EP2831888A1 - Method and mobile device for reducing the thermal resistance between two solids - Google Patents

Abstract

The invention relates to a substantially prismatic transmitter element (30, 32, 34, 36) for a nuclear fuel storage rack, comprising three main surfaces (303, 303', 305, 325, 345, 365), including a base and two secondary planar surfaces, and two side surfaces (301, 301') made of a heat-transmitting material, and which are provided, on the sides thereof, with a means for pulling the element in a direction parallel to the base.

Description

 METHOD AND MOBILE DEVICE FOR REDUCING RESISTANCE

 THERMAL BETWEEN TWO SOLIDS

DESCRIPTION TECHNICAL FIELD AND PRIOR ART

The invention relates to a storage basket for nuclear fuel assemblies consisting of a plurality of contiguous cells of great length in each of which can be introduced a fuel assembly or possibly the rods of several fuel assemblies.

 These storage baskets (also known as lockers or

"Racks") are intended for the storage and / or transport of said fuel assemblies, possibly in shielded or non-shielded packaging. They are suitable for used fuel, but can also be used for new fuel. They can be used in dry or wet conditions, for example when storing fuels in swimming pools or when they are introduced in transport or storage containers.

 Stacking various materials is the solution provided to the needs of the various functions of a fuel assembly transport ship (radiation protection, impact resistance, fire ...). In the case of high power to be discharged, a limit to the internal temperature results from the presence of games required for stacking.

 The issues related to the safety and transport of radioactive materials are set out in the documents "Safety of Transport of Radioactive Materials", by B. Lenail, Revue Générale Nucléaire n ° 1 2005; "Design, Manufacture and Testing of Packaging for the Transport of Radioactive Materials", by B.C. Bernardo, IAEA Bulletin Vol. 21, No. 6 or in EP 0 752 151.

In general, fuel assemblies are transported dry in castles containing up to 12 (or more) assemblies. These transport packagings have been approved by the competent French, British and Japanese authorities and meet the criteria imposed by the AI EA regulation for type packagings. B. This type of castle, used for nearly 40 years, is based on the intrinsic performance principle of the package (double barrier, fire resistance ...) that prevents any release of radioactivity.

 As illustrated in Figure 1, from the outside to the inside, a castle has, on its great length:

 an external zone 2, which may be provided with cooling fins 4,

 a layer 6 absorbing neutrons,

 a ferrule 8 made of steel,

 - And a storage basket 10 for nuclear fuel assemblies, comprising one or more contiguous cells 12, of great length, into which can be introduced a fuel assembly or possibly the rods of several fuel assemblies.

 Various types of cellular honeycomb baskets for nuclear fuel assemblies are known. They generally perform three functions:

 the control of criticality, in the dry state or in the presence of water, in the liquid or gaseous state (this water may contain neutron-containing compounds, based on boron for example), of all the assemblies which are stored therein ,

 - a sufficient mechanical resistance that serves two purposes: (i) maintain the geometry of the basket loaded with assemblies and avoid the deterioration of the fuel rods during normal use (handling, transport ...), (ii) ensure control of criticality by maintaining the geometry of the basket even in accident conditions (significant shock and drop) according to the regulations in force,

 - Thermal transfer, to evacuate the heat released in the case of irradiated assemblies.

The baskets are sometimes also designed to provide additional shielding against radiation. The basket generally consists of an association of several materials, each of them fulfilling at least one of the three functions mentioned above. The main materials used are, in general:

 - stainless steel or aluminum (or its alloys) for the mechanical strength function,

 - aluminum or copper (or their alloys) for the heat transfer function,

 - Boron compounds (such as B4C-based sintered alloys), copper, aluminum or stainless steel alloys containing boron for the criticality control function.

 From the point of view of the thermal performance of a castle, the evacuation of the internal power and the fire resistance of 800 ° C for 30 minutes is currently solved by playing on the materials (steel ferrule, aluminum basket. .) and their performance ("compound" crossed by fins, protection of joints ...).

 For a question of realization and especially of assembly, this system with interlocking different radial layers requires, in particular to more easily introduce an assembly or the basket in a castle, to play games at the interfaces between the different layers, in particular between assembly and cavity but also between the basket and the ferrule. These sets, for example about 5 mm and 2 mm, can be disadvantageous with respect to heat transfer requirements.

 In particular, in the case of high power to be evacuated, the presence of these games generates high thermal resistances, and therefore high thermal gradients, which greatly increases the maximum internal temperature when it is desired to increase the maximum allowable powers (which also depend on materials, burning rate ...).

Currently, the transport is under nitrogen but more conducive gases (helium) can be used, in this case, internal and external clearances, respectively 5 mm and 2 mm, are sufficient to transport PWR fuel (pressurized water reactor) since the powers are weak. But there is the problem of being able to transport higher power fuels (for example of the MOX fuel type or assemblies with actinides in the future).

 The possibility of a good evacuation of calories to the outside, without exceeding prohibitive internal temperatures, is therefore a key problem for the future.

 In this case, it is not so much the total power transported that poses a problem, but rather the thermal gradient that is created by the presence of the games mentioned above.

 Thus, using the current technology of a TN12 type structure, the maximum power of an assembly transported under helium would be limited to 2.5 kW without exceeding 450 ° C and 4.5 kW without exceeding 650 ° C while the need for power transported could to be much superior.

 The document WO 2011/161233 describes a system that makes it possible to reduce the thermal resistance of contact due to external games. In this system, the 4 parts of a basket come into contact with the steel ferrule. The result is a simple system, with improved radial transfers, but not so-called internal games. The gain, in terms of evacuable power, is therefore low.

 There is also the problem of so-called internal games (between assembly and basket).

 Indeed, if we take the case of the castle to a helium assembly, with conventional games (for example 5 mm internally and 2 mm externally) the power output at 650 ° C is 6.3 kW. If the external clearance is canceled, for example according to the teaching of document WO 2011/61233, it increases to 6.75 kW, ie an increase in the evacuable power of only 8%. If we cancel the 2 games then the power goes to 8.75 (an increase of + 40%). But in this technique, the contacted surfaces are important (about 1/4 of the external surface of the basket), so that, unless there are prohibitive manufacturing tolerances, the contact can be made only on a generator or just a few areas.

Therefore, the internal games at a storage or transport castle, whose game thicknesses create a significant contact resistance, as well as that the thermal criteria not to be exceeded greatly affect the evacuable power during a transport of fuel assemblies.

 A problem is therefore to improve internal heat exchange in a transport cask in order to reduce the temperatures reached in nominal mode. STATEMENT OF THE INVENTION

Here is a solution to this limitation.

 First described is a heat transmitting element for a substantially prismatic nuclear fuel storage container, comprising

3 main faces, including a base and 2 secondary flat surfaces, and two side faces, of a heat-transmitting material, laterally provided with means for providing traction of the element in a direction parallel to the base.

 Each transmitting element is made of a material which conducts heat, and therefore of good thermal conductivity, for example of a metallic material such as aluminum or copper.

 The means for ensuring traction of the element can be placed on the lateral faces. For example, each of these lateral faces is provided with at least 2 studs or 2 studs.

 Alternatively the means for providing traction of the element may comprise notches or lateral recesses made in the element, each recess opening into one of the secondary plane faces, and possibly in the corresponding lateral face. A wall of each notch comprises means, for example at least 2 studs or 2 studs.

 Such an element may comprise at least one pull rod, for example having a perforated interior, or not, and cooperating with the means to ensure traction of the element in a direction parallel to the base.

 Such an element may have, in a plane perpendicular to the base, a substantially triangular shape.

The base may be flat, or have at least one curvature about an axis substantially parallel to the direction of traction. A nuclear fuel storage basket element, may therefore include:

 a first stack of transmitter elements of the type described above, each secondary plane surface of an element facing a secondary plane surface of a neighboring transmitter element, so that the bases of the different transmitter elements are alternately turned towards one side of the stack then towards the other, each transmitting element being connected to its neighbors by the means to ensure traction of the element in a direction parallel to the base,

 means for exerting traction on all the transmitting elements.

 In such a storage basket element, each secondary flat surface of an element can:

 - Being in contact with a secondary planar surface of a neighboring transmitter element when no traction is exerted on all the transmitting elements, especially when pressure is exerted on all the elements,

 - And be removed from the secondary planar surface of a neighboring transmitter element, when traction is exerted on all the transmitter elements.

 The stack of transmitter elements may have a height (h) less than the total height of the basket element. In this case, the rest of the basket consists of a transmitting material, stacked above and below the transmitting elements described above. The height h is then substantially equal to or close to the length over which the fuel elements produce heat.

 The basket element may further comprise at least a second stack of transmitter elements as described above, arranged in a zone separated from the first stack by a continuous portion of material. This second stack then plays a mechanical role, but a lower thermal role.

An elementary nuclear fuel storage basket may comprise a plurality of storage basket elements of the type described above, arranged to delimit a substantially square central cavity or rectangular or hexagonal in a plane perpendicular to the direction of traction of each basket, according to the shape of the assembly for which it is intended.

 It is therefore possible to constitute a castle for storing and / or transporting nuclear fuel, comprising an elementary storage basket of the type as described above, the basket being surrounded by a peripheral protection layer for absorption. gamma rays and a peripheral protection layer to slow down the neutrons.

 It can also constitute a castle for storing and / or transporting nuclear fuel, comprising several basic storage baskets, for example in number between 2 and 12, each elementary basket being of the type as described above.

 The elementary baskets are placed in a fixed basket itself surrounded by a plurality of transmitting elements of the preceding type which ensure an effective thermal contact with the peripheral layers

 Also concerned here is a method for storing and / or transporting a nuclear fuel rod, comprising the following steps:

 - Traction on the basket elements of a storage basket as described above, so as to bring them from an initial position to a raised position and to generate a clearance between each transmitter element and each of the hot walls and cold,

 - introduce one or more assemblies in the central cavity,

releasing the tension, to bring the transmitting elements back to the initial position, in which the base of each transmitter element is positioned in contact with one or the other of the hot and cold walls. During this step, the effect of gravitation can be enough to bring the elements back to the initial position, because of their own weight. It may optionally add additional pressure, which keeps the elements in this position even when the basket is in a position other than the vertical position, for example when in a horizontal position during transport. Such a method may be preceded by a step of introducing the storage basket into a pool, and followed by a step of extracting the basket loaded with the rods to bring it out of the pool.

 In the invention, means are used to apply a force on a stack of transmitting elements, which allows the basket to modify its internal and external radii and thus reduce the gaps between assembly and basket and also between basket and the external environment, for example a ferrule.

 Thus the basket adapts its shape and marries any deformation of the assembly.

 The invention therefore makes it possible to maintain significant play during the introduction of the load and then to resorb them before a subsequent operation, for example handling or transport.

 In the case of the transport of assemblies, and in particular of high power, the system makes it possible to reduce, and even to cancel, the thermal contact resistances (directly related to the gas gap in the games and to the thermal conductivity of the gas ). But it has other advantages:

 - The veneer of the basket on the assembly allows a mechanical strength during transport; then we do not need to introduce shims as was the case before,

 - This basket will adapt its shape and marry any longitudinal deformation of the assembly,

 - it reduces the current machining costs of the basket,

 - In some cases (including that of an assembly in a case, we could replace the helium basket with dry air or nitrogen.

Compared to the technique described in WO 2011/161233, where, it is recalled, the contact can be made only on a generator or just a few areas, the invention described here allows, by the multiplicity of its basic surfaces d increase the number of contact points and have larger contact areas. The smaller the transmitter elements, the better the adaptation to the shape. The invention makes it possible to minimize the internal and external clearances in a basket, which makes it possible to carry out the transport storage and transportation of certain assemblies, whose powers (P> 8kW) are greater than those currently generated. It also makes it possible to optimize the number of transport assemblies, since both a single assembly, a plurality of assembly, can be made.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of nonlimiting examples, with reference to the accompanying drawings, in which:

 FIG. 1, already described, is an exploded view of a castle of known structure,

 FIGS. 2A-2D and 3A-3B are various views of transmitter elements as described,

 FIGS. 4A-4C represent two elements linked by a connecting rod and their relative movement,

 FIGS. 5A-5D are various views of transmitter elements,

FIGS. 6A and 6B show a stack of transmitting elements, linked by rods and their relative movement,

 FIGS. 7A and 7B are schematic views, respectively of a basket in the open position and of a basket in the closed position,

 FIGS. 8A and 8B are views of a basket containing an assembly,

 FIGS. 9A-9E are steps for introducing an assembly into a basket,

FIGS. 10A and 10B are top views of two systems, one of which contains several assemblies, each of these systems comprising at least one basket, a steel ferrule and a resin, FIGS. 11, 12 and 13, respectively, show the evolution of the maximum possible temperature as a function of the internal and external clearances and the power of an assembly, for one assembly, 7 and 12 assemblies, respectively.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS Referring first to FIGS. 2A (side view, in section along the plane

AA 'or xOz of Figure 2B) and 2B (seen from above, in section along the plane BB' or xOy of Figure 2A) which show a stack of transmitting elements 30, 32, 34, 36 of the heat of a basket system 20 according to a particular embodiment of the invention.

 In FIG. 2A, it can be seen that the various transmitter elements are stacked along a direction Oz of a trirectangular trihedron Oxyz. FIG. 2B also shows two walls 22, 24, which are respectively the hot and cold walls of the environment in which the stack is positioned (the wall 22, called the hot wall, is on the side a hot assembly, located in the interior of the basket, while the wall 24, called cold, is that of the environment immediately outside the basket). Outside this environment, the references 22 and 24 are two planes which delimit the lateral extension of the stack, according to Ox, when it is in the closed or lowered position, as explained below; in the following we refer to 2 walls, but we can also read 2 plans.

 The axis Ox is perpendicular to the two walls 22,24 while the axes Oz and Oy are parallel to them. The stack extends in a general direction according to Oz.

 Each element of the stack has a substantially prismatic shape, as illustrated in FIG. 2C for an embodiment of an individual element 30. The other elements of FIG. 2A are identical or similar to it and, for this reason, all the parts - similar or identical to those described in Figure 2C - these other elements are not described in detail.

More specifically, the element represented in FIG. 2C is substantially a pentahedron or a triangular prism, with three quadrilateral faces 303, 303 ', 305 adjacent in pairs and two triangular faces 301, 30 non-adjacent to each other and substantially perpendicular to one another. Oy axis. It comprises a base 305, which, in this embodiment, is flat and parallel to a stop 307 which extends along the axis Oy of the trirectangular trihedron Oxyz.

 According to one particular aspect, illustrated in FIG. 2D, the sides and the angles can be truncated: one will then use, nevertheless, the expression "stops" or "top".

 Between the edge 307, or the top, and the base 305 extend 2 surfaces 303, 303 'that can be designated, for convenience, respectively by "upper surface" and "lower surface". In the example shown, these surfaces are planar, but they may have other shapes, for example they may comprise corrugations or corrugations, intended to come into contact, or to assemble, with corrugations or corresponding corrugations a flat surface of a neighboring element.

 Laterally, along the axis Oy, the element is bounded by two walls or lateral faces 301, 30. In this embodiment, the latter two walls are substantially perpendicular to the base 305 and substantially parallel to the plane xOz. In a variant, shown schematically in plan view in FIGS. 3A and 3B, the side walls (here: 341, 34, the element represented being the element 34) are inclined and thus cut at the same time the Ox and Oy axes. In the plane zOx, each of these transmitter elements has a substantially triangular shape, each triangle having a large side and 2 small sides, which are preferably of substantially equal length, the triangle itself being substantially isosceles. More preferably, the three sides are truncated at their end, as illustrated in Figure 2D, or Figures 4A-4C. In the plane zOx, each one then, strictly, no longer a form substantially triangular, but rather hexagonal, with 3 long sides and 3 small sides which alternate with each other.

The height of this triangle, or the distance between the edge 307 or the top and the base 305, is smaller than the distance between the two walls 22, 24. Thus, when the element is positioned as illustrated in FIG. 2A, the maximum distance between the top 307 of the element and its base 305 makes it possible to maintain a clearance 27, 29 between this element and each of the two walls 22, 24. When the device is in the "closed" position (FIGS. 4C, 6B and 7B) there remain areas 270, 270 ', 290, 290' which are not filled with a portion of a transmitting element. These sets are dimensioned to avoid any contact between a transmitting element and the adjacent second-ranking element (for example, in FIG. 2A, all contact is avoided between the elements 30 and 34, between the elements 32 and 36, and so on. .). These areas do not pose a problem from the thermal point of view because the heat passes through the contacts created between the neighboring elements, between 30 and 32, between 32 and 34, between 34 and 36, etc. These zones are arranged, alternately, towards each of the walls 22, 24; even full of gas, and therefore insulating, their thermal influence is negligible because they are shunted by a parallel passage much more thermally conductive.

 In FIG. 2A, we see, in a manner similar to that presented in FIG.

2C, the base 325, 345, 365 of the other elements 32, 34, 36, and their edges, 327, 347, 367.

 The various elements 30, 32, 34, 36 are stacked as shown in FIG. 2A, the lower (respectively upper) planar surface of a first element being in contact with or facing the upper (respectively lower) plane surface of a second element immediately adjacent, but located under (respectively) on this first element, along the axis Oz.

 The long sides of the stacked elements are arranged, alternately, towards the wall 24 and towards the wall 22. In other words, a transmitting element 30 has a base directed towards the wall 24 while the base of the neighboring elements is directed towards the wall 22.

 In the closed or lowered position of the stack, two adjacent elements can be supported against one another by one of their lower and upper flat surfaces, according to an interface 40. This is in the form of a segment of straight line which defines, with a line parallel to the axis Ox, or perpendicular to the walls 22, 24, an acute angle A (for example between 30 ° and 60 °, for example still equal to, or close to, 45 °).

 In the example described above, the faces 305, 325, etc. are flat.

As a variant, this face may have a curvature, for example it may consist of a cylinder portion, as illustrated in FIGS. 3B, 5C and 5D with the faces 345 '(element 34, FIG. 3B), and 305' (element 30, 5C and 5D), the axis of the cylinder being parallel to the direction of traction of the entire stack. The thermal effect of the entire stack is not affected in the closed or lowered position of the stack, because the contacts between the plane surfaces adjacent to two neighboring elements remain identical to what has been described above. The section of this element, along a plane zOx, still has a triangular shape or that of Figure 2D, the base 305 of the triangle being a line segment. In the lowered position of the stack, the cylindrical portion of the wall 345 ', 305' is tangential to the outer wall or to the outer plane 24. Such a curvature may be useful to conform to the shape of a cylinder, the plans or walls 22 and 24 are often cylindrical (see for example the structures of Figures 10b) according to an axis parallel to the direction of traction.

 As can also be seen in FIGS. 2A-2C, 3A-3B and FIGS. 5A-5D, each of the lateral faces 301, 301 ', 321, 321', 341, 341 ', 361, 361' of each element may comprise two studs 30 ', 30 ", 32', 32", 34 ', 34 ", 36', 36", each stud being close to one of the lower and upper planar surfaces of the corresponding element. The two studs of the same lateral face are substantially aligned in a direction parallel to the base of this same element or along the edge 305 in the sectional view of FIG. 2D (or else: according to the direction of traction). Each post has a substantially cylindrical shape, the axis of the cylinder being directed substantially perpendicular to the side face on which the pin is located.

 A connecting rod or rod 40, 42, 44, 46 connects the two tenons closest to two neighboring elements. This link will define the maximum distance that can be between the two flat surfaces, lower and upper, the closest to two neighboring elements, when they are not in contact. It also defines the maximum amplitude of the possible sliding of a plane face of an element relative to the plane face opposite the neighboring element.

These rods, and the corresponding tenons, allow to apply to the element concerned a traction in a direction parallel or substantially parallel to the axis Oz and / or at the intersection 305 of the base with the plane zOx (case Figures 2D and 3B). In the case of Figure 4A, the force applied to each face has a component also according to Ox, but this is of no consequence because, in the traction position (Figure 4A) the elements are blocked. Therefore, the resulting force is again along the Oz axis. As seen in Figure 2A, and as explained below, a force F direction Oz can be applied or transmitted to each element, the base thereof remaining parallel to the corresponding hot or cold wall to which it is turned. Insofar as each element is arranged, along the Oz axis, between two other elements, each tenon undergoes a pulling force upwards, but also the weight of the elements which are situated beneath it.

 It is thus possible to ensure the relative displacement of the constituent elements of the basket, when they are stacked and arranged between the two walls such as the hot and cold walls 22, 24.

 These means will allow to separate the various elements relative to each of its neighbors and thus to induce between two side faces of two neighboring elements a distance e, these two lateral faces remaining parallel to each other. Likewise, during the spacing of the various elements, a positioning thereof occurs so that a space, or clearance 27, 29, is formed between the various elements and the walls 22,24.

A rod has for example the shape shown in Figure 2A or 6A, this shape is longitudinal and has a central opening, also longitudinal. The maximum amplitude of this opening, that is to say the distance between the internal faces of the two short sides of the rod is equal to the maximum distance desired between the external generatrices of the two neighboring studs of two transmitter elements immediately adjacent in stacking. The link and its lateral opening allow 2 neighboring elements to slide on one another, keeping their immediate neighboring faces in contact. For example, it can be seen in FIG. 2A that each of the links has a central opening which allows the two neighboring elements 301 and 321, 321 and 341, 341 and 361 to be spaced apart so that their neighboring lateral faces remain parallel to each other with a distance e. This distance, or this spacing, allows the transmitting elements to be in the "raised" position to allow the introduction of element bars in the basket. In the lowered position, the lateral faces of the neighboring elements are in contact with each other, as illustrated in FIG. 6B or 7B. The links are then in a relaxed position, the distance between two studs adjacent to two adjacent elements being less than the maximum amplitude defined by the internal opening of each link.

 Another embodiment of the rods is shown in Figures 4A-4C: each rod 47 has two openings, each of these openings for accommodating a stud 30 ", 32" of one of the transmitter elements. One of these openings, that which is around the tenon 30 ", allows the rod to move only in rotation around this tenon, but not in translation, while the other opening allows it to move in rotation around 32 "and allows the element 32 to move in translation: the corresponding opening extends over a greater length, approximately from the middle of the link (in the direction of its length) to the inner side from one of its lateral ends.

The distance between the two openings and the length of the 2 ^nd aperture are chosen so that the two neighboring transmitting elements can pass:

 a so-called initial position (FIG. 4A), in which the two neighboring faces of two adjacent elements are in contact, and a clearance 27, 29 is formed between the base of each of the elements and the wall or wall 22, 24 to which this base faces,

 at an intermediate position (FIG. 4B), in which the adjacent lateral faces of two neighboring elements are spaced apart from one another by a desired distance, and each of the bases approaches the corresponding wall 22, 24,

 and then to a "plating" position (FIG. 4C) in which two adjacent lateral faces are in contact with one another or pressed against each other, and the base of each of the elements is pressed against the wall 22, 24 corresponding.

 In this movement, the ends of the rod perform, under the action of the means 21 (Figure 7A), a substantially circular movement on a circle whose center is the center of the rod.

Another embodiment of a connection system between neighboring elements is illustrated in FIGS. 5A-5D, FIGS. 5A-5B corresponding to an embodiment with a base 305 in the form of a flat wall, FIGS. 5C-5D corresponding to a realization whose base 305 'has the shape of a cylinder portion. This time, the element 30 represented comprises:

 two lateral notches, or lateral recesses, 203, 204, which open into the upper planar face 303 and optionally (as is the case in FIGS. 5A-5D) in the corresponding lateral face 30, 301,

 two lateral notches, or lateral recesses, 205, 206, which open into the lower planar face 303 'and possibly into the corresponding lateral face 30, 301.

 In the inner wall of each lateral notch is here made a hole 203 ', 204' in which can be positioned a pin, intended to cooperate with the end of a rod or a rod, as already described above .

 A wall of each notch is therefore intended to be provided with means, for example at least 1 stud or 1 pin, to couple each element using, for example, two rods, as explained above. Each notch has a volume sufficient to accommodate an end portion of the corresponding link.

 As shown in FIG. 7A, means or a pulling mechanism 21 are positioned on one side of the basket at the top or bottom thereof. Means comprising for example one or more rods 210 and / or one or more jacks are connected to the end element of the stack of elements to communicate to all the elements upward or downward movement along the axis oz. The means 21 may allow to exert pressure on the entire stack, when the latter is in the closed or lowered position.

 When it is desired to introduce an assembly into the basket, an upward force is exerted, as shown schematically by the arrows F in FIGS. 2A, 6A and 7A, parallel to the axis Oz and to each of the walls 22, 24.

 Each element of the basket then separates from neighboring elements, in the manner explained above, in conjunction with FIGS. 4A-4C, 6A-6B and 7A-7B. This movement releases games 27, 29, 27 ', 29' in the radial direction (FIGS. 2A, 6A and 7A).

Once the assembly is in place, a force is applied downwards (always along the Oz axis), or it is the gravitational force which attracts the transmitting elements downwards, the plane faces of the transmitting elements come in contact with each other and the internal and external games disappear (as in Figures 4C, 6B and 7B). At the end of this phase, a pressing force can still be exerted on the stack of elements to reduce the thermal resistances at the solid-solid interface of each pair of neighboring elements and to guarantee the mechanical strength of the together, regardless of the position of the castle, including in a horizontal position.

 As seen in the top views of Figures 2B and 3 and in the perspective view of Figure 2C, each transmitting element extends over a limited length L, for example between 100 mm and 200 mm or 500 mm this length being chosen according to the surface qualities of the elements and the quality of the desired heat transfer. L can be the stretched length of an arc, especially in the case of a base such as the base 345 'of Figure 3B.

 Therefore, an assembly, which generally has a cylindrical shape, will be surrounded by a plurality of n basket members, arranged substantially circularly, each basket member covering an area of about 360 ° / n. Such an arrangement is shown in Figures 8A and 8B, for a hexagonal assembly, each basket member 60, 62, 64, 66, 68, 70 covering a sector of about 60 °. References 620-626 are the individual elements of two basket members 62. The two end members 620 and 626 are truncated to provide planar surfaces at both ends of the stack.

 In these figures 8A and 8B, there is shown the three-dimensional system, with a vertical array of transmitter elements eliminated (or a removed basket element) for better viewing. The set of basket elements is arranged to define an internal hexagonal opening at 17, in which a fuel element can be introduced.

 FIG. 8A corresponds to an opening situation, the transmitting elements being in disjoint position from each other, as illustrated in FIG. 2A and in FIG. 4A. A game, which can be important, is then created between the load, which is in the center of the basket, and the inner wall of this basket.

FIG. 8B corresponds to a closing situation, the neighboring transmitter elements being in the contact position with each other, as illustrated in FIG. Figure 4C and Figure 6B. In this position, any play, which was previously between the load and the inner surface of the basket, is canceled.

 In the embodiment of FIGS. 8A and 8B, the hexagon 15 is the load, its outer wall corresponds to the hot wall (walls 22) of FIG. 2A.

 In this embodiment, there is the presence of a zone, between two neighboring cells of the same stage, or between two elements (for example 62 and 64) basket, in which there are no transmitter elements. But for the same reason as that indicated above for the residual clearances 270, 290, this is not troublesome from the point of view of the thermal conduction; indeed, the heat passes "by side", in highly conductive areas from the thermal point of view (the ratio of the conductivity of aluminum to that of helium is 1000 and, on that of air, it is around 6000).

 Once the system is set up (FIGS. 7B, 8B), the evacuation of the calories in the radial direction is improved and this results in a significant decrease of the radial thermal gradients.

 Thus, by using a storage method implementing a basket as described above, the previously stated limit of 2.5 kW (Tmax <450 ° C) and 4.5 kW (Tmax <650 ° C) for a TN12 goes respectively to 3.5. kW and 6.5 kW. During a transport of an assembly, one can thus reach 5 kW for Tmax <450 ° C and 9 kW for Tmax <650 ° C.

 The embodiment illustrated in FIGS. 8A and 8B shows a basket (amputated from a column of elements only for questions of visibility of the drawing) and the hexagonal tube 15. But it is also possible to introduce several assemblies, as illustrated in FIG. 10B, which represents a view from above: in this case, the basket comprises:

 a plurality of elementary baskets 100-106,

 a fixed part 55 (a stack of discs of heat-conducting material, for example aluminum, each disc having the appropriate openings for passing the baskets to the desired positions),

a ring of basket elements 550 Each element being of the type according to the invention, as already presented above. The basket thus formed is disposed inside a castle, the assembly being surrounded by a shell 54 of steel and a layer 52 of resin. The assembly may be provided with vanes 56 for the removal of heat; these are the fins which, in Figure 10C, outwardly outwardly We find these references 52, 54 in Figure 10A, for the case of a single basket.

 A constituent assembly of a castle, may therefore comprise at least one elementary basket as described above, but also a set of absorbent layers, for example a layer 54 (which may be forged steel or lead) to absorb the gamma radiation, and a layer 52 (containing a lot of hydrogen) to slow the neutrons.

 An elementary basket may have the structure that has just been described above, over its entire height.

 It can also have such a structure over a limited height h, which corresponds to the power that one wants to evacuate, for example about 1 m, as it appears for example in FIG. 9A where it can be seen that the set 20 of movable elements extends over a limited height of each wall of the basket (it is the height on which the heat exchange takes place), the rest being constituted by two parts 20 ', 20 "uniform.

 As a variant, as illustrated in FIG. 9B, some elements may be arranged in a part in which there is little or no heat exchange, as in the zones 200, 200 '. These elements work as has been described above, but they have only a role of mechanical blocking, and not, or little, role from the thermal point of view. On the contrary, the set of moving elements has both a thermal and mechanical role. The zones 200 ', 200 are separated from the zone or the portion 20 by a portion of homogeneous and continuous material, not provided with transmitting elements as described above.

Figures 9A-9E show the steps of a fuel loading in a device according to the invention. In a first step (FIG. 9A), this assembly, which does not yet contain a fuel element, is immersed in a swimming pool 120 and the covers 130 of the various parts are open.

 Then (FIG. 9B) the transmitter elements of the basket are raised, in the manner already explained above, by pulling on all the elements, using the means 21. Their release is thus relaxed and games are introduced between the base of each element and the surface 22, 24 towards which it is turned (see the explanations given above).

 With the basket held in this raised position, a fuel element 15 (see FIG. 9C) can be introduced into the central opening 17.

 The support force is then reversed on the elements of the wall of the basket, as illustrated in FIG. 9D, so as to position the transmitting elements in contact with one another, and without leaving play between the bases of these elements. elements and walls.

 Finally, the assembly is closed, bringing the lids back to their original position (see FIG. 9E).

 The set can then be lifted from the pool for draining.

Numerical results are presented in the following for castles carrying 1, 7 or 12 assemblies. These castles are named TCl, TC2 or TC12 depending on whether they carry 1, 2 or 7 assemblies, they are inspired by current castle dimensions like IL49 or TN12.

 For a limit of 650 ° C, the power per assembly ranges from 4kW6 (TC12) to 6kW3 (TCl) for standard games. Cancel these games would get respectively 6kW6 to 8kw8.

 Below, the gains made in terms of evacuable power for a given temperature criterion are recorded for the case of assemblies loaded with minor actinides.

The geometry chosen for the castle is a multi-layer geometry: - TN12 type (used as soon as we have more than one assembly to transport), shown in top view in Figure 10B. In this geometry, the outside diameter layer 550 is the same as the basket used today which does not change the rest of the geometry. Reference 54 designates a steel ferrule,

or IL49 (for transporting a single assembly), shown in plan view in FIG. 10A. In this geometry, the outside diameter D _e of the layer 52 of resin, and the outside diameter of the basket 100 of aluminum are preserved

 Three cases have been studied: the case of a single assembly, that of 7 assemblies and that of 12 assemblies.

 For the case of a single assembly, the geometry is of type IL49.

 The study of the effect of Tmax parameters and games leads to the following results, given in FIG. 11 in which:

 curve I corresponds to 2 sets of 1 mm each,

 curve II corresponds to 1 internal clearance of 5 mm and 1 external clearance of

I mm,

 curve III corresponds to 1 internal clearance of 5 mm and 1 external clearance of 2 mm,

 the curve IV corresponds to 2 sets of 5 mm,

 the curve V corresponds to 2 sets of 0 mm, that is to say to a contact obtained according to the present invention,

 For example, for a maximum value of 650 ° C:

 - in the case of curve I, 8kW can be evacuated,

 - in the standard case (curve III) one can evacuate approximately 6.3kW,

- and the optimum is 8.7kW when the games disappear (curve V). For the case of 7 assemblies, the geometry is of TN12 type.

 During the parametric study, we studied only the standard case and the one where the games are null (the other cases being included between these 2 limit cases). The study of the effect of Tmax parameters and games leads to the following results, given in figure

II on which:

the curve Γ corresponds to 1 internal clearance of 5 mm and 1 external clearance of 1 mm; in this standard case 5.5kW can be evacuated per assembly, ie a total power of 39 kW and the resin has a temperature between 70 ° C and 88 ° C, the curve Ι Γ corresponds to 2 sets of 0 mm.

 Again, we see that the reduction of the games allows, at a given maximum center temperature, to increase the evacuable power.

 For the case of 12 assemblies, the TN12 type geometry was used. During the parametric study, we studied only the standard case and the one where the games are null (the other cases being included between these 2 limit cases). The study of the effect of Tmax parameters and games leads to the following results, given in FIG. 13 in which:

 - curve I "corresponds to 1 internal clearance of 5 mm and 1 external clearance of 1 mm, in this case it is possible to evacuate 4.5 kW per assembly, ie a total power of 54 kW, the center temperature being less than 650 ° VS,

 the curve M "corresponds to 2 sets of 0 mm.

 In this case of high power, the external resin reaches a temperature of 80 ° C.

 The results of FIG. 13 lead to the same conclusion: the reduction of the games makes it possible, at a given maximum temperature in the center, to increase the evacuable power.

 The evacuable power for the above three configurations and for 2 different maximum temperatures (450 ° C. and 650 ° C.) was synthesized in Table I below. The evacuable power is indicated for each of these cases, underlined when the games are null.

P evacuable by 1 assembly

1 assembly 7 assemblies 12 assemblies

Tmax = 450 oC 3,3kw (4,6kw) 2,9kw (4kw) 2,5kw (3,5kw)

Tmax = 650 ° C 6.3kw (8.8kw) 5.5kw (7.6kw) 4.6kw (6.6kw)

Water Tab II The invention applies in the field of storage and / or transport of high power radioactive materials, especially high-power generation IV fuels, for example still assemblies loaded with minor actinides.

Claims

Heat-transmitting element (30, 32, 34, 36) for a substantially prismatic nuclear fuel storage basket having 3 main faces (303, 303 ', 305, 325, 345, 365), of which a base and two secondary surfaces, and two lateral faces (301, 301 '), of a heat-transmitting material, laterally provided with means for providing traction of the element in a direction parallel to the base, and for bringing it an initial position, in which the transmitting element is released and is against a so-called hot or cold wall, at a raised position, separated therefrom from a space, or from a game (27, 29), and Conversely.

2. Element according to claim 1, the means for ensuring traction of the element:

 - being placed on the lateral faces,

 - or having lateral notches or lateral recesses

(203, 204, 205, 206) formed in the element, each recess opening into one of the secondary plane faces, and possibly in the corresponding lateral face (303).

3. Element according to claim 2, the means for ensuring traction of the element comprising at least 2 studs or 2 pins (30 ', 30 ", 32', 32", 34 ', 34 ", 36', 36" ), placed on each lateral face or on a wall of each lateral notch or lateral recess.

4. Element according to one of claims 1 to 3, comprising at least one connecting rod (40, 42, 44, 47) of traction cooperating with the means to ensure traction of the element in a direction parallel to the base.

5. Element according to the preceding claim, the pull rod having an interior at least partially perforated.

6. Element according to one of the preceding claims, having, in a plane perpendicular to the base, a substantially triangular shape.

7. Element according to one of the preceding claims, the base being flat or forming a cylinder portion (305 ').

8. Element according to one of the preceding claims, the secondary surfaces (303, 303 ') being flat or provided with corrugations.

9. Nuclear fuel storage basket element (60, 62, 64, 66, 68, 70), comprising:

 a first stack of transmitter elements according to one of the preceding claims, arranged between the two walls, each secondary surface of an element facing a secondary surface of a neighboring transmitter element, the bases of the different absorbing elements; being alternately turned towards one side of the stack, then towards the other, each transmitting element being connected to its neighbors by the means to ensure traction of the element in a direction parallel to the base,

 means (21) for exerting traction on all the transmitting elements.

10. Element (60, 62, 64, 66, 68, 70) of storage basket according to the preceding claim, each secondary surface of an element:

 - Being in contact with a secondary surface of a transmitting element when no traction is exerted on all the transmitter elements,

and being situated at a non-zero distance from said secondary surface, and substantially parallel thereto, when traction is exerted on all the transmitting elements.

The storage basket element (60, 62, 64, 66, 68, 70) according to claim 9 or 10, the stack of transmitting elements having a height (h) less than the total height of the storage element. basket.

Storage basket element (60, 62, 64, 66, 68, 70) according to one of claims 9 to 11, further comprising at least a second stack of transmitter elements according to one of claims 1 to 8, arranged in a zone (200, 200 ') separated from the first stack by a continuous portion of material.

13. Nuclear fuel storage basket, comprising a plurality of storage basket elements according to one of claims 9 to 12, arranged to define a central cavity (17) of substantially cylindrical or square or rectangular or hexagonal shape in a plane perpendicular to the direction of traction of each basket.

14. Castle for storing and / or transporting nuclear fuel, comprising at least one storage basket according to the preceding claim, surrounded by a peripheral protection layer (54) for the absorption of gamma rays and a layer (52). ) of peripheral protection to slow the neutrons.

15. Castle for the storage of nuclear fuel, according to the preceding claim, comprising several baskets in number between 2 and 12.

 16. A method for storing and / or transporting a nuclear fuel rod (15), comprising the following steps:

pulling on the transmitting elements of the basket elements of a storage basket according to claim 13, so as to bring them from an initial position to a raised position and to generate a play (27, 29) between each transmitting element and the two planes (22,24) which define the hot and cold surfaces, introducing one or more fuel rods into the central cavity (17),

 - Release the transmitter elements, to bring them back to the initial position, in which the base of each transmitter element is positioned in contact with one or the other of the two walls (22,24) hot and cold.

17. The method of claim 16, comprising a prior step of introduction of the storage basket in a pool (12), and a subsequent step of extracting the pool, the basket loaded with the rods.

18. The method of claim 16 or 17, wherein each fuel rod with a power of at least 7 kW or 8 kW.