FR2888231A1 - Installation for treating metallic sodium from fast neutron nuclear reactor, includes treatment enclosure equipped with gas inlet and outlet, circulating unit, horizontal and vertical plates, depositing unit, tank, removable lid and handle - Google Patents

Abstract

The installation for treating metallic sodium from a fast neutron nuclear reactor, comprises treatment enclosure equipped with a gas inlet (6) and outlet (8), a unit (10) to circulate a gas flow containing a steam in the enclosure, horizontal and vertical plates defining housings to receive thin layer liquid metallic sodium, and a unit (36, 52) to deposit treated liquid metallic sodium. The plates (14) forming between the gas circulation channels that are in contact with the treated sodium. A gas inlet is placed above the plates and a gas outlet is placed opposite to the inlet. The installation for treating metallic sodium from a fast neutron nuclear reactor, comprises treatment enclosure equipped with a gas inlet (6) and outlet (8), a unit (10) to circulate a gas flow containing a steam in the enclosure, horizontal and vertical plates defining housings to receive thin layer liquid metallic sodium, and a unit (36, 52) to deposit treated liquid metallic sodium. The plates (14) forming between the gas circulation channels that are in contact with the treated sodium. A gas inlet is placed above the plates and a gas outlet is placed opposite to the inlet. A passage of gas circulation is spared on the plates that are placed between the channels. The gas flow sweeps around the housing while circulating from the inlet to the outlet. The housing is opened to deposit the sodium at an inlet. The sodium liquid level in the housing exceeds the predetermined height. A tank (20) and a removable lid (24) are used to close the openings tightly. The liquid sodium is connected in a removable way at the inlet. A handle is used to transfer the plates between the treatment enclosure. The gas having volume of: nitrogen/air (94-99%), carbon dioxide (10-99%) and steam (1-6%). A thickness of the sodium film in the plates is lower than 40 mm.

Description

2888231 1

  The invention relates generally to metal sodium treatment plants, intended in particular for the treatment of sodium coming from fast neutron nuclear reactors.

  More specifically, the invention relates to a metal sodium treatment plant, of the type comprising a treatment chamber for-view of at least one gas inlet and at least one gas outlet, and means for circulating in the enclosure a flow of gas comprising at least water vapor, from the inlet to the outlet.

  EP-0.596.331 describes such an installation. The sodium metal to be treated is injected through a nozzle located in the upper part of the enclosure, in the form of a stream of sodium droplets directed down the enclosure. A first gas stream, mainly comprising an inert gas, oxygen and water vapor, is injected immediately below the nozzle and mixes with the stream of sodium droplets. A second gaseous flow essentially comprising CO2 is injected through the nozzles located in the central part of the enclosure, and mixes with the other streams. Sodium metal reacts with water vapor and with CO2 and transforms into solid sodium carbonate, which is collected at the bottom of the enclosure.

  This installation is complex and difficult to master. In particular, it is difficult to adequately control the size of the sodium droplets, and the mixing conditions of these droplets with the gas flows injected into the chamber.

  In this context, the invention aims to provide a simpler installation and easier to control operation.

  For this purpose, the invention relates to an installation of the aforementioned type, characterized in that it comprises a plurality of trays each defining a housing for receiving the liquid metal sodium in the form of a thin layer, and means for depositing the metallic sodium to treat in housing.

  The installation may also have one or more of the following characteristics, considered individually or in any technically possible combination: 2888231 2 - the trays are horizontal and stacked vertically, these trays defining between them channels of circulation of the gas in contact with the sodium to be treated; the gas inlet is located one from below or above the trays, and the gas outlet is located the other from below or above the trays, at least one gas circulation passage being provided at each platen between the channel above said platen and the channel below said platen, such that the gas stream scans all the housings while flowing from the inlet to the gas outlet; the housings are open towards the top, the means for depositing the sodium comprising at least one liquid sodium metal inlet provided in the treatment chamber capable of discharging the liquid sodium into the housing of the plate situated highest in the stack; , and spillways of predetermined heights provided on each tray, the one or more spoilers of a given tray being adapted to discharge by gravity the liquid sodium into the housing of the tray immediately below when the level of liquid sodium in the housing of said given plateau exceeds the predetermined height; the trays are integral with each other and are able to be evacuated from the enclosure in one piece; the treatment chamber comprises a tank presenting upwardly an opening for evacuating the trays, and a removable lid sealing the opening in a sealed manner; the installation comprises a sodium recovery chamber, and handling means capable of transferring the trays between the recovery chamber and the treatment chamber; the installation comprises a loading station comprising means for supplying the liquid sodium treatment chamber that can be connected removably to the liquid sodium inlet of the chamber, a treatment station comprising means for supplying the gas treatment enclosure and means for extracting the gas from the enclosure, capable of being releasably connected to the gas inlet and outlet of the enclosure, and a recovery station treated sodium 2888231 3 contained in the enclosure, the three stations being distant from each other, the treatment chamber being able to be moved from one station to another; the gas mainly comprises between 0% and 89% by volume of nitrogen, between 10% and 99% by volume of carbon dioxide and between 1% and 6% by volume of water vapor; the gas mainly comprises between 0% and 89% by volume of air, between 10% and 99% by volume of carbon dioxide and between 1% and 6% by volume of water vapor; the gas mainly comprises between 94% and 99% by volume of air or nitrogen, and between 1% and 6% by volume of water vapor; and the sodium film in the trays has a thickness of less than 40 millimeters.

  Other characteristics and advantages of the invention will emerge from the description which is given below, by way of indication and in no way limita-tif, with reference to the appended figures, among which: FIG. 1 is a general schematic representation of the installation according to the invention; - Figure 2 is a vertical sectional view of the processing chamber of Figure 1, revealing the trays; and FIGS. 3 to 5 are partial views in vertical section of the treatment area, showing alternative embodiments of the trays of FIG. 2.

  The installation 1 shown in Figure 1 is for the treatment of sodium metal. This metallic sodium comes for example from a nuclear reactor fast neutron type, and is the primary heat transfer fluid of this reactor.

  At the end of the life of the reactor, this sodium can not be sent directly to a disposal site for radioactive waste because it is not chemically inert. The metallic sodium is indeed likely to react with the oxygen of the air under certain conditions, according to an exothermic reaction which can be excited. The facility aims to transform the metallic sodium by carbonation into a stable chemical, sodium carbonate Na2CO3 and / or sodium carbonate NaHCO3, by reaction with H2O water and CO2 gas. The balance equations of these chemical reactions are as follows: 2Na + H2O + CO2 -> Na2CO3 + H2 Na + H2O + CO2-NaHCO3 +% H2 Sodium carbonates are solid at room temperature. The above reactions exhibit slow and steady overall kinetics.

  The sodium to be treated is substantially pure, or contains small amounts of impurities, for example particles of metal oxides torn from the equipment of the primary circuit of the nuclear reactor.

  Sodium can also include small amounts of radioactive elements, such as Na2O, Co60 or Fe55. These radioelements come from the activation of sodium in the nuclear reactor, or activated metal structures of the reactor.

  As shown in FIG. 1, the installation 1 comprises: a tank 2 for storing the metallic sodium to be treated in liquid form; a treatment chamber 4 provided with a gas inlet 6 and a gas outlet; , means 10 for circulating in the chamber 4 a flow of gas of a given composition, - a basket 12 provided with a plurality of trays 14 for receiving the liquid sodium metal to be treated, this basket 12 being capable of being received removably in the chamber 4, an enclosure 16 for the recovery of carbonated sodium, and - handling means 18 able to transfer the basket 12 between the recovery chamber 16 and the treatment chamber 4.

  The chamber 4 is shown in FIG. 2, and comprises a substantially cylindrical tank 20 having a vertical axis X, presenting upwardly an opening 22 for insertion or evacuation of the basket 12, and a removable cover 24 capable of to close the opening 22 in a sealed manner. The tank 20 is delimited downwards by a bottom slightly convex towards the outside of the enclosure 4. The tank 20 comprises a fastening flange 28 surrounding the orbital 22. The cover 24 is curved toward the outside of the enclosure 4, and comprises a counter-flange 30 complementary to the flange 28. The cover 24 is fixed to the tank 20 by a plurality of tie rods 32 solidarisant the flange 28 and the counter-flange 30 one to the other, with interposition of a seal not shown.

  The gas inlet 6 is disposed at the bottom of the tank 20, slightly above the bottom 26. The gas outlet 8 is disposed at the top of the tank 20, for example immediately below the flange 28.

  The cover 24 comprises a gripping lug 34 disposed on an outer side of the enclosure 4, in the center of the cover 24. It also comprises a branching 36 for supplying liquid sodium metal and a porthole 38. The tank 20 comprises a stitching 40 sodium evacuation from the chamber 4, carried by the bottom 26, and a drip tray 42 disposed inside the enclosure 4. This drip tray 42 is slightly sloped towards a low point, and present in this low point an evacuation port connected to the quilting 40. The enclosure 4 further comprises a sensor 43 for detecting the presence of sodium in the driester 42.

  The basket 12 comprises a rigid central upright 44, and a plurality of horizontal circular plates 14, arranged one above the other, and integral with the central upright 44.

  The trays 14 have an outside diameter slightly smaller than the internal diameter of the tank 20. Each plate 14 comprises a flat plate disk 46, and an edge 48 raised upwards surrounding the plate 46. Each plate 14 thus defines a housing 50 of reception of the liquid sodium metal to be treated, shallow, open upwards. Each plate 14 further comprises, at its periphery, a weir 52 of predetermined height. The spillway 52 includes a hole 54 in the plate 46 at the periphery thereof, and a flange 56, raised upward, around the hole 54, and having a predetermined height smaller than that of the edge 48.

  The predetermined height of the rim 56 is generally between 1 mm and 40 mm, typically between 1 mm and 5 mm, and preferably equal to 3 mm.

  Weirs 52 of two consecutive trays are arranged diametrically opposite. Thus, the weir 52 of a given first plate is diametrically opposed to the weir 52 of a second plate immediately greater than the first. The spillway 52 of a third plate immediately above the second is located above the spillway 52 of the first plate and diametrically opposite the weir 52 of the second plate.

  The spillway 52 of each plate 14 is disposed above the housing 50 of the plate 14 immediately below.

  The spillway 52 of the lower plate 14 is located above the dripping pan 42.

  The basket 12 also includes a foot 58 located under the plates 14, integral with the lower end of the upright 44, of a shape adapted to rest on the bottom 26.

  Finally, the basket 12 is provided with a gripping lug 62 rigidly attached to an upper end of the upright 44 situated above the plates 14.

  The total height of the stacked trays 14 is such that, when the basket 12 is disposed in the enclosure 4 and rests on the bottom 26 by the foot 58, the gas inlet 6 is located under the trays and the gas outlet 8 is located above the trays 14.

  The trays 14 are vertically spaced from each other so that they define between them gas circulation channels. These channels communicate with each other at each tray 14 by passages constituted by the holes 54.

  The tapping 36 arrival of the sodium opens overhanging the housing 50 of the highest plateau 14.

  The enclosure 4 further comprises heating means, for example a heating electric cord (not shown) wound on the ex-dull surface of the tank 20. Moreover, the enclosure 4 is insulated, for example by rolls of rock wool wrapped around the tank 20 (not shown), covering the electric heating cords.

  The storage tank 2 for the sodium to be treated comprises, as shown in FIG. 1, an inlet tap 64 provided with an isolation valve 66.

  This stitching 64 is capable of being placed in communication with a source of sodium to be treated, for filling the tank 2.

  The tank 2 is also equipped with a nipple 68 for feeding gaseous nitrogen, and means 70 for varying the pressure of the nitrogen supplying the tapping 68 in a predetermined pressure range. These means 70 comprise, for example, a high pressure nitrogen storage bottle, an adjustable expansion rate holder and an isolation valve.

  The tank 2 further comprises a gas outlet tap 72, equipped with a controlled isolation valve 74. The tap 72 is connected to a gas treatment device of a known type, which will not be described here.

  The tank 2 further comprises a sodium discharge tap 76 connected by a pipe 78 to the supply tap 36 of the enclosure 4. The tap 76 opens at the bottom of the tank 2. A controlled isolation valve 80 is interposed between the taps 76 and 36. The tank 2 also comprises a sodium recycle tap 82 connected to the exhaust tap 40 of the enclosure 4 by a pipe 83. A controlled isolation valve 84 is interposed between the taps 82 and 40.

  Finally, the tank 2 comprises heating means (not shown), for example of the electric heating cord type, making it possible to maintain the metallic sodium to be treated in the liquid state, and a heat insulation (not shown).

  Pipes 78 and 83 are also heated and insulated.

  The gas flowing in the outer enclosure 4 comprises nitrogen, water vapor and carbon dioxide, in the following proportions: N2 between 0% and 89% by volume, H2O between 1% and 6% by volume , and CO2 between 10% and 99% by volume. Preferably, the composition of the gas is as follows: N2 75% by volume, H2O 5% by volume and CO2 20% by volume.

  The means 10 for circulating the gas comprise cylinders 86 for storing carbon dioxide CO2 and N2 nitrogen, a cabinet 88 for preparing a dry gas stream from the gases stored in the bottles 86, a booster 90 ensuring the circulation of the dry mixture prepared by the cabinet 88 to the inlet 6 of the chamber 4, a humidifier 92 interposed between the booster 90 and the inlet 6, and heating means of the gas stream exiting the humidifier. The booster 90 controls the flow rate and pressure of the gas stream arriving at the inlet 6. The gas stream exiting the humidifier 92 has the appropriate composition mentioned above.

  The circulation means 10 further comprise a discharge cabinet 94 receiving the gas coming from the outlet 8, and transmitting these gases to a device for filtering and discharging into the environment.

  The filtration and rejection device is of known type and will not be described here.

  The reject cabinet comprises sensors for measuring the hydrogen content H2, carbon dioxide CO2, oxygen O2 and water vapor H20 in the gases leaving the enclosure 4, as well as pressure and flow sensors for the outgoing gas. of the enclosure 4.

  The installation further comprises a control cabinet 96, receiving the information from the sensors of the reject cabinet 94, and controlling the composition cabinet 88, the booster 90, the humidifier 92 and the heating means of the flow of gas, so as to obtain, at the inlet 6 of the enclosure 4, a mixture of composition, flow, pressure and temperature adapted.

  The control cabinet 96 also controls the means 70 for varying the nitrogen pressure in the tank 2, and the valves 74, 80 and 84, and is indicated by the means 43 for detecting the presence of sodium in the lick 42. The cabinet 96 controls the heating means of the tank 2 and the treatment chamber 4.

  The installation also comprises a safety device capable of injecting pure nitrogen inside the treatment enclosure 4. This device can be triggered by the control cabinet 96 if the cap is not in use. In the cabinet 94 there is a drift of some operating parameters of the plant, for example an increase in the hydrogen content H2 or in the water vapor H2O.

  The handling means 18 comprise a rail provided with a pa-lan 98 adapted to cooperate with the lug 34 of the lid 24 and with the lug 62 of the basket 12.

  The recovery chamber 16 has a roof provided with an access opening through which the basket 12 can be deposited inside the enclosure 16 by the hoist 98. It also includes a removable flap 100 likely to seal said opening sealingly. The recovery chamber 16 is equipped with different means for recovering the sodium carbonate found in the plates 14. These means are mechanical means (for example scrapers), spraying means (low water jets medium or high pressure), or tanks of sufficient size to immerse the basket 12. The spraying or immersion can be carried out using water containing additives promoting the dissolution of carbonates. In the case where the recovery of the carbonates is carried out by spraying or immersion, the enclosure comprises means for discharging the water loaded with dissolved carbonate to a liquid effluent treatment station. It is also equipped with means for drying the basket, for example by blowing hot air.

  The installation advantageously comprises two identical baskets 12 of the type described above. One of the baskets is used in the treatment chamber 4, while the other basket is cleaned in masked time in the recovery chamber 16.

  The entire installation, in particular the treatment chamber 4 and the cleaning chamber 16, is located in a room ensuring the confinement of the radioactive elements that could possibly be dispersed during the transfer of the baskets 12 of the treatment chamber 4 at the recovery chamber 16.

  We will now describe the operation of the installation above.

  Initially, the tank 2 is filled with sodium metal to be treated hot, liquid, one of the two baskets 12 is disposed inside the treatment chamber 4, and the other basket is waiting in the 'installation. The treatment chamber 4 is sealed.

  The first operation consists in filling the trays 14 of the basket 12 disposed inside the enclosure 4 with liquid metal sodium coming from the tank 2. For this purpose, the cabinet 96 closes the valve 74, opens the valve 80, and increases the nitrogen pressure in the tank 2, with the aid of the means 70. The increase in the nitrogen pressure pushes the liquid sodium in the line 78 to the supply tap 36. liquid sodium flows by gravity into the housing 50 of the highest plateau 14. When the sodium height in the housing 50 reaches the height of the flange 56 of the weir 52, the sodium flows through the orifice 54 by gravity and falls into the housing 50 of the tray 14 located immediately below. When the sodium height in this second plate 14 in turn reaches the predetermined height of the flange 56, the sodium overflows and flows by gravity in the third plate 14, located below the second. The sodium supply of the enclosure 4 continues until all the trays 14 of the basket 12 are filled with a predetermined height of sodium.

  When the lowest tray 14 is filled, the sodium flows into the pan 42. The sensor 43 detects the presence of sodium, and causes the isolation valve 80 to close, thereby interrupting the supply of the enclosure 4 in liquid sodium. The cabinet 96 then controls the opening of the valve 84 and lowers the nitrogen pressure inside the tank 2.

  After a delay, the isolation valve 84 is closed.

  In a second phase, the treated sodium is allowed to cool in the trays 14, until its solidification, that is to say up to a temperature of 90 C approximately.

  In a third phase, the means 10 circulate the flow of gas of determined composition indicated above inside the chamber 4, from the inlet 6 to the outlet 8. The gas successively scans the housings 50 of all the trays 14. It first sweeps the housing 50 of the lower tray 14 then passes through the opening 54 of the tray immediately above, sweeps the housing 50 of this tray and so on until at the highest plateau. It exits the enclosure 4 through the outlet 8, 2888231 11 through the discharge cabinet 94 and is released into the environment after filtration.

  The flow of gas enters the chamber 4 at a temperature of between 20 ° C. and 70 ° C. This temperature is controlled by the cabinet 96 so as to remain constantly lower than the internal temperature of the enclosure 4, so that the water vapor does not condense on the internal structures of the enclosure 4.

  In contact with the gas, the metallic sodium disposed in the housing 50 is converted into solid sodium carbonate, this reaction being accompanied by an evolution of hydrogen H 2. The hydrogen is removed from the wrap 4 by the circulation of gas.

  During the third phase, the enclosure 4 is heated, so as to maintain its internal temperature slightly above the temperature of the gas flow passing through the enclosure.

  The control cabinet 96 interrupts the humidification of the gas if the hydrogen level in the gas leaving the outlet 8 measured by the cabinet 94 exceeds a predetermined safety level.

  The flow of gas is stopped by the control cabinet 96 after a predetermined treatment time, or when the rejection cabinet 94 no longer detects H2 hydrogen in the gas flow leaving the enclosure 4.

  An operator then unscrews the tie rods 32, and the lid 24 is removed from the tank 20 using the hoist 98. The hoist 98 then grabs the basket 12 and carries it inside the recovery chamber 16. Then the hoist 98 deposits the second basket 12 inside the chamber 4 and replaces the cover 24. A new sodium treatment cycle can then begin.

  The basket 12 filled with sodium carbonate is, in turn, cleaned by operators inside the chamber 16, dried if necessary, then removed from the chamber 16 using the hoist 98 and placed on hold .

  The installation described above has many advantages.

  It is particularly simple and easy to master. The metallic sodium to be treated is placed in the trays in the form of a film. The means for introducing the sodium into the trays and to control the height of the film are very simple and reliable, since the sodium sinks 2888231 12 by plate gravity by weirs, the height of these weirs defining the height of the film.

  Sodium metal is converted into sodium carbonate according to slow global kinematic chemical reactions. The transformation of sodium can therefore be easily controlled by varying the gas flow rate and / or the composition of these gases.

  For the same reason, the flow of H2 hydrogen resulting from the conversion of sodium is low, so that the concentration of hydrogen in the gases leaving the enclosure 4 can easily be kept away from the upper limit of flammability. .

  The slowness of the reaction is compensated by the fact that the contact surface between the gas and the metallic sodium to be treated is very important. The installation thus has a good processing capacity.

  The small thickness of the sodium film in the trays ensures that all the metallic sodium is converted into carbonates.

  In addition, the installation involves only simple, inexpensive, and robust equipment.

  It is possible to treat, in the installation described above, sodium containing impurities, as specified above. It is also possible to treat in the installation a mixture of sodium and potassium, known as NaK or a mixture of sodium and any other alkali metal. The sodium can come from the primary circuit of a fast neutron nuclear reactor, or from another source, for example a laboratory, or a nuclear reactor of another type cooled with sodium.

  The plant is also suitable for treating solid waste contaminated with metallic sodium, for example pump bodies or pipe sections. In this case, the basket described above, provided with trays 14, is replaced by a hollow basket wire mesh, deep, salad basket type, in which are placed the waste to be treated.

  Finally, it will be noted that the arrangement of the trays inside the enclosure 4 makes it possible to scan the interior space of the enclosure which leaves no dead zone. Hydrogen can not accumulate in an area not swept by gas.

  The installation described above can have multiple variants.

  FIG. 3 illustrates a variant of the basket 12, which does not include a central upright 44. The openings 54 of the weirs 52 are not located on the periphery of the plates 14 but in the center, or at intermediate points between the center and the suburbs. Each plate is secured to the upper plate by spacers 110 cylindrical axis X. Each spacer 110 is secured at one end, the edges of an opening 54 of a plate 14, and, at its opposite end, the plate 46 of the upper plate 14. The vertical cylinders 110 are each provided with a side window 112 opening at the predetermined height above the plate 46. The portion of the tube 110 extending between the window 112 and the plate 46 constitutes the rim 56 of the weir 52. Sodium thus flows from tray 14 to lower tray 14 through window 112, through the interior of cylindrical spacer 110. Spacer 110 and its window 112 also create the gas flow passageway communicating with each other. the channel located under the plate 14 with the channel located above said plate 14. The gas flows in the opposite direction of the sodium, upwards. The spacers 110 of two consecutive trays are offset relative to each other, so that the spacers 110 of a given plate are not located under the spacers 110 of the upper plate.

  Figure 4 illustrates another variant of the basket. The basket 12 is devoid of a central upright 44. The plates 14 are secured to each other by a cylindrical outer shell 114, defining the edges 48 of the plates 14, and on which are welded the plates 46 of the plates 14.

  Weirs 52 are spaced apart from the peripheral edges of plates 14, and are offset relative to each other in two consecutive trays. As before, these weirs form gas circulation passages at each tray between the channel located under said plate and the channel above said plate.

  FIG. 5 illustrates yet another alternative embodiment of the basket 12 in which the gas circulation passages are dissociated from the weirs 52. The weirs 52 of the plates 14 are located at a distance from the peripheral edges of these plates 14. They have openings 54 of 2888231 14 small passage sections, thus offering a significant resistance to the flow of gas. Furthermore, each plate 14 has a gas passage lumen 116, formed on its peripheral edge, of much greater pas-wise section than that of the opening or openings 54 of the plate 14. The erected edge 48, which follows the periphery of the plate 14, extends along the edge of the light 116, so that the sodium can not flow through the opening 116 in the lower plate 14. The lights 116 of two consecutive trays 14 are diametrically opposed, so as to force the gas to travel through the housing 50 from a light 116 to the upper light 116.

  Alternatively, the gas flowing in the treatment chamber 4 may comprise air in place of nitrogen N2. The mass proportions of air, carbon dioxide CO2 and water vapor H2O are those indicated above. This is possible because of the low hydrogen flow rate H2 generated by the transformation of sodium, itself linked to the kinetics of the reaction. The risk of explosion of hydrogen in the presence of oxygen is extremely low and easy to control because of the low concentration of hydrogen in the gas leaving the chamber 4.

  It is also possible to use as treatment gas circulating in the enclosure 4 of nitrogen N 2 between 94% and 99% by volume, mixed with water vapor H 2 O, between 1% and 6% by volume, or air between 94% and 99% by volume mixed with water vapor between 1% and 6% by volume. Under these conditions, the sodium reacts on the water vapor contained in the gas to form anhydrous and solid sodium hydroxide.

  The enclosure 4 can also be mobile. It is then moved using a suitable trolley or a lifter suspended hoist 98. The installation comprises, in this case, a charging station of the sodium enclosure to be treated, a treatment station by circulation of gas and a station for recovering the oxidized sodium contained in the enclosure. The loading station is provided with means for supplying the treatment enclosure 4 made of liquid sodium which can be removably connected to the supply tap 36. The treatment station comprises feed means for feeding the liquid. 4 enclosure gas and 2888231 15 gas extraction means of the enclosure, may be removably connected to the inlet 6 and 8 gas outlet. The three stations are distant from each other, the wrap 4 being moved successively from one station to another. The recovery station may for example consist of a cell, under which the chamber 4 may be approached sealingly. The use of a mobile treatment chamber 4 is particularly advantageous for treating highly radioactive metallic sodium. Indeed, it makes it possible to avoid the confinement breaks created when the cover 24 of the enclosure is opened and the basket 12 is transferred to the recovery chamber 16.

  The installation may comprise a plurality of treatment tanks 4, mounted in parallel, fed by the same sodium tank 2, and by the same means 10 of gas circulation. It is thus possible to increase the treatment capacity of the installation. In the case of an installation comprising two treatment tanks 4, one can operate continuously, one of the two tanks being in process while the other tank is recovering.

  The treatment chamber 4 may not have a round section, but square, rectangular or prismatic.

2888231 16

Claims (12)

  1.- Sodium metal treatment plant, comprising a treatment chamber (4) provided with at least one gas inlet (6) and at least one gas outlet (8), and means (10) for circulating in the enclosure (4) a flow of gas comprising at least water vapor, from-then the inlet (6) to the outlet (8), characterized in that it comprises a plurality trays (14) each defining a housing (50) for receiving the liquid metallic sodium in the form of a thin layer, and means (36, 52) for depositing the metallic sodium to be treated in the housings (50).   2. Installation according to claim 1, characterized in that the trays (14) are horizontal and vertically stacked, these trays (14) defining between them channels of circulation of the gas in contact with the sodium to be treated.   3. Installation according to claim 2, characterized in that the gas inlet (6) is located below or above the trays (14), and the gas outlet (8) is located opposite the inlet (6) with respect to the trays (14), at least one gas circulation passage (54, 116) being formed at the level of each tray (14) between the channel located above said plate (14) and the channel below said platen (14), such that the gas stream scans all the housings (50) flowing from the inlet (6) to the gas outlet (8).   4. Installation according to claim 2 or 3, characterized in that the housings (50) are open upwards, the means for depositing the sodium comprising at least one inlet (36) of liquid sodium metal formed in the treatment chamber (4) capable of discharging the liquid sodium into the housing (50) of the topmost plate (14) in the stack, and weirs (52) of predetermined heights provided on each plate (14), the weir (s) (52) of a plate (14) being able to pour by gravity liquid sodium in the housing (50) of the tray (14) immediately below when the liquid sodium level in the housing (50) of said tray (14) ) given exceeds the predetermined height.   2888231 17 5. Installation according to any one of the preceding claims, characterized in that the plates (14) are integral with each other and are able to be removed from the enclosure (4) in one piece.   6. Installation according to claim 5, characterized in that the treatment chamber (4) comprises a tank (20) having upwardly an opening (22) for discharging trays (14), and a cover (24). removable opening closing the opening (22) sealingly.   7. Installation according to claim 5 or 6, characterized in that it comprises a chamber (16) for the recovery of treated sodium, and means (18) handling adapted to transfer the trays (14) between the recovery chamber (16) and the treatment chamber (4).   8. Installation according to claim 4, characterized in that it comprises a charging station comprising means for supplying the treatment chamber (4) in liquid sodium capable of being removably connected to the inlet ( 36) of liquid sodium from the enclosure (4), a treatment station comprising means (10) for supplying the treatment chamber (4) with gas and means for extracting the gas from the enclosure (4), connectable removably to the inlet (6) and outlet (8) of the gas chamber (4), and a station (16) recovery of treated sodium contained in the enclosure (4), the three stations being distant from each other, the treatment chamber (4) being able to be moved from one station to another.   9. Installation according to any one of the preceding claims, characterized in that the gas mainly comprises between 0% and 89% by volume of nitrogen, between 10% and 99% by volume of carbon dioxide and between 1% and 6% in volume of water vapor.   10. Installation according to any one of claims 1 to 8, characterized in that the gas comprises mainly between 0% and 89% by volume of air, between 10% and 99% by volume of carbon dioxide and between 1% and 6% by volume of water vapor.   11. Installation according to any one of claims 1 to 8, characterized in that the gas mainly comprises between 94% and 99% by volume of air or nitrogen, and between 1% and 6% by volume of steam. 'water.   2888231 18 12. Installation according to any one of claims 1 to 11, characterized in that the sodium film in the trays (14) has a thickness of less than 40 millimeters.