EP1317757B1 - Installation for storing irradiated fuel or radioactive materials - Google Patents

Description

Technical area

The invention relates to medium or long-term storage of irradiated nuclear fuel or various types of radioactive material. More specifically, it concerns storage facilities for radioactive materials where the residual heat released by the fission reactions (radioactive decays) is evacuated by natural convection, mixed or forced and where a number of subsystems (called wells, packages or containers) containing these irradiated nuclear fuels or these various types of radioactive materials are arranged in the same room or cavity.

State of the art

There are storage facilities for spent fuel or nuclear material operating according to the following general principle. Subsystems, usually metallic (for example "sinks" in these installations), containing spent fuel or radioactive material are regularly placed in a room. This room has a floor and a horizontal ceiling. The arrangement of subsystems is generally following a regular "network", for example square or triangular. An air intake system, which may include filters, burglar-proof grilles, and a number of other devices that provide various features, draws air from outside the room. The air thus brought heats up in contact with the subsystems and rises by natural or mixed convection, or driven by the overall movement of the air. An air outlet circuit, which may include a chimney to favor the draft or a fan and other devices to ensure other functionalities, draws air from the room (generally preferentially air in the vicinity of the ceiling, because that's where warm air accumulates) and throws it out.

These facilities can function satisfactorily. However, they have a number of disadvantages. The flow of air in the room is turbulent, multidimensional, very complex and difficult to predict. Since the ceiling of the room is horizontal, warm air tends to accumulate under the ceiling in areas farthest from the air outlet. Calculations showed that the hottest spots of the installation could be near the ceiling, far from the air outlet area. This is due to the fact that the air, to evacuate to the exit, only benefits from the Archimedes thrust created by the only gradient of thickness of the hot air layer under ceiling.

In cases where the arrangement of subsystems permits, preferential Air is formed in areas of lesser resistance without a subsystem that generates heat. This air bypassing the hot subsystems degrades the performance of the installation because it "clogs" the air inlet and outlet circuits without contributing to the cooling of the subsystems. This congestion results in a lowering of the air temperature in the chimney (and therefore a reduction in the draft, the flow motor), an unnecessary overflow and thus an expensive oversizing of the input and output circuits. air.

Transients (seasonal, daily or with characteristic times of up to a few minutes) of outdoor air temperature are filtered by the thermal inertia of the walls and other devices of the air intake circuit. When warmer air than the inlet circuit arrives, this results in a lowering of the air temperature between the outside and the entrance of the room. This lowering of temperature results in an increase in the relative humidity of the air entering the room. This increase in relative humidity favors condensation on the metal structures of the cold parts of the subsystems and on other surfaces. This condensation increases the risk of corrosion and degradation of metal structures in the cold parts of subsystems and other surfaces. These corrosions or degradations can limit the life of the installation. This phenomenon can be particularly troublesome because it is linked to the very complex structure of the flow and is therefore difficult to predict in a reliable quantitative manner.

When the subsystem is disposed vertically or has a vertical preferred direction and this subsystem releases power, a thermal boundary layer of natural and mixed convection develops and can go up to the ceiling it licks. The lower surface layer of the ceiling is therefore heated to a temperature above the mixing temperature of the overall air flow rate. The heat radiation from the wells can also cause additional heating, especially if the surfaces are very emissive. Either of these phenomena, or a combination of both, can lead to excessive ceiling temperature, requiring special and expensive precautions to prevent it from breaking down.

• Faible fiabilité de prédictions quantitatives de l'écoulement dans la salle.
• Température élevée de l'installation au voisinage du plafond, loin de la zone de sortie de l'air.
• De l'air contourne inutilement les sous-systèmes et encombre les circuits d'entrée et de sortie d'air.
• Les transitoires de température de l'air extérieur peuvent induire une condensation, elle-même génératrice de risques peu prédictibles de corrosion ou dégradation.
• La couche limite thermique issue du sous-système, disposé verticalement ou avec une direction privilégiée verticale sous ou à proximité d'un plafond, peut chauffer les couches superficielles inférieures du plafond à une température supérieure à la température de mélange du débit global d'air.

There is therefore the problem of overcoming the disadvantages mentioned above which can be summarized as follows:

• Low reliability of quantitative predictions of flow in the room.
• High temperature of the installation in the vicinity of the ceiling, far from the air outlet zone.
• Air unnecessarily bypasses the subsystems and clutters the air inlet and outlet circuits.
• Outdoor air temperature transients can induce condensation, itself generating risks that are unlikely to corrode or deteriorate.
• The thermal boundary layer derived from the subsystem, vertically or vertically preferred under or near a ceiling, may heat the lower surface layers of the ceiling to a temperature above the mixing temperature of the overall air flow rate. .

• la simplicité et la robustesse de fonctionnement.
• la passivité, c'est-à-dire le bon fonctionnement même sans surveillance continue.
• la stabilité de fonctionnement.
• L'expérience acquise grâce aux installations existantes.
• Le bon fonctionnement dans la durée : absence de pièces mécaniques mobiles, utilisation d'un principe physique très simple, etc.
• La facilité de gestion de l'installation, de l'entreposage ou du désentreposage de nouveaux combustibles irradiés ou de matières radioactives.

The reduction of the consequences of these disadvantages must not compromise the primary functionalities of the installation (evacuation of the power released, biological protection against ionizing radiation, secular durability, ease of loading and unloading the fuel, possibility of monitoring and maintaining the installation, etc.), nor the advantages of this type of installation, among which are:

• simplicity and robustness of operation.
• passivity, that is, good functioning even without continuous monitoring.
• the stability of operation.
• Experience gained from existing facilities.
• The good functioning in the duration: absence of moving mechanical parts, use of a very simple physical principle, etc.
• The ease of management of the installation, storage or de-storage of new spent fuel or radioactive material.

This type of installation is intended for radioactive materials. Specific regulations and especially the acceptability of the public require the ability to credibly calculate its thermo-aeraulic behavior. A strong constraint is therefore to be able to demonstrate in which measurements the sizing calculations are reliable and predictive. This constraint is particularly concerned with the description of the thermo-thermal operation complex of the installation and encourages the search for the solutions leading to the most structured and predictive flows, even at the cost of a slight complication of the system, or even a slight degradation of the thermal performances.

Document FR-A-2 721 430 discloses a device and a method for dry storage of heat-generating materials, in particular for radioactive materials. The disclosed device includes all features of the preamble of claim 1.

Presentation of the invention

To improve the predictive quality of thermoaerulic calculations in the room of the storage facility, it is proposed to voluntarily structure the flow in the vicinity of the subsystems by imposing a preferential direction to the flow of air. This preferential direction facilitates the modeling of the thermoaerulic flows of the air around the device and consequently makes the results obtained quantitatively more reliable.

• une salle pourvue d'un plancher, d'un plafond et de parois latérales,
• une pluralité de moyens de réception pour recevoir le combustible irradié ou les matières radioactives, ces moyens de réception étant disposés dans la salle de façon à pouvoir être soumis à la circulation d'un fluide gazeux de refroidissement,
• des moyens d'introduction de fluide gazeux dans la salle permettant d'introduire ledit fluide gazeux de refroidissement,
• des moyens d'évacuation de fluide gazeux hors de la salle pour évacuer ledit fluide gazeux de refroidissement après sa circulation sur les moyens de réception,
• des moyens permettant de canaliser ledit fluide gazeux de refroidissement pour lui donner une direction préférentielle de circulation lorsqu'il circule sur les moyens de réception, comportant des chemises entourant les moyens de réception en laissant un espace entre elles et les moyens de réception pour la circulation du fluide gazeux de refroidissement, ces chemises possédant des ouvertures d'entrée et de sortie pour assurer la circulation du fluide gazeux de refroidissement, l'installation étant caractérisée en ce que les moyens permettant de canaliser le fluide gazeux de refroidissement comprennent également des cloisons reliant des chemises, ces cloisons étant disposées selon une direction correspondant à la direction préférentielle de circulation du fluide gazeux de refroidissement.

The invention relates to an irradiated fuel storage facility or radioactive material comprising:

• a room with a floor, a ceiling and side walls,
• a plurality of receiving means for receiving the irradiated fuel or the radioactive materials, these receiving means being arranged in the room so as to be subject to the circulation of a gaseous cooling fluid,
• means for introducing gaseous fluid into the room for introducing said gaseous cooling fluid,
• means for evacuating gaseous fluid from the room to evacuate said gaseous cooling fluid after it has been circulated on the reception means,
• means for channeling said gaseous cooling fluid to give it a preferential direction of circulation as it circulates on the receiving means, comprising folders surrounding the receiving means leaving a space between them and the receiving means for the circulation cooling gaseous fluid, these jackets having inlet and outlet openings to ensure the circulation of gaseous cooling fluid, the installation being characterized in that the means for channeling the gaseous cooling fluid also comprise connecting partitions. shirts, these partitions being arranged in a direction corresponding to the preferred direction of circulation of the gaseous cooling fluid.

Advantageously, the receiving means adjacent the side walls of the room are arranged as close as possible to these side walls to prevent the gaseous cooling fluid form bypass currents. This can be done by arranging the receiving means (or subsystems) along a regular network to the walls by minimizing the distance between sidewall and adjacent subsystems.

Shirts can also be radiative screens.

The presence of partitions connecting shirts, these partitions being arranged in a direction corresponding to the preferred direction of circulation of the gaseous cooling fluid, has the effect of further improving the structuring of the flow of the gaseous cooling fluid.

The means for channeling the gaseous cooling fluid may also comprise partitions connecting at least one side wall of the room to adjacent shirts of this side wall, these partitions being arranged in a direction corresponding to the preferred direction of circulation of the gaseous fluid cooling. This contributes to further improving the structuring of the gas flow.

The installation may further comprise auxiliary means for channeling said gaseous cooling fluid, these auxiliary means being located between a side wall of the room and one or several folders and being arranged in a direction corresponding to the preferred direction of circulation of the gaseous cooling fluid. These ancillary means make it possible to reduce the bypass currents when the subsystems are arranged according to particular networks, for example according to a triangular network.

Preferably, if the gaseous fluid discharge means are located on the ceiling or near the ceiling, the ceiling is inclined and the gaseous fluid discharge means are located in the highest part of the room. This has the effect of reducing the maximum temperature of the gaseous fluid in the vicinity of the ceiling, away from the exit zone of the gaseous fluid. The angle of inclination of the ceiling can be between 10 ° and 20 ° relative to the horizontal. Preferably, this angle is equal to 15 °. This inclination allows the hot gas to evacuate more easily thanks to the buoyancy forces (Archimedes' thrust), to avoid its accumulation in these zones and thus to avoid the creation of hot spots.

The room may also be provided with an inclined floor rising towards the gaseous fluid evacuation means. This further improves the thermoaerulic behavior. An advantage of this solution is to leave a passage section for the gaseous fluid greater at the inlet than at the outlet. This promotes a more constant gas velocity to feed the various subsystems and ensure a more uniform fresh gaseous fluid supply of all subsystems.

The installation may further comprise a bypass circuit of the cooling gaseous fluid to recycle a portion of the gaseous cooling fluid, having circulated in the room or having been in thermal contact with the room. This portion of recycled gaseous cooling fluid can be taken from a discharge stack communicating with the gaseous fluid discharge means. This avoids that temperature transients of the gaseous fluid (air for example) induce a condensation generating risks of corrosion or degradation unpredictable. Part of the gaseous fluid heated and exiting the storage room is reintroduced into the input circuit, preferably as close as possible to the storage room to increase the temperature of the gas entering the room and therefore of decrease the relative humidity.

Adjustable pressure drop members may be provided in the bypass circuit or in the gaseous fluid discharge means for controlling the amount of recycled gaseous cooling fluid.

Thermal radiation plates may be associated with the receiving means, these plates being located near the ceiling to destructure the thermal boundary layer to the surface of the ceiling. This prevents the thermal boundary layer from a subsystem, arranged vertically or with a vertical preferred direction under or near the ceiling, to heat the surface layers. under the ceiling at a temperature above the mixing temperature of the overall flow of gaseous fluid. These plates play a dual role. By destabilizing the thermal boundary layer, they cause a mixture of the gaseous fluid and a drop in its temperature. They also act as radiative screens, at least partially protecting the ceiling of the thermal radiation from the receiving means.

Brief description of the drawings

• la figure 1 est une vue en coupe verticale d'une installation d'entreposage de combustible irradié ou de matières radioactives, selon la présente invention,
• la figure 2 est une vue en coupe transversale d'une partie de l'installation d'entreposage de combustible irradié ou de matières radioactives représentée à la figure 1,
• la figure 3 est une vue en coupe transversale d'une partie d'une autre installation d'entreposage de combustible irradié ou de matières radioactives, selon la présente invention.

The invention will be better understood and other advantages and particularities will appear on reading the following description, given by way of non-limiting example, accompanied by the appended drawings among which:

• FIG. 1 is a vertical sectional view of an irradiated fuel or radioactive material storage facility, according to the present invention,
• FIG. 2 is a cross-sectional view of a portion of the irradiated fuel or radioactive material storage facility shown in FIG.
• Fig. 3 is a cross-sectional view of a portion of another irradiated fuel or radioactive material storage facility according to the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Figure 1 is a vertical sectional view of an irradiated fuel or radioactive material storage facility in accordance with the present invention.

The installation comprises a room 1, buried in the example shown and provided with a floor 2, a ceiling 3 and side walls of which only two, the walls 4 and 5, are visible. In the room 1 are arranged a plurality of receiving means or well 6.

The wells 6 are, in the example of FIG. 1, tubular elements suspended from the floor 11 of the handling room 10 which is above the room 1. The foot of each well 6 can be debated in a limiter of clearance 7 via dampers not shown. The irradiated fuel or the radioactive materials are disposed in the wells from the handling room 10 according to packages known to those skilled in the art.

The wells 6 are each surrounded, in the heating part of the wells, with a jacket 8 whose role is multiple: radiative screen, chimney, structure of the flow. The jackets 8 surround the wells 6 so as to leave an annular space, between wells and corresponding jacket, sufficient to allow proper cooling of the wells. By way of example, for a well 90 cm in diameter, the corresponding liner may be 140 cm in diameter.

Partitions 9 connect the shirts 8 to each other. They do not play a direct thermal role but contribute to vertically structuring the flow of the cooling gaseous fluid and to avoiding the transverse currents of assembly. Other partitions, referenced 19, also connect the jackets 8 located near the side walls (for example the wall 5) to these side walls, both to structure the flow and to avoid bypass currents. The shirts 8 rest on the floor 2 and supports not shown and do not interfere with the circulation of the gaseous cooling fluid. The presence of the partitions 9 and 19 also ensures better stability of all the shirts.

The storage facility shown in Figure 1 is cooled by air. Fresh air enters through the air vent 20, passes through a grid 21 and an electrostatic filter 22 and is fed through a conduit 23 to the air inlet 24 of the room 1 The entrance is advantageously at the lowest part of room 1. Similarly, the air outlet 25 is advantageously at the highest part of room 1. It communicates with an exhaust stack 26. Between the air inlet 24 and the air outlet 25, the cooling air is thus channeled in a vertical direction by the folders 8 and the partitions 9 and 19.

Figure 1 shows that the floor 2 and the ceiling 3 are inclined to facilitate the flow of air. Floor 2 and ceiling 3 rise to the air outlet 25.

The ceiling 3 may be constituted by a sheet. Near the ceiling 3, the thermal boundary layer is destructured by plates 15 also acting as radiative screens. These plates may advantageously be arranged a few centimeters below the ceiling to be in contact by their two faces with the cooling fluid so that the heat exchange is done by these two faces

The installation shown in Figure 1 further comprises an air bypass circuit. This auxiliary air circuit, in natural convection, comprises a first vertical duct 31 which brings air between the ceiling 3 and the floor 11 of the handling room 10. The heated air then circulates in the second vertical duct 32 then in a horizontal duct 33 to return in the conduit 23. The air bypass circuit returns warm air to the entrance to the room 1, which slightly increases the temperature of the air at the entrance and reduces the risk of condensation. Another possible embodiment is to take the air directly into the outlet chimney.

This recirculation of air must moderately increase the air temperature at the inlet, typically a few degrees. The proportion of circulating air should be low at full power and increase when the power decreases to reach a proportion of 100% at zero power. To satisfy this condition, it is necessary to provide adjustable pressure drop members in the bypass circuit or the air outlet circuit or both circuits. The Adjustment of these organs could be done after each loading or unloading of nuclear material, to take into account the new power stored, or when the stored power has significantly decreased (usual radioactive decay). This last case can mean a period of a few years to a few tens of years between two consecutive adjustments.

FIG. 2 is a cross-sectional view of a portion of the installation shown in vertical section in FIG. 1. It is possible to recognize the wells 6 arranged in a regular triangular array, the folders 8, the partitions 9 between the shirts and the partitions 19 connecting the partitions 9 to the side wall 5. The wells 6 surrounded by their shirts 8 are arranged as close as possible to the side walls to avoid the presence of bypass currents. Elements 16 or "mannequins", equivalent to half-shirts (in the longitudinal direction) are present against the side wall 5 and are connected to the closest shirts by partitions 17. This arrangement allows to structure the flow of air, to ensure that the wells located near the side wall 5 see the same type of flow and avoid bypass currents.

Figure 3 is a cross-sectional and top view of a portion of another irradiated fuel or radioactive material storage facility. This installation differs from the previous one by the shape of the wells. Wells 41 of this variant have a square section. Shirts 42 surrounding them also have a square section. They are interconnected by partitions 43.

This configuration of the wells 41 makes it possible to arrange them according to a regular square network that is as close as possible to the lateral wall 50 in order to avoid the bypass currents. The set of folders can be surrounded by an envelope 44 connected to the adjacent folders by partitions 45 to further increase the structuring of the flow and reduce the bypass currents.

The arrows 51 symbolize the air flush with the ground and will penetrate from below into the network of shirts and partitions. The arrows 52 symbolize the air leaving the network of folders and partitions, under the ceiling and heading towards the air outlet symbolically represented in 53.

The invention therefore allows a better structuring of the flows, thus a better reliability of the calculations describing them. This implies that the safety performance demonstrations and certification procedures will be easier to do. Acceptability by the public should be increased.

The invention makes it possible to reduce the maximum temperatures of storage. In particular, it makes it possible to reduce the maximum temperatures to which the side walls and in particular the ceiling are subjected.

The invention also reduces the unnecessary flow bypass wells. It therefore makes it possible to dimension more economically the air inlet and outlet circuits while ensuring homogeneous and efficient cooling.

The invention also makes it possible to reduce the quantities of water coming from the humidity of the outside air condensed on the cold parts of the installation.

By allowing the temperature drop on the ceiling surface of the storage room, the design of this ceiling, its implementation, qualification and certification are facilitated.

Claims (13)

1. Storage installation for irradiated fuel or radioactive materials comprising:

   - a chamber (1) provided with a floor (2), a ceiling (3) and lateral walls (4, 5),

   - a plurality of reception means (6) for receiving the irradiated fuel or the radioactive materials, these reception means (6) being arranged in the chamber in such a way as to enable them to be submitted to the circulation of a cooling gaseous fluid,

   - means for introducing fluid (24) into the chamber (1) making it possible to introduce said cooling gaseous fluid,

   - means for evacuating gaseous fluid (25) outside the chamber (1) in order to evacuate said cooling gaseous fluid after its circulation over the reception means (6),

   - means (8, 9, 19) making it possible to channel said cooling gaseous fluid in order to impart it with a preferred circulation direction when it circulates over the reception means (6), comprising

   - sleeves (8) surrounding the reception means (6) leaving a space between them and the reception means (6) for the circulation of the cooling gaseous fluid, these sleeves (8) having intake and outlet openings to ensure the circulation of the cooling gaseous fluid, the installation being characterized in that the means making it possible to channel the cooling gaseous fluid also comprising

   - partitions (9) linking the sleeves (8), these partitions (9) being arranged according to a direction corresponding to the preferred direction for circulation of the cooling gaseous fluid.
2. Installation according to claim 1, characterized in that the reception means (6) next to the lateral walls (5) of the chamber (1) are arranged as close as possible to these lateral walls in order to avoid the cooling gaseous fluid forming bypass currents.
3. Installation according to claim 1, characterized in that the sleeves (8) also constitute radiating screens.
4. Installation according to any one of claims 1 to 3, characterized in that the means making it possible to channel the cooling gaseous fluid also comprise partitions (19) linking at least one lateral wall (5) of the chamber (1) to the sleeves (8) next to this lateral wall, these partitions (19) being arranged according to a direction corresponding to the preferred direction for circulation of the cooling gaseous fluid.
5. Installation according to any one of claims 1 to 4, characterized in that it further comprises supplementary means (16) making it possible to channel said cooling gaseous fluid, these supplementary means (16) being located between one lateral wall (5) of the chamber (1) and one or several sleeves (8) and being arranged according to a direction corresponding to the preferred direction for circulation of the cooling gaseous fluid.
6. Installation according to any one of claims 1 to 5, characterized in that the means for evacuating the gaseous fluid (25) being located at the ceiling or close to the ceiling (3), the ceiling is inclined and the means of evacuation of the gaseous fluid (250 are located in the highest part of the chamber.
7. Installation according to claim 6, characterized in that the ceiling (3) is inclined at an angle comprised between 10° and 20° relative to the horizontal.
8. Installation according to any one of claims 1 to 7, characterized in that the chamber (1) is provided with an inclined floor (2) rising towards the means for evacuation of the gaseous fluid (25).
9. Installation according to any one of claims 1 to 8, characterized in that it further comprises a branch circuit (31, 32, 33) for the cooling gaseous fluid to recycle part of the cooling gaseous fluid having circulated in the chamber (1) or having been in thermal contact with the chamber.
10. Installation according to claim 9, characterized in that the part of the cooling gaseous fluid recycled is extracted in an evacuation chimney (26) communicating with the means of evacuation of the gaseous fluid (25).
11. Installation according to one or the other of claims 9 or 10, characterized in that adjustable load loss elements are envisaged in the branch circuit or in the evacuation means for gaseous fluid, to control the quantity of cooling gaseous fluid recycled.
12. Installation according to any one of the preceding claims, characterized in that the thermal radiating plates (15) are associated with the reception means (6), these plates (15) being located close to the ceiling (30 to destructure the thermal boundary layer at the surface of the ceiling.
13. Installation according to any one of the preceding claims, characterized in that the cooling gaseous fluid is air.

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