A thermal generating reactor with a core comprising a liquid metal coolant and coolant-sealing tubes, each containing TRISO nuclear fuel particles.

Abstract

The present invention relates to a liquid metal-cooled reactor (1) comprising a vessel (2) called a primary vessel, which exhibits rotational symmetry about a central axis (X) and is filled with a coolant containing at least one liquid metal as a coolant for the primary circuit of the reactor, wherein the vessel comprises a core (3) comprising a plurality of sealed, fixed hollow tubes (4) arranged parallel to axis X so that the liquid metal circulates in contact with the external periphery of the reactor when the reactor is operating, each hollow tube (4) contains a stack of fuel assemblies (5) containing TRISO nuclear fuel particles (50) which are mixed with a matrix (51).

Description

Technical Field

[0001] The present invention relates to the field of solid fuel nuclear reactors cooled by one or more heat transfer fluids of the liquid metal type, specifically by liquid sodium.

[0002] Therefore, the present invention has as its main object to provide a heat generating nuclear reactor that operates at a low pressure, typically less than 5 bar, and is intended to provide a relatively high heat output of the order of several tens to several hundreds of MWth.

[0003] Specifically, the present invention aims to create mainly a thermal connection between a nuclear reactor and an industrial production site, such as chemical equipment for the production of, for example, ammonia or sodium carbonate.

[0004] As used herein, "heat generating" means, in the context of the present invention, a nuclear facility, nuclear power plant, or nuclear reactor in which most of the output can be dedicated to the supply of heat. The output of a heat generating reactor can be 100% dedicated to supplying heat. Nevertheless, in that heat generating configuration, a small percentage of its output can be used to supply electricity.

[0005] Although described with reference to a nuclear reactor cooled by liquid sodium, the present invention can be applied to any other liquid metal, such as lead, used as a heat transfer fluid in the primary circuit of a nuclear reactor.

[0006] Similarly, although described with reference to a reactor operating in a temperature spectrum, the present invention can also be applied to fast neutron reactors.

[0007] The present invention can also be applied to small modular reactors (SMRs) that typically operate at an output of 150 MWth or less.

[0008] In this specification, in the context of the present invention, “small modular reactor” has the usual technical meaning, that is, a fission reactor that is smaller in size and power than a conventional PWR reactor, manufactured in a factory and transported to a nuclear facility where it is installed. [Background technology]

[0009] One of the current areas of development regarding nuclear reactors concerns so-called thermal generator reactors, which are intended to provide thermal power.

[0010] Of the various existing technological solutions for supplying heat through nuclear fission, it is generally accepted that pressurized water reactors (PWRs) are currently the most suitable for supplying heat at relatively low temperatures.

[0011] In other words, PWRs enable the immediate supply of power at the tens of MWth level, primarily to supply the so-called urban heat, that is, to towns / urban areas with hundreds of thousands of residents in urban networks.

[0012] A boiling water reactor (BWR) is designed to generate steam in a primary circuit that is directly used by a turbine-AC generator group to produce electricity.

[0013] Industrial heat, generally exceeding 500°C and surpassing the levels required for urban heating, currently accounts for more than 20% of global energy demand.

[0014] More precisely, the global market for heat is approximately 57,000 TWh, of which roughly half is for industrial use, i.e., for industrial production sites.[1]

[0015] It is already acknowledged that solutions such as SMRs can contribute to some extent to replacing 75% of the industrial heat generated from oil, coal, and natural gas.

[0016] Aside from the simplicity of use and compactness of SMRs, which allow them to be transported via ground routes, the SMR-type reactors in question must provide inherent safety features.

[0017] The inventors have compiled a list of existing mature technologies that can be used in SMR reactors to supply heat at relatively high temperatures in industrial sites where carbon removal by electricity is difficult, such as facilities for the production of ammonia or sodium carbonate.

[0018] A high-temperature reactor (HTR) is a temperature-spectrum reactor in which a graphite moderator is cooled by a heat transfer fluid that is "permeable" to neutrons. HTRs offer the ability to achieve high heat transfer fluid temperatures, typically around 750°C, at the outlet from the core.

[0019] In some recent designs, this heat transfer fluid is pressurized helium. Another recent design, the Hermes demonstration reactor by Kairos Power, considers a so-called ionic heat transfer medium consisting of a molten salt based on fluoride salts.

[0020] In HTR reactors, the nuclear fuel used consists of triple-layered isotropic (TRISO) particles. Each particle is formed from a uranium oxide core coated with a layer based on a carbon-containing compound that serves as a first confinement barrier to hold fission products. The particles have the appearance of spheres approximately 1 millimeter in diameter. The particles are compressed in a graphite matrix (called a pebble bed) so that the heat transfer medium does not come into direct contact with the first confinement barrier.

[0021] The structure of an HTR-type reactor is generally loop-shaped, meaning that a heat exchanger is present between the primary and secondary circuits connected to the core by a tubular connection, and a fluid circulation system is used, which consists of a pump, a blower, and a heat exchanger that exchanges fluid and heat in the secondary circuit. The fluid can be helium, pressurized water, supercritical CO2, etc.

[0022] In an HTR-type reactor, heat transfer between the first confinement barrier and the heat transfer medium is brought about by conduction through an interface consisting of a graphite matrix on which TRISO particles are compressed.

[0023] The HTR type reactor has the following main advantages: - The TRISO fuel particles used can withstand high pressures and temperatures in the event of an incident or accident, with fuel temperatures typically exceeding 1500°C, and the internal pressure of the heat transfer medium (helium) being between 10 and 100 bar. - The neutron spectrum can become very thermal, which results in a high Doppler coefficient and a high moderator coefficient, typically equal to -15 pcm / °C, thus leading to abrupt changes in reactor power in the event of temperature changes in graphite and / or fuel. - The reactor core has high thermal inertia due to the mass of graphite, which allows for limiting the effects of high or low temperature thermal shocks. - Typically 2 W / cm 3 When combined with a low power-to-unit-volume value, the aforementioned advantages actually lead to the elimination of the risk of serious accidents, namely, the risk of core meltdown and molten fuel migration.

[0024] The main drawbacks of the HTR type reactor can be summarized as follows: - As already mentioned, in the case of rapid depressurization of the heat transfer gas, the maximum output per unit volume is low, partly due to the need to consider the integrity of the first confinement barrier. - In the case of air intrusion, there are residual safety risks linked to the risk of radioactive material dispersion, namely the risk of graphite fire or water hazards (the risk of steam explosion resulting from hydrogen production). Specifically, the overall dimensions of the relatively large steam supply system (primary vessel) are due to the relatively low density of the main heat transfer gas, which imposes large dimensions on the components for heat extraction and a loop configuration of the primary circuit with the components scattered across several separate buildings. - Specifically, for the supply of power to the primary gas circulation device, the on-site electrical output requirement, which typically amounts to several tens of MWe, depends on the output of the steam generation system and is essential for the operation of the facility. - The ratio of the generated thermal output to the consumed electrical power for the circulation of the primary fluid, which is less favorable for gas-cooled HTR-type reactors than for other reactor technologies that use cooling by incompressible fluids (such as water, liquid metals, etc.).

[0025] A fast neutron reactor (RNR) cooled by liquid metal, specifically by sodium (RNR-Na), and more precisely a fourth-generation one, supplies heat at a temperature that meets the requirements of industrial production sites. The temperature of the primary sodium at the outlet from the reactor core is typically about 550 °C.

[0026] Fast neutron reactors have been developed to enable better management of nuclear fuel, specifically by the long-term management of plutonium storage and the ability to monetize the inventory of uranium isotope 238, which is a relatively difficult isotope to monetize in thermal neutron reactors.

[0027] The solid fuel fast neutron reactor relies on the physical separation between the solid fuel and the liquid metal heat transfer medium by a casing (pencil shape or hypodermic needle shape) that forms the first physical confinement barrier (metal cladding). The fuel itself consists of materials that are solid at the intended operating temperature (specifically in the form of oxides of fissile materials, silicon carbide (SIC), or nitrides, or directly in the form of metal alloys). The casings are assembled into bundles and are submerged directly into the liquid metal heat transfer medium together with all other components of the primary circuit (neutron absorption material rods, exchangers, instruments), thus providing heat transfer.

[0028] The vessel of the RNR-type reactor is generally designed to be suspended from a metal slab connected to a civil engineering vessel well.

[0029] The main advantages of liquid metal-cooled RNR reactors, specifically RNR-Na reactors, are that they allow for the possibility of closing the fuel cycle (a breeding mode) and managing somewhat highly radioactive, long-lived waste (such as americium), and that RNR reactors typically produce 200 W / cm². 3 It has a high power density.

[0030] However, known RNR-Na type reactors have the following major drawbacks: - Due to the high power density, forced convective circulation of sodium is required. - The impossibility of a design that completely eliminates the risk of a core meltdown accident (the risk of overall or localized loss of primary flow, the risk of premature rise of neutron absorption rods). - The need to provide a substantial amount of equipment to prevent a core meltdown accident or to limit the associated consequences. Specifically, the complex physical properties of the reactor core due to a high level of linkage between thermal effects and the geometric properties of the core. - The need for specific neutron protection (for structures, corrosion products, secondary fluid activation, etc.) using fast neutron spectroscopy. - The high residual power of the fuel necessitates specific infrastructure for handling fuel transfer assemblies (gas-cooled reactor hoods) or for their storage (internal storage, reactor vessels, pound), as well as specific infrastructure for handling other sodium-containing components (washing wells, special handling of certain combustible assemblies, higher neutron protection if not sealed, etc.).

[0031] Therefore, specifically to mitigate the aforementioned drawbacks, there is a need to improve solid-fuel reactors cooled by liquid metal or gas for heat generation purposes, aimed at supplying heat to industrial production sites. [Overview of the project] [Problems that the invention aims to solve]

[0032] The objective of this invention is to at least partially address this need. [Means for solving the problem]

[0033] To that end, one aspect of the present invention relates to a liquid metal-cooled reactor comprising a vessel called a primary vessel, which is axially symmetric about a central axis (X) and filled with a fluid containing at least one liquid metal as a heat transfer fluid for the primary circuit of the reactor, wherein the vessel comprises a core comprising a plurality of hollow sealed fixed tubes arranged parallel to axis X so that the liquid metal circulates in contact with the external periphery of the reactor when the reactor is operating, and each hollow tube contains a stack of fuel assemblies containing so-called TRISO nuclear fuel particles mixed with a matrix.

[0034] In a favorable variant, the matrix into which the TRISO particles are mixed is in the form of a compact block.

[0035] In an advantageous embodiment, the reactor includes a structure that forms a flow restrictor with a central axis coinciding with the central axis of the primary vessel, the structure being positioned in the primary vessel such that when the reactor is operating, a liquid metal heat transfer fluid circulates from the bottom of the central region by natural convection in a closed loop, at the bottom of the central region where the reactor core is located and a fission reaction occurs, causing the liquid metal heat transfer fluid to rise to the top of the central region by heating, at the top of the central region, the liquid metal heat transfer fluid enters through an inlet into at least one heat exchanger outside the reactor vessel, exits through an outlet of the exchanger, and then moves toward the top of the peripheral region, descending toward the bottom of the peripheral region, and the liquid metal heat transfer fluid is redirected toward the reactor core.

[0036] In one operating configuration as a heat-generating reactor, the reactor core contains at least one moderator material.

[0037] The reactor core may also include reflectors made of moderator material, which are positioned below each sealing tube.

[0038] The reactor core may comprise at least two blocks of moderator material arranged around each sealing tube, with the liquid metal circulating around each sealing tube in contact with each sealing tube.

[0039] In an advantageous variant embodiment, each sealing tube comprises a bottomed tube component that forms an immersion sleeve into which fuel assemblies are stacked before the reactor begins operation.

[0040] The liquid metal of the heat transfer fluid can be selected from sodium (Na), lead (Pb), or lead-bismuth (Pb-Bi) alloys.

[0041] The material of the TRISO particle matrix, and / or the material of the reactor core, may be graphite.

[0042] The material that makes up the sealing tube may be ceramic.

[0043] In another advantageous embodiment, the reactor includes a reactivity control system comprising control rods in the primary vessel.

[0044] In the context of this invention, “moderator material” means any material capable of slowing down neutrons. In the usual sense, the kinetic energy of fast neutrons is greater than 1 MeV, and the kinetic energy of thermal neutrons is less than 1 eV, typically around 0.025 eV. See publication [2], specifically Figure 4 of that publication, which shows the thermal friction and fast neutron ratios of the neutron flow for several types of reactors.

[0045] Therefore, the present invention relates to a nuclear reactor comprising, in essence, a liquid metal which is specifically liquid sodium, a heat transfer medium, and solid fuel assemblies in the form of TRISO particles compressed in a matrix which are stacked with other assemblies in a sealing tube that separates the fuel from the flow of the liquid metal.

[0046] Therefore, the flow of liquid metal circulates outside the sealing barrier. This ensures that there is no contamination by fission products, as the two independent sealing barriers separate the liquid metal from the fissile material contained in the TRISO particles during the normal operation of the liquid metal, which is the primary heat transfer medium.

[0047] The reactor design according to the present invention substantially combines the advantages of an HTR-type reactor with the advantages of an RNR-type reactor cooled by liquid metal.

[0048] More specifically, the reactor design according to the present invention can significantly increase the power density of existing HTR-type reactors. In fact, the use of liquid metal at low pressures, typically 1 to 2 bar, instead of pressurized helium, which is typically 10 to 100 bar, allows for the normal operation of the reactor at higher fuel temperatures than the normal operation of existing HTR-type reactors, and TRISO particles can withstand these higher temperatures.

[0049] Furthermore, the physical separation between the fuel and liquid metal flows, accompanied by TRISO particles, offers considerable advantages.

[0050] Firstly, this allows for simple handling of the fuel (insertion in a fixed sealed tube) because the assembly does not come into contact with the liquid metal and consequently does not require cleaning. More broadly, most of the equipment, consisting of the fuel, control rods, and components that are "consumables" or consumables that require periodic replacement or inspection, is located in a fluid region separate from the fluid region of the primary heat exchange medium of the liquid metal. This feature protects most of the consumable components from interaction with the metal and prevents contamination by the heat transfer medium of the liquid metal.

[0051] The inventors have found that the power density is typically about 10 MW / m³ with liquid sodium. 3This is estimated to result in a value five times greater than that of an HTR-type reactor. When considered in conjunction with the thermal robustness of TRISO particles, this allows for radiation cooling during the operation of the irradiated fuel, even if there is a large residual power immediately after the cessation of the fission reaction. Given the large heat exchange coefficient between liquid sodium and power density (much smaller than that of a fast neutron reactor cooled by liquid metal), heat transfer between the fuel and liquid metal can be achieved by simple heat conduction.

[0052] The low neutron weight of the fuel assembly allows for single-line replenishment, i.e., replenishment at full power, without large neutron disturbances. This single-line replenishment enables increased reactor availability and reduces the inherent risks of replenishment operations by decreasing the temporal pressure in critical operation.

[0053] The properties of TRISO particles allow for dry storage in racks, where they are cooled solely by ventilation and then, when placed in a tank for several weeks after being removed from the reactor core, are cooled by radiation.

[0054] Finally, the reactor according to the present invention can operate with a primary liquid metal in liquid sodium at a typically low pressure and high temperature of about 750°C at the outlet from the core, which ultimately makes it possible to guarantee the heat generation mission of the reactor for the purpose of supplying heat to industrial production sites, such as chemical facilities for the production of ammonia or sodium carbonate.

[0055] Other advantages and features of the present invention will become more apparent by reading the following detailed description of embodiments of the invention, which are provided with non-limiting examples related to the following figures. [Brief explanation of the drawing]

[0056] [Figure 1] This is a schematic diagram of a longitudinal cross-section of a reactor according to the present invention, which is cooled by liquid metal in a loop exchanger configuration. [Figure 1A]Figure 1 is a detailed view of the height of the sealing tube that houses the TRISO particle assembly between two blocks of moderator material. [Figure 2] This is another perspective view of a cross-section of the reactor according to the present invention, which is cooled by liquid metal in a loop exchanger configuration. [Figure 2A] Figure 2 is a perspective view showing the insertion of the TRISO particle assembly into the core sealing tube. [Figure 3] This is a cross-sectional view of the reactor core according to the present invention, showing the relative arrangement between the fuel assembly, the sealing tube, and the block of moderator material. [Modes for carrying out the invention]

[0057] Throughout this application, the terms “vertical,” “downward,” “upward,” “top,” “bottom,” “below,” and “above” are understood to refer to the primary vessel filled with liquid metal of the reactor according to the present invention when in a vertical operating configuration.

[0058] The arrows symbolize the circulation of primary liquid sodium in the reactor vessel and in the exchanger between the primary and secondary circuits.

[0059] Figures 1 to 3 depict a nuclear reactor according to the present invention, cooled by liquid metal and containing fuel in the form of TRISO particles.

[0060] Such a reactor 1 comprises a reactor vessel filled with liquid sodium in the form of a straight cylindrical shape with a central axis X, which contains a primary vessel 2, or a core 3 containing a plurality of fixed sealing tubes 4 that house removable fuel assemblies 5 containing TRISO fuel particles 50 that generate thermal energy by the fission of fuel. The liquid sodium is the heat transfer fluid of the primary circuit, storing and transporting heat from the core 3.

[0061] As shown in Figure 1A, each fixed sealing tube comprises a bottomed tube component that forms an immersion sleeve through which the fuel assemblies 5 are stacked before the reactor begins operation. If necessary, the bottomed tube component can be replaced while the reactor is operating. The arrangement of each sealing tube 4 is such that the opening of the sealing tube 4 through which the fuel assemblies are stacked is away from the primary liquid metal.

[0062] The solid nuclear fuel is in the form of an assembly 5 comprising TRISO particles 50 compressed in a matrix 51 of a moderator material, preferably graphite. Each of these particles is formed from a uranium oxide core material coated with a layer based on a carbon-containing compound that serves as a first confinement barrier to hold fission products.

[0063] In particular, the cladding tube 52 made from graphite can optionally surround the matrix 51.

[0064] As can be seen in Figure 3, there are compact ring configurations 50, 51, and at the center of the compact ring configuration 51 is a volume 53 that is empty, or a volume 53 that is filled with an inert gas, preferably helium, at a low pressure. This volume 53 allows for limiting the core temperature of the fuel and further allows for expansion of the accepting matrix 51.

[0065] Each sealed assembly 5 may have a hexagonal external cross-section (Figure 2A) or a cylindrical external cross-section (Figure 3).

[0066] The TRISO particle outer covering constitutes the primary containment barrier for radioactive materials contained within core 3.

[0067] The support slab 6 supports the primary vessel 2, the weight of the liquid metal in the primary circuit, and the weight of the internal components. The slab 6 is aligned vertically with the core 3 and closes the primary vessel 2 to contain the liquid metal and serve as a barrier between the liquid metal and the surrounding environment.

[0068] The reactor vessel 2 is divided into two separate regions within its interior by a separation structure consisting of at least one shroud 7. This separation device is also known as a flow restrictor (redan).

[0069] As symbolized by the arrows in Figure 1, the flow restrictor 7 is located in the primary vessel 2, dividing the interior of the primary vessel 2 into a central region and a peripheral region, forming a central chimney-shaped section so that when the reactor is operating, the liquid metal circulates from the bottom of the central region by natural convection in a loop. At the bottom of the central region, the reactor core 3 is located above the floor 8, and heating causes the liquid metal to rise to the top of the central region. At the top of the central region, the liquid metal enters at least one heat exchanger 9 outside the reactor vessel 2 via an inlet 90, exits via an outlet 91 of the exchanger, and then moves towards the top of the peripheral region, descending towards the bottom of the peripheral region, from where the liquid metal is redirected towards the reactor core 3.

[0070] Therefore, under normal operation, the primary liquid metal circulates in the reactor vessel 2 and in a closed loop through at least one exchanger 9 solely by natural convection, exchanging its heat with the secondary fluid in the exchanger 9, which enters at a low temperature through the inlet 92 and exits at a high temperature through the outlet 93. The temperature of the secondary fluid at the outlet 93 can typically be equal to 700°C.

[0071] The shape of the flow restrictor 7 allows for improved circulation through natural convection of the liquid metal.

[0072] Reactor 1 is equipped with a reactivity control system which may consist of control rods inside the primary vessel 2, which are not described.

[0073] The reactor vessel 2 includes an upper section, usually called the core upper section, which may be filled with an inert gas such as argon or helium above the liquid metal. This upper section allows for the absorption of thermal expansion of the liquid metal in the reactor vessel when the liquid metal undergoes a change in height, and for the recovery of gaseous fission products generated by nuclear fission in the fuel.

[0074] A favorable configuration of a sealing tube 4 that houses a stack of fuel assemblies 5 is shown in Figure 1A. The sealing tube 4, preferably made of ceramic, is placed between at least two blocks 20 of a moderator material, preferably graphite. This configuration allows the primary liquid metal to be circulated in a clearly defined space E, in contact with the sealing tube.

[0075] A reflector 21, preferably made from a moderator material such as graphite, may be positioned below the sealing tube 4.

[0076] A favorable configuration for a sealing tube 4 and fuel assembly 5 with a straight cylindrical cross-section is shown in Figure 3. The tube 4 is positioned between two blocks 20 of moderator material, preferably graphite, which are placed adjacent to each other, leaving a gap e and a larger space E between them, through which the liquid metal circulates when the reactor is operating.

[0077] In Figure 3, a volume for filling with an inert gas, preferably helium, may be provided between the fuel assembly 5 and the sealing tube 4 to improve the thermal interface for heat conduction of the heat generated by the fission of TRISO particles.

[0078] The present invention is not limited to the examples described, and specifically, each of them can be combined with other features of the described examples in variations not described.

[0079] Other variations and embodiments can be considered without departing from the context of the present invention.

[0080] It is possible to consider liquid metals other than sodium for use as the primary fluid, which could be lead (Pb) or lead-bismuth (Pb-Bi) alloys.

[0081] Other materials besides graphite, such as aluminum, may be considered for the TRISO particle matrix and / or core.

[0082] As shown in Figure 2, the reactor 1 may be equipped with a sealed concrete enclosure 10 to house the primary vessel 2.

[0083] (References) [1] “High-temperature gas-cooled reactors and industrial heat applications”, NEA No.7629, OECD, Paris, 2022 [2] Jiri Krepel et al. “Self-Sustaining Breeding in Advanced Reactors: Characterization of Selected Reactors”, Encyclopedia of Nuclear Energy 2021, Pages 801-819. https: / / www.sciencedirect.com / science / article / pii / B9780128197257001239?via%3Dihub [Explanation of symbols]

[0084] 1 nuclear reactor 2 Primary vessel, reactor vessel 3. Reactor core 4 Sealed tube 5 Fuel assembly 6. Support slab 7 Shroud 8 beds 9 Heat exchanger 10 Encircling bodies 20 blocks 21 Reflector 90 Entrance 91 Exit 92 Entrance 93 Exit 50 TRISO fuel particles, compact ring configuration 51 matrix, compact ring configuration 52 Cladding tube 53 Volume e gap E space X center axis

Claims

1. A reactor (1) cooled by a liquid metal, comprising a vessel (2) called a primary vessel, which is axially symmetric about a central axis (X) and filled with a heat transfer fluid containing at least one liquid metal as a heat transfer fluid for the primary circuit of the reactor, wherein the vessel comprises a core (3) comprising a plurality of hollow sealed fixed tubes (4) arranged parallel to the axis X such that the liquid metal circulates in contact with the external surroundings of the reactor when the reactor is operating, and each hollow tube (4) contains a stack of fuel assemblies (5) containing so-called TRISO nuclear fuel particles (50) which are mixed with a matrix (51).

2. The reactor (1) according to claim 1, wherein the matrix into which the TRISO particles are mixed is in the form of a compact block.

3. A reactor (1) according to claim 1 or 2, comprising a structure that forms a flow restrictor (7) having a central axis coinciding with the central axis of the primary vessel, wherein the structure is positioned in the primary vessel such that the interior of the primary vessel is divided into a central region and a peripheral region, and when the reactor is operating, a liquid metal heat transfer fluid circulates from the bottom of the central region by natural convection in a closed loop, at the bottom of the central region where the core of the reactor is located, a nuclear fission reaction occurs, the liquid metal heat transfer fluid rises to the top of the central region by heating, at the top of the central region the liquid metal heat transfer fluid enters through an inlet (90) into at least one heat exchanger (9) outside the reactor vessel, exits through an outlet (91) of the exchanger, and then moves toward the top of the peripheral region, descends toward the bottom of the peripheral region, and the liquid metal heat transfer fluid is redirected toward the core of the reactor.

4. The reactor (1) according to any one of claims 1 to 3, wherein the reactor core contains at least one moderator material.

5. The reactor (1) according to claim 4, wherein the reactor core of the reactor comprises a reflector made of a moderator material, which is positioned below each sealing tube.

6. The reactor (1) according to claim 4 or 5, wherein the reactor core comprises at least two blocks of moderator material arranged around each sealing tube, and the liquid metal is circulated around each sealing tube in contact with each sealing tube.

7. The reactor (1) according to any one of claims 1 to 6, wherein each sealing tube comprises a bottomed tube component that forms an immersion sleeve into which the fuel assemblies are stacked before the reactor begins operation.

8. The reactor (1) according to any one of claims 1 to 7, wherein the liquid metal of the heat transfer fluid is selected from sodium (Na), lead (Pb), or a lead-bismuth (Pb-Bi) alloy.

9. The reactor (1) according to any one of claims 1 to 8, wherein the material of the matrix of the TRISO particles and / or the material of the core is graphite.

10. The reactor (1) according to any one of claims 1 to 9, wherein the material constituting the sealing tube is ceramic.

11. A reactor (1) according to any one of claims 1 to 10, comprising a reactivity control system consisting of control rods in the primary vessel.

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