Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F5/00—Transportable or portable shielded containers
  • G21F5/06—Details of, or accessories to, the containers
  • G21F5/10—Heat-removal systems, e.g. using circulating fluid or cooling fins
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
  • F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
  • F28D15/0233—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes the conduits having a particular shape, e.g. non-circular cross-section, annular

Definitions

• the invention relates to a storage installation, that is to say storage under surveillance and reversible, of very long duration (greater than 50 years), of heat products emitting a high thermal flux.
• Such a storage installation can in particular be used for the very long-term storage of nuclear waste such as irradiated nuclear fuels. Indeed, the storage of such products requires control of the temperature of the containers in which they are found.
• the high heat flux which is generated by the heat products must be evacuated by a cooling system which stabilizes the surface temperature of the containers. This ensures the durability of the structure of the containers and the heat products they contain. This also ensures the durability of the concrete of the walls surrounding.
• the cooling systems are preferably passive.
• this document proposes to tightly enclose each container, over its entire external cylindrical surface, by a flexible and removable jacket made, for example by a thin sheet stapled and tightened, which surrounds the container so that the surfaces smooth outer sides of the container and liner are normally in contact.
• a flexible and removable jacket made, for example by a thin sheet stapled and tightened, which surrounds the container so that the surfaces smooth outer sides of the container and liner are normally in contact.
• the application of the shirt to the outer surface of the container is ensured by tightening at several points when the shirt is closed (or stapled).
• the jacket is fitted externally, at regular intervals (for example about 20 cm), with vertical tubes of circular or square section. These tubes are intimately linked to the jacket, from the point of view of thermal conduction, so as to form an evaporator for the cooling fluid.
• this fluid operates in two-phase liquid-vapor regime and constitutes a heat pipe with the circuit in which it is confined.
• the heat pipe condenser is located outside the site, where a heat exchange takes place with the free air which circulates by natural convection.
• the tubes are integral with jacket sections, themselves assembled end to end by welding or by any other mechanical connection means.
• the thermal efficiency of the system only depends on the quality of the contact between the container and the juxtaposed jacket sections.
• the quality of the thermal transmission increases when the contact resistance decreases, that is to say when the contact between the surfaces is closer.
• good transmission of the heat flux between the container and the flexible jacket which surrounds it assumes that the thickness of the film of residual air between the two walls is limited to a fraction of a millimeter.
• a cooling supplement is normally provided by the surrounding air, in perpetual natural convection on the outside surface of the heat pipe jacket.
• means for setting the air in forced convection can be provided.
• the heat exchange increases with the outer surface of the jacket, when the latter is made of a heat-conducting material and when the contact resistance between the container and the jacket is low.
• the object of the invention is precisely a very long-term storage installation for heat products, comparable to the installation proposed in document FR-A-2 791 805 but the original design of which allows obtaining at least comparable performance in a significantly simpler and less costly manner, using traditional industrial means.
• a very long-term storage installation for heat products comprising at least one container for confining said products, an evaporator comprising a jacket surrounding the container and a plurality of tubes integral with the jacket and filled with a heat transfer fluid, and means for clamping the evaporator on the container, characterized in that the evaporator has an interior surface such that the clamping means keep the evaporator in close contact with a surface outside of the container only opposite each of the tubes.
• the interior surface of the evaporator has, between the tubes, a radius of curvature substantially greater than that of the exterior surface of the container.
• the contact zone between the container and each of the tubes has a well-defined surface and is not limited to a line, in particular in the case of tubes of circular section
• the interior surface of the evaporator comprises, in face of each of the tubes, a part of complementary shape to the outer surface of the container, maintained in close surface contact with said outer surface by the clamping means.
• the tubes are fixed, preferably by welding, inside a continuous structure, of substantially circular section, forming the jacket.
• the tubes may include cooling fins, located between the jacket and the container.
• each tube is produced in one piece with two sections of jacket and the sections of the neighboring tubes are joined together edge to edge to form the jacket.
• the sections of neighboring tubes can then be assembled either by welding, or by any mechanical connection means.
• the tubes can have either a substantially square or rectangular section, or a substantially circular section.
• the tubes advantageously have heels, one inner face of which is held in close surface support against the outer surface of the container by the clamping means.
• an outer surface of the evaporator may have cooling fins.
• the evaporator is moved away from the container so as to delimit vertical air circulation channels, by natural convection.
• the channels then form part of a closed circuit which constitutes an additional confinement barrier.
• FIG. 1 is a view in vertical section which very schematically represents part of an installation for storing heat products according to the invention
• FIG 2 is a sectional view, along a horizontal plane, schematically illustrating part of an evaporator according to the invention, in almost linear contact with a container stored in
• FIG. 3 is a view comparable to FIG. 2, schematically illustrating the case of an evaporator in surface contact with a container containing heat products;
• FIG 4 is a sectional view comparable to Figures 2 and 3, showing in more detail an evaporator according to a first embodiment of the invention, and the associated clamping means;
• FIG. 5 is a sectional view comparable to FIG. 4, showing side by side three possible section variants for the tubes of the evaporator as well as the optional presence of cooling fins on the jacket;
• FIG. 6 is a sectional view comparable to FIGS. 4 and 5, illustrating another variant of the first embodiment of the invention;
• FIG. 7 is a sectional view comparable to FIGS. 4 to 6, illustrating side by side three variants of a second embodiment of the invention.
• FIG. 9 represents the distribution of the heat flux (in / m 2 ) as a function of the distance (in mm) to the axis of a tube, in the direction of the circumference of the container, respectively in the case of a constant clearance of 0.01 mm (curve D), in the case of a constant clearance of 0.3 mm (curve E) and in the case of a contact in front of the tubes and an average clearance of 0, 3 mm (curve F); and FIG. 10 represents the change in the maximum temperature of the container (in ° C.) as a function of the clamping force applied to the evaporator (in Newton).
• FIG 1 there is shown schematically a part of an installation according to the invention, intended for the very long-term storage of heat products such as nuclear waste consisting, for example, of irradiated nuclear fuels.
• the installation comprises a closed cavity 10, delimited laterally and downwards by concrete walls 12.
• the cavity 10 is dimensioned so as to be able to accommodate one or more containers 14 in which the nuclear waste that is to be stored is conditioned.
• the containers 14 have the shape of cylindrical barrels and they are placed in the cavity 10 with their axes oriented substantially vertically.
• a space 16 is provided between each container 14 and the walls 12 of the cavity 10 to allow the circulation of the surrounding air, by natural convection.
• the container 14 rests on the bottom of the cavity 10 by means of a pedestal 17.
• the cavity 10 is closed upwards by a concrete slab 18, comprising a removable plug 20 above each of the containers 14.
• a heat pipe is associated with each container. More specifically, this heat pipe comprises an evaporator 22 which surrounds the container 14, an air condenser 24 placed above the slab 18 and two pipes 26 connecting the evaporator 22 to the air condenser 24 through the plug 20.
• the air condenser 24 may be common to several containers 14.
• a heat transfer fluid such as water to
• phase changes of this fluid (evaporation / condensation) in the heat pipe ensure the transfer of the heat emitted by the nuclear waste from the hot source constituted by the container 14 to the cold source constituted by the air condenser 24.
• the evaporator 22 comprises a jacket 28, which substantially entirely surrounds the outer peripheral surface 30 of the container 14, and a plurality of tubes 32 integral with the jacket 28.
• the tubes 32 are parallel to each other and to the substantially vertical axis of the container and they are regularly distributed substantially at equal distance from each other, over the entire periphery of the container.
• the tubes 32 are connected to an annular liquid water distributor 34 at their lower ends and in an annular manifold of vaporized water 36 at their upper ends.
• the distributor 34 and the manifold 36 are separately connected to the air condenser 24 by one of the pipes 26 and these comprise, below the plug 20, removable connectors 38.
• the tubes 32 and the collectors 34 and 36 are filled with the heat transfer fluid contained in the heat pipe.
• the evaporator 22 is mounted on the container 14, in a removable manner, by clamping means 40, an exemplary embodiment of which will be described later with reference to FIG. 4.
• the internal surface of the evaporator 22 that is to say the surface of the evaporator facing the container 14, is produced in such a way that the clamping means 40 keep the evaporator 22 in close contact with the outer surface 30 of the container 14 only opposite each of the tubes 32.
• the parts of the jacket 28 which are placed between the tubes 32 are spaced from the surface outer 30 of the container 14, so as to form vertical channels 42, of substantially uniform or variable thickness, between the jacket 28 and the container 14.
• These channels 42 constitute a kind of chimney which generates an air circulation, by natural convection, around container 14.
• This circulation air can be mainly laminar or turbulent depending on the specific power dissipated by the container, the height of the container and, to a lesser extent, the diameter of the container.
• the turbulent nature of the flow improves the cooling of the container. It is favored by a specific thermal power equal to or greater than 1 kw / m 2 and by the increase in the height of the container and the radial thickness of the vertical channels 42.
• Tests have been carried out with specific thermal powers ranging from 1 kw / m 2 to more than 3 kw / m 2 and, more particularly, around 2.5 kw / m 2 .
• the heights were between 2 m and 5 m, the greater height improving the efficiency of heat transfer.
• the radial thickness must be greater than 1 cm; this is why the tests were preferably carried out with radial thicknesses between 4 cm and 12 cm.
• the development of a chimney effect in natural convection is governed by three parameters which are:
• the height of the chimney is 5 to 6 meters when the container is filled with irradiated fuels, which generates a very efficient draft.
• a height of 1 meter corresponding to a container filled with hot objects of shorter length allows proportionally equal efficiency; -the presence of the cylindrical container generating the heat flow; the container is an excellent heat flux generator; this flow can be considered homogeneous on the cylindrical wall; and
• the movement of air is caused by the variation in density of the fluid subjected to a force field.
• the grouping which governs natural convection is the Grashof Gr number, but the commonly accepted correlations involve the Rayleigh number.
• ⁇ R 1 cm.
• the effect then increases with ⁇ R to reach an optimal value around 5 to 6 cm (the definition of this optimal value is based here on maximum use of a high efficiency heat pipe evaporator, coupled with an efficient cooling system by natural convection) .
• This optimal value corresponds to an extraction value by natural convection of approximately 40% of the total power extracted (conduction + radiation + natural convection in channels 42 + external natural convection).
• ⁇ R 4 cm
• the percentage of power extracted by the chimney-type effect is approximately 25 to 30% of the total. This value has been validated experimentally on a model 2 m in diameter, 1.5 m in height and a heat flux of 2.5 kW / m 2 .
• the value ⁇ R 4 cm corresponds to the external dimensions of a 40 mm X 40 mm square tube whose internal section is necessary for stable operation in two-phase siphon mode (passive mode).
• the performance gain of the system which is the subject of the invention is, at the optimum, around 20%. This results, at equal generated power in the container, by a significant lowering of the skin temperature of the container by approximately 10 to 20 ° C (depending on the nature of the different materials) and for heat fluxes of 2 to 3 kW / m 2 . This contribution is therefore very important.
• the contact between the evaporator 22 and the container 14 can be limited to almost linear zones corresponding to the generatrices of the container 14 located at the right of each of the tubes 32.
• the interior surface of the evaporator 22 may also include, at the level of each of the tubes 32, a portion 44, of limited width, the shape of which is complementary to that of the exterior surface 30 of container 14, as illustrated in FIG. 3.
• tightening means 40 (FIG. 4) then has the effect of maintaining these parts 44 in close surface contact with the external surface 30 of the container 14.
• the almost point contact of Figure 2 as the surface contact of Figure 3 can be obtained by giving the inner surface of the evaporator 22, between the tubes 32, a radius of curvature greater than that of the outer surface 30 of the container 14.
• the parts of the evaporator 22 located between the tubes 32 may have a radius of approximately 1200 mm.
• the maximum clearance between the evaporator and the container is then, for example, 0.85 mm.
• an average clearance of about 0.45 mm is obtained inside the channels 42.
• the jacket 28 is embodied by a continuous structure, of substantially circular section and of small thickness, which remotely surrounds the container 14.
• This structure is made, for example , by a sheet.
• the tubes 32 are then fixed inside the jacket 28 by any suitable means.
• this fixing is ensured by welding points.
• FIG. 4 also shows a possible embodiment of the clamping means 40.
• the evaporator 22 is open according to a generator and has two facing edges 22a, oriented parallel to the axis of container 14.
• the clamping means 40 are interposed between the two edges 22a. More specifically, the clamping means 40 comprise a plurality of bolts 46, which pass through holes formed in parts 48, attached along the edges 22a of the evaporator, on its surface facing outwards.
• a helical compression spring 50 is mounted on each of the bolts 46, so as to keep the clamping force substantially constant in the event of possible differential expansions between the container 14 and the evaporator 22.
• FIG. 5 different variants of the first embodiment described with reference to FIG. 4 have been shown simultaneously. In practice, it will be understood that these variants are alternative solutions, generally implemented separately from each other, unless indicated. otherwise.
• the different variants illustrated in FIG. 5 relate first of all to the shape of the tubes 32.
• these tubes can have either a circular, square or rectangular section, that is to say flattened in the direction of their thickness.
• the thermal evacuation is all the more effective as the contact surface between the container and the parts of the evaporator located in front of the tubes is large, that is to say going from the tubes of circular section to the tubes of rectangular section.
• the extent of this contact surface must remain sufficiently small so that close contact can be obtained without difficulty.
• the tubes 32 can be arranged every 200 mm and have a section of 40X40 mm or 60X60 mm, in the case of square tubes.
• the heat exchange between the tubes 32 and the air which circulates in the annular spaces 42 can be improved by equipping the tubes with cooling fins 32a, located between the jacket 28 and the container 14. These fins 32a can be attached to tubes 32 of any section or produced in one piece with said tubes, in the form of extruded profiles.
• the heat exchange can be improved by equipping each of the tubes 32 with heels 52, on the side of the container 14. The inner face of the heels 52 is then maintained in close surface support against the outer surface 30 of the container 14.
• the jacket 28 and the tubes 32 are made in one piece. More precisely, each of the tubes 32 is made in one piece with two sections 28a of the jacket 28. Each of the sections 28a has, in section along a horizontal plane, the shape of an arc of a circle whose length is equal to half the length of the jacket 28 between two consecutive tubes 32. The sections 28a of the neighboring tubes 32 are assembled together edge to edge, according to generatrices of the container 14, to form the jacket 28.
• the edge-to-edge assembly of the sections 28a can be ensured either by welds 54 or by mechanical connection means 56, such as jointing means or the like, as illustrated in FIG. 7.
• the tubes 32 may include heels 52, as described above with reference to FIG. 6, in the context of the first embodiment of the invention.
• the heels 52 then have an inner face whose shape is complementary to that of the outer cylindrical surface of the container 14.
• the clamping means associated with the evaporator maintain the inner face of each of the heels 52 in narrow surface support , that is to say without play, against the outer surface of the container 14.
• each of the integral parts comprising a tube 32 and two jacket sections 28a can also comprise one or more cooling fins 58, on its surface facing outwards , that is to say opposite the container 14.
• such cooling fins 58 ( Figure 5) may also be provided.
• the fins 58 are attached by welding to the outer surface of the sheet forming the jacket 28.
• clamping means can be similar to those used in the first embodiment, as described above with reference to FIG. 4.
• a finite element modeling made by the applicant has shown, surprisingly, that an evaporator 22 having limited surface contact with the container 14 (corresponding to a clearance of 0.01 mm), in line with the tubes 32 of the heat pipe, in accordance with the invention, makes it possible to obtain thermal properties substantially identical to those which are obtained using an evaporator in accordance with the prior art described in the document FR-A-2 791 805, in which a uniform clearance of 0.1 mm is obtained over the entire interface between the evaporator and the container.
• This result is particularly advantageous from an industrial point of view since it is much easier to ensure local contact limited to the right of the tubes 32 than to obtain a uniform clearance of 0.1 mm over the entire surface of the evaporator 22.
• the curve A corresponds to the case of an evaporator of the prior art, in which a constant clearance is provided between the evaporator and the container
• the curve B corresponds to the case of '' an evaporator which would be locally in contact with the container only between the tubes
• the curve C corresponds to the case of an evaporator 22 conforming to the invention, that is to say locally in contact with the container 14 only in front of the tubes 32.
• an average clearance of 0.5 mm with a contact between the evaporator 22 and the container 14 opposite the tubes 32 means that the clearance is zero at the level of the tubes 32 (c ' is to say equal to 0.01 mm in the modeling) and that it evolves linearly up to 1 mm in the middle of the circular arc formed in section by the evaporator between two neighboring tubes 32.
• Such an arrangement is perfectly achievable with traditional industrial means. Indeed, it allows, for equal thermal efficiency, to multiply by five the average clearance on the condition that the contact zones are located opposite the tubes 32.
• the contact zones can be almost linear or, preferably, have the form of narrow surfaces extending over the entire height of the container.
• An evaporator 22 according to the invention produced by combining the principle of the almost linear contact in FIG. 2 with the second embodiment described with reference to FIG. 7 (jacket sections 28a and tubes 32 in one piece), was first tested, with the numeric values shown previously with reference to FIG. 2 (container with a radius of 1000 mm, evaporator with a radius of curvature equal to 1200 mm, maximum clearance of 0.85 mm, almost linear contact under the tubes).
• this evaporator is thermally equivalent to an evaporator of the prior art, having an average clearance of 0.01 mm with the container, very difficult to obtain in practice.
• an evaporator 22 was produced combining the characteristics of FIG. 3 (surface contact) and the second embodiment of the invention.
• the contact surface in line with the tubes 32 must not be too wide, otherwise it will fall back on the implementation difficulties characteristic of the prior art.
• contact zones 40 to 60 mm wide constitute a good compromise between obtaining a greatly increased thermal efficiency and -an easy implementation.
• the first embodiment described above with reference to FIGS. 4 to 6 constituted a third stage of experimentation. Indeed, this embodiment allows, for a reduced cost, to maintain an acceptable thermal efficiency.
• the liner 28 By placing the liner 28 at a distance from the container 14 equal to the external dimensions of the tube 32, all the manufacturing tolerances are eliminated.
• the jacket 28 forms a continuous circular structure which allows the tubes 32 to be encircled and pressed against the container 14.
• annular space in the form of a crown, is created between the shirt and the container.
• This space corresponds to the channels 42 in FIG. 2. It promotes the development of a kind of chimney effect, which allows the ambient air thus channeled to circulate vertically under the effect of a natural convection whose engine is the thermal power of the container 14.
• a very efficient independent passive cooling is thus created, since it is carried out in direct contact with the container, that is to say without any contact resistance. The effect of this cooling is added to that of the heat pipe in contact with the container.
• the total yield of this embodiment is therefore higher than that of the prior art, at a much lower cost.
• Such turbulence in the vertical channels 42 is so effective that it can reduce the heat flow which the fluid circuit must evacuate. This reduction is advantageous in two cases: on the one hand, if an accidental failure affects the fluidic circuit, the time available to carry out an intervention is greatly extended; on the other hand, in the long term, the date on which we can stop using this fluid circuit given the decrease in heat flow is significantly anticipated.
• An alternative embodiment of the invention consists in extracting in a closed circuit the air circulating in the vertical channels 42, using means known to those skilled in the art. This variant also has the advantage of providing an additional sealed containment barrier, increasing safety in the event of an accident, and of avoiding thermal effects on the air in the warehouse.
• the jacket 28 also serves as a vis-à-vis the concrete structures of the site and that its temperature is lower than that of the jacket used in the prior art since it is cooled on its two faces and is not in thermal continuity with the tubes 32.
• the thermal conductivity of the materials present only participates very much little to thermal efficiency. The designer therefore has a much wider choice of materials than in the prior art.

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• 2002
  • 2002-01-23 FR FR0200805A patent/FR2835090B1/fr not_active Expired - Fee Related
• 2003
  • 2003-01-21 EP EP03715032A patent/EP1468425B1/de not_active Expired - Lifetime
  • 2003-01-21 US US10/500,460 patent/US7185512B2/en not_active Expired - Fee Related
  • 2003-01-21 DE DE60330649T patent/DE60330649D1/de not_active Expired - Lifetime
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  • 2003-01-21 WO PCT/FR2003/000184 patent/WO2003063180A2/fr active Application Filing
  • 2003-01-21 CA CA002473199A patent/CA2473199A1/fr not_active Abandoned
  • 2003-01-21 KR KR1020047011271A patent/KR100959297B1/ko not_active IP Right Cessation
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