Nuclear power plant equipped with a core catcher

Abstract

In a nuclear power plant (1) comprising a storage structure (2) and a pressure vessel (4) housed in the storage structure (2), the pressure vessel (4) houses the core (5) of the nuclear power plant (1) during normal operation of the nuclear power plant (1), and the storage structure (2) defines a diffusion compartment (6) configured to receive a molten material containing a molten core material from the core (5) in the event of a core meltdown. The nuclear power plant (1) further includes a core catcher (8) disposed in the diffusion compartment (6) and having side walls (16) and a bottom wall (18) that define an inner receiving space (20) intended to receive the molten material. The core catcher (8) includes a convection barrier (14) disposed in the receiving space (20) defined by the side walls (16) and the bottom wall (18).

Description

Technical Field

[0001] The present invention relates to a nuclear power plant including a pressure vessel and a core catcher.

[0002] The present invention relates to the containment function of a nuclear power plant in a nuclear power plant having a European pressurized water reactor or other nuclear power plants using a metal crucible for retaining the core melt during a severe accident.

Background Art

[0003] Generally, such a nuclear power plant includes a pressure vessel, which is located inside a containment structure and houses the core of the nuclear reactor of the nuclear power plant during normal operation of the nuclear power plant.

[0004] For the purpose of the containment function during a severe accident, such a nuclear power plant typically includes a core catcher. In fact, during a severe accident, the core may at least partially melt. Such an event is called a core melt. The core catcher is configured to receive the molten material from the core if the core melt progresses until the pressure vessel is damaged.

[0005] During such a core melt, a large amount of molten material such as steel and other materials of the core and the pressure vessel may flow back into the core catcher. Under extreme conditions, for example, due to a locally high heat flux from the molten material into the core catcher, local damage to the structure of the core catcher may occur.

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to prevent damage to the core catcher of a nuclear power plant and thus maintain the integrity of the containment vessel of the nuclear power plant when a severe accident causing a core melt occurs.

Means for Solving the Problems

[0007] For this purpose, a nuclear power plant comprises a containment structure and a pressure vessel accommodated within the containment structure, the pressure vessel containing the core of the nuclear power plant during normal operation of the nuclear power plant, the containment structure defining a diffusion compartment configured to receive molten material including molten core material from the core in the event of a core meltdown, and the nuclear power plant further comprising: - a core catcher disposed within the diffusion compartment and having side walls and a bottom wall that define an inner receiving space intended to receive molten material; - a cooling device configured to cool the side walls and the bottom wall of the core catcher; - a sacrificial material disposed in the core catcher so as to be melted by the molten material flowing toward and / or into it, the molten sacrificial material being intended to be mixed with the molten material to obtain a melt having a lower phase consisting of a molten metal phase and an upper phase consisting of a molten oxide phase.

[0008] The core catcher is further disposed within the receiving space defined by the side walls and the bottom wall and has a convection barrier protruding upward from the bottom wall of the core catcher, the convection barrier extending substantially parallel to the side walls of the core catcher and at a predetermined distance from the side walls, the convection barrier being made of a material adapted to withstand the molten metal phase of the melt, and the convection barrier being configured such that, in the event of a core meltdown, the molten material flows into both sides of the convection barrier in the receiving space.

[0009] The nuclear power plant according to the invention makes it possible to improve the protection of the containment vessel during a core meltdown by preventing local damage to the core catcher. In fact, the combination of the presence of the sacrificial material and the convection barrier reduces the heat flux to the side walls of the core catcher to a non-critical value. The reduction in the heat flux to the side walls of the core catcher causes a crust of solidified melt to form adjacent to the core catcher, reducing the risk of damage to the core catcher or its integrity.

[0010] In particular, when core melting occurs, the sacrificial melting material is mixed with the molten core material to form a melt, and the melt has a metallic molten phase and an oxide molten phase. By mixing with the sacrificial material, the density of the metallic molten phase is higher than that of the oxide molten phase, and in the melt, the metallic molten phase is positioned below the oxide molten phase. Due to this layer formation of the melt, the metallic molten phase is arranged to be cooled by the bottom of the core catcher and be able to form a crust on the bottom and side walls.

[0011] In the layer formation of the melt as described above, in the absence of a convection barrier, the upper part of the metallic molten phase of the melt may be heated by contacting the warmer oxide molten phase above, and due to natural convection in the lower phase of the melt, a locally strong heat flux may occur from the lower phase to the side wall. This convection is driven by the side wall that is at a lower temperature than the metallic molten phase of the melt, and the material from the metallic molten phase can move quickly to the side wall and / or transfer a large amount of heat to the side wall. These convections within the melt that result in a strong heat flux from the melt to the side wall of the core catcher may prevent the formation of a crust in at least some of the contact regions between the melt and the core catcher, particularly in the regions adjacent to the side wall.

[0012] By installing the convection barrier according to the present invention, such a strong heat flux caused by natural convection inside the lower phase of the melt to the side wall of the core catcher can be reduced. According to an embodiment, the convection barrier separates the molten metal phase into a narrow outer portion in contact with the side wall and a large central portion. The convection barrier particularly forms a heat insulation limit around the central portion and suppresses natural convection in the central portion. As a result, a stable stratification is formed in the central portion. For this reason, all the heat carried from above into the molten metal phase across the contact region between the upper and lower phases in the central portion is conducted to the cooled bottom. Therefore, the side wall is heated only by a very small part of the total heat coming from the oxide melt phase in contact with the outer portion of the molten metal phase. This makes it possible to prevent a strong heat flux from the molten metal phase to the side wall, and thus a crust can be formed in the region where the melt, particularly the molten metal phase, contacts the core catcher. Those skilled in the art understand that when core melting occurs, since the oxide melt phase is surrounded by a crust, such a strong heat flux is not observed in the oxide melt phase and a uniform boundary temperature is established.

[0013] Further embodiments may relate to one or more of the following features that can be combined in any technically feasible combination: - The height of the barrier of the convection barrier is strictly lower than the height of the wall of the side wall, and the height of the barrier and the height of the wall are each measured from the bottom wall. - The height of the wall is selected according to the predicted total volume of the melt to be held. - The height of the barrier of the convection barrier is selected according to the predicted maximum volume of the molten metal phase. - The material of the convection barrier has a melting point strictly higher than the temperature of the molten metal phase of the melt. - The material of the convection barrier has a thermal conductivity strictly lower than 3 W / m·K. - The material of the convection barrier includes sintered zirconia bricks. - The predetermined distance to the side wall of the convection barrier is determined according to at least one feature of the core catcher and / or the cooling device. - The peripheral region of the bottom wall is defined between the convection barrier and the side wall, and the central region of the bottom wall is defined by the convection barrier on the surface of the convection barrier on the side opposite to the peripheral region. The peripheral region has a surface area of 5 to 15% of the total surface area of the peripheral region and the central region. - The sacrificial material includes at least one oxide selected from, for example, silicon oxide, calcium oxide, aluminum oxide, and / or iron oxide. - The peripheral portion of the receiving space defined between the convection barrier and the side wall is empty during normal operation of the nuclear power plant or is at least partially filled with a filling material intended to melt in the event of a core meltdown. The filling material is, for example, concrete. - The convection barrier has a constant height measured parallel to the side wall from the bottom wall. - The core catcher includes at least one fixing device configured to fix the convection barrier to the bottom wall. The fixing device preferably includes at least one rail fixed to the bottom wall. - A coating is provided on the convection barrier. - The coating is made of metal. - The core catcher is arranged vertically below the pressure vessel, and the sacrificial material is arranged in the receiving space. - The containment structure includes a transfer space arranged vertically below the pressure vessel and a tunnel connecting the transfer space and the receiving space of the core catcher. The sacrificial material is arranged in the transfer space and / or in the receiving space of the core catcher.

[0014] These features and advantages of the present invention are further explained in the following description, given only by way of non-limiting example, with reference to the accompanying drawings as follows.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0016] In the following specification, the expression "substantially parallel" is understood to define an error with respect to parallelism of plus or minus 10 degrees, preferably plus or minus 5 degrees.

[0017] Referring to FIG. 1, a nuclear power plant 1 according to the first embodiment includes a containment structure 2, a reactor pressure vessel 4, hereinafter referred to as the pressure vessel 4, and a core 5 of the reactor.

[0018] The containment structure 2 defines a diffusion compartment 6 configured to receive a molten material including a molten core material from the core 5 in the event of core melting. In particular, the wall of the containment structure 2, preferably made of concrete, defines the diffusion compartment 6.

[0019] The nuclear power plant 1 further includes a core catcher 8, a cooling device 10, and a sacrificial material 12 disposed in the diffusion compartment 6.

[0020] FIG. 1 shows an example of the nuclear power plant 1 as seen in cross-section according to the first plane I.

[0021] The containment structure 2 is a different structure from the core catcher 8. For example, the containment structure 2 includes concrete and is preferably made of concrete, while the core catcher 8 preferably includes metal.

[0022] The pressure vessel 4 is stored by the containment structure 2, particularly within the internal volume defined by the containment structure 2 above the dispersion compartment 6.

[0023] The pressure vessel 4 contains the reactor core 5 during the normal operation of the nuclear power plant 1. The reactor core 5 is thus located inside the pressure vessel 4 during normal operation.

[0024] "Normal operation" is understood to mean the operation of a nuclear power plant in which no severe accident has occurred, particularly the absence of core melting.

[0025] The pressure vessel 4 further houses, for example, support elements made of metal, configured to support the reactor core 5 and / or guide the coolant of a reactor cooling system (not shown), and the reactor core cooling system.

[0026] The nuclear reactor is particularly a third-generation nuclear reactor. According to one example, the reactor core 5 is part of an European pressurized water reactor.

[0027] The core catcher 8 includes a convection barrier 14, side walls 16, and a bottom wall 18. The side walls 16 and the bottom wall 18 define an inner receiving space 20 intended to receive molten material.

[0028] The molten material includes molten core material from the reactor core 5 formed during core melting. The molten material further includes, for example, materials from other elements housed within the pressure vessel 4 during normal operation, such as a reactor cooling system, and / or materials from the pressure vessel 4 itself.

[0029] "Core melting" is understood to mean that at least a part of the reactor core 5 melts and becomes at least partially liquid.

[0030] The molten material has, in particular, a metal phase and an oxide phase. In the absence of mixing of the molten material and the sacrificial material 12, the oxide phase exhibits a higher density than the metal phase.

[0031] The core catcher 8 includes, for example, a metal such as iron, cast iron, or steel.

[0032] The core catcher 8 is arranged below the pressure vessel 4, for example, directly vertically below the pressure vessel 4 or offset downward laterally.

[0033] According to the first embodiment, the core catcher 8 is arranged directly vertically below the pressure vessel 4.

[0034] The "core catcher directly vertically below the pressure vessel" is understood such that the core catcher 8, and in particular the receiving space 20, faces the lower part of the pressure vessel 4. Preferably, in this case, the wall of the storage structure 2 is not arranged between the core catcher 8 and the pressure vessel 4.

[0035] The side wall 16 extends particularly vertically from the bottom wall 18. In particular, the side wall 16 and the bottom wall form a container having a bottom formed by the bottom wall 18 and a peripheral wall formed by the side wall 16.

[0036] Referring to FIG. 3 showing an example of the core catcher 8 as seen in a cross-section by a second plane II perpendicular to the first plane I, the side wall 16 has four wall portions and preferably forms a rectangle or a square.

[0037] Referring to FIGS. 1 and 2, the side wall 16 has, for example, a rectangular cross-section with a wall height H1 and a wall width W1. The wall height H1 of the side wall 16 is selected, for example, according to the predicted total volume of the melt (described below) to be held by the core catcher 8 in the event of a core melt.

[0038] The bottom wall 18 is arranged so as to connect two opposing portions of the side wall 16.

[0039] The bottom wall 18 and the side walls 16 are provided with cooling fins 22, for example, particularly on the lower surface of the bottom wall 18 and the surface of the side walls 16 opposite to the receiving space 20. The cooling fins 22 can extend vertically into a space intended to receive a coolant from the lower surface of the bottom wall 18 and from the surface of the side walls 16 opposite to the receiving space 20.

[0040] According to one embodiment, the side walls 16 and the bottom wall 18 are made of a plurality of pieces fixed to each other, for example, by a butt joint. According to another embodiment, the side walls 16, the bottom wall 18, and optionally, the cooling fins 22 are made integrally, for example, by casting. According to another embodiment, the side walls 16 are welded to the bottom wall 18 and optionally to the cooling fins 22.

[0041] The side walls 16, the bottom wall 18, and optionally the cooling fins 22 are preferably made using metal.

[0042] The cooling device 10 is configured to cool the side walls 16 and the bottom wall 18 of the core catcher 8.

[0043] Referring to FIG. 1, the cooling device 10 defines a coolant receiving space 24 for receiving a coolant 26, such as water, for example, and the coolant 26 contacts the side walls 16 and the bottom wall 18.

[0044] The coolant receiving space 24 is preferably arranged outside the core catcher 8, particularly below the bottom wall 18 and on the side of the side walls 16 opposite to the receiving space 20 of the core catcher 8.

[0045] The cooling device 10 further defines at least one coolant injection port 27 for injecting the coolant 26 into the coolant receiving space 24 during a severe accident.

[0046] The sacrificial material 12 is arranged to be melted by the molten material flowing towards and / or into the core catcher 8.

[0047] The sacrificial material 12 is intended to be mixed with the molten material to obtain a melt having a lower phase consisting of a molten metal phase 28 and an upper phase consisting of an oxide molten phase 29. Examples of the molten metal phase 28 and the oxide molten phase 29 are shown in FIGS. 5 and 6.

[0048] As used herein, the expression "melt" means a mixture obtained by mixing a molten material including a molten core material with the sacrificial material 12.

[0049] In particular, the sacrificial material 12 is a material configured to invert the densities of the metal phase and the oxide phase of the molten material when mixed with the molten material including the molten core material. The molten metal phase 28 has a higher density than the oxide molten phase 29 and is thus disposed below the oxide molten phase 29.

[0050] The sacrificial material 12 includes, for example, lightweight oxides so as to achieve an intended density inversion of the phases of the molten material when mixed with the molten material.

[0051] For example, the sacrificial material 12 includes oxides selected from silica (or silicon dioxide), calcia (or calcium oxide), alumina (or aluminum oxide), and / or iron oxide. According to one embodiment, the oxides are sintered or formulated, for example, in the form of concrete.

[0052] According to one embodiment, the sacrificial material 12 can include a metal, such as iron or steel, for example, in the form of reinforcing bars, to enhance mechanical stability.

[0053] According to a first embodiment, the sacrificial material 12 is disposed within the receiving space 20, as shown, for example, in FIG. 1. According to the first embodiment, the sacrificial material 12 is intended to be mixed with the molten material when received within the receiving space 20.

[0054] The sacrificial material 12 is not shown in FIG. 2 so that other parts can be seen better.

[0055] The convection barrier 14 is disposed within a receiving space 20 defined by a side wall 16 and a bottom wall 18.

[0056] The convection barrier 14 is made of a material adapted to withstand the metallic melt phase 28 of the melt.

[0057] The "convection barrier made of a material adapted to withstand the metallic melt phase of the melt" is understood in particular as a material fulfilling at least one, preferably both, of the following requirements: the melting point of the material is strictly higher than the temperature of the metallic melt phase 28 of the melt and / or the material of the convection barrier 14 exhibits a thermal conductivity strictly lower than 3 W / m·K.

[0058] According to one embodiment, the convection barrier 14 preferably comprises a refractory material selected from, for example, zirconia, in particular sintered zirconia, magnesium oxide, aluminum oxide, such as aluminum(III) oxide, or uranium dioxide. For example, the convection barrier consists of bricks of such a material.

[0059] According to one embodiment, the convection barrier 14 is provided with a coating 25. The coating 25 is configured in particular to protect the convection barrier 14 during normal operation of the nuclear power plant 1. The coating 25 preferably consists of a metal or a predefined sacrificial material.

[0060] The coating 25 is intended to be melted by the melt in the event of a core melt.

[0061] Referring to FIG. 2, the convection barrier 14 projects upward from the bottom wall 18.

[0062] The convection barrier 14 extends along at least one extending direction E. An example of the extending direction E is shown in FIG. 3.

[0063] Looking again at Fig. 2, the convection barrier 14 shows a cross-section perpendicular to the extending direction E of the convection barrier 14, which has a rectangular shape. In particular, the convection barrier 14 has a barrier height H2 measured from the bottom wall 18 and a barrier width W2.

[0064] Preferably, the barrier height H2 is selected according to the predicted maximum volume of the molten metal phase 28, in particular so as to form a separation for the molten metal phase 28 to be arranged on both sides of the convection barrier 14.

[0065] For example, the barrier height H2 is the same as or higher than the expected height of the molten metal phase 28.

[0066] For example, the barrier height H2 is constant when measured parallel to the side wall 16 and in particular along the extending direction E, for example along the horizontal direction. Preferably, the barrier height H2 is strictly smaller than the wall height H1.

[0067] Preferably, the convection barrier 14 has no openings or holes along the direction perpendicular to the extending direction E.

[0068] According to another embodiment, the convection barrier 14 has at least one opening along the direction perpendicular to the extending direction E.

[0069] According to one embodiment, the convection barrier 14 has a plurality of barrier sections arranged apart from each other. Preferably, in this case, the total length of the barrier sections defined parallel to the side wall 16 is strictly larger than the total length of the gaps of the convection barrier 14 between these sections.

[0070] The convection barrier 14 extends substantially parallel to the side wall 16 and at a predetermined distance D. For example, the predetermined distance D from the convection barrier 14 to the side wall 16 is determined according to at least one characteristic of the cooling device 10 such as the cooling capacity of the cooling device 10, and / or at least one characteristic of the core catcher 8 such as the material of the core catcher 8 or the wall width W1 of the side wall 16. The predetermined distance D is, for example, 20 to 40 cm.

[0071] Referring to FIG. 3, the convection barrier 14 has four portions, each extending parallel to a corresponding portion of the side wall 16 at a predetermined distance D. In particular, as is apparent in FIG. 3, each of the four portions of the convection barrier 14 is arranged perpendicular to the adjacent portion, forming a rectangle.

[0072] For example, the convection barrier 14 defines a central portion 30 of the receiving space 20 and a peripheral portion 31 of the receiving space 20. The central portion 30 is defined peripherally by the convection barrier 14 and further defined by a central region 32 of the bottom wall 18. The peripheral portion 31 is laterally defined by the convection barrier 14 and the side wall 16, and further defined by a peripheral region 33 of the bottom wall 18.

[0073] The peripheral region 33 of the bottom wall 18 is defined, for example, between the convection barrier 14 and the side wall 16. The central region 32 of the bottom wall 18 is particularly defined by the convection barrier 14 on the surface of the convection barrier 14 opposite to the peripheral region 33.

[0074] For example, the ratio of the surface area of the peripheral region 33 to the surface area of the central region 32 is determined by the size and / or capacity of the cooling device 10.

[0075] Preferably, the peripheral region 33 has a surface area of 5-15% of the total surface area of the peripheral region 33 and the central region 32.

[0076] The convection barrier 14 is configured such that when core melting occurs, the molten material flows into both sides of the convection barrier 14 in the receiving space 20, for example, into the central portion 30 and the peripheral portion 31.

[0077] According to one embodiment, the peripheral portion 31 is at least partially filled with a non-displayed filling material such as concrete intended to melt when core melting occurs. According to one embodiment, the filling material further covers the convection barrier 14.

[0078] This filling material can, in particular, protect the core catcher 8 and the convection barrier 14 during the normal operation of the nuclear power plant 1.

[0079] According to one embodiment, the filling material has a chemical composition such as to form at least a part of the sacrificial material 12 and, in particular, has oxides capable of inverting the density of the phases of the molten material.

[0080] According to another embodiment, the peripheral part 31 is empty during the normal operation of the nuclear power plant 2.

[0081] Referring to FIG. 2, the core catcher 8 comprises, for example, a fixing device 34 configured to fix the convection barrier 14 to the bottom wall 18.

[0082] The fixing device 34 preferably has at least one rail fixed to the bottom wall 18, for example welded to the bottom wall 18. The rail is configured to receive a plurality of elements forming the convection barrier 14, for example by sliding those elements along the rail.

[0083] Next, the operation of the nuclear power plant 1 according to the first embodiment when a core meltdown occurs will be described with reference to FIGS. 5 and 6.

[0084] When a core meltdown occurs, the core catcher 8 receives the molten material containing the molten core material from the core 5.

[0085] The molten material has, in particular, an initial metal phase and an initial oxide phase. In the absence of mixing between the molten material and the sacrificial material 12, the initial oxide phase exhibits a higher density than the initial metal phase.

[0086] As soon as the molten material is received within the core catcher 8, the molten material melts the sacrificial material 12 disposed therein and is mixed with this sacrificial material 12.

[0087] Referring to FIG. 5, the melt is received and mixed simultaneously, having a molten metal phase 28 in the lower phase and a molten oxide phase 29 in the upper phase. The mixing of the molten material and the sacrificial material 12 particularly leads to an inversion of the phase densities, i.e., the initial oxide phase of the molten material without the sacrificial material 12 has a higher density than the initial metal phase, whereas the oxide molten phase 29 of the melt containing the molten sacrificial material 12 has a lower density than the molten metal phase 28.

[0088] In the example of FIG. 5, the height H2 of the barrier of the convection barrier 14 corresponds to the height of the molten metal phase 28, forming a complete separation between the molten metal phase 28 in the central portion 30 and the molten metal phase 28 in the peripheral portion 31.

[0089] The convection barrier 14 restricts the heat flux to the side wall 16 as described below.

[0090] As indicated by the arrow 40 in FIG. 5, in the peripheral portion 31, local convection occurs within the molten metal phase 28. In particular, since the oxide molten phase 29 is at a higher temperature than the molten metal phase 28, the molten metal phase receives heat from the oxide molten phase 29, transfers this heat to the side wall 16, and then sinks until it is reheated by the oxide molten phase 29.

[0091] The convection barrier 14 thus restricts the heat flux of the molten metal phase 28 to the side wall 16 because the heat is not transferred to the side wall 16 by the molten metal phase 28 disposed within the central portion 30.

[0092] Since the heat flux within the molten metal phase 28 does not spread from the central portion 30 to the side wall 16, the melt forms a stable layer in the central portion 30 of the receiving space 20. The generation of such heat flux is blocked by the convection barrier 14.

[0093] Another example of the operation of the nuclear power plant 1 is shown in FIG. 6. This operation corresponds to the operation described with reference to FIG. 5, except for the differences described below.

[0094] In this case, the barrier height H2 of the convection barrier 14 is lower than the height of the molten metal phase 28. Since the heat flux 42 is such that a substantial portion of the melt is heated by the oxide melt phase 29, it is formed within the molten metal phase 28 from the central portion 30 towards the side wall 16, and then the heat is transferred to the side wall 16 following the heat flux 42.

[0095] In the example of FIG. 6, the backflow from the peripheral portion 31 to the central portion 30 is prevented, and thus only a small amount of heat is transferred to the side wall 16 by the molten metal phase 28, so the heat flux 42 is restricted by the convection barrier 14. In particular, since the height difference between the barrier height H2 of the convection barrier 14 and the height of the molten metal phase 28 is small, strong lateral heat transfer from the molten metal phase 28 to the side wall 16 does not occur.

[0096] Next, referring to FIG. 4, the nuclear power plant 1 according to the second embodiment will be described.

[0097] The nuclear power plant 1 and its operation are the same as those of the nuclear power plant 1 according to the first embodiment, except for the differences described below. In particular, the same or corresponding features of the nuclear power plant 1 according to the second embodiment compared to the first embodiment will not be described again. Only the differences will be described below.

[0098] The same or corresponding elements according to the second embodiment are denoted by the same reference numerals as those of the first embodiment, unless otherwise specified.

[0099] The containment structure 2 includes a transfer space 44 disposed vertically below the pressure vessel 4, a tunnel 46, and a diffusion compartment 48 that houses the core catcher 8 presenting the receiving space 20, hereinafter referred to as the remote diffusion compartment 48.

[0100] The remote diffusion compartment 48 preferably has dimensions that are larger than or equal to those of the diffusion compartment 6. The remote diffusion compartment 48 is defined, for example, by the walls of the containment structure 2, preferably made of concrete.

[0101] The tunnel 46 connects the transfer space 44 to a remote storage space 48, in particular to the receiving space 20 of the core catcher 8.

[0102] The tunnel 46 presents, for example, a refractory shroud 50 configured to transfer the melt from the transfer space 44 to a remote storage space 48.

[0103] The remote storage space 48 is preferably arranged in addition to and below the lateral direction of the pressure vessel 4.

[0104] According to the second embodiment, the sacrificial material 12 is arranged within the transfer space 44 and / or within the receiving space 20 of the core catcher 8 (not shown in FIG. 4 to enhance the visibility of other parts).

[0105] The operation of the nuclear power plant 1 according to the second embodiment is preferably the same as the operation according to the first embodiment.

[0106] According to one example, the operation according to the second embodiment differs from the operation of the nuclear power plant 1 according to the first embodiment in the case of a core melt in that the melt containing the core melt material melts the sacrificial material 12 inside the transfer space 44 and / or inside the receiving space 20 of the core catcher 8.

[0107] The resulting melt is received by the core catcher 8. The core catcher 8 and the convection barrier 14 are preferably the same as in the first embodiment.

[0108] The present invention has many advantages.

[0109] The convection barrier 14 makes it possible to prevent or at least reduce the appearance of a natural convection flow with a locally strong heat flux from the metal melt phase 28 to the side wall 16. Such a strong heat flux would prevent the formation of a crust in these regions and thus reduce the holding function of the core catcher 8.

[0110] The nuclear power plant 1 according to the invention, in particular the convection barrier 14, thus makes it possible to improve the protection of the containment vessel during severe accidents involving core melting.

Explanation of reference numerals

[0111] 1 Nuclear power plant 2 Containment structure 4 Pressure vessel 5 Reactor core 6 Diffusion compartment 8 Core catcher 10 Cooling device 12 Sacrificial material 14 Convection barrier 16 Side wall 18 Bottom wall 20 Receiving space 28 Molten metal phase 29 Molten oxide phase

Claims

1. In a nuclear power plant (1) comprising a storage structure (2) and a pressure vessel (4) housed within the storage structure (2), the pressure vessel (4) houses the core (5) of the nuclear power plant (1) during normal operation of the nuclear power plant (1), and the storage structure (2) defines a diffusion compartment (6, 48) configured to receive a molten material containing molten core material from the core (5) in the event of a core melt. The nuclear power plant (1) further comprises, hereinafter, - a side wall (16) and a bottom wall (18) that define an inner receiving space (20) intended to receive the molten material, and a core catcher (8) disposed within the diffusion compartment (6, 48), - a cooling device (10) configured to cool the side wall (16) and the bottom wall (18) of the core catcher (8), - a sacrificial material (12) disposed in the core catcher (8) so as to be melted by the molten material flowing toward and / or into it, the molten sacrificial material being intended to be mixed with the molten material to obtain a melt having a lower phase consisting of a molten metal phase (28) and an upper phase consisting of a molten oxide phase (29), comprising The core catcher (8) is further disposed within the receiving space (20) defined by the side wall (16) and the bottom wall (18), and comprises a convection barrier (14) protruding upward from the bottom wall (18) of the core catcher (8). The convection barrier (14) extends substantially parallel to the side wall (16) of the core catcher (8) and at a predetermined distance (D) from the side wall. The convection barrier (14) is made of a material adapted to withstand the molten metal phase (28) of the melt. The convection barrier (14) is configured such that, in the event of a core melt, the molten material flows into both sides of the convection barrier (14) within the receiving space (20). A nuclear power plant characterized by this.

2. The nuclear power plant (1) according to claim 1, wherein the height (H2) of the barrier of the convection barrier (14) is strictly lower than the height (H1) of the wall of the side wall (16), and the height (H2) of the barrier and the height (H1) of the wall are each measured from the bottom wall (18).

3. The nuclear power plant (1) according to claim 2, wherein the height (H1) of the wall is selected according to the predicted total volume of the melt to be retained, and / or the height (H2) of the barrier of the convection barrier (14) is selected according to the predicted maximum volume of the molten metal phase (28).

4. The material of the convection barrier (14) has a melting point that is strictly higher than the temperature of the metallic molten phase (28) of the melt, and / or the material of the convection barrier (14) has a thermal conductivity that is strictly lower than 3 W / m·K, and preferably the material of the convection barrier (14) includes sintered zirconia bricks, the nuclear power plant (1) according to any one of claims 1 to 3.

5. A nuclear power plant (1) according to any one of claims 1 to 4, wherein a predetermined distance (D) to the side wall (16) of the convection barrier (14) is determined according to at least one characteristic of the core catcher (8) and / or the cooling device (10).

6. A peripheral region (33) of the bottom wall (18) is defined between the convection barrier (14) and the side wall (16), and a central region (32) of the bottom wall (18) is defined by the convection barrier (14) on the surface of the convection barrier (14) on the side opposite to the peripheral region (33). The peripheral region (33) has a surface area that is 5 to 15% of the total surface area of the peripheral region (33) and the central region (32), the nuclear power plant (1) according to any one of claims 1 to 5.

7. A nuclear power plant (1) according to any one of claims 1 to 6, wherein the sacrificial material (12) includes at least one oxide selected from, for example, silicon oxide, calcium oxide, aluminum oxide, and / or iron oxide.

8. A peripheral portion (31) of the receiving space (20) defined between the convection barrier (14) and the side wall (16) is empty during normal operation of the nuclear power plant (2) or is at least partially filled with a filling material intended to melt in the event of core melting, and the filling material is, for example, concrete, the nuclear power plant (1) according to any one of claims 1 to 7.

9. A nuclear power plant (1) according to any one of claims 1 to 8, wherein the convection barrier (14) has a constant height (H2) measured parallel to the side wall (16) from the bottom wall (18).

10. A nuclear power plant (1) according to any one of claims 1 to 9, wherein the core catcher (8) includes at least one fixing device (34) configured to fix the convection barrier (14) to the bottom wall (18), and the fixing device (34) preferably includes at least one rail fixed to the bottom wall (18).

11. The convection barrier (14) is provided with a coating material (25), and the coating material (25) is preferably made of metal, the nuclear power plant (1) according to any one of claims 1 to 10.

12. The core catcher (8) is disposed vertically below the pressure vessel (4), and the sacrificial material (12) is disposed within the receiving space (20), the nuclear power plant (1) according to any one of claims 1 to 11.

13. The containment structure (2) includes a transfer space (44) disposed vertically below the pressure vessel (4) and a tunnel (46) connecting the transfer space (44) and the receiving space (20) of the core catcher (8), and the sacrificial material (12) is disposed within the transfer space (44) and / or within the receiving space (20) of the core catcher (8), the nuclear power plant (1) according to any one of claims 1 to 11.

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