FR3054922A1 - STORAGE BASKET FOR RADIOACTIVE MATERIALS, WITH AN OPTIMIZED SIZE - Google Patents

Abstract

The invention relates to a storage basket (1) for radioactive materials, the basket having an overall cylindrical shape of circular section and comprising a plurality of housings (4) parallel to a central axis of the basket, all the housing of the basket being arranged according to one or more concentric annular rows (R1, R2), centered on the central axis (6) of the basket. In addition, the basket comprises radial neutrophage plates (30) made of a material comprising neutron absorber elements, the radial neutrophage plates being disposed between at least some of the housings (4), in fictitious radial planes (PR) s'. intercepting in the same right confused with the central axis of the basket (9).

Description

DESCRIPTION

TECHNICAL AREA

The present invention relates to the field of transport and / or storage of radioactive materials. It may for example be fissile materials, such as uranium oxide powder highly enriched in U235, or even irradiated fuel assemblies of the MOX type, originating from the fast RNR sector.

STATE OF THE PRIOR ART

Such a basket, also called a “device” or “rack” for storage, comprises a plurality of adjacent housings each capable of receiving radioactive materials. It is housed in a cavity of a package, is designed to be able to simultaneously fulfill three essential functions, which will be briefly explained below.

First of all, it is the thermal transfer function of the heat given off by radioactive materials. Generally, aluminum or one of its alloys is used, due to its good thermal conduction properties.

The second function concerns neutron absorption, and the concern to maintain the subcriticality of the storage basket when it is loaded with fissile radioactive materials. This is achieved by using neutron absorbing materials called neutron-absorbing materials, such as boron. Additionally, the subcriticality can also be ensured by providing air spaces capable of being filled with water, for example inside the partitions situated between the basket housings.

Finally, the third essential function relates to the mechanical resistance of the device. It is noted that the overall mechanical strength of the basket must be compatible with the regulatory safety requirements for the transport / storage of radioactive materials, in particular with regard to the so-called “free fall” tests.

In the prior art, numerous designs have already been proposed aiming to fulfill all of these functions. In some solutions, it is planned to decorrelate all or part of the functions by providing separate elements to satisfy each of them. However, it follows from this principle a multiplicity of elements for the constitution of the basket, which has an impact on the overall size of the latter.

In the case of a basket of cylindrical overall shape of circular section, the housings are generally distributed along parallel and orthogonal lines between them. This classic arrangement lets appear at the periphery of the basket substantial spaces, free of housing. The overall size of the basket is thus also negatively impacted by a non-optimized arrangement of the housings.

STATEMENT OF THE INVENTION

The invention therefore aims to at least partially remedy the drawbacks mentioned above, relating to the embodiments of the prior art.

To do this, the invention relates to a storage basket for radioactive materials, the basket having an overall cylindrical shape of circular section and comprising a plurality of housings parallel to a central axis of the basket.

According to the invention, all the basket housings are arranged in one or more concentric annular rows, centered on the central axis of the basket, and the basket comprises a plurality of radial neutron absorbing plates made of a material comprising neutron absorbing elements, the radial neutron-absorbing plates being arranged between at least some of said housings, in fictitious radial planes intercepting in the same straight line merged with the central axis of the basket.

In other words, in view along the central axis of the basket, the central axes of all the housings are located on one or more concentric circles centered on the central axis of the basket. With this design implementing an original distribution of the housings according to annular rows, as well as a radial orientation of the neutron-absorbing plates, it follows a design which adapts perfectly to the circular nature of the basket. The size of the latter is advantageously optimized, and it therefore becomes possible to reduce its dimensions while retaining the same number of housings, while further increasing the number of housings without having too much impact on the dimensions of the basket.

The invention furthermore presents at least any one of the following optional characteristics, taken individually or in combination.

The annular row of housings having the smallest diameter consists of a number N of housings, each separated from the two adjacent housings within this row by two of the neutron-absorbing plates, the number N preferably being 1, 3, 5 or 6. Thus, in this preferred embodiment, all the housings are separated from their adjacent housings by radial neutron absorbing plates, even if it could be otherwise without departing from the scope of the invention. It is noted that this row of smaller diameter can be reduced to a single housing, the central axis of which would coincide with that of the basket, and therefore having a zero diameter. In this case with a single housing centered on the basket, the latter is completed by at least a second annular row provided with several housings, arranged around the central housing.

The basket comprises two concentric annular rows, and the total number of housings in these two rows is preferably between 8 and 16.

The basket has a number of rows greater than or equal to two, and each radial neutron absorbing plate crosses all the annular rows of housings. Alternatively, one or more radial neutron-absorbing plates could cross only one or some of the rows.

The basket includes additional neutron-absorbing plates arranged substantially perpendicular to the radial neutron-absorbing plates, each additional neutron-absorbing plate separating at least two housings belonging to two distinct annular rows.

According to a first possibility, two additional neutron-absorbing plates are associated with at least one radial neutron-absorbing plate by being arranged on either side thereof, the two additional neutron-absorbing plates being preferably arranged in the same fictitious plane.

Alternatively, at least one additional neutron absorbing plate and one radial neutron absorbing plate are intertwined.

Within at least one of the annular rows, the housings are regularly spaced from each other, and / or the radial neutron absorbing plates are regularly spaced from each other.

Preferably, the basket also includes:

- wafers made from a material devoid of neutron absorbing elements, the wafers being spaced from each other in a longitudinal direction of the basket and connected together by spacers; and

- liners passing through the wafers and forming said housings, each liner being made of a material devoid of neutron absorbing elements, clearances being preferably provided between the liners and the radial neutron-absorbing plates. Alternatively, the housings could be defined simply by the wafers, without the shirts.

This specific arrangement makes it possible to dissociate the subcriticality function from the mechanical resistance function. In fact, the mechanical function is provided by the liners, spacers and wafers, while the subcritical function is provided by the neutron absorbing plates. This results in an ease of certification and design of the basket.

In addition, the spacing between the wafers makes it possible to reduce the overall mass of the basket, compared to a full basket between the housings.

Also, since the liners are no longer intended to perform the subcriticality function, their shape can be fixed more freely in comparison with the liners of the prior art comprising boron, the manufacture of which turns out to be much more expensive, especially when the shape of the shirt becomes more complex.

More generally, the components of the basket are simple to manufacture, in particular the radial neutron absorbing plates. This advantageously results in a gain in terms of costs.

According to one possibility, at least one of the radial neutron-absorbing plates passes through at least one of the wafers, and preferably all the inner wafers of the basket.

According to another possibility, at least one of the radial neutron-absorbing plates is segmented into several axial segments each extending between two wafers directly consecutive from the basket, imprints being preferably provided on the wafers for housing the axial ends of the plate segments .

Preferably, the housings are of cylindrical shape and of circular section. Alternatively, they could for example be of polygonal shape, for example hexagonal, octagonal, etc.

The diameter of the basket "DP" and the largest width of each housing "LL" meet the following condition:

LL / DP> 0.1

This reflects a design in which the housing width is large relative to the diameter of the basket. This type of design requires an optimization of the distribution of the housings within the basket, this optimized distribution being offered by the arrangement in annular rows of the housings.

At least two radial neutron absorbing plates are arranged in parallel so as to define an air space between them. In this case, the water present in this blade is taken into account during a loading under water, for the criticality calculations.

Finally, the subject of the invention is a package for the transport and / or storage of radioactive materials, comprising a package and a storage basket as described above, housed in a cavity defined by the package.

Other advantages and characteristics of the invention will appear in the detailed non-limiting description below.

BRIEF DESCRIPTION OF THE DRAWINGS

This description will be made with reference to the accompanying drawings, among which;

FIG. 1 represents a package for the transport and / or storage of radioactive materials, in exploded perspective, according to a first preferred embodiment of the invention;

Figure IA shows a longitudinal sectional view of the storage basket shown on the package of Figure 1;

Figure 2 shows a sectional view taken along the line II-II in Figure 3;

Figure 3 shows a sectional view along line III-III of Figure 2;

Figure 4 shows the cooperation between one of the radial neutron absorbing plates and the wafers of the basket, according to an alternative embodiment to that shown in Figure 3;

Figure 5 shows a perspective view of the basket forming part of the package shown in Figure 1;

FIG. 6 represents an exploded perspective view of a radial neutron absorbing plate intended to cooperate with an additional neutron absorbing plate;

Figure 7 shows an alternative embodiment to that shown in Figure 6;

FIG. 8 represents yet another alternative embodiment for neutron-absorbing plates;

Figure 9 shows a storage basket in top view, according to a second preferred embodiment of the invention;

Figure 10 shows a storage basket in top view, according to a third preferred embodiment of the invention; and

FIG. 11 represents a top view of a storage basket according to a fourth preferred embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring firstly to Figure 1, there is shown a package 100 for the transport and / or storage of radioactive material according to a first preferred embodiment of the invention. This package 100 includes a storage basket 1 in which the radioactive materials 2 are intended to be stored, in housings 4 adjacent and parallel to a central axis 6 of the basket. Also, each housing 4 has a central axis 8 parallel to the central axis 6 of the basket 1.

The package 100 also includes a packaging 10 defining a cavity 12 in which the basket 1 is intended to be housed. Conventionally, the packaging is formed by an external lateral body 14, a fixed bottom 16 and a removable cover 18 closing the cavity 12.

The storage basket 1 is of generally cylindrical shape with an axis 6, and of circular section. The housings 4 also have a cylindrical shape of circular section, the largest width of each housing referenced “LL”, in FIG. 1, and corresponding to the internal diameter of each of these housings, is such that it has a large size at look at the outside diameter of the basket referenced “DP” in FIG. 1. More specifically, the ratio between the dimensions LL and DP is greater than or equal to 0.1, which in fact reflects the presence of housings of significant width within the basket.

The basket 1 is produced using various elements, including wafers 20a, 20b spaced apart from each other in a longitudinal direction 22 of the basket, parallel to its central axis 6. The wafers are spaced and held together by compared to the others using spacers 24 arranged in inter-pancake spaces.

These spacers 24 are therefore arranged in the longitudinal direction 22 and allow the wafers to be held relative to one another, as shown in FIG. IA. In this regard, it is noted that each spacer 24 is inserted into a wafer cavity at each of its ends. The wafers are thus arranged in columns, being separated from each other by wafers. Each column is also crossed by a tie rod 25 which passes through and retains between them all of the wafers 20a, 20b of the column, using upper 25a and lower 25b nuts.

The two end plates, namely the upper and lower closing plates 20b of the basket which carry the nuts 25a, 25b, are made of steel. Alternatively, an aluminum construction would also be possible for these wafers 20a, 20b. The other wafers 20a, called inner wafers, are made of aluminum. In both cases, it is preferably a material devoid of neutron absorbing elements, it being indicated that by "neutron absorbing elements" is meant elements which have an effective cross section greater than 100 barns for the thermal neutrons. As indicative examples, these are aluminum alloys free of boron, gadolinium, hafnium, cadmium, indium, etc.

The wafers are pierced with orifices crossing at the level of the housings 4, for the passage of liners 26 internally forming the housings 4. These liners preferably extend over the entire length of the basket 1 in the direction 22, crossing the galettes 20a . They are preferably made of a material devoid of neutron absorbing elements, for example stainless steel.

Thanks to this design, the mechanical function is provided jointly by the sleeves 26, the wafers 20a, 20b, the spacers 24 and the tie rods 25, while the subcriticality function is provided by radial neutron absorbing plates 30, one of which is visible in Figure 1.

Each plate 30 also extends along substantially the entire length of the basket 1 in the direction 22, possibly segmented as is the case in the embodiment of Figure 1. The plates 30 are said to be radial because they are arranged in the fictitious radial planes PR intercepting in the same straight line which coincides with the central axis 6 of the basket. In this embodiment, as shown in FIGS. 1, 2 and 3, each neutron absorbing pad 30 is therefore segmented into several axial segments which each extend between two wafers 20a directly consecutive. To maintain each of these plate segments 30a, the wafers 20a, 20b are provided with imprints of shape corresponding substantially to the cross section of each segment 30a, as is best visible in Figure 2. For example, it is made so that the clearance between each segment 20a and its footprint 32 is extremely small in the radial and tangential directions, but a more substantial axial clearance 34 can be provided in the longitudinal direction 22 between the upper axial end of the segment 30a and the bottom of borrows 32. However, a solution with a small clearance 34 is also possible, without departing from the scope of the invention.

According to an alternative embodiment shown in FIG. 4, the plate 30 passes through one or more internal wafers 20a passing through orifices 36 provided for this purpose, so that the radial neutron absorbing plate 30 extends over all or part of the length from the basket. In this case, imprints are preferably kept at the level of the upper and lower closing plates of the basket, for the reception of the axial ends of the plate 30.

FIG. 5 represents one of the particular features of the invention, namely the fact that the housings 4 defined by the liners 26 are arranged in one or more concentric annular rows, centered on the main axis 6 of the basket. These are two annular rows, referenced RI and R2. This design, in which in view along the central axis 10 of the basket, the central axes 8 of all the housings 4 are located on two concentric circles, makes it possible to adapt perfectly to the overall cylindrical shape of circular section of the basket, and therefore optimize the number of housings 4 in a given space.

In this first preferred embodiment, 15 housings are provided, 5 of which are arranged in the first annular row RI, and 10 housings provided within the second annular row R2. Within each of these rows, the housings are regularly spaced from each other, in the tangential direction. It is the same for the neutron-absorbing plates 30, provided for in number 5 in the fictitious radial planes PR. Thus, within the first row RI, there is provided a perfect alternation between the housings 4 and the radial neutron absorbing plates 30. In other words, each housing 4 of the first annular row RI is separated from the two adjacent housings 4 of this row by respectively two radial neutron-absorbing plates 30. In this regard, it is noted that to avoid weakening the mechanical resistance of the basket, clearances are preferably provided between the plates and the housings, and this for all the housings and all the basket plates. More specifically, the clearances are located between the plates and the external surface of the liners, the housings being defined by the internal surface of these same liners.

As can be seen in FIG. 5, additional neutron-absorbing plates 40 complete the radial neutron-absorbing plates, these additional plates 40 being arranged between the two annular rows of housings RI, R2. More specifically, each additional neutron absorbing plate is arranged perpendicular to the radial neutron absorbing plate with which it has been associated. The two associated plates 30, 40 thus form neutron sets of cross section in the form of a cross, the four branches of which have lengths which are preferably each greater than or equal to the diameter of the housings. Thus, in this first preferred embodiment, each additional neutron absorbing plate arranged in a tangential plane separates two housings of the first annular row RI, from two housings of the second annular row R2.

Here, the assemblies formed by the association of a radial neutron absorbing plate 30 and an additional plate 40, are distributed in a regular manner around the central axis 6 of the basket, this arrangement thus proving to be perfectly adapted to the general shape. cylindrical of circular section of this same basket.

For the production of neutron-absorbing sets of cross-section, it is first of all possible to use two plates, each having a notch 42 and arranged one on the other in a crisscross manner, by cooperation of the two notches 42. This embodiment is shown in Figure 6.

In an alternative embodiment shown in FIG. 7, there are two additional neutron-absorbing plates 40, and attached independently of each side of the neutron-absorbing plate 30.

The two additional plates 40 are therefore arranged in the same fictitious plane on either side of the radial plate 30 arranged in the radial plane PR. Finally, FIG. 8 shows yet another alternative in which each plate 30, 40 is replaced by two plates spaced from one another and arranged in parallel by defining between them an air gap 44. This blade air is intended to be filled with water when the basket is loaded with water, and the presence of this water is thus taken into account for the criticality calculations because it promotes the absorption of neutrons by the neutrophagous elements located in these plates 30, 40.

FIG. 9 shows a second preferred embodiment of the invention, in which 15 housings 4 are provided, including 6 housings provided in the first annular row RI, and 9 housings 4 located in the second annular row R2 at the periphery of the basket . In this second embodiment, 6 radial neutron absorbing plates 30 are provided, three of which cross the two rows RI, R2, and the other three of which are of shorter radial dimension, since they only cross the first row RI and have an outer radial edge located opposite one of the peripheral housings of the second row R2. The two types of radial plates 30 are arranged alternately around the central axis 6 of the basket. For the three longest plates in the radial direction, these are each associated with two additional neutron absorbing plates 40 disposed on either side thereof, in the manner of that described in the previous embodiment. It is however possible to provide a clearance between the radial plate 30 and each additional plate 40, as can be seen in FIG. 9.

In FIG. 10, the third preferred embodiment implements 12 housings 4, three of which are located within the first annular row RI, and the other 9 of which are located on the second annular row R2. Here, three radial neutron-absorbing plates 30 are provided, each extending through the two rows RI,

R2. Each plate 30 is associated with an additional neutron absorbing plate 40 in the manner of that mentioned in the first embodiment described above.

Finally, FIG. 11 shows a fourth embodiment in which a single annular row of housings is provided, here containing 6 housings. Radial neutron absorbing plates 30 are arranged between all these housings 4 defined by the liners.

Of course, various modifications can be made by those skilled in the art to the storage basket 1 which has just been described, only by way of indicative examples. In particular, the alternatives shown in Figures 4, 6, 7, 8 can be implemented in the second, third and fourth preferred embodiments of the invention.

Claims (15)

1. Storage basket (1) for radioactive materials, the basket having an overall cylindrical shape of circular section and comprising a plurality of housings (4) parallel to a central axis of the basket, characterized in that all the housings of the basket are arranged along one or more concentric annular rows (RI, R2), centered on the central axis (6) of the basket, and in that it comprises a plurality of radial neutron-absorbing plates (30) made of a material comprising absorbing elements of neutrons, the radial neutron-absorbing plates being arranged between at least some of said housings (4), in fictitious radial planes (PR) intercepted in the same straight line merged with the central axis of the basket (9). 2. Basket according to claim 1, characterized in that the annular row of housings (RI) having the smallest diameter consists of a number N of housings, each separated from the two adjacent housings within this row by two of the plates radial neutrophages (30), the number N preferably being 1, 3, 5 or 6. 3. Basket according to claim 1 or claim 2, characterized in that it comprises two concentric annular rows (RI, R2), and in that the total number of housings (4) in these two rows is preferably between 8 and 16. 4. Basket according to any one of the preceding claims, characterized in that it comprises a number of rows greater than or equal to two, and in that each radial neutron absorbing plate (30) passes through all the annular rows of housings (RI, R2). 5. Basket according to any one of the preceding claims, characterized in that it comprises additional neutron-absorbing plates (40) arranged substantially perpendicular to the radial neutron-absorbing plates (30), each additional neutron-absorbing plate (40) separating at least two housings ( 4) belonging to two separate annular rows (RI, R2). 6. Basket according to the preceding claim, characterized in that two additional neutron absorbing plates (40) are associated with at least one radial neutron absorbing plate (30) being arranged on either side thereof, the two additional neutron absorbing plates (40) preferably being arranged in the same fictitious plane. 7. Basket according to claim 5, characterized in that at least one additional neutron absorbing plate (40) and a radial neutron absorbing plate (30) are intertwined. 8. Basket according to any one of the preceding claims, characterized in that within at least one of the annular rows, the housings (4) are regularly spaced from each other, and / or in that the Radial neutron absorbing plates (30) are spaced regularly from each other. 9. Basket according to any one of the preceding claims, characterized in that it further comprises: - wafers (20a, 20b) made from a material devoid of neutron absorbing elements, the wafers being spaced apart from one another in a longitudinal direction (22) of the basket and connected together by spacers (24 ); and - sleeves (26) passing through the wafers (20a) and forming said housings (4), each sleeve being made of a material devoid of neutron absorbing elements, games are preferably provided between the sleeves (26) and the neutron absorbing plates radial (30). 10. Basket according to the preceding claim, characterized in that at least one of the radial neutron absorbing plates (30) passes through at least one of the wafers, and preferably all the inner wafers (20a) of the basket. 11. Basket according to claim 9, characterized in that at least one of the radial neutron absorbing plates (30) is segmented into several axial segments (30a) each extending between two wafers (20a, 20b) directly consecutive from the basket , indentations (32) being preferably provided on the wafers for housing the axial ends of the plate segments (30a). 12. Basket according to any one of the preceding claims, characterized in that the housings (4) are of cylindrical shape and of circular section. 13. Basket according to any one of the preceding claims, characterized in that the diameter of the basket "DP" and the largest width of each housing "LL" meet the following condition: LL / DP> 0.1 14. Basket according to any one of the preceding claims, characterized in that at least two radial neutron absorbing plates (30) are arranged in parallel so as to define an air space (44) therebetween. 15. Package (100) for the transport and / or storage of radioactive materials, comprising a packaging (10) and a storage basket (1) according to any one of the preceding claims, housed in a cavity (12 ) defined by the packaging. .60383 1/6