FR2844385A1 - System for preventing inflation of radioactive bitumen coatings in containers uses material that is porous to gases but impermeable to bitumen - Google Patents

Abstract

The system, used in the storage of low and medium-level radioactive waste mixed with a molten bitumen coating and poured into metal drum containers, comprises a material that is porous to gases but impermeable to liquid or solidified bitumen. The porous material traps the gases and allows them to be collected by a tube in the middle of the container and evacuated at the top. The plates are separated by radial spacers. The system, used in the storage of low and medium-level radioactive waste mixed with a molten bitumen coating and poured into metal drum containers (1) normally of 220 liters capacity, comprises a material (3) that is porous to gases but impermeable to liquid or solidified bitumen. The porous material, e.g. cellular concrete plates, traps the gases and allows them to be collected by a tube (4) in the middle of the container and evacuated at the top. The plates are separated by radial spacers (5) above and below them in the container.

Description

Method and device for inhibiting the swelling of radioactive coatings

bitumen contained in containers.

  The present invention relates to a method and a device for inhibiting the

  swelling of bituminous radioactive coatings confined in containers.

  The nuclear industry, and more particularly the power stations, generate, among other things, radioactive waste of low and average activities. Coating in bitumen and packaging in open containers for this waste for storage over time is a common means of treatment. During coating, the radioactive waste is hot-kneaded with bitumen. Io The asphalt thus obtained is heat-cast in metal fts generally

  with a capacity of 220 liters, of which it occupies at most 75% of the volume.

  These fts are then stored in appropriate premises.

  The asphalt coating of radioactive waste of low and medium activities has been retained because of the simplicity and stability over time of this process. However, this has the disadvantage of only accepting waste with a low concentration of radioactivity, relative to the volume of the bitumen. Indeed, the radioactive activity of the waste on the bitumen generates radiolysis gases and more particularly hydrogen. In time, hydrogen bubbles are formed in the bitumen. If the concentration of these bubbles is too great, the volume of the bitumen increases sharply, which can lead to the overflow of the ft. To mitigate this risk, the regulation limits the concentration of radio nuclide to a specific radioactive activity, as well as

  maximum filling of the fts at 80% of their capacity.

  In order to overcome this drawback, numerous research projects have been initiated and have made it possible to increase the radioactivity concentration of the waste.

  relative to a given volume of bitumen, by adding adjuvants in the bitumen such as, for example and more particularly, cobalt salts. The results, while representing progress, are not yet sufficient to release this process from the heavy technical and economic constraints of its operation.

  The present invention aims to overcome current deficiencies and

  to optimize the technique of the coating in the bitumen.

  According to the invention, this object is achieved by the implementation of a method according to which a capture of the radiolysis gases in the mass of the radioactive bituminous coating, confined in a container, by means of a material is carried out. gas porous and impervious to solid and liquid bitumen incorporated in said mass, the captured gases being, preferably, drained outward through a

  exhaust port formed in said container.

  The device according to the invention comprises a container provided with a loading opening, preferably sealingly sealed with bitumen and water, by means of a lid, this device being remarkable in that it

  contains a system for capturing radiolysis gases consisting of a material porous to gases and impervious to solid and liquid bitumen distributed over at least a portion of the height of the container, the latter preferably being provided with an exhaust orifice that can be in communication with the outside for draining the drained gases.

  Full scale experiments of the process and the device of the invention have made it possible to verify the possibility of quadrupling, at least, the concentration of the radioactive activity of the waste, in the bituminous coating without swelling or overflow. Thanks to the stabilization of the bitumen they provide, they also allow optimum filling of the fts or other containers. Another result obtained by the implementation of the invention is the possibility of closing the fts and thus make them airtight, which avoids the leaching of the coating and therefore a better hold in the air. the weather. The invention makes it possible to envisage long-term storage of radioactive waste of low and intermediate activity, or even a permanent storage of such waste. It is easily understood that the solution to this problem allows a very significant reduction in the number of fts for the same radioactive waste activity. This reduction automatically generates a very significant reduction in the economic cost of the entire processing chain. The economic interest combined with greater safety should, thanks to the invention, lead to an important development of the coating technique in the

  bitumen of low and medium level radioactive waste.

  Of course, all the advantages obtained by incorporating various adjuvants into the bitumen, such as cobalt salts, for example, can be preserved.

  to add to the advantages resulting from the method and the device of the invention.

  The foregoing and other objects, features and advantages will become more apparent from the following description and accompanying drawings in which:

  FIG. 1 is a front view with partial axial section of an exemplary embodiment of the device for inhibiting the swelling of radioactive coatings

  bitumen confined in containers, according to the invention.

  Figure 2 is an elevational view of the drainage system alone.

  FIG. 3 is a cross-sectional view along the line 3-3 of FIG. 2. FIG. 4 is a detail view, in axial section, showing the assembly

  a washer of porous material around the axial tubular collector of the drainage system.

  FIG. 5 is an axial sectional view illustrating the operation of the

  catching and draining device according to the invention.

  FIG. 6 is a detail view, in axial section, illustrating the orifice

  drain exhaust gas and valve equipping the orifice.

  FIG. 7 is a view similar to FIG. 6 and illustrating the operation

of the flap.

  Figure 8 is a detail view illustrating the conformation of the border

  device closing lid of the ft.

  Reference is made to the drawings to describe an interesting, although by no means limitative, example of the implementation of the method and of the embodiment of the device for inhibiting the swelling of bituminous radioactive coatings.

  confined in containers, according to the invention.

  In practice, it is expected that these containers will, as today, consist of standard fts trade or special fts with a capacity of about 220 liters, having a diameter of about 565 mm and a height of the order of 870 mm to be stored in the vertical position. For this reason, for a good understanding of the following discussion, words such as "vertical", "superior", "lower", etc. are used. He goes from

  however, these words have no limiting character.

  According to the process of the invention, the inhibition of the swelling of radioactive coatings confined in containers is obtained by the capture of the radiolysis gases in the mass of said coatings, by means of a device

capture embedded in said mass.

  The device according to the invention comprises a container 1, for example constituted by a cylindrical metal thread, open at its upper end and having a bottom end through which it can rest on the floor or other receiving surface S. within this ft, is positioned a sensing system 2 occupying at least a portion of the height of said ft and, preferably all or the

almost all of this height.

  This collection system preferably comprises one or more pieces 3 of a material porous to gas, impervious to solid and liquid bitumen, and insensitive to irradiation, this material may advantageously consist of cellular concrete such that, for example, a cellular concrete of the type marketed under the name of "SIPOREX" (Registered Trade Mark). The sensing system includes, for example, a plurality of spaced and superimposed plates 3 of porous material which may advantageously be cellular concrete. In view of the fact that the containers used for the storage of low and medium level radioactive waste are generally constituted by cylindrical bars, the plates 3 have

  preferably a circular shape.

  They have, for example, a thickness of the order of 20 to 30 mm and their spacing may be of the order of 130 mm. Their micropores allow a migration of the radiolysis gas bubbles towards a collection or drainage means via which communication with the outside can be established. According to the advantageous embodiment illustrated, the sensing plates 5 3 are fixedly mounted around an axial collector tube 4 constituting a drainage system radiolysis gases captured by said plates, outwardly. Each sensing plate 3 is immobilized around the collecting tube 4, by means of radiating wedges 5 consisting of a central ring 5a and 1o of a plurality of blade-shaped radial branches 5b. Each sensing plate 3 is taken between an upper wedge 5 'and a lower wedge 5 "The radiating wedges 5 are fixed on the collector tube 4, for example by means of pressure screws which screw into radial threads 6 formed in the

  ring 5a and resting on the side wall of said tube.

  Alternatively or jointly, the radiating wedges 5 could be immobilized on the collector tube 4, by means of circlips 7 engaged in

  peripheral grooves provided along said collection tube.

  The radiating wedges 5 furthermore allow the centering of the collection and drainage assembly in the ft 1. The outer end of the radial blades 5b of the lowest radiating wedge 5 "is provided with a chamfer 5c facilitating

  the introduction of the collection and drainage assembly, in the ft.

  The sensing plates 3 preferably have a diameter much smaller than the inside diameter of the fiber 1, for example a diameter of 525 mm for a diameter of about 565 mm, so that a gap of i "is located between the peripheral edge of the porous material plates 3 and the wall

internal side of the container 1.

  Laterally, the collector tube 4 has openings opening into

  view of the cylindrical wall delimiting the central hole of the sensing plates 3.

  In this way, a flow of gas can be established from the sensing plates 3 towards the inside of the collecting tube 4. For a good collection of gases, the openings are constituted by holes 8 formed in the bottom of gorges

  spaced peripherals 9 which is provided with the collector tube 4.

  In order to prevent the radioactive bituminous coating from penetrating into the collecting tube and blocking it, a seal 10 is placed around the collecting tube 4, on each edge of the central hole of the sensing plates 3 traversed by said tube, these seals which can advantageously be executed in plaster brick, or in

  braid of mineral fibers or glass.

  A mesh 11 of large mesh may be interposed between, on the one hand, the upper radiating wedges 5 'and lower 5 "and, on the other hand, the opposite faces 10 of each sensing plate. capture plates, on all their surfaces in contact with the bituminous radioactive coating, so that they are protected against

  any forces of rupture that could be applied to them.

  The lower end of the collector tube 4 is closed by a plug 12. Its upper end is secured to a lid 15 and may be provided with a valve 13 whose function is to prevent the moist vapors from being able to

  enter the drainage system.

  The upper end of the collector tube 4 passes, for example, a metal washer 15a to which it is secured by welding or otherwise 20 (Figure 6). This washer 15a can be made of steel and has a thickness greater than that of the cover 15 on which it is fixed, by

example by riveting.

  The plate 3 of the highest porous material is pressed against the face

  bottom of the cover 15, via the radiating wedge 5.

  The valve 13 comprises a fixed cap 14 provided with lateral exhaust holes 14a communicating with the outside. This cap surrounds the upper end of the collector tube and its base is fixed, for example by welding, on the washer 15a integral with the cover 15 constituting the upper element of the drainage assembly. The movable member of the valve 16, preferably formed by a very light metal part has a part of -7

  16a guide engaged in the upper end of the collector tube and a circular cap 16b resting on the upper edge of said collector tube and capable of occupying two positions, an upper position (pressed against the top of the cap 14) releasing the upper opening of said collecting tube (Figure 7) and a low position in which it rests on the edge of said opening by closing it (Figure 6).

  The periphery of the lid 15 is provided with a conical fall 15b extending downwards and intended to cap the conical upper edge 1a of the ft 1, when the drainage assembly which has just been described is introduced into the . The seal is provided by a peripheral seal 17 advantageously executed in a braid of rock fibers and disposed between said conical fallout and

said conical upper border.

  The veneer of the lid 15 on the upper edge of the ft is provided by a

  deformable metal strap 18 which encloses the edge of the lid and the upper end of the ft, by means of a clamping system known per se.

  The upper element 15-15a of the collection and drainage assembly serving as a lid, is provided with a handling loop 19 allowing it to be hooked to the hook of a lifting device during the introduction of said

  together in a ft or other container 1.

  It is easy to understand the implementation of the method and the device of the invention,

after the preceding statement.

  A quantity of radioactive asphalt coating E predetermined according to

  the volume occupied by the parts of the collection and drainage assembly intended to be immersed in said coating, is poured, in the liquid state, into the container 1.

  The collection and drainage assembly is then introduced into the container, so that the sensing plates 3 are embedded in the radioactive bituminous coating E. The upper opening of the container is then sealed by means of the lid 15 and the seal 30 17 and said container is stored or stored in a room or in a site -8

  during the period of activity of the waste thus treated.

  The hydrogen bubbles that form, in time, in the bituminous coating, during the storage period, are captured by the porous material plates 3 (see arrows of Figure 5). The gas then escapes from the plates of porous material 3 and is collected or drained by the collector tube 4 closed at its base. The collected gas circulates upwardly in the collecting tube 4 and when it reaches a predetermined pressure, it raises the movable member 16 of the valve 13 and escapes to the outside through the openings 14a.

  formed in the fixed cap 14 of said valve.

  It is understood that one thus removes any swelling and overflow of the mass of the bituminous radioactive coating contained in the container 1 and, taking into account the invariability of the volume of this coating, over time, said

  container can be filled almost to the brim.

Claims (17)

  A method of inhibiting the swelling of container-borne radioactive coatings, characterized in that the inhibition of swelling is achieved by capturing the radiolysis gases in the bulk of the bituminous radioactive coating (E) confined in said containers. (1), by means of one or more pieces (3) of a gas-porous material impervious to bitumen   solid and liquid, embedded in said mass.   2. Method according to claim 1, characterized in that the capture system (3) is placed in communication with the outside of the container (1) for   allow the escape of the drained gases.   3. Method according to one of claims 1 or 2, characterized in that the gases   captured by the capture system (3) are collected in the central part   container (1) and evacuated to the upper part of the latter.   4. Method according to any one of claims 1 to 3, characterized in that   that the capture of the radiolysis gases is carried out by a plurality of plates (3) superimposed and spaced, embedded in the mass of the coating   radioactive bitumen (E) contained in the container (1).   5. Method according to any one of claims 1 to 4, characterized in that one uses, to achieve the capture of radiolysis gases in the mass   bituminous radioactive coating, one or more plates (3) of cellular concrete. 6. Device for inhibiting the swelling of radioactive coatings confined in containers, characterized in that it comprises a container (1) and a means (3) for capturing the radiolysis gases, housed in this container (1), so as to be submerged by the mass of the bituminous radioactive coating (E) introduced into said container, this capturing means consisting of one or more pieces (3) of a gas-porous material and impervious to solid and liquid bitumen.   7. Device according to claim 6, characterized in that it comprises a collection means (4) for draining the gases captured by the capturing means (3), the collection means communicating with the outside for   allow the escape of the drained gases.   8. Device according to one of claims 6 or 7, characterized in that the   gas porous material and impervious to solid and liquid bitumen is constituted of cellular concrete.   9. Device according to any one of claims 6 to 8, characterized in that   the means for capturing the radiolysis gases comprises a plurality of superposed and spaced plates (3).   10. Device according to any one of claims 6 to 9, characterized   the superposed and spaced plates (3) of porous material are mounted around a central collecting tube (4) with which they are located in communication.   11. Device according to one of claims 9 or 10, characterized in that   interval (i) is provided between the peripheral edge of the material plates   porous (3) and the inner side wall of the container (1).   12. Device according to any one of claims 9 to 11, characterized in that   that the superposed and spaced plates (3) of porous material are immobilized around the central collecting tube (4) by means of upper (5 ') and lower (5 ") radiating wedges fixed on said collecting tube (4).   13. Device according to one of claims 10 or 12, characterized in that   seal (10), for example executed in plaster brick, or braided mineral fiber or glass, is placed around the collector tube (4), on each   central hole border of the sensing plates (3) traversed by said tube.   14. Device according to claim 12, characterized in that a grid (11) is interposed between, on the one hand, the upper radiating shims (5 ') and lower   (5 ") and, on the other hand, the opposite faces of each pickup plate (3).   Device according to one of Claims 6 to 14, characterized in that   the upper end of the collector tube (4) is provided with a valve (13).   16. Device according to any one of claims 6 to 15, characterized in that it comprises a lid (15) for sealing the container.   17. Apparatus according to claim 16, characterized in that the cover (15) is constituted by the upper element of the drainage system housed inside. said container.