Compact module for heat transfer between gas and liquid metal, for a liquid-metal-cooled, loop-type fast neutron nuclear reactor

Abstract

The invention relates to a heat transfer module (M) for a liquid-metal-cooled, loop-type fast neutron nuclear reactor (1), comprising an expansion tank (20), a heat exchanger (21) and an electromagnetic pump (22), the module alone forming a heat exchange loop between the primary liquid sodium circuit and the secondary circuit containing a gas, such as nitrogen, which is a closed Brayton cycle.

Description

[0001] Description

[0002] Title: Compact heat transfer module, between gas and liquid metal for liquid metal cooled fast neutron nuclear reactor, loop type.

[0003] technical field

[0004] The present invention relates to the field of so-called fast neutron nuclear reactors. It relates in particular to a fast neutron nuclear reactor cooled with liquid metal, in particular liquid sodium, known as SFR (Sodium Fast Reactor), lead, or a lead alloy, or generally known as LMBFR (Liquid Metal Breeder Fast Reactor), and which is part of the family of so-called fourth-generation reactors (GEN IV).

[0005] The invention relates even more particularly to the aforementioned loop-type reactor, that is to say, one in which the heat exchangers and the means for pumping the primary fluid, such as sodium, are located outside the reactor vessel.

[0006] The invention is preferably applicable to small or medium power reactors or SMRs (acronym for "Small Modular Reactor"), typically with an operating power between 50 and 400 MWe.

[0007] For the purposes of this invention, "SMR reactor" means the usual technological meaning, namely a nuclear fission reactor, smaller in size and power than conventional modular reactors (REL), whose reactor blocks are manufactured in a factory and transported to a nuclear site for installation.

[0008] By "reactor block", we mean here and within the framework of the invention, the vessel, called reactor vessel as well as all the components and part of the fluidic circuit, in particular the reactor core producing heat by nuclear fission reactions, which is housed inside the reactor vessel.

[0009] More specifically, the invention relates to a new design of a heat transfer module dedicated to such a loop reactor which is both compact and can be transported individually to a nuclear site.

[0010] Previous technique

[0011] The currently known sodium-cooled fast neutron reactors (SFRs) can be classified into two types:

[0012] - The most common type is called integrated because the primary liquid sodium circuit, including pumping equipment and heat exchangers, is entirely contained within a single primary vessel. An integrated reactor also includes secondary liquid sodium circuits (piping, pumps and steam generators) installed outside the primary vessel and a tertiary water / steam circuit which is associated with a steam turbine for electricity production;

[0013] The other type is called a loop reactor because the primary sodium circuit is installed in several tanks with intermediate heat exchangers and pumping equipment out of the primary tank. A loop reactor also includes secondary liquid sodium circuits (piping, pumps, and steam generators) and a tertiary water / steam circuit that is connected to a steam turbine for electricity generation.

[0014] These two types of reactors have architectures that lead to a large volume of components as well as a large footprint and buildings.

[0015] As part of the studies for the prototype liquid sodium cooled fast neutron nuclear reactor called ASTRID, an energy conversion circuit between liquid sodium and a gas, nitrogen, was considered.

[0016] A design solution for a heat exchanger between liquid sodium and a gas has been proposed, which uses compact plate heat exchanger modules. This solution is described, for example, in publication [1].

[0017] EP3039373B1 describes a compact heat exchanger which employs a sealed enclosure within which several plate exchanger modules as described in [1] are arranged.

[0018] Besides avoiding any presence of water in the reactor building and thus any risk of interaction with sodium, such a sodium / gas exchanger has the major advantages of being able to be integrated into the reactor building and of eliminating the intermediate sodium circuits as in known loop reactors and thus of being able to greatly reduce the cost of the reactor.

[0019] That being said, the sealed enclosure heat exchanger is not simple to manufacture and its qualification as nuclear equipment is not immediate. In addition, to finalize the heat exchange loop, assembly with other components (pump and piping) is necessary, which takes time and can be costly.

[0020] There is therefore a need to further improve fast neutron nuclear reactors, particularly liquid metal cooled, of the loop type in order to simplify the construction of said loops, to facilitate their nuclear qualification and to reduce the time and cost of in-situ assembly.

[0021] The aim of the invention is to meet at least part of this need.

[0022] Description of the invention

[0023] To this end, the invention relates, in one of its aspects, to a heat transfer module for a liquid-metal-cooled, loop-type fast neutron nuclear reactor, comprising:

[0024] - a tank called an expansion tank inside which are delimited two separate compartments called hot and cold, intended to be pressurized by a common gas head, each of the two compartments comprising an inlet port and an outlet port,

[0025] - a heat exchanger comprising a stack of metal plates assembled together and defining two fluid circuits, one of which is a liquid metal circuit and the other a gas circuit, in particular nitrogen, and an inlet manifold connected to the outlet port of the hot compartment of the expansion tank and an outlet manifold connected to the inlet port of the cold compartment of the expansion tank,

[0026] - an electromagnetic pump, designed to circulate the liquid metal, and connected upstream to the outlet of the cold compartment of the expansion tank,

[0027] - at least two fluid branches, one of which, upstream of the exchanger, is intended to be connected to a so-called hot manifold of the reactor block of the nuclear reactor and to the inlet port of the hot compartment of the expansion tank, and the other, downstream of the exchanger, is intended to be connected to a so-called cold manifold of the reactor block and to the electromagnetic pump.

[0028] Within the framework of the invention, a fluidic branch can be constituted by a piping with at least one pipe. Depending on the requirements, the electromagnetic pump can be arranged horizontally or vertically in a configuration installed in a nuclear reactor.

[0029] The invention also relates, in another aspect, to a liquid-metal-cooled, loop-type fast neutron nuclear reactor, comprising:

[0030] - at least one heat transfer module as described above, forming a primary / secondary heat exchange loop,

[0031] - a power conversion system (PCS) comprising a closed Brayton cycle with an inlet and outlet pipe connected respectively to the outlet and inlet manifolds of the module's heat exchanger gas circuit, the PCS comprising a gas turbine coupled to an alternator for generating electricity and a heat exchanger for producing high-temperature waste heat. "High temperature" herein, and within the scope of the invention, means a temperature higher than that of a conventional Rankine cycle (water / steam). Typically, the high-temperature waste heat is at least 80°C. Preferably, the gas in the closed Brayton cycle is nitrogen.

[0032] Advantageously, the pressurization gas for the gas head of the module's expansion tank is argon, preferably at very low pressure.

[0033] The invention also relates in another of its aspects to a method of operating the nuclear reactor described above, comprising circulating the liquid metal by the operating electromagnetic pump from the reactor block to within the heat transfer module and back to the reactor block.

[0034] Advantageously, the difference in elevation levels of the liquid metal between the two compartments within the expansion tank corresponds to the pressure drop induced by the heat exchanger of the module. The expansion tank is sized to allow the free expansion of the liquid metal within the primary heat exchange loop during the transition from the reactor shutdown state, in which the liquid metal is at a so-called cold temperature, to the reactor's normal operating state, in which the liquid metal is at a so-called hot temperature, with a constant gas mass in the common gas head. Preferably, the difference in elevation levels is between 60 and 100 cm. When the liquid metal is liquid sodium, the cold temperature in the reactor shutdown state is preferably approximately 200°C and the hot temperature is approximately 550°C.

[0035] The gas pressure in the common gas sky is preferably between 50 and 100 mbar relative.

[0036] Thus, the invention essentially consists of proposing for a fast neutron nuclear reactor, cooled with liquid sodium, a heat transfer module which by itself forms an exchange loop between the primary circuit of liquid sodium and the secondary circuit of gas, such as nitrogen which is a closed Brayton cycle.

[0037] The very compact module can be fully assembled in the factory for delivery and installation directly in the reactor building.

[0038] In conclusion, a heat transfer module according to the invention offers numerous advantages, including:

[0039] - high compactness and therefore a high power density of the module,

[0040] - the implementation of a loop architecture with several modules for a reactor whose compactness allows for a ratio between MWe of production and m 3 of concrete dedicated to the construction of the reactor building, which is high, better than integrated SFR-N reactors according to the state of the art and comparable to the ratio of a pressurized water reactor of the EPR type,

[0041] - an in-situ assembly on the site of a nuclear power plant, easier and faster than according to the state of the art.

[0042] The invention relates, in another aspect, to a liquid-metal cooled, loop-type fast neutron nuclear reactor, comprising:

[0043] - a central axis reactor block (X),

[0044] - a plurality of identical heat transfer modules, each forming a primary / secondary heat exchange loop, the plurality of heat transfer modules being arranged in an axisymmetric distribution around the reactor block, each of the heat transfer modules comprising: • a tank called the expansion tank within which are delimited two separate compartments called hot and cold, intended to be pressurized by a common gas head, each of the two compartments comprising an inlet port and an outlet port,

[0045] • a heat exchanger comprising a stack of metal plates assembled together and defining two fluid circuits, one of which is a liquid metal circuit and the other a gas circuit, in particular nitrogen, and an inlet manifold connected to the outlet port of the hot compartment of the expansion tank and an outlet manifold connected to the inlet port of the cold compartment of the expansion tank,

[0046] • an electromagnetic pump, designed to circulate the liquid metal, and connected upstream to the outlet of the cold compartment of the expansion tank,

[0047] • at least two fluid branches, one upstream of the exchanger is connected to a so-called hot manifold of the reactor block and to the inlet port of the hot compartment of the expansion tank, and the other downstream of the exchanger is connected to a so-called cold manifold of the reactor block and is connected upstream to the electromagnetic pump.

[0048] According to an advantageous embodiment, the reactor includes a sealed enclosure forming a third containment barrier within which all the heat transfer modules are arranged.

[0049] Advantageously, the reactor includes a reactor building forming a fourth containment barrier inside which the sealed containment structure is arranged.

[0050] According to another advantageous embodiment, the reactor includes an energy conversion system comprising a closed Brayton cycle in which an inlet fluidic branch and an outlet fluidic branch are connected respectively to the outlet manifold and the inlet manifold of the gas circuit of the exchanger of the module, the SCE system comprising a gas turbine coupled to an alternator to produce electricity and a heat exchanger to produce high-temperature waste heat.

[0051] Preferably, the gas in the closed Brayton cycle is nitrogen.

[0052] The pressurization gas for the expansion tank of each module is preferably argon. According to another advantageous embodiment, the reactor includes a liquid metal storage / discharge tank connected to the reactor block and to each of the heat transfer module expansion tanks. This facilitates the emptying and refilling of the primary circuit with liquid sodium.

[0053] The invention also relates to a method of operating the nuclear reactor as described above, comprising circulating the liquid metal by the operating electromagnetic pump from the reactor block to within all the heat transfer modules and back to the reactor block.

[0054] According to an advantageous embodiment, the difference in altimetric levels of the liquid metal between the two compartments within each expansion tank corresponds to the pressure loss induced by the heat exchanger of each module, the expansion tank being dimensioned is determined so as to allow the free expansion of the liquid metal within each exchange loop during the transition from the reactor shutdown state in which the liquid metal is at a so-called cold temperature, to the normal operating state of the reactor in which the liquid metal is at a so-called hot temperature, with a constant mass of gas in the common gas head.

[0055] Advantageously, the difference in altimetric levels in each expansion tank is between 60 and 100 cm.

[0056] When the liquid metal is liquid sodium, the cold temperature in the reactor shutdown state is approximately 200°C and the hot temperature is approximately 550°C.

[0057] The gas pressure in the common gas head is preferably between 50 and 100 mbar relative.

[0058] Thus, the invention in this second aspect consists of a nuclear reactor with identical primary / secondary exchange loops, each consisting of a heat transfer module as described above, and which are arranged in an axisymmetric distribution around the reactor block.

[0059] In conclusion, compared to state-of-the-art liquid metal-cooled nuclear reactors, a nuclear reactor according to the invention offers numerous advantages, including: - due to the compact heat transfer modules distributed axisymmetrically around the reactor block, a high degree of compactness resulting in a reduced footprint and the possibility of design modularity as desired,

[0060] - standardization of components (reactor block, identical heat transfer modules allowing for a reduction in costs and time for nuclear qualification by the authorities,

[0061] - Factory production of heat transfer modules enabling series production, - Due to the alternating current operating mode, a long fuel cycle with less frequent and centralized handling

[0062] - an increased level of safety with the presence of four containment barriers and a small footprint allowing installation near suburban areas and industries,

[0063] - a cogeneration of electricity and heat by a closed Brayton cycle allowing the production of low carbon energy at a competitive price.

[0064] The invention relates, in another aspect, to a liquid-metal cooled, loop-type fast neutron nuclear reactor, comprising:

[0065] - a central axis reactor block (X),

[0066] - at least one heat transfer module forming a primary / secondary heat exchange loop, and comprising:

[0067] • a tank called the expansion tank inside which are delimited two separate compartments called hot and cold, intended to be pressurized by a common gas head, each of the two compartments comprising an inlet port and an outlet port,

[0068] • a heat exchanger comprising a stack of interlocking metal plates defining two fluid circuits, one a liquid metal circuit and the other a gas circuit, in particular nitrogen, and an inlet manifold connected to the outlet of the hot compartment of the expansion tank and an outlet manifold connected to the inlet of the cold compartment of the expansion tank, • an electromagnetic pump, intended to circulate the liquid metal, and connected upstream to the outlet of the cold compartment of the expansion tank,

[0069] • at least two fluid branches, one upstream of the exchanger connected to a so-called hot manifold of the reactor block and to the inlet port of the hot compartment of the expansion tank, and the other downstream of the exchanger connected to a so-called cold manifold of the reactor block and to the electromagnetic pump,

[0070] - a gas discharge device for the exchanger circuit comprising a bursting membrane arranged in the upper part of the module's expansion tank and a discharge tank connected to the expansion tank by piping leading to the bursting membrane.

[0071] Preferably, the bursting membrane is in the form of a rupture disc.

[0072] According to an advantageous embodiment, the reactor comprises several heat transfer modules, the discharge tank connected to all the expansion tanks of the modules being in the form of a torus arranged around the reactor block.

[0073] Thus, the invention, in this third aspect, consists of a nuclear reactor with at least one primary / secondary heat exchange loop, comprised of a heat transfer module as described above, which includes a secondary circuit gas discharge device with a burst membrane located in the module's expansion tank. Such a discharge device allows for the control, or even the elimination, of the risk of gas bubbles entering the primary circuit in the event of a rupture in the module's heat exchanger gas circuit.

[0074] Other advantages and features of the invention will become clearer upon reading the detailed description of examples of implementations of the invention given by way of illustration and not limitation with reference to the following figures.

[0075] Brief description of the drawings

[0076] Figure 1 is a schematic view of a liquid sodium-cooled nuclear reactor (NSR-Na) according to the invention, with a heat exchange loop formed by a compact heat transfer module according to the invention and a closed Brayton cycle energy conversion system. Figure 2 is a schematic top view of the two-block nuclear reactor according to the invention, intended to operate alternately with respect to each other, with a closed Brayton cycle energy conversion system.

[0077] Figure 3 is a partial schematic view of the implementation of the gas circuit for a reactor block according to Figure 2.

[0078] Figure 4 illustrates in the form of a time diagram an example of an alternative operating mode of a power plant according to Figure 2.

[0079] Figure 5 illustrates in perspective view a heat transfer module in a mode where the electromagnetic pump of the module is arranged horizontally in a configuration installed in a reactor according to the invention.

[0080] Figure 6 illustrates in perspective view a heat transfer module in a mode where the electromagnetic pump of the module is arranged vertically in a configuration installed in a reactor according to the invention.

[0081] Figure 7 is an enlarged view of Figure 1 showing in detail the arrangement and fluidic connections of a heat transfer module according to the invention as part of a primary / secondary exchange loop between a reactor block and a closed Brayton cycle.

[0082] Figure 8 is a longitudinal side view of a heat exchanger of a heat transfer module according to the invention.

[0083] Figure 9 is a front view of the exchanger module as shown in Figure 8.

[0084] Figure 10 is a perspective view of a heat transfer module according to the invention as mounted on its support in a reactor according to the invention. Figure 11 is a perspective view of several heat transfer modules arranged around the reactor block according to the invention.

[0085] Figure 12 is a perspective view showing a reactor block connected to a heat transfer module according to the invention, as well as a liquid sodium storage tank for filling or emptying the reactor block vessel and a gas discharge device, intended to recover the gas in the event of a rupture of the heat exchanger of a heat transfer module. Figure 13 is a partial cross-sectional view of Figure 12.

[0086] Figure 14 is a schematic longitudinal cross-sectional view of a nuclear reactor with several primary exchange loops, each consisting of a heat transfer module according to the invention, with a liquid sodium storage tank and a gas discharge device.

[0087] Figure 15 is a perspective view of all the heat transfer modules as arranged around the reactor block, with the gas discharge device.

[0088] Figure 16 is a detailed view of a heat transfer module according to a variant of the invention.

[0089] Figure 17 is a front view of a heat exchanger according to a double gas tap embodiment.

[0090] Figure 18 is a detailed cross-sectional view of an exchanger according to Figure 17.

[0091] Figure 19 is a perspective view of a heat transfer module with an exchanger as shown in Figure 17.

[0092] Figure 20 is a perspective view of several heat transfer modules with a heat exchanger according to Figure 17, arranged around the reactor block according to the invention. Figure 21 is a perspective view of a heat exchanger according to another embodiment with a square-section sodium feed manifold.

[0093] Figure 22 is an exploded view showing a transfer module with a heat exchanger as shown in Figure 21.

[0094] Figure 23 is an exploded view showing the connection between a heat exchanger according to Figure 21 and the expansion tank by means of an additional welded part.

[0095] Detailed description

[0096] Throughout this application, the terms "horizontal," "vertical," "lower," "upper," "below," and "above" are to be understood with reference to a reactor vessel arranged vertically and its position relative to the cold or hot zone. Similarly, throughout this application, the terms "upstream" and "downstream" are to be understood with reference to the direction of sodium flow. Figure 1 shows a loop-type sodium-cooled fast reactor (SFR-Na), generally designated by reference numeral 1.

[0097] This nuclear power plant 1 comprises, firstly, at least one SMR-type reactor block 10, including a reactor vessel 11 with a central axis X, inside which is arranged a core 12 in which the heat is released as a result of the nuclear reactions. Typically, the core 12 is of low power, for example, on the order of 300 MWth.

[0098] Tank 11 can be closed by a plug called the "primary tank closure plug" which includes among other things the instrumentation necessary for the control and proper functioning of the nuclear reactions.

[0099] Core 12 consists of fuel assemblies. Advantageously, these assemblies are devoid of a casing or hexagonal tube around the needles that constitute them, and are made as described and claimed in the patent application filed by the applicant on November 19, 2024 under number FR2412649 and entitled "Fuel assembly for a nuclear reactor, of the type SFR-Na, devoid of a casing, comprising a bundle of fuel needles held laterally by honeycomb grids and longitudinally by stiffening rods, passing through the grids".

[0100] The circulation of liquid sodium within reactor block 10, in normal reactor operation, is advantageously as described in the patent application filed by the applicant on December 6, 2024 under number FR2413618 and entitled "Fast neutron nuclear reactor, in particular liquid metal cooled, with reactivity control system arranged on the periphery of the nuclear core".

[0101] As illustrated, the reactor architecture has primary / secondary exchange loops 2 allowing a high level of compactness of the reactor vessel 11, whose external diameter can be equal to 2.5m.

[0102] This reactor vessel 11 can typically be replaced every 20 years.

[0103] Figure 1 shows only a primary / secondary heat exchange loop 2. This heat exchange loop 2 is advantageously constituted by a heat transfer module M, described in detail below, which includes a heat exchanger 21.

[0104] The reactor includes an energy conversion system 3 featuring a closed Brayton cycle that directly constitutes the reactor's secondary circuit. In other words, in the reactor according to the invention, this closed Brayton cycle 3, combined with the heat exchanger of module M, eliminates the need for a sodium loop between the primary liquid sodium circuit and the energy conversion system 3.

[0105] This closed Brayton cycle 3 preferably operates with nitrogen. It includes an inlet fluidic branch 31 and an outlet fluidic branch 30 connected respectively to the outlet manifold 222 and the inlet manifold 221 of the gas circuit of the exchanger 21 of module M.

[0106] The SCE system comprises a gas turbine 32 coupled to an alternator to produce electricity and heat exchangers 33 to produce high-temperature waste heat. In other words, the nuclear reactor 1 with its closed Brayton cycle 3 makes it possible to produce both electricity and high-temperature waste heat by adapting to energy demand, without consuming water.

[0107] Various isolation valves 34, 36 and 35, 37 can be installed respectively on the inlet fluid branch 30, i.e., the cold gas branch, and on the outlet fluid branch 31, i.e., the hot gas branch. As shown in Figure 1, compressors 32 driven by the gas turbine shaft line allow the gas, such as nitrogen, to circulate in the Brayton cycle 3.

[0108] In the illustrated example, for a 300MWth reactor, the hot sodium exits reactor block 10 at a temperature of 550°C and the cold sodium entering reactor block 10 is at a temperature of approximately 400°C. In this primary circuit, the sodium can circulate at a very low pressure, typically on the order of 0.1 bar.

[0109] Cold nitrogen enters the heat exchanger 21 of module M at a temperature of approximately 380°C and hot nitrogen exits the heat exchanger 21 at a temperature of approximately 530°C. In the closed Brayton cycle secondary circuit 3, nitrogen can circulate at a high pressure, typically on the order of 180 bar.

[0110] As illustrated in Figure 1, the primary / secondary heat exchange loops 2 are all arranged within a sealed containment structure 4, which is axisymmetrically shaped around the X-axis of the reactor vessel 11. This sealed containment structure 4 constitutes a third containment barrier, with the fuel assemblies and the reactor vessel forming the first and second containment barriers, respectively. The reactor block 10 and the sealed containment structure 4 are arranged within a reactor building 5, consisting of an underground concrete infrastructure, which performs various functions, including contributing to the containment safety function. Thus, the reactor building 5 constitutes a fourth containment barrier.

[0111] Typically, the building envelope of reactor 5 can consist of several layers. As illustrated in Figure 1, the envelope can be a non-prestressed concrete wall, serving as the interface with the outside.

[0112] As also illustrated in Figure 1, reactor building 5 can be fully buried in soil S.

[0113] Thus, nuclear reactor 1 exhibits a significant level of safety, higher than that of all known Na-FRI reactors, due to:

[0114] - the presence of four containment barriers,

[0115] - the elimination of any possible reaction between sodium in the primary circuit and water, thanks to the gas Brayton cycle,

[0116] - the elimination of possible reactions between the sodium in the primary circuit and the air by the presence of nitrogen inside the sealed enclosure 4,

[0117] - the elimination of initiators of severe accidents, gas entry into the heart, thanks to the primary sodium circuit with a dual-level sodium expansion tank.

[0118] Figure 2 depicts a nuclear power plant with two reactor blocks 1.1, 1.2. Each of the blocks 1.1, 1.2 comprises a reactor vessel 10.1, 10.2 with heat exchange loops 2, as described previously, and housed within its own sealed containment structure 4.1, 4.2. More specifically, as shown in Figure 2, each of the reactor blocks 1.1, 1.2, with its own sealed containment structure 5, is housed within its own partitioned location 50.1, 50.2 of the reactor building 5.

[0119] As also illustrated, each of these two reactor blocks 1.1, 1.2 has a part of the secondary circuit which is its own with at least one tank forming a dedicated collector 38.1, 38.2; 39.1, 39.2 which allows respectively the injection of cold nitrogen into the exchangers or the collection of hot nitrogen from the exchangers before sending to the turbine, isolation valves 34.1 to 37.2 also allowing the part of each of the two secondary circuits to be isolated on the side of the tank 10.1, 10.2. The two parts of the secondary circuit are connected by a common fluidic branch 300 which allows the gas turbine and the heat exchanger of the closed Brayton cycle to be supplied.

[0120] Two isolation valves 380.1 and 380.2 allow one and / or the other of the part of the secondary circuit of the two reactor blocks 1.1, 1.2 to be isolated.

[0121] An advantageous embodiment of the secondary circuit for one of the blocks 1.1 is shown in Figure 3. At least one, preferably six, fluid branches carry the cold gas from a cold manifold 38.1 to each of the heat exchangers 21 of the modules M1 to M6 of the reactor block. At least one, preferably six, fluid branches carry the hot gas from each of the heat exchangers 21 of the modules M1 to M6 of the reactor block to a hot manifold 39.1.

[0122] This architecture allows the nuclear power plant to operate in an alternating mode between the two reactor blocks 1.1 and 1.2. An advantageous alternative operating mode is shown in Figure 4, with the various operations dedicated to one or both of the reactor blocks 1.1 and 1.2 over the plant's operating time. As can be seen, non-nuclear production operations are carried out in the background for the end customer, i.e., for the production of electricity and waste heat.

[0123] Typically, with this alternative operating mode, a plant availability factor exceeding 95% can be expected. Furthermore, a 10-year period of nuclear production without any refueling is conceivable.

[0124] A heat transfer module M forming a primary / secondary exchange loop 2 is shown in Figures 5 and 6. Figure 5 shows a variant in which the electromagnetic pump 22 of the module is arranged horizontally in a configuration installed in a reactor block, while in Figure 6 it is vertical.

[0125] Figure 7 illustrates this configuration installed with the electromagnetic pump 22 vertically with the hot primary sodium and the cold primary sodium inside the expansion tank 20.

[0126] As illustrated in these figures 5 to 7, a module M includes first of all an expansion tank 20 inside which are delimited two separate compartments 200, 201 called hot and cold, intended to be pressurized by a common gas head 202. The common gas head 202 can be pressurized with argon.

[0127] Each of the two compartments includes an inlet port and an outlet port.

[0128] Module M also includes a heat exchanger 21 with a stack of interlocking metal plates defining two fluid circuits, one a liquid sodium circuit and the other a gas circuit, specifically nitrogen. As shown in Figure 6, an inlet manifold of the exchanger 21 is connected to the outlet port of the hot compartment 200 of the expansion tank 20, and an outlet manifold is connected to the inlet port of the cold compartment 201 of the expansion tank 20.

[0129] An electromagnetic pump 22, designed to circulate the primary liquid sodium during the operation of reactor 1, is connected to the outlet of the cold compartment 201 of the expansion tank 20. The electromagnetic pump 22 is compact and preferably operates with high flow rates, typically on the order of 1200 m³ / s 3 / h.

[0130] A fluid branch 23 connected upstream to a so-called hot collector of the reactor block 10, is connected upstream to the inlet port of the hot compartment 200 of the expansion tank 20, to bring the hot liquid sodium there.

[0131] A fluidic branch 24 connected downstream to a so-called cold collector of the reactor block 10, is connected downstream of the electromagnetic pump 22 to reinject the cold liquid sodium into the reactor block 10.

[0132] A fluidic branch 25 connects the hot compartment of the expansion tank 20 to the inlet manifold of the exchanger 21 to bring the hot liquid sodium there.

[0133] In the configuration of the electromagnetic pump 22 in the vertical position, a fluidic branch 26 connects the outlet manifold of the exchanger 21 to the cold compartment 201 of the expansion tank 20 to bring the cold liquid sodium there.

[0134] Figures 8 and 9 show an advantageous example of the two-fluid-circuit heat exchanger 21, which is implemented for the exchange between liquid sodium (Na) from the primary circuit and gaseous nitrogen (N2) from the secondary Brayton cycle circuit. The module 21 consists of an alternating stack of metal plates 210, 220 assembled together by diffusion welding preferably using a CIC technique, or produced by additive manufacturing.

[0135] As shown in Figures 8 and 9, the heat exchanger 21, which extends along a central axis (XI), incorporates two manifolds 211 and 212, respectively for the inlet and outlet of liquid sodium (Na). One manifold is arranged on the top of the heat exchanger along axis XI, and the other is also arranged along axis XI, but on the underside. Each of the manifolds 211 and 212 opens onto a lateral base of the plate stack, onto which the channels of the Na circuit open, but not those of the N2 circuit.

[0136] The heat exchanger 21 also includes two nitrogen (N2) inlet and outlet manifolds 221 and 222, respectively, arranged on the same longitudinal face, at the bottom and top of the exchanger, respectively. Each of the inlet manifold 221 and outlet manifold 222 passes through the stack transversely to the (X) axis and opens into the channels of the N2 circuit but not into those of the Na circuit.

[0137] In such a heat exchanger 21, the circulation of the fluids (Na, N2) is therefore counter-current. Advantageously, the heat exchanger 21 is implemented as described in US patent 12152840B1 or patent application WO2024 / 132477.

[0138] Such an exchanger 21 implemented for primary liquid sodium, whose thermal conductivity at high temperature is very high, allows the module M to exchange a very high unit power, typically on the order of 50 MWth.

[0139] Figure 10 shows an advantageous example of a support structure 40 for a module M that is fixed directly inside the sealed enclosure 4. The heat exchanger 21 and the electromagnetic pump 22 are thus directly supported by this structure 40. The fluid branches 23 to 26 are free to expand relative to this structure 40. Figure 11 shows an advantageous example of an arrangement of six identical modules M1 to M6 around the reactor block 10.

[0140] To ensure an additional level of safety, the inventors considered an exchange loop architecture 2 that takes into account the risk of rupture of all or part of an exchanger 21 that could introduce gas from the exchanger 21 into the liquid sodium primary circuit. They therefore devised a gas discharge device 6 outside of any part of the primary circuit and thus not affecting the cooling of the reactor core 12.

[0141] This discharge device 6 includes first of all a bursting membrane 60 in the form of a rupture / burst disc arranged in the upper part of the expansion tank 20, as shown in Figure 6. Typically, the setting pressure of the rupture / burst disc is less than or equal to 500 mbar relative.

[0142] The discharge device 6 further includes a discharge fluid branch 61 connected on the one hand to the upper part of the reservoir 20 opposite the rupture disc 60 and on the other hand to a gas discharge reservoir 62.

[0143] As shown in figures 12 and 13 and detailed below with the compact architecture of reactor 1, the discharge tank 62 is advantageously in the form of a torus arranged around the reactor block 10.

[0144] Thus, in the event of a rupture of the gas circuit within the exchanger 21, it reaches the gas sky 202 of the tank 20 and breaks the disc 60 at its set pressure.

[0145] The gas is then discharged into the discharge tank 62 via branch 61.

[0146] In this way, the gas from the secondary circuit cannot move towards the reactor block and therefore impair the proper cooling of the reactor core 12.

[0147] Figures 14 and 15 show the set of primary / secondary exchange loops 2, each consisting of a heat transfer module M1 to M6. All modules M1 to M6 are identical.

[0148] As shown in Figure 10, the arrangement of modules M1 to M6 is made according to an axisymmetric distribution around the reactor block 10 inside the containment structure 4. Due to the adapted compact shapes of the components of modules M1 to M6, the arrangement itself makes the reactor 1 compact with a containment structure 4 whose diameter remains small compared to the diameter of the reactor block 10. Typically, the containment structure 4 has a diameter of 8m for an external diameter of the reactor vessel 11 of the order of 2.6m.

[0149] Reactor 1 further includes a device 7 for filling or emptying the primary circuit with liquid sodium. This device 7 includes a liquid metal storage / discharging tank 70 connected directly to the reactor block 10 by a fluidic branch 71. The gas head of the tank 70 is also connected to each of the heads of the expansion tanks 20 of the heat transfer modules M1 to M6 by means of a torus 72 filled with Argon blanket gas arranged at the periphery of the reactor block and preferably around the gas discharge torus 62.

[0150] More specifically, as illustrated, the torus 72 is connected by a fluidic branch 73 and to each of the expansion tanks 20 by one of the plurality of fluidic branches 74. Thus, the emptying / filling operations of the primary circuit with liquid sodium are easily carried out in situ. These filling and emptying operations of the primary circuit are performed via a lift pump connected to the sodium storage / emptying tank 70 and to the reactor block by the fluidic branch 71. Initially, the reactor block 10 and the primary circuit are filled with gas; during sodium filling, the gas is expelled from the primary circuit to the storage tank 70 by means of the balancing circuit of the storage tank heads and the heads of the primary loops, which includes the torus 72 and the fluidic branches 73 and 74.

[0151] The invention is not limited to the examples just described; in particular, features of the illustrated examples can be combined in unillustrated variants.

[0152] Other variations and improvements can be considered without going outside the scope of the invention.

[0153] Figure 16 shows an advantageous variant in which the outer wall of the electromagnetic pump 22 forms a calender 27 for circulating the cold liquid sodium. Indeed, the coils of the electromagnetic pump 22 can generate a significant amount of heat through Joule heating during operation. Thus, thanks to this calender 27, the cold liquid sodium comes into contact with the outer part of the electromagnetic pump 22, which houses the coils, before being pumped into the inner channel 28. Through this circulation, at least a large portion of the heat generated by the coils can be dissipated by the cold primary fluid.

[0154] Figures 17 to 20 show an advantageous embodiment of a heat exchanger 21 and its integration into a transfer module M, as well as a complete nuclear reactor with six modules M1 to M6 according to this embodiment. In this embodiment, the heat exchanger 21 is constructed with a duplication of the gas connections / manifolds.

[0155] As illustrated in Figure 17, the heat exchanger 21 comprises two nitrogen (N2) inlet / manifolds 221, 223 arranged on the same longitudinal face at the bottom of the exchanger and two nitrogen (N2) outlet / manifolds 222, 224 arranged on the same longitudinal face at the top of the exchanger. Each of the inlet manifolds 221, 223 and outlet manifolds 222, 224 passes through the stack transversely to axis (XI) and opens into the channels of the N2 circuit but not into those of the Na circuit.

[0156] This duplication of the connections / manifolds 221, 223 and 222, 224 allows:

[0157] - to improve the supply of gas circulation channels, and

[0158] - to reduce the thickness of the pipes 30 and 31, which is beneficial with regard to the thermomechanical stresses that these components and the heat exchanger 21 may experience. To further limit thermomechanical stresses, a portion of the primary fluid (Na) can be diverted into the structures of the branch connection(s). Indeed, certain transients can lead to significant temperature variations, and therefore thermomechanical stresses at these branch connections. The diversion is implemented to circulate the primary fluid within the wall of a branch connection. Note: I do not believe it is necessary to include diagrams for this aspect. Furthermore, those provided are not clear enough for a "patent" format.

[0159] Figures 21 to 23 show another advantageous embodiment of a heat exchanger 21 in which the upper longitudinal end 215 has a square cross-section, the interior of which directly forms the inlet manifold 211 for the primary fluid (Na) which exits hot from the expansion tank 20. This square cross-section allows for a more uniform supply of the internal channels of the heat exchanger 21. This is made possible by the low velocities in the expansion tank 20.

[0160] As illustrated in Figure 23, a connecting piece 29 comprising a cylindrical end 290 and another end with a square cross-section 291 is integrated between the outlet 2023 of the expansion tank 20 and the longitudinal end 215 with a square cross-section, different lines of welds S being made for the assembly of the module M.

[0161] List of references cited:[1]: "Innovative power conversion system for the French SFR prototype, ASTRID", L. Cachon et al. Proceedings of ICAPP'12, Chicago, USA, June 24-28, 2012, Paper 12300.

Claims

Demands 1. Heat transfer module (M) for a liquid-metal-cooled, loop-type fast neutron nuclear reactor (1), comprising: - a tank (20) called an expansion tank, inside of which are delimited two separate compartments called hot and cold, intended to be pressurized by a common gas head, each of the two compartments comprising an inlet orifice and an outlet orifice, - a heat exchanger (21) comprising a stack of metal plates assembled together and defining two fluid circuits, one of which is a liquid metal circuit and the other a gas circuit, in particular nitrogen, and an inlet manifold connected to the outlet port of the hot compartment of the expansion tank and an outlet manifold connected to the inlet port of the cold compartment of the expansion tank, - an electromagnetic pump (22), intended to circulate the liquid metal, and connected upstream to the outlet of the cold compartment of the expansion tank, - at least two fluid branches (23, 24), one of which (23), upstream of the exchanger, is intended to be connected to a so-called hot manifold of the reactor block (10) of the nuclear reactor and to the inlet port of the hot compartment of the expansion tank, and the other (24) downstream of the exchanger, is intended to be connected to a so-called cold manifold of the reactor block and to the electromagnetic pump.

2. Heat transfer module according to claim 1, the electromagnetic pump being arranged to be horizontal or vertical in configuration installed in a nuclear reactor.

3. Liquid-metal cooled, loop-type fast neutron nuclear reactor (1), comprising: - at least one heat transfer module according to claim 1 or 2, forming a primary / secondary heat exchange loop, - an energy conversion system comprising a closed Brayton cycle in which an inlet fluidic branch and an outlet fluidic branch are connected respectively to the outlet manifold and the inlet manifold of the gas circuit of the module exchanger, the SCE system comprising a gas turbine coupled to an alternator to produce electricity and a heat exchanger to produce high-temperature waste heat.

4. Nuclear reactor (1) according to claim 3, the gas of the closed Brayton cycle being nitrogen.

5. Nuclear reactor (1) according to any one of claims 3 or 4, the pressurization gas of the gas head of the pressurization tank of the module being argon.

6. Method of operating the nuclear reactor (1) according to any one of claims 3 to 5, comprising circulating the liquid metal by the operating electromagnetic pump from the reactor block to the heat transfer module and back to the reactor block.

7. Method according to claim 6, wherein the difference in altimetric levels of the liquid metal between the two compartments within the pressurization tank corresponds to the pressure drop induced by the heat exchanger of the module, the expansion tank being dimensioned so as to allow the free expansion of the liquid metal within the primary exchange loop during the transition from the reactor shutdown state in which the liquid metal is at a so-called cold temperature, to the normal operating state of the reactor in which the liquid metal is at a so-called hot temperature, with a constant mass of gas in the common gas head.

8. Method according to claim 7, the difference in altimetric levels being between 60 and 100 cm.

9. A process according to any one of claims 7 or 8, the liquid metal being liquid sodium, the cold temperature in the reactor shutdown state being substantially equal to 200°C and the hot temperature being substantially equal to 550°C.

10. Method according to any one of claims 6 to 9, the gas pressure in the common gas head being between 50 and 100 mbar relative.

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