Heat exchanger with at least two fluid circulation circuits, having a shell with two concentric cylinders between which plates of generally involute shape are arranged; use in a molten liquid salt nuclear reactor

Abstract

The invention relates to a heat exchanger (3) with two fluid circuits, comprising: - a shell (30) formed by two concentric hollow cylinders (31, 32), having a central axis (X), and defining therebetween an annular space; - plates (300) each having a straight cross-section perpendicular to the central axis X, in the form of a portion of the involute of a circle or of a curve having a radius of curvature that increases from the inner cylinder towards the outer cylinder and close to an involute of a circle, the plates each connecting the two cylinders of the shell and being parallel to one another in the annular space, while delimiting therebetween, on either side of the same plate, a channel (33) of one of the two fluid circuits, referred to as the first circuit and, within each of the plates, a channel (34) of the other one of the two fluid circuits, referred to as the second circuit.

Description

[0001] Description

[0002] Title: Heat exchanger with at least two fluid circulation circuits, with a jacket of two concentric cylinders between which are arranged plates of general involute shape; Use in a nuclear reactor with molten liquid salt(s).

[0003] technical field

[0004] The present invention relates to heat exchangers with at least two fluid circuits.

[0005] The invention relates more particularly to a new geometry of two-circuit fluid exchangers.

[0006] Known heat exchangers comprise either one or at least two internal fluid circulation channels. In single-circuit exchangers, heat exchange occurs between the circuit and a surrounding fluid in which it is immersed, or with an element from which heat must be supplied or extracted, such as in molds. In exchangers with at least two fluid circuits, heat exchange occurs between the two fluid circuits.

[0007] Chemical reactors are known to operate a continuous process in which a small quantity of co-reactants is simultaneously injected into the inlet of a first fluid circuit, preferably equipped with a mixer, and the resulting chemical product is recovered at the outlet of said first circuit. Among these known chemical reactors, some include a second fluid circuit, usually called a utility circuit, whose function is to thermally control the chemical reaction, either by supplying the heat necessary for the reaction or, conversely, by removing the heat released by it. Such chemical reactors with two fluid circuits and a utility circuit are usually called heat exchanger-reactors.

[0008] The present invention relates both to the implementation of heat exchangers with a sole function of heat exchange and to the implementation of reactor-exchangers. Therefore, the term "heat exchanger with at least one fluid circuit" should be understood, within the scope of the invention, to include both a heat exchanger with a sole function of heat exchange and a reactor-exchanger.

[0009] A heat exchanger according to the invention can also be implemented in any other application requiring an exchange between two fluids, such as a liquid and a gas, or two liquids or even two gases, in particular when rapid and / or large amplitude temperature variations are involved.

[0010] For the purposes of this invention, "primary fluid" means the usual meaning in thermal engineering, namely the hot fluid which transfers its heat to the secondary fluid which is the cold fluid.

[0011] Conversely, in the context of the invention, "secondary fluid" is understood in the usual sense in thermal engineering, namely the cold fluid to which heat is transferred from the primary fluid.

[0012] Although described with reference to a preferred application of heat exchanger of a molten salt reactor (MSR), particularly those of small or medium power or AMR (Advanced Modular Reactor), the invention can be implemented in all applications requiring heat exchangers, in particular those which must be immersed in a fluid circuit, for example primary, in which said fluid circulates in a closed loop from a central channel to an annular channel and vice versa.

[0013] By "molten salt reactor(s)", we mean here and within the framework of the invention, the usual technological meaning, namely a nuclear reactor in which the nuclear fuel is in liquid form, dissolved in molten salt(s), at a temperature typically between 500 and 900 °C, which acts as a heat transfer fluid.

[0014] Targeted applications include heat exchangers in the chemical and petrochemical industries, and integrated SMR type nuclear reactors.

[0015] Previous technique

[0016] In the nuclear field, two types of heat exchangers are currently used: shell and tube heat exchangers for critical and / or pressurized components, and plate heat exchangers for less critical components.

[0017] In general, existing plate heat exchangers have significant advantages over existing tube heat exchangers, particularly their thermal performance and compactness thanks to a favorablely high surface area to heat exchange volume ratio.

[0018] Examples of known tube-and-shell heat exchangers include shell-and-tube heat exchangers, in which a bundle of straight or U-shaped or helical tubes is mounted on perforated plates and arranged inside a shell-and-tube enclosure. In these shell-and-tube heat exchangers, one fluid flows inside the tubes while the other flows inside the shell. These shell-and-tube heat exchangers are easy to manufacture and inspect but have limitations in terms of compactness and require a significant volume.

[0019] Common plate heat exchangers are more compact and are made by stacking corrugated or uncorrugated plates with channels in prismatic order and assembling them together. Particularly due to the assembly techniques required—brazing, welding, or diffusion welding—plate heat exchangers are more complex to manufacture. They are also more difficult to inspect and repair.

[0020] In the nuclear field, plate heat exchangers appear to be an interesting approach, even for critical components, to increase power volume for power extraction.

[0021] The inventors of the present invention have designed a molten liquid salt(s) fast neutron type nuclear reactor, described and claimed in patent application 19 December 2022 under r1 FR2213882, entitled "Molten salt(s) fast neutron type nuclear reactor, whose primary circuit is by natural convection circulation."

[0022] Figure 1 of such a nuclear reactor 1 has been reproduced according to this patent application, which is a numerical simulation view obtained by coupling numerical fluid mechanics (MFN or CFD, an Anglo-Saxon acronym for "Computational Fluid Dynamics") and 3D neutronics, as explained below.

[0023] The reactor 1 with central axis X includes a tank 2 with a metal jacket preferably made of stainless steel or nickel-based alloy, with a thickness of approximately 10 to 20 mm, and formed of a hemispherical tank bottom and a vertical cylinder.

[0024] This reactor vessel 2 internally delimits a primary circuit of liquid fuel containing at least one molten salt. The interior of vessel 2 is devoid of moderator material. In other words, the molten salt fuel fills and circulates inside the vessel without being moderated.

[0025] As can be seen, the heat exchange zone (ZE) has an annular geometry between the reactor's primary circuit and a secondary circuit arranged inside reactor vessel 2. Optimally, this ZE zone consists of a single annular heat exchanger 3.

[0026] A first shell 4 in the form of at least one hollow cylinder, with its central axis coinciding with that of the reactor vessel, is arranged in the reactor vessel 2 to separate the interior of the latter into a central zone and a peripheral zone in which the heat exchanger 3 is arranged.

[0027] The thickness of the bottom of the ferrule 4, in the core area C, can be reduced compared to that of the top of the ferrule 4. As an example, for a total height H equal to 2.5m, the reduced height H' of the bottom of the ferrule 4 is equal to 1m.

[0028] A second ferrule 5 is arranged concentrically inside the first ferrule 4. The interior of the second ferrule 5 defines a space in which control and / or safety bars for nuclear reactions can extend.

[0029] Ferrules 4, 5 can be made of stainless steel or nickel-based alloy.

[0030] The ferrules 4, 5 are advantageously fixed by suspension to the cap-lid closing the reactor vessel 2.

[0031] At the bottom of reactor vessel 2, below the first shell 4, a first deflector 6, in the form of a portion of a torus.

[0032] At the top of reactor vessel 2, above the first shell 4, a second deflector 7, also in the form of a portion of a torus.

[0033] As symbolized by the arrows in Figure 1, with the shells 4, 5 and the deflectors 6, 7 as arranged, in reactor operation, the molten salt(s) fuel liquid circulates only by natural convection in a loop from the bottom of the central zone defining the reactor core C in which the fission reactions occur, from which it rises by heating to the top of the central zone between the shells 4 and 5 where it is deflected by the deflector 7 towards the top of the peripheral zone to cross horizontally and radially the top of the exchanger 3 then descends vertically towards the bottom of the peripheral zone where it is deflected by the deflector 7 towards the core of the reactor C.

[0034] The shell 5 allows the fuel liquid to be guided as it rises between the two areas where it is diverted, i.e. in the central area of ​​the reactor from the diversion area by the deflector 6 through the core C to the diversion area by the deflector 7. The deflectors 6, 7 by their shapes and their arrangement each allow the flow of the diverted molten salt fuel liquid to be distributed.

[0035] To make the single heat exchanger 3, one could consider a shell type and including a bundle of bayonet tubes defining the exchange part with the secondary circuit.

[0036] Now, as already mentioned, plate heat exchangers are an interesting avenue, particularly for increasing power volume in power extraction.

[0037] Thus, the inventors became interested in this plate heat exchanger technology to create heat exchanger 3 in Figure 1.

[0038] However, current geometries with plate stacks cannot be retained because the plates are flat and the resulting stacks are prismatic, which is incompatible with the geometry of reactor 1. Indeed, as illustrated in figure 3, the primary fluid circulation circuit (molten liquid salt(s)) and therefore the housing space ZE dedicated for the exchanger 3 is annular.

[0039] There is therefore a need to further improve heat exchangers with at least two fluid circuits, of the plate type in particular in order to be compatible with an annular geometry required for the fluid circuits and to best meet the specifications of applications in particular for a molten salt reactor, as envisaged in the aforementioned application FR2213882.

[0040] The aim of the invention is to at least partially meet this need.

[0041] Description of the invention

[0042] To achieve this, the invention relates to a two-circuit fluid heat exchanger comprising:

[0043] - an envelope formed by two concentric hollow cylinders, with a central axis (X), and defining an annular space between them;

[0044] - plates each having a straight cross-section perpendicular to the central axis X in the form of a portion of an involute of a circle or a curve with increasing radius of curvature from the inner cylinder towards the outer cylinder and close to an involute of a circle, the plates each connecting the two cylinders of the envelope and being parallel to each other in the annular space by delimiting between them on either side of the same plate, a channel of one of the two fluid circuits, called first circuit and within each of the plates a channel of the other of the two fluid circuits, called second circuit.

[0045] By "involute of a circle", we mean here and within the framework of the invention the usual mathematical definition according to which it is a plane involute curve, that is to say that its normals are the tangents of the circle.

[0046] For the purposes of this invention, a "curve with a close radius of curvature" is defined as a curve whose radius of curvature may deviate slightly from the involute of the circle as it moves outwards. Typically, the radius of curvature may deviate by no more than 20% from the involute of the circle, so as to vary the spacing between the plates by 20% between the inside and outside.

[0047] According to an advantageous embodiment, each plate consists of two parallel half-plates delimiting between them a channel of the second circuit which is open at one longitudinal end of the plate and closed by a closing partition at the other longitudinal end of the plate.

[0048] According to another advantageous embodiment, the inner cylinder of the envelope comprises, at one of its longitudinal ends, lateral openings, each opening onto a channel of the first circuit, forming the inlets of said first circuit, the outlets of said first circuit being formed by the longitudinal ends of the channels opposite the lateral openings of the inner cylinder.

[0049] According to an advantageous embodiment, the heat exchanger includes, within each channel connecting an inlet to an outlet of the first circuit, a deflector in the form of a curved fin adapted to redirect the fluid circulating in said first circuit from the lateral inlets to the longitudinal outlets. These flow-straightening fins for the fluid in the first circuit can preferably be metal overhangs the thickness between two adjacent plates. The curved shape of these deflectors serves to straighten the fluid flow from the lateral inlet in the inner cylinder to the longitudinal end of the annular space in the casing, advantageously maintaining the most homogeneous flow possible and without creating stagnant zones.For mechanical reasons, advantageously a fin is only attached to one of the two plates constituting the channel of the first circuit so as to allow for assembly and expansion of the plates relative to each other. According to an advantageous embodiment, the heat exchanger comprises inlet and outlet manifolds of the second circuit, arranged side-by-side, the outlet manifold comprising two concentric hollow cylinders, arranged in an annular shape extending from one of the longitudinal ends of the two cylinders of the casing to collect the second fluid exiting the channels of the second circuit, the inlet manifold comprising at least one concentric hollow cylinder arranged outside the outer cylinder of the outlet manifold to direct the second fluid towards the other longitudinal end of the plates.

[0050] Thus, according to this method, the second fluid circulates in the opposite direction to the first fluid inside the exchanger.

[0051] According to this method and a first advantageous embodiment, the inlet and / or outlet manifold is / are divided into n angular sectors, with two adjacent angular sectors being fluidly separated by a radial partition that is a portion of the same involute of a circle as a plate. This embodiment allows for the isolation of a portion of the heat exchanger in the event of a leak on a plate, even if this generates asymmetrical cooling, which can be minimized.

[0052] According to this method and a first advantageous embodiment, the inlet and / or outlet manifold is / are partitioned into N sub-manifolds, preferably regularly spaced. Two sub-manifolds are fluidly separated from each other by a cylindrical partition. Each channel of the second fluid circuit is partially blocked so that it is fluidly connected to only one inlet sub-manifold and one outlet sub-manifold. When the partitioning is angularly regular, this embodiment allows, in the event of a leak on a plate, the isolation of a portion of the heat exchanger without introducing an overall cooling asymmetry.

[0053] When required, the exchanger may include means for maintaining the spacing between plates so as to ensure a constant spacing over the height of the plates.

[0054] The exchanger may have one or both of the following advantageous characteristics: the width of a channel in the first fluid circuit is between 2 and 5 mm; the width of a channel in the second fluid circuit is between 1 and 2 mm; - the number of channels in the first and second fluid circuits is between 10 and 5000;

[0055] - the number of plates is between 500 and 1500;

[0056] - the thickness of a plate is between 0.5 and 3 mm;

[0057] - the heat exchange width defined by the width of the annular space between the two cylinders of the envelope is between 1 and 100cm.

[0058] Advantageously, the material constituting the shell, the plates and where applicable the collectors is a nickel-based alloy, preferably Inconel® 625. In an application where the exchanger is used for a molten salt reactor, this material has the advantages of exhibiting low swelling under irradiation and being compatible with combustible molten salt.

[0059] The invention also relates to the use of the heat exchanger as described above, the fluid of the first circuit, as the primary fluid, being molten liquid salt(s) and the fluid of the second circuit, as the secondary fluid, being a liquid salt.

[0060] Preferably, the molten salt(s) liquid of the first circuit is selected from a mixture of NaCl-UC13, preferably in proportions of 5 to 36 mol% for FUC13, and PuC13, preferably in proportions of 5 to 30 mol%, as salts, with depleted uranium, preferably less than 0.3 atomic percent, or a mixture of NaCl-UC13, preferably at 34 mol%, as a salt with enriched uranium U235 (HALEU), preferably in proportions of 5 to 20%. The molten salt(s) may also contain ThC14.

[0061] Preferably, the liquid salt in the second circuit is based on a mixture of molten salts NaCl-MgCh or NaCl-MgC12-KCl or NaCl-MgC12-KCl-ZnC12. A heat exchanger according to the invention can of course operate with liquid salts other than chloride salts.

[0062] In one preferred application, the fluid in the first or second circuit comes from a nuclear reactor.

[0063] The heat exchanger as described above is advantageously that of a molten salt nuclear reactor of the fast neutron type. The invention also relates to a molten liquid salt nuclear reactor of the fast neutron type, comprising:

[0064] - an axisymmetric reactor vessel around a central axis, internally delimiting a primary circuit of fuel in liquid form in which at least one salt is melted, the interior of the vessel being devoid of a moderator material;

[0065] - at least one heat exchanger as described above, arranged inside the reactor vessel;

[0066] - a first shell in the form of at least one hollow cylinder, with the central axis coinciding with that of the reactor vessel, the first shell being arranged in the reactor vessel to separate the interior of the latter into a central zone and a peripheral zone in which the heat exchanger is arranged so that in the operation of the reactor, the molten salt(s) fuel liquid circulates by natural convection in a loop from the bottom of the central zone defining the reactor core in which the fission reactions occur, from which it rises by heating to the top of the central zone where it is deflected to the top of the peripheral zone to pass through the exchanger and then descends to the bottom of the peripheral zone where it is deflected to the reactor core.

[0067] Thus, in this reactor, the exchanger is arranged vertically in the peripheral zone and the primary molten salt(s) which rise(s) by natural convection in the central zone corresponding to the inside of the inner cylinder of the exchanger jacket is deflected, preferably by the deflectors within the plates of the exchanger, to descend back down towards the bottom of the peripheral zone.

[0068] The fluid of the second exchanger circuit, preferably a liquid salt, circulates by thermosiphon effect from the inlet manifold preferably located in the pile head zone of the reactor vessel, descending downwards to the periphery of the exchanger shell and then is diverted into the channels delimited by the plates to ascend to the outlet manifold also preferably located in the pile head zone of the reactor vessel.

[0069] In other words, the fluid from the second circuit circulates inside the exchanger by thermosiphon effect and against the current of the fluid from the first circuit.

[0070] Such a reactor can have a thermal power output between 10 and 500 MWth. The temperature of the molten salt(s) within the reactor vessel can be between 500 and 750°C.

[0071] The temperature of the secondary fluid at the inlet of the exchanger according to the invention can be around 420°C while its temperature at the outlet of the exchanger is around 620°C.

[0072] Thus, the invention is essentially a two-fluid-circuit heat exchanger comprising a shell delimited by two concentric hollow cylinders between which are arranged parallel plates in the shape of a portion of an involute of a circle, the space between one plate and an adjacent plate defining a channel of one of the two circuits, the space between this same plate and the other adjacent plate defining a channel of the other of the two circuits.

[0073] The heat exchanger is preferably configured to operate with the fluid from one of the two circuits, which enters from inside the inner cylinder of the casing and circulates in the opposite direction to the fluid from the other circuit, which is preferably the one that removes the heat. This counter-current circulation is the most efficient in terms of the amount of heat that can be removed.

[0074] This defines a heat exchanger that operates in an annular circulation configuration of one of the two fluids.

[0075] The operating regime of the exchanger can be such that the flow rate of the primary fluid within it is advantageously between 0.25 m / s and 5 m / s.

[0076] The thermal power that can be evacuated by an exchanger according to the invention can be between 2 kWth and 2000 MWth.

[0077] The pressure drop within an exchanger according to the invention is advantageously less than 4 bars.

[0078] In general, an exchanger according to the invention can be used in any application where annular circulation of at least one of the two fluids is required.

[0079] An exchanger according to the invention offers numerous advantages, including:

[0080] - heat exchange in an annular circulation configuration of one of the fluids circulating in the exchanger, with reduced pressure losses; - the possibility of counter-current circulation of the fluids which allows the evacuation of a significant amount of thermal power;

[0081] - in vertically installed configuration, the possibility of thermosiphon circulation of one of the two fluids within the exchanger.

[0082] Other advantages and features of the invention will become clearer upon reading the detailed description of examples of implementation of the invention given by way of illustration and not limitation with reference to the following figures.

[0083] Brief description of the drawings

[0084] [Fig 1] Figure 1 is a view from a simulation coupling computational fluid dynamics (CFD) and 3D neutronics, showing the circulation of the primary fluid with the temperature field within a molten salt nuclear reactor, of the fast neutron type according to patent application FR2213882.

[0085] [Fig 2] Figure 2 shows a schematic longitudinal section view of the top of the reactor vessel from Figure 1.

[0086] [Fig 3], [Fig 3 A] Figures 3 and 3 A are partial perspective and detail views of a portion of a parallel plate heat exchanger in the form of portions of involutes of a circle according to the invention.

[0087] [Fig 4] Figure 4 is a schematic longitudinal cross-sectional view of a space between two adjacent plates showing the circulation of fluid from a first circuit within a heat exchanger according to the invention.

[0088] [Fig 5] Figure 5 is a schematic longitudinal cross-sectional view of a plate showing the circulation of the fluid from the second circuit within a heat exchanger according to the invention.

[0089] [Fig 6] Figure 6 is a schematic cross-sectional view taken at the level of adjacent plates of a heat exchanger according to the invention.

[0090] [Fig 7A], [Fig 7B] Figures 7A and 7B are longitudinal and transverse sectional views, respectively, showing an embodiment of a heat exchanger according to the invention, which incorporates an inlet manifold and an outlet manifold for the fluid of the second circuit. [Fig 8] Figure 8 is a transverse sectional view showing a first alternative embodiment of the inlet and outlet manifolds for the fluid of the second circuit.

[0091] [Fig 9] Figure 9 is a cross-sectional view showing a second variant of the embodiment of the fluid inlet and outlet manifolds of the second circuit.

[0092] Detailed description

[0093] Throughout this application, the terms "vertical", "lower", "upper", "bottom", "top", "below" and "above" are to be understood by reference to a fast neutron molten salt nuclear reactor and the exchanger according to the invention, as provided for in the vertical operating configuration.

[0094] For clarity, the same references designating the same elements of an exchanger according to the invention are used for all figures 1 to 9. In figure 9, the plates and channels are shown upright for clarity.

[0095] It is specified that the different elements according to the invention are represented only for the sake of clarity and that they are not necessarily to scale.

[0096] In the figures, the arrows illustrate the path of the fluids (Fluid 1, Fluid 2) within an exchanger 3 according to the invention.

[0097] Figure 1 has already been discussed in the introduction. It will therefore not be detailed further below.

[0098] Figure 2 reproduces the upper part of figure 1 and clearly illustrates the exchanger design specifications that the inventors had to propose.

[0099] The molten liquid salt(s), which constitute(s) the primary fluid, rises inside the central channel delimited by the ferrule 4. This molten salt(s) fuel liquid of the primary circuit can be a mixture of NaCl, 25% UC13, 9% PuC13 in molar proportions as salts, with depleted uranium U235 at 0.7% atomic.

[0100] This molten salt(s) enters horizontally and radially through the inner lateral end of the top of the exchanger 3 (where it cools), which is in the annular part of the reactor vessel 2, then passes vertically through the exchanger at the bottom of which it exits to return inside the reactor vessel 2.

[0101] Heat exchanger 3 must have a low pressure drop to allow the molten salt(s) to circulate, even if only by natural convection. The dimensions of heat exchanger 3 may advantageously be as follows:

[0102] RI between 30 and 80 cm;

[0103] R2 between 100 and 150 cm;

[0104] R3 between 20 and 70 cm;

[0105] H1 between 50 and 300 cm;

[0106] H2 between 20 and 50 cm.

[0107] As shown in figures 3 to 6, the inventors considered creating a plate exchanger with 300 plates arranged vertically in the configuration of figure 2.

[0108] The exchanger 3 includes first of all an envelope 30 formed by two concentric hollow cylinders 31, 32, with a central axis (X), and defining between them an annular space.

[0109] Each of the 300 plates has a straight cross-section perpendicular to the central X axis in the form of a portion of an involute of a circle.

[0110] As shown in Figures 3 and 3A, the plates 300 are parallel to each other along two involutes of the same circle, parallel to each other in the sense that the perpendicular distance, i.e., the smallest distance between the two curves, remains constant. These involutes ensure that the space between the plates is constant regardless of the distance R from the central axis X.

[0111] These plates 300 each connect the two cylinders 31, 32 of the envelope and are parallel to each other in the annular space, delimiting between them on either side of the same plate, a channel 33 of one of the two fluid circuits (Fluid 1) and within each of them a channel 34 of the other of the two fluid circuits (Fluid 2).

[0112] For example, the plates are made of Inconel® 625.

[0113] The effective heat exchange width L of such an exchanger can be up to 1m.

[0114] The inner cylinder 31 of the envelope includes, at one of its longitudinal ends, one or more lateral openings 310, each opening onto a channel 33 of the first fluid circuit (Fluid 1). This opening or these openings 310 form the inlets of the first circuit, the outlets of the first circuit being formed by the longitudinal ends of the channels 330 opposite the lateral opening(s) 310. As illustrated in Figure 4, inside each channel 33 delimited by a space between two adjacent plates 300 connecting an inlet to an outlet of the first circuit, a deflector 35 is arranged in the form of a curved fin adapted to redirect the fluid circulating in the first circuit from the lateral inlets 310 to the longitudinal outlets 330. These flow straightening fins 35 can be metal oversizing the thickness of a plate 300.Thus, their curved shape serves to straighten the flow of Fluid 1 from the first circuit to make it pass from horizontal to vertical while maintaining the most laminar flow possible and without creating turbulence.

[0115] A deflector 35 extends only partially over the width of a channel 33, on the one hand to allow the mounting of the plates and on the other hand to leave a space E for the expansion of the plates between them (figure 6).

[0116] Thus, as illustrated in figure 4, the fluid (Fluid 1) of the first circuit enters laterally into the exchanger 3 through the lateral opening(s) 310 and is then deflected by the fins 35 into each of the channels 33 of the first circuit to make it parallel to the X axis (vertical in the configuration of figure 2) and thus exit through the longitudinal ends 330 of the channels 33.

[0117] Each plate 300 consists of two parallel half-plates 301, 302 delimiting between them a channel 34 which is open at one longitudinal end of the plate 300 and closed by a closing partition 303 at the other longitudinal end of the plate 300.

[0118] Inside the space between the two half-plates 301, 302, there are partition walls 304 dividing the Fluid 2 circulation channel 34 into several sub-channels 340.

[0119] The 300 plates according to the invention can be made by diffusion welding.

[0120] As shown in Figure 5, the fluid (Fluid 2) of the second circuit can enter, in a cold state, a longitudinal end 320 of a channel 34 which is the one delimited within the same plate 300.

[0121] When it reaches the opposite longitudinal end, it is deflected into the distribution space between the subchannels 340 and the closing partition 303. This distribution space serves to distribute the flow of the cold fluid into the different subchannels 340. As illustrated in Figure 5, the cross-section of this distribution space is variable so as to distribute the flow evenly between the different subchannels 340.

[0122] Then the fluid (Fluid 2) is discharged in a hot state through the longitudinal end 341 of the sub-channels 34 in parallel with the inlet 320.

[0123] This results in a predominantly counter-current exchanger between Fluid 1 and Fluid 2, which guarantees high efficiency for heat exchange.

[0124] In the configuration of Figure 2, the fluid (Fluid 2) can circulate by thermosiphon effect inside the channels 34, from its inlet at the top to the horizontal distribution space at the bottom of the exchanger and then its outlet also at the top.

[0125] Figure 6 shows the counter-current flows of the two fluids (Fluid 1, Fluid 2) in the areas of the channels 33, 34 delimited by the involute plates 300. As an example, each of the half-plates 301 and 302 has a thickness of 0.5 mm, the width of a channel 33 between the two adjacent plates 300 is equal to 2 mm, and the width of a channel 34 between the half-plates 301 and 302 is equal to 1 mm.

[0126] Figures 7A and 7B illustrate an embodiment where inlet manifolds 38 and outlet manifolds 39 of the fluid (Fluid 2) are integrated into the exchanger 3.

[0127] In this mode, these collectors 38, 39 are arranged side-by-side. The outlet collector 39 comprises two concentric hollow cylinders, arranged in an annular shape extending from one of the longitudinal ends of the two cylinders 31, 32 of the casing 30 to collect the second fluid (Fluid 2) at the outlet 330 of the channels 33.

[0128] The inlet manifold 38 includes at least one concentric hollow cylinder 37 arranged outside the outer cylinder of the outlet manifold to bring the second fluid (Fluid 2) towards the other of the longitudinal ends of the plates 300, opposite the outlets 330.

[0129] Thus, with these cross-sections of the fuel exchanger, the following cross-sections are shown: vertical (left), horizontal in the plane of the manifold (A) and the plates (B) (right). The cold primary fluid enters the outer part of the manifold, then descends into the outer part of the heat exchanger plates. After a change of direction at the bottom, it rises into the inner part of the plates and is then recovered in the inner part of the manifold. In Figure 7B, the constant width 1 of the channels 33 is visible across the entire width of the annular space between the cylinders 31 and 32 of the casing.

[0130] Figure 8 shows an advantageous variant in which the inlet manifold 38 and the outlet manifold 39 are each divided into n angular sectors. Thus, in each of these manifolds 38, 39, two adjacent angular sectors are fluidly separated from each other by a radial partition 380, 390, which is a portion of the same involute of a circle as a plate 300.

[0131] Figure 9 shows another advantageous variant in which the inlet manifold 38 and the outlet manifold 39 are partitioned into a number N of sub-manifolds, two sub-manifolds being fluidly separated from each other by a cylindrical partition, each of the channels 34 of the second fluid circuit (Fluid 2) being partially closed so as to be fluidly connected with a number at most equal to Nl of sub-manifolds. With parts 382, ​​392 of the channels 34 being closed, each of the channels 34 is fluidly connected with only one inlet or outlet sub-manifold.

[0132] For the production of an exchanger 3 according to the invention, it is possible to produce plates 300 individually and then weld them to the two concentric hollow cylinders 31, 32 forming the envelope 30.

[0133] Also, the secondary fluid collectors can be attached and welded to the casing already fitted with the plates inside.

[0134] Other variations and improvements can be made without going outside the scope of the invention.

[0135] For example, one can also consider fluid circulations with co-current flow.

[0136] Other installed configurations of heat exchangers besides vertical ones can be considered.

Claims

Demands 1. Heat exchanger (3) with two fluid circuits comprising: - an envelope (30) formed by two concentric hollow cylinders (31, 32), with a central axis (X), and defining between them an annular space; - plates (300) each having a straight cross-section perpendicular to the central axis X in the form of a portion of an involute of a circle or a curve with a radius of curvature increasing from the inner cylinder to the outer cylinder and close to an involute of a circle, the plates each connecting the two cylinders of the casing and being parallel to each other in the annular space, delimiting between them on either side of the same plate a channel (33) of one of the two fluid circuits, called the first circuit, and within each of the plates a channel (34) of the other of the two fluid circuits, called the second circuit, each plate (300) being made up of two parallel half-plates (301, 302) delimiting between them a channel (34) of the second circuit which is open at one longitudinal end of the plate (300) and closed by a closing partition (303) at the other longitudinal end of the plate (300), the inner cylinder of the casing comprising,at one of its longitudinal ends, one or more lateral openings (310), each opening onto a channel (33) of the first circuit, forming the inlets of said first circuit, the outlets of said first circuit being formed by the longitudinal ends of the channels (330) opposite the lateral opening(s) of the inner cylinder.

2. Heat exchanger according to claim 1, comprising, inside each channel connecting an inlet to an outlet of the first circuit, a deflector (35) in the form of a curved fin adapted to redirect the fluid circulating in said first circuit from the lateral inlets to the longitudinal outlets.

3. Heat exchanger according to any one of the preceding claims, comprising: inlet (38) and outlet (39) manifolds of the second circuit, arranged side-by-side, the outlet manifold comprising two concentric hollow cylinders arranged in an annular shape extending from one of the longitudinal ends of the two cylinders of the casing to collect the second fluid at the outlet of the channels of the second circuit, the inlet manifold comprising at least one concentric hollow cylinder arranged outside the outer cylinder of the outlet manifold to bring the second fluid towards the other of the longitudinal ends of the plates.

4. Heat exchanger according to claim 3, the inlet manifold and / or outlet manifold being divided into a number of n angular sectors, two adjacent angular sectors being fluidly separated from each other by a radial partition which is a portion of the same involute of a circle as a plate.

5. Heat exchanger according to claim 4, the inlet manifold and / or outlet manifold being partitioned into a number N of sub-manifolds, two sub-manifolds being fluidly separated from each other by a cylindrical partition, each of the channels of the second fluid circuit being partially closed so as to be fluidly connected only with a single inlet sub-manifold and a single outlet sub-manifold.

6. Heat exchanger according to any one of the preceding claims, the width of a channel of the first fluid circuit being between 2 and 5 mm.

7. Heat exchanger according to any one of the preceding claims, the width of a channel of the second fluid circuit being between 1 and 2 mm.

8. Heat exchanger according to any one of the preceding claims, the number of channels in the first and second fluid circuits being between 10 and 5000.

9. Heat exchanger according to any one of the preceding claims, the number of plates being between 500 and 1500.

10. Heat exchanger according to any one of the preceding claims, the thickness of a plate being between 0.5 and 3 mm.

11. Heat exchanger according to any one of the preceding claims, the heat exchange width defined by the width of the annular space between the two cylinders of the envelope being between 1 and 100cm.

12. Heat exchanger according to any one of the preceding claims, the material constituting the casing, the plates and where applicable the collectors being nickel-based alloy, preferably Inconel® 625.

13. Use of the heat exchanger according to any one of the preceding claims, the fluid of the first circuit, as primary fluid, being liquid molten salt(s) and the fluid of the second circuit, as secondary fluid, being liquid salt.

14. Use according to claim 13, the molten salt(s) liquid of the first circuit being selected from a mixture of NaCl-UC13, preferably in proportions of 5 to 36 mol% for FUC13, and PuC13, preferably in proportions of 5 to 30 mol%, as salts, with depleted uranium, preferably less than 0.3 atomic percent, or a mixture of NaCl-UC13, preferably at 34 mol%, as a salt with enriched uranium U235 (HALEU), preferably in proportions of 5 to 20%.

15. Use according to claim 13 or 14, the liquid salt of the second circuit being based on a mixture of molten salts NaCl-MgCh or NaCl-MgC12-KCl or NaCl-MgC12-KCl-ZnC12.

16. Use according to any one of claims 13 to 16, as a heat exchanger for a molten salt nuclear reactor, of the fast neutron type.

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