Storage device for storing and/or transporting nuclear fuel assemblies

Abstract

The invention relates to a storage device for storing and/or transporting nuclear fuel assemblies, which includes recesses (2) defined by separating partitions (9) defining first and second recesses (2), the partition comprising: two first walls (22) defining the first and second recesses and made of an aluminium-alloy material which is free of neutron-absorbing elements, and defining therebetween a first inter-wall space (28); two second walls (30) arranged in the first space (28) and made of a material which comprises neutron-absorbing elements, the distance between the inner (36) and outer (34) surfaces of each second wall (30) defining a thickness (e2), and a distance (E) being defined between the outer surface (34) of each second wall and a median partition plane (20), the values meeting the condition 0.1e2/E0.43.

Claims

1. A storage device for temporarily storing and/or transporting PWR type nuclear fuel assemblies, said device being intended to be housed in a cavity of a package and including a plurality of adjacent housings each intended to receive a nuclear fuel assembly, the housings being delimited by separating partitions at least one of which delimits on either side of the same first and second housings, wherein said at least one separating partition includes: two first walls each partly delimiting, respectively with its external surface, said first and second housings, both first walls being made of a first material of aluminium alloy free of neutron absorbing elements, both first walls delimiting a first inter-wall space therebetween; two second walls arranged in the first inter-wall space and made of a second material comprising neutron absorbing elements and distinct from the first material, each second wall having an external surface facing one of both first walls, as well as an internal surface arranged such that both internal surfaces of both second walls are facing each other and delimit a second inter-wall space therebetween, the distance between the internal and external surfaces of each second wall defining a thickness (e2), whereas a distance (E) is defined between the external surface of each second wall and a median partition plane parallel to the first and second walls, said device being also characterised in that the thickness (e2) and the distance (E) meet the following condition:
1e2/E0.43.

2. The storage device according to claim 1, wherein the thickness (e2) and the distance (E) meet the following condition:
0.15e2/E0.32.

3. The storage device according to claim 1, wherein the distance (E) is between 20 and 30 mm.

4. The storage device according to claim 1, wherein the second material comprises neutron absorbing elements chosen from boron and cadmium.

5. The storage device according to claim 1, wherein each second wall is pressed against the first associated wall, taking the form of a coating deposited onto the internal surface of the first wall.

6. The storage device according to claim 1, wherein a clearance (J) is present between each second wall and the first associated wall, the clearance (J) being between 1 and 5 mm.

7. The storage device according to claim 1, wherein it has a number of housings between four and twenty-four housings, each housing being intended to receive a nuclear fuel assembly.

8. The storage device according to claim 1, wherein at least one of the housings has a quadrilateral shaped cross-section.

9. The storage device according to claim 1, wherein at least some of said partitions are made using notched structural assemblies, the structural assemblies being interlaced and stacked along a stacking direction parallel to the axes of the housings.

10. The storage device according to claim 1, wherein at least some of said partitions are partly made using tubular elements each internally defining one of said housings, the walls of these tubular elements making up said first walls of the partitions.

11. The storage device according to claim 10, wherein the second walls are externally secured to the tubular elements.

12. A package for temporarily storing and/or transporting PWR type nuclear fuel assemblies, the package comprising a cavity in which a storage device according to claim 1 is housed.

13. A pack comprising a package according to claim 12 as well as fuel assemblies arranged in the housings of the storage device of this package.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) This description will be made with regard to the appended drawings in which:

(2) FIG. 1 represents a perspective view of a storage device for temporarily storing and/or transporting nuclear fuel assemblies, according to the present invention;

(3) FIG. 2 is a partial cross-section view taken along the transverse plane P of FIG. 1;

(4) FIG. 3 represents a transverse cross-section view of a partition of the storage device shown in FIG. 2;

(5) FIG. 4 is a graph comprising three curves showing the content of boron carbide in the second walls of the partition, as a function of a ratio of dimensions associated with these second walls;

(6) FIGS. 5a and 5b show a first possible design for the partitions of the storage device; and

(7) FIG. 6 represents a second possible design for partitions of the storage device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(8) In reference to FIGS. 1 and 2, a storage device 1 is represented, provided to be placed in the cavity of a package (not represented) for transporting and/or temporarily storing PWR type irradiated nuclear fuel assemblies (not represented). Conventionally, when the package receives the storage device 1 and that this is loaded with irradiated fuel assemblies, all of these elements form a pack, which is also an object of the invention.

(9) As is visible in FIGS. 1 and 2, the storage device 1 comprises a plurality of adjacent housings 2 disposed in parallel, the latter each extending along a longitudinal axis 4. The housings 2 are each capable of receiving at least one square cross-section fuel assembly, and preferably a single one. The housings are provided in a number between four and twenty-four, for example twelve housings as in FIG. 1.

(10) The housings 2 are thus provided so as to be juxtaposed to each other. They are made through a plurality of separating partitions 9, 11 parallel to the axes 4, and also parallel to a longitudinal axis of the package passing through its bottom and its lid. The partitions 9, 11 are formed using notched structural assemblies 6a, 6b, stacked along a stacking direction 8 which is preferably parallel to the longitudinal axes 4 of the housings 2. By convention, in the following of the description, it is assumed that the notion of height is to be associated with the stacking direction 8.

(11) The partitions 9, 11 are arranged parallel and perpendicular to each other, such that the assemblies 6a are located parallel to each other, whereas the assemblies 6b are also located parallel to each other, but perpendicular to the assemblies 6a.

(12) When the structural assemblies 6a, 6b are stacked along the stacking direction 8, the partitions 9, 11 resulting therefrom delimit together the housings 2, each having a substantially square shaped transverse cross-section. Of course, the housings 2 could have any other shape allowing a differently shaped fuel assembly to be held, such as a hexagonal shape.

(13) In the storage device 1 represented in FIGS. 1 and 2 where the housings 2 are of a square cross-section, the structural assemblies 6a form separating partitions 9 parallel to a direction 10, whereas the structural assemblies 6b form separating partitions 11 parallel to a direction 12, the directions 8, 10 and 12 being perpendicular to each other.

(14) Preferably, each of the assemblies 6a, 6b extends between two peripheral partitions 14 to which it is secured, these peripheral partitions 14 enabling the storage device 1 to be closed sideways. By way of indicating example and as represented, these peripheral partitions 14 can be provided four in number, each extending on the entire height of the device 1, and partly delimiting the peripheral housings 2 of this device 1.

(15) On the other hand, as is clearly apparent from the above, the partitions 9, 11 participate in delimiting several housings 2 on either side of the same. In this regard, FIG. 3 shows a part of one of the separating partitions 9, delimiting on either side of the same a first housing 2 as well as a second housing 2, their two axes 4 being located in a dummy plane orthogonal to that of the partition 9. Only two housings 2 are represented in FIG. 3, but as previously mentioned, it is to be understood that this partition 9 is preferably provided to delimit one or more other housings 2 on either side of the same. The partition 9 of FIG. 3 will now be described in more detail, and it is to be considered that the other partitions 9, as well as the abovementioned partitions 11, have an identical or similar design.

(16) The partition 9 has a symmetry along a median plane 20 orthogonal to the transverse plane P of FIG. 1. On each side of this plane 20, the partition 9 includes a first wall 22 parallel to the median plane 20, and comprising an external surface 24 as well as an internal surface 26. The external surface 24 partly delimits the associated housing 2, whereas the two internal surfaces 26 of both walls 22 delimit a first inter-wall space 28 therebetween.

(17) The first walls 22 are made of an aluminium alloy free of neutron absorbing elements. It is indicated that by neutron absorbing elements, it is meant elements which have an effective cross-section higher than 100 barns for the thermal neutrons. By way of indicating examples, this is an aluminium alloy free of boron, gadolinium, hafnium, cadmium, indium, etc.

(18) In the case of a design with stacked and interlaced notched assemblies, each first wall 22 is thus segmented along the height direction of the device 1.

(19) The thickness e1 of each first wall 22 is for example between 5 and 25 mm, whereas the distance a separating both external surfaces 24 is in the order of 40 to 100 mm, whereas the distance d separating both internal surfaces 26 is in the order of 30 to 60 mm.

(20) In the first inter-wall space 28, with each first wall 22, a second wall 30 parallel to the median plane 20 is associated. Each wall 30 comprises an external surface 34 as well as an internal surface 36. The external surface 34 faces the internal surface 26 of its first associative wall, whereas both internal surfaces 36 face each other and delimit a second inter-wall space 38 therebetween.

(21) The second walls 30 are made of a second material comprising neutron absorbing elements, for example an alloy comprising boron carbide (B.sub.4C), preferably an aluminium based alloy.

(22) In the case of a design with stacked and interlaced notched assemblies, each second wall 22 is also segmented along the height direction of the device 1.

(23) In the embodiment exhibited in FIG. 3, a clearance J is provided between the internal surface 26 and the external surface 34 facing it. This clearance J is for example between 1 and 5 mm, so as to provide a proper drying efficiency between both walls 22, 30, once the package is drained off. Alternatively, the second wall 30 can be pressed against the internal surface 26 of its first associated wall, so as to limit water infiltrations. To do this, a technique of depositing the second wall 30 onto the first wall 22 can be implemented, for example such that the latter takes the form of a coating deposited onto the internal surface 26. For example, this can be a composite comprising a particle loaded metal matrix comprising neutron absorbing elements.

(24) The thickness e2 of each first wall 22 is for example between 2 and 10 mm, whereas the distance E separating the external surface 34 from the median plane 20 is for example between 15 and 40 mm, and further preferentially between 20 and 30 mm.

(25) One the features of the invention lies in the choice of the dimensions for the thickness e2 and the distance E, such that they satisfy the condition 0.1e2/E0.43, and more preferentially 0.15e2/E0.32, corresponding to the case where E is 23.5 mm and e2 values for which Keff+3 is satisfied with a maximum content of boron carbide (B.sub.4C) of 25%.

(26) Indeed, it has been noticed that these ranges of dimension ratios advantageously result in partitions satisfying cost, mass and sub-criticality criteria.

(27) In reference to FIG. 4 now, it is shown a graph in which the curves (a) and (b) and (c) represent, as a function of the ratio e2/E, the volume content of boron carbide in an aluminium alloy required for achieving a criticality factor Keff+3 of a 0.95 value.

(28) For curve (a), the distance E is set to 23.5 mm, whereas for curve (b), the distance E is set to 20 mm, and for curve (c), the distance E is set to 30 mm.

(29) Surprisingly, these curves show that for e2/E ratios between 0.1 and 0.43, the volume content of boron carbide sufficient to satisfy the sub-criticality criterion does not exceed 26%, which enables the second walls 30 to be manufactured at a reasonable cost.

(30) Further surprisingly, these curves show that the minimum content to satisfy the sub-criticality criterion corresponds to an identical e2/E ratio regardless of the E value, this optimum ratio Rop being substantially equal to 0.23. The three curves are thus axially offset, along the ordinate axis corresponding to the content of boron carbide. The higher is the E value, the lower is the required volume content of boron carbide, and reversely.

(31) This content is even reduced to around 25% when the e2/E ratio is 0.23, and E values higher than 20.

(32) For E values higher than or equal to 23.5 mm, this content is further reduced to less than 23% when the e2/E ratio is set between 0.2 and 0.25.

(33) In reference now to FIGS. 5a and 5b, the assemblies 6a, 6b for forming the partitions 9, 11 are shown, in two distinct configurations upon assembling. These assemblies 6a, 6b each have spacers 40 separating the two second walls 30. They are equipped with notches 42 made at the first walls 22, so as to allow assembling by stacking and interlacing, in the way described in document FR 2 872 922. In addition, it is indicated that the second walls 22 do not extend at the interlaced portions, such that they are interrupted along each assembly 6a, 6b. This enables a financial saving to be generated, without embrittling the sub-criticality criterion insofar as the interlaced zones have only a low on the criticality factor.

(34) According to another embodiment shown in FIG. 6, square transverse cross-section tubular elements 50 are provided, each defining one of the housings 2. All or only some of the four walls of a tubular element 50 form the first walls 22, which are externally coated with a second wall 30. The partition 9 is thereby formed by the facing parts of two adjacent tubes 50.

(35) Of course, various modifications could be provided by those skilled in the art to the storage devices 1 just described, only by way of non-limiting examples.