device 21 is required to realize high cooling performance with a material quantity reduction and an inexpensive material from the viewpoints of manufacturability, maintainability, economy and the like. According to this embodiment, there is no significant increase in physical quantity. Further, it becomes possible to provide a core melt holding device 21 capable of reducing or eliminating expensive sacrificial materials and heat-resistant materials as compared with a structure that can withstand erosion only with sacrificial materials and heat-resistant materials.

Further, according to the present embodiment, since the recess 33a is formed in the upper lid 33 of the closed container 30, the core melt 5 can be reliably held when the core melt 5 falls.

Further, according to the present embodiment, the porous body 35 may be impregnated with water in advance before the start of operation of the nuclear reactor, and the porous body 35 may be cooled without detecting a sign or occurrence of an accident, controlling the amount of water injection, or the like. Performance can be improved.

(Modified example of the first embodiment)
A modified example of the first embodiment will be described with reference to FIG. In this modification, the water injection pipe 23 is directly connected to the closed container 30, and water is directly injected into the closed container 30. According to the configuration of this modification, water can be reliably supplied to the porous body 35 regardless of the state of the upper lid 33 after dropping.

Here, the first embodiment and the present modification may be used together. More specifically, the water injection pipe 23 may branch in the middle, one branch pipe may inject water from above the core meltdown device 21, and the other branch pipe may be directly connected to the closed container 30. good. As a matter of course, the water injection pipe 23 for injecting water from above the core melt holding device 21 and the water injection pipe 23 directly connected to the closed container 30 may be provided as independent piping systems.

(Second Embodiment)
FIG. 6 is a schematic vertical cross-sectional view showing an enlarged view of the core meltdown device of the second embodiment. The same or corresponding parts as those in the first embodiment are designated by the same reference numerals, and duplicated description will be omitted, and configurations and operations different from those in the first embodiment will be described. The same applies to other embodiments and modifications.

As shown in FIG. 6, in the present embodiment, a plurality of divided porous bodies 35 are spread along the upper surface of the bottom surface portion 31 of the closed container 30 and the inner surface (predetermined installation surface) of the side surface portions 32. There is. Each porous body 35 is formed in a block shape.

When the upper surface of the bottom surface portion 31 is substantially circular as a whole, the upper surface shape of the porous body 35 may be made trapezoidal, for example, and arranged so as to be circular as a whole. In this case, for example, a regular polygonal columnar porous body 35 (not shown) may be arranged at the center in the radial direction.

Therefore, in the present embodiment, after the bottom surface portion 31 and the side surface portion 32 of the closed container 30 are installed in the pedestal 17, a plurality of porous bodies 35 are arranged in the closed container 30. Then, after the porous body 35 is impregnated with a predetermined amount of water, the opening of the closed container 30 is sealed by the upper lid 33. The upper lid 33 functions to prevent the evaporation of water contained in the plurality of porous bodies 35 at normal times, and also considers the impact when the core melt 5 is dropped and the worker working on the upper lid 33. It suffices as long as it is the strength given.

In the present embodiment, when the core melt holding device 21 is installed in the pedestal 17, the porous body 35 divided into a plurality of parts can be carried into the closed container 30 and installed. Therefore, in addition to the effect of the first embodiment, it becomes easy to add to the existing nuclear facility.

(Modified example of the second embodiment)
FIG. 7 is a schematic vertical cross-sectional view showing an enlarged core melt holding device of a modified example of the second embodiment.

As shown in FIG. 7, in this modified example, the porous body 35 is divided into a plurality of parts and is installed in multiple layers in the vertical direction. These porous bodies 35 are formed in a block shape. The porous bodies 35 of the upper and lower layers are alternately arranged so as not to be in the same position in the vertical direction.

As described above, according to the present modification, since the porous body 35 is divided into a plurality of parts and is installed in multiple layers in the vertical direction, in addition to the effect of the second embodiment, each porous body 35 is formed. It is possible to reduce the size of 35. This makes it easier to carry in the porous body 35.

(Third Embodiment)
FIG. 8 is a schematic vertical cross-sectional view showing an enlarged view of the core meltdown device of the third embodiment.

As shown in FIG. 8, in this embodiment, in addition to the configuration of the second embodiment, each porous body 35 holds a tank (water tank) 40 inside. Water or a water absorbing material containing water is housed in these tanks 40. As the constituent material of the tank 40, for example, a synthetic resin or metal is used as in the closed container 30, and it is desirable that the material is inert to the core melt 5.

In this embodiment, since the tank 40 contains water or a water absorbing material containing water, the porous body 35 does not have to contain water.

Further, although the example in which the porous body 35 and the tank 40 of the present embodiment are each divided into a plurality of parts is shown, the present invention is not limited to this, and the porous body 35 and the tank 40 may be integrally formed. Further, the structure covering the upper part of the tank 40 may have a lid structure so that the tank 40 can be installed after the porous body 35 is installed. In that case, the lid does not have to be a porous body. Further, the inside of the tank 40 may be exposed without installing a lid on the upper part of the tank 40.

Next, the operation of this embodiment will be described.

When a core meltdown accident occurs and the core melt 5 falls to the upper part of the core melt holding device 21, the water in the tank 40 absorbs heat due to its heat conduction, expands in volume, and then starts boiling. Then, even if the upper surface of the tank 40 melts, the core melt 5 falls into the tank 40, is submerged in water, and is cooled.

As described above, for example, it takes 10 minutes from the fall of the core melt 5 to the injection of water. If the decay heat of the core melt 5 is 10 MW, the amount of evaporated water required to hold the core melt 5 is 2.66 × 10 ³ kg from the latent heat of water. Since the density of water at 100 ° C. is about 960 kg / m ³ , 2.77 ^{m 3} of water needs to be evaporated.

If the inner diameter of the pedestal 17 is 6 m, the water depth per area of the pedestal bottom 18 may be about 10 cm. Therefore, when holding for 10 minutes until water injection, the water depth of the tank 40 may be 0.9 m or less. It is expected to be established.

Further, if water injection is started from the water injection pipe 23 and the porous body 35 is impregnated with water before the water in the tank 40 is completely evaporated, the core melt 5 does not reach the pedestal bottom 18. , Cooled and held by the porous body 35.

In this embodiment, instead of the water contained in the tank 40, a water-absorbing material such as a super absorbent polymer, cloth, or paper that has sufficiently absorbed water may be used.

As described above, according to the present embodiment, since the porous body 35 holds the tank 40 inside and the water or the water absorbing material containing water is housed in the tank 40, the core melts even before the injection of the cooling water. It becomes possible to further improve the cooling performance for the object 5.

Further, as a modification of the present embodiment, the tank 40 may be configured so that its lower portion is damaged by a predetermined internal pressure. More specifically, the tank 40 is sealed in the installation before the core melt 5 falls, and the sealing is broken by the increase in internal pressure, and a safety device (not shown) that leaks water inside. ) Is provided. As this safety device, for example, a fusible plug or the like is used.

With this configuration, the internal pressure of the tank 40 rises due to the volume expansion and boiling of water, and the tank 40 is damaged. Then, since the water in the tank 40 permeates into the porous body 35, it is possible to shift to the state described in the first embodiment and prevent the core melt 5 from reaching the pedestal bottom 18. can.

(Fourth Embodiment)
FIG. 9 is a schematic enlarged vertical cross-sectional view showing an enlarged main part of the core melt holding device of the fourth embodiment.

As shown in FIG. 9, in this embodiment, in addition to the configuration of the first embodiment, a plurality of communication flow paths 41 communicating in the horizontal direction are provided in the porous body 35 in the vertical direction. These communication flow paths 41 are connected to the water injection flow path 42. The water injection flow path 42 is connected to the water injection pipe 23. That is, the inflow port of the water injection flow path 42 and the water injection port of the water injection pipe 23 are connected. Therefore, each communication flow path 41 communicates with the water injection pipe 23 through the water injection flow path 42.

Each communication flow path 41 is arranged vertically and horizontally in the horizontal direction. The water injection flow path 42 is provided in the vertical direction in the side wall portion 37 and the horizontal portion 36 of the porous body 35.

As for the communication flow path 41, for example, when the porous body 35 is a block of alumina, calcium silicate, or the like, the communication flow path 41 may be provided by excavation or the like. Alternatively, the porous body 35 is laminated so as to form a gap by providing a downward convex portion on the block placed on the lower block as a stack of a plurality of blocks, and the gap is formed. The communication flow path 41 may be used.

In the state shown in FIG. 3 described in the first embodiment, the water in the porous body 35 in contact with the core melt 5 evaporates, but the water having a high water level in the porous body 35 is not present. , Flows downward due to low water level due to gravity.

However, since the flow resistance of the porous body 35 is large, the flow speed of water is slow, and the distribution of the dropped core melt 5 on the core melt holding device 21 causes a bias in the position where cooling is required.

Therefore, by providing the communication flow path 41 in the porous body 35 as in the present embodiment, the speed of water supply to the contact portion with the core melt 5 is increased. As a result, the water contained in the porous body 35 can be effectively used to cool the core melt 5.

Further, in the present embodiment, the water injection flow path 42 is provided in the porous body 35, and the inflow port of the water injection flow path 42 and the water injection port of the water injection pipe 23 are connected to each other. Therefore, the water injection after the start of water injection quickly flows into the porous body 35 through the communication flow path 41 communicating with the water injection flow path 42. As a result, the porous body 35 between the core melt 5 and the pedestal 17 is filled with water, and the core melt 5 is cooled and held. As a result, the pedestal 17 can be protected.

As described above, according to the present embodiment, by providing the communication flow path 41 in the porous body 35, in addition to the effect of the first embodiment, the water in the porous body 35 for cooling the core melt 5 is provided. It will be possible to make effective use of it.

Further, according to the present embodiment, since the water injection pipe 23 communicates with the communication flow path 41 through the water injection flow path 42, water can be quickly supplied into the porous body 35. As a result, the cooling effect on the core melt 5 can be enhanced.

(Fifth Embodiment)
FIG. 10 is a schematic vertical cross-sectional view showing an enlarged view of the core meltdown device of the fifth embodiment.

As shown in FIG. 10, in this embodiment, in addition to the configuration of the first embodiment, a plurality of metal lattice plates 43 are horizontally installed inside the porous body 35 and in the vertical direction. .. The metal lattice plate 43 may be, for example, a punching plate or a metal member in which a plurality of metal rods are arranged in parallel or in a lattice pattern, and is not limited thereto. However, it is desirable that water can pass through the metal grid plate 43 in the vertical (vertical) direction when the metal grid plate 43 is installed.

In the state shown in FIG. 3 described in the first embodiment, the water in the porous body 35 in contact with the core melt 5 evaporates, but the water having a high water level in the porous body 35 is present. , Flows downward due to low water level due to gravity.

However, since the flow resistance of the porous body 35 is large, the flow speed of water is slow, and there is a possibility that the water supply to the contact portion between the core melt 5 and the porous body 35 cannot be made in time.

Therefore, by providing the porous body 35 with a metal lattice plate 43 having a higher thermal conductivity than the porous body 35 as in the present embodiment, the heat generated by the core melt 5 is diffused in the horizontal direction, and the inside of the porous body 35. Reduce the bias of water evaporation. As a result, the water contained in the porous body 35 for cooling the core melt 5 can be effectively used for cooling the core melt 5.

As described above, according to the present embodiment, by providing the metal lattice plate 43 in the porous body 35, the water in the porous body 35 is effective for cooling the core melt 5 as in the fourth embodiment. It will be possible to utilize it.

(Sixth Embodiment)
FIG. 11 is a schematic vertical cross-sectional view showing an enlarged view of the core meltdown device of the sixth embodiment.

As shown in FIG. 11, in this embodiment, in addition to the configuration of the first embodiment, the porous body 35 is covered with the porous block 44 which is divided into a plurality of parts and contains water. .. The porous body 35 has an integral structure as in the first embodiment.

When the porous block 44 is not spread on the upper surface of the porous body 35, a sudden heat load is applied to the core melt holding device 21 immediately after the core melt 5 falls, and a sudden temperature change occurs. Therefore, the upper surface of the porous body 35 expands due to a rapid temperature rise, and a large thermal stress is generated.

Even if cracks are formed in the porous body 35, the core melt 5 immediately solidifies when it invades the cracks in the porous body 35 containing water. Therefore, although it is considered that the core melt 5 does not easily penetrate into the inside of the porous body 35, the crack itself of the porous body 35 is not preferable.

Therefore, in the present embodiment, the excessive thermal stress is alleviated by laying the porous block 44 on the upper surface having a large heat load or laying the crushed porous body.

As described above, according to the present embodiment, since the porous block 44 divided into a plurality of pieces and containing water is spread on the upper surface of the porous body 35, in addition to the effect of the first embodiment, it is excessive. Thermal stress can be relieved.

In this embodiment, sand, gravel, or the like containing water may be layered on the upper surface of the porous body 35 instead of the divided porous block 44.

(Modified example of the sixth embodiment)
FIG. 12 is a schematic vertical cross-sectional view showing an enlarged core melt holding device of a modified example of the sixth embodiment.

As shown in FIG. 12, in this modified example, a water absorbing member 45 that has absorbed water in advance is laid on the upper surface of the porous body 35. The water absorbing member 45 is made of, for example, a wet cloth. The water absorbing member 45 is not limited to cloth, but a soft material that absorbs water, such as paper or sponge, can provide the same effect.

As described above, according to the present modification, by laying the water absorbing member 45 made of, for example, a wet cloth on the upper surface of the porous body 35, the same effect as that of the sixth embodiment can be obtained.

(7th Embodiment)
FIG. 13 is a schematic vertical cross-sectional view showing an enlarged view of the core meltdown device of the seventh embodiment.

The amount of water that can be retained in the porous body 35 depends on the volume and porosity of the porous body 35. In order to retain the core melt 5 for a long period of time, it is necessary to increase the volume of the porous body 35 and use one having a higher porosity. However, there is an upper limit to the porosity, and the volume of the porous body 35 is also restricted by the installation location.

In order to avoid these restrictions, as shown in FIG. 13, in the present embodiment, a water supply pipe 46 communicating with the inside of the porous body 35 is installed, and a water supply tank 47 as a water source is connected to the water supply pipe 46. There is. The water supply tank 47 is separated from the external space except for communicating with the inside of the porous body 35 through the water supply pipe 46. The water supply tank 47 is installed on, for example, the pedestal side wall 19.

With this configuration, the water supply tank 47 holds water during normal operation in which the airtightness of the closed container 30 is maintained. When the core melt 5 falls into the closed container 30, the heat of the core melt 5 melts the closed container 30 and makes it less airtight, the water in the porous body 35 evaporates, and the water level in the closed container 30 drops. do.

Therefore, in the present embodiment, when the closed container 30 is melted and is no longer airtight, water is allowed to flow from the water supply tank 47 into the closed container 30 through the water supply pipe 46, and the water is automatically made into the porous body 35. I try to supply it. As a result, the water level in the porous body 35 can be pushed up.

Further, the surface of the water supply tank 47 on the falling side of the core melt 5 is heated by the radiant heat from the core melt 5. Then, the temperature of the water in the water supply tank 47 rises, and the pressure in the water supply tank 47 also rises, thereby promoting the discharge of the water in the water supply tank 47 and supplying the water to the porous body 35.

By such an action, the porous body 35 can secure water having a volume and a porosity or more. As a result, the porous body 35 can hold the core melt 5 for a long time. Specifically, the time until the static containment cooling system (PCCS: Passive Containment Cooling System) is started, the cooling water is supplied from the water injection pipe 23, or the water is injected from the outside, the core melt 5 is charged. It becomes possible to hold.

As described above, according to the present embodiment, the water supply pipe 46 communicating with the porous body 35 is provided, and since the water supply pipe 46 is connected to the water supply tank 47, the porous body 35 has a volume and a porosity or more. Water can be secured, and the porous body 35 can hold the core melt 5 for a long time.

(8th Embodiment)
FIG. 14 is a schematic vertical cross-sectional view showing an enlarged configuration of a nuclear facility to which the core meltdown device of the eighth embodiment is applied.

In the present embodiment, instead of the water supply tank 47 of the seventh embodiment, the water in the pressure suppression pool (suppression pool) 14 shown in FIG. 14 is supplied to the core meltdown device 21 as a water source.

As described above, the amount of water that can be retained in the porous body 35 depends on the volume and porosity of the porous body 35. In order to retain the core melt 5 for a long period of time, it is necessary to increase the volume of the porous body 35 and use one having a higher porosity. However, there is an upper limit to the porosity, and the volume of the porous body 35 is also restricted by the installation location.

In order to avoid these restrictions, as shown in FIG. 14, in the present embodiment, when the water level of the pressure suppression pool 14 as the water supply tank is higher than the core meltdown device 21, the pressure suppression pool 14 and the inside of the closed container 30 of the core melt holding device 21 are connected by a water supply pipe 46.

Since the closed container 30 has a watertight structure, the water in the pressure suppression pool 14 does not leak out. When the core melt 5 falls onto the core melt holding device 21 and the closed container 30 is no longer watertight, the water in the pressure suppression pool 14 is supplied to the core melt holding device 21 through the water supply pipe 46.

With this configuration, a large amount of water source can be secured for the porous body 35 of the closed container 30. Therefore, the core melt 5 can be held on the core melt holding device 21 for a long time, and the pedestal 17 can be protected.

In this embodiment, an on-off valve 48 is provided in the middle of the water supply pipe 46. The on-off valve 48 may be opened before the start of operation, opened when the core melt 5 is expected to fall, or the on-off valve 48 may be used as a melting valve. In the case of the melting valve in this way, when the core melt 5 falls, it is heated by the radiant heat from the core melt 5 and the melting valve is automatically opened.

As described above, according to the present embodiment, the pressure suppression pool 14 and the inside of the closed container 30 of the core meltdown device 21 are connected by the water supply pipe 46, so that the porous body 35 is similar to the seventh embodiment. Can hold the core melt 5 for a long time.

(Other embodiments)
Although each embodiment of the present invention has been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other embodiments, and various omissions, replacements, changes, and combinations can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, as well as in the scope of the invention described in the claims and the equivalent scope thereof.

In each of the above embodiments, if the closed container 30 is made of a flexible material such as synthetic resin, the closed container 30 may be folded and carried into the pedestal 17 and then expanded and installed.

Further, the features of the second embodiment, its modifications, and the third to eighth embodiments can be appropriately combined and implemented.

1 ... Nuclear facility, 5 ... Core melt, 10 ... Reactor pressure vessel, 11 ... Core, 12 ... Reactor containment vessel, 13 ... Dry well, 14 ... Pressure suppression pool (water supply tank), 15 ... Wet well, 16 ... Vent pipe, 17 ... pedestal, 18 ... pedestal bottom, 19 ... pedestal side wall, 20 ... pedestal space, 21 ... core melt holding device, 23 ... water injection pipe, 24 ... water injection valve, 30 ... closed container, 31 ... bottom part , 32 ... side surface, 33 ... top lid, 33a ... recess, 35 ... porous body, 36 ... horizontal part, 37 ... side wall, 40 ... tank (water tank), 41 ... communication flow path, 42 ... water injection flow path, 43 ... metal lattice plate (metal member), 44 ... porous block, 45 ... water absorbing member, 46 ... water supply pipe, 47 ... water supply tank, 48 ... on-off valve

Claims (11)

A core melt holding device that is installed below the nuclear pressure vessel in the containment vessel that houses the nuclear pressure vessel that houses the core and holds the core melt that occurs when the core melts in the event of an accident. hand,
A closed container installed on a predetermined installation surface and
A porous body that is stored in the closed container and contains water,
The porous body is a core melt holding device installed in multiple layers in the vertical direction. The core melt holding device according to claim 1, wherein the porous body is divided into a plurality of parts. The core meltdown device according to claim 1 or 2 , further comprising a water tank installed in the porous body and containing water. The core melt holding device according to claim 3 , wherein the water tank is provided with a safety device in which the sealed state is destroyed by an increase in internal pressure. The core melt holding device according to claim 1 or 2 , further comprising a plurality of porous blocks that are spread on the upper surface of the porous body and have absorbed water in advance. The core melt holding device according to claim 1 or 2 , further comprising a water absorbing member which is laid on the upper surface of the porous body and has absorbed water in advance. The core melt holding device according to any one of claims 1 to 6 , wherein a communication flow path through which water flows is provided in the porous body. The core melt retention according to any one of claims 1 to 6 , wherein a metal member having a higher thermal conductivity than the porous body is embedded in the porous body in the horizontal direction. Device. The core meltdown device according to any one of claims 1 to 8 , further comprising a water supply pipe connected to the porous body and supplying water from a water source into the porous body. The core meltdown device according to claim 9 , wherein the water source is a pressure suppression pool installed in the reactor containment vessel. With the core
Reactor pressure vessel containing the core and
A core melt holding device installed below the reactor pressure vessel in the reactor pressure vessel and holding a core melt generated when the core melts in the event of an accident.
It is a nuclear facility that has
The core melt holding device is
A closed container installed on a predetermined installation surface and
A porous body that is stored in the closed container and contains water,
The porous body is a nuclear facility installed in multiple layers in the vertical direction.

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