FR3094549A1 - SET INCLUDING A PACKAGING FOR THE STORAGE OF RADIOACTIVE MATERIALS, AND ITS SUPPORT SYSTEM - Google Patents

Abstract

The invention relates to an assembly (100) comprising a packaging (1) for storing radioactive materials, as well as its support system (3) comprising a radiative screen (20) for thermal protection of the ground, this screen comprising at at least one air passage (24) providing communication between a zone (32) of circulation of cooling air of the ground defined under a first face (28) of the screen, and a zone (34) of circulation of cooling air of the packaging bottom defined between a second face (30) of the screen and the packaging bottom (4). The support system (3) includes support members (36) of the package bottom, each projecting from the second face (30) of the radiative screen (20) and extending through the area (34). , and it also comprises support elements (38) projecting into the area (32). Figure for the abstract: Figure 1.

Description

ASSEMBLY COMPRISING PACKAGING FOR THE STORAGE OF RADIOACTIVE MATERIALS, AND ITS SUPPORT SYSTEM

The present invention relates to the field of storage containers for radioactive materials, for example radioactive waste placed in drums, or even nuclear fuel assemblies.

The invention relates more particularly to an assembly formed by such a packaging with its support system, the latter providing the interface between the bottom of the packaging in the vertical storage position, and the floor of the storage site.

Usually, packages are stored in an upright position in a storage site, also referred to as a storage hall or building. These packages are generally placed on the floor in the storage building, involving direct contact between the bottom of the package and the ground. Consequently, the part of the floor facing the bottom of the packaging can reach high temperatures, likely to exceed the average and maximum tolerated floor temperatures.

To lower the average and maximum temperatures of the ground vis-à-vis a package, the subject of the invention is an assembly comprising a storage package for radioactive materials as well as a package support system intended, in a packaging storage configuration, to be arranged between a bottom of the packaging and a floor of a storage building.

According to the invention, the support system comprises a radiative shield for thermal protection of the ground having a first lower face as well as a second upper face opposite the first, the radiative shield comprising a central part provided with at least one passage of air providing communication between a floor cooling air circulation zone defined under the first face of the radiation shield, and a cooling air circulation zone of the packaging bottom defined between the second face of the radiative screen and the bottom of the packaging.

In addition, the support system further comprises a plurality of spaced apart package bottom support members, each support member protruding from the second face of the radiation shield and extending through the cooling air circulation zone of the bottom of the packaging until it comes into contact with the latter.

Finally, the support system also comprises a plurality of support elements protruding into the floor cooling air circulation zone, from the first face of the radiative screen.

The invention thus makes it possible to reduce the average and maximum temperatures of the part of the ground located opposite the assembly, thanks first of all to the support system whose radiative screen limits the radiation of the packaging towards the ground. In addition to forming a screen against this radiation, the support system makes it possible to cool the floor by means of air suction within the floor cooling air circulation zone defined under the first face of the radiative screen. , this suction taking place radially from the outside towards the inside until this air passes through the central air passage(s), then until it is discharged by the bottom cooling air circulation zone packaging.

In other words, the invention provides in a simple way to combine the effects of heat shielding and cooling by natural convection, to limit the rise in temperature of the ground and the bottom of the packaging.

The invention may provide for the implementation of one of the following optional features, taken in isolation or in combination.

The central part of the radiation screen, in which each air passage is circumscribed, has a first diameter D1 smaller than the largest transverse dimension D2 of the packaging, so as to satisfy the following relationship:
D1<0.5. D2

This dimensioning further improves the cooling efficiency of the bottom of the packaging and the floor, by combining the two effects of heat shielding and cooling by natural convection.

Said at least one air passage has a cumulative surface S1 for air circulation, the packaging in the storage configuration has a central longitudinal axis orthogonal to the ground and to the radiation screen and centered with respect to the latter, the packaging has a projected surface S2 on the ground, along the central longitudinal axis, and the surfaces S1 and S2 correspond to the following relationship:
S1<0.25. S2

Here again, this dimensioning contributes to improving the cooling efficiency of the bottom of the packaging and the ground, by combining the two effects of heat shielding and cooling by natural convection.

The support elements of the bottom of the packaging and the support elements form two by two feet crossing the radiation shield for thermal protection.

This advantageously results in simplicity of design. Each foot is then preferably made in one piece, except possibly to integrate a layer of thermal insulation at its end in contact with the bottom of the packaging. Alternatively, the support elements of the bottom of the packaging and the support elements could be produced by elements independent of each other, aligned or not aligned two by two according to the direction of the central longitudinal axis of the packaging. in storage configuration.

In this storage configuration, the support system comprises an envelope carried around the periphery of the radiation screen, the envelope defining an air suction channel around the packaging.

This envelope promotes cooling by natural convection, and provides a chimney effect for the air coming from the cooling air circulation zone of the bottom of the packaging.

The support elements and/or the support elements are oriented radially or substantially radially with respect to the longitudinal central axis of the packaging on which the support system is also centered.

This feature provides better circulation of fresh air towards the air passage(s), as well as better evacuation of heated air after it has passed through this/these passage(s). In other words, the particular orientation of the support and support elements limits the physical barriers generated by the presence of these elements, vis-à-vis the flow of air within the support system.

The supporting elements and/or the support elements are arranged radially outwards with respect to the central part of the radiation screen.

This makes it possible to avoid direct heat conduction between the central part of the bottom of the packaging, which is the hottest, and the ground, and limits the size of the central part of the radiation screen which includes the air passage(s) .

The radiative screen is equipped with a plurality of mechanical reinforcement elements interconnecting at least part of the bottom support elements and/or the support elements.

The mechanical reinforcement elements have radially inner ends connected together at the level of a central connecting member around which several air passages are delimited radially inwards, each of them also being delimited circumferentially by two reinforcement elements directly consecutive mechanics.

Each mechanical reinforcement element is secured, at its radially outer end, to one of the support elements and/or to one of the bottom support elements.

The assembly comprises hooking means allowing reversible hooking of the support system on the packaging, the hooking means preferably comprising fixing elements intended to cooperate with handling pins provided on the packaging.

This makes it possible to secure the packaging to the support system, so that the assembly can be moved in the storage building when handling the packaging vertically, and thus avoid having to move the packaging separately. and the support system. Once the packaging is placed on the support system, the latter is then preferentially attached to the dowels of the packaging.

Each support element has an end in contact with the bottom of the packaging taking the form of a layer of thermal insulation.

This makes it possible to reduce heat conduction through the support elements in contact with the bottom of the packaging, and limits any damage caused to this bottom of the packaging by these same support elements.

Finally, the subject of the invention is a method for storing a packaging belonging to an assembly as described above, the method comprising the positioning of the packaging on the support system arranged on the ground, so as to reveal the cooling air circulation zone of the bottom of the packaging.

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

This description will be given with regard to the appended drawings, among which;

shows a view in longitudinal axial section of an assembly according to a preferred embodiment of the present invention;

shows a sectional view taken along the line II-II of Figure 1;

shows a sectional view taken along the line III-III of Figure 1;

shows a view similar to that of Figure 1, with the assembly in the form of another preferred embodiment;

shows a top view of a radiative screen similar to that fitted to the assembly shown in the preceding figures, but according to another embodiment;

shows a top view of a radiation screen, according to yet another embodiment;

shows a perspective view of a support system intended to equip the assembly shown in Figure 4, but in the form of another preferred embodiment of the invention;

depicts a perspective view of part of the support system shown in Figure 7;

shows a bottom view of the support system shown in Figures 7 and 8; And

shows a schematic view of a reversible mechanical connection between the package and its support system.

DETAILED DISCUSSION OF PREFERRED EMBODIMENTS

Referring first to Figures 1 to 3, there is shown an assembly 100 according to a preferred embodiment of the invention, this assembly comprising a packaging 1 for storing radioactive materials, and its support system 3 on floor 5 of a storage building 7.

The packaging 1 is shown in a vertical storage position, in which its longitudinal central axis 2 is oriented vertically, namely orthogonally to the ground 5. Conventionally, it comprises a packaging bottom 4 opposite a removable cover 6 according to the direction of the height 8, parallel to the longitudinal central axis 2. extending around this axis 2. The bottom 4 and the cover 6 axially delimit a housing cavity 12 within which the radioactive materials (not shown) are received.

The assembly 100 also includes the support system 3 which, in the packaging storage configuration as shown in FIG. 1, is located between the bottom 4 of the packaging and the floor 5. This support system 3 can reside in a movable system placed on the ground 5, or, alternatively, in a system secured to the ground. The latter case is particularly advantageous for responding to seismic constraints.

The support system 3 comprises a radiative screen 20 serving for the thermal protection of the ground 7. This screen 20 has the shape of a plate, of identical or homothetic geometry to that of the bottom of the packaging 4. Here, it is of an overall disc shape centered on the longitudinal central axis 2 of the packaging, this axis 2 also corresponding to the longitudinal central axis of the system 3 and of the assembly 100.

The screen 20 has a central part 22 centered on the axis 2, and of diameter D1 less than an outer diameter D2 of the side packaging body. The ratio between the two diameters D1 and D2 is preferably less than 0.5. The external diameter D3 of the screen 20 is for its part greater than or equal to the external diameter D2 of the lateral packaging body, the ratio between D3 and D2 preferably being between 1 and 1.3.

The central part 22 mentioned above corresponds to the part of the screen 20 through which is made one or more air passages 24. In this preferred embodiment, there is provided a single air passage 24, of circular shape and centered on axis 2. This passage 24 has a diameter D4 generating a surface S1. Furthermore, the projected surface S2 of the packaging on the ground 5, along the axis 2, is such that the ratio between the surfaces S1 and S2 is preferably less than 0.25. This projected surface S2 can also be considered as the projected surface of the packaging on the radiation screen 20, still along the axis 2, but without taking into account the opening formed by the air passage 24.

The screen 20 has a first lower face 28, as well as a second upper face 30 opposite the first face. The air passage 24 connects these two faces 28, 30. The first lower face 28 is located parallel to and at a distance from the floor 5, so as to axially delimit between them a zone 32 of air circulation for cooling the floor. Similarly, the second upper face 30 is located parallel and at a distance from the bottom of the packaging 4, so as to axially delimit between them a zone 34 for the circulation of air for cooling the bottom of the packaging. The air passage 24 thus ensures communication between the two zones 32, 34, each open radially outwards.

The support system 3 also comprises, in the zone 34, a plurality of support elements 36 of the bottom of the packaging, spaced from one another. These support elements 36 are for example provided four in number, even if a different number can be adopted, without departing from the scope of the invention. Furthermore, each support element 36 projects vertically from the second face 30 of the screen 20, extending upwards through the area 34 until it contacts the bottom of the packaging 4. As is best visible in Figure 3, each support element 36 is oriented radially or substantially radially in relation to the axis 2, so as to better channel the flow of air within the zone 34 of circulation of cooling air of the wrapping background. In addition, these support elements 36 are arranged radially outwards with respect to the central part 22 of the screen 20. At its upper end of contact resting on the bottom of the packaging 4, each support element 36 can integrate a layer of thermal insulation so as to limit the direct transfer of heat from the bottom 4 to the floor 7.

Similarly, the support system 3 comprises in the area 32 a plurality of support elements 38 on the ground 5, spaced from each other. These support elements 38 are for example provided four in number, even if a different number can be adopted, without departing from the scope of the invention. Furthermore, each support element 38 projects vertically from the first face 28 of the screen 20, extending downwards through the zone 32 until it contacts the ground 5. The contact can be direct, or a layer of thermal insulation can be interposed between the support elements and the ground. Alternatively, the support elements 38 can be connected to a plate at their lower end, which plate would then be in contact with the ground to further standardize the temperature. Indeed, this plate makes it possible to limit the risks of hot spots on the ground, opposite the support elements 38.

As best seen in Figure 2, each support element 38 is oriented radially or substantially radially in relation to the axis 2, so as to better channel the air flow within the zone 32 of circulation floor cooling air. In addition, these support elements 38 are arranged radially outwards with respect to the central part 22 of the screen 20.

In this preferred embodiment, the support elements 36 and the support elements 38 are grouped together two by two so as to form feet 40 passing through the radiation screen 20, and extending vertically between the bottom of the packaging 4 and ground 5.

With this preferred embodiment, the outside fresh air is sucked into the zone 32 in which it circulates radially inwards, in the direction of the passage 24 and being channeled between the feet 40. During this circulation, the air cools the floor 5 which thus sees its temperature decrease, this decrease being accentuated by the effect of limiting the heat radiation procured by the radiative screen 20 arranged between the bottom of the packaging 4 and the floor 5. After having crossed the passage 24, the air enters the zone 34 in which it circulates radially outwards, also being channeled by the feet 40. This air circulation occurs by natural convection. In addition, this circulation of air in the zone 34 contributes to the cooling of the bottom of the packaging 4 married by this same moving air.

To further accentuate the suction effect by natural convection, the support system 3 may also comprise, at the periphery of the screen 20, an envelope 46 surrounding the side body 10 of the packaging. This envelope 46 is visible in Figure 4, and here adopts a cylindrical shape. It defines with the side body 10 an annular air suction channel 48 around the package. This envelope 46, centered on the axis 2 and of a shape homothetic to that of the side body 10, can extend over a length greater than the height of the support elements 36 of the bottom of the packaging, that is to say say be longer than the height of the zone 34. Preferably, this length of the envelope 46 is less than a quarter of the total length of this package in the storage configuration. Alternatively, the envelope 46 may not be cylindrical in shape, but take on a conical shape widening towards the top of the packaging, still being centered on the axis 2. This solution is particularly preferred in the case where the ratio between the aforementioned diameters D3 and D2 tends towards 1.

The support system may also comprise, at the outer periphery of the casing 46, an annular ring for radiological protection, the height of which is at least greater than that of the support elements 36 of the bottom of the packaging. In addition to its radiological protection role, this crown, which can extend over all or part of the height of the casing 46, also makes it possible to thermally insulate the casing 46 vis-à-vis the outside, to improve the draft due to the increase in internal/external temperature difference.

In the previously described modes, the radiative screen 20 is traversed by a single circular air passage. However, several passages 24 can be provided within the central part 22 of the screen 20, such as for example several circular passages 24 regularly distributed around the axis 2 as shown in FIG. 5. According to another embodiment possible shown in Figure 6, the air passages 24 may correspond to angular sectors of rings, separated from each other by ligaments of material 50.

Referring now to Figures 7 to 9, there is shown a support structure 3 according to another preferred embodiment of the invention. In this embodiment, six feet 40 are provided, all arranged radially and regularly distributed around the axis 2. These feet can rest directly on the ground, or else be covered with a layer of thermal insulation 52 intended to form the interface with the ground.

Furthermore, the radiation screen 20 is made by alternating, in the circumferential direction, angular screen sectors 54 and mechanical reinforcement elements 56. More specifically, the angular sectors 54 are ring sections, while that the mechanical reinforcement elements 56 are beams oriented radially and arranged at the interface between two directly consecutive ring sections 54, so as to secure them.

The beams 56 also perform the connecting function between the feet 40, since each of the latter is secured to the radially outer end of one of the beams.

On the other hand, at its radially inner end, each beam 56 is secured to a central connecting member 58 forming an integral part of the screen 20, this member 58 being cylindrical and centered on the axis 2. Thus, passages of air 24 are distributed in a manner similar to that shown on the screen of Figure 6, each being delimited radially inwardly by the central member 58, radially outwardly by a ring section 54 , and circumferentially by the radially inner ends of two directly consecutive beams 56.

FIG. 10 schematically represents a step in a method for storing the packaging 1 in the building 7, aimed at putting this packaging in place on the support system 3 already placed on the ground 5. In this respect, it is noted that for its storage, the packaging 1 is freed from its shock-absorbing covers which usually equip its axial ends during its transport.

The simple fact of placing the packaging 1 on the system 3 reveals the cooling air circulation zone 34 of the bottom of the packaging. Once installed, the packaging 1 is preferably fixed temporarily to the support system 3, so that these two entities can be moved simultaneously during the handling operations carried out during the storage period in the building 7.

To achieve this connection between the packaging 1 and the system 3, the latter can be equipped with reversible attachment means comprising fixing elements 64 intended to enclose pins 62 of the packaging. These dowels correspond to the handling dowels usually provided near the bottom of the packaging.

Of course, various modifications can be made by those skilled in the art to the invention which has just been described, solely by way of non-limiting examples and according to the scope defined by the appended claims. In particular, the different preferred embodiments can be combined with each other.

Claims (13)

Assembly (100) comprising a cask (1) for storing radioactive materials as well as a cask support system (3) intended, in a cask storage configuration, to be arranged between a bottom ( 4) packaging and a floor (5) of a storage building (7),
characterized in that the support system (3) comprises a radiative shield (20) for thermal protection of the ground having a first lower face (28) as well as a second upper face (30) opposite the first, the radiative shield (20) comprising a central part (22) provided with at least one air passage (24) providing communication between a zone (32) for the circulation of air for cooling the floor defined under the first face (28) of the radiative screen, and a cooling air circulation zone (34) for the packaging bottom defined between the second face (30) of the radiative screen (20) and the packaging bottom (4),
the support system (3) further comprising a plurality of spaced-apart package bottom support members (36), each support member (3) projecting from the second face (30) of the radiative screen (20) and extending through the cooling air circulation zone (34) of the bottom of the packaging (4) until it comes into contact with the latter,
the support system (3) also comprising a plurality of support elements (38) projecting into the zone (32) of circulation of air for cooling the floor, from the first face (28) of the radiation screen (20). Assembly according to Claim 1, characterized in that the central part (22) of the radiation screen, in which each air passage (24) is circumscribed, has a first diameter D1 smaller than the greatest transverse dimension D2 of the packaging (1), so as to meet the following relationship:
D1<0.5. D2 Assembly according to Claim 1 or Claim 2, characterized in that the said at least one air passage (24) has a cumulative surface S1 for air circulation, in that the packaging (1) in the storage configuration has a longitudinal central axis (2) orthogonal to the ground (5) and to the radiation screen (20) and centered with respect to the latter, in that the packaging has a projected surface S2 on the ground (5), along the central longitudinal axis (2), and in that the surfaces S1 and S2 correspond to the following relationship:
S1<0.25. S2 Assembly according to any one of the preceding claims, characterized in that the support elements (36) of the bottom of the packaging and the support elements (38) form two by two feet (40) passing through the radiative screen ( 20) thermal protection. Assembly according to any one of the preceding claims, characterized in that in the storage configuration, the support system (3) comprises an envelope (46) carried at the periphery of the radiation screen (20), the envelope defining an air suction channel (48) around the package (1). Assembly according to any one of the preceding claims, characterized in that the support elements (38) and/or the support elements (36) are oriented radially or substantially radially with respect to the central longitudinal axis (2) of the packaging on which the support system (3) is also centered. Assembly according to any one of the preceding claims, characterized in that the support elements (38) and/or the support elements (36) are arranged radially outwards with respect to the central part (22) of the radiation screen (20). Assembly according to any one of the preceding claims, characterized in that the radiation screen is equipped with a plurality of mechanical reinforcement elements (56) connecting together at least a part of the support elements (36) of the bottom and /or support elements (38). Assembly according to the preceding claim, characterized in that the mechanical reinforcement elements (56) have radially inner ends connected to each other at the level of a central connecting member (58) around which are delimited radially inwards several passages of air (24), each of them also being delimited circumferentially by two directly consecutive mechanical reinforcement elements (56). Assembly according to Claim 8 or 9, characterized in that each mechanical reinforcement element (56) is secured, at its radially outer end, to one of the support elements (38) and/or to one of the elements support (36) of the bottom (4). Assembly according to any one of the preceding claims, characterized in that it comprises attachment means allowing reversible attachment of the support system (3) on the packaging (1), the attachment means preferably comprising elements fastening (64) intended to cooperate with handling pins (62) provided on the packaging (1). Assembly according to any one of the preceding claims, characterized in that each support element (36) has an end in contact with the bottom of the packaging taking the form of a layer of thermal insulation. Method for storing a packaging (1) belonging to an assembly (100) according to any one of the preceding claims, characterized in that it comprises placing the packaging (1) on the support system (3) arranged on the ground (5), so as to reveal the area (34) of cooling air circulation of the bottom of the packaging (4).