WO2024012675A1 - Nuclear power plant comprising a core catcher - Google Patents

Nuclear power plant comprising a core catcher Download PDF

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Publication number
WO2024012675A1
WO2024012675A1 PCT/EP2022/069655 EP2022069655W WO2024012675A1 WO 2024012675 A1 WO2024012675 A1 WO 2024012675A1 EP 2022069655 W EP2022069655 W EP 2022069655W WO 2024012675 A1 WO2024012675 A1 WO 2024012675A1
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WO
WIPO (PCT)
Prior art keywords
power plant
nuclear power
core
molten
convection barrier
Prior art date
Application number
PCT/EP2022/069655
Other languages
French (fr)
Inventor
Manfred Fischer
Torsten Keim
Original Assignee
Framatome Gmbh
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Framatome Gmbh filed Critical Framatome Gmbh
Priority to PCT/EP2022/069655 priority Critical patent/WO2024012675A1/en
Publication of WO2024012675A1 publication Critical patent/WO2024012675A1/en

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Classifications

    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C9/00—Emergency protection arrangements structurally associated with the reactor, e.g. safety valves provided with pressure equalisation devices
    • G21C9/016—Core catchers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00—Energy generation of nuclear origin
    • Y02E30/30—Nuclear fission reactors

Definitions

  • Nuclear power plant comprising a core catcher
  • the present invention concerns a nuclear power plant comprising a pressure vessel and a core catcher.
  • the present invention relates to a containment function of a nuclear power plant in the case of a severe accident in the nuclear power plant having an EPR reactor or of another reactor that uses a metallic crucible for core melt retention in case of a severe accident.
  • such nuclear power plants comprise a pressure vessel, which is located inside a containment structure and contains, during normal operation of the nuclear power plant, the reactor core of the nuclear power plant.
  • such nuclear power plants typically comprise a core catcher.
  • the core may at least partially melt.
  • Such an event is called core meltdown.
  • the core catcher is configured for receiving molten material from the core in the event of a core meltdown that progresses up to the failure of the pressure vessel.
  • An objective of the present invention is to prevent the failure of a core catcher of a nuclear power plant and thus to maintain the integrity of the containment of the nuclear power plant, in the event of a severe accident resulting in a core meltdown.
  • a nuclear power plant comprising a containment structure and a pressure vessel received in 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 spreading compartment configured for receiving molten material including molten core material from the core in the event of a core meltdown, wherein the nuclear power plant furthermore comprises:
  • a core catcher arranged in the spreading compartment and comprising a lateral wall and a bottom wall interiorly delimiting a reception space intended for receiving the molten material;
  • a cooling device configured for cooling the lateral wall and the bottom wall of the core catcher
  • a sacrificial material arranged so as to be molten by the molten material flowing towards and/or into the core catcher, the molten sacrificial material being intended to be mixed with said molten material so as to obtain a melt comprising a lower phase consisting of a metal molten phase and an upper phase consisting of an oxide molten phase.
  • the core catcher further comprises a convection barrier, arranged within the reception space delimited by the lateral wall and the bottom wall, and protruding upwards from the bottom wall of the core catcher, the convection barrier extending substantially parallel to and at a predetermined distance from the lateral wall of the core catcher, the convection barrier consisting of a material adapted to resist the metal molten phase of the melt, the convection barrier being configured in such a manner that the molten material flows, in the event of the core meltdown, into the reception space on both sides of the convection barrier.
  • the nuclear power plant according to the invention allows improving containment protection in case of a core meltdown, because local failure of the core catcher is prevented.
  • the combination of the presence of the sacrificial material together with the convection barrier reduces heat fluxes into the lateral wall of the core catcher to non-critical values. Thanks to the reduction of heat fluxes into the lateral wall of the core catcher, a crust of solidified melt develops adjacent to the core catcher, which reduces the risk of failure or damage to the integrity of the core catcher.
  • the molten sacrificial material is mixed with the molten core material forming a melt, which has a metal molten phase and an oxide molten phase. Thanks to the mixing with the sacrificial material, the density of the metal molten phase is higher than the density of the oxide molten phase, such that the metal molten phase is located below the oxide molten phase in the melt. Due to this melt layering, the metal molten phase is arranged so as to be cooled through the bottom of the core catcher so that crusts may form at the bottom and sidewalls.
  • an upper part of the metal molten phase of the melt may be heated due to its contact with the warmer oxide molten phase above, and locally strong heat fluxes out of the lower phase into the lateral wall may occur, due to natural convection in the lower phase of the melt.
  • This convection is propelled by the lateral walls, which are cooler than the metal molten phase of the melt, and material from the metal molten phase may move quickly to the lateral wall and/or transfer high amounts of heat into the lateral wall.
  • These convection currents inside the melt resulting in strong heat fluxes from the melt to the lateral wall of the core catcher may prevent the formation of crusts at least in some areas of contact between the melt and the core catcher, in particular adjacent to the lateral wall.
  • a convection barrier allows reducing such strong heat fluxes caused by natural convection inside the lower phase of the melt to the lateral wall of the core catcher.
  • the convection barrier separates the metal molten phase into a narrow outer part in contact with the lateral wall and a large central part.
  • the convection barrier forms in particular an adiabatic limitation around the central part, which inhibits natural convection in the central part. As a consequence, a stable stratification forms in the central part. Because of this, all heat carried into the metal molten phase from above across a contact area between the upper phase and the lower phase in the central part is conducted into the cooled bottom.
  • the lateral walls are only heated by the small fraction of the total heat coming from the oxide molten phase in contact with the outer part of the molten metal phase.
  • This allows preventing strong heat fluxes from the metal molten phase into the lateral wall and crusts may thus be formed in the areas of contact of the melt, in particular of the metal molten phase, with the core catcher.
  • the skilled person understands that such strong heat fluxes are not observed in the oxide molten phase in the event of a core meltdown, because the oxide molten phase is surrounded by a crust, which establishes uniform boundary temperatures.
  • a barrier height of the convection barrier is strictly smaller than a wall height of the lateral wall, the barrier height and the wall height being each measured from the bottom wall;
  • the wall height is chosen depending on a predicted total volume of the melt to be retained
  • the barrier height of the convection barrier is chosen depending on a predicted maximum volume of the metal molten phase
  • the material of the convection barrier has a melting point strictly higher than a temperature of the metal molten 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 comprises sintered zirconia bricks
  • the predetermined distance of the convection barrier to the lateral wall is determined depending on at least one feature of the core catcher and/or the cooling device;
  • a peripheral area of the bottom wall is delimited between the convection barrier and the lateral wall, and a central area of the bottom wall is delimited by the convection barrier on a side of the convection barrier opposite the peripheral area, the peripheral area having a surface area comprised between 5% and 15% of the sum of the surface areas of the peripheral area and the central area;
  • the sacrificial material comprises at least one oxide, for example chosen from silicium oxide, calcium oxide, aluminum oxide and/or iron oxide;
  • a peripheral part of the reception space, defined between convection barrier and the lateral wall is empty during the normal operation of the nuclear power plant or is at least partially filled with a filling material intended to be molten in the event of the core meltdown, the filling material being for example concrete;
  • the convection barrier has a constant height, measured from the bottom wall and in parallel to the lateral wall;
  • the core catcher comprises at least one fixing device configured for fixing the convection barrier to the bottom wall, the fixing device comprising preferably at least one rail fixed to the bottom wall;
  • the convection barrier is provided with a sheathing
  • the sheathing consists of metal
  • the core catcher is arranged vertically below the pressure vessel, the sacrificial material being arranged in the reception space;
  • the containment structure comprises a transfer space arranged vertically below the pressure vessel and a tunnel connecting the transfer space and the reception space of the core catcher, wherein the sacrificial material is arranged in the transfer space and/or in the reception space of the core catcher.
  • FIG. 1 is a schematic sectional view according to a first plane I of a part of a nuclear power plant according to a first embodiment of the invention, comprising a core catcher with a convection barrier according to the invention;
  • FIG. 2 is a schematic sectional view of the core catcher of Figure 1 according to the first plane I, illustrating details of the core catcher;
  • FIG. 3 is a schematic view from above of the core catcher of Figure 1 , according to a second plane II perpendicular to the first plane I;
  • FIG. 4 is a schematic sectional view of a part of a nuclear power plant similar to the view of Figure 1 , according to a second embodiment
  • FIG. 5 is a schematic sectional view of the core catcher of any one of Figures 1 to
  • FIG. 6 is a view similar to the view of Figure 5, according to a second example.
  • the expression “substantially parallel to” is understood to specify a deviation to parallelism of plus or minus 10 degrees, preferably of plus or minus
  • a nuclear power plant 1 according to a first embodiment comprises a containment structure 2, a reactor pressure vessel 4, called pressure vessel 4 in the following, and a reactor core 5.
  • the containment structure 2 defines a spreading compartment 6 configured for receiving molten material including molten core material from the core 5 in the event of a core meltdown.
  • the nuclear power plant 1 furthermore comprises a core catcher 8 arranged in the spreading compartment 6, a cooling device 10 and sacrificial material 12.
  • Figure 1 illustrates an example of the nuclear power plant 1 as seen in cross-section according to a first plane I.
  • the containment structure 2 is a structure distinct from the core catcher 8.
  • the containment structure 2 comprises concrete, preferably is made of concrete and the core catcher 8 comprises preferably metal.
  • the pressure vessel 4 is received by the containment structure 2, in particular in an inner volume defined by the containment structure 2 above the spreading compartment 6.
  • the pressure vessel 4 contains the core 5 during normal operation of the nuclear power plant 1.
  • the core 5 is thus arranged inside the pressure vessel 4 during normal operation.
  • the pressure vessel 4 furthermore contains, for example, a core cooling system and support elements, for example made from metal, configured to support the core 5 and/or to guide coolant of the reactor cooling system (not shown).
  • a core cooling system and support elements for example made from metal, configured to support the core 5 and/or to guide coolant of the reactor cooling system (not shown).
  • the nuclear reactor is in particular a generation III reactor.
  • the core 5 is part of an EPR reactor.
  • the core catcher 8 comprises a convection barrier 14, a lateral wall 16 and a bottom wall 18.
  • the lateral wall 16 and the bottom wall 18 interiorly delimit a reception space 20 intended for receiving molten material.
  • the molten material includes molten core material from the core 5 formed during the core meltdown.
  • the molten material additionally comprises, for example, material from other elements received in the pressure vessel 4 during normal operation, such as the reactor cooling system and/or from the pressure vessel 4 itself.
  • core meltdown it is understood that at least parts of the core 5 melt and become at least partially liquid.
  • the molten material comprises in particular a metal phase and an oxide phase.
  • the oxide phase presents a higher density than the metal phase.
  • the core catcher 8 comprises for example metal, such as for example iron, cast iron or steel.
  • the core catcher 8 is arranged below the pressure vessel 4, for example vertically below or laterally offset below the pressure vessel 4.
  • the core catcher 8 is arranged vertically below the pressure vessel 4.
  • core catcher vertically below the pressure vessel
  • the core catcher 8 and in particular the reception space 20, faces a lower part of the pressure vessel 4.
  • no walls of the containment structure 2 are arranged between the core catcher 8 and the pressure vessel 4 in this case.
  • the lateral wall 16 extends in particular perpendicularly from the bottom wall 18.
  • the lateral wall 16 and the bottom wall form a vessel having a bottom formed by the bottom wall 18, and a circumferential wall formed by the lateral wall 16.
  • the lateral wall 16 comprises four wall parts, preferably forming a rectangle or a square.
  • the lateral wall 16 comprises for example a rectangular section having a wall height H1 and a wall width W1 .
  • the wall height H1 of the lateral wall 16 is for example chosen depending on a predicted total volume of a melt (described below) to be retained by the core catcher 8 in the event of a core meltdown.
  • the bottom wall 18 is arranged to connect two opposite parts of the lateral wall 16.
  • the bottom wall 18 and the lateral wall 16 are for example provided with cooling fins 22, in particular on a lower surface of the bottom wall 18 and on a surface of the lateral wall 16 opposite to the reception space 20.
  • the cooling fins 22 may extend perpendicularly from the lower surface of the bottom wall 18 and from the surface of the lateral wall 16 opposite to the reception space 20, into a space intended to receive coolant.
  • the lateral wall 16 and the bottom wall 18 are made of several pieces that are fixed to each other, for example by tongue-and-groove connections.
  • the lateral wall 16, the bottom wall 18 and optionally the cooling fins 22, are made in one piece, for example by casting.
  • the lateral wall 16, the bottom wall 18 and optionally the cooling fins 22, are welded together.
  • the lateral wall 16, the bottom wall 18 and optionally the cooling fins 22 are preferably made out of metal.
  • the cooling device 10 is configured for cooling the lateral wall 16 and the bottom wall 18 of the core catcher 8.
  • the cooling device 10 defines for example a coolant reception space 24 for reception of a coolant 26, such as water, so that the coolant 26 is in contact with the lateral wall 16 and the bottom wall 18.
  • a coolant 26 such as water
  • the coolant reception space 24 is arranged preferably outside the core catcher 8, in particular below the bottom wall 18 and on a side of the lateral wall 16 opposite to the reception space 20 of the core catcher 8.
  • the cooling device 10 defines furthermore at least one coolant inlet 27 for the inlet of the coolant 26 into the coolant reception space 24 in case of a severe accident.
  • the sacrificial material 12 is arranged so as to be molten by the molten material flowing towards and/or into the core catcher 8.
  • the molten sacrificial material 12 is intended to be mixed with the molten material so as to obtain a melt comprising a lower phase consisting of a metal molten phase 28 and an upper phase consisting of an oxide molten phase 29.
  • a melt comprising a lower phase consisting of a metal molten phase 28 and an upper phase consisting of an oxide molten phase 29. Examples of the metal molten phase 28 and the oxide molten phase 29 are illustrated in Figures 5 and 6.
  • melt designates the mix obtained by mixing the molten material including molten core material together with the sacrificial material 12.
  • the sacrificial material 12 is a material configured to invert the density of the metal phase and the oxide phase of the molten material, when being mixed with this molten material including the molten core material, so that the metal molten phase 28 has a higher density than the oxide molten phase 29, and is thus arranged below the oxide molten phase 29.
  • the sacrificial material 12 comprises for example light-weight oxides so as to achieve the intended density inversion of the phases of the molten material when being mixed with it.
  • the sacrificial material 12 comprises oxides chosen from silica (or silicon dioxide) calcia (or calcium oxide), alumina (or aluminum oxide), and/or iron oxide.
  • the oxides are sintered, or otherwise compounded, e.g. in the form of concrete.
  • the sacrificial material 12 may contain metal, e.g. iron or steel, for example in the form of reinforcing bars to enhance mechanical stability.
  • the sacrificial material 12 is arranged in the reception space 20, as for example illustrated in Figure 1 . According to the first embodiment, the sacrificial material 12 is intended to be mixed with the molten material upon reception in the reception space 20.
  • the sacrificial material 12 is not shown in Figure 2 for better visibility of other parts.
  • the convection barrier 14 is arranged within the reception space 20 delimited by the lateral wall 16 and the bottom wall 18.
  • the convection barrier 14 consists of a material adapted to resist the metal molten phase 28 of the melt.
  • the convection barrier consisting of a material adapted to resist the metal molten phase of the melt
  • a material which fulfills at least one, preferably both of the followings requirements: the melting point of the material is strictly higher than a temperature of the metal molten phase 28 of the melt, and/or the material of the convection barrier 14 presents a thermal conductivity strictly lower than 3 W/m.K.
  • the convection barrier 14 comprises, preferably consists of, a refractory material, for example chosen from zirconia, in particular sintered zirconia, magnesium oxide, aluminum oxide, e.g. aluminum(lll) oxide, or uranium dioxide.
  • a refractory material for example chosen from zirconia, in particular sintered zirconia, magnesium oxide, aluminum oxide, e.g. aluminum(lll) oxide, or uranium dioxide.
  • the convection barrier consists of bricks of such material.
  • the convection barrier 14 is provided with a sheathing 25.
  • the sheathing 25 is in particular configured for protecting the convection barrier 14 during normal operation of the nuclear power plant 1 .
  • the sheathing 25 consists preferably of metal or a predefined sacrificial material.
  • the sheathing 25 is intended to be melted by the melt in the event of a core meltdown.
  • the convection barrier 14 protrudes upwards from the bottom wall 18.
  • the convection barrier 14 extends along at least one extension direction E. Examples of the extension direction E are illustrated in Figure 3.
  • the convection barrier 14 presents a section, perpendicular to the extension direction E of the convection barrier 14, having a rectangular form.
  • the convection barrier 14 has a barrier height H2 measured from the bottom wall 18, and a barrier width W2.
  • the barrier height H2 is chosen depending on a predicted maximum volume of the metal molten phase 28, in particular so as to form a separation for the metal molten phase 28 arranged on both sides of the convection barrier 14.
  • the barrier height H2 is identical to or higher than an expected height of the metal molten phase 28.
  • the barrier height H2 is constant, measured in parallel to the lateral wall 16, and in particular along the extension direction E, e.g. along a horizontal direction.
  • the barrier height H2 is strictly smaller than the wall height H1 .
  • the convection barrier 14 is deprived of openings or holes along a direction perpendicular to the extension direction E.
  • the convection barrier 14 presents at least one opening along the direction perpendicular to the extension direction E.
  • the convection barrier 14 comprises a plurality of barrier sections having a distance one to another.
  • a total length of the barrier sections, defined in parallel to the lateral wall 16, is strictly greater than a total length of interruptions of the convection barrier 14 between these sections.
  • the convection barrier 14 extends substantially parallel to and at a predetermined distance D from the lateral wall 16.
  • the predetermined distance D of the convection barrier 14 to the lateral wall 16 is determined depending on at least one feature of the cooling device 10, such as a cooling capacity of the cooling device 10, and/or at least one feature of the core catcher 8, such as the wall width W1 of the lateral wall 16 or a material of the core catcher 8.
  • the predetermined distance D is for example comprised between 20 cm and 40 cm.
  • the convection barrier 14 comprises four parts, each extending in parallel and at the predetermined distance D to a corresponding part of the lateral wall 16.
  • each of the four parts of the convection barrier 14 is arranged perpendicularly to a neighboring part, so as to form a rectangle, as visible in Figure 3.
  • the convection barrier 14 defines a central part 30 of the reception space 20 and a peripheral part 31 of the reception space 20.
  • the central part 30 is delimited circumferentially by the convection barrier 14, and further delimited by a central area 32 of the bottom wall 18.
  • the peripheral part 31 is delimited laterally by the convection barrier 14 and the lateral wall 16, and further delimited by a peripheral area 33 of the bottom wall 18.
  • the peripheral area 33 of the bottom wall 18 is for example delimited between the convection barrier 14 and the lateral wall 16.
  • the central area 32 of the bottom wall 18 is in particular delimited by the convection barrier 14 on a side of the convection barrier 14 opposite the peripheral area 33.
  • a ratio of a surface area of the peripheral area 33 to a surface area of the central area 32 is determined in function of a size and/or capacity of the cooling device 10.
  • the peripheral area 33 has a surface area comprised between 5% and 15% of the sum of the surface areas of the peripheral area 33 and the central area 32.
  • the convection barrier 14 is configured in such a manner that the molten material flows, in the event of the core meltdown, into the reception space 20 on both sides of the convection barrier 14, e.g. into the central part 30 and the peripheral part 31 .
  • the peripheral part 31 is at least partially filled with a filling material, not shown, such as concrete, intended to be molten in the event of the core meltdown.
  • the filling material covers, in addition, the convection barrier 14.
  • This filling material allows in particular protecting the core catcher 8 and the convection barrier 14 during normal operation of the nuclear power plant 1 .
  • the filling material comprises a chemical composition so as to form at least part of the sacrificial material 12, in particular comprises oxides which allow inverting the density of the phases of the molten material.
  • the peripheral part 31 is empty during the normal operation of the nuclear power plant 2.
  • the core catcher 8 comprises for example a fixing device 34 configured for fixing the convection barrier 14 to the bottom wall 18.
  • the fixing device 34 comprises preferably at least one rail fixed to the bottom wall 18, for example welded to the bottom wall 18.
  • the rail is configured for receiving a plurality of elements forming the convection barrier 14, for example by sliding the elements along the rail.
  • the core catcher 8 receives the molten material including molten core material from the core 5.
  • the molten material comprises in particular an initial metal phase and an initial oxide phase.
  • the initial oxide phase presents a higher density than the initial metal phase.
  • the molten material melts the sacrificial material 12 arranged therein and is mixed with this sacrificial material 12.
  • the melt is received upon mixing, and comprises the metal molten phase 28 in a lower phase and the oxide molten phase 29 in an upper phase.
  • the mixing of the molten material with the sacrificial material 12 leads in particular to an inversion of density of the phases, i.e. the oxide molten phase 29 of the melt, comprising the molten sacrificial material 12, has a lower density than the metal molten phase 28, whereas the initial oxide phase of the molten material, without the sacrificial material 12, has a higher density than the initial metal phase.
  • the barrier height H2 of the convection barrier 14 corresponds to the height the metal molten phase 28, so as to form a complete separation between the metal molten phase 28 in the central part 30 from the metal molten phase 28 in the peripheral part 31 .
  • the convection barrier 14 limits heat fluxes to the lateral wall 16 as described in the following.
  • a local convection inside the metal molten phase 28 occurs, as illustrated by arrows 40 in Figure 5.
  • the oxide molten phase 29 being hotter than the metal molten phase 28, the latter receives heat from the oxide molten phase 29, transfers this heat to the lateral wall 16, and then sinks down until being heated again by the oxide molten phase 29.
  • the convection barrier 14 limits thus heat fluxes of the metal molten phase 28 to the lateral wall 16, because no heat is transferred by the metal molten phase 28 arranged in the central part 30 to the lateral wall 16.
  • the melt forms stable layers, because no heat flux in the metal molten phase 28 extends form the central part 30 to the lateral wall 16. A generation of such heat flux is prevented by the convection barrier 14.
  • FIG. 6 Another example of the operation of the nuclear power plant 1 is shown in Figure 6. The operation corresponds to the operation as described with reference to Figure 5, with the exception of the difference described below.
  • the barrier height H2 of the convection barrier 14 is smaller than a height of the metal molten phase 28.
  • a heat flux 42 is formed in the metal molten phase 28 from the central part 30 to the lateral wall 16, as the corresponding part of the melt is heated by the oxide molten phase 29 and the heat is then transferred according to the heat flux 42 to the lateral wall 16.
  • the heat flux 42 is limited by the convection barrier 14, because the backflow from the peripheral part 31 to the central part 30 is impeded and thus only small quantities of heat are transferred by the metal molten phase 28 to the lateral wall 16.
  • the difference in height between the barrier height H2 of the convection barrier 14 and the height of the metal molten phase 28 is small, so that no strong lateral heat transfer occurs from the metal molten phase 28 into the lateral wall 16.
  • the nuclear power plant 1 and its operation is identical to the nuclear power plant 1 according to the first embodiment, with the exception of differences described hereafter.
  • the same or corresponding features of the nuclear power plant 1 according to the second embodiment compared with the first embodiment are not described again. Only the differences are described hereafter.
  • the containment structure 2 comprises a transfer space 44 arranged vertically below the pressure vessel 4, a tunnel 46 and the spreading compartment 48, called distant spreading compartment 48 in the following, receiving the core catcher 8 presenting the reception space 20.
  • the distant spreading compartment 48 has preferably larger or the same dimensions as the spreading compartment 6.
  • the distant spreading compartment 48 is for example defined by walls of the containment structure 2, preferably made of concrete.
  • the tunnel 46 connects the transfer space 44 with the distant containment space 48, in particular with the reception space 20 of the core catcher 8.
  • the tunnel 46 presents for example a refractory shroud 50 configured to transport the melt from transfer space 44 to the distant containment space 48.
  • the distant containment space 48 is preferably arranged laterally besides and below the pressure vessel 4.
  • the sacrificial material 12 is arranged in the transfer space 44 and/or in the reception space 20 of the core catcher 8 (not shown in Figure 4 for better visibility of other parts).
  • the operation of the nuclear power plant 1 according to the second embodiment is preferably identical to the operation according to first embodiment.
  • the operation according to the second embodiment differs from the operation of the nuclear power plant 1 according to the first embodiment in the event of a core meltdown in that the molten material including the core molten material melts the sacrificial material 12 inside the transfer space 44 and/or inside the reception space 20 of the core catcher 8.
  • the obtained melt is received by the core catcher 8.
  • the core catcher 8 and convection barrier 14 are preferably identical to the first embodiment.
  • the invention presents many advantages.
  • the convection barrier 14 allows to prevent or at least to reduce the occurrence of natural convection currents implying locally strong heat fluxes from the metal molten phase 28 to the lateral wall 16. Such strong heat fluxes would prevent the formation of crusts in these areas and thus reduce the retention function of the core catcher 8.
  • the nuclear power plant 1 according to the invention, and in particular the convection barrier 14, allows thus to improve containment protection in case of a severe accident implying a core meltdown.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Structure Of Emergency Protection For Nuclear Reactors (AREA)

Abstract

The invention relates to a nuclear power plant (1) comprising a containment structure (2) and a pressure vessel (4) received in the containment structure (2), the pressure vessel (4) containing the core (5) of the nuclear power plant (1) during normal operation of the nuclear power plant (1), the containment structure (2) defining a spreading compartment (6) configured for receiving molten material including molten core material from the core (5) in the event of a core meltdown, wherein the nuclear power plant (1) furthermore comprises a core catcher (8) arranged in the spreading compartment (6) and comprising a lateral wall (16) and a bottom wall (18) interiorly delimiting a reception space (20) intended for receiving the molten material. The core catcher (8) comprises a convection barrier (14), arranged within the reception space (20) delimited by the lateral wall (16) and the bottom wall (18).

Description

Nuclear power plant comprising a core catcher
The present invention concerns a nuclear power plant comprising a pressure vessel and a core catcher.
The present invention relates to a containment function of a nuclear power plant in the case of a severe accident in the nuclear power plant having an EPR reactor or of another reactor that uses a metallic crucible for core melt retention in case of a severe accident.
In general, such nuclear power plants comprise a pressure vessel, which is located inside a containment structure and contains, during normal operation of the nuclear power plant, the reactor core of the nuclear power plant.
For the purpose of a containment function in the case of a severe accident, such nuclear power plants typically comprise a core catcher. Indeed, in case of a severe accident, the core may at least partially melt. Such an event is called core meltdown. The core catcher is configured for receiving molten material from the core in the event of a core meltdown that progresses up to the failure of the pressure vessel.
During such a core meltdown, large quantities of the molten material, such as steel and other material of the core and the pressure vessel, may be reversed into the core catcher. Under extreme conditions, local failure of the structure of the core catcher may occur, for example due to locally high heat fluxes from the molten material into the core catcher.
An objective of the present invention is to prevent the failure of a core catcher of a nuclear power plant and thus to maintain the integrity of the containment of the nuclear power plant, in the event of a severe accident resulting in a core meltdown.
To this end, a nuclear power plant comprising a containment structure and a pressure vessel received in 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 spreading compartment configured for receiving molten material including molten core material from the core in the event of a core meltdown, wherein the nuclear power plant furthermore comprises:
- a core catcher arranged in the spreading compartment and comprising a lateral wall and a bottom wall interiorly delimiting a reception space intended for receiving the molten material;
- a cooling device, configured for cooling the lateral wall and the bottom wall of the core catcher,
- a sacrificial material arranged so as to be molten by the molten material flowing towards and/or into the core catcher, the molten sacrificial material being intended to be mixed with said molten material so as to obtain a melt comprising a lower phase consisting of a metal molten phase and an upper phase consisting of an oxide molten phase.
The core catcher further comprises a convection barrier, arranged within the reception space delimited by the lateral wall and the bottom wall, and protruding upwards from the bottom wall of the core catcher, the convection barrier extending substantially parallel to and at a predetermined distance from the lateral wall of the core catcher, the convection barrier consisting of a material adapted to resist the metal molten phase of the melt, the convection barrier being configured in such a manner that the molten material flows, in the event of the core meltdown, into the reception space on both sides of the convection barrier.
The nuclear power plant according to the invention allows improving containment protection in case of a core meltdown, because local failure of the core catcher is prevented. Indeed, the combination of the presence of the sacrificial material together with the convection barrier reduces heat fluxes into the lateral wall of the core catcher to non-critical values. Thanks to the reduction of heat fluxes into the lateral wall of the core catcher, a crust of solidified melt develops adjacent to the core catcher, which reduces the risk of failure or damage to the integrity of the core catcher.
In particular, in the event of a core meltdown, the molten sacrificial material is mixed with the molten core material forming a melt, which has a metal molten phase and an oxide molten phase. Thanks to the mixing with the sacrificial material, the density of the metal molten phase is higher than the density of the oxide molten phase, such that the metal molten phase is located below the oxide molten phase in the melt. Due to this melt layering, the metal molten phase is arranged so as to be cooled through the bottom of the core catcher so that crusts may form at the bottom and sidewalls.
With the above-mentioned melt layering, in the absence of a convection barrier, an upper part of the metal molten phase of the melt may be heated due to its contact with the warmer oxide molten phase above, and locally strong heat fluxes out of the lower phase into the lateral wall may occur, due to natural convection in the lower phase of the melt. This convection is propelled by the lateral walls, which are cooler than the metal molten phase of the melt, and material from the metal molten phase may move quickly to the lateral wall and/or transfer high amounts of heat into the lateral wall. These convection currents inside the melt resulting in strong heat fluxes from the melt to the lateral wall of the core catcher may prevent the formation of crusts at least in some areas of contact between the melt and the core catcher, in particular adjacent to the lateral wall.
The provision of a convection barrier according to the invention allows reducing such strong heat fluxes caused by natural convection inside the lower phase of the melt to the lateral wall of the core catcher. According to embodiments, the convection barrier separates the metal molten phase into a narrow outer part in contact with the lateral wall and a large central part. The convection barrier forms in particular an adiabatic limitation around the central part, which inhibits natural convection in the central part. As a consequence, a stable stratification forms in the central part. Because of this, all heat carried into the metal molten phase from above across a contact area between the upper phase and the lower phase in the central part is conducted into the cooled bottom. Therefore, the lateral walls are only heated by the small fraction of the total heat coming from the oxide molten phase in contact with the outer part of the molten metal phase. This allows preventing strong heat fluxes from the metal molten phase into the lateral wall and crusts may thus be formed in the areas of contact of the melt, in particular of the metal molten phase, with the core catcher. The skilled person understands that such strong heat fluxes are not observed in the oxide molten phase in the event of a core meltdown, because the oxide molten phase is surrounded by a crust, which establishes uniform boundary temperatures.
Further embodiments may relate to one or more of the following features, which may be combined in any technical feasible combination:
- a barrier height of the convection barrier is strictly smaller than a wall height of the lateral wall, the barrier height and the wall height being each measured from the bottom wall;
- the wall height is chosen depending on a predicted total volume of the melt to be retained;
- the barrier height of the convection barrier is chosen depending on a predicted maximum volume of the metal molten phase;
- the material of the convection barrier has a melting point strictly higher than a temperature of the metal molten 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 comprises sintered zirconia bricks;
- the predetermined distance of the convection barrier to the lateral wall is determined depending on at least one feature of the core catcher and/or the cooling device;
- a peripheral area of the bottom wall is delimited between the convection barrier and the lateral wall, and a central area of the bottom wall is delimited by the convection barrier on a side of the convection barrier opposite the peripheral area, the peripheral area having a surface area comprised between 5% and 15% of the sum of the surface areas of the peripheral area and the central area;
- the sacrificial material comprises at least one oxide, for example chosen from silicium oxide, calcium oxide, aluminum oxide and/or iron oxide; - a peripheral part of the reception space, defined between convection barrier and the lateral wall is empty during the normal operation of the nuclear power plant or is at least partially filled with a filling material intended to be molten in the event of the core meltdown, the filling material being for example concrete;
- the convection barrier has a constant height, measured from the bottom wall and in parallel to the lateral wall;
- the core catcher comprises at least one fixing device configured for fixing the convection barrier to the bottom wall, the fixing device comprising preferably at least one rail fixed to the bottom wall;
- the convection barrier is provided with a sheathing,
- the sheathing consists of metal;
- the core catcher is arranged vertically below the pressure vessel, the sacrificial material being arranged in the reception space;
- the containment structure comprises a transfer space arranged vertically below the pressure vessel and a tunnel connecting the transfer space and the reception space of the core catcher, wherein the sacrificial material is arranged in the transfer space and/or in the reception space of the core catcher.
These features and advantages of the invention will be further explained in the following description, given only as non-limiting examples, and with reference to the attached drawings, on which:
- Figure 1 is a schematic sectional view according to a first plane I of a part of a nuclear power plant according to a first embodiment of the invention, comprising a core catcher with a convection barrier according to the invention;
- Figure 2 is a schematic sectional view of the core catcher of Figure 1 according to the first plane I, illustrating details of the core catcher;
- Figure 3 is a schematic view from above of the core catcher of Figure 1 , according to a second plane II perpendicular to the first plane I;
- Figure 4 is a schematic sectional view of a part of a nuclear power plant similar to the view of Figure 1 , according to a second embodiment;
- Figure 5 is a schematic sectional view of the core catcher of any one of Figures 1 to
4 according to a first example, when a melt in the event of a core meltdown is received by the core catcher, and
- Figure 6 is a view similar to the view of Figure 5, according to a second example.
In the following specification, the expression “substantially parallel to” is understood to specify a deviation to parallelism of plus or minus 10 degrees, preferably of plus or minus
5 degrees. With reference to Figure 1 , a nuclear power plant 1 according to a first embodiment comprises a containment structure 2, a reactor pressure vessel 4, called pressure vessel 4 in the following, and a reactor core 5.
The containment structure 2 defines a spreading compartment 6 configured for receiving molten material including molten core material from the core 5 in the event of a core meltdown. In particular, walls of the containment structure 2, preferably made of concrete, delimit the spreading compartment 6.
The nuclear power plant 1 furthermore comprises a core catcher 8 arranged in the spreading compartment 6, a cooling device 10 and sacrificial material 12.
Figure 1 illustrates an example of the nuclear power plant 1 as seen in cross-section according to a first plane I.
The containment structure 2 is a structure distinct from the core catcher 8. For example, the containment structure 2 comprises concrete, preferably is made of concrete and the core catcher 8 comprises preferably metal.
The pressure vessel 4 is received by the containment structure 2, in particular in an inner volume defined by the containment structure 2 above the spreading compartment 6.
The pressure vessel 4 contains the core 5 during normal operation of the nuclear power plant 1. The core 5 is thus arranged inside the pressure vessel 4 during normal operation.
By “normal operation”, it is understood an operation of the nuclear power plant without any severe accidents, in particular the absence of a core meltdown.
The pressure vessel 4 furthermore contains, for example, a core cooling system and support elements, for example made from metal, configured to support the core 5 and/or to guide coolant of the reactor cooling system (not shown).
The nuclear reactor is in particular a generation III reactor. According to an example, the core 5 is part of an EPR reactor.
The core catcher 8 comprises a convection barrier 14, a lateral wall 16 and a bottom wall 18. The lateral wall 16 and the bottom wall 18 interiorly delimit a reception space 20 intended for receiving molten material.
The molten material includes molten core material from the core 5 formed during the core meltdown. The molten material additionally comprises, for example, material from other elements received in the pressure vessel 4 during normal operation, such as the reactor cooling system and/or from the pressure vessel 4 itself.
By “core meltdown”, it is understood that at least parts of the core 5 melt and become at least partially liquid. The molten material comprises in particular a metal phase and an oxide phase. In the absence of mixing of the molten material with the sacrificial material 12, the oxide phase presents a higher density than the metal phase.
The core catcher 8 comprises for example metal, such as for example iron, cast iron or steel.
The core catcher 8 is arranged below the pressure vessel 4, for example vertically below or laterally offset below the pressure vessel 4.
According to the first embodiment, the core catcher 8 is arranged vertically below the pressure vessel 4.
By “core catcher vertically below the pressure vessel”, it is understood that the core catcher 8, and in particular the reception space 20, faces a lower part of the pressure vessel 4. Preferably, no walls of the containment structure 2 are arranged between the core catcher 8 and the pressure vessel 4 in this case.
The lateral wall 16 extends in particular perpendicularly from the bottom wall 18. In particular, the lateral wall 16 and the bottom wall form a vessel having a bottom formed by the bottom wall 18, and a circumferential wall formed by the lateral wall 16.
With reference to Figure 3 showing an example of the core catcher 8, as seen in crosssection according to a second plane II perpendicular to the first plane I, the lateral wall 16 comprises four wall parts, preferably forming a rectangle or a square.
With reference to Figures 1 and 2, the lateral wall 16 comprises for example a rectangular section having a wall height H1 and a wall width W1 . The wall height H1 of the lateral wall 16 is for example chosen depending on a predicted total volume of a melt (described below) to be retained by the core catcher 8 in the event of a core meltdown.
The bottom wall 18 is arranged to connect two opposite parts of the lateral wall 16.
The bottom wall 18 and the lateral wall 16 are for example provided with cooling fins 22, in particular on a lower surface of the bottom wall 18 and on a surface of the lateral wall 16 opposite to the reception space 20. The cooling fins 22 may extend perpendicularly from the lower surface of the bottom wall 18 and from the surface of the lateral wall 16 opposite to the reception space 20, into a space intended to receive coolant.
According to an example, the lateral wall 16 and the bottom wall 18 are made of several pieces that are fixed to each other, for example by tongue-and-groove connections. According to another example, the lateral wall 16, the bottom wall 18 and optionally the cooling fins 22, are made in one piece, for example by casting. According to another example, the lateral wall 16, the bottom wall 18 and optionally the cooling fins 22, are welded together. The lateral wall 16, the bottom wall 18 and optionally the cooling fins 22 are preferably made out of metal.
The cooling device 10 is configured for cooling the lateral wall 16 and the bottom wall 18 of the core catcher 8.
With reference to Figure 1 , the cooling device 10 defines for example a coolant reception space 24 for reception of a coolant 26, such as water, so that the coolant 26 is in contact with the lateral wall 16 and the bottom wall 18.
The coolant reception space 24 is arranged preferably outside the core catcher 8, in particular below the bottom wall 18 and on a side of the lateral wall 16 opposite to the reception space 20 of the core catcher 8.
The cooling device 10 defines furthermore at least one coolant inlet 27 for the inlet of the coolant 26 into the coolant reception space 24 in case of a severe accident.
The sacrificial material 12 is arranged so as to be molten by the molten material flowing towards and/or into the core catcher 8.
The molten sacrificial material 12 is intended to be mixed with the molten material so as to obtain a melt comprising a lower phase consisting of a metal molten phase 28 and an upper phase consisting of an oxide molten phase 29. Examples of the metal molten phase 28 and the oxide molten phase 29 are illustrated in Figures 5 and 6.
In the present document, the expression “melt” designates the mix obtained by mixing the molten material including molten core material together with the sacrificial material 12.
In particular, the sacrificial material 12 is a material configured to invert the density of the metal phase and the oxide phase of the molten material, when being mixed with this molten material including the molten core material, so that the metal molten phase 28 has a higher density than the oxide molten phase 29, and is thus arranged below the oxide molten phase 29.
The sacrificial material 12 comprises for example light-weight oxides so as to achieve the intended density inversion of the phases of the molten material when being mixed with it.
For example, the sacrificial material 12 comprises oxides chosen from silica (or silicon dioxide) calcia (or calcium oxide), alumina (or aluminum oxide), and/or iron oxide. According to an example, the oxides are sintered, or otherwise compounded, e.g. in the form of concrete.
According to an example, the sacrificial material 12 may contain metal, e.g. iron or steel, for example in the form of reinforcing bars to enhance mechanical stability.
According to the first embodiment, the sacrificial material 12 is arranged in the reception space 20, as for example illustrated in Figure 1 . According to the first embodiment, the sacrificial material 12 is intended to be mixed with the molten material upon reception in the reception space 20.
The sacrificial material 12 is not shown in Figure 2 for better visibility of other parts.
The convection barrier 14 is arranged within the reception space 20 delimited by the lateral wall 16 and the bottom wall 18.
The convection barrier 14 consists of a material adapted to resist the metal molten phase 28 of the melt.
By “the convection barrier consisting of a material adapted to resist the metal molten phase of the melt” it is understood in particular a material, which fulfills at least one, preferably both of the followings requirements: the melting point of the material is strictly higher than a temperature of the metal molten phase 28 of the melt, and/or the material of the convection barrier 14 presents a thermal conductivity strictly lower than 3 W/m.K.
According to an example, the convection barrier 14 comprises, preferably consists of, a refractory material, for example chosen from zirconia, in particular sintered zirconia, magnesium oxide, aluminum oxide, e.g. aluminum(lll) oxide, or uranium dioxide. For example, the convection barrier consists of bricks of such material.
According to an example, the convection barrier 14 is provided with a sheathing 25. The sheathing 25 is in particular configured for protecting the convection barrier 14 during normal operation of the nuclear power plant 1 . The sheathing 25 consists preferably of metal or a predefined sacrificial material.
The sheathing 25 is intended to be melted by the melt in the event of a core meltdown.
With reference to Figure 2, the convection barrier 14 protrudes upwards from the bottom wall 18.
The convection barrier 14 extends along at least one extension direction E. Examples of the extension direction E are illustrated in Figure 3.
Turning again to Figure 2, the convection barrier 14 presents a section, perpendicular to the extension direction E of the convection barrier 14, having a rectangular form. In particular, the convection barrier 14 has a barrier height H2 measured from the bottom wall 18, and a barrier width W2.
Preferably, the barrier height H2 is chosen depending on a predicted maximum volume of the metal molten phase 28, in particular so as to form a separation for the metal molten phase 28 arranged on both sides of the convection barrier 14.
For example, the barrier height H2 is identical to or higher than an expected height of the metal molten phase 28. For example, the barrier height H2 is constant, measured in parallel to the lateral wall 16, and in particular along the extension direction E, e.g. along a horizontal direction. Preferably, the barrier height H2 is strictly smaller than the wall height H1 .
Preferably, the convection barrier 14 is deprived of openings or holes along a direction perpendicular to the extension direction E.
According to another example, the convection barrier 14 presents at least one opening along the direction perpendicular to the extension direction E.
According to an example, the convection barrier 14 comprises a plurality of barrier sections having a distance one to another. Preferably, in this case, a total length of the barrier sections, defined in parallel to the lateral wall 16, is strictly greater than a total length of interruptions of the convection barrier 14 between these sections.
The convection barrier 14 extends substantially parallel to and at a predetermined distance D from the lateral wall 16. For example, the predetermined distance D of the convection barrier 14 to the lateral wall 16 is determined depending on at least one feature of the cooling device 10, such as a cooling capacity of the cooling device 10, and/or at least one feature of the core catcher 8, such as the wall width W1 of the lateral wall 16 or a material of the core catcher 8. The predetermined distance D is for example comprised between 20 cm and 40 cm.
With reference to Figure 3, the convection barrier 14 comprises four parts, each extending in parallel and at the predetermined distance D to a corresponding part of the lateral wall 16. In particular, each of the four parts of the convection barrier 14 is arranged perpendicularly to a neighboring part, so as to form a rectangle, as visible in Figure 3.
For example, the convection barrier 14 defines a central part 30 of the reception space 20 and a peripheral part 31 of the reception space 20. The central part 30 is delimited circumferentially by the convection barrier 14, and further delimited by a central area 32 of the bottom wall 18. The peripheral part 31 is delimited laterally by the convection barrier 14 and the lateral wall 16, and further delimited by a peripheral area 33 of the bottom wall 18.
The peripheral area 33 of the bottom wall 18 is for example delimited between the convection barrier 14 and the lateral wall 16. The central area 32 of the bottom wall 18 is in particular delimited by the convection barrier 14 on a side of the convection barrier 14 opposite the peripheral area 33.
For example, a ratio of a surface area of the peripheral area 33 to a surface area of the central area 32 is determined in function of a size and/or capacity of the cooling device 10.
Preferably, the peripheral area 33 has a surface area comprised between 5% and 15% of the sum of the surface areas of the peripheral area 33 and the central area 32. The convection barrier 14 is configured in such a manner that the molten material flows, in the event of the core meltdown, into the reception space 20 on both sides of the convection barrier 14, e.g. into the central part 30 and the peripheral part 31 .
According to an example, the peripheral part 31 is at least partially filled with a filling material, not shown, such as concrete, intended to be molten in the event of the core meltdown. According to an example, the filling material covers, in addition, the convection barrier 14.
This filling material allows in particular protecting the core catcher 8 and the convection barrier 14 during normal operation of the nuclear power plant 1 .
According to an example, the filling material comprises a chemical composition so as to form at least part of the sacrificial material 12, in particular comprises oxides which allow inverting the density of the phases of the molten material.
According to another example, the peripheral part 31 is empty during the normal operation of the nuclear power plant 2.
With reference to Figure 2, the core catcher 8 comprises for example a fixing device 34 configured for fixing the convection barrier 14 to the bottom wall 18.
The fixing device 34 comprises preferably at least one rail fixed to the bottom wall 18, for example welded to the bottom wall 18. The rail is configured for receiving a plurality of elements forming the convection barrier 14, for example by sliding the elements along the rail.
The operation of the nuclear power plant 1 according to the first embodiment in the event of the core meltdown is now described with reference to Figures 5 and 6.
In the event of a core meltdown, the core catcher 8 receives the molten material including molten core material from the core 5.
The molten material comprises in particular an initial metal phase and an initial oxide phase. In the absence of mixing of the molten material with the sacrificial material 12, the initial oxide phase presents a higher density than the initial metal phase.
Upon reception of the molten material in the core catcher 8, the molten material melts the sacrificial material 12 arranged therein and is mixed with this sacrificial material 12.
With reference to Figure 5, the melt is received upon mixing, and comprises the metal molten phase 28 in a lower phase and the oxide molten phase 29 in an upper phase. The mixing of the molten material with the sacrificial material 12 leads in particular to an inversion of density of the phases, i.e. the oxide molten phase 29 of the melt, comprising the molten sacrificial material 12, has a lower density than the metal molten phase 28, whereas the initial oxide phase of the molten material, without the sacrificial material 12, has a higher density than the initial metal phase. In the example of Figure 5, the barrier height H2 of the convection barrier 14 corresponds to the height the metal molten phase 28, so as to form a complete separation between the metal molten phase 28 in the central part 30 from the metal molten phase 28 in the peripheral part 31 .
The convection barrier 14 limits heat fluxes to the lateral wall 16 as described in the following.
In the peripheral part 31 , a local convection inside the metal molten phase 28 occurs, as illustrated by arrows 40 in Figure 5. In particular, the oxide molten phase 29 being hotter than the metal molten phase 28, the latter receives heat from the oxide molten phase 29, transfers this heat to the lateral wall 16, and then sinks down until being heated again by the oxide molten phase 29.
The convection barrier 14 limits thus heat fluxes of the metal molten phase 28 to the lateral wall 16, because no heat is transferred by the metal molten phase 28 arranged in the central part 30 to the lateral wall 16.
In the central part 30 of the reception space 20, the melt forms stable layers, because no heat flux in the metal molten phase 28 extends form the central part 30 to the lateral wall 16. A generation of such heat flux is prevented by the convection barrier 14.
Another example of the operation of the nuclear power plant 1 is shown in Figure 6. The operation corresponds to the operation as described with reference to Figure 5, with the exception of the difference described below.
In this case, the barrier height H2 of the convection barrier 14 is smaller than a height of the metal molten phase 28. A heat flux 42 is formed in the metal molten phase 28 from the central part 30 to the lateral wall 16, as the corresponding part of the melt is heated by the oxide molten phase 29 and the heat is then transferred according to the heat flux 42 to the lateral wall 16.
In the example of Figure 6, the heat flux 42 is limited by the convection barrier 14, because the backflow from the peripheral part 31 to the central part 30 is impeded and thus only small quantities of heat are transferred by the metal molten phase 28 to the lateral wall 16. In particular, the difference in height between the barrier height H2 of the convection barrier 14 and the height of the metal molten phase 28 is small, so that no strong lateral heat transfer occurs from the metal molten phase 28 into the lateral wall 16.
With reference to Figure 4, a nuclear power plant 1 according to a second embodiment is now described.
The nuclear power plant 1 and its operation is identical to the nuclear power plant 1 according to the first embodiment, with the exception of differences described hereafter. In particular, the same or corresponding features of the nuclear power plant 1 according to the second embodiment compared with the first embodiment are not described again. Only the differences are described hereafter.
The same or corresponding elements according to the second embodiment are designated with the same reference signs as in the first embodiment, except described otherwise.
The containment structure 2 comprises a transfer space 44 arranged vertically below the pressure vessel 4, a tunnel 46 and the spreading compartment 48, called distant spreading compartment 48 in the following, receiving the core catcher 8 presenting the reception space 20.
The distant spreading compartment 48 has preferably larger or the same dimensions as the spreading compartment 6. The distant spreading compartment 48 is for example defined by walls of the containment structure 2, preferably made of concrete.
The tunnel 46 connects the transfer space 44 with the distant containment space 48, in particular with the reception space 20 of the core catcher 8.
The tunnel 46 presents for example a refractory shroud 50 configured to transport the melt from transfer space 44 to the distant containment space 48.
The distant containment space 48 is preferably arranged laterally besides and below the pressure vessel 4.
According to the second embodiment, the sacrificial material 12 is arranged in the transfer space 44 and/or in the reception space 20 of the core catcher 8 (not shown in Figure 4 for better visibility of other parts).
The operation of the nuclear power plant 1 according to the second embodiment is preferably identical to the operation according to first embodiment.
According to an 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 event of a core meltdown in that the molten material including the core molten material melts the sacrificial material 12 inside the transfer space 44 and/or inside the reception space 20 of the core catcher 8.
The obtained melt is received by the core catcher 8. The core catcher 8 and convection barrier 14 are preferably identical to the first embodiment.
The invention presents many advantages.
The convection barrier 14 allows to prevent or at least to reduce the occurrence of natural convection currents implying locally strong heat fluxes from the metal molten phase 28 to the lateral wall 16. Such strong heat fluxes would prevent the formation of crusts in these areas and thus reduce the retention function of the core catcher 8. The nuclear power plant 1 according to the invention, and in particular the convection barrier 14, allows thus to improve containment protection in case of a severe accident implying a core meltdown.

Claims

1. Nuclear power plant (1 ) comprising a containment structure (2) and a pressure vessel (4) received in the containment structure (2), the pressure vessel (4) containing the core (5) of the nuclear power plant (1 ) during normal operation of the nuclear power plant (1 ), the containment structure (2) defining a spreading compartment (6, 48) configured for receiving molten material including molten core material from the core (5) in the event of a core meltdown, wherein the nuclear power plant (1 ) further comprises:
- a core catcher (8) arranged in the spreading compartment (6, 48) and comprising a lateral wall (16) and a bottom wall (18) interiorly delimiting a reception space (20) intended for receiving the molten material;
- a cooling device (10), configured for cooling the lateral wall (16) and the bottom wall (18) of the core catcher (8),
- a sacrificial material (12) arranged so as to be molten by the molten material flowing towards and/or into the core catcher (8), the molten sacrificial material being intended to be mixed with said molten material so as to obtain a melt comprising a lower phase consisting of a metal molten phase (28) and an upper phase consisting of an oxide molten phase (29), characterized in that the core catcher (8) further comprises a convection barrier (14), arranged within the reception space (20) delimited by the lateral wall (16) and the bottom wall (18), and protruding upwards from the bottom wall (18) of the core catcher (8), the convection barrier (14) extending substantially parallel to and at a predetermined distance (D) from the lateral wall (16) of the core catcher (8), the convection barrier (14) consisting of a material adapted to resist the metal molten phase (28) of the melt, the convection barrier (14) being configured in such a manner that the molten material flows, in the event of the core meltdown, into the reception space (20) on both sides of the convection barrier (14).
2. Nuclear power plant (1 ) according to claim 1 , wherein a barrier height (H2) of the convection barrier (14) is strictly smaller than a wall height (H1 ) of the lateral wall (16), the barrier height (H2) and the wall height (H1 ) being each measured from the bottom wall (18).
3. Nuclear power plant (1 ) according to claim 2, wherein the wall height (H1 ) is chosen depending on a predicted total volume of the melt to be retained, and/or wherein the barrier height (H2) of the convection barrier (14) is chosen depending on a predicted maximum volume of the metal molten phase (28).
4. Nuclear power plant (1 ) according to any one of the preceding claims, wherein the material of the convection barrier (14) has a melting point strictly higher than a temperature of the metal molten phase (28) of the melt, and/or wherein the material of the convection barrier (14) has a thermal conductivity strictly lower than 3 W/m.K, and preferably wherein the material of the convection barrier (14) comprises sintered zirconia bricks.
5. Nuclear power plant (1 ) according to any one of the preceding claims, wherein the predetermined distance (D) of the convection barrier (14) to the lateral wall (16) is determined depending on at least one feature of the core catcher (8) and/or the cooling device (10).
6. Nuclear power plant (1 ) according to any one of the preceding claims, wherein a peripheral area (33) of the bottom wall (18) is delimited between the convection barrier (14) and the lateral wall (16), and a central area (32) of the bottom wall (18) is delimited by the convection barrier (14) on a side of the convection barrier (14) opposite the peripheral area (33), the peripheral area (33) having a surface area comprised between 5% and 15% of the sum of the surface areas of the peripheral area (33) and the central area (32).
7. Nuclear power plant (1 ) according to any one of the preceding claims, wherein the sacrificial material (12) comprises at least one oxide, for example chosen from silicium oxide, calcium oxide, aluminum oxide and/or iron oxide.
8. Nuclear power plant (1 ) according to any one of the preceding claims, wherein a peripheral part (31 ) of the reception space (20), defined between convection barrier (14) and the lateral wall (16) is empty during the normal operation of the nuclear power plant (2) or is at least partially filled with a filling material intended to be molten in the event of the core meltdown, the filling material being for example concrete.
9. Nuclear power plant (1 ) according to any one of the preceding claims, wherein the convection barrier (14) has a constant height (H2), measured from the bottom wall (18) and in parallel to the lateral wall (16).
10. Nuclear power plant (1 ) according to any one of the preceding claims, wherein the core catcher (8) comprises at least one fixing device (34) configured for fixing the convection barrier (14) to the bottom wall (18), the fixing device (34) comprising preferably at least one rail fixed to the bottom wall (18).
1 1 . Nuclear power plant (1 ) according to any one of the preceding claims, wherein the convection barrier (14) is provided with a sheathing (25), the sheathing (25) consisting preferably of metal.
12. Nuclear power plant (1 ) according to any one of the preceding claims, wherein the core catcher (8) is arranged vertically below the pressure vessel (4), the sacrificial material (12) being arranged in the reception space (20).
13. Nuclear power plant (1 ) according to any one of claims 1 to 11 , wherein the containment structure (2) comprises a transfer space (44) arranged vertically below the pressure vessel (4) and a tunnel (46) connecting the transfer space (44) and the reception space (20) of the core catcher (8), wherein the sacrificial material (12) is arranged in the transfer space (44) and/or in the reception space (20) of the core catcher (8).
PCT/EP2022/069655 2022-07-13 2022-07-13 Nuclear power plant comprising a core catcher WO2024012675A1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5049352A (en) * 1990-10-15 1991-09-17 Associated Universities, Inc. Nuclear reactor melt-retention structure to mitigate direct containment heating
US5263066A (en) * 1991-11-06 1993-11-16 Commissariat A L'energie Atomique Nuclear reactor equipped with a core catcher
EP3905262A2 (en) * 2018-12-26 2021-11-03 Joint Stock Company "Atomenergoproekt" Melt confinement device

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5049352A (en) * 1990-10-15 1991-09-17 Associated Universities, Inc. Nuclear reactor melt-retention structure to mitigate direct containment heating
US5263066A (en) * 1991-11-06 1993-11-16 Commissariat A L'energie Atomique Nuclear reactor equipped with a core catcher
EP3905262A2 (en) * 2018-12-26 2021-11-03 Joint Stock Company "Atomenergoproekt" Melt confinement device

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
FISCHER MANFRED ET AL: "Retrofitting of ex-vessel core catchers into operating nuclear power plants at the example of a Mark-I BWR", ANNALS OF NUCLEAR ENERGY, PERGAMON PRESS, OXFORD, GB, vol. 146, 28 June 2020 (2020-06-28), XP086214225, ISSN: 0306-4549, [retrieved on 20200628], DOI: 10.1016/J.ANUCENE.2020.107646 *

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