RU2608765C2 - Method and mobile device for reducing thermal resistance between two solids - Google Patents

Abstract

FIELD: packaging industry.

SUBSTANCE: invention relates to elements of containers for transportation and storage of nuclear fuel. Prismatic heat transfer element of a nuclear fuel storage rack (30, 32, 34, 36) comprises three main surfaces (303, 303', 305, 325, 345, 365), includes a base and two side flat surfaces, as well as two end surfaces (301, 301'), made from heat-transfer material. End faces are provided with means for pulling element in a direction parallel to base.

EFFECT: technical result is efficient heat removal from container.

25 cl, 30 dwg

Description

FIELD OF THE INVENTION

The invention relates to a rack for storing fuel assemblies of nuclear fuel composed of a plurality of contacting cells of large lengths, into each of which a fuel assembly of nuclear fuel can be inserted, or, optionally, rods of several fuel assemblies.

The above storage racks (also known as storage baskets) are intended for storage and / or transportation of the above fuel assemblies, optionally in protective or non-protective packaging. They adapt for irradiated fuel, but can also be used for new fuel. They can be used in a dry or liquid environment, for example, during storage of fuel in a pool, or during their introduction into packaging for transportation or storage.

If it is necessary that the container for transporting fuel assemblies be multifunctional (radiation protection, impact resistance, fire resistance, etc.), then a set of various materials is an appropriate solution. In the event that it is necessary to divert a large power, the limit value of the internal temperature is determined by the presence of gaps necessary for the container.

The problems associated with the safety and transport of radioactive materials are described in La sureté des transports de matières radioactives (Safe transport of radioactive materials, B. Lenail, Revue Générale Nucléaire No. 1 2005; "Conception, fabrication et essais des emballages pour le transport des matières radioactives" (Design, construction and testing of packages for transporting radioactive materials, "Design, construction and testing of packages for the transport of radioactive materials"), B.C. Bernardo, IAEA Bulletin (IAEA, International Atomic Energy Agency), Volume 21, No. 6; or instead, in document EP 0752151.

In general, fuel assemblies are transported dry in containers containing up to 12 or more fuel assemblies. These transport packages have been approved by the relevant French, British and Japanese administrative authorities, and they meet the criteria prescribed by the IAEA (International Atomic Energy Agency) guidelines for Type B packages. This type of container, used for nearly 40 years, is based on the principle of performance characteristics essential for packaging (double barrier, nature of fire spread, etc.) that prevent any leakage of radioactivity.

As illustrated in FIG. 1, from the outer part to the inner container contains along its entire length:

- the outer zone 2, which may be provided with ribs 4 for cooling,

- layer 6 for neutron absorption,

- steel ring 8, and

- a rack 10 for storing fuel assemblies of nuclear fuel containing one or more adjacent cells 12 of large length into which a fuel assembly of nuclear fuel can be inserted, or, if necessary, rods of several fuel assemblies.

Various types of struts with a cellular structure are known for fuel assemblies of nuclear fuel. In general, they guarantee three functions:

- criticality control, in a dry state or in the presence of water, in a liquid or gaseous state (this water is capable of containing chemical compounds that absorb neutrons, for example, based on boron) of a set of heat-generating assemblies that are stored in a rack,

- maintaining significant mechanical strength, which meets two goals: 1) ensuring the geometry of the rack loaded with assemblies, which avoids damage to the fuel rods during normal use (handling, transportation, etc.), 2) guarantee criticality control through support rack geometry, even under conditions of accidental impact (significant impact and fall), in accordance with instructions for perceived efforts,

- thermal transfer, in order to remove heat generated in the case of irradiated fuel assemblies.

Sometimes racks are also designed with the expectation that protection against radioactivity will be added.

The stand as a whole is formed by the combined use of several materials, each of which performs at least one of the three above functions. In general, the main materials used here are:

- stainless steel or aluminum (or their alloys) for the function of maintaining mechanical strength,

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

- chemical boron compounds (such as B4C based on sintering), copper, aluminum or stainless steel alloys containing boron to provide criticality control functions.

In terms of the thermal performance of the container, the removal of internal energy and a fire resistance temperature of 800 ° C for 30 minutes are currently permitted for use with materials (steel ring, aluminum stand, etc.) and for their performance (“chemical connection ”, crossed by ribs, protection of connections, etc.).

Regarding the implementation issue and especially the assembly, this system with the connection of different radial layers requires, especially for easier insertion of the assembly or rack into the container, the location of the gaps at the interface between the different layers, in particular between the assembly and the cavity, but also between the rack and the ring . These gaps, for example about 5 mm and 2 mm, may be unfavorable to the needs of thermal transfer.

In particular, in the case when it is necessary to divert a lot of power, the presence of these gaps creates high thermal resistances, and thus, large thermal gradients that significantly increase the maximum internal temperature, when it is desirable to increase the maximum allowable power levels (which also depend on materials, combustion rates, etc.).

Currently, transportation is carried out with nitrogen filling, but transportation with gases having a higher conductivity (helium) can be used. In this case, internal and external clearances of 5 mm and 2 mm, respectively, are sufficient for transporting fuel for a PWR (pressurized water reactor), since the power levels are low.

But the problem is that it is possible to transport high-energy fuels (for example, MOX (mixed oxide fuel) fuels or instead fuel assemblies with actinides in the future).

Thus, the ability to divert calories well to the outside without exceeding completely unacceptable internal temperatures is a key issue for the future.

In this case, the total transmitted power does not cause the problem to the same extent as the temperature difference, which occurs due to the presence of the gaps mentioned above.

Thus, using existing technology, the maximum assembly power transmitted in helium will be limited to 2.5 kW without exceeding a temperature of 450 ° C, and 4.5 kW without exceeding a temperature of 650 ° C, while the need for transmitted power may to be much taller.

Document WO 2011/161233 describes a system that makes it possible to reduce contact thermal resistances due to external clearances. In this system, 4 rack parts come in contact with a steel ring. The result is a simple system with improved radial transfers, but not gaps known as internal. Thus, the change in the amount of heat, in terms of power output, is low.

Thus, the problem also lies in the gaps called internal (between the assembly and the rack).

In fact, re-examining the case of a container with assembly in helium medium, with traditional clearances (for example, 5 mm — internal clearances and 2 mm — external clearances), 6.3 kW at 650 ° can be allocated in it. If the external clearance is canceled, for example, in accordance with the ideas of document WO 2011/161233, the power reaches 6.75 kW, i.e. power output increases by only 8%. If 2 gaps are canceled, then the power reaches 8.75 (i.e. increases by 40%). But in this technology, the surfaces that are in contact (about ¼ from the outer surface of the rack) are important, so, with the exception of completely unacceptable production gaps, the contact can take place only on one generatrix or just in several areas.

Therefore, the gaps inside the container for storage or transportation, in which the thickness of the gap creates a significant contact resistance, and in addition, the thermal criterion is not exceeded, largely satisfies the condition of the possibility of power removal during transportation of fuel assemblies.

Thus, the problem is to improve the heat exchange processes inside the transport container in order to reduce the temperatures reached in the nominal mode.

Disclosure of invention

The solution to this restriction is provided in the future.

First of all, a heat transfer element of a rack for storing nuclear fuel of essentially prismatic shape is described, comprising three main surfaces, including a base and two side flat surfaces, as well as two end surfaces made of heat transfer material and provided laterally with means for pulling the element into direction parallel to the base.

Each heat transfer element is made of a material that conducts heat, so it has good heat conductivity, and is made, for example, of a metal material such as aluminum or copper.

Means for pulling the element can be located on the end surfaces. For example, each of these end surfaces is provided with at least two pins or two protrusions.

Alternatively, the means for pulling out the element may include recesses or end recesses formed in the element, with each recess extending onto one of the side flat surfaces, and optionally, in the corresponding end surface. The wall of each recess contains appropriate means, for example, at least two pins or two protrusions.

Such an element may contain at least one traction connecting link, for example, having an internal cutout or not, and interacting with means for pulling the element in a direction parallel to the base.

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

The base may be flat, or have at least one bend around an axis substantially parallel to the direction of traction.

Thus, an element of a rack for storing nuclear fuel may contain:

- the first set of heat transfer elements of this type, which was described above, each side flat surface of the element is opposite to the side flat surface of the adjacent heat transfer element, so the bases of the various heat transfer elements alternately rotate in the direction of one side of the set, then in the direction of the other, with each heat transfer element being attached to adjacent elements using means for pulling the element in a direction parallel to the base,

- Means for actuating the traction force on the assembly of heat transfer elements.

In such an element of the fuel storage rack, each side flat surface of the element may:

- be in contact with the side flat surface of the adjacent heat transfer element when the traction is not exerted on the assembly of heat transfer elements, and in the particular case when pressure is exerted on the assembly of elements,

- move away from the side flat surface of the adjacent heat transfer element when the pulling force is on the assembly of heat transfer elements.

A set of heat transfer elements may have a height (h) that is lower than the total height of the rack element. In this case, the remainder of the rack is composed of a heat transfer material laid above and below the heat transfer elements described above. The height h in this case is substantially equal to or close to the length at which the fuel cells generate heat.

The rack element may further comprise at least one second set of heat transfer elements, as described above, located in an area separated from the first set by a continuous section of material. This second set in this case performs the function of maintaining mechanical strength, and to a lesser extent the thermal function.

An elementary nuclear fuel storage rack may comprise a plurality of fuel storage rack elements of the type described above, arranged so as to delimit the central cavity in a substantially square, or rectangular, or hexagonal shape in a plane perpendicular to the pulling direction of each rack, depending from the form of the assembly for which it was intended.

Thus, the container can be created for storing and / or transporting nuclear fuel and may contain an elementary storage rack of the type described above, the rack being surrounded by a peripheral protective layer for absorbing gamma radiation, and a peripheral protective layer for slowing down neutrons.

It is also possible to create a container for storing and / or transporting nuclear fuel containing several elementary racks for storage, for example containing a number of such racks from 2 to 12, each of the elementary racks being a rack of the type described above.

Elementary racks are placed in a fixed rack, and this rack itself is surrounded by many heat transfer elements of the above type, which guarantee effective thermal contact with the peripheral layers.

The present invention also relates to a method for storing and / or transporting nuclear fuel rods, comprising the following steps:

- providing traction on the rack elements of the above racks for storing fuel, in order to bring them from the initial position to the upper position and create a gap between each heat transfer element and each of the hot and cold walls,

- the introduction of one or more assemblies in the Central cavity,

- cessation of traction in order to transfer the heat transfer elements back to their original position, in which the base of each heat transfer element is positioned in contact with one or the other of the hot and cold walls. During this phase, the effect of gravity may be sufficient to bring the elements back to their original position due to their own weight. Optionally, additional pressure may be added which makes it possible to support the elements in this position, even when the strut is in a different position other than a vertical position, for example, when it is in a horizontal position during transport.

Such a method may be preceded by the step of introducing the storage rack into the pool, followed by the step of removing the rack loaded with rods to remove it from the pool.

In the invention, the means are applied in such a way as to exert force on the set of heat transfer elements, which allows you to change the internal and external radii of the rack, and thus reduce the space between the assembly and the rack, as well as between the rack and the external environment, for example, a ring.

Thus, the rack adapts its shape and holds potential assembly deformations.

Thus, the invention makes it possible to preserve important gaps during the introduction of the load, and then re-absorb them before the last operation, for example, before handling or transportation.

In the case of transportation of assemblies, and in particular, assemblies with high power levels, the system makes it possible to reduce contact thermal resistances and even annul them (they are directly connected with gas play in the gaps and with the thermal conductivity of the gas). But it has other advantages:

- the conclusion of the rack in the shell on the assembly allows to increase the mechanical strength during transportation; therefore, there is no longer any need to introduce inserts, as was previously the case in this case;

- this rack allows you to adapt your shape and holds potential assembly deformations;

- The current rack processing costs are reduced;

- in certain cases (in particular, assembly in the housing *), the helium in the rack can be replaced with dry air or nitrogen.

Compared with the technology described in document WO 2011/161233, as described previously, contact can take place on only one generator or just a few areas, while the invention described here makes it possible, due to the multiplicity of base surfaces, to increase the number of contact points and have more contact surfaces. The fewer heat transfer elements, the better the adaptation to the form.

The invention makes it possible to minimize the internal and external gaps in the rack, which make it possible to store and transport certain assemblies whose power levels (P> 8 kW) exceed the indicators currently produced. It also makes it possible to optimize the number of transported assemblies, since not only one assembly can be implemented, but also many assemblies.

Brief Description of the Drawings

Embodiments of the invention will be described below solely as non-limiting examples, with reference to the attached drawings.

In FIG. 1 (already described) shows a container of known construction, a view with a spatial separation of the parts;

in FIG. 2A-2D and 3A-3B show the above-described heat transfer elements;

in FIG. 4A-4C show 2 elements connected by a connecting link and their relative movement;

in FIG. 5A-5D show heat transfer elements of various kinds;

in FIG. 6A and 6B show a set of heat transfer elements connected by connecting links and their relative movement;

in FIG. 7A and 7B schematically show racks in an open position and in a closed position, respectively;

in FIG. 8A and 8B show a rack containing an assembly;

in FIG. 9A-9E show the steps of introducing an assembly into a rack;

in FIG. 10A and 10B show two systems, where one system contains several assemblies, each of these systems containing at least one rack, one steel ring and one synthetic resin, top view;

in FIG. 11, 12 and 13, respectively, shows the change in the maximum possible temperature as a function of internal and external gaps and assembly power, respectively, for one assembly, for 7 and 12 assemblies.

The implementation of the invention

First, FIGS. 2A (side view, with a cut along the plane AA 'or xOz in Fig. 2B) and 2B (top view, with a cut along the plane BB' or xOy in Fig. 2A), which represent a set of heat transfer elements 30, 32, 34, 36 rack systems 20 in accordance with a separate embodiment of the invention.

In FIG. 2a, it can be seen that various heat transfer elements are stacked along the Oz direction of the Oxyz spatial coordinate system. In this figure and FIG. 2B also presents two walls 22, 24, which are respectively the hot and cold walls of the surrounding space in which the kit is positioned (wall 22, called the hot wall, is on the side of the hot assembly located inside the rack; while wall 24, called the cold wall, is the immediate environment on the outside of the rack). Outside of this environment, digital planes 22 and 24 indicate two planes that delimit the lateral extent of the assembly along the Ox direction when it is in the closed or lowered position, as will be explained later; later reference is made to two walls, but this can also mean two planes.

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

Each element of the kit has a substantially prismatic shape, as illustrated in FIG. 2C for an embodiment of the individual element 30. Other elements of FIG. 2A are identical or similar, therefore, all details similar or identical to those described with reference to FIG. 2C of these and other elements are not described in detail.

More specifically, the element shown in FIG. 2C is a substantially pentahedral or triangular prism with three quadrangular surfaces 303, 303 ′, 305 pairwise adjacent, and two triangular surfaces 301, 301 ′ not adjacent to each other and substantially perpendicular to the Oy axis.

The element comprises a base 305, which in this embodiment is flat and parallel to the rib 307, which extends along the Oy axis of the Oxyz spatial coordinate system.

In accordance with a separate aspect illustrated in FIG. 2D, sides and angles can be blunt, however, the expression “edge” or “vertex” will be used.

Between the edge 307, or the apex, and the base 305, there are two surfaces 303, 303 ', which may be designated for convenience, respectively, "upper surface" and "lower surface". In the present example, these surfaces are flat, but they can also have other shapes, for example, they may contain irregularities or undulations intended to come into contact, or for assembly with corresponding irregularities or undulations of the flat surface of an adjacent element.

In the transverse direction, along the Oy axis, the element is bounded by two walls or end surfaces 301, 301 '. In this example embodiment, these two side walls are substantially perpendicular to the base 305 and substantially parallel to the xOz plane. In an embodiment schematically shown in plan view of FIG. 3A and 3B, the side walls (here they are 341, 341 ', the element represented is element 34) are inclined and thus intersect both axes Ox and Oy. In the xOz plane, each of these heat transfer elements has a substantially triangular shape, with each triangle having a large side and two small sides, which are preferably substantially equal in length and the triangle itself is essentially isosceles. It is also preferred that the three sides are truncated at the end, as illustrated in FIG. 2D, or in FIG. 4A-4C. In the zOx plane, each of them, strictly speaking, no longer has a substantially triangular shape, but rather is a hexagon, with three large sides and three small sides that alternate with each other.

The height of this triangle, or the distance between the rib 307, or the top, and the base 305, is less than the distance between the two walls 22, 24. Thus, when the element is positioned in such a way as shown in FIG. 2A, the maximum distance between the vertex 307 of the element and its base 305 makes it possible to maintain a gap 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), zones 270, 270 ', 290, 290' remain unfilled with a part of the heat transfer element. For these gaps, dimensions are selected that make it possible to avoid any contact between the heat transfer element and the element from the second adjacent row (for example, in Fig. 2A, the contact between elements 30 and 32, between elements 32 and 36, etc., is completely prevented). These areas do not pose a problem from a thermal point of view, since heat passes through contacts created between adjacent elements, for example, between elements 30 and 32, between 32 and 34, between 34 and 36, etc. Alternatively, these areas are located in the direction of each of the walls 22, 24; even when filled with gas, and thus with insulating properties, their thermal effect is negligible, as they are shunted through a much more heat-conducting parallel passage.

In FIG. 2A can be seen, similarly to that shown in FIG. 2C, bases 325, 345, 365 of other elements 32, 34, 36, and their ribs 327, 347, 367.

Various elements 30, 32, 34, 36 are connected as a set, as shown in FIG. 2A, wherein the lower (respectively, upper) flat surface of the first element is in contact or opposite to the upper (respectively lower) flat surface of the second element immediately adjacent to it, but located below (respectively above) this first element along the Oz axis.

Alternatively, the large sides of the stacked elements are located in the direction of the wall 24 and in the direction of the wall 22. In other words, the heat transfer element 30 has a base directed towards the wall 24, while the base of adjacent elements is directed to the wall 22.

In the closed or lowered position of the kit, two adjacent elements can be pressed against each other through one of their lower or upper flat surfaces along the interface 40. This may take the form of a straight segment, which defines, together with a straight line parallel to the Ox axis or perpendicular to the walls 22, 24, an acute angle A (for example, from 30 ° to 60 °, for example equal to 45 °, or close to such an angle) .

In the above example, surfaces 305, 325, etc. are flat. Alternatively, this surface may have a curvature, for example, it may consist of a cylindrical portion, as illustrated in FIG. 3B, 5C and 5D with surfaces 345 '(element 34, Fig. 3B), and 305' (element 30, Figs. 5C and 5D), while the axis of the cylinder is parallel to the direction of traction of the entire set. The thermal efficiency of the entire kit is not affected in the closed or lowered position of the kit, since the contacts between adjacent flat surfaces of two adjacent elements remain identical to those described above. The cross section of this element along the zOx plane also has a triangular shape, or similar to that shown in FIG. 2D, the base 305 of the triangle is a straight segment. In the lowered position of the kit, the cylindrical part of the wall 345 ', 305' is tangent to the outer wall or to the outer plane 24. Such curvature may be useful to press the shape of the cylinder, planes or walls 22 and 24, which are often cylindrical (see, for example, the structures of FIG. . 10, 10b) along an axis parallel to the direction of traction.

As can also be seen in FIG. 2A-2C, 3A-3B and 5A-5D, each of the end surfaces 301, 301 ', 321, 321', 341, 341 ', 361, 361' of each element may contain two protrusions 30 ', 30ʺ, 32', 32ʺ , 34 ', 34ʺ, 36', 36ʺ, each of these protrusions is located near one of the lower or upper flat surfaces of the corresponding element. Two protrusions of the same end surface are substantially aligned in a direction parallel to the base of the same element or along a face 305 in a sectional view of FIG. 2D (or instead, along the direction of traction). Each of the protrusions has a substantially cylindrical shape, while the axis of the cylinder is directed essentially perpendicular to the end surface on which this protrusion is located.

A connecting rod or link 40, 42, 44, 46 connects the two nearest projections of two adjacent elements. Thus, this connecting link should determine the maximum distance that can be between two flat surfaces, lower or upper, the nearest surfaces of two adjacent elements, when they are not in contact. It also determines the maximum amplitude of the possible sliding of the flat surface of the element relative to the opposite flat surface of the neighboring element.

These connecting links and corresponding protrusions make it possible to apply a pulling force to the element in question in a direction parallel or substantially parallel to the Oz axis and / or to the intersection 305 of the base with the zOx plane (the case shown in Fig. 2D and 3B). In the case shown in FIG. 4A, the force exerted on each surface also has a component along the Ox direction, but this is without consequences since in the position (Fig. 4A), the traction forces are blocked. Therefore, the resulting force here again is directed along the Oz axis. As can be seen in FIG. 2A, and as explained hereinafter, a force F in the direction of the Oz axis can thus be applied or transmitted to each element, while the base remains parallel to the corresponding hot or cold wall in the direction in which it rotates. Since each element is located along the Oz axis, between two other elements, each protrusion is subjected to upward pulling force, but also the weight of the elements that are located below.

In this way, relative displacement of the constituent elements of the rack can be guaranteed when they are packaged and placed between two walls, for example, such as hot or cold walls 22, 24.

These means make it possible to separately move the various elements relative to each of the neighboring elements, and thus create a gap between the two end surfaces of the two adjacent elements, and these two end surfaces remain parallel to each other. Similarly, during the separate movement of various elements, they are positioned in such a way that the space or gap 27, 29 is located between the various elements and walls 22, 24.

The connecting link, for example, has the form shown in FIG. 2A or 6A. This shape is longitudinal and contains a central hole, also having a longitudinal shape. The maximum amplitude of this hole, in other words, the distance between the inner surfaces of the two small sides of the connecting link, is equal to the maximum desired distance between the external generators of two adjacent protrusions of the two heat transfer elements directly adjacent to each other in the kit. The connecting link and its end hole allows one element to slide on an adjacent element, while at the same time keeping directly adjacent flat surfaces in contact. For example, in FIG. 2a, it can be seen that each of the connecting links has a central hole that allows two adjacent elements 301 and 321, 321 and 341, 341 and 361 ... to move separately so that their adjacent end surfaces remain parallel to each other at a distance e. This distance or this gap allows the heat transfer elements to be in the “upper” position to allow the introduction of element rods into the rack. In the lowered position, the end surfaces of adjacent elements contact each other, as illustrated in FIG. 6B or 7B. Then the connecting links are in the released position and the distance between two adjacent protrusions of two adjacent elements becomes less than the maximum amplitude determined by the inner hole of each connecting link.

Another embodiment of the invention is shown in FIG. 4A-4C: each connecting link 47 contains two holes, each of these holes allows you to accommodate the protrusions 30ʺ, 32ʺ of one of the heat transfer elements. One of these holes, which surrounds the protrusion 30ʺ, allows the link to move only rotating around this protrusion, but not in translational movement, while the other hole allows the link to rotate around the protrusion 32ʺ and allows the element 32 to move in translational motion: corresponding the hole extends a greater length, from approximately the middle of the connecting link (in the direction of its length) to the inside of one of its end ends.

The distance between the two holes and the length of the second hole is selected so that two adjacent heat transfer elements can pass:

- from a position called initial (Fig. 4A), in which two adjacent surfaces of two adjacent elements are in contact, and a gap 27, 29 is located between the base of each of the elements and the wall or walls 22, 24 that are facing this base,

- to the intermediate position (Fig. 4B), in which the adjacent end surfaces of two adjacent elements move apart from each other at the desired distance, and each of these bases comes closer to the corresponding wall 22, 24,

- then to the position of the "shell" (Fig. 4C), in which two adjacent end surfaces are in contact with each other or pressed against each other, and the base of each of the elements is pressed against the corresponding wall 22, 24.

With this movement, the ends of the connecting link under the action of means 21 (Fig. 7A) essentially produce a circular movement, on the circumference of which the center is the center of the connecting link.

Another embodiment of the system of connection between adjacent elements is illustrated in FIG. 5A-5D, wherein FIG. 5A-5B correspond to an embodiment of the invention with a flat-wall base 305, and FIG. 5C-5D correspond to an embodiment of the invention in which the base 305 ′ is in the form of a portion of a cylinder.

This time, the presented element 30 contains:

- two end recesses, or end recesses 203, 204, which extend into the upper flat surface 303 and optionally (as in the case shown in Figs. 5A-5D) in the corresponding end surface 301, 301 ',

- two end recesses, or end recesses 205, 206, which extend in the lower flat surface 303 ′ and optionally in the corresponding end surface 301 ′, 301.

Here, an opening 203 ', 204' is formed in the inner wall of each end recess, in which a protrusion can be positioned to interact with the end of the connecting rod or link, as already described.

Thus, the walls of each recess are intended to be provided with means, for example, at least one pin or one protrusion, in order to connect each element using, for example, two connecting links, as described previously. Each recess has a sufficient volume to accommodate the final part of the corresponding connecting link.

As shown in FIG. 7A, the means or mechanism 21 for generating traction is positioned on one side of the strut, above or below it. The means comprise, for example, one or more rods 210 and / or one or more clamps attached to the end element of a set of elements for interacting with an assembly of elements when moving up or down along the Oz axis. Means 21 may create the ability to exert pressure on the entire kit when it is in a closed or lowered position.

When it is necessary to insert the assembly into the rack, the force is applied in the upward direction, as schematically shown by the arrows F in FIG. 2A, 6A and 7A, parallel to the axis Oz and each of the walls 22, 24.

Then, each rack element is separated from neighboring elements in a manner that has been explained above with reference to FIG. 4A-4C, 6A-6B, and 7A-7B. This movement releases the gaps 27, 29, 27 ', 29' in the radial direction (Fig. 2A, 6A and 7A).

As soon as the assembly is in place, a downward force is applied (still along the Oz axis), or gravity acts instead, which pulls the heat transfer elements down, the flat surfaces of the heat transfer elements begin to contact each other, while the internal and external gaps disappear ( as in Fig. 4C, 6B and 7B). At the end of this phase, the perceived load can again be applied to the set of elements in order to reduce the thermal resistance at the interface of the solid-phase media of each pair of neighboring elements and to guarantee the mechanical strength of the assembly in any position of the container, including the horizontal position.

As can be seen in the top view of FIG. 2B and 3, and also in perspective view in FIG. 2C, each heat transfer element extends for a limited length L, for example, a component value between 100 mm and 200 mm, or instead 500 mm, this length being selected as a function of the surface quality of the elements as well as the quality of the desired thermal conductivity. L may be the length of the unfolded arc, in particular when a base such as 345 'in FIG. 3B.

Therefore, the assembly, which has a generally cylindrical shape, must be surrounded by a plurality of n rack elements arranged substantially in a circle, with each rack element covering a sector of approximately 360 ° / n. Such an arrangement is shown in FIG. 8A and 8B, for a hexagonal assembly, each pillar element 60, 62, 64, 68, 70 covers a sector of approximately 60 °. The numerals 620-626 indicate the individual components of the two rack members 62. The two end members 620 and 625 are truncated to provide flat surfaces at the two ends of the kit.

In these FIGS. 8A and 8B, the system is presented in three dimensions with a remote vertical row of heat transfer elements (or a remote rack element) for better visualization. The assembly of the rack elements is positioned so as to define an internal hexagonal hole 17 into which a fuel element can be inserted.

FIG. 8A corresponds to the open position, with the heat transfer elements being in a position where they are separated from each other, as illustrated in FIG. 2A and FIG. 4A. The gap, which may be important, in this case is created between the load, which is in the center of the rack, and the inner wall of this rack.

FIG. 8B corresponds to the closed position, wherein adjacent heat transfer elements are in a position where they are in contact with each other, as illustrated in FIG. 4C and FIG. 6B. In this position, any gap that was previously between the load and the inner surface of the rack is canceled.

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

In this embodiment, the presence of an area between two adjacent cells of the same stage, or between two rack elements (e.g., 62 and 64) in which there are no heat transfer elements, can be noted. But for the same reasons that have been indicated above for the residual gaps 270, 290, this is not a disturbing factor in terms of thermal conductivity. In fact, heat passes nearby ("nearby") in areas of high conductivity in terms of thermal conductivity (the ratio of thermal conductivity of aluminum with respect to helium is 1000, and with respect to air - about 6000).

As soon as the system returns to its place (Figs. 7B, 8B), the abduction of calories in the radial direction improves and the result is a significant reduction in thermal radial gradients.

Thus, through the use of a storage method using such a rack, as described above, the previously announced limitation of 2.5 kW (Tmax <450 ° C) and 4.5 kW (Tmax <650 ° C) passes, respectively, to the values 3.5 kW and 6.5 kW. Thus, during transportation of fuel assemblies, for Tmax <450 ° С the power can reach 5 kW, and for Tmax <650 ° С it can reach 9 kW.

Illustrated in FIG. 8A and 8B, an embodiment of the invention shows a stand (the column of elements was removed solely for the purpose of readability of the drawing) and a hexagonal tube 15. However, it is also possible to introduce several assemblies, as illustrated in FIG. 10B, which is a plan view. In this case, the rack contains:

- many elementary racks 100-106,

- a fixed part 55 (a set of disks made of heat-conducting material, for example, aluminum, with each disk having corresponding openings to allow the racks to pass to the desired positions),

- the crown of the elements 550 racks, with each element having a type in accordance with the invention, as already described above.

The rack thus formed is located inside the container, the assembly is surrounded by a steel ring 54 and a resin layer 52. Assembly may be provided with fins 56 for heat dissipation; for example, ribs such as those shown in FIG. 10C protruding outward toward the outside. These digital positions 52, 54 reappear in FIG. 10A, for a single rack option.

Thus, the assembly constituting the container may contain at least one elementary rack, as described above, but may also comprise an assembly of absorbent layers, for example, layer 54 (which may be made of wrought iron or lead) to absorb gamma radiation, as well as layer 52 (consisting of a large amount of hydrogen) to slow down neutrons.

The elementary stand may have the structure described above, extending over its entire height.

It can also have such a structure at a limited height h, which corresponds to the power that it is desirable to divert, for example, about 1 m, as shown, for example, in FIG. 9A, or as can be seen in Fig., The assembly 20 of the movable elements extends to the limited height of each rack wall (this is the height through which heat transfer occurs). The remaining part is composed of two homogeneous parts 20 ', 20ʺ.

In the embodiment illustrated in FIG. 9B, several elements may be located in that part in which heat exchange does not exist or is insignificant, as in regions 200, 200 ′. These elements function in the manner described above, but in this case they only have a mechanical blocking function and do not have a function in terms of heat transfer or it is insignificant. Conversely, the assembly of 20 movable elements has at the same time a thermal and mechanical function. The regions 200, 200 'are separated from the region or region 20 by a portion of a homogeneous and continuous material not provided with heat transfer elements, as described above.

FIG. 9A-9E represent the steps of loading fuel into a device in accordance with the invention.

At first (Fig. 9A) this assembly, which still does not contain a fuel element, is immersed in the pool 120, while the covers 130 of its various parts remain open.

Then (Fig. 9B), the heat transfer elements of the rack are lifted in such a way, as already explained above, due to the pulling force to assemble the elements using means 21. In this way, they are maintained, between the base of each element and the surface 22, 24, in the direction by which it rotates (see the above explanations), gaps are created.

The stand is maintained in such an elevated position and the fuel element 15 (see Fig. 9C) can be introduced into the Central hole 17.

The perceived load on the elements of the rack wall in this case is inverted, as illustrated in FIG. 9D, in order to position the heat transfer elements in contact with each other, without leaving any gap between the bases of these elements and the walls.

And at the last stage, the assembly closes again, while the covers are moved back to their original position (see Fig. 9E).

Then the assembly can be lifted from the pool to dry.

Subsequently, the results for containers transporting 1, 7, or 12 assemblies are digitally presented. These containers are designated TC1, TC2 or TC12 depending on the number of transported assemblies, respectively 1, 2 or 7 assemblies.

To limit 650 ° C, the assembly power is from 4.6 kW (TC12) to 6.3 kW (TC1) for standard clearances. Cancellation of these gaps will allow, respectively, from 6.6 kW to 8.8 kW.

The following are estimates of the gains in terms of power output for a given temperature criterion for the case of assemblies loaded with minor actinides.

The geometry selected for the container is multi-layer geometry:

- shown in a plan view in FIG. 10B: in this geometry, the outer diameter of the layer 550 is the same as the diameter of the currently used rack, which in no way alters the geometry of the remaining part. Numeral 54 indicates a steel ring,

- or represented in a plan view in FIG. 10A: in this geometry, the outer diameter D _{e of the} resin layer 52 and the outer diameter of the aluminum strut 100 are maintained.

These three cases were studied: the case of a single assembly, the cases of seven assemblies and twelve assemblies.

For the case of a single assembly, the study of the effects of the parameters Tmax and gaps led to the following results shown in FIG. 11 in which:

- curve I corresponds to two gaps of 1 mm in each,

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

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

- curve IV corresponds to two 5 mm gaps,

- curve V corresponds to two clearances of 0 mm, in other words, corresponds to the contact obtained in accordance with the present invention.

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

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

- in the standard case (curve III) about 6.3 kW can be allocated,

- and 8.7 kW is optimal when the gaps disappear (curve V).

For the case of 7 assemblies, during the parametric study, only the standard case and the case when the gaps were equal to zero were studied (other cases are located between these two limiting cases). The study of the effects of Tmax parameters and gaps led to the following results shown in FIG. 11 in which:

- curve I 'corresponds to one internal clearance of 5 mm and one external clearance of 1 mm; in this standard case, 5.5 kW can be allocated to one assembly, i.e. the total power is 39 kW, and the resin has a temperature between 70 ° C and 88 ° C,

- curve I 'corresponds to two clearances of 0 mm.

Here you can again see that reducing gaps makes it possible at a given maximum temperature in the center to increase the power output.

For the case of 12 assemblies, during the parametric study, only the standard case and the case where the gaps were equal to zero were studied (other cases are located between these two limiting cases). The study of the effects of Tmax parameters and gaps led to the following results shown in FIG. 13, in which:

- curve Iʺ corresponds to one internal clearance of 5 mm and one external clearance of 1 mm; in this standard case, 4.5 kW can be allocated per assembly, i.e. the total power is 54 kW, and the temperature in the center is less than 650 ° C,

- curve IIʺ corresponds to two clearances of 0 mm.

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

The results shown in FIG. 13 lead to the same conclusion: reducing the gaps makes it possible at a given maximum temperature in the center to increase the power output.

The table below summarizes the results of power dissipation for the three configurations above and for two different maximum temperatures (450 ° C and 650 ° C). The power output is indicated for each of these cases, while the underline indicates the case of zero clearance.

The invention is applicable in the field of storage and / or transportation of high-level radioactive materials, in particular, fourth-generation high-level fuels, in addition, for example, fuel assemblies charged with minor actinides.

Claims (34)

1. The heat transfer element (30, 32, 34, 36) of the rack for storing nuclear fuel, having a substantially prismatic shape, containing three main surfaces (303, 303 ', 305, 325, 345, 365), which are the base and two side surfaces, and two end surfaces (301, 301 ') made of heat transfer material, while these two end surfaces are provided with means for pulling the element in a direction parallel to the base, and for its transfer from the initial position in which the heat transfer element is released and is on the contrary into walls, called hot or cold, in the raised position, in which it is separated from the wall by space or a gap (27, 29), and vice versa. 2. The item according to claim 1, in which the means for pulling the element: - are placed on the end surfaces, - or contain end recesses or end recesses (203, 204, 205, 206) formed in the element, with each recess extending to one of the side flat surfaces and optionally to the corresponding end surface (303). 3. The element according to claim 2, in which the means for pulling out the element contain at least two pins or two protrusions (30 ', 30ʺ, 32', 32ʺ, 34 ', 34ʺ, 36', 36ʺ), placed on each end surface or on the wall of each end recess or end recess. 4. The item according to one of paragraphs. 1-3, containing at least one traction connecting link (40, 42, 44, 47), interacting with means for pulling the element in a direction parallel to the base. 5. The element according to claim 4, in which the traction connecting link has an inner part at least partially perforated. 6. The item according to one of paragraphs. 1-3, 5, having in the plane perpendicular to the base, essentially triangular shape. 7. The element according to claim 4, having in the plane perpendicular to the base, essentially triangular shape. 8. The item according to one of paragraphs. 1-3, 5, 7, in which the base is flat, or forming a section of the cylinder (305 '). 9. The element according to claim 4, in which the base is flat, or forming a section of the cylinder (305 '). 10. The element according to claim 6, in which the base is flat, or forming a section of the cylinder (305 '). 11. The item according to one of paragraphs. 1-3, 5, 7, 9, 10, in which the side surfaces (303, 303 ') are flat or have a wavy shape. 12. The element according to claim 4, in which the side surfaces (303, 303 ') are flat or have a wavy shape. 13. The element according to claim 6, in which the side surfaces (303, 303 ') are flat or have a wavy shape. 14. The element according to claim 8, in which the side surfaces (303, 303 ') are flat or have a wavy shape. 15. Element (60, 62, 64, 66, 68, 70) of a rack for storing nuclear fuel, containing: - the first set of heat transfer elements according to one of paragraphs. 1-14, located between two walls, with each side surface of the element opposite the side surface of the adjacent heat transfer element, and the bases of the various absorbing elements alternately rotate in the direction of one side of the kit, then in the direction of the other, with each heat transfer element connected to adjacent elements by means for pulling the element in a direction parallel to the base, - means (21) for the impact of traction on the site of heat transfer elements. 16. The element (60, 62, 64, 66, 68, 70) for storage according to claim 15, in which each side surface of the element: - is in contact with the side surface of the heat transfer element when the traction does not act on the node of the heat transfer elements, - is located at a non-zero distance from the specified side surface and essentially parallel to it when the pulling force acts on the node of the heat transfer elements. 17. The storage element (60, 62, 64, 66, 68, 70) according to claim 15 or 16, wherein the set of heat transfer elements has a height (h) less than the total height of the rack element. 18. Element (60, 62, 64, 66, 68, 70) for storage according to one of paragraphs. 15 or 16, further comprising at least one second set of heat transfer elements according to one of claims. 1-14 located in the area (200, 200 '), separated from the first set by a continuous section of material. 19. The storage element (60, 62, 64, 66, 68, 70) according to claim 17, further comprising at least one second set of heat transfer elements according to one of claims. 1-14 located in the area (200, 200 '), separated from the first set by a continuous section of material. 20. Rack for storing nuclear fuel containing many elements of the rack for storing fuel in one of the paragraphs. 15-19, located so as to delimit the Central cavity (17), essentially cylindrical, square, rectangular, or hexagonal in a plane perpendicular to the direction of traction of each rack. 21. A container for storing and / or transporting nuclear fuel, comprising at least one fuel storage rack according to claim 20, surrounded by a peripheral protective layer (54) for absorbing gamma radiation, and a peripheral protective layer (52) for slowing down neutrons . 22. The container for storing nuclear fuel according to claim 21, containing several racks, the number of which is in the range from 2 to 12. 23. A method for storing and / or transporting rods (15) of nuclear fuel, comprising the following steps, in which: - act by pulling force on the heat transfer elements of the fuel storage rack according to claim 20, in order to transfer them from the initial position to the upper position and create a gap (27, 29) between each heat transfer element and two planes (22, 24) that define the hot and cold surface - introduce one or more fuel rods into the Central cavity (17), - release the heat transfer elements in order to return them to their original position, in which the base of each heat transfer element is installed with the possibility of contact with one or the other of the two hot and cold walls (22, 24). 24. The method according to p. 23, containing the preliminary step of introducing the rack for storing fuel into the pool (12) and the subsequent step of removing from the pool the rack loaded with fuel rods. 25. The method according to p. 23 or 24, in which each fuel rod has a power of at least equal to 7 kW or 8 kW.

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