FR2721430A1 - Containers for dry storage of heat-releasing materials - Google Patents

Abstract

Containers of heat-releasing materials are placed in leaktight, vertical storage tubes and cooling air passes over the outside of the tubes. To ensure good cooling air contact, an enclosure is welded to the tubes. The convective air flow rate is determined by the temp. generated in a storage tube and is auto-compensating.

Description

 The present invention is directed to a device and method for dry storage of heat generating materials. The device and method are particularly suitable for storing radioactive materials with high thermal clearance. They are suitable for said storage even under adverse seismic conditions. Such materials may in particular be in the form of containers containing glasses in which fission products are immobilized.

 The invention will be described in the following text with reference to the storage of this type of material, but it will be readily understood by those skilled in the art that the invention is not limited to this context. The device and method currently claimed are suitable for storing any type of material, radioactive or not, toxic or otherwise, solid or liquid ... with high heat release; the technical problem solved by the invention being that of the evacuation of the released calories.

 The storage, at least temporarily, of nuclear waste is, according to a first variant, a storage under water. Said waste is immersed in the water of a pond, which must be permanently decontaminated and cooled.

The installation that includes said pond and its annexes generates high volumes of effluents, requires significant investments and has high operating costs.

 According to a second variant, dry storage is used. Such dry storage advantageously involves, for the evacuation of the heat released by the waste, forced or natural air circulation. Said heat is evacuated by convection. Devices for implementing such a dry storage have been described in particular in patent applications FR-A-2 384 325, GB-A-2 096 937, EP-AO 151 035 and FR-A-2. 601,809.

 More particularly, the teaching of the last of these documents describes a dry storage device, in which is implemented a storage type storage in casemate. According to this storage method, the waste is placed inside wells (vertical tubes), themselves distributed inside a closed room by a biological protection barrier, for example a concrete wall. Said wells are closed at their lower part and open at their upper part; the irradiated waste being introduced into said wells by means of a transfer machine which makes it possible to pass them through orifices suitably arranged in the biological protection barrier. These orifices are located in the upper wall of the room and therefore allow access to the interior of the wells, from a handling room located above said room.They can of course be closed sealingly, at the help of adequate means type plugs.

 The outer walls of said wells are cooled by the circulation, by natural convection, of a coolant, generally air. The cold air supply is usually at the bottom of the room while the hot air extraction can be at the top of the room or in a side wall. According to said application FR-A-2 601 809, the arrangement of the wells is such that the cooling of each of them is ensured independently.

 The present invention is in this context of dry storage, in casemate, with convection or draft cooling, natural or forced.

 More specifically, according to its first object, it proposes a device for dry storage of materials giving off heat in wells, using natural or forced cooling means which make it possible to maintain the temperature of said materials within prescribed limits and this, independently on the one hand the filling rate of said wells and the storage itself and on the other hand the heat output and its distribution.

 The dry storage device according to the invention comprises a) an enclosure which has at least one inlet opening for a heat transfer fluid, cold, in its lower part and at least one outlet opening for said hot heat transfer fluid, in its upper part and b) at least one well, disposed in the room defined by said enclosure; said well being adapted to contain, in a sealed manner, the materials to be stored.

 Characteristically, said well is provided, over at least part of its height, with an outer envelope, comprising at least one opening at its lower part and at least one opening at its upper part; said envelope delimiting a circulation duct of said heat transfer fluid.

 In known manner, the storage device of the invention comprises at least one well in a room defined by an enclosure.

 It generally comprises a network of wells inside said room. The wells of said network may be arranged in various configurations. As an illustration, mention is made of the staggered arrangement.

 In each well, the materials to be stored are available. Said materials have generally been preconditioned. They often come in the form of containers. Such containers are stacked, one above the other, in the well. Whatever the conditioning of said materials, the wall of the well, in which it is stored, constitutes a sealed barrier.

 Most often, in the nuclear context, as described in FR-A-2 601 809, the wells extend to the upper wall of the room and are not filled in their upper part. The "unfilled" zone, in the upper part, promotes the evacuation of the hot heat transfer fluid towards the outlet opening. Generally, said wells are not, either, filled in their lower part. The "unfilled" zone, in the lower part, promotes the distribution of cold heat transfer fluid in the storage room.

 Said storage room is delimited by an enclosure. This enclosure has the appropriate openings for the convective circulation (natural or forced) of the heat transfer fluid or cooling fluid. Its exact nature depends on the nature of the materials stored in the wells. In the nuclear context, said enclosure generally consists of concrete walls.

 More specifically, in this context, the storage room is often a pit, located between two slabs, delimiting an upper plenum and a lower plenum; the assembly being preferably made of concrete.

 The lower plenum communicates with the coolant inlet while the upper plenum communicates with its outlet.

 Said pit contains the wells. Each well is closed by a plug, at the level of the upper slab. Said slab has an upper face which constitutes the floor of the handling room and a lower face which constitutes the ceiling of the storage room. This lower face may be horizontal or advantageously inclined, arranged so as to rise as one approaches the outlet opening. Such an arrangement has the effect of promoting the evacuation of the hot heat transfer fluid towards said outlet opening. The same result can be obtained with a horizontal lower face equipped with a deflector.

 The heat transfer fluid most often used in the dry storage device of the invention (as in devices of this type of the prior art) is air.

 However, it would not be outside the scope of the present invention to use another fluid, for example another gas. The expression "heat transfer fluid, cold" used in the present text refers to the fluid that enters the room via one (or) cold coolant inlet opening (s) and which is at a certain temperature. = external ambient temperature, in the case of air) whereas the expression "hot heat transfer fluid" designates said fluid which has been heated by coming into contact with the heat-generating wells, which is at a temperature 62 (82> 81) at the outlet opening (s) of said hot heat transfer fluid.

 As in some devices of the prior art, the circulation of said coolant can be done, within the storage device according to the invention, naturally, by convection. The outlet opening (s) of the hot heat transfer fluid is connected to a chimney. Said chimney assures under the effect of its height, a setting vacuum, which ensures the circulation of heat transfer fluid in the storage device. Said chimney optionally allows additional depression to compensate for the effects of wind between its outlet and the air intake. A special device can be provided at the top of the chimney to enhance the beneficial effect of the wind.

 Circulation of said heat transfer fluid can also be done, at least in part, forcibly in the storage device according to the invention.

To this end, the appropriate means (fans, pumps, etc.) will be used at the inlet (s) and / or outlet (s) of the coolant. By implementing such a forced circulation of said fluid, generally more homogeneous temperatures are obtained throughout the storage. You can also operate with a lower chimney.

 Characteristically, according to the invention, the well is provided, over at least a portion of its height, with an outer envelope delimiting a circulation duct of said heat transfer fluid. Said envelope intervenes, preferably, on the loading height of said well, to the right of thermal release packages stored therein.

 The intervention of such a conduit has proved advantageous, particularly in case of low filling rate of the storage device, with implementation of natural or forced cooling means.

 Said envelope, provided with openings allowing in the lower part the penetration of the fluid in the duct generated and in the upper part its output of said duct, can exist in different forms.

 The well may be of any shape and in particular of cylindrical or prismatic shape.

 According to a preferred variant, said storage well is a cylindrical or parallelepipedic well and said envelope is coaxial with said wells.

According to this variant, said well thus has a circular, square or rectangular section.

 Whatever the shapes of said well (advantageously cylindrical with a circular or parallelepipedal section with a square section) and the envelope (advantageously cylindrical with a circular or parallelepipedic section with a square section) surrounding it, said envelope is connected to said well, at its or its outer walls. Such a connection can be made by any conventional means, since said means does not significantly disturb the free circulation of the heat transfer fluid. Such a means must ensure stably maintaining said envelope around said well.

 The connection can be direct and involve, as such means, parts of the envelope (for example, at the ends of said envelope, it can be provided in the structure thereof, cuts, with folding of the material , towards the axis of the well). It can be indirect and involve, as such means, spacers, gussets ... It can be both direct and indirect ..

 To secure the various elements of the assembly, it is generally performed welds, given the nature of the materials involved (usually stainless steel).

 Advantageously, the outer casing surrounding the well has open upper and lower ends.

 Incidentally, it will be noted here that it is possible, according to a variant of the invention, to provide, inside the heat transfer fluid circulation duct - duct delimited between the well and the envelope associated therewith according to the invention. invention - means forming baffle, to impose said fluid a specific movement. One may wish to improve thus its action.

 According to a preferred variant, said outer casing is a tube, at the lower and upper ends open.

 Advantageously, such a tube surrounds a cylindrical well, said tube and said well having a circular section. Thus, each well is surrounded by an outer envelope which delimits a coaxial annular space, open at its lower and upper ends. Such an arrangement, concentric, is particularly advantageous in that it facilitates the seismic dimensioning; the relative movements of the well and its envelope being authorized both seismically and thermally.

 Whatever the respective shape of the well and the envelope, which according to the invention is attached thereto, said envelope intervenes on at least a portion of the height of said well. On its intervention height, it channels the heat transfer fluid. It allows it to reinforce its action of cooling the walls of the well.

 To obtain an optimum result, at the level of the evacuation of the calories, said envelope is disposed over the entire filling height of the well.

 As indicated above in the present text, said well extends generally to the upper wall of the room and is not filled in its upper part. Thus, particularly in the nuclear context, the filling height of the well is always lower than its total height.

 In any case, it is advantageously provided that said well is not provided with an envelope at its upper part; which promotes the evacuation of the hot heat transfer fluid to the outlet opening.

 However, in the nuclear context - with another layout of the room and wells - or in a non-nuclear context, the intervention of the outer shell, according to the invention, over the entire height of the wells, can not be excluded. at least up to their upper end; said wells being filled or not filled to their full height.

 As regards their lower part, advantageously it is not surrounded by said outer casing. It thus provides a free circulation space cold coolant. It is distributed perfectly throughout the lower part of the room.

 Incidentally, it will be noted here that generally said lower part of the wells is not filled with materials. It advantageously comprises means for stabilizing stored materials and wells and means for anchoring said wells to the lower slab (wall) of the room.

 As specified above, the storage device according to the invention comprises at least one storage well in the room. It usually includes a network of such wells. In this hypothesis, the most common of a plurality of wells, it will be readily understood that advantageously the invention is implemented at each well; i.e. that each well of the network is provided, on at least part of its height, with an outer envelope.

 Said invention can, moreover, be implemented in a storage device comprising several premises, contiguous to their side wall (s).

 The thickness of the duct, to be provided according to the invention, for the circulation of the coolant between the wells and their respective shells, will be easily optimized by the skilled person, who will have previously determined the flow of said coolant necessary for the evacuation of calories.

 On reading the above description, to consider with the accompanying drawings, the description thereof and the example which follow, the skilled person will not fail to grasp the merit of the present invention.

 In general, the channeling of the heat transfer fluid in forced or natural circulation strengthens its action.

 For a given well, its thermal load created in the space, generated between said well (more precisely, its external wall or its external walls) and the corresponding envelope (more precisely its internal wall or its internal walls), an upward movement said fluid that heats in contact with the well. The vertical component of said movement is largely preponderant.

The flow rate resulting from this effect is all the more important as the heat load is high. The system is, from this point of view, self-regulated.

 Incidentally, it will be noted here that, within the devices of the prior art, described in documents FR-A-2 384 325, GB-A-2 096 937 and EP-A-0 151 035, the circulation of the fluid of cooling is rather transverse (compared to the wells).

 Moreover, in the event of unequal distribution of waste in the premises containing a network of wells, and thus of unequal distribution of the heat load of the various wells of the network, a preferential circulation of the cooling fluid is obtained along the hottest wells. In the same way, in the case of incomplete storage, it is shown that, as the filling rate decreases, the overall flow rate decreases but, on the other hand, the flow rate along the hottest wells increases. This shows that an incomplete filling rate does not penalize the performance of the system vis-à-vis the temperature of the materials stored and that the system is, from this point of view also (relative to the filling ratio), self -régulé. The coolant is always, even with a low overall flow, sucked strongly around hot spots ...

 The device of the invention makes it possible to ensure good homogeneity of the temperatures of the materials stored, even for partial fillings and with materials of different thermal powers.

 Note finally that, remarkably, the circulation of the fluid, in the spaces generated between the wells and their outer shell, does not have to be imposed: a horizontal wall separating the wells, forcing the fluid to pass into said spaces, is not necessary. Said fluid, of itself, naturally, preferentially goes up in said spaces along the loaded wells. The effectiveness of such a horizontal wall is only marginal.

Even in the absence of such a wall, the distance between the wells, provided with their outer shell, has little influence and is, in fact, determined by the constraints of implementation.

 The device of the invention, by involving at the level of the wells an outer envelope, thus decisively improves the result obtained, both with a circulation of the natural and forced cooling fluid.

 The subject of the invention is a method for storing heat-releasing materials used in a storage device, as described above; device which involves, typically, around the wells, an outer envelope. Said second object could equally well be described as a process for cooling heat-generating materials.

 Such a method is particularly advantageous in that it is of simple management.

 In fact, the presence of the envelopes makes it possible to overcome the thermal constraints: whatever is the case, when filling the wells, the distribution of the materials to be stored within said wells, storage is ensured under good conditions.

 We do not have to respect a filling order to avoid local overheating. The materials to be stored can be distributed, in the available places, randomly.

 According to a preferred variant of the method of the invention, the wells are thus filled without a distribution key; key imposed, in the processes of the prior art, by thermal stresses.

 Such filling, without distribution key, allows easier management, more flexible operation ... at the convenience of the operator.

 The method of the invention is advantageously used, both with natural circulation of the heat transfer fluid with forced circulation thereof.

 It is now proposed to describe the invention with reference to the appended figures in which: FIG. 1 is a general diagram of a storage installation according to the invention; - Fig. 2 is a longitudinal section, on a larger scale, of a well of the storage facility according to FIG.

 The description below is to be considered while referring simultaneously to the two figures.

 The storage of containers 1 containing radioactive materials is carried out in a pit 2 cooled by natural draft of air. Said containers 1 are shown in FIG. 2. Said pit 2 comprises an air intake 3, wells 4 and a chimney 5.

 It is bounded by concrete biological protection walls.

Said walls have, in the lower part, an inlet port 3 'of coolant (air) cold and, in the upper part, an outlet or extraction port 5' of said fluid, hot. The facing horizontal walls respectively constitute the lower slab 6 and the upper slab 7. Under said upper slab 7, due to the high temperatures generated, a layer of heat-insulating material 8 has been disposed. Said material is represented in FIG.

 The upper slab 7 has orifices for communicating the interior of the wells 4 and a handling hall 9. For the handling of the containers 1 - their placement in a well 4 or their extraction of a well 4 - one uses a ferry 10. The ports communicating said wells 4 and said handling hall 9 are closed by removable caps 1 1 (manipulable from said handling hall 9)).

 In the upper part of the pit 2 or upper plenum, said wells 4 are empty. Said upper plenum communicates with the chimney 5 by 5 '.

In the lower part of the pit 2 or lower plenum, the bottom of the wells 4, containing the containers 1, is not directly on the lower slab 6. The bottom of each of said wells 4 is in fact equipped with different means: - a damper 13, damper of falling containers;
a compensator 14, allowing significant expansion, inherent to the temperature conditions prevailing in the wells 4 (high temperatures);
an anchoring device 15, to ensure the stability of said wells 4, particularly in the event of an earthquake.

 Through said dampers 13 and said anchor plate 15, each well 4 is secured to the lower slab 6. Said lower plenum communicates with the air intake 3 by 3 '.

 Characteristically, each of said wells 4 is surrounded, at a distance, over its entire filling height, with an outer envelope 20. It thus delimits, around said wells 4, annular spaces 21 in which the coolant circulates from the bottom to the top.

 The outer shells 20 are secured to the wells 4 by welding, by means of gussets 22, for example 3 to 120, at their top and spacers 23, for example 4 to 90-, at least one level of their height. .

 In Figure 1, there is shown in 12 additional premises.

 The invention is illustrated by the example below.

 The storage of glass packages (containers containing vitrified fission products) is implemented in a pit cooled by natural draft of air. The air enters said pit, at the bottom, at 19-C. Said pit is delimited by a concrete enclosure.

 Said pit has 180 wells, divided into 18 rows of 10 wells.

Each of said wells has a diameter of 482 mm and a useful height of about 15.2 m. On said useful height, there is coaxially, the outer casing with a diameter of 610 mm. The walls of the wells and the outer shells are made of stainless steel.

We can store 12 containers, stacked on each other, in each well.

So 2160 containers are stored in the pit, in nominal operation (full load).

 The lower plenum has a height of about 1.8 m, the upper plenum a height of about 2 m.

The installation is sized to ensure:
- in nominal operation, an air temperature, at the exit of the pit, of 1400C, maximum;
- in disturbed operation, a core temperature of the packages, always lower than 5100C (in any circumstance).

 It has been verified that the natural draft ensures, according to the invention, the required cooling whatever the loading of the pit.

Calculations have been made for typical easily modelable configurations, allowing to cover all configurations:
- full load (nominal operation)
- half loading (every other row)
- loading 1/18 (single row)
- loading 1/180 (one well).

The results summarized in the table below were obtained.

<Tb>

<SEP> Any <SEP> char <SEP> e <SEP> Mid-loaded <SEP> 1 <SEP> row <SEP> 1 <SEP> well
<tb> Temperature <SEP> heart <SEP> 432 <SEP> 410 <SEP> 403.4 <SEP> 384
<tb><SEP> maxit <SEP>
<tb> Temperature <SEP> max. <SEP> of <SEP> 136.2 <SEP> 106.5 <SEP> 75 <SEP> 55
<tb><SEP> plenum2 <SEP> C) <SEP>
<tb> Temperature <SEP> in <SEP> foot <SEP> of <SEP> 111.4 <SEP> 78 <SEP> 33 <SEP> 22
<tb> chimney <SEP> (C) <SEP>
<tb> Overall <SEP> Flow <SEP> (kg / s) <SEP> 43.6 <SEP> 35.2 <SEP> 17.3 <SEP> 8
<tb> 1. This is the maximum temperature at the core of the glass in the highest package of the hottest well.

2. This is the maximum air temperature in the upper plenum.

 These results show that, typically, cooling efficiency - by natural convection - increases with low loading.

 It has also been verified that the cooling is also provided with a single heat pump in the installation which is sufficient to create a heat engine in the concerned well.

 The full load therefore remains always the hottest and it is in this case that we will dimension an installation designed according to the present invention.

Claims (10)

- Claims  1. Dry storage device, of materials (1) generating heat, comprising: - an enclosure having at least one inlet opening (3 ') for a heat transfer fluid, cold, in its lower part and at least one outlet opening (5 ') for said hot heat transfer fluid in its upper part; - At least one well (4) disposed in the room (2) defined by said enclosure; said well being adapted to seal said materials (1); characterized in that said well (4) is provided, over at least a portion of its height, with an outer envelope (20), having at least one opening at its lower part and at least one opening at its upper part; said outer casing (20) delimiting a circulation duct (21) of said heat transfer fluid.  2. Device according to claim 1, characterized in that said well (4) is a well (4) cylindrical or parallelepipedic and in that said casing (20) is coaxial with said well (4).  3. Device according to one of claims 1 or 2, characterized in that said outer casing (20) is a tube at the lower and upper ends open.  4. Device according to any one of claims 1 to 3, characterized in that said outer casing (20) is disposed over the entire filling height of said well (4); said filling height being generally less than the total height of said well (4).  5. Device according to any one of claims 1 to 4, characterized in that said well (4) is not provided with said outer casing (20) at its upper part, so as to promote the evacuation of the heat transfer fluid hot towards the outlet opening (5 ').  6. Device according to any one of claims 1 to 5, characterized in that said well (4) is not provided with said outer casing (20) at its lower part, so as to promote the distribution of cold coolant in said room (2).  7. Device according to any one of claims 1 to 6, characterized in that baffles are disposed in said circulation duct (21) of said heat transfer fluid.  8. Device according to any one of claims 1 to 7, characterized in that it comprises a well network (4) inside the room (2) defined by said enclosure; each well (4) of said network being provided with an outer envelope (20).  9. A method for dry storage of materials (1) generating heat characterized in that it is implemented within a storage device according to any one of claims 1 to 8 with natural or forced circulation of coolant.  10. Storage method according to claim 9, characterized in that the filling of the wells (4) is performed without distribution key.