JP6239586B2 - Method and mobile device for reducing thermal resistance between two solids - Google Patents

Description

  The present invention relates to a storage rack for a nuclear fuel assembly comprised of a plurality of elongated adjacent cells into which a fuel assembly or optionally several fuel assembly rods may be introduced.

  The storage rack (also known as a storage basket) is for storage and / or transportation of the fuel assembly in packages that are optionally shielded or unshielded. They are suitable for spent fuel, but can also be used for unused fuel. They can be used in a dry or wet medium, for example when storing fuel in a pool or when introducing them into a transport or storage package.

  The solution provided for the need for various functions (radiation protection, impact resistance, fire resistance, etc.) of the cask for transporting the fuel assembly is a stack of diverse materials. When high power is discharged, the presence of the necessary clearance for the stack results in a limit to the internal temperature.

  For issues related to the safety and transport of radioactive materials, see “La surete des transports de matieres radioactives” (Safe transport of radioactive materials), by B. Lenail, Revue Generale Nucleaire n ° 1 2005, “Conception, fabrication et essais des emballages pour le transport des matieres radioactives ”(Design, construction and testing of packages for transporting radioactive materials), by BC Bernardo, IAEA Bulletin Vol. 21, n ° 6, or described in EP 0 752 151 Yes.

  In general, fuel assemblies are transported dry in a cask containing up to 12 (or more) assemblies. These shipping packages are approved by the relevant French, British and Japanese authorities and meet the standards imposed by the IAEA regulations for Type B packages. This type of cask, which has been used for about 40 years, is based on the principle that the package is inherently equipped with the ability to prevent any release of radioactivity (double barrier, fire behavior, etc.).

As shown in FIG. 1, the cask has a long length from the outside to the inside.
An outer zone 2, which can be provided with cooling fins 4,
-Neutron absorption layer 6,
・ Steel collar 8,
As well as a storage rack 10 for a nuclear fuel assembly that includes one or more elongated adjacent cells 12 into which fuel assemblies or optionally several fuel assembly rods may be introduced.
Is provided.

Various types of racks having a cell structure for nuclear fuel assemblies are known. They generally guarantee the following three functions.
In the presence of water in a series of assemblies stored in a rack, either in a dry state or in a liquid or gaseous state (this water may contain neutron absorbing compounds based on eg boron) • Control of criticality at the time • Sufficient mechanical strength to fulfill the following two objectives: (i) To ensure the maintenance of the rack geometry with the assembly, and during normal use (handling, transportation, etc.) Avoid fuel rod degradation (ii) ensure critical control by maintaining rack geometry in accordance with current regulations, even in accidental situations (severe impacts or drops);
Heat transfer to exhaust heat released in the case of used assemblies

  The rack is also optionally designed to provide a complement that shields radiation.

The rack is generally composed of a combination of several materials, each of which fulfills at least one of the three functions listed above. The main materials used are generally as follows.
Stainless steel or aluminum (or their alloys) for mechanical strength function
-Aluminum or copper (or their alloys) for heat transfer function
Boron compounds (eg, B4C-based frit), copper alloys, boron-containing aluminum or stainless steel for critical control functions

  From the perspective of the cask's thermal performance, the discharge of internal power and the fire resistance for 30 minutes at 800 ° C. are currently based on materials (steel collars, aluminum racks, etc.) and their performance (the “composite” that the fins traverse, It is solved by adapting the protection of the connection part).

  Especially in the case of assembly realization problems, this system with the connection of different layers in the radial direction particularly requires that the assembly or rack be introduced into the cask more easily, so that between the different layers, in particular the assembly. Clearance is provided at the boundary between the rack and the collar as well as between the cavity and the cavity. These clearances, for example about 5 mm and 2 mm, can be disadvantageous to the need for heat transfer.

  The presence of these clearances, particularly when exhausting high power, results in high thermal resistance, resulting in high thermal gradients, which are the highest internal temperatures when it is desired to increase the maximum allowable power level. (Which also depends on the material, the burning rate, etc.).

  At present, the transport is performed under nitrogen, but a more conductive gas (helium) can be used, and in this case, the power level is low in the transport of PWR (Pressurized Water Reactor) fuel. , Internal and external clearances of 5 mm and 2 mm, respectively, are sufficient.

  However, there are problems with enabling transport of higher power fuels (eg, MOX fuel type, or alternatively future actinide assemblies).

  Therefore, the possibility of good discharge of heat to the outside without completely exceeding the unacceptable internal temperature is an important issue in the future.

  In this case, the total power transmitted is not so much a problem, but rather the thermal gradient caused by the presence of the aforementioned clearances.

Therefore, by using the present state technology, the maximum output of the assembly to be transported under helium, would be reduced to 4.5kW if not exceeded when not exceeding 450 ° C. 2.5 kW, and 650 ° C. On the other hand, even higher power transport may be required.

  WO 2011/161233 describes a system that makes it possible to reduce the thermal contact resistance due to external clearance. In this system, the four parts of the rack are in contact with the steel collar. The result is a simple system with improved radial transmission, but no known internal clearance. Therefore, the gain is small with respect to the output that can be discharged.

  Therefore, there is also a problem with the clearance (between the assembly and the rack) called internal clearance.

  In fact, reconsidering the case of a cask with conventional clearances (eg, 5 mm internal and 2 mm external) where the assembly is under helium, the power that can be discharged at 650 ° C. is 6.3 kW. For example, according to the teaching of WO 2011/161233, if the external clearance is eliminated, the dischargeable output will be 6.75 kW, i.e. the dischargeable output will increase by 8%. If two clearances are lost, the output will be 8.75 (ie an increase of + 40%). However, in this technique, the surface located in contact is important (about ¼ of the outer surface of the rack), and so there is only one generator or simply as long as there are no completely unacceptable manufacturing tolerances. Contact can only occur in some zones.

  As a result, the clearance inside the storage or transport cask, whose thickness results in significant contact resistance as well as an upper limit for thermal criteria, will likely adjust the dischargeable power during transportation of the fuel assembly.

  The challenge is therefore to improve the heat exchange inside the transport cask in order to reduce the temperature that can be reached in the nominal specification.

  A solution to this limitation is provided herein.

  First, a heat transfer element for a nuclear fuel storage rack, which is substantially prism-shaped and has three main surfaces including a bottom surface and two second planes and two side surfaces, A heat transfer element is described which is made of material and has means on its side for pulling the element in a direction parallel to the bottom surface.

  Each transfer element is made of a material that transfers heat, and thus has good thermal conductivity, for example, made of a metallic material such as aluminum or copper.

  The means for pulling the element may be located on the side. For example, each of these sides comprises at least two pins or two protrusions.

  In a variant, the means for pulling the element may comprise notches or side recesses formed in the element, where each recess is in one of the second planes, as well as optional It also exists on the corresponding side. Each notch wall comprises means such as at least two pins or two protrusions.

  Such an element may comprise at least one traction link, for example with or without internal cutouts, cooperating with means for pulling the element in a direction parallel to the bottom surface.

  Such an element has a substantially triangular shape in a plane perpendicular to the bottom surface.

  The bottom surface may be planar or may have at least one curvature about an axis that is substantially parallel to the direction of traction.

Therefore, the nuclear fuel storage rack element is
Each second plane of the element faces the second plane of an adjacent transfer element so that the bottom face of the different transfer element is directed towards one side of the stack and then towards the other side; A first stack of transfer elements of the type described above, alternately inverted, each transfer element being connected to its adjacent transfer element by means for pulling the element in a direction parallel to the bottom surface; ,
Means for exerting traction on the assembly of transmission elements.

In such storage rack elements, each second plane of the element is
If the traction is not exerted on the assembly of transmission elements, especially when pressure is applied to the assembly of elements, the second plane of the adjacent transmission element may be contacted;
As well as away from the second plane of the adjacent transmission element when traction is exerted on the assembly of transmission elements.

  The stack of transmission elements may have a height (h) that is less than the total height of the rack elements. In this case, the remaining part of the rack is made up of transmission material stacked above and below the transmission element described above. The height h is substantially equal to or close to the length at which the fuel element generates heat.

  The rack element may further include at least one second stack of transmission elements as described above, disposed in a zone spaced from the first stack by a continuous portion of material. This second stack plays a mechanical role, but plays little thermal role.

  The basic nuclear fuel storage rack is arranged to delimit a substantially square, rectangular or hexagonal central cavity in a plane perpendicular to the direction of traction of each rack, depending on the shape of the assembly in question. A plurality of storage rack elements of the type described above may be included.

  Thus, the cask may be configured for storage and / or transport of nuclear fuel and includes a basic storage rack of the type described above, in which case the rack is a perimeter protection for absorbing gamma radiation. Surrounded by a layer and a peripheral protective layer for moderating neutrons.

  It is also possible to configure a cask for the storage and / or transport of nuclear fuel, including several, for example 2-12 basic storage racks, where each basic rack is as described above Of the type.

  The basic rack is located in a fixed rack itself surrounded by a plurality of transmission elements of the type described above that ensure efficient thermal contact with the surrounding layers.

The invention also relates to a method for storing and / or transporting nuclear fuel rods comprising the following steps.
-By using traction on the rack elements of the storage rack as described above, they are moved from the initial state to the raised state, between each transmission element and each of the hot and cold walls. Creating clearance; introducing one or more assemblies into the central cavity; releasing the traction such that the bottom surface of each transmission element contacts one or the other of the hot and cold walls. Step of returning to the initial position to be positioned During this step, the action of the attractive force may be sufficient to return the element to the initial position due to their own weight. Even if the rack is in a state other than a portrait orientation, for example, in a landscape orientation during transportation, additional pressure is optionally applied to allow the element to remain in this state. Also good.

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

  In the present invention, means are applied to apply a force to the stack of transmission elements, which allows the rack to change its inner and outer radii, so that the space between the assembly and the rack And it also makes it possible to reduce the space between the rack and the external environment, for example the collar.

  Thus, the rack adapts its shape to accommodate the potential deformation of the assembly.

  The present invention thus maintains important clearances during the introduction of loads and then allows them to be reabsorbed prior to subsequent operations such as handling or shipping.

Especially for transport of high power level assemblies, the system allows to reduce or even eliminate contact thermal resistance (which is directly related to the gas gap in clearance and the thermal conductivity of the gas). However, the system also has another advantage:
• The rack covers the assembly to allow mechanical strength during transport. • No need to introduce a wedge as it did previously. • This rack adapts its shape, Adapt to potential longitudinal deformations in the assembly-Reduce the current machining cost of the rack-In certain cases (especially in the case of assemblies) the rack helium can be replaced with dry air or nitrogen

  Compared to the technique described in US Pat. No. 6,057,089, where the contact is conceived to occur only in one generator or only in several zones, the present invention described herein By increasing the contact point, it is possible to have a larger contact area. The smaller the transmission element, the better the fit to the shape.

  The present invention makes it possible to minimize internal and external clearances in the rack, which makes it possible to carry out storage and transport of certain assemblies, whose power level (P> 8 kW) is currently released Greater than what is being done. Since not only a single assembly but also multiple assemblies can be realized, the present invention also allows optimization of the number of assemblies transported.

  In the following, embodiments of the present invention will be described by way of non-limiting examples with reference to the accompanying drawings.

The exploded three-dimensional view of the cask of the well-known structure already demonstrated. Fig. 4 represents various views of the transfer element as described. Fig. 4 represents various views of the transfer element as described. Fig. 4 represents various views of the transfer element as described. Fig. 4 represents various views of the transfer element as described. Fig. 4 represents various views of the transfer element as described. Fig. 4 represents various views of the transfer element as described. Represents two elements connected by links and their relative motion. Represents two elements connected by links and their relative motion. Represents two elements connected by links and their relative motion. Various diagrams of transmission elements. Various diagrams of transmission elements. Various diagrams of transmission elements. Various diagrams of transmission elements. Represents a stack of transmission elements connected by links and their relative motion. Represents a stack of transmission elements connected by links and their relative motion. The schematic of the rack of the open state. Schematic of the rack in the closed state. Illustration of a rack containing the assembly. Illustration of a rack containing the assembly. Introducing the assembly into the rack. Introducing the assembly into the rack. Introducing the assembly into the rack. Introducing the assembly into the rack. Introducing the assembly into the rack. 1 is a top view of a system containing at least one rack, one steel collar, and one resin that houses one assembly. FIG. FIG. 3 is a top view of a system that houses several assemblies, including at least one rack, one steel collar, and one resin that houses multiple assemblies. It represents the highest possible temperature discharge as a function of internal and external clearances and the output of one assembly. It represents the highest possible temperature discharge as a function of the internal and external clearances and the output of the seven assemblies. It represents the highest possible temperature discharge as a function of the internal and external clearances and the output of the 12 assemblies.

  Initially, FIG. 2A (side view, cross-section along plane AA ′ or xOz in FIG. 2B), representing a stack of heat transfer elements 30, 32, 34, 36 of rack system 20 according to certain embodiments of the invention and Reference is made to 2B (top view, cross-section along plane BB ′ or xOy in FIG. 2A).

  In FIG. 2A it can be seen that the various transfer elements are stacked along the direction Oz of the cube corner Oxyz. Also shown in this figure and FIG. 2B are two walls 22, 24, which are the hot and cold walls of the environment in which the stack is placed, respectively (the wall 22 called hot wall is hot The side of the assembly, located inside the rack, while the wall 24, called the cold wall, is the side of the surrounding environment outside the rack). Outside this environment, reference numerals 22 and 24 are two planes that delimit the side extension of the stack along Ox when they are closed or lowered, as will be explained later. Yes, in the following, reference is made to two walls, which can also be meant as two planes.

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

  Each element of the stack is substantially prismatic, as shown in FIG. 2C for the individual element 30 embodiment. The other elements in FIG. 2A are the same or similar to it, and for this reason for all parts of these other elements (similar or identical to those described in FIG. 2C) Will not be described in detail.

  More specifically, the elements represented in FIG. 2C are substantially pentahedral or triangular prisms, in which case the three rectangular surfaces 303, 303 ′, 305 are two of them and with respect to the axis Oy. Adjacent to two triangular faces 301, 301 ′ that are substantially perpendicular and not adjacent to each other.

  The element also has a bottom surface 305, which in this embodiment is planar and parallel to a ridge 307 extending along the axis Oy of the cube corner Oxyz.

  Depending on the particular embodiment shown in FIG. 2D, the sides and corners may be truncated, and the expression “ridge” or “top” will still be used.

  The two surfaces 303, 303 ′ extend between the ridge line portion 307 or the topmost portion and the bottom surface 305, and the surfaces may be referred to as “upper surface” and “lower surface”, respectively, for convenience. . In the illustrated embodiment, these planes are planar, but they may have other shapes, for example, they contact the corresponding corrugations or undulations in the plane of adjacent elements Or may have corrugations or undulations intended to be combined therewith.

  The element is limited by two walls or sides 301, 301 'laterally along the axis Oy. In the example of this embodiment, these two latter walls are substantially perpendicular to the bottom surface 305 and substantially parallel to the plane xOz. In the variant represented diagrammatically in the top views of FIGS. 3A and 3B, the sidewalls (here 341, 341 ′, the element represented is the element 34) are inclined, and thus the axes Ox and Oy Intersect with both. Each of these transfer elements has a substantially triangular shape in the plane zOx, each triangle having one large side and two small sides, preferably of substantially the same length, The triangle itself is substantially an isosceles triangle. More preferably, the three sides are truncated at their ends, as shown in FIG. 2D or FIGS. In the plane zOx, each strictly no longer has a substantially triangular shape, but rather has a hexagon in which three long sides and three short sides are arranged alternately.

  The height of this triangle, or the distance between the ridge 307 or the top and the bottom surface 305 is shorter than the distance between the two walls 22, 24. Thus, if the element is positioned as shown in FIG. 2A, the distance between the top 307 of the element and its bottom surface 305 is between this element and each of the two walls 22,24. The clearances 27 and 29 can be held. When the device is in a “closed” state (FIGS. 4C, 6B, and 7B), zones 270, 270 ', 290, 290' are left unfilled by some of the transfer elements. These clearances are dimensions that allow avoiding any contact between the transmission element and the adjacent second row of elements (eg, between elements 30 and 34, element 32 in FIG. 2A). And all contacts such as between 36 and 36 are avoided). Since heat is transferred through contact that occurs between adjacent elements, for example, between elements 30 and 32, between elements 32 and 34, between elements 34 and 36, these zones are No problem from a thermal point of view These zones are interleaved toward each of the walls 22, 24, whether adjacent to the gas, and as a result, are adiabatic, the adjacent elements have much more heat conduction. These thermal effects are negligible because they are connected via parallel sex passages.

  In FIG. 2A, the bottom surfaces 325, 345, 365 and their ridges 327, 347, 367 of other elements 32, 34, 36 can be seen, similar to that presented in FIG. 2C.

  The various elements 30, 32, 34, 36 are stacked as shown in FIG. 2A, and the lower (respectively upper) plane of the first element is below this first element along the axis Oz (respectively , Above) is in contact with or opposite the upper (respectively lower) plane of the immediately adjacent second element.

  The large sides of the stacked elements are arranged alternately towards the walls 24 and 22. In other words, the transmission element 30 has a bottom surface facing the wall 24, while the bottom surface of an adjacent element faces the wall 22.

  When the stack is closed or lowered, two adjacent elements can press each other along interface 40 via one of their lower and upper planes. This makes an acute angle A (eg 30 ° -60 °, eg again equal to or close to 45 °) relative to a straight line parallel to the axis Ox or perpendicular to the walls 22, 24. It has the shape of a straight line to be formed.

  In the embodiment described above, the surfaces 305, 325, etc. are flat.

  In a variant, this surface may have a curvature, for example, it is shown in FIGS. 3B, 5C and 5D by surfaces 345 ′ (element 34, FIG. 3B) and 305 ′ (element 30, FIGS. 5C and 5D). As can be seen, it may consist of part of a cylinder, in which case the axis of the cylinder is parallel to the direction of traction of the entire stack. Since the contact between adjacent planes in two adjacent elements remains the same as described above, the thermal effect of the entire stack is affected when the stack is closed or lowered. Not receive. The cross section of this element along the plane zOx is also a triangle similar to the shape of FIG. 2D, and the base 305 of the triangle is a straight line. With the stack lowered, the cylindrical portion of the walls 345 ′, 305 ′ contacts the outer wall or outer plane 24. Such a curvature may be useful for encasing the shape of a cylinder, and the planes or walls 22 and 24 are often cylindrical along an axis parallel to the direction of traction (eg, FIG. (See structures 10, 10b).

  As can be seen from FIGS. 2A-2C, 3A-3B, and FIGS. 5A-5D, each of the side surfaces 301, 301 ′, 321, 321 ′, 341, 341 ′, 361, 361 ′ of each element has two Protrusions 30 ′, 30 ″, 32 ′, 32 ″, 34 ′, 34 ″, 36 ′, 36 ″, each protrusion being one of the lower and upper planes of the corresponding element In the vicinity. Two protrusions on the same side are substantially parallel to the bottom surface of the same element, or along the ridge 305 in the cross-sectional view of FIG. 2D (or alternatively, along the direction of traction). Are aligned. Each protrusion has a substantially cylindrical shape, and the axis of the cylinder is oriented substantially perpendicular to the side surface on which the protrusion is located.

  Connecting rods or links 40, 42, 44, 46 connect to the two nearest projections of two adjacent elements. This link will thus form the maximum distance that can exist between the two upper and lower planes of the two nearest neighboring elements (if they are not in contact). The link also determines the maximum slidable amplitude of one element plane relative to the opposing plane of an adjacent element.

  This link and the corresponding protrusion are of interest in a direction parallel or substantially parallel to the axis Oz and / or to the bottom intersection 305 with the plane zOx (in the case of FIGS. 2D and 3B). Allows application of traction to elements. In the case of FIG. 4A, the force applied to each face also has a component along Ox, but in the traction state (FIG. 4A), the element is blocked and is irrelevant to the result. As a result, the resulting force is again along the axis Oz. Thus, as can be seen from FIG. 2A, and as explained below, a force F in the direction Oz is applied or transmitted to each element, in which case their bottom surfaces have corresponding high temperatures to which they are directed. It remains parallel to the wall or cold wall. As long as each element is arranged along the axis Oz between two other elements, each protrusion receives an upward traction force but also receives the weight of the element located below it .

  Thus, when the rack is stacked and aligned between two walls, such as hot and cold walls 22, 24, the relative displacement of the components of the rack is ensured.

  These means allow different elements to be separated from each of its neighboring elements, resulting in a gap e between the two sides of the two neighboring elements, in which case these two sides are They remain parallel to each other. Similarly, when different elements are separated, their positioning occurs such that the spaces or clearances 27, 29 are aligned between the different elements and the walls 22, 24.

  The link has, for example, the shape shown in FIG. 2A or 6A, which is vertically long and has a central opening, in which case the central opening is also vertically long. The maximum amplitude of this opening, in other words, the distance between the inner surfaces of the two small sides of the link, is the external generator of the two adjacent protrusions of the two immediately adjacent transfer elements in the stack. Equal to the desired maximum distance between. The link and its side openings allow the two adjacent elements to slide relative to each other while keeping the immediately adjacent planes of the two adjacent elements in contact. For example, each link has two adjacent elements 301 and 321, 321 and 341, 341 and 361. . . It can be seen from FIG. 2A that it has a central opening that allows them to be spaced apart so as to keep adjacent sides parallel to each other at a distance e. This distance or this gap makes it possible to put the transmission element in the “lifted” state in order to allow the introduction of the rod of the element into the rack. In the lowered state, the sides of adjacent elements are in contact with each other, as shown in FIGS. 6B and 7B. The link is then released, in which case the distance between two adjacent protrusions in the two adjacent elements is less than the maximum amplitude determined by the internal opening of each link.

  Another embodiment of the link is depicted in FIGS. 4A-4C, where each link 47 has two openings, each of which has a ring of the transmission element. It makes it possible to accommodate one protrusion 30 ″, 32 ″. One of these openings around the protrusion 30 "allows only rotational movement of the link around this protrusion, but does not allow translational movement, whereas the other opening The part allows a rotational movement of the link around the protrusion 32 "and a translational movement of the element 32, i.e. the corresponding opening is near the center of the link (in the direction of its length) on its side It extends longer to the inner end of one of the ends.

The distance between two openings and the length of the second opening is such that the two adjacent transfer elements are
A state called initial (FIG. 4A) (in this state, two adjacent surfaces of two adjacent elements are in contact, and clearances 27, 29 are the respective bottom surfaces and walls of the elements or the bottom surfaces are surfaces. Between the walls 22 and 24)
To an intermediate state (FIG. 4B) (in this state, adjacent side surfaces of two adjacent elements move away from each other the desired distance and each bottom surface approaches the corresponding wall 22, 24),
Then "covered" state (Fig. 4C) (in this state two adjacent sides touch each other or press each other, the bottom of each element pressed against the corresponding wall 22, 24) Selected to be able to move on.

  In this movement, the end of the link undergoes a substantially circular movement under the action of the means 21 (FIG. 7A), such that the center of the circle is the center of the link.

  Another embodiment of a system of connections between adjacent elements is shown in FIGS. 5A-5D, where FIGS. 5A-5B correspond to the embodiment of a planar wall-shaped bottom surface 305, and FIG. ~ 5D corresponds to an embodiment in which the bottom surface 305 'has the shape of a part of a cylinder.

This time, the represented element 30 is
Two side notches or side recesses 203, 204 present in the upper plane 303 and optionally in the corresponding side surfaces 301 ′, 301 (as in FIGS. 5A-5D);
It has two side notches or side recesses 205, 206 that are present on the lower plane 303 ′ and optionally on the corresponding side surfaces 301 ′, 301.

  Here, as already explained above, the inner wall of each side notch is formed with holes 203 ′, 204 ′ in which the protrusions can be positioned, the holes being connected to the end of the connecting rod or link It is intended to work together.

  Thus, the walls of each notch are intended to comprise means for connecting each element, for example by two links, as described above, for example at least one pin or one protrusion. Each notch has a volume sufficient to accommodate the end portion of the corresponding link.

  As shown in FIG. 7A, the traction means or mechanism 21 is positioned on one side of the rack above or below the rack. Means including, for example, one or more rods 210 and / or one or more jacks are connected to the end elements of the stack of elements in order to convey the ascent or descent movement along the axis Oz to the assembly of elements. Is done. The means 21 may allow pressure to be applied to the entire stack when it is in a closed or lowered state.

  When trying to introduce the assembly into the rack, an upward force is applied parallel to the axis Oz and each of the walls 22, 24, as shown schematically by arrows F in FIGS. 2A, 6A, and 7A. It is done.

  Then, as described above with reference to FIGS. 4A-4C, 6A-6B, and 7A-7B, each element of the rack is separated from the adjacent elements. This movement releases clearances 27, 29, 27 ', 29' (FIGS. 2A, 6A, and 7A) in the radial direction.

  When the assembly is in place, a downward force (still along the axis Oz) is applied, or alternatively gravity that pulls the transfer element downward, so that the planes of the transfer elements come into contact with each other. Thus, the internal clearance and the external clearance disappear (as in FIGS. 4C, 6B, and 7B). At the end of this phase, again to reduce the thermal resistance at the solid-solid interface of each pair of adjacent elements, regardless of the state of the cask, including the sideways state, and to ensure the mechanical strength of the assembly , A pressing force can be applied to the stack of elements.

  As can be seen from the top view of FIGS. 2B and 3 and the perspective view of FIG. 2C, each transmission element extends over a limited length L, such as 100 mm to 200 mm or 500 mm, which length is It is selected depending on the surface quality of the element and the desired heat transfer quality. L may be an extended length of an arc, particularly in the case of a bottom surface such as the bottom surface 345 'of FIG. 3B.

  As a result, an assembly having a generally cylindrical shape will be surrounded by a plurality of n rack elements arranged in a substantially circular shape, with each rack element covering a portion of approximately 360 ° / n. Such an arrangement is depicted in FIGS. 8A and 8B, for example, in the case of a hexagonal assembly, each rack element 60, 62, 64, 66, 68, 70 covers a portion of about 60 °. Reference numerals 620 to 626 are individual elements of the two rack elements 62. The two end elements 620 and 626 are truncated to obtain a plane at the two ends of the stack.

  In these FIGS. 8A and 8B, the system is represented in three dimensions, where a vertical row of transfer elements is omitted (or one rack element is omitted for better visualization). Have been). The rack element assembly is arranged to form an internal hexagonal opening 17 into which fuel elements can be introduced.

  FIG. 8A corresponds to an open situation where the transfer elements are spaced apart from each other as shown in FIGS. 2A and 4A. Therefore, a clearance that may be important is formed between the load in the center of the rack and the inner wall of the rack.

  FIG. 8B corresponds to a closed situation where adjacent transfer elements are in contact with each other as shown in FIGS. 4C and 6B. In this state, any clearance previously found between the load and the inner surface of the rack is lost.

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

  In this embodiment, the existence of a zone with no transfer element between adjacent cells or between two rack elements (eg 62 and 64) can be described. However, for the same reasons given above for the remaining clearances 270, 290, this has no effect from the point of view of heat conduction, and in fact, from the point of view of heat, heat is in the higher conductivity zone. It travels "near" (the ratio of heat transfer of aluminum to helium is 1000 and about 6000 for air).

  When the system is in place (FIGS. 7B, 8B), the radial heat output is improved and, as a result, the radial thermal gradient is significantly reduced.

Thus, by using a storage method using a rack as described above, limits published in previously 2.5kW (Tmax <450 ℃) and 4.5kW (Tmax <650 ℃), respectively 3.5 kW and 6.5 kW. Thus, when transporting the assembly, it can reach 5 kW for Tmax <450 ° C. and 9 kW for Tmax <650 ° C.

The embodiment shown in FIGS. 8A and 8B shows a rack (only one row of elements has been omitted due to drawing readability issues) and a hexagonal tube 15. However, it is also possible to introduce several assemblies, as shown in FIG. 10B representing the top view, in which case the rack is
A plurality of basic racks 100 to 106;
Fixed component 55 (a stack of disks made of a thermally conductive material, e.g. made of aluminum, each disk has an appropriate opening to allow the rack to pass to the desired position And)
A rack element crown 550 (each element is of the type according to the invention, as already presented above).

  The rack constituted thereby is arranged inside the cask, and the assembly is surrounded by a steel collar 54 and a resin layer 52. The assembly may include heat exhaust fins 56, which are fins protruding outward in FIG. 10C. These symbols 52, 54 are also found in FIG. 10A for a single rack.

  Thus, the assembly comprising the cask may include at least one basic rack as described above, but also an assembly of absorber layers, for example a layer 54 for absorbing gamma radiation (which is forged And layer 52 (which contains a lot of hydrogen) for moderating neutrons and the like.

  The base rack may have the structure described above over its entire height.

  It may have such a structure at a limited height h, for example about 1 m, corresponding to the output to be discharged, as seen for example in FIG. 9A, ie an assembly of mobile elements 20 extends at the limited height of each wall of the rack (which is the height at which heat exchange takes place), and the rest can be composed of two isomorphic parts 20 ′, 20 ″. I understand.

  In a variation, as shown in FIG. 9B, some elements may be placed in a portion where there is little or no heat exchange, such as zones 200, 200 '. These elements function as already described above, but they have only a mechanical protection role and play no or little role from a thermal point of view. In contrast, one movable element assembly 20 has both a thermal role and a mechanical role at the same time. Zones 200 ', 200 are spaced from the zone or portion 20 by a uniform, continuous portion of material that does not include a transmission element as described above.

  9A-9E represent the process of loading the fuel into the device according to the invention.

  Initially (FIG. 9A), the assembly does not yet contain fuel elements, is immersed in the pool 120, and the covers 130 of the various parts are opened.

  Then (FIG. 9B), pulling of the assembly of elements by means 21 pulls up the transmission element of the rack, as already explained above. Thus, their maintenance is released and a clearance is introduced between the bottom surface of each element and the surfaces 22, 24 to which they face (see description given above).

  The rack is maintained in this raised state and the fuel element 15 (see FIG. 9C) can be introduced into the central opening 17.

  Then, as shown in FIG. 9D, to position the transmission elements in contact with each other without leaving any clearance between the bottom surface and the walls of these elements, The pressing force is reversed.

  Finally, the covers are returned to their initial state and the assembly is closed again (see FIG. 9E).

  The assembly can then be lifted from the pool for drainage.

In the following, the numerical results are presented for a cask carrying 1, 7, or 12 assemblies. These cask, they one, two, or depending on whether the transport seven assemblies, TC1, TC2, or TC12 and Ru named.

If 650 ° C is the limit, the output per assembly will be 4 for standard clearance . 6 kW ( TC12) to 6 . Increase to 3 kW ( TC1). By eliminating these clearances, 6 . 6 k W or et al 8. It would be possible to obtain 8 kW.

  In the following, the gain made with respect to the output that can be discharged is evaluated for a given temperature criterion for the case of an assembly with minor actinides.

The geometric structure selected for the cask is
- Figure 10B that are represented in the top view of (in this geometry, the outer diameter of the layer 550 is the same as the outer diameter of the rack in use today, geometry of the remainder is not at all changed No. 54 indicates a steel collar),
- or, that are represented in the top view of FIG. 10A (in this geometry, the outer diameter of the outer diameter D _e and aluminum rack 100 of the resin layer 52 is held),
It is a multi-layered geometric structure.

  Three of these cases were considered: a single assembly, seven assemblies, and twelve assemblies.

For the case of a single assembly, a study of the effect of parameter Tmax and clearance results in the following results as shown in FIG.
・ Curve I corresponding to two clearances of 1 mm each
Curve II corresponding to one internal clearance of 5 mm and one external clearance of 1 mm
Curve III corresponding to one internal clearance of 5 mm and one external clearance of 2 mm
・ Curve IV corresponding to two clearances of 5 mm
A curve V corresponding to two clearances of 0 mm (in other words contact obtained according to the invention)
Is obtained.

For example, for a maximum value of 650 ° C .:
-In the case of curve I, 8 kW is discharged,
In the standard case (curve III), about 6.3 kW is discharged,
When the clearance is lost (curve V), the optimum value is 8.7 kW.

The case of 7 assemblies was considered during the parametric study only for the standard case and when the clearance was zero (other cases are between these two limited cases). A study of the effect of the parameter Tmax and clearance results in the following results shown in FIG.
Curve I ′ corresponding to one internal clearance of 5 mm and one external clearance of 1 mm; for this standard, 5.5 kW per assembly, ie a total output of 39 kW, can be discharged and the resin is 70 ° C. Having a temperature of ~ 88 ° C,
・ Curve II 'corresponding to two clearances of 0 mm
Is obtained.

  Again, it can be seen that the reduction in clearance makes it possible to increase the power that can be discharged at a given maximum temperature in the center.

The case of 12 assemblies was considered during the parametric study only for the standard and zero clearance cases (other cases are between these two limited cases). A study of the effect of parameter Tmax and clearance showed the following results shown in FIG. 13:
A curve I ″ corresponding to one internal clearance of 5 mm and one external clearance of 1 mm; in this standard case, 4.5 kW per assembly, ie a total output of 54 kW, can be discharged, the central temperature Is less than 650 ° C.,
・ Curve II corresponding to two clearances of 0 mm
Is obtained.

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

  The result of FIG. 13 leads to the same conclusion, i.e. the reduction in clearance makes it possible to increase the dischargeable power at a given maximum temperature in the middle.

  Table II below summarizes the dischargeable power for the above three configurations and two different maximum temperatures (450 ° C. and 650 ° C.). The dischargeable output is shown for each of these cases and is underlined when the clearance is zero.

  The invention applies to the field of storage and / or transport of high levels of radioactive material, in particular fourth generation high level fuels, for example assemblies also filled with minor actinides.

Claims (18)

Column-shaped or block-shaped heat transfer elements (30, 32, 34, 36) for nuclear fuel storage racks,
It has three main surfaces (303, 303 ′, 305, 325, 345, 365) and two side surfaces (301, 301 ′) including a bottom surface and two second surfaces, and the column shape or block shape is Including three main surfaces including at least the bottom surface and the two second surfaces on a surface to be formed;
Made of thermally conductive material,
The two sides are
Means for pulling the heat transfer element in a pulling direction parallel to the bottom surface and perpendicular to the extending direction of the columnar or block shape;
The means for pulling the heat transfer element is from an initial position where the bottom surface of the heat transfer element is in contact with a wall called a hot wall or a cold wall, and the bottom surface of the heat transfer element is the hot wall or a low temperature. To transfer the heat transfer element to a raised state facing the wall called the wall and separated from the wall called the hot or cold wall by a space or clearance (27, 29) and vice versa A heat transfer element provided for. The means for pulling the element comprises:
Is located on the side,
Or side recesses (203, 204, 205, 206) formed in the element, each recess being in one of the second planes and optionally in the corresponding side surface (303) , With side notches or side recesses,
The element of claim 1.   The means for pulling the element includes at least two pins or two protrusions (30 ', 30 ", 32', 32" located on each side or on the wall of each side notch or side recess. 34 ', 34 ", 36', 36").   4. At least one traction link (40, 42, 44, 47) cooperating with the means for pulling the element in a direction parallel to the bottom surface. Listed elements.   The element according to claim 1, wherein the tow link has an opening cut out at least partially.   The element according to claim 1, wherein each of the two side surfaces is formed in a triangular shape.   7. Element according to any one of the preceding claims, wherein the bottom surface is planar, forms part of a cylinder (305 ') or has a curvature.   8. Element according to any one of the preceding claims, wherein the second surface (303, 303 ') is planar or comprises wavy undulations. 9. A first stack of transfer elements according to any one of the preceding claims, disposed between the two walls, wherein each second surface of the element is a second of adjacent transfer elements. Facing the surface, the bottom surfaces of the different absorbent elements are alternately inverted towards one side and then the other side of the stack, each transfer element being in a direction parallel to the bottom surface A first stack connected to its adjacent elements by means for pulling the elements
Means (21) for exerting traction on said assembly of transmission elements;
A nuclear fuel storage rack element (60, 62, 64, 66, 68, 70). Each second surface of the element
-In contact with the second surface of the transmission element when no traction is exerted on said assembly of the transmission element;
If traction is exerted on the assembly of transmission elements, it is located at a non-zero distance from the second surface, parallel to them,
Storage rack element (60, 62, 64, 66, 68, 70) according to claim 9.   Storage rack element (60, 62, 64, 66, 68, 70) according to claim 9 or 10, wherein the stack of transmission elements has a height (h) shorter than the total height of the rack element.   9. A second stack on at least one of the transfer elements according to any one of claims 1 to 8, further arranged in a zone (200, 200 ') spaced from the first stack by a continuous portion of material. 12. Storage rack element (60, 62, 64, 66, 68, 70) according to any one of claims 9 to 11, comprising.   13. The arrangement according to claim 9, arranged to delimit a cylindrical or square or rectangular or hexagonal central cavity (17) in a plane perpendicular to the direction of traction of each rack. A nuclear fuel storage rack comprising a plurality of storage rack elements.   Nuclear fuel storage and / or comprising at least one storage rack according to claim 13 surrounded by a peripheral protective layer (54) for the absorption of gamma rays and a peripheral protective layer (52) for moderating neutrons. Cask for transportation.   15. A cask for storage of nuclear fuel according to claim 14, comprising a number of racks between 2 and 12. The following steps:
The two planes (22), wherein the transmission elements of the rack elements of the storage rack according to claim 13 are shifted from an initial state to a raised state to form each transmission element and the hot and cold surfaces. , 24) to exert a clearance (27, 29) with respect to the transmission element, introducing a nuclear fuel rod (15) into the central cavity (17),
The transmission elements to return to their initial state in which the bottom surface of each transmission element is positioned so that it contacts one or the other of the two of the hot and cold walls (22, 24); Releasing elements,
A method for storing and / or transporting nuclear fuel rods (15). The method according to claim 16, comprising a pre-step of introducing the storage rack into the pool (12) and a post-step of removing the rack carrying the nuclear fuel rods (15) from the pool. The method according to claim 16 or 17, wherein the nuclear fuel rod (15) has an output of 7 kW or more .

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