JP6775382B2 - Core catcher - Google Patents

Description

The present invention relates to a core catcher installed in a reactor containment vessel.

The reactor is equipped with engineering safety equipment consisting of a reactor containment facility and an emergency core cooling facility that prevent the emission of fission products due to fuel damage in the reactor. For example, in a light water reactor, the containment facility has a first boundary of fuel rods with sealed nuclear fuel pellets and a second boundary of a reactor pressure vessel containing a core loaded with fuel assemblies that bundle fuel rods. It is composed of triple boundaries of the airtight reactor containment vessel that houses the reactor pressure vessel. In addition, the emergency core cooling system cools the core with a high-pressure water injection system, an automatic decompression system, a core spray system, and a low-pressure water injection system when the coolant is lost. Even if the external power supply is lost due to an earthquake, wind and flood damage, etc., the emergency core cooling system will still function due to the emergency generator. However, in the unlikely event that the emergency core cooling system does not operate and a severe accident occurs in which the core melts, the core melt (debris) penetrates the bottom of the reactor pressure vessel and the lower section of the reactor containment vessel. It is necessary to suppress the emission of fission products even if they fall into the reactor. On the other hand, for example, there is a method in which a heat-resistant core catcher is placed on the floor surface of the reactor containment vessel to receive and cool debris having a temperature of 2000 K to 2500 K falling from the reactor pressure vessel.

By the way, debris generates decay heat even after the reactor is shut down, so even a core catcher with heat resistance needs cooling to remove the decay heat. As described in Non-Patent Document 1, accident management (AM) measures for strengthening the safety function of a nuclear reactor have been proposed based on the knowledge obtained in the past severe accidents. As a measure against AM, in order to cool debris that is hot and the temperature rises due to decay heat, the method of injecting water from the condensate storage tank into the lower section of the containment vessel and the lower part of the containment vessel for spray water to the containment vessel drywell. There is a method that uses the inflow to the containment. Patent Document 1 discloses a technique of applying cooling water to the outer periphery of a core catcher to cool the water. In Patent Document 2, an upper support core catcher is provided in the pedestal space below the reactor pressure vessel, and thermal stress applied to the vessel by debris, specifically deformation due to thermal expansion and creep, is applied in the lower space of the vessel, which is the free end. Absorb to prevent damage to the core catcher. Further, Patent Document 3 describes a technique of arranging a high melting point material in the inner surface layer and a low thermal conductive material in the intermediate layer for heat resistance and heat insulation in order to maintain the soundness of the high ductility member of the outermost layer of the core catcher wall. Has been done.

JP-A-59-13987 Japanese Unexamined Patent Publication No. 2010-271261 Japanese Unexamined Patent Publication No. 2008-241657

Japan Nuclear Energy Safety Organization, "1", JNES / SAE05-061, 05 Solution Report-0061, pp. 3-1-3-21, 2004 Bal Raj Sehgal, Natural convection heat convection heat in a stratified melt with volume with heat generation, Proc. MASCA Seminar 2004, Aix-en-Provence, France, 10-11 June 2004 F. B. Cheung, et al. , Critical Heat Flux (CHF) Phenomenon on a Downward Facing Curved Surface, NUREG / CR-6507, p. 17 (1997) Masanori Kadode, et al., "Limited Heat Flux in Pool Boiling on a Vertical Heating Plane", JSME Proceedings (Vol. B), Vol. 63, No. 605, pp. 256-260 (1997-1) Tatsu Oka, "Basics of Plastic Injection Molding <Part 4>", Skills and Technology, No. 4, 2000, Japan Organization for Employment of the Elderly, Disabled, and Job Seekers, Vocational Ability Development College Infrastructure Development Center, 2000

FIG. 1 shows a vertical cross-sectional view of a hemispherical core catcher whose outer circumference is filled with cooling water. Liquid debris that falls from the upper reactor pressure vessel creates natural convection due to heat generation and cooling inside the core catcher. Debris retention and cooling conditions by the core catcher become strict when a large amount of debris falls.
Generally, the natural convection heat transfer coefficient is high for vertical plates and top heating plates, and low for bottom heating plates. For this reason, the debris from the lower part to the central part where the amount of cooling is small causes an ascending flow due to the decrease in density due to the temperature rise, and the wall surface is cooled well and the density increases and decreases. Since the high temperature debris that has risen in the center of the debris collides with the side surface of the core catcher, the heat flux on the side wall (when the hemispherical core catcher is filled with debris, the position at an angle of 90 degrees in FIG. 1) is high. On the other hand, the heat flux at the bottom of the core catcher (position at an angle of 0 degrees in FIG. 1) decreases. In the measurement of the heat flux with respect to the cross section of the semicircular wall and the inclination angle of the internal melt, including the experiment using the eutectic salt shown in FIG. 2 (from Non-Patent Document 2) as the working fluid, the inclination angles are 0 degrees and 90 degrees. A difference in heat flux (standardized value based on the average heat flux) of up to 5 times has been reported. In addition, the increase in heat flux is remarkable in the region where the inclination angle of the wall surface exceeds 30 degrees. On the other hand, on the outer surface of the core catcher, a high heat flux causes boiling and heat is transferred to the cooling water. The boiling steam generated at the bottom of the core catcher tends to stay because the buoyancy vector intersects the flow direction, and the wall surface is covered with steam, which reduces the heat transfer coefficient. At the side wall, the vector of the buoyancy of boiling steam coincides with the flow direction, so the steam easily separates from the wall surface, and the wall surface comes into contact with the cooling water, increasing the heat transfer coefficient. In addition, the heat flux (marginal heat flux) that causes a film boiling state in which the wall surface is covered with steam and the heat transfer coefficient is greatly reduced also has a low bottom and a high side wall. In the evaluation of Non-Patent Document 3 shown in Equation 1, the critical heat flux Qchf at the bottom of the semicircular container (inclination angle Θ: 0 ° of the wall surface) is 500 kW / m2 and the side wall (side wall) under the steady heating conditions of the natural circulation cooling system. The maximum value of the critical heat flux is 1500 kW / m2 at the inclination angle Θ: 90 °), and the difference between the critical heat flux at the inclination angle of 0 degree and 90 degrees is about 3 times as in the tendency of the heat flux of Non-Patent Document 2. is there. Here, the evaluation formula of the critical heat flux Qchf is not limited to the formula 1, and an appropriate formula may be selected depending on the heat transfer system, the type of fluid, and the atmospheric conditions. For example, in Non-Patent Document 3, in the case of the pool boiling system, the critical heat flux Qchf at an inclination angle of 0 to 5 degrees is 300 kW / m2, and in the case of a vertical flat plate (inclination angle of 90 °), it is described in Non-Patent Document 4. The critical heat flux Qchf is 1400 kW / m2 when the evaluation formula is used.

(Equation 1) Qchf (kW / m2) = 500 + 13.3 × Θ (0 ° <Θ <15 °),
Qchf (kW / m2) = 540 + 10.7 × Θ (15 ° <Θ <90 °)

FIG. 3 shows the temperature profile from the cooling water to the debris across the core catcher wall. The high and low temperatures are expressed in the vertical direction. Here, L is the core catcher wall thickness (m), Td is the debris temperature (K), Ti is the core catcher wall inner surface temperature (K), To is the core catcher wall outer surface temperature (K), and Tm is the core catcher. The melting point of the wall (K), Tw is the cooling water temperature (K), ΔT is the wall superheat degree (K) of boiling heat transfer, Qb is the heat flux of boiling heat transfer (W / m2), and Qc is the heat flux of heat conduction. (W / m2) and Qn represent the heat flux of natural convection heat transfer (W / m2) when the debris is liquid, and the heat flux of heat conduction (W / m2) when the debris is solid. Heat is transferred from the cooling water to the outer surface of the core catcher wall by boiling heat transfer, and the outer surface temperature To becomes a value higher than the water temperature by the degree of superheat ΔT. Heat is transferred inside the core catcher wall by heat conduction. From debris to the inner surface of the core catcher wall, heat is transferred by natural convection heat transfer when the debris is liquid, and by heat conduction when the debris is solid. Since water has a large specific heat and latent heat of vaporization and good heat transfer, the amount of heat transfer is dominated by boiling heat transfer on the outer surface of the core catcher wall. When the heat transfer amount is balanced in this heat transfer system and the quasi-steady state is reached, the heat fluxes Qb, Qc, and Qn become equal.

Given the heat flux Qc, the outer surface temperature To of the core catcher wall, the thermal conductivity R of the core catcher material, and the melting point Tm, the wall thickness L where the inner surface temperature reaches the melting point according to the heat conduction equation (Equation 2). Is required. Equation 2 is a modification of the general equation for heat conduction on the wall surface.

(Equation 2) L = R × (Tm-To) / Qc

In the above equation, when the initial core catcher wall thickness L is increased, Qc decreases (assuming that Qc does not change, it is equivalent to an increase in the core catcher wall inner surface temperature Ti), and the core catcher inner wall surface that received debris It shows that the wall thickness is reduced by melting beyond the melting point. From the shape of the equation, the higher the thermal conductivity of the material and the lower the heat flux, the smaller the amount of wall thinning and the thicker the inner wall surface after melting. As long as the heat flux on the outer surface of the core catcher does not reach the limit heat flux and shift to film boiling, the temperature balance shown in Equation 2 is maintained.

When the heat flux distribution shown in FIG. 2 is applied to Equation 2, the cross section of the core catcher is relatively thick up to the bottom 30 degrees (region A in FIG. 4) as shown in FIG. 4, and the side wall portion exceeds 30 degrees. Becomes thinner (region B in FIG. 4). The minimum thickness at which the core catcher is sound is the value when the heat flux reaches the critical heat flux, and from Equation 2, the higher the heat flux, the thinner the minimum thickness. For example, in a stainless steel core catcher, the limit heat flux is 1500 kW / m2 at an inclination angle of 90 degrees, the outer surface temperature is 400 K (assuming a degree of superheat with cooling water of 30 ° C.), the thermal conductivity of stainless steel is 16 W / mK, and that of stainless steel. Substituting the melting point of 1700 K, the thickness of the wall surface of the core catcher having an inclination angle of 90 degrees after thinning becomes about 14 mm from Equation 2. On the other hand, at the bottom, when the inclination angle is 0 degrees and the critical heat flux of 500 kW / m2 is substituted, it is about 42 mm. As shown in FIG. 2, this thickness distribution includes the conditions below the critical heat flux because the amount of heat transfer on the wall surface is about 3.5 times different between the inclination angles of 0 degrees and 90 degrees. It is considered that the thickness differs by about 3 to 3.5 times between the bottom and the side wall.

Based on the above evaluation, in a core catcher whose outer circumference is filled with cooling water, the wall material is a stainless steel case and the side wall is reduced to 20 mm or less at the minimum, so the total amount of the core weighing a hundred and several tens of tons at high temperatures near the melting point Assuming a case of holding, it is considered necessary to reinforce the wall surface.
In response to such a problem, Patent Document 2 provides a core catcher for supporting the upper part in the pedestal space, allows expansion and creep deformation of the container due to debris, and absorbs the deformation in the lower space of the container which is a free end. However, when the side wall of the core catcher is thinned, tensile stress is applied downward due to the weight of the debris, which may cause further wall thinning or breakage of the side wall.
In general, it is effective to make the side wall portion have a rib structure as shown in Non-Patent Document 5 as a reinforcing measure for preventing such progress of wall thinning and breakage of the side wall portion. In particular, in the reinforcement of the core catcher, the vertical ribs are effective and reduced because the shape of the thinned portion of the side wall is formed in a part of the vertical cross section in the height direction (the inclination angle from the vertical axis is above 30 degrees). Lateral ribs are also needed to support the circumferential elongation of the core catcher wall due to meat and temperature rise.

FIG. 5 shows a horizontal cross-sectional view of the wall when vertical ribs are attached to support the load on the wall surface. As explained with reference to FIG. 3, the increase in the wall thickness due to the joining of the ribs is the same as the case where the wall thickness L is increased in Equation 2, and when the wall is thicker than the heat flux removal heat flux, FIG. As shown in (1), the wall thickness through which the heat of debris passes increases apparently (the broken line indicates the distance corresponding to the wall thickness after thinning with respect to the wall surface in contact with the cooling water). As a result, as shown in FIG. 5 (2), a defect may occur due to the thinning of the inner wall surface, which may lead to a decrease in the wall surface strength of the core catcher.
When the horizontal ribs are attached, not only is the inner wall surface thinned to cause defects as in the vertical ribs, but also the rise along the outer wall surface driven by the density difference due to the buoyancy of the generated steam as shown in FIG. The flow is blocked by the lateral ribs as an obstacle. For this reason, cooling of the wall in the wake portion of the lateral rib is hindered, the heat transfer form of the wall surface shifts to film boiling, and the wall may be melted and damaged.
As shown in Fig. 1, the flow of cooling water filled on the outside of the core catcher wall is such that the steam generated by the nucleate boiling at the bottom gradually moves from the slightly inclined bottom to the side with a large inclination angle along the wall surface. Then, add more nucleate boiling steam and ride on the flow accelerated by buoyancy and escape upward. If vertical ribs are provided from the bottom in such a flow state, the vertical ribs intersect at the lowest point of the hemisphere, so that a space partitioned at the vertices of the intersecting ribs is formed. There is no problem if the steam generated at the bottom moves to the open side of the intersecting ribs, but if it moves to the apex side of the intersecting ribs and stays and accumulates, the critical heat flux may decrease and the membrane may boil. There is. As mentioned above, the fibers to the membrane boiling lead to melting and thinning of the core catcher wall.

Next, in Patent Document 3, since the heat insulating member and the heat insulating member enhance the heat insulating property of the debris, the debris temperature rises due to the decay heat if there is no other cooling source. In addition, since the heat-resistant member and the heat-insulating member overlap to make the wall thicker, the inner wall temperature corresponds to the heat-removing heat flux corresponding to the decay heat according to the characteristics shown in Equation 2, compared to the case where the heat-resistant member and the heat-insulating member are not arranged. Increase. When the debris temperature in contact with the heat-resistant material reaches the melting point of the heat-resistant member, the heat-resistant member melts, and then the heat-resistant member and the outer layer member melt. Further, if the melting point of the heat insulating member is low, the heat insulating member may melt before the heat resistant member melts.
When holding a heat-generating substance with a high vaporization temperature such as debris, even if heat-insulated with a heat-resistant material, the temperature rises unless the amount of heat removed is balanced with the amount of heat generated, the heat-resistant material melts, and the heat load on the wall surface increases. .. In addition, even if the wall is thickened, the wall melts until the temperature of the inner and outer walls is balanced between the amount of heat removed and the amount of heat generated. Therefore, the semi-steady wall thickness is the minimum value that depends on the physical properties such as the thermal conductivity of the member. It will not exceed. For this reason, it is effective to promote heat removal so that the debris temperature drops rather than to insulate, or to consume the heat of debris to melt the sacrificial material.
On the other hand, when the debris falls or in a transient state until the semi-steady heat balance is reached, when the initial debris temperature is high, the heating amount of the core catcher wall surface is the semi-steady state described with reference to FIG. The amount of heat removed may be exceeded. As a result, the wall thickness may be thinner than the value based on the balance between the amount of heat removed and the amount of heat generated. It is also necessary to prevent such transient heating of the wall surface.

The present invention has been made in view of the above. In the outer surface cooling type core catcher installed in the reactor containment vessel, when a high temperature debris is received, the wall surface of the core catcher is surely cooled and the debris is debris. The purpose is to prevent debris from falling onto the containment vessel floor and prevent damage to the containment vessel by ensuring the structural strength of the wall against erosion.

In order to achieve the above object, the core catcher of the present invention is composed of a core catcher wall surface that receives the heat load of debris and vertical ribs that are joined to the outer wall surface to support the load on the debris wall.
The thickness of the core catcher wall joint in the circumferential direction of the vertical rib is made thinner than the core catcher wall thickness, preferably thinner than the core catcher wall thickness after thinning corresponding to the critical heat flux calculated by Equation 2.
A horizontal rib that supports the vertical rib is provided through a gap with the outer wall surface of the core catcher.
The vertical rib circumferential thickness of the horizontal rib joint portion may be thicker than the vertical rib circumferential thickness of the core catcher wall joint portion.
The core catcher wall is made of a material with high thermal conductivity, high melting point, and high toughness. Specifically, it is composed of stainless steel, carbon steel, tungsten steel, or molybdenum steel.
The core catcher wall has a multi-layer structure, the inner wall is made of a material with high thermal conductivity, high melting point, and high toughness (stainless steel, carbon steel, tungsten steel, or molybdenum steel), and the outer wall is ultra-high thermal conductivity ( It may be made of a material (copper, brass, or aluminum).
A sacrificial material with a melting point lower than that of the wall material is attached to the inside of the core catcher wall surface. Specifically, concrete or silicon dioxide is attached. Further, a sacrificial material having a melting point lower than that of the wall material may be placed inside the core catcher. Specifically, a concrete block or a silicon dioxide block is placed.
In a core catcher whose wall surface is hemispherical, the vertical rib is 30 degrees or less (perimeter in the longitudinal direction is 1/3 from the bottom) or less from the contact point between the vertical axis at the center of the core catcher and the horizontal plane of the hemispherical center axis. It is characterized by joining outer wall surfaces up to 90 degrees (upper end) or more.
A core catcher having a cylindrical wall surface is characterized in that the vertical ribs join the outer wall surface from the bottom of the upper and lower ends of the core catcher to the lower end of the core catcher from below 1/3.
The core catcher mount is characterized in that it supports the vertical axis and the outer wall surface of the core catcher at 30 degrees or less with the contact point between the vertical axis at the center of the core catcher and the horizontal plane of the hemispherical central axis as a base point. Further, the frame of the core catcher is joined to the vertical ribs to support the core catcher. The core catcher pedestal is joined to the lateral ribs to support the core catcher. Further, the core catcher mount is supported by the above combination.
The outer wall surface of the core catcher may be shaped like an outer folding rib that protrudes outward, and a horizontal rib that supports the tip of the outer folding rib via a gap with the outer wall surface of the core catcher may be provided.
Preferably, a flow guide plate having an upward inclination from the outer peripheral side to the inner peripheral side of the vertical rib is joined to the outer wall surface of the core catcher while maintaining a gap in a direction substantially orthogonal to the vertical surface of the vertical rib. Is also good.
A waterproof plate with a central part protruding downward may be joined to the upper end of the core catcher all around. At the upper end of the core catcher, a guide plate that is joined to the upper end of the core catcher wall all around and extends over the space above the lateral rib may be provided.
The outer wall surface of the core catcher may be shaped like an outer folding rib that protrudes outward, and a horizontal rib that supports the tip of the outer folding rib via a gap with the outer wall surface of the core catcher may be provided.

According to the present invention, it is possible to catch the debris falling from the reactor pressure vessel, cool it reliably for a long period of time, and prevent the debris from falling to the floor surface of the reactor containment vessel to prevent damage to the reactor containment vessel. ， Can provide a core catcher that enhances the safety of the reactor.

It is a vertical cross-sectional view which shows the core catcher which concerns on 1st Example of this invention, and the fluid behavior inside and outside the core catcher. It is a numerical graph which shows the heat flux distribution of the core catcher wall surface which concerns on 1st Example of this invention. It is a schematic diagram which shows the temperature profile inside and outside the core catcher wall which concerns on 1st Example of this invention. It is a vertical cross-sectional view which shows the melt thinning behavior of the core catcher wall which concerns on 1st Example of this invention. It is sectional drawing which shows the interaction of melting of a core catcher wall and a rib which concerns on 1st Example of this invention. It is a vertical cross-sectional view which shows the schematic structure of the nuclear reactor to which the core catcher which concerns on embodiment of this invention is applied. It is a bird's-eye view which shows the appearance of the core catcher which concerns on 1st Embodiment of this invention. It is a vertical sectional view and a horizontal sectional view which show the structure of the core catcher which concerns on 1st Example of this invention. It is a horizontal cross-sectional view which shows the vertical rib shape which concerns on 1st Example of this invention. It is a horizontal cross-sectional view which shows the vertical rib shape which concerns on the modification of 1st Example of this invention. It is a vertical sectional view and a horizontal sectional view which show the structure of the core catcher which concerns on 2nd Embodiment of this invention. It is a vertical cross-sectional view which shows the structure of the core catcher which concerns on 3rd Example of this invention. It is a vertical cross-sectional view which shows the structure of the core catcher which concerns on 4th Embodiment of this invention. It is a vertical cross-sectional view which shows the structure of the core catcher which concerns on the modification of 4th Example of this invention. It is a vertical cross-sectional view which shows the structure of the core catcher pedestal which concerns on 5th Embodiment of this invention. It is a vertical cross-sectional view which shows the structure of the core catcher pedestal which concerns on the modification of 5th Example of this invention. It is a vertical cross-sectional view which shows the structure of the core catcher pedestal which concerns on the modification of 5th Example of this invention. It is a vertical sectional view and a horizontal sectional view which represent the vertical rib shape which concerns on 6th Example of this invention. It is a horizontal cross-sectional view which shows the vertical rib shape which concerns on 7th Example of this invention. It is a vertical cross section which represents the structure of the core catcher which concerns on 8th Embodiment of this invention.

<First Example>
FIG. 6 is a vertical cross-sectional view showing a schematic configuration of a configuration example of a nuclear reactor to which the core catcher according to the present embodiment is applied. FIG. 6 illustrates a boiling water reactor. Hereinafter, the case where the present invention is applied to a boiling water reactor will be described, but the present invention is applied to other types of reactors such as light water reactors such as pressurized water reactors, fast breeder reactors, advanced thermal reactors, and HTGRs. It is also applicable to this.

As shown in FIG. 6, the reactor 40 includes a reactor pressure vessel (pressure vessel) 1, a reactor containment vessel (containment vessel) 41, and a reactor building 42. The reactor building 42 is provided on the outer peripheral side of the containment vessel 41 so as to surround the containment vessel 41. The pressure vessel 1 is stored in the containment vessel 41.

The pressure vessel 1 houses the core shroud 55. In the core shroud 55, a core 50 loaded with a plurality of fuel assemblies 56 is stored. The lower end of the plurality of fuel assemblies 56 is supported by the core support plate 57, and the upper end is held by the upper grid plate 58. The fuel assembly 56 has, for example, a fuel rod in which a plurality of pellets of uranium fuel are vertically filled in a Zircaloy cladding tube as a nuclear fuel material. A plurality of control rod guide pipes 59 are provided below the core 50 in the pressure vessel 1. In each control rod guide pipe 59, control rods 60 that are taken in and out between the fuel assemblies 56 to control the reactor output are provided. A plurality of control rod drive mechanism housings 5 for accommodating control rod drive mechanisms (not shown) are attached to the lower mirror 61 of the pressure vessel 1.

The containment vessel 41 is formed in a cylindrical shape so as to have airtightness. An upper lid 43 is detachably attached to the upper part of the containment vessel 41. The containment vessel 41 includes a pressure suppression chamber (wet well) 45 or the like having a pressure suppression pool filled with cooling water. A dry well 44, a storage container lower space 2, and the like are provided inside the storage container 41. The dry well 44 is provided so as to surround the pressure vessel 1 and the like. The containment vessel lower space 2 is provided below the pressure vessel 1 and accommodates a plurality of control rod drive mechanism housings 5, and the like. The dry well 44 and the containment vessel lower space 2 are partitioned by a tubular pedestal 62 that is erected upward from the concrete containment vessel floor surface (floor surface) 3 formed at the bottom of the containment vessel 41. A core catcher 10 is arranged on the floor surface 3 below the pressure vessel 1 in the containment vessel 41. Hereinafter, the core catcher 10 will be described.

FIG. 7 is a bird's-eye view showing the appearance of the core catcher of the present invention, FIG. 8 is a vertical sectional view (AA'vertical section) and a horizontal sectional view (BB'horizontal section) showing the structure of the core catcher, and FIG. 9 is a horizontal sectional view. It is a horizontal sectional view showing a vertical rib shape.
In this embodiment, as shown in FIG. 7, the core catcher 10 that receives the debris D1 has a hemispherical core catcher wall 11, a vertical rib 12 joined to the wall surface, and a gap 14 with respect to the core catcher wall 11. It is composed of horizontal ribs 13 joined to the outer peripheral side of the vertical ribs 12 through the holes. The structural point of the lateral rib 13 is that it is not in contact with the core catcher wall 11. Here, the number of vertical ribs 12 and horizontal ribs 13 is not particularly limited, and the required number may be determined by evaluating the heat load and structural strength of the core catcher wall 11 after receiving the debris D1.

As shown in the vertical cross-sectional view of FIG. 8, the vertical rib 12 is 30 degrees from the vertical axis (the circumference in the longitudinal direction is 1/3 from the bottom) with respect to the contact point between the vertical axis at the center of the core catcher 10 and the horizontal plane of the hemispherical central axis. ) From the outer surface of the core catcher wall 11 to the outer surface up to 90 degrees (upper end) or more. Since the vertical rib 12 compensates for the decrease in the structural strength of the core catcher wall 11 due to melting and thinning on the wall surface having an inclination angle of 30 degrees or more described with reference to FIGS. 2 and 4, the function of holding the debris D1 is provided. Be kept. On the other hand, due to melting and thinning, stress extending in the circumferential direction is generated on the core catcher wall 11 due to the heat and load of the debris D1. On the other hand, since the horizontal rib 13 supports the core catcher wall 11 via the vertical rib 12, the core catcher wall 11 is prevented from extending in the circumferential direction.
The flow path of the cooling water W1 outside the core catcher wall 11 having an inclination angle of 30 degrees or more is restricted in the vertical direction by the vertical ribs 12, but as described with reference to FIG. 1, the cooling water along the outer surface of the core catcher wall 11 Since the flow of W1 is a vertical flow driven by the buoyancy of boiling steam, the influence on the outer surface cooling of the core catcher wall 11 is small.
On the outer surface of the bottom of the core catcher wall 11, the vector of the buoyancy of boiling steam intersects the surface of the wall, so that the flow velocity of the steam is slow and it tends to stay on the outer surface of the bottom of the core catcher wall 11. If there is an obstacle on the outer surface of the bottom, it may be difficult for the retained steam to escape and the film may boil. However, in this embodiment, the vertical rib 12 joint is limited to an inclination angle of 30 ° or more and the core catcher is used. By making the outer surface of the bottom of the wall 11 unobstructed, the movement of steam from the outer surface of the bottom is smoothed.

Further, as shown in the horizontal cross section of FIG. 9 (1), the distance shown by the broken line from the outer surface of the core catcher wall 11 is the range in which the wall surface temperature is maintained at the melting point of the core catcher wall 11 by cooling the cooling water W1. .. By making the vertical rib 12 thinner than the thickness of the core catcher wall 11, cooling from both sides of the vertical rib 12 alleviates the melting and thinning of the core catcher wall 11 shown in FIG. 9 (2), and the defect C1 is alleviated. Since the 12 also functions as a heat transfer fin, melting and thinning at the joint portion of the vertical rib 12 of the core catcher wall 11 are prevented.

FIG. 10 is a horizontal cross-sectional view showing a vertical rib shape according to a modified example of the first embodiment. It is necessary to make the vertical ribs 12 thinner in order to prevent the above-mentioned melting and thinning, but there is a problem that the strength of the vertical ribs 12 is lowered. On the other hand, there is a method of narrowing the width of the gap 14, but if the gap 14 is extremely narrowed, the flow of the cooling water W1 may be hindered. In a modified example of this embodiment, as shown in FIG. 10, the shape of the vertical rib 12 is thin at the joint portion of the core catcher wall 11 and thick at the horizontal rib 13 side. As a result, the structural strength of the vertical rib 12 is increased without causing the core catcher wall 11 shown in FIG. 5 to be damaged. FIG. 10 (1) is an example in which the thickness is increased from the middle of the vertical rib 12, and FIG. 10 (2) is an example in which the thickness of the vertical rib 12 is changed stepwise.

The material of the core catcher wall 11 is suitable to have high thermal conductivity, high melting point, and high toughness, and is made of stainless steel, carbon steel, tungsten steel, or molybdenum steel. For example, when stainless steel is used, the heat flux at the position of an inclination angle of 90 degrees calculated in Equation 1, the physical properties of stainless steel, and the outer surface temperature of the core catcher wall 11 based on the cooling water conditions at atmospheric pressure are substituted into Equation 2. Then, the wall thickness after thinning is about 15 mm. When carbon steel is used, it is about 40 mm.

According to the above embodiment, an external cooling type core catcher that cools and holds the core melt (debris) that has fallen from the reactor pressure vessel in the event of a severe accident in which the core melts and the reactor pressure vessel is damaged. In this case, the wall surface of the core catcher can be reliably cooled, and the structural strength of the core catcher wall can be ensured against melting and thinning of the wall due to the heat of debris. This prevents debris from falling to the floor of the containment vessel and prevents damage to the containment vessel, thus improving the safety of the reactor.

<Second Example>
A second embodiment of the present invention will be described in detail with reference to FIG. FIG. 11 is a vertical sectional view (AA'longitudinal section) and a horizontal sectional view (BB'horizontal section) showing the structure of the core catcher according to the second embodiment of the present invention. In this embodiment, the core catcher 18 that receives the debris D1 has a cylindrical core catcher wall 19, a vertical rib 20 joined to the wall surface, and an outer circumference of the vertical rib 20 with respect to the core catcher wall 19 via a gap 22. It is composed of lateral ribs 21 joined to the side. Here, the number of the vertical ribs 20 and the horizontal ribs 21 is not particularly limited, and the required number may be determined by evaluating the heat load and structural strength of the core catcher wall 19 after receiving the debris D1. By making the shape cylindrical, the amount of debris retained increases, although corners are created. Also, if the debris retention amount is the same, the height and diameter of the core catcher can be reduced.

As shown in the vertical cross-sectional view of FIG. 11, the vertical rib 20 is joined to the side wall of the core catcher 18, but in the case where the heat load of the received debris D1 is large, the upper part of the side wall when a large amount of debris falls. When the position above 30 ° of the hemispherical shape where the heat flux increase shown in FIG. 2 is applied to the cylindrical shape, the vertical rib 20 is 1 / of the total height from the upper end of the core catcher wall 19 to the bottom of the core catcher wall 19. It suffices to join below the height of 3. Since the vertical rib 20 compensates for the decrease in structural strength due to melting and thinning of the upper part of the core catcher wall 19 described with reference to FIGS. 2 and 4, the function of holding the debris D1 is maintained. On the other hand, due to melting and thinning, a stress extending in the circumferential direction is generated on the core catcher wall 19 due to the heat and load of the debris D1. On the other hand, since the horizontal rib 21 supports the core catcher wall 19 via the vertical rib 19, the core catcher wall 11 is prevented from extending in the circumferential direction.
The flow path of the cooling water W1 outside the core catcher wall 19 is restricted in the vertical direction by the vertical rib 20, but the flow of the cooling water W1 along the outer surface of the core catcher wall 11 is boiling steam as described with reference to FIG. Since the flow is in the vertical direction driven by the buoyancy of the vertical rib 20, the influence of the vertical rib 20 on the cooling of the outer surface of the core catcher wall 19 is small.
On the outer surface of the bottom of the core catcher wall 19, if there is an obstacle on the outer surface of the bottom, it may be difficult for the retained steam to escape and the film may boil. Since the outer surface of the bottom of the core catcher wall 19 is limited to the side surface of the core catcher wall 19 and has a structure without obstacles, the movement of steam from the outer surface of the bottom is smooth.

According to the above-described embodiment, in addition to the effect of the first embodiment, the core catcher can be miniaturized, so that the degree of freedom of installation is improved and the economic efficiency is improved.

<Third Example>
A third embodiment of the present invention will be described in detail with reference to FIG. FIG. 12 is a vertical cross-sectional view showing the structure of the core catcher according to the third embodiment of the present invention. The core catcher 10 that receives the debris D1 includes a hemispherical core chatter inner wall 23, a multiple wall of the core chatter outer wall 24 joined to the outer surface thereof, a vertical rib 25 joined to the core chatter outer wall 24, and a core. Although not shown with respect to the outer wall 24 of the chacchar, it is composed of horizontal ribs 26 joined to the outer peripheral side of the vertical ribs 25 through a gap as in FIG. In this embodiment, the core chatter inner wall 23 is made of a material having the same high thermal conductivity, high melting point, and high toughness as in the first embodiment, and the core chatcher outer wall 24 is made of a material having ultra-high thermal conductivity, as a specific example. Use copper, brass, or aluminum.
Since the material of the core chatter outer wall 24 has a low melting point, if it is used directly on the core chatter inner wall 23, it tends to melt when the temperature of the wall rises transiently. On the other hand, since the thermal conductivity is high, the wall thickness after wall thinning increases in proportion to the thermal conductivity as long as the melting point is not exceeded with respect to the heat flux from debris. Since the core chatter outer wall 23 has a high melting point, it is expected that by combining the materials of these walls, it is possible to cope with a transient temperature rise and the structural strength is improved by thickening the wall.

For the thickness of the core chatter inner wall 23, the heat flux calculated in Equation 1 is used, and in Equation 2, the core catcher wall outer surface temperature To is replaced with a temperature below the melting point of the material of the core catcher outer wall 24 (assumed to be Tx). Calculate and find. The thickness of the core chatter outer wall 24 is calculated by using the heat flux similarly calculated by Equation 1 and replacing the melting point Tm of the core catcher wall with the above temperature Tx in Equation 2. The thickness of the core chucker inner wall 23 obtained by the above procedure is thinner than that when a material having high thermal conductivity, high melting point, and high toughness similar to that in the first embodiment is used, but the core chatter outer wall Since the thickness of 24 becomes thicker in proportion to the thermal conductivity, the thickness of the core chatcher wall including the inner wall and the outer wall becomes thicker than the case of the first embodiment.
For example, when stainless steel (thermal conductivity 16 W / mK) is used for the inner wall 23 of the core chatcher and brass (thermal conductivity 106 W / mK) is used for the outer wall 24 of the core chatcher, and the temperature Tx is 1140 K, the first implementation is performed. When calculated by Equation 2 under the same conditions as in the example, the wall thickness of the core chatcher inner wall 23 after thinning is about 5 mm, and the wall thickness of the core chatter outer wall 24 is about 50 mm. The chacchar increases to 55 mm. This embodiment is applicable not only to the hemispherical core catcher but also to the cylindrical core catcher shown in the second embodiment.
In addition, ignoring the influence of the transient temperature rise of the core chatcher wall, the evaluation formula of heat flux as shown in Equation 1 on the wall made of the material with ultra-high thermal conductivity was obtained, and the wall thickness obtained by Equation 2 was obtained. If the structural strength can be evaluated, the core chatter wall 11 of the first embodiment can be constructed only with a material having an ultra-high thermal conductivity.

According to the above-mentioned embodiment, in addition to the effect of the first embodiment, the wall thickness of the core catcher can be increased, so that the structural strength is secured, and the debris is prevented from falling to the floor surface of the containment vessel. The safety of the reactor is improved because the performance to prevent damage is improved.

<Fourth Example>
A fourth embodiment of the present invention will be described in detail with reference to FIGS. 13 and 14. 13 and 14 are vertical cross-sectional views showing the structure of the core catcher according to the fourth embodiment of the present invention. The core catcher 10 that receives the debris D1 is attached to the hemispherical core chatter wall 11, the sacrificial material 27 installed on the inner surface thereof, the vertical ribs 12 joined to the core chatcher wall 11, and the core chatcher wall 11. On the other hand, although not shown, it is composed of horizontal ribs 13 joined to the outer peripheral side of the vertical ribs 12 through a gap as in FIG. In this embodiment, the core chatter wall 11 is made of a material having the same high thermal conductivity, high melting point, and high toughness as in the first embodiment, and the sacrificial material 27 is made of a material having a melting point lower than that of the core chatcher wall 11. , Concrete, silicon dioxide, etc. are used as specific examples.

In order to prevent the temperature of the core catcher wall 11 from rising with respect to the debris D1 that continuously releases decay heat, the amount of heat removed from the cooling water W1 for external cooling should be increased and the temperature of the debris itself should be lowered. Is valid. For example, a heat-resistant material can be used to temporarily reduce the amount of heat transferred from the debris D1 to the core catcher wall 11, but the decay heat of the debris D1 that could not dissipate heat raises the temperature of the debris itself. When the temperature of the debris D1 rises and the heat-resistant material melts, the core catcher wall 11 is exposed to the heat of the high temperature debris D1. Therefore, it is effective to bring a sacrificial material such as concrete or silicon dioxide having a melting point lower than that of the core catcher wall 11 into contact with the debris D1 to lower the temperature of the debris by its heat capacity and latent heat of melting.
Even during the melting of the sacrificial material 27, the heat of the debris D1 is transferred to the core catcher wall 11 by heat conduction, and the heat is further transferred from the outer surface of the core catcher wall 11 to the cooling water W1 to remove the heat. After the sacrificial material 27 is melted, the core catcher wall 11 is melted to the thickness calculated by the equation 2 by heat transfer between the debris D1 whose temperature has dropped and the core catcher wall 11. Even at this time, the temperature of the debris D1 is lowered by removing heat equivalent to the latent heat of melting of the wall surface. After that, since the debris D1 and the core catcher wall 11 continue to remove heat equivalent to the decay heat, the core catcher wall 11 maintains the soundness of the core catcher wall 11 without causing transient melting due to the high temperature debris D1. Dripping.

FIG. 14 shows an example in which the sacrificial material 27a is arranged inside the core catcher 10 in addition to the sacrificial material 27 installed on the inner surface of the core chatter wall 11 of FIG. The upper limit of the volume of the sacrificial material 27a is set based on the maximum drop volume of the debris D1 so that the upper surface 17 of the debris D1 after melting the sacrificial material 27a does not exceed the upper surface of the core catcher 10. The shape of the sacrificial material 27a is preferably a structure restrained by mutual contact, for example, a tetrapod shape so as not to scatter due to the impact when the debris falls. This embodiment is applicable not only to the hemispherical core catcher but also to the cylindrical core catcher shown in the second embodiment.
According to the above-mentioned embodiment, in addition to the effect of the first embodiment, the debris temperature is lowered and the heat is continuously removed from the cooling water for external cooling, so that the structural strength of the core catcher wall is secured. ， The performance to prevent the debris from falling to the floor of the containment vessel and the damage to the containment vessel is improved, and the safety of the reactor is improved.

<Fifth Example>
A fifth embodiment of the present invention will be described in detail with reference to FIGS. 15 to 17. 15 to 17 are vertical cross-sectional views showing a gantry structure of a core catcher according to a fifth embodiment of the present invention. The hemispherical core catcher 10 has a core catcher wall support portion 29 in contact with the outer surface of the core catcher wall 11 having a temperature of 30 degrees or less with the vertical axis at the contact point between the vertical axis at the center of the core catcher 10 and the horizontal plane of the hemispherical central axis. It is installed on the floor by a catcher 28. As described with reference to FIG. 4, the cross section of the core catcher wall 11 is relatively thick up to the bottom 30 degrees (region A in FIG. 4), and the side wall becomes thin above 30 degrees from the base point (FIG. 4). Area B). Further, as described with reference to FIG. 5, when a member comes into contact with the outer surface of the core catcher wall 11, it becomes a thermal resistance and the wall is thinned. Since this effect is large in the side wall portion exceeding 30 degrees from the base point where the wall thickness is thin, it is effective to support the gantry at a point 30 degrees or less from the base point as shown in FIG. The number of core catcher wall support portions 29 is preferably set to an appropriate interval and number after calculating the structural strength of the core catcher wall 11.

On the other hand, the contact of the core catcher wall support portion 29 with the wall surface is not preferable in terms of thermal resistance, but it is appropriate to use the vertical ribs and the horizontal ribs as the support portions because the ribs are the support members of the wall surface and have strength. FIG. 16 shows an example in which the core catcher wall support portion 29 of the gantry 28 is attached to the vertical rib 12, and FIG. 17 shows an example in which the core catcher wall support portion 29 of the gantry 28 is attached to both the vertical rib 12 and the horizontal rib 13. is there.
The gantry of this embodiment is not limited to the hemispherical core catcher, but also the cylindrical core catcher shown in the second embodiment, and the mounting location of the gantry 28 is the total height from the bottom of the cylindrical core catcher wall 19. It is applicable by setting the height below 1/3 of the height, the outer surface of the bottom, and the vertical rib 20 and the horizontal rib 21.

According to the above-mentioned examples, in addition to the effects of the first to fourth embodiments, the debris in the core catcher can be supported on the floor while maintaining the strength of the core catcher wall, so that the structural strength is secured. The performance of preventing debris from falling to the floor of the containment vessel and preventing damage to the containment vessel is improved, and the safety of the reactor is improved.

<Sixth Example>
A sixth embodiment of the present invention will be described in detail with reference to FIG. FIG. 18 is a vertical sectional view and a horizontal sectional view showing a vertical rib shape according to a sixth embodiment of the present invention. In the configuration of the core catcher wall 11, the vertical rib 12, and the horizontal rib 13 shown in the first to fifth embodiments, the plate surface orthogonal to the joint surface of the vertical rib 12 faces the inner peripheral side from the outer peripheral side of the vertical rib 12. The guide plate 30 having an upward inclination is joined to the outer surface of the core catcher wall 11 while maintaining a gap. As described with reference to FIG. 2, there is a surface where the core catcher wall 11 does not come into direct contact with the cooling water W1 due to the vertical rib 12, and the cooling in the corner region R1 where the vertical rib 12 and the core catcher wall 11 intersect is insufficient. If there is, a defective portion C1 may occur inside the core catcher wall 11. In this embodiment, the direction of the flow of the cooling water W1 that has risen in the gap 22 along the vertical rib 12 is bent by the flow guide plate 30, and the flow W2 of the cooling water in the corner region R1 is increased. As a result, the core catcher wall 11 near the joint of the vertical ribs 12 is sufficiently cooled, and it is possible to prevent defects due to local wall thinning inside the core catcher wall 11.

According to the above-described embodiment, in addition to the effects of the first to fifth embodiments, the structural strength of the core catcher wall is ensured, debris is prevented from falling to the containment vessel floor surface, and the containment vessel is damaged. The performance to prevent the above is improved, and the safety of the reactor is improved.

<7th Example>
A seventh embodiment of the present invention will be described in detail with reference to FIG. FIG. 19 is a horizontal cross-sectional view showing a vertical rib shape according to a seventh embodiment of the present invention. In the configuration of the core catcher wall 11 and the horizontal rib 13 shown in the first to sixth embodiments, the vertical rib 31 has a part of the core catcher wall 11 having an outer folding rib shape protruding outward, and the outer surface of the core catcher wall 11 A lateral rib 13 that points-supports the tip of the outer folding portion via the gap 22 is provided. The tip of the outer folded portion of the vertical rib 31 is spot-bonded to the joint portion 32 on the surface of the horizontal rib 13. Since it is a spot joint, the inner surface of the core catcher wall 11 is unlikely to be damaged. Further, by integrating the core catcher wall 11 and the vertical rib 31, the strength of the core catcher wall 11 is increased, and the deformation of the core catcher wall 11 due to the heat of the debris D1 can be absorbed by the space R2 of the outer folding portion. Deformation of the core catcher is prevented. In this embodiment, unlike the defect shown in FIG. 5 (2), the core catcher wall 11 is not defective and the continuous structure of the wall is maintained.

According to the above-mentioned embodiment, in addition to the effects of the first to sixth embodiments, the core catcher can be prevented from being deformed, so that the debris can be prevented from falling to the floor surface of the containment vessel and the containment vessel can be damaged. The prevention performance is improved and the safety of the reactor is improved.

<8th Example>
An eighth embodiment of the present invention will be described in detail with reference to FIG. FIG. 20 is a vertical cross-sectional view showing the structure of the core catcher according to the eighth embodiment of the present invention. In the first to seventh embodiments, the core catcher 10 is not shown with respect to the hemispherical core chatter wall 11, the vertical rib 12 joined to the core chatter wall 11, and the core chatter wall 11, although not shown. Similar to No. 8, it is composed of horizontal ribs 13 joined to the outer peripheral side of the vertical ribs 12 via a gap. In this embodiment, a cylindrical support wall 34 having a plurality of through holes 33 is attached to the upper end of the core chatter wall 11, and a funnel shape having a negative inclination toward the center of the core catcher 10 is attached to the upper end of the support wall 34. The guide plate 36 of the above is provided. The flow guide plate 36 has a shape and dimensions such that the projection circle vertically below the upper end passes outside the outer edge of the lateral rib 13 and the projection circle vertically below the upper end passes inside the inner surface of the core chatter wall 11. Take. Further, the through hole 33 is formed so that the height of the upper edge thereof is higher than the lower end of the flow guide plate 36.

An inverted conical waterproof plate 35 that covers the entire upper surface of the core catcher 10 is provided above the upper portion of the core chatter wall 11 and below the lower edge of the through hole 33. The entire circumference of the circular edge of the waterproof plate 35 is joined to the core chatter wall 11 or the support wall 34. The waterproof plate 35 is made of a lightweight material, and its dimensions, structure, and material are set so that the minimum strength thereof can be retained even if water collects from the inside of the cone of the waterproof plate 35 to the height of the through hole 33. For the maximum strength, the structure and material are set so that the waterproof plate 35 is damaged or melted due to the debris weight or heat load while debris is accumulated in the conical space of the waterproof plate 35.

When debris falls from the reactor pressure vessel 1, if the debris falls not in the center of the core catcher 10 but in the peripheral portion, the falling debris closes the gap 14 (not shown) between the core chatter wall 11 and the lateral rib 13 of the present invention. , The flow of the cooling water W1 along the outer surface of the core chatter wall 11 may be hindered. Insufficient cooling of the core chatter wall 11 causes damage due to wall thinning. The flow guide plate 36 has a function of guiding the falling debris to the inside of the core chatter 10 by the installation position covering the core chatter wall 11 and the lateral rib 13 over the entire circumference and the inclination of the surface thereof.
On the other hand, since the core catcher 10 has an open upper part and a closed lower part, water such as steam condensed water that falls into the lower space 2 of the containment vessel during reactor operation may collect. When debris that has fallen from the reactor pressure vessel 1 during a severe accident falls into the water inside the core catcher 10, it is necessary to assume the occurrence of a steam explosion depending on the conditions of water temperature and atmospheric pressure. In the core catcher 10 of this embodiment, steam condensed water can be stored in a space surrounded by the waterproof plate 35, the core chatter wall 11, and the support wall 34, and the increased water can be drained from the through hole 33 to the outside of the core catcher 10. .. When the debris falls, the waterproof plate 35 is damaged or melted when the debris accumulates in the conical space of the waterproof plate 35, and the debris falls into the core catcher 10. As a result, it is possible to prevent steam explosion at the start of debris fall and to secure the debris holding function by the core catcher 10.

According to the above embodiment, in addition to the effects of the first to seventh embodiments, steam explosion due to debris falling into the water accumulated in the core catcher can be prevented, so that the debris can be placed on the floor surface of the containment vessel. The performance to prevent falling and damage to the containment vessel is improved, and the safety of the reactor is improved.

In the above-mentioned first to eighth embodiments, an example of a core catcher that catches debris falling from the reactor pressure vessel to the floor surface of the containment vessel is shown. However, the essence of the present invention is to reliably retain the high-temperature thermal fluid in the vessel structure, and the present invention can also be applied to the lower structure of the reactor pressure vessel and the bottom structure of the containment vessel.

1 ... Reactor pressure vessel 2 ... Containment vessel lower space 3 ... Containment vessel floor 5 ... Control rod drive mechanism housing 10 ... Core catcher 11 ... Core catcher wall 12 ...・ Vertical rib 13 ・ ・ ・ Horizontal rib 14 ・ ・ ・ Gap 15 ・ ・ ・ Vertical rib 16 ・ ・ ・ Vertical rib 17 ・ ・ ・ Debris top surface 18 ・ ・ ・ Core catcher 19 ・ ・ ・ Core chatter wall 20 ・ ・ ・Vertical rib 21 ... Horizontal rib 22 ... Gap 23 ... Core catcher inner wall 24 ... Core catcher outer wall 25 ... Vertical rib 26 ... Horizontal rib 27, 27a ... Sacrificial material 28 ... Stand 29 ... Core catcher wall support 30 ... Conduction plate 31 ... Vertical rib 32 ... Joint 33 ... Through hole 34 ... Support wall 35 ... Waterproof plate 36 ... Conduction plate 40 ... Reactor 41 ... Reactor containment vessel 42 ... Reactor building 43 ... Reactor containment vessel top lid 44 ... Drywell 45 ... Pressure suppression chamber (Wetwell)
46 ... Vent passage 47 ... Shield plug 48 ... Reactor pressure vessel top lid 50 ... Core 51 ... Air-water separator 52 ... Steam dryer 55 ... Core shroud 56 ...・ Fuel assembly 57 ・ ・ ・ Core support plate 58 ・ ・ ・ Upper lattice plate 59 ・ ・ ・ Control rod guide tube 60 ・ ・ ・ Control rod 61 ・ ・ ・ Lower mirror 62 ・ ・ ・ Pedestal 64 ・ ・ ・ Reactor well 65 ... Dryer separator pool 66 ... Spent fuel pool 67 ... Driver's floor 68 ... Refueling machine W1 ... Cooling water W2 ... Cooling water flow R1 ... Corner area R2 ... Space C1 ... Missing part D1 ... Debris

Claims (19)

It is located below the reactor pressure vessel in the reactor containment vessel, and when the reactor pressure vessel is damaged due to a core meltdown accident of the reactor, it receives and holds the dropped core melt, and the core melt from the outer surface. In the core catcher that dissipates the heat of
A core catcher wall that holds the core melt, a vertical rib that joins the core catcher outer wall surface to support the load on the core melt wall, and a horizontal rib that supports the vertical rib through a gap with the core catcher outer wall surface. A core catcher characterized by being composed. In the core catcher according to claim 1,
Core catcher A core catcher characterized in that the thickness of the wall joint in the circumferential direction of the vertical ribs is thinner than the thickness of the core catcher wall. In the core catcher according to claim 1 ,
A core catcher characterized in that the vertical rib circumferential thickness of the horizontal rib joint portion is made thicker than the vertical rib circumferential thickness of the core catcher wall joint portion. In the core catcher according to any one of claims 1 to 3 ,
The wall shape of the core catcher is formed in a hemispherical shape, and the vertical rib is 30 degrees with the vertical axis from the point of contact between the vertical axis at the center of the core catcher and the horizontal plane of the hemispherical center axis (perimeter in the longitudinal direction is 1/3 from the bottom). A core catcher characterized by joining outer walls from the following to 90 degrees (upper end) or higher. In the core catcher according to any one of claims 1 to 3 ,
A core catcher characterized in that the wall surface shape of the core catcher is formed into a cylindrical shape, and the vertical ribs join the outer wall surface from the bottom of the upper and lower ends of the core catcher to the lower end of the core catcher from below 1/3 to the upper end of the core catcher. In the core catcher according to any one of claims 1 to 5 ,
Core catcher A core catcher characterized in that the wall is made of a material with high thermal conductivity, high melting point, and high toughness. In the core catcher according to claim 6 ,
Core catcher A core catcher characterized in that the wall is made of stainless steel, carbon steel, tungsten steel, or molybdenum steel. In the core catcher according to any one of claims 1 to 5 ,
The core catcher wall has a multiple structure,
A core catcher characterized in that the inner wall is made of stainless steel, carbon steel, tungsten steel, or molybdenum steel, and the outer wall is made of copper, brass, or aluminum. In the core catcher according to any one of claims 1 to 8 .
Core catcher A core catcher that features a sacrificial material with a lower melting point than the wall material attached to the inside of the wall. In the core catcher according to claim 9 ,
Core catcher A core catcher characterized in that the material of the sacrificial material attached to the inside of the wall is concrete or silicon dioxide. In the core catcher according to any one of claims 1 to 10 .
A core catcher characterized in that a sacrificial material having a melting point lower than that of the wall material is placed inside the core catcher. In the core catcher according to claim 11,
A core catcher characterized in that the sacrificial material placed inside the core catcher is a concrete block or a silicon dioxide block. In the core catcher according to any one of claims 1 to 12 ,
A core catcher characterized in that the gantry supports the vertical axis and the outer wall surface of the core catcher at 30 degrees or less based on the contact point between the vertical axis at the center of the core catcher and the horizontal plane of the hemispherical central axis. In the core catcher according to any one of claims 1 to 13 .
A core catcher characterized in that a gantry is joined to the vertical ribs to support the core catcher. In the core catcher according to any one of claims 1 to 14 .
A core catcher characterized in that the gantry is joined to horizontal ribs to support the core catcher. In the core catcher according to any one of claims 1 to 15 .
The thickness of the core catcher wall joint of the vertical ribs is the difference between the melting point temperature of the core catcher wall material and the core catcher outer wall temperature multiplied by the thermal conductivity of the core catcher wall material, and the cooling water in contact with the core catcher outer wall and the core catcher outer wall. A core catcher characterized by being thinner than the calculated value of the critical heat flux between. It is located below the reactor pressure vessel in the reactor containment vessel, and when the reactor pressure vessel is damaged due to a core meltdown accident of the reactor, it receives and holds the dropped core melt, and the core melt from the outer surface. In the core catcher that dissipates the heat of
A core catcher characterized in that the core catcher wall that holds the core melt has a protruding outer folding rib shape on the outside, and a horizontal rib that supports the outer folding rib tip via a gap with the outer wall surface of the core catcher is provided. In the core catcher according to any one of claims 1 to 17 .
A core catcher characterized in that a waterproof plate with a central part protruding downward is provided at the upper end of the core catcher, and a flow guide plate is provided at the upper end of the core catcher wall, which is joined all around and extends to the space above the lateral rib. In the core catcher according to any one of claims 1 to 5 ,
Core catcher A core catcher characterized in that the walls are made of copper, brass, or aluminum.

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