Heat removal system for a nuclear facility

Abstract

The present invention relates to a cooling module (201) suitable for cooling a liquid (25) of a storage pool (21) configured to store fuel elements (24) that have a residual thermal power to be removed, the cooling module comprising a heat pipe (230) designed to be positioned in at least one medium (26, 27) outside the storage pool and to be coupled to the storage pool via at least one heat exchanger (211, 212) of the cooling module, the liquid forming a hot source for the heat pipe, and the medium forming a cold source for the heat pipe; the heat pipe (230) extending in a longitudinal direction (Z).

Description

[0001] DESCRIPTION

[0002] Thermal evacuation system of a nuclear installation. This application claims priority from French patent application FR2415256 filed on December 24, 2024, entitled "Thermal evacuation system of a nuclear installation", which is considered to be an integral part of this description within the limits provided by law.

[0003] technical field

[0004]

[0001] The present description relates in general to the thermal evacuation of a nuclear installation.

[0005]

[0002] The present description relates in particular to the cooling of combustible elements having residual thermal power to be evacuated, in a storage pool, or cooling pool, and the cooling of the storage pool by a thermal evacuation system.

[0006]

[0003] The storage pool may be part of a nuclear power plant comprising at least one nuclear reactor. The nuclear reactor may be, for example, a power reactor and / or a research reactor.

[0007] Previous technique

[0008]

[0004] A nuclear reactor uses fuel elements containing energetic fissile materials, or even fertile materials which, under the action of neutrons, can partially transform into fissile materials. The fuel elements are generally installed in the core of the nuclear reactor, the core being located within a vessel, in a circuit called the primary circuit. The fuel elements are, for example, grouped into assemblies. A heat transfer fluid circulates in the vessel and in the core, from which it extracts the thermal energy released by the fission of the fissile materials. The heat transfer fluid carries the extracted heat and transfers it via a heat exchanger to a secondary fluid which circulates in a secondary circuit, so as to vaporize the secondary fluid. The secondary circuit typically includes a turbine and a generator to generate electricity from the vaporized secondary fluid.In water-cooled reactors, the primary circuit coolant is water, and the secondary circuit coolant is also water. In pressurized water reactors (PWRs), the heat exchanger is integrated into a steam generator, which is generally part of the primary circuit. The steam generator transfers all or part of the heat from the primary circuit coolant to the water in the secondary circuit, converting it into steam.

[0009]

[0005] When fuel elements are no longer in use, for example when the irradiation cycle of these fuel elements is completed, they are extracted from the reactor core and vessel, then removed from the reactor vessel and stored in a storage facility, where they are cooled for several months to reduce their thermal power before being removed from the nuclear power plant. Fuel elements with residual thermal power may be designated as "spent" or "hot" fuel elements.

[0010]

[0006] In a nuclear reactor whose fuel elements are compatible with water, typically water-cooled reactors, the storage facility includes a storage pool, or cooling pool, which is filled with water, in which the fuel elements are cooled. A storage pool ensures the storage of fuel elements removed from the core of the nuclear reactor, while also providing radiation protection and cooling of these fuel elements before they can be transported and removed from the nuclear power plant.The removal of residual heat from the fuel elements relies on keeping them submerged in the water of the storage pool and on a cooling circuit for this water. This circuit must include at least one pumping and heat exchange system connected to an external cold source. This is essential to continue cooling the fuel elements and prevent the water from boiling. For example, the fuel elements are stored at the bottom of the storage pool where a large volume of water actively circulates, cooled by one or more cooling circuits that include one or more heat exchangers and one or more circulation pumps.In the event of boiling, the combustible elements could be partially exposed, meaning they would no longer be completely covered by water (this is called dewatering), leading to their degradation to varying degrees, according to a kinetic profile dependent on their residual heat output at the time of partial or total dewatering. Each cooling circuit for the storage pool water is typically sized to maintain the average temperature of the storage pool water, under normal operating conditions, at a maximum value of approximately 50°C.

[0011]

[0007] Figure 1 is a cross-sectional view representing in a simplified manner an example of a nuclear power plant 100. This nuclear power plant 100 comprises a reactor building 110 and an annex building 120, or fuel building, adjoining the reactor building 110.

[0012]

[0008] The reactor building 110 includes side walls 111 and a bottom wall, or base, 112. The fuel building 120 includes side walls 121 and a bottom wall, or base, 122. In general, roofs (not shown in Figure 1) of the reactor and fuel buildings rest on the side walls.

[0013]

[0009] The reactor building 110 includes a vessel 113 which contains a nuclear reactor core containing fuel elements (core and fuel elements not shown in Figure 1), and a reactor pool 114 filled with water for loading and unloading fuel elements into and from vessel 113.

[0014]

[0010] The fuel building 120 includes a storage pool 124 filled with water. In the example shown, the storage pool 124 has three compartments which can be separated from each other by a door or a cofferdam 125: a storage compartment 124A, a transfer compartment 124B and a loading compartment 124C.

[0015]

[0011] The transfer compartment 124B communicates with the reactor pool 114 by means of a transfer device 131 which passes in a sealed manner through side walls 111, 121 opposite the reactor and fuel buildings 110, 120, so as to connect the reactor pool 114 with the transfer compartment 124B of the storage pool 124, in particular to transport the fuel elements between the vessel 113 and the storage pool 124.

[0016]

[0012] The loading compartment 124C allows the fuel elements to be removed once cooled. For example, the cooled fuel elements are removed via a transport package loaded underwater into the loading compartment 124C, or docked beneath the loading compartment 124C.

[0013] The storage compartment 124A includes a storage rack 123 which can hold several fuel elements. The storage rack 123 comprises several locations, or slots, for example between 300 and 1200 locations depending on the type of nuclear reactor. The water level in the storage compartment 124A is, for example, between 10 and 20 meters.

[0017]

[0014] The nuclear power plant 100 includes a cooling circuit 140 connected to an outlet of the storage pool 124, for example, to an outlet of storage compartment 124A. Indeed, when the pool water heats up in contact with the fuel elements, it contributes less effectively to the cooling function of these fuel elements and can even boil, which can lead to at least partial unflooding of these fuel elements. It must therefore be continuously cooled. The cooling circuit 140 includes a pump 141 for circulating the water and a heat exchanger 142 for cooling the water in the storage pool 124. Another cooling circuit 140', including another pump 141' and another heat exchanger 142', can be connected in parallel with the cooling circuit 140.Each exchanger 142, 142' communicates with a cold source (not shown in Figure 1) to which the water from the storage pool 124 gives up all or part of its heat and is continuously cooled.

[0018]

[0015] Each cooling circuit 140, 140' is connected to an inlet of the storage pool 124 by an injection circuit 143 intended to reinject the cooled water into each of the compartments 124A, 124B, 124C of the storage pool 124. The filling circuit 143 has several pipes each plunging into one of the compartments 124A, 124B, 124C of the storage pool 124, in particular a pipe 144 plunging into the lower part of the storage compartment 124A, under the storage rack 123.

[0019]

[0016] Maintaining the water temperature in the storage pool below the threshold, typically a maximum of around 50°C, is thus contingent upon the proper functioning of at least one of the cooling circuits, in particular the cooling circuit pump, the heat exchanger, and even the availability of the cold source. For example, if no pump is operating, the water can boil, and combustible materials can be exposed, leading to their more or less significant and rapid degradation, depending on the kinetics of their residual heat at the time of dewatering, and even damage to the storage pool and related installations. For example, during the Fukushima accident in 2011, the cooling system became inaccessible due to failures of both the main equipment and the backup equipment, caused by the earthquake and flooding.Although it was not possible to continuously measure the temperature of the storage pool, the condition of the combustible elements strongly suggests that some of them were not properly cooled, suggesting partial dewatering following localized boiling in the storage pool.

[0020]

[0017] A system for cooling the fuel elements in a storage pool is therefore sought which is not dependent on active external sources, typically a source of electricity, while allowing safe and continuous cooling of the fuel elements.

[0021]

[0018] In particular, a thermal evacuation system is sought that allows heat to be extracted from the storage pool, in particular allowing the fuel elements to continue to be cooled, even in the event of unavailability or malfunction of the cooling circuit(s).

[0022] Summary of the invention

[0023]

[0019] There is a need for a heat evacuation system that would allow heat to be extracted safely and continuously from a storage pool filled with hot combustible materials.

[0024]

[0020] One embodiment would overcome all or part of the disadvantages of known thermal evacuation systems.

[0025]

[0021] One embodiment provides a cooling module adapted to cool a liquid in a storage pool configured to store combustible elements having residual thermal power to be removed, the cooling module comprising a heat pipe adapted to be positioned in at least one medium external to the storage pool and to be coupled to said storage pool via at least one heat exchanger of the cooling module, the liquid forming a hot source of the heat pipe, and the at least one medium forming a cold source of the heat pipe; the heat pipe extending in a longitudinal direction.

[0026]

[0022] According to one embodiment, the at least one heat exchanger comprises a first heat exchanger and a second heat exchanger connected together and adapted for the circulation of a first fluid, and the heat pipe is configured for the circulation of a second fluid in liquid and gaseous form;

[0027] the first heat exchanger being adapted to be positioned in the storage pool liquid to transfer all or part of the heat from the liquid to the first fluid, and the second heat exchanger being positioned in the heat pipe to transfer all or part of the heat from the first fluid to the second fluid, so as to transform a first portion of said second fluid from a liquid phase to a vapor phase.

[0028]

[0023] According to one embodiment, the cooling module further comprises at least one other heat exchanger in at least one medium, the at least one other heat exchanger being coupled to the heat pipe to cool the second fluid.

[0029]

[0024] According to one embodiment, the cooling module comprises:

[0030] - a first circuit adapted to the circulation of the first fluid, the first circuit including the first heat exchanger, the second heat exchanger, and a fluid network linking said first and second heat exchangers; and

[0031] - a second circuit adapted to the circulation of the second fluid, the second circuit including the heat pipe;

[0032] the second circuit being coupled to the first circuit by the second heat exchanger.

[0033]

[0025] According to one embodiment, the heat pipe comprises a chamber elongated in the longitudinal direction and including:

[0034] - an inner tube in which the second heat exchanger is positioned, the inner tube being sized so as to allow a phase change effect, by the first portion in vapor phase of the second fluid, of a second portion in liquid phase of the second fluid from the second heat exchanger towards an upper end of the inner tube;

[0035] - an outer tube around the inner tube and in fluidic communication with the inner tube; and an annular space between the outer tube and the annular tube.

[0036]

[0026] According to one embodiment, the second heat exchanger is positioned in a lower portion of the inner tube connected to an upper portion of said inner tube, said upper portion being sized to allow the first and second portions of the second fluid to be driven towards the upper end of the inner tube.

[0037]

[0027] According to one embodiment, the inner tube includes an outer portion which extends longitudinally outside the outer tube, the cooling module including a third heat exchanger positioned in a first medium among at least one medium, for example air, and coupled to the outer portion of the inner tube to cool the second fluid, for example condense the first portion in vapor phase of the second fluid.

[0038]

[0028] According to one embodiment:

[0039] - the upper end of the external tube is closed by a cover, for example a bell-shaped cover;

[0040] - the lower end of the outer tube is closed;

[0041] - the upper end of the inner tube is closed; and - the lower end of the inner tube is open in the outer tube, at a non-zero distance from the lower end of the outer tube.

[0042]

[0029] According to one embodiment, the cooling module includes at least one first fluid passage between the cover and the annular space and at least one second fluid passage between the inner tube and the cover.

[0043]

[0030] According to one embodiment, the cooling module further comprises a fourth heat exchanger positioned in a second external medium among water less a medium, for example soil, and coupled to a lower portion of the external tube to cool the second fluid.

[0044]

[0031] According to one embodiment, the inner tube has a tubular shape in the longitudinal direction.

[0045]

[0032] According to one embodiment:

[0046] - the first fluid is water or an organic fluid, for example a refrigerant, for example a hydrofluoroolefin-based refrigerant; and / or

[0047] - the second fluid is an organic fluid, for example a refrigerant, for example a hydrofluoroolefin-based refrigerant.

[0048]

[0033] According to one embodiment, the distance in the longitudinal direction between the second heat exchanger and the first heat exchanger is defined to promote natural convection of the first fluid between the first heat exchanger and the second heat exchanger, while minimizing the average level of the second heat exchanger in the heat pipe.

[0049]

[0034] One embodiment provides a thermal evacuation system comprising:

[0050] at least one cooling module as described previously;

[0051] - a storage pool at least partially filled with a liquid suitable for storing combustible elements in the liquid; said combustible elements having residual thermal power to be evacuated; a first heat exchanger among the at least one heat exchanger of the at least one cooling module being positioned in the storage pool.

[0052]

[0035] According to one embodiment, at least one cooling module comprises several cooling modules. Brief description of the drawings

[0053]

[0036] These features and advantages, as well as others, will be described in detail in the following description of particular embodiments, given by way of non-limiting example, in relation to the accompanying figures, among which:

[0054]

[0037] Figure 1 is a cross-sectional view representing in a simplified manner an example of a nuclear power plant;

[0055]

[0038] Figure 2A is a longitudinal cross-sectional view representing a heat evacuation system according to one embodiment; and

[0056]

[0039] Figure 2B is a longitudinal sectional view representing a module of the thermal evacuation system of Figure 2A.

[0057] Description of the implementation methods

[0058]

[0040] The same elements have been designated by the same reference numerals in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same reference numerals and may have identical structural, dimensional and material properties.

[0059]

[0041] For the sake of clarity, only the steps and elements necessary for understanding the described embodiments have been shown and are detailed. In particular, the components of a nuclear reactor are not detailed. Furthermore, not all the components of a storage pool, including one or more cooling circuits, are detailed, as they can be carried out by a person skilled in the art.

[0060]

[0042] Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than connectors or conductors, and when referring to two elements coupled together, this means that these two elements can be connected or linked through one or more other elements.

[0061]

[0043] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "superior", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures or to a heat dissipation system in a normal operating position.

[0062]

[0044] Unless otherwise specified, the expressions "approximately", "roughly", "about", and "in the order of" mean to within 10% or 10°, preferably to within 5% or 5°.

[0063]

[0045] In the following description, when reference is made to a reactor, it refers, unless otherwise specified, to a nuclear reactor.

[0064]

[0046] Figure 2A is a longitudinal cross-sectional view representing a thermal evacuation system 200 according to one embodiment. Figure 2B is a longitudinal cross-sectional view representing a module 201 of the thermal evacuation system of Figure 2A.

[0065]

[0047] The heat dissipation system 200 is installed at a nuclear site, for example a nuclear power plant, comprising a pool building 20 which houses a storage pool 21 for holding hot fuel elements 24. The fuel elements 24 are, for example, in a storage rack 23 which includes several locations for storing several fuel elements 24, for example between 300 and 1200 locations depending on the type of nuclear reactor. The storage pool 21 is filled with a liquid 25, generally water, for example demineralized water, in which the fuel elements 24 must be kept to cool them. In the remainder of this description, this liquid 25 may be referred to as water 25 or liquid 25.

[0066]

[0048] The nuclear site may further include one or more nuclear reactors, generally in one or more reactor buildings, and / or one or more other storage pools.

[0067]

[0049] The combustible elements 24 are, for example, in the form of irradiated fuel assemblies. The combustible elements 24 have residual thermal power to be removed. By residual thermal power, it is understood that thermal power exceeds a limit, related to its removal, typically between 5 and 10 kW. t h, for example equal to approximately 7 kW t h (for fuels of the uranium oxide (UO2) type or of the MOX type from the English mixed oxides, mixture of oxides). Thus, the combustible elements 24 can release heat, or thermal energy, which must be able to be removed.

[0068]

[0050] The heat dissipation system 200 comprises at least one cooling module 201, or module 201. Only one module 201 has been shown in Figure 2A, although there may be several, as explained later.

[0069]

[0051] The cooling module 201 includes a first fluidic circuit 210 configured to circulate a first fluid 215.

[0070]

[0052] The first circuit 210 includes a first heat exchanger 211, a second heat exchanger 212, and a fluid network connecting the first and second exchangers. The fluid network shown in this example comprises two fluid lines: a line 213 (supply line) to circulate the first fluid 215 between the first exchanger 211 and the second exchanger 212, and a line 214 (return line) to circulate the first fluid 215 between the second exchanger 212 and the first exchanger 211. The fluid lines 213 and 214 are designed to withstand the pressure and temperature of the first heat transfer fluid 215.

[0071]

[0053] The fluid lines 213 and 214 are, for example, metallic. Each fluid line 213, 214 may advantageously have a shape adapted to promote natural convection in that fluid line, for example, an elongated shape, with, for example, at least one vertical portion. The supply line 213 may advantageously be insulated. The return line 214 may also be insulated. The return line 214 may advantageously be configured to allow the return of the first fluid 215 to the first heat exchanger 211 by gravity.

[0072]

[0054] The first exchanger 211 is positioned in the water 25 of the storage pool 21. The liquid 25 circulates around the first exchanger 211 in which the first fluid 215 circulates.

[0073]

[0055] The second interchange 212 is positioned in an enclosure 224 which is located outside the pool building 20, as described later. Thus, lines 213 and 214 pass through a wall of the pool building 20 to emerge outside this pool building.

[0074]

[0056] The cooling module 201 includes a second fluidic circuit 220 configured to circulate a second fluid 225. The second circuit 220 is coupled to the first circuit 210 by the second heat exchanger 212. The second fluid 225 circulates around the second heat exchanger 212, through which the first fluid 215 circulates.

[0057] The second fluid 225 may be different from the first fluid 215, or perhaps similar to the first fluid 215. The first and second fluids may, for example, be organic fluids. Examples of fluids are given later.

[0075]

[0058] During operation, the fuel elements 24 transfer all or part of their heat to the water 25 in the storage pool 21, which in turn transfers all or part of its heat to the first fluid 215 via the first heat exchanger 211, and the first fluid 215 transfers all or part of its heat to the second fluid 225 via the second heat exchanger 212. The water 25 in the pool 21 forms a heat source for the cooling module 201 and the heat removal system 200.

[0076]

[0059] The second circuit 220 includes a container 224 in which the second fluid 225 circulates.

[0077]

[0060] The enclosure 224 comprises an outer tube 221 (crown), an inner tube 222 (central column) which extends longitudinally at least partially inside the outer tube 221, and a cover 223, for example bell-shaped, joined to the outer tube 221 at its upper end 221A. The lower end 221B of the outer tube 221 is closed. The upper end 222A of the inner tube 222 is closed and the lower end 222B of the inner tube 222 is open in the outer tube 221. The open lower end 222B of the inner tube 222 is at a non-zero distance d from the lower end 221B of the outer tube 221. Preferably, the enclosure 224, the inner tube 222 and the outer tube 221 have an elongated shape in the longitudinal direction Z.

[0078]

[0061] The second heat exchanger 212 is positioned inside the inner tube 222, preferably in a lower portion 222D of the inner tube 222. The inner tube 222 has an upper portion 222C connected to the lower portion 222D above the second heat exchanger 212. The inner tube 222 has a length L2. The upper portion 222C has a length L3 and the lower portion 222D has a length L4. The lengths are taken in the longitudinal direction Z.

[0079]

[0062] An annular space 228 is included between the outer tube 221 and the inner tube 222.

[0080]

[0063] One or more fluid passage(s) 229A is / are formed between the cover 223 and the inside of the outer tube 221, more specifically the annular space 228. This may be openings formed in an upper wall of the outer tube 221 around the inner tube 222 inside the cover 223, or an absence of an upper wall of the outer tube 221 around the inner tube 222 inside the cover 223.

[0081]

[0064] One or more opening(s) 229B is / are formed in the inner tube 222, more precisely between the inner tube 222 and the cover 223, so as to form at least one fluid passage between the inner tube 222 and the cover 223. It may be a continuous opening or several discontinuous openings along a circumference of the inner tube 222.

[0082]

[0065] As shown in Figures 2A and 2B, the inner tube 222 comprises a portion 222E (outer portion), included within the upper portion 222C, which extends longitudinally outside the outer tube 221, for example into an upper portion 224A of the enclosure 224. The inner tube 222 passes through the cover 223, preferably in a sealed manner, at the level of this outer portion 222E. This outer portion 222E has a length L5.

[0083]

[0066] Preferably, the enclosure 224, formed by this assembly of outer tube 221, inner tube 222, and cover 223, is sealed.

[0067] The cooling module 201 includes a third heat exchanger 226, for example in the form of horizontal tubes that may be fitted with horizontal fins, around the outer portion 222E of the inner tube 222. Other types of air-based heat exchangers may be considered by those skilled in the art. The medium 26 (first medium) located around the upper portion 224A of the enclosure 224 is air in this example. The air 26 forms a first cold source for cooling the second fluid 225 circulating in the upper portion 224A of the enclosure 224 through the third heat exchanger 226.

[0084]

[0068] The third exchanger 226 can in particular condense the second fluid 225 when it is in vapor form, as explained later.

[0085]

[0069] Once condensed by the third exchanger 226, the second fluid 225 can exit the inner tube 222 and pass into the annular space 228 via the fluid passages 229A and 229B.

[0086]

[0070] The enclosure 224 can be partially buried in soil 27 (second medium). For example, a lower portion 224B of the enclosure 224, preferably located under the second exchanger 212, can be buried in soil 27.

[0087]

[0071] The lower end 221B of the outer tube 221 can be extended, or connected to, a fourth heat exchanger 227 of the cooling module 201 positioned in the ground 27. The fourth exchanger 227 is, for example, in the form of vertical tubes or vertical fins through which the second fluid 225 can circulate. Other types of buried exchangers may be considered by those skilled in the art. The ground 27 can thus form a second cold source to cool the second fluid 225 circulating in the lower portion 224B of the enclosure 224 through the fourth exchanger 227.

[0072] The fourth exchanger 227 allows, by cooling the second fluid 225 in the lower portion 224B of the enclosure 224, to draw the second fluid 225 from top to bottom in the annular space 228, the second fluid 225 then being drawn from the bottom of the annular space 228 into the internal tube 222 by thermosiphon effect.

[0088]

[0073] The assembly formed by the third exchanger 226, which cools the second fluid 225 in the upper portion 224A of the enclosure 224 and draws it into the annular space 228, and the fourth exchanger 227 which cools the second fluid 225 in the lower portion 224B of the enclosure 224 and draws it downwards into the annular space 228, then into the inner tube 222, thus ensures a thermal pumping phenomenon.

[0089]

[0074] The third and fourth interchanges 226 and 227 can be part of the second circuit 220.

[0090]

[0075] The first fluid 215 in the second exchanger 212 forms, for example, a so-called warm source, that is to say, an intermediate source between the hot source and the cold source(s) of the cooling module 201, or of the thermal evacuation system 200.

[0091]

[0076] The swimming pool building 20 can also be partially buried in the ground 27.

[0092]

[0077] In the example shown, the enclosure 224 has a substantially straight, circular cylindrical geometry with a diameter Dl, which corresponds to the diameter of the outer casing 221. The inner tube 222 has a diameter D2 smaller than the diameter Dl of the outer tube 221. The diameter D2 is, for example, on the order of one meter. Furthermore, the outer tube 221 and the inner tube 222 may be substantially concentric. This example is not limiting; the enclosure 224 could have another geometry, for example, a parallelepiped with a square, rectangular, or other cross-section, a non-circular cylindrical shape, or any other geometry conceivable by a person skilled in the art, and, for example, the inner and outer tubes might not necessarily have the same geometry. Moreover, the inner and outer tubes might not be concentric.

[0093]

[0078] The first circuit 210, and respectively the second circuit 220, may include a safety device 216 (not shown for the second circuit) to prevent overpressure in this fluid circuit, for example a valve. For example, the safety device 216 of the first circuit 210 is configured to discharge the primary fluid 215 outside the building 20.

[0094]

[0079] Figure 2B represents only the cooling module 201, or module 201, which includes the primary circuit 210 and the secondary circuit 220, including the heat exchangers 211, 212, 226, 227. In Figure 2B, the first 215 and second 225 fluids which circulate in the module 201 when it is in operation in the thermal exhaust system 200 have not been shown.

[0095]

[0080] In the example shown in Figure 2A, the heat removal system 200 comprises a single cooling module 201. Alternatively, the heat removal system 200 may comprise several cooling modules similar to module 201 for the same storage pool 21, for example distributed around the storage pool 21. In a heat removal system 200 with several modules 201, the first heat exchanger 211 in the storage pool 21 may be common to several modules 201, or a first heat exchanger 211 may be dedicated to each module 201. Similarly, a person skilled in the art may construct a fluid network, between each first heat exchanger 211 and each second heat exchanger 212, which includes common fluid lines or portions of common fluid lines.

[0096]

[0081] During operation, when the first fluid 215 has transferred all or part of its heat to the second fluid 225 via the second heat exchanger 212, the second fluid 225, which is initially in liquid phase L, is at least partially vaporized, forming a mixed phase L+V. Since the vapor phase V is less dense than the liquid phase L, it causes the second fluid 225 to rise in its liquid phase by a phase transition effect. During operation, the enclosure 224 therefore behaves like a heat pipe, as explained later. The second fluid 225 rises from the second heat exchanger 212 in the upper portion 222C of the inner tube 222, to the outer portion 222E where it releases all or part of its heat to the air 26 via the third heat exchanger 226.The second fluid 225 thus cooled is condensed to return to liquid phase L and is drawn into the annular space 228 between the outer tube 221 and the inner tube 222, due to the presence of the mixed phase L+V inside the inner tube 222 which blocks any passage.

[0097]

[0082] The second fluid 225 is carried, for example by the fourth exchanger 227, down the annular space 228, and then is drawn into the inner tube 222. A new vaporization / condensation cycle of the second fluid 225 can then begin.

[0098]

[0083] In its operation, the enclosure 224 forms a heat pipe 230, that is to say a heat transfer device in which a heat transfer fluid takes heat from a hot source by changing from a liquid to a gaseous state (vaporization), then transfers it to a cold source by returning to a liquid state (condensation).

[0099]

[0084] The thermal evacuation system 200 thus makes it possible to evacuate all or part of the calories from the water 25 of the pool 21, and thus to cool the combustible elements 204 which are in the pool 21, in a passive manner, without it being necessary to add an external gas source and / or an external electrical source, in particular without an external means of fluid circulation, such as a pump.

[0100]

[0085] Thus, even in the event of a complete loss of cooling for the pool 21, for example in the event of a loss of the external power supply, the thermal dissipation system 200 allows the water 25 in the pool 21 to continue to be cooled, in particular to prevent the water temperature 25 from rising above a critical limit, for example between 50 and 90°C. This allows the fuel elements 24 stored in the storage pool 21 to continue to be cooled, in particular preventing the fuel elements 24 from becoming uncovered and from degrading, which could otherwise lead to radioactive contamination and the production of hydrogen by radiolysis of the water.

[0101]

[0086] Preferably, the enclosure 224 has a vertical tubular shape, of length L1. The length L1 considered corresponds to the sum of the length of the external tube 221 (without the heat exchanger tubes 227) and the cover 223, taken in the longitudinal direction Z.

[0102]

[0087] Preferably, the inner tube 222 has a vertical tubular shape, so as to promote the upward circulation of the second fluid 225, and thus the heat pipe effect.

[0103]

[0088] Preferably, the first exchanger 211 is positioned in the upper part of the pool 21, for example to receive water 25 that is warmer than in the lower part, and to improve heat transfer to the first fluid 215.

[0104]

[0089] The first exchanger 211 may advantageously have a large exchange surface, so as to optimize the heat exchange between the water 25 of the pool 21 and the first fluid 215, and thus maximize the temperature of the first fluid 215.

[0105]

[0090] Preferably, the average level z4 of the second heat exchanger 212 in the inner tube 222 is defined relative to the average level z5 of the first heat exchanger 211 so as to promote natural convection of the first fluid 215 in the first circuit 210, while optimizing the operation of the heat pipe 230. Preferably, a minimum level difference Az between z4 and z5 is defined to promote natural convection while minimizing the average level z4 of the second heat exchanger 212 in order to optimize the operation of the heat pipe 230.

[0106]

[0091] The second exchanger 212 can advantageously be a compact exchanger so as to optimize its exchange surface, in a limited section which is that of the inner tube 222, and over a height which is also limited in the lower portion 222D of the inner tube 222.

[0107]

[0092] The third exchanger 216, respectively the fourth exchanger 217, can advantageously have a large exchange surface, so as to optimize the heat exchange between the second fluid 225 and the air 26, respectively between the second fluid 225 and the ground 27, and thus optimize the cooling of the second fluid 225, and the thermal pumping effect.

[0108]

[0093] A person skilled in the art will be able to size the various exchangers and determine the dimensions and levels of the different elements of the heat pipe 230 to obtain the desired convection effects.

[0109]

[0094] Preferably, the enclosure 224 extends to a depth z6 in the soil 27 greater than or equal to 2 meters, for example to have a substantially stable cooling temperature in the soil 27, and to optimize the heat exchange surface with the soil 27.

[0110]

[0095] Preferably, the first fluid 215 is a fluid that does not vaporize during the operation of the heat dissipation system 200, typically not vaporizing below a temperature of approximately 60°C. Preferably, the first fluid 215 is an organic fluid. The first fluid 215 may be, for example, a refrigerant, for example, a hydrofluoroolefin (HFO)-based refrigerant.

[0111]

[0096] Preferably, the second fluid 225 is a fluid with a low latent heat of vaporization, to promote the operation of the heat pipe. Preferably, the second fluid 225 has a vaporization temperature below 70°C, for example, in the range of 30 to 40°C. Preferably, the second fluid 225 is an organic fluid. The second fluid 225 may, for example, be a refrigerant, for example, a hydrofluoroolefin (HFO)-based refrigerant.

[0112]

[0097] Table 1 below shows different temperature assumptions (in degrees Celsius (°C)) according to different operating configurations (CONFIG) and according to the season: T1 is the water temperature 25 in the pool 21 (hot source), T2 is the air temperature 26 (first cold source), T3 is the ground temperature 27 (second cold source), and T4 is the temperature of the primary fluid 215 in the second exchanger 212 (warm source).

[0113]

[0098] [Table 1]

[0114]

[0115]

[0116]

[0099] Table 1 shows that the water temperature Tl 25 varies according to the operating conditions of the pool 21 (nominal: Tl at 35°C, limit: Tl at 50°C, degraded: Tl at 90°C), resulting in a variation of the temperature T4 of the primary fluid 215, that the air temperature T2 26 obviously varies according to the seasons, while the ground temperature T3 27 remains substantially stable at about 15°C.

[0117]

[0100] The temperature difference T1-T4 between the hot source and the warm source is between 5 and 10°C. The temperature difference T4-T2 between the warm source and the first cold source is between -5 and 80°C. The temperature difference T4-T3 between the warm source and the second cold source is between 15 and 65°C.

[0118]

[0101] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will be apparent to those skilled in the art. In particular, several heat evacuation systems, each comprising one or more modules, can be implemented, for example, dedicated to one or more storage pools.

[0119]

[0102] Finally, the practical implementation of the embodiments and variants described is within the reach of a person skilled in the art, based on the functional indications given above.

Claims

25 DEMANDS 1. Cooling module (201) adapted to cool a liquid (25) from a storage pool (21) configured to store combustible elements (24) having residual thermal power to be removed, the cooling module comprising a heat pipe (230) adapted to be positioned in at least one medium (26, 27) external to the storage pool and to be coupled to said storage pool via at least one heat exchanger (211, 212) of the cooling module, the liquid (25) forming a hot source of the heat pipe, and the at least one medium (26, 27) forming a cold source of the heat pipe; the heat pipe (230) extending in a longitudinal direction (Z); in which at least one heat exchanger comprises a first heat exchanger (211) and a second heat exchanger (212) connected together and adapted for the circulation of a first fluid (215), and the heat pipe (230) is configured for the circulation of a second fluid (225) in liquid and gaseous form; the first heat exchanger being adapted to be positioned in the liquid (25) of the storage pool (21) to transfer all or part of the heat from the liquid to the first fluid, and the second heat exchanger being positioned in the heat pipe (230) to transfer all or part of the heat from the first fluid to the second fluid, so as to transform a first portion of said second fluid from a liquid phase to a vapor phase.

2. Cooling module (201) according to claim 1, further comprising at least one other heat exchanger (226, 227) in at least one medium (26, 27), the at least one other heat exchanger being coupled to the heat pipe (230) to cool the second fluid (225).

3. Cooling module (201) according to claim 1 or 2, comprising: - a first circuit (210) adapted to the circulation of the first fluid (215), the first circuit including the first heat exchanger (211), the second heat exchanger (212), and a fluidic network (213, 214) linking said first and second heat exchangers; and - a second circuit (220) adapted to the circulation of the second fluid (225), the second circuit including the heat pipe (230); the second circuit (220) being coupled to the first circuit (210) by the second heat exchanger (212).

4. Cooling module (201) according to any one of claims 1 to 3, wherein the heat pipe (230) comprises an enclosure (224) elongated in the longitudinal direction (Z) and including: - an inner tube (222) in which the second heat exchanger (212) is positioned, the inner tube being dimensioned so as to allow a phase change effect drive, by the first vapor phase portion of the second fluid (225), of a second liquid phase portion of the second fluid from the second heat exchanger towards an upper end (222A) of the inner tube; - an external tube (221) around the internal tube and in fluidic communication with the internal tube; and - an annular space (228) between the outer tube and the annular tube.

5. Cooling module (201) according to claim 4, wherein the second heat exchanger (212) is positioned in a lower portion (222D) of the inner tube (222) connected to an upper portion (222C) of said inner tube, said upper portion being dimensioned to allow the first and second portions of the second fluid (225) to be driven towards the upper end of the inner tube.

6. Cooling module (201) according to claim 4 or 5, wherein the inner tube (222) comprises an outer portion (222E) which extends longitudinally outside the outer tube (221), the cooling module comprising a third heat exchanger (226) positioned in a first medium (26) among at least one medium, for example air, and coupled to the outer portion (222E) of the inner tube (222) to cool the second fluid (225), for example condensing the first portion in vapor phase of the second fluid.

7. Cooling module (201) according to any one of claims 4 to 6, wherein: - the upper end (221A) of the external tube (221) is closed by a cover (223), for example a bell-shaped cover; - the lower end (221B) of the external tube (221) is closed; - the upper end (222A) of the inner tube (222) is closed; and - the lower end (222B) of the inner tube is open in the outer tube (221), at a non-zero distance (d) from the lower end of the outer tube.

8. Cooling module (201) according to claim 7, comprising at least one first fluid passage (229A) between the cover (223) and the annular space (228) and at least 28 a second fluid passage (229B) between the inner tube (222) and the cover (223).

9. Cooling module (201) according to any one of claims 4 to 8, further comprising a fourth heat exchanger (227) positioned in a second external medium (27) among at least one medium, for example a soil, and coupled to a lower portion of the external tube (221) to cool the second fluid (225).

10. Cooling module (201) according to any one of claims 4 to 9, wherein the inner tube (222) has a tubular shape in the longitudinal direction (Z).

11. Cooling module (201) according to any one of claims 1 to 10, wherein: the first fluid (215) is water or an organic fluid, for example a refrigerant, for example a hydrofluoroolefin-based refrigerant; and / or - the second fluid (225) is an organic fluid, for example a refrigerant, for example a hydrofluoroolefin-based refrigerant.

12. Cooling module (201) according to any one of claims 1 to 11, wherein the distance (Az) in the longitudinal direction (Z) between the second heat exchanger (212) and the first heat exchanger (211) is defined to promote natural convection of the first fluid (215) between the first heat exchanger (211) and the second heat exchanger (212), while minimizing the average level (z4) of the second heat exchanger (212) in the heat pipe (230).

13. Thermal evacuation system (200) comprising: - at least one cooling module (201) according to one29 any of claims 1 to 12; - a storage pool (21) at least partially filled with a liquid (25) adapted to store combustible elements (24) in the liquid; said combustible elements having residual thermal power to be evacuated; a first heat exchanger (211) among the at least one heat exchanger of the at least one cooling module being positioned in the storage pool.

14. Heat dissipation system (200) according to claim 13, wherein at least one cooling module (201) comprises several cooling modules.

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